Feasibility of biogas production from anaerobic co-digestion of herbal-extraction residues with swine manure

The objective of this work was to examine the feasibility of biogas production from the anaerobic co-digestion of herbal-extraction residues with swine manure. Batch and semi-continuous experiments were carried out under mesophilic anaerobic conditions. Batch experiments revealed that the highest specific biogas yield was 294 mL CH₄ g⁻¹ volatile solids added, obtained at 50% of herbal-extraction residues and 3.50 g volatile solids g⁻¹ mixed liquor suspended solids. Specific methane yield from swine manure alone was 207 mL CH₄ g⁻¹ volatile solid added d⁻¹ at 3.50 g volatile solids g⁻¹ mixed liquor suspended solids. Furthermore, specific methane yields were 162, 180 and 220 mL CH₄ g⁻¹ volatile solids added d⁻¹ for the reactors co-digesting mixtures with 10%, 25% and 50% herbal-extraction residues, respectively. These results suggested that biogas production could be enhanced efficiently by the anaerobic co-digestion of herbal-extraction residues with swine manure.     

Kinetic study of dissociation of Eu(III) complex with H8dotp (H8dotp = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis(methylphosphonic acid))

The dissociation kinetics of the europium(III) complex with H₈dotp ligand was studied by means of molecular absorption spectroscopy in UV region at ionic strength 3.0 mol dm⁻³ (Na,H)ClO₄ and in temperature region 25-60 °C. Time-resolved laser-induced fluorescence spectroscopy (TRLIFS) was employed in order to determine the number of water molecules in the first coordination sphere of the europium(III) reaction intermediates and the final products. This technique was also utilized to deduce the composition of reaction intermediates in course of dissociation reaction simultaneously with calculation of rate constants and it demonstrates the elucidation of intimate reaction mechanism. The thermodynamic parameters for the formation of kinetic intermediate (ΔH⁰ = 11 ± 3 kJ mol⁻¹, ΔS⁰ = 41 ± 11 J K⁻¹ mol⁻¹) and the activation parameters (E_a = 69 ± 8 kJ mol⁻¹, ΔH^≠ = 67 ± 8 kJ mol⁻¹, ΔS^≠ = −83 ± 24 J K⁻¹ mol⁻¹) for the rate-determining step describing the complex dissociation were determined. The mechanism of proton-assisted reaction was proposed on the basis of the experimental data.     

Computational investigation of ethene trimerisation catalysed by cyclopentadienyl chromium complexes

Intermediates and transition states of the reaction cycle for the trimerisation of ethene catalysed by the initial catalyst precursor [η⁵-CpCrCl₂]₂ have been characterised by modeling, starting from the species η⁵-CpCrMe₂. This is a simplified model system of the actual catalytically active system containing bulky cyclopentadienyls. The ground-state multiplicity configuration was determined to be that of a quartet, in the case of non-chlorinated Cr(III) species, and a triplet for corresponding chlorinated Cr(IV) analogues. Geometry optimizations were performed on all intermediates, using their ground-state multiplicity, and all relevant transition states were located and subsequently optimised. The effect of an additional chlorine ligand on the chromium centre (viz. species of the form η⁵-CpCrClL_n) on the activation energy barriers was also determined for two key high energy transformations. It was found that the activation energy barriers are lowered significantly upon the addition of a chlorine ligand to the chromium centre. The rate determining step for the non-chlorinated, Cr(III) system, was calculated as requiring a free energy value of 88 kJ mol⁻¹, with the chlorinated Cr(IV) analogue at 56 kJ mol⁻¹ in the same step. The process of ethene tetramerisation was found to be unfeasible with the system, with a free energy barrier of 162 kJ mol⁻¹ associated with this transformation.     

