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International audience; During the last two decades, numerous observed data obtained by various physical techniques, also supported by molecular modeling approaches, have highlighted the structuring features of tripeptides, as well as their aggregation properties. Herein, we focus on the structural dynamics of four trimers, i.e., Gly-Gly-Gly, Gly-Ala-Gly, Ala-Ala-Ala and Ala-Phe-Ala, in an aqueous environment. Density functional theory calculations (DFT) were carried out to assess the stability of four types of secondary structures, i.e., β-strand, polyproline-II (pP-II), α-helix and γ-turn, of which the formation had been described in these tripeptides. Both implicit and explicit hydration effects were analyzed on the conformational and energetic features of trimers. It has been shown that the use of M062X functional (versus B3LYP) improve the stability of intramolecular H-bonds, especially in inverse γ-turn structures, as well as the energetic and conformational equilibrium in all tripeptides. Explicit hydration reflected by the presence of five water molecules around the backbone polar sites (NH3+, N-H, CO and NH2) considerably changes the conformational landscapes of the trimers. Characteristic intramolecular and intermolecular interactions evidenced by the calculations, were emphasized.

Primarily known as the inhibitor of growth hormone release, the role of somatostatin in many other inhibiting activities upon binding to its five G-protein-coupled receptors has been elucidated. Because of the short half-life of somatostatin, a number of synthetic analogues were elaborated for this peptide hormone. Herein, after recalling the main somatostatin therapeutic interests, we present the dynamical behavior of somatostatin-14 and its two currently used synthetic cyclic analogues, octreotide and pasireotide. Physical techniques, such as fluorescence, UV-visible absorption, circular dichroism, Raman spectroscopy, surface-enhanced Raman spectroscopy, and transmission electron microscopy, were jointly used in order to get information on the solution structural features, as well as on the anchoring sites of the three peptides on silver colloids. While somatostatin-14 adopts a rather unordered chain within the submillimolar concentration range, its cyclic analogues were revealed to be ordered, i.e., stabilized either in a type-II' β-turn (octreotide) or in a face-to-face γ-turn/type-I β-turn (pasireotide) structure. Nevertheless, a progressive structuring trend was observed in somatostatin-14 upon increasing concentration to the millimolar range. Because of their cationic character, the three peptides have revealed their capability to bind onto negatively charged silver nanoparticles. The high affinity of the peptides toward metallic particles seems to be extremely promising for the elaboration of somatostatin-based functionalized plasmonic nanoparticles that can be used in diagnosis, drug delivery, and therapy.

Primarily known as the inhibitor of growth hormone release, the role of somatostatin in many other inhibiting activities upon binding to its five G-protein-coupled receptors has been elucidated. Because of the short half-life of somatostatin, a number of synthetic analogues were elaborated for this peptide hormone. Herein, after recalling the main somatostatin therapeutic interests, we present the dynamical behavior of somatostatin-14 and its two currently used synthetic cyclic analogues, octreotide and pasireotide. Physical techniques, such as fluorescence, UV-visible absorption, circular dichroism, Raman spectroscopy, surface-enhanced Raman spectroscopy, and transmission electron microscopy, were jointly used in order to get information on the solution structural features, as well as on the anchoring sites of the three peptides on silver colloids. While somatostatin-14 adopts a rather unordered chain within the submillimolar concentration range, its cyclic analogues were revealed to be ordered, i.e., stabilized either in a type-II' β-turn (octreotide) or in a face-to-face γ-turn/type-I β-turn (pasireotide) structure. Nevertheless, a progressive structuring trend was observed in somatostatin-14 upon increasing concentration to the millimolar range. Because of their cationic character, the three peptides have revealed their capability to bind onto negatively charged silver nanoparticles. The high affinity of the peptides toward metallic particles seems to be extremely promising for the elaboration of somatostatin-based functionalized plasmonic nanoparticles that can be used in diagnosis, drug delivery, and therapy.

