Polyhedral boron nitride molecules

The geometrical and electronic structures of two isomers (1 and2) of the polyhedral boron nitride molecule, B₁₂N₁₂, have been calculated using the MNDO method. Structure1 having the form of a truncated octahedron is more energetically preferable (ΔH _f ⁰=−128 kcal mol⁻¹) than isomer2, which hasC _6v symmetry. The equilibrium geometries of the N₆B₆(CH₂)₆ isomers (3 and4), which simulate fragments of structure2, have been calculated. The stabilization mechanism of the N₆ nitrogen cluster (hexaazabenzene) in polyhedral structures is discussed. The parameters calculated for molecules1 and2 have been correlated with the corresponding characteristics of their carbon analogs. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1712–1714, October, 1993.     

Preparation and Characterization of 61,6n-DI-O-(α-D-Galactopyranosyl)Cyclomaltooctaoses

ABSTRACT

Four positional isomers of 6¹,6ⁿ-di-O-(D-galactopyranosyl)cyclomaltooctaoses (cG₈s, γ-cyclodextrins) (n = 2?5) were chemically synthesized using the trichloroacetimidate method. The desired compounds having two α-(1→6)-linkages were isolated from a mixture of configurational isomers by HPLC, and their structures were confirmed by ¹³C NMR spectroscopy and FAB-high resolution mass spectra (HRMS). The elution behavior of their four positional isomers on an ODS column by HPLC is discussed.     

Potentiometric discrimination of organic amines by liquid membrane electrodes based on a long alkyl chain derivative of β-cyclodextrin

A long alkyl chain derivative of -cyclodextrin (6^A,6^B,6^C,6^D,6^E,6^F,6^G-hepta-S-dodecyl-6^A, 6^B,6^C,6^D,6^E,6^F,6^G-heptathio--cyclodextrin tetradecaacetate) was examined as a new type of sensory element of an ion-selective electrode for organic amines. Poly(vinyl chloride) (PVC) matrix liquid membrane electrodes based on this host were prepared by using several membrane solvents, among which 2-fluoro-2-nitrodiphenyl ether (FNDPE) was found to be by far most effective for potentiometric responses by the cyclodextrin host. Guest-induced potential changes were examined at pH 5.0 for several groups of protonated organic amine guests having different types of nonpolar moieties. The magnitude of the guest-induced potential change was in the order of 2-phenylethylamine > 1-adamantanamine > benzylamine > cyclohexanamine > dopamine. Potentiometric discrimination was also observed for the positional isomers of di- and trimethoxybenzylamines, though the discrimination between the isomers of monomethoxybenzylamines was negligible. These potentiometric selectivities were quite different from those for a liquid membrane electrode containing no particular sensory element. No appreciable effect was observed by addition of potassium tetrakis(p-chlorophenyl)borate as a fixed anionic site. Such a characteristic feature of this cyclodextrin-based liquid membrane electrode was explained in terms of the availability of an inclusion complex between the cyclodextrin host and each guest in a geometry that would be stable at the membrane surface.Presented in part at the IUPAC 2nd International Symposium on Bioorganic Chemistry, Fukuoka, Japan, June 6–10, 1993. Abstracts, p. 239     

Carbon-carbon double bond in pillar[5]arene cavity: Selective binding of cis/trans-olefin isomers

The binding behavior of pillar[5]arenes (P5As) towards a series of olefin guests ((E)-1,4-dichlorobut-2-ene (1E), (Z)-1,4-dichlorobut-2-ene (1Z), (E)-but-2-ene-1,4-diol (2E), and (Z)-but-2-ene-1,4-diol (2Z), as well as an alkyne derivative 1,4-dichlorobut-2-yne (3)) have been studied in organic solution. P5As exhibit considerable selectivities for the trans-olefin isomers (1E and 2E) over their cis-isomers (1Z and 2Z). The cis/trans-selective interactions hold the potential of utilizing P5As to separate olefin isomers.     

