Free-radical decarboxylation of carboxylic acids as a concerted abstraction and fragmentation reaction

Two variants of the reaction of radicals with the carboxyl group of carboxylic acids, namely, RO ₂ ^? + R _i COOH → ROOH + R _i CO ₂ ^? and RO _i ^? + R _j COOH → ROOH + R _i ^? + CO₂ are theoretically analyzed. It is demonstrated by the intersecting-parabolas method that if the reaction proceeded via the formation of an intermediate carboxyl radical, it would be much slower than is actually observed. Quantum-chemical calculations carried out by the density functional method using the nonempirical functional PBE have shown that the reactions of the methyl radical with the carboxyl group of acetic, butyric and vinylacetic acids include concerted H atom abstraction and C-C bond breaking. In the framework of the intersecting-parabolas model, an algorithm has been developed to calculate the activation energy and rate constant for X^? + R _i COOH → XH + CO₂ + R _i ^? reactions, where X = R^?, RO^?, HO^?, ArO^?, Ar₂N^? or H^?     

Effects of electric fields and electric field-gradients on X-ray scattering factors and the compton profile of hydrogenic atoms

Analytic expressions for the modification of the hydrogenic atom X-ray atomic scattering factor and Compton profile due to a proton at distance R are derived. It is shown that electric field-gradient effects (order R^?3) are comparable in importance to electric field effects (order R^?2).     

The pair polarizabilities of Li+/Li+ and Cl−/Cl−

Ab initio SCF MO energies and pair polarizabilities are reported for the pairs Li⁺/Li⁺ and Cl^?/Cl^? over the ranges of internuclear separation which are of importance in molten LiCl. The shapes of the β(R) curves resemble those of inert gas diatoms. The Cl^?/Cl^? interaction is predicted to make a rather small contribution to those properties of molten LiCl which depend on $\text{α}$⁽²⁾(R), and a larger contribution to properties which depend on β(R). The Li⁺/Li⁺ interaction contributes almost nothing to the bulk polarizability.     

Effect of the long-range potential on ion mobility measurements

The temperature dependence of ion mobilities in helium was studied by using the ion chromatography method to investigate the effect of long-range terms in the ion-buffer gas interaction. Experimental cross sections thus determined increased significantly as the temperature was lowered from 300 to 80 K for all ions investigated, which were fullerene C ₆₀ ⁺ , cationized PEG polymers, cationized crown ethers, and protonated and sodiated oligoglycines. The temperature dependence of the collision cross sections was successfully modeled by employing simple atom-atom interaction potentials including a repulsive R ^?12 term and the attractive long-range R ^?6 and R ^?4 terms, R being the distance between the colliding particles.     

On the validity of a modified Buckingham potential for the rare gas dimers at intermediate distances

The Buckingham potential has been modified to include the R^?8 and R^?10 dispersion terms. All the potential parameters are known for the rare gas dimers either from SCF or TFD calculations at short distances or perturbation calculations at long distances. Computed well potential parameters R₀ and R_m are found to be in excellent agreement (< 5%), while ? values are in reasonable agreement (≈ 25%) with the most recent experimental results.     

The polarizability of a pair of hydrogen atoms at long range

The coefficients of R^?6 and R^?9 in the long-range expansion of the parallel and perpendicular components of the polarizability of a pair of hydrogen atoms at a separation R have been calculated. The results are A⁽⁶⁾₆ = 2558.59. A⁽⁶⁾_⊥ = 1268.25, A⁽⁸⁾₆ = 90639.5 and A⁽⁸⁾_⊥ = 22010.3 au. The values of A⁽⁶⁾₆ and A⁽⁶⁾₆ and A⁽⁶⁾_| are somewhat larger than previous theoretical estimates and much larger than the classical values of 729 and 182.25 au. The terms in R^?8 arise from distortion associated with the dispersion forces and from the field of the quadrupole moment induced by the field-gradient at each atom.     

Xanthate anions in salts of biscyclopentadienylzirconium(IV) chelates

A series of [Cp ₂ZrL]⁺[ROCS₂]^? complexes whereL is the conjugate base of acetylacetone, benzoylacetone or 8-hydroxyquinoline andR=Me,Et ori-Pr have been synthesised in aqueous medium by the reaction of [Cp ₂ZrL]⁺Cl^? withROCS ₂ ^? K⁺. Various physico-chemical studies carried out for these complexes indicate that all the complexes are 1:1 electrolytes in which the ligandL is bidentate, consequently there is a tetrahedral coordination about the zirconium atom.     

