Stereoselective preparation of mono- and bis-derivatives of pentacyclo[6.3.0.02,6.03,10.05,9] undecane (D 3-trishomocubane)

The rearrangement of easily accessible Cookson’s diketone with chlorosulfonic acid in chloroform followed by the acidic hydrolysis gave 6-chloro-7-hydroxy-dichloropentacyclo[6.3.0.0^2,6.0^3,10.0^5,9]undecane-4-one, whose syn-stereochemistry was assigned through the X-ray crystal structure analysis. This key structure was used for the stereoselective synthesis of the D ₃-trishomocubane derivatives as well as for the preparation of potential drugs bearing hydroxy- and amino-functional groups. A new multigram preparative synthesis of D ₃-trishomocubane was developed.      

Thermodynamic transfer functions for urea and thiourea from water to water-tetrahydrofuran mixtures from precise vapor-pressure measurements

The rate of change of the standard chemical potential with solvent composition, \(\partial \bar G_0 /\partial Z\) , has been calculated from precise vapor-pressure measurements for urea at three temperatures and for thiourea at 298.15°K in water-tetrahydrofuran (THF) mixtures. From these results the standard free energy of transfer ΔG _t ^o of the solutes from water to various water-THF mixtures has been obtained together with the standard molar entropy ΔS _t ^o and the standard molar enthalpy ΔH _t ^o of transfer at 298.15°K in the case of urea. The quantity ΔG _t ^o for urea is negative in the water-rich region and positive for mole fractions THF>0.2. There is a nearly complete compensation between ΔH _t ^o andTΔS _t ^o at 298.15°K up to mole fraction THF=0.5. These phenomena can be partly related to the structure in H₂O-THF mixtures.     

Dynamic solvation effects on surface-impact dissociation of I 2 - (CO2)n

Surface-impact dissociation of I ₂ ^- (CO₂)n was studied by a molecular dynamics simulation in comparison with the experimental results. The branching fraction, ? _dis, of the I ₂ ^- dissociation was calculated as a function of the parent cluster size, n. This computational result reproduces the experimental one. We calculated a number of the I ₂ ^- dissociation events starting from given initial orientations. The most favorable molecular orientation obtained supports the wedge effect in which a CO₂ molecule located at the waist position of the I ₂ ^- core ion splits the I ₂ ^- bond as if a piece of wood is split by a mechanical thrust against a wedge. The time profile of the wedge action calculated for the I ₂ ^- (CO₂) impact shows that more than 20 % of the collision energy is converted to the vibrational energy of the I ₂ ^- .     

The first synthesis of 3-deoxyoripavine and its utilization in the preparation of 10-deoxyaporphines and cyprodime

The synthesis of 3-deoxyoripavine (7) was realized as a novel and promising intermediate towards the synthesis of the important class of dopaminergic and/or serotonergic 10-deoxyaporphines and the special pharmacological tool µ opioid antagonist cyprodime. Generally, the preparation of these valuable biologically active compounds was achieved in remarkable yields.      

Organoruthenium(II) thiosemicarbazone complexes: synthesis, spectral characterization, DNA binding and DNA cleavage studies

A series of new ruthenium(II) complexes were synthesized with Schiff bases derived from salicylaldehyde / o-hydroxyacetophenone/ o-vanillin / 2-hydroxy-1-naphthaldehyde with thiosemicarbazide and acetyl furan. They are characterized by elemental analysis, IR, electronic, ¹H NMR, ¹³C NMR and mass spectral studies. The elemental analysis suggests the stoichiometry to be 1:1 (metal:ligand). Four of these complexes were tested for its binding with CT-DNA using absorption spectroscopic studies and two of these complexes exhibit efficient DNA cleavage activity.      

Extraction of gold(III) by sulfur-containing calix[4,6]arenes from hydrochloric acid solutions

Thiacalixarenes 1 and 2, thiacalixarene thioether 5, and calixarene thioethers 3a–3c, 4a, and 4b are compared with respect to gold(III) extraction from hydrochloric acid solutions. The gold extractability increases in the following order: 1,2 5 3a–3c, 4a, 4b. The effect of the substituents at the sulfur atom in R₂S and in 3a–3c, 4a, and 4b is identical when cooperative effects (CE) appear for calixarene thioethers. On the basis of the extraction stoichiometry and the activities of the components of the aqueous phase, the gold distribution in the form of (AuCl₃)_nL (n = 1?4) species is quantified for c_HCl from 0.5 to 6 mol/L. A correlation is found between the gold distribution constants into various diluents and the Kamlet-Taft parameter π*.     

