A potentiometric and spectrofluorimetric approach to unravel inhibitory effects of semi- and thiosemicarbazones on mushroom tyrosinase activity.

The inhibitory effects on mushrooms tyrosinase activity of some semi- and thiosemicarbazones were investigated. While the semicarbazones are inactive, the thiosemicarbazones are, in general, more active than the reference (kojic acid, IC50 = 70 µM), with maximum activity obtained with benzaldehyde thiosemicarbazone (IC50 = 7 µM). These inhibitors probably act by coordination of the copper(II) metal ions in the active site of tyrosinase: effectively, potentiometric studies conducted in water solutions confirm that the most active thiosemicarbazone is a good ligand for copper(II) ions. The tyrosinase CD spectra do not show any significant difference by addition of an inhibitor or an inactive compound. On the contrary, interesting results were obtained by spectrofluorimetric titrations of mushrooms tyrosinase aqueous solutions with some of the investigated compounds, giving helpful information about possible mechanism of action. The thiosemicarbazones here reported are not cytotoxic on human fibroblasts and do not activate cells in a pro-inflammatory way.

Hydroxyphenyl thiosemicarbazones as inhibitors of mushroom tyrosinase and antibrowning agents.

Tyrosinase is a metalloenzyme involved in o-hydroxylation of monophenols and oxidation of o-diphenols to o-quinones, with formation of brown or black pigments (melanines). Tyrosinase inhibitors are of great interest in medicine and cosmetics (skin whitening compounds), but also in food and beverage industry (antibrowning agents). Here we report on the activity as mushroom tyrosinase inhibitors of a series of hydroxyphenyl thiosemicarbazones (1-5): one of them revealed an inhibitory activity stronger than kojic acid, used as reference. Enzymatic inhibition activity was confirmed by colorimetric measurements on small wheels of Fuji apples treated with the hydroxyphenyl thiosemicarbazones. The mechanism of action of compounds 1-5 was investigated by molecular modelling and by studying in solution their speciation with Cu(II) ions, the ions in the active site of the enzyme. Finally, compounds 1-5 were tested on human fibroblasts: they are not cytotoxic and they do not activate cells in a pro-inflammatory way.

Antiviral activity and metal ion-binding properties of some 2-hydroxy-3-methoxyphenyl acylhydrazones.

Here we report on the results obtained from an antiviral screening, including herpes simplex virus, vaccinia virus, vesicular stomatitis virus, Coxsackie B4 virus or respiratory syncytial virus, parainfluenza-3 virus, reovirus-1 and Punta Toro virus, of three 2-hydroxy-3-methoxyphenyl acylhydrazone compounds in three cell lines (i.e. human embryonic lung fibroblast cells, human cervix carcinoma cells, and African Green monkey kidney cells). Interesting antiviral EC50 values are obtained against herpes simplex virus-1 and vaccinia virus. The biological activity of acylhydrazones is often attributed to their metal coordinating abilities, so potentiometric and microcalorimetric studies are here discussed to unravel the behavior of the three 2-hydroxy-3-methoxyphenyl compounds in solution. It is worth of note that the acylhydrazone with the higher affinity for Cu(II) ions shows the best antiviral activity against herpes simplex and vaccinia virus (EC50 ~ 1.5 µM, minimal cytotoxic concentration = 60 µM, selectivity index = 40).

A versatile salicyl hydrazonic ligand and its metal complexes as antiviral agents.