Theoretical sstudy on the Co2+OH2+/Co3+OH2+ electron transfer reactivity

This paper presents a contact distance dependence analysis scheme and an abinitio calculation application for the electron transfer (ET) reactivity of Co²⁺OH₂/Co³⁺OH² reacting pair. The applicability of these schemes and the corresponding models has been discussed. The contact distance (R _CoCo) dependence of the relevant quantities has been analyzed. The results indicate that the activation energy from the accurate PES method agrees well with that from the anharmonic potential method, and they are obviously better than that from the harmonic potential method. The pair distribution function varies from 10^?2 to 10^?5 along withR _CoCo changing from 1.20 to 0.35 nm. The coupling matrix element exponentially decays along with the increase ofR _CoCo, and the effective electronic coupling requiresR _CoCo smaller than 0.75 nm. In the range from 0.50 to 0.75 nm forR _CoCo, the corresponding electronic transmission coefficient falls within 1.0—10^?6. The local ET rate also exponentially decays along with the increase ofR _CoCo due to the electronic factor. Since the contribution from the pair distribution function to the total ET rate is an inverse measure of that from the electronic factor, the variation of the spherically averaged local ET rate along withR _CoCo exhibits a parabola with a maximum at 0.50 nm ofR _CoCo. This maximum is close to the overall observed ET rate value. For this mono-hydrated transition metal ionic system, the ET rate generally is about 10⁶ L·mol^?1·s^?1 in gaseous process. Further, since it is impossible to experimentally determine the structures and their PESs of these hydrated systems, especially for the unstable intermediate species,ab initio calculations can play an effective auxiliary role in discussing the ET reactivities of these kinds of reacting systems.     

Production of <Emphasis Type="Italic">R</Emphasis>-Mandelic Acid Using Nitrilase from Recombinant <Emphasis Type="Italic">E. coli</Emphasis> Cells Immobilized with Tris(Hydroxymethyl)Phosphine

Recombinant Escherichia coli cells harboring nitrilase from Alcaligenes faecalis were immobilized using tris(hydroxymethyl)phosphine (THP) as the coupling agent. The optimal pH and temperature of the THP-immobilized cells were determined at pH 8.0 and 55 °C. The half-lives of THP-immobilized cells measured at 35, 40, and 50 °C were 1800, 965, and 163 h, respectively. The concentration of R-mandelic acid (R-MA) reached 358 mM after merely 1-h conversion by the immobilized cells with 500 mM R,S-mandelonitrile (R,S-MN), affording the highest productivity of 1307 g L^?1 day^?1 and the space-time productivity of 143.2 mmol L^?1 h^?1 g^?1. The immobilized cells with granular shape were successfully recycled for 60 batches using 100 mM R,S-MN as substrate at 40 °C with 64% of relative activity, suggesting that the immobilized E. coli cells obtained in this study are promising for the production of R-MA.     

Elementary derivation of long-range moments of two coupled centrosymmetric systems

The expression for the long-range dipole moment of a pair of non-identical centrosymmetric systems (varying as R^?7) in terms of frequency-dependent polarizabilities and hyperpolarizabilities is recovered more simply than hitherto. An expression in terms of frequency-dependent quantities for the quadrupole moment of an identical pair (∞ R^?6) is given for the first time.     

Selective transport of zinc and copper ions by synthetic ionophores using liquid membrane technology

This work highlights the role of synthetic carrier (ionophore) in the separation of heavy metal ions. A new series of ionophores; 4,4′-nitrophenyl-azo-O,O′-phenyl-3,6,9-trioxaundecane-1,10-dioate (R₁), bis[4,4′nitro-phenylazo-naphthyl-(2,2-dioxydiethylether)] (R₂) 1,8-bis-(2-naphthyloxy)-3,6-dioxaoctane (R₃), 1,11-bis-(2-naphthyloxy)-3,6,9-trioxaunde-cane (R₄), 1,5-bis-(2-naphthyloxy)-3-oxa-pentane (R₅) have been synthesized and used as extractant as well as carrier for the transport of various metal ions (Na⁺, K⁺, Mg²⁺, Ni²⁺, Cu²⁺ and Zn²⁺) through liquid membranes. Effect of various parameters such as metal ion concentration, ionophore concentration, liquid–liquid extraction, back extraction, comparison of transport efficiency of BLM and SLM and different membrane support (hen’s egg shell and PTFE) have been studied. In BLM ionophores (R₂–R₅) transport Zn⁺ at greater extent and the observed trend for the transport of Zn²⁺ is R₂?>?R₄?>?R₃?>?R₅ respectively. Further transport efficiency is increased in SLM. In egg shell membrane ionophores (R₂–R₅) transport Zn⁺ due to their non-cyclic structure and pseudo cavity formation while ionophore R₁ transports Cu²⁺ ions at greater extent due to its cyclic structure and cavity size. Among the membrane support used egg shell membrane is found best for the transport of zinc ions because of its hydrophobic nature and exhibits electrostatic interactions between positively charged zinc ions and –COOH group of egg shell membrane. Thus structure of ionophores, hydrophobicity and porosity of the membrane support plays important role in separation of metal ions.     