Adduct formation of [(η-C7H7)Zr(η-C5H5)] with phosphines and N-heterocyclic carbenes: An experimental and theoretical study

The reaction of [(η⁷-C₇H₇)Zr(η⁵-C₅H₅)] with two Lewis bases, tetramethylimidazolin-2-ylidene and PMe₃, is reported and their stability probed via spectroscopic and theoretical methods. The strongly σ-basic N-heterocyclic carbene forms a stable adduct which has been structurally characterised, whilst the PMe₃ ligand coordinates weakly to the metal centre. Variable temperature ³¹P NMR spectroscopy has been used to determine the activation energy for this process (ΔG^‡ = 40.5 ± 1.9 kJ mol⁻¹). DFT calculations have been performed on both complexes and the structures discussed. In addition, the enthalpies for the formation of these compounds have been calculated [ΔH⁰(Zr-IMe) = −56.3 kJ mol⁻¹; ΔH⁰(Zr-PMe₃) = −2.3 kJ mol⁻¹] and show that the N-heterocyclic carbene forms a thermodynamically much more stable adduct than that with PMe₃.     

Cross-linked succinyl chitosan as an adsorbent for the removal of Methylene Blue from aqueous solution

Removal of a basic dye (Methylene Blue) from aqueous solution was investigated using a cross-linked succinyl-chitosan (SCCS) as sorbent. The chemical structures of chitosan and its derivatives were testified by FT-IR. X-ray diffraction, DTG analysis and swelling measurements were conducted to clarify the characteristics of the chemically modified chitosan. The effect of process parameters, such as pH of the initial solution, and concentrations of dyes on the extent of Methylene Blue (MB) adsorption was investigated. The Langmuir isotherm model was used to fit the equilibrium experimental data, giving a maximum sorption capacity of 289.02 mg/g at 298 K. Kinetic studies showed that the kinetic data were well described by the pseudo-second-order kinetic model. Thermodynamic parameters such as enthalpy change (ΔH°), free energy change (ΔG°) and entropy change (ΔS°) were determined to be −25.32 kJ mol⁻¹, −6.76 kJ mol⁻¹ and −62.36 J mol⁻¹ K⁻¹, respectively, which leads to a conclusion that the adsorption process is spontaneous and exothermic.     

Thermodynamic analysis of hydration in human serum heme-albumin

Ferric human serum heme-albumin (heme-HSA) shows a peculiar nuclear magnetic relaxation dispersion (NMRD) behavior that allows to investigate structural and functional properties. Here, we report a thermodynamic analysis of NMRD profiles of heme-HSA between 20 and 60 °C to characterize its hydration. NMRD profiles, all showing two Lorentzian dispersions at 0.3 and 60 MHz, were analyzed in terms of modulation of the zero field splitting tensor for the S = ⁵/₂ manifold. Values of correlation times for tensor fluctuation (τ_v) and chemical exchange of water molecules (τ_M) show the expected temperature dependence, with activation enthalpies of −1.94 and −2.46 ± 0.2 kJ mol⁻¹, respectively. The cluster of water molecules located in the close proximity of the heme is progressively reduced in size by increasing the temperature, with ΔH = 68 ± 28 kJ mol⁻¹ and ΔS = 200 ± 80 J mol⁻¹ K⁻¹. These results highlight the role of the water solvent in heme-HSA structure-function relationships.     

Structural studies of trans-N2S2 copper macrocycles

The X-ray crystal structures of two related trans-N₂S₂ copper macrocycles are reported. One was isolated with the copper in the divalent form and the other with copper in its univalent form affording a valuable insight into the changes of geometry and metrical parameters that occur during redox processes in macrocyclic copper complexes. A variable temperature NMR study of the copper(I) complex is reported, indicative of a chair-boat conformational change within the alkyl chain backbone of the macrocycle. It was possible to extract the relevant kinetic and thermodynamic parameters (ΔG^‡, 57.8 kJ mol⁻¹; ΔH^‡, 52.1 kJ mol⁻¹; ΔS^‡, −19.2 J K⁻¹ mol⁻¹) for this process at 298 K. DFT molecular orbital calculations were used to confirm these observations and to calculate the energy difference (26.2 kJmol⁻¹) between the copper(I) macrocycle in a planar and a distorted tetrahedral disposition.     

