U.S. patent application number 13/078633 was filed with the patent office on 2011-08-04 for nano-reagents with cooperative catalysis and their uses in multiple phase reactions.
This patent application is currently assigned to SOUTHERN ILLINOIS UNIVERSITY CARBONDALE. Invention is credited to Yong Gao.
Application Number | 20110190506 13/078633 |
Document ID | / |
Family ID | 38334756 |
Filed Date | 2011-08-04 |
United States Patent
Application |
20110190506 |
Kind Code |
A1 |
Gao; Yong |
August 4, 2011 |
NANO-REAGENTS WITH COOPERATIVE CATALYSIS AND THEIR USES IN MULTIPLE
PHASE REACTIONS
Abstract
Nano-reagents with catalytic activity are provided herein. The
nanocatalyst comprises at least one amino acid attached to a
nanoparticle, wherein the reactive side chain of the amino acid
catalyzes a chemical or biological reaction. Methods of using these
nano-reagents to catalyze reactions in solution or in multiple
phases are also provided, as are methods of making these
nanocatalysts.
Inventors: |
Gao; Yong; (Carbondale,
IL) |
Assignee: |
SOUTHERN ILLINOIS UNIVERSITY
CARBONDALE
Carbondale
IL
|
Family ID: |
38334756 |
Appl. No.: |
13/078633 |
Filed: |
April 1, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11668151 |
Jan 29, 2007 |
7951744 |
|
|
13078633 |
|
|
|
|
60763123 |
Jan 27, 2006 |
|
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Current U.S.
Class: |
548/106 ;
556/146 |
Current CPC
Class: |
B01J 31/062 20130101;
B01J 2231/4266 20130101; A62D 2101/04 20130101; B01J 2531/824
20130101; B01J 2231/4261 20130101; B01J 2231/40 20130101; A62D 3/35
20130101; B01J 31/1633 20130101; B01J 35/0013 20130101; B01J 23/745
20130101; B01J 35/023 20130101; B01J 2231/4211 20130101; B01J
31/0254 20130101; A62D 2101/02 20130101; B01J 35/0033 20130101 |
Class at
Publication: |
548/106 ;
556/146 |
International
Class: |
C07F 15/02 20060101
C07F015/02; C07F 19/00 20060101 C07F019/00 |
Goverment Interests
GOVERNMENTAL RIGHTS
[0002] This invention was made with government support under grant
numbers CHE-0343440 and CHE-0534321 awarded by the National Science
Foundation CAREER Award Program. The Government has certain rights
in this invention.
Claims
1. A process for making a nanocatalyst comprising at least one
reactive species attached to a metal oxide nanoparticle, the
process comprising mixing at least one hydroxyl-containing compound
carrying the reactive species with a metal oxide nanoparticle
coated with a hydrophobic surfactant, whereby the
hydroxyl-containing compound replaces the hydrophobic surfactant on
the surface of the metal oxide nanoparticle and the nanocatalyst is
produced.
2. The process of claim 1, wherein the mixing comprises sonication
for about six hours.
3. The process of claim 1, wherein the hydrophobic surfactant is
chosen from a saturated long chain fatty acid, an unsaturated long
chain fatty acid, and a mixture thereof, the fatty acid comprising
about 14 to about 22 carbons.
4. The process of claim 1, wherein the hydroxyl-containing compound
is chosen from an alcohol, a diol, a carboxylic acid, and a
hydroxide.
5. The process of claim 1, wherein the reactive species is an amino
acid chosen from aspartic acid, cysteine, glutamic acid, histidine,
lysine, and serine.
6. The process of claim 1, wherein the reactive species is a
palladium-containing compound.
7. The process of claim 4, wherein the metal oxide nanoparticle is
an iron oxide nanoparticle, the hydrophobic surfactant is oleic
acid, and the hydroxyl-containing compound is dopamine.
8. The process of claim 7, wherein the reactive species is an amino
acid chosen from aspartic acid, cysteine, glutamic acid, histidine,
lysine, and serine.
9. The process of claim 4, wherein the wherein the metal oxide
nanoparticle is an iron oxide nanoparticle, the hydrophobic
surfactant is oleic acid, and the hydroxyl-containing compound is
silicon hydroxide.
10. The process of claim 9, wherein the reactive species is a
palladium-containing compound.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional application of U.S. patent
application Ser. No. 11/668,151 filed Jan. 19, 2007, which claims
benefit of priority to U.S. Provisional Application Ser. No.
60/763,123 filed Jan. 27, 2006, each of which is hereby
incorporated by reference in its entirety.
FIELD OF THE INVENTION
[0003] The present invention provides nano-reagents with catalytic
activity and methods of using these nanocatalysts to catalyze
chemical and biological reactions.
BACKGROUND OF THE INVENTION
[0004] Catalysts are widely used in many industrial applications,
such as pharmaceutical and fine chemicals manufacturing. A catalyst
may be necessary for a reaction to occur or for the process to be
economically viable. Many catalysts are expensive because they are
made from precious metals, such as platinum or palladium, or
because of the processing required to make a catalyst of a
particular size, shape, or crystal phase. Because of the scale of
industrial process and the expense of the catalysts it is desirable
to be able to recover and reuse catalysts. Tradition methods of
recovery have met limited success, however.
[0005] Furthermore, enzymes catalyze some industrially important
reactions. The limited stability, high substrate specificity, and
limited availability of sufficient quantities of some enzymes,
however, have tended to limit their use. Thus, a need exists for
small, stable, biomimetic catalysts that also could be recovered
and reused.
SUMMARY OF THE INVENTION
[0006] Among the various aspects of the present invention is the
provision of a method for making a nanocatalyst comprising at least
one reactive species attached to a metal oxide nanoparticle. The
process comprises mixing at least one hydroxyl-containing compound
carrying the reactive species with a metal oxide nanoparticle
coated with a hydrophobic surfactant. During the mixing step the
hydroxyl-containing compound replaces the hydrophobic surfactant on
the surface of the nanoparticle, whereby the nanocatalyst is
produced.
[0007] Other aspects and features of the invention are detailed
below.
DESCRIPTION OF THE FIGURES
[0008] FIG. 1 presents schematic diagrams of nanocatalysts of the
invention. A. A nanocatalyst comprising a carboxylic
acid-containing amino acid (aspartic acid, Asp) attached via a
dopamine linker to an iron oxide nanoparticle. B. A nanocatalyst
comprising an imidazole-containing amino acid (histidine, His)
attached via a dopamine linker to an iron oxide nanoparticle. C. A
nanocatalyst comprising a thiol-containing amino acid (cysteine,
Cys) attached via a dopamine linker to an iron oxide nanoparticle.
D. A nanocatalyst comprising three different amino acids (Asp, His,
Cys) attached via silicon hydroxide linkers to an iron oxide
nanoparticle. E. A nanocatalyst comprising two amino acids (Asp,
His) attached via dopamine linkers to an iron oxide nanoparticle.
F. A nanocatalyst comprising a palladium-containing compound
[N-heterocyclic carbene (Pd--NHC)] attached via a silicon hydroxide
linker to an iron oxide nanoparticle. G. A nanocatalyst comprising
a nanoparticle coated with a polymer, with amino acids attached to
the polymer. H. A nanocatalyst comprising a nanoparticle coated
with a polymer, with polypeptides attached to the polymer. I. A
nanocatalyst comprising a nanoparticle coated with a polymer linked
to reactive species. J. A nanocatalyst comprising a nanoparticle
embedded in a matrix comprising polymer to which the reactive
species are attached.
[0009] FIG. 2 illustrates the surface-exchange reaction during the
synthesis of a nanocatalyst comprising amino acids (AA) attached to
an iron oxide nanoparticle. The amino acid-derived dopamine
molecules replace the oleic acid molecules on the surface of the
nanoparticle.
