Investigating the possibility of simultaneously finding an electron-hole and an electron-pair in a molecule: Delocalization,competition of ionic vs. covalent character,and related effects in push–pull ethylenes

This work examines the possibility of finding an electron-hole and an electron-pair simultaneously in a π-system substituted by an electron-donating (NH₂) and/or electron-withdrawing (NO₂) group. The contributions of various ionic [(+), ( ↑ ↓ )] structures are calculated from ab initio SCF –CI wave functions, using a recently developed general multielectron population analysis. The molecules studied are two monosubstituted ethylenes, aminoethylene and nitroethylene, and a disubstituted ethylene, the 2-nitroethenamine (push–pull ethylene) in its two configurational forms. The influence of the NH₂ and/or NO₂ group in delocalization and ionic (vs. covalent) character of the C?C double bond are investigated, along with examining the experimental chemist formalism of electron-pair “displacements” in several resonance structures. Analysis of mutual dependence of an electron-hole and an electron-pair, at short and long distances, leads to the conclusion that a push–pull π-system can stimulate the simultaneous existence of an electronhole and an electron-pair even for nonvicinal positions. The relationship between the electronpair distributions and contributions of the corresponding structures are also examined; the effects of electronic correlation are analyzed as well. © 1992 John Wiley & Sons, Inc.     

Synthesis of 6H-pyrrolo[3',4':2,3][1,4]diazepino[6,7,1-hi]indole-8,10(7H,9H)-diones using 3-bromo-4-(indol-1-yl)maleimide scaffold

Series of 3-arylalkyl- or 3-alkylamino-4-(indol-1-yl)maleimides and bis(indol-1-yl)maleimides were synthesised. The cyclization of the 3-substituted 4-(indol-1-yl)maleimides under the action of acids resulted in the formation of diazepine[1,4] derivatives with indoline and maleimide nuclei annelated. These compounds readily produced the corresponding indolomaleimidodiazepines[1,4] after dehydrogenation.     

Synthesis and biological evaluation of spongistatin/altohyrtin analogues: E-ring dehydration and C46 side-chain truncation

Simplified analogues of the potent antimitotic marine macrolide spongistatin 1/altohyrtin A were synthesised and evaluated as growth inhibitory agents against a range of human tumour cell lines, including Taxol-resistant strains, revealing that E-ring dehydration leads to enhanced cytotoxicity at the low picomolar level while truncation of the side-chain at C46 results in a drastic decrease in activity.     

Control of the Properties of Carbon Nanotubes Synthesized by CVD for Application in Electrochemical Biosensors

Interest in carbon nanotubes (CNT) has grown at a very rapid rate in the last decade. Their interesting physical and chemical properties open attractive possibilities in many application areas. These properties depend on the process conditions during synthesis and on subsequent purification steps. Recent studies have demonstrated that CNT can promote the electron transfer of biomolecules. These exceptional properties make them attractive for use in electrochemical biosensors. Multi walled nanotubes have been synthesized by the Chemical Vapor Deposition (CVD) method using methane as a carbon source and Ni–Al₂O₃–SiO₂ as the catalyst. The influence of the variation of certain reaction parameters such as feed gas composition, catalyst mass, temperature and reaction time in the yield of the CVD process has been established. In addition, the structural and chemical characteristics of the CNTs have been studied and a purification process to eliminate the catalyst and amorphous carbon has been developed that involves a gaseous oxidative process and acid treatment. The efficiency of the purification step has been determined by analytical techniques. Atomic force microscopy, Raman scattering, thermogravimetric analysis, inductively coupled plasma atomic spectroscopy are the characterization techniques employed in this work.     

Oxygen sensitivity of algal H2- production

Applied Biochemistry and Biotechnology - Photoproduction of H2 by green algae utilizes electrons originating from the photosynthetic oxidation of water and does not require metabolic intermediates....     

