Stabilities,solubility, and kinetics and mechanism for formation and hydrolysis of some palladium(II)and platinum(II) iodo complexes in aqueous solution

Complex formation between Pd(II), Pt(II) and iodide has been studied at 25 °C for an aqueous 1.00 M perchloric acid medium. Measurements of the solubility of PdI₂(s) in aqueous mercury(II) perchlorate and of AgI(s) and PdI₂(s) in aqueous solutions of Pd²⁺(aq) and Ag⁺(aq) gave the solubility product of PdI₂(s) as K_s^o=(7±3) × 10⁻³² M³, which is much smaller than previous literature values.The stability constants β₁=[MI(H₂O)₃⁺]/([M(H₂O)₄²⁺][I⁻]) for the two systems were obtained as the ratio between rate constants for the forward and reverse reactions of (i).

The following values of k₁ (s⁻¹ M⁻¹), k₋₁ (s⁻¹) and β₁ (M⁻¹) were obtained at 25 °C: (1.14±0.11) × 10⁶, (0.92±0.18), (12±4) × 10⁵ for MPd, and (7.7±0.4), (8.0±0.7) × 10⁻⁵, (9.6±1.3) × 10⁴ for MPt. Combination with previous literature data gives the following values of log(β₁ (M⁻¹)) to log(β₄ (M⁻⁴)): 6.08, ∼22, 25.8 and 28.3 for MPd, and 4.98, ∼25, ∼28, and ∼30 for MPt. The present results show that the large overall stability constants β₄ observed for the M²⁺I⁻ systems are most likely due to a very large stability of the second complex MI₂(H₂O)₂, which is probably a cis-isomer. A distinct plateau in the formation curve for mean ligand number 2 is obtained both for MPd and Pt. The other iodo complexes are not especially stable compared to those of chloride and bromide.ΔH^≠ (kJ mol⁻¹) and ΔS^≠ (JK⁻¹ mol⁻¹) for the forward reaction of (i), MPd, are (17.3±1.7) and (−71±5), and for the reverse reaction of (i) MPd, (45±3) and (−95±6), respectively. The kinetics are compatible with associative activation (I_a). The contribution from bond-breaking in the formation of the transition state seems to be less important for Pd than for Pt.     

Supramolecular interaction between adenosine 5′-triphosphate (ATP) and polycharged tetraazamacrocycles. Thermodynamic and 31P NMR studies

The interaction of adenosine 5′-triphosphate (ATP) with the tetraammonium macrocyclic receptors 1,1,4,4,7,7,10,10-octamethyl-1,4,7,10-tetraazacyclododecane tetrakis(iodide) (L1·4I) and 1,6,11,16-tetraazacycloeicosane (L2) in its fully protonated form, has been studied by potentiometry and ³¹P NMR in water at I = 0.15 mol dm⁻³ and 25 °C H₄L2⁴⁺ reacts both with ATP⁴⁻ and HATP³⁻ to produce H₄L2·ATP and (H₄L2·HATP)⁺ whose equilibrium constants are 6.46 × 10³ and 1.10 x 10³, respectively. In the case of L1, in which the quaternarization of the nitrogen atoms prevents the formation of hydrogen bonds, no detectable interactions arise with ATP. These results are consistent with the hypothesis that the formation of hydrogen bonds play a role of major importance in the interaction between ATP and tetrammonium receptors.     

Kinetics and mechanism of aluminum(III)/siderophore ligand exchange: mono(deferriferrioxamine B)aluminum(III) formation and dissociation in aqueous acid solution

