First-principles calculation of pKa for cocaine, nicotine, neurotransmitters, and anilines in aqueous solution

The absolute pKa values of 24 representative amine compounds, including cocaine, nicotine, 10 neurotransmitters, and 12 anilines, in aqueous solution were calculated by performing first-principles electronic structure calculations that account for the solvent effects using four different solvation models, i.e., the surface and volume polarization for electrostatic interaction (SVPE) model, the standard polarizable continuum model (PCM), the integral equation formalism for the polarizable continuum model (IEFPCM), and the conductor-like screening solvation model (COSMO). Within the examined computational methods, the calculations using the SVPE model lead to the absolute pKa values with the smallest root-mean-square-deviation (rmsd) value (1.18). When the SVPE model was replaced by the PCM, IEFPCM, and COSMO, the rmsd value of the calculated absolute pKa values became 3.21, 2.72, and 3.08, respectively. All types of calculated pKa values linearly correlate with the experimental pKa values very well. With the empirical corrections using the linear correlation relationships, the theoretical pKa values are much closer to the corresponding experimental data and the rmsd values become 0.51-0.83. The smallest rmsd value (0.51) is also associated with the SVPE model. All of the results suggest that the first-principles electronic structure calculations using the SVPE model are a reliable approach to the pKa prediction for the amine compounds.     

Constructions of stable equivalences of Morita type for finite-dimensional algebras III

In this paper, we provide a new method to produce stable equivalencesof Morita type. Our main results can be stated as follows. LetA and B be two finite-dimensional k-algebras over a field k.Suppose that two bimodules _AM_B and _BN_A define a stable equivalenceof Morita type between A and B and that R is a generator forA-modules. Then there is a stable equivalence of Morita typedefined by X and Y between the endomorphism algebra End_A(R)of the module R and the endomorphism algebra End_B(N_AR) of themodule N_AR. If M and N satisfy the property that both (N_A–,M_B–) and (M_B–, N_A–) are adjoint pairs of functors,then so do the modules X and Y. Moreover, we show that the self-injectivedimension and the Gorenstein property are invariant under stableequivalences of Morita type with the above-mentioned adjointproperty.     

A theoretical study of the photodetachment and intramolecular hydrogen-bonding energies of hydrogen maleate anions

Three low-lying conformers of the hydrogen maleate anions (HMAs) regarding cis-HMA(HB) having the O-...HO intramolecular hydrogen bond (HB), cis-HMA(nHB) without the HB, and trans-HMA are studied by density functional theory (B3LYP) combined with natural bond orbital (NBO) and atoms-in-molecules (AIM) analyses. The photoelectron spectra of cis- and trans-HMA conformers recorded by Woo et al. (J. Phys. Chem. A 2005, 109, 10633) are reassigned on the basis of the present electron propagator theory calculations, indicating the significant energy differences between the Dyson orbitals and canonical molecular orbitals due to the electron-correlation and orbital relaxation effects considered in the electron propagator theory. The NBO associated with the natural resonance theory analyses and AIM electron topological study show that the strong O-...HO in cis-HMA(HB) has the remarkable characteristics of three-center four-electron hyperbond, and the bonding strength of ca. 30 kcal/mol is recommended with the reference calculations of the HO-...HOH complex. The further calculations for the microhydrated cis-HMA(HB) clusters indicate that the O-...HO bonding strength decreases in water solution.     

Probing the structure and bonding in Al6N- and Al6N by photoelectron spectroscopy and ab initio calculations

The electronic and geometrical structure of a nitrogen-doped Al6- cluster (Al6N-) is investigated using photoelectron spectroscopy and ab initio calculations. Photoelectron spectra of Al6N- have been obtained at three photon energies with seven resolved spectral features. The electron affinity of Al6N has been determined to be 2.58 +/- 0.04 eV. Global minimum structure searches for A6N- and its corresponding neutral form are performed using several theoretical methods. Vertical electron detachment energies, calculated using three different methods for the lowest energy structure and a low-lying isomer, are compared with the experimental data. The ground-state structure of Al6N- is established from the joint experimental and theoretical study to consist of an Al2 dimer bonded to the top of a quasi-planar tetracoordinated N unit, Al4N-, or it can be viewed as a distorted trigonal prism structure with the N atom bonded in one of the prism faces. For neutral Al6N, three low-lying isomers are found to compete for the global minimum, two of which are built from the tetracoordinated Al4N unit. The chemical bonding in Al6N- is discussed on the basis of molecular orbital and natural bond analyses.     

Reactions of late lanthanide metal atoms with water molecules: a matrix isolation infrared spectroscopic and theoretical study

The reactions of late lanthanide metal atoms (Gd-Lu) with water molecules have been investigated using matrix isolation infrared spectroscopy. The reaction intermediates and products were identified on the basis of isotopic substitution experiments and density functional theory calculations. All of the metal atoms except Lu react with water to form the M(H2O) complexes spontaneously upon annealing (M = Gd, Tb, Dy, Ho, Er, Tm, and Yb). The Dy(H2O) and Ho(H2O) complexes are able to coordinate a second water molecule to form the Dy(H2O)2 and Ho(H2O)2 complexes. The M(H2O) complexes isomerize to the inserted HMOH isomers under visible light irradiation, which further decompose to give the MO and/or HMO molecules upon UV light irradiation. The M(OH)2 molecules (M = Gd-Lu) were also produced. The results have been compared with our earlier work covering the early lanthanide metal atoms (Nd, Sm, Eu) to observe the existent trends for the lanthanide metal atom reactions.     

