In situ-preparation and characterization of silver-HEMA/PEGDA hydrogel matrix nanocomposites: Silver inclusion studies into hydrogel matrix

Poly(ethylene glycol) diacrylate (PEGDA) of different molecular weights (Mn = 575 and 700) was used as crosslinking agent for the photopolymerization of 2-hydroxyethyl methacrylate (HEMA) in order to obtain HEMA/PEGDA-based hydrogels. Composites were synthesized in situ employing a new methodology that implies the addition of different quantities of silver nitrate aqueous solution to the monomer mixture with the finality to obtain hydrogels with different silver nanoparticles’ spatial density and distribution. Samples were characterized by thermal, optical, spectroscopic and structural/morphological methods. Thermal studies showed that the increase of PEGDA molecular weight and the AgNO₃ concentration in the reaction mixture enhance the glass transition temperature and the thermal stability of the composites. This behavior could be related to the silver coordination with the polymer network. Infrared spectroscopy with Fourier transform and Raman analyses were realized in order to corroborate the sample chemical structure by the identification of specific functional groups. Surface hydrogel morphology was visualized with scanning electron microscopy analysis, detecting a homogeneous micro-porous surface for the samples obtained from high molecular weight PEGDA. Presence of silver nanoparticles was established by X-ray fluorescence spectroscopy and UV/Vis methods. In this last case, the characteristic silver nanoparticle plasmon was observed. Using Transmission Electron Microscopy it was possible to visualize a homogeneous spatial distribution of spherical silver nanoparticles with very narrow diameter distribution that rounds about 14–21 ± 5 nm. In general, the silver nanoparticle presence in the compounds enhances considerably their thermal/morphological characteristics.     

Diastereoselective multicomponent Amine-Aldehyde-Dienophile (AAD) process for the synthesis of polysubstituted cyclohex-2-enylamines

The multicomponent Amine-Aldehyde-Dienophile reaction is optimized employing benzyl or 4-methoxybenzylamine. The interest of the transformation consist in the synthesis of polysubstituted cyclohex-2-enylamines. The study of the scope of this AAD process is carried out, as well as the diastereoselective version, employing commercially available chiral benzylic amines and a maleimide with the chiral information at the N-substituent. VCD spectroscopy is a very useful tool for the determination of the absolute configuration of the isolated enantiomerically enriched compounds.     

Trifluoroacetylsulfenyl trifluoroacetate,CF(3)C(O)-S-O-C(O)CF(3), a novel compound with a symmetrically substituted S-O bond: synthesis,spectroscopic characterization,and quantum chemical calculations

The new compound trifluoroacetylsulfenyl trifluoroacetate, CF(3)C(O)SOC(O)CF(3), which possesses two identical carbonyl substituents attached to the S-O bond, has been synthesized. The IR and UV spectra of the gas phase as well as the (13)C NMR spectrum of the solution in CDCl(3) were recorded and assigned. Quantum chemical calculations were performed with the ab initio methods HF and MP2 and the density functional approach B3LYP. The 6-31G basis set was chosen in all calculations. The molecule possesses a skew structure, and according to all computational methods, the syn-syn structure (C=O bonds of both C(O)CF(3) groups synperiplanar to S-O bond) represents the most stable conformer. In agreement with the quantum chemical calculations, the presence of small amounts (< or =5%) of a second conformer (anti-syn) cannot be excluded on the basis of the IR spectrum. The calculated values for the torsional angle around the S-O bond (delta(C-S-O-C)) of the syn-syn form are smaller than 80 degrees (72-78 degrees). Comparison with theoretical results for the corresponding disulfide CF(3)C(O)SSC(O)CF(3) and peroxide CF(3)C(O)OOC(O)CF(3) indicates that the structural properties of sulfenyl compounds are more similar to those of disulfides than to those of peroxides.     

