Crystal Structure of Sodium Deoxyinosine Monophosphate

The crystal and molecular structure of sodium deoxyinosine monophosphate (5'-dIMP) has been determined by x-ray crystallographic methods. The crystals belong to orthorhombic space group P212121, with a = 21.079(5) Aring, b = 9.206(3) Aring and c = 12.770(6) Aring. This deoxynucleotide shows common nucleotide features namely anti conformation about the glycosyl bond, C2' endo pucker for the deoxyribose sugar and gauche-gauche orientation for the phosphate group. The sodium ion is directly coordinated to the O3' atom, a feature observed in many crystal structures of sodium salts of nucleotides.

Influence of acetyl and bromine substitutions on stacking. Crystal and molecular structures of 8-bromo-2',3',5'-triacetyl adenosine and 8-bromo 2',3',5'-triacetyl guanosine

The three dimensional structures of 8-bromo 2',3',5' triacetyl adenosine (8-Br Tri A) and 8-bromo 2',3',5'-triacetyl guanosine (8-Br Tri G) have been determined by single crystal X-ray diffraction methods to study the combined effect of bromine and acetyl substitutions on molecular conformation and interactions. The ribose puckers differ from those found in unbrominated Tri A and Tri G and unacetylated 8-Br A and 8-Br G analogues

Stereoselections in cyclic β-ketoester alkylations

A hyperconjugative influence may be an additional factor in Z-alkylation being promoted by a syn-axial ester in enolates formed from conformationally immobilised 6-cyclic beta-ketoesters.

Topology of wolfgram proteins and 2?, 3?-cyclic nucleotide 3?-phosphodiesterase in CNS myelin: Studies with proteases

The topological disposition of Wolfgram proteins (WP) and their relationship with 2', 3'-cyclic nucleotide 3'-phosphodiesterase (CNPase) in human, rat, sheep, bovine, guinea pig and chicken CNS myelin was investigated. Controlled digestion of myelin with trypsin gave a 35KDa protein band (WP-t) when electrophoresed on dodecyl sulfate-polyacrylamide gel in all species. Western blot analysis showed that the WP-t was derived from WP. WP-t was also formed when rat myelin was treated with other proteases such as kallikrein, thermolysin and leucine aminopeptidase. Staining for CNPase activity on nitrocellulose blots showed that WP-t is enzymatically active. Much of the CNPase activity remained with the membrane fraction even after treatment with high concentrations of trypsin when WP were completely hydrolysed and no protein bands with M.W > 14KDa were detected on the gels. Therefore protein fragments of WP with M.W < 14KDa may contain CNPase activity. From these results, it is suggested that the topological disposition of all the various WP is such that a 35KDa fragment is embedded in the lipid bilayer and the remaining fragment exposed at the intraperiod line in the myelin structure which may play a role in the initiation of myelinogenesis.

Antibodies raised against guanosine bind to double-stranded DNA

Antibodies elicited against guanosine have been reported to bind to single-stranded DNA. Using an avidin-biotin microELISA, we report that these antibodies also bind to double-stranded DNA. The binding is specific and is completely inhibited by the homologous hapten. The cross-reactivity of double-stranded DNA binding antibodies to single-stranded DNA is low. The antibodies are shown to bind to the topoisomers of plasmid DNA as assessed by a gel retardation assay.

A simple strategy for spirocyclopentannullation of cyclic ketones. Formal total synthesis of (+/-)-acorone

A general and simple methodology for spirocyclopentannulation of cyclic ketones (or 4,4-disubstituted cyclopentenones from acyclic ketones) and its application in the synthesis of the spirodienone 7 via a prochiral precursor constituting a formal total synthesis of (+/-)-acorone (6), are described.

Elasto-plastic contact stress analysis of joints subjected to cyclic loading

Rigorous elastic-plastic finite element analysis of joints subjected to cyclic loading is carried out. An incremental-iterative algorithm is developed in a modular form combining elasto-plastic material behaviour and contact stress analysis. For the case of the interference fit, the analysis sequentially carries out insertion of the pin and application of the load on the joint, covering possible initiation of separation (and/or yielding) and progressively the receding/advancing contact at the pin-plate interface. Deformations of both the plate and the pin are considered in the analysis. Numerical examples are presented for the case of an interference fit pin in a large plate under remote cyclic tension, and for an interference fit pin lug joint subjected to cyclic loading. A detailed study is carried out for the latter problem considering the effect of change in contact/separation at the pin-plate interface on local stresses, strains and redistribution of these stresses with the spread of a plastic zone. The results of the study are a useful input for the estimation of the fatigue life of joints. Copyright (C) 1996 Elsevier Science Ltd

Molecular dynamics studies on nucleoside 2',3'-cyclic phosphates

2',3'-cyclic nucleotides are intermediates and substrates of Ribonuclease (RNase)-catalysed reactions. The characterization of the equilibrium conformation as well as the flexibility inherent in these molecules helps in understanding the enzymatic action of RNases. The present study explores parameters like phase angle, glycosydic torsion angle and hydrogen bond to find possible interrelationship between them through Molecular Dynamics (MD) simulations on 3'-GMP, 3'-UMP, A>p, G>p, U>p, C>p, GpA>p and UpA>p. Interesting results of the effect of cyclisation and other constraints such as hydrogen bond between certain groups on the equilibrium ribose conformation have emerged from this study.

