Oxidation of copper(II)-coordinated diethylenetriamine by hexacyanoferrate(III) ion. A kinetic investigation

The stoichiometry and kinetics of the reaction between [Cu(dien)(OH)]⁺ and [Fe(CN)₆]³⁻ in aqueous alkaline medium are described. The rate equation − (d[Fe(III)]/dt = {k₁[OH⁻]²[[Cu(dien)(OH)]⁺] + k₂[OH⁻] × [[Cu(dien)(OH)]⁺]²}([Fe(III)]/[Fe(II)]) (Fe(III) = [Fe(CN)₆]³⁻; Fe(II) = [Fe(CN)₆]⁴⁻, the 4:4:1 OH⁻/Fe(III)/[Cu(dien)(OH)]⁺ stoichiometric ratio and the nature of the ultimate products identified in the reaction solution suggest the fast formation of a doubly deprotonated Cu(III)-diamido complex which slowly undergoes an internal redox process where the ligand is oxidised to the Schiff base H₂NCH₂CH₂NCHCHNH.The [[Cu(dien)(OH)]⁺]² term in the rate equation is explained with the formation of a transient μ-hydroxo mixed-valence Cu dimer. A two-electron internal reduction of the Cu(III) complex yielding a Cu(I) intermediate is suggested to account for the presence of monovalent copper in a precipitate which forms at relatively high reactant concentrations and in the absence of dioxygen.     

Theoretical study about the 5-azido-1H-tetrazole and its ion salts

Periodic DFT method has been firstly used to calculate the bulk structure, electronic structure, electrical transferring and thermodynamic properties of crystalline 5-azido-1H-tetrazole (HCN₇) and its four different salts. The anion CN₇ ^? was included in all of the salts such as ammonium 5-azidotetrazolate ([NH₄]⁺[CN₇]^?), hydrazinium 5-azidotetrazolate ([N₂H₅]⁺[CN₇]^?), guanidinium 5-azidotetrazolate ([CH₆N₃]⁺[CN₇]^??·?H₂O) and 1-aminoguanidinium 5- azidotetrazolate ([CH₇N₄]⁺[CN₇]^?). The simulation is in reasonable agreement with the experimental results. It is found the salts of HCN₇ are more stable than itself because the band gap of the salts is larger. The density of state shows the p states of them (including HCN₇ and its four salts) have played a very significant role in the reaction.

Electrolyte effects on the intervalence transition within discrete binuclear cyano-bridged complexes. An estimation of activation free energy from static, optical and electrochemical data

A study of the metal-to-metal charge-transfer (MMCT) transition within the binuclear cyano-bridged complexes cis-[L¹³Co^III(μ-NC)Fe^II(CN)₅]⁻ (L¹³ = 12-methyl-1,4,7,10-tetraazacyclotridecan-12-amine), trans-[L¹⁴Co^III(μ-NC)Fe^II(CN)₅]⁻ (L¹⁴ = 6-methyl-1,4,8,11-tetraazacyclotetradecan-6-amine) and trans-[L¹⁵Co^III(μ-NC)Fe^II(CN)₅]⁻ (L¹⁵ = 10-methyl-1,4,8,12-tetraazacyclopentadecan-10-amine) has been carried out in electrolyte solutions at varying concentrations. Using these data, as well as the reaction free energies obtained from electrochemical measurements, the reorganisation and activation free energies for the forward and reverse thermal electron-transfer processes have been estimated. The changes of these parameters with the electrolyte concentration, as well as those of the energy of the maximum MMCT band and the reaction free energy, are mainly due to ion-pairing effects.     

