Accurate steady-state and zero-time fluorescence spectra of large molecules in solution by a first-principle computational method

We report the first-principle calculation and analysis of the vibrationally resolved steady-state absorption and fluorescence spectra, and of the zero-time fluorescence spectrum of a sizable molecule, coumarin C153, in two different solvents. Our approach, bringing together the most recent developments in the fields of time-dependent density functional theory and of polarizable continuum solvent models, with an efficient method for the computation of vibrational contributions to transition intensities, allows a remarkable agreement with experiments, both concerning the line shapes and the solvatochromic and Stokes shifts. The method is also able to nicely describe the solvent relaxation effect on the fluorescence spectra, perfectly reproducing the energy shift between zero-time and steady-state fluorescence.     

Genetic microheterogeneity of human transthyretin detected by IEF

Mutations of the human transthyretin (TTR) gene have attracted medical interest as a cause of amyloidosis. Recently, we have described in detail an electrophoretic procedure with PAGE followed by IEF in urea gradients for the study of the microheterogeneity of TTR monomers (Altland, K., Winter, P., Sauerborn, M. K., Electrophoresis 1999, 20, 1349-1364). In this paper, we present a study on 49 different mutations of TTR including 33 that result in electrically neutral amino acid substitutions. The aims of the investigation were to test the sensitivity of the procedure to detect TTR variants in patients with TTR amyloidosis and their relatives and to identify some common characteristics that could explain the amyloidogenicity of these variants. We found that all tested amyloidogenic mutations could be detected by our method with the exception of those for which the corresponding variant was absent in plasma samples. Most of the electrically neutral amyloidogenic TTR variants had in common a reduced conformational stability of monomers by the activity of protons and urea. For three variants, e.g. TTR-F64L, TTR-I107V and TTR-V122I, the monomers had a conformational stability close to that of normal monomers but we found experimental and structural arguments for a weakening of the monomer-monomer contact. All types of amyloidogenic mutations affected the stability of TTR tetramers.     

HPLC with diode-array detection for the simultaneous determination of di(2-ethylhexyl)phthalate and mono(2-ethylhexyl)phthalate in seminal plasma

A high-performance liquid chromatographic method for the simultaneous determination of di(2-ethylhexyl)phthalate (DEHP) and its major metabolite mono(2-ethylhexyl)phthalate (MEHP) in seminal plasma was developed and validated. The method involves liquid-liquid extraction followed by isocratic reversed-phase chromatography with diode-array detection. The recovery, selectivity, linearity, precision and accuracy of the method were evaluated from the analysis of spiked seminal plasma samples. The effect of mobile-phase composition and pH on the retention of the target analytes was investigated. The limits of detection were 0.010 and 0.015 microg/mL, for DEHP and MEHP, respectively. This method was used to analyze real samples in support of clinical studies on these potential endocrine disruptors.     

Special matchings and Coxeter groups

In the recent paper [Adv. Applied Math., 38 (2007), 210–226] it is proved that the special matchings of permutations generate a Coxeter group. In this paper we generalize this result to a class of Coxeter groups which includes many Weyl and affine Weyl groups. Our proofs are simpler, and shorter, than those in [loc. cit.] All authors are partially supported by EU grant HPRN-CT-2001-00272. Received: 30 October 2006     

Quadratic description of conical intersections: characterization of critical points on the extended seam

In this paper, we present a practical approach for the characterization of critical points on conical intersection seams as either local minima or saddle points using second-derivative technology. The utility of this methodology is illustrated by the analysis of seven S0/S1 (2Ag/1Ag) conical intersection points involved in the photochemistry of butadiene. The characterization of critical points on the crossing seam requires second derivatives computed in curvilinear coordinates. Using such coordinates, we can represent the branching space and the intersection space to second order. Although these curvilinear coordinates are conceptually important, they also give rise to two additional practical applications. First, such coordinates yield information on the nature of vibrational modes that are stimulated following radiationless decay at a crossing point. Second, the second-order force field is directly comparable to experimental spectroscopic data for Jahn-Teller systems. We will illustrate the latter idea for the cyclopentadienyl radical.     

Silica nanoparticles for fluorescence sensing of Zn(II): exploring the covalent strategy

Silica nanoparticles (about 15 nm diameters), which contain a derivative of 6-methoxy-8-(p-toluensulfonamido)-quinoline (TSQ) as a Zn(II) fluorescent probe covalently linked to the silica network, were prepared and studied as Zn(II) fluorescent chemosensors. The systems selectively detect Zn(II) ions in water rich solutions with a submicromolar sensitivity: 0.13 microM concentrations of Zn(II) can be measured with the only interference of Cu(II) and Cd(II) ions. Compared with free TSQ, the nanoparticles based systems have the advantage that they can be employed in aqueous solutions without aggregation problems while at the same time, they maintain a similar Zn(II) affinity and sensing ability. Addition of a second, substrate insensitive, fluorophore to the particles leads to the realization of a ratiometric sensor.     

Intramolecular interchain reactions in bidesmosidic glycosides, a new insight into carbohydrate rearrangements induced by electrospray ionisation

Glycoconjugates are a class of complex molecules that are widely distributed in the plant kingdom and in some marine organisms. This class of compounds has a wide range of biological activities such as anti-inflammatory, antimicrobial, antifungal, anticancer, antiulcer, and immunoenhancing actions.1-3 Some of them also show various toxic activities such as cytotoxic, hemolytic, cardiotoxic, and teratogenic. Among these compounds, steroidal and triterpenoid saponins have long been known as components of widely used herbal drugs and pharmaceutical preparations; ginseng, Tribulus terrestris, Quillaja saponaria, and Digitalis ssp. are just a few examples. Thus, identification of saponins in herbal drugs used worldwide is of significance in phytochemical and toxicological quality control studies, and for the production of safe health products. Therefore, there is continuing demand for methods to rapidly identify and characterize these natural products.