[0010] FIG. 3 diagrams reactions catalyzed by nanocatalysts
comprising iron oxide nanoparticles linked to one or two amino
acids. The black circle represents the nanocatalyst, which was
removed by applying an external magnet (horseshoe symbol) upon
completion of each reaction. A. Hydrolysis of the carboxylic ester
bond of paraoxon (diethyl p-nitrophenylphosphate). B. Hydrolysis of
the phosphoester bond of 4-nitrophenyl acetate. C. Hydrolysis of
the phosphodiester bond in the RNA construct, UpU. D. Hydrolysis of
the phosphodiester bond in the DNA construct, dApdT.
[0011] FIG. 4 diagrams a solid phase Suzuki coupling reaction
catalyzed by a magnetic Pd nanocatalyst (diagramed in FIG. 1F).
Substrate X was immobilized on the resin, which was contacted with
the nanocatalyst and substrate B. The magnetic nanocatalyst was
removed by applying an external magnet. The produce P was released
from the resin and purified.
DETAILED DESCRIPTION OF THE INVENTION
[0012] A nanocatalyst has been discovered that comprises at least
one amino acid residue attached to a nanoparticle, wherein the
reactive side chain of the amino acid catalyzes a chemical
reaction. Furthermore, it has been discovered that these
nano-reagents also catalyze biological reactions that are generally
catalyzed by enzymes. The reactive groups of the amino acid side
chains may interact cooperatively to catalyze the reaction, in a
manner similar to the active sites of many enzymes. The reactions
catalyzed by these nanocatalysts may be in solution or they may be
in multiple phases. Additionally, nanocatalysts comprising a
magnetic nanoparticle may be magnetically separated from the
reaction products, byproducts, and excess reagents that are in
solution or in one of the orthogonal matrices, such that the
nanocatalysts may be recovered, recycled, and reused again.
I. Nanocatalyst
[0013] (a) Nanoparticle
[0014] One aspect of the present invention provides a nanocatalyst
comprising a nanoparticle attached to at least one reactive
species, whereby the reactive species functions as a catalyst. In
one embodiment the nanoparticle may be a magnetic material.
Non-limiting examples of suitable magnetic materials include a
metal, a metal oxide, a metal dioxide, a metallic salt, a metal
alloy, an intermetallic alloy, an organic magnetic material, a
derivative thereof, or a combination thereof. Suitable metals
include iron, cobalt, manganese, nickel, or a rare earth metal.
Alloys are typically combinations of two or more compounds, of
which at least one is a metal. Suitable alloys, therefore, include
alloys of iron, alloys of cobalt, alloys of manganese, and alloys
of nickel. Intermetallic alloys are generally mixtures of two or
more metals in a certain proportion. Suitable examples of an
intermetallic alloy include cementite (Fe.sub.3C), alnico (a blend
of aluminum, nickel, and cobalt), or Ni.sub.3Al. Among the suitable
metal oxides include iron oxides, such as magnetite
(Fe.sub.3O.sub.4) or maghemite (Fe.sub.2O.sub.3). Other suitable
magnetic materials include ferrofluids or spinel ferrites. The
magnetic material may also be an organic material, such as
7,7,8,8-tetracyano-p-quinodimethane or tetrathiafulvalenium
tetracyanoqinomethane. In a preferred embodiment, the nanoparticle
comprises an iron oxide.
[0015] In another embodiment, the nanoparticle may comprise a
non-magnetic material. The non-magnetic material may be inorganic
or organic. Suitable examples of an inorganic material include, but
are not limited to, silver, gold, titanium, aluminum, cadmium,
selenium, silicon, silica, or mixtures thereof. The inorganic
material may be formulated into a nanocrystal, a nanosphere, a
quantum dot, an electric semiconductor, and the like. An organic
non-magnetic material may be a synthetic polymer, a semisynthetic
polymer, or a natural polymer. Non-limiting examples of synthetic
organic polymers include polyacrylate, polyacrylamide,
poly(acrylamide sulphonic acid), polyacrylonitrile, polyamine,
poly(amidoamine), poly(arylamine), polycarbonate, poly(ethylene
glycol), poly(ester), poly(ethylene imine), poly(ethylene oxide),
poly(ethyloxazoline), polyhydroxyethylacrylate, polymethacrylate,
polymethacrylamide, poly(oxyalkylene oxide), poly(phenylene),
poly(propylene imine), poly(propylene oxide), polystyrene,
polyurethane, poly(vinyl alcohol), and poly(vinyl pyrrolidone). An
example of a suitable natural polymer is cellulose and its
(semisynthetic) derivatives, such as methylcellulose,
carboxymethylcellulose, hydroxyethylcellulose,
hydroxypropylcellulose, and hydroxy-propylmethylcellulose. Other
examples of natural polymers include polysaccharides or
carbohydrate polymers, such as hyaluronic acid, dextran, dextrin,
heparan sulfate, chondroitin sulfate, heparin, alginate, agar,
carrageenan, xanthan, and guar. The non-magnetic material may also
be a micelle comprising an aggregate of surfactant molecules
dispersed in a liquid.
[0016] One skilled in the art will appreciate that the size of a
nanoparticle can and will vary depending on the nature of the
material comprising the nanoparticle and the intended use of the
nanocatalyst. The average diameter of a nanoparticle may range from
about 0.01 nanometers (nm) to about 100,000 nm, preferably from
about 0.1 nm to about 1,000 nm, and more preferably from about 1 nm
to about 100 nm. In a preferred embodiment the average diameter of
a nanoparticle may range from about 2 nm to about 25 nm.
[0017] (b) Reactive Species
[0018] The nanoparticle is linked to at least one reactive species,
which functions as a catalyst. The reactive species may be an
acidic functional group, a basic functional group, a nucleophilic
functional group, or a catalyst atom.
[0019] In one embodiment, the reactive species may be an acidic
functional group. In general, an acid functional group refers to a
proton (H.sup.+) donor. Examples of acidic groups include, but are
not limited to, borate, carboxylate, hydroxamic acid, phenol,
phosphoric acid, phosphorous acid, seleninic acid, sulfinate,
sulfonate, thiol acid, or derivatives thereof.
[0020] In another embodiment, the reactive species may be a basic
functional group. In general, a basic functional group refers to a
proton (H.sup.+) acceptor. Examples of basic groups include, but
are not limited to, amino groups including primary, secondary and
tertiary amines, heterocyclic amines, guanidines, or derivatives
thereof.
[0021] In yet another embodiment, the reactive species may be a
nucleophilic group. Generally, a nucleophilic group has an unshared
pair of electrons, and the group may be neutral or have a negative
charge. Examples of nucleophilic functional groups include, but are
not limited to, amide, amino (including primary, secondary, or
tertiary amines), borate, carboxylate, guanidine, heterocyclic
amine, hydroxyl, hydroxylamine, hydroxamic acid, hydrazine,
o-iodosylcarboxylate, phenol, phosphine, phosphine oxide, phosphine
sulfide, phosphine sulfoxide, phosphorate, phosphorous acid,
seleninic acid, sulfinate, sulfonate, thio, thiol acid, or
derivatives thereof. In another aspect of this embodiment, the
nucleophilic group may comprise --X.sup.1--OH (or
--X.sup.1--O.sup.-), --X.sup.1--NH.sub.2, or --X.sup.1--SH (or
--X.sup.1--S.sup.-) structures, where X.sup.1 may be P, I, Br, Cl,
B, Al, N, O, S, Se, As, Si, or Ge.
[0022] In an alternate embodiment, the reactive species may be a
catalyst atom. In general, a catalyst atom is a metal or non-metal
that exhibits catalytic activity. Non-limiting examples of a
suitable catalyst atom include platinum, palladium, iridium, gold,
osmium, ruthenium, rhodium, or rhenium. In a preferred embodiment,
the catalyst atom forming the reactive species may be
palladium.
[0023] One skilled in the art will appreciate that the
aforementioned reactive species may be part of a larger molecule.
Essentially, the reactive species may be attached to a hydrocarbyl
moiety or a substituted hydrocarbyl moiety. In one embodiment, the
reactive species may be part of a larger chemical compound, e.g.,
palladium N-heterocyclic carbene (Pd--NHC) (see FIG. 1F). In
another embodiment, the reactive species may be part of an amino
acid or a polypeptide. In yet another embodiment, the reactive
species may be part of a nucleic acid. In still another embodiment,
the reactive species may be part of a carbohydrate. In a preferred
embodiment, the reactive species comprises at least one amino acid.
