Identification of block copolymers and determination of their purity by thin-layer chromatography

The application of adsorption, precipitation and extraction thin-layer chromatography to the identification of block copolymers, determination of their homogeneity (mixtures of homopolymers), and evaluation of their compositional homogeneity by one- and two-dimensional, multistage and gradient methods, is described. To detect the polymers on the thin-layer plate, various methods of detection are used, including those specific for each component of the block copolymer. Examples of analysis of the following block copolymers by thin-layer chromatography are reported: PS-PMMA, PS-PB, PS-PAN, PS-PBG, PI-PMS-PI, PMMA-PBMA, PMMA-PBG, PS-PEO.     

Determination of molecular-weight distribution and average molecular weights of block copolymers by gel-permeation chromatography

The problem of preparation of a block copolymer of precise molecular-weight distribution (MWD) and with heterogeneous composition on the basis of gel-permeation chromatography (GPC) data has been investigated. It has been shown that in MWD calculations the distribution f(p) of the composition p in individual GPC fractions should be taken into account. The type of the f(p) functions can be simultaneously established by an independent method, such as use of adsorption-column or thin-layer chromatography sensitive to the composition of the copolymer. It has also been shown that the actual f(p) may be replaced by a corresponding piecewise distribution, of simple form, without decrease in the precision of calculation of the MWD and average molecular weights of most known block copolymers.     

Displacement affinity chromatography of protein phosphatase one (PP1) complexes

Background  

Protein phosphatase one (PP1) is a ubiquitously expressed, highly conserved protein phosphatase that dephosphorylates target protein serine and threonine residues. PP1 is localized to its site of action by interacting with targeting or regulatory proteins, a majority of which contains a primary docking site referred to as the RVXF/W motif.     

Phase transition and anisotropy of thermal expansion in TlInS2

Linear expansion coefficients parallel and perpendicular to the layer plane of TlInS₂ layer crystal were measured in the temperature range 20–250 K at T { 200 K a strong anomaly in α⊥ behaviour was observed—the value of α6 increased abruptly up to the 200 × 10^?6 K^?1 due to phase transition in this crystal. It was shown that there is no anomaly in the behaviour of linear expansion coefficient α_z.dfnc;. This fact allowed to conclude that the phase transition in TlInS₂ is caused by changes in interlayer distances.     

Use of combined chromatographic methods including thin-layer chromatography for analysis of complex polymer systems. Determination of the polydispersity of block copolymers of styrene and methyl methacrylate by gel permeation, thin-layer and pyrolysis gas chromatography.

A combination of gel permeation chromatography (GPC), thin-layer chromatography (TLC) and pyrolysis gas chromatography (PGC) has been used for investigations of a polymethyl methacrylate-polystyrene-polymethyl methacrylate block copolymer. Continuous distribution of the polymer (40-mg sample) was attained according to the content of the styrene and methyl methacrylate units and of the block copolymer and according to the composition of the copolymer as functions of the hydrodynamic radius of the macromolecules. The polymer was subjected to a preliminary fractionation with an analytical gel chromatograph. The fractions were investigated by TLC, which permitted the separation of the block copolymer and the homopolymers. The composition of the fractions obtained by GPC and TLC was determined by PGC. As a result, it was possible to establish the composition of the block copolymer and its ratio to polymethyl methacrylate in each fraction. This investigation was based on a combination of highly effective fractionation by chromatographic methods with precise quantitative ratios obtained from Benoit's universal calibration graph and from determinations of the composition of the polymer fractions by PGC. The mechanism of the TLC of polymers, including the appearance of artefacts that distort the results of analysis, is also discussed.     

High-performance liquid chromatography of proteins on short capillary columns

A microchromatographic procedure for highly sensitive analysis of proteins has been developed by using short capillary columns with reverse-phase, ion-exchange, and hydrophobic interaction sorbents. The high analytical mass sensitivity on the level of several nanograms was attained by the miniaturization of the column and the optimization of gradient steepness.     

Chemo- and regioselective cyclohydrocarbonylation of alpha-keto alkynes catalyzed by a zwitterionic rhodium complex and triphenyl phosphite

alpha-Keto alkynes react with CO and H(2) in the presence of catalytic quantities of the zwitterionic rhodium complex (eta(6)-C(6)H(5)BPh(3))(-)Rh(+)(1,5-COD) and triphenyl phosphite affording either the 2-, 2(3H)-, or 2(5H)-furanones in 61-93% yields. The cyclohydrocarbonylation is readily accomplished using substrates containing alkyl, aryl, vinyl, and alkoxy groups at the acetylenic terminal, as well as a variety of primary, secondary, and tertiary alkyl, aryl, and heteroaryl groups connected to the ketone functionality. Structural and electronic properties present in the starting materials mediate the chemo- and regioselectivity of the reaction.     

Review. Use of laser detectors in capillary liquid chromatography

The main relationship of high-performance liquid chromatography (HPLC) are considered. It is shown that the optimum conditions of ultrasensitive trace analysis should be achieved by using packed capillary columns manufactured from flexible quartz capillaries with dc approximately less than 0.2 mm. The main features of these columns (v opt = 0.6 v opt of that for conventional HPLC columns with double the hydraulic permeability) make it possible to obtain two or three times higher plate numbers for the same analysis time and column pressure characteristic of conventional HPLC, as a result of using a submicrometre sorbent. The main features of laser detection in capillary liquid chromatography (laser-induced fluorescence and cross-beam thermal lens absorption detectors) are considered. The requirements that should be met by a modern capillary liquid chromatograph based on using flexible quartz capillary columns with a submicrometre sorbent and laser detectors are formulated. Examples of using these systems for femtomole and attomole analyses of biological samples (amino acids and prostaglandins) are given.     

The nature of temperature dependence of energy gaps in layer semiconductors

The temperature dependences of direct and indirect energy gaps in layer semiconductors GaS, GaSe and GaS_xSe_1?x are investigated in the temperature range 5–150 K. The nonmonotonous behaviour of E_g(T) dependences is observed in these crystals. It is shown that the effect of thermal expansion cannot in itself explain the observed anomalies. A new model of electron-phonon interaction explaining the E_g(T) behaviour in layer crystals is proposed.