Acid Complexes In Solution Research Articles

Novel procedures for preparing 99mTc(III) complexes with tetradentate/monodentate coordination of varying lipophilicity and adaptation to 188Re analogues.

Improved methods are presented for the preparation of 99mTc and 188Re mixed-ligand complexes with tetradentate and monodentate ligands of the general formula [MIII(Lm)(Ln)] (M = Tc, Re; Lm = NS3 or NS3COOH; Ln = isocyanide or phosphine). To avoid the undesired formation of reduced-hydrolyzed species of both metals, the preparation of complexes is performed in a two-step procedure. At first the Tc(III)- or Re(III)-EDTA complex is formed which reacts in a second step with the tripodal ligand 2,2',2' '-nitrilotris(ethanethiol) (NS3) or its carboxyl derivative NS3COOH (a) and the monodentate phosphine ligands (triphenylphosphine L1, dimethylphenylphosphine L2) or isocyanides (tert-butyl isonitrile L3, methoxyisobutyl isonitrile L4, 4-isocyanomethylbenzoic acid-L-arginine L5, 4-isocyanomethylbenzoic acid-L-arginyl-L-arginine L6, 4-isocyanomethylbenzoic acid-neurotensin(8-13) L7) to the so-called '4+1' complex. Copper(I) isocyanide complexes are used for preparing the '4+1' complexes. That facilitates storage stability and allows kit formulations, and, moreover, enables the formation of 188Re complexes in acidic solution. Only micromolar amounts of the monodentate ligand are needed, and that results in high specific activity labeling of interesting molecules. The lipophilicity of complexes can be controlled by introducing a carboxyl group into the tetradentate ligand and/or derivatization of the monodentate ligands. Furthermore, the carboxyl group enables the conjugation of biomolecules. As an example, the neurotensin derivative CN-NT(8-13) was prepared and labeled with 99mTc according to the '4+1' approach, and its behavior in vivo was studied.

Cobalt(III) Tetraazamacrocyclic Complexes with Pendant Amino Groups: Synthesis, Structure and Electrochemical Properties

AbstractTwo isomeric cis‐2,9‐bis(aminomethyl)‐5,7,7,12,14,14‐hexamethyl‐1,4,8,11‐tetraazacyclotetradecane (1 and 2) and two 2‐aminomethyl‐2‐methyl‐1,4,8,11‐tetraazacyclotetradecane (3 and 4) cobalt(III) complexes have been prepared and characterised. During the synthesis of 2 a minor oxidation product 5 was formed. The structures of 3, 4 and 5 have been determined by X‐ray crystallography, and the UV/Vis spectra of 1−5 have been analysed. The average Co−N distances in 1 and 2 have been estimated from the correlation between the average Co−N bond lengths and position of the maximum absorption for hexaamine complexes given in literature. The electrochemical behaviour of 1−5 in neutral and acidic solutions has been studied by cyclic voltammetry. In complexes displaying electronic maxima at higher energy, cobalt(III) was reduced at more negative potentials. Small differences in the conformation of ligand between 3 and 4 explain the different behaviour of these complexes in acidic solutions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Multiparameter single-molecule fluorescence spectroscopy reveals heterogeneity of HIV-1 reverse transcriptase:primer/template complexes.

By using single-molecule multiparameter fluorescence detection, fluorescence resonance energy transfer experiments, and newly developed data analysis methods, this study demonstrates directly the existence of three structurally distinct forms of reverse transcriptase (RT):nucleic acid complexes in solution. Single-molecule multiparameter fluorescence detection also provides first information on the structure of a complex not observed by x-ray crystallography. This species did not incorporate nucleotides and is structurally distinct from the other two observed species. We determined that the nucleic acid substrate is bound at a site far removed from the nucleic acid-binding tract observed by crystallography. In contrast, the other two states are identified as being similar to the x-ray crystal structure and represent distinct enzymatically productive stages in DNA polymerization. These species differ by only a 5-A shift in the position of the nucleic acid. Addition of nucleoside triphosphate or of inorganic pyrophosphate allowed us to assign them as the educt and product state in the polymerization reaction cycle; i.e., the educt state is a complex in which the nucleic acid is positioned to allow nucleotide incorporation. The second RT:nucleic acid complex is the product state, which is formed immediately after nucleotide incorporation, but before RT translates to the next nucleotide.