Kinetics of the complexation of nickel(II) with 1,10-phenanthroline and its derivatives in acetonitrile-water mixed solvents

The kinetics of the complexation of Ni(II) with 1,10-phenanthroline(phen), 4,7-dimethyl-1,10-phenanthroline(dmphen), and 5-nitro-1,10-phenanthroline(NO₂phen) in acetonitrile-water mixed solvents of acetonitrile mole fraction x_AN = 0, 0.05, 0.1, 0.2 and 0.3 at 288, 293, 298 and 303 K have been studied by stopped-flow method at ionic strength of 1.0 (NaClO₄) and pH 7.4. The corresponding activation enthalpy, entropy, and free energy were determined from the observed rate constants. The complexation of Ni(II) with the three ligands has comparable observed rate constants; in pure water the observed rate constants are (×10³ dm³ mol⁻¹ s⁻¹) 2.31, 2.57, and 1.38 for phen, dmphen and NO₂phen, respectively. The corresponding activation parameters for the three ligands are, however, considerably different; in pure water the ΔH^‡/ΔS^‡ (kJ mol⁻¹/J K⁻¹ mol⁻¹) are 44.7/−30.2, 19.5/−114.1, and 32.2/−76.9 for phen, dmphen, and NO₂phen, respectively. The effects of solvent composition on the kinetics are also markedly different for the three ligands. The ΔH^‡ and ΔS^‡ showed a minimum at x_AN = 0.1 for phen; for dmphen and NO₂phen, however, maxima at x_AN = 0.2 were observed. Nevertheless, there is an effective enthalpy-entropy compensation for the ΔH^‡/ΔS^‡ of all the three ligands, demonstrating the significant effects of the changes in solvation and solvent structure on the complexation kinetics. As the rate-determining step of Ni(II) complexation is the dissociation of a water molecule from Ni(II), the solvent and ligand dependencies in the Ni(II) complexation kinetics are ascribed to the change in solvation status of the ligands and the altered solvent structures upon changing solvent composition.     

The Contribution of a Covalently Bound Cofactor to the Folding and Thermodynamic Stability of an Integral Membrane Protein

The factors controlling the stability, folding, and dynamics of integral membrane proteins are not fully understood. The high stability of the membrane protein bacteriorhodopsin (bR), an archetypal member of the rhodopsin photoreceptor family, has been ascribed to its covalently bound retinal cofactor. We investigate here the role of this cofactor in the thermodynamic stability and folding kinetics of bR. Multiple spectroscopic probes were used to determine the kinetics and energetics of protein folding in mixed lipid/detergent micelles in the presence and absence of retinal. The presence of retinal increases extrapolated values for the overall unfolding free energy from 6.3 ± 0.4 kcal mol^− 1 to 23.4 ± 1.5 kcal mol^− 1 at zero denaturant, suggesting that the cofactor contributes 17.1 kcal mol^− 1 towards the overall stability of bR. In addition, the cooperativity of equilibrium unfolding curves is markedly reduced in the absence of retinal with overall m-values decreasing from 31.0 ± 2.0 kcal mol^− 1 to 10.9 ± 1.0 kcal mol^− 1, indicating that the folded state of the apoprotein is less compact than the equivalent for the holoprotein. This change in the denaturant response means that the difference in the unfolding free energy at a denaturant concentration midway between the two unfolding curves is only ca 3-6 kcal mol^− 1. Kinetic data show that the decrease in stability upon removal of retinal is associated with an increase in the apparent intrinsic rate constant of unfolding, k_u^H2O, from ~1 × 10^− 16 s^− 1 to ~1 × 10^− 4 s^− 1 at 25 °C. This correlates with a decrease in the unfolding activation energy by 16.3 kcal mol^− 1 in the apoprotein, extrapolated to zero SDS. These results suggest that changes in bR stability induced by retinal binding are mediated solely by changes in the activation barrier for unfolding. The results are consistent with a model in which bR is kinetically stabilized via a very slow rate of unfolding arising from protein-retinal interactions that increase the rigidity and compactness of the polypeptide chain.     

