Search results for "Method"
showing 10 items of 13253 documents
On the Glass Transition in Polymer Films: Recent Monte Carlo Results
1998
AbstractThis paper reports results of a Monte Carlo simulation for a simplified lattice modelof a supercooled polymer film. The film geometry is realized by two opposite hard walls.The distance between the walls is varied. The chains exhibit a strong tendency to orientparallel to the walls and are flattened when being very close to them. This deviation of thepolymer structure with respect to the bulk is accompanied by an acceleration of local densityfluctuations. On the other hand, the diffusion coefficient of a chain remains unaffected.
Molecular structures and vibrations of m-methylaniline in the S0 and S1 states studied by laser induced fluorescence spectroscopy and ab initio calcu…
2000
Abstract The UV fluorescence excitation and dispersed fluorescence spectra of a jet-cooled m-methylaniline have been obtained for the S1←S0 transition, in which some of the bands have been observed for the first time. The main spectral bands have been assigned by comparison with those of other relevant substituted benzenes. It was found that the spectra exhibit an important feature which is the internal rotation of the methyl group in the electronic ground and excited states. Ab initio calculations at MP2/6-31G* and CIS/6-31G* show that the optimized structure of m-methylaniline in the ground state is not planar with the amino group having sp3 hybridation-like character due to the existence…
Fractionated precipitation of acid macropolyanions by dialysis, a simple method for the estimation of DNA in complex biological samples.
1976
Abstract After efficient extraction by para-aminosalicylate, (hopping, grinding and eventual sonication, the macropolyanions are transformed into their cetyltrimethylammonium salts. These have differing solubilities, strongly depending on ionic strength. The cationic detergent-macropolyanionic salts are solubilized by high salt concentration. Salt is then dialysed out, rendering the polyanions highly insoluble in a sequential fashion. The insolubilized components are determined quantitatively by monitoring turbidity, which in case of DNA is strictly proportionate to its concentration. This relation is not affected by other components. This makes DNA determination possible even in crude aque…
High pressure processing of fruit juice mixture sweetened with Stevia rebaudiana Bertoni: Optimal retention of physical and nutritional quality
2013
Abstract The impact of high pressure processing (HPP) technology on physicochemical properties (color, browning index, turbidity index), bioactive compounds (ascorbic acid, total phenolic compounds, total anthocyanins, total carotenoids) and antioxidant capacity of a fruit juice mixture (papaya (32.5%, v/v), mango (10%, v/v) and orange (7.5%, v/v)) sweetened with Stevia rebaudiana Bertoni at different percentages was studied. The experimental design comprised a response surface methodology according to a central composite face-centered design. The variable ranges were 300–500 MPa (pressure), 5–15 min (time), 0–2.5% Stevia percentage. This design was used to determine the optimal high pressu…
Bulk and interfacial properties in colloid-polymer mixtures
2005
Large-scale Monte Carlo simulations of a phase-separating colloid-polymer mixture are performed and compared to recent experiments. The approach is based on effective interaction potentials in which the central monomers of self-avoiding polymer chains are used as effective coordinates. By incorporating polymer nonideality together with soft colloid-polymer repulsion, the predicted binodal is in excellent agreement with recent experiments. In addition, the interfacial tension as well as the capillary length are in quantitative agreement with experimental results obtained at a number of points in the phase-coexistence region, without the use of any fit parameters.
Biophysical approaches for the study of metal-protein interactions
2019
Protein-protein interactions play important roles for a variety of cell functions, often involving metal ions; in fact, metal-ion binding mediates and regulates the activity of a wide range of biomolecules. Enlightening all of the specific features of metal-protein and metal-mediated protein-protein interactions can be a very challenging task; a detailed knowledge of the thermodynamic and spectroscopic parameters and the structural changes of the protein is normally required. For this purpose, many experimental techniques are employed, embracing all fields of Analytical and Bioinorganic Chemistry. In addition, the use of peptide models, reproducing the primary sequence of the metal-binding …
Momentum-dependent interfacial tension in polymer solutions
2002
A model for the interface between a concentrated and a very dilute polymer solution is studied by Monte Carlo simulations at temperatures below the Theta temperature (in bad solvent conditions). The wave-number–dependent interfacial tension γ(q) is extracted from an analysis of the capillary wave amplitudes. It is shown that γ(q) decreases monotonically with q2, while no evidence is found for the predicted increase γ(q) ∝ κq2 with a positive bending rigidity κ of the interface at large q. Consequences for the interpretations of simulations and experiments on interfacial widths are briefly discussed.
‘Intrinsic’ profiles and capillary waves at interfaces between coexisting phases in polymer blends
2001
Abstract Lateral fluctuations in the local position of the center of the interface between coexisting phases in unmixed polymer blends lead to a broadening of interfacial widths; comparing self-consistent field predictions for the ‘intrinsic’ profile to simulations (or experiments), this ‘capillary wave’ broadening needs consideration. This problem has been studied by extensive Monte Carlo simulations of the bond fluctuation model for symmetrical polymer mixtures, both for free interfaces (between bulk phases) and for confined interfaces (in thin films between parallel walls). While the capillary wave predictions at large length scales are confirmed, the extraction of the ‘intrinsic’ profil…
Interfaces between coexisting phases of polymer mixtures: Comparison between Monte Carlo simulations and theoretical predictions
1997
Large scale Monte Carlo investigations of the interface between A-rich and B-rich phases of symmetric binary (AB) polymer mixtures are presented, using the bond fluctuation model of flexible chains with NA=NB=N=32 effective monomers. The temperature range studied, 0.144<T/Tc0.759, includes both the strong and the weak segregation limit. Interfacial free energy and interfacial structure are studied, and compared to predictions based on the selfconsistent field theory. Also the broadening of the interfacial width due to capillary waves is considered, and finite size effects due to the confinement of interfaces in thin films of polymer blends are discussed.
A practical entry to β-aryl-β-alkyl amino alcohols: application to the synthesis of a potent BACE1 inhibitor
2012
The 1,2-addition of alkyl Grignard reagents to readily available N-tert-butanesulfinyl ketimines, bearing an α-silyloxy substituent, proceeds in high yields and excellent diastereocontrol. The utility of the present method was demonstrated by the synthesis, in enantiomerically pure form, of one recently disclosed β-secretase (BACE1) inhibitor.