Preparation and characterization of cellulose hybrids grafted with the polyhedral oligomeric silsesquioxanes (POSS)

The cellulose hybrids with polyhedral oligomeric silsesquioxane (POSS) are synthesized by cross-linking graft reaction. Dimethylol dihydroxy ethylene urea (DDEU) as cross-linking agent is used in the graft reaction. The chemical and surface morphological structures of the am-POSS grafted cellulose hybrids are characterized with micro-FT-IR spectra, silicon element analysis, X-ray diffraction, SEM, AFM, and DSC. The results show that the am-POSS grafted cellulose hybrids form new macromolecular structures containing POSS nano-silica particles. POSS particles are evenly dispersed at the nanometer scale in the cellulose host matrix, bonding to the cellulose through covalent bonds. The thermal properties of the am-POSS grafted cellulose hybrids are improved.     

Atomistic simulation of the sol formation during synthesis of organic/inorganic hybrid materials

Atomistic modelling was employed to investigate interactions between the precursors used in preparation of organic/inorganic polymer hybrids. Three molecular systems composed of different kinds of organofunctionalised silanes and an organic polymer in aqueous solution have been simulated, representing various model stages of the hydrolysis reaction during the sol/gel processing. The equilibrium configurations obtained by Molecular Dynamics were analysed in order to elucidate the extent of the hydrogen bonding network and clustering of components within the systems. Diffusion coefficients were obtained to estimate the mobility of the components and the stability of the molecular associations. It has been concluded that the molecular mechanism of the initial stages of the sol/gel process used for preparation of the organic/inorganic hybrids involves clustering of the organofunctionalysed inorganic components as a first step and then progressive hydrolysis as consequent steps. The organic polymer component plays a role of the cluster "wrap" and thus prevents the particles from unlimited growth and precipitation from the solution.     

Application of a lipase-immobilized silica monolith bioreactor to the production of fatty acid methyl esters

We developed a highly efficient bioreactor loaded with a lipase-immobilized non-shrinkable silica monolith by adopting a two-step sol–gel method, i.e., preparing a methyltrimethoxysilane (MTMS)-based silica monolith followed by coating of the latter with more hydrophobic alkyl-substituted silicates that entrapped lipase. We applied this type of bioreactor to the production of fatty acid methyl esters through methanolysis of rapeseed oil in n-hexane by Rhizopus oryzae lipase. As the result of screening alkyltrimethoxysilanes mixed with tetramethoxysilane (TMOS) during sol–gel coating, propyltrimethoxysilane (PTMS) gave the best performance, and the lipase immobilized therein exhibited ca. 10 times higher activity than non-immobilized lipase powder. The amount of the PTMS-based silicates with which the MTMS-based silica monolith was coated was optimized by adjusting the molar ratio of silanes (mixture of PTMS and TMOS at 4:1) to 100 mol of water. Conversion rate was highest at the molar ratio of 0.4 mol silanes to 100 mol of water, which was ca. 10 times higher than that with lipase deposited on the MTMS-based silica monolith. Conversion rate was approximately 1.5 times higher in the flow-through monolith bioreactor than in the batch slurry reactor.     

Immobilization of horseradish peroxidase on chitosan/silica sol-gel hybrid membranes for the preparation of hydrogen peroxide biosensor

A simple and effective strategy for fabrication of hydrogen peroxide (H₂O₂) biosensor has been developed by entrapping horseradish peroxidase (HRP) in chitosan/silica sol–gel hybrid membranes (CSHMs) doped with potassium ferricyanide (K₃Fe(CN)₆) and gold nanoparticles (GNPs) on platinum electrode surface. The hybrid membranes are prepared by cross-linking chitosan (CS) with 3-aminopropyltriethoxysilane (APTES), while the presence of GNPs improved the conductivity of CSHMs, and the Fe(CN)₆^3−/4− was used as a mediator to transfer electrons between the electrode and HRP due to its excellent electrochemistry activity. UV–Vis absorption spectroscopy was employed to characterize the different components in the CSHMs and their interaction. The parameters influencing the performance of the resulting biosensor were optimized and the characteristic of the resulting biosensor was characterized by cyclic voltammetry and chronoamperometry. Linear calibration for hydrogen peroxide was obtained in the range of 3.5 × 10^− 6 to 1.4 × 10^− 3 M under the optimized conditions with the detection limit (S/N = 3) of 8.0 × 10^− 7 M. The apparent Michaelis–Menten constant of the enzyme electrode was 0.93 mM. The enzyme electrode retained about 78% of its response sensitivity after 30 days. The system was applied for the determination of the samples, and the results obtained were satisfactory.     

