Anionic oligomerization of methacrylonitrile

The anionic oligomerization of methacrylonitrile by alcoholic solutions of sodium alkoxide in dimethyl sulfoxide, methanol and ethanol was studied. The DP of the oligomers was directly proportional to the monomer concentration and inversely proportional to the alcohol concentration, in accordance with the equation DP = K[MAN]/[ROH], K being equal to K_p/K_tr. The value of K in DMSO (with sodium methoxidemethanol) was 2.9 ± 0.2, in methanol was 1.5 ± 0.1, and in ethanol (with sodium ethoxide as initiator) was 1.9 ± 0.1. The physical properties of the oligomers are given.     

Détermination des modèles d'imperfections de différentes variétés allotropiques du sulfure cuivreux (digénite cubique,chalcocite hexagonale “haute et basse température”, chalcocite orthorhombique)

From the study of the CuCuBrCu_2?εSC solid cell in the range of cubic digenite and “high temperature” hexagonal chalcocite we have deduced the laws of variation of the deviation from stoichiometry and the holes concentration with the equilibrium partial pressure of sulfur (δ and p are found to be proportional to ). The electronic model corresponding to the formation of associations (V^×_CuV′_Cu) in the presence of neutral vacancies V^×_Cu allows one to explain these laws. In the low temperature range (range of “low temperature” hexagonal chalcocite and orthorhombic chalcocite) the study of thermal variations of Hall coefficient permits us to propose the following models: (a) the deviation from stoichiometry of the “low temperature” hexagonal chalcocite is due to the simple ionized vacancies V′_Cu; (b) the deviation from stoichiometry of the orthorhombic chalcocite is due to the vacancies V′_Cu and to the associations (V^×_CuV^×_Cu).     

SciFinder-guided rational design of fluorescent carbon dots for ratiometric monitoring intracellular pH fluctuations under heat shock

Intracellular pH plays a significant role in various biological processes, including cell proliferation, apoptosis, metabolism, enzyme activity and homeostasis. In this work, a novel design strategy for the preparation of pH responsive carbon dots (CDs-pH) for ratiometric intracellular imaging was reported. By using SciFinder database, fluorescent CDs-pH with the required pK_a value of 6.84 were rationally designed, which is vital important for precise sensing of intracellular pH. As a result, the synthesized CDs-pH demonstrated robust ability to test pH fluctuations within the physiological range of 5.4-7.4. The CDs-pH was further utilized for fluorescent ratiometric imaging of pH in living HeLa cells, effectively avoided the influence of autofluorescence from native cellular species. Moreover, real-time monitoring of intracellular pH fluctuation under heat shock was successfully realized. This SciFinder-guided design strategy is simple and flexible, which has a great potential to be used for the development of other types of CDs for various applications.     

Force field and 13C-NMR investigations of substituted cyclopentanes. A concept for the adaption of 13C NMR shifts to varying torsional arrangements in flexible conformers

MM2 Exploration of the conformational space for methylcyclopentane, in contrast to cyclopentanone yields more and flatter minima than known previously. Calculations of cyclopentanes with substituents X = F, Cl, CHMe₂, and CMe₃ with two stable conformations indicate <2° torsional angle changes with the different substituents. Cyclopentanes bearing not more than 2 substituents can accommodate all groups in pseudoequatorial positions without changing the basic envelope and twist chair geometries significantly. A model for ¹³C-shift calculation is proposed in which shift increments for the different torsional arrangements are obtained by linear interpolation between corresponding cyclohexane values. After correction for the nonequivalent carbon shifts in the hydrocarbon itself, again using the linear interpolation, a significant improvement of the shift correlations is observed. For disubstituted cyclopentanes these predict the shifts within ± 1.7 ppm with Me, CHMe₂, CMe₃, Cl, Br and OH as substituents. Configurational assignments are difficult with 1,3-di-substituted cyclopentanes, but straightforward with 1,2-di- and trisubstituted compounds. Thus, due to the presence of smaller torsional angles between, e.g. diequatorial vicinal substituents in the 1,2- cis series as compared to the trans compounds, the latter show deshielding, particularly at C2, by 1–4 ppm. Several epimers are stereo-selectively prepared by suitable ketone reduction and displacement methods.     

Sensing the physicochemical nature of he and ne in micropores by adsorption measurements

He and Ne in contact with molecular sieves in the form of crystalline A zeolites and amorphous carbon molecular sieves fibers (CMSF) were studied by adsorption measurements. Classification of the effective enclosure of zeolitic apertures and of graphitic constrictions, as determined by recent temperature-programmed desorption mass spectrometry (TPD-MS) studies of adsorption of He and Ne onto these materials, was utilized in making a prudent choice of samples and experimental conditions. In view of the former TPD information, the behaviors of adsorption and volumetric measurements reported herein are straightforwardly interpreted. The combined TPD, adsorption isotherms, and dead volume data deepen the understanding of the physicochemical nature of adsorbed gas, where gas adsorption in the vicinity of pore constrictions and/or apertures as well as on the inner surface areas of pores and/or cages could be resolved. Previous conclusions that the huge activation energies measured for Ne/CMSF at high temperatures are unlikely to characterize chemical desorption but reflect those required for overcoming the barrier of effectively constricted apertures were confirmed by the volumetric data presented here. At 77 K, considerable He adsorption was observed in the porous solids and found to be responsible for abnormal deduced values of dead volumes. The occurrence of significant adsorption of He onto A zeolites and CMSF at 77 K warrants the realization that in cases concerning porous materials, volumetrically deduced quantities should not be taken for granted, but should be carefully considered and uniquely interpreted in relation to the specific experimental conditions under which they are taken.     

