Algebraic characterization of bridged polycyclic compounds

An approach based on the topological distance matrix is used for algebraic characterization of bridged polycyclic compounds. The classical bridged structures which have external bridges between cycles were examined together with the more complicated three-dimensional polycyclic systems regarded as containing internal bridges. Thirteen rules are given for characterizing the main types of structural rearrangements in these compounds. The important topological characteristic of (poly)cyclic systems, the molecular cyclicity, is examined in the polycyclic condensed, spiro- and bridged structures, respectively.     

On interference of orbital communications in molecular systems

The atomic orbitals (AO) contributed by bonded atoms of molecular systems emit or receive the “signals” of electronic allocations to these basis functions, thus acting as the signal source (input) or receiver (output), respectively, in the associated communication network. Each orbital simultaneously participates in both the through-space and through-bridge probability propagations: the former involve direct communications between two AO while the latter are realized indirectly via orbital intermediates. This work examines the interference effects of the amplitudes of molecular probability scatterings, and introduces the operator representation of AO communications. The eigenvalue problem of the associated Hermitian operator combining the forward and reverse information propagations defines the stationary modes (“standing” waves) of the molecular propagation of electronic conditional probabilities. The combined effect of interference between the multiple (direct and indirect) information scatterings, which establishes the stationary distribution of electronic probabilities, is probed. The wave-superposition principle for the conditional-probability amplitudes of the generalized through-bridge information propagation is linked to the idempotency relations of the system density matrix. It explicitly demonstrates that the resultant effect of the probability propagations involving bridges containing all basis functions, at arbitrary bridge orders indeed generates the (stationary) molecular distribution of conditional probabilities.     

Quantitative multi-element mapping of ancient glass using a simple and robust LA-ICP-MS rastering procedure in combination with image analysis

The surface of two glass artefacts in mosaic style, probably fragments of conglomerate glass bowls dating back two millennia, was investigated by laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS). By rastering with the laser beam over a selected area of the surface of the glass artefacts, elemental oxide maps were generated. Quantification of the elemental oxides in the maps was achieved using a so-called sum normalization procedure, summating the elements—54 in total—as their oxides to 100% (w/w), without using an internal standard and applying only one external standard (NIST SRM glass 610). This results in a robust mapping procedure which automatically corrects for drift and defocusing issues. Sum normalization was applied to each pixel in the map separately and required a custom source code to process all the data in the tens of thousands of pixels to generate the elemental oxide concentration maps. The digital element maps generated upon rastering of the two glass artefacts are very compelling and are an excellent entry point to gain detailed insight into their fabrication and provenance using image analysis software for retrieval of localized elemental oxide concentrations and correlations.     

Relationship between the structure and thermal properties of 4-n-alkyl-4’-cyanobiphenyls

The relationship between the molecular structure and thermal properties in the homologous series nCB with n = 5–10 is investigated by the Monte Carlo and atom — atomic potential methods by dividing the thermodynamic properties of liquid crystal systems into inter- and intramolecular increments. An explicit even-odd correlation between the intermolecular term of the inner configuration energy U^inter, heat capacity C _v ^inter , and the anisotropy of the geometrical form (Σ/Σ) of nCB molecules is established. It is shown that internal degrees of freedom are responsible to a certain extent for the even-odd effect of some physicochemical properties of nCB. The major contribution to the heat capacity Cy is made by the vibrational motion.     

Raman scattering spectra and molecular conformations of bis(quaternaryammonium bromide)-water systems

