Preparation of Organosoluble Silica−Polypeptide Particles by “Click” Chemistry

Silica hairy nanoparticles: a promising material for self-assembling processes

"Hairy" nanoparticles (HNPs), i.e. inorganic NPs functionalized with polymer chains, are promising building blocks for the synthesis of advanced nanocomposite (NC) materials having several technological applications. Recent evidence shows that HNPs self-organize in a variety of anisotropic structures, resulting in an improvement of the functional properties of the materials, in which are embedded. In this paper, we propose a three-step colloidal synthesis of spherical SiO₂-HNPs, with controlled particle morphology and surface chemistry. In detail, the SiO₂ core, synthesized by a modified Stöber method, was first functionalized with a short-chain amino-silane, which acts as an anchor, and then covered by maleated polybutadiene (PB), a rubbery polymer having low glass transition temperature, rarely considered until now. An extensive investigation by a multi-technique analysis demonstrates that the synthesis of SiO₂-HNPs is simple, scalable, and potentially applicable to different kind of NPs and polymers. Morphological analysis shows the overall distribution of SiO₂-HNPs with a certain degree of spatial organization, suggesting that the polymer coating induces a modification of NP-NP interactions. The role of the surface PB brushes in influencing the special arrangement of SiO₂-HNPs was observed also in cis-1,4-polybutadiene (cis-PB), since the resulting NC exhibited the particle packing in "string-like" superstructures. This confirms the tendency of SiO₂-HNPs to self-assemble and create alternative structures in polymer NCs, which may impart them peculiar functional properties.

Poly(ethylene oxide) grafted silica nanoparticles: efficient routes of synthesis with associated colloidal stability

In this study, poly(ethylene oxide) monomethyl ether (MPEO) of molecular weight of 5000, 10 000, and 20 000 g mol-1 were grafted onto colloidal silica nanoparticles (NPs) of a 27.6 nm diameter using two distinct "grafting to" processes. The first method was based on the coupling reaction of epoxide-end capped MPEO with amine-functionalized silica NPs, while the second method was based on the condensation of triethoxysilane-terminated MPEO onto the unmodified silica NPs. The influence of PEO molecular weight, grafting process and grafting conditions (temperature, reactant concentration, reaction time) on the PEO grafting density was fully investigated. Thermogravimetric analysis (TGA) was used to determine the grafting density which ranged from 0.12 chains per nm2 using the first approach to 1.02 chains per nm2 when using the second approach. 29Si CP/MAS NMR characterization indirectly revealed that above a grafting density value of 0.3 PEO chains per nm2, a dendri-graft PEO network was built around the silica surface which was composed of PEO chains directly anchored to the silica surface and those grafted to silica NPs by intermediate of >CH-O-Si- bonds. The colloidal stability of the particles during different steps of the grafting process was characterized by small-angle X-ray scattering (SAXS). We have found that the colloidal systems are stable whatever the achieved grafting density due to the strong repulsions between the NPs, with the strength of repulsion increasing with the molecular weight of the grafted MPEO chains.

Adsorption of Myoglobin and Corona Formation on Silica Nanoparticles

The adsorption of proteins from aqueous medium leads to the formation of protein corona on nanoparticles. The formation of protein corona is governed by a complex interplay of protein-particle and protein-protein interactions, such as electrostatics, van der Waals, hydrophobic, hydrogen bonding, and solvation. The experimental parameters influencing these interactions, and thus governing the protein corona formation on nanoparticles, are currently poorly understood. This lack of understanding is due to the complexity in the surface charge distribution and anisotropic shape of the protein molecules. Here, we investigate the effect of pH and salinity on the characteristics of corona formed by myoglobin on silica nanoparticles. We experimentally measure and theoretically model the adsorption isotherms of myoglobin binding to silica nanoparticles. By combining adsorption studies with surface electrostatic mapping of myoglobin, we demonstrate that a monolayered hard corona is formed in low salinity dispersions, which transforms into a multilayered hard + soft corona upon the addition of salt. We attribute the observed changes in protein adsorption behavior with increasing pH and salinity to the change in electrostatic interactions and surface charge regulation effects. This study provides insights into the mechanism of protein adsorption and corona formation on nanoparticles, which would guide future studies on optimizing nanoparticle design for maximum functional benefits and minimum toxicity.