Raman data collected from free amino acid and peptide chains permit assignment of the seven markers located at approximately 1616, 1606, 1210, 1178, 850, 830, and 643 cm−1 to tyrosine. The effects induced by labile hydrogen deuteration, temperature, concentration, and protonation–deprotonation on these Raman markers were analyzed. Following closely a recent multiconformational analysis on phenylalanine, we could confirm the predominance of gauche-/gauche- rotamers with respect to the side chain χ1/χ2 torsion angles in both tyrosine and tyrosinate. Calculated Raman spectra, based on the consideration of both implicit and explicit hydration models, have revealed the effect of hydrogen bonding of water molecules to the phenol ring hydroxyl group of tyrosine. A special attention has been paid to the 850/830 cm−1 tyrosine doublet, for which no intensity ratio inversion could be remarked when the phenol hydroxyl group acts as a hydrogen bond donor or acceptor. On the contrary, this intensity ratio appeared to be strongly dependent on the hydrophobic/hydrophilic balance of the interactions, in which the phenol ring is involved. Based on the present theoretical calculations, the components of the tyrosine doublet might originate from two independent fundamental modes of the phenol ring: one with an in-plane character and the other with an out-of-plane character. As a consequence, the widely spread Fermi resonance-based description of the tyrosine doublet appears to be unjustified. The latter interpretation simply results from the insufficiencies of the simple model compound used at that time for analyzing the vibrational features of a more complex molecular system such as tyrosine. Copyright © 2015 John Wiley & Sons, Ltd.

International audience; Acetylcholine is the first discovered neurotransmitter that has received a great attention regarding its capability of binding to several cellular targets. The chemical composition of acetylcholine, including a positively charged trimethylammonium and a carbonyl group, as well as its conformational flexibility was pointed out as the key factors in the stabilization of its interactions. Here, the possibilities offered by a Raman scattering-based multiconformatioal analysis to access the most stable conformers of acetylcholine, is discussed. To control the validity of this protocol, acetylcholine and one of its closely structured analogues, acetylthiocholine, were simultaneously analyzed. Solution Raman spectra revealed distinct and well resolved strong markers for each molecule. Density functional theory calculations were consistent with the fact that the energy order of the low energy conformers is considerably affected by the acyloxy oxygen sulfur atom substitution. Raman spectra were calculated on the basis of the thermal average of the spectra arising from the low energy conformers. It has been evidenced that the carbonyl and trimethylammonium groups are the most favorable hydration sites in aqueous environment. Taking into account the large gap between the carbonyl bond-stretch and aliphatic bending bands, Raman spectra also allowed separation of the HOH bending vibrations arising from the bound and bulk water molecules. (C) 2017 Elsevier B.V. All rights reserved.

Water interaction with peptide chains is one of the key structure stabilizing factors in an aqueous environment. Because of its strong polar character, water can bind to both anionic and cationic sites via electrostatic interactions. It can also act as a hydrogen-bond donor or acceptor according to its interactions with different polar groups in the backbone and side chains of peptides and proteins. Based on density functional theory calculations, the present report aims at illustrating the most energetically favorable interaction sites of aromatic side chains of phenylalanine, tyrosine, tryptophan, and histidine (neutral and protonated species) with surrounding water molecules. It was shown that beyond the strong interactions occurring between water and the aromatic ring acceptor/donor sites, such as O–H, N–H and –N groups, weaker interactions with π-electron clouds should also be considered. The latter type of binding, hereafter referred to as Hw⋯π interaction, involves one of the water hydrogen atoms (Hw) pointing toward the aromatic ring. Upon comparison between the theoretical data obtained from a purely implicit hydration model, i.e. a polarized solvent continuum, and those collected from a mixture of implicit and explicit hydration models, it has been shown that the explicit water molecule binding to aromatic rings affects the relative energies of the rotamers generated by the two side chain torsion angles (χ1 and χ2).