The dimeric bis(quaternaryammonium bromide) surfactants, [Br⁻(CH₃)₂N⁺(C _m H_{2 m +1})—(CH₂) _s —(C _m H_{2 m +1})N⁺(CH₃)₂Br⁻, s = 2, 3 and m = 4, 6, 10 and 12, s = 6 and m = 8, 10, 12], have been synthesized and the phase maps of the sm6-8-water, sm6-10-water and sm6-12-water binary systems have been determined (sm6-8 implies s = 6, m = 8). In order to examine the molecular structures of these solid samples and of their dimeric surfactant-water binary systems, Raman spectra of the simple dimeric surfactants, sm2-4 and sm3-4, in which crystal structures of the trans- and cis-type conformations have been determined by single-crystal X-ray diffraction analysis, have been investigated, and Raman bands characteristic of these skeletal structures were found in the skeletal deformation region. On the basis of these characteristic Raman bands for the two conformations, it has been concluded that the dimeric surfactants, sm6-8, sm6-10 and sm6-12 also take up a cis-type conformation in the crystalline state. Furthermore, it has been found that the Raman bands in the C—H stretching, skeletal stretching and CH₂ scissoring regions are sensitive to phase structure. Received: 21 July 1998 Accepted in revised form: 9 November 1998     

Structural characterization and prediction of Kovats retention indices (RI) for alkylbenzene compounds

A new molecular structural characterization (MSC) method called the molecular vertex eigenvalue correlative index (MVECI) is constructed and used to describe the structures of 122 alkylbenzene compounds. Through multiple linear regression (MLR) and stepwise multiple regression (SMR), a quantitative structure-retention relationship (QSRR) model with correlation coefficient (R) of 0.995 is obtained. Through partial least-square regression (PLS), another QSRR model with correlation coefficient (R) of 0.991 is obtained. The estimation stability and prediction ability of the two models are strictly analyzed by both internal and external validations. For the internal validation, the cross-validation (CV) correlation coefficients (R _CV) of the two models are 0.993 and 0.988. For the external validation, the correlation coefficients (R _test) of the two models are 0.996 and 0.995, respectively. The results show that the stability and predictability of the models are good, and the molecular vertex eigenvalue correlative index can successfully describe the structures of alkylbenzene compounds.     

Structural studies of 3-chloro-N-(8′-quinolyl)×benzo[b]thiophene-2-carboxamide

3-Chloro-N-(8′-quinolyl)benzo[b]thiophene-2-carboxamide was synthesized from 3-chlorobenzo[b] thiophene -2-carboxyl chloride and 8-aminoquinoline in the presence of triethylamine. The single crystal X-ray structure determination confirmed the earlier proposed structure and also characterized by ¹HNMR, and Mass spectroscopy. Crystallographic study reveals that the structure crystallizes in monoclinic system, a = 14.878(4) ?, b = 8.4292(15) ?, c = 25.461(7) ?, β = 112.022(18)°, Z = 8, V = 2960.20(12) ?³ with space group C2/c (No. 15). In the structure packing, three kinds of interactions are responsible for the stability of the structure. Infinite two-dimensional stair-like layered chains are formed by relatively strong intermolecular hydrogen bonds [C14—H14...O1]. These parallel chains are connected by several π—π and CH—π interactions, alternatively. There are two such parallel chains with 70.53°, which are in contact by van der Waals interactions.     

Photochemical generation of triplet—triplet nitrene pairs in aromatic diazide crystals

The molecular and crystal structures of 4-amino-2,6-diazido-3,5-dichloropyridine and 6-amino-2,4-diazido-1,3,5-triazine, as well as the paramagnetic photolysis products of their crystals at 77 K, were studied using X-ray diffraction analysis and ESR spectroscopy. Triplet nitrenes generated during the photolysis of diazidopyridine form triplet—triplet nitrene pairs, whose ESR spectrum corresponds to the quintet spin state. The high-spin state (S = 2) results from the exchange interaction between two triplet molecules with the zero-field splitting parameters |D| = 1.0280 cm⁻¹ and |E| = 0.0038 cm⁻¹ and the γ angle between two C—N nitrene bonds equal to 133°. This angle is close to an angle of 136.2° between the C-N bonds of two adjacent molecules in the crystal structure. No formation of the triplet—triplet nitrene pairs is observed during the photolysis of crystalline diazidotriazine, whose molecules lie in the parallel planes. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 513–520, March, 2008.     

