The use of immobilized Saccharomyces cerevisiae on radiation crosslinked acrylamide–maleic acid hydrogel carriers for production of ethyl alcohol

Radiation crosslinked acrylamide/maleic acid (AAm/MA) copolymers were prepared by γ-irradiation. They were used in experiments on swelling, diffusion, and immobilization of yeast cells (Saccharomyces cerevisiae) for the production of ethyl alcohol. AAm/MA hydrogels containing different amount of MA, irradiated at different doses, were used for swelling and diffusion studies. The parameters of swelling, diffusional exponents, network constants, diffusion coefficients and percent porosity of the hydrogel/penetrant systems were calculated and evaluated. Yeast cells were immobilized on to the hydrogels by adsorption during multiplication, and ethyl alcohol production by the hydrogels was investigated. Swelling of AAm/MA increased with increase in MA content. Ethyl alcohol production also increased with increasing MA in the hydrogels but decreased with an increase of irradiation dose.     

Structure of Co2(CO)6(dppm) and Co2(CO)5(CHCO2Et)(dppm) (dppm = Ph2PCH2PPh2) and exchange reaction with CO: An experimental and computational study

Crystal structures of Co₂(CO)₆(dppm) (1) and Co₂(CO)₅(CHCO₂Et)(dppm) (2) (dppm = Ph₂PCH₂PPh₂) show asymmetry with respect to the orientation of the phenyl groups in 1 and owing to the bridging ethoxycarbonylcarbene ligand in 2. The effect of this asymmetry was recognized in the solid-state ³¹P NMR spectra of 1 and 2 and in the solid-state and solution ¹³C NMR spectra of 2 as well, but not in the solid-state and solution ¹³C NMR spectra of 1. In CH₂Cl₂ solution under an atmosphere of ¹³CO, the CO ligands of both complexes exchange with ¹³CO. The overall rate of ¹³CO exchange at 10 °C was found to be k_obs = 0.107 × 10⁻³ s⁻¹ for 1 and k_obs = 0.243 × 10⁻³ s⁻¹ for 2. Two-layered ONIOM(B3LYP/6-31G(d):LSDA/LANL2MB) studies revealed fluxional behavior of 1 with rather small barriers of activation of the rearrangements. Four possible isomers have been computed for 2, close to each other energetically.     

Structure of the exudate gum from Meryta sinclairii

A gum that exudes from the wounded trunk of the New Zealand native tree Meryta sinclairii has been isolated. The gum was completely precipitated by the β-glucosyl Yariv reagent and was thus determined to be an arabinogalactan-protein (AGP). It contained >95% w/w carbohydrate and only 2% w/w protein with a high level of hydroxyproline. SEC-MALLS showed that the gum had a weight-average molecular weight of 4.45×10⁶ Da compared with 6.02×10⁵ Da for gum arabic. Constituent sugar and linkage analyses were consistent with polymers comprised of a highly branched backbone of 1,3-linked galactopyranosyl (Galp) residues, with side-chains made up of arabinofuranose- (Araf) containing oligosaccharides, terminated variously by rhamnopyranosyl (Rhap), arabinopyranosyl (Arap), Galp and glucuronopyranosyl (GlcpA) residues. Analysis by one-dimensional and two-dimensional ¹H and ¹³C NMR experiments confirmed the linkage analyses. The structure of the gum is discussed in comparison with the structure of gum arabic and other AGPs.     

Modulate the phase transition temperature of hydrogels with both thermosensitivity and biodegradability

The synthesis and characterization of thermoresponsive hydrogels on the basis of N-isoproplyarylamide (NIPAAm) and acrylamide (AAm) copolymers crosslinked with a novel biodegradable crosslinker (PEG-co-PLA) were carried out in this study. Swelling measurement results demonstrated that four gels of PNAM5, PNAM10, PNAM12 and PNAM15 are thermoresponsive. The equilibrium swelling ratio and degradation of the hydrogels strongly depend on hydrogels composition. The morphology of the hydrogels was observed by scanning electron microscopy (SEM), and their thermal property was characterized by differential scanning calorimetry (DSC). The results show that the proportion of AAm in the copolymer has notable effect on the low critical solution temperature (LCST) of the hydrogel. When the molar ratio of AAm to NIPAAm was increased from 1:10 to 3:10 the LCST of the copolymer increased from 39.7 to 64.2 °C. The compression modulus of PNAM15 is of the highest among other hydrogels, because PNAM15 hydrogel has a more compact structure.     