This work was granted access to the HPC resources of CINES (Montpellier, France) under the allocations c2013075065 and c2014085065 made by GENCI (Grand Equipement National de Calcul Intensif). The authors would like to acknowledge CSIC for the Project I-LINK 0646 facilitating the collaboration between the Spanish and French groups.

Because of the absence of the side chain in its chemical structure and its well defined Raman spectra, glycine was selected here to follow its backbone protonation–deprotonation. The scan of the recorded spectra in the 1800–300 cm−1 region led us to assign those obtained at pH 1, 6 and 12 to the cationic, zwitterionic and anionic species, respectively. These data complete well those previously published by Bykov et al. (2008) [16] devoted to the high wavenumber Raman spectra (>2500 cm−1). To reinforce our discussion, DFT calculations were carried out on the clusters of glycine + 5H2O, mimicking reasonably the first hydration shell of the amino acid. Geometry optimization of 141 initial clusters, reflecting plausible combinations of the backbone torsion angles, allowed exploration of the conformational features, as well as construction of the theoretical Raman spectra by considering the most stable clusters containing each glycine species.

Thanks to a considerable modulation of electronic polarizability, six phenylalanine (Phe) vibration modes located at ca. 1606, 1586, 1207, 1031, 1004 and 622 cm−1 appear as intense or medium bands in the Raman spectra of peptides and proteins, as confirmed by the Raman data collected from free amino acid, somatostatin and bovine serum albumin (BSA). To get information on the nature and location of these lines, we resorted to a multiconformational analysis which consists in a systematic investigation of the structural and vibrational features of hydrated Phe in a conformational space depending on four angular variables: φ, ψ, χ1 and χ2. The first two variables correspond to the Phe backbone torsion angles, whereas the latter two refer to its side chain. Based on a protocol described in an accompanying report on glycine and its protonated and deprotonated species, we have prepared an initial set of 123 initial clusters of Phe + 5H2O, including all plausible values of the above mentioned conformational angles. The results of their geometry optimization, by means of the density functional theory using the B3LYP hybrid functional, were first analyzed through the comparison between the E(χ1, χ2) energy maps obtained either by an explicit or by an implicit hydration model. Then, a set of nine doubly minimized clusters corresponding to the deepest local minima were used for further structural and vibrational analysis. Beyond providing a reliable assignment for the above mentioned characteristic Raman lines, the theoretical spectrum allowed us to carry out an overview of the whole observed data of Phe in aqueous solution. Copyright © 2013 John Wiley & Sons, Ltd.

14 págs.; 10 figs.; 2 tabs., Octreotide and pasireotide are two cyclic somatostatin analogues with an important clinical use in the treatment and diagnosis of neuroendocrine tumors. Herein, by the combined use of several techniques (UV-visible absorption, fluorescence, circular dichroism, ζ-potential, transmission electron microscopy, Raman scattering, surface-enhanced Raman scattering, and quantum mechanical calculations) we have followed the structural dynamics of these analogues in the bulk, as well as their binding sites on plasmonic (gold and silver) colloids. In contrast to the previously derived conclusions, the two peptides seem to possess completely different conformational features. Octreotide, a cyclic octapeptide, is formed by a moderately flexible type-II′ β-turn maintained by a deformable disulfide linkage. Pasireotide, in which the cyclic character is made possible by peptide bonds, manifests a rigid backbone formed by two oppositely placed tight turns of different types, i.e. γ-turn and type-I β-turn. Owing to their cationic character, both analogues induce aggregation of negatively charged gold and silver colloids. Nevertheless, despite their notable structural differences, both peptides bind onto gold nanoparticles through their unique d-Trp residue. In contrast, their binding to silver colloids seems to be of electrostatic nature, as formed through monodentate or bidentate ionic pairs. © the Owner Societies 2016, The authors would like to thank Novartis Pharma (Basel, Switzerland) for generously providing the lyophilized sample of pasireotide. This work was granted access to the HPC resources of IDRIS (Orsay, France) under the allocations c2016085065 by GENCI (Grand Equipement National de Calcul Intensif). A. C. was supported by a Pasteur Innov (PIV15-197) and a PTR grant (PTR451) from Institut Pasteur. S. S. C. acknowledges the Spanish Ministerio de Economia y Competitividad for the project FIS2014-52212-R.

