13C‐NMR detection of STD spectra

We have investigated the use of ¹³C for the detection of saturation transfer difference (STD) NMR spectra. By detecting the STD spectrum in the ¹³C channel it is possible to eliminate the residual water signal in the STD‐NMR spectrum. We have employed an INEPT transfer in order to shift the magnetization from the proton channel to ¹³C. As a sample system to check our method we have used human serum albumin and phenylalanine. We have shown that such a transfer can be accomplished and gives reasonable signal intensities. Copyright © 2009 John Wiley & Sons, Ltd.     

Two-dimensional liquid chromatography of diblock copolymers: Simulation at various adsorption interaction conditions

Diblock copolymers, which are heterogeneous in both molar mass and composition, can be fully characterized by using two-dimensional chromatography. Since the size-exclusion, the adsorption, and the critical interaction based modes of chromatography are possible for each of the polymers A and B, this leads to a variety of options for 2D-chromatography of copolymers AB. Using the theory of chromatography of block copolymers, 2D-chromatograms are simulated that correspond to the most interesting of these options. Orthogonal 2D-chromatograms are expected, if in the 1st dimension the critical condition is created for A, while in the 2nd dimension – for B. The situations, where A and B are both adsorbable, as well as those where the conditions of adsorption for A and SEC for B are created, are also considered. In particular, it is shown that the 2nd dimension combination of the critical condition for A and SEC – for B is preferable than that with SEC condition for both A and B. The simulated 2D-chromatograms of low- and high molar mass diblock copolymers, as well as of copolymers with one short block are compared with the reported real ones; it is concluded that the corresponding virtual and real 2D-chromatograms are qualitatively very similar.     

Possible mechanisms of formation of long-periodic magnetic structure in high-symmetry crystals

On the example of a crystal with point symmetry group and based on the method of integral rational basis of invariants, linear and nonlinear invariants of first spatial derivatives with respect to the order parameters of the exchange origin have been calculated. It is shown the competition of what kind of parameters can initiate modulated magnetic structures in crystals of this symmetry.     

PbII 4,4,4-trifluoro-1-naphthyl-1,3-butanedione complexes of 1,10-phenanthroline and 2,2′-bipyridine ligands

Lead(II) 4,4,4-trifluoro-1-naphthyl-1,3-butanedione (Htfnb) complexes of 1,10-phenanthroline (phen) and 2,2′-bipyridine (bpy), [Pb₂(bpy)₂(tfnb)₂] (1) and [Pb₂(phen)₂(tfnb)₂] (2), have been synthesized and characterized by elemental analysis, IR, spectroscopy and X-ray crystallography. The self-assembly of 1 and 2 is likely to be caused by C–H ··· F–C, C–H ··· O and π–π stacking interactions.     

Retention of β blockers on native titania stationary phase

In recent years, metal oxides such as titania have been commercially available as chromatographic beds that can potentially be used to achieve novel separations of polar compounds. For example β blockers, which are more often encountered in environmental sciences, have a wide range of polarity, and their basic character leads to difficult sample treatment and separation on conventional silica‐based sorbents. The contribution of titania to the selective analysis of nine β blockers was evaluated in terms of retention mechanisms observed in hydrophilic interaction LC using acetonitrile/water mobile phases with various additives. The mobile phase additives enabled to control the β blocker charge as well as the titania surface charge. Depending on their respective ionic state, various retention mechanisms were identified at low water contents (<40%), including mainly adsorption mixed with hydrophilic interaction LC partition, ion exchange and ion exclusion. An unexpected retention was also observed for high water content and high pH, changing the selectivity of the support.     

Tripod molecules build molecular networks and open-dimer capsules by weak interactions

Three tripod molecules, tris(2-methoxy-5-nitrobenzyl)phosphine oxide (1), tris(2-butoxy-3-methyl-5-nitrobenzyl)phosphine oxide (2), and tris(3-nitrobenzyl)amine (TNBA), were synthesized and crystallized. The structures of 1, 2, and their comparison (TNBA) were determined by X-ray crystallography. It is noteworthy that compound 1 interacted with adjacent molecules via π-π stacking and C-H···π interactions to yield an open supramolecular network with the porosity P in 8.9%, whereas compound 2 gathered closely...     

Vector meson rescattering effect in understanding the threshold enhancement observed in J/ψ→γp(p)

We propose one possible mechanism,i.e.,the vector meson(VV)rescattering effects,to interpret the near threshold narrow enhancement observed in J/ψ→γp(p).The estimate indicates that these effects can give sizeable contributions to this channel,and a destructive interference between different rescattering amplitudes is required to reproduce the line shape of the data.     

Simulation of two‐phase flow with moving immersed boundaries

A two‐dimensional multi‐phase model for immiscible binary fluid flow including moving immersed objects is presented. The fluid motion is described by the incompressible Navier–Stokes equation coupled with a phase‐field model based on van der Waals' free energy density and the Cahn–Hilliard equation. A new phase‐field boundary condition was implemented with minimization of the free energy in a direct way, to specifically improve the physical behavior of the contact line dynamics for moving immersed objects. Numerical stability and execution time were significantly improved by the use of the new boundary condition. Convergence toward the analytical solution was demonstrated for equilibrium contact angle, the Lucas–Washburn theory and Stefan's problem. The proposed model may be used for multi‐phase flow problems with moving boundaries of complex geometry, such as the penetration of fluid into a deformable, porous medium. Copyright © 2010 John Wiley & Sons, Ltd.     

Development and validation of a hydrophilic interaction chromatography–tandem mass spectrometry for quantification of nicotine and its metabolites in human maternal and cord sera

A selective and sensitive HILIC‐MS/MS method for the simultaneous quantification of nicotine and its metabolites in human maternal and cord sera was developed and validated. After solid‐phase extraction, LC separation was achieved on a hydrophilic interaction chromatography. The validated method is capable of selective identification as well as accurate and sensitive quantification. Analyte recovery ranged from 86.2 to 107.7% and intra‐ and inter‐day assay precision were less than 15% relative standard deviation. This sensitive HILIC‐MS/MS method can be used to determine nicotine and its metabolic profile in smokers. This validated method is useful for the determination of nicotine and its metabolites in human serum in future studies of the effects of nicotine exposure on neonatal outcome. Copyright © 2010 John Wiley & Sons, Ltd.