Kinetics of the cis-to-planar interconversion of cis-diaqua(1,4,7,11-tetraazacyclotetradecane)nickel(II) ion

In order to examine the effects of coordinated hydroxide ion and free hydroxide ion in configurational conversion of a tetraamine macrocyclic ligand complex, the kinetics of the cis-to-planar interconversion of cis-[Ni(isocyclam)(H₂O)₂]²⁺ (isocyclam, 1,4,7,11-tetraazacyclotetradecane) has been studied spectrophotometrically in basic aqueous solution. The interconversion requires the inversion of one sec-NH center of the folded cis-complex to have the planar species. Kinetic data are satisfactorily fitted by the rate law, R = k_OH[OH⁻][cis-[Ni(isocyclam)(H₂O)₂]²⁺], where k_OH = 3.84 × 10³ dm³ mol⁻¹ s⁻¹ at 25.0 ± 0.1 °C with I = 0.10 mol dm⁻³ (NaClO₄). The large ΔH^≠, 61.7 ± 3.2 kJ mol⁻¹, and the large positive ΔS^≠, 30.2 ± 10.8 J K⁻¹ mol⁻¹, strongly support a free-base-catalyzed mechanism for the reaction.     

Molecular sensing behavior of the first Mn(I)-compound of di-2-pyridylketone-p-nitrophenylhydrazone (dpknph), fac-[Mn(CO)3(dpknph)Br]

The reaction between [Mn(CO)₅Br] and di-2-pyridylketone-p-nitrophenylhydrazone (dpknph) in diethyl ether under ultrasonic conditions gave fac-[Mn(CO)₃(dpknph)Br] in good yield. Optical and thermodynamic measurements on fac-[Mn(CO)₃(dpknph)Br] in non-aqueous polar solvents revealed reversible interconversion between two intense charge transfer absorption bands due to π-π* (dpk), followed by dpk → nitro intraligand charge transfer transition (ILCT), mixed with metal ligand charge transfer transition (MLCT) due to . In non-polar solvents, a single absorption band appeared. Extinction coefficients of 46 200 ± 2000 and 28 400 ± 2000 M⁻¹ cm⁻¹ were calculated in DMSO for the low- and high-energy electronic states of fac-[Mn(CO)₃(dpknph)Br] using excess NaBF₄. Changes in enthalpy (ΔH^ø) of +14.0 and −12.1 kJ mol⁻¹, entropy (ΔS^ø) of +28.65 and −64.30 J mol⁻¹ K⁻¹, and free energy (ΔG^ø) of +5.48 and +7.08 kJ mol⁻¹ at 298 K were calculated for the interconversion between the high and low energy electronic states of fac-[Mn(CO)₃(dpknph)Br]. These results allow for the use of these systems (fac-[Mn(CO)₃(dpknph)Br] and surrounding solvent or solute molecules) as optical sensors for a variety of physical and chemical stimuli that include metal ions. Group 12 metal ions in concentrations as low as 1.00 × 10⁻⁹ M can be detected and determined using fac-[Mn(CO)₃(dpknph)Br] in dmso in the presence and absence of NaBH₄.     

Effect of temperature on phosphorus sorption to sediments from shallow eutrophic lakes

The availability of phosphorus (P) in lakes is dependent on the sorption characteristics of the underlying sediments. Temperature is a crucial factor affecting the P sorption in sediments. The objective of this study was to evaluate the effect of temperature on sorption of P by sediments from two eutrophic lakes. The study was carried out using short-term batch experiments at 4, 20 and 30 °C. Phosphorus sorption kinetics, isotherms, fractionation and desorption were investigated. The P sorption was dependent on sediment type and temperature (p < 0.001). The Mei sediments showed a higher sorption rate and sorption capacity than Hua sediments. The P sorption kinetics were best described by a pseudo second order model (R² > 0.97). Activation energies derived from the kinetics rate constant indicated that P sorption onto the two sediments was controlled by a diffusion process. For both sediments, Freundlich model fit the P sorption isotherms well and the calculated apparent sorption heat was 6.37 kJ mol⁻¹ for Mei sediments and 8.67 kJ mol⁻¹ for Hua sediments. This indicated that P sorption onto both sediments was endothermic. Adding P significantly increased the soluble and loosely bound P (S/L-P), aluminum-bound P (Al-P) and iron-bound P (Fe-P) (p < 0.05). The amount of Al-P and Fe-P was markedly higher at 30 °C than at 4 °C (p < 0.05). Subsequent P desorption indicated that adsorbed P was highly labile, in particular for Hua sediment. The degree of P mobility that occurred during sediment sorption was inversely related to the temperature at the time of sorption. A significant relationship (R² = 0.978) between phosphorus sorption maximum and oxalate-extractable Fe and Al at different temperatures reflects that the amorphous contents of Fe and Al are responsible for the temperature effect on P sorption.     

