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.     

Role of c-fos gene in vasoactive intestinal peptide promoted synthesis of pulmonary surfactant phospholipids

We previously reported that vasoactive intestinal peptide (VIP) promoted synthesis of phosphatidylcholine (PC) in alveolar type II (ATII) cells. But the intracellular mechanism for this effect was unknown. In this work, we investigated the intracellular signal transduction pathway for VIP promoted synthesis of PC, the major lipid component of pulmonary surfactant (PS), by using an antagonist of VIP receptors, inhibitor of protein kinase C (PKC) and antisense oligonucleotides (AS-ODN) for c-fos oncogene. Our results showed that: ① [D-P-Cl-Phe(6)-Leu(17)]-VIP (10^− 6 mol/l), an antagonist of VIP receptors, could decrease the quantity of [³H] choline incorporation, microsomal choline-phosphate cytidylyltransferase (CCT) mRNA expression and CCT activity induced by VIP (10^− 8 mol/l) in cultured lung explants to the control levels; ② VIP (10^− 8 mol/l) upregulated c-Fos protein expression in ATII cells. AS-ODN for c-fos oncogene (9 × 10^− 6 mol/l) could block the elevation of [³H] choline incorporation, microsomal CCT mRNA expression and CCT activity induced by VIP in cultured lung explants and in ATII cells; ③ H7 (10^− 5 mol/l), a PKC inhibitor could also reduce VIP induced [³H] choline incorporation, microsomal CCT mRNA expression and CCT activity in cultured lung explants and in ATII cells. These results demonstrated that VIP receptors, PKC and c-Fos protein played important roles in the signaling pathway through which VIP promoted the synthesis of PC.     

Synthesis and NMR structural analysis of O-succinyl derivative of low-molecular-weight κ-carrageenan

Low-molecular-weight (LMW) κ-carrageenan was achieved through mild hydrochloric acid hydrolysis of κ-carrageenan. The acylation of LMW κ-carrageenan was performed by use of tetrabutylammonium (TBA) salt of the anionic polysaccharide fragments, succinic anhydride, 4-dimethylaminopyridine and tributylamine under homogeneous conditions in N,N-dimethylformamide at 80 °C. Investigation of FT-IR spectrum of the succinylated LMW κ-carrageenan showed that a monoester derivative with succinyl group was formed when LMW κ-carrageenan reacted with succinic anhydride. The ¹H and ¹³C NMR spectroscopy has been used to characterize the fine structure of O-succinyl derivative of the LMW κ-carrageenan. The ¹³C and ¹H NMR chemical shifts of disaccharide unit of O-succinyl LMW κ-carrageenan have been fully assigned using 2D NMR spectroscopic techniques.     

DNA buoyant density shifts during 15N-DNA stable isotope probing

DNA-based stable isotope probing (SIP) is a novel technique for the identification of organisms actively assimilating isotopically labeled compounds. Herein, we define the limitations to using ¹⁵N-labeled substrates for SIP and propose modifications to compensate for these shortcomings. Changes in DNA buoyant density (BD) resulting from ¹⁵N incorporation were determined using cultures of disparate GC content (Escherichia coli and Micrococcus luteus). Incorporation of ¹⁵N into DNA increased BD by 0.015±0.002 g mL⁻¹ for E. coli and 0.013±0.002 g mL⁻¹ for M. luteus. The DNA BD shift was greatly increased (0.045 g mL⁻¹) when dual isotope (¹³C plus ¹⁵N) labeling was employed. Despite the limited DNA BD shift following ¹⁵N enrichment, we found the use of gradient fractionation, followed by a comparison of T-RFLP profiles from fractions of labeled and control treatments, facilitated detection of enrichment in DNA samples from either cultures or soil.     