Amino acids with suitably reactive side chains include aspartic
acid (Asp), cysteine (Cys), glutamic acid (Glu), histidine (His),
lysine (Lys), and serine (Ser) (see FIG. 1A-C).
[0024] While at least one reactive species is attached to a
nanoparticle, generally many reactive species will be attached to
the nanoparticle. For example, a nanoparticle may be surrounded by
a shell of reactive species. One skilled in the art will appreciate
that the number of reactive species attached to a nanoparticle can
and will vary depending upon the size of the nanoparticle and the
density of reactive groups on the surface of the nanoparticle. The
reactive species attached to the nanoparticle may be of the same
type. For example, all of the reactive species attached to a
nanoparticle may comprise acidic groups; they all may comprise
carboxyl groups; they all may comprise palladium; and so forth.
Alternatively, the reactive species attached to a nanoparticle may
be of different types. For example, the reactive species attached
to a nanoparticle may comprise a mixture of acidic groups and basic
groups; they may comprise a mixture of acidic, basic, and
neutrophilic groups; they may comprise a mixture of carboxyl groups
and imidazole groups; they may comprise a mixture of different
amino acids; and so forth.
[0025] In a preferred embodiment, a nanocatalyst may comprise a
single type of amino acid. In an exemplary embodiment, a
nanocatalyst may comprise two different types of amino acids,
selected from the group consisting of Asp, Cys, Glu, His, Lys, and
Ser. In an especially preferred embodiment, a nanocatalyst
comprises aspartic acid and histidine attached to a nanoparticle
(see FIG. 1E). Furthermore, a nanocatalyst may comprise three or
more different amino acids, selected from the group listed above.
In embodiments comprising two or more different amino acids, the
amino acids may be attached to the nanoparticle such that their
side chains are positioned in close proximity to each other,
whereby the reactive side chains may interact cooperatively to
catalyze a chemical reaction. In particular, the interaction
between an acidic group and a basic group on the side chains of two
adjacent amino acids may cooperatively catalyze a reaction.
Alternatively, the interaction between an acidic group and a
neutrophilic group on the side chains of two adjacent amino acids
may cooperatively catalyze a reaction. The ratio of the amino acids
attached to the nanoparticle can and will vary depending upon the
application. For most applications, however, an equimolar amount of
each amino acid may be optimal.
[0026] (c) Linkage Between the Reactive Species and the
Nanoparticle
[0027] Depending upon the embodiment, the reactive species may be
attached to the nanoparticle by a variety of chemical bonds,
including but not limited to, covalent bonding, dative bonding,
ionic bonding, hydrogen bonding, or van der Waals bonding. In an
exemplary embodiment, the reactive species is attached by a
covalent bond.
[0028] The reactive species or the compound comprising the reactive
species may be attached directly to the nanoparticle. One skilled
in the art will appreciate that the nature of the nanoparticle
material will determine the type of bond utilized for a direct
attachment. Alternatively, the reactive species may be attached to
the nanoparticle by a linker. Typically, a linker is a molecule
having at least two functional groups, such that the linker is
disposed between the reactive species and the nanoparticle. Thus,
one functional group of the linker forms an attachment with the
nanoparticle, and another functional group of the linker forms an
attachment with the reactive species or the compound comprising the
reactive species. The type of bonds linking the reactive species to
the nanoparticle via the linker can and will vary depending upon
the reactive species, the linker, and the material of the
nanoparticle. Furthermore, the size, length, charge, and/or
hydrophilicity/phobicity of the linker can and will vary depending
on the nanoparticle material, the reactive species, and the
intended uses of the nanocatalyst.
[0029] In a preferred embodiment, the nanoparticle material
comprises a metal oxide. A suitable linker comprises a molecule
containing at least one hydroxyl group. Without being bound by any
particular theory, hydroxyl groups have affinity for the
undercoordinated surface sites of the metal oxide. Non-limiting
examples of suitable hydroxyl-containing molecules include
alcohols, diols, ethendiols, carboxylic acids, and hydroxides. In
an especially preferred embodiment, the nanoparticle comprises the
iron oxide, maghemite (Fe.sub.2O.sub.3) and the linker comprises
the ethenediol, dopamine (4-(2-aminoethyl)benzene-1,2-diol) (see
FIG. 1). In another especially preferred embodiment, the
nanoparticle comprises maghemite and the linker comprises silicon
hydroxide (see FIG. 1).
[0030] In yet another embodiment, the nanoparticle may be coated
with a polymer, and the reactive species is attached to the
nanoparticle via the polymer (see FIG. 1H, I). The polymer may be a
synthetic polymer, a semisynthetic polymer, or a natural polymer.
Suitable polymers were listed above in section (I)(a). The reactive
species may be attached directly to the polymer, via a reactive
group in the polymer. Alternatively, the reactive species may be
attached to the polymer via a linker, as detailed above.
[0031] In still another embodiment, the nanoparticle may be
dispersed in at least one type of polymeric matrix, with the
reactive species being attached to either the nanoparticle or the
polymer of the matrix (see FIG. 1J).
[0032] (d) Preferred Embodiments
[0033] As detailed above, a nanocatalyst of the invention comprises
at least one reactive species attached to a nanoparticle. Table A
lists various combinations of nanoparticles and reactive species
that form nanocatalysts. Preferred nanocatalysts comprise amino
acids with reactive side chains attached to a metal oxide
nanoparticle. An exemplary nanocatalyst comprises equimolar amounts
of aspartic acid and histidine attached to an iron oxide
(maghemite) nanoparticle. Another exemplary nanocatalyst comprises
a palladium-containing compound attached to an iron oxide
(maghemite) nanoparticle.
