Intramolecular H-transfer in CH2OO and cis-HO3

Intramolecular H-transfer reactions in cis-HO₃ and CH₂OO were studied at the MP2 and B3LYP levels of theory. Activation energies (E _a) and Gibbs free energies of activation (?G ^#) of the H-transfer reactions were calculated. The activation energies of the H-transfer in cis-HO₃ and CH₂OO were about 110 and 130 kJ/mol, respectively. Catalytic effects of some protic molecules including HCOOH, CH₃OH, NH₃, CH₃NH₂, HOCl, H₂O₂, and H₂O, on the activation energies and transition state structures were studied. The more stable transition state structures were obtained in the presence of the protic molecules. Our calculations showed that the protic molecules decrease the activation energies of the H-transfer reactions about 50 kJ/mol.     

Hydrophobic interaction chromatography of proteins: Thermodynamic analysis of conformational changes

For BSA and β-lactoglobulin adsorption to hydrophobic interaction chromatography (HIC) stationary phases leads to conformational changes. In order to study the enthalpy (ΔH_ads), entropy (ΔS_ads), free energy (ΔG_ads) and heat capacity (Δc_p,ads) changes associated with adsorption we evaluated chromatographic data by the non-linear van’t Hoff model. Additionally, we performed isothermal titration calorimetry (ITC) experiments. van’t Hoff analysis revealed that a temperature raise from 278 to 308 K increasingly favoured adsorption seen by a decrease of ΔG_ads from −12.9 to −20.5 kJ/mol for BSA and from −6.6 to −13.2 kJ/mol for β-lactoglobulin. Δc_p,ads values were positive at 1.2 m (NH₄)₂SO₄ and negative at 0.7 m (NH₄)₂SO₄. Positive Δc_p,ads values imply hydration of apolar groups and protein unfolding. These results further corroborate conformational changes upon adsorption and their dependence on mobile phase (NH₄)₂SO₄ concentration. ITC measurements showed that ΔH_ads is dependent on surface coverage already at very low loadings. Discrepancies between ΔH_ads determined by van’t Hoff analysis and ITC were observed. We explain this with protein conformational changes upon adsorption which are not accounted for by van’t Hoff analysis.     

Bond dissociation energies and radical heats of formation in CH3Cl,CH2Cl2, CH3Br,CH2Br2, CH2FCl,and CHFCl2

An analysis of thermochemical and kinetic data on the bromination of the halomethanes CH_4–nX_n (X = F, Cl, Br; n = 1–3), the two chlorofluoromethanes, CH₂FCl and CHFCl₂, and CH₄, shows that the recently reported heats of formation of the radicals CH₂Cl, CHCl₂, CHBr₂, and CFCl₂, and the C? H bond dissociation energies in the matching halomethanes are not compatible with the activation energies for the corresponding reverse reactions. From the observed trends in CH₄ and the other halomethanes, the following revised ΔH°_f,298 (R) values have been derived: ΔH°_f(CH₂Cl) = 29.1 ± 1.0, ΔH°_f(CHCl₂) = 23.5 ± 1.2, ΔH_f(CH₂Br) = 40.4 ± 1.0, ΔH°_f(CHBr₂) = 45.0 ± 2.2, and ΔH°_f(CFCl₂) = ?21.3 ± 2.4 kcal mol^?1. The previously unavailable radical heat of formation, ΔH°_f(CHFCl) = ?14.5 ± 2.4 kcal mol^?1 has also been deduced. These values are used with the heats of formation of the parent compounds from the literature to evaluate C? H and C? X bond dissociation energies in CH₃Cl, CH₂Cl₂, CH₃Br, CH₂Br₂, CH₂FCl, and CHFCl₂.     

