“One-Pot” In Situ Formation of Gold Nanoparticles within Poly(acrylamide) Hydrogels

Peptide Stereochemistry Effects from pKa-Shift to Gold Nanoparticle Templating in a Supramolecular Hydrogel

The divergent supramolecular behavior of a series of tripeptide stereoisomers was elucidated through spectroscopic, microscopic, crystallographic, and computational techniques. Only two epimers were able to effectively self-organize into amphipathic structures, leading to supramolecular hydrogels or crystals, respectively. Despite the similarity between the two peptides' turn conformations, stereoconfiguration led to different abilities to engage in intramolecular hydrogen bonding. Self-assembly further shifted the pKa value of the C-terminal side chain. As a result, across the pH range 4-6, only one epimer predominated sufficiently as a zwitterion to reach the critical molar fraction, allowing gelation. By contrast, the differing pKa values and higher dipole moment of the other epimer favored crystallization. The four stereoisomers were further tested for gold nanoparticle (AuNP) formation, with the supramolecular hydrogel being the key to control and stabilize AuNPs, yielding a nanocomposite that catalyzed the photodegradation of a dye. Importantly, the AuNP formation occurred without the use of reductants other than the peptide, and the redox chemistry was investigated by LC-MS, NMR, and infrared scattering-type near field optical microscopy (IR s-SNOM). This study provides important insights for the rational design of simple peptides as minimalistic and green building blocks for functional nanocomposites.

Acrylamide: New Organic Solvent with Chemically Tunable Viscosity for Rapid Gram-Scale Synthesis of Gold Nanoparticles

Noble metal nanoparticles have demonstrated various biomedical, optical, and electronic applications owing to their unique chemical and physical properties. However, their gram-scale synthesis remains a challenge. We have developed a method for the gram-scale synthesis of gold nanoparticles (AuNPs) using acrylamide (AAm) as a solvent. AAm possesses unique properties such as low melting temperature, high solvating power, and high solubility of its polymer (polyacrylamide(pAAm)) in water. The viscosity of the AAm solvent can be chemically tuned by the polymerization of AAm and addition of a low-volatile diluent, which can stabilize highly concentrated as-synthesized AuNPs in gram quantities. The synthesized AuNPs are substantially stable and catalytically active under high ionic strength conditions owing to the pAAm protection on the particle surface. Further, the synthesis mechanism of the AuNPs has been thoroughly investigated. The versatility of the synthesis method is proved by synthesizing other mono-(Ag and Pd) and bimetallic (Au + Pd and Ag + Pd) nanoparticles using the AAm solvent with controlled viscosity. Importantly, the productivity of this synthetic strategy is the highest among the previously reported gram-scale synthesis methods of AuNPs. To the best of our knowledge, our study presents the use of acrylic monomer as a solvent for the gram-scale synthesis of noble metal nanoparticles for the first time. This study significantly extends the list of solvents with chemically tunable viscosity by including other acrylic reagents for nanomaterial synthesis, functionalization, and catalytic, optical, and electrical reactions under highly localized reaction conditions.

Exploring new avenues in physical chemistry of hydrophilic polymers: to the 70th anniversary of Professor Sarkyt Elekenovich Kudaibergenov

This paper is dedicated to 70th anniversary of the prominent Kazakh chemist – professor Sarkyt Elekenovich Kudaibergenov. The information of biographical nature, showing the development of S.E. Kudaibergenov as a scientist, as well as his main research contributions to the field of physical chemistry of hydrophilic polymers and colloidal systems are presented in this paper. This is written in the form of a review of the most important and prominent publications of Prof S.E. Kudaibergenov, published in the journals indexed by Web of Knowledge. Professor S.E. Kudaibergenov has made a substantial contribution to the studies of synthetic and natural polyelectrolytes, their complexes with different compounds, polymeric hydrogels, stimuli-responsive materials, nanoparticles and nanocomposites, as well as applications of different polymeric materials and colloidal systems as catalysts, specialty chemicals, and drug delivery systems. This paper also includes information about the research conducted by Professor S.E. Kudaibergenov on various projects, funded by different organisations, his membership in different journals’ editorial boards, his role in the establishment of the Institute of Polymer Materials and Technologies, his participation in research councils and committees, as well as supervision of numerous students and researchers. The paper includes some photographs of Professor S.E. Kudaibergenov with several international collaborators.

