Search results for "Effects"
showing 10 items of 2634 documents
Experimental and theoretical studies on the electronic spectra of indole-3-acetic acid and its anionic and protonated species
1991
Abstract The geometrical and electronic structure of indole-3-acetic acid (IAH) have been investigated using the MINDO/3 molecular orbital method, the geometries being optimized by Rinaldi's method. The UV spectrum of IAH has been recorded in different solvents. The corresponding spectra of IAH + 2 and IA − were also respectively obtained, from IAH in different H 2 SO 4 /water mixtures and NaOH solutions. The agreement of experimental spectra with the ones theoretically calculated by the CNDO/M-Cl method after optimization of the κ parameter, is discussed. The p K a values of IAH have also been determined from the IAH + 2 spectra and are compared with literature data.
Potato pulp as a composting substrate
2014
Potato pulp is a waste, which is produced in considerable quantities by starch manufacturing industry. Addition of pulp fibre residue to soil results in beneficial effects on soil physical and biochemical properties. In this study, organic potato pulp was mixed with organic grass in three concentrations (75:25 (A), 50:50 (B) and 25:75 (C) % w/w) with the aim of comparing the dynamics of the composting process during a 30-day period. A mini-field experiment was conducted in 0.7 m 3 windrows which were left without covering and additional mixing during composting process, except sampling procedure. During 30-days’ experiment the C:N ratio decreased from 25÷30 to 13÷17 indicating the active co…
DNA nucleobase properties and photoreactivity: Modeling environmental effects
2009
Abstract The accurate ab initio quantum chemical (QM) method multiconfigurational second-order perturbation (CASSPT2)/complete active space self-consistent field (CASSCF) has been used in conjunction with molecular mechanics (MM) procedures to compute molecular properties and photoinduced reactivity of DNA/RNA nucleobases (NABs) in isolation and within a realistic environment, in which the double helix strand, the aqueous media, and the external counterions are included. It is illustrated that the use of an MM model is helpful both to account for short- and long-range effects of the system surrounding the QM molecular core and to provide the proper structural constraints that allow more acc…
FT-IR investigation of the state of iron (III) chloride clusters confined in AOT reverse micelles dispersed in carbon tetrachloride
2007
The state of the water-soluble salt iron(III) chloride in AOT reverse micelles dispersed in carbon tetrachloride has been investigated by FT-IR spectroscopy. Interestingly, while the entrapment of a lot of water-soluble inorganic salts in AOT reverse micelles requires preliminarily the presence of significant amounts of water within the micellar core, solubilization of FeCl3 occurs without the need to add water in the micellar solution reaching the very high solubility value, expressed as the maximum salt-to-surfactant molar ratio, of 1.30. The analysis of the spectral features of the investigated samples leads to hypothesize that iron(III) chloride is confined within the reverse micellar c…
Supramolecular chirality in organogels: a detailed spectroscopic, morphological, and rheological investigation of gels (and xerogels) derived from al…
2010
This Article addresses the formation of chiral supramolecular structures in the organogels derived from chiral organogelator 1R (or 2R), and its mixtures with its enantiomer (1S) and achiral analogue 3 by extensive circular dichroism (CD) spectroscopic measurements. Morphological analysis by atomic force microscopy (AFM) and scanning electron microscopy (SEM) were complemented by the measurements of their bulk properties by thermal stability and rheological studies. Specific molecular recognition events (1/3 vs 2/3) and solvent effects (isooctane vs dodecane) were found to be critical in the formation of chiral aggregates. Theoretical studies were also carried out to understand the interact…
Cooperative High-Temperature Spin Crossover Accompanied by a Highly Anisotropic Structural Distortion
2016
Spin transitions are a spectacular example of molecular switching that can provoke extreme electronic and structural reorganizations in coordination compounds. A new 3D cyanoheterometallic framework, [Fe(pz)(Au(CN)2)2], has been synthesized in which a highly cooperative spin crossover has been observed at 367 and 349 K in heating and cooling modes, respectively. Mössbauer spectroscopy revealed a complete transition between the diamagnetic and paramagnetic states of the iron centres. The low-spin-to-high-spin transition induced a drastic structural distortion involving a large one-directional expansion (ca. 10.6%) and contraction (ca. 9.6%) of the lattice. Negative thermal expansion along th…
Twisting of the resorcinarene core due to solvent effects upon crystallization
2009
The effect of the crystallization conditions on the conformation of the tetramethoxy resorcinarene skeleton was investigated in acetone solutions, to which was added a second component (less favorable solvent or salt) to promote crystallization. The resorcinarene core was found to adopt three different conformations: crown (I), a pinched crown (II) and a twisted pinched crown (III). In addition, the flexibility of the resorcinarene core was compared with a tetramethoxy resorcinarene derivative, resorcinarene bis-crown, which is in a fixed boat conformation.
Synthese sterisch gehinderter Peptide und Depsipeptide nach einem Säurechlorid-Verfahren mit 2-Phosphonioethoxycarbonyl-(Peoc-)Aminosäuren und -Hydro…
1982
2-(Triphenylphosphonio)ethoxycarbonyl-(Peoc-)aminosauren 1 und -hydroxysauren 5 werden mit Oxalylchlorid in bei Raumtemp. stabile Saurechloride 2 bzw. 6 ubergefuhrt. Mit diesen aktivierten Verbindungen werden sterisch gehinderte Amidbindungen — z. B. in den geschutzten Valin-Peptiden 3a—g und in Hydroxyacyl-Dipeptiden 7 — hergestellt. Nach Schutzgruppenabspaltung aus der voll geschutzten Form 7a entsteht so die Sporidesmolsaure B (9a), die in ihren Eigenschaften mit dem Abbauprodukt aus dem Sporidesmolid I ubereinstimmt. Trotz zweimaliger Anwendung der Saurechlorid-Kondensation ist keine Racemisierung eingetreten. Syntheses of Sterically Hindered Peptides and Depsipeptides by Means of an Ac…
Characterization of a fiber-reinforced new fully aromatic liquid crystalline polymer
1998
A new rigid liquid crystalline polymer that demonstrates good mechanical and thermomechanical properties and acceptable processing temperature has been recently synthesized and characterized. The melting temperature and some thermomechanical properties do not seem, however, suitable for use in some applications at high temperature or in the presence of aggressive fluids. The use of appropriate inorganic fillers can overcome these shortcomings. In this work the new LCP, polymerized in a bench-scale apparatus, and the same sample filled with carbon fibers are characterized. The properties of the carbon fiber filled LCP are compared with those of another filled wholly aromatic commercial LCP,…
A DFT study of the role of the Lewis acid catalysts in the [3 + 2] cycloaddition reaction of the electrophilic nitrone isomer of methyl glyoxylate ox…
2015
The molecular mechanism and stereoselectivity of the BF3 Lewis acid catalyzed [3 + 2] cycloaddition (32CA) reaction between C-methoxycarbonyl nitrone and cyclopentene has been theoretically studied using DFT methods at the MPWB1K/6-31G(d) computational level. The BF3 catalyst accelerates the 32CA reaction by decreasing the activation energy leading to the formation of the trans cycloadduct as the kinetic product, in agreement with the experimental data. Inclusion of solvent effects slightly increases the activation energy and decreases the exothermic character of the 32CA reaction as a consequence of a better solvation of nitrone than the transition state and the cycloadduct. The use of the…