Effects of heteroatoms on the electronic,sensor, and adsorption properties of graphene

The effects of doping heteroatoms on the structure, electronic and adsorption properties of graphene are investigated using density functional theory calculations. Six different doped graphenes (with Al, B, Si, N, P, and S) are considered, and to obtain the interaction and adsorption properties, three sulfur-containing molecules (H₂S, SO₂, and thiophene) were interacted with selected graphenes. The adsorption energies (E _ad) in the gas phase and solvents show the exothermic interaction for all complexes. The maximum E _ad values are observed for aluminum doped graphene (AG) and silicon doped graphene (SiG), and adsorption energies in the solvent are not so different from those in the gas phase. NBO calculations show that the AG and SiG complexes have the highest E ⁽²⁾ interaction energies and simple graphene (G) and nitrogen doped graphene (NG) have the least E ⁽²⁾ energies. Population analyses show that doping heteroatoms change the energy gap. This gap changes more during the interaction and these changes make these structures useful in sensor devices. All calculated data confirm better adsorption of SO₂ by graphenes versus H₂S and thiophene. Among all graphenes, AG and then SiG are the best adsorbents for these structures.     

The distonic ion ˙CH2CH2CO+ and its formation from ionized cyclopentanone

Collisional activation decomposition (CAD) spectra are interpreted as indicating that formation of ˙CH₂CH₂CO⁺ (1) from ionized cyclopentanone, succinic anhydride arid butyrolactone is important at 70 eV electron energy. However, photoionization appearance energy measurements and CAD spectra demonstrate that CH₃CH?C?O^+· (3) is formed from ionized cyclopentanone near threshold. Ab initio molecular orbital calculations place ΔH _f (1) about 36 kJ mol^?1 above ΔH _f (3).     

Experimental and theoretical studies of media effects on copper corrosion in acidic environments containing 2-amino-5-mercapto-1,3,4-thiadiazole

Corrosion behaviour of copper metal in acid solutions (HCl, H₂SO₄ and H₃PO₄) containing 2-amino-5-mercapto-1,3,4- thiadiazole (AMT) was investigated experimentally and theoretically via gravimetric, potentio-dynamic and quantum electrochemical approaches. Similar behavior was observed for H₂SO₄ and H₃PO₄ media, and related to the nature of anions at metal/solution interface. With regard to HCl, however, the rate of corrosion was determined to be low at initial stages, but high later on using an auto-catalyzing mechanism. In the presence of AMT, the experimental studies revealed that this molecule was a good anodic-type inhibitor causing substantial changes in corrosion potential. Moreover, its adsorption obeys the Langmuir isotherm. The values of ΔG _ads were determined and correlated to the inhibitor powers. Finally, the influence of media (anions) on metal corrosion was also investigated from molecular point of view by calculations of the copper-anions interaction using density functional theory.     

Cooperative atomic migrations in the associates of formic acid molecule with H2O...X systems (X=CH3OH,NH2OH,H2O2, HOF,and H2O)

The pathways and activation barriers of cooperative biproton migrations in the associates of the formic acid molecule with H₂O and X molecules (X=CH₃OH, NH₂OH, H₂O₂, FOH, and H₂O) are calculated by an ab initio method (3-21G and 6-31G^** basis sets). A cooperative triproton transfer occurs in the system with X=H₂O. The activation barriers of this transfer calculated in the 3-21G and 6-31G^** basis sets are 6.94 and 27.29 (through the structure of C₂ symmetry) or 7.99 and 26.08 kcal/mole (through the structure of C_s symmetry), respectively. In the systems with X=H₃COH, HOOH, and FOH, the biproton transfer is accompanied by synchronous shifts of two hydroxyl groups and overcomes high activation barriers (>40 kcal/mole), which is accounted for by poor stereochemical similarity for the low-barrier cooperative processes in the given molecular associates. Scientific Research Institute of Physical and Organic Chemistry, Rostov State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 5, pp. 845–858, September–October, 1996. Translated by I. Izvekova     

