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The 2D phase transition of thymine, uracil, guanine and coumarin, adsorbed at the Hg electrode/aqueous solution interface, is rationalised on the basis of the model proposed in Part 1, J. Chem. Soc., FaradayTrans., 1994, 90, 2925. The results together with that obtained for adenine, are compared with the relevant quantities calculated by using molecular descriptors (dipole moments and polarizabilities). Finally, a value of the standard enthalpy phase-transition variation, averaged over the results collected for the five compounds is estimated and discussed.

The dissociation of the 4-chlorotoluene radical anion, in the corresponding arylic open-shell and chloride closed-shell species, has been studied using semiempirical and ab initio methods, in both cases ROHF and UHF calculations have been performed. It is shown that semiempirical PESs are not reliable. While, at least a 3–21g basis set is needed to obtain an ab initio single determinant global dissociative path (which is qualitatively consistent with the experimental evidence). In addition, UMP2, ROMP2, SOCI dissociative PESs are discussed, suggesting that ROHF-based methods are preferable to UHF-based ones. This is shown to depend on the spin contamination affecting the UHF wavefunction.

The Frumkin interaction parameter between aromatic molecules (neutral form) adsorbed from aqueous solution on mercury electrode, is related to the balance of energy dispersion terms (adsorbate-adsorbate) and water-water molecular interaction reflecting the role played by substitution on the electrode surface of water by the aromatic molecule. The interaction among adsorbed aromatics (in neutral form) is always attractive, so that the sign of a F (Frumkin parameter, positive or negative) arises from that kind of balance. For aromatic anions, taking into account a large partial charge transfer from the adsorbate to the metal surface, the change of ΔG ADS 0 at varying the coverage (θ) is mainly due to electrostatic repulsion among charge adsorbed particles.

Significance The role of the electron spin in chemistry and biology has been receiving much attention because of a plausible relation to electromagnetic field effects on living organisms. Part of the difficulty in studying the subject arises from the lack of a physical model that can rationalize these phenomena. Recently the chiral-induced spin selectivity effect was observed in electron transmission through organic molecules. The question is to what extent the effect takes place in proteins. In the present study, we probed bacteriorhodopsin embedded in its native membrane environment. We observed clear evidence for spin-dependent electron transmission through this system. The results point to the possibility that the effect may play a role in electron transfer in biological systems.

Glassy carbon (GC) surfaces are functionalized exploiting the electrochemical reduction of asymmetric iodonium salts of the general formula [4-Z C6H4 I+ C C(CH2)4Cl, Z = NO2, Br, F, H, or CH3]. The range of Z groups was selected aiming to examine the Caryl I bond energy as a function of the “electron withdrawing/electron donating” ability of the Z-group, with the ultimate purpose of controlling the alkynyl/aryl grafting ratio. The electroreduction mechanism and the characteristics of the grafted surface are studied by means of cyclic voltammetry and X-ray photoelectron spectroscopy. It is shown that the alkynyl/aryl grafting ratio decreases with the increasing electron withdrawing nature of Z, which induces a weakening of the Caryl I bond. Ab initio DFT vertical electron affinities (EAv) allowed to rationalize the electroreduction potentials of both the bulk and surface functionalised redox couples. Moreover, the alkynyl/aryl grafting ratio is assessed, at a molecular level, on the basis of ab initio DFT potential energy surfaces.

The co-adsorption of sodium dodecyl sulfate (SDS) and sodium dodecylbenzenesulfonate (SDBS), on the 1-decanethiol self-assembled monolayer (SAM)-functionalized polycrystalline gold surface, is investigated by electrochemical techniques. The peak current (cyclic voltammetry) and charge transfer resistance (impedance spectra) variations are measured, concerning the [Fe(CN)6]3−/[Fe(CN)6]4− couple redox process. SDBS is found to yield a more efficient inhibiting barrier (towards the charge transfer process), when compared to the SDS one. Thus, it is suggesting that a higher tendency of SDBS to be co-adsorbed within the 1-decanethiol SAM with respect to SDS.