TABLE-US-00001 TABLE A Nanoparticle Material Reactive Species
nonmagnetic catalyst atom nonmagnetic palladium nonmagnetic acidic
group nonmagnetic basic group nonmagnetic nucleophilic group
nonmagnetic amino acid nonmagnetic Asp nonmagnetic Cys nonmagnetic
Glu nonmagnetic His nonmagnetic Lys nonmagnetic Ser nonmagnetic a
combination of any two of the following: Asp, Cys, Glu, His, Lys,
Ser nonmagnetic Asp, His nonmagnetic a combination of any three of
the following: Asp, Cys, Glu, His, Lys, Ser magnetic catalyst atom
magnetic palladium magnetic acidic group magnetic basic group
magnetic nucleophilic group magnetic amino acid magnetic Asp
magnetic Cys magnetic Glu magnetic His magnetic Lys magnetic Ser
magnetic a combination of any two of the following: Asp, Cys, Glu,
His, Lys, Ser magnetic Asp, His magnetic a combination of any three
of the following: Asp, Cys, Glu, His, Lys, Ser metal oxide catalyst
atom metal oxide palladium metal oxide acidic group metal oxide
basic group metal oxide nucleophilic group metal oxide amino acid
metal oxide Asp metal oxide Cys metal oxide Glu metal oxide His
metal oxide Lys metal oxide Ser metal oxide a combination of any
two of the following: Asp, Cys, Glu, His, Lys, Ser metal oxide Asp,
His metal oxide a combination of any three of the following: Asp,
Cys, Glu, His, Lys, Ser iron oxide catalyst atom iron oxide
palladium iron oxide acidic group iron oxide basic group iron oxide
nucleophilic group iron oxide amino acid iron oxide Asp iron oxide
Cys iron oxide Glu iron oxide His iron oxide Lys iron oxide Ser
iron oxide a combination of any two of the following: Asp, Cys,
Glu, His, Lys, Ser iron oxide Asp, His iron oxide a combination of
any three of the following: Asp, Cys, Glu, His, Lys, Ser magnetite
(Fe.sub.3O.sub.4) catalyst atom magnetite (Fe.sub.3O.sub.4)
palladium magnetite (Fe.sub.3O.sub.4) acidic group magnetite
(Fe.sub.3O.sub.4) basic group magnetite (Fe.sub.3O.sub.4)
nucleophilic group magnetite (Fe.sub.3O.sub.4) amino acid magnetite
(Fe.sub.3O.sub.4) Asp magnetite (Fe.sub.3O.sub.4) Cys magnetite
(Fe.sub.3O.sub.4) Glu magnetite (Fe.sub.3O.sub.4) His magnetite
(Fe.sub.3O.sub.4) Lys magnetite (Fe.sub.3O.sub.4) Ser magnetite
(Fe.sub.3O.sub.4) a combination of any two of the following: Asp,
Cys, Glu, His, Lys, Ser magnetite (Fe.sub.3O.sub.4) Asp, His
magnetite (Fe.sub.3O.sub.4) a combination of any three of the
following: Asp, Cys, Glu, His, Lys, Ser maghemite (Fe.sub.2O.sub.3)
catalyst atom maghemite (Fe.sub.2O.sub.3) palladium maghemite
(Fe.sub.2O.sub.3) acidic group maghemite (Fe.sub.2O.sub.3) basic
group maghemite (Fe.sub.2O.sub.3) nucleophilic group maghemite
(Fe.sub.2O.sub.3) amino acid maghemite (Fe.sub.2O.sub.3) Asp
maghemite (Fe.sub.2O.sub.3) Cys maghemite (Fe.sub.2O.sub.3) Glu
maghemite (Fe.sub.2O.sub.3) His maghemite (Fe.sub.2O.sub.3) Lys
maghemite (Fe.sub.2O.sub.3) Ser maghemite (Fe.sub.2O.sub.3) a
combination of any two of the following: Asp, Cys, Glu, His, Lys,
Ser maghemite (Fe.sub.2O.sub.3) Asp, His maghemite
(Fe.sub.2O.sub.3) a combination of any three of the following: Asp,
Cys, Glu, His, Lys, Ser
II. Method for Using a Nanocatalyst to Catalyze a Chemical
Reaction
[0034] A further aspect of the invention encompasses methods for
using the nanocatalysts of the invention to catalyze chemical
reactions. These nanocatalysts may catalyze many different types of
chemical reactions, but more importantly, these nanocatalysts may
catalyze biological reactions that are generally catalyzed by
enzymes. Furthermore, magnetic nanocatalysts may be readily
separated and recovered from the reaction mix or the product using
an external magnet, such that the nanocatalyst may be recycled and
reused.
[0035] (a) Types of Reactions
[0036] Nanocatalysts may be engineered to catalyze a plethora of
chemical reactions. The chemical reaction may be a combination
reaction, a decomposition reaction, or a replacement reaction. Many
such reactions are widely used in industry. Non-limiting examples
of such reactions include oxidative-reductive reactions,
condensation reactions, coupling reactions, hydrolysis reactions,
and dehydration reactions.
[0037] It has been discovered that nanocatalysts of the invention
may be used to catalyze the hydrolysis of ester bonds, phosphoester
bonds, and phosphodiester bonds (see Example 2). One skilled in the
art will appreciate that the hydrolysis of many other types of
bonds may be catalyzed by these nanocatalysts. Non-limiting
examples of other hydrolysable bonds include thioester, acyl
halide, alkyl halide, aryl halide, amide, acidic anhydride, ether,
thioether, phosphohalide, sulfonyl halide, sulfinyl halide,
sulfenyl halide, acetal, thioacetal, thioketal, ketal, hemiacetal,
thiohemiacetal, hemiketal, thiohemiketal, cyano bonds, and
derivatives thereof. Another bond whose hydrolysis may be catalyzed
by these nanocatalysts may be diagrammed as --X.sup.2-LG, wherein
X.sup.2 is I C, P, I, Br, Cl, B, Al, N, O, S, Se, As, Si, or Ge and
"LG" is a leaving group. A leaving group generally relates to the
part of a substrate molecule that is cleaved and generally has the
ability to attract electrons and/or negative charges. Non-limiting
examples of leaving groups include acetate (--OCOCH.sub.3),
halogens (--F, --Cl, --Br, and --I), trifluoroactetate
(--OCOCF.sub.3), methansulfonate (--O--SO.sub.2CH.sub.3), tosylate
(--OSO.sub.2C.sub.6H.sub.4CH.sub.3), nitrosulfonate
(--OSO.sub.2C.sub.6H.sub.4NO.sub.2), and triflate
(--OSO.sub.2CF.sub.3).
[0038] (b) Reaction Conditions
[0039] The nanocatalysts of the invention generally function under
mild reaction conditions. Traditionally, many chemical reactions
are performed at extreme pH values, elevated temperatures, in the
presence of caustic reagents, toxic organic solvents, and/or heavy
metals. In contrast, reactions catalyzed by the nanocatalysts of
the invention are generally performed at a neutral pH, a moderate
temperature, and in an aqueous solution (see Example 2). Depending
upon the application, a reaction mixture may further comprise a
buffering agent, a cation, a surfactant, an organic solvent, a
reducing agent, or a co-reactant. As will be appreciated by one
skilled in the art, the reactions conditions and reaction
components will vary depending upon the application.
[0040] The pH of the reaction may range from about 5.0 to about
9.0, preferably from about 6.0 to about 8.0, and more preferably at
about 6.5 to about 7.5. The temperature of the reaction may range
from about 20.degree. C. to about 80.degree. C., preferably from
about 25.degree. C. to about 65.degree. C., and more preferably
from about 30.degree. C. to about 45.degree. C. The duration of the
reaction may range from about 1 hour to about 96 hours, preferably
from about 6 hours to about 72 hours, and more preferably about 12
hours to about 48 hours. In one embodiment, the pH of the reaction
may be about 6.5 to about 7.5, the temperature of the reaction may
be about 25.degree. C. to about 30.degree. C., and the duration of
the reaction may be about 24 hours to about 48 hours. In yet
another embodiment, the pH of the reaction may be about 6.5 to
about 7.5, the temperature of the reaction may be about 37.degree.
C., and the duration of the reaction may be about 24 hours to about
48 hours.
[0041] The efficiency of the nanocatalyst, which may be assessed as
the percent of conversion of the substrate to the product, will
generally be at least 50%. The percent of conversion may be about
60%, 70%, 80%, 85%, 90%, 95%, or 99%. Preferably, the percent of
conversion may be at least 75%.
[0042] (c) Recovery of the Nanocatalyst
[0043] Magnetic nanocatalysts may be separated from the reaction
mixture or the product by applying an external magnet. Thus, the
nanocatalyst may be readily recovered, concentrated, recycled, and
reused repeatedly. The product of the reaction may be isolated
and/or purified from the reaction mixture by a variety of
techniques well known in the art.
[0044] (d) Applications
[0045] In one embodiment, a nanocatalyst of the invention may be
used to catalyze the hydrolysis of an environmental pollutant,
whereby the environmental pollutant is inactivated. The
environmental pollutant may be a pesticide, an insecticide, an
herbicide, or an insect repellent. Non-limiting examples of
environmental pollutants include paraoxon, parathion, methyl
parathion, malathion, methoprene, DEET, atrazine, azinophos-methyl,
diazinon, O-chlorobenzylmalononitrile, and derivatives thereof (see
Table B). The environmental pollutant may be in surface water,
ground water, or the soil. Alternatively, the environmental
pollutant may not be dispersed in the environment but may still be
in need of inactivation (e.g., in a storage facility). Thus, a
nanocatalyst of the invention may hydrolyze and inactivate the
environmental pollutant in water, soil, or another medium at
ambient temperatures. Additional reagents, such as divalent
cations, may be also be added. Upon completion of the reaction, a
magnetic nanocatalyst may be recovered magnetically from the
reaction medium, recycled, and reused.