Crystal structure, spectroscopic and magnetic properties, and antimicrobial activities of cobalt(II) 2-methylthionicotinate complexes with N-heterocyclic ligands

Synthesis and characterization of 10 new 2-methylthionicotinate (2-MeSnic) Co(II) complexes, namely, [Co(2-MeSnic)₂L₂(H₂O)₂] · nH₂O (L is N,N-diethylnicotinamide—Et₂nia, ethylnicotinate—Etnic, nicotinamide—nia, isonicotinamide—isonia, N-methylnicotinamide—N-Menia, furo[3,2-c]pyridine—fpy, 2,3-dimethylfuro[3,2-c]pyridine—Me₂fpy or benzo[4,5]furo[3,2-c]pyridine—Bfp; n is 0, 1 or 2) as well as [Co(2-MeSnic)₂L₂] (L is ronicol—ron or 2-methylfuro[3,2-c]pyridine—Mefpy), are reported. The characterizations were based on physico-chemical and spectroscopic methods. The crystal structure of one of the complexes has been determined. In the molecular complex [Co(2-MeSnic)₂(Me₂fpy)₂(H₂O)₂], the Co(II) central atom, located at a symmetry centre, is octahedrally coordinated by an oxygen atom of the unidentate 2-MeSnic carboxyl group, the nitrogen atom of the pyridine ring of Me₂fpy, a water molecule and the corresponding centrosymmetrically located atoms. Also, biological activity of the complexes against various strains of bacteria and filamentous fungi has been investigated. It is concluded that by complexation of these nicotinate derivatives their biological activities are elevated. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Thermal,physicochemical and microstructural studies of binary organic eutectic systems

Solid–liquid phase equilibrium data of three binary organic systems, namely, 3-hydroxybenzaldehyde (HB)—4-bromo-2-nitroanilne (BNA), benzoin (BN)—resorcinol (RC) and urea (U)—1,3-dinitrobenzene (DNB), were studied by the thaw–melt method. While the former two systems show the formation of simple eutectic, the third system shows the formation of a monotectic and a eutectic with a large immiscibility region where two immiscible liquid phases are in equilibrium with a liquid of single phase. Growth kinetics of the pure components, the monotectic and the eutectics, studied by measuring the rate of movement (v) of solid–liquid interface in a thin U-tube at different undercoolings (ΔT) suggests the applicability of the Hillig–Turnbull’s equation: v = u (ΔT) ⁿ , where v and n are the constants depending on the nature of the materials involved. The thermal properties of materials such as heat of mixing, entropy of fusion, roughness parameter, interfacial energy, and excess thermodynamic functions were computed from the enthalpy of fusion values, determined by differential scanning calorimeter (Mettler DSC-4000) system. The role of solid–liquid interfacial energy on morphologic change of monotectic growth has also been discussed. The microstructures of monotectic and eutectics were taken which showed lamellar and federal features.     

Determination of the adsorption volume and surface of carbon adsorbents with developed mesoporosity

The isotherms of excess adsorption of CH₄ (atP=0.001–160 MPa), SF₆ (atP=0.001–2.4 MPa), and C₆H₆ (atP=0.0001–0.1 MPa) on carbon adsorbents—microporous carbons CMS and FAS with developed mesoporosity and graphitized soot—were measured in the 298–408 K temperature region. Calculation of the isotherms of absolute adsorption of the total content of these substances requires knowledge of the adsorption volume, which was determined by different methods: by the Dubinin—Radushkevich equation; by the experimental isotherm of excess adsorption and the equation of absolute adsorption; by the method using the intersection of nonlinear isosteres of excess adsorption and isosteres of absolute adsorption; by the comparative plot of values of the excess C₆H₆ adsorption Γ_FAS—Γ_soor; by the method using the difference of molecular radii of adsorptives and the surface of the specific adsorbent; and by the calculation of the adsorption layer thickness using the FHH equation for mesoporous systems. The results of determination of the adsorption volume for microporous systems of these carbons agree well with each other and with the passport data for the adsorbents. Analysis of the results revealed the peculiarity of the sulfur hexafluoride adsorption related to the formation of associates on the surface of the carbon adsorbents. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 4, pp. 688–696, April, 2000.     