The adsorption of the nonanoic acid at the electrified Hg/aqueous solution interface is studied by means of capacity and surface tension measurements. Comparison of the experimental Γ max value with the calculated more favoured solvated conformation suggests that the acid is adsorbed in a partially coiled conformation. The adsorption free energy here determined, together with previously reported values found in the literature concerning other saturated acids and alcohols, is compared with reactivity and calculated molecular descriptors. The collected evidence suggests that the hydrophobic nature of the acid is responsible for the adsorption, while the electric field/molecule interaction, occurring at the electrified interface, governs the desorption. Lastly, some experimental (capacitive transients, effect of the temperature on the tensammetric curves) and theoretical findings are discussed which indicate that the adsorbed acid monolayer should be regarded as a usual, in the field of adsorption at electrodes, disordered network. Thus excluding the occurrence of a two-dimensional phase transition involving the formation of a 2D solid-like film

GC/OligoThiophene/Ag(NP) hybrid interfaces are synthesized and characterized: GC is the glassy carbon surface; OligoThiophene stands for both an ultrathin bithiophene grafted film and a 4-Br-Bithiophene grafted polymer; Ag(NP) stands for silver nanoparticles. The hybrid interface preparation involves different steps: first, the electrode surface is functionalized through a combination of electrochemically assisted grafting (under reduction regime) and polymerization (under oxidation regime); then, silver nanoparticles are chemisorbed by dipping. In particular, an ultrathin film of grafted bithiophene can be obtained by applying one cyclic voltammetry reduction cycle (GC/BT surface), while subsequent cyclic voltammetry cycling under oxidation regime yields an immobilized 4Br-Bithiophene polymer (GC/4BrBT surface). AFM and TEM images were recorded to investigate the morphology and chemical composition of the Ag(NP). Fe(II)/Fe(III) cyclic voltammetry, Zn underpotential deposition (UPD), XPS, LA-ICP-MS, and Raman techniques were exploited to characterize both the GC/OligoThiophene and GC/OligoThiophene/Ag(NP) interfaces. Theoretical calculation, at the B3LYP/6-311G** level of the theory, enabled rationalization of the electroreduction mechanism and the Raman results.

Glassy carbon (GC) electrode surfaces are functionalized through electrochemical assisted grafting, in oxidation regime, of six amino acids (AA): β-alanine (β-Ala), l -aspartic acid (Asp), 11-aminoundecanoic acid (UA), 4-aminobenzoic acid (PABA), 4-(4-amino-phenyl)-butyric acid (PFB), 3-(4-amino-phenyl)-propionic acid (PFP). Thus, a GC/AA interface is produced featuring carboxylic groups facing the solution. Electrochemical (cyclic voltammetry and electrochemical impedance spectroscopy) and XPS techniques are used to experimentally characterize the grafting process and the surface state. The theoretical results are compared with the experimental evidence to determine, at a molecular level, the overall grafting mechanism. Ionization potentials, standard oxidation potentials, HOMO and electron spin distributions are calculated at the CCD/6-31G* level of the theory. The comparison of experimental and theoretical data suggests that the main electroactive species is the “zwitterionic” form for the three aliphatic amino acids, while the amino acids featuring the amino group bound to the phenyl aromatic moiety show a different behaviour. The comparison between experimental and theoretical results suggests that both the neutral and the zwitterionic forms are present in the acetonitrile solution in the case of 4-(4-amino-phenyl)-butyric acid (PFB) and 3-(4-amino-phenyl)-propionic acid.

The analysis of the polarographic, voltammetric and coulometric results shows that the overall reduction mechanism of benzamide occurs with the cleavage of the CN bond. However, the first step of the electrochemical process leads to the formation of a radical anion which undergoes protonation by another benzamide molecule in DMF and DMSO or by the solvent in CH 3 CN and C 2 H 5 OH. Theoretical calculations have been performed to clarify the mechanism. Halobenzamide reduction involves the Chalogen bond breaking as the first reduction step to give benzamide.

The adsorbability of a wide series of aromatic derivatives (38) on mercury from aqueous solution at constant potential ( E pzc or close to it) cannot be simply accounted for by the “aromaticity” of the compounds, at any rate modulated by substituent groups on the aromatic moiety, even if the adsorbates show a common planar disposition on the surface in the adsorbed state. The interfacial activity can be successfully related to the process of formation of a “soft-soft” couple (in the Pearson's concept) between mercury and the organic, in competition with the “hard-soft” couple between the metal and water. Desorption is then explained with a higher “hard” character of mercury at increasing negative potential. In this view, the feasibility of a partial charge transfer, as expressed by λ, calculated for neutral organic adsorbates, corresponding to a positive Δ N value (Δ N , fractional number of electrons transferred from the adsorbate to the mercury) can be confirmed. A simple relation between adsorbability and “bulkyness” of the compounds, in relation to the dislodgement of water molecules from the surface occurring in the adsorption process is proposed and discussed.

