MEKC: an update focusing on practical aspects

This paper reviews recent methodological and instrumental advances in MEKC. Improvements in sensitivity arising from the use of on-line sample concentration (sweeping, stacking, and combination of both protocols) and derivatization (in-capillary reactions and coupling with flow-injection systems) and improvements in resolution obtained by changing the composition of the BGE (e.g., with organic modifiers, ionic liquids, nonionic and zwitterionic surfactants, mixed micelles, and vesicles) or using coated capillaries are discussed in detail. In addition, MS and LIF spectroscopy are examined in relation to their advantages and restrictions as applied to MEKC analysis. Some thoughts on potential future directions are also expressed.     

Photodynamics and time-resolved fluorescence of azobenzene in solution: a mixed quantum-classical simulation

We have simulated the photodynamics of azobenzene by means of the Surface Hopping method. We have considered both the trans → cis and the cis → trans processes, caused by excitation in the n → π* band (S(1) state). To bring out the solvent effects on the excited state dynamics, we have run simulations in four different environments: in vacuo, in n-hexane, in methanol, and in ethylene glycol. Our simulations reproduce very well the measured quantum yields and the time dependence of the intensity and anisotropy of the transient fluorescence. Both the photoisomerization and the S(1) → S(0) internal conversion require the torsion of the N═N double bond, but the N-C bond rotations and the NNC bending vibrations also play a role. In the trans → cis photoconversion the N═N torsional motion and the excited state decay are delayed by increasing the solvent viscosity, while the cis → trans processes are less affected. The analysis of the simulation results allows the experimental observations to be explained in detail, and in particular the counterintuitive increase of the trans → cis quantum yield with viscosity, as well as the relationship between the excited state dynamics and the solvent effects on the fluorescence lifetimes and depolarization.     

Advances in CE-mediated microanalysis: an update

This review, as a continuation of two earlier reports, gives an overview of the recent developments, over the period from 2005 until now, in the use of electrophoretically mediated microanalysis (EMMA) methodology for the on-line study of enzymatic reaction and derivatization. The article is divided into two parts: (i) on-line enzymatic reaction by EMMA and (ii) on-line derivatization by EMMA. Following a brief introduction, a literature overview on enzymatic reaction is provided. The second part starts with an introduction of the purpose of derivatization and the nomenclature used in the area of in-capillary derivatization based on EMMA. The development of more integrated analytical platform that combines in-capillary derivatization and sample preconcentration is discussed. Reported derivatization procedures are summarized.     

Confinement Effects of Cyclodextrin on the Photodynamics of Few Selected Systems

In this contribution, we discuss the effect of cyclodextrins (CDs) on the photorelaxation of three molecules showing proton and charge transfer reactions. Using steady-state and picosecond time-resolved emission spectroscopy, we show that the confinement due to the restriction of CDs and the H-bonding network of their OH-groups involving water molecules found at its gates play an important role for both spectral and time domains. Anisotropy experiments give different rotational times following the nature and stoichiometry of the formed complexes.     

Capillary electrophoresis of inorganic ions: an update

This review as a sequel of three earlier similar reports gives a summary of the progress and significant methodological developments, starting from 2002, in the use of capillary electrophoresis (CE) for inorganic ion analysis. As substantiated by the illustrative number of relevant references, improvements in sensitivity achieved both in and outside a CE system, advances in manipulating the separation selectivity, novel hardware configurations, and system performance innovations are continually being reported over the review period. Specifically viewed are the recent advancements in elemental (bio)speciation analysis, which remains one of the most fertile areas of CE research, as well as in three recently booming research topics: contactless conductivity detection, separations on microchips, and transient isotachophoretic preconcentration. A state-of-the-art picture of technique's potentialities within the field of interest presented here demonstrates that CE has become recognized and is growing in acceptance as a reliable alternative to traditional analytical methods such as high-performance liquid chromatography (HPLC).     

Human D-amino acid oxidase: an update and review

The flavoprotein D-amino acid oxidase (DAO) degrades the gliotransmitter D-Ser, a potent activator of N-methyl-D-aspartate-type glutamate receptors. A body of evidence suggests that DAO, together with its activator, G72 protein, may play a key role in the pathophysiology of schizophrenia. It has also been suggested that 3,4-dihydroxy-D-phenylalanine (D-DOPA), the stereoisomer of 3,4-dihydroxy-L-phenylalanine (L-DOPA), is oxidized by DAO and converted to dopamine via an alternative biosynthetic pathway. We determined the crystal structures of human DAO in complex with the reaction products of two clinically important substrates, D-Ser and D-DOPA. Kinetic data show that the maximum velocity is much greater for D-DOPA than that for D-Ser, which strongly supports the proposed alternative pathway for dopamine biosynthesis in the treatment of Parkinson's disease. In addition, biochemical characterization of human DAO indicates that it binds FAD more weakly than does porcine D-amino acid oxidase (pDAO) and exists as a stable homodimer, even in the apoprotein form. Determination of the structures of human DAO in various states reveals that, in contrast to pDAO, the hydrophobic-Val-Ala-Ala-Gly-Leu (VAAGL) stretch (residues 47-51, structurally ambivalent peptide) located at the si-face of the flavin ring assumes a uniquely stable conformation, which provides a structural basis for the unique kinetic features of human DAO.     

