Complexation of Ag+ ions with L-cysteine

The complexation of Ag⁺ ions with L-cysteine anions (Cys^2?) at 25°C was studied potentiometrically against the background of 0.1 M KNO₃. The AgCys^? (log?? = 11.14 ± 0.10), AgHCys (log?? = 20.77 ± 0.06), Ag₂Cys (log?? = 20.32 ± 0.17), and Ag₂HCys⁺ (log?? = 27.28 ± 0.12) soluble complexes were found to be formed.     

Stability constants for aqueous silver/bromide/thiocyanate complexes

Stability constants for aqueous Ag⁺/Br^?, Ag⁺/SCN^?, and mixed Ag⁺/Br^?/SCN^? complexes are determined at 25° C by using data generated potentiometrically in solutions having ionic strengths of 0.4, 1.0, and 2.0 m. Monte Carlo numerical methods which yield apparent stability constants for these complexes as well as confidence limits are described in detail. Explicit consideration of speciation shows that under useful precipitation conditions (high bromide and low thiocyanate), a significant fraction of soluble silver is present as AgBr_n (SCN)^1?n?m_m complexes. The most prevalent mixed complexes under these conditions are AgBr (SCN)^? (log β₁₁=8.0 ± 0.5) and AgBr₂(SCN)^2? (log β₂₁=9.2 ± 0.3). The free energies of formation of the other tri- and tetra-coordinate mixed complexes are nearly indistinguishable (log β₁₂=9.3 ± 0.5; log β₃₁=9.0 ± 0.6; log β₂₂=9.6 ± 0.9; log β₁₃=10.3 ±0.5).     

Gas-phase elimination kinetics of 1-substituted ethyl acetates. Effect of polar substituents at the α carbon of secondary acetates

The gas-phase elimination of several polar substituents at the α carbon of ethyl acetates has been studied in a static system over the temperature range of 310–410°C and the pressure range of 39–313 torr. These reactions are homogeneous in both clean and seasoned vessels, follow a first-order rate law, and are unimolecular. The temperature dependence of the rate coefficients is given by the following Arrhenius equations: 2-acetoxypropionitrile, log k₁ (s^?1) = (12.88 ± 0.29) – (203.3 ± 2.6) kJ/mol (2.303RT)^?1; for 3-acetoxy-2-butanone, log ±₁(s^?1) = (13.40 ± 0.20) – (202.8 ± 2.4) kJ/mol (2.303RT)^?1; for 1,1,1-trichloro-2-acetoxypropane, log ?₁ (s^?1) = (12.12 ± 0.50) – (193.7 ± 6.0) kJ/mol (2.303RT)^?; for methyl 2-acetoxypropionate, log ?₁ (s^?1) = (13.45 ± 0.05) – (209.5 ± 0.5) kJ/mol (2.303RT)^?1; for 1-chloro-2-acetoxypropane, log ?₁ (s^?1) = (12.95 ± 0.15) – (197.5 ± 1.8) kJ/mol (2.303RT)^?1; for 1-fluoro-2-acetoxypropane, log ?₁ (s^?1) = (12.83 ± 0.15)– (197.8 ± 1.8) kJ/mol (2.303RT)^?1; for 1-dimethylamino-2-acetoxypropane, log ?₁ (s^?1) = (12.66 ± 0.22) –(185.9 ± 2.5) kJ/mol (2.303RT)^?1; for 1-phenyl-2-acetoxypropane, log ?₁ (s^?1) = (12.53 ± 0.20) – (180.1 ± 2.3) kJ/mol (2.303RT)^?1; and for 1-phenyl?3?acetoxybutane, log ?₁ (s^?1) = (12.33 ± 0.25) – (179.8 ± 2.9) kJ/mol (2.303RT)^?1. The C_α? O bond polarization appears to be the rate-determining process in the transmition state of these pyrolysis reactions. Linear correlations of electron-releasing and electron-withdrawing groups along strong σ bonds have been projected and discussed. The present work may provide a general view on the effect of alkyl and polar substituents at the C_α? O bond in the gas-phase elimination of secondary acetates.     

