Search results for "THERMODYNAMICS"
showing 10 items of 2774 documents
Diffusion technique for the generation of gaseous halogen standards
2009
Abstract Halogens are known to play an important role in the tropospheric ozone-depletion chemistry and are of special interest because of their influence on the atmospheric oxidation capacity. In this paper, we investigate the application of a capillary diffusion technique for the generation of gaseous halogen standards like Br 2 , IBr, ICl and I 2 . The influence of capillary dimension (i.e. length and inner diameter), ambient pressure and headspace volume of the diffusion vessel on the test gas output has been evaluated. The experimental output rates are determined from the mass loss of the analyte vessel on a regular schedule and compared with their respective theoretical predictions. W…
Thermodynamic Study of Small Hydrophobic Ions at the Water–Lipid Interface
2001
Abstract The thermodynamics of binding of two small hydrophobic ions such as norharman and tryptophan to neutral and negatively charged small unilamellar vesicles was investigated at pH 7.4 using fluorescence spectroscopy. Vesicles were formed at room temperature from dimyristoyl phosphatidylcholine (DMPC) or DMPC/dimyristoylphosphatidic acid and DMPC/dimyristoylphosphatidylglycerol. The changes in fluorescence properties were used to obtain association isotherms at variable membrane surface negative charge and at different ionic strengths. The binding of both ions was found to be quantitatively enhanced as the percentage of negative phospholipid increases in the membrane. Also, a decrease …
Application of a Novel Refinement Method for Accurate Determination of Chemical Diffusion Coefficients in Electroactive Materials by Potential Step T…
2005
We describe application of a novel refinement method for an accurate determination of the chemical diffusion coefficient, D, and the generalized kinetic parameter, A, from experimental potentiostatic intermittent titration technique (PITT) data suited for a variety of electrochemically doped electroactive polymers and inorganic intercalation host materials. The proposed, simple, two-step refinement procedure, based on earlier derived analytical expressions for the PITT response, is exemplified by the analysis of chronoamperometric responses to small-amplitude potential perturbation for p- and n-doped poly(fluorenone-bithiophene) (PFDOBT-HH) thin film electrode. The initial p-doping and the …
A second strain gradient elasticity theory with second velocity gradient inertia – Part II: Dynamic behavior
2013
Abstract This paper is the sequel of a companion Part I paper devoted to the constitutive equations and to the quasi-static behavior of a second strain gradient material model with second velocity gradient inertia. In the present Part II paper, a multi-cell homogenization procedure (developed in the Part I paper) is applied to a nonhomogeneous body modelled as a simple material cell system, in conjunction with the principle of virtual work (PVW) for inertial actions (i.e. momenta and inertia forces), which at the macro-scale level takes on the typical format as for a second velocity gradient inertia material model. The latter (macro-scale) PVW is used to determine the equilibrium equations …
A gradient elasticity theory for second-grade materials and higher order inertia
2012
Abstract Second-grade elastic materials featured by a free energy depending on the strain and the strain gradient, and a kinetic energy depending on the velocity and the velocity gradient, are addressed. An inertial energy balance principle and a virtual work principle for inertial actions are envisioned to enrich the set of traditional theoretical tools of thermodynamics and continuum mechanics. The state variables include the body momentum and the surface momentum, related to the velocity in a nonstandard way, as well as the concomitant mass-accelerations and inertial forces, which do intervene into the motion equations and into the force boundary conditions. The boundary traction is the …
NMR Spectroscopic Evidence for the Intermediacy of XeF3− in XeF2/F− Exchange, Attempted Syntheses and Thermochemistry of XeF3− Salts, and Theoretical…
2010
The existence of the trifluoroxenate(II) anion, XeF(3)(-), had been postulated in a prior NMR study of the exchange between fluoride ion and XeF(2) in CH(3)CN solution. The enthalpy of activation for this exchange, ΔH(⧧), has now been determined by use of single selective inversion (19)F NMR spectroscopy to be 74.1 ± 5.0 kJ mol(-1) (0.18 M) and 56.9 ± 6.7 kJ mol(-1) (0.36 M) for equimolar amounts of [N(CH(3))(4)][F] and XeF(2) in CH(3)CN solvent. Although the XeF(3)(-) anion has been observed in the gas phase, attempts to prepare the Cs(+) and N(CH(3))(4)(+) salts of XeF(3)(-) have been unsuccessful, and are attributed to the low fluoride ion affinity of XeF(2) and fluoride ion solvation in…
Theoretical Study on the Photo-Oxidation and Photoreduction of an Azetidine Derivative as a Model of DNA Repair
2021
Photocycloreversion plays a central role in the study of the repair of DNA lesions, reverting them into the original pyrimidine nucleobases. Particularly, among the proposed mechanisms for the repair of DNA (6-4) photoproducts by photolyases, it has been suggested that it takes place through an intermediate characterized by a four-membered heterocyclic oxetane or azetidine ring, whose opening requires the reduction of the fused nucleobases. The specific role of this electron transfer step and its impact on the ring opening energetics remain to be understood. These processes are studied herein by means of quantum-chemical calculations on the two azetidine stereoisomers obtained from photocyc…
Thermodynamic parameters of the interaction between Co(II) bovine carbonic anhydrase and anionic inhibitors
1992
The pH dependence of the apparent affinity constants of perchlorate for cobalt(II)bovine carbonic anhydrase II has been measured by electronic absorption spectroscopy. The obtained data have been analyzed in terms of the ionization of two acidic groups of CoBCAII, and the affinity of perchlorate for the two water-containing species of the enzyme have been estimated. Furthermore, the affinity constants of nitrate, perchlorate, and azide for CoBCAII in the temperature range 5 degrees C-30 degrees C have been determined by spectrophotometric titrations at pH 7. The affinity constants for these ligands decrease with increasing temperatures. The temperature dependence of binding was used to esti…
Water Structure Recovery in Chaotropic Anion Recognition: High-Affinity Binding of Dodecaborate Clusters to γ-Cyclodextrin
2015
Dodecaborate anions of the type B12X12(2-) and B12X11Y(2-) (X=H, Cl, Br, I and Y=OH, SH, NH3(+), NR3(+)) form strong (K(a) up to 10(6) L mol(-1), for B12Br12(2-)) inclusion complexes with γ-cyclodextrin (γ-CD). The micromolar affinities reached are the highest known for this native CD. The complexation exhibits highly negative enthalpies (up to -25 kcal mol(-1)) and entropies (TΔS up to -18.4 kcal mol(-1), both for B12I12(2-)), which position these guests at the bottom end of the well-known enthalpy-entropy correlation for CDs. The high driving force can be traced back to a chaotropic effect, according to which chaotropic anions have an intrinsic affinity to hydrophobic cavities in aqueous …
Fractional-order constitutive equations in mechanics and thermodynamics
2019
This chapter is devoted to the application of fractional calculus in mechanics of materials and thermodynamics. The use of fractional calculus in mechanics is related to the definition of fractional-order constitutive equations leading to the class of fractional hereditariness. In this regard, a brief description of the classical rheological models of material hereditariness and a comparison with the fractional elements are reported. It is shown that a rheological hierarchy corresponding to the fractional order stress-strain relation may be defined. Such a model provides a multi-scale mechanical picture of the power-law hereditariness and it leads toward an unique definition of material fre…