Fluorescence Study of the Conformational Properties of Recombinant Tick Anticoagulant Peptide (Ornithodorus moubata) Using Multifrequency Phase Fluorometry

Abstract— Steady-state and multifrequency phase fluorometry were used to characterize the conformational state and conformational dynamics of recombinant tick anticoagulant peptide ( Ornithodorus moubata ) (TAP). The TAP contains two tryptophan residues at positions 11 and 37. The fluorescence emission varies sigmoidally as a function of pH with a pK_a of 6.01 ± 0.07. This pH dependency suggests that tryptophan fluorescence is quenched by His43 at low pH. This is confirmed by modification of the his-tidine with diethylpyrocarbonate. At pH 9 the fluorescence decay is well described by a sum of three exponentials (0.52,1.9 and 5.4 ns), which decrease all three at pH 4 (0.25, 1.61 and 4.4 ns). From the reactivity of the fluorescence lifetimes toward N -bromosuccinimide and from the calculation of the accessibility we can attribute the long lifetime to Trpll, the short one to Trp37 and the middle one to both. The anisotropy decay was resolved into two components of 3.85 ns and 0.27 ns at pH 4 and 4.5 ns and 0.6 ns at pH 9. The long anisotropy decay time corresponds to the rotational correlation time of the protein, the short one to local mobility of the tryptophan residues.     

A cyclobutadiene—palladium complex with a non-planar cyclobutadiene ring obtained from the palladium catalyzed dimerization of an ynamine

A cyclobutadiene—palladium complex, obtained by dimerization of an ynamine is described. The crystal structure of this compound shows, as salient feature, that the cyclobutadiene ring is not planar, but highly puckered. Anti-bonding interactions have been suggested as an explanation for this puckering.     

L'ernploi du tétrafluoroborate de triéthyloxonium et ses limites,dans l'éthylation d'oxo-2 indolinc earboxanilides et thioearboxanilides

The reaction of triethyloxonium tetrafluoroborate (Meerwein's reagent) with 2-oxo indoline 3-carboxanilides ( 4 ) gives mainly the 2-ethoxyindole derivatives, together with other C- and O-ethyl compounds. In the same time, difluoro indolyloxyboranes are formed by the reaction of the anilides 4 with boron trifluoride resulting from the decomposition, in situ, of the Meerwein's reagent. These results clearly indicate some limitation for synthetic applications of this reagent.     

Synthesis of iminoaziridines from carbodiimides and diazoesters : A new example of transition metal salt catalysed reactions of carbenes

Alkyl diazoacetates react with N,N′-diisopropylcarbodiimide in the presence of transition metal salts (e.g. copper triflate or rhodium (II) acetate) to give 1-isopropyl-2-alkoxycarbonyl-3- isopropyliminio-aziridine in good yield. The reaction takes place at room temperature without formation of the formal dimer of the carbene (maleate and fumarate).     

Synthesis and cytotoxic and antitumor activity of 1,2-dihydroxy-1,2-dihydrobenzo[b]acronycine diacid hemiesters and carbamates

A series of cis-1,2-dihydroxy-1,2-dihydrobenzo[b]acronycine diacid hemiesters and dicarbamates were prepared by acylation of cis-1,2-dihydroxy-6-methoxy-3,3,14-trimethyl-1,2,3,14-tetrahydro-7H-benzo[b]pyrano[3,2-h]acridin-7-one. The cytotoxicity of the dicarbamates depended on the steric hindrance of the esterifying groups at positions 1 and 2. Diacid hemiesters displayed significant in vitro cytotoxic activities and induced cell cycle perturbations similar to those obtained with cis-1,2-diacetoxy-1,2-dihydrobenzo[b]acronycine (S23906-1) currently under preclinical development. cis-1-Acetoxy-2-hemiglutaryloxy-1,2-dihydrobenzo[b]acronycine was the most promizing compound of the series, inducing complete inhibition of tumor growth when tested against C38 colon adenocarcinoma implanted in mice.     

Synthèses en une seule etape de nouvelles molécules heptacycliques à partir de sels de 2-aryl-4-méthyl-1-benzopyrylium. Structures radiocristallographiques de composés renfermant le squelette d'une 1-benzoxépine methano-pontée et condensée à deux entités de 1-benzopyrane

One-Step Synthesis of Novel Heptacyclic Molecules Starting from 2-Aryl-4-methyl-1-benzopyrylium Salts. X-Ray Crystal Structures of These Compounds Containing a Methano-Bridged 1-Benzoxepine Fused to Two 1-Benzopyran Moieties The chemical reduction of 4-methyl-2-(ortho-hydroxyaryl)-1-benzopyrylium chlorides with Zn in MeCN and HCl led to a mixture of diastereoisomeric heptacyclic molecules. The structures of two of them were determined by X-ray analysis. These methano-bridged 1-benzoxepines fused to two 1-benzopyran moieties were formed from intermediate biflavene species.     

The First Synthesis of Organic Diselenolates: Application to the Synthesis of Diorganyl Diselenides

The addition of elemental selenium to organolithium compounds 1 or organic selenates 2 gives organic diselenolates 3 . The reactions proceed by the insertion of two selenium atoms into the carbon–metal bonds or of one selenium atom into a selenolate. Evidence for the existence of n-butyldisilenol has also been obtained.     

Influence of the molecular weight on the elongational behaviour of polypropylene and on the fibre orientation factors

This study shows that the elongational behaviour depends upon molecular weight and upon elongational rate. If the molecular weight is low, elongational viscosity reaches rapidly a steady value but, if the molecular weight is high, the viscosity (or the elongational stress) increases continuously with the time. These behaviours may be explained in comparison of the relaxation rate determined by shear rheology as the reciprocal relaxation time with the elongation rate ϵ. If the elongation rate is lower than the relaxation rate the polypropylene chains may relax and the elongational viscosity reaches a steady value with the time. For high fluidity polypropylene the range of elongation rates within of which the elongational viscosity is constant with time is very large. On the contrary, if the elongational rate is higher than relaxation rate the polypropylene chains undergo a continuous deformation and then the elongational viscosity increases with time. The range of elongational rates within of which the stress is constant is narrow for high-molecular-weight polypropylene. Furthermore, the elongational behaviour influences the chain orientation in the crystalline and amorphous phases of the fibres. If the polymer chains are quenched in a relaxed state the orientation is lowered as shown with high fluidity polypropylenes. On the contrary, if the chains are cooled in extended state their orientation may subsist during crystallisation and the orientation factors may reach high values as shown with high-molecular-weight polypropylene.