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A comprehensive study of saturated vapors of 4-n-propyloxybenzoic acid (POBA) by gas electron diffraction (GED) and mass spectrometric (MS) methods supplemented by quantum chemical (QC) calculations was carried out for the first time. An attempt was made to detect dimeric forms of the acid in the gaseous state. It has been established that at the temperature of GED experiment, vapor over a solid sample contains up to 20 mol.% of cyclic dimers with two O-H...O hydrogen bonds. The main geometrical parameters of gaseous monomers and dimers of POBA are obtained. The distance r(O…O) = 2.574(12) Å in the cyclic fragment of the gaseous dimer is close to that in the crystal structure (2.611 Å). In the mass spectrum of the POBA recorded the ions of low intensity with a mass exceeding the molecular mass of the monomer were detected. The presence of ions, whose elemental composition corresponds to the dissociative ionization of the dimer, confirms the results of the GED experiment on the presence of POBA dimers in the gas state. The results of GED studies of acetic acid, benzoic acid, and POBA were compared. It is shown that the COOH fragment saves its geometric structure in monomers, as well as the COOH...HOOC fragment with two hydrogen bonds in dimers of different acids. The intermolecular interaction energy in considered acid dimers was estimated using QC calculations (B97D/6-311++G **). The significant value of last (>84 kJ/mol) is the reason for the noticeable presence of dimers in the gas phase.

The enthalpies of sublimation of five substituted pyridine N-oxides were determined by the Knudsen effusion method with mass spectrometric control of the vapor composition within the framework of the second law of thermodynamics. The sublimation enthalpy of mono-substituted compounds 4-X-PyO depends on the nature of the substituent X and increases in the order CH3→NO2→OCH3. A difference is noted in the nature of dissociative ionization of disubstituted derivatives 2-CH3-4-NO2PyO and 3-CH3-4-NO2PyO. The relationship between the packing of molecules in crystals and the ΔH°subl values is considered.

Complexes of sodium dodecyl sulfate dimer (SDS)2 with β-alanyl-3-methyl-L-histidine dipeptide (balenine) in zwitterionic and cationic forms are simulated by the quantum chemical method DFT/B97D using the 6-311++G(3d,3p) basis set. The most stable configurations of these complexes are found. The complexes are shown to be stabilized by electrostatic forces and hydrogen bonds between the peptide and the dimer. Energy changes and hydrogen bond characteristics during complexation are analyzed. It is established that complexes with cationic balenine are more energy preferable. Balenine complexes and complexes formed by the isomeric peptide β-alanyl-1-methyl-L-histidine (anserine) are compared. As far as the formation of H-bonds with the dimer, position 1 of the balenine imidazole ring is more sterically favorable for the NH group than position 3 in the anserine ring. Structural changes in the peptide during the complexation are analyzed.

The densities of solutions of L-tryptophan (Trp) in water and sodium dodecyl sulfate (SDS) in Trp aqueous solutions are measured in a wide range of temperatures (293.15, 298.15, 303.15, 308.15, and 313.15) K using a DMA 5000 М density meter (Anton Paar).The apparent molar volumes ( $${{V}_{{\varphi ,{\text{SDS}}}}}$$ ) of sodium dodecyl sulfate in the 0.0010–0.0199 mol kg−1 range of concentrations and its limiting apparent molar volumes at infinite dilution ( $$V_{{\varphi ,{\text{SDS}}}}^{^\circ }$$ ) in solutions containing the amino acid (at a fixed concentration of 0.01 mol kg–1) are determined. A rise in the first critical micelle concentration from m = 0.0080 for SDS solutions in water to m = 0.0099 for SDS solutions with Trp is observed. Values of derivatives ( $$\partial V_{{\varphi ,{\text{SDS}}}}^{^\circ }$$ /∂T)p and ( $${{\partial }^{2}}V_{{\varphi ,{\text{SDS}}}}^{^\circ }$$ /∂T 2)p, and the partial molar volumes of SDS transfer from water to amino acid aqueous solutions, are calculated. Results are discussed by considering different types of intermolecular interaction in the given solutions. Quantum-chemical DFT/B97D modeling of the complexes between SDS and L-tryptophan zwitterion is done using a combination of basis set 6-311++G(2d,2p) and Grimme’s functional hybrid exchange correlation with a dispersion correction. The polarizable continuum model (PCM) is used to determine the structure and energies of formation of the SDS…Trp complexes with allowance for hydration effects.

Dipeptide complexes of β-alanyl-histidine (carnosine) and β-alanyl-1-methyl-histidine (anserine) with the sodium dodecyl sulfate dimer (SDS)2 are studied by the DFT/B97D quantum chemical method using the 6-311++G(3d,3p) basis set. The most stable configurations of peptide complexes in cationic and zwitterionic forms with the (SDS)2 dimer are found. The changes in peptide structures and energies as a result of the complexation are analyzed. It is shown that both ionic forms of carnosine can participate in the reaction with the SDS dimer in aqueous solution. The influence of the methyl substituent in the imidazole ring of anserine is noticeably manifested in the lengths of H-bonds formed by the $$\text{NH}^+_3$$ group of the peptide with SDS due to high steric barriers encountered by the substituted peptide as it adjusts to the dimer structure. The complexation energies have close values for anserine and carnosine cations.

The DFT/B3LYP method is used to study geometric and electronic structures of ions formed in the mass spectrum upon electron ionization of molecular forms in the vapor of aluminum tris-dipivaloylmethanate (Al(C11H19O2)3, Al(dpm)3). It is shown that the most energetically favorable processes upon dissociative ionization of molecular form AlL3 (L = dpm) are related to the detachment of radicals CH3•, t-Bu• and the anionic form of the ligand dpm–. It is established that one chelate ring is broken upon the formation of ions [AlL3–t-Bu]+, [AlL3–2t-Bu]+, [AlL3–6t-Bu]+ and the structure of the latter contains one monodentate ligand and two bidentate ligands. In the ions with compositions [AlL2]+, [AlL2–CH3]+, [AlL2–2CH3]+, [AlL2–4CH3]+, and [AlL2–2t-Bu–CH3]+, the cores of two bidentate ligands are located in mutually perpendicular planes. The energies of reactions leading to the formation of the above ions are calculated. The energies of frontier orbitals of these ions are considered; the reasons of high-intensity [AlL2]+ current are revealed. Detailed examination of ions in the mass spectrum of aluminum tris-dipivaloylmethanate (a typical representative of tris-β-diketonate complexes) reveals a number of structural features that can be used to predict the structure of such ions in the mass spectra of numerous similar complexes belonging to the ML3 type.