Acylhydrazones are very versatile ligands and their coordination properties can be easily tuned, giving rise to metal complexes with different nuclearities. In the last few years, we have been looking for new pharmacophores able to coordinate simultaneously two metal ions, because many enzymes have two metal ions in the active site and their coordination can be a successful strategy to inhibit the activity of the metalloenzyme. As a part of this ongoing research, we synthesized the acylhydrazone H2L and its complexes with Mg(II), Mn(II), Co(II), Ni(II), Cu(II) and Zn(II). Their characterization, both in solution--also by means of potentiometric studies--and in the solid state, evidenced the ability of the o-vanillin hydrazone scaffold to give rise to different types of metal complexes, depending on the metal and the reaction conditions. Furthermore, we evaluated both the free ligand and its metal complexes in in vitro studies against a panel of diverse DNA- and RNA-viruses. In particular, the Mg(II), Mn(II), Ni(II) and Zn(II) complexes had EC50 values in the low micromolar range, with a pronounced activity against vaccinia virus.

Hydrophobic hydration processes thermal and chemical denaturation of proteins.

The hydrophobic hydration processes have been analysed under the light of a mixture model of water that is assumed to be composed by clusters (W(5))(I), clusters (W(4))(II) and free water molecules W(III). The hydrophobic hydration processes can be subdivided into two Classes A and B. In the processes of Class A, the transformation A(-ξ(w)W(I)→ξ(w)W(II)+ξ(w)W(III)+cavity) takes place, with expulsion from the bulk of ξ(w) water molecules W(III), whereas in the processes of Class B the opposite transformation B(-ξ(w)W(III)-ξ(w)W(II)→ξ(w)W(I)-cavity) takes place, with condensation into the bulk of ξ(w) water molecules W(III). The thermal equivalent dilution (TED) principle is exploited to determine the number ξ(w). The denaturation (unfolding) process belongs to Class A whereas folding (or renaturation) belongs to Class B. The enthalpy ΔH(den) and entropy ΔS(den) functions can be disaggregated in thermal and motive components, ΔH(den)=ΔH(therm)+ΔH(mot), and ΔS(den)=ΔS(therm)+ΔS(mot), respectively. The terms ΔH(therm) and ΔS(therm) are related to phase change of water molecules W(III), and give no contribution to free energy (ΔG(therm)=0). The motive functions refer to the process of cavity formation (Class A) or cavity reduction (Class B), respectively and are the only contributors to free energy ΔG(mot). The folded native protein is thermodynamically favoured (ΔG(fold)≡ΔG(mot)<0) because of the outstanding contribution of the positive entropy term for cavity reduction, ΔS(red)≫0. The native protein can be brought to a stable denatured state (ΔG(den)≡ΔG(mot)<0) by coupled reactions. Processes of protonation coupled to denaturation have been identified. In thermal denaturation by calorimetry, however, is the heat gradually supplied to the system that yields a change of phase of water W(III), with creation of cavity and negative entropy production, ΔS(for)≪0. The negative entropy change reduces and at last neutralises the positive entropy of folding. In molecular terms, this means the gradual disruption by cavity formation of the entropy-driven hydrophobic bonds that had been keeping the chains folded in the native protein. The action of the chemical denaturants is similar to that of heat, by modulating the equilibrium between W(I), W(II), and W(III) toward cavity formation and negative entropy production. The salting-in effect produced by denaturants has been recognised as a hydrophobic hydration process belonging to Class A with cavity formation, whereas the salting-out effect produced by stabilisers belongs to Class B with cavity reduction. Some algorithms of denaturation thermodynamics are presented in the Appendices.

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 W(I) and W(II) accompanied by free molecules W(III). The principle of thermal equivalent dilution (TED) is the potent tool (Ergodic Hypothesis) employed to monitor the water equilibrium and to determine the number xi(w) of water molecules W(III) involved in each process. The hydrophobic hydration processes can be subdivided into two Classes: Class A includes those processes for which the transformation A(-xi(w)W(I)-->xi(w)W(II)+xi(w)W(III)+cavity) takes place with the formation of a cavity, by expulsion of xi(w) water molecules W(III) whereas Class B includes those processes for which the opposite transformation B(-xi(w)W(II)-xi(w)W(III)-->xi(w)W(I)-cavity) takes place with reduction of the cavity, by condensation of xi(w) water molecules W(III). The number xi(w) depends on the size of the reactants and measures the extent of the change in volume of the cavity. Disaggregating the thermodynamic functions DeltaH(app) and DeltaS(app) as the functions of T (or lnT) and xi(w) has enabled the separation of the thermodynamic functions into work and thermal components. The work functions DeltaG(Work), DeltaH(Work) and DeltaS(Work) only refer specifically to the hydrophobic effects of cavity formation or cavity reduction, respectively. The constant self-consistent unitary (xi(w)=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 DeltaH(Th) and DeltaS(Th) refer exclusively to the passage of state of water W(III). Essential mathematical algorithms are presented in the appendices.