Correlation of acid–base chemistry of phytochelatin PC2 with its coordination properties towards the toxic metal ion Cd(ii)

The acid–base properties and cadmium binding abilities of (γ-Glu-Cys)2-Gly (PC2), a short phytochelatin, were studied in solution, using potentiometry, 1H NMR and UV-vis spectroscopy. Macroscopic and microscopic constants established by potentiometry and NMR allowed the complete dissociation processes of the hexaprotic PC2 molecule to be explained. The stoichiometry of the complexes formed by phytochelatin with cadmium depends very strongly on reactant ratios. For different amounts of ligand with respect to the metal ion the CdH2L and CdHL species exist in almost the same molar fractions. Above pH 6 complexes with one (CdL) or two ligand molecules bound (CdH3L2, CdH2L2, CdHL2 and CdL2, respectively) were found depending on the Cd(II) ∶ peptide ratio. 1H NMR and UV-vis spectroscopy show coordination of four sulfur atoms from two molecules of PC2 to one cadmium(II) ion (RCd–S: 2.52 A). Amino groups, glutamic acid and glycine deprotonated carboxyls also participate in cadmium coordination, in contrast to thiolate groups, in monomeric complexes in acidic solutions. Quantitative comparison of metal ion binding strength by PC2 with low molecular weight peptide thiols (LMWT), glutathione and its fragments show that over a wide range of pH phytochelatin binds to cadmium(II) ions several times more strongly than LMWT.

Equilibrium studies on the protonation and Cu(II) complexation by an hexaaza macrocycle containing p-xylyl spacers. The crystal structure of the hexaprotonated ligand and the kinetics of decomposition of the Cu(II) complexes

The protonation constants of the ligand 3,6,9,16,19,22-hexaazatricyclo[22.2.2.2 11,14]triaconta-1(26),11(12),13,24,27, 29-hexaene (L, BPXD) have been determined in water at 25°C by potentiometric procedures and indicate a lower basicity than that corresponding to the analogue ligand with m-xylyl spacers between the diethylenetriamine subunits (BMXD). The crystal structure of a salt of H 6L 6+ containing Br − and NO 3 − as anions has been solved by X-ray diffraction procedures and reveals that the macrocycle adopts an almost planar configuration. The protonated amine groups are involved in a complex network of hydrogen bonds with the anions and water molecules, with two anions being placed close to the cavity of the macrocycle. Despite the lower basicity of BPXD, the stability of the mononuclear CuL 2+ and HCuL 3+ complexes is several log units higher than that corresponding to the analogous BMXD complexes, which suggests the possibility of a different coordination mode for both closely related ligands. Actually, the whole set of stability constants for the mono and binuclear Cu(II)–L complexes can be rationalised by considering that the macrocycle acts as tetradentate in the mononuclear species. In contrast, the kinetic parameters for decomposition of the mono and binuclear Cu(II)–L complexes in acid solutions are only slightly different from those previously determined for the BMXD complexes.

Speciation of gold(III)-L-histidine complex: a multi-instrumental approach.

The formation and structure of gold (III)-L-histidine complex was investigated with the use of carbon (13C) and proton (1H) nuclear magnetic resonance (NMR), infrared (IR) spectroscopy, capillary electrophoresis (CE), capillary electrophoresis-inductively coupled plasma-mass spectroscopy (CE-ICP-MS), X-ray fluorescence spectroscopy (XRF), matrix-assisted laser desorption/ionization (MALDI), and laser desorption mass spectroscopy (LDMS). It was found that two L-histidine molecules and one gold ion slowly form a complex in acidic solution. Each L-histidine molecule provided two nitrogen ligands; one was the alpha-amino group and the other from the imidazole ring. The Au(III)-bis-L-histidine complex precipitates after deprotonation of the free carboxylic group, resulting in an increase in the solution acidity. Determination of the exact sequence of events and the identity of the complex was a comprehensive instrumental analysis problem involving the above techniques.

