A comprehensive conformational analysis of tryptophan,its ionic and dimeric forms

Tryptophan is an essential amino acid, and understanding the conformational preferences of monomer and dimer is a subject of outstanding relevance in biological systems. An exhaustive first principles investigation of tryptophan ( W ) and its ionized counterparts cations (WC) , anions (WA) , and zwitterions (WZ) has been carried out. A comprehensive and systematic study of tryptophan dimer (WD) conformations resulted in about 62 distinct minima on the potential energy surface. The hydrogen bonds and a variety of noncovalent interactions such as OH‐π, NH‐π, CH‐π, CH‐O, and π‐π interactions stabilized different forms of tryptophan and its dimers. Over all in monomeric conformers which have NH‐O, hydrogen bonds showed higher stability than other conformers. A cursory analysis reveal that the most stable dimers stabilized by hydrogen bonding interactions while the less stable dimers showed aromatic side chain interactions. Protein Data Bank analysis of tryptophan dimers reveals that at a larger distance greater than 5 Å, T‐shaped orientations (CH‐π interactions) are more prevalent, while stacked orientations (π‐π interactions) are predominant at a smaller distance. © 2013 Wiley Periodicals, Inc.     

New Helical Folds in α‐Peptides with Alternating Chirality

In α‐peptides, the 8/10 helix is theoretically predicted to be energetically unstable and has not been experimentally observed so far. Based on our earlier studies on ‘helical induction’ and ‘hybrid helices’, we have adopted the ‘end‐capping’ strategy to induce the 8/10 helix in α‐peptides by using short α/β‐peptides. Thus, α‐peptides containing a regular string of α‐amino acids with alternating chirality were end capped by α/β‐peptides with 11/9‐helical motifs at the termini. Extensive NMR spectroscopy studies of these peptides revealed the presence of a hitherto unknown 8/10‐helical pattern; the H‐bonds in the shorter pseudorings were rather weak. The approach of using short helical motifs to induce new mixed helices in α‐peptides could provide avenues for more versatile design strategies.     

Novel Schiff bases–based thiophenes: Design,synthesis and biological evaluation

2-amino-5-(3-fluoro-4-methoxyphenyl)thiophene-3-carbonitrile derivatives have been synthesized from 1-(3-fluoro-4-methoxyphenyl)ethanone, malononitrile, mild base, and sulfur powder using the Gewald method through a multistep reaction sequence. The structures of newly synthesized compounds were established on the basis of their elemental analyses, IR, ¹H NMR, ¹³C NMR, and mass spectral data, and then synthesized compounds were screened for their in vitro antimicrobial activity. Among them, derivatives 3b (thiphene), 3f (pyrazole), and 3d (halogen) showed good activity and remaining derivatives exhibited moderate activity.     

Stereoselective Total Synthesis of Dodoneine

A simple and highly efficient stereoselective total synthesis of dodoneine ( 1 ), a naturally occurring bioactive 5,6‐dihydro‐2H‐pyran‐2‐one, was achieved. The synthesis involved Keck's asymmetric allylation, iodine‐induced electrophilic cyclization, and Grubbs' catalyzed ring‐closing metathesis as key steps.     

First Stereoselective Synthesis of the Cytotoxic Polyketide (4R)‐1‐(3,5‐Dihydroxyphenyl)‐4‐hydroxypentan‐2‐one

The first stereoselective synthesis of the cytotoxic polyketide (4R)‐1‐(3,5‐dihydroxyphenyl)‐4‐hydroxypentan‐2‐one ( 1 ) was achieved from readily available propylene oxide and 3,5‐dimethoxybenzyl alcohol. The synthesis involves Jacobsen's hydrolytic kinetic resolution (HKR) and Grignard reaction as key steps.     