The effect of hexahydrated monovalent and divalent cations on the geometrical and vibrational features of dimethyl phosphate, dimethyl phosphorothioate and dimethyl phosphorodithioate anions (simple suitable model compounds representing the anionic moieties of natural and some modified nucleic acids) was studied. For this purpose, density functional theory (DFT) calculations were carried out at the B3LYP/6-31++G* level. Our results indicate that only K(+) and Mg(2+) prefer to be located in the bisector plane of the PO(2)(-) angle, whereas Li(+) and Na(+) deviate from this plane. Monovalent and divalent cations are slightly deviated from the OPS(-) bisector plane and are found closer to the free oxygen atom. Moreover, the present calculations have shown that in contrast to the general belief, the g(-)g(-) conformer (with respect to the torsion angles defined around the P-O ester bonds) is not always the energetically most favorable. For instance, the g(-)t conformer presents the lowest energy in the case of dimethyl phosphorothioate. The calculated vibrational wavenumbers obtained for dimethyl phosphate and dimethyl phosphorothioate interacting with hydrated sodium counterion, were compared with those previously recorded by Raman scattering and infrared absorption (IR) in aqueous solutions. It has been evidenced that the use of explicit solvent versus dielectric continuum, considerably improves the agreement between the theoretical and observed characteristic wavenumbers.

Since the late 1950s, metformin is the worldwide first-line pharmacologic treatment for type 2 diabetes. Beyond the fact that the mode of action of this drug has always been very difficult to elucidate, little is known about its physicochemical properties in aqueous solution. Herein, we focus on the protonation-deprotonation features of metformin by using jointly Raman scattering and theoretical calculations. Vibrational markers evidence the fact that within a wide pH interval extended at either side of the physiological one, i.e. ∼7 ± 4, metformin is mainly monoprotonated. Although the biprotonated form appears as major population at very low pH values (1.5), Raman markers of neutral species do not dominate even at very high pH values (13), presumably because of the extreme basicity of metformin as described by recent NMR measurements. Density functional theory calculations using both explicit and implicit hydration models, have led to presume a possible coexistence of two possible monoprotonated forms in aqueous environment. In conclusion, the biophysical features of this molecule and the amount used in clinical practice might certainly explain the pleiotropic actions toward several targets where metformin could be a permanent cationic partner, a proton donor/acceptor, as well as a good candidate for stabilizing the so-called π→π interactions.

The kinetic study of copolymers synthesis is important to understand how a material is built and how it can get some particular properties. The radical copolymerization of one, two or more monomers can be simulated with classical analytic models, but can also be simulated by a Monte Carlo model that allows a bigger flexibility and is a lot easier to compute and use. We have shown that this Monte Carlo simulation gives the same results of the kinetic stud of the terpolymerization as the analytic model, and it can create easily a bank of virtual copolymers for all the compositions needed to analyze the structure of the macromolecular chains in term of sequence of monomers occurring as a function of the global composition. The search for the sequences is very simple to compute as it consists in a simple reading of the virtual chains previously simulated. This result can thus be applied to make appear a simple correlation between the distribution of functional groups and some specific observed biological activities of biospecilic copolymers.

Previous results obtained have shown that it was possible to create biospecific sites onto polymers through statistic modifications of polystyrene derivatives copolymer with given chemical groups or through synthesis of random methacry late-based copolymers. Such polymers show biological activities (anticoagulant, cell proliferation modulation...) dependent of the global composition and thus of the statistical distribution of the functional groups, and the number of biospecific sites is simply correlated to the observed biological activity. The study of the radical terpolymerization allow us to use a Monte Carlo based synthesis simulation and to determine the occurrence frequency of three to twenty monomers sequence as a function of the conversion rate and the global composition. The comparison of the sequences occurrence curves as a function of the global composition of the polymers with the experimental cell proliferation inhibition curve led us to extract a series of eight monomers sequence with similar structure properties representing a group of biospecific sites responsible for the observed biological activity.