The kinetics and mechanism of a linear trihydroxamic acid siderophore (deferriferrioxamine B, H₄DFB⁺) ligand exchange with Al(H₂O)₆³⁺ to form mono(deferriferrioxamine B)aluminum(III) (Al(H₂O)₄H₃DFB)³⁺ have been investigated at 25 °C over the [H⁺] range 0.001−1.0 M and I = 2.0 M (HClO₄/NaClO₄) by ²⁷Al NMR. Kinetic results are consistent with Al(H₂O)₄(H₃DFB)³⁺ formation and dissociation proceeding through a parallel path mechanistic scheme involving Al(H₂O)₆³⁺(k₂/k₋₁) and Al(H₂O)₅(OH)²⁺(k₂/k₋₂) where k₁ = 0.13 M⁻¹ s⁻¹, k₋₁ = 8.7 × 10⁻³ M⁻¹ s⁻¹, k₂ = 2.7 × 10³ M⁻¹ s⁻¹, and k₋₂ = 9.6 × 10⁻⁴ s⁻¹. Relative complex formation rates at Al(H₂O)₆³⁺ and Al(H₂O)₅OH²⁺, and comparison with kinetic data for a series of synthetic hydroxamic acids, suggest that an interchange mechanism is operative. These results are also discussed in relation to kinetic data for the corresponding iron(III)-deferriferrioxamine B system.     

The formation constants of dimethylthallium(III)-glutathione complexes in aqueous solution

The complexes formed in the dimethylthallium(III) (Me₂Tl⁺), glutathionate (EGC³⁻) and hydrogen ion system in aqueous solution at 37 °C and I = 150 mmol dm⁻³ (NaCl) have been characterised by means of glass-electrode potentiometry. Glutathione protonation constants were found to be 9.123 ± 0.007, 17.42 ± 0.01, 20.78 ± 0.02, and 22.93 ± 0.02. Formation constants for the complexes [(Me₂Tl)EGCH]⁻ and [(·Me₂Tl) EGC]²⁻ were found to be 11.19 ± 0.03 and 2.39 ± 0.02, respectively. Particular attention has been paid to the evaluation of the effect of possible systematic errors on the constant values determined. Reliable standard deviation estimations have been made by applying a Monte Carlo calculation technique.     

Dynamics of molecular organization in agarose sulphate

Nongelling solutions of structurally regular chain segments of agarose sulphate show disorder–order and order–disorder transitions (as monitored by the temperature dependence of optical rotation) that are closely similar to the conformational changes that accompany the sol–gel and gel–sol transitions of the unsegmented polymer. The transition midpoint temperature (T_m) for formation of the ordered structure on cooling is ～25 K lower than T_m for melting. Salt-induced conformational ordering, monitored by polarimetric stopped-flow, occurs on a millisecond time scale, and follows the dynamics expected for the process 2 coil ? helix. The equilibrium constant for helix growth (s) was calculated as a function of temperature from the calorimetric enthalpy change for helix formation (ΔH_cal = ?3.0 ± 0.3 kJ per mole of disaccharide pairs in the ordered state), measured by differential scanning calorimetry. The temperature dependence of the nucleation rate constant (k_nuc), calculated from the observed second-order rate constant (k_obs) by the relationship k_obs = k_nuc(1 ? 1/s) gave the following activation parameters for nucleation of the ordered structure of agarose sulphate (1 mg mL^?1; 0.5M Me₄NCl or KCl): ΔH* = 112 ± 5 kJ mol^?1; ΔS* = 262 ± 20 J mol^?1 K^?1; ΔG*₂₉₈ = 34 ± 6 kJ mol^?1; (k_nuc)₂₉₈ = (7.5 ± 0.5) × 10⁶ dm³ mol^?1 s^?1. The endpoint of the fast relaxation process corresponds to the metastable optical rotation values observed on cooling from the fully disordered form. Subsequent slow relaxation to the true equilibrium values (i.e., coincident with those observed on heating from the fully ordered state) was monitored by conventional optical rotation measurements over several weeks and follows second-order kinetics, with rate constants of (2.25 ± 0.07) × 10^?4 and (3.10 ± 0.10) × 10^?4 dm³ mol^?1 s^?1 at 293.7 and 296.2 K, respectively. This relaxation is attributed to the sequential aggregation processes helix + helix → dimer, helix + dimer → trimer, etc., with depletion of isolated helix driving the much faster coil–helix equilibrium to completion. Light-scattering measurements above and below the temperature range of the conformational transitions indicate an average aggregate size of 2–3 helices.     