An unusual thermostable aspartic protease from the latex of Ficus racemosa (L.)

The most extensively studied ficins have been isolated from the latex of Ficus glabrata and Ficus carica. However the proteases (ficins) from other species are less known. The purification and characterization of a protease from the latex of Ficus racemosa is reported. The enzyme purified to homogeneity is a single polypeptide chain of molecular weight of 44,500 ± 500 Da as determined by MALDI-TOF. The enzyme exhibited a broad spectrum of pH optima between pH 4.5-6.5 and showed maximum activity at 60 ± 0.5 °C. The enzyme activity was completely inhibited by pepstatin-A indicating that the purified enzyme is an aspartic protease. Far-UV circular dichroic spectra revealed that the purified enzyme contains predominantly β-structures. The purified protease is thermostable. The apparent T_m, (mid point of thermal inactivation) was found to be 70 ± 0.5 °C. Thermal inactivation was found to follow first order kinetics at pH 5.5. Activation energy (E_a) was found to be 44.0 ± 0.3 kcal mol⁻¹. The activation enthalpy (ΔH^∗), free energy change (ΔG^∗) and entropy (ΔS^∗) were estimated to be 43 ± 4 kcal mol⁻¹, −26 ± 3 kcal mol⁻¹ and 204 ± 10 cal mol⁻¹ K⁻¹, respectively. Its enzymatic specificity studied using oxidized B chain of insulin indicates that the protease preferably hydrolyzed peptide bonds C-terminal to glutamate, leucine and phenylalanine (at P₁ position). The broad specificity, pH optima and elevated thermal stability indicate the protease is distinct from other known ficins and would find applications in many sectors for its unique properties.     

Cyanide and chloride exchange on homoleptic gold(III) square-planar complexes: variable pressure kinetic investigation by heteronuclear NMR

Kinetic studies of X⁻ exchange on [AuX₄]⁻ square-planar complexes (where X=Cl⁻ and CN⁻) were performed at acidic pH in the case of chloride system and as a function of pH for the cyanide one. Chloride NMR study (330-365 K) gives a second-order rate law on [AuCl₄]⁻ with the kinetic parameters: (k₂^Au,Cl)²⁹⁸=0.56±0.03 s⁻¹ mol⁻¹ kg; ΔH₂^‡ Au,Cl=65.1±1 kJ mol⁻¹; ΔS₂^‡ Au,Cl=−31.3±3 J mol⁻¹ K⁻¹ and ΔV₂^‡ Au,Cl=−14±2 cm³ mol⁻¹. The variable pressure data clearly indicate the operation of an I_a or A mechanism for this exchange pathway. The proton exchange on HCN was determined by ¹³C NMR as a function of pH and the rate constant of the three reaction pathways involving H₂O, OH⁻ and CN⁻ were determined: k₀^HCN,H=113±17 s⁻¹, k₁^HCN,H=(2.9±0.7)×10⁹ s⁻¹ mol⁻¹ kg and k₂^HCN,H=(0.6±0.2)×10⁶ s⁻¹ mol⁻¹ kg at 298.1 K. The rate law of the cyanide exchange on [Au(CN)₄]⁻ was found to be second order with the following kinetic parameters: (k₂^Au,CN)²⁹⁸=6240±85 s⁻¹ mol⁻¹ kg, ΔH₂^‡ Au,CN=40.0±0.8 kJ mol⁻¹, ΔS₂^‡ Au,CN=−37.8±3 J mol⁻¹ K⁻¹ and ΔV₂^‡ Au,CN=+2±1 cm³ mol⁻¹. The rate constant observed varies about nine orders of magnitude depending on the pH and HCN does not act as a nucleophile. The observed rate constant of X⁻ exchange on [AuX₄]⁻ are two or three orders of magnitude faster than the Pt(II) analogue.     