Lanreotide, a synthetic cyclic octapeptide, analogue of the peptide hormone somatostatin-14 (SST-14), is routinely used as a long-acting medication in the management of neuroendocrine tumors. Despite its therapeutic importance, low concentration structural data is still lacking for lanreotide. In fact, the major part of the previous structural investigations were focused on the remarkable aggregation properties of this peptide, appearing at high concentrations (5 mM). Here, we have applied three optical spectroscopic techniques, i.e. fluorescence, circular dichroism and Raman scattering, for analyzing the structural dynamics at the concentrations below 5 mM, where lanreotide exists either in a monomer state or at the first stages of aggregation. The obtained data from lanreotide were discussed through their comparison with those collected from SST-14, leading us to the following conclusions: (i) The central D-Trp residue, forming with its adjacent Lys the main receptor interacting part of lanreotide, keeps a constant high rotational freedom whatever the environment (water, water/methanol, methanol). (ii) A solvent-dependent tight β-turn, belonging to the type-II' family, is revealed in lanreotide. (iii) Raman data analyzed by band decomposition in the amide (I and III) regions allowed estimation of different secondary structural elements within the millimolar range. Interestingly, the applied protocol shows a perfect agreement between the structural features provided by the amide I and amide III Raman markers.

We present a set of new data allowing elucidation of the energetic, conformational and vibrational features of cysteine (Cys) and methionine (Met), i.e. two natural amino acids (AAs) containing a sulfur atom in their side chains. Special attention has been paid to cysteine, for which vibrational features were analysed in a wide pH range (6-to-12), where its backbone can switch from a zwitterionic to an anionic form, and its side chain SH group can be deprotonated. Through a detailed discussion on the relative acidity of the three protonation sites of this AA, as well as on the vibrational markers arising from zwitterionic and anionic backbones, we could assign the spectra recorded at pH 6, 9.2 and 12 to three species, referred to as Cys(0), Cys(1-)(a) and Cys(2-), where the superscripts designate their global net charges. To bring clarification to the structural and vibrational features, quantum mechanical calculations based on the Density Functional Theory (DFT) were carried out, allowing (i) a quasi exhaustive energetic and side chain conformational analysis through 804 clusters of explicitly hydrated AAs; (ii) simulation of the observed aqueous solution vibrational spectra of Cys(0), Cys(-2) and Met by means of the theoretical data obtained from their conformationally distinct lowest energy clusters.

A comprehensive description of the energetic, conformational, and vibrational features of the two amino acids (AAs) with polar side chains, i.e., serine and threonine, in aqueous environment, is provided. To adequately analyze the side chain conformational flexibility of these amino acids, we resorted to quantum mechanical calculations with the use of density functional theory, which allowed the determination of the energetic features of these AAs through 236 clusters. Each cluster contains a zwitterionic AA surrounded by seven explicit water molecules. The obtained data could evidence the effect of the side chain conformational angle (χ(1) and χ(2)) as well as the location of water molecules on the energy landscapes of both AAs. Four of the lowest energy clusters of each AA, which give rise to distinct side chain conformations, were selected in order to reproduce the FT-IR and Raman spectra recorded in aqueous solutions and to assign the vibrational modes responsible of the main observed bands.