Spectroscopic characterization of coaxially and π—π stacked binuclear copper(II) complexes of ω,ω′-bis(pyridine-2-carboxamido)alkanes in acidic solution

Using electron spin resonance (ESR) and visible spectroscopies, coaxially stacked binuclear copper(II) complexes of ω,ω′-bis(pyridine-2-carboxamido)alkanes in acidic aqueous solution (pH 3.8–5.0), H 2peda (alkane = ethane), H 2ppda (alkane = propane), and H 2pbda (alkane = butane), were characterized. trans-1,2-Bis(pyridine-2-carboxamido)cyclohexane or trans-H 2pcyhda (alkane = trans-1,2-cyclohexane) did not provide coaxially stacked binuclear complex, because of the lower conformational freedom at the HNCH-CHNH bond. The coaxially stacked structure causes π—π stacking between the pyridyl rings. The conformation of the propanediyl chain is gauche—gauche, while the ethanediyl and butanediyl chains contain an eclipsed conformation. The driving force for the formation of these binuclear complexes in acidic solution is intramolecular π—π stacking interaction between the pyridyl rings in concert with hydrophobic interaction. Although H 2ppda gave crystals of a binuclear complex with many lattice water molecules, H 2peda and H 2pbda ligands provided crystals of copper(II) polymer complexes from the respective acidic solution. The trans-H 2pcyhda ligand forms a copper(II) binuclear complex with open-chain structure in acidic solution. Crystal structures of the polymer complexes are also presented.

Experimental investigation of aluminum-silica aqueous complexing at 300°C

Equilibrium constants for aqueous Al–Si complexes at 300°C and saturated water vapour pressure (86 bar) were generated experimentally from the difference between the solubility of boehmite in silica-free and silica-bearing solutions. At strongly acidic (pH<2) and near-neutral to basic (pH>4.5) conditions aluminum silica aqueous complexes form according to Al 3++H 4SiO 4 0=AlH 3SiO 4 2++H + and Al(OH) 4 −+H 4SiO 4 0=Al(OH) 3H 3SiO 4 −+H 2O for which the logarithm of the equilibrium constants was found to be 3.23±0.25 and 2.32±0.20, respectively. No solubility increase following addition of aqueous silica was observed in the slightly acidic range (2.5<pH<4), indicating that Si complexation with Al(OH) 2+, Al(OH) 2 +, and Al(OH) 3 0, is negligible. The equilibrium constant obtained for AlH 3SiO 4 2+ formation at 300°C was combined with published values for this complex at 25 to 150°C [Pokrovski, G.S., Schott, J., Harrichoury, J.-C., Sergeyev, A.S., 1996. The stability of aluminum silicate complexes in acidic solutions from 25 to 150°C. Geochim. Cosmochim. Acta 60, 2495–2501.] to generate standard partial molal thermodynamic properties at 25°C and 1 bar and HKF (revised Helgeson–Kirkham–Flowers model; [Tanger, J.C., Helgeson, H.C., 1988. Calculation of the thermodynamic and transport properties of aqueous species at high pressures and temperatures: revised equations of state for the standard partial molal properties of ions and electrolytes. Am. J. Sci., 288, 19–98; Shock, E.L., Helgeson, H.C., 1988. Calculation of the thermodynamic and transport properties of aqueous species at high pressures and temperatures: correlations algorithms for ionic species and equation of state predictions to 5 kbar and 1000°C. Geochim. Cosmochim. Acta, 52, 2009–2036; Shock, E.L., Oelkers, E.H., Johnson, J.W., Sverjensky, D.A., Helgeson, H.C., 1992. Calculation of the thermodynamic properties of aqueous species at high pressures and temperatures. J. Chem. Faraday Trans. 88 (6), 803–826.] equation of state parameters for this complex. Calculations indicate that Al–Si complexing can increase Al solubility of up to 1/2 an order of magnitude at 500°C and 1 kbar. As a consequence, Al–Si complexes should be taken into account to accurately model chemical equilibria in hydrothermal and metamorphic fluids.