Thermodynamics of micelle formation in water, hydrophobic processes and surfactant self-assemblies.

The critical micelle concentration (c.m.c.) for four cationic surfactants, alkyl-trimethyl-ammonium bromides, was determined as a function of temperature by conductivity measurements. The values of the standard free energy of micellisation DeltaG degrees(mic) at different temperatures were calculated by using a pseudo-phase transition model. Then, from the diagram (-DeltaG degrees(mic)/T)=f(1/T), the thermodynamic functions DeltaH(app) and DeltaS(app) were calculated. From the plots DeltaH(app)=f(T) and DeltaS(app) = f(ln T) the slopes DeltaC(p) = n(w(H))C(p,w) and DeltaC(p)=n(w(S))C(p,w) were calculated, with the numbers n(w(H)) and n(w(S)) negative and equal and therefore defined simply as n(w). The number n(w)<0, indicating condensed water molecules, depends on the reduction of cavity that takes place as a consequence of the coalescence of the cavities previously surrounding the separate aliphatic or aromatic moieties. The analysis, based on a molecular model consisting of three forms of water, namely W(I), W(II), and W(III), respectively, was extended to several other types of surfactants for which c.m.c. data had been published by other authors. The results of this analysis form a coherent scheme consistent with the proposed molecular model. The enthalpy for all the types of surfactant is described by DeltaH(app)= -3.6 + 23.1xi(w)-xi(w)C(p,w)T and the entropy by DeltaS(app)= +10.2+428xi(w)-xi(w)C(p,w) ln T where xi(w)= |n(w)| represents the number of molecules W(III) involved in the reaction. The term Deltah(w)= +23.1 kJ mol(-1) xi(w)(-1) indicates an unfavourable endothermic contribution to enthalpy for reduction of the cavity whereas the term Deltas(w)= +428 J K(-1) mol(-1) xi(w)(-1) represents a positive entropy contribution for reduction of the cavity, what is the driving force of hydrophobic association. The processes of non polar gas dissolution in water and of micelle formation were found to be strictly related: they are, however, exactly the opposite of one another. In micelle formation no intermolecular electronic short bond is formed. We propose, therefore, to substitute the term "hydrophobic bond" with that of "hydrophobic association".

Self-assembly and anion encapsulation properties of cavitand-based coordination cages.

Two novel classes of cavitand-based coordination cages 7a--j and 8a--d have been synthesized via self-assembly procedures. The main factors controlling cage self-assembly (CSA) have been identified in (i) a P--M--P angle close to 90 degrees between the chelating ligand and the metal precursor, (ii) Pd and Pt as metal centers, (iii) a weakly coordinated counterion, and (iv) preorganization of the tetradentate cavitand ligand. Calorimetric measurements and dynamic (1)H and (19)F NMR experiments indicated that CSA is entropy driven. The temperature range of the equilibrium cage-oligomers is determined by the level of preorganization of the cavitand component. The crystal structure of cage 7d revealed the presence of a single triflate anion encapsulated. Guest competition experiments revealed that the encapsulation preference of cages 7b,d follows the order BF(4)(-) > CF(3)SO(3)(-) >> PF(6)(-) at 300 K. ES-MS experiments coupled to molecular modeling provided a rationale for the observed encapsulation selectivities. The basic selectivity pattern, which follows the solvation enthalpy of the guests, is altered by size and shape of the cavity, allowing the entrance of an ancillary solvent molecule only in the case of BF(4)(-).

