Purification and properties of an NADP+-specific isocitrate dehydrogenase from Rhizobium meliloti

An NADP+-specific isocitrate dehydrogenase has been purified and characterized from Rhizobium meliloti. The enzyme showed Mn++ or Mg++ requirement. The apparent Km values were 2.00×10-5 m and 1.51×10-5 m for dl-isocitrate and NADP+, respectively. The enzyme was inhibited by ATP, to a lesser extent by ADP and AMP. agr-Ketoglutarate also inhibited the enzyme activity. Oxalacetate and glyoxylate together inhibited the enzyme activity. The inhibition was competitive. Studies with thiol inhibitors suggested that the enzyme contained a sulfhydryl group at or near the active site. The enzyme has an approximate molecular weight of 60 000. Fluorescence studies suggested that the enzyme contained tryptophan.

Dilute solution properties of methyl methacrylate�acrylonitrile copolymer (MA1)

This paper deals with studies on the dilute solution properties of methyl methacrylate�acrylonitrile copolymer of 0.289 mole fraction (mf) of acrylonitrile composition. Mark�Houwink parameters for this copolymer have been evaluated in acetonitrile (MeCN), 2-butanone (MEK), dimethylformamide (DMF) and γ-butyrolactone (γ-BL). The solvent power is found to be in the order of MEK < MeCN < DMF < γ-BL at 30°C. Herein, probably for the first time, the steric factor for the copolymer is found to be lower than that for the parent homopolymers and the excess interaction parameter, �AB is found to be negative. This probably suggests that the units are compatible to each other.

Some properties of indium-tin oxide-films

Thin films of indium-tin oxide have been deposited by DC diode sputtering from an indium-tin alloy target in an argon, hydrogen and oxygen atmosphere. Films with sheet resistance of 11 ohms/square and 80% light transmission have been obtained. The effect of cathode composition and gas mixture on sheet resistance and optical transmission properties of the films have been studied.

Coarse-Grained Molecular Dynamics Simulation of the Aggregation Properties of Multiheaded Cationic Surfactants in Water

The aggregation property of multiheaded surfactants has been investigated by constant pressure molecular dynamics (MD) simulation in aqueous medium. The model multiheaded surfactants contain more than one headgroup (x = 2, 3, and 4) for a single tail group. This increases the hydrophilic charge progressively over the hydrophobic tail which has dramatic consequences in the aggregation behavior. In particular, we have looked at the change in the aggregation property such as critical micellar concentration (cmc), aggregation number, and size of the micelles for the multiheaded surfactants in water. We find with increasing number of headgroups of the Multiheaded surfactants that the cmc values increase and the aggregation numbers as well as the size of the micelles decrease. These trends are in agreement with the experimental findings as reported earlier with x = 1, 2, and 3. We also predict the aggregation properties of multiheaded surfactant With four headgroups (x = 4) for which no experimental studies exist yet.

Dielectric properties of Li2O-3B(2)O(3) glasses

The frequency and temperature dependences of the dielectric constant and the electrical conductivity of the transparent glasses in the composition Li2O-3B(2)O(3) were investigated in the 100 Hz-10 MHz frequency range. The dielectric constant and the loss in the low frequency regime were electrode material dependent. Dielectric and electrical relaxations were, respectively, analyzed using the Cole-Cole and electric modulus formalisms. The dielectric relaxation mechanism was discussed in the framework of electrode and charge carrier (hopping of the ions) related polarization using generalized Cole-Cole expression. The frequency dependent electrical conductivity was rationalized using Jonscher's power law. The activation energy associated with the dc conductivity was 0.80 +/- 0.02 eV, which was ascribed to the motion of Li+ ions in the glass matrix. The activation energy associated with dielectric relaxation was almost equal to that of the dc conductivity, indicating that the same species took part in both the processes. Temperature dependent behavior of the frequency exponent (n) suggested that the correlated barrier hopping model was the most apposite to rationalize the electrical transport phenomenon in Li2O-3B(2)O(3) glasses. These glasses on heating at 933 K/10 h resulted in the known nonlinear optical phase LiB3O5.

Synthesis, X-ray structure and properties of [Ru2O(MeCN)4(O2CMe)2(PPh3)2](ClO4)2

The diruthenium(III) complex [{(PPh3)(MeCN)2Ru}2(μ-O)(μ-O2CMe)2](ClO4)2 (1) has been prepared from Ru2O(O2CMe)4(PPh3)2, which is obtained from a reaction of Ru2Cl(O2CMe)4 and PPh3 in MeCN. The crystal structure of 1 was determined by X-ray studies and the complex has an {Ru2(μ-O)(μ-O2CMe)22+} core and the facial sites on each metal centre are occupied by two MeCN and one PPh3 ligands. The Ru—b. Ru and Ru—Ooxo distances and Ru—O—Ru angle are 3.240(1), 1.866(4) Å and 120.6(2)°, respectively. The cis and trans Ru—N distances in 1 are 2.040(6) and 2.116(5) Å, respectively. The visible spectral band in 1 is observed at 574 nm (var epsilon, 10,800 M−1 cm−1). The 1H NMR spectrum of the diamagnetic complex 1 in CD3CN is in agreement with the X-ray structure.