Kinetics and mechanism of malonate replacement in bis(malonato)oxovanadate(IV) by oxalate

The kinetics of malonate replacement in bis- (malonato)oxovanadate(IV), [VO(mal)₂H₂O]²⁻(hereafter water molecule will be omitted), by oxalate has been studied by the stopped-flow method. The reaction was found to consist of two consecutive steps (k₁ and k₂: first-order rate constants) passing through a mixed ligand complex, [VO(mal)(ox)]²⁻. The rates for each step depended linearly on the concentrations of free oxalate species, Hox⁻ and ox²⁻. The second-order rate constants for the replacement by ox²⁻ were much larger in the k₁ step than in the k₂ step and the activation parameters were determined as follows: ΔH^≠= 43.5 ± 5.6 kJ mol⁻¹, ΔS±-53 ± 19 J K⁻¹ mol⁻¹ and ΔH≠= 43.6 ± 0.5 kJ mol⁻¹, δS≠ = -62 ± 2 J K^−l mol⁻¹ for the k₁ and k₂ steps, respectively. The volume of activation was determined to be -0.65 ± 0.75 cm³ mol⁻¹ at 20.2 °C by the high-pressure stopped-flow method for the apparent rate constants.     

Activation parameters for directly determined first order rate constants for outer sphere electron transfer reactions,and crystal structure of a pertinent pentaammine of CoIII

The outer sphere reductions of Co(NH₃)₅B³⁺ by Fe(CN)₅A³⁻ have been studied. The observed pseudo first order rate constants (Co complex in excess) obey the dependence k_obs=K_osk_et[Co]/(1 +K_os[Co]), as expected for outer sphere electron transfer reactions. Values of the fundamental electron transfer rate constants k_et have been determined, along with the equilibrium constant K_os for a range of reactions in which A and B are pyridyl ligands of different sizes. The first order electron transfer rate constants vary in a manner that is consistcnt with adiabatic electron transfer. The outer sphere ion pairing equilibrium constants K_os have been calculated: K_os=8.6 ± 0.1 × 10² M⁻¹ when A and B=pyridine; K_os=1.07 ± 0.09 × 10³ M⁻¹ where A=pyridine, B=1-phenyl-3-(4-pyridyl)propane; K_os=1.86 ± 0.11 × 10³ M⁻¹ when A=4,4′-bipyridine, B=pyridine; K_os=1.27 ± 0.08 × 10³ M⁻¹ when A=4,4′-bipyridine, B=4-phenylpyridine. Distances of closest approach between the metal centers in the reactive ion pairs are compared, and it is concluded that there is a common mechanism, in which the ammonia side of the cobalt complex approaches the cyano side of the iron complex in each reactive ion pair.The distance of closest approach between the two metal centers (a) was calculated from the experimental values for the ion pairing equilibrium constant K_os at 25 °C: 5.2 Å when A=4,4′-bipyridine, B=pyridine; 5.4 Å when A=4,4′-bipyridine, B=4-phenylpyridine; 5.5 Å when A=pyridine, B=1-phenyl-3-(4-pyridyl)propane; 5.7 Å when A=B=pyridine. These relatively short metal-metal distances, when compared to the X-ray structure of the compound [Co(NH₃)₅(4-phenylpyridine)]₂[S₂O₆]₃· 4H₂O, do not support an ion pair orientation in which the two substituted pyridine ligands A and B are oriented toward each other. [P2₁/c,a=7.399(3), b=22.355(10), c=13.776(4) Å, β=92.02(3)°, R=0.070.] The crystallographic results show that if the two pseudo-octahedral coordination spheres are oriented in the reactive ion pair so that an ammonia face of the cobalt complex is at hydrogen bonding distance from a cyano face on the iron complex, the metal-metal distance is 5.3 Å, a distance which is in agreement with the kinetic results.     

