Adenosine-5'-carboxylic Acid

The two molecules in the asymmetric unit of adenosine-5'-carboxylic acid, C10H11N5O5, exist as zwitterions with N1 protonated and the carboxyl groups ionized. Both molecules are in an anti conformation with glycosyl torsion angles of -161.4(3) and -155.5(3)degrees. The ribose moieties adopt a C3-endo-C2-exo twist conformation. The pseudo-rotation parameters are P = 0.01(1) and 6.58(1)degrees, and tau(m) = 36.2(2) and 34.6(2)degrees, for molecules A and B, respectively. The carboxyl groups of A and B are not in the standard g(+), g(-) or t conformations. Both Watson-Crick sites, N1 and N6, of the adenine bases are involved in a pair of hydrogen bonds with the dissociated carboxyl groups, forming a cyclic tetramer. The adenine base of molecule A stacks on the ribose O4' atom of a symmetry-related B molecule at a distance of 2.88 Angstrom; the adenine base of B stacks in an analogous way at a distance of 2.91 Angstrom.

1H NMR study of [N(CH3)4]2ZnCI4 at high pressures and low temperatures

Wide-line proton NMR studies on polycrystalline tetramethylammonium tetrachlorozincate have been carried out at high hydrostatic pressures up to 15 kbar in the temperature range 77-300 K and at ambient pressure down to 4.2 K. A second-moment transition is observed to occur starting around 161 K, the temperature for the V-VI phase transition. This transition temperature is seen to have a negative pressure coefficient up to 2 kbar, beyond which it changes sign. At 77 K the second moment decreases to 4 kbar and then increases again as a function of pressure. The results are explained in terms of the dynamics of the N(CH3)4 groups.

Flexure of composite plates

A new higher order shear deformation theory of laminated composite plates is developed. The basic displacement variables in this theory are two partial normal displacements and two in-plane displacement parameters. The governing equations are presented in the form of four simultaneous partial differential equations. The shear deformation theories of Bhimareddy and Stevens, and of Reddy are special cases of this formulation. In their models, transverse shear strains will become zero at points in the plate where displacements are constrained to be zero such as those on fixed edges. This limitation has been overcome in the present formulation.

Microprocessor-based transient analyser

An 8085-based microprocessor system readily available in the laboratory has been developed in conjunction with a slow A/D converter to digitize repetitive transient signals arising in a solid-state physics experiment. The unit has been successfully used to measure the domain switching time in ferroelectric crystals, the duration of which is of the order of milliseconds-seconds.

Complexes of lanthanide perchlorates with 2-N-(pyridyl)benzamide

New complexes of lanthanide perchlorates with 2-N-(pyridyl) benzamide (PyBA) of the type Ln(PyBA)3(ClO4)3 where Ln = Y and La---Yb have been synthesised and characterised by analyses, conductance, IR, 13C NMR (for diamagnetic complexes only) and electronic spectra. The molar conductance and IR data point to the ionic nature of the perchlorate groups in the complexes. IR data along with the 13C NMR data unequivocally proves that the coordination of the ligand to the metal ions taken place in a bidentate fashion through the oxygen of the benzamide group and the nitrogen of the heterocyclic ring. From a comparison of the visible electronic spectral shapes of the Nd3+, Ho3+ and Er3+ complexes with those reported in the literature, a 6-coordinate geometry around the metal ion has been assigned in all the complexes.

Dendritic structures produced on solidification of multicomponent aqueous solutions

