The gauche effect : On the nature of the interaction between electronegative substituents in trans-1,2-disubstituted cyclohexanes

The positions of the aa/ee conformational equilibria of a series of trans-1,2-disubstituted cyclohexanes containing etectronegative substituents have been determined experimentally by NMR, and calculated theoretically by classical means. It is found that the classical analysis of the results, which takes into account explicitly steric and electrostatic interactions between gauche substituents, is not adequate, because residual attraction remains between the substituents.     

Zeta matrices of elliptic curves

Let $\text{O =}\text{lim}{}_{\mathrm{n}}\text{Z/p}{}^{\mathrm{n}}\text{Z}$, let $\text{A}\text{= O[g}{}_2\text{, g}{}_3\text{]}{}_{\mathrm{\Delta }}$, where g₂ and g₃ are coefficients of the elliptic curve: Y² = 4X³ ? g₂X ? g₃ over a finite field and Δ = g₂³ ? 27g₃² and let $\text{B}\text{=}\text{A}\text{[X, Y]}\text{(Y}{}^2\text{? 4X}{}^3\text{+ g}{}_2\text{X + g}{}_3\text{)}$. Then the p-adic cohomology theory will be applied to compute explicitly the zeta matrices of the elliptic curves, induced by the pth power map on the free $\text{A}{}^2\text{?}{}_{\mathrm{Z}}\text{Q}$-module $\text{H}{}^1\text{(X,}\text{A}{}^2\text{?}{}_{\mathrm{Z}}\text{Q)}$. Main results are; Theorem 1.1: X²dY and YdX are basis elements for $\text{H}{}^1\text{(}\text{X}\text{, Γ}{}_{\mathrm{<mtext>A</mtext>}}{}^1\text{(}\text{X}\text{)}{}^2\text{?}{}_{\mathrm{Z}}\text{Q)}$; Theorem 1.2: YdX, X²dY, Y^?1dX, Y^?2dX and XY^?2dX are basis elements for $\text{H}{}^1\text{(}\text{X}\text{? (Y = 0), Γ}{}_{\mathrm{<mtext>A</mtext>}}{}^1\text{(}\text{X}\text{)}{}^2\text{?}{}_{\mathrm{Z}}\text{Q)}$, where $\text{X}$ is a lifting of X, and all the necessary recursive formulas for this explicit computation are given.     

CPT noninvariance: a model for an initial lepton asymmetry due to unequal masses for lepton and antilepton

A primary lepton-antilepton asymmetry provides the seed for the present empirical baryon-antibaryon asymmetry in a phenomenological model with a small, effectively spontaneous violation of CPT invariance at the origin. An experimentally accessible possibility is that the mass of a charged lepton, measured in the present era, can differ slightly from the mass of the antilepton, with a maximum possible difference at the level of (10 ^?9 - 10 ^?8). For electron and positron this is a mass difference with magnitude (0.001 - 0.01) eV, somewhat below the present empirical upper limit of 0.02 eV.     

Energie des orgitales et interactions orbitalaires : effet anomere de la nojirimycine

The anomeric effect in Nojirimycin (5-amino-$\text{D}$-glucopyranose) in water solvent is greater than that in $\text{D}$-glucopyranose by approximately 0.7 k cal/mol ; the direction of the difference accords with the predictions of qualitative perturbational molecular orbital theory.     

Hypervirial theorems and symmetry

It is pointed out that to ensure that an optimal variational wave function having a certain symmetry satisfies the hypervirial theorem forW, it is sufficient thatiSW, whereS is the projector onto the symmetry type in question, be a possible variation of . Application is made to the tensor hypervirial theorem for atoms.     

Evaluation of a new automated cleanup system for the analysis of polychlorinated dibenzo-p-dioxins and dibenzofurans in environmental samples

An automated cleanup system (Power-Prep, Fluid Management Systems, Inc.) was evaluated for the analysis of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/PCDF) in environmental samples. The study was firstly carried out against standard mixtures containing labeled and unlabeled PCDD/PCDF and a certified reference material (fly ash CRM 490). Next, a comparison between a conventional cleanup procedure and the new automated system for PCDD/PCDF analysis in environmental samples such as flue gas emissions, fly ashes, sludges, ambient air and soils was also made. The suitability of the system was finally assessed from the participation in an interlaboratory exercise. Owing to its capability to successfully perform the sample cleanup the Power-Prep apparatus is an alternative to the conventional methods.     

Synthesis and properties of palladium(II) complexes with sulfur ligands

Complexes of L-2 thiolhistidine (th) and 2-mercaptoimidazole (miz) with Pd(II) were synthesized, Pd(th)₄(NO₃)₂ and Pd(miz)₄Cl₂, and their structure determined by FTIR, UV/VIS, NMR, mass spectroscopy, and X-ray crystallography. For comparison, a Pd(II) complex with thiourea (tu), Pd(tu)₄Cl₂, was prepared. This compound has been reported in the literature. Spectral evidence indicates a single coordination site between the Pd(II) and S for all complexes. A Pd-S stretch band was identified for all complexes. NMR spectra provided evidence for deshielding effects in the complexes from that of its ligands. Charge transfer bands were identified in the UV/VIS spectra for the new complexes as well. The crystal structure for Pd(miz)₄Cl₂ was determined. Unit cell data was found to be:a=8.102(3)Å,b=8.300(3)Å,c=8.304(3)Å. The crystal system is triclinic and the space group isP ¯1.     

Investigation of the species-dependent in vitro metabolism of BAL30630 by stable isotope labeling and isotope exchange experiments analyzed by capillary liquid chromatography coupled to mass spectrometry

The in vitro metabolic profile of BAL30630, an antifungal piperazine propanol derivative, which inhibits the 1,3-beta-d-glucansynthase, was investigated by incubation with microsomes of several species and with rat hepatocytes. For the spotting of the metabolites, mixtures of BAL30630 with a stable isotope (deuterium) labeled analogue were incubated. The metabolic pattern comprises several oxidized metabolites. Based on isotope exchange experiments, their structures could be assigned to epoxide- and hydroxylated metabolites. In hepatocyte incubations, several glucuronides formed from these oxidized metabolites could be observed. From the analysis of the metabolic pattern in microsomes, products of carbamate hydrolysis were characterized. This hydrolysis was highly species dependent. In activated incubations and in rat hepatocytes, those metabolites were further oxidized. In incubations without NADPH activation, the resulting hydrolytic metabolites could be enriched without the subsequent oxidation. Final structural elucidation of the metabolites was performed using accurate mass determination and isotope exchange experiments, in which incubations were analyzed by deuterium exchange and capillary HPLC–QTof-MS and MS/MS. The use of non-radioactive, stabile isotope labeled drug analogues in combination with isotope exchange studies was essential in particular for a defined assignment of the functional groups in the structures of the investigated metabolites.