Gelation of n3p3[nh(ch2)3si(oet)3]6-n [x]n x = nh(ch2)3si(oet)3, nch3(ch2)3cn and oc6h4(ch2)cn, n = 0 or 3 at the liquid/air/interface

Indexación: ScieloThe compounds N3P3[NH(CH2)3Si(OEt)3]6 (1), N3P3[NH(CH2)3Si(OEt)3]3[NCH3(CH2)3CN]3 (2) and N3P3[NH(CH2)3Si(OEt)3]3 [HOC6H4(CH2)CN]3 (3) undergo slow gelation at the interface oil/air at low temperatures to give perfect gels G1, G2 and G3 respective ly. TEM analysis reveals nanoparticles of silica with mean size of about 10 nm. Pyrolysis under air at 800 °C of these gels affords a mixture of mainly Si5(PO4)6O, SiP2O7 and SiO2. Gelation and pyrolysis products were characterized by IR, solid-state NMR, TEM, SEM-EDAX microscopy and X-ray diffraction. The sol-gel process in the interface liquid /air is discussed in comparison with the usual sol-gel solution process.http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072010000300031&nrm=is

A CMOS 0.8- µm transistor-only 1.63-MHz switched-current bandpass ΣΔ modulator for AM signal A/D conversion

This paper presents a CMOS 0.8-/spl mu/m switched-current (SI) fourth-order bandpass /spl Sigma//spl Delta/ modulator (BP-/spl Sigma//spl Delta/M) IC capable of handling signals up to 1.63 MHz with 105-bit resolution and 60-mW power consumption from a 5-V supply voltage. This modulator Is intended for direct A/D conversion of narrow-band signals within the commercial AM band, from 530 kHz to 1.6 MHz. Its architecture is obtained by applying a low-pass-to-bandpass transformation (z/sup -1//spl rarr/-z/sup -2/) to a 1-bit second-order low-pass /spl Sigma//spl Delta/ modulator (LP-/spl Sigma//spl Delta/M). The design of basic building blocks is based upon a detailed analysis of the influence of SI errors on the modulator performance, followed by design optimization. Memory-cell errors have been identified as the dominant ones. In order to attenuate these errors, fully differential regulated-folded cascode memory cells are employed. Measurements show a best SNR peak of 65 dB for signals of 10-kHz bandwidth and an intermediate frequency (IF) of 1.63 MHz. A correct noise-shaping filtering is achieved with a sampling frequency of up to 16 MHz.This work has been supported by the Spanish CICYT Project TIC 97-0580

Photothermally controlled methotrexate release system using β-cyclodextrin and gold nanoparticles

The inclusion compound (IC) of cyclodextrin (CD) containing the antitumor drug Methotrexate (MTX) as a guest molecule was obtained to increase the solubility of MTX and decrease its inherent toxic effects in nonspecific cells. The IC was conjugated with gold nanoparticles (AuNPs), obtained by a chemical method, creating a ternary intelligent delivery system for MTX molecules, based on the plasmonic properties of the AuNPs. Irradiation of the ternary system, with a laser wavelength tunable with the corresponding surface plasmon of AuNPs, causes local energy dissipation, producing the controlled release of the guest from CD cavities. Finally, cell viability was evaluated using MTS assays for β-CD/MTX and AuNPs + β-CD/MTX samples, with and without irradiation, against HeLa tumor cells. The irradiated sample of the ternary system AuNPs + β-CD/MTX produced a diminution in cell viability attributed to the photothermal release of MTX

Functionalization of gold nanostars with cationic ß-cyclodextrin-based polymer for drug co-loading and SERS monitoring

