Structure-Memorization Phenomenon During the Hygrolysis of a Spirophosphorane to a Phosphonate

Abstract

Phosphonate II is obtained by hydrolysis of the spirophosphorane I (1). IR, ¹H and ³¹P NMR spectra confirm the phosphonate structure. However, one question remains about the relative position of the amide and ester fonction relative to the phosphonate group. In front of this difficulty, we resolved it through X-Ray crystallography of 11. Phosphonate II structure shows a slightly distorted figure of the spirophosphorane I of which it comes from. This observation is quite astonishing because of the lot of possible carbonyl positions of the new ester fonction. We can reasonably rationalize this phenomenon as a memory effect, phosphonate II “keeping in mind” even in solid state, i.e. in the more comfortable conformation, the memory of the phosphorane structure.     

A further contribution to the study of sagittamide a: synthesis of a pivotal intermediate belonging to a rare L-series

A key saggitamide intermediate corresponding to a rare sugar framework has been obtained. This approach should help to establish the overall configuration of more complex structures of the sagittamide family.     

INAA applied to the multielemental characterization of a sedimentary column: a contribution to oceanographic studies

The environmental changes that occurred in different periods can be identified through the increase or decrease of the concentrations of metals and other substances throughout sediment cores. The purpose of this study was to determine Al, As, Ba, Br, Cs, Eu, K, La, Mn, Sb, Sc, Sm, Th, Ti, U and V in a sediment core collected from S?o Paulo State South Seashore. Instrumental neutron activation analysis followed by gamma-ray spectrometry was the analytical method used. Results showed an abrupt decrease in the concentration of all elements in the 132–134 cm layer depth. This finding indicates an impact of anthropic activity.     

Determining the temperature to initiate the explosion of a propellant

Summary Gun propellants are per definition instable substances. During their lifetime a slow decomposition process is going-on. During this decomposition process the heat that is generated accelerates the process, which could result to an unsafe situation, or an unexpected explosion of the material. The temperature to initiate the explosion of a propellant is of importance for the storage conditions of such a substance. The method used so far to evaluate this temperature is based on an extrapolation of the Kissinger equation at zero heating rate. A new proposal is the use of the invariant kinetic parameters (IKP) method to determine the iso-kinetic temperature and extrapolating it to zero heating rate as an alternative method. The results are discussed for some examples.     

Relation of the force constant of a bond to the electric field at a nucleus

The change in the electric field at a nucleus in a molecule due to bond stretch is related to the force constant of the stretched bond. The validity of this relationship using approximate wave functions at the SCF and MP2 levels of theory is tested for the diatomic molecules H₂, HF, CO, and N₂. The effect of basis set variation on H₂ is also investigated. © 1997 John Wiley & Sons, Inc. J Comput Chem 18 : 1664–1667, 1997     

Molecular view of the isothermal transformation of a stable glass to a liquid

We have used neutron reflectivity to measure translational motion on the nanometer length scale in exceptionally stable glasses of tris(naphthylbenzene). These glasses are prepared by vapor deposition onto a substrate held somewhat below the glass transition temperature (T(g) = 342 K). When the most stable samples are annealed at 345 K, no translational motion is observed on the 12 nm length scale for over 10,000 s and full mixing requires more than 60,000 s. For comparison, the equilibrium supercooled liquid mixes in 1000 s at this temperature and on this length scale. These measurements provide insight into the mechanism by which a stable glass transforms into a liquid. "Melting" of the stable glass appears to occur by the growth of liquid regions into the surrounding glassy matrix, perhaps by a surface-initiated growth process. At 345 K, translational motion in the stable glass is at least 100 times slower than motion in the supercooled liquid.     

Investigations of the use of a mussel-inspired compatibilizer to improve the matrix-fiber adhesion of a biocomposite

Vegetable fibers have several positive aspects, such as low production costs, biodegradability and good mechanical properties, which make them very attractive in the field of composite reinforcement. The aim of this study is to introduce into a l-poly-(lactic-acid) (PLLA) – hemp biocomposite a new compatibilizer, inspired from the mussels' adhesive capacity, to improve the fiber-matrix bonding. As a first step, we carried out atomic force microscopy (AFM) and surface energy measurements in order to prove the compatibilizer's presence. Secondly, tensile tests were performed. The results show a significant increase of Young's modulus and the breaking strength when using polydopamine. Observations made through scanning electronic microscopy (SEM) confirmed an improvement of the fiber-matrix coupling in the presence of poly-(dopamine).     

