Uncertainties in crystallization of hen‐egg white lysozyme: reproducibility issue

The reproducibility of biomacromolecular crystallization (tetragonal and orthorhombic lysozyme crystals) was studied by monitoring the evolution of protein concentration during the crystallization process using Mach‐Zehnder interferometer. It was found that formation of both tetragonal and orthorhombic crystals exhibited poor reproducibility. When the crystallization occurred under isothermal conditions, the protein concentration in the solution varied differently in different experiments under identical conditions (for both types of crystals). Moreover, in the case of orthorhombic lysozyme crystallization (under either isothermal or thermal gradient conditions), it is clear that the crystals could not be always readily formed. When formation of tetragonal lysozyme crystals was conducted at a temperature gradient condition, however, the evolution of concentration was reproducible. The phenomena found in this study revealed that biomacromolecular crystallization can be uncertain, which is probably caused by the process of nucleation. Such uncertainties will be harmful for the efforts of screening crystallization conditions for biomacromolecules. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

On a set of generating relations of the full transformation semigroups

A set of generating relations of the full transformation semigroup Σ_n consisting of all mappings of the set $\text{Ω = {1, …, n}}$ into itself with respect to a natural system of generators {γ_jⁱ, σ_jⁱ} (defined in Section 1) is given. The set of relations (1)～(15) given in Section 1 turns out to be a set of generating relations.     

Exponential two server queue withN-policy and general vacations

AnM/M/2 queueing system with vacations is studied in which two servers keep working until there are no customers, and then one of the two servers takes a vacation. The remaining server does not leave the system during the vacation, and keeps serving the arriving customers. The duration of vacation is general. We study both theN-policy multiple vacation model and the single vacation model. This paper is concerned with the determination of the stationary distribution of the number of customers in the systems, and their decomposition structures.     

Enantiospecific and diastereoselective synthesis of syn-β-amino-α-hydroxy acids

The reaction of chiral α-hydroxy β,γ-unsaturated esters with tosyl isocyanate followed by cyclization of the resulting allylic carbamates with iodine in the presence of sodium carbonate provided trans-4,5-disubstituted 2-oxazolidinone derivatives in a highly diastereoselective manner. The subsequent removal of the iodo group and the protective functionality afforded the syn-β-amino-α-hydroxy acids. Using the reaction sequence, (2R,3S)- and (2S,3R)-3-amino-2-hydroxy acids were synthesized with high enantioselectivity.     

Carrier doping effect into quasi-one-dimensional bromo-bridged Ni(III) complexes with strong electron-correlation by Cu(II) ions, [Ni1-xCux(chxn)2Br]Br2-x

This communication will describe the electron doping effect into Ni(III) complexes by Cu(II) ions, [Ni(1-x)Cu(x)(chxn)(2)Br]Br(2-x) (x = 0.038 and 0.101) by using an electrochemical oxidation method. A drastic increase of electrical conductivity as well as a new absorption band around 0.5 eV in single crystal reflectance spectra was observed by doping Cu(II) ions, indicating the electron doping was successfully made. An ESR result shows unpaired electrons locate in the d(x2-y2) orbitals of Cu(II) and have almost no interaction with those of other ions.     

Tungsten and molybdenum nitrosyl cations in fluorosulfonic acid

The tungsten and molybdenum hexacarbonyls, M(CO)(6) (M = W, Mo), dissolve in fluorosulfonic acid, HSO(3)F, to generate the tungsten and molybdenum carbonyl cations, [M(CO)(4)](2+)(solv), which are transformed, by exposure to an NO atmosphere, into the tungsten and molybdenum carbonyldinitrosyl cations, [M(CO)(NO)(2)](2+)(solv), respectively. These complexes have been characterized by NMR ((183)W, (13)C, and (15)N), IR, and Raman spectroscopy, and they are the first well-characterized metal nitrosyl cations in strong acids or superacids although the spectroscopic techniques do not address the number or coordination mode of the solvent molecules. Their formation suggests that strong acids and superacids can hopefully be used to generate a number of metal nitrosyl cations as they have been successfully used for preparing a series of metal carbonyl cations.     

Analytical applications of condensed phosphoric acid-III Iodometric determination of sulphur after reduction of sulphate with sodium hypophosphite and either tin metal or potassium iodide in condensed phosphoric acid

Novel methods for the reduction of sulphate to hydrogen sulphide with hypophosphite-tin metal or hypophosphite-iodide in condensed phosphoric acid (CPA) are proposed. The reduction of sulphate with hypophosphite alone does not proceed quantitatively. Sulphate, however, is quantitatively decomposed with hypophosphite when tin metal or potassium iodide is used together with it. The determination of sulphur by the hypophosphite-tin metal-CPA and tin(II)-CPA methods is interfered with by copper on account of the stabilization of copper(I) sulphide, but this interference can be eliminated by adding iodide, e.g. potassium and lead salts. Alum and barytes are quantitatively decomposed within 15 min at 140 and 280 degrees , respectively. The hydrogen sulphide evolved is absorbed in zinc acetate solution at pH 4.5 and then determined by iodometry.     

Organocatalytic Asymmetric Nitroaldol Reaction: Cooperative Effects of Guanidine and Thiourea Functional Groups

Catalytic enantio‐ and diastereoselective nitroaldol reactions were explored by using designed guanidine–thiourea bifunctional organocatalysts under mild and operationally simple biphasic conditions. These catalytic asymmetric reactions have a broad substrate generality with respect to the variety of aldehydes and nitroalkanes. Based on this catalytic nitroaldol process, straightforward syntheses of cytoxazone and 4‐epi‐cytoxazone were achieved. These catalytic nitroaldol reactions require KI as an additive for highly asymmetric induction; it operates by inhibiting the retro mode of the reaction. On the basis of studies of structure and catalytic‐activity relationships, a plausible guanidine–thiourea cooperative mechanism and a transition state of the catalytic reactions are proposed. Drastic substituent effects on the catalytic properties of this catalyst may lead to the development of new chiral surfactants.