The swelling behavior and network parameters of guar gum/poly(acrylic acid) semi-interpenetrating polymer network hydrogels

Guar gum/poly(acrylic acid) semi-interpenetrating polymer network (IPN) hydrogels have been prepared via free radical polymerization in the presence of a crosslinker of N,N′-methylene bisacrylamide (MBA). The kinetics of swelling and the water transport mechanism were studied as a function of the composition of the hydrogels and the pH of the swelling medium. Hydrogels showed enormous swelling in aqueous medium and displayed swelling characteristics, which were highly dependent on the chemical composition of the hydrogels and pH of the medium in which hydrogels were immersed (ionic strength I = 0.15 mol/L). The semi-INP hydrogels were characterized by evaluating various network parameters such as average molecular weight between crosslinks (M_c) crosslink density (ρ) and mesh size ξ.     

Cell adhesion and proliferation on poly(N-vinylacetamide) hydrogels and double network approaches for changing cellular affinities

Poly(N-vinylacetamide) hydrogels (PNVA gels) were synthesized to investigate their basic characteristics for biomedical applications such as water contact angles, protein uptake, and mouse fibroblasts (L-929) cell adhesion. Because PNVA gels show hydrophilic features, double network (DN) hydrogels were prepared by the secondary polymerization of N-vinylacetamide (NVA) or acrylamide (AAm) in PNVA gels (NVA/NVA DN gels and NVA/AAm DN gels, respectively), in order to vary PNVA gel features for biocompatibility. Contact angles for both DN gels decreased to around 20 degrees, whereas both PNVA and PAAm gels were over 30 degrees. On the other hand, more protein tended to adsorb to DN gels than single network hydrogels. Compared to PNVA gel, cell adhesion and proliferation on NVA/NVA DN gel were improved with less swelling ratio and much protein uptake, while no significant difference was observed on NVA/AAm DN gel, probably due to more hydrophilic character, supported by lowest water contact angle. These complicated structure change in DN gels would provide a new methodology for tuning the biocompatibility of hydrogels and for controlling surface hydrophilic characteristics and network structures.     

Molybdenocene-oligonucleotide binding study at physiological pH using NMR spectroscopy and cyclic voltammetry

The self-complementary oligonucleotide CGCATATATGCG was used as a model to establish the binding interactions of antitumor molybdenocene dichloride and DNA. The free dodecamer was first characterized using ¹H, NOESY, and DQF-COSY NMR experiments, which enable to pinpoint the guanines and adenines as well as the cytosines and thymines signals in the aromatic region. Molybdenocene dichloride was characterized in saline and buffer solutions as function of pH by ¹H NMR spectroscopy. In 10 mM NaCl/D₂O solution at pH of 6.5 and above, Cp₂Mo(OD)(D₂O)⁺ is in equilibrium with its dimeric species, [Cp₂Mo(μ-OH)₂MoCp₂]²⁺. In 25 mM Tris/4 mM NaCl/D₂O at physiological pH, a new stable species is formed, coordinated by the buffer, Tris(hydroxymethyl)aminomethane. The interactions of molybdenocene dichloride species with CGCATATATGCG were studied at different pH. At pH 6.5, in 4 mM NaCl/D₂O solution, ¹H NMR spectra of CGCATATATGCG exhibit downfield shifts in the signals associated mainly to adenines and guanines, upon addition of molybdenocene dichloride. At pH 7.4, in 25 mM Tris/4 mM NaCl/D₂O, molybdenocene species causes broadening and small downfield shifts to the purines and pyrimidine signals, suggesting that molybdenocene dichloride can get engaged in binding interactions with the oligonucleotide in a weak manner. ³¹P NMR spectra of these interactions at pH 7.4 showed no changes associated to Mo(IV)-OP coordination, indicating that molybdenocene–oligonucleotide binding interactions are centered, most likely, on the bases. Cyclic voltammetry titration showed a 4.9% of molybdenocene–oligonucleotide interaction. This implicates that possible binding interactions with DNA are weak.     