The TD-DFT/B97-D/6-311G** method is used to calculate the electronic absorption spectra of А⋯Х⋯А supramolecules with intermolecular hydrogen bonds (HBs), where А is 4-n-propoxycinnamic acid, Х is a nonmesogen molecule with bifunctional HB acceptors. Nonmesogens Х (B, C, D, E) consist of two pyridyl fragments connected by bridging groups of different natures: 4,4′-bipyridine (В), 1,2-bis(4-pyridyl)ethane (С), 1,2-bis(4-pyridyl)ethylene (D), 4,4′-azopyridine (Е). It is shown that the introduction of bridging groups (–CН2–CН2–, –CН=СН–, –N=N–) significantly affects the energy of frontier orbitals and electronic absorption spectra (EAS) of nonmesogens Х in the near-UV region. The EAS of two structural units A⋯В⋯A, A⋯A, which may be formed due to the self-assembly in two-component mesogen А–nonmesogen В systems, are compared. Due to hydrogen bonds (O–H⋯N and O–H⋯O), having different types and strengths in these complexes, the high-intensity band shifts to shorter wavelengths in complex А⋯В⋯А and to longer wavelengths in complex А⋯А with respect to the λ = 333 nm band of monomer А. It is shown that EAS of hydrogen-bonded complexes А⋯Х⋯А are not superpositions of EAS of individual components. The spectra show electronic transitions related to charge transfer between the components of the complexes. Using nonmesogens Х of different nature in supramolecules А⋯Х⋯А will allow one to change purposefully their electro-optical properties and to achieve intense absorption in particular regions of UV spectra.

The molecular structure and conformational properties of tryptophan have been investigated by gas-phase electron diffraction and theoretical methods. Quantum chemical calculations realized by program Gaussian 03 (B3LYP/cc-pVTZ) have been predicted the existence of six conformers at the temperature of experiment (T = 495 K). The ability of gas-phase electron diffraction method to distinguish the structure of conformers was estimated theoretically. Conformers have different orientations of carboxylic and amine group, backbone and indole fragment to each other. These conformers can be divided on two groups: distinguishable parameters (with different torsion angle C(OOH)-C(HNH2)-C(H2)-C(ind)) and weekly distinguishable ones (with different torsion angles H-N-C-C and H-O-C-C) by gas-phase electron diffraction. The molecular parameters of the conformers were determined. The conformers have intramolecular hydrogen bonding of the H2N···HO. The analysis of the gas-phase electron diffraction data have been carried out assuming the saturated vapor of tryptophan at T = 495 K consists of mixture at least of two conformers with lowest energy. It was shown that optimal ratio between conformers I : II was 50 : 50, respectively. The geometrical parameters of amino acids molecules (glycine, alanine, tryptophan) obtained by gas-phase electron diffraction were compared. The influence of the intramolecular hydrogen bond was established onto the structural parameters of the backbone of the above amino acids molecules.

The structure of PdTPP and ZnTPP molecules have been studied at first time by a combined gas-phase electron diffraction and mass spectrometry (GED/MS) complemented by quantum-chemical calculations. Four conformers have been found in which four phenyl fragments are turned in different directions from their perpendicular position relative to the porphyrin plane. The structures with turned orientation of phenyl fragments demonstrate an energy balance between orbital conjugation of phenyls with porphyrin framework and steric repulsion of the phenyl and pyrrole fragments. Comparison of PdTPP and unsubstituted PdP as well as ZnTPP and ZnP complexes within the framework of NBO analysis shows that characteristics of the M N coordination bond do not practically change when meso-substituents are introduced. In contrast, the Cα-Cm bond lengths at the meso-substituent, the Cα-Cm-Cα bond angle, and the energy of the frontier orbitals are changed significantly. The change in these parameters indicates the electron-donor nature of the phenyl fragments. Strong donor-acceptor interactions between LP(N) and both 4dx2-y2 and 5s AO (Pd) causes a significant transfer of the electron density from the donor atom N on Pd resulting the extremely low effective net charge on the palladium atom and determining the high donor and acceptor properties of PdP and PdTPP complexes.

The variants of structural organization in the systems “mesogen – nonmesogen” are considered. The systems contain p-n-propyloxycinnamic acid (A), as a mesogenic component, and nonmesogenic Ph–X–Ph compounds: phenyl benzoate (B, where X = –COO–), azobenzene (C, where X = –N=N–) and N-benzylideneaniline (D, where X = –CH=N–). Quantum-chemical modeling of possible structural units in such systems has been performed. It was shown that all assumed A∙∙∙X(Ph)2 H-complexes do not have electronic and geometric anisotropy and have a lower intermolecular interaction energy than the cyclic dimer of acid A∙∙∙A. The calculated values of the Gibbs free energy of complexation reactions also indicate a low probability of the formation of A∙∙∙X(Ph)2 type H-complexes. It is noted that the “length” of the A∙∙∙A dimer is comparable with the doubled “length” of Ph–X–Ph molecules, which, like the acid dimer, have a rod-like structure favorable for the formation of nematic and smectic LC phases. Based on the analysis of the quantum chemical calculations, it was assumed that Ph–X–Ph can be embedded between acid cyclic dimers A∙∙∙A and can facilitate reduce intermolecular interactions in the system, which reduces the temperature of Cr–LC transitions. The proposed structural organization of systems A: Ph–X–Ph is confirmed by an experimental IR spectrum for a similar system, in which the bands corresponding to the vibrational frequencies of the acid dimer and to individual molecules of alkyloxy substituted phenyl benzoate B are recorded.