Kinetics of reaction between acetic acid and Ag2+ in nitric acid medium

The reaction kinetics between acetic acid and Ag²⁺ in nitric acid medium is studied by spectrophotometry. The effects of concentrations of acetic acid (HAc), H⁺, NO^?₃, and temperature on the reaction are investigated. The rate equation has been determined to be –dc(Ag²⁺)/dt = kc(Ag²⁺)c(HAc)c^?1(H⁺), where k = (610 ± 15) (mol/L)^?1 min^?1 with an activation energy of about (48. 8 ± 3.5) kJ mol^?1 when the reaction temperature is 25°C and the ionic strength is 4.0 mol L^?1. The reduction rate of Ag²⁺ increases with the increase in HAc concentration and/or temperature and the decrease in HNO₃ concentration. However, the effect of NO^?₃ concentrations within 0.5–2.5 mol L^?1 on the reaction rate is negligible. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 45: 47–51, 2013     

Experimental study and computer modeling of Ni(II) and Cu(II) complexation with ceftazidime

The protonation constants of the anion of the cephalosporin antibiotic ceftazidime Ctzd^– and formation constants of its complexes with Ni²⁺ and Cu²⁺ have been determined by pH metric titration at 25°С and ionic strength 0.1 (KNO₃): logβ(HCtzd) = 4.82 ± 0.04, logβ(H₂Ctzd⁺) = 7.62 ± 0.06, logβ(H₃Ctzd²⁺) = 9.23 ± 0.09, logβ(NiCtzd⁺) = 4.04 ± 0.03, logβ(Ni(Ctzd)₂) = 6.41 ± 0.06, and logβ(CuCtzd⁺) = 5.03 ± 0.06. The potentiometric method has failed to reveal the complexation of Ctzd^– with Co²⁺, Zn²⁺, and Cd²⁺. The composition of the [Ni(Ctzd)₂] and [CuCtzd]⁺ complexes has been confirmed by spectrophotometry. The computer models of the [NiCtzd]⁺ and [CuCtzd]⁺ complexes have been calculated by the DFT method with the use of the B3LYP hybrid functional and the LACV3P**++ basis set.     

Extraction of silver from water into nitrobenzene using sodium dicarbollylcobaltate in the presence of valinomycin

Summary From extraction experiments andg-activity measurements, the extraction constant corresponding to the Ag⁺(aq) + NaL⁺(nb)?AgL⁺(nb) + Na⁺(aq) equilibrium in the two-phase water-nitrobenzene system (L=valinomycin; aq=aqueous phase, nb=nitrobenzene phase) was evaluated as log K_ex(Ag⁺,NaL⁺)=-0.6±0.1. The stability constant of the valinomycin-silver complex in nitrobenzene saturated with water was calculated: log b_nb(AgL⁺)=4.6±0.1. The stability constants of complexes of some univalent cations with valinomycin were summarized and discussed.     

Stability of diammine and chloroammine gold(I) complexes in aqueous solution

The substitution equilibria AuCl ₂ ^? + iNH ₄ ⁺ = Au(NH₃)_iCl_{2 ? i} + iCl^? + iH⁺, β _i ^* . were studied pH-metrically at 25°C and I = 1 mol/L (NaCl) in aqueous solution. It was found that logβ ₁ ^* = ?5.10±0.15 and logβ ₂ ^* = ?10.25±0.10. For equilibrium AuNH₃Cl_solid = AuNH₃Cl, log K _s = ?3.1±0.3. Taking into account the protonation constants of ammonia (log K _H = 9.40), the obtained results show that for equilibria AuCl ₂ ^? + iNH₃ = Au(NH₃)_iCl_{2 ? i} + iCl^?, logβ₁ = 4.3±0.2, and logβ₂ = 8.55±0.15. The standard potentials E ₀ ^1/0 of AuNH₃Cl⁰ and Au(NH₃) ₂ ⁺ species are equal to 0.90±0.02 and 0.64±0.01 V, respectively.     

