Book Review The End of Certainty: Time,Chaos, and the New Laws of Nature. Ilya Prigogine. New York: Free Press, 1997. Pp. viii + 228

Nonlinear Dynamics, Psychology, and Life Sciences -     

Enantiopure β3-neopentylglycine: synthesis and resolution

A procedure has been developed for the large scale synthesis of enantiopure β³-neopentylglycine and its Cbz-protected derivative. The synthetic route developed in our laboratory features Cbz-protection of the racemic β-amino acid followed by resolution with l-norephedrine and provides the enantiomerically pure Cbz-β-neopentylglycine in good yield and excellent enantiopurity. No toxic or dangerous chemicals are used, allowing the scale-up of this procedure without major safety concerns.     

Collaborative study of an liquid chromatographic method for the determination of R-timolol and other related substances in S-timolol maleate

A collaborative study applying an enantiomeric liquid chromatographic (LC) method was carried out to determine the content of the enantiomeric impurity R-timolol and other related substances in three different S-timolol maleate samples. Eight laboratories, all located in Europe, participated in the study. The quantitative results obtained were used to estimate the uncertainty on the content of the different impurities. For that purpose, a set-up was adapted from the ISO guidelines 5725-2, which allowed the estimation of the different variances, i.e. the between-laboratories (), the between-days () and the between-replicates (). The variances of repeatability () and reproducibility () were then calculated using the equations and . For the timolol impurities, it was found that the estimated uncertainty seem to be concentration-dependent. Since the LC method which combines the compendial ones for enantiomeric purity and related substances testing was applied to evaluate uncertainty in this collaborative study, it was shown how a laboratory can evaluate the uncertainty of its results when applying the method in the future.     

Definition and system implementation of strategies for method development of chiral separations in normal- or reversed-phase liquid chromatography using polysaccharide-based stationary phases

This paper proposes strategies in normal- and reversed-phase liquid chromatography (NP-HPLC or NPLC and RP-HPLC or RPLC), which were developed using three polysaccharide-based stationary phases. Those strategies are implemented in a knowledge-based system for the chiral separation of drug enantiomers. Each strategy includes a screening and an optimisation stage. The screening stage allows a fast evaluation of separation possibilities and enantioselectivity for many drugs in a short period of time, while the optimisation stage gives the opportunity to enhance, if needed, the initially obtained separation. Different examples demonstrate the effectiveness of the strategies for fast method development.     

Screening approach for chiral separation of pharmaceuticals part II. Reversed-phase liquid chromatography

A screening strategy for the rapid separation of drug enantiomers by reversed-phase liquid chromatography was developed using three cellulose/amylose stationary phases. The key point to achieve enantioselectivity is the control of the compound ionisation. Only two mobile phases, i.e. an acidic phosphate buffer (pH 2.0) containing a chaotropic salt (KPF6) and a borate buffer (pH 9.0) mixed with acetonitrile, are used in the proposed strategy. This strategy was successfully applied to a set of 37 diverse chiral pharmaceuticals. Satisfactory enantioselectivity was achieved for 89% of them.     

Monitoring the hygrothermal response of poly(vinyl methyl ether) submicron films using AFM

Films with submicron thickness of the thermoresponsive polymer poly(vinyl methyl ether) (PVME) are prepared by spin-coating and measured with AFM. The change of film thickness, work of adhesion (WOA), and modulus of elasticity (MOE) are monitored below and above the lower critical solution temperature (LCST) in controlled atmosphere. The film thickness decreases above the LCST at high relative humidity, but not at low humidity. Simultaneously, the MOE increases by 3 orders of magnitude due to conformational transition. The WOA shows a hysteretic behavior due to changes in surface wettability and film compressive strength. Hygrothermal cycling is found to facilitate the relaxation of initially arrested entanglements. The proposed hypothesis of hygrothermally induced partial disentanglement is further supported with cyclic DSC measurements of concentrated aqueous PVME solutions. This work is an important contribution to understand the local and macroscopic behavior of thermoresponsive polymers in dry and humidified atmosphere.     

Tools for Malliavin Calculus in UMD Banach Spaces

In this paper we study the Malliavin derivatives and Skorohod integrals for processes taking values in an infinite dimensional space. Such results are motivated by their applications to SPDEs and in particular financial mathematics. Vector-valued Malliavin theory in Banach space E is naturally restricted to spaces E which have the so-called umd property, which arises in harmonic analysis and stochastic integration theory. We provide several new results and tools for the Malliavin derivatives and Skorohod integrals in an infinite dimensional setting. In particular, we prove weak characterizations, a chain rule for Lipschitz functions, a sufficient condition for pathwise continuity and an Itô formula for non-adapted processes.     

Liquid Chromatographic Determination of Cationic Surfactants in Environmental Samples using a Continuous Post-Column Ion-Pair Extraction Detector with a Sandwich Phase Separator

Abstract

A new detection technique is described for the quantitative analysis of cationic surfactants by HPLC via post-column ion-pair formation. A new sandwich type phase separator, as part of the extraction detector, was successfully introduced. The method was used to determine ditallowdimethylammonium chloride (DTDMAC) in various environmental samples. Detection limits of DTDMAC in river water were about 2 μg/1 (60 ng absolute; S/N = 5) and 10 ng/1 (260 pg absolute; S/N = 5), using methyl orange and 9,10-dimethoxyanthracene-2-sulphonate (DAS) as ion-pairing reagents, respectively. The environmental concentration of DTDMAC found on random samples from two Belgian rivers range from 30 to 40 μg/1. The reproducibility of the determination of DTDMAC in river water was 4.2% (RSD) (n = 20).