Antimicrobial activity of AgCl embedded in a silica matrix on cotton fabric

An antimicrobial finishing for cotton fabric was prepared from commercial (iSys AG, Germany) silver chloride (Ag) dispersed at different concentrations in a reactive organic–inorganic binder (RB) (iSys MTX (CHT, Germany). Pad-dry-cure and exhaustion methods were used for the sols application, giving Ag-RB coating with Ag concentration from ca. 48 to ca. 290 ppm on the cotton fabric. The presence of silver on the cotton finishes was confirmed by measuring its concentration in the fabrics with the help of inductively coupled plasma mass spectroscopy (ICP-MS). The morphology of the finished fabrics was investigated by SEM, while their composition was established from EDXS measurements combined with the results of FT-IR spectral analysis. The antimicrobial activity of variously treated cotton fabrics was assessed before and after repetitive (up to 10×) washing by the application of standard tests: for the fungi Aspergillus niger (ATCC 6275) and Chaetomium globosum (ATCC 6205) by the modified DIN 53931 standard method, while the presence of Gram-negative bacterium Escherichia coli (ATCC 25922) was followed by using ISO 20645:2004 (E) and AATCC 100-1999 standard methods. Results revealed that the antimicrobial activity of the coatings strongly depended on the concentration of Ag in the corresponding Ag-RB dispersions, indirectly depending on the preparation method (pad-dry-cure vs. exhaustion) and that the Ag-RB coatings were more effective for bacteria than for fungi. The Ag concentrations on the cotton fabrics achieved by the pad-dry-cure method (48 and 52 ppm) were not sufficient to impart satisfactory antifungal activity to the cotton fabrics, though they assured excellent reduction of the bacterium E. coli (98–100%). A minimal inhibitory concentration of Ag in the coating providing a sufficient bacterial reduction of 60% was ca. 24 ppm. Effective antifungal activity was achieved only by applying the exhaustion method, enabling high initial Ag concentration in the Ag-RB coating (>100 ppm). The antibacterial activity depended on the washing treatment. No antifungal activity was noted for washed cotton fabric, even those with highly concentrated Ag (290 ppm) in the Ag-RB coating, but a 94% bacterial reduction was obtained for the corresponding cotton fabric, after 10 repetitive washings, corroborated by the Ag concentration on washed fabric of about 65 ppm.     

Synthesis and characterization of guar gum templated hybrid nano silica

The objective of the present study was the fabrication of green adsorbent hybrids for which native guar gum was used as template to polymerize tetraethoxysilane. The properties and performances of the hybrids could be tailored by using varying molecular sizes of the partially depolymerized guar gum templates of various molecular sizes as control. Zn(II) uptake from aqueous solution was used as a criterion for evaluating the adsorbent efficiency. The optimum material (H4) in terms of maximum Zn(II) uptake, was obtained when the template size used was 375 kDa at a calcination temperature of 700 °C. H4 was also evaluated for Ca(II), Mg(II), Cd(II) and Hg(II) adsorption. To explore the other applicability areas, the hybrids have been extensively characterized using FTIR, XRD, TGA-DTA, PL, SEM, TEM and BET analyses. H4 was found to be as efficient as previously reported vinyl modified-silica nanohybrids. It had a high surface area (264 m²/g) with silica nanoparticles in the size range of 90-140 nm. Being thermally very stable and photoluminescent, the material can be potentially used for many biological, medical and environmental applications.     

A series of POM-based hybrid materials with different copper/aminotriazole motifs

By controlling the reaction temperature, pH value of the system and the polyanion templates, three inorganic-organic hybrid materials based on Keggin polyoxometalate building blocks combined with Cu^I/II and 4-amino-1,2,4-triazole (4atrz) have been obtained by hydrothermal methods, namely, [Cu₃(μ₃-OH)(4atrz)₆][SiW₁₂O₄₀]·I·3H₂O (1), [Cu₄(4atrz)₆][SiW₁₂O₄₀] (2) and [Cu₆(4atrz)₆][PMo₁₂O₄₀]₂·H₂O (3). Crystal structure analysis reveals that the Cu^I/II/4atrz complexes in the three materials show tri-, tetra- and hexanuclear models, respectively. In compound 2, the copper clusters link the polyoxometalates into the chains by weak Cu-O bonds; while in the compounds 1 and 3, the copper clusters and the polyoxometalates stack by the ionic interactions. These compounds are further characterized by powder XRD, elemental analyses, FT-IR and thermogravimetric (TG) analyses. The electrochemical behavior of 3-CPE has been studied in the 1 M H₂SO₄ solution. The results exhibit that there are four pairs of redox waves attributable to the four consecutive two-electron processes of Mo(VI/V) couples and the redox process is surface-controlled.     