Dendrite structures of ice produced on undirectional solidification of ternary and quaternary aqueous solutions have been studied. Upon freezing, solutions containing more than one solute produce plate-shaped dendrites of ice. The spacing between dendrites increase linearly with the distance from the chill surface and the square root of local solidification time (or square root of inverse freezing rate) for any fixed composition. For fixed freezing conditions, the dendrite spacings from multicomponent aqueous solutions were a function of the concentrations and diffusion coefficients of the individual solutes. The dendrite spacing produced by freezing of a solution was changed by the addition of a solute different from those already present. If the main diffusion coefficient of the added solute is higher than that of solutes already present, the dendrite spacing is increased and vice versa. The dendrite spacing in multi-component systems increases with the total solute concentration if the constituent solutes are present in equal amounts. The dendrite spacing obtained on freezing of these dilute multicomponent solutions can be expressed by regression equations of the type Image Full-size image (2K) where L is the dendrite spacing in microns, C1, C2 and C3 are concentrations of individual solutes, Θf is the total freezing time and A1 −A8 are constants. A Yates analysis of the dendrite spacings in a factorial design of quaternary solutions indicates that there are strong interactions between individual solutes in regard to their effect on the dendrite spacings. A mass transport analysis has been used to calculate the interdendritic supersaturation ΔC of the individual solutes, the supercooling in the interdendritic liquid ΔT, and the transverse growth velocity of the dendrites, VT. In ternary solutions if two solutes are present in equal amount the supersaturation of the solute with higher main diffusion coefficient is lower, and vice versa. If a solute with higher main diffusion coefficient is added to a binary solution, the interface growth velocity, the interdendritic supersaturation of the base solute and the interdendritic supercooling increase with the quantity of solute added.

X-ray studies on crystalline complexes involving amino acids. IV. The structure of L-arginine L-ascorbate

L-Arginine ascorbate, C6HIsN40+.C6H706, a 1"1 crystalline complex between the amino acid arginineand the vitamin ascorbic acid, crystallizes in the monoclinic space group P21 with two formula units in a cell of dimensions a = 5.060 (8), b = 9.977 (9), c = 15.330 (13) A, fl = 97.5 (2) °. The structure was solved by the symbolic addition procedure and refined to an R of 0.067 for 1501 photographically observed reflec- tions. The conformation of the arginine molecule in the structure is different from any observed so far. The present structure provides the first description of the ascorbate anion unaffected by the geometrical constraints and disturbances imposed by the requirements of metal coordination. The lactone group and the deprotonated enediol group in the anion are planar and the side chain assumes a conformation which appears to be sterically the most favourable. In the crystals, the arginine molecules and the ascorbate anions aggregate separately into alternating layers. The molecules in the arginine layer are held together by interactions involving a-amino and ~t-carboxylate groups, a situation analogous to that found in proteins. The two layers of unlike molecules are interconnected primarily through the interactions of the side-chain guanidyl group of arginine with the ascorbate ion. These involve a specific ion-pair interaction accompanied by two convergent hydrogen bonds and another pair of nearly parallel hydrogen bonds.

Cosmological Constant and Scalar Gravitons

If a cosmological term is included in the equations of general relativity, the linearized equations can be interpreted as a tensor-scalar theory of finite-range gravitation. The scalar field cannot be transformed away be a gauge transformation (general co-ordinate transformation) and so must be interpreted as a physically significant degree of freedom. The hypothesis that a massive spin-two meson (mass m2) satisfied equations identical in form to the equations of general relativity leads to the prediction of a massive spin-zero meson (mass m0), the ratio of masses being m0 / m2 = 3*3.

A note on the application of a radiation condition for a source in a rotating stratified fluid

The motion due to an oscillatory point source in a rotating stratified fluid has been studied by Sarma & Naidu (1972) by using threefold Fourier transforms. The solution obtained by them in the hyperbolic case is wrong since they did not make use of any radiation condition, which is always necessary to get the correct solution. Whenever the motion is created by a source, the condition of radiation is that the sources must remain sources, not sinks of energy and no energy may be radiated from infinity into the prescribed singularities of the field. The purpose of the present note is to explain how Lighthill's (1960) radiation condition can be applied in the hyperbolic case to pick the correct solution. Further, the solution thus obtained is reiterated by an alternative procedure using Sommerfeld's (1964) radiation condition.

Arginine Decarboxylase from Lathyrus sativus Seedlings Purification and Properties