The mass spectra of tetrakis(1,1,1,5,5,5-hexafluoro-2,4-pentanedionato)lanthanide(III)-potassium complexes KLn(C5HF6O2)4, where Ln = La, Gd, Lu, (hereinafter referred to as KLn(hfa)4), have been recorded at different temperatures. The presence of the high-intensity ions KLn(hfa)3+ generated by elimination of one ligand from the parent species due to electron ionization indicates that the saturated vapours of all three complexes consist of the only KLn(hfa)4 species. The sublimation enthalpies were determined by effusion Knudsen method in frame of second law of thermodynamics. The vaporization was studied over temperature ranges 414 ÷ 471 К for KLa(hfa)4, 401 ÷ 453 К for KGd(hfa)4, and 399 ÷ 442 К for KLu(hfa)4. The values of ΔsubH°(T) equal 170.6 ± 2.1, 166.4 ± 3.6, and 161.8 ± 2.3 kJ/mol for the complexes of La, Gd and Lu respectively. DFT/PBE0 calculations show, that the shortening of the M O bond length due to lanthanide contraction is accompanied by a decrease in the negative net charge on the oxygen atoms bounded with potassium. The potassium ions play the role of the bridges between the [Ln(hfa)4]− anions in the crystal, and weakening the K O ionic bonds can explain the decrease in the enthalpy of sublimation of the lutetium complex in comparison with the lanthanum one.

The structure of free manganese(II) bis-acetylacetonate [Mn(acac)2] was determined experimentally by gas-phase electron diffraction. The vapor at 197(5) °C is composed of a single conformer of Mn(a...

IR spectra of individual 4-n-dodecyloxybenzoic acid (A) and 4-pyridyl 4′-n-dodecyloxybenzoate (B) compounds as well as IR spectra of 2A:1B and 1A:1B systems were recorded. For the assignment of the experimental vibrational spectra a series of quantum chemical calculations of DFT(B97-D)/6-311++G** level was carried out. Hydrogen-bonded complexes of types A⋯A, A⋯B, as well as various trimers that can be formed at different component ratios in system A-B were simulated. The geometric structure of these complexes was optimized and the vibrational frequencies were calculated. The conclusions on the molecular organization of system A-B for different ratios of the components A and B were based on the interpretation of IR spectra and the analysis of calculated thermodynamic characteristics of self-assembly processes. Thus, it is determined that the system A consists of cyclic A⋯Acycl dimers; in 1A:1B system the H-complexes of A⋯B type are formed. In the 2A:1B system in the process of self-assembly, instead of the complexes A⋯A⋯B and A⋯B⋯A of stoichiometric composition, the complexes A⋯B and A⋯Acycl are formed in the ratio 2:1. These results are confirmed by the dilatometric method data.

By DFT method with B3LYP, PBE, CAM-B3LYP, and B97D functionals, it was found that the molecule 4-(4-tritylphenoxy)phthalonitrile (TPPN) has four conformers. The geometric structure, vibrational frequencies, electronic characteristics, and thermodynamic functions of conformers, as well as the structure and energy of transition states, were determined. IR spectrum of TPPN film contains vibrational bands belonging to different conformers. The assignment of bands was performed basing the distribution of normal vibration energy on internal coordinates. A synchronous electron diffraction/mass spectrometric experiment was performed to determine the structure of conformers in a saturated TPPN vapor. The elemental composition of the ions recorded in the mass spectrum indicates the thermal stability of TPPN at least up to T = 200 °C. The difference in the structure of tetrasubstituted metal phthalocyanines, which can be synthesized from different TPPN conformers, has been shown.

The molecular structures of potassium tetrakis(hexafluoroacetylacetonato)lanthanide(III) complexes [KLn(hfa)4] (Ln=La, Gd, Lu; hfa=C5HF6O2,) were studied by synchronous gas‐phase electron diffraction/mass spectrometry (GED/MS) supported by quantum‐chemical (DFT/PBE0) calculations. The compounds sublime congruently and the vapors contain a single molecular species: the heterobinuclear complex [KLn(hfa)4]. All molecules are of C 1 symmetry with the lanthanide atom in the center of an LnO8 coordination polyhedron, while the potassium atom is coordinated by three ligands with formation of three K−O and three K−F bonds. One hfa ligand is not bonded to the potassium atom. Topological analysis of the electron‐density distributions confirmed the existence of ionic‐type K−O and K−F bonding. The structures of the free [KLn(hfa)4] molecules are compared with those of the related compounds [KDy(hfa)4] and [KEr(hfa)4] in their crystalline state. The complex nature of the chemical bonding is discussed on the basis of electron‐density topology analyses., Gas phase and solid state of potassium tetrakis(hexafluoroacetylacetonato) lanthanid complexes [KLn(hfa)4] (Ln: lanthanide) are very different. The structures of the of salt‐like [KLn(hfa)4] (Ln=La, Gd, Lu) have now been determined by gas electron diffraction, and the nature of the bonding by quantum‐chemical methods. The gas phase of such compounds is seldom studied, but highly relevant to applications in gas‐phase metal transport or deposition techniques.

For the first time, the molecular structure of 3-aminophthalimide has been determined by the gas electron diffraction (GED) method supported by a mass-spectrometric analysis of the gas phase and results of quantum-chemical computations up to coupled-cluster level of theory, CCSD(T). The semiexperimental equilibrium structure, rsee, has been derived from the GED data by taking into account harmonic and anharmonic vibrational corrections estimated from the quantum-chemical force field (up to cubic terms). High accuracy structures have been exploited for the observation of fine structural effects arising due the presence of the electron-donating amino group and the formation of a hydrogen bond. Natural bond orbital (NBO) analysis and quantum theory of atoms in molecules (QTAIM) have been applied to explain these effects.