Synthesis, spectral and electrochemical properties of donor/acceptor substituted fluoroarylporphyrins

Spectroscopic and electrochemical redox properties of a series of fluorinated porphyrins bearing donor-acceptor groups and their Zn(II) and Cu(II) derivatives are presented. The magnitude of the ring reduction potentials and charge transfer properties derived from spectral data depend on the nature and position of the substituent(s), (nitro/dimethylamino) and the central metal ions.

Electrochromic, magnetotransport and AC transport properties of vapor phase polymerized PEDOT(VPP PEDOT)

Poly(3,4-ethylenedioxy)thiophene (PEDOT) doped with tosylate ion (PEDOT-tosylate or VPP PEDOT) was synthesized by vapor phase polymerization (VPP) technique on glass as well as on glass/ITO and the electrochromic properties were investigated. Compared with that of PEDOT-PSS spin-coated on glass/ITO, the studies showed that VPP PEDOT has a lower work function and better electrochromic properties. The magneto and AC transport properties studies were done on VPP PEDOT coated on glass substrate. The system shows 2-dimensional variable range hopping and wave function shrinkage of charge carriers.

Influence of Hydrophilic Surface Specificity on the Structural Properties of Confined Water

The influence of chemical specificity of hydrophilic surfaces on the structure of confined water in the subnanometer regime is investigated using grand canonical Monte Carlo Simulations. The structural variations for water confined between hydroxylated silica surfaces are contrasted with water confined between mica surfaces. Although both surfaces are hydrophilic, our Study shows that hydration of potassium ions on the mica surface has a strong influence on the water Structure and solvation force response of confined water. In contrast to the disrupted hydrogen bond network observed for water confined between Mica Surfaces, water between silica surfaces retains its hydrogen bond network displaying bulklike structural features down to surface separations as small as 0.45 nm. Hydrogen bonding of all invariant contact water layer with the surface silanol groups aids in maintaining a constant number of hydrogen bonds per water molecule for the silica surfaces. As a consequence water depletion and rearrangement upon decreasing confinement is a strong function of the hydrophilic surface specificity, particularly at smaller separations. An oscillatory solvation force response is only observed for water confined between Silica surfaces, and bulklike features are observed for both Surfaces above a surface separation of about 1.2 nm. We evaluate and contrast the water density, dipole moment distributions, pi pair correlation functions, and solvation forces as a function of the surface separation.

Rapid quenching and glass formation in chalcogenide glasses: Preparation and properties of Ge-As-Te glasses over an extended composition ranges

In Ge-As-Te system, the glass forming region determined by normal melt quenching method has two regions (GFR I and GFR II) separated by few compositions gap. With a simple laboratory built twin roller apparatus, we have succeeded in preparing Ge7.5AsxTe92.5-x glasses over extended composition ranges. A distinct change in T-g is observed at x = 40, exactly at which the separation of the glass forming regions occur indicating the changes in the connectivity and the rigidity of the structural network. The maximum observed in glass transition (T-g) at x = 55 corresponding to the average coordination number (Z(av)) = 2.70 is an evidence for the shift of the rigidity percolation threshold (RPT) from Z(av) = 2.40 as predicted by the recent theories. The glass forming tendency (K-gl) and Delta T (=T-c-T-g) is low for the glasses in the GFR I and high for the glasses in the GFR II.

Effect of oxygen partial pressure on the structural and optical properties of dc reactive magnetron sputtered molybdenum oxide films

Molybdenum oxide films (MoO3) were deposited on glass and crystalline silicon substrates by sputtering of molybdenum target under various oxygen partial pressures in the range 8 × 10−5–8 × 10−4 mbar and at a fixed substrate temperature of 473 K employing dc magnetron sputtering technique. The influence of oxygen partial pressure on the composition stoichiometry, chemical binding configuration, crystallographic structure and electrical and optical properties was systematically studied. X-ray photoelectron spectra of the films formed at 8 × 10−5 mbar showed the presence of Mo6+ and Mo5+ oxidation states of MoO3 and MoO3−x. The films deposited at oxygen partial pressure of 2 × 10−4 mbar showed Mo6+ oxidation state indicating the films were nearly stoichiometric. It was also confirmed by the Fourier transform infrared spectroscopic studies. X-ray diffraction studies revealed that the films formed at oxygen partial pressure of 2 × 10−4 mbar showed the presence of (0 k 0) reflections indicated the layered structure of α-phase MoO3. The electrical conductivity of the films decreased from 3.6 × 10−5 to 1.6 × 10−6 Ω−1 cm−1, the optical band gap of the films increased from 2.93 to 3.26 eV and the refractive index increased from 2.02 to 2.13 with the increase of oxygen partial pressure from 8 × 10−5 to 8 × 10−4 mbar, respectively.

