Versatile and facile synthesis of diverse semisynthetic tetracycline derivatives via Pd-catalyzed reactions

A diverse collection of tetracycline derivatives has been synthesized utilizing Heck, Suzuki, and other palladium-coupling reactions via tetracycline arenediazonium and iodoarene salts. Large numbers of tetracyclines are now possible via these reactions, including numerous upper periphery derivatives of doxycycline, minocycline, sancycline, and methacycline modified at positions C7, C9, and C6-C13 on the tetracycline naphthacene ring. Application of palladium-coupling reactions to the tetracyclines has yielded new tetracycline classes with differing structural attributes, greatly increasing the structural diversity of this family of antibiotics, one of the last of the early antibiotic families to be expanded by organic and medicinal chemistry.     

Characterization of enantiospecific chemisorption on chiral Cu surfaces vicinal to Cu(111) and Cu(100) using density functional theory

Surfaces of simple fcc metals such as Cu with nonzero and unequal Miller indices are intrinsically chiral. Density functional theory (DFT) calculations are a useful way to study the enantiospecific adsorption of small chiral molecules on these chiral metal surfaces. We report DFT calculations of seven chiral molecules on several structurally distinct chiral Cu surfaces. These surfaces include two surfaces with (111)-oriented terraces and one with (100)-oriented terraces. Calculations are also described on a surface that was modified to mimic the surface structures that typically appear on real metal surfaces following thermally driven fluctuations in step edges. Our results provide initial information on how variation in the surface structure of intrinsically chiral metal surfaces can affect the enantiospecific adsorption of small molecules on these surfaces.     

A heterogeneous model for gas transport in carbon molecular sieves

A dual resistance model with distribution of either barrier or pore diffusional activation energy is proposed in this work for gas transport in carbon molecular sieve (CMS) micropores. This is a novel approach in which the equilibrium is homogeneous, but the kinetics is heterogeneous. The model seems to provide a possible explanation for the concentration dependence of the thermodynamically corrected barrier and pore diffusion coefficients observed in previous studies from this laboratory on gas diffusion in CMS. The energy distribution is assumed to follow the gamma distribution function. It is shown that the energy distribution model can fully capture the behavior described by the empirical model established in earlier studies to account for the concentration dependence of thermodynamically corrected barrier and pore diffusion coefficients. A methodology is proposed for extracting energy distribution parameters, and it is further shown that the extracted energy distribution parameters can effectively predict integral uptake and column breakthrough profiles over a wide range of operating pressures.     

Gravitational Instability of a Rotating Viscous Thermally Conducting Plasma

This paper deals with the gravitational instability of an infinite homogeneous viscous rotating plasma of finite electrical conductivity in the combined presence of effects of Hall currents, finite Larmor radius (FLR) and thermal conductivity. The ambient magnetic field is assumed to be uniform and acting along the vertical direction. Both longitudinal and transverse modes of wave propagation have been studied. It is shown that Jean's criterion determines the gravitational instability even in the presence of the effects of thermal conductivity, viscosity, finite electrical conductivity, FLR, rotation and Hall currents. Further it is found that while FLR, viscosity and rotation have a stabilizing influence, both the thermal and the electrical conductivities have a destabilizing influence on the gravitational instability of a plasma.     

How and Why to Solve the Operator Equation AX-XB = Y

The entities A, B, X, Y in the title are operators, by whichwe mean either linear transformations on a finite-dimensionalvector space (matrices) or bounded (= continuous) linear transformationson a Banach space. (All scalars will be complex numbers.) Thedefinitions and statements below are valid in both the finite-dimensionaland the infinite-dimensional cases, unless the contrary is stated.1991 Mathematics Subject Classification 15A24, 47A10, 47A62,47B47, 47B49, 65F15, 65F30.     

Solvent extraction of Re/VII/ with methylene blue into nitrobenzene

A method has been developed for the extraction of rhenium/VII/ with methylene blue. Nitrobenzene was found to be the most effective extractant for Re/VII/. The stoichiometry of metal to reagent determined by the method of substoichiometric extraction and slope-ratio method was found to be 11.     

Thermodynamics of binary mixtures of non-electrolytes containing a salt

Molar excess volume V ^E and enthalpy H ^E data have been measured at 25°C for pyridine A saturated with anhydrous cupric chloride (S) [A(S)]+ B [where B is aniline or o-toluidine (OT) or formamide (FD) or N, N-dimethylformamide (NND)] mixtures on the assumption that while the standard state of B is that of pure components B, the standard state of A(S) is that of A saturated with the salt S. The excess volume or enthalpy data for an equimolar mixture at a given temperature have been utilized to evaluate the interactional parameter X₁₂ of the Sanchez and Lacombe theory of fluid mixtures at that temperature, and the same has been combined with V ^E (x _A ) data for a good prediction not only of the coresponding H ^E (x _A ) data for the mixture but also the extent of unlike interactions between the A(S) and B components of these A(S)+B mixtures.