Synthesis and characterization of triaminecobalt(III) complexes and acid hydrolysis kinetics of fac-[Codpt(H2O)nX3−n]n+ (X = Cl,Br; n = 0,1,2)

The complexes CodptX₃ and [Codpt(H₂O)X₂]ClO₄ (X = Cl, Br; dpt = dipropylenetriamine = NH(CH₂CH₂CH₂NH₂)₂) have been prepared and characterized. Rate constants (s⁻¹) for aqueous solution at 25 °C and μ = 0.5 M (NaClO₄), for the acid-independent sequential ractions.

have been measured spectrophotometrically. For X = Cl: k₁ ⋍ 2 × 10⁻², k₂ = 1.7 × 10⁻⁴ and k₃ = 4.8 × 10⁻⁶, and for X = Br: k₁ ⋍ 2 × 10⁻², k₂ = 5.25 × 10⁻⁴ and k₃ = 2.5 × 10⁻⁵ The primary equation was found to be acid independent, while the secondary and tertiary aquations were acid-inhibited reactions. For the second step, the rate of the reaction was given by the rate equation

where C_t is the complex concentration in the aqua-and hydroxodihalo species, k′₂ is the rate constant for the acid-dependent pathway and K_a is the equilibrium constant between the hydroxo and aqua complex ions. The activation parameters were evaluated, for X = Cl: ΔH^≠₂ = 106.3 ± 0.4 kJ mol⁻¹ and ΔS^≠₂ = 40.2 ± 1.7 J K⁻¹ mol⁻, and for X = Br: ΔH^≠₂ = 91.6 ± 0.4 kJ mol⁻¹ and ΔS^≠₂ = 0.4 ± 1.7 J K⁻¹ mol⁻¹. The results are discussed and detailed comparisons of the reactivities of these complexes with other haloaminecobalt(III) species are presented.     

Kinetics of imidazole addition to the axial site of the iron(II) complex of 2, 3, 9,10-tetraphenyl-1,4, 8,11-tetraaza-1,3, 8,10-cyclotetradecatetraene in dimethyl sulfoxide. Evidence for a dissociative-interchange mechanism

The axial adduct formation of the iron(II) complex of 2,3,9,10-tetraphenyl-l,4,8,11-tetraaza-1,3,8,10-cyclotetradecatetraene (L) with imidazole in dimethyl sulfoxide has been investigated spectrophotometrically at various temperatures and pressures. In the presence of a large excess of imidazole the reaction with the two phases has been observed. The first faster reaction is the formation of the monoimidazole complex of FeL²⁺, and the second slower reaction corresponds to the formation of the bisimidazole complex. Activation parameters are as follows: for the first step with k₁ (25.0°C) = (6.8 ±0.2)×10⁵ mol⁻¹ kg s⁻¹, ΔH³₁ = 47.5 ± 4.9 kJ mol⁻¹, ΔS³₁ = 26±16 J K⁻¹ mol⁻¹, and ΔV³₁ (30.0°C) = 27.2±1.5 cm³ mol⁻¹; for the second step with k₂ (25.0°C) = 26.8±0.8 mol⁻¹ kg s⁻¹, ΔH³₂ = 91.6± 0.8 kJ mol⁻¹, ΔS³₂ = 90±3 J K⁻¹ mol⁻¹, and ΔV³₂ (35.0°C) = 21.8±0.9 cm³ mol⁻¹. The large positive activation volumes strongly indicate a dissociative character of the activation process.     

Stepwise Frontal Analysis Coupled with Affinity Chromatography: A Fast and Reliable Method for Potential Ligand Isolation and Evaluation from Mahuang-Fuzi-Xixin Decoction

