Nonlinear analysis of dynamic binding in affinity capillary electrophoresis demonstrated for inclusion complexes of beta-cyclodextrin

The stability of the molecular host-guest inclusion complexes of beta-cyclodextrin with benzoate and four different hydroxybenzoates is investigated. For the measurement of the binding constants an experimental method is devised that is based on affinity capillary electrophoresis (ACE) with indirect UV absorbance detection. We derive an explicit equation for effective mobilities in ACE experiments without violation of rigorous mass balance. This equation is employed in the nonlinear least-squares analyses of the experimental data yielding binding constants of 48+/-2 M(-1) for benzoate, 299+/-38 M(-1) for 2-hydroxybenzoate, 37+/-1 M(-1) for 3-hydroxybenzoate, 228+/-9 M(-1) for 4-hydroxybenzoate, and 895+/-110 M(-1) in the case of 2,4-dihydroxybenzoate.     

Perfluoroalkylene-linked aromatic polyimides. I. Synthesis,structure, and some general physical characteristics

This paper describes the preparation of a series of novel perfluoroalkylene- and ether-linked aromatic polyimides. Depending on the nature of the precursor diamine, the polyimides were prepared by either melt or solution techniques, the latter via the corresponding poly(amic acids). The polymers were characterized by a variety of methods, and their structure is discussed.     

Simultaneous analysis of prostanoids using liquid chromatography/high-field asymmetric waveform ion mobility spectrometry/tandem mass spectrometry

A liquid chromatography/high-field asymmetric waveform ion mobility spectrometry/tandem mass spectrometry (LC-FAIMS-MS/MS) semi-quantitative method was developed for the simultaneous determination of prostaglandin (PG) E2, PGD2, PGF(2alpha), 6-keto-PGF(1alpha), and thromboxane (TX) B2. Diluted samples containing these prostanoids and their tetra-deuterium-substituted internal standards were analyzed by LC followed by either selected reaction monitoring (LC-SRM) or FAIMS and selected reaction monitoring (LC-FRM). FAIMS reduced background noise, separated the isobaric ions PGE2 and PGD2, and separated dynamically interchanging TXB2 anomers. This is the first report of the separation of interconverting anomers by FAIMS. Generally, the LC-FRM chromatograms were more selective than the LC-SRM chromatograms. Its potential was demonstrated by analysis of prostanoids in guinea pig lumbar spinal cord homogenate.     

Chemical potentials and phase equilibria of Lennard-Jones chain fluids

Computer simulations (molecular dynamics) were performed for ensembles of flexible tangent Lennard-Jones chains consisting of n sites (n = 1, 2, 4, 8, and 16). From these simulations, the orthobaric liquid and vapour densities were calculated not only with the traditional method of simulating a liquid film in coexistence with vapour, but also using the rigorous thermodynamic condition of satisfying the chemical potential equality between the phases in equilibrium. The agreement with literature data, as far as such exist, is excellent.     

Viscosity and normal stress forces of Lennard-Jones chains using reverse non-equilibrium molecular dynamics

Reverse non-equilibrium molecular dynamics was applied for the calculation of the viscosity for different chain lengths. Each chain consisted of m tangent spherical sites, where m was 1, 2, 4, 8 or 16, respectively. From these results, shear thinning was observed at high shear rates. The normal stress forces were also estimated via the calculation of the total stress tensor, and they were related to the shear thinning effect depending on the length of the chain. Furthermore, a power law equation was used to fit the rheological curves of each chain, making possible the calculation of the viscoelasticity as a function of the sites involved in the chains.     

Raman spectroscopic study of bacterial endospores

Endospores and endospore-forming bacteria were studied by Raman spectroscopy. Raman spectra were recorded from Bacillus licheniformis LMG 7634 at different steps during growth and spore formation, and from spore suspensions obtained from diverse Bacillus and Paenibacillus strains cultured in different conditions (growth media, temperature, peroxide treatment). Raman bands of calcium dipicolinate and amino acids such as phenylalanine and tyrosine are more intense in the spectra of sporulating bacteria compared with those of bacteria from earlier phases of growth. Raman spectroscopy can thus be used to detect sporulation of cells by a characteristic band at 1,018 cm^–1 from calcium dipicolinate. The increase in amino acids could possibly be explained by the formation of small acid-soluble proteins that saturate the endospore DNA. Large variations in Raman spectra of endospore suspensions of different strains or different culturing conditions were observed. Next to calcium dipicolinate, tyrosine and phenylalanine, band differences at 527 and 638 cm^–1 were observed in the spectra of some of the B. sporothermodurans spore suspensions. These bands were assigned to the incorporation of cysteine residues in spore coat proteins. In conclusion, Raman spectroscopy is a fast technique to provide useful information about several spore components. Figure A difference spectrum between Raman spectra of B. licheniformis LMG 7634 cultured for 6 days and 1 day, together with the reference Raman spectrum of calcium dipicolinate