Synthesis and surface and antimicrobial properties of novel cationic surfactants.

A series of surfactants with tuned polarity were prepared, including a new class of compounds: gluco-pyridinium surfactants. Pure anomers were obtained by chromatographic separation. The conductivity and surface tension of surfactant solutions in water were measured, and provided interesting information regarding their aggregation behavior. Peculiarities were observed in the premicellar range. Tensidic parameters correlated with antimicrobial activity. A few parameters, mainly the hydrophobicity of the headgroup, may play a role in finding more efficient antimicrobial structures.

Synthesis and correlations between experimental and calculated lipophilic indices of new 1,2-benzisothiazole derivatives with potential antimicrobial activity.

Five series of new hydrazones (1a-m, 2a-m, 3a-m, 4a-m, 5a-m) with potential antimicrobial activity were synthesized from cyclic (1 and 4) or acyclic (2, 3 and 5) 1,2-benzisothiazolylhydrazides and characterized. Condensation of the appropriate hydrazide with aldehydes afforded the designed compounds. Aldehydes carrying different hydrophobic substituents were used and the five series were designed so that the hydrophobicity also varied among congeners. Retention parameters were measured by HPLC employing a deactivated alkyl-bonded silica column and different eluent systems (methanol-aqueous buffer, acetonitrile-water). The hydrophobicity chromatographic parameters (log k') were compared with those provided by measurement of partitioning of solutes between n-octanol and water (log P), and with theoretical partition coefficients, calculated by a fragmental method and scaled according to the experimental values. Correlations between different hydrophobicity indices are reported and discussed.

Effect of drying methods on retention of moist sucralfate gel properties.

The aim of this work was to find a drying procedure for moist sucralfate gel capable of producing dried sucralfate gel that retains the original gel properties of bioadhesion, rheology, and micromeritics. Spray-drying and microwave-drying procedures were employed. Mannitol was used as a gel-protective substance during the drying processes. The spray drying of moist sucralfate gel gave rise to a powder whose water suspensions showed significantly reduced viscosity. The bioadhesion of spray-dried sucralfate gel was strongly reduced by drying. When mannitol was used as a gel protector, the spray-dried sucralfate in part maintained the original bioadhesion of moist sucralfate gel. The preparation of a dried sucralfate gel retaining the bioadhesion characteristics, avoiding the use of mannitol, was made possible using the microwave-drying procedure. The microwave-dried product possesses a granular morphology suitable for direct compression because it is a free flowing and strongly coherent granular powder.

A software for the estimation of binding parameters of biochemical equilibria based on statistical probability model.

An algorithm is proposed for the estimation of binding parameters for the interaction of biologically important macromolecules with smaller ones from electrometric titration data. The mathematical model is based on the representation of equilibria in terms of probability concepts of statistical molecular thermodynamics. The refinement of equilibrium concentrations of the components and estimation of binding parameters (log site constant and cooperativity factor) is performed using singular value decomposition, a chemometric technique which overcomes the general obstacles due to near singularity. The present software is validated with a number of biochemical systems of varying number of sites and cooperativity factors. The effect of random errors of realistic magnitude in experimental data is studied using the simulated primary data for some typical systems. The safe area within which approximate binding parameters ensure convergence has been reported for the non-self starting optimization algorithms.

