Visualization of enantiomers using natural abundant 13C-filtered single and double quantum selective refocusing experiments: Application to small chiral molecules

The routine use of proton NMR for the visualization of enantiomers, aligned in the chiral liquid crystal solvent poly-γ-benzyl-l-glutamate (PBLG), is restricted due to severe loss of resolution arising from large number of pair wise interaction of nuclear spins. In the present study, we have designed two experimental techniques for their visualization utilizing the natural abundance 13C edited selective refocusing of single quantum (CH-SERF) and double quantum (CH-DQSERF) coherences. The methods achieve chiral discrimination and aid in the simultaneous determination of homonuclear couplings between active and passive spins and heteronuclear couplings between the excited protons and the participating 13C spin. The CH-SERF also overcomes the problem of overlap of central transitions of the methyl selective refocusing (SERF) experiment resulting in better chiral discrimination. Theoretical description of the evolution of magnetization in both the sequences has been discussed using polarization operator formalism.

ESR studies of phase transitions in double propionates

Detailed ESR investigations of Mn2+ substituting for Ca2+ in Ca2Sr(C2H5COO)6 (DSP), Ca2Pb(C2H5COO)6 (DLP) and Ca2Ba(C2H5COO)6 (DBP), in single crystals and powders, over the temperature range from 200°C to -180°C have been carried out to study the successive phase transitions in these compounds. (DSP: [Tetragonal] ← 8.5°C → [tetragonal, ferroelectric] [tetragonal] ← -169°C → [monoclinic, ferroelectric]; DLP : [tetragonal] ← 60°C → [tetragonal, ferroelectric] ← -71.5°C → [monoclinic, ferroelectric]; [Cubic] ← -6°C → [orthorhombic] ← -75°C → [?]). Spectra have been analysed in terms of axial spin Hamiltonians and the temperature dependences of the parameters studied. In DSP and DLP across the I ↔ II transition, new physically and chemically inequivalent sites appear indicating the disappearance of the diad axes on which the propionate groups are located, bringing out the connection between the motional states of the propionate groups and the occurence of ferroelectricity. The II ↔ III transition also causes chemically inequivalent sites to develop, indicating that the transitions may not be isomorphous as believed previously. In DBP, the -6°C transition leads to (i) a doubling of both physically and chemically inequivalent sites (ii) a small (150 G at -6°C to 170 G at -8°C), but abrupt change in the magnitude of the zero-field splitting tensor D, and (iii) displacements of the orientations of the D tensors. Results are interpreted in terms of alternate rotations of the oxygen octahedra, showing participation of the carboxyl oxygens in the transition. No drastic changes in the parameters occur across the -75°C transition consistent with its second order nature. Similarities and dissimilarities of the ESR spectra of the three compounds in relation to the phase transitions, are discussed.

Existence theorem for a generalized Hammerstein type equation

An existence theorem is obtained for a generalized Hammerstein type equation

Anthranilate Hydroxylase from Aspergillus niger: Evidence for the Participation of Iron in the Double Hydroxylation Reaction

Evidence was obtained for the participation of iron in the double hydroxylation reaction catalyzed by anthranilate hydroxylase from Aspergillus niger (UBC 814). Omission of iron from the growth medium gave inactive preparations of anthranilate hydroxylase which could be reactivated by incubating the enzyme preparations with ferric citrate. The enzyme was susceptible to inhibition by metal chelating agents. The Ki for o-phenanthroline, which inhibited the enzyme activity non-competitively with respect to anthranilate, was calculated to be 0.9 mM. The inhibition by o-phenanthroline was counteracted by ferric complexes such as ferric-ethylenediaminetetraacetic acid and ferric citrate. Anthranilate afforded protection against inhibition by o-phenanthroline.

Wavefront filter for double-exposure holographic interferometry

Measurements of small phase shifts by double-exposure holographic interferometry are facilitated, and ambiguities in the sign of the phase shift eliminated, by introducing a background pattern of interference fringes. A simple and reliable optical system for this purpose utilizing a rotating wedge is described, with which fringes of any desired orientation and spacing can conveniently be obtained. It is shown how this system can be used under certain conditions for measurements of small mechanical deformations.

