1,354,707 research outputs found
Molecular thermodynamics of the denaturation of lysozyme
No full textThe macromol. system where denaturation takes place, is considered from a mol. thermodn. point of view as a convolution of a grand canonical ensemble, gce and a canonical ensemble ce. The former corresponds to the solute, the latter to the solvent. The properties of this system can be represented by a convoluted partition function obtained by the product of a grand canonical partition function, and a canonical partition function. The process of denaturation seems to be related to the formation of a cage of water mols. around the denatured protein
Analysis of variance in determinations of equivalence volume and of the ionic product of water in potentiometric titrations
No full textBy: Braibanti, Antonio; Bruschi, Claudio; Fisicaro, Emilia; Pasquali, Marzia
Homogeneous sets of data from strong acid-strong base potentiometric titrns. in aq. soln. at various const. ionic strengths were analyzed by statistical criteria to see whether the error distribution matches that for the equil. consts. detd. by competitive potentiometric methods using the glass electrode. The titrn. curve can be defined when the estd. equivalence vol. (VEM), with std. deviation (s.d.) σ(VEM), the std. potential E0, with s.d. σ(E0), and the operational ionic product of water Kw* in mV), with s.d. σ(Kw*) [or σ(Ew*)] are known. A special computer program, BEATRIX, was written which optimizes the values of VEM, E0 and Kw* by linearization of the titrn. curve as a Gran plot. Anal. of variance applied to a set of 11 titrns. in 1.0M NaCl medium at 298 K demonstrated that the value of VEM belong to a normal population of points corresponding to individual potential/vol. data-pairs (Ei·,vi) of any titrn., whereas the values of pKw* (or of Ew*) belong to a normal population with members corresponding to individual titrns., which is also the case for the equil. consts. The intertitrn. variation is attributable to the electrochem. component of the system and appears as signal noise distributed over the titrns. The correction for junction-potentials, introduced in a further stage of the program by optimization in a Nernst equation, increases the noise, i.e., σ(pKw*). This correction should therefore be avoided whenever it causes an increase of σ(pKw*). The influence of the ionic medium was examd. by processing data from acid-base titrns. in 0.1M KCl and 0.5M KNO3 media. The titrns. in KCl medium showed the same behavior as those in NaCl medium, but with an s.d. for pKw* that was smaller and close to the expected instrumental noise, whereas the titrns. in nitrate medium had a high noise level and even the detn. of VEM was less certain. Procedures are also proposed for obtaining ref. sets of data and checking the conformity of the solns. and app. to the chosen ref
Hydrophobic hydration processes. General thermodynamic model by thermal equivalent dilution determinations
No full textE. Fisicaro, C. Compari , A. Braibanti
Biophysical Chemistry 151 (2010) 119–138
Hydrophobic hydration processes
General thermodynamic model by thermal equivalent dilution determinations
The “hydrophobic hydration processes” can be satisfactorily interpreted on the basis of a common molecular model for water, consisting of two types of clusters, namely WI and WII accompanied by free molecules WIII. The principle of thermal equivalent dilution (TED) is the potent tool (Ergodic Hypothesis) employed to monitor the water equilibrium and to determine the number ξw of water molecules WIII involved in each process. The hydrophobic hydration processes can be subdivided into two Classes: Class A includes those processes for which the transformation A(−ξwWI→ξwWII+ξwWIII+cavity) takes place with the formation of a cavity, by expulsion of ξw water molecules WIII whereas Class B includes those processes for which the opposite transformation B(−ξwWII−ξwWIII→ξwWI−cavity) takes place with reduction of the cavity, by condensation of ξw water molecules WIII. The number ξw depends on the size of the reactants and measures the extent of the change in volume of the cavity. Disaggregating the thermodynamic functions ΔHapp and ΔSapp as the functions of T (or lnT) and ξw has enabled the separation of the thermodynamic functions into work and thermal components. The work functions ΔGWork, ΔHWork and ΔSWork only refer specifically to the hydrophobic effects of cavity formation or cavity reduction, respectively. The constant self-consistent unitary (ξw=1) work functions obtained from both large and small molecules indicate that the same unitary reaction is taking place, independent from the reactant size. The thermal functions ΔHTh and ΔSTh refer exclusively to the passage of state of water WIII. Essential mathematical algorithms are presented in the appendices
Potentiometric titrations in methanol/water medium: intertitration variablity