Synthesis and characterization of a photoresponsive doxorubicin/combretastatin A4 hybrid prodrug

To explore the application of photoremovable protecting groups (PPGs) in the field of combination chemotherapy, we designed and synthesized a photoresponsive hybrid prodrug 4 that bearing both doxorubicin (DOX) and combretastatin A4 (CA4). Light triggered drug release investigation found that DOX release was mainly accomplished by 405?nm light while CA4 release was mainly triggered by 365?nm light, i.e., prodrug 4 exhibited a quasi-sequential release behavior when a sequential light irradiation strategy was applied. Cell viability evaluation confirmed the increased cytotoxicity of prodrug 4 compared with individual drugs towards MDA-MB-231cells, indicating that a synergistic effect was achieved.     

Synthesis,characterization and sol–gel entrapment of a crown ether‐styryl fluoroionophore

The synthesis and initial evaluation of a new dye‐functionalized crown‐ether, 2‐[2‐(2,3,5,6,8,9,11,12,14,15‐decahydro‐1,4,7,10,13,16‐benzohexaoxacyclooctadecin)ethenyl]‐3‐methyl benzothiazolium iodide (denoted BSD), are reported. This molecule contains a benzyl 18‐crown‐6 moiety as the ionophore and a benzothiazolium to spectrally transduce ion binding. Binding of K⁺ to BSD in methanol causes shifts in the both absorbance and fluorescence emission maxima, as well as changes in the molar absorptivity and the emission intensity. Apparent dissociation constants (K_d) in the range 30–65 µ m were measured. In water and neutral buffer, K_d values were approximately 1 m m . BSD was entrapped in sol–gel films composed of methyltriethoxysilane (MTES) and tetraethylorthosilicate (TEOS) with retention of its spectral properties and minimal leaching. K⁺ binding to BSD in sol–gel films immersed in pH 7.4 buffer causes significant fluorescence quenching, with an apparent response time of approximately 2 min and an apparent K_d of 1.5 m m . Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis,characterization, and photoluminescence property of Nd–TUD‐1

Here, five different samples of neodymium (Nd) incorporated 3D‐mesoporous siliceous materials were fabricated using a single‐step hydrothermal technique. Typically, all samples were subjected to several qualitative elemental and quantitative analyses such as X‐ray diffraction, N₂‐adsorption/desorption, scanning electron microscopy, energy dispersive X‐ray, mapping, high resolution transmission electron microscopy, diffuse reflectance ultraviolet–visible, and Raman spectroscopy. The characterization results showed that at small loading of Nd (i.e. Si/Nd < 20), only isolated centres of trivalent neodymium ions were tetrahedrally coordinated in the TUD‐1 matrix. However, with increasing neodymium loading, additional nanoparticles of neodymium oxide with size 10–20 nm were embedded into silica host pores. Detailed photoluminescence (PL) analysis of all samples was carried out by recording the emission profiles at two diverse excitation wavelengths, 333 and 343 nm, to understand the effect of the Nd³⁺ environment on the PL emission spectra with special attention to the area between 400 and 600 nm. Most importantly, different peaks of the emission spectrum of each sample exhibited a distinct shape based on the Nd³⁺ environment. This performance was superior evidence that PL can be applied as a simple and efficient characterization tool to understand the nature of Nd³⁺ ion linkage with a silica matrix.     

Synthesis, structure, and characterization of two polyoxometalate-photosensitizer hybrid materials

Two hybrid materials based on the tris(bipyridine)ruthenium(II), [Ru(bpy)₃]²⁺ and Keggin-type polyoxometalates, [PW₁₁O₃₉]⁷⁻ and [PW₁₂O₄₀]³⁻, namely, [Ru(bpy)₃][K₅PW₁₁O₃₉] (1) and [Ru(bpy)₃][KPW₁₂O₄₀] (2) were synthesized. X-ray crystallographic study of the red-colored complex, 2, shows that it crystallizes in the orthorhombic space group P_bcn and the polyanions are associated with the [Ru(bpy)₃]²⁺ counterions by Coulombic forces and supramolecular interactions. The molecular complex is further connected and forms a three-dimensional framework through C-H?O_POM and other weak interactions. These complexes were further characterized by FT-IR, UV-Vis, ¹H and ³¹P NMR, luminescent spectra and computational studies. Significantly, these combined spectroscopic studies show that these polyoxometalate-dye hybrids have strong electronic interactions between the cationic dye and polyanion units.     