Technological quality determination of pharmaceutical disintegrant by DSC cooling and DSC photovisual

A number of disintegrants are available on the market. They improve tablets’ disintegration. The objective of this work is the comparison of the technological quality parameters of disintegrants using different analytical techniques. Three batches of disintegrants and their binary mixtures (water:disintegrants) were investigated. Cooling experiments were used from –30 up to 200°C. The data obtained showed calorimetric differences between the samples. In the binary mixtures water showed different crystallization behaviour from the one found in the literature. According to the results DSC technique helped the quality control of different disintegrants.     

Graft copolymerisation of acrylamide onto cashew gum

The synthesis of cashew gum-g-polyacrylamide was carried out at 60 °C by a radical polymerisation using potassium persulphate as the redox initiator under N₂ atmosphere. A series of graft copolymers, varying in acrylamide concentration and keeping the concentration of the initiator and polysaccharide constant, was prepared. These graft copolymers were characterised by elemental analysis, infrared and ¹³C NMR spectroscopy, rheological studies, differential scanning calorimetry and thermogravimetric analysis. Comparisons amongst grafting parameters of the reaction of various natural polysaccharides with polyacrylamide (PAM) were carried out. High percentages of acrylamide conversion (%C) and grafting efficiency (%E) were obtained for cashew gum (CG), even with a low acrylamide/gum ratio. All copolymers had intrinsic viscosity and thus the hydrodynamic volume much higher than the CG value and closer to the PAM. The CG-g-PAM solution had an absolute viscosity at 2.5% concentration (wt./vol.) up to 33 and 3.3 times the CG and PAM values, respectively. Grafting of PAM chains onto the polysaccharide enhances its thermal stability.     

OH radical oxidation of the sorbitylfurfural furanic ring to sugar derivatives induced by radiolysis in aerobic environment

Chemical radiolytic oxidation induced by OH addition on 1-(2-furan-2-yl-5-hydroxy-6-hydroxymethyl-[1,3]dioxan-4-yl)-ethan-1,2-diol (sorbitylfurfural, SF) leads, in the presence of controlled amounts of oxygen, to a permanent functional modification of the target molecule. The yield of conversion reaches 60% of the starting material. LC-MS analysis allowed the identification, as final products, of carboxylic acids, butenal and hydroxy-furan derivatives in which the sugar chain remains unbroken, while the furanic ring is attacked first by OH and then by oxygen, giving in succession an intra-/inter-molecular rearrangement of the allylperoxyl radicals thus formed. The proposed oxidation of the furanic ring envisages the peroxyl intermediates undergoing mono- and/or bi-molecular reactions; a reaction path has been outlined and is reported here. The presence of unsaturated bonds in the final products could provide a further site for radical scavenger activity. Therefore, the fast reaction with O₂ and the rearrangement of the produced peroxyl radicals to species, which are likely to be effective OH-capturers, reinforces the antioxidant ability of SF.     

1,4-dioxane as a solvent in spectroscopy and photochemistry

Commercially available 1,4-dioxane, even of spectroscopic grade, contains various impurities that arise mostly from reaction of the solvent with oxygen. Aspects relevant to the spectroscopy and photochemistry of the dioxane/oxygen system are discussed. Methods of purification and storage of the solvent are presented.     

Self-organization of a sulfonamido-porphyrin in Langmuir monolayers and Langmuir-Blodgett films

Langmuir monolayers (LM) and Langmuir-Blodgett (LB) films of pure lipophilic meso-tetra(4-dodecylaminosulfophenyl)porphyrin (PC12) and mixed with the anionic surfactant sodium hexadecylsulfate (SHS) were studied. The molecular packing and structure of PC12 and PC12-4SHS with variable surface pressure were investigated by surface pressure-area measurements, steady-state absorption, fluorescence emission and anisotropy, as well as by fluorescence lifetime imaging microscopy (FLIM). At low surface pressure, the porphyrin molecules are organized with the rings tilted on the water surface whereas at high surface pressure the porphyrin rings achieve a more perpendicular arrangement. Using the FLIM images a gradual change of aggregates into large "islands" is observed. Different patterns are observed in the pure PC12 multilayer films (n = 3 and 5) with ordered patches superimposed which are not observed in the PC12-4SHS multilayer LB films.