Strong solute-solute dispersive interactions in a protein-ligand complex

The contributions of solute-solute dispersion interactions to binding thermodynamics have generally been thought to be small, due to the surmised equality between solute-solvent dispersion interactions prior to the interaction versus solute-solute dispersion interactions following the interaction. The thermodynamics of binding of primary alcohols to the major urinary protein (MUP-I) indicate that this general assumption is not justified. The enthalpy of binding becomes more favorable with increasing chain length, whereas the entropy of binding becomes less favorable, both parameters showing a linear dependence. Despite the hydrophobicity of the interacting species, these data show that binding is not dominated by the classical hydrophobic effect, but can be attributed to favorable ligand-protein dispersion interactions.     

Minimax risk overl p -balls forl p -error

Summary Consider estimating the mean vector from dataN _n (, ² I) withl _q norm loss,q1, when is known to lie in ann-dimensionall _p ball,p(0, ). For largen, the ratio of minimaxlinear risk to minimax risk can bearbitrarily large ifp. Obvious exceptions aside, the limiting ratio equals 1 only ifp=q=2. Our arguments are mostly indirect, involving a reduction to a univariate Bayes minimax problem. Whenp, simple non-linear co-ordinatewise threshold rules are asymptotically minimax at small signal-to-noise ratios, and within a bounded factor of asymptotic minimaxity in general. We also give asymptotic evaluations of the minimax linear risk. Our results are basic to a theory of estimation in Besov spaces using wavelet bases (to appear elsewhere).     

THE REARRANGEMENT OF ARYLSELENENAMIDES

Abstract

Attempts to synthesize N-phenylbenzeneselenena mide always produced the isomeric p-aminodiphenyl selenide, probably as a result of an acid catalyzed rearrangement. The ease with which this rearrangement occurs is contrasted with the forcing conditions required for the analogous rearrangement of sulfenamides.     

The power of visual imagery in synthesis planning. Stereocontrolled approaches to CGP-60536B,a potent renin inhibitor

Two strategies were developed toward the stereocontrolled synthesis of 8-aryl-3-hydroxy-4-amino-2,7-diisopropyloctanoic acids with predetermined stereogenic centers. This is a generic motif in a new class of potent inhibitors of the enzyme renin, exemplified by CGP-60536B. The synthesis relies on the utilization of L-pyroglutamic acid as chiron, and proceeds through the incorporation of required functionality by exploiting internal induction. One of the strategies shows the power of visual imagery in synthesis planning, akin to a Dali-like representation of objects that can be viewed in more than one way. Thus, the entire carbon skeleton of the target molecule is encompassed in a partially functionalized bicyclic indolizidinone precursor. In a second strategy, an intermediate common to the first approach is elaborated into an appended gamma-lactone which is alkylated through enolate chemistry and ultimately transformed into the intended target compound. X-ray crystallography was used to corroborate the structures and stereochemistries of several intermediates.     

Stoneley waves in three-layered cylindrical solid media

This paper considers the propagation of Stoneley modes along the interfaces of three-layered concentric cylindrical solid media in order to assist in the design of ultrasonic transmission rods. The phase velocity dispersion curves and amplitude distributions are numerically analyzed. The modes are analogous to non-dispersive Stoneley waves and are confined to the vicinities of the two interfaces at high frequency. A key finding is that the peak amplitude location for each mode transfers between the two interfaces as a function of frequency. A simplified model is introduced, giving the peak amplitude locations of each mode in different frequency ranges efficiently.     

4‐(3‐Azaniumylpropyl)morpholin‐4‐ium chloride hydrogen oxalate: an unusual example of a dication with different counter‐anions

The mixed organic–inorganic title salt, C₇H₁₈N₂O²⁺·C₂HO₄⁻·Cl⁻, forms an assembly of ionic components which are stabilized through a series of hydrogen bonds and charge‐assisted intermolecular interactions. The title assembly crystallizes in the monoclinic C2/c space group with Z = 8. The asymmetric unit consists of a 4‐(3‐azaniumylpropyl)morpholin‐4‐ium dication, a hydrogen oxalate counter‐anion and an inorganic chloride counter‐anion. The organic cations and anions are connected through a network of N—H...O, O—H...O and C—H...O hydrogen bonds, forming several intermolecular rings that can be described by the graph‐set notations R₃³(13), R₂¹(5), R₁²(5), R₂¹(6), R₂³(6), R₂²(8) and R₃³(9). The 4‐(3‐azaniumylpropyl)morpholin‐4‐ium dications are interconnected through N—H...O hydrogen bonds, forming C(9) chains that run diagonally along the ab face. Furthermore, the hydrogen oxalate anions are interconnected via O—H...O hydrogen bonds, forming head‐to‐tail C(5) chains along the crystallographic b axis. The two types of chains are linked through additional N—H...O and O—H...O hydrogen bonds, and the hydrogen oxalate chains are sandwiched by the 4‐(3‐azaniumylpropyl)morpholin‐4‐ium chains, forming organic layers that are separated by the chloride anions. Finally, the layered three‐dimensional structure is stabilized via intermolecular N—H...Cl and C—H...Cl interactions.     

Bacterial Reduction of Chromium

A mixed culture was enriched from surface soil obtained from an eastern United States site highly contaminated with chromate. Growth of the culture was inhibited by a chromium concentration of 12 mg/L. Another mixed culture was enriched from subsurface soil obtained from the Hanford reservation, at the fringe of a chromate plume. The enrichment medium was minimal salts solution augmented with acetate as the carbon source, nitrate as the terminal electron acceptor, and various levels of chromate. This mixed culture exhibited chromate tolerance, but not chromate reduction capability, when growing anaerobically on this medium. However, this culture did exhibit chromate reduction capability when growing anaerobically on TSB. Growth of this culture was not inhibited by a chromium concentration of 12 mg/L. Mixed cultures exhibited decreasing diversity with increasing levels of chromate in the enrichment medium. An in situ bioremediation strategy is suggested for chromate contaminated soil and groundwater.