Spectroscopic Properties of Morin in Various CH3OH–H2O and CH3CN–H2O Mixed Solvents

The specific fluorescence properties of morin (3,2′,4′,5,7‐pentahydroxyflavone) were studied in various CH₃OH–H₂O and CH₃CN–H₂O mixed solvents. Although the dihedral angle is large in the S₀ state, morin has an almost planar molecular structure in the S₁ state owing to the very low rotational energy barrier around the interring bond between B and the A, C ring. The excited state intramolecular proton transfer (ESIPT) at the S₁ state cannot occur immediately after excitation, S₁ → S₀ fluorescence can be observed. Two conformers, Morin A and B have been known. At the CH₃OH–H₂O, Morin B will be the principal species but at the CH₃CN–H₂O, Morin A is the principal species. At the CH₃OH–H₂O, owing to the large Franck–Condon (FC) factor for S₂ → S₁ internal convernal (IC) and flexible molecular structure, only S₁ → S₀ fluorescence was exhibited. At the CH₃CN–H₂O, as the FC factor for S₂ → S₁ IC is small and molecular structure is rigid, S₂ → S₀ and S₁ → S₀ dual fluorescence was observed. This abnormal fluorescence property was further supported by the small pK₁ value, effective delocalization of the lone pair electrons of C(2′)–OH to the A, C ring, and a theoretical calculation.     

Optically active organoaluminum based inclusion compounds. Synthesis and characterization of (S)-(−)-α-[(C6H5)CH(CH3)N(CH3)3][Al2R6I] (R=CH3, C2H5)

The optically active quaternary ammonium salt (S)-(?)-α-[(C₆H₅)CH(CH₃)N(CH₃)₃I] reacts with AlR₃ to afford optically active organoaluminum based inclusion compounds, liquid clathrates, of the formula (S)-(?)-α-[(C₆H₅)CH(CH₃)N(CH₃)₃][Al₂R₆I] (R=CH₃, C₂H₅). Specific rotation ([α] ₂₅ ^D ) for the Al(CH₃)₃ compound was determined to be ?13.19° while that for the Al(C₂H₅)₃ analog was determined to be ?14.30°. There are 13.8 toluene molecules per anionic moiety for the trimethylaluminum based liquid clathrate while there are 15.0 toluene molecules per anion for the corresponding triethylaluminum inclusion compound.     

Inhibition Effect of N-(Pyridin-2-yl-Carbamothioyl) Benzamide on the Corrosion of C-Steel in Sulfuric Acid Solutions

N-(Pyridin-2-yl-carbamothioyl)benzamide (PCMB) was newly synthesized and tested as a corrosion inhibitor for C-steel in 0.5 M H₂SO₄ using chemical and electrochemical techniques. Polarization measurements showed that the synthesized compound acted as a mixed inhibitor. The inhibition efficiencies obtained from the different methods were in good agreement. The inhibitive action of this compound is discussed in terms of blocking the electrode surface by adsorption of the inhibitor according to the Langmuir isotherm. The effect of temperature on the corrosion behavior in the absence and presence of 2.5 × 10^?5 M of PCMB was studied (283–308 K). The associated activation energies (E _a) and the thermodynamic parameters (ΔH*, ΔS*, K _ads, ΔG°_ads) for the adsorption process were determined. The ΔG°_ads value is ?36.55 kJ/mol, which indicated that the adsorption mechanism of PCMB on C-steel in 0.5 M H₂SO₄ solution was combined between physisorption and chemisorption processes.     