Four out of the 20 natural α-amino acids (α-AAs) contain aromatic rings in their side chains. In a recent paper (J. Phys. Chem. B 2010, 114, 9072-9083), we have analyzed the structural and vibrational features of l-histidine, one of the potent elements of this series. Here, we report on the three remaining members of this family, i.e., l-phenylalanine, l-tyrosine, and l-tryptophan. Their solution (H(2)O and D(2)O) Raman scattering and Fourier transform infrared absorption attenuated total reflection (FT-IR ATR) spectra were measured at room temperature from the species corresponding to those existing at physiological conditions. Because of the very low water solubility of tyrosine, special attention was paid to avoid any artifact concerning the report of the vibrational spectra corresponding to nondissolved powder of this AA in aqueous solution. Finally, we could obtain for the first time the Raman and FT-IR spectra of tyrosine at very low concentration (2.3 mM) upon long accumulation time. To clarify this point, those vibrational spectra of tyrosine recorded either in the solid phase or in a heterogeneous state, where dissolved and nondissolved species of this AA coexist in aqueous solution, are also provided as Supporting Information . To carry out a discussion on the general geometrical and vibrational behavior of these AAs, we resorted to quantum mechanical calculations at the DFT/B3LYP/6-31++G* level, allowing (i) determination of potential energy surfaces of these AAs in a continuum solvent as a function of the torsion angles χ(1) and χ(2), defining the conformation of each aromatic side chain around C(α)-C(β) and C(β)-C(γ) bonds, respectively; (ii) analysis of geometrical features of the AAs surrounded by clusters of n explicit (n = 5-7) water molecules interacting with the backbone and aromatic rings; and (iii) assignment of the observed vibrational modes by means of the theoretical data provided by the lowest energy conformers of explicitly hydrated amino acids.

In manuscript VI of the same series (J. Phys. Chem. B 2010, 114, 1077-1088), we reported the geometrical and vibrational features of lysine and arginine, that is, two alpha-amino acids (alpha-AAs) with positively charged side chains, at physiological conditions. Here, we report our results on histidine, one of the most biologically important alpha-AAs, whose side chain can be neutral or positively charged through a protonation-deprotonation process of the nitrogens involved in its cyclic side chain at pH values in the physiological range. We have recorded at room temperature Raman scattering and Fourier-transform infrared (FT-IR) absorption spectra from the aqueous solutions of the AA at pH values 4, 6.8, and 8. It has been shown that a Raman spectrum recorded at the intermediate pH (6.8) can be perfectly reconstituted by a linear combination of those observed at two extreme pH values (4 and 8), allowing determination of the populations of histidine with protonated and neutral side chains in solution. The above-mentioned experimental data were completed by the vibrational spectra recorded in D(2)O. On the other hand, quantum mechanical calculations at the DFT/B3LYP/6-31++G* allowed us to analyze the energetic, geometrical, and vibrational features of histidine. Through a discussion on the basis of experimental and theoretical results, we comment on (i) the potential energy surfaces of histidine placed in a polarizable dielectric continuum, providing molecular energy landscapes as a function of its side chain orientations around C(alpha)-C(beta) and C(beta)-C(gamma) bonds; (ii) the full geometry optimization of the low energy conformers placed in a solvent continuum or in the presence of n explicit water molecules (n = 3, 7); (iii) the energy value separating the two histidine forms with neutral side chains; (iv) the determination of the side chain pK(a) by means of Raman spectra; and (v) the assignment of the observed vibrational modes by means of the lowest-energy conformers of hydrated histidine.

In two recent reports of the same series (J. Phys. Chem. B 2007, 111, 1470-1477 and J. Phys. Chem. B 2009, 113, 3169-3178), we have described the geometrical and vibrational analysis of glycine and amino acids (AAs) with hydrophobic side chains through the joint use of optical spectroscopy and quantum mechanical calculations. Here, we report Raman scattering and Fourier-Transform Infrared (FT-IR) Attenuated Total Reflectance (ATR) spectra measured from the aqueous solutions (H(2)O and D(2)O) of L-lysine and L-arginine, i.e. two alpha-AAs with positively charged hydrophilic side chains. The discussion on the vibrational features of both AAs could be carried out thanks to the theoretical calculations performed by means of the Density Functional Theory (DFT) approach at the B3LYP/6-31++G* level. We have analyzed the influence of implicit (with a polarizable dielectric continuum) and explicit (by means of an H(2)O cluster interacting with H-donor and H-acceptor sites of AAs) hydration models. In addition, through the calculated geometrical parameters and vibrational wavenumbers, a discussion was performed on the effect of the Cl(-) anion interacting with the positively charged side chains of explicitly hydrated AAs.

