Electronic structure of Ti<Subscript>4</Subscript>Fe<Subscript>2</Subscript>O as determined from <Emphasis Type="Italic">ab initio</Emphasis> calculations and X-ray spectroscopy studies

The TiL _α, FeL _α and OK _α ultrasoft X-ray emission bands obtained in experiment reflect, respectively, the energy distribution of mainly the Ti3d, Fe3d and O2p electronic states in Ti₄Fe₂O compound, which is an efficient hydrogen absorber for energy cells. Full and partial densities of electronic states for all atoms constituting the indicated oxide were calculated by a modified method of associated plane waves (APW) using the WIEN2k software package. The APW calculation data for Ti₄Fe₂O compound as well as superposition of TiL _α, FeL _α and OK _α ultrasoft X-ray emission bands on a single energy scale indicate that O2p states in the oxide are localized mainly near the bottom of the valence band, the major contribution near the ceiling of the valence band belonging to Fe3d and Ti3d states. According to the APW calculation, the major contribution to the bottom of Ti₄Fe₂O conduction band is made by Fe3d* and Ti3d* states. The APW data for Ti₄Fe₂O are supported by the cluster calculation performed for this compound using a FEFF82 software package.     

Constants of acid‒base equilibria in an aqueous amikacin aminoglycoside solution at 298 K

The acid dissociation constants of form pK₁ = 7.34 ± 0.01, pK₂ = 7.84 ± 0.01, pK₃ = 8.77 ± 0.01, pK₄ = 9.49 ± 0.01, and pK₅ = 10.70 ± 0.02 of cationic amikacin are determined by pH-metric titration at 25°C against the background of 0.1 mol/L KNO₃. K₁, K₂, K₃, and K₄ correspond to the dissociation of protons coordinated to amino groups, while K₅ characterizes the dissociation of the hydroxyl hydrogen atom, testifying to the amphoteric character of amikacin molecules. Applying density functional theory (DFT) with the B3LYP hybrid functional and the 6-311G**++ basis set, the partial charges on the atoms of an amikacin molecule are calculated. It is concluded that the dissociation of H(55)hydrogen atom occurs with a greatest partial charge of +0.53631.     

Electrical conductivity and ionic association of lithium and sodium perchlorates in tetrahydrofuran

The total limiting molar electrical conductivities of ions and triads of ions and the association constants of ions with the formation of ion pairs and triads of ions were calculated from the concentration dependences of the electrical conductivity of solutions of lithium and sodium perchlorates in tetrahydrofuran at 278.15–318.15 K with the use of the method specially developed earlier. The experimental total limiting electrical conductivities were used to calculate the limiting molar electrical conductivities and attraction friction factors of separate ions (Li⁺, Na⁺, ClO ₄ ^? , Li₂ClO ₄ ⁺ , Na₂ClO ₄ ⁺ , Li(ClO₄) ₂ ^? , and Na(ClO₄) ₂ ^? ). The constants of ion association into ion pairs were used to calculate the Gibbs energy of non-Coulomb interionic interaction (ΔG*_+?), and the constants of association into triads of ions, to determine the a ₃ distance parameter between the centers of the ion and the dipole of the ion pair. Positive ΔG*_+?), values and deviations of the experimental a ₃ value from the distance parameter calculated theoretically (a ₃ ⁰ ) for the triad of ions (Δa ₃ = a ₃ ? a ₃ ⁰ ) were related to non-Coulomb repulsion in the region of overlap of the solvation shells of ions and the influence of temperature and ion charge density on this repulsion.     

Resonant photoemission and absorption spectroscopy study of the Cu<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>TiSe<Subscript>2</Subscript> electronic structure

The Cu3p and Cu2p resonance photoelectron spectra of the valence bands and core levels as well as Ti and CuL _2,3 absorption spectra for monocrystals 1T-Cu _x TiSe₂ were studied. The valence spectra obtained at Cu3p and Cu2p resonance drastically differ from each other. For Cu 3p-3d resonance, there are several bands corresponding to different channels of excited state decay. Spectra of the valence bands at Cu 2p-3d resonance are virtually identical to the spectra of pure TiSe₂. As follows from the absorption spectra, titanium atoms have the oxidation state 4+, whereas copper atoms are close to the free ion state.     