Supramolecular catalytic systems based on anionic amphiphiles and polyethyleneimine for hydrolytic cleavage of phosphorus ester bonds

Self-organization in individual and binary systems based on polyethyleneimine (PEI) and amphiphilic sulfonatocalix[4]resorcinarene was studied by conductometry, tensiometry, dynamic light scattering, and ¹H NMR spectroscopy. The critical concentrations of micelle formation and aggregate sizes were determined. The enhancement of the catalytic effect on the hydrolysis of O-ethyl O-p-nitrophenyl chloromethylphosphonate was shown in the following series of the systems: PEI-water < PEI—calixarene-water < PEI—calixarene—La^III—water. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 366–373, February, 2008.     

Hidden rearrangement processes in short-lived negative molecular ions

The study of resonant electron capture by nitrobenzene molecules showed that some fragmentary negative ions are unstable toward electron autodetachment. The measured appearance energy of the neutral component of an [M — H]⁻ ion beam does not agree with the energetics of direct dissociation in a molecular ion. The estimation calculations show that the low appearance energy of [M — H]⁰ neutral components is caused by isomerization of a molecular ion of nitrobenzene to the 2-nitrobenzene structure followed by the formation of a phenoxide ion in the autodetachment state. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 367–370, February, 2006.     

The equivalence of bond-energy schemes and the determination of resonance energies

 It is argued that the preservation of algebraic equivalence between the Allen and Laidler bond-energy schemes for nonconjugated alkenes logically determines that the Allen scheme should apply to a classical structure of a conjugated hydrocarbon exactly as it stands, i.e. no additional parameters are needed. Extending the requirement of equivalence to conjugated alkenes implies that, in the Laidler scheme, the bond energy of the pure single CC bond in a conjugated system is a combination of the bond-energies of the semiconjugated and normal CC single bonds: E(C_d—C_d)=2E(C_d—C)−E(C—C). This result is a deduction and is not an independent hypothesis. The equivalence of the two schemes for conjugated hydrocarbons is demonstrated numerically, by calculating the resonance energies of some selected molecules by both methods. Received: 5 December 1999 / Accepted: 5 March 2000 / Published online: 5 June 2000     

Supramolecular systems of amphiphilic derivatives of calix[4]resorcinarenes and surfactants in chloroform

Aggregation of amphiphilic calix[4]resorcinarenes (CRA) modified by carboxymethyl (1), 2-hydroxyethyl (2), methylamino acetal (3), and aminomethyl (4) fragments and their interaction with some synthetic (5, 6) and natural (7, 8) surfactants in the low-polarity solvent (chloroform) were studied by permittivity measurements and FT-IR spectroscopy. Compounds 1–4 and surfactants form aggregates at critical micelle concentrations (CMC) of 2.0·10⁻⁵–7.5·10⁻⁵ and 1.7·10⁻⁵–2.0·10⁻³ mol L⁻¹, respectively. The CMC values of CRA—surfactant mixed aggregates depend on the surfactant structure and the structure and concentration of CRA. Analysis of the IR spectra of solutions of a series of amphiphilic CRA (2–4, 9, 10) and their mixtures with the cationic surfactant N-cetyl-N,N-dimethyl-N-(2-hydroxyethyl)ammonium bromide (5) showed that an increase in the concentration of the solutions in individual and mixed systems is accompanied by a decrease in the molar integral intensities and intensities in the maxima of the absorption bands of the O—H and C—H bonds down to the CMC point, after which these values change slightly. The discovered effect, which is differently pronounced for all systems studied, indicates that both the polar “head” groups and nonpolar fragments of CRA and surfactant are involved in the formation of supramolecules of the reverse micelle type in all cases. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 459–466, March, 2007.     