Double walled carbon nanotubes as ultrafast optical switches

Pristine and molybdenum filled double walled carbon nanotubes (DWNTs) suspended in D2O show excellent ultrafast optical switching properties investigated through femtosecond Z-scan and degenerate pump-probe method using 50 fs pulses with central photon energy of 1.57 eV. For pristine-DWNT, the two photon absorption coefficient, beta and nonlinear refraction coefficient, n2 are 4.9×10−8 cm/W, and 9.5×10−11 cm2/W, respectively, which yield one photon figure of merit, W=133 and two photon figure of merit, T=0.4. The degenerate pump-probe measurements show strong photoinduced bleaching with biexponential decay with time constants ~150 and 600 fs. ©2009 American Institute of Physics

Double standard polynucleotides: two typical alternative conformations for nucleic acids

Two typical alternative conformations for double strandee polynucleotides with Watson-Crick base pairing scheme are presented. these types avoid tangling of the chains. Representative models of these types with two different views, to show the similarity and dissimilarity between these models and the Watson-Crick model, are given.

New light on the optical equivalence theorem and a new type of discrete diagonal coherent state representation

In many instances we find it advantageous to display a quantum optical density matrix as a generalized statistical ensemble of coherent wave fields. The weight functions involved in these constructions turn out to belong to a family of distributions, not always smooth functions. In this paper we investigate this question anew and show how it is related to the problem of expanding an arbitrary state in terms of an overcomplete subfamily of the overcomplete set of coherent states. This provides a relatively transparent derivation of the optical equivalence theorem. An interesting by-product is the discovery of a new class of discrete diagonal representations.

Conformation of polypeptide-chains containing both l-residues and D-residues .2. Double-helical structures of poly-ld-peptides

Polypeptides with alternating L- and D-amino acid residues can take up stereochemically satisfactory coaxial double-helical structures, both antiparallel and parallel, which are stabilized by systematic interchain NH O hydrogen bonds. Semiempirical energy calculations over allowed regions of conformational space have yielded the characteristics of these double-helices. There are four possible types of antiparallel double-helices - A3, A4, A5 and A6, with n, the number of LD peptide units per turn, around 2.8, 3.6, 4.5 and 5.5 respectively, while for the parallel double-helices there are two types, P3 and P4, having similar helical parameters as in A3 and A4. The hydrogen-bonding scheme restricts the pitch in all the models to the narrow range of 10.0 to 11.5 Å. All these helices have large central cores whose radii increase proportionately with n. In this respect, A3 and A4 are suitable models for the structure of gramicidin A. In terms of their relative energies, antiparallel double-helices are marginally more stable than those with parallel strands. Our results indicate that the energy differences amongst the members in the antiparallel family are not significant and thus provide an explanation for the polymorphism reported for poly(γ-benzyl-LD-glutamate).

The Noether-Lefschetz theorem for the divisor class group

Let X be a normal projective threefold over a field of characteristic zero and vertical bar L vertical bar be a base-point free, ample linear system on X. Under suitable hypotheses on (X, vertical bar L vertical bar), we prove that for a very general member Y is an element of vertical bar L vertical bar, the restriction map on divisor class groups Cl(X) -> Cl(Y) is an isomorphism. In particular, we are able to recover the classical Noether-Lefschetz theorem, that a very general hypersurface X subset of P-C(3) of degree >= 4 has Pic(X) congruent to Z.

Self-Assembly of a Pd-6-Molecular Double-Square and a Cu-3-Trigonalbipyramidal Cage via a New Tripodal Flexible Ligand

A new tripodal flexible ligand (L) containing pyrazolyl functionality has been prepared and successfully used to obtain a pd(6) (1) molecular double-square and a cu(3) trigonalbipyramidal cage (2), where complex 1 represents the first example of a double-square obtained using a flexible tripodal ligand.