Anion Effects on the Kinetics of Mercury Underpotential Deposition on Au(111) Electrodes

The kinetics and mechanism of mercury underpotential deposition (UPD) on Au(111) electrodes have been investigated in the presence and absence of strongly interacting anions including bi-sulfate, chloride, and acetate. In the absence of strongly interacting anions, i.e. in perchloric acid, the mercury UPD process is largely controlled by mercury−gold surface interactions. The presence of sulfuric acid in the supporting electrolyte alters the kinetics of the initial and final stages of mercury deposition/dissolution. The presence of two well-ordered structures at potentials below (a mercurous sulfate √3×√19 structure) and above (a √3×√7 bi-sulfate structure) mercury deposition leads to the appearance of two pairs of sharp spikes in the cyclic voltammogram. Analysis of the current transients obtained for deposition and dissolution processes reveals that three different processes are taking place during the adsorption/desorption of the mercury bi-sulfate layer: adsorption/desorption processes governed by Langmuir kinetics, a nucleation and growth process linked to an order/disorder transition to form the mercury bi-sulfate adlayer, and an order/disorder transition related to the formation/disruption of the √3×√7 bi-sulfate layer. In chloride medium, the voltammetric profile is very similar to that obtained in sulfuric acid solution, with the presence of two sharp spikes. However, no nucleation and growth kinetics mechanism was found linked to the process of formation/disruption of the mercury chloride adlayer. The transients show a clear deviation from the ideal Langmuir behavior, probably associated with the presence of attractive interactions in the mercury chloride adlayer. The kinetics of mercury UPD in acetate media are significantly slower than in the previous media, as revealed by voltammetric and chronoamperometric measurements. The slow kinetics appear to be related to the formation of Hg2+−acetic acid complexes in solution. Although ordered structures are formed at potentials below the main UPD peak, no nucleation and growth mechanism was observed.

The stability of aluminum silicate complexes in acidic solutions from 25 to 150°C

The equilibrium constant of the reaction Al 3+ + H 4SiO 4 0, (aq) = AlH 3SiO 4 2+ + H + (K 1) has been determined at temperatures from 25 to 150°C from the pH of aqueous solutions containing H 4SiO 4(aq), HCI, and KCl with and without added AlCl 3. Log K 1 values obtained in this study at 25, 90, and 150°C are −2.38 ± 0.10, −0.35 ± 0.20, and 1.07 ± 0.30, respectively. These values are linearly related to the reciprocal temperature and yield an association enthalpy of 66.6 kJ/mol. The K 1 value derived at 25°C is in close agreement with that determined by Farmer and Lumsdon (1994) and implies that aluminum silicate complexes do not play a significant role in most surficial natural waters. However, thermodynamic calculations indicate that these complexes form in significant amounts in acid (pH < 3) hydrothermal solutions where they can affect the solubility of Al/Si-bearing minerals.

Copper(II) and nickel(II) complexes of hexacyclen (1,4,7,10,13,16-hexa-azacyclo-octadecane) and the kinetics of dissociation of the copper(II) and nickel(II) complexes in acidic solution

The copper(II) and nickel(II) complexes of hexacyclen (1,4,7,10,13,16-hexa-azacyclo-octadecane, [18]aneN 6) have been characterized as their perchlorate salts, [ML](ClO 4) 2·H 2O. Analytical, conductivity, spectral and magnetic measurements are reported. The kinetics of dissociation of the copper(II) and nickel(II) complexes in acidic solution have been studied in detail. For the copper complex at high acidities ([H +] = 0.075-0.275 M) a single kinetic process is observed which displays a first order dependence on the hydrogen ion concentration with rate = k H[CuL 2+][H +] and k H = 73 M −1s −1 at 25°C and I = 1.0 M. The temperature dependence of k H gives ΔH ‡ = 30.5 kJ mol −1 and ΔS 298 ‡ = −107 JK −1 mol −1 . Cleavage of the first equatorial CuN bond is slow with all of the subsequent steps being rapid. At lower acidities ([H +] ca 1 × 10 −3 M) only the monoprotonated complex CuLH 3+ is expected to occur in solution. The reaction displays a second order dependence on the hydrogen ion concentration with rate = k′ H[CuLH 3+][H +] 2 and k′ H = 8.5 × 10 3 M −2 s −1 at 25°C and I = 1.0 M. The equilibrium constant for the second protonation equilibrium CuLH 3+ + H + ⇌ CuLH 2 4+ is given by K = k′ H/ k H = 116 M −1 at 25°C. Dissociation of CuL 2+ in 1 M acid is some 10-fold slower than CuN cleavage in [Cu(2,2,2,-tet)] 2+ (2,2,2-tet = 1,8-diamino-3,7-diazoctane). The acid hydrolysis of [NiL] 2+ is biphasic at both low and high acidities. At high acidities (0.05-0.4 M [H +]) both reactions display saturation kinetics and it was possible to determine the equilibrium constant K 2 for the second protonation equilibrium NiLH 3+ + H + ⇌ NiLH 2 4+ as 2.5 M −1 at 25°C and I = 1.0M. For the dissociation of NiLH 2 4+ the rate constant is 59 s −1, while for the reaction NiLH 2 4+ + H + → Ni 2+ + LH 6 6+ the rate constant is 6.4 M −1 s −1 at 25°C and I = 0.1 M. At low acidities the two reactions display a second order dependence on the hydrogen ion concentration and the rate constants are 95 ± 3 M −2 s −1 and 24±2 M −2 s −1 at 25°C. The temperature dependence of the rate constant for the slower reaction gives ΔH ‡ = 44.6±2 kJ mol −1 and ΔS 298 ‡ = −70±5 JK −1 mol −1 .