Nature-Inspired and "Water-Skating" Paper and Polyester Substrates Enabled by the Molecular Structure of Poly(γ-stearyl-α,l-glutamate) Homopolypeptide

We demonstrate that the molecular structure of a synthetic homopolypeptide that resembles the leg architecture of water strider insects is effective to impart flexible polymeric surfaces with superhydrophobic behavior. Filter paper (FP) and polyester (PET) were modified with a coating consisting of low-molecular weight α-helical poly(γ-stearyl-α,l-glutamate) (PSLG, M_w = 4500 Da) homopolypeptide. PSLG-coated substrates displayed near to and superhydrophobic behavior (≥150°) as reflected by the contact angle values. Despite being physically adsorbed, the PSLG coating uniformly covered and was strongly adhered to the substrate surfaces. The thin coating layer displayed remarkable mechanical abrasion resistance and was insensitive to long-time exposure to ambient conditions. PLSG-coated textile fibers exhibited useful and interesting properties. Under an iron-containing load, PSLG-coated PET was able to float and "walk" on water when exposed to a magnet. The PSLG coating was able to reduce the adhesion of Escherichia coli, model Gram-negative bacteria. The results indicated that the molecular geometry of PSLG homopolypeptide, which possesses a α-helical backbone sprouting out of highly hydrophobic stearyl side chains, was the key feature responsible for the observed behaviors. This study is relevant for a broad range of potential applications: from crop and drinking water management in arid geographic areas to biomedical devices and implants.

Fabrication of device with poly(N-isopropylacrylamide)-b-ssDNA copolymer brush for resistivity study

In this study, we grafted bromo-terminated poly(N-isopropylacrylamide) (PNIPAAm) brushes onto thin gold films deposited on silicon, and then reacted with NaN₃ to produce azido-terminated PNIPAAm brushes. A probe sequence of single-stranded DNA (ssDNA) with a 4-pentynoic acid succinimidyl ester unit was grafted onto the azido-terminated PNIPAAm brushes through a click reaction, resulting in the formation of block copolymer brushes. The PNIPAAm-b-ssDNA copolymer brushes formed supramolecular complexes stabilized by bio-multiple hydrogen bonds (BMHBs), which enhanced the proton transfer and thereby decreased the resistivity of the structures. In addition, the optimal operation window for DNA detection ranges from 0 to 0.2 M of NaCl concentration. Therefore, the specimens were prepared in the PBS solution at 150 mM NaCl concentration for target hybridization. The supramolecular complex state of the PNIPAAm-b-ssDNA copolymer brushes transformed into the phase-separated state after the hybridization with 0.5 ng/µL of its target DNA sequence owing to the competition between BMHBs and complementary hydrogen bonds. This phase transformation of the PNIPAAm and probe segments inhibited the proton transfer and significantly increased the resistivity at 25 °C. Moreover, there were no significant changes in the resistivity of the copolymer brushes after hybridization with the target sequence at 45 °C. These results indicated that the phase-separated state of the PNIPAAm-b-ssDNA copolymer brushes, which was generally occurred above the LCST, can be substantially generated after hybridization with its target DNA sequence. By performing the controlled experiments, in the same manner, using another sequence with lengths similar to that of the target sequence without complementarity. In addition, the sequences featuring various degrees of complementarity were exploited to verify the phase separation behavior inside the PNIPAAm-b-ssDNA copolymer thin film.