A computational investigation and the conformational analysis of dimers, anions, cations, and zwitterions of L-phenylalanine

The structure and stability of various conformations of L-phenylalanine (PheN) and its zwitterions (PheZ), along with their ionized counterparts, cation (PheC) and anion (PheA), generated by adding and removing a proton respectively, have been investigated using first principle calculations in vacuum and in solution. This is followed by an extensive study on various possible dimer (PheD) conformations, which are noncovalently bound units without a peptide bond. This study results in 52, 31, 12, 9, and 11 minimum energy structures on the potential energy surfaces of PheD, PheN, PheC, PheA, and PheZ, respectively. Several important nonbonded interactions such as hydrogen bonds, NH-π, CH-π, OH-π, and π-π interactions, which impart stability to the monomeric and dimeric units, have been analyzed. The capability and strength of the nonbonded interactions drastically changing the conformational orientations of monomeric units has been illustrated.     

Die Änderung der Trübung wÄhrend der Flockung von Mangandioxydsolen mit Quecksilbersulfatlösungen

Zusammenfassung Es wird über Versuchsergebnisse berichtet, die bei der Koagulation von Mangandioxydsolen mit Quecksilbersulfatlösungen verschiedener Konzentration erhalten wurden. In übereinstimmung mit den Ergebnissen Joshi's und seiner Mitarbeiter lie\ sich feststellen, da\ die Änderung der Trübung wÄhrend der Koagulation zonal, d. h.: diskontinuierlich über die Koagulationsdauer war. Dieser Effekt wird um so deutlicher, je langsamer die Flockung ist. Im Gegensatz zu den üblichen Erfahrungen nahm die Trübung wÄhrend der Flockung mit Quecksilbersulfatlösungen ab.übersetzt von H. Kauffmann (Leipzig).Zum Schlu\ möchte ich Herrn Professor Dr. S. S. Joshi für die Anregungen zu dieser Arbeit und für stÄndige Unterstützung und Hilfe wÄhrend der ganzen Dauer dieser Untersuchung danken.     

On intrinsic properties of steady gas flows

Summary Considering the geometric theory of triply orthogonal spatial curves, the basic equations governing a steady gas flow are transformed into the intrinsic form and the results obtained are:(1) The pressure is uniform along the binormal to the stream line and the radius of curvature varies as the square of the velocity along it, for the baratropic fluids.(2) Acceleration is irrotational field when the fluid is compressible but baratropic or incompressible, in which case the relations existing between the flow quantities, curvature and torsions of the curves under consideration are obtained.(3) Considering incompressible flows, it is observed that either velocity in magnitude is uniform or the vorticity lies in the normal plane, in which case the stream lines are orthogonal to the vortex lines.Stream lines are observed to be either right circular helices or circles or straight lines.If the stream lines are not straight then the torsions of the binormal congruences and stream lines are equal.(4) The compatibility conditions of Berker¹) are transformed into intrinsic form, involving the curvatures and torsions of the above curves.     

Effect of lattice strain on the Debye-Waller factors of Mg, Zn and Cd

Lattice strains in Mg, Zn and Cd powders produced by grinding have been analyzed by X-ray powder diffraction. The lattice strain (ɛ) and Debye-Waller factor (B) are determined from the half-widths and integrated intensities of the Bragg reflections. In all three cases viz. Mg, Zn and Cd, the Debye-Waller factor is found to increase with the lattice strain. From the correlation between the strain and effective Debye-Waller factor, the Debye-Waller factors for zero strain have been estimated for Mg, Zn and Cd. The variation of energy of vacancy formation as a function of lattice strain has been studied.     

A crystallization-induced stereoselective glycosidation reaction in the synthesis of the anticancer drug etoposide

The anticancer drug etoposide, 1, is prepared in 79% overall yield from readily available 4'-demethyl-4-epipodophyllotoxin, 3, and 4, 6-O-ethylidene-2,3-O-dibenzyl-D-glucose, 4, via a crystallization-induced stereoselective glycosidation reaction followed by catalytic hydrogenation.