Chemical modification of Cassia occidentalis seed gum: carbamoylethylation

The seeds of Cassia occidentalis, an annual weed occurring throughout India, is a rich source of galactomannan gum. The gum derived from seed endosperm can be potentially utilized in a number of industries to replace the conventional gums. With a view to utilize the gum for broader applications, carbamoylethylation of C. occidentalis seed gum was carried out with acrylamide in presence of sodium hydroxide under different reaction conditions. Variables studied were concentration of sodium hydroxide, acrylamide, gum–solvent ratio, reaction time and temperature. The nitrogen content, carboxyl content and total ether content were determined. The optimum condition for preparing carbamoylethyl C. occidentalis seed gum (%N=2.57) comprised concentration of acrylamide (0.070 mol), sodium hydroxide (0.125 mol), C. occidentalis seed gum (0.03 mol) at 30 °C for 3 h. Rheological properties of carbamoylethyl C. occidentalis seed gum solution showed non-Newtonian pseudo-plastic behavior, relatively high viscosity, cold water solubility and solution clarity vis-à-vis unmodified C. occidentalis seed gum.     

Characterization of a H-arginine-vasopressin binding site in the cingulate gyrus of the rat pup

Autoradiographic analysis of 1, 8, 16 and 26-day-old rat brains showed ³H-arginine⁸-vasopressin (³H-AVP) binding to the cingulate gyrus-dorsal hippocampus (CG) only in the 8-day-old rat brain. Saturation analysis of CG membranes prepared from pups (7–10 days) and adults (90 days) revealed a small but significant increase in binding site concentration in adults compared to pups. However, the K_d of the ³H-AVP binding site increased significantly with age. The K_d of ³H-AVP binding to pup CG membranes was 0.9±0.1 nM, while the adult CG was 5.7±1.0 nM. The pharmacological specificity of ³H-AVP binding sites in the pup and adult CG was similar, but differed markedly from the profile observed in adult septal membranes. The primary specificity difference between the pup CG and septum was the reduced potency of certain V₁ receptor antagonists. In competition experiments the CG binding site showed a reduced affinity for the V₁ antagonist, [d(CH₂)₅, Tyr(Me)]AVP. This reduced affinity for the V₁ antagonist was also documented autoradiographically using ³H-[d(CH₂)₅, Tyr(Me)]AVP. The data suggest that the ³H-AVP binding site expressed in the pup CG is not identical to the V₁ type receptor present in the periphery and brain of the adult rat.     

Modification of Okra mucilage with acrylamide: Synthesis, characterization and swelling behavior

In the present communication, the synthesis and characterization of Okra mucilage, a food grade and water-soluble polysaccharide, based-materials are described. Okra mucilage has been modified by grafting acrylamide (AAm) for developing the new green polymeric materials of specialty applications. Grafting has been done under N₂ atmosphere using redox initiator and hydrogels were prepared by using N,N-methylenebisacrylamide (NN-MBAAm) as crosslinker. The effect of monomer concentration, initiator concentration, reaction time and temperature in terms of grafting efficiency (%GE), percent grafting (PG) and percent gel (%G) has been investigated. The grafted polymers and hydrogels were characterized by SEM, XRD and FTIR techniques to study various structural aspects. The swelling behavior of the crosslinked polymeric material has also been studied as a function of time, temperature and pH. The application area of these polymers is varied from biomaterials to the wastewater treatment.