Domed Silica Microcylinders Coated with Oleophilic Polypeptides and Their Behavior in Lyotropic Cholesteric Liquid Crystals of the Same Polypeptide

Liquid crystals can organize dispersed particles into useful and exotic structures. In the case of lyotropic cholesteric polypeptide liquid crystals, polypeptide-coated particles are appealing because the surface chemistry matches that of the polymeric mesogen, which permits a tighter focus on factors such as extended particle shape. The colloidal particles developed here consist of a magnetic and fluorescent cylindrically symmetric silica core with one rounded, almost hemispherical end. Functionalized with helical poly(γ-stearyl-l-glutamate) (PSLG), the particles were dispersed at different concentrations in cholesteric liquid crystals (ChLC) of the same polymer in tetrahydrofuran (THF). Defects introduced by the particles to the director field of the bulk PSLG/THF host led to a variety of phases. In fresh mixtures, the cholesteric mesophase of the PSLG matrix was distorted, as reflected in the absence of the characteristic fingerprint pattern. Over time, the fingerprint pattern returned, more quickly when the concentration of the PSLG-coated particles was low. At low particle concentration the particles were "guided" by the PSLG liquid crystal to organize into patterns similar to that of the re-formed bulk chiral nematic phase. When their concentration increased, the well-dispersed PSLG-coated particles seemed to map onto the distortions in the bulk host's local director field. The particles located near the glass vial-ChLC interfaces were stacked lengthwise into architectures with apparent two-dimensional hexagonal symmetry. The size of these "crystalline" structures increased with particle concentration. They displayed remarkable stability toward an external magnetic field; hydrophobic interactions between the PSLG polymers in the shell and those in the bulk LC matrix may be responsible. The results show that bio-inspired LCs can assemble suitable colloidal particles into soft crystalline structures.

Intimate organic-inorganic nanocomposites via rationally designed conjugated polymer-grafted precursors

Semiconducting organic-inorganic nanocomposites comprising the conjugated polymer poly(3-hexylthiophene) (P3HT) in intimate contact with CdSe nanocrystals were crafted by exploiting rationally designed P3HT-grafted cadmium precursors (i.e., Cd-P3HT complexes). The bifunctional ligand 4-bromobenzyl phosphonic acid (BPA-Br) that possesses two terminal functional groups at each end was employed, enabling the coordination of BPA-Br with Cd first to yield Cd-phosphonic acid complexes (Cd-BPA-Br) followed by the subsequent substitution of the bromide moiety into the azide (N3) group to form N3-functionalized Cd-phosphonic acid complexes (Cd-BPA-N3). Cd-P3HT complexes were then synthesized via a click reaction between Cd-BPA-N3 and ethynyl-terminated P3HT (P3HT-[triple bond, length as m-dash]). The success of the click reaction was confirmed by spectroscopic measurements. The morphology of CdSe nanocrystals (i.e., quantum dot and multi-branched) in P3HT-CdSe nanocrystal nanocomposites can be altered by tuning the concentration of Cd-P3HT complexes and the addition of excess Cd-BPA-Br (i.e., Cd-P3HT solely for the synthesis of CdSe quantum dots, and Cd-P3HT and Cd-BPA-Br at the ratio Cd-P3HT : Cd-BPA-Br = 1 : 1 for the synthesis of multi-branched CdSe nanocrystals). The photophysical properties of the resulting P3HT-CdSe nanocomposites were examined via absorption and photoluminescence studies. In comparison with P3HT-[triple bond, length as m-dash], the significant emission quenching of nanocomposites suggested the efficient charge transfer at the P3HT/CdSe interface. It is noteworthy that the implementation of judiciously synthesized Cd-P3HT complexes as precursors rendered the in situ synthesis of P3HT-CdSe nanocrystal nanocomposites, dispensing with the need for the use of insulating aliphatic ligands and tedious ligand exchange procedures for the preparation of functional polymer-tethered nanocrystals.

