Thermal,morphostructural and spectrometric characterization of an antibacterial kaolinite-based filter modified with silver for water treatment

Journal of Thermal Analysis and Calorimetry - The aim of this work is to synthesize and characterize a new structured silver–clay dried, calcined or sintered at different temperatures...     

Synthesis, structure and conformation of partially-modified retro- and retro-inverso psi[NHCH(CF3)]Gly peptides

Partially modified retro- (PMR) and retro-inverso (PMRI) psi[NHCH(CF(3))]Gly peptides, a conceptually new class of peptidomimetics, have been synthesized in wide structural diversity and variable length by aza-Michael reaction of enantiomerically pure alpha-amino esters and peptides with enantiomerically and geometrically pure N-4,4,4-trifluorocrotonoyl-oxazolidin-2-ones. The factors underlying the observed moderate to good diastereocontrol have been investigated. The conformations of model PMR-psi[NHCH(CF(3))]Gly tripeptides have been studied in solution by (1)H NMR spectroscopy supported by MD calculations, as well as in the solid-state by X-ray diffraction. Remarkable stability of turn-like conformations, comparable to that of parent malonyl-based retropeptides, was evidenced, as a likely consequence of two main factors: 1) severe torsional restrictions about sp(3) bonds in the [CO-CH(2)-CH(CF(3))-NH-CH(R)-CO] module, which is biased by the stereoelectronically demanding CF(3) group and the R side chain; 2) formation of nine-membered intramolecularly hydrogen-bonded rings, which have been clearly detected both in CHCl(3) solution and in some crystal structures. The former factor seems to be more important, as turn-like conformations were found in the solid-state even in the absence of intramolecular hydrogen bonding. The relative configuration of the -C*H(CF(3))NHC*H(R)- stereogenic centers has a major effect on the stability of the turn-like conformation, which seems to require a syn stereochemistry. X-ray diffraction and ab initio computational studies showed that the [-CH(CF(3))NH-] group can be seen as a sort of hybrid between a peptide bond mimic and a proteolytic transition state analogue, as it combines some of the properties of a peptidyl -CONH- group (low NH basicity, CH(CF(3))-NH-CH backbone angle close to 120 degrees, C-CF(3) bond substantially isopolar with the C=O) with some others of the tetrahedral intermediate [-C(OX)(O(-))NH-] involved in the protease-mediated hydrolysis reaction of a peptide bond (high electron density on the CF(3) group, tetrahedral backbone carbon).     

Synthesis of anticonvulsant sulfamides. Theoretical study of the related mechanism

A theoretical study of the mechanisms associated with the synthesis of anticonvulsant symmetric N,N-substituted sulfamides is presented. Two possible synthetic routes are compared, which mainly differ in the use of pyridine as a nucleophilic agent in the reaction mechanism. Geometry optimization techniques and transition-state detection at the B3LYP/6-31G** level, modeling the solvent by means of an isodensity polarizable continuum approach, allow the most suitable method for the experimental process to be discerned.From the Proceedings of the 28th Congreso de Químicos Teóricos de Expresión Latina (QUITEL 2002)     

Synthesis of stereo-defined α-trifluoromethyl (Tfm)-malic units

Aldol reactions of titanium enolates of N-acyl-1,3-oxazolidin-2-ones with ethyl trifluoropyruvate occurred with low to good stereoselectivity depending on the steric properties of the N-acyl group. Attempts to transform the resulting aldols into peptidomimetics incorporating stereo-defined α-trifluoromethyl (Tfm)-malic units are described.     

Studies on the synthesis of heterocyclic compounds. VII. Action of acyl halides on heterocyclic compounds containing the O-M-O (M  P,As, Sb) bond in the ring

The action of acyl halides on heterocyclic compounds of five-membered rings containing an O-M-O (M ? P, As, Sb) linkage is described. The reactions were either carried out in the presence of a solvent (benzene or toluene) or by direct heating of the reagent with the substrate. In the case of arsole, stibole and stannole derivatives, the cleavage of O-M bond and the formation of the respective mono- and diesters were always obtained, while with the phospholes, no cleavage of the compounds was observed. The products IIa-c (M = Sb) have been obtained in excellent yields starting from VIa-c and antimony trichloride. The structure of the compounds which were prepared was determined by analytical and spectroscopic methods and also by comparations with authentic samples where possible.     