Subtle Modification of Imine-linked Helical Receptors to Significantly Alter their Binding Affinities and Selectivities for Chiral Guests

Aromatic helical receptors P- 1 and P- 2 were slightly modified by aerobic oxidation to afford new receptors P- 7 and P- 8 with right-handed helical cavities. This subtle modification induced significant changes in the binding properties for chiral guests. Specifically, P- 1 was reported to bind d -tartaric acid (K_a=35500 M⁻¹), used as a template, much strongly than l -tartaric acid (326 M⁻¹). In contrast, its modified receptor P- 7 exhibited significantly reduced affinities for d -tartaric acid (3600 M⁻¹) and l -tartaric acid (125 M⁻¹). More dramatic changes in the affinities and selectivities were observed for P- 2 and P- 8 upon binding of polyol guests. P- 2 was determined to selectively bind d -sorbitol (52000 M⁻¹) over analogous guests, but P- 8 showed no binding selectivity: d -sorbitol (1890 M⁻¹), l -sorbitol (3330 M⁻¹), d -arabitol (959 M⁻¹), l -arabitol (4970 M⁻¹) and xylitol (4960 M⁻¹) in 5% (v/v) DMSO/CH₂Cl₂ at 25±1 °C. These results clearly demonstrate that even subtle post-modifications of synthetic receptors may significantly alter their binding affinities and selectivities, in particular for guests of long and flexible chains.     

Crystal structures of inclusion compounds of 4-aminobenzenesulfamidine (sulfaguanidine) with two dicyclohexano-18-crown-6 isomers

The crystal structures of inclusion compounds of 4-aminobenzenesulfamidine (sulfaguanidine) (L) with two dicyclohexano-18-crown-6 (DCH-6) isomers A(cis-syn-cis) and B(cis-anti-cis) have been determined by X-ray methods. The complexes exhibit 1:2 host-guest ratios. In fact the complex of isomer A is formulated as [DCH-6^A·[L]H₂O]L (complexI), while that of isomerB is DCH-6 ^B L₂ (complex I1).In the crystals, host and guests are connected by O-H...0 and N-H...O bonds.     

Toxic metal complexes of macrocyclic cyclen molecule – synthesis,structure and complexing properties

Toxic metal (Cd²⁺, Hg²⁺, Pb²⁺, and Ag⁺) complexes with the tetradentate macrocyclic ligand - cyclen (1,4,7,10-tetraazacyclododecane, [12]aneN₄, L) were prepared and studied in the solid state by IR, X-ray diffraction, elemental and thermal analysis. Diffraction results have yielded three molecular structures, [Cd([12]ane-κ⁴N^1,4,7,10)(NO₃)₂)] (1), [Hg([12]ane-κ⁴N^1,4,7,10)(NO₃-κ²O,O`)]NO₃ (2), [Pb₂([12]ane-κ⁴N^1,4,7,10)₂][Pb(NO₃)₆] (3) and one polymeric structure {[Ag₂([12]ane-κ³N^1,4,7)(μ₂-[12]aneN¹⁰)](NO₃)₂?2H₂O)}_n (4) featuring a unique coordination mode not observed before with cyclen as a ligand. The monodentate (1) and chelate (with small bite angle 50.3(3)°, (2) coordination modes of nitrate ligands were confirmed. Stereochemically active 6s² lone pair was suggested in 3 and DFT results confirmed no significant metal–metal covalent bond. The stability constants of the complexes with Cd²⁺ and Pb²⁺ ions were determined by potentiometric methods in aqueous solutions. Additionally, the structures of complexes in solution were observed by ¹H NMR. Both methods confirm similar cyclen complexing properties toward Zn²⁺ biometal and Cd²⁺, Pb²⁺ toxic metals.     