Arginine decarboxylase which makes its appearance in Lathyrus sativus seedlings after 24 h of seed germination reaches its highest level around 5–7 days, the cotyledons containing about 60% of the total activity in the seedlings at day 5. The cytosol enzyme was purified 977-fold from whole seedlings by steps involving manganese chloride treatment, ammonium sulphate and acetone fractionations, positive adsorption on alumina C-γ gel, DEAE-Sephadex chromatography followed by preparative disc gel electrophoresis. The enzyme was shown to be homogeneous by electrophoretic and immunological criteria, had a molecular weight of 220000 and appears to be a hexamer with identical subunits. The optimal pH and temperature for the enzyme activity were 8.5 and 45 °C respectively. The enzyme follows typical Michaelis-Menten kinetics with a Km value of 1.73 mM for arginine. Though Mn2+ at lower concentrations stimulated the enzyme activity, there was no dependence of the enzyme on any metal for the activity. The arginine decarboxylase of L. sativus is a sulfhydryl enzyme. The data on co-factor requirement, inhibition by carbonyl reagents, reducing agents and pyridoxal phosphate inhibitors, and a partial reversal by pyridoxal phosphate of inhibition by pyridoxal · HCl suggests that pyridoxal 5'-phosphate is involved as a co-factor for the enzyme. The enzyme activity was inhibited competitively by various amines including the product agmatine. Highest inhibition was obtained with spermine and arcain. The substrate analogue, l-canavanine, homologue l-homoarginine and other basic amino acids like l-lysine and l-ornithine inhibited the enzyme activity competitively, homoarginine being the most effective in this respect.

L-Tyrosyl-L-glutarnie Acid Monohydrate, C14H18N206.H20

Mr=328.32, triclinic, P1, a=5.801 (1), b=7.977(1), c=9.110(2)A, ~t=102.33 (1), fl= 97.92 (1), y= 109.82 (1) °, v= 377.2 (1) A 3 at 293 K, Z=I, D x=1.45, D m=1.45 g cm -3, 2(MoKs)= 0.7107 A, ~ = 0.74 cm -1, F(000) = 174.0. R = 0.046 for 990 unique observed [F o > 4O(Fo)] reflections. The crystal structure is stabilized by extensive hydrogen bonding involving all N and O atoms.

Triplet repeat polymorphism & fragile X syndrome in the Indian context

Mental retardation due to fragile X syndrome is one of the genetic disorders caused by tripler repeat expansion, CGG repeat involved in this disease is known to exhibit polymorphism even among normal individuals. Here we describe the development of suitable probes for detection of polymorphism in CGG repeat at FMR1 locus as well as the diagnosis of fragile X syndrome. Using these methods polymorphism at the FMR1 locus has been examined in 161 individuals. Ninety eight patients with unclassified mental retardation were examined, of whom 7 were found to have the expanded (CGG) allele at the FMR1 locus, The hybridization pattern for two patients has been presented as representative data.

Influence of Temperature and High Electric Field on Power Consumption by Piezoelectric Actuated Integrated Structure

The influence of electric field and temperature on power consumption of piezoelectric actuated integrated structure is studied by using a single degree of freedom mass-spring-damper system model coupled with a piezoactuator. The material lead zirconate titanate, is considered as it is capable of producing relatively high strains (e.g., 3000 mu epsilon). Actuators are often subject to high electric fields to increase the induced strain produced, resulting in field dependant piezoelectric coefficient d(31), dielectric coefficient epsilon(33) and dissipation factor delta. Piezostructures are also likely to be used across a wide range of temperatures in aerospace and undersea operations. Again, the piezoelectric properties can vary with temperature. Recent experimental studies by physics researchers have looked at the effect of high electric field and temperature on piezoelectric properties. These properties are used together with an impedance based power consumption model. Results show that including the nonlinear variation of dielectric permittivity and dissipation factor with electric field is important. Temperature dependence of the dielectric constant also should be considered.

Modeling of heat and mass transfer for solid state fermentation process in tray bioreactor

A mathematical model is developed to simulate oxygen consumption, heat generation and cell growth in solid state fermentation (SSF). The fungal growth on the solid substrate particles results in the increase of the cell film thickness around the particles. The model incorporates this increase in the biofilm size which leads to decrease in the porosity of the substrate bed and diffusivity of oxygen in the bed. The model also takes into account the effect of steric hindrance limitations in SSF. The growth of cells around single particle and resulting expansion of biofilm around the particle is analyzed for simplified zero and first order oxygen consumption kinetics. Under conditions of zero order kinetics, the model predicts upper limit on cell density. The model simulations for packed bed of solid particles in tray bioreactor show distinct limitations on growth due to simultaneous heat and mass transport phenomena accompanying solid state fermentation process. The extent of limitation due to heat and/or mass transport phenomena is analyzed during different stages of fermentation. It is expected that the model will lead to better understanding of the transport processes in SSF, and therefore, will assist in optimal design of bioreactors for SSF.