Calorimetric and Laser Induced Fluorescence Investigation of the Complexation Geometry of Selected Europium-gem-Diphosphonate Complexes in Acidic Solutions

Details of the coordination chemistry of europium complexes with methanediphosphonic acid (MDPA), vinylidene-1,1-diphosphonic acid (VDPA), and 1-hydroxyethane-1,1-diphosphonic acid (HEDPA) in acidic aqueous solutions have been investigated by titration calorimetry and laser-induced fluorescence. For the 1:1 complexes, thermodynamic parameters and complex hydration are consistent with those previously reported for europium complexes with the carboxylate structural analog malonate. In the 1:2 complexes, markedly different thermodynamic parameters and cation dehydration are observed. The second diphosphonate ligand adds to the 1:1 complex displacing four additional water molecules from the primary coordination sphere (as compared with two for the addition of a second malonate). This reaction is also characterized by a nearly zero entropy change. The results are rationalized using molecular mechanics to suggest an unusual geometry in which the diphosphonate ligands and bound water molecules are appreciably segregated in the europium coordination sphere. Intramolecular hydrogen bonding and second hydration sphere ordering are suggested to explain the low complexation entropies.

Hydrogen/Hydrogen Exchange and Formation of Dihydrogen Derivatives of Rhenium Hydride Complexes in Acidic Solutions

Hydrogen/Hydrogen Exchange and Formation of Dihydrogen Derivatives of Rhenium Hydride Complexes in Acidic Solutions

Structural investigations on lewis acid mediated solubilization of poly(p‐phenylenebenzobisthiazole) in an aprotic solvent

AbstractInvestigations on aluminum chloride‐mediated solubilization of poly(p‐phenylenebenzo‐bisthiazole), PBZT, in nitromethane revealed that, in general, dilute solutions of the polymer prepared in nitromethane with a large molar excess of the Lewis acid with respect to PBZT were relatively stable and thus suitable for processing into films and coatings via regeneration with hydroxylic nosolvents while polymer solutions with minimum stoichiometrically required (PBZT:AlCl3 molar ratio 1:4) or marginal molar excess of AlCl3 relative to PBZT tended to gel during handling. Structural studies on polymer–Lewis acid complex solutions were performed using 1H and 27Al NMR. 1H NMR of the protonated structure of the model compound 2,6‐diphenylbenzo [1,2‐d:4,5‐d′] bisthiazole was useful for confirming the 1H NMR assignments of PBZT‐AlCl3 complex solution in CD3NO2. 27Al NMR was particularly useful in probing the different tetrahedrally coordinated environments of the Al nucleus in the polymer solution, pointing to a complexation interaction between the polymer molecule and the Lewis acid and also between the solvent and the Lewis acid. Direct evidence in the solid state for the presence of a reversible electron donor–acceptor complex (EDA complex) was obtained from FTIR spectra of complexed films, isolated and handled in an inert atmosphere. The structural changes upon PBZT complexation caused significant frequencly shifts in both aromatic as well as heteroring stretching modes relative to PBZT itself, and intensity variations indicative of changes in the resonance configuration between the 1,4‐phenylene moiety and the aromatic heterocyclic ring were also observed upon complexation. A preliminary comparison between the pristine PBZT fibers and regenerated PBZT by dilute solution viscometry indicates that the process results, to some extent, in polymer degradation leading to a decrease in the molecular weight of the polymer © 1993 John Wiley &amp; Sons, Inc.

