Sorption of metal ions by poly(ethylene glycol)/β-CD hydrogels leads to gel-embedded metal nanoparticles

Role of Ligand Shell Density in the Diffusive Behavior of Nanoparticles in Hydrogels

The diffusion coefficients of poly(ethylene glycol) methyl ether thiol (PEGSH)-functionalized gold nanoparticles (NPs) with different effective grafting densities were measured in polyacrylamide hydrogels. The NP core size was held constant, and the NPs were functionalized with mixtures of short oligomeric ligands (254 Da PEGSH) and longer (either 1 or 2 kDa PEGSH) ligands. The ratio of short and long ligands was varied such that the grafting density of the high-molecular-weight (MW) ligand ranged from approximately 1 to 100 high-MW ligands/NP. The diffusion coefficients of the NPs were then measured in gels with varying average mesh sizes. The measured diffusion coefficients decreased with higher MW ligand density. Interestingly, the diffusion coefficients for NPs with high effective grafting densities were well-predicted by their hydrodynamic diameters, but the diffusion coefficients for NPs with low effective grafting densities were higher than expected from their hydrodynamic diameters. These results suggest that crowding in the NP ligand shell influences the mechanism of diffusion, with lower grafting densities allowing ligand chain relaxations that facilitate movement through the gel. This work brings new insights into the factors that dictate how NPs move through hydrogels and will inform the development of models for applications such as drug delivery in complex viscoelastic biological materials.

Self-assembly of new cobalt complexes based on [Co (SCN)4], synthesis, empirical, antioxidant activity, and quantum theory investigations

The cobalt (II) complexes have been synthesized from the reaction of the cationic entities (3,4-dimethylaniline (1) and histamine (2)) with metallic salt CoCl2⋅6H2O and thiocyanate ion (SCN-) as a ligand in H2O/ethanolic solution and processing by the evaporation crystal growth method at room temperature to get crystals. The synthesized complex has been fully characterized by single-crystal X-ray diffraction. UV-Visible, FTIR spectroscopy, TGA analysis, and DFT circulations were also performed. The crystal structural analysis reveals that the solid (1) {[Co(SCN)4] (C8H12N)3}·Cl crystallizes in the monoclinic system with the space group P21/n and the solid (2) {[Co(SCN)4](C5H11N3)2}·2Cl crystallizes in the monoclinic space group P21/m. Metal cations are joined into corrugated chains parallel to the b-axis direction in (1) and (2) by four thiocyanate anions. The crystal structures of (1) and (2) were calculated using XRPD data, indicating that they are closely connected to the DRX mono-crystal results. Different interactions pack the system into a ring formed by N-H⋯Cl and N-H⋯S hydrogen bonds. C-H⋯π and the π⋯π stacking of anilinuim ring for (1) and N-H⋯S intermolecular interactions for (1) and (2) increase the crystals' robustness. Hirshfeld surface analysis cum 2D fingerprint plots visualize the main intermolecular interactions with their contributions in the solid-state phase. The molecular geometries of both complexes obtained from the crystal structure were used for quantum chemical calculation. Here, frontier orbital analysis and electrostatic potential illustrate the chemical reactivities of metal-organic complexes. QTAIM and NCI analysis reveal the strength of interactions at the electronic level.

Evaluation of the Accessibility of Molecules in Hydrogels Using a Scale of Spin Probes

In this work, we explored by means of electron paramagnetic resonance (EPR) spectroscopy the accessibility of a series of spin probes, covering a scale of molecular weights in the range of 200–60,000 Da, in a variety of hydrogels: covalent network, ionotropic, interpenetrating polymer network (IPN) and semi-IPN. The covalent gel network consists of polyethylene or polypropylene chains linked via isocyanate groups with cyclodextrin, and the ionotropic gel is generated by alginate in the presence of Ca²⁺ ions, whereas semi-IPN and IPN gel networks are generated in a solution of alginate and chitosan by adding crosslinking agents, Ca²⁺ for alginate and glutaraldehyde for chitosan. It was observed that the size of the diffusing species determines the ability of the gel to uptake them. Low molecular weight compounds can diffuse into the gel, but when the size of the probes increases, the gel cannot uptake them. Spin-labelled Pluronic F127 cannot be encapsulated by any covalent gel, whereas spin-labelled albumin can diffuse in alginate gels and in most of the IPN networks. The EPR spectra also evidenced the specific interactions of spin probes inside hydrogels. The results suggest that EPR spectroscopy can be an alternate method to evaluate the mesh size of gel systems and to provide information on local interactions inside gels.

Synthesis, crystal structure, and characterization of cyclohexylammonium tetraisothiocyanatocobaltate(II): A single-source precursor for cobalt sulfide and oxide nanostructures

We successfully synthesized 3D supramolecular structure of cyclohexylammonium tetraisothiocyanatocobaltate(II) complex, (C6H11NH3)2[Co(NCS)4], in almost a quantitative yield by using metathesis and ligand addition reactions. The new complex was characterized by various techniques such as FTIR, UV-Visible, PXRD, SXRD, and CV electrochemical analysis to investigate mainly its structure. Based on the results of these techniques, the formation of the desired complex was confirmed. The TGA for this complex indicated the utilization of this complex as a single-source precursor for the synthesis of cobalt sulfide (CoS) under helium atmosphere and tricobalt tetraoxide (Co3O4) under air. Investigation of pyrolysis products by PXRD proved the formation of CoS and Co3O4. Furthermore, morphology studies by SEM and TEM displayed the formation of CoS and Co3O4 nanoparticles with various shapes.