Purification and properties of protocatechuate-3,4-dioxygenase from Tecoma stans L

Protocatechuate-3,4-dioxygenase from the leaves of Tecoma stans was purified to near homogeneity and some of its properties studied. It was optimally active at pH 5.2 and at 40°C. Its molecular weight of approx. 150 000 was determined by gel filtration on a Sephadex G-150 column. The Km value for protocatechuate was found to be 330 μM and for ferrous sulfate, 40 μM. The enzyme was highly specific for protocatechuate and did not attack any of the substrate analogues. None of the substrate analogues tested inhibited the enzyme activity. Sulfhydryl reagents inhibited the enzyme activity which could be partially reversed by sulfhydryl compounds. The dioxygenase activity was not associated with polyphenol oxidase activity.

Structural, dielectric, impedance and optical properties of CaBi2B2O7 glasses and glass-nanocrystal composites

Optically clear glasses were fabricated by quenching the melt of CaCO3-Bi2O3-B2O3 (in equimolecular ratio). The amorphous and glassy characteristics of the as-quenched samples were confirmed via the X-ray powder diffraction (XRD) and differential scanning calorimetric (DSC) studies These glasses were found to. have high thermal stability parameter (S). The optical transmission studies carried out in the 200-2500 nm wavelength range confirmed both the as-quenched and heat-treated samples to be transparent between 400 nm and 2500 nm. The glass-plates that were heat-treated just above the glass transition temperature (723 K) for 6 h retained approximate to 60% transparency despite having nano-crystallites (approximate to 50-100 nm) of CaBi2B2O7 (CBBO) as confirmed by both the XRD and transmission electron microscopy (TEM) studies. The dielectric properties and impedance characteristics of the as-quenched and heat-treated (723 K/6 h) samples were studied as a function of frequency at different temperatures. Cole-Cole equation was employed to rationalize the impedance data.

Fluorescence properties of Baltic Sea phytoplankton

To obtain data on phytoplankton dynamics with improved spatial and temporal resolution, and at reduced cost, traditional phytoplankton monitoring methods have been supplemented with optical approaches. In this thesis, I have explored various fluorescence-based techniques for detection of phytoplankton abundance, taxonomy and physiology in the Baltic Sea. In algal cultures used in this thesis, the availability of nitrogen and light conditions caused changes in pigmentation, and consequently in light absorption and fluorescence properties of cells. In the Baltic Sea, physical environmental factors (e.g. mixing depth, irradiance and temperature) and related seasonal succession in the phytoplankton community explained a large part of the seasonal variability in the magnitude and shape of Chlorophyll a (Chla)-specific absorption. The variability in Chla-specific fluorescence was related to the abundance of cyanobacteria, the size structure of the phytoplankton community, and absorption characteristics of phytoplankton. Cyanobacteria show very low Chla-specific fluorescence. In the presence of eukaryotic species, Chla fluorescence describes poorly cyanobacteria. During cyanobacterial bloom in the Baltic Sea, phycocyanin fluorescence explained large part of the variability in Chla concentrations. Thus, both Chla and phycocyanin fluorescence were required to predict Chla concentration. Phycobilins are major light harvesting pigments for cyanobacteria. In the open Baltic Sea, small picoplanktonic cyanobacteria were the main source of phycoerythrin fluorescence and absorption signal. Large filamentous cyanobacteria, forming harmful blooms, were the main source of the phycocyanin fluorescence signal and typically their biomass and phycocyanin fluorescence were linearly related. Using phycocyanin fluorescence, dynamics of cyanobacterial blooms can be detected at high spatial and seasonal resolution not possible with other methods. Various taxonomic phytoplankton pigment groups can be separated by spectral fluorescence. I compared multivariate calibration methods for the retrieval of phytoplankton biomass in different taxonomic groups. Partial least squares regression method gave the closest predictions for all taxonomic groups, and the accuracy was adequate for phytoplankton bloom detection. Variable fluorescence has been proposed as a tool to study the physiological state of phytoplankton. My results from the Baltic Sea emphasize that variable fluorescence alone cannot be used to detect nutrient limitation of phytoplankton. However, when combined with experiments with active nutrient manipulation, and other nutrient limitation indices, variable fluorescence provided valuable information on the physiological responses of the phytoplankton community. This thesis found a severe limitation of a commercial fast repetition rate fluorometer, which couldn t detect the variable fluorescence of phycoerythrin-lacking cyanobacteria. For these species, the Photosystem II absorption of blue light is very low, and fluorometer excitation light did not saturate Photosystem II during a measurement. This thesis encourages the use of various in vivo fluorescence methods for the detection of bulk phytoplankton biomass, biomass of cyanobacteria, chemotaxonomy of phytoplankton community, and phytoplankton physiology. Fluorescence methods can support traditional phytoplankton monitoring by providing continuous measurements of phytoplankton, and thereby strengthen the understanding of the links between biological, chemical and physical processes in aquatic ecosystems.