The stability and solubility of cadmium(II)-8-oxyquinoline complexes in water and micellar solutions of sodium dodecyl sulfate

The formation of cadmium 8-oxyquinoline (HOx) complexes in water and a 0.01 M aqueous solution of sodium dodecyl sulfate (293 K, 0.01) was studied by pH-metric titration. Mathematical simulation of the most probable equilibria gave complex formation constants logβ₁ = 6.17 ± 0.32 (CdOx⁺) and logβ₂ = 14.60 ± 0.14 (CdOx₂) in aqueous solution and apparent stability constants logβ₁ = 8.64 (CdOx⁺) and logβ₂ = 17.59 (CdOx₂) in a solution of dodecyl sulfate. The solubility of cadmium dioxyquinolate in water at pH from 3 to 6 and a micellar sodium dodecyl sulfate medium was determined by the method of saturated solutions. The solubility product pL _p = 21.3 ± 0.9 (H₂O, 293 K) was calculated by modeling the solution of CdOx₂ with taking into account all acid-base interactions and complex formation reactions.     

Autoionizing rydberg states of. The Li2 molecule: Molecular constants for Li2+

Autoionizing Rydberg series of Li₂ have been observed in the two-step optical cxcitation of a supersonic lithium beam. The series limits are vibrational states of Li₂⁺. In the most probable assignment IP(Li₂) = 41236.4 ± 2.5 cm^?1 and for Li₂⁺ω_e = 263.45 ± 1.3 cm^?1; ω_eχ_e = 1.35 ± O.2 cm^?1; r_e = 3.032 ± 0.01 Å; D_e = 10807 ± 150 cm^?1.     

Cation-Induced dimerization of nickel(II), platinum(II), and palladium(II) meso-tetra(benzo-15-crown-5)porphyrinates

Cation-induced dimerization of nickel(II), platinum(II), and palladium(II) meso-tetra(benzo-15-crown-5)porphyrinates (Ni(II)TCP, Pd(II)TCP, and Pt(II)TCP) on treatment with potassium thiocyanate in a chloroform-methanol solution has been studied by electronic absorption spectroscopy. The formation of [{MTCP}₂(K⁺)₄](SCN^?)₄ in solution induces a hypsochromic shift of the Soret band and a bathochromic shift of the β-band with respect to their positions in the spectrum of MTCP. The equilibrium constants (K) for the 2MTCP + 4K⁺ = [{MTCP}₂(K⁺)₄] processes at 20°C are determined to be as follows: log K _Ni(II)TCP = 27.31 ± 1.67, logK _Pd(II)TCP = 27.16 ± 1.43, and logK _Pt(II)TCP = 26.15 ± 1.56.     

Cuprous complexes and dioxygen,VII. Competition between one- and two-electron reduction of O2 in the autoxidation of Cu(1-methyl-2-hydroxymethyl-imidazole)2+

The complexation of 1-methyl-2-hydroxymethyl-imidazole (L) with Cu(I) and Cu(II) has been studied in aqueous acetonitrile (AN). Cu(I) forms three complexes, Cu(AN)L⁺, CuL₂⁺, and Cu(AN)H_?1L, with stability constants logK(Cu(AN)⁺ + L ? Cu(AN)L⁺) = 4.60 ± 0.02, logβ₂ = 11.31 ± 0.04, and logK(Cu(AN)H_?1L+H⁺ ? Cu(AN)L⁺) = 10.43 ± 0.08 in 0.15M AN. The main species for Cu(II) are CuL²⁺, CuH_?1L⁺, CuH_?1L₂⁺, and CuH_?2L₂. The autoxidation of CuL₂⁺ was followed with an oxygen sensor and spectrophotometrically. Competition between the formation of superoxide in a one-electron reduction of O₂ and a path leading to H₂O₂ via binuclear (CuL₂)₂O was inferred from the rate law with k_a = (2.31 ± 0.12) · 10⁴M ^?2S ^?1, k_b = (1.0 ± 0.2) · 10³M ^?1, k_c = (2.85 ± 0.07) · 10²M ^?2S ^?1, k_d = 3.89 ± 0.14M ^?1S ^?1, k_e = 0.112 ± 0.004, k_f = (2.06 ± 0.24) · 10^?10M S ^?1, k_g = (1.35 ± 0.07) · 10^?7 S ^?1, and k_h = (6.8 ± 1.4) · 10^?7M ^?1 S ^?1.     