Effect of different reaction parameters on the lipase-catalyzed selective acylation of polyhydroxylated natural compounds in ionic liquids

The effect of various reaction parameters on the enzymatic acylation of plant polyhydroxylated compounds, including phenolic and flavonoid glucosides (salicin, helicin, esculin and naringin), was investigated in imidazolium-based ionic liquids (1-butyl-3-methylimidazolium tetrafluoroborate [bmim]BF₄ and 1-butyl-3-methylimidazolium hexafluorophosphate [bmim]PF₆), using immobilized lipase B from Candida antarctica. The conversion yield, the regioselectivity and the reaction rate of the biocatalytic process strongly depended on the ionic liquid used, their water content, the incubation temperature, as well as the solubility and the concentration of substrates. For most glucosides tested, one major product (monoacylated derivative) was detected as a result of the acylation of the primary hydroxyl group of glucose moiety. The acylation rate and the regioselectivity of the process are higher in [bmim]BF₄, where the solubility of all glucosides is significantly higher than in [bmim]PF₆ or acetone. Response surface methodology (RSM) based on a five level-three variable central composite circumscribed design, was employed to evaluate the interactive effect of the molar ratio of substrates (MR), the initial concentration of glucoside (N) and the reaction time (RT), as well as for their optimization in [bmim]BF₄. At the optimal reaction conditions the maximum acylation yield was 87%. The amount of monoacylated derivatives produced in a single-step biocatalytic process reached values up to 31.6 g/l which is considerably higher than those reported for organic media.     

A high-spin Fe(II)/low-spin Fe(III) redox couple featuring the hydro[tris(4-chloro-3,5-dimethyl-pyrazolyl)]borate ligand: Synthesis, spectroscopic and X-ray crystallographic characterization

The white homoleptic high-spin iron(II) complexes Fe[Tp^Me2,4Cl]₂ (1) was isolated in quantitative yield from reaction mixtures containing 1 equiv of FeCl₂(THF)_1.5 and 2 equiv of K[Tp^Me2,4Cl] (Tp^Me2,4Cl = hydrotris[(4-chloro-3,5-dimethyl-pyrazolyl)]borate). Its purple low-spin iron(III) counterparts 1[O₃SCF₃] and 1[PF₆] were synthesized and isolated in 85% yields upon treatment of 1 with 1 equiv of silver triflate and silver hexafluorophosphate, respectively. The three paramagnetic compounds are air and thermally stable as solids and in solution; they were characterized by elemental analyses, IR, magnetic susceptibility measurements, ¹H NMR, and Mössbauer spectroscopy. In addition, 1[PF₆] was authenticated by a single-crystal X-ray diffraction. The two scorpionate ligands are κ³-N,N′,N′′ ligated to the central Fe^III ion, forming an almost perfect FeN₆ octahedron with an average Fe-N bond distance of 1.9551(18) Å. In addition, complex 1 which oxidizes reversibly at E_1/2 = 0.483 V/SCE (ΔE_p = 94 mV), remains high-spin (S = 2) when the temperature is lowered to 2 K.     

Penicillium expansum lipase-catalyzed production of biodiesel in ionic liquids

Penicillium expansum lipase (PEL) was used to catalyze biodiesel production from corn oil in [BMIm][PF₆]¹ (an ionic liquid, IL) and tert-butanol. Both systems were optimized in terms of MeOH/oil molar ratio, reaction temperature, enzyme loading, solvent volume, and water content. The high conversion obtained in the IL (86%) as compared to that in tert-butanol (52%) demonstrates that the IL is a superior solvent for PEL-catalyzed biodiesel production. Poor yields were obtained in a series of hydrophilic ILs. Addition of salt hydrates affected biodiesel production predominantly through the specific ion (Hofmeister) effect. The impact of methanol on both activity and stability of PEL in the IL and in hexane was investigated, in comparison to the results obtained by two commonly used lipases, Novozym 435 and Lipozyme TLIM. The results substantiate that while different lipases show different resistance to methanol in different reaction systems, PEL is tolerant to methanol in both systems.     

Identification of acylation products in SHAPE chemistry

SHAPE chemistry (selective 2′-hydroxyl acylation analyzed by primer extension) has been developed to specifically target flexible nucleotides (often unpaired nucleotides) independently to their purine or pyrimidine nature for RNA secondary structure determination. However, to the best of our knowledge, the structure of 2′-O-acylation products has never been confirmed by NMR or X-ray data. We have realized the acylation reactions between cNMP and NMIA under SHAPE chemistry conditions and identified the acylation products using standard NMR spectroscopy and LC–MS/MS experiments. For cAMP and cGMP, the major acylation product is the 2′-O-acylated compound (>99%). A trace amount of N-acylated cAMP has also been identified by LC–UV–MS². While for cCMP, the isolated acylation products are composed of 96% of 2′-O-acylated, 4% of N,O-diacylated, and trace amount of N-acylated compounds. In addition, the characterization of the major 2′-O-acylated compound by NMR showed slight differences in the conformation of the acylated sugar between the three cyclic nucleotides. This interesting result should be useful to explain some unexpected reactivity of the SHAPE chemistry.     