No full textHomogeneous sets of data from strong acid-strong base potentiometric titrns. in a mixed solvent medium (9:1 vol./vol., methanol/water), performed by means of the glass electrode, at various const. ionic strengths and with different ref. electrodes, were analyzed by statistical criteria. A standardized procedure was established to obtain reliable potentiometric data in mixed solvents. It has been demonstrated how, with the aid of a proper linearized model, anal. of variance (ANOVA) applied to the standardization titrns. can be used to test the reliability of a potentiometric chain in a medium other than pure water. The error expected in the stability consts. thus evaluated is related to the intertitration error of the operational pKw*, for the same medium and the same chain. The results obtained by applying ANOVA to the mixed solvent data substantially confirm the trend found for aq. media, the intertitration error being larger than the intratitration error for all the parameters investigated (E'0, pKw*', mean equivalence vol.). The stochastic error thus obtained depends on the ionic medium used and on the kind of ref. electrode employed in the electrochem. chain
Swelling efficiency of disintegrants: A direct evaluation through calorimetric analyses
No full textThe behavior of some disintegrants used in pharmaceutical formulations (sodium carboxymethylstarch, sodium carboxymethylcellulose, polyvinylpyrrolidone) and of a new candidate disintegrant (a polymeric derivative of β-cyclodextrin) has been investigated. Calorimetric measurements have been performed on powdered samples of these materials by water addition and allowed the interpretation of the mechanism of interaction with water in terms of two distinct contributions: heat of wetting and heat of swelling
Norme intese a conferire diritti ai singoli e tutela risarcitoria di interessi diffusi: una riflessione a margine della sentenza JP c Ministre de la Transition écologique
No full textThis Insight takes the Court of Justice’s ruling in JP v Ministre de la Transition écologique and Premier Ministre (case C-61/21) as a starting point to reflect, more broadly, on the interpretation of the first condition of State liability for breaches of EU law, i.e. that the rule breached shall be intended to confer rights on individuals. Most notably, it focuses on the implications of such condition on the use of the Francovich remedy in defence of general or ‘diffuse’ interests and criticises the Court’s sharp distinction between general and individual interests in this context. It also observes how the Court’s recent case law traces a distinction between the scope of substantive protection and that of the action for damages: on the one hand, it ensures broad access to national courts to vindicate general or diffuse interests protected by EU law; on the other hand, it excludes the right to damages when the provision in question is not aimed directly and specifically to protect the interests of the individual
A spectroscopic study of anatase properties. II. Characterization of a via-sulfate preparation
No full textTiO2 (anatase), prepd. via a sulfate process was characterized by IR transmittance and UV, visible, and near-IR diffuse reflectance spectroscopy. The spectrum of surface OH groups and of undissociated coordinated water is quite different from that of a via chloride prepn. and from that of most TiO2 prepns. reported in the literature. The redox properties are also different from those of the via chloride prepn. S-contg. impurities, which are quite abundant in samples taken in the early stages of prepn., occur mainly in the form of surface sulfates. These possess variable structure and are highly sensitive to the surface hydration degree and, more in general, to the overall polarity of the surface layer
Flow microcalorimetry applied to solution equilibria: a computer program for the evaluation of enthalpies
No full textA computer program in BASIC language on an IBM XT personal computer, for the evaluation of the enthalpies of proton-ligand-metal equil. reactions directly from flow microcalorimetric data, and the fundamental math. equations underlying it are described. The detn. of the protonation enthalpies of ephedrine and norephedrine in aq. and MeOH/H2O (9:1 vol./vol.) solns, is reported
Cooperativity functions and site binding constants in polyprotic acids
No full textThe partition function ΣA = 1 + β1[H] + β2[H]2 + ... + βi[H]i + ... + βt[H]t was used to interpret the variation in the stepwise formation consts. for the equil. between base A and proton H. The cumulative protonation const. of the satd. complex HtA, βt = [HtA]/([H]t[A]), is equal to the ratio between the formation partition function ΣA and the dissocn. partition function ΣAD, the former giving the probability of finding compds. HiA of the ligand H binding to A and the latter giving the probability of finding species AiA by dissocn. of protons from HtA. The satn. function βt = ΣA/ΣAD can be factorized as a product of stepwise consts. βt = K1.K2...Ki...Kt. Comparisons between K1 and the geometric means βi1/i enable a calcn. to be made of the av. cooperativity consts. Kγ(i) which are explicit functions of i. The cooperativity functions γ(i) require that the equil. are described by means of model partition functions depending on the site affinity const. k and the coeffs. of the cooperativity function γ(i) = exp{2.302[a + b(i-1)]}. By analyzing the cumulative protonation consts. of polysite receptors, it is possible to det. if there actually are sep. classes of sites each with site const. kj and class cooperativity function γ(ij). The anal. of the equil. consts. of some polyprotic acids shows how both the site affinity consts. k and the slope b of log γ(i) depend on the charge d. of the base. The importance of the electrostatic effect in the binding of the proton to the base is clearly apparent. The anal. of the contribution of enthalpy to the cooperativity effect for the same compds. shows varying behavior
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