Asymmetric nitrogen

The¹H NMR spectra ofO-derivatives of 1-hydroxy-2,2-bis(trifluoromethyl)aziridine containing such substituents as EtO₂CCH₂, (R/S)-RO₂CCH(Me) (R=Me, Prⁱ, or Bu^t), (R/S)-H₂NC(O)CH(Me), and (R)-H₂NC(O)CH(Me) were analyzed. Both of the diastereomerically pure amides of the latter type were isolated. The validity of the¹H NMR criteria, which were suggested for the determination of absolute configurations of diastereomers ofN-alkoxyaziridines, was confirmed by X-ray diffraction study of the (R,R)-amide.     

Acremines A-F, novel secondary metabolites produced by a strain of an endophytic Acremonium, isolated from sporangiophores of Plasmopara viticola in grapevine leaves

Six novel metabolites, acremines A-F have been isolated from agar cultures of a strain of Acremonium sp. Their structures and stereochemistry were elucidated using a combination of ¹³C and ¹H homo and heteronuclear 2D NMR experiments and X-ray analysis. Acremines A-D inhibited the germination of sporangia of Plasmopara viticola.     

Designed Beta‐Turn Mimic Based on the Allylic‐Strain Concept: Evaluation of Structural and Biological Features by Incorporation into a Cyclic RGD Peptide (Cyclo(‐L‐arginylglycyl‐L‐α‐aspartyl‐))

The (3R,5S,6E,8S,10R)‐11‐amino‐3,5,8,10‐tetramethylundec‐6‐enoic acid (ATUA; 1 ), which was designed as a βII′‐turn mimic according to the concepts of allylic strain and 2,4‐dimethylpentane units, was incorporated into a cyclic RGD peptide. The three‐dimensional structure of cyclo(‐RGD‐ATUA‐) (=cyclo(‐Arg‐Gly‐Asp‐ATUA‐)) 4 in H₂O was determined by NMR techniques, distance geometry calculations and molecular‐dynamics simulations. The RGD sequence of 4 shows high conformational flexibility but some preference for an extended conformation. The structural features of the RGD sequence of 4 were compared with the RGD moiety of cyclo(‐RGDfV‐) (=cyclo(‐Arg‐Gly‐Asp‐D ‐Phe‐Val‐)). In contrast to cyclo(‐RGDfV‐), which is a highly active αvβ3 antagonist and selective against αIIbβ3, cyclo(‐RGD‐ATUA‐) shows a lower activity and selectivity. The structure of the ATUA residue in the cyclic peptide resembles a βII′‐turn‐like conformation. Its middle part, adjacent to the C?C bond, strongly prefers the designed and desired structure.     

Solvent dependent conformational isomerism and ligand oxidation of novel Ru(II) cyclen complexes

The synthesis of cis-[Ru(II)(cyclen)(L)(x)](n+) (cyclen = 1,4,7,10-tetraazacyclododecane and L = 2,2'-bipyridine (bpy), phenanthroline (phen) or 4-cyanopyridinium (4-NCpyH(+))) is reported. The freshly prepared complexes are stable in aprotic solvents and cyclen undergoes oxidative dehydrogenation reaction at high pH. These compounds also present solvent dependent conformational isomerization.     

Evaluation of recombinant green fluorescent protein, under various culture conditions and purification with HiTrap hydrophobic interaction chromatography resins

To determine the influence of various culture conditions, transformed cells of Escherichia coli expressing recombinant green fluorescent protein (GFPuv) were grown in nine cultures with four variable conditions (storage of inoculated broth at 4°C prior to incubation, agitation speed, isopropyl-β-d-thiogalactopyranoside [IPTG] concentration, and induction time). The pelleted cells were resuspended in extraction buffer and subjected to the three-phase partitioning (TPP) extraction method. To determine the most appropriate purification resin, protein extracts were eluted through one of four types of HiTrap hydrophobic interaction chromatography (HIC) columns prepacked with methyl, butyl, octyl, or phenyl resins and analyzed further on a 12% sodium dodecylsulfatepolyacrylamidegel. With Coomassie staining, a single band between 27 (standard GFPuv) and 29 kDa (molecular weight standard) was visualized for every HIC column sample. TPP extraction with HIC elution provided about 90% of the GFPuv recovered and eight-fold GFPuv enrichment related to the specific mass. Rotary speed and IPTG concentration showed, respectively, greater negative and positive influences on GFPuv expression at the beginning of the logarithmic phase for the set culture conditions (37°C, 24-h incubation).