Internal stresses and chemical binding in the H molecule

Following an interpretive formalism presented earlier, chemical binding in the H molecule has been studied in terms of the variations, with respect to R, of electrostatic field and stress components at five selected points on the interuclear axis. At three points phenomena analogous to those recorded earlier for H₂ have been observed. In particular, the existence of extremal relationships for the difference density field and the total field, as well as for the corresponding stresses, at R ? R_eq for certain specific points on the internuclear axis has been confirmed. As in the case of H₂, chemical binding in H occurs due to local variations of electrostatic pressure from point to point in such a manner as to cause the vanishing of either the total electrostatic force density or the difference force density at certain points on the internuclear axis.     

Raman scattering study of LiKSO4—phases II and III

Detailed Raman scattering investigation of LiKSO₄ in phases II and III across the transition temperatureT _c ? 700 K is reported. Abrupt change in frequency and line width of the external and internal modes have been observed. Analysis of the results suggests lithium positional disorder and sulphate orientational disorder in the high temperature phase (II). The results also throw some light on the existence of twin domains in the crystal.     

New phase transition in LiKSO4

A subtle first order phase transition in LiKSO₄ has been discovered with the help of a temperature dependent study of the Raman intensity measurements of certain polar modes in different polarization configurations. The room temperature hexagonal C⁶₆ (P6₃) phase transforms to trigonal C⁴_3v (P31c) phase at 201°K while cooling; the reverse transformation (on heating) takes place at 242°K. The phase transition appears to be primarily associated with a cooperative reorientation of SO₄ tetrahedra in the crystal.     

A facile domino metathetic route to a thapsigargin skeleton

A facile synthesis of a 5,7,5-fused ring system that is present in thapsigargins belonging to a novel family of sesquiterpene lactones, guainanolides, using domino enyne-RCM is reported here.     

Is multiscaling an artifact in the stochastically forced Burgers equation?

We study turbulence in the one-dimensional Burgers equation with a white-in-time, Gaussian random force that has a Fourier-space spectrum approximately 1/k, where k is the wave number. From very high-resolution numerical simulations, in the limit of vanishing viscosity, we find evidence for multiscaling of velocity structure functions which cannot be falsified by standard tests. We find a new artifact in which logarithmic corrections can appear disguised as anomalous scaling and conclude that bifractal scaling is likely.     

Dynamics of passive-scalar turbulence

We present the first study of the dynamic scaling or multiscaling of passive-scalar turbulence. For the Kraichnan version of passive-scalar turbulence we show analytically, in both Eulerian and quasi-Lagrangian frameworks, that simple dynamic scaling is obtained but with different dynamic exponents. By developing the multifractal model we show that dynamic multiscaling occurs in passive-scalar turbulence only if the advecting velocity field is itself multifractal. We substantiate our results by detailed numerical simulations in shell models of passive-scalar advection.     

Varieties of dynamic multiscaling in fluid turbulence

We show that different ways of extracting time scales from time-dependent velocity structure functions lead to different dynamic-multiscaling exponents in fluid turbulence. These exponents are related to equal-time multiscaling exponents by different classes of bridge relations, which we derive. We check this explicitly by detailed numerical simulations of the Gledzer-Ohkitani-Yamada shell model for fluid turbulence. Our results can be generalized to any system in which both equal-time and time-dependent structure functions show multiscaling.     

Asymmetric synthesis and translational competence of L-alpha-(1-cyclobutenyl)glycine

[reaction: see text] L-alpha-(1-Cyclobutenyl)glycine (1-Cbg) was targeted as a potentially translatable analogue of isoleucine and valine and as a useful building block for peptides. An enantioselective synthesis was executed in which the key step was diastereoselective addition of 1-cyclobutenylmagnesium bromide to the sulfinimine 2b derived from (S)-t-butanesulfinimide and tert-butyl glyoxylate. 1-Cbg was found to substitute efficiently for isoleucine and valine, but not leucine, in the translation of green fluorescent protein in vitro.     

New strategies for exploring RNA's 2'-OH expose the importance of solvent during group II intron catalysis

The 2'-hydroxyl group contributes inextricably to the functional behavior of many RNA molecules, fulfilling numerous essential chemical roles. To assess how hydroxyl groups impart functional behavior to RNA, we developed a series of experimental strategies using an array of nucleoside analogs. These strategies provide the means to investigate whether a hydroxyl group influences function directly (via hydrogen bonding or metal ion coordination), indirectly (via space-filling capacity, inductive effects, and sugar conformation), or through interactions with solvent. The nucleoside analogs span a broad range of chemical diversity, such that quantitative structure activity relationships (QSAR) now become possible in the exploration of RNA biology. We employed these strategies to investigate the spliced exons reopening (SER) reaction of the group II intron. Our results suggest that the cleavage site 2'-hydroxyl may mediate an interaction with a water molecule.