Reactivity of Singlet Oxygen Toward Proteins: The Effect of Structure in Basic Pancreatic Trypsin Inhibitor and in Ribonuclease A

The reactions of singlet oxygen, ¹O₂, with large peptides have been described previously. It was found that even in these systems, which in their native form are generally not supposed to possess a stable structure in solution, the polypeptide does impede the access of ¹O₂ to the amino acids that react readily with ¹O₂. Here we describe the ¹0₂ reaction with two proteins of well-defined structure. The quenching of ¹O₂ by bovine pancreatic trypsin inhibitor (BPTI) and by ribonuclease A (RNase A) was compared to that of a solution at the same concentration as those of its constituent amino acids that react readily with ¹O₂. The proteins were studied in their native form, when partly denatured by splitting their S-S bonds and when fully denatured. It was found that while in the native form the quenching rate constant was seven times lower in BPTI (2.2 vs 15.2 times 10⁷WM^-1 s^-1) and three times lower in RNase A (11.0 vs 32 times 10⁷M^-l s^-1) than in a mixture of its constituent amino acid residues, it increased upon denaturation reaching in the fully denatured state the value of the corresponding amino acid mixture. More striking is the effect of the protein structure when comparing the fraction of the encounters between ¹O₂ and protein, which cause damage to the protein, as reflected in the decrease of its biological activity. This decrease is assumed to be due to the chemical (oxidative) reactions of ¹O₂ in the protein. In the exceptionally stable BPTI the fraction of such encounters was 0.05 and in RNase A it was 0.2, whereas for the amino acid tryptophan in solution, 0.7 of the collisions with ¹O₂ led to a chemical reaction.     

Metal complexes with macrocyclic ligands. Part XXII. Synthesis two of bis-tetraaza-macrocycles and study of the structures,electrochemistry, VIS and EPR spectra of their binuclear Cu2+ and Ni2+ complexes

The two bis-macrocycles 4 and 5 in which the tetraaza units are separated by a chain of different length, have been synthesized using 1,4,7-tritosyl-1,4,7,11-tetraazacyclotetradecane as starting compound and bifunctional alkylating agents. The bis-macrocycles give binuclear complexes with Ni²⁺ and Cu²⁺, the properties of which have been studied to obtain information about the interaction of the two subunits as a function of the distance. The VIS spectra of the Ni²⁺ and Cu²⁺ complexes indicate that both metal ions are in a square-planar geometry as expected from the results of the analogous complexes with 1,4,7,11-tetraazacyclotetradecane 7 . Cyclic voltammetry and differential pulse polarography of the binuclear Ni²⁺complexes in CH₃CN show a single two-electron step for ligand 5 , whereas two distinct one-electron redox processes can be observed for ligand 4 , indicating that the two metal ions interact with each other when the chain length is shorter. Similarly, the EPR studies of frozen solutions of the binuclear Cu²⁺ complexes clearly show that a magnetic dipolar interaction between the two paramagnetic centers exists, and that the strength of it depends upon the length of the bridge. Finally, from the X-ray structures of the binuclear Ni²⁺ complexes with 4 and 5 , it is seen that the two rings are kept apart as far as possible, the distances between the two metal ions determined in the solid correlate well with the observations in solution.     

Vectorization of a classical trajectory code on a floating point systems,Inc. Model 164 attached processor

A triatomic classical trajectory code has been modified by extensive vectorization of the algorithms to achieve much improved performance on an FPS 164 attached processor. Extensive timings on both the FPS 164 and a VAX 11/780 with floating point accelerator are presented as a function of the number of trajectories simultaneously run. The timing tests involve a potential energy surface of the LEPS variety and trajectories with 1000 time steps. The results indicate that vectorization results in timing improvements on both the VAX and the FPS. For larger numbers of trajectories run simultaneously, up to a factor of 25 improvement in speed occurs between VAX and FPS vectorized code.     

Preparation,Characterisation, and Structure of N-Methylated Derivatives of 1,3,5-Triamino-1,3,5-trideoxy-cis-inositol: Polyalcohols with Unusual Acidity

1,3,5-Trideoxy-1,3,5-tris(dimethylamino)-cis-inositol (TDCI) and 1,3,5-trideoxy-1,3,5-tris(trimethylammonio)-cis-inositol (TTCI) were prepared by methylation of 1,3,5-triamino-1,3,5-trideoxy-cis-inositol (TACI). The ability of TDCI to form both intermolecular and intramolecular H-bonds, as demonstrated by X-ray diffraction, is probably responsible for the good solubility of TDCI in almost every common solvent. TTCI was found to be a polyol of unusual high acidity (pK₁ = 8.14 ± 0.02, pK₂ = 13.0 ± 0.2). This phenomenon could be explained by electrostatic interactions between the charged substituents of the cyclohexane residue.     

N,N,N′,N′-Tetrabutyl-3,6-dioxaoctan-dithioamid,Ionophor mit Selektivität für Cd2+

N,N,N′,N′-Tetrabutyl-3,6-dioxaoctane-dithioamide, an Ionophore with Selectivity for Cd²⁺ The dioxa-dithioamide 3 behaves as a highly selective ionophore for Cd²⁺ in solvent polymeric membranes. It induces cation-permselectivity in these membranes with a transference number of 1 for Cd(NO₃)₂- and of 2 for CdCl₂-solutions. In the presence of a proton carrier, 3 may be used to selectively pump Cd²⁺ through membranes by coupling with a pH gradient.