Preparation of Metalloporphyrin-Bound Superparamagnetic Silica Particles via "Click" Reaction

A facile approach using click chemistry is demonstrated for immobilization of metalloporphyrins onto the surface of silica-coated iron oxide particles. Oleic-acid stabilized iron oxide nanocrystals were prepared by thermal decomposition of iron(III) acetylacetonate. Their crystallinity, morphology, and superparamagnetism were determined using X-ray diffraction, transmission electron microscopy, and a superconducting quantum interference device. Monodisperse core-shell particles were produced in the silica-coating of iron oxide via microemulsion synthesis. Surface modification of these particles was performed in two steps, which included the reaction of silica-coated iron oxide particles with 3-bromopropyltrichlorosilane, followed by azido-functionalization with sodium azide. Monoalkylated porphyrins were prepared using the Williamson ether synthesis of commercially available tetra(4-hydroxyphenyl) porphyrin with propargyl bromide in the presence of a base. (1)H NMR and matrix-assisted laser desorption ionization confirmed the identity of the compounds. The prepared monoalkyne porphyrins were zinc-metalated prior to their introduction to azide-functionalized, silica-coated iron oxide particles in the click reaction. X-ray photoelectron spectroscopy, thermogravimetric analysis, and Fourier transform infrared spectroscopy were used to characterize the surface chemistry after each step in the reaction. In addition, particle size was determined using dynamic light scattering and microscopy. The presented methodology is versatile and can be extended to other photoreactive systems, such as phthalocyanines and boron-dipyrromethane, which may lead to new materials for optical, photonic, and biological applications.

Efficient synthesis of polyoxazoline-silica hybrid nanoparticles by using the “grafting-onto” approach

The first preparation of silica hybrid nanoparticles by comparing the click chemistry approach with the silane coupling of α-telechelic poly(2-methyl-2-oxazoline)s is reported.

Advances in click chemistry for silica-based material construction

Click chemistry is undoubtedly the most powerful 1,3-dipolar cycloaddition reaction in organic synthesis.

Amphiphilic glycosylated block copolypeptides as macromolecular surfactants in the emulsion polymerization of styrene

Bio-inspired amphiphilic block copolymer surfactants fully derived from amino acids and sugars are synthesised. The materials are successfully employed in the synthesis of polystyrene latexes by emulsion polymerization.

Surface-initiated controlled radical polymerizations from silica nanoparticles, gold nanocrystals, and bionanoparticles

This review summarizes recent progress in surface-initiated controlled radical polymerizations from silica nanoparticles, gold nanocrystals, and bionanoparticles.

Polymer-nanocomposite brush-like architectures as an all-solid electrolyte matrix

Herein, we report on polymer-nanocomposites with brush-like architectures and evaluate their feasibility as an all-solid electrolyte matrix supporting Li(+)-ion conduction. Showcased as a first example in the domain of electrolyte research, the study probes several key factors, such as (i) core morphology, (ii) surface modifiers/functionality, (iii) grafting length, and (iv) density of the brushes, and determines their role on the overall electrochemical properties of these nanostructured organic-inorganic hybrids. Nanostructured titania was synthesized via wet-chemical approaches using either controlled hydrolysis or hydrothermal methods. Exercising suitable control on reaction parameters led to well-defined morphologies/phases, such as nanoparticles, nanospindles, nanourchins, nanorods or nanotubes, in either anatase, rutile or mixed forms. Covalent anchoring on titania nanostructures was achieved using dopamine, gallic acid and glycerol as small organic moieties. A one-pot process of priming the available surface functional groups postmodification with isocyanate chemistry was followed by grafting polyethylene glycol monomethyl ethers of desired chain lengths. Finally, complexation with lithium salt yielded electrolyte compositions where the ethylene oxide (EO) fractions aid in ion-solvation with ease. The synthesized materials were characterized in detail employing XRD, TEM, DRS-UV, FTIR, micro-Raman, TG-DTA and DSC at each stage to confirm the products and ascertain the physicochemical properties. Comprehensive evaluation using temperature-step electrochemical impedance spectroscopy (EIS) of these brush-like nanocomposites provided crucial leads toward establishing a plausible physical model for the system and understanding the mechanism of ion transport in these all-solid matrices. The preliminary results on ionic conductivity (σ) obtained for some of the compositions are estimated to be within the range of ∼10(-4) to 10(-5) S cm(-1) in the temperature window of the study that holds excellent promise for further improvement.