Experimental and theoretical evidence suggests carbamate intermediates play a key role in CO2 sequestration catalysed by sterically hindered amines

The chemisorption of CO₂ by aqueous-hindered amines has been investigated experimentally and theoretically. Negative-ion ESI–MS analysis of solutions containing a sterically hindered amine and a source of ¹³CO₂ reveals peaks corresponding to [M–H + 45]^?. These ions readily lose 45 Da when subjected to collisional activation, and together with other key fragments confirms the generation of the ¹³C-labelled carbamate derivatives. The thermochemistry of the two key capture reactions: $$2.{\text{amine }} + {\text{ CO}}_{ 2} { \leftrightarrows }{\text{amine}} - {\text{CO}}_{ 2}^{ - } + {\text{ amine}} - {\text{H}}^{ + } {\kern 1pt} \quad 1:{\text{carbam}}$$ $${\text{amine }} + {\text{ CO}}_{ 2} + {\text{ H}}_{ 2} {\text{O}}{ \leftrightarrows }{\text{HCO}}_{ 3}^{ - } + {\text{ amine}} - {\text{H}}^{ + } \quad 2:{\text{ bicarb}}$$ at 298 K was modelled using composite chemistry methods, CCSD(T), DFT, and SM8 free energies of solvation. The aqueous reaction free energies (ΔG ₂₉₈) for reaction 1 are predicted to be more negative than ΔG ₂₉₈ for reaction 2 when amine = ammonia, 2-aminoethanol (MEA), 2-amino-2-methyl-1-propanol (AMP), 2-amino-2-hydroxymethyl-propane-1,3-diol (tris), and 2-piperidinemethanol (2-PM). For AMP, tris, and 2-PM, activation free energies ΔG ₂₉₈ ^? for reaction 1 (SM8 + CCSD(T)/6-311 ++G(d,p)//M08-HX/MG3S: 38–67 kJ mol^?1) are smaller than the corresponding values for 2 (109–113 kJ mol^?1). For 2-PM, the computed carbamate ΔG ₂₉₈ ^? (38 kJ mol^?1) is comparable to the MEA value (45 kJ mol^?1), whereas the primary amines with tertiary alpha carbons have slightly larger values (60–70 kJ mol^?1). The organic amine values are much lower than the value for ammonia (93 kJ mol^?1). The results indicate CO₂ chemisorption proceeds via a carbamate intermediate for all aqueous primary and secondary amines. Hindered carbamates are susceptible to further chemical transformations following their formation.     

Synthesis and spectral characterization of stannocanes of the type [O(CH2CH2S)2SnR2](R=Me1,Bun2,Ph3)

The stannocanes of the type [O(CH₂CH₂S)₂SnR₂](R=Me1,Buⁿ 2,Ph3) have been synthesized in an improved method by the reaction of R₂SnCl₂ with 2, 2′-oxydiethanethiol O(CH₂CH₂SH)₂ in molar ratio of 1:1 at the presence of sodium ethoxide in anhydrous ethanol. The reactions are carried out under inert atmosphere. These compounds have been extensively characterized by FT-IR, UV-Vis spectrophotometry, multi-nuclear (¹H, ¹³C, ¹¹⁹Sn) NMR, elemental analysis and mass spectrometry. The obtained data clearly indicates that, there is a strong interaction between oxygen atom of the ligand as a donor and Sn atom of the organotin species as a Lewis acid acceptor. Therefore, the resulted dithiostannocanes possess a transannular secondary bonding and hypervalency at the central Sn atom which leads to an increase in the coordination number of tin from four to five-coordinated tin.      

Aerobic oxidation of cumene catalysed by 4-alkyloxycarbonyl-N-hydroxyphthalimide

4-Hexyloxycarbonyl-, 4-dodecyloxycarbonyl- and 4-hexadecyloxycarbonyl-N-hydroxyphthalimides were synthesised using trimellitic anhydride chloride as the starting material. The obtained lipophilic derivatives of N-hydroxyphthalimide were applied as catalysts of the cumene oxidation reaction with oxygen performed in polar acetonitrile, in non-polar tert-butylbenzene and in the absence of a solvent. The courses of reactions catalysed by N-hydroxyphthalimide and its derivatives were compared.      

Enthalpy of formation of wulfenite (natural lead molybdate)

A thermochemical study of wulfenite, i.e., natural lead molybdate PbMoO₄ (Kyzyl-Espe field deposit, Central Kazakhstan), is performed on a Setaram high-temperature heat-flux Tian-Calvet microcalorimeter (France). Enthalpies of the formation of wulfenite from oxides Δ_f H _ox ^o (298.15 K) = ?88.5 ± 4.3 kJ/mol and simple substances Δ_f H°(298.15 K) = ?1051.2 ± 4.3 kJ/mol were determined by means of melt calorimetry. The Δ_f G°(298.15 K) of wulfenite corresponding to ?949.1 ± 4.3 kJ/mol was calculated using data obtained earlier for S°(298.15 K) = 161.5 ± 0.27 J/(K mol).     