TABLE-US-00002 TABLE B Common Chemical Structure Name Chemical Name
##STR00001## Paraoxon (diethyl p-nitrophenylphosphate) ##STR00002##
Parathion (diethyl p-nitrophenyl monothiophosphate) ##STR00003##
Methyl parathion (dimethyl p-nitrophenyl monothiophosphate)
##STR00004## O-chlorobenzyl-malononitirile ##STR00005## Malathion
([(dimethoxyphosphinothioyl)thio] butanedioic acid, diethyl ester)
##STR00006## Methoprene ((E,E)-11-methoxy-3,7,11-
trimethyl-2,4-do-decadienoic acid, 1-methylethyl ester)
##STR00007## DEET (N,N-diethyl-3-methylbenzamide) ##STR00008##
Atrazine (2-chloro-4-ethylamino-6- isopropyl-amine-s-triazine)
##STR00009## Azinphos- methyl (phosphorodithioic acid, O,O-
dimethyl S-[(4-oxo-1,2,3- benzotriazin-3(4H)-yl)methyl]ester)
##STR00010## Diazinon phosphorothioic acid O,O-diethyl
O-[6-methyl-2-(1-methylethyl)-4- pyrimidinyl] ester
[0046] In an alternate embodiment, a nanocatalyst of the invention
may be used to catalyze the hydrolysis or inactivation of a
chemical warfare agent. Non-limiting examples of chemical warfare
agents include Sarin, Lewisite, Soman, Tabun, VX,
chloroacetophenone (ClC.sub.6H.sub.4COCH.sub.3), bromobenzylcyanide
(BrC.sub.6H.sub.4CH.sub.2CN), and derivatives thereof. These and
other examples of chemical warfare agents are presented in Table C.
As described above for the environmental pollutants, a nanocatalyst
may inactivate a chemical warfare agent in water or soil under mild
reaction conditions. Furthermore, a magnetic nanocatalysts may be
magnetically recovered and recycled.
TABLE-US-00003 TABLE C Common Chemical Structure Name Chemical Name
##STR00011## Sarin (GB) (methylphosphonofluoridic acid
1-methylpropylester) ##STR00012## Lewisite dichloro((E)-2-
chlorovinyl)arsine ##STR00013## Soman (GD)
(methylphosphonofluoridic acid, 1,2,2- trimethylpropylester)
##STR00014## Tabun (GA) (dimethylphosphoramido- cyanidic acid,
ethyl ester) ##STR00015## VX (methylphosphonothioic acid,
S-[2-[bis-(1- methylethyl)amino]-o-ethyl ester]) ##STR00016##
cyclohexyl methylphosphonofluoridate (GF) ##STR00017##
phosphonofluoridic acid, ethyl-, isopropyl ester (GE) ##STR00018##
Phosphonothioic acid, ethyl- S-(2-(diethylamino)ethyl) O- ethyl
ester ##STR00019## Amiton S-2-(diethylamino)ethyl O,O-diethyl
phosphorothioate ##STR00020## VM S-2-(diethylamino)ethyl O- ethyl
methyl- phosphonothioate ##STR00021## Russian VX
S-2-(diethylamino)ethyl O- isobutyl methyl- phosphonothioate
##STR00022## (ethylbis(2- chloroethyl)amine) ##STR00023##
Mechloreth- amine (2-chloro-N-(2-chloroethyl)- N-methylethanamine)
##STR00024## Trichlormethine (tris(2-chloroethyl)amine)
##STR00025## Dichloroformo- xine hydroxycarbonimidic dichloride
##STR00026## diphenylcyanoarsine ##STR00027## cyanogen chloride
.ident.N hydrogen cyanide Cl--Cl chlorine ##STR00028##
trichloronitromethane ##STR00029## Diphosgene (trichloromethyl
chloroformate) ##STR00030## methyldichloroarsine ##STR00031##
phosgene ##STR00032## Sulfur Mustard (1,1'-thiobis(2-
chloroethane)) ##STR00033## (1-(2-(2-(2- chloroethylthio)ethoxy)-
ethylthio)-2-chloroethane) ##STR00034## ethyldichloroarsine
AsH.sub.3 Arsine (arsenic trihydride)
[0047] In still another embodiment, a nanocatalyst of the invention
may be used to catalyze the hydrolysis of esters in chemical
industrial processes. As an example, a magnetic nanocatalyst may be
utilized in an industrial saponification process. In general,
industrial saponification refers to the hydrolysis of a fatty acid
ester into an alcohol and the salt of a carboxylic acid (also
called a soap). Generally, vegetable oils and animal fats, which
are primarily triglycerides comprising glycerol esterified with
three fatty acids, are the starting materials. Typically, an
industrial saponification process is performed in the presence of a
strong base (NaOH or KOH) and heat. The products comprise free
glycerol and fatty acid salts. A nanocatalyst of the invention may
be used to catalyze the hydrolysis of the triglycerides at a
neutral pH and at a moderate temperature in the presence of a
cation. A magnetic nanocatalyst may be recovered and reused.
[0048] In yet another embodiment, a nanocatalyst of the invention
may be used to catalyze the hydrolysis of a phosphodiester bond in
a nucleic acid. The nucleic acid may comprise deoxyribonucleotides
or ribonucleotides, or a combination thereof. The nucleic acid may
be single-stranded or double-stranded. Non-limiting examples of
ribonucleic acids (RNA) include messenger RNA (mRNA), micro RNA
(miRNA), short interfering RNA (sRNA), and viral RNA. The
hydrolysis of a phosphodiester bond in a nucleic acid may be
targeted to a specific sequence by also attaching an
oligonucleotide, whose sequence is complementary to the sequence of
the target nucleic acid, to the nanoparticle. Thus, the
oligonucleotide attached to the nanoparticle may hybridize with the
target nucleic acid, such that the reactive species attached to the
nanoparticle catalyzes the hydrolysis of a phosphodiester bond in
the target nucleic acid.
[0049] The oligonucleotide attached to the nanoparticle may
comprise deoxyribonucleotides, ribonucleotides, or a combination
thereof. The nucleotides comprising the oligonucleotide may be
standard nucleotides or non-standard nucleotides, and the
nucleotides may be modified or derivatized nucleotides. The
nucleotides may be linked by phosphodiester bonds or
non-hydrolysable bonds, such as phosphorothioate or
methylphosphonate bonds. The oligonucleotide may also comprise
morpholinos, which are synthetic molecules in which bases are
attached to morpholino rings that are linked through
phosphorodiamidate groups. The oligonucleotide may also comprise
alternative structural types, such as peptide nucleic acids (PNA)
or locked nucleic acids (LNA). The length of the oligonucleotide
may range from about 4 nucleotides to about 30 nucleotides, and
more preferably from about 8 nucleotides to about 18
nucleotides.
[0050] As detailed above, the nucleic acid hydrolysis reactions may
be performed under mild conditions. The reactions may be performed
in vitro. The reactions may also be performed in vivo, for example,
in humans, animals, or plants. The method may further comprise an
initial heating step to denature the target nucleic acid, such that
the target nucleic acid may hybridize with the oligonucleotide
attached to the nanoparticle. Upon completion of the reaction, the
method may further comprise another heating step to denature and
release the cleaved product from the oligonucleotide attached to
the nanoparticle. Magnetic nanocatalysts may be recovered and
reused, as described above. One skilled in the art will appreciate
the applications of this embodiment. For example, a nanocatalyst
may be targeted to cleave a viral RNA molecule, such as HIV-1 tar
RNA. Further, nanocatalysts may be engineered for use in antisense
therapies for disease treatments.
(III) Method for Using a Nanocatalyst to Catalyze a Multiple Phase
Reaction
[0051] Yet another aspect of the present invention provides methods
for using the nanocatalysts of the invention to catalyze multiple
phase reactions. Multiple phase reactions may comprise two phases,
wherein a first reagent is immobilized on a matrix and a second
reagent is immobilized on a nanoparticle. Alternatively, multiple
phase reactions may comprise three phases, wherein a first reagent
is immobilized on a matrix, a second reagent is immobilized on a
nanoparticle, and a third reagent is either in solution or
immobilized on a second matrix. One skilled in the art will
appreciate that multiple phase reactions may also comprise four
phases, five phases, and so forth.