Evaluation of the accessible inclusion sites in copolymer materials containing β-cyclodextrin

The accessible inclusion sites of insoluble copolymers containing β-cyclodextrin (β-CD) were studied in aqueous solutions by measuring the absorbance changes (decolourization) of phenolphthalein (phth) at pH 10.5. The various copolymers were reacted at different β-CD:crosslinker mole ratios with five individual types of crosslinker agents (epichlorohydrin (EP), sebacoyl chloride (SCL), terephthaloyl chloride (TCL), glutaraldehyde (GLU), and poly(acrylic) acid (PAA), respectively). The decolourization provided estimates of the 1:1 binding constants (K₁) for the β-CD monomer/phth complex. Comparable values of K₁ were measured for copolymer/phth complexes with highly accessible β-CD inclusion sites as compared with the 1:1 β-CD/phth complex. The surface accessibility of the β-CD inclusion binding sites for the polymers ranged from ∼10 to 72%. The observed variability of the inclusion sites was attributed to: (i) steric effects in the annular hydroxyl region of β-CD, (ii) the degree of crosslinking of the copolymer and (iii) the accessibility of the micropore sites within the copolymers. The Gibbs free energy (ΔG°) and site occupancy (θ) of phth adsorbed to the copolymer materials was estimated independently using the Sips isotherm model. The ΔG° values ranged between −27.6 and −30.9 kJ mol⁻¹ for the copolymers and are in close agreement with the value for the 1:1 β-CD/phth complexes (ΔG° = −27 kJ mol⁻¹) in aqueous solution.     

Pyrolysis characteristics and kinetics of Arundo donax using thermogravimetric analysis

The increase of the price of fossil means, as well as their programmed disappearing, contributed to increase among appliances based on biomass and energy crops. The thermal behavior of Arundo donax by thermogravimetric analysis was studied under inert atmosphere at heating rates ranging from 5 to 20 °C min⁻¹ from room temperature to 750 °C. Gaseous emissions as CO₂, CO and volatile organic compounds (VOC) were measured and global kinetic parameters were determined during pyrolysis with the study of the influence of the heating rate. The thermal process describes two main phases. The first phase named active zone, characterizes the degradation of hemicellulose and cellulose polymers. It started at low temperature (200 °C) comparatively to wood samples and was finished at 350 °C. The pyrolysis of the lignin polymer occurred during the second phase from 350 to 750 °C, named passive zone. Carbon oxides are emitted during the active zone whereas VOC are mainly formed during the passive zone. Mass losses, mass loss rates and emission factors were strongly affected by the variation of the heating rate in the active zone. It was found that the global pyrolysis of A. donax can be satisfactorily described using global independent reactions model for hemicellulose and cellulose in the active zone. The activation energy for hemicellulose was not affected by a variation of the heating rate with a value close to 110 kJ mol⁻¹ and presented a reaction order close to 0.5. An increase of the heating rate decreased the activation energy of the cellulose. However, a first reaction order was observed for cellulose decomposition. The experimental results and kinetic parameters may provide useful data for the design of pyrolytic processing system using A. donax as feedstock.     

Synthesis, crystal structure and interaction with DNA and HSA of (N,N'-dibenzylethane-1,2-diamine) transition metal complexes