Mahuang-Fuzi-Xixin Decoction (MFXD) is widely used in the treatment of asthma, however, the functional components in the decoction targeting beta2-adrenoceptor (β₂-AR) remain unclear. Herein, we immobilized the haloalkane dehalogenase (Halo)-tagged β₂-AR on the 6-chlorocaproic acid-modified microspheres. Using the affinity stationary phase, the interactions of four ligands with the receptor were analyzed by stepwise frontal analysis. The association constants were (4.75±0.28)×10⁴ M⁻¹ for salbutamol, (2.93±0.15)×10⁴ M⁻¹ for terbutaline, (1.23±0.03)×10⁴ M⁻¹ for methoxyphenamine, (5.67±0.38)×10⁴ M⁻¹ for clorprenaline at high-affinity binding site, and (2.73±0.05)×10³ M⁻¹ at low-affinity binding site. These association constants showed the same rank order as the radioligand binding assay, demonstrating that immobilized β₂-AR had capacity to screen bioactive compounds binding to the receptor while stepwise frontal analysis could predict their binding affinities. Application of the immobilized receptor in analysis of MFXD by chromatographic method revealed that ephedrine, aconifine, karakoline, and chasmanine were the bioactive compounds targeting β₂-AR. Among them, ephedrine and chasmanine exhibited association constants of (2.94±0.02)×10⁴ M^-1and (4.60±0.15)×10⁴ M⁻¹ to the receptor by stepwise frontal analysis. Molecular docking analysis demonstrated that ephedrine, chasmanine, and the other two compounds interact with β₂-AR through the same pocket involving the key amino acids such as Asn312, Asp113, Phe289, Trp286, Tyr316, and Val114. As such, we reasoned that the four compounds dominate the therapeutic effect of MFXD against asthma through β₂-AR mediating pathway. This work shed light on the potential of immobilized β₂-AR for drug discovery and provided a valuable methodology for rapid screening.     

Temperature and pressure dependent equilibrium studies of 1, 4, 8, 11-tetramethyl-1, 4, 8, 11-tetraazacyclotetradecane nickel(ii) in coordinating solvents

In coordinating solvents, the complex 1, 4, 8, 11- tetramethyl-1, 4, 8, 11-tetraazacyclotetradecane nickel(II) bisperchlorate exists as an equilibrium mixture involving four coordinate R,S,R,S-[Ni(tmc)]²⁺ and five coordinate R,S,R,S-[Ni(tmc)(solvent)]²⁺ species. Spectrophotometric measurements of this equilibrium in a number of solvents have been conducted over a range of temperatures and pressures. The stability order for the five coordinate complex in the solvents investigated is CH₃CN>DMF>DMSO>C₆H₅CN> H₂O>ClCH₂CN at 25 °C. Differences in stability are considered in terms of the measured thermodynamic parameters ΔH° and ΔS°. Both steric and electronic factors were found to influence solvent coordination with the macrocyclic complex.For the equilibrium in CH₃CN, C₆H₅CN, DMF and H₂O, reaction volumes, ΔV°, of −3.2±0.5, −4.2±0.5, −0.2±0.5 and −0.5±0.5 cm³ mol⁻¹ respectively have been determined. Each is significantly smaller than the corresponding solvent molar volume. The ΔV° for the equilibrium in CH₃CN is comparable with the previously determined activation volume for exchange of this solvent on R, S, R, S- [Ni(tmc)(CH₃CN)]²⁺. The equilibrium and measured volume parameters are discussed in relation to the mechanism for solvent exchange.     

Kinetic investigation of the base hydrolysis of the chloropentaamminecobalt(III) ion in micellar sodium dodecyl sulfate solution

The kinetics of the base hydrolysis of the complex ion chloropentaamminecobalt(III) have been studied by conventional spectrophotometry at 25.0 °C in water and in the presence of the anionic surfactant sodium dodecyl sulfate (SDS) over the SDS concen- tration range from 1.0 × 10⁻³ to 7.5 × 10⁻² mol dm⁻³. The hydrolysis rate is strongly inhibited by the surfactant, fitting a model in which the cobalt- (III) complex is distributed between water and the micellar pseudo-phase with a binding constant equal to 3.7 × 10³ dm³ mol⁻¹. The effects of different added electrolytes on the critical micelle concentra- tion of the surfactant and on the hydrolysis rate have also been investigated and discussed.     

