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...     

Minimal, rigid foliations by curves on ℂℙ n

We prove the existence of minimal and rigid singular holomorphic foliations by curves on the projective space ℂℙ ⁿ for every dimension n≥2 and every degree d≥2. Precisely, we construct a foliation ℱ which is induced by a homogeneous vector field of degree d, has a finite singular set and all the regular leaves are dense in the whole of ℂℙ ⁿ . Moreover, ℱ satisfies many additional properties expected from chaotic dynamics and is rigid in the following sense: if ℱ is conjugate to another holomorphic foliation by a homeomorphism sufficiently close to the identity, then these foliations are also conjugate by a projective transformation. Finally, all these properties are persistent for small perturbations of ℱ.?This is done by considering pseudo-groups generated on the unit ball 𝔹 ⁿ ⊆ℂ ⁿ by small perturbations of elements in Diff(ℂ ⁿ ,0). Under open conditions on the generators, we prove the existence of many pseudo-flows in their closure (for the C ⁰-topology) acting transitively on the ball. Dynamical features as minimality, ergodicity, positive entropy and rigidity may easily be derived from this approach. Finally, some of these pseudo-groups are realized in the transverse dynamics of polynomial vector fields in ℂℙ ⁿ . Received March 7, 2002 / final version received November 26, 2002?Published online February 7, 2003 Most of this work has been carried out during a visit of the first author to IMPA/RJ and a visit of the second author to the University of Lille 1. We would like to thank these institutes for hospitality and express our gratitude to CNPq-Brazil and CNRS-France for the financial support which made these visits possible. We are also indebted to Paulo Sad, Marcel Nicolau and the referee whose comments helped us to improve on the preliminary version. Finally, the second author has partially conducted this research for the Clay Mathematics Institute.     

Phase separation of p53 precedes aggregation and is affected by oncogenic mutations and ligands

Mutant p53 tends to form aggregates with amyloid properties, especially amyloid oligomers inside the nucleus, which are believed to cause oncogenic gain-of-function (GoF). The mechanism of the formation of the aggregates in the nucleus remains uncertain. The present study demonstrated that the DNA-binding domain of p53 (p53C) underwent phase separation (PS) on the pathway to aggregation under various conditions. p53C phase separated in the presence of the crowding agent polyethylene glycol (PEG). Similarly, mutant p53C (M237I and R249S) underwent PS; however, the process evolved to a solid-like phase transition faster than that in the case of wild-type p53C. The data obtained by microscopy of live cells indicated that transfection of mutant full-length p53 into the cells tended to result in PS and phase transition (PT) in the nuclear compartments, which are likely the cause of the GoF effects. Fluorescence recovery after photobleaching (FRAP) experiments revealed liquid characteristics of the condensates in the nucleus. Mutant p53 tended to undergo gel- and solid-like phase transitions in the nucleus and in nuclear bodies demonstrated by slow and incomplete recovery of fluorescence after photobleaching. Polyanions, such as heparin and RNA, were able to modulate PS and PT in vitro. Heparin apparently stabilized the condensates in a gel-like state, and RNA apparently induced a solid-like state of the protein even in the absence of PEG. Conditions that destabilize p53C into a molten globule conformation also produced liquid droplets in the absence of crowding. The disordered transactivation domain (TAD) modulated both phase separation and amyloid aggregation. In summary, our data provide mechanistic insight into the formation of p53 condensates and conditions that may result in the formation of aggregated structures, such as mutant amyloid oligomers, in cancer. The pathway of mutant p53 from liquid droplets to gel-like and solid-like (amyloid) species may be a suitable target for anticancer therapy.

Mutant p53 tends to form aggregates with amyloid properties, especially amyloid oligomers inside the nucleus, which are believed to cause oncogenic gain-of-function (GoF).     

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.     

A rapid and sensitive method for simultaneous determination of lamivudine and zidovudine in human serum by on-line solid-phase extraction coupled to liquid chromatography/tandem mass spectrometry detection

A method based on solid-phase extraction (SPE) coupled to high-performance liquid chromatography (HPLC) with positive ion electrospray ionization tandem mass spectrometry (ESI-MS/MS) detection was developed for the simultaneous determination of lamivudine (3TC) and zidovudine (AZT) in human serum, using didanosine (ddI) as internal standard. The acquisition was performed in multiple reaction monitoring (MRM) mode, monitoring the transitions m/z 230.0 --> 111.8 for 3TC, m/z 268.1 --> 126.8 for AZT, and m/z 237.2 --> 136.8 for ddI. The limits of detection and quantitation were 3 and 10 ng/mL for 3TC, and 5 and 15 ng/mL for AZT. The method was linear in the studied ranges (10-1500 ng/mL for 3TC and 15-3000 ng/mL for AZT), with r(2) > 0.99 for each drug, and the run time was 4 min. The intra-assay precisions (%) were in the ranges 1.9-8.7 (3TC) and 2.2-8.9 (AZT), the inter-assay precisions were in the ranges 2.6-9.0 (3TC) and 4.2-8.1 (AZT), and the intra- and inter-assay accuracies were >97% for both drugs. The absolute recoveries were 95-99% for 3TC (45, 600 and 1200 ng/mL) and 104-112% for AZT (45, 1000 and 2400 ng/mL). The analytical method was applied to a bioequivalence study in which 24 healthy adult volunteers received single oral doses of the reference formulation and two test combined AZT/3TC tablets, in an open, three-period, balanced, randomized, crossover protocol. Based on the 90% confidence interval of the individual ratios (test formulation/reference formulation) for C(max) (peak serum concentration) and AUC(0-inf) (extrapolated area under the serum concentration vs. time curve from time zero to infinity), it was concluded that the two test formulations are bioequivalent to the reference formulation with respect to the rate and extent of absorption of both 3TC and AZT.     

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.     

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.