Polyelectrolyte complex-silica hybrid colloidal particles decorated with different polyelectrolytes

We report the synthesis of polyelectrolyte-decorated hybrid colloidal particles by using negatively charged polyelectrolyte complex (PEC) micelles as colloidal templates for silica mineralization under ambient conditions. The negatively charged polyelectrolytes including poly(acrylic acid) (PAA), poly(L-glutamic acid) (PLGA), and poly(styrene sulfonate) (PSS) were complexed with poly(L-lysine) at non-stoichiometric mixing weight percentage to form negatively charged PEC micelles. Varying the mixing weight percentage and molecular weight of polyelectrolytes led to the changes in the size and charge of the PEC particles. Silica mineralization in the complex core resulted in the colloidally stable hybrid particles decorated with different negatively charged polyelectrolytes. The colloidal properties of these polyelectrolyte-decorated hybrid particles were determined by the composition and decorated polyelectrolyte. This approach provided a simple and facile method to prepare polymer-decorated hybrid colloidal particles comprised of different polymers and their colloidal properties can be easily tuned by varying the decorated polymer and synthesis condition.

Synthesis and surface functionalization of silica nanoparticles for nanomedicine

There are a wide variety of silica nanoformulations being investigated for biomedical applications. Silica nanoparticles can be produced using a wide variety of synthetic techniques with precise control over their physical and chemical characteristics. Inorganic nanoformulations are often criticized or neglected for their poor tolerance; however, extensive studies into silica nanoparticle biodistributions and toxicology have shown that silica nanoparticles may be well tolerated, and in some case are excreted or are biodegradable. Robust synthetic techniques have allowed silica nanoparticles to be developed for applications such as biomedical imaging contrast agents, ablative therapy sensitizers, and drug delivery vehicles. This review explores the synthetic techniques used to create and modify an assortment of silica nanoformulations, as well as several of the diagnostic and therapeutic applications.

X-Ray Photoelectron Spectroscopy Investigation of the Nitrogen Species in Photoactive Perfluorophenylazide-Modified Surfaces

X-ray Photoelectron Spectroscopy (XPS) was used to characterize the nitrogen species in perfluorophenylazide (PFPA) self-assembled monolayers. PFPA chemistry is a novel immobilization method for tailoring the surface properties of materials. It is a simple route for the efficient immobilization of graphene, proteins, carbohydrates and synthetic polymers onto a variety of surfaces. Upon light irradiation, the azido group in PFPA is converted to a highly reactive singlet nitrene species that readily undergoes CH insertion and C=C addition reactions. Here, the challenge of characterizing the PFPA modified surfaces was addressed by detailed XPS experimental analyses. The three nitrogen peaks detected in the XPS N1s spectra were assigned to amine/amide (400.5 eV) and azide (402.1 and 405.6 eV) species. The observed 2:1 ratio of the areas from the 402.1 eV to 405.6 eV peaks suggests the assignment of the peak at 402.1 eV to the two outer nitrogen atoms in the azido group and assignment of the peak at 405.6 eV to the central nitrogen atom in the azido group. The azide decomposition as the function of x-ray exposure was also determined. Finally, XPS analyses were conducted on patterned graphene to investigate the covalent bond formation between the PFPA and graphene. This study provides strong evidence for the formation of covalent bonds during the PFPA photocoupling process.

Assembly of free-standing polypeptide films via the synergistic combination of hyperbranched macroinitiators, the grafting-from approach, and cross-chain termination

Cross-linked polypeptide-based films are fabricated via a novel and robust method employing surface-initiated ring opening polymerization of α-amino acid N-carboxyanhydrides (NCA-ROP). The judicious combination of amine-based hyperbranched macroinitiators and benzyl ester-protected NCA derivatives promotes network formation by cross-chain terminations, which allows the formation of stable cross-linked peptide-based capsules in a one-pot system.