A Search for a Direct Relationship Between Chromatographic and Adsorption Data

Shifts of chromatographic peak maxima and centres of gravity have been investigated for different amounts of propane injected on to a chromatographic column in ideal, non-linear chromatography. Specific retention volumes (V _{g (273)}, corrected to the standard temperature, 273.15 K), propane adsorption isotherms, and the first and second derivatives of the isotherms, (da/dp) _T and (d²a/dp²) _T , were determined for samples of active carbon and for different amounts of propane injected on column. Relationships between specific retention volume and the molar differential work of adsorption, A, were calculated on the basis of the propane isotherms and using the retention times of the peak maxima and the centres of gravity of the peaks. The equations obtained, ln V _{g (273)}=f₁(A) and(dW/dA) _{T, F c} = f₂(ln V _{g (273)}), have been used to explain the relationships between (i) chromatographic peak profiles and (ii) the distribution function of pore volumes filled with propane and the molar differential work of adsorption at different column temperatures (303–318 K).     

Compositions and structures of nanoparticles of trigonal symmetry <Emphasis Type="Italic">D</Emphasis><Subscript>3<Emphasis Type="Italic">d</Emphasis></Subscript>: Nanotubes

A method has been developed for the determination of the structure and number of atoms in the shells of nanoparticles as a function of the arrangement of atoms at the symmetry elements of a symmetry group. The formulas for calculation of the number of particles of symmetry D _3d have been reported. It has been shown that the number of atoms in trigonal shells is determined by three structurally invariant numbers and the quantum number of the group order n. All possible nanostructures of symmetry D _3d have been classified: C_{θ + 6z} , z = 0, 1, 2, ..., where the basic shells are C_θ = C₆, C₈, and C₁₄. A sum rule has been obtained for the coordination numbers of the shell sites located on symmetry axes. Trigonal nanoparticles are parent ones for obtaining (3,0), (6,0), and (9,0) nanotubes of trigonal type. The general formulas of these nanotubes with icosahedral, dodecahedral, and cubic caps are N_{8 + 12p} , N_{20 + 24p} , and N_{60 + 36p} (p = 1, 2, ...), respectively. The graphical constructions of all classes of trigonal nanoparticles and nanotubes are reported.     

SAMPL6: calculation of macroscopic p<Emphasis Type="Italic">K</Emphasis><Subscript>a</Subscript> values from ab initio quantum mechanical free energies

Macroscopic pK_a values were calculated for all compounds in the SAMPL6 blind prediction challenge, based on quantum chemical calculations with a continuum solvation model and a linear correction derived from a small training set. Microscopic pK_a values were derived from the gas-phase free energy difference between protonated and deprotonated forms together with the Conductor-like Polarizable Continuum Solvation Model and the experimental solvation free energy of the proton. pH-dependent microstate free energies were obtained from the microscopic pK_as with a maximum likelihood estimator and appropriately summed to yield macroscopic pK_a values or microstate populations as function of pH. We assessed the accuracy of three approaches to calculate the microscopic pK_as: direct use of the quantum mechanical free energy differences and correction of the direct values for short-comings in the QM solvation model with two different linear models that we independently derived from a small training set of 38 compounds with known pK_a. The predictions that were corrected with the linear models had much better accuracy [root-mean-square error (RMSE) 2.04 and 1.95 pK_a units] than the direct calculation (RMSE 3.74). Statistical measures indicate that some systematic errors remain, likely due to differences in the SAMPL6 data set and the small training set with respect to their interactions with water. Overall, the current approach provides a viable physics-based route to estimate macroscopic pK_a values for novel compounds with reasonable accuracy.     

Physicochemical Properties of Mesoporous Silicas Modified with Hydrazide and Amide Functional Groups

Physicochemical properties of mesoporous silicas modified with hydrazide and amide functional groups were studied. It was found that the main properties of the sorbents under study, characterized by pK_a1, are weakly pronounced. The replacement of the counter ion with a hydroxide occurs in a less alkaline medium, compared with monomer analogs. The sorbent modified with N', N'-dimethylhydrazide groups by the impregnation method has pK_a2 = 11.78, which is indicative of a sufficient strength of bonding between the counter ion and the silica matrix. The temperature limits, heat effects, and decomposition stages of the sorbents were determined.     