The rate of decomposition of the ferric-thiosulfate complex in acidic aqueous solutions

The rate of decomposition of the ferric thiosulfate complex varies as the square of the concentration of the complex. The rate of decomposition of the complex was determined by following the change in absorbance due to the complex as a function of time. Regression of log rate vs. log m FeS 2O 3 + at 20°C produced the rate law dm FeS 2O + 3 dt = − 2.0(±0.3)m 2.0(±0.1) FeS 2O 3. The decomposition of this complex in acid solutions is strongly dependent on temperature, E a = 120(±15) kJ mol −. The rate of reaction increases with increasing ionic strength, which is consistent with the interaction of two positively charged ions to form the activated complex. This study resolves many of the inconsistencies found in earlier studies and shows that reaction with H + is a more important sink for S 2O 3 2− than reaction with Fe 3+ when pH > ~1.7.

Gold bromide complexes in acidic aqueous solutions from 25� to 300�C. A laser raman spectroscopic study

Raman spectra of gold bromide complexes in acidic solutions (pH=−0.3–3) have been recorded at 25° to 300°C and at pressures on the liquid vapor curve for the system. At 25°C, only the square planar Au(III) bromide complex, AuBr 4 − , is present in solution with bands at approximately 105, 197 and 215 cm−1. However, in these acidic solutions, when the temperature is 50°C or higher, the square planar Au(III) bromide complex is partially transformed into the linear Au(I) bromide complex, AuBr 2 − , with a single band near 208 cm−1. The transformation of the Au(III) square planar tetrabromo complex into the Au(I) linear dibromo complex is also favored by a reduction of the oxygen fugacity and an increase in pH.

Studies of Chromium(III)-Gluconate Complexes in Acidic Solutions by Liquid-Liquid Extraction

Article Studies of Chromium(III)-Gluconate Complexes in Acidic Solutions by Liquid-Liquid Extraction was published on July 1, 1989 in the journal Zeitschrift für Physikalische Chemie (volume 270O, issue 1).

Studies of Chromium(III)-Gluconate Complexes in Acidic Solutions by Liquid-Liquid Extraction

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Effect of gamma radiation on folic acid and its cobalt complex solutions

Gamma-radiolysis of folic acid and its cobalt complex were studied in aqueous solutions at doses ranged from 2 to 10 krad and from 2 to 10 Mrad using60Co source. The variations in their spectra of IR, UV, and visible due to their radiolysis were shown. Also the change in pH after radiolysis was determined. The results showed that decomposition of folic acid by gamma-radiation occurred without variation of pH. Fine measurements of pH for irradiated CoCl2 and cobalt-folic acid complex solutions can be utilized for dose determination in the studied range of 2–10 Mrad. IR spectra showed that addition of cobalt chloride to folic acid decreased its decomposition by gamma-radiation. This result proved the importance of addition of cobalt chloride in keeping foodstuffs, which contain folic acid, by irradiation. The mechanism for the effect of radiation on cobalt chloride and cobalt-folic acid complex was discussed.

Anodic stripping voltammetry with mercury electrodes in extracts of cadmium, lead, thallium and indium diethyldithiocarbamate complexes and analysis of mixtures

The selectivity of the determination of traces of cadmium, lead, thallium and indium is improved by direct coupling of liquid/liquid extraction and anodic stripping voltammetry. Metals are extracted from aqueous solution to benzene or chloroform after the addition of sodium or zinc diethyldithiocarbamate. Stripping voltammetry of Cd, Tl and Pb at a hanging mercury drop electrode or mercury film electrode is done in benzene/methanol medium (1:1) with 0.1 M NaClO 4 as supporting electrolyte. For indium, the medium is chloroform/ethanol/water (1:4:1) with 0.005 M sodium acetate/0.06 M KBr/0.06 M HCl as supporting electrolyte. The complexes in acidic solution can be decomposed by mercury (II) ions, which provides useful shifts of deposition potentials. Calibration graphs are linear at concentrations of about 10 −7 M with a detection limit of 1×10 −8 M. The method is applied to determine a single metal in the presence of a large amount (1000-fold) of interfering metal.