Anticyanobacterial phenolic constituents from the aerial parts of Eupatorium fortunei Turcz

Four thymol derivatives and two phenolic compounds were isolated from the aerial parts of Eupatorium fortunei. The new structures were elucidated to be 7,8,9-trihydroxythymol (1), and 8,10-didehydro-7,9-dihydroxythymol (2) by means of MS and NMR analysis. The known compounds were identified as 8,9,10-trihydroxythymol (3), 10-acetoxy-8,9-dihydroxythymol (4), o-coumaric acid (5) and 4-(2-hydroxyethyl)benzaldehyde (6). Compound 3 showed strongest inhibitory effect on the growth of Microcystis aeruginosa in comparison with CuSO₄.     

Five unusual natural carbohydrates from <Emphasis Type="Italic">Actinosynnema pretiosum</Emphasis>

Five unusual hexose derivatives were isolated from the carbohydrate portion of the solid-state fermentation extract of Actinosynnema pretiosum ssp. auranticum ATCC 31565, which is a producing strain of maytansinoids that are a family of 19-membered macrocyclic lactams having extraordinary cytotoxic and antineoplastic activities. Their structures were determined to be 2-deoxy-α-D-arabino-hexopyranose (1), 2-deoxy-β-D-arabino-hexopyranose (2), 3,6-anhydro-2-deoxy-α-D-arabino-hexcofuranose (3), 3,6-anhydro-2-deoxy-β-D-arabino-hexofuranose (4), and 2-(D-glycerol-1,2-dihydroxyethyl)furan (5) by NMR spectroscopic experiments. Published in Khimiya Prirodnykh Soedinenii, No. 5, pp. 481–483, September-October, 2008.     

大环金属铜(II)、镍(II)配合物的模板合成与晶体结构

用模板法合成了1个大环金属铜(II)配合物[CuLCl₂]·3H₂O (1)和3个大环金属镍(II)配合物[NiLCl₂] (2)，[NiL](ClO₄)₂ (3)和[NiLH₂](ClO₄)₄ (4)(L=3,10-二乙基-1，3，5，8，10，12-六氮杂十四烷)，通过X-射线衍射单晶结构分析测定了它们的晶体结构。晶体结构显示：配合物1和2的金属离子与大环配体的4个氮原子及大环平面轴向的2个氯离子以八面体配位方式配位；配合物3和4的金属离子与大环配体的4个氮原子以平面正方形配位方式配位，配合物4的侧链氮原子的质子化导致侧链结构翻转，使得其侧链与大环平面共面。     

Three new pterocarpans from the aerial parts of Abrus Precatorius

Abstract

Three new pterocarpans, named abrusprecatins A-C (1–3), along with three known ones, namely medicarpin (4), maackiain (5), and 4-hydroxy-3-methoxy-8,9-methylenedioxypterocarpan (6) were isolated from the aerial parts of Abrus precatorius. The structures of these compounds were established by extensive analysis of mass spectrometric data, 1?D and 2?D NMR spectroscopic data. In addition, the absolute configurations were determined by a combination of single crystal X-ray diffraction analysis and circular dichroism spectroscopy.     

Selectivity comparisons of monolithic silica capillary columns modified with poly(octadecyl methacrylate) and octadecyl moieties for halogenated compounds in reversed-phase liquid chromatography

Stationary phase selectivities for halogenated compounds in reversed-phase HPLC were compared using C18 monolithic silica capillary columns modified with poly(octadecyl methacrylate) (ODM) and octadecyl moieties (ODS). The preferential retention of halogenated benzenes on ODM was observed in methanol/water and acetonitrile/water mobile phases. In selectivity comparison of selected analytes on ODM and ODS, greater selectivities for halogenated compounds were obtained with respect to alkylbenzenes on an ODM column, while similar selectivities were observed with a homologous series of alkylbenzenes on ODM and ODS columns. These data can be explained by greater dispersive interactions by more densely packed octadecyl groups on the ODM polymer coated column together with the contribution of carbonyl groups in ODM side chains. For the positional isomeric separation of dihalogenated benzenes (ortho-, meta-, para-), the ODM column also provided better separation of these isomers for the adjacently eluted isomers that cannot be completely separated on an ODS column in the same mobile phase. These results imply that the ODM column can be used as a better alternative to the ODS column for the separation of other halogenated compounds.     

