Rational design and molecular diversity for the construction of anti-alpha-bungarotoxin antidotes with high affinity and in vivo efficiency

The structure of peptide p6.7, a mimotope of the nicotinic receptor ligand site that binds alpha-bungarotoxin and neutralizes its toxicity, was compared to that of the acetylcholine binding protein. The central loop of p6.7, when complexed with alpha-bungarotoxin, fits the structure of the acetylcholine binding protein (AChBP) ligand site, whereas peptide terminal residues seem to be less involved in toxin binding. The minimal binding sequence of p6.7 was confirmed experimentally by synthesis of progressively deleted peptides. Affinity maturation was then achieved by random addition of residues flanking the minimal binding sequence and by selection of new alpha-bungarotoxin binding peptides on the basis of their dissociation kinetic rate. The tetra-branched forms of the resulting high-affinity peptides were effective as antidotes in vivo at a significantly lower dose than the tetra-branched lead peptide.     

Direct thermal extraction and gas chromatographic-mass spectrometric determination of volatile compounds of extra-virgin olive oils

The instrumental performances of a Thermo Desorption-Cooled Injection System coupled with a gas chromatography-mass spectrometer (GC-MS) were improved by a Plackett-Burman experimental design for the direct thermal extraction of volatile compounds from extra-virgin olive oils. The obtained experimental conditions were applied to the analysis of samples from West Liguria (cv. Taggiasca > or = 90%) and Spain (cv. Arbequina), which shared such similar sensorial features that Taste Panel did not distinguish them. Principal component analysis (PCA) was then applied to the experimental data. Three linear combinations of the amounts of the lipoxygenase oxidation products proved to be decisive and sufficient in the differentiation of the two groups of samples.     

Redox and complexation chemistry of the Cr(VI)/Cr(V)-D-galacturonic acid system

The oxidation of d-galacturonic acid by Cr(VI) yields the aldaric acid and Cr(III) as final products when a 30-times or higher excess of the uronic acid over Cr(VI) is used. The redox reaction involves the formation of intermediate Cr(IV) and Cr(V) species, with Cr(VI) and the two intermediate species reacting with galacturonic acid at comparable rates. The rate of disappearance of Cr(VI), Cr(IV) and Cr(V) depends on pH and [substrate], and the slow reaction step of the Cr(VI) to Cr(III) conversion depends on the reaction conditions. The EPR spectra show that five-coordinate oxo-Cr(V) bischelates are formed at pH < or = 5 with the uronic acid bound to Cr(V) through the carboxylate and the alpha-OH group of the furanose form or the ring oxygen of the pyranose form. Six-coordinated oxo-Cr(V) monochelates are observed as minor species in addition to the major five-coordinated oxo-Cr(V) bischelates only for galacturonic acid : Cr(VI) < or =10 : 1, in 0.25-0.50 M HClO(4). At pH 7.5 the EPR spectra show the formation of a Cr(V) complex where the vic-diol groups of Galur participate in the bonding to Cr(V). At pH 3-5 the Galur-Cr(V) species grow and decay over short periods in a similar way to that observed for [Cr(O)(alpha-hydroxy acid)(2)](-). The lack of chelation at any vic-diolate group of Galur when pH < or = 5 differentiates its ability to stabilise Cr(V) from that of neutral saccharides that form very stable oxo-Cr(V)(diolato)(2) species at pH > 1.     

Block copolymers of ethylene oxide and phenyl glycidyl ether: micellization, gelation, and drug solubilization

Three triblock copolymers of ethylene oxide and phenyl glycidyl ether, type E(m)G(n)E(m), where G = OCH2CH(CH2OC6H5) and E = OCH2CH2, were synthesized and characterized by gel-permeation chromatography, matrix-assisted laser desorption ionization time-of-flight mass spectrometry, and NMR spectroscopy. Their association properties in aqueous solution were investigated by surface tensiometry and light scattering, yielding values of the critical micelle concentration (cmc), the hydrodynamic radius, and the association number. Gel boundaries in concentrated micellar solution were investigated by tube inversion, and for one copolymer, the temperature and frequency dependence of the dynamic moduli served to confirm and extend the phase diagram and to highlight gel properties. Small-angle X-ray scattering was used to investigate gel structure. The overall aim of the work was to define a block copolymer micellar system with better solubilization capacity for poorly soluble aromatic drugs than had been achieved so far by use of block copoly(oxyalkylene)s. Judged by the solubilization of griseofulvin in aqueous solutions of the E(m)G(n)E(m) copolymers, this aim was achieved.     

A guideline to the design of molecular-based materials with long-lived photomagnetic lifetimes

Materials presenting a stable and reversible switch of physical properties in the solid state are of major interest either for fundamental interests or potential industrial applications. In this context, the design of metal complexes showing a light-induced crossover from one spin state to another, leading to a major change of magnetic and optical properties, is probably one of the most appealing challenges. The so-denoted spin-crossover materials undergo, in some cases, a reversible photoswitch between two magnetic states, but, unfortunately, lifetimes of the photomagnetic states for compounds known so far are long enough only at low temperatures; this prohibits any applications. We have measured and collected the temperatures above which the photomagnetic effect disappears for more than sixty spin-crossover compounds. On the basis of this large data base, a correlation between the nature of the coordination sphere of the metal and the photomagnetic lifetime can be drawn. Such correlation allows us to propose here a general guideline for the rational design of materials with long-lived photomagnetic lifetimes. This result clearly opens the way towards room-temperature photonic materials, based on the spin-crossover phenomenon, which will be of great interest for future communication devices.     