Synthese und Kristallstruktur von Praseodympropionat-trihydrat,Pr(CH3CH2COO)3(H2O)3

Synthesis and Crystal Structure of Praseodymium Propionate Trihydrate, Pr(CH₃CH₂COO)₃(H₂O)₃ Single crystals of Pr(CH₃CH₂COO)₃(H₂O)₃ were obtained by dissolving freshly prepared praseodymium hydroxide in diluted propionic acid. The crystal structure (monoclinic, P2₁/c, Z = 4, a = 1034.2(2) pm, b = 1521.2(3) pm, c = 2086.3(7) pm, β = 102.87(2)°, R1 = 0.0864, wR2 = 0.1196) consists of one-dimensional infinite chains parallel [010]. Pr1 and Pr2 are coordinated by four tridentate-bridging propionate groups. Additionally, Pr1 is coordinated by three “coordination water” molecules, Pr2 by two bidentate propionate groups. There are, in addition, three “crystal water” molecules so that praseodymium propionate trihydrate should be formulated as [(H₂O)₃Pr1(CH₃CH₂COO)₄Pr2(CH₃CH₂COO)₂] (H₂O)₃.     

Alkyl- und aryl-komplexe des iridiums und rhodiums: X. Chelatphosphin-stabilisierte rhodiumorganyle Rh(R)[PhP(CH2CH2CH2PPh2)2]: synthese,NMR-spektroskopischer cis,trans-einfluss und molekülstruktur von Rh(2-MeC6H4)[PhP(CH2CH2CH2PPh2)2]

The organorhodium(I) complexes Rh(R)[PhP(CH₂CH₂CH₂PPh₂)₂] (R  CH₂CMe₃, CH₂SiMe₃; 2-MeC₆H₄, 4-MeC₆H₄, 2,4-Me₂C₆H₃, 2,4,6-Me₃C₆H₂; C₂Ph) have been prepared and characterized by ³¹P and ¹H NMR spectroscopy and an X-ray structure determination of the tolyl derivative Rh(2-MeC₆H₄)-[PhP(CH₂CH₂CH₂PPh₂)₂].For these compounds, the relative ³¹P coordination shifts Δ(PPh₂) > Δ(PPh) distinctly reflect the electron-releasing properties of the organoligands σ-bonded trans to PPh. As expected, coupling between the ¹⁰³Rh nucleus and phenylphosphino P atoms is weak and varies only little as the strong trans influence groups R are changed. In contrast to this insensitivity of ¹J(Rh-PPh) to R, Rh-P coupling within the Ph₂P-Rh-PPh₂ moieties shows considerable dependence upon the nature of the C-donor producing the cis influence series sp³-C <sp²-C < sp-C.The ortho-tolyl complex crystallizes from toluene as 1/1 solvate Rh(2-MeC₆H₄)[PhP(CH₂CH₂CH₂PPh₂)₂] · C₇H₈. Crystals are orthorhombic, space group Pbc2₁, with a 1017.9(7), b 1974.3(14), c 2177.6(11) pm, and Z = 4. The structure has been refined to R = 0.079 for 2249 unique data with F₀ > 3σ(F₀). Metal-phosphorus distances are 225.7(5) and 229.6(6) pm for Rh-PPh₂ and 227.3(6) pm for Rh-PPh.     

Absolute and relative emission cross sections for electron impact on CH3F,CH2F2 and CHF3

Emission spectra following electron impact on CH₃F, CH₂F₂ and CHF₃ at various energies have been investigated in the spectral region from 200 nm to 700 nm. Emission thresholds and excitation functions for atomic and molecular fragments have been determined. Absolute emission cross sections were obtained for two band systems, ^{A 2} Δ → X ² Π, C ² Σ⁺ → X ² Π, observed in the emission spectrum of CH₃F and for the H-Balmer radiation, H _α ? H _γ, in the spectra of all compounds. The continuous emission between 200 nm and 400 nm in the spectra of CH₂F₂ and CHF₃ has been examined systematically. It was found that CF₂(Ã) is the main precursor in both spectra.     