The electroreductive potential values of the o-, m- and p- dibromobenzenes (DBBs) follow an unusual pattern in that, unlike the structurally related dichlorobenzene (DCB) derivatives, these three isomers exhibit a strong ‘ortho effect’ and are accompanied by a large difference in the E1/2 values. Any interference with the mechanism of reduction on the part of the chemical environment can be safely ruled out, given the consistency of the E1/2 values obtained in four different solvents. The use of theoretical indices calculated by the PM3 method enables the experimental behaviour of the DBBs to be rationalised on the basis of the electronic structure of the neutral isolated molecule. Remarkably, PM3 indicates the formation of a σ-type radical anion in the case of the reduction of the bromobenzene derivatives.

The paper reports a systematic study concerning the role played by different organic compounds (glycolic acid, oxalic acid, glycerol) on the electrochemical oxidation process of aluminium in sulphuric acid solution. The result of the experiment as a whole provides a clear indication of the deep influence exerted by the three selected organic compounds on the aluminium oxide structure, leading to the formation of a more compact oxide layer. Electrochemical impedance spectroscopy results appear of particular interest; they are discussed in the light of a model proposed by Bojinov. The relevant parameters, half-jump distance a and cross-capture section S, are found consistently related to variations in the oxide structure (porosity). This gives a sounder basis to the physically correct nature of the assumptions underlying the Bojinov model, also suggesting that organic compounds are adsorbed at the aluminium oxide/aqueous solution interface.

We describe the synthesis of alternating bithiophene–fluorene copolymers (P1–P3) with different regiochemistry of the bithienyl unit and different alkylsulfanyl chain lengths. The structural, electrochemical and photophysical properties of these polymers were investigated by gel permeation chromatography (GPC), differential scanning calorimetry (DSC), NMR, UV/Vis and photoluminescence (PL) spectroscopy and cyclic voltammetry (CV), and the polymers were used to assemble organic solar cells (OSCs), in combi-nation with the fullerene derivative methyl [6,6]-phenyl-C61- butyrate (PCBM). P3, with a head-to-head bithienyl unit, shows a broader absorption and a lower band gap with respect to P1 and P2, which have tail-to-tail bithienyl units. The PL intensity of P1–P3 is dramatically quenched in the presence of PCBM, demonstrating that an efficient charge transfer between donor and acceptor occurs. The best OSC device was obtained with P3

The design of a catalyst for one of the most important electrocatalytic reactions, the oxygen reduction reaction (ORR), was done following the most recent guidelines of theoretical studies on this topic. Aim of this work was to achieve a synergic effect of two different metals acting on different steps of the ORR. The catalytic activity of Ag, already known and characterized, was enhanced by the presence of a monolayer of cobalt subdivided into nanosized islands. To obtain such a controlled nanostructure, a novel method utilizing self-assembled monolayers (SAMs) as templates was employed. In a recent study, we were able to perform a confined electrodeposition of cobalt onto Ag(111) in a template formed by selectively desorbing a short-chain thiol (3-mercaptopropionic acid, MPA) from binary SAMs using 1-dodecanthiols (DDT). [32] This method allows for an excellent control of the morphology of the deposit by varying the molar ratio of the two thiols. Becausecobalt does not deposit on silver at an underpotential, the alternative approach of surface limited redox replacement (SLRR) was used. This method, recently developed by Adz?ic´ et al.,[13] consists of the use of a monolayer of a third metal, which can be deposited at an underpotential, as a template for the spontaneous deposition of a more noble metal. Herein, we choose zinc as template for the deposition of cobalt. Ag(111) crystals were covered by monolayer islands consisting of cobalt, with the surface atomic ratios ranging from 12 to 39% for cobalt. The catalytic activity of such samples towards ORR was evaluated and the best improvement in activity was found to be that of the sample with a cobalt percentage of approximately 30% with respect to the bare silver, which is in good agreement with theoretical hypotheses.

The electrochemical dehalogenation of a variety of halogenated aromatic compounds is studied by means of semiempirical (AM1) and ab initio(ROHF 3-21G*) calculations. Comparison of the electrochemical half-wave potential values (E1/2) and calculated theoretical indices indicates the formation of a π radical following the electron uptake. Moreover, the relationship observed between the half-wave potential, in dimethylformamide (DMF) and dimethyl sulfoxide (DMSO), and the electron affinity suggests that the reduction potential is determined by the first electron uptake and that kinetic factors play a minor role, their influence being constant or negligible.