A new ligand, N,N′-dibenzylethane-1,2-diamine (L) and its four transition metal(II) complexes, ML₂(OAc)₂ · 2H₂O (M = Cu, Ni, Zn, Co), have been synthesized and characterized by elemental analysis, mass spectra, molar conductivity, NMR and IR. Moreover, the crystals structure of Cu(II) and Ni(II) complexes characterized by single crystal X-ray diffraction showed that the complexes have a similar molecular structure. Ni(II) has an regular octahedral coordination environment complexes, but typical Jahn Teller effect influenced Cu(II) in an elongated octahedral environment. The interaction between complexes and calf thymus DNA were studied by UV and fluorescence spectra measure, which showed that the binding mode of complexes with DNA is intercalation. Under physiological pH condition, the effects of Cu(OAc)₂L₂ · 2H₂O and Ni(OAc)₂L₂ · 2H₂O on human serum albumin were examined by fluorescence. The results of spectroscopic measurements suggested that the hydrophobic interaction is the predominant intermolecular force. The enthalpy change ΔH⁰ and the entropy change ΔS⁰ of Cu(OAc)₂L₂ · 2H₂O and Ni(OAc)₂L₂ · 2H₂O were calculated to be −11.533 kJ mol⁻¹ and 46.339 J mol⁻¹ K⁻¹, −11.026 kJ mol⁻¹ and 46.396 J mol⁻¹ K⁻¹, respectively, according to the Scatchard’s equation. The quenching mechanism and the number of binding site (n ≈ 1) were also obtained from fluorescence titration data.     

Mechanistic studies on monodentate-ligand substitution of five-coordinate trigonal-bipyramidal platinum (II) complexes with tris[2-(diphenylphosphino)ethyl]phosphine

Reaction of the five-coordinate trigonal-bipyramidal platinum(II) complex, [Pt(pt)(pp₃)](BF₄) (pt = 1-propanethiolate, pp₃ = tris[2-(diphenylphosphino)ethyl]phosphine), with I⁻ in chloroform gave the five-coordinate square-pyramidal complex with a dissociated terminal phosphino group and an apically coordinated iodide ion in equilibrium. The thermodynamic parameters for the equilibrium between the trigonal-bipyramidal and square-pyramidal geometries, [Pt(pt)(pp₃)]⁺ + I⁻ ? [PtI(pt) (pp₃)], and the kinetic parameters for the chemical exchange were obtained as follows: , ΔH⁰ = − 10 ± 2.4 kJ mol⁻¹, ΔS⁰ = − 36 ± 10 J K⁻¹ mol⁻¹, , ΔH^‡ = 34 ± 4.7 kJ mol⁻¹, ΔS^‡ = − 50 ± 21 J K⁻¹ mol⁻¹. The square-planar trinuclear platinum(II) complex was formed by bridging reaction of one of the terminal phosphino groups of trigonal-bipyramidal [PtCl(pp₃)]Cl with trans-[PtCl₂(NCC₆H₅)₂] in chloroform. From these facts, ligand substitution reactions of [PtX(pp₃)]⁺ (X = monodentate anion) are expected to proceed via an intermediate with a dissociated phosphino group. The rate constants for the chloro-ligand substitution reactions of [PtCl(pp₃)]⁺ with Br⁻ and I⁻ in chloroform approached the respective limiting values as concentrations of the entering halide ions are increased. These kinetic results confirmed the preassociation mechanism in which the square pyramidal intermediate with a dissociated phosphino group and an apically coordinated halide ion is present in the rapid pre-equilibrium.     

A kinetic investigation of the oxidative addition reactions of the dimeric Bu4N[Ir2(μ-Dcbp)(cod)2] complex with iodomethane

The kinetic results of the oxidative addition of iodomethane to Bu₄N[Ir₂(μ-Dcbp)(cod)₂] (Dcbp = 3,5-dicarboxylatepyrazolate anion) show that oxidative addition can occur via a direct equilibrium pathway (K₁ = 88(22) acetone, 51(3) 1,2-dichloroethane, 55(4) dichloromethane, 52(12) acetonitrile and 43(5) M⁻¹ chloroform) or a solvent-assisted pathway (k₂, k₃). Oxidative addition occurs mainly along the direct pathway, which is a factor 10-40 faster than the solvent-assisted pathway. The observed solvent effect cannot be attributed to the donosity or polarity of the solvents. The fairly negative ΔS^≠ value (−110(7) J K⁻¹ mol⁻¹) and the positive ΔH^≠ value (+47(2) kJ mol⁻¹) for the oxidative addition step are indicative of an associative process.