Synthesis and Stabilization of Gold Nanoparticles Using Water-Soluble Synthetic and Natural Polymers

Gold nanoparticles (AuNPs) were synthesized and stabilized using the one-pot method and growth seeding, through utilization of synthetic polymers, including poly(N-vinylpyrrolidone) (PVP), poly(ethylene glycol) (PEG), and poly(vinylcaprolactame) (PVCL), as well as natural polysaccharides, including gellan, welan, pectin, and κ-carrageenan. The absorption spectra, average hydrodynamic size, ζ-potential, and morphology of the gold nanoparticles were evaluated based on various factors, such as polymer concentration, molecular mass of polymers, temperature, and storage time. The optimal polymer concentration for stabilization of AuNPs was found to be 4.0 wt % for PVP, 0.5 wt % for gellan, and 0.2 wt % for pectin, welan, and κ-carrageenan. The values of the ζ-potential of polymer-stabilized AuNPs show that their surfaces are negatively charged. Most of the AuNPs are polydisperse particles, though very monodisperse AuNPs were detected in the presence of a 0.5 wt % gellan solution. At a constant polymer concentration of PVP (4 wt %), the average size of the PVP-AuNPs decreased with the decrease of molecular weight, and in the following order: PVP 350 kDa (~25 nm) > PVP 40 kDa (~8 nm) > PVP 10 kDa (~4 nm). The combination of Fourier-transform infrared spectroscopy (FTIR) and Raman spectroscopy revealed that the functional groups of polymers that are responsible for stabilization of AuNPs are lactam ring in PVP, carboxylic groups in gellan and welan, esterified carboxylic groups in pectin, and SO2 groups in κ-carrageenan. Viscometric and proton nuclear magnetic resonance (1H NMR) spectroscopic measurements showed that the temperature-dependent change in the size of AuNPs, and the gradual increase of the intensity of AuNPs at 550 nm in the presence of gellan, is due to the rigid and disordered conformation of gellan that affects the stabilization of AuNPs. The AuNPs synthesized in the presence of water-soluble polymers were stable over a period of 36 days. Preliminary results on the synthesis and characterization of gold nanorods stabilized by polymers are also presented.

Mapping Nanoparticles in Hydrogels: A Comparison of Preparation Methods for Electron Microscopy

The distribution of noble metal nanoparticles (NMNPs) in hydrogels influences their nanoplasmonic response and signals used for biosensor purposes. By controlling the particle distribution in NMNP-nanocomposite hydrogels, it is possible to obtain new nanoplasmonic features with new sensing modalities. Particle positions can be characterized by using volume-imaging methods such as the focused ion beam-scanning electron microscope (FIB-SEM) or the serial block-face scanning electron microscope (SBFSEM) techniques. The pore structures in hydrogels are contained by the water absorbed in the polymer network and may pose challenges for volume-imaging methods based on electron microscope techniques since the sample must be in a vacuum chamber. The structure of the hydrogels can be conserved by choosing appropriate preparation methods, which also depends on the composition of the hydrogel used. In this paper, we have prepared low-weight-percentage hydrogels, with and without gold nanorods (GNRs), for conventional scanning electron microscope (SEM) imaging by using critical point drying (CPD) and hexamethyldisilazane (HMDS) drying. The pore structures and the GNR positions in the hydrogel were characterized. The evaluation of the sample preparation techniques elucidate new aspects concerning the drying of hydrogels for SEM imaging. The results of identifying GNRs positioned in a hydrogel polymer network contribute to the development of mapping metal particle positions with volume imaging methods such as FIB-SEM or SBFSEM for studying nanoplasmonic properties of NMNP-nanocomposite hydrogels.