Pseudomonas cepacia lipase catalyzed esterification and transesterification of 3-(furan-2-yl) propanoic acid/ethyl ester: A comparison in ionic liquids vs hexane

A comparison of the Pseudomonas cepacia lipase (lipase PS) catalyzed esterification of 3-(furan-2-yl) propanoic acid and transesterification of ethyl 3-(furan-2-yl) propanoate with six straight chain alcohols (propanol to octanol) in ionic liquids and hexane was carried out. The ionic liquids selected, [Bmim]BF₄, [Bmim]PF₆, and [Bmim]Tf₂N, consisted of an identical cation and different anions. This is the first report on the biocatalyzed synthesis of these esters. In all the media, lipase PS catalyzed esterification of 3-(furan-2-yl) propanoic acid resulted in high yields of the esters compared to the transesterification of ethyl 3-(furan-2-yl) propanoate. [Bmim]Tf₂N proved to be the best; yielding 98–67% of the product by lipase PS catalyzed esterification. The lipase PS–[Bmim]Tf₂N and lipase PS–[Bmim]PF₆ mixture was recycled five times without any decrease in the yields of the products and was found to be operationally stable up to 10 months at room temperature.     

Biocatalytic synthesis of poly(ε‐caprolactone) using modified lipase in ionic liquid media

Ionic liquids have been used as exceptional nonaqueous reaction media for enzymatic transformation. The ring‐opening polymerization of ε‐caprolactone catalyzed by Novozyme‐435 lipase was successfully conducted in 1‐butyl‐3‐methylimidazolium hexafluorophosphate ([Bmim]PF₆) ionic liquid. ¹H‐NMR and MALDI‐TOF analyses of poly(ε‐caprolactone) (PCL) formed by Novozyme‐435 lipase‐catalyzed reaction revealed an asymmetric telechelic α‐hydroxy‐ω‐carboxylic acid end group. The effects of enzyme concentration, temperature, reaction time, and water activities on monomer conversion and M_n were systematically evaluated. Through the optimization of reaction conditions, PCL was produced in 85% monomer conversion, with an M_n of 5942, in [Bmim]PF₆ at 60°C for 48 h. DSC results demonstrated that high‐molecular‐weight PCL exhibited an excellent thermal property. SEM results showed that PCL had a clear spherulites structure, which could provide a large surface area for cell adhesion. These results showed that [Bmim]PF₆ ionic liquid was suitable for the biocatalytic synthesis of PCL using Novozyme‐435 lipase, and could be used as alternative environmentally friendly media to replace the traditional organic solvents.     

Syntheses, spectroscopic properties and crystal structures of two organoruthenium (II) complexes of bipyridines: [{Cp*Ru(2,2′-bipy)}2(μ-Cl)][PF6] and [{(η-p-cymene)Ru}2(μ-OH)2(4,4′-bipy)]2[BF4]4

Interaction of [Cp*RuCl(μ-Cl)]₂ with 2,2′-bipyridine (2,2′-bipy) in the presence of Na[PF₆] gave a chloride bridging dinuclear complex [{Cp*Ru(2,2′-bipy)}₂(μ-Cl)][PF₆] (1). In the crystal structure, the cation [{Cp*Ru(2,2′-bipy)}₂(μ-Cl)]⁺ contains a bent Ru-Cl-Ru linkage with an angle of 141.87(12)°. The tris(μ-hydroxo)diruthenium complex [{(η⁶-p-cymene)Ru}₂(μ-OH)₃][BF₄] in acetone solution was treated by 4,4′-bipyridine (4,4′-bipy) to give a hydroxo-bridged tetranuclear complex [{(η⁶-p-cymene)Ru}₂(μ-OH)₂(μ-4,4′-bipy)]₂[BF₄]₄ (2). Complex 2 consists of four (η⁶-p-cymene)Ru moieties connected by two 4,4′-bipy and four hydroxo-bridging groups, forming a novel metallomacrocycle with alternating hydroxyl and 4,4′-bipy bridges between the ruthenium atoms. Spectroscopic properties along with electrochemistry of two organoruthenium (II) complexes 1 and 2 are reported.     