Complexation of nickel (II) ion with B3 vitamin in aqueous dimethyl sulfoxide

The stability change of nickel(II) ion complexes including one and two nicotinamide (B₃ vitamin) molecules in aqueous dimethyl sulfoxide (X_DMSO = 0–0.85 m.f.) was studied at 298.2±0.1 K and 0.25 ionic strength value (NaClO₄) using the potentiometric method. The first stage constant of complexation increased until organic solvent concentration was 0.5 m.f. and reduced at higher DMSO content. The difference between complex and central ions solvation is a dominating contribution into the Gibbs energy change of mononicotinamide complex formation reaction. When the second ligand molecule was bonded into the coordination compound, the nicotinamide contribution to Δ_trG_r rose and became prevailing at X_DMSO = 0.7–0.85. The ligand was found to replace a water molecule in the coordination sphere of the cation according to spectrophotometric study results.      

Effect of feedback inhibition on the behavior of multienzyme monolinear reaction chains

The multiplicity characteristics of the simple two-enzyme reaction chain are investigated numerically for simple lumped and distributed reaction systems. The quasisteady state response of the concentration within each of the two systems to changes in environmental concentration is generated for a range of kinetic parameters. The effect of product inhibition in suppressing the region of multiple steady-state behavior is followed quantitatively.     

Ionization of aqueous benzoic acid: Conductance and thermodynamics

Molar conductances of dilute aqueous benzoic acid solutions are presented for temperatures from 5 to 80°C. The data have been analyzed to give acid dissociation constants as well as ΔH ^o, ΔS ^o, and ΔC _p ^o for the ionization process and the limiting conductance of the benzoate ion. The conductance-viscosity product changes less than 4% over the temperature range, indicating that the interaction of the benzoate ion with the solvent changes little if at all with increasing temperature. The pK _a(m) vs.T data show that ΔH ^o decreases quadratically while ΔC _p ^o increases linearly withT although, over the 75°C range, ΔC _p ^o increases only about 6 cal-mole^?1 deg^?1 around an average of ?37 cal-mole^?1deg^?1. The acid dissociation constants as derived from the conductance-molal concentration analysis show an average uncertainty of about 0.1% and are fitted to within about 0.01% by the equation $$p{\text{K}}_{\text{a}} (m) = - 75.5422 + 3136.34/T + 28.7965 log T - 6.8139 {\text{x}} 10^{ - 3{\text{T}}} $$ whereT is the absolute temperature.     

The nature and the mechanism of ion transfer in tungstates Me2+{WO4} (Ca, Sr, Ba) and Me 2 3+ {WO4}3 (Al, Sc, In) according to the data acquired by the tubandt method

The Tubandt method of electrolysis is used for studying the nature of ionic carriers in ceramics of tungstates Me²⁺{WO₄} (Ca, Sr, Ba) and Me ₂ ³⁺ {WO₄}₃ (Al, Sc, In) which are solid electrolytes. These compounds have the salt-like islet structure with isolated tetrahedrons {WO ₄ ^2? } and are crystallized in the allied structural types of scheelite (CaWO₄) for Me²⁺ and Sc tungstate (Sc₂{WO₄}₃) for Me³⁺. The electrolysis is carried out in 2- or 3-section cells (?)Pt|M ₂ ^n/n+ {WO₄}|Me ₂ ^n/n+ {WO₄}|Pt(+) in air atmosphere at the temperature of ～900°C and cell voltage of 4 and 300 V. All experiments without exception demonstrate a decrease in the mass of the cathodic section of cells. This points to the negative charge of ionic mass carriers and their transfer towards the Pt⁽⁺⁾ electrode. The cathodic briquette mass loss Δm ^(?) depends linearly on the charge passed through a cell. In all experiments with MeWO₄ tungstates, the anodic disk mass remains constant. The electrolysis of Me₂(WO₄)₃ cells is always accompanied by an increase in the anolyte mass Δm ⁽⁺⁾; however, in all experiments, Δm ^(?) > Δm ⁽⁺⁾. All data on mass variation and the results of studying the composition of nearelectrode electrolyte layers by XRD and SEM methods correspond to the condition $t_{WO_4^{2 - } } > t_C $ (C is the cation), i.e., {WO ₄ ^2? } anions pertain to the major ionic carriers. The transport number $t_{WO_4^{2 - } } $ is calculated based on the Faraday law from Δm ^(?). It is shown that the second ionic carrier with the mobility even higher than that of {WO ₄ ^2? } is the O^2? ion. For middle values of transport numbers, their ratio is shown to be $t_{O^{2 - } } $ (0.5–0.8) > (0.2–0.5) $t_{WO_4^{2 - } } $ . No results that would confirm the involvement of Me²⁺ and Me³⁺ ions in conduction are obtained.     