Sensitive and specific liquid chromatography-tandem mass spectrometry method for assay of fluoxetine and its metabolite norfluoxetine in human plasma and application of method to pharmacokinetic analysis

A simple, specific and sensitive high-performance liquid chromatography — electrospray tandem mass spectrometry method is developed for the simultaneous determination of fluoxetine and its metabolite norfluoxetine in human plasma. Plasma samples were simply treated with acetonitrile to precipitate and remove proteins and the isolated supernatants were directly injected into the high-performance liquid chromatography — electrospray tandem mass spectrometry system. Chromatographic separation of the analytes was achieved on a Discovery C₁₈ (100 × 2.1 mm I.D., particle size 3.0 μm) column using 0.1% formic acid in water — acetonitrile (40: 60) as mobile phase with a flow rate of 0.2 mL/min. Diazepam was used as the internal standard. The compounds were ionized in the electrospray ionization source of the mass spectrometer and were detected by selected reaction ion monitoring of the transitions of m/z 310 → m/z 44.3 for fluoxetine, m/z 296 → m/z 134 for norfluoxetine and m/z 285 → m/z 193 for the internal standard. The method has low limit of detection (LOD) of 0.02 ng/mL and 0.03 ng/mL for fluoxetine and norfluoxetine, respectively. The inter- and intra-run precision was measured to be below 5.3% (relative standard deviation) for both fluoxetine and norfluoxetine. The developed method was successfully used to investigate plasma concentrations of fluoxetine and norfluoxetine in the pharmacokinetic study of Chinese volunteers who received fluoxetine orally.     

Direct determination of the primary binding site of cisplatin on cytochrome c by mass spectrometry

Protein—cisplatin interactions lie at the heart of both the effectiveness of cisplatin as a therapeutic agent and side effects associated with cisplatin treatment. Because a greater understanding of the protein—cisplatin interactions at the molecular level can inform the design of cisplatin-like agents for future use, mass spectrometric determination of the binding site of cisplatin on a model protein, cytochrome c, was undertaken in this paper. The monoadduct cytochrome c—Pt(NH₃)₂(H₂O) is found to be the primary adduct produced by the cytochrome c—cisplatin interactions under native conditions. To locate the primary binding site of cisplatin, both free cytochrome c and the cytochrome c adducts underwent trypsin digestion, followed by Fourier transform mass spectrometry (FT-MS) to identify unique fragments in the adduct digest. Four such fragments were found in the adduct digest. Tandem mass spectrometry (MS/MS and MS³ indicates that two fragments are Pt(NH₃)₂(H₂O) bound peptides (Gly56-Glu104 and Asn54-Glu104) with one water associated at the peptide bond Lys79∼Met80, and the other two fragments are heme containing peptides (acety1-Gly1-Lys53 and acety1-Gly1-Lys55). The product-ion spectra of the four fragments reveal that Met65 is the primary binding site of cisplatin on cytochrome c.     

Dimerization and Coordination Properties of Zinc(II)tetra-4-alkoxybenzoyloxiphthalocyanine in Relation to DABCO in <Emphasis Type="Italic">o</Emphasis>-Xylene and Chloroform

For the first time the interactions between zinc(II)tetra-4-alkoxybenzoyloxiphthalocyanine (Zn(4—O—CO—C₆H₄—OC₁₁H₂₃)Pc) and 1,4-diazabicyclo[2.2.2]octane (DABCO) in o-xylene and chloroform have been studied by calorimetric titration and NMR and electron absorption spectroscopic methods. It has been found that in o-xylene at concentrations of Zn(4—O—CO—C₆H₄—OC₁₁H₂₃)Pc higher than 6×10⁻⁴ mol⋅L⁻¹ π–π dimers species are formed (λ _max= 685 nm). Additions of DABCO to the solution up to mole ratio 1 : 8 (Zn(4—O—CO—C₆H₄—OC₁₁H₂₃)Pc : DABCO) lead to a shift of the aggregation equilibrium towards monomer species due to formation of monoligand axial complexes. Further increasing the DABCO concentration results in formation of Zn(4—O—CO—C₆H₄—OC₁₁H₂₃)Pc—DABCO—Zn(4—O—CO—C₆H₄—OC₁₁H₂₃)Pc sandwich dimers (λ _max= 675 nm).