Compositions and structures of nanoparticles of pentagonal axial symmetry <Emphasis Type="Italic">D</Emphasis><Subscript>5<Emphasis Type="Italic">d</Emphasis></Subscript>: Nanotubes

The method of determination of the structure and the number of atoms in the shells of nanoparticles as a function of the arrangement of atoms at the symmetry elements of a symmetry group has been developed. The formulas for the calculation of the number of particles with symmetry group D _5d are reported. The number of particles in these shells is determined by three structurally invariant numbers and the “quantum number” of the group order n. The classification of all possible nanostructures with symmetry group D _5d is given: C _θ+10z , z = 0, 1, 2, …, where the basic shells are C _θ = C ₂, C ₁₀, C ₁₂. The sum rule has been obtained for the coordination numbers of shell sites located at symmetry axes. Pentagonal axial nanoparticles are shown to be the initial shells for obtaining (5,5) and (10,10) armchair nanotubes or (5,0) and (10,0) zigzag nanotubes. The general formula of these nanotubes closed with icosahedral and dodecahedral caps is N _20+10p , N _60+10p (p = 1, 2, …). The graphical constructions of all classes of nanoparticles and nanotubes of the pentagonal axial type are reported.     

Ab Initio Theoretical Studies on the Kinetics of Hydrogen Abstraction Type Reactions of Hydroxyl Radicals with CH<Subscript>3</Subscript>CCl<Subscript>2</Subscript>F and CH<Subscript>3</Subscript>CClF<Subscript>2</Subscript>

The hydrogen abstraction reactions from CH₃Cl₂F (R-141b) and CH₃CClF₂ (R-142b) by OH radicals are studied theoretically by semi-classical transition state theory. The stationary points for the reactions are located by using KMLYP density functional method along with 6-311++G(2d,2p) basis set and MP2 method along with 6-311+G(d,p) basis set. Single-point energy calculations are performed by the CBS-Q and G4 combination methods on the geometries optimized at the KMLYP/6-311++G(2d,2p) level of theory. Vibrational anharmonicity coefficients, x _ij , which are needed for semi-classical transition state theory calculations, are computed at the KMLYP/6-311++G(2d,2p) and MP2/6-311+G(d,p) levels of theory. The computed barrier heights are slightly sensitive to the quantum-chemical method. Thermal rate coefficients are computed over the temperature range from 200 to 2000 K and they are shown to be in accordance with available experimental data. On the basis of the computed rate coefficients, the tropospheric lifetime of the CH₃CCl₂F and CH₃CClF₂ are estimated to be about 6.5 and 12.0 years, respectively.     

Structural and electronic properties of heptachlor

In this work, the molecular geometry of heptachlor is investigated using ab initio HF, DFT, LDA, and GGA methods. The natural bond orbital (NBO) analysis is performed at the B3LYP/6-311++G(d,p) level of theory. The first order hyperpolarizability β_total, the mean polarizability Δα, the anisotropy of the polarizability Δα, and the dipole moment μ, are calculated by B3LYP/6-311++G(d,p) and HF/6- 311++G(d,p) methods. The first order hyperpolarizability (β_total) is calculated based on the finite field approach. UV spectral parameters along with HOMO, LUMO energies for heptachlor are determined in vacuum and the solvent phase using HF, DFT, and TD-DFT/B3LYP methods implemented with the 6-311++G(d,p) basis set. Atomic charges and electron density of heptachlor in vacuum and ethanol are calculated using DFT/B3LYP and TD-DFT/B3LYP methods and the 6-311++G(d,p) basis set. In addition, after the frontier molecular orbitals (FMOs), the molecular electrostatic potential (MEP), the electrostatic potential (ESP), the electron density (ED), and the solvent accessible surface of heptachlor are visualized as a results of the B3LYP/6-311++G(d,p) calculation. Densities of states (DOS), the external electric field (EF) effect on the HOMO-LUMO gap, and the dipole moment are investigated by LDA and GGA methods.     

Evaluation of Acid Dissociation Constants in DMSO and DMF by Quantum-Chemical Methods

We have calculated total electronic energies (E) and Gibbs energies (G) of a large number of acids and their anions in water, dimethylsulfoxide, and dimethylformamide using the hybrid B3LYP functional DFT method in the 6-31++G(d,p) basis set, taking into account the solvent effect by the conductor-like polarizable continuum model method. A linear correlation has been found between the experimental values of acid dissociation constants (pK_a) of different nature and the difference between anion and acid E values, and between pK_a and the difference between anion and acid G values. The obtained correlations allowed us to evaluate the pK_a values of both inorganic and organic acids. Such an evaluation is of special importance for nonaqueous solvents as it is quite problematic to determine these dissociation constants.     

