Search results for " Capacity"
showing 10 items of 902 documents
Heat capacities, volumes and solubilities of pentanol in aqueous alkyltrimethylammonium bromides
1988
Apparent molar heat capacities and volumes of pentanol, 0.05m in decyl-, tetradecyl- and hexadecyltrimethylammonium bromides micellar solutions, were measured at 25°C. They were assumed to approach the standard infinite dilution values and rationalized by means of previously reported equations following which the distribution constant between the aqueous and the micellar phase, heat capacity, and volume of pentanol in both phases are simultaneously derived. The present results show that the volume of the micellar core does not seem to have a significant effect on the apparent molar volume and heat capacity of pentanol in the micellar phase and on the free energy of transfer of pentanol from…
Effects of ultrasound-assisted extraction on physicochemical properties, bioactive compounds, and antioxidant capacity for the valorization of hybrid…
2021
Samples of tree hybrid mandarins (´Clemenvilla`, ´Ortanique` and ´Nadorcott`) were employed to determine the physicochemical properties (increase of conductivity, brix° and pH), bioactive compounds (total phenolic, flavonoid, ascorbic acid and carotenoids content) and antioxidant capacity (DPPH and TEAC) of peels. Mandarin peel extracts were prepared employing ultrasound assisted extraction (400 W, 80% v/v duty cycle, 40ºC). The results were compared to the values of control extraction method. Aqueous ethanol solution (50%, v/v) was used as solvent in solid-liquid ratio of 1:10 (w/v). A 5, 15 and 30 min were applied in both methods to stablish the most effective extraction time. The increas…
Potential role of branched-chain amino acid catabolism in regulating fat oxidation.
2013
Insulin-resistant or obese individuals have increased serum branched-chain amino acid (BCAA) levels. Recent findings relate increased BCAA catabolism to increased fatty acid oxidation and better metabolic health in physically active individuals. We hypothesize that, via glyceroneogenesis, BCAA catabolism mediates increased constitutive use of fatty acids for β-oxidation in subjects with increased inherent or acquired aerobic capacity both during exercise and at rest.
Thermodynamic Properties of Sodium n-Alkanecarboxylates in Water and in Water + Cyclodextrins Mixtures
1998
Densities and heat capacities of water−substrate, water−cyclodextrin, and water−substrate−cyclodextrin systems were determined at 298 K. The substrates studied are sodium n-alkanecarboxylates (CnCOONa) (from sodium acetate to sodium decanoate) and the cyclodextrins are hydroxypropyl-α-cyclodextrin (HP-α-CD), hydroxypropyl-β-cyclodextrin, (HP-β-CD), hydroxypropyl-γ-cyclodextrin (HP-γ-CD) and β-cyclodextrin (β-CD). The apparent molar volumes and heat capacities of CnCOONa in water were calculated as functions of concentration. The standard partial molar properties agree with those obtained by using the additivity rule. HP-β-CD essentially does not affect the thermodynamic properties of C1COON…
N,N,N-Alkyloctyldimethylammonium Chlorides in Water: A Thermodynamic Investigation
1993
Abstract Specific conductivities, densities, heat capacities and enthalpies of dilution at 298 K and osmotic coefficients at 310 K were measured for N,N,N -octylbutyldimethylammonium, N,N,N -octylpentyldimethylammonium, and N,N -dioctyldimethylammonium chlorides in water as functions of concentration. From the specific conductivity data, the CMC and the degree of the counterion dissociation have been calculated. It is shown that additional CH 2 groups in the variable alkyl chain affect both CMC and β less than they do in the single chain surfactants. The partial molar volumes, heat capacities, relative enthalpies, nonideal free energies, and entropies at 298 K were derived as functions of t…
Volume and heat capacity studies to evidence interactions between cyclodextrins and nicotinic acid in water
2008
Density and heat capacity of the water+cyclodextrin (CD), water+nicotinic acid (NA) and water+CD+NA mixtures were determined at 298.15 K. CDs with different cavity size and alkylation were selected. From the experimental data the apparent molar properties were calculated. Assuming the formation of inclusion complexes of 1:1 stoichiometry, these properties were modeled and provided the stability constants of CD/NA inclusion complexes and the corresponding property change. The binding of NA with the smallest sized alpha-cyclodextrin (alpha-CD) generates more stable complexes accompanied by the lower volume and the heat capacity changes. These results are in agreement with earlier proposed bin…
Volumes and heat capacities of the aqueous sodium dodecanoate/sodium perfluorooctanoate mixtures in the presence of β-cyclodextrin
2003
Apparent molar volumes (VΦ) and heat capacities (CΦ) of the sodium dodecanoate (NaL)/sodium perfluorooctanoate (NaPFO) mixtures in the water/β-cyclodextrin (β-CD) solvent as functions of the surfactant total molality (mt) were determined at 25°C. For a given surfactant mixture, VΦ decreases with mt to ca. 0.05 mol kg−1 thereafter it increases tending to a constant value. CΦ displays a behaviour opposite to VΦ. The mt values where the apparent molar properties exhibit extrema are nearly coincident with the critical micellar concentrations determined by conductivity. An equation correlating VΦ to mt was derived by assuming that the equilibria for the 1∶1 surfactant/cyclodextrin complex format…
Environmentally sustainable production of cellulose-based superabsorbent hydrogels
2006
The development of new products and materials, especially those which are non-petrolchemical reserves and based on renewable organic resources, using innovative sustainable processes is nowadays of increasing interest and deserves the attention of both academic and industrial research. Cellulose and its derivatives, as renewable organic resources, have been used to synthesize novel superabsorbent hydrogels. Although the production of cellulose is one of the causes connected to deforestation, the production of suitably engineered cellulose superabsorbent hydrogel materials has been proposed to preserve water in typically arid areas in the world. Paradoxically, divinylsulfone (DVS), a small d…
Thermodynamics of binary mixtures: Volumes, heat capacities, and dilution enthalpies for then-pentanol+2-methyl-2-butanol system
1983
The densities, heat capacities, and dilution enthalpies ofn-pentanol+2-methyl-2-butanol mixtures have been measured, in many cases as a function of temperature, over the complete mole fraction range. Excesses thermodynamic properties, apparent and partial molar heat capacities, volumes and expansibilities were derived. The concentration and temperature dependences of these functions are discussed in terms of the variations of the structure of the system caused by the participation of the two alcohol molecules (with quite different steric hindrance of the alkyl chain around the-OH group) in the dynamic intermolecular association process through hydrogen bonding.
Heat capacities of butanol and pentanol in aqueous dodecyltrimethylammonium bromide solutions
1987
Heat capacities of the ternary systems water-dodecyltrimethylammonium bromide (DTAB)-butanol and water-DTAB-pentanol were measured at 25°C. The standard partial molar heat capacities of pentanol in micellar solutions show a maximum at about 0.35 mol-kg−1 DTAB that has been attributed to a micellar structural transition. This maximum tends to vanish by increasing the alcohol concentration and by decreasing the alcohol alkyl chain length; in the case of butanol it was not detected. The behavior of the standard partial molar heat capacities of alcohols in micellar solutions in the region above the cmc and below the structural transition was explained using a previously reported mass-action mod…