Molecular orbital momentum distributions and binding energies for H2O using an electron impact coincidence spectrometer

The construction and operation of an instrument which uses the techniques of coincidence counting and electron impact spectroscopy is reported for the study of molecular ionization at large momentum transfer in which the two outgoing electrons are detected at 45° to the incident beam. Variation of the incident energy provides binding-energy spectra for Xe, CH₄ and H₂O up to 45 eV. Alternatively variation of the azimuthal angle (symmetric, non-coplanar geometry) gives a measure of the electron momentum distribution for any selected orbital in the binding-energy spectrum. Momentum distributions for the four valence orbitals of H₂O are compared with various wavefunctions from the literature.     

Correlation effects and electron momentum distributions in the valence orbitals of ethylene

The non-coplanar symmetric (e, 2e) reaction has been applied to C₂H₄ at 1000-eV incident electron energy. An ion state at 27.4 eV separation en     

A second-order iterative technique for differential-integral systems

This note considers the optimal control of a system represented by nonlinear differential-integral equations with a general cost function. A second-order iterative method of solution based on the fixed-point contraction mapping principle is proposed.     

An Air‐Stable Na3SbS4 Superionic Conductor Prepared by a Rapid and Economic Synthetic Procedure

All‐solid‐state sodium batteries, using solid electrolyte and abundant sodium resources, show great promise for safe, low‐cost, and large‐scale energy storage applications. The exploration of novel solid electrolytes is critical for the room temperature operation of all‐solid‐state Na batteries. An ideal solid electrolyte must have high ionic conductivity, hold outstanding chemical and electrochemical stability, and employ low‐cost synthetic methods. Achieving the combination of these properties is a grand challenge for the synthesis of sulfide‐based solid electrolytes. Design of the solid electrolyte Na₃SbS₄ is described, realizing excellent air stability and an economic synthesis based on hard and soft acid and base (HSAB) theory. This new solid electrolyte also exhibits a remarkably high ionic conductivity of 1 mS cm^?1 at 25 °C and ideal compatibility with a metallic sodium anode.     

The area-code hypothesis: the immune system provides clues to understanding the genetic and molecular basis of cell recognition during development

Numberous studies of embryogenesis have provided evidence for highly specific cell-surface recognition phenomena. These include both the interactions of neighboring cells and the specific cellular migrations which occur as the developmental program of the embryo progresses. The area-code hypothesis elaborate here is an attempt to provide a framework for understanding cell-recognition phenomena in development. This hypothesis is based on extensive genetic, molecular, and cellular studies of the immune system. These studies suggest that the following events occur during the differentiation of antibody-producing cells. 1) Somatic cell lines of antibody-producing cells undergo a modification of their DNA as they become committed to synthesize a particular type of antibody molecule. This chromosomal modification event is probably a DNA translocation which leads to a somatic rearrangement of certain antibody genes. 2) In each of the specific cell lineages the new arrangement of DNA is inherited by all subsequent generations of cells. 3) The developmental programs which control these genetic alterations may be employed in a programmed and reproducible fashion. This programming of antibody development is suggested because different embryos appear to become committed to the production of identical antibody molecules in the same developmental sequence. 4) Antibody molecules are initially displayed on the cell surface where they serve as highly specifici receptors to trigger the cell to proliferate and differentiate upon interacting with appropriate external molecular signals. 5) Antibody-producing cells display combinations of different molecules on their surfaces which cause each of a very large number of different cells to interact differently with their environment. 6) The genes which code for many of these cell-surface molecules are organized into multigene families. These observations as well as information from other developmental systems have led us to propose the area-code hypothesis. This hypothesis is concerned with the structure, function, and regulation of cell-surface molecules that mediate recognition phenomena during embryogenesis. Area-code molecules are cell-surface molecules which are involved in the specific recognition phenomena during growth and development. These molecules provide cells with distinct cell-surface addresses or phenotypes, and provide the basis for the specificity in cell-cell recognition during cell migrations and cell-cell interactions, as well as serving as receptors for diffusible differentiation signals. The area-code hypothesis has 3 main postulates. i) There is a progressive display of specific combinations of area-code molecules on the surfaces of cells during development. ii) The genetic programs which determine the specific expression of area-code molecules are in part controlled by DNA modifications. These chromosomal modifications are believed to channel cells into specific lineages uith progressively restricted developmental options...     

CoMFA modeling of enzyme kinetics: K(m) values for sulfation of diverse phenolic substrates by human catecholamine sulfotransferase SULT1A3

Three-dimensional QSAR models were developed for predicting kinetic Michaelis constant (K(m)) values for phenolic substrates of human catecholamine sulfating sulfotransferase (SULT1A3). The K(m) values were correlated to the steric and electronic molecular fields of the substrates utilizing Comparative Molecular Field Analysis (CoMFA). The evaluated SULT1A3 substrate data set consisted of 95 different substituted phenols, catechols, catecholamines, steroids, and related structures for which the K(m) values were available. The data set was divided in three different subgroups in the initial analysis: (1). for the first CoMFA model substrates with only one reacting hydroxyl group were selected (n = 51), (2).the second model was build with structurally rigid substrates (n = 59), and (3). finally all substrates of the data set were included in the analysis (n = 95). Substrate molecules were aligned using the aromatic ring and the reacting hydroxyl group as a template. After the initial analysis different substrate alignment rules based on the existing knowledge of the SULT1A3 active site structure were evaluated. After this optimization a final CoMFA model was built including all 95 substrates of the data set. Cross-validated q(2) values (leave-one-out and leave-n-out) and coefficient contour maps were calculated for all derived CoMFA models. All four CoMFA models were statistically significant with q(2) values up to 0.624. These predictive QSAR models will provide us information about the factors that affect substrate binding at the active site of human catecholamine sulfotransferase SULT1A3.