Multiply charged carbon ions produced from C2H2 and CH4 molecules in energetic,heavy ion impact

Multiply charged carbon ions up to C⁵⁺ ions have been observed from C₂H₂ and CH₄ molecules in 1.05 MeV/amu Ar¹²⁺ ion impact. These ions are believed to be produced through processes where multiply charged molecular ions are produced first by direct ionization and, then, dissociate via Coulomb explosion into atomic ions. The peak positions of ions from C₂H₂ molecules are found to be shifted with respect to those of ions from CH₄ molecules and this shift is understood to be due to the initial kinetic energy provided through the Coulomb potential between the dissociating ions.     

A Computational Understanding of Solvent Effect on the Structure,Electronic, Thermochemical,and Spectroscopic Properties of Ni(η2‐C6H4)(H2PCH2CH2PH2) Complex

Here we report the density functional calculations of the molecular parameters including the energy, geometries, electric dipole moments, vibrational IR frequencies, and ¹H and ¹³C NMR chemical shifts of Ni(η²‐C₆H₄ )(H₂PCH₂CH₂PH₂ ) (a benzyne complex). Based on the polarizable continuum model (PCM ), the effect of polarity of the solvent on these parameters was explored. The wavenumbers of υ(C1–C2 ) as well as the ¹H and ¹³C NMR chemical shift values of complex in various solvents were calculated and correlated with the Kirkwood–Bauer–Magat equation (KBM ), the solvent acceptor numbers (ANs ), and the linear solvation energy relationship (LSER ). The bonding interaction between the benzyne and Ni(H₂PCH₂CH₂PH₂ ) fragment was analyzed by means of the energy decomposition analysis (EDA ). The character of the Ni–C bonds of the molecules was analyzed by natural bond orbital (NBO ) analysis. Also, Monte Carlo simulations were used for the calculation of the total energy and solvation free energy of the complex in water.     

Assembly of succinic acid and isoxazolidine motifs in a single entity to mitigate CO2 corrosion of mild steel in saline media

Inhibition of CO₂ corrosion of mild steel in 0.5 M NaCl under atmospheric pressure at 40 °C as well as high pressure (10 bar) at 120 °C by 2-[2-methyl-4(or 5)-alkylisoxazolidin-5(or 4)-yl)methyl]succinic acids, a new class of molecules having inhibitive motifs of succinic acid, isoxazolidine and hydrophobic alkyl chain assembled in a single entity, has been examined by gravimetric and electrochemical methods. Inhibitor molecule containing CH₃(CH₂)₈ outperformed its counterpart with a shorter hydrophobe CH₃(CH₂)₄ and two other commercial imidazoline-based inhibitors. The effectiveness of these new inhibitors was also evaluated by electrochemical impedance spectroscopy. The inhibition efficiency by EIS was found to be 75%, 91% and 98% in the presence of 1, 5 and 20 ppm, respectively, at 40 °C. The potentiodynamic polarization studies indicated that the new inhibitors act as anodic inhibitors. The adsorption of the synthesized inhibitors follows Temkin adsorption isotherm model with favorable high values of –ΔG°_ads and −ΔH°_ads pointing the inhibitors adsorbed on the metal surface by chemisorption process. The XPS study confirmed the adsorption of the inhibitors on the metal surface.     

Calculation of the isotropic nuclear spin spin coupling constants for H2O,NH3 and CH4

Isotropic nuclear spin spin coupling constants have been evaluated for all possible couplings in H₂O, NH₃ and CH₄ by two different double perturbation techniques. All calculations were performed employing bases of detors constructed with SCF canonical and, for H₂O, localized orbitals, produced by extended STO basis set calculations.     

Secondary isotope effects in the mass spectra of C2D5OC2H5 and CD3CH2OC2H5

Secondary isotope effects were examined in the loss of methyl from the molecular ions of C₂D₅OC₂H₅ and CD₃CH₂OC₂H₅ for ion source processes and collisional activation (CA) processes. In the ion source loss of CH₃ was slightly favored over loss of CD₃, but in CA the CH₃ loss was favored to a much larger extent than expected. A possible explanation is given which invokes an energy distribution function peaked near the appearance energy for the methyl loss process.     