Homogeneous phase synthesis of cellulose carbamate silica hybrid materials using 1-n-butyl-3-methylimidazolium chloride ionic liquid medium

Cellulose carbamate silica hybrid materials can be prepared in 78–84% yield using the homogeneous phase reaction of 3-(triethoxysilyl)propyl isocyanate with cellulose dissolved in 1-n-butyl-3-methylimidazolium chloride ionic liquid and then using NH₄OH catalyzed hydrolysis of triethoxysilyl groups and the sol–gel process. New cellulose carbamate silica hybrid materials produced were characterized by elemental analysis, FT-IR, and TG-DTA. The hydrophilic affinity of these materials is shown to decrease with the degree of substitution of the cellulose hydroxyl groups with carbamate groups.     

Induction of cell-mediated immunity against B16-BL6 melanoma in mice vaccinated with cells modified by hydrostatic pressure and chemical crosslinking

In the preceding paper we have demonstrated an increase in presentation of both major histocompatibility complex antigens (MHC) and a tumor-associated antigen of the weakly immunogenic B16 melanoma by a straight-forward technique. The method consists in modulating the tumor cell membrane by hydrostatic pressure and simultaneous chemical crosslinking of the cell-surface proteins. In B16-BL6 melanoma, the induced antigenic modulation was found to persist for over 48 h, which permitted the evaluation of the ability of modified B16-BL6 cells to induce immunity against unmodified B16-BL6 cells. In the present study, we have shown that a significant systemic immunity was induced only in mice that were immunized with modified B16-BL6 melanoma cells, whereas immunization with unmodified B16-BL6 cells had only a marginal effect when compared to the results in control sham-immunized mice. The induced immunity was specific since a single immunization affected the growth of B16-BL6 tumors but had no effect on MCA 106, an antigenically unrelated tumor. The addition of interleukin-2 to the immunization regimen had no effect on the antitumor responses induced by the modified B16-BL6 cells. The cell-mediated immunity conferred by immunization with treated B16-BL6 cells was confirmed in experiments in vitro where splenocytes from immunized mice could be sensitized to proliferate by the presence of B16-BL6 cells. In addition, the altered antigenicity of these melanoma cells appeared to correlate with their increased susceptibility to specific effectors. Thus,⁵¹Cr-labeled B16-BL6 target cells, modified by pressure and crosslinking, in comparison to control labeled target cells, were lysed in much greater numbers by effectors such as lymphokine-activated killer cells and allogeneic cytotoxic lymphocytes (anti-H-2^b), while such cells remained resistant to lysis by natural killer cells. Our findings indicate that the physical and chemical modifications of the tumor cells that are described here may be considered as a simple yet effective method for the preparation of tumor vaccines, which could be applied in tumor-bearing hosts.     

Synthesis,characterization and optical properties of polymer‐based ZnS nanocomposites

Nanostructured polymer–semiconductor hybrid materials such as ZnS–poly(vinyl alcohol) (ZnS–PVA), ZnS–starch and ZnS–hydroxypropylmethyl cellulose (Zns–HPMC) are synthesized by a facile aqueous route. The obtained nanocomposites are characterized using various techniques such as X‐ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), UV/vis spectroscopy and photoluminescence (PL). XRD studies confirm the zinc blende phase of the nanocomposites and indicate the high purity of the samples. SEM studies indicate small nanoparticles clinging to the surface of a bigger particle. The Energy Dispersive Analysis by X‐rays (EDAX) spectrum reveals that the elemental composition of the nanocomposites consists primarily of Zn:S. FTIR studies indicate that the polymer matrix is closely associated with ZnS nanoparticles. The large number of hydroxyl groups in the polymer matrix facilitates the complexation of metal ions. The absorption spectra of the specimens show a blue shift in the absorption edge. The spectrum reveals an absorption edge at 320, 310 and 325 nm, respectively. PL of nanocomposites shows broad peaks in the violet–blue region (420–450 nm). The emission intensity changes with the nature of capping agent. The PL intensity of ZnS–HPMC nanocomposites is found to be highest among the studied nanocomposites. The results clearly indicate that hydroxyl‐functionalized HPMC is much more effective at nucleating and stabilizing colloidal ZnS nanoparticles in aqueous suspensions compared with PVA and starch. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis and characterization of drug–saccharide conjugates by enzymatic strategy in organic media