An ‘intrinsic’ value of the adsorption Gibbs energy (ΔG°int)∥, not directly proportional to the measured ΔG∥ads, has been evaluated for a set of 28 aromatic, heterocyclic and naphthalenic derivatives. The structural feature of (ΔG°int)∥ is rationalised in terms of a ‘soft’ interaction with mercury at the point of zero charge, on the basis of the parr and Pearson concept, accounting on a quantitative basis for the different adsorbability of the compounds. Moreover, the partial charge-transfer coefficient, λ, has been related in a satisfactory way to ΔN(the fractional number of electrons transferred) calculated taking into account the absolute electronegativitiy, χ, and the hardness, η, both of the adsorbate and of mercury.

The voltammetric generation of corannulene anions was investigated over a large range of experimental conditions comprising either "traditional" electrochemical solvents, such as dimethylformamide, acetonitrile, and tetrahydrofuran, or "unconventional" solvents, such as liquid ammonia, liquid methylamine, or liquid dimethylamine, and several different supporting electrolytes. Strong ion pairing effects were found to dominate the electrochemical generation of corannulene higher anions, and through the suitable choice of the solvent/electrolyte system, we observed, for the first time, the reversible electrochemical generation of up to the triply reduced corannulene. The standard potentials obtained experimentally compared rather well with the theoretical values calculated by ab initio and density functional methods, in which solvation and ion pairing effect were explicitly taken into account. In particular, the calculations considered the effect of the electrolyte cation size on ion pairing in order to rationalize the occurrence of the third reduction within the experimental potential window.

The adsorption at the mercury/aqueous solution interface of the 3-, 4-, 5-indolecarboxylic acids in their anionic form has been characterized. The thermodynamic analysis has shown that the process is mainly determined by the interaction of the planar aromatic system with the mercury surface and well described by a Frumkin type isotherm. From the experimental values of the electrosorption valency (γN) and using the model proposed by Schultze a relation between the partial charge transfer (λ) and the repulsive Frumkin interaction parameter has been found. At least, the interfacial activity of the aromatic anions is also discussed on the basis of localized (charge densities) and delocalized (frontier MO energies) theoretical parameters.

The anodic dissolution of the mercury electrode in 1,10-phenanthroline (phen) aqueous solution has been investigated by polarographic and voltammetric methods. The adsorption processes affecting the entire mechanism of oxidation and the complex formation have been observed and analysed introducing the random adsorption model (Frumkin isotherm) and the nucleation-growth collision model. The results suggest the occurrence of different surface structures of phenanthroline itself (the ligand) as well as of the product of the oxidative process, [Hg(phen) 2 ] 2+ , upon varying the ligand concentration in the bulk.

The behaviour of alkynil(aryl)iodonium salts upon electrochemical reduction, on glassy carbon electrodes, is here studied by comparing both theoretical and experimental results. In particular, experimental results are obtained by means of cyclic voltammetry and chronocoulometric measurements as well as by collecting XPS spectra, while the standard electrode potential and different dissociation paths (I‐C, arylic, compared to the I‐C, alkynil, bond cleavage) have been characterized theoretically at the B3LYP/3‐21g** level of the theory (the solvation free Gibbs energy of the cation and of the neutral radical species have been calculated by using the CPCM method).

The 2,3-bis(2′-pyridyl)pyrazine (2,3-dpp) and 2,5-bis(2′-pyridyl)pyrazine (2,5-dpp) have been successfully used as bridging ligands for building up ruthenium (II) and osmium (II) polypyridyl redox and luminescent active dendrimers. Such ligands have been herein investigated by ab initio and DFT theoretical calculations both in gas phase and with the solvent effect. The different molecular conformations exhibited by 2,3-dpp, which depend on whether it is free or coordinated to one or two metal centres, have been explored by performing the scan of the potential energy surface. The spectra of the neutral and the radical anion species of the relevant conformers have been calculated at DFT and semiempirical level of the theory. The results have been assessed by correlating them with electrochemical and UV–Vis–NIR spectroelectrochemical experimental ones, obtained in highly aprotic and dry conditions.