Quantum chemistry was used to simulate a fragment of α-glycine crystal consisting of 5 and 6 glycine molecules. The α-glycine crystal fragment model was constructed using X-ray diffraction data contained in the Cambridge Crystallographic Database (CCDC). Theoretical IR spectra were obtained. It was shown that in a fragment of a crystal, glycine molecules in zwitterionic form form N-H...O hydrogen bonds of different strength, which correspond to different frequencies of stretching vibrations νst (N-H) of the NH3+ group. Full optimization of glycine crystal fragments consisting of a small number of molecules, regardless of the method of calculation, leads to the agglomeration of the structure. The system forms the maximum possible number of the most durable hydrogen bonds, thereby lowering the overall energy of the system, which leads to disruption of the crystal structure of the fragment, distortion of the parameters of hydrogen bonds in the crystal, and, consequently, to an unsystematic shift in the frequencies of N-H vibrations. To avoid this process, further modeling was performed by partially optimizing the geometry of the crystal fragment, with the positions of heavy nitrogen atoms, carbon and oxygen atoms being fixed, and only the positions of hydrogen atoms involved in the formation of hydrogen bonds were varied. Using the DFT/B3LYP/6-311G** method, the energies of donor–acceptor interaction in a fragment of a crystal, as well as its oscillation frequencies, are calculated. The calculated frequencies are consistent with the three experimental frequencies in the indicated X-ray region. A comparison was made between the calculated and experimental frequencies of the stretching vibrations of the N-H group of the NH3+ group. According to the geometric characteristics of the HB and the energy of donor-acceptor interaction between the lone electron pairs of oxygen atoms and the *(N-H) loosening orbitals, it was found that the hydrogen bonds of N-H...O between molecules in one layer are stronger than between molecules in different layers of a crystal.

1-(N,N-dimethylamino)-1-silacyclohexane 1 was synthesized. Contributions of the conformers of 1, Eq-trans: Eq-gauche: Ax-trans, were found to be 55(15):15(15):30(15) mol.% in gas phase at 288 K from gas electron diffraction. The enthalpy ΔH = 0.29(15) kcal/mol for Ax-to-Eq transition was measured by temperature dependent Raman spectroscopy of liquid 1 and its solutions. Geometry, conformational properties and intramolecular conversion were explored by theoretical calculations. The nitrogen bond configurations for 1 was found to be close to planar, with a sum of the bond angles of ca. 350-355° that is quite different from those analogs in which the N atom is connected to a carbon atom rather than to a silicon atom.

А dynamic vibrational task has been solved with taking into account the interaction of vibrational coordinates on the base of the calculated PES. The vibrational level energies and corresponding wave functions of LaI3 molecule have been determined by the solution of three-dimensional Schrodinger equations. Theoretical calculations were performed by the DFT/PBE0, DFT/B3LYP and MP2 methods using relativistic effective pseudopotentials and a good quality basis sets for inner and outer atomic shells. Six-dimensional PES was numerically calculated by the DFT/PBE0 approach. Available gas-phase electron diffraction (GED) data were simulated by the original methodology based on the full dimensional PES. A good agreement between experimental and theoretical thermal average structural parameters supports the reliability of the theoretical data and the efficiency of the methodology implemented. It is shown that the standard approaches based on the use of the harmonic approximation, to calculate of the vibrational corrections necessary for the interpretation of GED results, at high temperatures lead to either significantly overestimated or underestimated values of equilibrium geometrical parameters. An analysis of the anharmonic vibrational levels obtained indicates the absence of Fermi resonances and the suitability of the harmonic approximation for describing fundamental vibrational transitions.

Complexes formed by leucine (Leu) and the dimer of sodium dodecyl sulfate (DDSNa)2 are studied by the quantum chemical method DFT using the hybrid exchange-correlation functional B97 with Grimme's dispersion correction D2 and the 6-311++G(2d,2p) basic set. The complexes formed by Leu and the dimer of DDSNa (considered as a micelle fragment) are studied in terms of their spatial structures and the energies of intermolecular interactions ЕIMI, depending on the penetration depth of Leu inside the micelle model. The highest energy ЕIMI is exhibited by the complex formed by the zwitterionic form of the amino acid and the hydrophilic part of sodium dodecyl sulfate. When the hydrophilic environment is replaced by the hydrophobic one, the intramolecular hydrogen bond in the amino acid changes in terms of its type and strength: N–H…O (weak) → N…H…O (strong) → N…O–H (weak). The energies of frontier orbitals and, therefore, redox properties of leucine also undergo changes in the course of the process.

Particular features of the geometrical and electronic structure of six possible conformers of dansylamide ((CH3)2N–C10H6–SO2NH2) are considered. The electronic absorption spectra of the conformers of dansylamide in the free state and taking into account the influence of an aqueous solvent (in terms of the PCM model) are calculated by the TDDFT method. It is shown that, as a result of taking into account solvation, the electronic absorption spectra of the conformers exhibit a bathochromic shift, and the difference in the values of λ of the conformers reaches 16 nm. The calculated electronic absorption spectra in an aqueous medium agree qualitatively with the obtained experimental spectra. An analysis of molecular orbitals involved in the first three electronic transitions of the conformers is carried out. It is suggested that the broadening of the band with λmax = 326 nm in the experimental spectrum may be caused by the presence of dansylamide conformers in the aqueous solution. It is shown that the calculated values of λ in the electronic absorption spectra of dansylamide in the aqueous solvent depend substantially on the DFT functional type.

Dansylamide is perhaps the most ubiquitous fluorophore due to its donor-acceptor bifunctionality and its ability to form intra- and intermolecular hydrogen bonding. Among the diversity of its applications is the development of new generation of biosensors for the in vivo monitoring of traces of metals. The structure and conformational stability of dansylamide in the gas phase were investigated for the first time by a combined gas-phase electron diffraction-mass spectrometry (GED/MS), complemented by quantum chemical calculations. GED data indicate that different skewed conformers exist at T = 464 K, which are characterized by the deviation of two S–N bonds from the perpendicular orientation relative to the naphthalene plane. Maybe the most indicative structural parameters for electronic interactions between the donor-acceptor substituents and the aromatic naphthalene and the subsequent stabilization of the favorable skewed eclipsed-syn conformer are the dihedral angles C9–C1–S–N and C10–C5–N–C with the experimentally determined values of 66.8° (32) and 68.1° (72), respectively. The role of –SO2NH2 by forming intramolecular hydrogen bonds was scrutinized by employing the natural bond orbital approach (NBO), quantum theory atoms in molecules (QTAIM), and molecular electrostatic potential (MESP). The non-planarity of the naphthalene skeleton due to the electronic interactions with the substituents and its consequence for the fluorescence activity of dansylamide have been discussed.