Effect of the Counterion on Thermodynamic Properties of Aqueous Micellar Solutions of 1-(3,3,4,4,5,5,6,6,6-Nonafluorohexyl) Pyridinium Halides

We report a thermodynamic study of the aqueous solutions of 1-(3,3,4,4,5,5,6,6,6-nonafluorohexyl) pyridinium chloride, bromide, and iodide and N-octyl pyridinium iodide. Dilution enthalpies and osmotic coefficients of the aqueous solutions of these cationic surfactants have been measured at 313 K as a function of the concentration. The experimental data are expressed in terms of apparent and partial molar quantities. The changes in thermodynamic properties upon micellization have been obtained from the experimental data by using a pseudo phase transition approach. The cmc at 313 K have been evaluated from the plot of the milliosmolality, the measured quantity, vs molality. From the comparison with the trends of the enthalpies at 298 K of the same set of compounds, the effect of temperature on the energetics of their solutions can be derived. The trends of thermodynamic properties vs molality and the micellization parameters confirm that the effect of the counterions, however strong and inversely proportional to the radius of the hydrated counterion, seems to be reduced with respect to the hydrogenated analogs. The curves of the apparent and partial molar enthalpies vs m for the bromide and the iodide are lowered, with respect to the curve of the chloride, by an amount comparable to that at 298 K. This observation suggests that the changes in the absolute trends of the curves and in the micellization enthalpies are due to the modification of the more mobile hydrophobic hydration shell of the perfluoroalkyl chain, whereas the hydration sphere of the counterions is practically unaffected. The heat capacity data and the comparison with the behaviour of hydrogenated analogs is in agreement with the above observation. The trends of the free energies confirm that the degree of counterion binding, beta, and the aggregation number, n, increase with the increasing of the radius of the hydrated counterion.

Thermodynamic Study of Aqueous Micellar Solutions of Biologically Active Bisquaternary Ammonium Chlorides

Thermodynamic properties of aqueous solution of bisquaternary ammonium salts, which are derivatives of N,N-bisdimethyl-1,2-ethanediamine (bis-Cn-BEC), of general formula/CnH2n+1OOCCH2(CH3)2N$^{\oplus}CH2CH2N$^{\oplus}(CH3)2CH2COOCn-H2n+1/2Cl-(bis-Cn-BEC, where the subscript n stands for the number of carbon atoms of the alkyl chain bound to the carboxyl group) are here reported and compared with those of the corresponding monomers. Dilution enthalpies have been measured by means of a flow type microcalorimeter at 313 K, and densities have been measured by means of a vibrating tube densimeter at 298 K. Apparent and partial molar quantities have been obtained from the experimental data and expressed as a function of molalities, assuming the infinite dilution as standard state. The changes in enthalpy and in volume upon micellization have been evaluated by assuming the pseudo-phase transition model. From the calculated enthalpy changes at 313 K and that previously reported at 298 K, the changes in heat capacity for micellization has been evaluated. The data suggest the hypothesis that the alkyl chain in the dimers are already partially associated in solution. Moreover, the trends of the cmc as a function of the chain length for monomers and dimers suggest that the association of the chains probably leaves out the first three methylene groups of the alkyl chains bound to the carboxylic groups. The packing parameter, P, gives 0.37 for bis-C10-BEC, and the formation of rod-like micelles is therefore suggested.

Interaction between model membranes and a new class of surfactants with antioxidant function.

The effect of two series of amphiphilic quaternary ammonium salts on some properties of phospholipid membranes was studied. The compounds of one series, N-benzyl-N,N-dimethyl-N-alkyl ammonium bromides, exert a destructive effect on membranes and are treated as reference compounds. The compounds of the other series, N-(3,5-di-t-butyl-4-hydroxy)benzyl-N,N-dimethyl-N-alkyl ammonium bromides, are derivatives of the former ones, exhibit antioxidant properties, and do only relatively slight damage to the membranes. The aim of the work was to explain the difference in molecular interaction with membranes between the two kinds of hydrophobic compounds. Thermodynamic methods, a new mixing technique, and monolayer and quantum calculation methods were used. It has been shown that the antioxidant molecules are less hydrophobic than those of the reference compounds and disturb the membrane organization to a lesser extent. On the basis of monolayer data, we suggest that the studied antioxidant behaves like a substitutional impurity, whereas the reference behaves like an interstitial one.