Heavy metals removal using hydrogel-supported nanosized hydrous ferric oxide: Synthesis, characterization, and mechanism

A new polymer-supported hybrid adsorbent (HFO-P(TAA/HEA)) for highly efficient removal of Pb²⁺, Cu²⁺, Cd²⁺ and Ni²⁺ from wastewater was developed by supporting hydrous ferric oxide (HFO) nanoparticles onto a porous poly(trans-Aconitic acid/2-hydroxyethyl acrylate) hydrogel (P(TAA/HEA)) with in situ precipitation method. Swelling kinetics, scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), thermo-gravimetric analysis (TGA), Fourier transform infrared spectra (FTIR) and X-ray photoelectron spectroscopy (XPS) were used for characterization of the prepared HFO-P(TAA/HEA). The characterization data demonstrated that the hybrid hydrogel HFO-P(TAA/HEA) was successfully fabricated, and swelling ability as well as thermal stability was promoted after loading. The results of batch equilibrium experiments indicated that pH and temperature significantly influenced the adsorption process and adsorption of heavy metals was better fitted to Langmuir and pseudo-second-order models. Selectivity of HFO-P(TAA/HEA) towards heavy metals was greatly improved under the calcium ions competition at higher concentration compared to P(TAA/HEA). Competitive adsorption evidenced the priority order in multifold metal species system was Pb²⁺>Cu²⁺>Ni²⁺>Cd²⁺. What's more, FTIR and XPS analyses manifested that heavy metals might mainly be adsorbed via inner sphere complexation. These findings revealed that hydrogel HFO-P(TAA/HEA) is a potential adsorption material to remove the heavy metals from polluted water.

Sunlight induced unique morphological transformation in graphene based nanohybrids: appearance of a new tetra-nanohybrid and tuning of functional property of these nanohybrids

In this study, sunlight was used for in situ preparation of gel-based various nanohybrid systems. A naturally occurring amino acid, l-phenylalanine derivative formed a hydrogel with graphene oxide (GO)/reduced graphene oxide (rGO) at physiological pH. This hydrogel was then used in the presence of silver ions and diffuse sunlight to form initially a tri-nanohybrid system consisting of six atom silver nanoclusters, nanosheets, and nanofibers. Interestingly, a time-dependent morphological transformation occurs in this nanohybrid system to form one tri-nanohybrid to another tri-nanohybrid with the appearance of a novel, nanoscopic intermediate tetra-nanohybrid system consisting of four distinctly different nanomaterials (nanofibers, nanosheets, nanospheres, and nanoparticles). UV-Vis and fluorescence spectroscopic analyses, transmission electron microscopic, X-ray photo electron spectroscopic and MALDI-TOF mass spectral analyses with time were applied to characterise these morphological transformations in gel based nanohybrids. Time-dependent X-ray photo electron spectroscopic (XPS) analysis was used to uncover the mechanism for the transformation of silver nanoclusters to silver nanoparticles in the hydrogel matrix. Sunlight was used to trigger time-dependent structural transformation in the nanohybrid systems. Interestingly, one of these tri-nanohybrid systems (silver nanoparticles containing rGO based hydrogel) shows a catalytic property of reducing nitroarenes to aminoarenes and the catalytic efficiency can be modulated by changing the size of the silver nanoparticles with time in diffuse sunlight. The mechanism for different catalytic activities for different hybrids with varying size of silver nanoparticles has also been deciphered.

Enhanced ALP activity of MG63 cells cultured on hydroxyapatite-poly(ethylene glycol) hydrogel composites prepared using EDTA-OH

In order to obtain a hydroxyapatite (HAp)-poly(ethylene glycol) (PEG) composite, tetra amine-terminated PEG was crosslinked using disuccinimidyl tartrate to obtain a PEG hydrogel. Using two kinds of chelators with different stability constants for Ca ion (N-(2-hydroxyethyl) ethylenediamine-N,N',N'-triacetic acid (EDTA-OH, 8.14), and ethylenediamine-N,N,N',N'-tetraacetic acid (EDTA, 10.96)), calcium phosphate was deposited within PEG hydrogels by heating the chelator-containing calcium phosphate solution at 90 °C. X-ray diffraction analysis showed that the deposited calcium phosphate was HAp. The crystallinity of the HAp deposited using EDTA-OH was low compared with that obtained using EDTA, but the amount of HAp deposited within the PEG hydrogel using EDTA-OH was higher than that deposited using EDTA. Significantly more human osteoblast-like MG-63 cells adhered on the HAp-PEG composite prepared using EDTA-OH than on the HAp-PEG composites prepared using EDTA. Furthermore, the alkaline phosphatase activity of MG-63 cultured on the HAp-PEG composite prepared using EDTA-OH was four times higher than that on the HAp-PEG composite prepared using EDTA. Therefore, the HAp-PEG composite prepared using EDTA-OH has potential as a bone substitute material.

Properties of polyethylene glycol/cyclodextrin hydrogels revealed by spin probes and spin labelling methods

The properties of a gel consisting of a covalent network formed by the reaction of isocyanate end-capped polyethylene glycol (PEG) with β-cyclodextrin, were investigated by EPR spectroscopy. Spin-labelled cyclodextrin was incorporated into the cross-link points of the gel and at the chain ends. The dynamics of the gel fibres as reported by the spin label, was found to be sensitive to the H-bonding ability of the solvent, density of cross-links and temperature. Addition of spin probes (e.g., TEMPO and adamantane-TEMPO) to the unlabelled gel made it possible to characterise the solvent pools in the gel. While TEMPO was uniformly distributed throughout the solvent pools, the adamantane derivative was located at the gel fibre-solvent pool interface; these two probes thus reported on the different locations in the solvent pools. At low temperature, the gels were shown to prevent ice crystallisation in the solvent pools resulting in the formation of supercooled water. Both probes showed that the water froze at ca. 250 K, thus suggesting that the properties of the supercooled water are uniform across the solvent pools.