Studies on the reactions of PtCl2en,cis-Pt(NH3)2Cl2 and their aqua species with adenosine,deoxyadenosine and adenine using ion-pair HPLC

The reactions of PtCl₂en or cis-Pt(NH₃)₂Cl₂ and their aqua species with adenine and adenosine were studied by means of ion-pair HPLC. From the chromatograms, it was found that the first binding site of Pt(II) was the N(7) site of adenine under both acidic and neutral conditions. The rates of Pt(II) binding at the (N7) site of adenosine and deoxyadenosine were measured. The rate constants, k₁, were obtained for the reactions of PtCl₂en or cis-Pt(NH₃)₂Cl₂ with adenosine and deoxyadenosine at pH 3 and 7 over the temperature range 9–25 °C. The k₁ values were 6.8–7.7 × 10⁻⁴ dm³ mol⁻¹ s⁻¹ at 25 °C. For the aqua species, the rate of [cis-Pt(NH₃)₂ClH₂O]⁺ with adenosine N(7) was measured. The rate constants, k₂ which were found to be smaller than those of hydrolysis, k_h, were calculated at pH 3 over the temperature range 25–40 °C. The k₂ value obtained at 25 °C was 1.1 × 10⁻² dm³ mol⁻¹ s⁻¹, 15 time larger than k¹. The activation parameters were also calculated.     

Kinetic and equilibrium studies of cyclomalto-octaose (γ-cyclodextrin)-methyl orange inclusion complexes

Measurements of the equilibrium and temperature-jump u.v., visible, and induced c.d. spectra of Methyl Orange (MO) in the presence of cyclomalto-octaose (γ-cyclodextrin, γ-CD) have been carried out. Three mechanistic steps were detected through the temperature-jump data (25.0°):

where K₁, K₂, and K₃ are 45 (±7), 2.0 (±1.1) × 10⁶, and 6.1 (±2.5) × 10³ dm³.mol^?1, respectively, k₂ = 9.4 (±5.1) × 10⁹ dm³.mol^?1.s^?1, and k_?2 = 4.8 (±0.8) × 10³ s^?1. The equilibrium u.v./visible data are also consistent with this reaction scheme. The high stability of the dimer inclusion complex (MO)₂ · γ-CD compared to that of the monomer inclusion complex MO · γ-CD appears to be related to the annular diameter of γ-CD and demonstrates a degree of selectivity in cyclodextrin inclusion complexes. The (MO)₂ · (γ-CD)₂ complex also contains a dimer, included by both γ-CD molecules.     

Equilibrium constants under physiological conditions for the reactions of the nonphosphorylated pathway of L-serine biosynthesis

The observed equilibrium constants (K_obs) for the reactions of d-2-phosphoglycerate phosphatase, d-2-Phosphoglycerate^3? + H₂O → d-glycerate^? + HPO₄^2?; d-glycerate dehydrogenase (EC 1.1.1.29), d-Glycerate^? + NAD⁺ → NADH + hydroxypyruvate^? + H⁺; and l-serine:pyruvate aminotransferase (EC 2.6.1.51), Hydroxypyruvate^? + l-H · alanine^± → pyruvate^? + l-H · serine^±; have been determined, directly and indirectly, at 38 °C and under conditions of physiological ionic strength (0.25 m) and physiological ranges of pH and magnesium concentrations. From these observed constants and the acid dissociation and metal-binding constants of the substrates, an ionic equilibrium constant (K) also has been calculated for each reaction. The value of K for the d-2-phosphoglycerate phosphatase reaction is 4.00 × 10³m [ΔG⁰ = ?21.4 kJ/mol (?5.12 kcal/mol)]([H₂0] = 1). Values of K_obs for this reaction at 38 °C, [K⁺] = 0.2 m, I = 0.25 M, and pH 7.0 include 3.39 × 10³m (free [Mg²⁺] = 0), 3.23 × 10³m (free [Mg²⁺] = 10^?3m), and 2.32 × 10³m (free [Mg²⁺] = 10^?2m). The value of K for the d-glycerate dehydrogenase reaction has been determined to be 4.36 ± 0.13 × 10^?13m (38 °C, I = 0.25 M) [ΔG⁰ = 73.6 kJ/mol (17.6 kcal/mol)]. This constant is relatively insensitive to free magnesium concentrations but is affected by changes in temperature [ΔH⁰ = 46.9 kJ/mol (11.2 kcal/mol)]. The value of K for the serine:pyruvate aminotransferase reaction is 5.41 ± 0.11 [ΔG⁰ = ?4.37 kJ/mol (?1.04 kcal/mol)] at 38 °C (I = 0.25 M) and shows a small temperature effect [ΔH⁰ = 16.3 kJ/ mol (3.9 kcal/mol)]. The constant showed no significant effect of ionic strength (0.06–1.0 m) and a response to the hydrogen ion concentration only above pH 8.5. The value of K_obs is 5.50 ± 0.11 at pH 7.0 (38 °C, [K⁺] = 0.2 m, [Mg²⁺] = 0, I = 0.25 M). The results have also allowed the value of K for the d-glycerate kinase reaction (EC 2.7.1.31), d-Glycerate^? + ATP^4? → d-2-phosphoglycerate^3? + ADP^3? + H⁺, to be calculated to be 32.5 m (38 °C, I = 0.25 M). Values for K_obs for this reaction under these conditions and at pH 7.0 include 236 (free [Mg²⁺] = 0) and 50.8 (free [Mg²⁺] = 10^?3m).     