Theoretical study on the mechanism for the thermal rearrangement reactions of 2‐silylethyl acetate H3SiCH2CH2OCOCH3

The thermal rearrangement mechanisms of 2‐silylethylacetate H₃SiCH₂CH₂OOCCH₃ were investigated by ab initio molecular orbital theory for the first time. All structures of reactant, transition states, and products were located and fully optimized at the B3LYP/6‐311+G(d, p) levels, and harmonic vibrational frequencies for the involved stationary points on the potential energy surface were obtained. The reaction pathways were analyzed and confirmed by intrinsic reaction coordinate (IRC) calculations. Furthermore, atomic charges were determined by using the natural bond orbital (NBO) analysis. The calculational results show that H₃SiCH₂CH₂OOCCH₃ can rearrange thermally in two ways. One is [1,3] rearrangement (Reaction A), in which silyl group transfers from carbon to oxygen(in C? O? C) via a four‐membered ring transition state, forming silyl acetate and ethylene, the other way, [1,5] rearrangement (Reaction B), happens with transferring of silyl group from carbon to oxygen (in C?O) via a six‐membered ring transition state, forming the same products as in Reaction A. The energy barriers of the Reactions A and B were calculated to be 188.9 and 191.6 kJ/mol at the B3LYP/6‐311+G(d,p) levels, respectively. Changes in thermodynamic functions (ΔS, ΔH, and ΔG), equilibrium constant K(T), as well as preexponential factor A(T), and reaction rate constant k(T) in Eyring transition state theory were calculated over a temperature range of 200–1600 K, and then thermodynamic and kinetic properties of the reactions were analyzed. It can be suggested that Reactions A and B are noncompetitive, and both happen only at elevated temperature. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Ab initio molecular orbital study on structures and energetics of CH3O−(H2O)n and CH3S−(H2O)n in gas phase

The purpose of this article was to calculate the structures and energetics of CH₃O⁻(H₂O)_n and CH₃S⁻(H₂O)_n in the gas phase; the maximum number of water molecules that can directly interact with the O of CH₃O⁻; and when n is larger, we asked how the CH₃O⁻ and CH₃S⁻ moiety of CH₃O⁻(H₂O)_n and CH₃S⁻(H₂O)_n changes and how we can reproduce experimental ΔH ⁰_{n−1, n}. Using the ab initio closed-shell self-consistent field method with the energy gradient technique, we carried out full geometry optimizations with the MP2/aug-cc-pVDZ for CH₃O⁻(H₂O)_n (n=0, 1, 2, 3) and the MP2/6–31+G(d,p) (for n=5, 6). The structures of CH₃S⁻(H₂O)_n (n=0, 1, 2, 3) were fully optimized using MP2/6–31++G(2d,2p). It is predicted that the CH₃O⁻(H₂O)₆ does not exist. We also performed vibrational analysis for all clusters [except CH₃O⁻(H₂O)₆] at the optimized structures to confirm that all vibrational frequencies are real. Those clusters have all real vibrational frequencies and correspond to equilibrium structures. The results show that the above maximum number of water molecules for CH₃O⁻ is five in the gas phase. For CH₃O⁻(H₂O)_n, when n becomes larger, the C—O bond length becomes longer, the C—H bond lengths become smaller, the HCO bond angles become smaller, the charge on the hydrogen of CH₃ becomes more positive, and these values of CH₃O⁻(H₂O)_n approach the corresponding values of CH₃OH with the n increment. The C—O bond length of CH₃O⁻(H₂O)₃ is longer than the C—O bond length of CH₃O⁻ in the gas phase by 0.044 Å at the MP2/aug-cc-pVDZ level of theory. The structure of the CH₃S⁻ moiety in CH₃S⁻(H₂O)_n does not change with the n increment. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 1138–1144, 1999