The synthesis and results of gas electron diffraction (GED), temperature-dependent Raman spectroscopy, along with detailed quantum chemical (QC) study of 1-methoxy-1-silacyclohexane 1 are reported. Within the series of the QC results, DFT(B3LYP, PBE0, M06, M062X), and MP2, the conformational preference predictions are rather contradictive. From the both GED and Raman experimental methods applied, the vapour and liquid phases of 1 were found to exist as a mixture of two conformers, gauche- axial and gauche -equatorial, with almost equal contributions, while the trans -forms are much less stable. In addition, theoretical calculations on the cyclohexane analog, methoxycyclohexane 2 , are performed in order to compare with the conformational properties of 1 . The latter is predicted not to diminish the axial/equatorial ratio, as contrasted to the expectations at switching the point of the substituent attachment from Si to C.

The results of quantum-chemical modeling of the self-assembly process in the system based on 4-alkylbenzenesulfonic acids and 4-pyridyl 4′-alkyloxybenzoates are presented. It has been shown that the interaction of the pyridyl fragment of 4-pyridyl 4′-alkyloxybenzoat and the sulfonic group of 4-alkylbenzenesulfonic acid leads to the strongest H-complexes. The potential function of proton transfer from the sulfonic group to the pyridyl fragment was simulated both in the gas phase and in a solvent (ethanol). It was found that an H-complex with a hydrogen bond of the O∙∙∙H–N type is formed between the compounds under study. FTIR spectra of the 1(4-alkylbenzenesulfonic acid) : 1(4-pyridyl 4′-alkyloxybenzoate) systems confirm the results of quantum chemical calculations. The mesomorphic properties of the 1(4-methylbenzenesulfonic acid) : 1(4-pyridyl 4′-heptyloxybenzoate) supramolecular complex were studied using DSC and polarizing microscopy. It is shown that the H-complex formed by 4-methylbenzenesulfonic acid and 4-pyridyl 4′-heptyloxybenzoate has a smectic mesophase with expanded temperature range (59o) in comparison with the 4-pyridyl 4′-heptyloxybenzoate (28o).

The quantum chemical modeling of sodium dodecylsulfate (DDSNa) complexes with glycine (Gly) and cysteine (Cys) is carried out at the DFT/B97D level using the Grimme hybrid exchange-correlation functional with a dispersion correction and the 6-311++G(2d,2p) basis set. The structure of the Gly and Cys molecular and zwitterionic forms is examined. The structures and the formation energies of DDSNa…Gly and DDSNa…Cys complexes are determined. The effect of the amino acid structural features on the stability of the complexes they form with DDSNa is analyzed. The NBO analysis of the electron density distribution in the DDSNa molecule is performed.

The structure of free manganese(III) tris(acetylacetonate) [Mn(acac)3] was determined by mass-spectrometrically controlled gas-phase electron diffraction. The vapor of Mn(acac)3 at 125(5)°C is composed of a single conformer of Mn(acac)3 in C2 symmetry with the central structural motif of a tetragonal elongated MnO6 octahedron and 47(2) Mol% of acetylacetone (Hacac) formed by partial thermal decomposition of tris(acetylacetonate). Three types of Mn-O distances have been refined (rh1 = 2.157(16), 1.946(5) and 1.932(5) A. We have found no indication of significant deviations of the -C-C-C-O-Mn-O- six-membered rings from planarity, which is observed in the solid state.

Geometrical and electronic structure and optical properties of several substituents and derivatives of 1,8-naphthosultam are studied by quantum-chemical DFT and TDDFT. It is found that the substituents –NO2, –CF3, and –N(CH3)2 affect the geometrical and electronic structure the most. It is shown that the Stokes shift is greatest (≈260 nm) for compounds with the strong donor substituent –N(CH3)2, while strong acceptor substituents provide a quite small Stokes shift. The dependence of the Stokes shift on the difference in energies of the frontier orbitals of the ground and excited states of molecules is found. Of the 1,8-naphthosultam substituents considered, compounds with –N(CH3)2 substituent, which emit in the biological window region, can be advised for use in optical bioimaging. The results can be used as a basis for the development and creation of new functional materials and biologically active compounds.

The influence of the chalcogen atom (X) on the molecular and electronic structures for the series of Mg[Formula: see text] tetra(1,2,5-chalcogenadiazolo)porphyrazines [TXDPzMg] (X [Formula: see text] O, S, Se, Te) and their monoaqua complexes [TXDPzMg(OH[Formula: see text]] was studied using DFT methods (B3LYP and PBE0 functionals) with cc-pVTZ basis sets. The chalcogen atom X changes strongly the geometry of the fused 1,2,5-chalcogenadiazole rings, but has only a weak influence on the dimensions of the coordination cavity of the porphyrazine macrocycle in [TXDPzMg] leading to its slight expansion in the sequence S < Se < Te < O. The electron density distribution was considered in terms of the natural bond order (NBO) and the natural population analysis (NPA). The frontier molecular orbitals are destabilzed along with the decrease of electronegativity of the chalcogen atoms. The a[Formula: see text] and e[Formula: see text] orbitals (HOMO and LUMO) are mainly localized on atoms constituting the internal 16-membered macrocycle, while the chalcogen atoms have the strongest effect on the composition of the filled [Formula: see text]-MOs having the a[Formula: see text] symmetry – 2a[Formula: see text] and lower lying 1a[Formula: see text] orbitals. The Gouterman type a[Formula: see text] orbital with predominant localization on the nitrogen atoms of the internal 16-membered macrocycle is 2a[Formula: see text] for the O- and S-containing complexes and for the Se- and Te-analogs it becomes 1a[Formula: see text], while the higher lying 2a[Formula: see text] orbital resides mainly on the fused heterocycles (Se/Te and C[Formula: see text] atoms). The lowest excited states have been calculated for [TXDPzMg] and used for the explanation of the peculiarities and tendencies observed in the experimental electronic absorption spectra available for the S, Se- and Te-containing Mg[Formula: see text] complexes.

Electronic, geometrical, vibrational and energetic characteristics of the ice I TDT fragment consisted of dodecahedron H2O[512] (D) fused with two tetrakaidecahedrons H2O[51262] (T) and of the TDT cluster with three encapsulated CH4 molecules (3CH4·TDT) were calculated using a DFT/B97-D/6-311++G(2d,2p) approach. Binding energies, hydrogen bonding energies, energies of encapsulation of methane molecules into small D- and large T-cages of the TDT fragment, energies of frontier orbitals, the translational and librational frequencies, as well as the intramolecular vibrations of methane within the cages of different sizes were studied. Similar characteristics of isolated D- and T-cages and clathrates CH4·D and CH4·T were studied as function of compression/expansion of their oxygen skeletons using DFT/B97-D, LC-B3LYP, B3LYP-D2 methods.