[0052] The composition of the matrix can and will vary depending
upon the application and the reaction being catalyzed. The matrix
may comprise a synthetic solid phase resins, such as 1-2%
divinylbenzene crosslinked polystyrene and its derivatives, or
non-crosslinked polystyrene and its derivatives. The matrix may
also comprise a synthetic or a semisynthetic polymer, as detailed
above in section (I)(a). Another suitable polymer is a ROMP gel,
which is synthesized by ring-opening metathesis polymerization
reactions. The matrix may comprise sol-gels, which are porous
materials consisting of inorganic oxides such as silica, alumina,
zirconia, stannic or tungsten oxide, or mixtures thereof. Sol-gels
that contain uniform pore dimensions are generally termed
monolithic sol-gels. The matrix may also comprise aerogels, which
are porous materials consisting of inorganic oxides such as silica,
alumina, zirconia, stannic or tungsten oxide, or mixtures thereof.
The pores of aerogels are usually filled with air instead of
solvents and water. The matrix may also comprise silica gels, glass
beads, zeolites, graphites, or derivatives thereof. Lastly, the
matrix may also comprise fluorotags, which usually refer to organic
functionalities or molecules containing multiple fluoro atoms or
polymers that have multiple fluoro atoms. Examples of molecules
containing fluorotags are 4-[3-(perfluorooctyl)propyl-1-oxy]benzyl
alcohol and
bis[diphenyl-[4-(1H,1H,2H,2H-perfluorodecyl)phenyl]phosphine]palladium
(II) chloride. Both molecules contain a C.sub.8F.sub.17 group.
[0053] A wide variety of chemical reactions may be performed using
multiple phase technologies. Non-limiting examples include coupling
reactions, condensation reactions, replacement reactions,
dehydration reactions, and hydrolysis reactions. In particular,
multiple phase reactions may be used to synthesize many different
types of molecules. For example, biopolymers (i.e., polypeptides,
nucleic acids), synthetic polymers, small organic molecules, etc.
may be synthesized in multiple phases. Thus, the nanocatalysts of
the invention, rather than traditional catalysts, may be used in a
variety of multiple phase chemical reactions.
[0054] In one embodiment, the method comprises contacting a
nanocatalyst with a substrate immobilized on a matrix. The
nanocatalyst comprises at least one reactive species attached to a
nanoparticle, whereby the reactive species catalyzes the reaction
to generate a product. The product may be immobilized on the matrix
or the product may be in solution. If the nanocatalyst is magnetic,
then the nanocatalyst may be magnetically separated from the matrix
and the product, such that the nanocatalyst may be recycled and
reused.
[0055] In another embodiment, the method further comprises
contacting the nanocatalyst and the immobilized first substrate
with a second substrate. The second substrate may be in solution or
the second substrate may be immobilized on a second matrix. As an
example, the reaction may be a Suzuki cross-coupling reaction (see
Example 4). For this reaction, the first substrate that is
immobilized on a matrix may be an aryl halogen, and the second,
soluble, substrate may be an arylboronic acid. The nanocatalyst may
comprise palladium (i.e., Pd--NHC) attached to a metal oxide
nanoparticle (see Example 3). The reaction may be performed at pH
values that range from about 6.0 to about 9.0. The temperature of
the reaction may range from about 20.degree. C. to about
100.degree. C. The duration of the reaction may range from about 1
hour to about 10 days. In a preferred embodiment, the pH of the
reaction may be about 7.0, the temperature of the reaction may be
about 80.degree. C., and the duration of the reaction may be about
6 days.
IV. A Process for Making a Nanocatalyst
[0056] Still another aspect of the present invention encompasses a
method for making a nanocatalyst comprising at least one reactive
species attached to a metal oxide nanoparticle. The method
comprises mixing one hydroxyl-containing compound carrying the
reactive species with a metal oxide nanoparticle coated with a
hydrophobic surfactant. During the mixing step, the
hydroxyl-containing compound replaces the hydrophobic surfactant on
the surface of the metal oxide nanoparticle, thus forming the
nanocatalyst (see Example 1 and Example 3).
[0057] The hydroxy-containing compound may be an alcohol, a diol,
an ethenediol (e.g, dopamine), a carboxylic acid, or a hydroxide.
In a preferred embodiment, the hydroxy-containing compound may be
dopamine. In another preferred embodiment, the hydroxy-containing
compound may be silicon hydroxide.
[0058] The reactive species may be an amino acid with a reactive
side chain, such as aspartic acid, cysteine, glutamic acid,
histidine, lysine, and serine. The reactive species may also be a
compound containing a catalyst atom, such as palladium. Methods
known in the art may be used to couple the reactive
species-containing compound to the hydroxy-containing compound.
[0059] The hydrophobic surfactant coating the metal oxide
nanoparticle may be a saturated long chain fatty acid, an
unsaturated long chain fatty acid, or a mixture thereof. The fatty
acid may comprise from about 14 carbons to about 22 carbons. In a
preferred embodiment, the hydrophobic surfactant may be oleic acid.
The metal oxide nanoparticle may be an iron oxide, such as
magnetite (Fe.sub.3O.sub.4) or maghemite (Fe.sub.2O.sub.3).
[0060] The process comprises mixing the derivatized
hydroxyl-containing compound and the coated nanoparticle. The
mixing may comprise sonication for a period of time. The time may
range from about 0.5 hour to about 15 hours, preferably from about
2 hours to 10 hours, and more preferably about 6 hours. During the
mixing step the hydroxyl-containing compounds replace the oleic
acid molecules coating the surface of the nanoparticle, such that
the hydroxyl-containing compounds become attached to the surface of
the nanoparticle.
DEFINITIONS
[0061] To facilitate understanding of the invention, a number of
terms are defined below:
[0062] The term "alkyl" embraces linear, cyclic or branched
hydrocarbon radicals having one to about twenty carbon atoms or,
preferably, one to about twelve carbon atoms. Examples of such
radicals include methyl, ethyl, n-propyl, isopropyl, n-butyl,
isobutyl, sec-butyl, tert-butyl, pentyl, iso-amyl, hexyl and the
like.
[0063] The term "alkenyl" embraces linear or branched hydrocarbon
radicals having at least one carbon-carbon double bond of two to
about twenty carbon atoms or, preferably, two to about twelve
carbon atoms. Examples of alkenyl radicals include ethenyl,
propenyl, allyl, propenyl, butenyl and 4-methylbutenyl.
[0064] The term "alkynyl" denotes linear or branched carbon or
hydrocarbon radicals having at least one carbon-carbon triple bond
of two to about twenty carbon atoms or, preferably, two to about
twelve carbon atoms. Examples of such radicals include propargyl,
butynyl, and the like.
[0065] The term "aryl" as used herein alone or as part of another
group denote optionally substituted homocyclic aromatic groups,
preferably monocyclic or bicyclic groups containing from 6 to 12
carbons in the ring portion, such as phenyl, biphenyl, naphthyl,
substituted phenyl, substituted biphenyl or substituted
naphthyl.
[0066] A "catalyst" refers to a substance that enables a chemical
or biological reaction to proceed at a faster rate or under
different conditions (as at a lower temperature) than otherwise
possible. The catalyst itself is not consumed during the overall
reaction.
[0067] "Complimentary" refers to the natural association of nucleic
acid sequences by base-pairing (5'-A G T-3' pairs with the
complimentary sequence 3'-T C A-5'). Complementarity between two
single-stranded molecules may be partial, if only some of the
nucleic acids pair are complimentary, or complete, if all bases
pair are complimentary.
[0068] The term "heterocyclic" as used herein alone or as part of
another group denote optionally substituted, fully saturated or
unsaturated, monocyclic or bicyclic, aromatic or nonaromatic groups
having at least one heteroatom in at least one ring, and preferably
5 or 6 atoms in each ring.
[0069] The term "hydrocarbyl" as used herein describe organic
compounds or radicals consisting exclusively of the elements carbon
and hydrogen. These moieties include alkyl, alkenyl, alkynyl, and
aryl moieties. These moieties also include alkyl, alkenyl, alkynyl,
and aryl moieties substituted with other aliphatic or cyclic
hydrocarbon groups, such as alkaryl, alkenaryl and alkynaryl.