Organic molecules with sulfur-containing headgroups interacting with noble metal surfaces represent a fruitful class of systems with potential relevance in new device technology. Within this context, the room temperature adsorption of 2-mercaptobenzoxazole (MBO) on the Cu(1 0 0) surface has been studied by high-resolution electron energy-loss spectroscopy (HREELS) as a function of molecular exposure. At low coverage, the HREEL spectra present only one mode at 93 meV (750 cm−1), which is attributed to the out-of-plane C–H bending γCH. Its off-specular angular dependence indicates that the molecules lie almost flat on the surface. At higher coverage, the MBO layer orders in a p(2 × 2) superstructure, and energy loss peaks at higher energies appear. These features can be assigned to in-plane vibrations indicating that the molecular axis tilts toward a more vertical position, thus allowing a closer molecular packing. Assignment of the HREELS peaks is confirmed by estimation of the gas phase normal modes of the free molecule, evaluated by ab initio methods. The absence of the N–H stretching mode in the HREEL spectra indicates that the H atom bonded to nitrogen in the gas-phase molecule is lost upon adsorption, suggesting that MBO molecule adsorbs on the Cu surface as a thiolate.

The electrochemical reduction of a series of thio- and oxopyrimidine derivatives has been investigated in organic solvents on mercury electrodes. In all cases the electrochemical process gave a dimeric species as the major product. The overall reduction mechanism is the same for oxo and thio derivatives, and is found to be dependent only on the nature of the ring nitrogen substituent. A ‘father–son reaction’ is observed when hydrogen is bound to the ring nitrogen atom: the radical anion obtained from the first electron transfer draws out the nitrogen proton of a non-reduced molecule and this then dimerizes. In the presence of a protonating agent as well as for the N-substituted derivatives, the ‘father–son reaction’ is not observed. Theoretical calculations have been performed to gain insight into the proposed mechanisms: the LUMO energy and the vertical electron affinity show a linear correlation with the reduction potentials. Analysis of the theoretical parameters has allowed step-by-step determination of the electrochemical reduction process. The manner in which solvent properties influence electrochemical behaviour has been examined, and the role of the acceptor number (AN) has been discussed.

We report the results of an investigation, using electrochemical and spectroelectrochemical techniques, into redox properties of uncoordinated free bis-chelating 2,3- and 2,5-bis(2-pyridyl)pyrazine ligands (2,3- and 2,5-dpp) and of the complexes of the [Ru(2,3-dpp)n(bpy)3−n]2+ and [Ru(2,5-dpp)n(bpy)3−n]2+ families (bpy=2,2′-bipyridine), which are used as building blocks for obtaining polynuclear complexes. For comparison purposes, the electrochemical behaviour of the [Ru(2,3-dpp)(DCE-bpy)2]2+complex, where DCE-bpy is 5,5′-dicarboxyethyl-2,2′-bipyridine, has also been investigated. Correlations of the E1/2 values observed for the compounds examined (genetic diagrams) have allowed us to assign all the ligand-based reduction processes as well as to discuss electronic interactions. The localisation of the first three reduction processes for each complex has also been established on the basis of the spectroelectrochemical results. Theoretical calculations (AM1 semiempirical and ab-initio level) carried out for the 2,5-dpp and 2,3-dpp ligands show that, in the uncoordinated state, the former ligand does not exhibit any substantial conformation arrangement, whereas the latter has a stable conformation for a large (56°) dihedral angle between the pyridyl and pyrazine rings. The changes in conformation upon mono- and bis-coordination of 2,3-dpp can account for its peculiar electrochemical behaviour consisting in a change of the number of redox processes with varying coordination state.

The standard Gibbs energy of adsorption of pure liquid ethylene glycol (EG) on mercury is assessed to range between −50 and −60 kJ mol−1, about two–three times with respect to water (−21 kJ mol−1). This evidence is obtained on the basis of a series of indirect and independent experimental results. Moreover, ab-initio calculations are performed to account for the interaction energy relating the isolated EG molecule and a cluster of seven (or four) Hg atoms: three different geometrical approaches of the EG molecule with respect to the cluster are considered (top, hollow, bridge) as well as three EG conformations (trans, cis, cis-OH, the last one with an intramolecular hydrogen bond). The deepest minimum in the energy versus (Hgcluster–EGmolecule) distance potential energy curve, amounting to −80 kJ mol−1, is obtained in the case of the cis conformation of EG. In particular, it is found that this stabilizing energy is essentially due to the oxygen–mercury atoms interaction, giving rise also to an appreciable charge transfer coefficient from the EG molecule to the Hg cluster. Finally, in this conformation, the EG adsorbed layer is also stabilized by an attractive energy term effective among vicinal interacting molecules.