A facile and efficient strategy to prepare drug derivatives with saccharides was developed, and 12 drug–saccharide conjugates were obtained by selective enzymatic synthesis methods. When the transesterification of chlorphenesin vinyl esters with glucose was chosen as a model reaction, the influence of reaction conditions was optimized. Then, we successfully prepared a series of chlorphenesin–saccharide derivatives of three monosaccharides (glucose, mannose and galactose) and three disaccharides (maltose, lactose and sucrose). In order to study the relationship between the solubility of drug–saccharide conjugates and the structure of parent drugs, five hydrophobic drugs (chlorphenesin, mephenesin, guaifenesin, propranolol and clorprenaline) were chosen as substrates to synthesize drug–saccharide conjugates. The results indicated that the aqueous solublity of drug–saccharide derivatives was greatly improved, which was changed by different saccharides and the structure of parent drugs.     

Expression of recombinant hybrid peptide cecropinA(1-8)-magainin2(1-12) in Pichia pastoris: purification and characterization

Hybrid antibacterial peptide CA-MA (cecropinA(1-8)-magainin2(1-12)) is a linear cationic peptide that has potent antimicrobial properties without hemolytic activity. To explore a new approach of expression of hybrid peptide CA-MA in methylotrophic yeast, Pichia pastoris, the gene of CA-MA was obtained by recursive PCR (rPCR) and cloned into the vector pPICZalpha-A. The SalI-linearized plasmid pPICZalpha-CA-MA was transformed into P. pastoris SMD1168 by electroporation. The expression was induced for 96h with 1.0% methanol at 28 degrees C, pH 5.0. Recombinant CA-MA was purified by reversed-phase HPLC and 22 mg pure active CA-MA was obtained from 1L fermentation culture. Tricine-SDS-PAGE indicated that recombinant CA-MA protein molecular weight is 2.6 kDa. Mass spectrometry of purified CA-MA demonstrated a single large signal for the molecular ion [M+2H+](2+) at 1281.07 m/z, identical to that of the putative protein (2.56 kDa). Antimicrobial assays showed that CA-MA has a broad spectrum of antimicrobial property against fungi, as well as Gram-positive and Gram-negative bacteria. This is the first report on the heterologous expression of a hybrid antibacterial peptide with molecular weight below 3.0 kDa in P. pastoris. Our results demonstrate that functional CA-MA can be produced in sufficient quantities using P. pastoris for use in further studies on functionality and diagnostic applications.     

Synthesis and characterization of a new biotinylated gramicidin

A new linear gramicidin analog bearing a biotinyl group grafted on C-terminal part was designed to study ligand–receptor interactions. The C-terminal alcohol in the native peptide was first replaced by an amino group. Then the peptide was synthesized on a polystyrene resin functionalized by the 2-chlorotrityl chloride following a biotinylation performed in solution. This new N′-biotinyl-(EDA)¹⁵-Gramicidin A was reconstituted in planar lipid bilayers and exhibited channel activities similar to those of natural gramicidin, with unitary conductance value about 30 ps in 1 m KCl. Furthermore this ionophore activity was quenched by addition of streptavidin in the surrounding medium. Our system is an outstanding tool for monitoring ligand–receptor interactions and could be used for designing a new biosensor. © 1998 European Peptide Society and John Wiley & Sons, Ltd.     

Synthesis and cytotoxic activities of novel hybrid 2-phenyl-3-alkylbenzofuran and imidazole/triazole compounds

A series of novel hybrid compounds of 2-phenyl-3-alkylbenzofuran and imidazole or triazole were prepared and evaluated in vitro against a panel of human tumor cell lines. The results suggest that the 2-ethyl-imidazole ring, and substitution of the imidazolyl-3-position with a 2-bromobenzyl or naphthylacyl group, were vital for modulating inhibitory activity. In particular, hybrid compound 31 was found to be the most potent derivative with IC₅₀ values of 0.08–0.55 μM against five strains human tumor cell lines and was found to be more selective against breast carcinoma (MCF-7) and colon carcinoma (SW480) (IC₅₀ values 40.8-fold and 40.1-fold lower than cisplatin (DDP)).