Conformational composition of the vapor (T = 413(5) K) and the conformer structures of 1,5-naphthalenedisulfonylchloride (1,5-NaphDSC) have been studied by a combined gas-phase electron diffraction and mass spectrometry (GED/MS) method complemented by quantum chemical calculations. According to quantum chemical calculations at DFT/B3LYP/cc-pVTZ and MP2/cc-pVTZ theory levels, the molecule 1,5-NaphDSC possesses four conformers differing mutual orientation of the two SO 2 Cl groups. GED data clearly indicate that only two conformers, whose structures are characterized by deviation of two S Cl bonds from perpendicular position relative to the plane of the naphthalene skeleton (syn-symmetry C 2 and anti-symmetry C i ), are present in vapor at 413 K. The following geometrical parameters of these conformers were obtained from the experiment (A and degrees; uncertainties are in parentheses): r h1 (C H) = 1.098(9), r h1 (C C) = 1.405(3), r h1 (C S) = 1.781(4), r h1 (S O) = 1.426(3), r h1 (S Cl) = 2.056(4), ∠C C S C = 122.9(1), ∠C S S Cl = 101.8(6); C9 C1 S Cl = 71.2(12), C10 C5 S Cl = 71.2(12)-syn conformer; C9 C1 S Cl = 71.2(12), C10 C5 S Cl = −71.2(12) -anti-conformer. The presence of C 9 H n + ions in the mass spectra of naphthalenesulfonyl chlorides, which are absent in the mass spectrum of naphthalene, may be attributed to the weakening of two C C bonds adjacent to the substituent of the naphthalene skeleton. This reflects in the geometric parameters of 1,5-NaphDSC. The barriers to internal rotation of sulfonyl chloride groups were calculated. It is shown that the low-energy syn- and anti-conformers are structurally rigid, in contrast to high-energy conformers with one or two S Cl bonds, lying in the plane of the naphthalene skeleton. The dependence of C1 C2, C S, S Cl bond lengths from SO 2 Cl groups orientation relative to naphthalene skeleton is discussed in terms of NBO-analysis of electron density distribution. The relationship between conformational properties of molecule and some physicochemical characteristics of the 1,5-NaphDSC compound is discussed.

Conformational properties of a benzenesulfonic acid hydrazide molecule and its para-nitro and para-methyl derivatives, which have found wide application as porofors and biologically active compounds, are studied. It is found that the benzenesulfonic acid hydrazide molecule has six conformers with relative energies of 0//0 kcal/mol, 0.34//0.98 kcal/mol, 2.51//2.25 kcal/mol, 2.54//2.56 kcal/mol, 2.90//3.28 kcal/mol, 6.64//6.43 kcal/mol (MP2//DFT(B3LYP) with the cc-pVTZ basis set), each conformer has enantiomer. The conformers differ from each other in the relative orientation of the fragments of the–SO2NHNH2 group, the energies of the frontier orbitals, the direction and value of the dipole moments. It is shown that the introduction of a nitro or methyl group into the para-position practically does not affect the conformational properties of the sulfonyl hydrazide group. Change in the structure of benzenesulfonic acid hydrazide during the crystal–gas transition is considered and it is revealed that in the crystal the conformation similar in structure to one of the high-energy conformers of the free molecule is stabilized. The NBO analysis of the electron density distribution is performed and it is shown that the occurrence of the gauche effect in all conformers of the molecules under study can be interpreted by the manifestation of the total action of strong anomeric effects between the lone pairs of nitrogen atoms and antibonding orbitals of S=O, N–H, C–S, and N–S bonds.

The molecular structure of Y, La, and Lu complexes with hemihexaphyrazine (Нр), a six-link heteroazaporphyrinoid of АВАВАВ type, has been studied by DFT. It has been found that these MHp (M = Y, La, Lu) complexes have a non-planar structure of Cs symmetry with the metal atom dislocated from the center of the cavity to one of the thiadiazole rings. The average lengths of coordination bonds formed by the metal atom with six nitrogen atoms of the thiadiazole moieties are 2.389, 2.566, and 2.358 A in YHp, LaHp, and LuHp, respectively. Different degrees of deviation from planar structure have been determined in La complex and Y and Lu complexes, characterized by the values of the N N...N N torsion angle between nonequivalent N N bonds in two thiadiazole rings (38.2, 56.0, and 58.6°, respectively). At the same time the internal circumferences of the macrocycle are the same in all three complexes. It has been shown that the planar structures of the complexes of the D3h symmetry are saddle points on the PES. The transition barriers between the structures of Cs and D3h symmetries have been computed (40.5, 4.6, and 52.4 kJ/mol for YHp, LaHp, and LuHp, respectively). An NBO analysis of the electron density distribution in MHp complexes has been carried out and the nature of coordination bonds in the complexes has been examined. We suppose the coordination bonds in the complexes as three-center ones involving atom M and two nitrogen atoms of Nt-Nt bond in the thiadiazole moieties, and the Hp ligand as a quasi tridentate one, despite the fact that the metal atom is bonded to six nitrogen atoms of the ligand. The value of the lanthanide contraction ΔrLn (0.208 A) in the examined LnHp complexes with one ligand has been determined, which turned out to be close to ΔrLn values in the series of lanthanide halogenides with three monovalent ligands and in the series of lanthanide compounds with three bidentate ligands.