Responsive hybrid hydrogels with volume transitions modulated by a titin immunoglobulin module

The I28 immunoglobulin (Ig)-like module of human cardiac titin, an elastic muscle protein, was used to cross-link acrylamide (AAm) copolymers into hybrid hydrogels. Cross-linking was accomplished through metal coordination bonding between terminal histidine tags (His tags) of the I28 module and metal-chelating nitrilotriacetic acid (NTA)-containing side chains on the copolymer. In solution, the beta-sheet structure of the I28 module unfolded with a transition midpoint of about 58 degrees C as the temperature was elevated. Hydrogels cross-linked with the I28 module demonstrated positive temperature responsiveness; they swelled to 3 times their initial volume at temperatures above the melting temperature of the cross-links. Positive temperature responsiveness is unusual for synthetic hydrogels. The I28 hybrid hydrogels demonstrate that cross-linking synthetic polymers with natural, well-characterized protein modules is a practical strategy for creating new materials with unique environmental responsiveness predictably determined by the mechanical properties of the protein cross-links. These new materials may be useful for controlled chemical delivery.     

Alkaline extractability of pectic arabinan and galactan and their mobility in sugar beet and potato cell walls

The organisation of sugar beet and potato cell walls was studied using alkaline extractions following a response surface methodology, simultaneously with solid-state ¹³C NMR spectroscopy. The influence of two extraction parameters: NaOH concentration (0.05, 0.275, 0.5 M) and temperature (40, 65, 90 °C) on the composition (neutral and acidic sugars) of the residues recovered was established. Treatments of increasing harshness progressively washed off non-cellulosic polysaccharides from the cell walls. Alkaline treatments applied to sugar beet cell wall material (SB-CWM) revealed the presence of diverse pectin populations. The existence of distinct pectin populations in potato cell wall material (P-CWM) was less outstanding. Solid-state ¹³C NMR applied to SB-CWM and P-CWM and residues after treatment by 0.275 M NaOH at 65 °C revealed two fractions of pectic arabinan and galactan side chains. One fraction was highly mobile, whereas the other one displayed restricted mobility.     

Developmental toxicity assessment of thermoresponsive poly(N-isopropylacrylamide-co-acrylamide) oligomers in CD-1 mice

BACKGROUND: Although polymers and hydrogels are used successfully in biomedical applications, including implants and drug delivery devices, smaller molecular weight oligomers, such as those investigated here, have not been extensively studied in vivo. Poly(N‐isopropylacrylamide‐co‐acrylamide), or P(NIPAAm‐co‐AAm), has a unique thermoresponsive behavior and is under investigation as a novel drug delivery system for metastatic cancer treatment. To date, no studies have been published regarding the safety of P(NIPAAm‐co‐AAm) to the conceptus. METHODS: From gestation days (GD) 6–16, pregnant CD‐1 mice were dosed via i.p. injection with aqueous solutions containing 500, 750, or 1,000 mg/kg/d P(NIPAAm‐co‐AAm). Dams were sacrificed on GD 17 and their litters were examined for abnormalities. RESULTS: P(NIPAAm‐co‐AAm) caused no statistically significant difference in maternal weight gain or percent resorbed or dead fetuses compared to control values, but fetal weight was significantly decreased in the two highest dosage groups. CONCLUSIONS: At the highest dosages employed, maternal exposure to P(NIPAAm‐co‐AAm) was associated with decreased fetal weight. However, as the estimated human exposure levels for persons using this system would be some 1,500‐fold lower than the lowest dosage administered in this study, the authors feel that this oligomer was not shown to pose a biologically significant risk at relevant human dosages. Birth Defects Res (Part B), 2008. © 2008 Wiley‐Liss, Inc.     