sp C-H and sp C-H agostic ruthenium complexes: a combined experimental and theoretical study

Halide abstraction from the 18 electron Ru(II) complex RuCl(CO)₂[2,6-(CH₂P^tBu₂)₂C₆H₃] (2) with AgPF₆ results in the exclusive formation of the cationic complex {Ru(CO)₂[2,6-(CH₂P^tBu₂)₂C₆H₃]}⁺PF₆⁻ (3). The molecular structures of 2 and 3 were determined by complete single-crystal diffraction studies. X-ray crystallographic analysis of 3 reveals that the “open” coordination site is occupied by an agostic interaction between the metal center and an sp³ C-H bond of a tert-butyl substituent. DFT gas phase calculations (B97-1/SDD) show the necessity of two sterically demanding tert-butyl substituents on one P donor atom for the agostic interaction to occur. The reaction of 3 with H₂ results in the quantitative conversion to {Ru(H)(CO)₂[2,6-(CH₂P^tBu₂)₂C₆H₄]}⁺PF₆⁻ (4) where the aromatic C_ipso-H bond is η²-coordinated to the metal center. Treatment of the agostic complex 4 with Et₃N results in the formation of the neutral complex Ru(H)(CO)₂[2,6-(CH₂P^tBu₂)₂C₆H₃] (5). The mechanistic details of 3 + H₂ → 4 were investigated by DFT calculations at the B97-1/SDB-cc-pVDZ//B97-1/SDD level of theory.     

Rb2[B12(OH)12]·2H2O and Rb2[B12(OH)12]·2H2O2: Hydrate and perhydrolate of rubidium dodecahydroxo-closo-dodecaborate

The orthorhombically crystallizing salts Rb₂[B₁₂(OH)₁₂]·2H₂O (a = 1576.81(9), b = 813.08(5), c = 1245.32(7) pm) and Rb₂[B₁₂(OH)₁₂]·2H₂O₂ (a = 1616.54(9), b = 814.29(5), c = 1260.12(7) pm) could be prepared from Rb₂[B₁₂H₁₂] and hydrogen peroxide. Both crystal structures were determined by X-ray single crystal diffraction and refined in the space group Cmce. They are not isostructural to the other compounds containing icosahedral dodecahydroxo-closo-dodecaborate dianions [B₁₂(OH)₁₂]²⁻ and potassium, rubidium or cesium cations already known to literature, but both title compounds crystallize quasi-isotypically exhibiting Rb⁺ cations in 10-fold oxygen coordination. The hydrogen peroxide adduct (Rb₂[B₁₂(OH)₁₂]·2H₂O₂) is explosive on shock and heat, while the hydrate (Rb₂[B₁₂(OH)₁₂]·2H₂O) is not.     

Reactions of dichloroaluminium acetylacetonate with lewis bases. 1. Ionic complex of Cl2alacac with tetrahydrofurane

The reaction of dichloroaluminium acetylacetonate with THF has been studied. The ionic complex [(acac)₂Al·2THF]⁺[AlCl₄]⁻ was found to result from the reaction. The structure of the complex has been investigated by the variable temperature ¹H NMR technique, as well as by ¹³C and ²⁷Al NMR spectroscopy. The cation complex [(acac)₂Al·2THF]⁺ is predominantly trans in dichloromethane solution (75% trans and 25% cis). In the presence of an excess of THF a fast exchange proceeds at room temperature in the cation complex between the free THF molecules and those present in the complex, which is accompanied by a stereo-chemical rearrangement of the cation complex.     