Conformational properties of the main part (excluding OC 3 H 7 radicals) of the p-n -propyloxybenzoic (A 1 ) and p-n -propyloxycinnamic (A 2 ) acids molecules (relating to mesomorphic compounds) as well as p-n -propyloxybenzoic acid pyridine ester (B 1 ) and p-n -propyloxyphenylazopyridine (B 2 ) molecules (relating to non-mesomorphic compounds) were studied by DFT(B3LYP)/cc-pVTZ method. It was shown that the main parts of A 1 and A 2 acids are rigid. The barrier to internal rotation of pyridine fragment in the B 1 and B 2 molecules depends on the nature of the bridging group. It was determined that all studied A 1 ⋯B 1 , A 2 ⋯B 1 and A 2 ⋯B 2 complexes are characterized by a strong hydrogen bond. The binding energy of complexes (≈14 kcal/mol, with BSSE corrections, DFT(B97D)/6-311++G**) exceeds the energy per hydrogen bond in the corresponding acid dimers (≈10 kcal/mol). The structural non-rigidity of A⋯B complexes is mainly caused by possibility of OC 3 H 7 radicals internal rotation and A and B molecules rotation about the (H)O⋯N line. The characteristics of intermolecular hydrogen bonds were determined by NBO-analysis. The obtained results indicate that examined complexes correspond to the basic requirements to mesogen molecular forms. The thermodynamic functions of the gas-phase complexation reactions (idealized model of the complexes formation in the condensed state) were calculated. Preliminary studies of mesogen–non-mesogen A 1 ⋯B 2 system by differential scanning calorimetry and polarizing optical microscopy, showed that it has mesomorphic properties.

The structure of free manganese(II) bis-acetylacetonate [Mn(acac)

The conformational properties of p-n-propyloxybenzoic acid and p-n-propyloxy-p′-cyanobiphenyl molecules, which can exhibit liquid crystalline properties in the formation of Н-complexes, are studied (DFT/B3LYP)/cc-pVTZ method). It is found that a molecule of p-n-propyloxybenzoic acid has 16 conformers that can be divided into four groups with respect to relative energies (0 kcal/mol, 1.6 kcal/mol, 6.5 kcal/mol, and 8.1 kcal/mol), and a molecule of p-n-propyloxy-p′-cyanobiphenyl has six conformers with relative energies of 0 kcal/mol (two conformers, φ(СPh–O–C–C)=180°) and 1.6 kcal/mol (four conformers, φ(СPh–O–C–C)=64.4°). In all conformers of the 3-AOCB molecule, phenyl rings are turned at 35° relative to each other. A conformation with the planar arrangement of two rings has a higher energy by 1.5 kcal/mol. Barriers to the internal rotation of different groups are determined and it is established that the structural nonrigidity of the molecules is mainly due to the possible rotation of the–C2Н5 moiety about the C–C bond. It is shown that with increasing temperature the vibrational amplitudes of the OC3H7 substituent, which enhance the probabilities of transitions between the conformers, become appreciably larger. It is found that p-n-propyloxybenzoic acid and p-n-propyloxy-p′-cyanobiphenyl can form Н-complexes with the medium hydrogen bond. Two types of the structural organization of Н-complexes are considered: linear and angular. The similarity of energies of Н-complexes with different structures (NBO analysis) can be the reason for the occurrence of two liquid crystalline subphases of p-n-propyloxybenzoic acid and p-n-propyloxy-p′-cyanobiphenyl system.

Quantum chemical investigation of α- l -alanyl-α- l -alanine and β-alanyl-β-alanine complexes with SDS dimer as an anion micelle fragment in polarizable continuum has been carried out by using of DFT method with B97-D/6-311++G(3d,3p) level. The variation of peptide structure and the difference in energies of free peptides, SDS dimer and their complexes have been analyzed. Optimized configurations of complexes are stabilized by hydrogen bonds of (H2)N H…O(S) type. The localization of α- l -alanyl-α- l -alanine among the charged groups of SDS dimer is more preferable. The localization of β-alanyl-β-alanine among the charged groups or in the dimer hydrophpbic canal results in close values of the complex formation energy. More favorite change of energy and shorter length of hydrogen bond of (H2)N H…O(S) type have been revealed for complex formation between SDS dimer and β-alanyl-β-alanine as opposed to α- l -alanyl-α- l -alanine. Molecular dynamics simulation of adsorption of the peptides on SDS micelle has been performed in NPT ensemble at 0.1 MPa and 298 K. The cell under study contained 14,678 water molecules, one peptide zwitter-ion, and the micelle including 64 SDS monomers. Most probable localization of peptide atoms relative the micelle has been analyzed. The peptide – SDS micelle interaction is accompanied by diminish of average number of peptide – water H-bonds and the formation of at the mean two H-bonds with SDS. Some peculiarities of adsorption of the isomolecular peptides on SDS micelle are appeared in different values of H-bond lifetimes, different probability of formation of H-bond of NH3+…−O3S O or NH3+… O (SO3−) types, and localization of peptide zwitter-ions outside or within double electrical layer of the micelle.

By mass spectrometry it is found that naphthalene, 1-naphthalenesulfonyl chloride, 2-naphthalenesulfonyl fluoride, 2-naphthalenesulfonyl chloride, 1,5-naphthalenedisulfonyl chloride, 1-naphthalenesulfonamide, and 2-naphthalenesulfonamide evaporate congruently on heating and their saturated vapor is presented by the corresponding monomeric molecular forms. The relationship is established between the character of the fragmentation of molecules during electron ionization and the specific features of their geometric and electronic structures.

The molecular structure and conformational variety of the zinc(II) etioporphyrin have been studied by the combination of gas-phase electron diffraction (GED), mass spectrometry and quantum chemical calculations. The DFT (B3LYP and PBE) calculations predict six conformers, which differ in the orientation of the ethyl groups relative to the porphyrin skeleton. The energy differences between conformers I–V do not exceed 0.3 kJ mol−1; the conformer VI has relatively high energy. Our investigation has shown that GED is not able to solve the conformational problem of the isolated zinc(II) etioporphyrin molecules. At the same time, this method allows to obtain reliable structural parameters of the macrocycle, as well as to determine the position of the ethyl groups with respect to the porphyrin core. Selected experimental parameters are as follows: r h1(Zn–N) = 2.042 (5) A, r h1(N–Cα) = 1.374 (5) A, r h1(Cα–Cβ) = 1.453 (4) A, r h1(Cα–Cm) = 1.396 (4) A, r h1(Cβ–Cβ) = 1.376(4) A, ∠ZnNCα = 126.8 (2)°, ∠CαNCα = 106.3 (3)°, ∠CαCmCα = 127.0 (4)°.