b1Σ+ Emissions from group V–VII diatomic molecules. b 0+ → X1 0+, X2 1 emissions of AsI and SbI

Chemiluminescence from the b 0⁺ → X₁ 0⁺ band system of AsI and of the b 0⁺ → X₁ 0⁺, X₂ 1 systems of SbI in the near-infrared spectral region has been observed in a discharge flow system. Analysis of the spectra led to the spectroscopic constants (in cm^?1) of AsI: ω_e(X₁, X₂) = 257 ± 2, ω_ex_e(X₁, X₂) = 0.82 ± 0.2, T_e(b 0⁺) = 11738 ± 5, ω_e(b 0⁺) = 271 ± 2, ω_ex_e(b 0⁺) = 0.66 ± 0.2, and of SbI: T_e(X₂ 1) = 965 ± 10, ω_e(X₁, X₂) = 206 ± 6, T_e(b 0⁺) = 12328 ± 10, ω_e(b 0⁺) = 211 ± 6. The intensity ratio of the two sub-systems b 0⁺ → X₂ 1 and b 0⁺→ X₁ 0⁺ was found to be ≈0.013 in the case of SbI and ? 0.01 for AsI.     

The retro-aldol mechanism in the pyrolysis kinetics of primary,secondary, and tertiary β-hydroxy ketones in the gas phase

The pyrolysis kinetics of primary, secondary, and tertiary β-hydroxy ketones have been studied in static seasoned vessels over the pressure range of 21–152 torr and the temperature range of 190°–260°C. These eliminations are homogeneous, unimolecular, and follow a first-order rate law. The rate coefficients are expressed by the following equations: for 1-hydroxy-3-butanone, log k₁(s^?1) = (12.18 ± 0.39) ? (150.0 ± 3.9) kJ mol^?1 (2.303RT)^?1; for 4-hydroxy-2-pentanone, log k₁(s^?1) = (11.64 ± 0.28) ? (142.1 ± 2.7) kJ mol^?1 (2.303RT)^?1; and for 4-hydroxy-4-methyl-2-pentanone, log k₁(s^?1) = (11.36 ± 0.52) ? (133.4 ± 4.9) kJ mol^?1 (2.303RT)^?1. The acid nature of the hydroxyl hydrogen is not determinant in rate enhancement, but important in assistance during elimination. However, methyl substitution at the hydroxyl carbon causes a small but significant increase in rates and, thus, appears to be the limiting factor in a retroaldol type of mechanism in these decompositions. © John Wiley & Sons, Inc.     

Silbermercaptide und -mercaptokomplexe

The complex formation of silver(I) has been studied with the anions of simple mercaptans RSH which have been rendered soluble by replacing some H in the substituent R by OH. All equilibria constants refer to a solvent of ionic strength μ = 0,1 and 20°C. Monothioglycol HO? CH₂? CH₂? SH (pK = 9.48) forms an amorphous insoluble mercaptide {AgSR} (s), ionic product [Ag⁺] [SR^?] = 10^?19.7. The solution in equilibrium with the solid contains the molecule AgSR at a constant concentration of 10^?6.7 M which furnishes the formation constant of the 1:1-complex: K₁ = 10^{13. 0}. The solid is soluble in excess of mercaptide (AgSR+SR^? → Ag(SR)₂^?: K₂ = 10^{4. 8}) as well as in an excess of silver ion (AgSR + Ag⁺ → Ag₂SR⁺K ≈? 10⁶). With the bulky monothiopentaerythrite (HO? CH₂? )₃C? CH₂? SH (pK = 9.89) no precipitation occurs with silver when the mercaptan concentration is below 10^{?3. 2}M. A single polynuclear Ag₁₀(SR)₉⁺ (β_10.9 = 10¹⁷⁵) is formed in acidic solutions which breaks up with the formation of Ag₂SR⁺ (β_2.1 = 10^19.0) when an excess of silver ion is added. Below the mononuclear wall ([RS]_total < 10^?6) Ag₂SR⁺ is formed via the mononuclear AgSR (K₁ = 10¹³). At higher mercaptan concentrations ([RS]_tot > 10^?3.2) an amorphous precipitate is formed which has almost the same solubility product as silver thioglycolate ([Ag⁺] [SR^?] = 10^?19.1). Apparently silver(I) forms with mercaptans always the complexes Ag₂SR⁺, AgSR and Ag(SR)₂^?. Above the mononuclear wall, these species condense to chain-like polynuclears which are cations Ag(SRAg)_n⁺ in presence of an excess of Ag⁺, and anions SR (AgSR)_n^? when the concentration [RS^?] is larger than [Ag⁺]. Usually n becomes rapidly very large as soon as the condensation starts (n → ∞: precipitate). The decanuclear Ag(SRAg)₉⁺ formed with thiopentaerythrit is somewhat more stable than the shorter chains (n < 9) and larger chains (n > 9), because it can tangle up to a ball by coordination of bridging mercapto-sulfur to the terminal silver ions (figure 12, page 2179). This ball seems to be further stabilized by hydrogen bonds between the many alcoholic OH groups of the substituent R = (HO? CH₂)₃C? CH₂? . The stability of the bonds Ag? S, however, is little influenced by the substituent R which carries the mercaptide sulfure.     