The dynamics of the dissociation of the benzyl chloride radical anion to a benzyl radical and chloride anion was studied theoretically. To this end two different conformations of benzyl chloride were examined: one featuring a 90° angle between the Cl–C bond and the aromatic ring (conformation S), the other with the Cl–C bond and the aromatic moiety lying coplanar (conformation E). The potential-energy (PE) surface shows the existence of a conical intersection when studied as a function of the C–Cl bond length and of the rotation angle around the C(sp 2 )–C(sp 3 ) bond. Information on the dynamics of this process was obtained using the dynamic reaction coordinate (DRC) algorithm for tracing reaction paths. The DRC method shows a qualitative difference in the dissociation mechanism of the two conformers. The lifetime of conformation E depends on the amount of kinetic energy assigned to the internal rotational mode motion, whereas that of conformation S does not.

The chemical and physical nature of the stages preceding the massive electrochemical reduction of chromium is studied combining electrochemical, scanning electron microscopy (SEM) and vibrational spectroscopy (IR) techniques. The collected evidence indicates that the formation of intermediate species occurs in the adsorbed phase.

The electrochemical behavior of a family of polynuclear ruthenium(II) bipyridine-type complexes with 2,3-bis(2-pyridyl)pyrazine (2,3-dpp) and 2,5-bis(2-pyridyl)pyrazine (2,5-dpp) as bridging ligands has been investigated in highly purified N,N-dimethylformamide solution. The compounds studied contain two, three, four, and six metal centers and have general formula [Run(bpy)n+2(2,X-dpp)n-1]2n+, where n = 2, 3, 4, or 6, X = 3 or 5, and bpy is 2,2‘-bipyridine. The wide cathodic potential window explored (up to ca. −3.1 V vs SCE) has allowed us to observe the most extensive ligand-centered redox series so far reported, comprising up to 26 reversible reduction processes for the hexanuclear complex. The redox standard potentials for overlapping processes in multielectron waves have been obtained from the analysis of the voltammetric curves and their digital simulation. The localization of each redox process and the mutual interactions of the redox centers have been elucidated through the analysis and comparison...

The interfacial behaviour of benzaldehyde and p -methyl phenyl acetic acid in ethyleneglycol (EG), as well as that of o -dimethyltoluidine in water, has been investigated to obtain a number of adsorption parameters necessary to discuss the reliability, on a quantitative ground, of the “intrinsic” value of Gibbs adsorption energy, Δ G int °, relating, for a group of aromatic derivatives adsorbed on mercury, to the process: A pure +Hg⇌Hg(A adsorbed ). It has been shown that this quantity does not depend on the solvent in use, so that it is really “intrinsic” and can be usefully related to structural molecular parameters of the adsorbate alone, allowing the interfacial behaviour to be foreseen a priori. As a consequence the solvation in the adsorption state of the interfacial active species, either in EG and in water, can be considered to contribute little to the whole adsorption Gibbs energy. Eventually, EG itself shows an interfacial activity almost the double of that of water, ∼−50 and ∼−21 kJ mol −1 , respectively. So that, within this view the adsorption of aromatics from EG on mercury can be fully rationalized with respect their behaviour on Hg from water.

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The electrochemical behaviour of 2-methylsulphonyl-3-phenyloxaziridine (1) and 2-tbutyl-3-phenyloxaziridine (2) has been investigated by polarographic techniques in aprotic solvent. The electroreductive center appears to be the oxaziridine ring but the rearrangement following the electron uptake yields benzaldehyde and imine for the derivatives (1) and (2) respectively. This peculiar behaviour has been discussed on the basis of calculated theoretical indices (CNDO/2 method), like energy values and “shapes” of frontier molecular orbitals, which suggest the NO bond breaking as the first step of the overall reduction process.

The electrochemical behaviour of 12 polychlorobenzene derivatives is discussed on the basis of calculated quantum-mechanical indexes (CNDO/2, MNDO, AM1 methods) and of pure structural parameters reckoned by means of graph theory (Wierner, Balaban, Randic, PID and Wrms numbers). Even the existence of good relationships between reduction potentials and energies of virtual molecular orbitals, π* or σ*(closed-shell calculations), does not account for the details of the electron uptake at the molecular level. Open-shell calculations (MNDO) regarding unrelaxed radical anions are much more promising in this respect, the occurrence of the so-called ‘ortho effect’ can be so justified. The reductive process (at least in the experimental conditions considered here) is shown to be scarcely affected by solvent-shell or internal molecular rearrangements; this view is supported by the good description of the process, strictly on structural grounds regarding the whole of the molecule, provided by the graph-theoretical indexes.