Efficient production of glycyrrhetic acid 3-O-mono-β-d-glucuronide by whole-cell biocatalysis in an ionic liquid/buffer biphasic system

Hydrolysis of glycyrrhizin (GL) to glycyrrhetic acid 3-O-mono-β-d-glucuronide (GAMG) by whole-cell biocatalysts in a system containing non-conventional solvents was performed. Three whole-cell biocatalysts were used, including wild-type Penicillium purpurogenum Li-3 (w-PGUS) and recombinant strains Escherichia coli BL21 and Pichia pastoris GS115. The biotransformation of GL to GAMG by w-PGUS in a 1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim]PF₆)/buffer biphasic system was the main focus of this study because w-PGUS showed a higher GAMG yield and a higher relative activity in this system than the other two whole-cell biocatalysts. Using the optimized reaction conditions determined as a pH 5.2 buffer, a 6.0 mM substrate concentration, a reaction temperature of 30 °C, and a 60 g/L (1.23 U/g) cell concentration, a GAMG yield of 87.63% was achieved after 60 h. After eight reaction cycles, [Bmim]PF₆ retained a high recovery percentage (85.48%)_[0], indicating the reusability of this IL. The biotransformation activity of w-PGUS was not significantly affected, even after two batch reaction cycles. Furthermore, the product GAMG and the byproduct glycyrrhetinic acid were spontaneously separated in the biphasic system. In conclusion, the combination of whole cells and ionic liquid is a promising approach for economical and industrial-scale production of GAMG.     

Candida antarctica lipase B catalyzed enantioselective acylation of pyrimidine acyclonucleoside

Abstract

The influence of solvent and acyl group donor on selectivity of the transesterification reaction of 1-[1′,3′-dihydroxy-2′-propoxymethyl]-5-methyluracil, a structural analogue of ganciclovir was examined. Lipase (EC 3.1.1.3) B from Candida antarctica (CALB) enabled desymmetrization of prochiral hydroxyl groups when 1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim][PF₆]) was used as a reaction medium. It was observed that CALB was up to 2.7–4 times more enantioselective in the ionic liquid [Bmim][PF₆] than in conventional organic solvents.     

The role of different anions in ionic liquids on Pseudomonas cepacia lipase catalyzed transesterification and hydrolysis

Lipase Pseudomonas cepacia (PS) catalyzed transesterification of ethyl 3-phenylpropanoate with eleven alcohols was investigated in three ionic liquids [ILs], [Bmim]BF₄, [Bmim]PF₆, and [Bmim]Tf₂N, consisting of an identical cation and different anions. The yields were higher in hydrophobic ILs [Bmim]Tf₂N (55–96%) and [Bmim]PF₆ (22–95%), than in hydrophilic [Bmim]BF₄ (0–19%). The incubation of lipase PS in hydrophobic ILs for a period of 20–300 days at room temperature resulted in an increased yield of 62–98% in [Bmim]Tf₂N and 45–98% in [Bmim]PF₆, respectively. The lipase PS-hydrophobic IL mixture was recycled five times without any decrease in the yield of the products. In another set of experiments, the hydrolytic activity of the enzyme was determined after incubation in each of the three ILs and in hexane for 20 days at room temperature. It was found to be 1.8- and 1.6-fold higher in [Bmim]Tf₂N and [Bmim]PF₆, respectively, remained unchanged in [Bmim]BF₄ and was 1.6 times lower in hexane as compared to the non-incubated enzyme.     

Synthesis of fac-[Os(CO)3(L)Me2] (L = THF or MeCN) and some reactions with PPh3 and trityl salts

The reaction of cis-[Os(CO)₄Me₂] with Me₃NO in the THF or MeCN yields the complexes fac-[Os(CO)₃(L)Me₂] (where L = THF or MeCN). Whereas the THF complex is unstable and only characterised spectroscopically, fac-[Os(CO)₃(MeCN)Me₂] has been isolated as a white solid and fully characterized by both analytical and spectroscopic methods. These complexes fac-[Os(CO)₃(L)Me₂] are shown to be useful intermediates. Thus, reaction with PPh₃ gives fac-[Os(CO)₃(PPh₃)Me₂] in good yield.Reactions of fac-[Os(CO)₃(L)Me₂] (L = CO or MeCN) with CPh₃PF₆ or B(C₆F₅)₃ have been investigated. Whereas cis-[Os(CO)₄Me₂] showed no reaction with either CPh₃PF₆ or B(C₆F₅)₃, the reaction of fac-[Os(CO)₃(MeCN)Me₂] with CPh₃PF₆ in CH₂Cl₂ occurred over 16 h at room temperature to give an unstable cationic product and CPh₃Me. The reaction was monitored by both IR and NMR spectroscopies. When this reaction of fac-[Os(CO)₃(MeCN)Me₂] was carried out in the presence of a trapping ligand such as MeCN, the stable cationic product [Os(CO)₃(MeCN)₂Me]⁺ could be isolated and identified spectroscopically.     