Planar Chromatographic and Electrophoretic Study of Thermally Induced Conformational Modifications of Protein Structure

JPC – Journal of Planar Chromatography – Modern TLC -     

Determination of the amino acid tryptophan and the biogenic amine tryptamine in foods by the heavy atom induced-room temperature phosphorescence methodology

Very simple and selective methods are presented to determine the amino acid tryptophan (Trp) and the biogenic amine tryptamine (Tryp), both compounds with an indole-type molecular structure by the methodology named Heavy Atom Induced-Room Temperature Phosphorescence (HAI-RTP) which constitutes the first time that HAI-RTP has been used to detect compounds with non-naphthalenic structures in their molecules. Different variables affecting the phosphorescence signal (heavy atom perturber and sodium sulfite concentration) were carefully studied. The analytical curves give a linear dynamic range of 15-100 ng ml(-1) and a detection limit of 4 ng ml(-1) for Trp and 94-400 ng ml(-1) and 28 ng ml(-1) for Tryp. The methods have been successfully applied to the analysis of complex food matrices such as the presence of tryptophan in yoghurt and tryptamine in bottled beer. A single alkaline hydrolysis to release Trp from yoghurt proteins and two methods for extracting Tryp from beer samples are proposed and optimised. A total Trp content of 374 mg of Trp per kg of yoghurt was quantified by the standard addition method of calibration and a recovery of 90% was obtained for 250 ng ml(-1) of Tryp in spiked non-alcoholic beer samples.     

Light-Induced Tetrazole-Quinone 1,3-Dipolar Cycloadditions

Quinones were firstly used as dipolarophiles in a photoclick 1,3-cycloaddition with 2,5-diaryltetrazoles, as photoactivatable predipoles, providing a novel and efficient access to three types of pyrazole-fused quinones (indazoledione derivatives). Distinctive features of this protocol include the use of light as the unique reagent and readily available, stable, and easy to handle starting materials and good to excellent yields. Photophysical and electrochemical properties of the quinones and their potential application as photoredox catalysts are also detailed.     

Thermal,spectral and biological characterisation of copper(II) complexes with isoniazid-based hydrazones

Journal of Thermal Analysis and Calorimetry - A series of complexes [Cu(L)(CH3COO)2]·nH2O (L: isonicotinic acid 2-(2-hydroxy-8-substituted-tricyclo[7.3.1.02.7]tridec-13-ylidene)-hydrazones)...     

1-Alkyl-2,4-dihydro-1H-pyrazino[2,1-b]quinazoline-3,6-diones as glycine templates. Synthesis of Fiscalin B

An excess of base allows the regio- and diastereoselective alkylation at C(4) of the glycine templates 1-methyl(isopropyl)-2,4-dihydro-1H-pyrazino[2,1-b]quinazoline-3,6-diones 9a and 9b without the need for N(2)-protecting groups. While the alkylation of 9a gave exclusively the 1,4-anti-isomers, the isopropyl derivative 9b required much longer reaction times and occurred with lower diastereoselectivity. Fiscalin B 3 was obtained by alkylation of 9b with N-Boc-3-indolylmethyl bromide followed by indole deprotection.     

An insight into the aromaticity of fullerene anions: experimental evidence for diamagnetic ring currents in the five-membered rings of C(60)(6-) and C(70)(6-)

Reduction of the two "closed" [6,6] methanofullerenes, [6,6]C(61)H(2) (1) and [6,6]C(71)H(2) (5), to the corresponding hexaanions with lithium metal causes the bridgehead-bridgehead bonds to open, at least partially, and this change gives rise to diamagnetic ring currents in the resulting homoconjugated six-membered rings (6-MRs). These new ring currents shield the overlying hydrogen atoms on the methylene bridge and induce upfield shifts of 1.60 and 0.11 ppm in their (1)H NMR resonances, respectively. Analogous reduction of the already "open" [5,6]methanofullerenes, [5,6]C(61)H(2) (2) and [5,6]C(71)H(2) (3 and 4), only slightly enhances the shielding of the hydrogen atoms over the homoconjugated 6-MRs (upfield shifts of 0.13, 0.68, and 0.14 ppm, respectively) but leads to exceptionally strong diamagnetic ring currents in the homoconjugated five- membered rings (5-MRs), as evidenced by dramatic shielding of the hydrogen atoms situated over them (upfield shift of 5.01, 6.78, and 1.63 ppm, respectively). The strongest shielding is seen for the hydrogen atom sitting over the 5-MR at the pole of C(71)H(2)(6)(-) (delta = -0.255 ppm) indicating that the excess charge density is concentrated at the poles.