Photodynamics of polyene-polymethine transformations and spectral fluorescent properties of merocyanine dyes

Absorption and fluorescence spectrum band moments (center of gravity, width, asymmetry, excess, and fine structure) have been determined in a wide range of solvents with different polarities for inverse solvatochromic di-, tetra-, and hexamethinemerocyanines derived from 1,3-diphenyl-2,3-dihydro-1H-benzimidazole. Juxtaposition of the quantum-chemically calculated (by the semiempirical AM1 method) charges, bond orders, and dipole moments of the merocyanine molecules in the ground and excited singlet states with the experimentally observed spectral fluorescent characteristics suggests that the molecular electronic structure in the two states can vary from a nonpolar polyene via a polymethine to a charge-separated polyene, depending on the length of the polymethine chain and the medium polarity. As shown, solvatofluorochromism gives rise to smaller spectral band shifts than those of solvatochromism. This effect is attributable to weaker intermolecular solute-solvent interactions in the fluorescent excited state due to the more equalized charges as compared to those of the ground state. A lack of mirror symmetry of the absorption and fluorescence spectra has been revealed for di- and tetramethinemerocyanines (broadened fluorescence bands) as well as for hexamethinemerocyanines (narrowed fluorescence bands); the two cases are accounted for by the different behavior of vibronic and intermolecular interactions in the course of absorption and emission. As found for merocyanines, the electronic structure of their fluorescent state approaches the cyanine limit and the ground state becomes increasingly polyene-like with lengthening of the polymethine chain. A close vicinity of the excited state to the cyanine limit causes a dramatic increase in fluorescence quantum yields and a decrease in Stokes shifts observed for higher merocyanine vinylogues.     

BODIPY-bridged push-pull chromophores: optical and electrochemical properties

A series of BODIPY bridged push-pull chromophores were prepared by a sequence of reactions involving: i) cross-coupling reactions promoted by palladium complexes; ii) Knoevenagel condensation leading to dicyano derivatives; iii) [2+2] cycloaddition. The last reaction is regioselective, providing mono-derivatives with anisole substituents. With dimethylaminophenyl donor groups, double addition is feasible, providing highly colored dyes displaying remarkable electrochemical properties.     

Direct optical detection in bioanalysis: an update

In biomolecular interaction analysis, direct optical detection is attracting increasing interest in academia and industry. Therefore, a previous review has been updated. Optical principles are given in brief, focussing especially on modern and frequently used techniques. Commercialized methods are listed with some specific applications. In addition, some of the many applications found in the literature are listed; others which have been reviewed elsewhere are cited. Overall, the growing interest in direct optical monitoring of biomolecular interaction is demonstrated and future trends are outlined. Because optical methods is a very wide field, the paper concentrates on the currently most common methods, microrefractometry and microreflectivity.     

Highly fluorinated thermotropic liquid crystals: an update

Fluorine is used in liquid crystal materials in order to give them particular properties as compared to their hydrocarbon homologues. This leads to use of the new compounds as materials mainly in display devices such as Twisted Nematic Liquid Crystals Display (TNLCD) or for the development of Surface Stabilized Ferroelectric smectic C* display (SSFLCDs). In this paper, we describe recent studies and research effort concerning the liquid crystalline behavior of compounds incorporating a highly fluorinated part with more than one fluoromethylene units. We examine some of their mesophase properties and the impact of molecular shape on the resulting liquid crystal behavior.     

Sensitive chiral analysis by CE: an update

A general view of the different strategies used in the last years to enhance the detection sensitivity in chiral analysis by CE is provided in this article. With this purpose and in order to update the previous review by García-Ruiz et al., the articles appeared on this subject from January 2005 to March 2007 are considered. Three were the main strategies employed to increase the detection sensitivity in chiral analysis by CE: (i) the use of off-line sample treatment techniques, (ii) the employment of in-capillary preconcentration techniques based on electrophoretic principles, and (iii) the use of alternative detection systems to the widely employed on-column UV-Vis absorption detection. Combinations of two or three of the above-mentioned strategies gave rise to adequate concentration detection limits up to 10(-10) M enabling enantiomer analysis in a variety of real samples including complex biological matrices.     

Water-soluble, self-assembling container molecules: an update

Over the past five years, an important development in the area of self-assembling containers has been the increase in interest in those containers that function in aqueous solution. This progress is a reflection of a similar trend within supramolecular chemistry in general, and is driven in part by the need to address issues and challenges within the biological sciences, as well as a desire to develop new strategies for greener chemistries carried out in water. It is also an opportunity to learn more about fundamental topics such as the hydrophobic effect. In this critical review we discuss progress in aqueous-based self-assembling container molecules since 2005 (177 references).     

Derivatization trends in capillary electrophoresis: an update

This survey as a sequel of two earlier reports gives an overview of recent developments, starting from 1999, in the use of derivatization protocols in capillary electrophoretic (CE) analysis. Derivatization is mainly used for enhancement of the detection sensitivity in CE, for which a combination of fluorescence labeling and laser-induced fluorescence detection is favorable. Moreover, especially in the field of saccharide assay, derivatization to introduce charge into the molecule, is common. Derivatization procedures are classified in tables, focused on precapillary, on-line, on-capillary and postcapillary arrangements and divided in sections concerning the functional group that is derivatized. The most frequently reported groups are amines and the reducing end of (oligo)saccharides, but thiols, carbonyl and carboxyl groups, steroids and inorganic ions have also been reported about. Other reasons for derivatization are to enhance chiral separation, introduction of a suitable charge into the molecule or to improve mass spectrometric detection. The use of derivatization techniques for special cases, such as the analysis of neurotransmitters, insulin antibodies and mitochondria has also been incorporated as well as a study on the adsorption of proteins onto capillary walls during CE in which derivatization plays a role.