Calculations of thermodynamic stability of CpCoC<Subscript>2</Subscript>B<Subscript>9</Subscript>H<Subscript>11</Subscript> cobaltacarborane isomers

Quantum-chemical calculations of the geometry and energies of nine possible isomers of 12-vertex cobaltacarborane CpCoC₂B₉H₁₁ (1) were carried out by the DFT method (PBEPBE/DGDZVP/DGA1). Thermodynamic stability of the isomers increases with increasing distance between the carbon atoms in the cage and is virtually independent of the position of the CpCo vertex. The relative stabilities of the 1,2,3-(17.57 kcal mol⁻¹), 1,2,4-(3.72 kcal mol⁻¹), and 1,2,9-isomers of 1 (0 kcal mol⁻¹) are similar to the corresponding values for the ortho (17.61 kcal mol⁻¹), meta (3.21 kcal mol⁻¹), and para isomers (0 kcal mol⁻¹) of carborane C₂B₁₀H₁₂. The results of the present study confirm a close similarity of the CpCo and BH fragments in metallacarborane chemistry. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1557–1559, July, 2005.     

Molecular structures of 8,8′-dithioureido-2,2′-binaphthalene derivatives and their anions recognition: an ONIOM investigation

The structures of 8,8′-bis(3-phenylthioureidomethyl)-2,2′-binaphthalene (1), 8,8′-bis(3-butylthioureidomethyl)-2,2′-binaphthalene (2) and their complexes with anionic guests such as carboxylate ions (acetate, oxalate, malonate, succinate, glutarate, adipate, pimelate, suberate, and azelate), inorganic oxygen-containing anions (nitrate, sulfate, bicarbonate, hydrogen phosphate, and dihydrogen phosphate), and halide ions (fluoride, chloride, and bromide) were obtained using the ONIOM approach. The binding abilities of receptors 1 and 2 to anionic species in terms of binding energy, thermodynamic properties, and selectivity coefficient were obtained at the ONIOM(B3LYP/6-31G(d):AM1) and BSSE-corrected B3LYP/6-31G(d)//ONIOM(B3LYP/6-31G(d):AM1) levels of theory. The multipoint hydrogen bonding between receptors (either the receptor 1 or 2) and anionic guests were found. The hydrogen phosphate is the most preferable ion to bind with either the receptor 1 or 2.     

六、七元瓜环与苯二胺及硝基苯胺异构体相互作用的HPLC研究

利用HPLC法考察了六、七元瓜环(Q[6], Q[7])与邻苯二胺(g1)、间苯二胺(g2)、对苯二胺(g3)、邻硝基苯胺(g4)、间硝基苯胺(g5)、对硝基苯胺(g6)的相互作用. 实验结果表明: Q[6]可与客体g1～g3, g5形成1∶1的包结配合物; Q[7]与客体g1～g6形成1∶1包结配合物, 同时计算了包结配合物的包结稳定常数, 探讨了主-客体的相互作用模式, 并利用¹H NMR、紫外吸收光谱法进行了佐证.     

Two new labdane diterpenoids from the rhizomes of Isodon yuennanensis

Two new labdane diterpenoids, s-trans-8(17),12E,14-labdatrien-20-oic acid (1), s-trans-12E,14-labdadien-20,8β-olide (2), along with 10 known compounds, hinokiol (3), ursonic acid (4), 2α,3α-dihydroxyolean-12-en-28-oic acid (5), 2α,3β,23-trihydroxyolean-12-en-28-oic acid (6), ethyl 3-(3,4-dihydroxyphenyl)lactate (7), ethyl rosmarinate (8), (Z,E)-2-(3,4-dihydroxyphenyl)ethenyl caffeic ester (9), tridecanoic acid (10), β-sitosterol (11) and daucosterol (12), were isolated from the 70% acetone extract of the rhizomes of Isodon yuennanensis. Their structures were elucidated based on the analyses of extensive spectroscopic data and physicochemical properties.     