Determination of enthalpies of formation of organic free radicals from bond dissociation energies 1. Hydrocarbon radicals

The enthalpies of formation (ΔH _f ^o) for 24 hydrocarbon radicals (R^?), mainly polycyclic aromatic radicals with the complex structure, were determined from the published data on bond dissociation energies. The ΔH _f ^o values of the corresponding molecules were calculated, in the majority of cases, by the macroincrement method. Calculations by the group contribution method were performed. Some ΔH _f ^o(R^?) values were compared to those calculated by the additive-group method. Calculations were performed, and the conjugation energies of the radicals were discussed. The errors of determination of the ΔH _f ^o(R^?) values found were estimated. Due to this work, the database for ΔH _f ^o values of hydrocarbon radicals was increased more than by 25%.     

Enantiomeric Separation of Moxifloxacin and Its (R,R)-Isomer by Ligand-Exchange Chiral Chromatography

A new stereospecific LC method for the separation and quantification of moxifloxacin and its (R,R)-enantiomer in bulk drug was developed and validated by ligand-exchange liquid chromatography on a reversed phase column using aqueous mobile phase containing the chiral reagent l-isoleucine-Cu(II). The UV detector was operated at 293 nm. The flow rate of mobile phase was set at 0.9 mL min^?1. The achiral ODS column offers good separation of the two enantiomers in less than 20 min. The test concentration was 1,000 μg mL^?1 in the mobile phase. This method was capable of detecting the (R,R)-enantiomer of moxifloxacin up to 0.1 μg mL^?1 for a 20 μL injection volume. The drug was subjected to stress conditions of hydrolysis, oxidation, photolysis and thermal degradation. There was no interference of degradants with the (R,R)-enantiomer in the developed method. The developed chiral RP-LC method was validated with respect to linearity, accuracy, precision and robustness. The percentage recovery for the (R,R)-enantiomer in bulk drug samples ranged from 98.1 to 104.4%. The test solution was found to be stable in the mobile phase for 48 h after preparation.     

Electrochemical intercalation kinetics of lithium ions for spinel LiNi0.5Mn1.5O4 cathode material

The crystal structure and electrochemical intercalation kinetics of spinel LiNi_0.5Mn_1.5O₄ such as the resistance of a solid electrolyte interphase (SEI) film, charge transfer resistance (R _ct), surface layer capacitance, exchange current density (i ₀), and chemical diffusion coefficient are evaluated by Fourier transform infrared (FT-IR) and electrochemical impedance spectroscopy (EIS), respectively. FT-IR shows that LiNi_0.5Mn_1.5O₄ thus obtained has a cubic spinel structure, which can be indexed in a space group of Fd3m with a disordering distribution of Ni. EIS indicates that R _s is almost a constant at different states of charge. The thickness of SEI film increases with increasing of the cell voltage. R _ct values evidently decreases when lithium ions deintercalated from the cathode in the voltage range from OCV to 4.6 V, and R _ct value increases with increasing potential of deintercalation over 4.7 V. i ₀ varies between 0.2 and 1.6 mA cm^?2, and the solid phase diffusion coefficient of Li⁺ changed depending on the electrode potential in the range of 10^?11–10^?9 cm² s^?1.     

Lifetime and collisional depopulation of the metastable 5D 3/2-state of Yb+

The lifetime and collisional depopulation rates of the metastable 5D _3/2 state of Yb⁺ have been determined in a radiofrequency ion trap by observation of the fluorescence count rate after ion excitation by a short laser pulse. From measurements using He, N₂ and H₂ as buffer gases between 10^?8 and 10^?6 mbar pressure and linear extrapolation to zero pressure we obtain a lifetime of τ=52.15±1.00 ms and rate constants ofR(H₂)=(1.02±0.10)×10^?9 cm³/s andR(N₂)=(1.78±0.19)×10^?10 cm³/s. The lifetime is in fair agreement with a calculated value of 74 ms.     