X-ray photoelectron spectra and structure of polynuclear nickel complexes

Mono- and binuclear nickel complexes of different stoichiometry have been studied by X-ray photoelectron spectroscopy (XPS). The Ni2p, Ni3p, and N1s X-ray photoelectron spectra have been examined, and the role of a ligand in their formation has been determined. As distinct from a low-spin Ni(II) complex, the Ni2p spectra of high-spin Ni(II) compounds show strong satellite lines. For high-spin Ni(II) complexes, which have unpaired 3d electrons, the Ni2p _1/2-Ni2p _3/2 spin-orbit splitting is larger than that for a low-spin Ni(II) compound. The presence or absence of the satellite structure has made it possible to classify these complexes with regard to their magnetic properties. The difference between the Ni2p _3/2 and N1s binding energies has made it possible to estimate the covalence of the metal-ligand bond. The XPS results are consistent with X-ray crystallography data.     

Investigation of Solution p<Emphasis Type="Italic">K</Emphasis><Subscript>a</Subscript> and Thermodynamic Values of Lamivudine and Pefloxacin Drugs by Ab initio and DFT Methods

In this work we investigate the thermodynamic properties and pK_a value of lamivudine and pefloxacin drugs, in aqueous solutions, by ab initio and density functional theory (DFT) methods at different temperatures. Molecular structures and solute–solvent effects of the anions, cations, and neutral molecules of lamivudine and pefloxacin were studied by the polarizable continuum model (PCM). The calculation was done at the DFT-B3LYP/6-31+G(d) level of theory using Tomasi’s method to analyze the formation of intermolecular hydrogen bonds (IHB) in aqueous solution. The pK_a1 values of lamivudine and pK_a2 values of pefloxacin increase with temperature increase. In contrast, the pK_a1 values of pefloxacin decrease when the temperature increases. Further, the thermodynamic properties of the ionization processes (?H, ?S and ?G) of the drugs in aqueous solution were determined and discussed. The results of this work are in good agreement with the literature data at 298.15 K.     

Absolute and relative p<Emphasis Type="Italic">K</Emphasis><Subscript>a</Subscript> predictions via a DFT approach applied to the SAMPL6 blind challenge

In this work, quantum mechanical methods were used to predict the microscopic and macroscopic pK_a values for a set of 24 molecules as a part of the SAMPL6 blind challenge. The SMD solvation model was employed with M06-2X and different basis sets to evaluate three pK_a calculation schemes (direct, vertical, and adiabatic). The adiabatic scheme is the most accurate approach (RMSE?=?1.40 pK_a units) and has high correlation (R²?=?0.93), with respect to experiment. This approach can be improved by applying a linear correction to yield an RMSE of 0.73 pK_a units. Additionally, we consider including explicit solvent representation and multiple lower-energy conformations to improve the predictions for outliers. Adding three water molecules explicitly can reduce the error by 2–4 pK_a units, with respect to experiment, whereas including multiple local minima conformations does not necessarily improve the pK_a prediction.     

X-ray spectroscopy of lanthanum manganites: Nature of doping holes,correlation effects,and orbital ordering

The Mn3s X-ray photoelectron spectra of manganites were studied. It was shown that for the formal valence of manganese from 3+ to 3.3+, the doping holes are O2p in character; as the valence of manganese increases further, the Mn3d states acquire holes. For La_0.7Sr_0.3MnO₃, the Mn3p-3d resonance spectra provided information about the occupied and unoccupied Mn3d states, and the correlation energy U = 6.7 eV was determined experimentally. An analysis of X-ray dichroism on the L absorption spectra of three-dimensional La_7/8Sr_1/8MnO₃ showed that the cooperative Jahn Teller distortion of the orthorhombic phase at 240 K was related to (x ² ? z ²)/(y ² ? z ²) type orbital ordering.     

Electrical-percolation effects in micellar solutions of alkyltrimethylammonium bromides

Specific conductivity K of aqueous solutions of alkyltrimethylammonium bromides has been studied in a wide range of concentrations c of surfactants containing 10, 12, 14, and 16 carbon atoms in alkyl chains. In general, three break points have been observed in the K(с) dependences. The first point observed upon increasing overall solution concentration corresponds to critical micelle concentration CMC₁. The CMC₁ values of alkyltrimethylammonium bromides decrease with an increase in the alkyl chain length. They are in satisfactory agreement with the published data. It has been supposed that the second break point in the K(с) dependences corresponds to the formation micellar structures as clusters and the appearance of channels with a higher specific conductivity, which is provided by the contribution from the overlap of electrical double layers existing in the vicinities of micelles. Surfactant concentrations corresponding to these break points have been called “critical percolation concentrations” (CPCs). The position of a CPC in the concentration scale strongly depends on alkyl radical length. All K(с) curves exhibit a third break, which corresponds to second critical micelle concentration CMC₂, at which the properties of ionic-surfactant solutions may substantially change because of the appearance of supramicellar structures. The experimental data obtained have been used to evaluate the parameters of the model of electrical percolation for micellar solutions, i.e., effective conductivity \({\tilde K_m}\) and effective micelle radius r ₀.     