Development of a general approach to the synthesis of a library of isoflavonoid derivatives

Isoflavonoids are a class of organic compounds that act primarily as antioxidants. They are produced almost exclusively by various members of the bean family including soybeans, tofu, peanuts, chick peas, and alfalfa. The antioxidant characteristics that isoflavonoids exhibit help hinder the progression of certain cancers, primarily breast, prostate, and colon cancer. We have developed a three-five step synthesis for obtaining a suite of isoflavonoid derivatives. The synthesis involves an enamine formation, a ring closure and halogenation, a Suzuki coupling, and finally a global deprotection to obtain the respective isoflavonoid derivatives.     

New approach to the synthesis of a trifurylcarbonium perchlorate

Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1141–1142, August, 1992.     

How to compute the Wiener index of a graph

The Wiener index of a graphG is equal to the sum of distances between all pairs of vertices ofG. It is known that the Wiener index of a molecular graph correlates with certain physical and chemical properties of a molecule. In the mathematical literature, many good algorithms can be found to compute the distances in a graph, and these can easily be adapted for the calculation of the Wiener index. An algorithm that calculates the Wiener index of a tree in linear time is given. It improves an algorithm of Canfield, Robinson and Rouvray. The question remains: is there an algorithm for general graphs that would calculate the Wiener index without calculating the distance matrix? Another algorithm that calculates this index for an arbitrary graph is given.     

Rearrangement of a cyclohexyl radical to a cyclopentylmethyl radical on the avermectin skeleton

The rearrangement of a substituted cyclohexyl radical to a cyclopentylmethyl radical on the skeleton of avermectin B1 was observed experimentally and explored computationally. The Stork-Nishiyama methodology was applied to the macrocycle of interest followed by a Tamao oxidation. The expected 5-6 fused ring product was observed in minor amounts. The major product was a 5-5 fused ring resulting from apparent conversion of the initially formed cyclohexyl radical to a cyclopentylmethyl radical. Preliminary computational results indicate that substituents in the macrocycle induce the rearrangement.     

Optimization of a capillary electrophoresis method to determine the chiral purity of a drug

Capillary electrophoresis (CE) using hydroxypropyl-β-cyclodextrin (HP-β-CD) in the separation buffer was investigated to determine the overall chiral purity of a drug containing a single stereogenic center. The effects of primary factors —pH, buffer components, buffer concentration, cyclodextrin concentration and sample amount (concentration and injection volume) — on the resolution of the enantiomers were investigated. Secondary factors such as the HP-β -CD source, lot and degree of substitution that were expected to affect the robustness of the assay were investigated also. The linearity, quantitation limit for the trace enantiomer and the precision of the measurements were determined. This study shows that understanding and optimizing the assay conditions leads to a chiral CE separation that is comparable to that obtained by chiral HPLC. However, chiral CE separations achieved with buffer additives have the advantages of shorter run times, higher numbers of theoretical plates (greater resolution), smaller amounts of chiral additive (less cost) and greater ruggedness (separation virtually independent of column properties unlike HPLC).     

From a biogenetic scenario to a synthesis of the ABC ring of manzamine A

On the basis of a biogenetic proposal for explaining the biogenesis of manzamine A, the cycloaddition of dihydropyridinium salt 26 with diene derivative 5 leads to adducts 27. These adducts, as well as their related and previously described analogues 9, are now shown to be precursors of diene derivatives such as 10, 13, and 28. Treatment of diene 32 with sodium azide resulted in a one-step formation of the tricyclic imino derivative 34. This key intermediate was further transformed into tricyclic derivative 40, which possesses the essential features of the ABC ring of manzamine A.     

Rearrangement of a pyranone to a benzothiazole

The conversion of 2-chloromethyl-5-methoxy-4H-pyran-4-one to 2-amino-5-hydroxy-6-methoxybenzothiazole hydrochloride under mild reaction conditions has been observed. The synthesis of the identical benzothiazole by an alternate unequivocal method is also reported.