Piperidinium tetrathiotungstate as sulfur transfer reagent: synthesis of cyclic disulfides

Piperidinium tetrathiotungstate has been found to react with a number of 1,n-dihalo compounds to afford the corresponding cyclic disulfides in good yields, under mild reaction conditions. This new methodology has been used as a key step in the synthesis of (+/-)-lipoic acid (35) and asparagusic acid (37).

Role of elasto-plastic analysis under cyclic loading in fatigue crack growth studies

Linear Elastic Fracture Mechanics (LEFM) has been widely used in the past for fatigue crack growth studies, but this is acceptable only in situations which are within small scale yielding (SSY). In many practical structural components, conditions of SSY could be violated and one has to look for fracture criteria based on elasto-plastic analysis. Crack closure phenomenon, one of the most striking discoveries based on inelastic deformations during crack growth, has significant effect on fatigue crack growth rate. Numerical simulation of this phenomenon is computationally intensive and involved but has been successfully implemented. Stress intensity factors and strain energy release rates lose their meaning, J-integral (or its incremental) values are applicable only in specific situations, whereas alternate path independent integrals have been proposed in the literature for use with elasto-plastic fracture mechanics (EPFM) based criteria. This paper presents certain salient features of two independent finite element (numerical) studies of relevance to fatigue crack growth, where elasto-plastic analysis becomes significant. These problems can only be handled in the current day computational environment, and would have been only a dream just a few years ago.

Thermally Controlled Cyclic Insertion/Ejection of Dopant Ions and Reversible Zinc Blende/Wurtzite Phase Changes in ZnS Nanostructures

We report a reversible phase transformation of platelet-shaped ZnS nanostructures between wurtzite (WZ) and zinc blende (ZB) phases by reversible insertion/ ejection of dopant Mn(II) ions induced by a thermocyclic process. In a reaction flask loaded with WZ ZnS platelets and Mn molecular precursors, during heating Mn ions are incorporated and change the phase of the host nanostructures to ZB; during cooling Mn ions are spontaneously ejected, returning the host nanoplatelets to the original WZ phase. These reversible changes are monitored for several cycles with PL, EPR, XRD, and HRTEM. Interestingly, the (0001) WZ platelets transform to (110) ZB following a nucleation and growth process triggered by a local increase/depletion of the Mn2+ concentration in the nanocrystals.

Thermally Controlled Cyclic Insertion/Ejection of Dopant Ions and Reversible Zinc Blende/Wurtzite Phase Changes in ZnS Nanostructures

We report a reversible phase transformation of platelet-shaped ZnS nanostructures between wurtzite (WZ) and zinc blende (ZB) phases by reversible insertion/ ejection of dopant Mn(II) ions induced by a thermocyclic process. In a reaction flask loaded with WZ ZnS platelets and Mn molecular precursors, during heating Mn ions are incorporated and change the phase of the host nanostructures to ZB; during cooling Mn ions are spontaneously ejected, returning the host nanoplatelets to the original WZ phase. These reversible changes are monitored for several cycles with PL, EPR, XRD, and HRTEM. Interestingly, the (0001) WZ platelets transform to (110) ZB following a nucleation and growth process triggered by a local increase/depletion of the Mn2+ concentration in the nanocrystals.

ChemInform Abstract: Sodium Perborate/Acetic Anhydride: A Convenient Reagent for the Conversion of Cyclic Acetals to Esters

A facile oxidative cleavage of cyclic acetals to their respective esters using an inexpensive reagent system, sodium perborate/acetic anhydride is described.

Effect of Constant and Cyclic Current Stressing on the Evolution of Intermetallic Compound Layers

In this paper the effects of constant and cyclic power loads on the evolution of interfacial reaction layers in lead-free solder interconnections are presented. Firstly, the differences in the growth behavior of intermetallic compound (IMC) layers at the cathode and anode sides of the interconnections are rationalized. This is done by considering the changes in the intrinsic fluxes of elements owing to electromigration as well as taking into account the fact that the growth of Cu3Sn and Cu6Sn5 are coupled via interfacial reactions. In this way, better understanding of the effect of electron flux on the growth of each individual layer in the Cu-Sn system can be achieved. Secondly, it is shown that there is a distinct difference between steady-state current stressing (constant current, constant temperature) and power cycling with alternating on- and off-cycle periods (accompanied by a change of temperature). The reasons behind the observed differences are subsequently discussed. Finally, special care is taken to ensure that the current densities are chosen in such a way that there is no risk for even partial melting of the solder interconnections.

Cyclic Prefix Based Cooperative Sequential Spectrum Sensing Algorithms for OFDM

This paper considers the problem of spectrum sensing in cognitive radio networks when the primary user is using Orthogonal Frequency Division Multiplexing (OFDM). For this we develop cooperative sequential detection algorithms that use the autocorrelation property of cyclic prefix (CP) used in OFDM systems. We study the effect of timing and frequency offset, IQ-imbalance and uncertainty in noise and transmit power. We also modify the detector to mitigate the effects of these impairments. The performance of the proposed algorithms is studied via simulations. We show that sequential detection can significantly improve the performance over a fixed sample size detector.