In the framework of our investigations on the analysis of vibrational spectra of amino acids (AAs) in hydrated media, Raman scattering and Fourier transform infrared (FT-IR) attenuated transmission reflectance (ATR) spectra of three alpha-amino acids with hydrophobic hydrocarbon side chains, i.e., alanine, valine, and isoleucine, were measured in H2O and D2O solutions. The present data complete those recently published by our group on glycine and leucine. This series of observed vibrational data gave us the opportunity to analyze the vibrational features of these amino acids in hydrated media by means of the density functional theory (DFT) calculations at the B3LYP/6-31++G* level. Harmonic vibrational modes calculated after geometry optimization on the clusters containing five water molecules interacting with H-donor and H-acceptor sites of amino acids are performed and allowed the observed main Raman and infrared bands to be assigned. Additional calculations on a cluster formed by leucine (L) and five water (W) molecules and the comparison of the obtained data with those recently published by our group on L+12W, allowed us to justify the number of hydration considered in the present report.

1 - Article; Raman scattering and Fourier-transform infrared (FT-IR) attenuated transmission reflectance (ATR) spectra of two alpha-amino acids (alpha-AAs), i.e., glycine and leucine, were measured in H2O and D2O (at neutral pH and pD). This series of observed vibrational data gave us the opportunity to analyze vibrational features of both AAs in hydrated media by density functional theory (DFT) calculations at the B3LYP/6-31++G* level. Harmonic vibrational modes calculated after geometry optimization on the clusters containing each AA and 12 surrounding water molecules, which represent primary models for hydration scheme of amino acids, allowed us to assign the main observed peaks.

Thrombus formation on blood-contacting artificial surfaces is a major problem. Antithrombogenic polymer surfaces have been obtained either by heparin binding, or by grafting sulphonate and/or amino acid sulphonamide groups on insoluble polystyrene. In addition to their capacity to adsorb thrombin, such surfaces were shown to be able to catalyse its inhibition by antithrombin III (AT), i.e. they are endowed with heparin-like activity. The results were mainly obtained by using clotting assays. In many cases, delineating adsorption and catalytic processes by such assays is not possible when evaluating anticoagulant polymer surfaces. To overcome this problem, the kinetics of thrombin adsorption and inhibitions by AT and heparin cofactor II (HC) in the presence of such surfaces have been measured by using an assay performed with a thrombin-specific chromogenic substrate. A simple kinetic model of thrombin consumption is proposed. The relevant calculations, carried out with the help of a computer program, lead to determination of relative second order rate constants of thrombin adsorption and inhibitions by AT and HC in the presence of the polymers. In addition to thrombin adsorption, polystyrene surfaces bearing only sulphonate groups catalyse inhibition by AT, whereas polystyrene surfaces bearing either aspartate, glycinate or isophthalate sulphonamide groups catalyse both inhibitions by AT and HC.

The kinetics of oxidative addition of zerovalent palladium to aromatic iodides in tetrahydrofuran in the presence of the ligand triphenylphosphine have been studied by amperometry on the oxidation wave of palladium. The reaction is first order in aromatic iodide and first order in palladium and the rate constant is inversely proportional to the free ligand concentration. The reactive palladium intermediate is assumed to be Pd{P(C 6 H 5 ) 3 } 2 . This assumpion is compatible with the observed activation parameters Δ H ‡  +77 kJ mol −1 ; Δ S ‡  13 J mol −1 K −1 . With substituted aromatic iodides, the rate constants give a linear Hammett relationship with ϱ  +2. The suggested mechanism can be regarded as related to an aromatic nucleophilic substitution with some assitance from halogen—palladium interaction.