The synthesis and reaction kinetics of some Co(IIl) and Cr(III) chloro complexes of 1,4,8-Triazaoctane (2,3-tri) and the isolation of chiral trans-dichloro [CoCl2(NH3)(2,3-tri)] ClO4

The reaction of 2,3-tri with CrCl₃·6H₂O₁, dehydrated in boiling DMF, results in the formation of mer-CrCl₃(2,3-tri) and anation of hydrolysed solutions of mer-MCl₃(2,3,-tri) (M=Co, Cr) with 6 M HCl containing HClO₄, forms trans-dichloro- mer-[MCl₂(2,3-tri)(OH₂)]ClO₄·H₂O (M=Cr, Co; I, II). trans-Dinitro-mer-[Co(NO₂)₂(NH₃)(2,3-tri)] ClO₄ crystallises from the reaction between mer-Co(NO₂)₃(2,3-tri) and aqueous 7 M ammonia, on addition of NaClO₄·H₂O, and trans-dichloro-mer-[CoCl₂(NH₃)(2,3-tri)]ClO₄ (III) can be isolated by treatment of the dinitro with 12 M HCl. Reaction of mer-CoCl₃(2,3-tri) with C₂O₄₂⁻, followed by addition of aqueous NH₃ and NaClO₄·H₂O results in the isolation of racemic mer-[Co(ox)(NH₃)(2,3-tri)]ClO₄· H₂O. This complex was resolved into its enantiomeric forms and treatment of these with SOCl₂/MeOH/ HClO₄ gave the chiral forms of trans-dichloro-mer- [CoCl₂(NH₃)(2,3-tri)]ClO₄ (R or S at the see-NH center). The rates of loss of the first chloro ligand from these dichloro complexes have been measured spectrophotometrically in 0.1 M HNO₃ over a 15 K temperature range to give the following kinetic parameters; (I) k_H(298)=7.25 × 10⁻⁵ s⁻¹, E_a=78.5 kJ mol⁻¹, δS₂₉₈^#=₋69 J K⁻¹ mol⁻¹; (II) k_H(298)=4.00 × 10⁻³ s⁻¹, E_a=89.9, δS₂₉₈^#= +87.5; (III) k_H(298)=3.09 × 10⁻⁴ s⁻¹, E_a=103, δS₂₉₈^#=+27. Treatment of the dichloro cations with Hg²⁺/HNO₃ results in the generation of mer- M(2,3-tri)(OH₂)₃³⁺ (M=Cr, Co; IV, V) and trans- diaqua-mer-Co(NH₃)(2,3-tri)(OH₂)₂³⁺ (VI). The Co(III) cations isomerise to the fac configuration with (V) K_isom(298) μ=1.0 M)=2.97 × 10⁻⁵ s⁻¹, E_a=115, δS₂₉₈^#=+46. (VI) K_isom(298) (μ=1.0 M)=4.13 × 10⁻⁵ s⁻¹, E_a=113, δS₂₉₈^#=+52.     