Change in size, morphology and stability of DNA polyplexes with hyperbranched poly(ethyleneimines) containing bulky maltose units

Polyplexes between Salmon DNA and non-modified hyperbranched poly(ethyleneimines) of varying molar mass, i.e., PEI(5 k) with 5000 g/mol and PEI(25 k) with 25,000 g/mol, and modified PEI(5 k) with maltose units (PEI-Mal) were investigated in dependence on the molar N/P ratio by using dynamic light scattering (DLS), zeta potential measurements, micro differential scanning calorimetry (μ-DSC), scanning-transmission electron microscopy (STEM), and cryo-scanning electron microscopy (cryo-SEM). A reloading of the polyplexes can be observed by adding the unmodified PEI samples of different molar mass. In excess of PEI a morphological transition from core-shell particles (at N/P 8) to loosely packed onion-like polyplexes (at N/P 40) is observed. The shift of the DSC melting peak from 88 °C to 76 °C indicates a destabilization of the DNA double helix due to the complexation with the unmodified PEI. Experiments with the maltose-modified PEI show a reloading already at a lower N/P ratio. Due to the presence of the sugar units in the periphery of the polycation electrostatic interactions between DNA become weaker, but cooperative H-bonding forces are reinforced. The resulting less-toxic, more compact polyplexes in excess of the PEI-Mal with two melting points and well distributed DNA segments are of special interest for extended gene delivery experiments.

Effective Electrochemistry of Human Sulfite Oxidase Immobilized on Quantum-Dots-Modified Indium Tin Oxide Electrode

The bioelectrocatalytic sulfite oxidation by human sulfite oxidase (hSO) on indium tin oxide (ITO) is reported, which is facilitated by functionalizing of the electrode surface with polyethylenimine (PEI)-entrapped CdS nanoparticles and enzyme. hSO was assembled onto the electrode with a high surface loading of electroactive enzyme. In the presence of sulfite but without additional mediators, a high bioelectrocatalytic current was generated. Reference experiments with only PEI showed direct electron transfer and catalytic activity of hSO, but these were less pronounced. The application of the polyelectrolyte-entrapped quantum dots (QDs) on ITO electrodes provides a compatible surface for enzyme binding with promotion of electron transfer. Variations of the buffer solution conditions, e.g., ionic strength, pH, viscosity, and the effect of oxygen, were studied in order to understand intramolecular and heterogeneous electron transfer from hSO to the electrode. The results are consistent with a model derived for the enzyme by using flash photolysis in solution and spectroelectrochemistry and molecular dynamic simulations of hSO on monolayer-modified gold electrodes. Moreover, for the first time a photoelectrochemical electrode involving immobilized hSO is demonstrated where photoexcitation of the CdS/hSO-modified electrode lead to an enhanced generation of bioelectrocatalytic currents upon sulfite addition. Oxidation starts already at the redox potential of the electron transfer domain of hSO and is greatly increased by application of a small overpotential to the CdS/hSO-modified ITO.

Preparation of a novel high-strength polyzwitterionic liquid hydrogel and application in catalysis

A new polymeric hydrogel P(PVIS–AA) based on zwitterionic liquids (1-propyl-3-vinyl imidazole sulfonate) (PVIS) and acrylic acid (AA) was prepared by free-radical polymerization.

Supramolecular hybrid hydrogel based on host-guest interaction and its application in drug delivery

In this work, we developed a simple, novel method for constructing gold nanocomposite supramolecular hybrid hydrogels for drug delivery, in which gold nanocrystals were utilized as building blocks. First, methoxypoly(ethylene glycol) thiol (mPEG-SH, molecular weight (MW)=5 K) capped gold nanocrystals (nanospheres and nanorods) were prepared via a facile one-step ligand-exchange procedure. Then, the homogeneous supramolecular hybrid hydrogels were formed, after adding α-cyclodextrin (α-CD) into PEG-modified gold nanocrystal solutions, due to the host-guest inclusion. Both gold nanoparticles and inclusion complexes formed between α-CD and PEG chain provided the supra-cross-links, which are beneficial to the gelation formation. The resulting hybrid hydrogels were fully characterized by a combination of techniques including X-ray diffraction, rheology studies, and scanning electron microscopy. Meanwhile, the hybrid hydrogel systems demonstrated unique reversible gel-sol transition properties at a certain temperature caused by the temperature-responsive reversible supramolecular assembly. The drug delivery applications of such hybrid hydrogels were further investigated in which doxorubicin was selected as a model drug for in vitro release, cytotoxicity, and intracellular release studies. We believe that the development of such hybrid hydrogels will provide new and therapeutically useful means for medical applications.