Poly(L-glutamic acid)-decorated hybrid colloidal particles from complex particle-templated silica mineralization

We report the synthesis of polyelectrolyte complex (PEC) particles by mixing the negatively and positively charged polyelectrolytes, poly(L-glutamic acid) (PGA) and poly(2-(N,N-diethylamino) ethylmethacrylate) (PDEAEMA), and the use of negatively charged PEC particles as colloidal templates for silica mineralization under ambient conditions. The structure and property of PEC particles, as well as polypeptide chain conformation, were found to depend on the mixing weight percentage, polymer molecular weight, and solution condition. The negatively charged PEC micelles can be deposited with silica without loss colloid stability, leading to PGA-decorated hybrid particles. These hybrid particles were negatively charged at neutral and basic condition and become positively charged, accompanying the conformational changes of the grafted PGA, upon decreasing pH below isoelectric points due to the protonation/deprotonation of PGA and PDEAEMA. Functional nanoparticles such as gold NPs could be incorporated using polypeptides as the mediating agents. These hybrid particles loaded with drug exhibited noticeable pH-responsive behavior with accelerated release at acidic condition, demonstrating the potential for use as pH-responsive delivery vehicles. This type of polypeptide-decorated hybrid particles represents an interesting class of organic-inorganic hybrids in which the functional properties of polypeptides such as biocompatibility, stimuli responsiveness, and directed growth of metal nanoparticles can be incorporated.

Photoreactive azido-containing silica nanoparticle/polycation multilayers: durable superhydrophobic coating on cotton fabrics

In this study, we report the functionalization of silica nanoparticles with highly photoreactive phenyl azido groups and their utility as a negatively charged building block for layer-by-layer (LbL) electrostatic assembly to produce a stable silica nanoparticle coating. Azido-terminated silica nanoparticles were prepared by the functionalization of bare silica nanoparticles with 3-aminopropyltrimethoxysilane followed by the reaction with 4-azidobenzoic acid. The azido functionalization was confirmed by FTIR and XPS. Poly(allylamine hydrochloride) was also grafted with phenyl azido groups and used as photoreactive polycations for LbL assembly. For the photoreactive silica nanoparticle/polycation multilayers, UV irradiation can induce the covalent cross-linking within the multilayers as well as the anchoring of the multilayer film onto the organic substrate, through azido photochemical reactions including C-H insertion/abstraction reactions with surrounding molecules and dimerization of azido groups. Our results show that the stability of the silica nanoparticle/polycation multilayer film was greatly improved after UV irradiation. Combined with a fluoroalkylsilane post-treatment, the photoreactive LbL multilayers were used as a coating for superhydrophobic modification of cotton fabrics. Herein the LbL assembly method enables us to tailor the number of the coated silica nanoparticles through the assembly cycles. The superhydrophobicity of cotton fabrics was durable against acids, bases, and organic solvents, as well as repeated machine wash. Because of the unique azido photochemistry, the approach used here to anchor silica nanoparticles is applicable to almost any organic substrate.

Synthesis of poly-L-glutamic acid grafted silica nanoparticles and their assembly into macroporous structures

Polypeptide-coated silica nanoparticles represent an interesting class of organic-inorganic hybrids since the ordered secondary structure of the polypeptide grafts imparts functional properties to these nanoparticles. The synthesis of a poly-l-glutamic acid (PLGA) silica nanoparticle hybrid by employing N-carboxyanhydride (NCA) polymerization to synthesize the polypeptide chains and Cu catalyzed azide alkyne cycloaddition reaction to graft these chains onto the silica surface is reported. This methodology enables the synthesis of well-defined polypeptide chains that are attached onto the silica surface at high surface densities. The PLGA-silica conjugate particles are well dispersed in water, and have been thoroughly characterized using multinuclear ((13)C, (29)Si) solid state NMR, thermogravimetric analysis, Fourier transform infrared, dynamic light scattering, and transmission electron microscopy. The pH-dependent reversible aggregation of the PLGA-silica particles, driven by the change in PLGA structure, has also been studied. Preliminary results on the use of aqueous dispersions of silica-PLGA for the preparation of three-dimensional macroporous structures with oriented pores by ice templating methodology are also demonstrated. These macroporous materials, comprising a biocompatible polymer shell covalently attached to rigid inorganic cores, adopts an interesting lamellar structure with fishbone-type architecture.