Unless otherwise indicated, these moieties preferably comprise 1 to
20 carbon atoms.
[0070] The term "hybridize" refers to the process of annealing,
base pairing, or hydrogen bonding between the nucleotides of two
single stranded nucleic acids.
[0071] The term "hydrolyzing" or "hydrolyze" or "hydrolysis" refers
to a chemical process of decomposition involving the splitting of a
bond and the addition of the hydrogen cation and the hydroxide
anion of water or the alkoxide or aryloxide anion of an alcohol or
the thiolate ion of a thiol alcohol.
[0072] The term "linker" as used herein refers to a molecule with
at least two functional groups, such that the linker is disposed
between the reactive species (or a compound containing the reactive
species) and the nanoparticle.
[0073] The term "nucleic acid," as used herein, refers to sequences
of linked nucleotides. The nucleotides may be deoxyribonucleotides
or ribonucleotides. The nucleic acid may be single-stranded or
double-stranded.
[0074] The term "oligonucleotide" refers to a short nucleic acid,
i.e., less than about 50 nucleotides.
[0075] A "polymer" is a chemical compound or mixture of compounds
consisting essentially of repeating structural units. Polymers
include, but are not limited to natural, synthetic, and
semi-synthetic polymers.
[0076] The "substituted hydrocarbyl" moieties described herein are
hydrocarbyl moieties which are substituted with at least one atom
other than carbon, including moieties in which a carbon chain atom
is substituted with a hetero atom such as nitrogen, oxygen,
silicon, phosphorous, boron, sulfur, or a halogen atom. These
substituents include halogen, carbocycle, aryl, heterocyclo,
alkoxy, alkenoxy, alkynoxy, aryloxy, hydroxy, protected hydroxy,
keto, acyl, acyloxy, nitro, amino, amido, nitro, cyano, thiol,
ketals, acetals, esters and ethers.
[0077] The following examples are included to demonstrate preferred
embodiments of the invention. It should be appreciated by those of
skill in the art that the techniques disclosed in the examples that
follow represent techniques discovered by the inventors to function
well in the practice of the invention. However, those of skill in
the art should, in light of the present disclosure, appreciate that
many changes can be made in the specific embodiments that are
disclosed and still obtain a like or similar result without
departing from the spirit and scope of the invention, therefore all
matter set forth or shown in the accompanying drawings is to be
interpreted as illustrative and not in a limiting sense.
EXAMPLES
[0078] The following examples illustrate various embodiments of the
invention.
Example 1
Synthesis of Iron Oxide Nanoparticle-Amino Acid Complexes
[0079] Chemicals and organic solvents mentioned below were
purchased from Aldrich (Milwaukee, Wis.) or Acros Organics
(Pittsburgh, Pa.) and used as received. Water was obtained from a
Milli-Q water system purchased from Millipore Corporation (Milford,
Mass.). The heavy metal and bacterial contaminant levels in Milli-Q
water were below 10 parts per billion. Permanent magnets were
purchased from Dexter Magnetic Technologies Inc. (Elk Grove
Village, Ill.).
[0080] To generate amino acid-linked nanocatalysts, amino acids
with a carboxylate, a basic or a nucleophilic group on the side
chain, such as Asp, Glu, His, and Lys, were attached to dopamine
(4-(2-aminoethyl)benzene-1,2-diol) using standard procedures
(Organic Letters 2006, 8, 3215). The .alpha.-amino groups of the
amino acids were acylated to mimic the amide bonds of the enzyme
backbones. Exchange-replacement reactions were conducted by mixing
0.06 mmol of an amino acid dopamine derivative in 1 mL of
CHCl.sub.3 and 1 mL of methanol with 60 mg of .about.12-nm
maghemite (Fe.sub.2O.sub.3) nanoparticles coated with oleate
(Nature Mater. 2004, 3, 891; J. Colloid Interface Sci. 2003, 258,
427). For nanoparticles coated with two amino acids, 0.03 mmol of
each amino acid residue was utilized in the exchange reaction. The
mixture was sonicated for 6 h. The reaction is diagrammed in FIG.
2. Magnetic nanoparticles were magnetically concentrated and washed
with CH.sub.2Cl.sub.2 (20 mL.times.4) and methanol (20 mL.times.4)
sequentially.
Example 2
Catalysis of Phosphoester, Carboxylic Ester, and Phosphodiester
Bonds by Iron Oxide Nanoparticle-Amino Acid Complexes
[0081] The maghemite nanoparticle-amino acid complexes prepared in
Example 1 were used to catalyze hydrolysis reactions using paraoxon
(diethyl p-nitrophenylphosphate), 4-nitrophenyl acetate, an RNA
construct (UpU), or a DNA construct (dApdT) as substrates (FIG. 3).
The general procedure involved introducing a nanocomplex (amino
acid concentration 0.06 mM) to a solution of substrate (0.5 mM) in
2 mL of Milli-Q water at 37.degree. C. After 48 h, the nanocomplex
was magnetically concentrated and removed from the solution (Org.
Lett. 2006, 8, 3215). The solution was then subjected to HPLC
analyses using an internal standard for the conversion yield of the
substrate. The structures of the hydrolytic products were confirmed
by LC-MS experiments. Each experiment was repeated at least two
times.
[0082] The hydrolysis of the phosphoester bond of paraoxon (FIG.
3A) by the different nanoparticle-amino acid complexes is presented
in Table 1. Nanoparticles coated with Asp and His analogues
(Fe.sub.2O.sub.3-Asp-His) (Entry 8, Table 1) exhibited the highest
catalytic activity. For example, after 48 h, 77% of paraoxon was
hydrolyzed using Fe.sub.2O.sub.3-Asp-His; after 96 h, a conversion
yield of 92% was achieved. In contrast, a mixture of Asp and His
without a nanoparticle support (Entry 20) led to a conversion yield
of less than 1%. Within the margin of experimental error, the
unsupported amino acid pair showed no catalytic activity in the
hydrolysis of paraoxon. On the other hand, the nanoparticle support
itself does not appear to be a catalyst, as entry 1 showed that
after 48 h less than 1% of paraoxon was hydrolyzed by maghemite
nanoparticles without a shell of amino acid coatings. Nanoparticles
protected with other dyad pairs of amino acids (Entries 9-19, Table
1) were less active catalysts than Fe.sub.2O.sub.3-Asp-His. For
example, the nanocomplex with Glu and His led to a conversion yield
of 51% after 48 h (Entry 12), which is lower than that of a dyad of
Asp and His despite the fact that the structures of Asp and Glu are
similar to each other. Kinetic studies suggested that the
hydrolysis of paraoxon by Fe.sub.2O.sub.3-Asp-His fits into the
Michaelis-Menten model. Analysis of the Lineweaver-Burk plot gave
K.sub.M=1.1 mM and k.sub.cat=4.3.times.10.sup.-5s.sup.-1 in a pH
7.4 buffer at 40.degree. C. for Fe.sub.2O.sub.3-Asp-His. The
Fe.sub.2O.sub.3-Asp-His nanocomplex was also used to catalyze the
hydrolysis of paraoxon at ambient temperature (25.degree. C.), and
it was found to be about 10-fold slower than at 37.degree. C.
TABLE-US-00004 TABLE 1 Cleavage of Paraoxon by 12 nm Maghemite
Nanoparticle-Supported Amino Acids Conversion Entry Amino Acid
Yield (%) 1 Nanoparticle.sup.a <1 2 Asp 5 3 Cys 15 4 Glu <1 5
His 6 6 Lys 2 7 Ser 4 8 Asp + His 77/92.sup.b 9 Asp + Lys 27 10 Asp
+ Cys 25 11 Asp + Ser 28 12 Glu + His 51 13 Glu + Lys 50 14 Glu +
Cys 44 15 Glu + Ser 45 16 His + Cys 30 17 His + Ser 40 18 Lys + Ser
17 19 Lys + Cys 39 20 Asp, His.sup.c <1 .sup.a12 nm maghemite
nanoparticles coated with oleate (no amino acids attached).