Kinetics of acid-catalysed dissociation of lead(II) and copper(II) complexes of ethylenebis(oxyethylenenitrilo)tetraacetic acid (EGTA)

The acid-catalysed dissociation rate constants for PbEGTA²⁻ and CuEGTA²⁻ complexes (where EGTA is ethylenebis(oxyethylenenitrilo) tetraacetic acid) were measured in acetic acid-acetate buffer medium (pH: 3.0–4.8) and perchloric acid solutions ([H⁺] = 0.05–0.15 M), respectively, at a constant ionic strength of 0.15 (NaClO₄). The rate laws shown by the lead(II) and copper(II) complexes are of the form, Rate = {k_d + k_H[H⁺]}[complex] and Rate = {k_d + k_H²[H⁺]²}[complex], respectively. Enthalpy and entropy of activation for acid-independent and acid-catalysed pathways for both the complexes were obtained by the temperature-dependence studies of resolved rate constants in the 16–45°C range. The rate of dissociation of PbEGTA²⁻ is not enhanced by increasing the concentration of acetate ion in the buffer, and the amount of total electrolyte in the reaction mixture has no pronounced effect on the dissociation rates of their the lead(II) or copper(II) complex. Attempts to study the kinetics of stepwise ligand unwrapping in the binuclear Cu₂EGTA complex were unsuccessful due to the extremely rapid dissociation of this complex to yield mononuclear CuEGTA²⁻.     

Hydrolysis of adenylyl imidodiphosphate in the presence of Na+ + Mg+ by (Na+ + K+)-activated ATPase

(1) Contrary to what has usually been assumed, (Na⁺ + K⁺)-ATPase slowly hydrolyses AdoPP[NH]P in the presence of Na⁺ + Mg²⁺ to ADP-NH₂ and P_i. The activity is ouabain-sensitive and is not detected in the absence of either Mg²⁺ or Na²⁺. The specific activity of the Na⁺ + Mg²⁺ dependent AdoPP[NH]P hydrolysis at 37°C and pH 7.0 is 4% of that for ATP under identical conditions and only 0.07% of that for ATP in the presence of K⁺. The activity is not stimulated by K⁺, nor can K⁺ replace Na⁺ in its stimulatory action. This suggests that phosphorylation is rate-limiting. Stimulation by Na⁺ is positively cooperative with a Hill coefficient of 2.4; half-maximal stimulation occurs at 5–9 mM. The K_m value for AdoPP[NH]P is 17 μM. At 0°C and 21°C the specific activity is 2 and 14%, respectively, of that at 37°C. AMP, ADP and AdoPP[CH₂]P are not detectably hydrolysed by (Na⁺ + K⁺)-ATPase in the presence of Na⁺ + Mg²⁺. (2) In addition, AdoPP[NH]P undergoes spontaneous, non-enzymatic hydrolysis at pH 7.0 with rate constants at 0, 21 and 37°C of 0.0006, 0.006 and 0.07 h^?1, respectively. This effect is small compared to the effect of enzymatic hydrolysis under comparable conditions. Mg²⁺ present in excess of AdoPP[NH]P reduces the rate constant of the spontaneous hydrolysis to 0.005 h^?1 at 37°C, indicating that the MgAdoPP[NH]P complex is virtually stable to spontaneous hydrolysis, as is also the case for its enzymatic hydrolysis. (3) A practical consequence of these findings is that AdoPP[NH]P binding studies in the presence of Na⁺ + Mg²⁺ with enzyme concentrations in the mg/ml range are not possible at temperatures above 0°C. On the other hand, determination of affinity in the (Na⁺ + K⁺)-ATPase reaction by competition with ATP at low protein concentrations (μg/ml range) remains possible without significant hydrolysis of AdoPP[NH]P even at 37°C.