Preparation of highly (111)-oriented (Pb,La)(Zr,Sn,Ti)O<Subscript>3</Subscript> (PLZST) antiferroelectric thin films by modified sol-gel process using a novel tin source,dibutyloxide of tin

Highly (111)-oriented Pb_0.97La_0.02Zr_0.85Sn_0.13 Ti_0.02O₃(PLZST) antiferroelectric thin films were deposited on Pt(111)/Ti/SiO₂/Si(100) substrates through a modified sol-gel process technique. The electric field-induced antiferroelectric-to-ferroelectric (AFE‐FE) phase transformation behaviour was examined by C-V measurement. The results indicated that antiferroelectric (AFE) to ferrroelectric (FE) switching field , FE to AFE switching field were 315 kV/cm and 240 kV/cm respectively. The temperature dependence of the dielectric constant showed that the Curie temperature (T _c) of the PLZST antiferroelectric thin films was 171°C. The voltage dependent current density of the highly (111)-oriented PLZST film was less than 1.3 × 10⁻⁶ A/cm² over electric field range from 0 to ± 427 kV/cm.     

Adsorbed para-nitrophenol on HDTMAB organoclay--a TEM and infrared spectroscopic study

para-Nitrophenol adsorbed on hexadecyltrimethylammonium bromide modified montmorillonite has been studied using a combination of X-ray diffraction TEM and infrared spectroscopy. Upon formation of the organoclay, the properties change from hydrophilic to hydrophobic. It is proposed that para-nitrophenol is adsorbed onto the water in the cation hydration sphere of the organoclay. As the cation is replaced by the surfactant molecules the para-nitrophenol replaces the surfactant molecules in the clay interlayer. Significant changes in the water vibrations occur in this process. Bands attributed to CH stretching and bending vibrations in general decrease as the concentration of the surfactant (CEC) increases up to 1.0 CEC. After this concentration the bands increase approaching a value the same as that of the surfactant. Strong changes occur in the HCH deformation modes of the methyl groups of the surfactant. These changes are attributed to the methyl groups locking into the siloxane surface of the montmorillonite. Such a concept is supported by changes in the SiO stretching bands of the montmorillonite siloxane surface. This study demonstrates that para-nitrophenol will penetrate into the untreated clay interlayer and replace the intercalated surfactant in surfactant modified clay, resulting in the change of the arrangement of the intercalated surfactant.     

Changes in the surfaces of adsorbed p-nitrophenol on methyltrioctadecylammonium bromide organoclay--an XRD, TG, and infrared spectroscopic study

Water purification is of extreme importance worldwide. p-Nitrophenol was used as a test chemical to design and test an organoclay for the removal of p-nitrophenol from an aqueous solution. Synthesis of the organoclay with methyltrioctadecylammonium bromide [CH(3)(CH(2))(17)](3)NBr(CH(3)) labeled as MTOAB results in multiple expansions of the montmorillonite clay from 1.24 nm to a maximum of 5.20 nm as is evidenced by the XRD patterns. Thermal analysis shows strong bonding of the surfactant to the clay siloxane layers and the interaction of the p-nitrophenol with the clay surfaces. It is proposed that the p-nitrophenol penetrates the siloxane layer of the clay and bonds through the ditrigonal space of the siloxane hexagonal units to the inner OH units. Such a concept is supported by the observation of an additional infrared band at 3652 cm(-1) for the organoclay. Shifts in the p-nitrophenol OH stretching vibrations mean a strong interaction of the p-nitrophenol molecule. Significant changes in the siloxane stretching bands are also observed.     

Modification of the surfaces of Wyoming montmorillonite by the cationic surfactants alkyl trimethyl, dialkyl dimethyl, and trialkyl methyl ammonium bromides

Surfaces of a Wyoming SWy-2 sodium montmorillonite were modified using microwave radiation through intercalation with the cationic surfactants octadecyl-trimethyl ammonium bromide, dimethyldioctadecylammonium bromide, and methyl-tri-octadecyl ammonium bromide by an ion exchange mechanism. Changes in the surfaces and structure were characterized using X-ray diffraction (XRD), thermal analysis (TG) and infrared (IR) spectroscopy. Different configurations of surfactants within montmorillonite interlayer are proposed based on d(001) basal spacings. A range of surfactant molecular environments within the surface-modified montmorillonite are proposed based upon their thermal decomposition. IR spectroscopy using a smart endurance single bounce diamond attenuated total reflection (ATR) cell has been used to study the changes in the spectra of CH asymmetric and symmetric stretching modes of the surfactants to provide more information of the surfactant molecular configurations.