The formation of an adsorbed condensed film on mercury of 1,10-phenanthroline from aqueous solution has been characterized by a.c. polarography at a dropping mercury electrode and the kinetic of the transition from the liquid-like to the solidlike adsorptive state characterized, on a quantitative ground, by the analysis of the capacitance-time transients. The Avrami model of nucleation and growth of the compact layer reveals to be unadequate to fit the experimental Θ (coverage) versus time dependence, while a better description is obtained using a relation accounting for a surface-diffusion controlled growth process. This evidence can be related to the stacking process occurring in solution giving rise to stable oligomers (mainly dimers) of 1,10-phenanthroline.

The electrochemical behaviour of 12 polychlorobenzene derivatives is discussed on the basis of calculated quantum-mechanical indexes (CNDO/2, MNDO, AM1 methods) and of pure structural parameters reckoned by means of graph theory (Wierner, Balaban, Randic, PID and Wrms numbers). Even the existence of good relationships between reduction potentials and energies of virtual molecular orbitals, π* or σ*(closed-shell calculations), does not account for the details of the electron uptake at the molecular level. Open-shell calculations (MNDO) regarding unrelaxed radical anions are much more promising in this respect, the occurrence of the so-called ‘ortho effect’ can be so justified. The reductive process (at least in the experimental conditions considered here) is shown to be scarcely affected by solvent-shell or internal molecular rearrangements; this view is supported by the good description of the process, strictly on structural grounds regarding the whole of the molecule, provided by the graph-theoretical indexes.

The adsorption of N-dansylglycine in its monoanionic and dianionic molecular forms has been characterized in aqueous solution (1 M NaClO 4 as base electrolyte) at the mercury electrode, for concentration values lower than 7 mM

The combined effect of temperature, bulk concentration and applied potential, on the stability of the condensed phase of adenine adsorbed at the mercury/aqueous solution interface, is rationalized assuming that the occurrence of a 2D phase transition involves only two distinct adsorbed phases. The chemical potential, µ, which drives the equilibrium at the phase transition, is expressed by means of an equation which accounts explicity for the electric field–adsorbed molecule interaction. The approach enables the standard entropy variation of the overall process to be determined. The findings are consistent with the ordered nature of the adsorbed phase, with which the appearance of a low and constant capacity region in the capacity vs. potential curves is associated. The standard entropy variation for the 2D ‘flat → perpendicular (solid-like)’ phase transition is estimated and discussed.

The electroadsorptive behaviour of benzoic acid, investigated by means of a.c. phase selective polarography under different experimental conditions (1 mol dm–3 NaClO4, 1 mol dm–3 NaCl), shows a marked dependence on the temperature, indicating the existence of a two-dimensional phase transition ‘gas-like’(disordered disposition of the adsorbed molecules)→‘solid-like’(ordered disposition of the adsorbed molecules). The experimental results in terms of the variation induced by different temperatures on the capacity vs. potential curves are analysed, leading to the determination of a repulsive intermolecular energy, IµAA, in contrast with the experimental evidence presented and with previously obtained data concerning the Frumkin interaction factor. Values of IµAA that are attractive are calculated by the atom–atom potential method, thus supporting theoretically the experimental evidence for condensation of the adsorbed benzoic acid molecules.

The electrochemical behaviour in protic and aprotic solvents of some tosylaminoacids bearing a lateral electroinactive chain confirms that the reduction mechanism conforms to that one already proposed for tosyl- and dansylglycine and benzenesulphonamide derivatives. The E 1 2 value reveals to be a good structural index and relationships between empirical and calculated structural parameters show that the presence of the carboxylate group in tosylaminoacids causes an increase of NH bond acidity with respect to benzenesulphonamide derivatives. The pK values of the amide group are influenced by the kind of the lateral chains and by the position of carboxylic group in the molecular frame.

The analysis of polarographic and coulometric results shows that the overall reduction mechanism of chlorobenzenesulphonamide derivatives occurs with the cleavage of the CCl bond followed by the reduction of the benzenesulphonamide involving the SN bond breaking. However, the E sol1 2 values fit the structural relation E 1 2 -ELUMO for the series of benzenesulphonamides and not that of the cholorobenzene derivatives and the shape of the LUMO of cholorobenzenesulphonamides is similar to that of the benzenesulphonamide, so that it is sensible to suggest that the first step of the reduction mechanism is the same for all the benzenesulphonamide derivatives and involves the CSN moiety of the molecules.