Gold nanostars (AuNSs) exhibit modulated plasmon resonance and have a high SERS enhancement factor. However, their low colloidal stability limits their biomedical application as a nanomaterial. Cationic ß-cyclodextrin-based polymer (CCD/P) has low cytotoxicity, can load and transport drugs more efficiently than the corresponding monomeric form, and has an appropriate cationic group to stabilize gold nanoparticles. In this work, we functionalized AuNSs with CCD/P to load phenylethylamine (PhEA) and piperine (PIP) and evaluated SERS-based applications of the products. PhEA and PIP were included in the polymer and used to functionalize AuNSs, forming a new AuNS-CCD/P-PhEA-PIP nanosystem. The system was characterized by UV–VIS, IR, and NMR spectroscopy, TGA, SPR, DLS, zeta potential analysis, FE-SEM, and TEM. Additionally, Raman optical activity, SERS analysis and complementary theoretical studies were used for characterization. Minor adjustments increased the colloidal stability of AuNSs. The loading capacity of the CCD/P with PhEA-PIP was 95 ± 7%. The physicochemical parameters of the AuNS-CCD/P-PhEA-PIP system, such as size and Z potential, are suitable for potential biomedical applications Raman and SERS studies were used to monitor PhEA and PIP loading and their preferential orientation upon interaction with the surface of AuNSs. This unique nanomaterial could be used for simultaneous drug loading and SERS-based detection

S-S cleavage in disulphides by the fragment CpFe(dppe)+

The reaction of CpFe(dppe)l with disulphides S2R2 R = CH3, C3H7, CH2-C6H5, C6H5 in presence of NH4PF6 afford the unexpectedly oxidized thiolate complexes [CpFe(dppe)SR]PF6 instead the expected disulphide complexes. The paramagnetic 17 ē complexes were characterized by elemental analysis, IR, UV, visible spectral data as well as magnetic methods

Coordinating properties of some solvents in Cr(CO)5L complexes

The influence of the donor-acceptor properties of several solvents on the Cr(CO)5 group in the solid [Cr(CO)5·solvent] complexes has been examined by spectroscopic methods. Relationships were found between the acceptor number of solvent with the π acceptor ability (Graham π parameter) and with the λmax for the ligand field 1A1 → 1E transition, in the carbonyl chromium complexes. These relations are discussed in terms of the dative metal-ligand π bonding. From these results, it is possible to demonstrate the π contribution in the acceptor number. © 1988 Pergamon Press plc

Análisis y restauración de retablos

Los retablos pertenecen a la colección de la Facultad de Artes de la Universidad de Chile

Preferential salvation in N-methylthiourea

The chemical shifts of the NH and NH2 protons in N-methylthiourea dissolved in binary mixed solvents show a dependence on the solvent molar fractions typical of preferential solvation processes. The degree of preferential salvation determined from the NH resonance depends mainly on the donor properties of the components of the mixture; however, those obtained from the NH2 protons show also the influence of the solvent acceptor properties. These results, as well as some deviations from the general behaviour, are discussed considering the different degree of the electron delocalization along both branches of the thioure

Metal-metal interaction through CH2-CN bridge: Synthesis and characterization of [CpM(L2) NCCH2Fc]PF6 complexes (Fc = ferrocenyl; L = 1/2 dppe, PPh3; M = Fe,Ru)

The new complexes [CpM(L2)NCCH2Fc]PF6 (M = Fe 1, Ru 2; Fc = ferrocenyl), have been prepared from reaction of CpM(L2)X and the ligand Fc-CH2CN 3 in methanol and in the presence of NH4PF6. The compounds were characterized by elemental analysis as well as spectroscopic methods. Electrochemical as well as near-IR measurements suggest a weak metal-metal interaction for the Fe(II)-Fe(III) complex. Hush parameters for this mixed-valence complex suggest a class II Robin-Day type with a moderate metal-metal interaction similar to that observed in the related pyridine bridged systems (η5-C5H5)Fe-η5-C5H4-C5H4N-ML(n). The unusual electron transfer through a insulating CH2 group is the first such example for an asymmetric binuclear system. (C) 2000 Elsevier Science S.A

Ionization of the FeX bond in polar solvents: A spectroscopic study of CpFe(dppe)X complexes

Electronic absorption spectra for complexes CpFe(dppe)X [with X = Cl, I and CN; dppe = (Ph)2PCH2CH2P(Ph)2; Cp = η5-C5H5] and the cationic derivative [CpFe(dppe)NCCH3]PF6 in different solvents have been measured. The lower energy bands were assigned to iron d-d orbital transitions on the bais of intensities, solvent effects ad extended Hückel MO calculations. The complexes CpFe(dppe)X (with X = Cl and I) undergo ionization in polar solvents to give the cationic solvated species [CpFe(dppe) (solvent)]+. This behaviour can be explained on the basis of the theoretical calculations. © 1993