Versatility of alkyne-modified poly(glycidyl methacrylate) layers for click reactions

Functional soft interfaces are of interest for a variety of technologies. We describe three methods for preparing substrates with alkyne groups, which show versatility for "click" chemistry reactions. Two of the methods have the same root: formation of thin, covalently attached, reactive interfacial layers of poly(glycidyl methacrylate) (PGMA) via spin coating onto silicon wafers followed by reactive modification with either propargylamine or 5-hexynoic acid. The amine or the carboxylic acid moieties react with the epoxy groups of PGMA, creating interfacial polymer layers decorated with alkyne groups. The third method consists of using copolymers comprising glycidyl methacrylate and propargyl methacrylate (pGP). The pGP copolymers are spin coated and covalently attached on silicon wafers. For each method, we investigate the factors that control film thickness and content of alkyne groups using ellipsometry, and study the nanophase structure of the films using neutron reflectometry. Azide-terminated polymers of methacrylic acid and 2-vinyl-4,4-dimethylazlactone synthesized via reversible addition-fragmentation chain transfer polymerization were attached to the alkyne-modified substrates using "click" chemistry, and grafting densities in the range of 0.007-0.95 chains nm(-2) were attained. The maximum density of alkyne groups attained by functionalization of PGMA with propargylamine or 5-hexynoic acid was approximately 2 alkynes nm(-3). The alkyne content obtained by the three decorating approaches was sufficiently high that it was not the limiting factor for the click reaction of azide-capped polymers.

Silica-polypeptide composite particles: controlling shell growth

A method is presented for preparing core-shell silica-polypeptide composite particles with variable and controllable shell growth. The procedure is demonstrated using poly(carbobenzoxy-L-lysine) and poly(benzyl-L-glutamate); after deprotection, these can lead to the most common basic and acidic homopolypeptides, poly(L-lysine) and poly(L-glutamic acid). Control over shell thickness is made possible by sequential addition of N-carboxyanhydride peptide monomer to surfaces that have been functionalized with an amino initiator combined with a surface passivation agent. This results in a series of particles having different shell thicknesses. Variation of shell thickness was evident both in light scattering and in thermogravimetric assays. The shells were visible by transmission electron microscopy; these images along with light scattering measurements suggest the polymers in the shells are highly solvated.

Synthesis and characterization of poly-L-lysine-grafted silica nanoparticles synthesized via NCA polymerization and click chemistry

Polypeptide polymer-grafted silica nanoparticles are of considerable interest because the ordered secondary structure of the polypeptide grafts imparts novel functional properties onto the nanoparticle composite. The synthesis of poly-L-lysine-grafted silica nanoparticles would be of particular interest because the high density of cationic charges on the surface could lead to many applications such as gene delivery and antimicrobial agents. In this work, we have developed a "grafting-to" approach using a combination of NCA polymerization and "click chemistry" to synthesize poly-L-lysine-grafted silica nanoparticles with a high graft density of 1 chain/nm(2). The covalent attachment of poly-L-lysine to silica nanoparticles (PLL-silica) was confirmed using a variety of techniques such as (13)C CP MAS NMR, TGA, and IR. This methodology was then extended to graft poly-L-lysine-b-poly-L-leucine copolymer (PLL-b-PLLeu-silica) and poly-L-benzylglutamate (PLBG-silica) onto silica nanoparticles. All of these polypeptide-grafted nanoparticles show interesting aggregation properties in solution. The efficacy of PLL-silica and PLL-b-PLLeu-silica as antimicrobial agents was tested on both gram-negative E. coli and gram-positive Bacillus subtilis.