[Spontaneous hematoma of the rectus muscle]. / L'ematoma spontaneo del muscolo retto.

The possibility of heart surgery and vascular surgery and the increased number of dialyzed patients receiving dicourmarin and heparin treatment raises the question of the probable rupture of the abdominal muscles, in particular the rectus muscles, following the onset of lancing abdominal pain. The authors report a clinical case referred to them in emergency conditions. They examine the possible etiopathogenetic causes and underline the symptoms of acute abdomen in patients being treated with anti-coagulating drugs.

Calculation of site affinity constants and cooperativity coefficients for binding of ligands and/or protons to macromolecules. I. Generation of partition functions and mass balance equations.

The thermodynamics of binding of a ligand A and/or proton H to a macromolecule M is treated by the partition function method. In complex systems, the representation of the equilibria by means of cumulative constants beta PQR used as coefficients in partition functions ZM, ZA, and ZH is ill-suited to least-squares refinement procedures because the cumulative constants are interrelated by common cooperativity functions gamma j(i) and common site affinity constants kappa j. There is therefore the need to express ZM, ZA, ZH as functions of site constants kappa j and cooperativity coefficients bj. This is done by developing an algebra of partition functions based on the following concepts: (i) factorability of partition functions; (ii) binary generating function Jj = (1 + kappa j[Y])i tau for each class j of sites, represented by column (Jj) and row (Jj) vectors; (iii) cooperativity between sites of one class described by functions gamma j(i), represented by diagonal matrices gamma j; (iv) probability of finding microspecies represented by elements of tensor product matrix Ll = (J1)[J2]; (v) statistical factors mij obtained from Newton polynomials, Jj; (vi) power operators Oi', O(i-l)', and O(i tau-l)', transforming vectors Jj; and (vii) operators Oi or O(i-l) indicating tensor products of i or (i-l) vectors Jj. Vectors Jj combined in tensors Ll give rise to both an affinity/cooperativity space and a parallel index space. The partition functions ZM, ZA, and ZH and the total amounts TM, TA, and TH can be obtained as an appropriate sum of elements of matrices Ll, each of which is represented in an index space by a combination p1, p2,...q1, q2,...r1, r2,... of indices ij. From these indices the contribution of that element to partition function ZM, ZA, or ZH and to total amount TM, TA, or TH is calculated in the affinity/cooperativity space as product of factors: [i tau !/i !(i tau-i)!]kappa ij(exp[bj (i-1)i])[X]i, i being any index p, q, r and X any component M, A, or H. Future applications of this algorithm to practical problems of macromolecule-ligand-proton equilibria are outlined.

Calculation of site affinity constants and cooperativity coefficients for binding of ligands and/or protons to macromolecules. II. Relationships between chemical model and partition function algorithm.

The relationships between the chemical properties of a system and the partition function algorithm as applied to the description of multiple equilibria in solution are explained. The partition functions ZM, ZA, and ZH are obtained from powers of the binary generating functions Jj = (1 + kappa j gamma j,i[Y])i tau j, where i tau j = p tau j, q tau j, or r tau j represent the maximum number of sites in sites in class j, for Y = M, A, or H, respectively. Each term of the generating function can be considered an element (ij) of a vector Jj and each power of the cooperativity factor gamma ij,i can be considered an element of a diagonal cooperativity matrix gamma j. The vectors Jj are combined in tensor product matrices L tau = (J1) [J2]...[Jj]..., thus representing different receptor-ligand combinations. The partition functions are obtained by summing elements of the tensor matrices. The relationship of the partition functions with the total chemical amounts TM, TA, and TH has been found. The aim is to describe the total chemical amounts TM, TA, and TH as functions of the site affinity constants kappa j and cooperativity coefficients bj. The total amounts are calculated from the sum of elements of tensor matrices Ll. Each set of indices (pj..., qj..., rj...) represents one element of a tensor matrix L tau and defines each term of the summation. Each term corresponds to the concentration of a chemical microspecies. The distinction between microspecies MpjAqjHrj with ligands bound on specific sites and macrospecies MpAqHR corresponding to a chemical stoichiometric composition is shown. The translation of the properties of chemical model schemes into the algorithms for the generation of partition functions is illustrated with reference to a series of examples of gradually increasing complexity. The equilibria examined concern: (1) a unique class of sites; (2) the protonation of a base with two classes of sites; (3) the simultaneous binding of ligand A and proton H to a macromolecule or receptor M with four classes of sites; and (4) the binding to a macromolecule M of ligand A which is in turn a receptor for proton H. With reference to a specific example, it is shown how a computer program for least-squares refinement of variables kappa j and bj can be organized. The chemical model from the free components M, A, and H to the saturated macrospecies MpAQHR, with possible complex macrospecies MpAq and AHR, is defined first.(ABSTRACT TRUNCATED AT 250 WORDS)

