Immobilization of growing cells by polyethyleneimine-modified alginate

A unique polymer matrix that is suitable for immobilizing growing cells has been developed. Alginate was chemically modified with polyethyleneimine (PEI), and the resultant polymer aggregate was evaluated as a cell carrier. Our method of immobilization depends on reversible gelation of the PEI-modified alginate. Our hypothesis is that immobilized cells grow by dissolving the surrounding gel matrix; the dissolved polymer adduct is displaced peripherally and gelled again by the influx of calcium ion from the surrounding fermentation broth, retaining both cells and carrier polymer in the gel beads. Thus, the immobilized cells gain space for growth by expanding the carrier matrix. The PEI modification offers the following advantages: (1) improved mechanical strength; (2) improved cell retention; (3) increased catalyst life; (4) ease of pelletization; and (5) an apparent bacteriostatic capability. When immobilized yeast cells were applied to a continuous ethanol fermentation, 94% theoretical conversion of glucose to ethanol was observed, with a reactor productivity of 15–30 g/L/h in a nonsterile reactor. A 3-mo catalyst life and minimal cell washout were observed.     

CO Hydrogenation by K-Promoted Coprecipitated Co/Al2O3

Effect of K promotion on the CO hydrogenation activity and selectivity of coprecipitated Co/Al₂O₃ has been studied. K addition is found to lower total activity while enhancing C₂-C₄ olefins selectivity; kinetic data indicate that the reaction mechanism is not affected.     

Reactivity of Al3O3- cluster toward H2O studied by density functional theory

Density functional theory calculations (Becke's three parameter hybrid functional) have been done on a wide range of possible structures for the complexes formed in the reaction between Al(3)O(3) (-) and one or two water molecules. Both energetically competitive structural isomers of Al(3)O(3) (-) (kitelike and distorted rectangle) were considered. The structures of neutral complexes accessed from detachment of the stable anion structures were also optimized. The calculations predict that hydroxide complexes are energetically favored over Lewis acid-base and charge-dipole complexes. For Al(3)O(3) (-)/H(2)O complexes, the kite-based hydroxide and rectangle-based hydroxide are predicted to be nearly isoenergetic, while for Al(3)O(3) (-)/(H(2)O)(2), the rectangle-based dihydroxide emerges as being 0.5 eV more stable than the lowest energy kite-based dihydroxide. The structures of these and their neutrals are used to analyze anion PE spectra of Al(3)O(4)H(2) (-) and Al(3)O(5)H(4) (-) obtained previously [F. A. Akin and C. C. Jarrold, J. Chem. Phys. 118, 5841 (2003)].     

Comparison of transition probabilities calculated using different parameters on WBEPM theory for some p‐d and d‐p transitions in excited atomic nitrogen

The transition probabilities between individual and multiplet lines for some quartet terms of excited p‐d and d‐p transition arrays of nitrogen atom have been calculated using the weakest bound electron potential model (WBEPM) theory. For determination relevant parameters, we employed both numerical Coulomb approximation (NCA) method and numerical nonrelativistic Hartree–Fock (NRHF) wave functions for expectation values of radii. The necessary energy values have been taken from experimental energy data in the literature. The expectation values of radii obtained using the two different methods have been employed in the calculation of transition probabilities of all transition arrays. The results obtained have been compared with either each other or NIST data. Good agreement with accepted values taken from NIST has been observed for related excited transitions. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Comparison of nickel-group metal cyanides and acetylides and their anions using anion photoelectron spectroscopy and density functional theory calculations

The photoelectron spectra of NiCN-, PdCN-, PtCN-, HNiC2H-, Ni(C2H)2(-), PdC2H-, and PtC2H- are presented along with density functional theory calculations. Linear structures are predicted for all anions and neutrals. NiCN- and NiCN are predicted to have 3delta and 2delta ground states, respectively. HNiC2H- and Ni(C2H)2(-) are predicted to have 2delta and 2delta(g) anion and 3delta and 3pi(g) neutral ground states, respectively. The palladium and platinum cyanide and acetylides have 1sigma+ anion and 2sigma+ neutral ground states. Simulations generated from the calculated parameters are compared to observed spectra, and molecular orbital diagrams are presented to compare the bonding in these species.     

β-Hydroxyamide derivatives of salicylic acid as organocatalysts for enantioselective reductions of prochiral ketones

In order to find the most effective catalyst for the enantioselective reduction of a prochiral ketone, a series of novel β-hydroxyamide derivatives of salicylic acid and chiral amino alcohols were synthesized. Different substituted prochiral ketones have been reduced in high yield (up to 99%) and the corresponding secondary alcohols are formed with good enantiomeric excess (up to 86%). The mechanism of this type of catalyst can be explained by considering the reaction mechanism for the CBS catalyst.     

Aqueous pathways for formation of zinc oxide particles in the presence of carboxymethyl inulin

In this study, zinc oxide (ZnO) crystals were obtained by a simple wet chemical method using zinc nitrate hexahydrate (Zn(NO₃)₂·6H₂O) and hexamethylenetetramine as the starting materials in the presence of the water-soluble biopolymer carboxymethyl inulin (CMI). We investigated the effect of reaction temperature and CMI concentration on the morphology, surface area, particle size, and size distribution of zinc oxide. X-ray diffraction analysis showed the XRD patterns for all the samples were similar to that of ZnO with the wurtzite structure, irrespective of the geometric shape of the particle. The ZnO rod grows preferentially along the [001] direction in the absence of the CMI. The biopolymer affects the ZnO crystals in a concentration-dependent manner by altering the growth rate of the particles along the c-axis and a-axis. The vast majority of the crystals have a central grain boundary in the presence of CMI. The precipitate consisted of micrometer-sized hexagonally shaped bipyramidal ZnO crystals and nanocrystals.     

Modelling of calcium dynamics in brain energy metabolism and Alzheimer's disease

Functional imaging techniques play a major role in the study of brain activation by monitoring the changes in blood flow and energy metabolism. In order to interpret functional neuroimaging data better, the existing mathematical models describing the links that may exist between electrical activity, energy metabolism and hemodynamics in literature are thoroughly analyzed for their advantages and disadvantages in terms of their prediction of available experimental data. Then, these models are combined within a single model that includes membrane ionic currents, glycolysis, mitochondrial activity, exchanges through the blood-brain barrier, as well as brain hemodynamics. Particular attention is paid to the transport and storage of calcium ions in neurons since calcium is not only an important molecule for signalling in neurons, but it is also essential for memory storage. Multiple efforts have underlined the importance of calcium dependent cellular processes in the biochemical characterization of Alzheimer's disease (AD), suggesting that abnormalities in calcium homeostasis might be involved in the pathophysiology of the disease. The ultimate goal of this study is to investigate the hypotheses about the physiological or biochemical changes in health and disease and to correlate them to measurable physiological parameters obtained from functional neuroimaging data as in the time course of blood oxygenation level dependent (BOLD) signal. When calcium dynamics are included in the model, both BOLD signal and metabolite concentration profiles are shown to exhibit temporal behaviour consistent with the experimental data found in literature. In the case of Alzheimer's disease, the effect of halved cerebral blood flow increase results in a negative BOLD signal implying suppressed neural activity.