Optically active chromium(III) complexes. VII. Chiroptical and kinetic properties of chloro(1,5-diazahexane)( 1,4,7-triazaheptane)chromium(III) tetrachlorozincate(II), [CrCl(NMetn)(dien)]ZnCl4

One isomer of [CrCl(N-Me-tn)(dien)]ZnCl₄ has been isolated from the reaction of CrCl₃·6H₂O, dehydrated in DMF, with the polyamines N-methyl- 1,3-diaminopropane and diethylenetriamine. This complex is isomorphous with δλ-(R,S)usft-[CoCl(N-Me-tn)(dien)] ZnCl₄ and thus has the unsym-fac- configuration with the N-Me group trans to the sec-NH group of the coordinated triamine. The Cr(III) complex has been resolved with NH₄BCS and the chiroptical parameters of (-)₄₈₈-[CrCl(N-Me-tn)(dien)]- ZnCl₄, derived from the less soluble diastereoisomeride by metathesis, are similar to those obtained for the less soluble (-)₅₃₄-λ-(S)-a,cb,edf-Co(III) analogue, of known absolute configuration. Kinetic parameters for the rates of thermal aquation (μ= 1.0 M, HClO₄) and Hg²⁺-assisted chloride release (μ= 1.0 M) for usft-[CrCl(N-Me-tn)(dien)]ZnCl₄ are k_H= 3.7 × 10⁻⁶ s⁻¹, E_a=93 ± 8 kJ mol⁻¹, ΔS_2984t^#= −45 ± 16 J K⁻¹ mol⁻¹ and k_Hg=2.01 × 10⁻³ M⁻¹ s⁻¹, E_a=64.2 ± 3.3, ΔS₂₉₈^#=−89.5 ± 7, respectively at 298 K.     

PHOTOSYNTHESIS AND CALCIFICATION BY EMILIANIA HUXLEYI (PRYMNESIOPHYCEAE) AS A FUNCTION OF INORGANIC CARBON SPECIES

To test the possibility of inorganic carbon limitation of the marine unicellular alga Emiliania huxleyi (Lohmann) Hay and Mohler, its carbon acquisition was measured as a function of the different chemical species of inorganic carbon present in the medium. Because these different species are interdependent and covary in any experiment in which the speciation is changed, a set of experiments was performed to produce a multidimensional carbon uptake scheme for photosynthesis and calcification. This scheme shows that CO₂ that is used for photosynthesis comes from two sources. The CO₂ in seawater supports a modest rate of photosynthesis. The HCO is the major substrate for photosynthesis by intracellular production of CO₂ (HCO+ H⁺→ CO₂+ H₂O → CH₂O + O₂). This use of HCO is possible because of the simultaneous calcification using a second HCO, which provides the required proton (HCO+ Ca²⁺→ CaCO₃+ H⁺). The HCO is the only substrate for calcification. By distinguishing the two sources of CO₂ used in photosynthesis, it was shown that E. huxleyi has a K_½ for external CO₂ of “only” 1.9 ± 0.5 μM (and a V_max of 2.4 ± 0.1 pmol·cell⁻¹·d⁻¹). Thus, in seawater that is in equilibrium with the atmosphere ([CO₂]= 14 μM, [HCO]= 1920 μM, at fCO₂= 360 μatm, pH = 8, T = 15° C), photosynthesis is 90% saturated with external CO₂. Under the same conditions, the rate of photosynthesis is doubled by the calcification route of CO₂ supply (from 2.1 to 4.5 pmol·cell⁻¹·d⁻¹). However, photosynthesis is not fully saturated, as calcification has a K_½ for HCO of 3256 ± 1402 μM and a V_max of 6.4 ± 1.8 pmol·cell⁻¹·d⁻¹. The H⁺ that is produced during calcification is used with an efficiency of 0.97 ± 0.08, leading to the conclusion that it is used intracellularly. A maximum efficiency of 0.88 can be expected, as NO uptake generates a H⁺ sink (OH⁻ source) for the cell. The success of E. huxleyi as a coccolithophorid may be related to the efficient coupling between H⁺ generation in calcification and CO₂ fixation in photosynthesis.