Total synthesis of (+)-pericosine B and (+)-pericosine C and their enantiomers by using the Baylis–Hillman reaction and ring-closing metathesis as key steps

A simple and divergent route for the total synthesis of pericosine B and pericosine C and their enantiomers from d-ribose by using the Baylis–Hillman reaction and ring-closing metathesis reactions as key steps has been described.     

Spectroscopic study of inhibition of calcium oxalate calculi growth by Larrea tridentata

Urolithiasis, the category of diseases associated with the formation of kidney stones, has many causes. However, only a few have been documented as aggravating calculi depositions and aggregations. This amply justifies continued work in developing effective and efficient inhibition and treatment techniques. The recent resurgence in reviews on plant antiurolithiatic activity has given credence to the application of modern spectroscopic analysis, and has led us to this study. Results obtained from Raman and infrared (IR) absorption analysis of inhibited calculi growth resulting from laboratory synthesis of calcium oxalate crystals accompanied by the natural infusion of Larrea tridentata are reported. A visible decrease in calcium oxalate crystal growth with increasing amounts of L. tridentata herbal infusion was observed in photomicrographs, as well as a color change from white‐transparent for pure crystals to light orange‐brown for crystals with inhibitor. Both Raman and IR absorption spectra reveal a monohydrate structure for the crystals grown alone, which transform to a dihydrate morphology with the addition of the L. tridentata inhibitor. Furthermore, the resulting data support the possibilities of the influences, in this complex process, of the nordihydroguaiaretic acid (NDGA) and its derivative compounds from L. tridentata and the bonding of the magnesium of the inhibitor with the oxalate ion on the surface of the calculi crystals. This assumption corroborates well with the micrographs obtained under higher magnification, which show that the separated small crystallites consist of a darker brownish core, which we attribute to the dominance of growth inhibition by NDGA, surrounded by light transparent thin shells, which possibly correspond to passivation of the crystals by magnesium oxalate. Copyright © 2010 John Wiley & Sons, Ltd.     

Stereoselective synthesis of the densely functionalized C1-C9 fragment of amphidinolides C and F

The synthesis of the C1-C9 subunit of amphidinolides C and F is described. Key steps include tandem Sharpless asymmetric dihydroxylation-S_N2 cyclization reaction, Lewis acid-mediated epoxide opening, Wittig reaction, and Wacker oxidation.     

Quantitative accounting for the medium effect at the catalytic decomposition of H<Subscript>2</Subscript>O<Subscript>2</Subscript> in hydrophilic solvents

The experimental data on the effect of physicochemical properties of solvent on the rate of hydrogen peroxide decomposition catalyzed by cobalt ions were obtained using a method of adding inhibitors and were generalized quantitatively by the application of multiparametric linear equations.     

N-heterocyclic carbene-mediated hydroacylation-Sonogashira/Heck/Suzuki coupling in a single pot: a new cascade reaction

A dually NHC-catalyzed reaction cascade comprising an initial hydroacylation of an activated ketone and subsequent Sonogashira/Heck/Suzuki coupling in the same pot is reported. The reaction mechanism and scope of the methodology is presented.     

On the photomagnetism of nitronyl nitroxide, imino nitroxide, and verdazyl-substituted azobenzene

The cis- and trans-azobenzenes are known as photochromic isomers with the trans- converting into the cis-form and vice versa upon irradiation with specific wavelengths. We have quantum chemically investigated the cis- and trans-forms of substituted azobenzene diradicals, with two nitronyl nitroxides, imino nitoxides, or verdazyls at para positions and serving as monoradical centers, to determine whether they can exhibit a photoassisted magnetic crossover. Geometries of both substituted and unsubstituted molecules have been optimized by density functional (DF) method UB3LYP using the 6-311G(d,p) basis set. Optimization of the geometry of the cis isomers has required special care. Single point singlet, triplet, and broken symmetry calculations have been done using 6-311++G(3df, 3pd) basis set. The magnetic exchange coupling constants have been estimated from the broken symmetry calculations. Absorption wavelengths have been estimated for both substituted and unsubstituted species from time-dependent DF treatment using restricted spin-polarized methodology RB3LYP and 6-311++G(3df, 3pd) basis set. From the similarity in the calculated absorption wavelengths for the unsubstituted and substituted azobenzenes, and the increased oscillator strengths (f) for the substituted species, we predict that the diradical isomers would be strongly photochromic. From our triplet state and broken symmetry calculations, we predict that both the cis- and the trans-diradicals are antiferromagnetically coupled. This prediction is consistent with the spin alternation rule, and the possibility of a magnetic crossover is nonexistent for these species.     

An alternative approach of developing a frequency encoded optical tri-state multiplexer with broad area semiconductor optical amplifier (BSOA)

During the last few decades several logic gates, sequential and combinational logic devices, have been developed using light signals. For this work several encoding as well as decoding techniques are proposed for data handling and information processing with optics as information carrying signal. Frequency encoding technique is one such type of encoding processes, which gives a very good response for long distance communication of logically processed data because frequency is a fundamental character of light and it remains unchanged for long distance communication. Here in this paper the authors propose a frequency encoded multiplexer with the proper use of semiconductor optical amplifier in tri-state logic.     

A novel synthesis of beta-lactam fused cyclic enediynes by intramolecular Kinugasa reaction

A general synthetic route to beta-lactam-fused enediynes by intramolecular Kinugasa reaction has been successfully developed. The method has widened the scope of Kinugasa reaction in the synthesis of sensitive systems like the one described in this communication.     

Stable Tin (n = 2-15) clusters and their geometries: DFT calculations

We present a detailed structural analysis for small Tin (n = 2-15) clusters based on ab initio quantum mechanical calculations of their binding energies, frontier orbital gaps, and second energy derivatives. Local density approximation calculations revealed that while the smaller clusters (n < or = 8) prefer hexagonal atomic arrays with bulklike crystal symmetry, the bigger clusters prefer pentagonal atomic arrays. From the stability criteria of the magic number clusters we could identify three magic number clusters Ti7, Ti13, and Ti15. While the most stable configuration of Ti7 is a decahedral bipyramid induced by tetrahedral atomic arrays, the most stable configuration of Ti13 is an icosahedron. The other stable cluster Ti15 takes a closed-shell icosahedron-like configuration with both pentagonal and hexagonal symmetries. The stability of the Tin clusters strongly depends on their geometries and charge states. The HOMO-LUMO gap of the Tin clusters approaches its bulk value for n > 8. While there is not much difference between the HOMO and LUMO isosurface charge distributions for the Ti7 and Ti13 clusters in their most stable configurations, they are very different in the case of Ti15. Such a distinct charge distribution in Ti15 indicates its singular chemical selectivity over the other two magic number clusters.