Protolytic properties of cyanic and thiocyanic acids and their isoforms

The electronic structure of HOCN, HSCN, HNCO, and HNCS molecules and [OCN]^? and [SCN]^? anions has been studied by ab initio calculations at HF/6-31G(d), HF/6-31G(d, p), MP2/6-31G(d)//HF/6-31G(d), and MP2/6-31G(d, p)//HF/6-31G(d, p) levels of theory. The HNCO and HNCS molecules are shown to have higher thermodynamic stability than HOCN and HSCN, respectively. The protolyte strength series are substantiated: HSCN > HOCN, HNCS > HNCO, HOCN > HNCO, HSCN > HNCS. Computations including electron correlation [MP2/6-31G(d)//HF/6-31G(d) and MP2/6-31G(d, p)//HF/6-31G (d, p)] reproduce the general sequence of proton-donor properties: HSCN > HOCN > HNCS > HNCO, which coincides with the hydrophobicity series for the compounds. The relative proton-donor capacity of these acids in water solutions is generally governed by the electronic structure and by the size of their molecules and [OCN]^? and [SCN]^? anions, but not by medium effects.     

p<Emphasis Type="Italic">K</Emphasis><Subscript>a</Subscript> measurements for the SAMPL6 prediction challenge for a set of kinase inhibitor-like fragments

Determining the net charge and protonation states populated by a small molecule in an environment of interest or the cost of altering those protonation states upon transfer to another environment is a prerequisite for predicting its physicochemical and pharmaceutical properties. The environment of interest can be aqueous, an organic solvent, a protein binding site, or a lipid bilayer. Predicting the protonation state of a small molecule is essential to predicting its interactions with biological macromolecules using computational models. Incorrectly modeling the dominant protonation state, shifts in dominant protonation state, or the population of significant mixtures of protonation states can lead to large modeling errors that degrade the accuracy of physical modeling. Low accuracy hinders the use of physical modeling approaches for molecular design. For small molecules, the acid dissociation constant (pK_a) is the primary quantity needed to determine the ionic states populated by a molecule in an aqueous solution at a given pH. As a part of SAMPL6 community challenge, we organized a blind pK_a prediction component to assess the accuracy with which contemporary pK_a prediction methods can predict this quantity, with the ultimate aim of assessing the expected impact on modeling errors this would induce. While a multitude of approaches for predicting pK_a values currently exist, predicting the pK_as of drug-like molecules can be difficult due to challenging properties such as multiple titratable sites, heterocycles, and tautomerization. For this challenge, we focused on set of 24 small molecules selected to resemble selective kinase inhibitors—an important class of therapeutics replete with titratable moieties. Using a Sirius T3 instrument that performs automated acid–base titrations, we used UV absorbance-based pK_a measurements to construct a high-quality experimental reference dataset of macroscopic pK_as for the evaluation of computational pK_a prediction methodologies that was utilized in the SAMPL6 pK_a challenge. For several compounds in which the microscopic protonation states associated with macroscopic pK_as were ambiguous, we performed follow-up NMR experiments to disambiguate the microstates involved in the transition. This dataset provides a useful standard benchmark dataset for the evaluation of pK_a prediction methodologies on kinase inhibitor-like compounds.     

Disperse systems based on chloracetophos in the low concentration range: self-organization,physicochemical properties and influence on representatives of higher plants and hydrobionts

A set of physicochemical methods was used to establish that aqueous solutions of chloracetophos fungicide and bactericide (1) in the range of calculated concentrations from 1?10^–18 to 1?10^–4 mol L^–1 are disperse systems in which a dispersed phase hundreds of nanometers in size is formed above and below a threshold concentration of 1?10^–9 mol L^–1. Upon dilution disperse systems 1 are capable of non-monotonic changing the physicochemical properties and changing the toxicity profile (inhibition–stimulation) when influencing the growth and development of unicellular algae Chlorella vulgaris. The formation of domains and nanoassociates is accompanied by the appearance in the UV spectrum of an absorption band at 210–300 nm with a maximum at ~220 nm (A₂₂₀). The interrelated concentration dependences of A₂₂₀, the size of the dispersed phase, and electrical conductivity indicates that the observed spectral features of systems 1 are caused by the properties of the domains and nanoassociates.