Mutational analysis of active-site residues in the Mycobacterium leprae RecA intein, a LAGLIDADG homing endonuclease: Asp(122) and Asp(193) are crucial to the double-stranded DNA cleavage activity whereas Asp(218) is not

Mycobacterium leprae recA harbors an in-frame insertion sequence that encodes an intein homing endonuclease (PI-MleI). Most inteins (intein endonucleases) possess two conserved LAGLIDADG (DOD) motifs at their ctive center. A common feature of LAGLIDADG-type homing endonucleases is that they recognize and cleave the same or very similar DNA sequences. However, PI-MleI is distinctive from other members of the family of LAGLIDADG-type HEases for its modular structure with functionally separable domains for DNA-binding and cleavage, each with distinct sequence preferences. Sequence alignment analyses of PI-MleI revealed three putative LAGLIDADG motifs; however, there is conflicting bioinformatics data in regard to their identity and specific location within the intein polypeptide. To resolve this conflict and to determine the active-site residues essential for DNA target site recognition and double-stranded DNA cleavage, we performed site-directed mutagenesis of presumptive catalytic residues in the LAGLIDADG motifs. Analysis of target DNA recognition and kinetic parameters of the wild-type PI-MleI and its variants disclosed that the two amino acid residues, Asp(122) (in Block C) and Asp(193) (in functional Block E), are crucial to the double-stranded DNA endonuclease activity, whereas Asp(218) (in pseudo-Block E) is not. However, despite the reduced catalytic activity, the PI-MleI variants, like the wild-type PI-MleI, generated a footprint of the same length around the insertion site. The D122T variant showed significantly reduced catalytic activity, and D122A and D193A mutations although failed to affect their DNA-binding affinities, but abolished the double-stranded DNA cleavage activity. On the other hand, D122C variant showed approximately twofold higher double-stranded DNA cleavage activity, compared with the wild-type PI-MleI. These results provide compelling evidence that Asp(122) and Asp(193) in DOD motif I and II, respectively, are bona fide active-site residues essential for DNA cleavage activity. The implications of these results are discussed in this report.

An adiabatic model for a two-stage double-inlet pulse tube refrigerator

A numerical modelling technique for predicting the detailed performance of a double-inlet type two-stage pulse tube refrigerator has been developed. The pressure variations in the compressor, pulse tube, and reservoir were derived, assuming the stroke volume variation of the compressor to be sinusoidal. The relationships of mass flowrates, volume flowrates, and temperature as a function of time and position were developed. The predicted refrigeration powers are calculated by considering the effect of void volumes and the phase shift between pressure and mass flowrate. These results are compared with the experimental results of a specific pulse tube refrigerator configuration and an existing theoretical model. The analysis shows that the theoretical predictions are in good agreement with each other.

Holomorphic Sobolev spaces, Hermite and special Hermite semigroups and a Paley-Wiener theorem for the windowed Fourier transform

The images of Hermite and Laguerre-Sobolev spaces under the Hermite and special Hermite semigroups (respectively) are characterized. These are used to characterize the image of Schwartz class of rapidly decreasing functions f on R-n and C-n under these semigroups. The image of the space of tempered distributions is also considered and a Paley-Wiener theorem for the windowed (short-time) Fourier transform is proved.

Critical test for Altshuler-Aronov theory: Evolution of the density of states singularity in double perovskite Sr2FeMoO6 with controlled disorder

With high-resolution photoemission spectroscopy measurements, the density of states (DOS) near the Fermi level (E-F) of double perovskite Sr2FeMoO6 having different degrees of Fe/Mo antisite disorder has been investigated with varying temperature. The DOS near E-F showed a systematic depletion with increasing degree of disorder, and recovered with increasing temperature. Altshuler-Aronov (AA) theory of disordered metals well explains the dependences of the experimental results. Scaling analysis of the spectra provides experimental indication for the functional form of the AA DOS singularity.