Polymerization of methyl methacrylate by charge-transfer complex using n-butyl amine and carbon tetrachloride in dimethylsulphoxide

The charge-transfer complex formed by the interaction of an aliphatic amine, such as n-butylamine (nBA), and carbon tetrachloride (CCl₄) in dimethylsulphoxide (DMSO) initiates polymerization of methyl methacrylate (MMA) at 30°. The rate of polymerization is given by R_p = k[MMA]^0.83 [nBA]^0.5 [CCl₄]^0.5 when [CCl₄]/[nBA] is ? 1. When [CCl₄]/[nBA] > 1, R_p is independent of [CCl₄] and R_p = k[MMA]^1.46 [nBA]^0.5. The average rate constants are (1.42 ± 0.05) × 10^?6 1 mol^?1 sec^?1 in terms of MMA and (2.20 ± 0.06) × 10^?6 sec^?1 at 30° for higher and lower concentration of carbon tetrachloride respectively. A charge-transfer mechanism for polymerization is suggested.     

The first two excited 1Σg+ states of Cs2

Laser-induced fluorescence Of Cs₂ molecules in the infrared region (4000–9000 cm^?1) has been observed using several exciting wavelengths from an argon-ion laser and from a ring dye laser. Accurate molecular constants for the first two excited ¹Σ_g⁺ electronic states are derived from spectra recorded at high resolution by Fourier transform spectroscopy. Main molecular constants are: (2)¹Σ_g⁺: T_c = 12114.090 cm^?1, ω_e = 23.350 cm^?1, B_c = 7.4.5 × 10^?3 cm^?1, R_c = 5.8316 Å; (3)¹Σ_g⁺: T_e = 15975.450 cm^?1, ω_e = 22.423 cm^?1 , B_e = 8.23 × 10^?3 cm^?1, R_c = 5.5569 Å.     

Semiclassical variational study of size effects in neutral and charged jellium droplets

An analytic expression for the total energy of metallic clusters composed ofN identical atoms of valencev and with net chargeQ is obtained by means of a variational solution of the Thomas-Fermi-Weizsäcker energy density functional within the spherical jellium model. The minimum energy is given as an expansion in decreasing powers of the cluster radiusR=r _s Z ^1/3, withZ=vN andr _s the radius per electron of the bulk metal. The coefficients are obtained as functions ofr _s . Terms of volume (R ³), surface (R ²), curvature (R), constant (R ⁰), (1/R) and (1/R ²) are clearly separated in the formula, as well as the different contributions (kinetic, coulombic and exchange-correlation) to each of them. The asymptotic values (R→∞) for the work functions,W(r _s ), and surface energies σ(r _s ), are compared to analogous semiclassical and Kohn-Sham calculations of jellium-like surfaces and to the experimental values. The size dependent behaviour of chemical potentials, μ(R), electron affinities,AF(R), and ionization potentials,IP(R), are easily obtained for any kind of metallic clusters. In particular we discuss the Coulomb and quantum corrections to the coefficients β, δ in the asymptotic formulae:IP?W+β/R andAF?W+δ/R.     

Raman optical activity of tartaric acid and related molecules

The Raman optical activity spectra of (2R, 3R) (+)- and (2S,3S) (?)-tartaric acid, (2R, 3R) (+)-dimethyl tartrate, (2R,3R) (?)-2,3-butanediol and (2S, 3S) (+)-dibenzoyl tartaric acid are presented. A large couplet at about 500cm^?1 in the first three molecules, which probably originates in deformations of a chiral structural unit, might serve as an indicator of conformation and absolute configuration.     

An improved absorption correction based on a Gaussian ionization distribution model for electron probe microanalysis

The electron range equation R, employed in a Gaussian absorption correction, is optimized making use of f(χ) values which were calculated from ionization distributions determined experimentally by Brown and Parobek. A new expression of R[R = $\text{(1 + 2}\text{h}\text{)}\text{(1 +}\text{h}$)2.59 × 10^?5(E^1.3₀ ?E^1.3_c)] g cm^?2 is proposed in this paper.The absorption correction using the new electron range equation R is applied to oxygen determination in several silicates and sulfates with greater accuracy than other methods. This equation also predicts one of the most accurate mean depths of ionization at an accelerating voltage of 25 kV for Zn and Cd tracers in Al, Cu, Ag and Au matrices.