The molecular structure of copper(II) 2,9,16,23-tetra-tert-butyl phthalocyanine (Cu(pc t )) was investigated by gas-phase electron diffraction with mass spectrometric control of vapor composition. Two conformers of C 4h symmetry and three conformers of C s symmetry are predicted by quantum chemical calculations using the hybrid DFT method UB3LYP with 6-31G* and cc-pVTZ basis sets. According to the relative energies at the temperature of GED experiments (436 °C), the two C 4h symmetric conformers occur in 1.1 and 2.3 % abundance in the gas phase. The highest mole fraction (66.6 %) and lowest R-factor (4.25 %) correspond to one of the C s symmetric conformers; however, the two C 4h symmetric models cannot be disproved by the Hamilton R-factor ratio test. The GED structural data of the three models mentioned reliably confirm approximate local D 4h symmetry of the phthalocyanine ligand core.

Quantum chemical calculations using DFT (B3LYP and PBE0) and MP2 approximations with cc-pVTZ basis sets have been performed for 10 N-oxides with different substituents. The influence of the substituent nature on the geometry and redox properties of the compound, as well as on the parameters of the semipolar N → O bond, has been analyzed. The presence of strong electron-withdrawing substituents on the pyridine ring results in increase in the electron affinity value and, consequently, in the enhancement of the antifungal activity of the compound. The compounds with the electron-donating substituents have greater complexation ability. The main conclusions based on the calculation results are in good agreement with the available experimental data.

Molecular structure of beryllium diiodide, BeI2, was studied by combined gas-phase electron diffraction/mass spectrometry experiment at two temperatures, 501(5) and 722(10) K, and by theoretical calculations. Equilibrium structure of the monomer was found to be linear; thermal-averaged bond distance r g(Be–I) = 2.163(6) and 2.172(7) A was determined for the low- and high-temperature experiment, respectively. Quantum chemical approaches DFT-B3LYP, MP2 and CCSD(T) were applied to calculate the geometric and vibration parameters of monomeric and dimeric Be2X4 (X = F, Cl, Br, I) molecules. Enthalpies of the dimerization processes 2BeX2(g) = Be2X4(g) were estimated on the base of quantum chemical results with the basis set superposition error (BSSE) taken into account and compared with the experimental thermodynamic values.

The gas-phase molecular structure of the magnesium octa(m-trifluoromethylphenyl)porphyrazine (MgC 72 H 32 N 8 F 24 ) has been studied by a synchronous gas-phase electron diffraction and mass spectrometric experiment at T = 667(10) K in combination with DFT calculations using B3LYP hybrid method and triple-ζ valence basis sets. The molecule has an equilibrium structure of D 4 symmetry. The following values of selected internuclear distances have been determined: r h1 , A: r(Mg–N) = 1.979(5), r(N–C) = 1.363(3), r(N mezo –C) = 1.334(4), r(C pyr –C Ph ) = 1.469(3), r(C Ph –CF 3 ) = 1.510(5), r(C–F) = 1.349(3), r(C α –C β ) = 1.466(3), r(C β –C β ) = 1.380(7). A slight (less than 1 to 2 degrees) twisting deformation of the macrocycle from planarity, caused by the presence of the eight bulky PhCF 3 substituents, planes of which are turned by 132.6(9) degrees relative to the adjacent pyrrole rings, has been found. The deviation of phenyl ring planes from 90 degrees orientation is caused by stabilizing donor–acceptor interactions between π-natural orbitals of pyrrole and phenyl moieties. Substitution effects and coordination bonding in magnesium porphyrazine complexes, MgPz, MgPzPh 8 and MgPz(CF 3 Ph) 8 , are discussed. Sensitivity of GED data to long range interatomic distances of large molecules has been shown.

The conformational properties of a dansyl amide molecule (CH3)2N–C10Н6–SO2NH2, which is widely used for fluorescent labeling of compounds, e.g., amino acids or nucleotides and compounds able to form liquid crystals, are studied. It is found that the molecule has six conformers with relative energies 0/0.13, 1.13/1.38, 0.06/0.06, 0.31/0, 2.95/2.70, 0.31/0 (B3LYP/cc-pVTZ and МР2/cc-pVTZ methods respectively). In all conformers the naphthalene core becomes non-planar under the effect of two substituents. The effect of the nature of substituents on the geometric parameters of the conformers is considered. In terms of the NBO analysis a substantial deviation of the S–N bond in the –SO2NH2 substituent from orthogonality and also the asymmetrical position of the –N(СH3)2 group with respect to the naphthalene core are explained. The paths and barriers of conformational transformations of the dansyl amideа molecule are determined. The structure of the (CH3)2N–C10H6–SO2NН–X moiety in the crystals is analyzed and the relationship between the relative energy of the conformers of a free molecule and the probability of the occurrence of their structures in the crystals is determined.

The conformational composition of the vapor ( T = 380(5) K) and the conformer structures of ortho -nitromethylbenzenesulfonate (NO 2 С 6 H 4 SO 2 OCH 3 , 2-NMBS) molecule have been studied by a combined gas-phase electron diffraction and mass spectrometry (GED/MS) method complemented by the results of quantum chemical calculations. According to calculations (MP2/B3LYP, cc-pVTZ), the molecule 2-NMBS possesses six conformers with relative energies Δ Е = 0/0; 0.54/1.08; 0.69/0.89; 0.81/1.77; 1.68/2.22 and 2.94/2.91 kcal/mol. The geometrical parameters (A and degrees) of the prevailing conformer were determined by GED (uncertainties are in parentheses): r h 1 (C C) av = 1.400(5), r h 1 (C S) = 1.781(6), r h 1 (S O) = 1.588(5), r h 1 (S O) av = 1.427(10), r h 1 (C N) = 1.469(15), r h 1 (C O) = 1.487(16), r h 1 (N O) av = 1.236(10), φ (C C S O) = −96(7), φ (C S O C) = 139(9). It is shown that the relative orientation of SO 2 OCH 3 and NO 2 groups in the structure of each of the six conformers is determined by ortho - and cog wheel effects and by anomeric effects inside the SO 2 OCH 3 group. The reliability of the structure estimation of free 2-NMBS molecules on the base of X-ray data is discussed.