Coordination Features of a Polyaza-Bipyridine-Macrocyclic Ligand toward Co(II) and Cd(II) in Water and Dimethylsulfoxide

The coordination features of a polyaza macrocycle, containing the diverse bipyridine unit 4,4′-(2,5,6,11,14-pentaaza[15]-[15](2,2′)-bipyridylophane (L3), with Co(II) and Cd(II) have been studied in aqueous solution and in the aprotic solvent dimethylsulfoxide (DMSO). The study was carried out at 298 K by means of potentiometric, spectrophotometric and calorimetric techniques. The formation of the dinuclear species M₂ L3 is observed for Co(II) both in water and in DMSO, whereas Cd(II) is able to form this type of dinuclear complex only in DMSO. The FT-IR spectra of the mononuclear species ML3, formed in both solvents, provide evidence that the rigid structure of the polyaminic chain prevents metal ions from being coordinated by all of the nitrogens of the macrocyclic cavity, in good agreement with the behavior suggested by the thermodynamic parameters. The results are compared with those for the complexation of Co(II) and Cd(II) with similar polyazamacrocycles containing a bipyridine unit directly inside the cavity. Semi-empirical calculations were also performed to obtain structural information.     

New pyranosyl cembranoid diterpenes from Sarcophyton trocheliophorum

During our continual searching programme for novel bioactive metabolites from Sarcophyton trocheliophorum, collected from Red Sea, we describe herein the isolation and structural elucidation of further two new pyrane-based cembranoid diterpenes: 9-hydroxy-7,8-dehydro-sarcotrocheliol (1) and 8,9-expoy-sarcotrocheliol acetate (2), along with the well-known sarcotrocheliol acetate (3), (+)-sarcophine (4), (+)-sarcophytoxide (5) and (-)-sarcophytoxide (6). The chemical structures of compounds 1 and 2 were determined on the basis of 1D and 2D NMR (¹H, ¹³C, ¹H–¹H COSY, HMQC, HMBC and NOE), mass spectra (ESI and HR-ESIMS) and by comparison with related structures. The antimicrobial activities of the reported compounds 1–6 were investigated. According to the molecular docking study of compounds 1–6 using 3D structure of α,β tubulin in complex with taxol (PDB code 1JFF) and epothilone A (PDB code 1TVK), sarcophine (4) displayed the highest affinity towards both crystal structures, followed by 5 and 6, meanwhile pyrane-based cembranoid diterpenes (1–3) showed less affinity.     

Synthesis and Evaluation of Potentiometric Properties of Pyridylthiazole Derivatives

Synthesis of 2-pyridylthiazole ethers 2, 3), 4-nonyl-2-pyridylthiazole 4), 2-nonyl-4-pyridylthiazole 5) and 2-pyridylthiazole imine 6), potentially useful as effective cation-binding ligands, is described. The potentiometric properties of ion-selective membranes prepared with 30–32 wt% PVC, 66 wt% 2-nitrophenyloctyl ether and 2–4 wt% pyridylthiazole derivatives have been examined. While the membranes containing 2-pyridylthiazole ethers 1-4) exhibited high selectivity toward silver(I) ion, that prepared with 2-pyridylthiazole imine 6) resulted in negligible potentiometric reponse to most mono- and divalent cations.     

Inclusion of nitriles inside and outside the molecular bowls of tetrabromo calix[4]arene hosts

New tetrabromo calix[4]arene derivatives 2 and 5a/5b have been synthesised and found to function as inclusion hosts for nitrile guests. The X-ray structures of (2)₂ · (pivalonitrile)₃ and (5a) · (acetonitrile)₃ · (water) show that, in each compound, molecular inclusion occurs by a combination of complexation within the calixarene bowl and lattice inclusion outside the bowl. Racemic 5a/5b crystallises as a conglomerate, with chiral discrimination between these enantiomers being assisted by the propeller-shaped molecular conformation they adopt in the solid state.