Search results for "Kinetic"
showing 10 items of 3064 documents
Photosensitization of DNA by β-carbolines: Kinetic analysis and photoproduct characterization
2012
β-Carbolines (βCs) are a group of alkaloids present in many plants and animals. It has been suggested that these alkaloids participate in a variety of significant photosensitized processes. Despite their well-established natural occurrence, the main biological role of these alkaloids and the mechanisms involved are, to date, poorly understood. In the present work, we examined the capability of three important βCs (norharmane, harmane and harmine) and two of its derivatives (N-methyl-norharmane and N-methyl-harmane) to induce DNA damage upon UV-A excitation, correlating the type and extent of the damage with the photophysical characteristics and DNA binding properties of the compounds. The r…
AN ENZYME-ENHANCED EXTRACTION OF ANTHOCYANINS FROM RED CABBAGE AND THEIR THERMAL DEGRADATION KINETICS
2020
There is a great demand for developing efficient anthocyanins extraction related to each plant material. Conventional methods have been replaced by novel techniques, but they might remain attractive when combined with the latter. Anthocyanins extraction from fresh and dried red cabbage was investigated by maceration, ultrasonication, and with enzymes. Pre-treatments through drying determined an improved extraction with respect to fresh samples, freeze-drying emerging as the best method. Combined enzyme-assisted extraction with maceration resulted in higher yield by conducting several extractions (1078.8±12.5 mg/100 g DW). The kinetic studies revealed good stability of anthocyanins at 50 °C,…
Aggregation Processes and Formation of Silico-calco-alkaline Gels under High Ionic Strength
2002
This paper presents a systematic in situ study of the process of formation of silico-calco-alkaline gels starting from a liquid colloidal solution containing different alkaline ions and different calcium concentration until the final gel state. The combined use of X-ray and neutron small-angle scattering (SAS) and dynamical rheometry techniques lead to a consistent description of the structure of the aggregates and of the mechanisms of aggregation involved in gel formation. SAS results indicate that the aggregates are fractal objects, their structure strongly depending on calcium ion concentration. The differences in gelation kinetics for systems containing different alkaline ions were attr…
Kinetics of 4-Methoxybenzyl Alcohol Oxidation in Aqueous Solution in a Fixed Bed Photocatalytic Reactor
2010
WOS: 000280384800004
Investigation of Multicomponent Sorption in Polymers from Fluid Mixtures at Supercritical Conditions: The Case of the Carbon Dioxide/Vinylidenefluor…
2008
The simultaneous sorption of carbon dioxide and vinylidene fluoride (VDF) in poly(vinylidenefluoride) from their supercritical (sc) mixtures was studied using an experimental method, already described in a previous publication, based on the gas-chromatographic determination of the equilibrium composition of the fluid phase in contact with the polymer. Argon was added to the system as a nonabsorbable molecular probe in the polymer to take into account the effect of the volume swelling on the measurement. Sorption behavior has been studied at 50 °C by changing the composition and the density of the supercritical phase. We have found that VDF dissolves in its polymer with concentrations much l…
Relationships between kinetic constants and the amino acid composition of enzymes from the yeast Saccharomyces cerevisiae glycolysis pathway
2012
The kinetic models of metabolic pathways represent a system of biochemical reactions in terms of metabolic fluxes and enzyme kinetics. Therefore, the apparent differences of metabolic fluxes might reflect distinctive kinetic characteristics, as well as sequence-dependent properties of the employed enzymes. This study aims to examine possible linkages between kinetic constants and the amino acid (AA) composition (AAC) for enzymes from the yeast Saccharomyces cerevisiae glycolytic pathway. The values of Michaelis-Menten constant (K M), turnover number (k cat), and specificity constant (k sp = k cat/K M) were taken from BRENDA (15, 17, and 16 values, respectively) and protein sequences of nine…
Cu2+ Coordination Properties of a 2-Pyridine Heptaamine Tripod: Characterization and Binding Mechanism
2009
The synthesis, protonation, and Cu(2+) coordination chemistry of a tripodal heptaamine ligand (L(1)) functionalized with 2-pyridine fragments at the ends of its three branches are reported. L(1) presents six relatively high protonation constants followed by much more reduced constant that as indicated by the UV-vis and NMR data, occur on the pyridine fragments. p[H]-metric, ESI/MS(+), EPR and UV-vis data show that L(1) is able to form mono-, di-, and trinuclear Cu(2+) complexes. Slippage movements and molecular reorganizations have been observed to occur as a function of p[H] in the 1:1 Cu(2+) complexes. The kinetic studies showed that the complex formation is fast and proceeds through a di…
Multiple interactions between molecular and supramolecular ordering
1999
We report studies of the interplay among processes of molecular conformational changes, spinodal demixing of the solution, and molecular crosslinking involved in the physical gelation of a biopolysaccharide-water system. Multiple interactions and kinetic competition among these processes were studied under largely different absolute and relative values of their individual rates by appropriate choices of the quenching temperature at constant polymer concentration. Quenching temperature strongly affects the rate of growth but not the final value of the fractal dimension of the gel. Kinetic competition plays a central role in determining the final conformation of individual molecules and the s…
Effect of ionic liquid organizing ability and amine structure on the rate and mechanism of base induced elimination of 1,1,1-tribromo-2,2-bis(phenyl-…
2006
Abstract The kinetics of the elimination reaction of 1,1,1-tribromo-2,2-bis(phenyl-substituted)ethanes into the corresponding 1,1-dibromo-2,2-bis(phenyl-substituted)ethenes induced by amines were studied in three room temperature ionic liquids ([BMIM][BF 4 ], [BMIM][PF 6 ], [BdMIM][BF 4 ]). In order to have information about reagent–ionic liquid interactions, the reaction was carried out over the temperature range (293.1–313.1 K). To study the effect of the amine on the rate and occurrence of the elimination reaction, several primary, secondary and tertiary amines with different structure (cyclic and acyclic), basicity and steric requirements were used. The data collected show that the reac…
Kinetically Controlled Sequential Growth of Surface-Grafted Chiral Supramolecular Copolymers.
2016
We report a facile strategy to grow supramolecular copolymers on Au surfaces by successively exposing a surface-anchored monomer to solutions of oppositely charged peptide comonomers. Charge regulation on the active chain end of the polymer sufficiently slows down the kinetics of the self-assembly process to produce kinetically trapped copolymers at near-neutral pH. We thereby achieve architectural control at three levels: The β-sheet sequences direct the polymerization away from the surface, the height of the supramolecular copolymer brushes is well-controlled by the stepwise nature of the alternating copolymer growth, and 2D spatial resolution is realized by using micropatterned initiatin…