.sup.bReaction time: 96 h. .sup.cUn-supported Asp (0.14 mM) and His
(0.14 mM) and paraoxon (0.5 mM) in 2 mL of Milli-Q water at
37.degree. C. for 48 h.
[0083] Table 2 presents the cleavage of the carboxylic ester bond
of 4-nitrophenyl acetate (FIG. 3B) by the nanoparticle-amino acid
complexes. Most of the nanocomplexes coated with pairs of amino
acids were effective catalysts (Entries 8-18, Table 2), with
conversion yields generally greater than 50%. The
Fe.sub.2O.sub.3-Cys-Lys, Fe.sub.2O.sub.3-Lys-Ser, and
Fe.sub.2O.sub.3-Asp-His nanocomplexes had the highest catalytic
activity of 84%, 76%, and 67%, respectively. Nanoparticles coated
with oleic acid and no attached amino acids (Entry 19) had no
catalytic activity.
TABLE-US-00005 TABLE 2 Cleavage of 4-Nitrophenyl Acetate by 12 nm
Maghemite Nanoparticle- Supported Amino Acids Conversion Entry
Amino Acid Yield (%) 1 blank <1 2 Asp 30 3 Cys 27 4 Glu 12 5 His
24 6 Lys 19 7 Ser 28 8 Asp + His 67 9 Asp + Ser 54 10 Asp + Lys 54
11 Cys + His 57 12 Cys + Glu 54 13 Glu + Lys 56 14 Glu + Ser 55 15
Cys + Lys 84 16 His + Ser 54 17 Lys + Ser 76 18 Glu + His 10 19
Nanoparticle- <1 oleate.sup.a .sup.ap-nitrophenyl acetate (1 mM)
and maghemite nanoparticles coated with oleate (no amino acid
residues on the surfaces) (2 mg) in 2 mL of pH 7.4 phosphate buffer
(0.05 mM) at 35.degree. C. for 12 h.
[0084] RNA or DNA constructs were exposed to the
Fe.sub.2O.sub.3-Asp-His nanocomplex as detailed above. This
nanocomplex completely hydrolyzed the phosphodiester bond of UpU
(FIG. 3C) and dApdT (FIG. 3D).
Example 3
Synthesis of Iron Oxide Nanoparticle-Pd Complexes
[0085] To make the Pd-containing nanocomplexes, about 60 mg of
11-nm .gamma.-Fe.sub.2O.sub.3 nanocrystals coated with oleate in 50
mL of chloroform was treated with (3-chloropropyl)trimethoxysilane
(1 mL, 5.48 mmol). The resulting solution was then brought to
reflux. After 12 h, the solution was cooled down to ambient
temperature. Nanoparticles were magnetically concentrated by using
an external permanent magnet and washed with toluene (2.times.50
mL), 0.1 M HCL (2.times.50 mL) and methanol (2.times.50 mL). The
resulting nanoparticles were air-dried. Such nanoparticles were
re-dissolved in 45 mL of dry toluene and then N-methylimidazole
(0.75 mL, 9.41 mmol) in 5 mL of toluene was added. The resulting
solution was brought to reflux and after 16 h, it was cooled down
to room temperature. Nanoparticles were then magnetically
concentrated and washed with toluene, HCl and methanol
sequentially.
[0086] About 100 mg of the aforementioned magnetic nanoparticles
were re-dissolved in a mixture of DMF (2 mL) and Na.sub.2CO.sub.3
aqueous solution (0.5 M, 2 mL) in the presence of Pd(OAc).sub.2 (22
mg, 98 .mu.mol). After 16 h at 50.degree. C., the mixture was
cooled down to room temperature. The nanoparticle-Pd complexes were
magnetically concentrated and washed with water (3.times.50 mL),
0.1 M HCl (3.times.50 mL), methanol (3.times.50 mL) and air-dried.
The amount of Pd on the nanoparticles was determined via elemental
analysis. TEM measurements and elemental analyses were employed for
the structure of Iron Oxide-Pd.
Example 4
Use of Iron Oxide-Pd Complexes in Solid Phase Suzuki Cross-Coupling
Reactions
[0087] The reaction scheme is presented in FIG. 4. A typical
solid-phase Suzuki cross-coupling reaction was as follows. First, a
solid phase polystyrene resin (1% divinylbenzene crosslinked,
200-400 mesh) was loaded with aryl halogens (J. Org. Chem. 2006,
71, 537). Then, the aforementioned resin (1.22 g) loaded with an
aryl halogen (1 mmol) was added to a mixed suspension of the
arylboronic acid (2 mmol) and K.sub.2CO.sub.3 (2 mmol) in 20 mL of
DMF containing Iron Oxide-Pd (4 nm) (30 mg, 0.87 mol %). The
mixture was heated to 80.degree. C. and was maintained at this
temperature for 6 days. Iron Oxide-Pd was magnetically concentrated
using an external permanent magnet. To this end, the mixture was
vigorously shaken. A permanent magnet was then applied externally.
Magnetic nanoparticles were concentrated on the sidewalls of the
tube (horizontal direction) while some resins were suspended in
solution or precipitate at the bottom of the tube (vertical). The
suspended and precipitated resins, as well as the solution, were
transferred out of the tube using a pipette. This process usually
needed to be repeated more than eight times to ensure that most of
nanoparticles were removed from resins. Iron Oxide-Pd was then
washed with methanol (10.times.200 mL). Afterwards, magnetic
nanoparticles were further washed with water (5.times.100 mL) and
methanol (5.times.100 mL). The nanoparticles were then air-dried
and used directly for a new round of Suzuki reaction.
[0088] The resins and excessive arylborate were separated via
filtration. The beads were recovered as the filter and subsequently
washed with methanol (5.times.100 mL) and water (5.times.100 mL).
The cleavage of the Suzuki product out of the resins was achieved
by adding the solid-phase beads (1.18 g) and NaOH (2 mmol) to a
mixture of ethanol (15 mL) and water (15 mL). The mixture was
heated to reflux and stirred at this temperature for 2 days. After
cooling down to ambient temperature, resins were filtered off and
the filtrate was neutralized with 1 M HCl to pH 7. Solvents were
removed in vacuo and the residues were extracted with ethyl acetate
(10.times.50 mL). The combined organic solutions were dried over
anhydrous Na.sub.2SO.sub.4 and subjected to HPLC and NMR analyses.
A simple recrystallization step was also employed using
EtOH/H.sub.2O to improve the purity of the Suzuki product. The
structures of isolated Suzuki products were determined by .sup.1H
NMR, IR and high-resolution MS. HPLC analyses of isolated products
after recrystallization showed that high purity (>99%) was
obtained. A UV detector with a fixed wavelength of 254 nm was
employed for signal detection. A typical HPLC analysis program used
a solvent gradient starting from 40% H.sub.2O in CH.sub.3CN to 10%
H.sub.2O in CH.sub.3CN in 6 min followed by 10% H.sub.2O in
CH.sub.3CN for additional 9 min with a flow rate of 0.5 mL/min.
[0089] The yields of the solid-phase cross-coupling products were
summarized in Table 3. The Iron Oxide-Pd nanocomplex effectively
catalyzed these reactions.
TABLE-US-00006 TABLE 3 Suzuki Cross-Coupling of Aryl Halogens (on
Resins) and Arylboronic Acids (in Solution) under Iron Oxide-Pd (4
nm). Suzuki product.sup.b entry Y.sup.a borate yield (%).sup.c
purity (%).sup.d 1 o-I ##STR00035## 78 >99 2 o-I ##STR00036## 63
>99 3 o-I ##STR00037## 71 >99 4 o-I ##STR00038## 77 >99 5
o-Br ##STR00039## 62 >99 .sup.aSee FIG. 4, Y = substitution on
phenyl ring. .sup.bSuzuki products were cleaved from resins and
purified via recrystallization steps. .sup.cAverage of at least two
runs. .sup.dPurity was determined by HPLC analyses and the
structures of Suzuki products were confirmed by .sup.1H NMR and
MS.
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