Features of the Diels-Alder reaction between 9,10-diphenylanthracene and 4-phenyl-1,2,4-triazoline-3,5-dione

The Diels-Alder reaction between substituted anthracenes 1a?1j and 4-phenyl-1,2,4-triazoline-3,5 (2) is studied. In all cases except one, the reaction proceeds on the most active 9,10-atoms of substituted anthracenes. The orthogonality of the two phenyl groups at the 9,10-position of diene 1a is found to shield 9,10-reactive centers. No dienophiles with C=C bonds are shown to participate in the Diels-Alder reaction with 1a; however, the reaction 1a + 2 proceeds with the very active dienophile 2,4-phenyl-1,2,4-triazoline-3,5-dione. It is shown that attachment occurs on the less active but sterically accessible 1,4-reactive center of diene 1a. The structure of adduct 3a is proved by ¹H and ¹³C NMR spectroscopy and X-ray diffraction analysis. The following parameters are obtained for reaction 1a + 2 ? 3a in toluene at 25°C: K _eq = 2120 M^?1, ΔH _f ^≠ = 58.6 kJ/mol, ΔS _f ^≠ = ?97 J/(mol K), ΔV _f ^≠ = ?17.2 cm³/mol, ΔH _b ^≠ = 108.8 kJ/mol, ΔS _b ^≠ = 7.3 J/(mol K), ΔV _b ^≠ = ?0.8 cm³/mol, ΔH _r-n = ?50.2 kJ/mol, ΔS _r-n = ?104.3 J/(mol K), ΔV _r-n = ?15.6 cm³/mol. It is concluded that the values of equilibrium constants of the reactions 1a?1j + 2 ? 3a?3j vary within 4 × 10¹?10¹¹ M^?1.     

Thermochemistry of aqueous solutions of nucleic acid bases and their alkylated derivatives

Enthalpy of solution, ΔH _sol ^o , enthalpy of sublimation, ΔH _subl ^o , apparent partial molar volume and heat capacities,V ₂ ^o andC _p,2 ^o were determined for aqueous solutions of thirty alkylated derivatives of uracyl and adenine, eight derivatives of cytosine and guanine. Calculated accessible surface areas and molar volumes are presented, too. The values of enthalpy of solution, enthalpy of sublimation can be useful in the studies on the nature of interaction between these compounds and water molecules. Apparent partial molar volume and heat capacity give a new aspect on hydrophob properties of the examined nucleic acid base derivatives.     

Stability of 3<Emphasis Type="Italic">d</Emphasis>-element cyclotetraphosphates in water

The hydrolysis kinetics of the anion in 3d-element cyclotetraphosphates is considered. The thermodynamic functions of formation (Δ _f H ⁰, Δ _f G ⁰, and Δ _f ? _at ⁰ ) of the cyclotetraphosphates are calculated using the ion increment method. A linear correlation is established between and log K Δ _f ? _at ⁰ for these compounds.     

Polymer conjugates with potential biological activity based on new derivatives of 2-mercaptobenzoxazole-synthesis and characterization

New potentially biologically active compounds derived from 2-mercapto-benzoxazole were synthesized and coupled on polymeric support of poly (maleic anhydride-alt-vinyl acetate) for the preparation of polymer-drug conjugates with controlled drug release. All compounds were characterized by elemental and spectroscopy (FT-IR, ¹H-NMR) analysis. The toxicological tests recommend the products for further laboratory screening.      

Regio- and stereoselectivity of polar [2+3] cycloaddition reactions between (Z)-C-(3,4,5-trimethoxyphenyl)-N-methylnitrone and selected (E)-2-substituted nitroethenes

[2+3] Cycloaddition reactions of the highly reactive (Z)-C-(3,4,5-trimethoxyphenyl)-N-methylnitrone with (E)-2-R-nitroethenes proceed under mild conditions and yield mixtures of stereoisomeric 2-methyl-3-(3,4,5-trimethoxyphenyl)-4-nitro-5-R-isoxazolidines. The effect of regiospecificity of the cycloadditions may be accounted for by the theory of electrophilicity indexes. Stereoselectivity, however, is determined by a compilation of steric and secondary orbital effects.