Potentiometric titrations in methanol/water medium: Intertitration variability.

Homogeneous sets of data from strong acid-strong base potentiometric titrations in a mixed solvent medium (9:1 v/v methanol/water), performed by means of the glass electrode, at various constant ionic strengths and with different reference electrodes, have been analysed by statistical criteria. A standardized procedure has been established to obtain reliable potentiometric data in mixed solvents. It has been demonstrated how, with the aid of a proper linearized model, analysis of variance (ANOVA) applied to the standardization titrations can be used to test the reliability of a potentiometric chain in a medium other than pure water. The error expected in the stability constants thus evaluated is related to the intertitration error of the operational pK*(')(w), 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 aqueous media, the intertitration error being larger than the intratitration error for all the parameters investigated (E(')(0), pK*(')(w), mean equivalence volume). The stochastic error thus obtained depends on the ionic medium used and on the kind of reference electrode employed in the electrochemical chain.

Analysis of variance in determinations of equivalence volume and of the ionic product of water in potentiometric titrations.

Homogeneous sets of data from strong acid-strong base potentiometric titrations in aqueous solution at various constant ionic strengths have been analysed by statistical criteria. The aim is to see whether the error distribution matches that for the equilibrium constants determined by competitive potentiometric methods using the glass electrode. The titration curve can be defined when the estimated equivalence volume VEM, with standard deviation (s.d.) sigma (VEM), the standard potential E(0), with s.d. sigma(E(0)), and the operational ionic product of water K(*)(w) (or E(*)(w) in mV), with s.d. sigma(K(*)(w)) [or sigma(E(*)(w))] are known. A special computer program, BEATRIX, has been written which optimizes the values of VEM, E(0) and K(*)(w) by linearization of the titration curve as a Gran plot. Analysis of variance applied to a set of 11 titrations in 1.0M sodium chloride medium at 298 K has demonstrated that the values of VEM belong to a normal population of points corresponding to individual potential/volume data-pairs (E(i); v(i)) of any titration, whereas the values of pK(*)(w) (or of E(*)(w)) belong to a normal population with members corresponding to individual titrations, which is also the case for the equilibrium constants. The intertitration variation is attributable to the electrochemical component of the system and appears as signal noise distributed over the titrations. The correction for junction-potentials, introduced in a further stage of the program by optimization in a Nernst equation, increases the noise, i.e., sigma(pK(*)(w)). This correction should therefore be avoided whenever it causes an increase of sigma(pK(*)(w)). The influence of the ionic medium has been examined by processing data from acid-base titrations in 0.1M potassium chloride and 0.5M potassium nitrate media. The titrations in potassium chloride medium showed the same behaviour as those in sodium chloride medium, but with an s.d. for pK(*)(w) that was smaller and close to the expected instrumental noise, whereas the titrations in nitrate medium had a high noise level and even the determination of VEM was less certain. Procedures are also proposed for obtaining reference sets of data and checking the conformity of the solutions and apparatus to the chosen reference.