Purification of a synthetic myristylated peptide by counter-current chromatography

A preparative purification of myristyl-Gly-Asn-Ile-Phe-Ala-Asn-Leu-Phe-Lys-Gly-Leu-Phe-Gly-Lys-Lys-Glu -NH2 was accomplished using the multi-coil counter-current chromatograph. A partition coefficient was determined in the n-butanol-acetic acid-water (4:1:5) system. Chromatographic runs were made in this system and one modified with ethyl acetate. The peptide material showed anomalous elution behavior due to its surfactant properties. It was found that by loading the sample exclusively in the stationary phase, satisfactory retention of the compound occurred. Finally, conditions utilizing the upper phase as the mobile phase successfully separated the impurities.     

Ion-ion reactions for charge reduction of biopolymer at atmospheric pressure ambient

Extractive electrospray ionization source(EESI)was adapted for ion-ion reaction,which was demonstrated by using a linear quadrupole ion trap mass spectrometer for the first ion-ion reaction of biopolymers in the atmospheric pressure ambient.     

钴希夫碱配合物的合成及其氧合机制的研究——Ⅰ.配合物及其氧加合物的合成和表征

本文合成了一系列以水杨醛或萘酚醛同多胺缩合的四齿(N₂O₂)或五齿(N₃O₂)希夫碱为配体的钴希夫碱配合物及它们的氧加合物,用元素分析、红外光谱、磁化率以及ESR谱进行了表征,在续篇中将继续讨论配合物的吸氧行为和氧合机制。     

Engineering reactions in crystalline solids: predicting photochemical decarbonylation from calculated thermochemical parameters

A detailed thermochemical analysis of the alpha-cleavage and decarbonylation reactions of acetone and several ketodiesters was carried out with the B3LYP/6-31G* density functional method. The heats of formation of several ground-state ketones and radicals were calculated at 298 K to determine bond dissociation energies (BDE) and radical stabilization energies (RSE) as a function of substituents. Results show that the radical-stabilizing abilities of the ketone substituents play a very important role on the thermodynamics of the alpha-cleavage and decarbonylation steps. An excellent correlation between calculated values and previous experimental observations suggests that photochemical alpha-cleavage and decarbonylation in crystals should be predictable from knowledge of excitation energies and the RSE of the substituent.     

Reversible wettability of a chemical vapor deposition prepared ZnO film between superhydrophobicity and superhydrophilicity

A superhydrophobic ZnO thin film was fabricated by the Au-catalyzed chemical vapor deposition method. The surface of the film exhibits hierarchical structure with nanostructures on sub-microstructures. The water contact angle (CA) was 164.3 degrees, turning into a superhydrophilic one (CA < 5 degrees) after UV illumination, which can be recovered through being placed in the dark or being heated. The film was attached tightly to the substrate, showing good stability and durability. The surface structures were characterized by scanning electron microscopy and atomic force microscopy.     

Diffusioosmosis of electrolyte solutions along a charged plane wall

The steady diffusioosmotic flow of an electrolyte solution along a dielectric plane wall caused by an imposed tangential concentration gradient is analytically examined. The plane wall may have either a constant surface potential or a constant surface charge density of an arbitrary quantity. The electric double layer adjacent to the charged wall may have an arbitrary thickness, and its electrostatic potential distribution is determined by the Poisson-Boltzmann equation. The macroscopic electric field along the tangential direction induced by the imposed electrolyte concentration gradient is obtained as a function of the lateral position. A closed-form formula for the fluid velocity profile is derived as the solution of a modified Navier-Stokes equation. The direction of the diffusioosmotic flow relative to the concentration gradient is determined by the combination of the zeta potential of the wall and the properties of the electrolyte solution. For a given concentration gradient of an electrolyte along a plane wall, the magnitude of fluid velocity at a position in general increases with an increase in its electrokinetic distance from the wall, but there are exceptions. The effect of the lateral distribution of the induced tangential electric field in the double layer on the diffusioosmotic flow is found to be very significant and cannot be ignored.     

On the exactness of a theorem of G.A. Fomin

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Purines, pyrimidines, and related fused systems. 20. Heterocyclizations of 6-alkynyl-1,3-dimethyllumazines. Synthesis of pyrrole and thiophene analogs of some natural pteridines

Sonogashira cross-coupling of 6-chloro-1,3-dimethyllumazine with terminal alkynes gave 6-alkynyl derivatives in good yields. Oxidative amination of the latter with primary alkylamines was accompanied by the pyrrole-ring closure to form 1-R"-2-R-6,8-dimethylpyrrolo[3,2-g]pteridine-5,7(6H,8H)-diones. The addition of bromine to 6-alkynyllumazines afforded the corresponding dibromoalkenes whose treatment with sodium trithiocarbonate gave rise to 2-R-6,8-dimethylthieno[3,2-g]pteridine-5,7(6H,8H)-diones. The latter compounds are close analogs of the metabolite of molybdenum cofactor (molybdopterine).     

Creeping motion of an assemblage of composite spheres relative to a fluid

The sedimentation of a homogeneous distribution of spherical composite particles and the fluid flow through a bed of these particles are investigated theoretically. Each composite particle is composed of a spherical solid core and a surrounding porous shell. In the fluid-permeable porous shell, idealized hydrodynamic frictional segments are assumed to distribute uniformly. The effect of interactions among the particles is taken into explicit account by employing a fundamental cell-model representation which is known to provide good predictions for the motion of a swarm of nonporous spheres within a fluid. In the limit of a small Reynolds number, the Stokes and Brinkman equations are solved for the flow field in a unit cell, and the drag force exerted by the fluid on the particle is obtained in a closed form. For a distribution of composite spheres, the normalized mobility of the particles decreases or the particle interactions increase monotonically with a decrease in the permeability of their porous shells. The effect of particle interactions on the creeping motion of composite spheres relative to a fluid can be quite significant in some situations. In the limiting cases, the analytical solutions describing the drag force or mobility for a suspension of composite spheres reduce to those for suspensions of solid spheres and of porous spheres. The hydrodynamic behavior for composite spheres may be approximated by that for permeable spheres when the porous layer is sufficiently thick, depending on the permeability.