Ionic conductivity of and Raman spectroscopy investigation in binary oxosalts (1 − x)AgPO3xAg2SO4 glasses

(1 ? x)AgPO₃xAg₂SO₄ homogeneous glasses obtained by quenching of a melt of the two salts are pure ionic Ag⁺ conductors. The RT conductivity is increased from 2.5 × 10^?7 to 4 × 10^?6 (Ω cm)^?1 when the ratio of Ag₂SO₄ is increased from 0 to 0.3. Raman spectroscopy shows that no modifications of the (PO₃)^∞ chain skeleton occur by adding Ag₂SO₄. The low-frequency Raman band lying at about 55 cm^?1 is quantitatively correlated to Ag⁺ oscillations, the hopping distance decreasing from 3.0 to 2.7 Å if a jump process between regular Ag⁺ sites is considered.     

Hydrolysis of methyltin(IV) trichloride in aqueous NaCl and NaNO3 solutions at different ionic strengths and temperatures

The hydrolysis of methyltin(IV) trichloride (CH₃SnCl₃) has been studied in aqueous NaCl and NaNO₃ solutions (0 < I/mol dm⁻³ ≤ 1), at different temperatures (15 ≤ T/°C ≤ 45) by­potentiometric measurements (H⁺‐glass electrode). By considering the generic hydrolytic <?tw=97.2%>reaction pCH₃Sn³⁺ + qH₂O = (CH₃Sn)_p(OH)_q^3p−q<?tw>­+ qH⁺ (logβ_pq), we have the formation of five species and logβ₁₂ = −3.36, logβ₁₃ = −8.99, logβ₁₄ = −20.27 and logβ₂₅ = −7.61. The first hydrolysis step is measurable only at very low pH values and was not determined: a rough estimate of the hydrolysis constant is logβ₁₁ = −1.5 (± 0.5). The dependence on ionic strength of logβ_pq is quite different in NaNO₃ and NaCl solutions, and the formation at low pH values of the species CH₃Sn(OH)Cl⁺ has been found with logβ = −1.40. Hydrolysis constants strongly depend on temperature and from the relationships logβ_pq = f(T), ΔH ° values have been calculated. Speciation problems of CH₃Sn³⁺ in aqueous solution are discussed. Copyright © 1999 John Wiley & Sons, Ltd.     

Layered coordination polymer of silver methanesulfonate with 2,3,5,6-tetramethylpyrazine

The complex [Ag₂(Me₄-Pyz)(CH₃SO₃)₂]·2H₂O is synthesized, and its structure is determined. The crystals are monoclinic, space group P2₁ /n,a = 11.821(1), b = 4.906(1), c = 15.782(1) Å,β = 94.34(1) °, V = 912.5(2) ų, ρ(calcd) = 2.104 g/cm³, Z = 2. The Ag⁺ ion is coordinated at the vertices of the distorted tetrahedron by the nitrogen atom of tetramethylpyrazine and three oxygen atoms of two methanesulfonate ions (Ag(1)-N(1) 2.283(2), Ag (1)-O(RSO ₃ ^? )2.386(3)-2.451(2) Å, angles at the Ag atom 86.8(1)°–129.1(1)°). The structure contains layers of sulfonate-silver chains and tetramethylpyrazine molecules extended along the direction [101].     