Synthesis and solution behavior of the trinuclear palladium(II) unsaturated carboxylate complexes triangle-Pd3[μ-O2CC(R′) = CHMe]6 (R′ = Me, H): X-ray structure of palladium(II) tiglate (R′ = Me)

The first examples of binary palladium(II) derivatives of unsaturated carboxylic acids are reported. It was found that the interaction of Pd₃(μ-OAc)₆ with the ,β-unsaturated 1-methylcrotonic (tiglic) and crotonic acids leads to the corresponding carboxylates of composition Pd₃[μ-O₂CC(R′) = CHMe]₆, where R′ = Me (1) or H (2). The new compounds have been characterized by elemental analysis, solid and solution IR, ¹H and ¹³C NMR, and ESI mass spectrometry. The crystal structure of 1 has been determined. This molecule displays a central Pd₃ cyclic core with Pd–Pd distances of 3.093–3.171 Å. Each Pd–Pd bond is bridged by a pair of carboxylate ligands, one above and the other below the Pd₃ plane, providing a square planar coordination for each Pd atom in an approximate D_3h overall symmetry arrangement. Solution spectroscopic data show that the bridging η¹:η¹:μ₂ interaction of the carboxylates of 1 and 2 is readily displaced, with a change of the ligand to the terminal (η¹) coordination mode.     

Contribution of the heme propionate groups to the electron transfer and electrostatic properties of myoglobin

The role of the heme propionate groups in determining the electron transfer and electrostatic properties of myoglobin have been studied by thermodynamic, kinetic, and spectroscopic studies of horse heart myoglobin in which the heme propionate groups are esterified. Spectroelectrochemical analysis has established that the E_m,7 of dimethylester heme-substituted Mb (DME-Mb) (E_m,7 = 100.2(2) mV vs. NHE (Normal Hydrogen Electrode) (25 °C) is increased  40 mV relative to that of the native protein with ΔH° = −12.9(2) kcal/mol and ΔS° = −51.0(8) cal/mol/deg (pH 7.0, μ = 0.1 M (phosphate)). The second order rate constant for reduction of DME-metMb by Fe(EDTA)²⁻ is increased  > 400-fold relative to that for reduction of native metMb to a value of 1.34(2) × 10³ M⁻¹ s⁻¹ with ΔS^‡ = −13(1) cal/mol/deg and ΔH^‡ = 9.2(3) (pH 7.0, μ = 0.1 M (phosphate)). Analysis of the pH dependences of the reduction potential and rate constant for reduction by Fe(EDTA)²⁻ demonstrates that heme propionate esterification introduces significant changes into the electrostatic interactions in myoglobin. These changes are also manifested by differences in the pH dependences of the ¹H NMR spectra of native and DME-metMb that reveal shifts in pK_a values for specific His residues as the result of heme propionate esterification. In sum, the current results establish that heme propionate esterification not only affects the electron transfer properties of myoglobin but also influences the titration behavior of specific His residues.     

Preparation and physicochemical characteristics of self-assembled nanoparticles of deoxycholic acid modified-carboxymethyl curdlan conjugates

Various deoxycholic acid (DOCA)-modified-carboxymethylated (CM)-curdlan (DCMC) were synthesized and characterized by FTIR, ¹H NMR and XRD. The degree of DOCA substitution (DS), as spectrophotometrically determined, was 2.1, 3.2, 4.1, or 6.3 DOCA groups per hundred sugar residues of CM-curdlan. The physicochemical properties of the self-assembled nanoparticals in aqueous media were investigated using ¹H NMR, dynamic light scattering, zeta potential, transmission electron microscopy (TEM) and fluorescence spectroscopy. DCMC conjugates provided monodispersed self-assembled nanoparticles in water, with mean diameter decreasing from 192 to 347 nm with DOCA DS increasing. Moreover, the mean diameter also increased with decreasing pH in PBS. Zeta potential of DCMC self-assembled nanoparticles exhibited near −60 mV in distilled water and −26 to −36 mV in PBS, indicating these nanoparticles were covered with negatively charged CM-curdlan shells. The critical aggregation concentration (cac) of the DCMC were dependent on the degree of substitution (DS) of DOCA and were slightly lower in PBS than in distilled water. The TEM images demonstrated that these self-assembled nanoparticles were of spherical shape.