Isolation of C-H...C(pi) complexes from the reaction of stable carbenes with hydrocarbons

Several imidazolium-hydrocarbon salts have been isolated from the reaction of stable carbenes with hydrocarbons and some of the products have been structurally characterized showing ion pair formation in the solid state characterized by the presence of well defined and transferable C-H...C(pi) interactions.     

Application of tandem Ugi multi-component reaction/ring closing metathesis to the synthesis of a conformationally restricted cyclic pentapeptide

A conformationally restricted cyclic pentapeptide, containing an unsaturated 9-membered lactam as a semi-rigid scaffold, was prepared in a very convergent manner, through tandem Ugi reaction/ring closing metathesis.     

Fluorimetric Flow-Through Sensing of Quinine and Quinidine

We describe a single continuous-flow method for the determination of Quinine (QN) and Quinidine (QD) based on the enhancement of their native fluorescence by on-line transitory retention on a solid support placed in a flow cell. KCl solution was used as carrier/self-eluting solution. The active solid surface is regenerated by the carrier itself which also acts as eluting solution, thus making the microsensing zone reusable for subsequent measurements.In the range of 40 to 1260µL, the response of the sensor (_exc/_em=250/450nm) was directly proportional to the sample volume injected. The sensor was calibrated for three injection volumes: 40, 600 and 1000µL, responding linearly in the range of 40–800, 2–40 and 0.4–20µgL^–1 of QN and 20–600, 5–40 and 0.9–20µgL^–1 of QD with detection limits of 2.2, 0.2 and 0.1µgL^–1 (QN) and 3.9, 0.4 and 0.2µgL^–1 (QD), respectively. The relative standard deviation for ten independent determinations is 1.0% (QN) and 3.9% (QD). The sampling frequency ranges between 40 and 22h^–1 depending on the sample volume injected. This sensor was satisfactorily applied to the determination of QN in soft drink samples and a shampoo, and to the determination of QD in pharmaceutical preparations with equally satisfactory results.     

Capillary electrophoresis investigation of a partially unfolded conformation of beta(2)-microglobulin

Dialysis-related amyloidosis is a disease in which partial unfolding of beta(2)-microglobulin plays a key pathogenetic role in the formation of the amyloid fibrils. We have recently demonstrated that a partially unfolded conformer of beta(2)-microglobulin is involved in fibrillogenesis and that this species is significantly populated under physiological conditions. In this work capillary electrophoresis has been used to measure the equilibrium between the native protein and this conformer in samples known to have a higher or lower amyloidogenic potential, namely full-length beta(2)-microglobulin, two truncated species and a mutant, created by replacing histidine in position 31 with thyrosine. In addition, for all protein species folding stability experiments have been carried out by monitoring the secondary structure by circular dichroism at increasing concentrations of guanidinium chloride. The values of free energy of unfolding in the absence of denaturant, obtained by elaboration of these experiments, were found to be inversely correlated to the area percent of the partially unfolded conformer, as measured by capillary electrophoresis. Affinity capillary electrophoresis experiments have been also carried out under nondenaturing conditions to assess the affinity of copper and suramin to either the native form or the conformational intermediate of full-length beta(2)-microglobulin.     

PHYTOCHROME MODELS,PART 9. CONFORMATION SELECTIVITY OF THE PHOTOCYCLIZATION OF THE BILIVERDIN IX γ and IX δ DIMETHYL ESTERS*

Abstract— The photocyclization of the biliverdin IX γ and IX δ dimethyl esters to phorcabilin and neobiliverdin IX δ dimethyl ester, respectively, markedly depends on the irradiation wavelength within the first electronic absorption band. The quantum yields of reaction are highest on irradiation at575–600 nm. As judged from fluorescence excitation studies, absorption by the stretched conformations of the biliverdins is relatively important at these wavelengths. At longer wavelengths, where the reaction efficiency sharply declines, absorption by the coiled form predominates. Based on these findings and on supporting evidence from the solvent and temperature influence on the reaction, the photocyclization is proposed to occur selectively from a stretched conformation (an example of the principle of nonequilibration of excited rotamers), competing with E-Z isomerization of the centralC–10 double bond. A kinetic hydrogen isotope effect on the photochemical reaction rate of N,N,N-trideuteriated biliverdin IX δ dimethyl ester indicates that the primary photoproduct in the cyclization reaction is labile and reacts via two competing processes: reopening to the starting material and a solvent-mediated proton shift. The latter process leads to the phorcabilin and neobiliverdin IX δ esters. The results suggest, as a general rule, that the stretching of coiled biliverdins is confined to thermal and photochemical transformations within the B/C partial structure, while the Z-syn geometry of the A/B and C/D moieties is retained.