Unsymmetrical selenides from selenocyanates and methyl grignard

The addition of methyl Grignard to diethyl acetamido(cyanoselenobenzyl)malonates 3 and 4 at ?78° followed by hydrolysis yields the 3-(4-and 3-methylselenophenyl)alanines 1 and 2.     

Synthesis,Crystal Structure,and Spectral Properties of a Cobalt(II) Complex with N‐Salicylidene‐p‐Toluidine

The complex Co(C₁₄H₁₃NO)₂Cl₂ with the protonated N‐salicylidene‐p‐toluidine ligand was synthesized from an ethanolic solution of CoCl₂·6H₂O and N‐salicylidene‐p‐toluidine. The crystal structure was determined from X‐ray single crystal data (monoclinic, space group Cc, a = 1496.2(3) pm, b = 1257.4(4) pm, c = 1544.6(3) pm, β = 115.01(1)°, Z = 4). Co²⁺ adopts a distorted tetrahedral geometry. The UV‐Vis and IR spectra of the complex are discussed.     

Synthesis and Structure of a 1,3-alternate-Thiacalix[4]arene diamide Derivative

A novel receptor possessing two complexation sites and bearing 1,3-alternate conformation based on thiacalix[4]arene, confirmed by single crystal X-ray analysis, was prepared. The tetrathiacalix[4]arene diamide shows strong intramolecular hydrogen bonding. The binding behavior towards K⁺ and halides has been examined by ¹H NMR titration experiments.     

Oxygen isotope corrections for online delta(34)S analysis

Elemental analyzers have been successfully coupled to stable-isotope-ratio mass spectrometers for online measurements of the delta(34)S isotopic composition of plants, animals and soils. We found that the online technology for automated delta(34)S isotopic determinations did not yield reproducible oxygen isotopic compositions in the SO(2) produced, and as a result calculated delta(34)S values were often 1-3 per thousand too high versus their correct values, particularly for plant and animal samples with high C/S ratio. Here we provide empirical and analytical methods for correcting the S isotope values for oxygen isotope variations, and further detail a new SO(2)-SiO(2) buffering method that minimizes detrimental oxygen isotope variations in SO(2).     

Parametric studies of interaction strengths in polymer/CO2 systems: discontinuous molecular dynamics simulations

Discontinuous molecular dynamics simulations are performed on homopolymer/solvent and surfactant/solvent systems. The homopolymer and surfactant molecules are modeled as freely jointed square-well chains. Solvent molecules are modeled as both hard spheres and square-well spheres. We explore how the various interaction parameters affect the types of phase behavior and micellization observed in the homopolymer/solvent and surfactant/solvent systems. Increasing the packing fraction of homopolymers in both hard-sphere solvents and square-well solvents increases the solvent's ability to dissolve homopolymers only when the segment-solvent interaction strength exceeds a critical value. Although only upper critical solution temperature (UCST) behavior is observed for homopolymers in hard-sphere solvents, both UCST and lower critical solution temperature (LCST) behavior are observed for homopolymers in square-well solvents, depending upon the interaction strengths and chain length. This indicates that it is necessary to account for the solvent-solvent attraction to model LCST behavior in supercritical CO2. Our simulation results on surfactants in hard-sphere solvents show that it is necessary to account for the interactions experienced by both the head and tail blocks in order to capture the essential features of surfactant/supercritical CO2 systems.     

as-Triazin-Derivate,die möglicherweise therapeutische Wirkung besitzen, 15. Mitt.: Synthese von neuen “blockierten 5-substituierten 4-thio-6-azauridinen”

5-Substituted 4-thio-6-azauracils [I, 6-alkylthio-3,4-dihydro-5-thioxo-1,2,4-triazin-3(2H)-ones] have been converted with hexamethyldisilazane in 3-trimethylsilyloxy-5-trimethylsilylthio-derivatives(II). These were condensed with 1-O-acetyl-2,3,5-tri-O-benzoyl-d-ribofuranose in the presence of anhydrous stannic chloride to afford the corresponding 1-(2,3,5-tri-O-benzoyl--d-ribofuranosyl)-4-thioxo-5-substituted-6-azauracil (III).     

Synthesis and conformational analysis by 1H NMR and restrained molecular dynamics simulations of the cyclic decapeptide [Ser-Tyr-Ser-Met-Glu-His-Phe-Arg-Trp-Gly]

Summary The design of enzyme mimics with therapeutic and industrial applications has interested both experimental and computational chemists for several decades. Recent advances in the computational methodology of restrained molecular dynamics, used in conjunction with data obtained from two-dimensional ¹H NMR spectroscopy, make it a promising method to study peptide and protein structure and function. Several issues, however, need to be addressed in order to assess the validity of this method for its explanatory and predictive value. Among the issues addressed in this study are: the accuracy and generizability of the GROMOS peptide molecular mechanics force field; the effect of inclusion of solvent on the simulations; and the effect of different types of restraining algorithms on the computational results. The decapeptide Ser-Tyr-Ser-Met-Glu-His-Phe-Arg-Trp-Gly, which corresponds to the sequence of ACTH_1–10, has been synthesized, cyclized, and studied by two-dimensional ¹H NMR spectroscopy. Restrained molecular dynamics (RMD) and time-averaged restrained molecular dynamics (TARMD) simulations were carried out on four different distance-geometry starting structures in order to determine and contrast the behavior of cyclic ACTH_1–10 in vacuum and in solution. For the RMD simulations, the structures did not fit the NOE data well, even at high values of the restraining potential. The TARMD simulation method, however, was able to give structures that fit the NOE data at high values of the restraining potential. In both cases, inclusion of explicit solvent molecules in the simulation had little effect on the quality of the fit, although it was found to dampen the motion of the cyclic peptide. For both simulation techniques, the number and size of the NOE violations increased as the restraining potential approached zero. This is due, presumably, to inadequacies in the force field. Additional TARMD vacuum-phase simulations, run with a larger memory length or with a larger sampling size (16 additional distance-geometry structures), yielded no significantly different results. The computed data were then analyzed to help explain the sparse NOE data and poor chymotryptic activity of the cyclic peptide. Cyclic ACTH_1–10, which contains the functional moieties of the catalytic triad of chymotrypsin, was evaluated as a potential mimic of chymotrypsin by measurement of the rate of hydrolysis of esters of L-and d-phenylalanine. The poor rate of hydrolysis is attributed to the flexibility of the decapeptide, the motion of the side chains, which result in the absence of long-range NOEs, the small size of the macrocycle relative to that of the substrate, and the inappropriate orientation of the Gly, His, and Ser residues. The results demonstrate the utility of this method in computer-aided molecular design of cyclic peptides and suggest structural modifications for future work based on a larger and more rigid peptide framework.