The elimination kinetics and mechanisms of ethyl piperidine‐3‐carboxylate,ethyl 1‐methylpiperidine‐3‐carboxylate,and ethyl 3‐(piperidin‐1‐yl)propionate in the gas phase

The gas‐phase elimination kinetics of the above‐mentioned compounds were determined in a static reaction system over the temperature range of 369–450.3°C and pressure range of 29–103.5 Torr. The reactions are homogeneous, unimolecular, and obey a first‐order rate law. The rate coefficients are given by the following Arrhenius expressions: ethyl 3‐(piperidin‐1‐yl) propionate, log k₁(s^?1) = (12.79 ± 0.16) ? (199.7 ± 2.0) kJ mol^?1 (2.303 RT)^?1; ethyl 1‐methylpiperidine‐3‐carboxylate, log k₁(s^?1) = (13.07 ± 0.12)–(212.8 ± 1.6) kJ mol^?1 (2.303 RT)^?1; ethyl piperidine‐3‐carboxylate, log k₁(s^?1) = (13.12 ± 0.13) ? (210.4 ± 1.7) kJ mol^?1 (2.303 RT)^?1; and 3‐piperidine carboxylic acid, log k₁(s^?1) = (14.24 ± 0.17) ? (234.4 ± 2.2) kJ mol^?1 (2.303 RT)^?1. The first step of decomposition of these esters is the formation of the corresponding carboxylic acids and ethylene through a concerted six‐membered cyclic transition state type of mechanism. The intermediate β‐amino acids decarboxylate as the α‐amino acids but in terms of a semipolar six‐membered cyclic transition state mechanism. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 106–114, 2006     

Nature et stabilité des complexes métalliques de cryptands dinucléants en solution II. Polythiamacrotricycles et monocycles apparentés

Nature and Stability of Some Metallic Complexes of Dinucleating Cryptands in Solution II. Polythiamacrotricycles and Related Monocyclic Subunits The stability constants of the Cu²⁺ and Ag⁺ complexes of the cylindrical macrotricycle 1a (1,7,13,19-tetraaza 4,16-dioxa 10,22,27,32-tetrathiatricyclo[17.5.5.5]tetratriacontane) have been determined by pH-metry, as well as those of the Cu²⁺, Co²⁺, Zn²⁺, Cd²⁺, Pb²⁺, and Ag⁺ complexes of the monocyclic subunit 2a (1,7-dimethyl-1,7-diaza 4,10-dithiacyclododecane), in aqueous solutions (NaClO₄) at 25°. In the Cu(II) systems, equilibria were reached slowly, and the results established by pH-metry were confirmed by UV/VIS spectrophotometric studies. The tricycle 1a forms dinuclear cryptates with copper and silver, with overall stability constants log β₂₁₀ (Cu₂- 1a )⁴⁺ = 18.5, log β_21-2 (Cu₂- 1a (OH)₂)²⁺ = 4.8, log β₂₁₀(Ag₂- 1a )²⁺ = 23.0. Ag⁺ also forms a mononuclear (Ag- 1a )⁺ complex, with log β₁₁₀ = 13.1, but no mononuclear species were detected in the Cu- 1a system. The absorption spectra of the bis-Cu(II) complexes of 1a and 2a in aqueous medium, MeOH and propylene carbonate (PC) are given, as well as those, in MeOH and PC, of the bis-copper complexes of the related monocycles 3 and 4 (1,7-diaza-4,10,13-trithiacyclopentadecane and 1.10-diaza 4,7,13,16-tetrathiacyclooctadecane, respectively), and tricycle 5 with two benzyl groups in the lateral chains. The complexing properties of the polyoxa- and polythia macrotricycles (Parts I and II of this series) are compared to those of other bis-chelating ligands, the bicyclic bis-tren and the monocyclic bis-dien.