The adsorption of N -dansylglycine (5-dimethylaminonaphthalene-1-sulphanylglycine) in monoanionic and dianionic forms has been characterized in aqueous solution at a mercury electrode. At pH 6 (only the monoamonic form present in the bulk), N -dansylglycine is arranged on the metal surface in a perpendicular manner through the naphthyl moiety, and an attractive interaction factor among the adsorbed molecules is observed. At pH 12 (dianionic form), the molecules still arranged in a perpendicular way show a greater molecular area and no interaction factor is revealed. These features, together with those regarding a series of other N -substituted glycine derivatives previously studied, are related to some calculated structural indices, and a relationship is obtained between the adsorption Gibbs energy and Δ E l-h (the energy difference between the lowest unoccupied molecular orbital and the highest occupied one). Moreover, some local theoretical indices (net atomic charges, partial net π charges) are used in a tentative molecular interpretation of the disposition of the sorbate on the surface and of the significance of the Frumkin interaction factor. To offer a more general grounding to the argument, a group of naphthyl and benzoyl derivatives studied by Bockris and co-workers (J. Phys. Chem., 65 (1961) 2000) in very similar conditions is also considered.

The comparison of the electrochemical behaviour of N-tosylglycine and N-dansylglycine with that of the corresponding amides and the benzenesulphonamide in protic and aprotic media has shown that the RSO2- protected aminoacids, in their neutral form, can be considered as benzenesulphonamide derivatives and their E 1 2 values fit the structural correlations among experimental and theoretical parameters already discussed in previous papers. Using these correlations, the role of the RSO2- and carboxylate groups on the amidic acidity of the free and complexed aminoacid has been determined also on the basis of calculated differences in total energy (ΔEtot) of dissociated and undissociated acidic species. All these results confirm the main role played by the carboxylate group on the formation of NO bidentate complexes.

Abstract The phenomenon of tin dioxide doping by antimony, Sb(V), atoms in semiconductive glazes is discussed. In particular, the impedance spectra of the glaze surface at room temperature were experimentally determined, and the results were analysed in terms of equivalent circuits. The parameters resulting from the fitting procedure were related to the SnO 2 Sb(V) relative content, the SnO 2 Sb (V) percentage in the glaze, and the microstructure as observed by SEM. It is proposed that the addition of SnO 2 and Sb 2 O 3 to a common glaze for ceramic tile results in a semiconductive continuous phase, whose electrical characteristics fulfil the antistatic floor regulation, as far as surface conductivity is concerned. As a whole the obtained results suggest that the thermal cycle used in fast firing technology is capable to promote the oxidation of Sb 2 O 3 to Sb 2 O 4 , resulting in a sufficient amount of Sb(V) capable of generating a semiconductive behaviour of the SnO 2 crystalline phase dispersed in the glaze.

The electrochemical reduction of α,α,α-trichlorotoluene (benzotrichloride) and of the corresponding isomeric pyridine derivatives has been investigated by cyclic voltammetry and microcoulometry. Three irreversible diffusion controlled reduction waves have been observed in the voltammetry of the trichloromethyl derivatives and are found to correspond to the progressive two-electron reduction of derivatives where a chlorine atom is substituted by a hydrogen atom. The peak potentials E p show that reduction of the pyridine derivatives is easier than that of the benzene derivatives with the same number of chlorine atoms, the more positive shift occurring for the 4-substituted compounds. The experimental findings would indicate a concerted electron transfer-bond breaking (C–Cl) mechanism for all the compounds examined, as well as for the chloromethyl and dichloromethyl derivatives formed after Cl/H substitution. Electron uptake appears to be the rate-determining step of the reductive cleavage of these molecules. The effects of the different aromatic rings and of the degree of halogen substitution of the methyl group on the reduction potentials are discussed.

Coronene, a polyaromatic hydrocarbon, has been crystallized for the first time in a different polymorph using a crystal growth method that utilizes magnetic fields to access a unit cell configuration that was hitherto unknown. Crystals grown in magnetic field of 1 T are larger, have a different appearance to those grown in zero field and retain their structure in ambient conditions. We identify the new form, beta-coronene, as the most stable at low temperatures. As a result of the new supramolecular configuration we report significantly altered electronic, optical and mechanical properties., 32 pages, 17 figures