Supramolecular aggregates between carboxylate anions and an octaaza macrocyclic receptor

The 28-membered octaazamacrocycle Me2[28]py2N6 was used as a receptor for the molecular recognition of aromatic and aliphatic carboxylate substrates. The receptor-substrate binding behaviour of (H6Me2[28]py2N6)6+ with an aliphatic (-O2C(CH2)nCO2-, n=0 to 4) and an aromatic (phthalate, isophthalate, terephthalate, 4,4'-dibenzoate, benzoate, 3- and 4-nitrobenzoate) series of carboxylate anions was evaluated by 1H NMR spectroscopy (carried out in DMSO-d6 at 300 K). Two association constants were found for most of the studied cases, except for 3- and 4-nitrobenzoate for which only K1 was determined. For oxalate, malonate, benzoate and dibenzoate anions only the beta2 constants could be obtained. The values of the first association constant cover a range from 2.86 to 3.69 (log units), and the second stepwise constant from 2.15 to 2.89 (also in log units). No special selectivity was found but the highest values were determined for adipate and the lowest for the monoprotic 3- and 4-nitrobenzoates. Single crystal X-ray structures of H6Me2[28]py2N6 6+ with terephthalate, 1, and 4,4'-dibenzoate (2) were determined showing supramolecular entities with general formula (H6Me2[28]py2N6).(substrate)2(PF6)2.4H2O. These anions are the building blocks of an extensive 3-D network of hydrogen bonds.     

Correlation between quasielastic Raman scattering and configurational entropy in an ionic liquid

Low-frequency (5-200 cm(-1)) Raman spectra are reported for the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate, [bmim]PF(6), in glassy, supercooled liquid, and normal liquid phases (77-330 K). Raman spectra of [bmim]PF(6) agree with previous results obtained by optical Kerr effect spectroscopy and molecular dynamics simulation. Both the superposition model and the coupling model give reasonable fit to low-frequency Raman spectra of [bmim]PF(6). The configurational entropy of [bmim]PF(6) has been evaluated as a function of temperature using recently reported data of heat capacity. The calculated configurational entropy is inserted in the Adam-Gibbs theory for supercooled liquids, giving a good fit to non-Arrhenius behavior of viscosity and diffusive process, with the latter revealed by a recent neutron scattering investigation of [bmim]PF(6). There is a remarkable linear dependence between intensity of quasielastic Raman scattering and configurational entropy from 77 K up to the melting point of [bmim]PF(6). This correlation offers insight into the nature of dynamical processes probed by low-frequency Raman spectra of ionic liquids.     

Ruthenium-catalyzed cycloaddition between propargylic alcohols and cyclic 1,3-dicarbonyl compounds via an allenylidene intermediate

Thiolate-bridged diruthenium complexes such as [Cp*RuCl(mu(2)-SR)(2)RuCp*Cl] (Cp* = eta(5)-C(5)Me(5); R = Me, (n)Pr, (i)Pr) and [Cp*RuCl(mu(2)-S(i)Pr)(2)RuCp*(OH(2))]OTf (OTf = OSO(2)CF(3)) promote the cycloaddition between propargylic alcohols and cyclic 1,3-dicarbonyl compounds to give either the corresponding 4,6,7,8-tetrahydrochromen-5-ones or 4H-cyclopenta[b]pyran-5-ones in high yields with complete regioselectivity. This catalytic cycloaddition provides a simple and one-pot synthetic protocol for a variety of substituted chromenones and cyclopenta[b]pyranones.     

Gas phase reaction between chromones and solvent in an electrospray ionization source

Chromones were measured by using electrospray ionization mass spectrometry in negative mode. Interestingly, in addition to the deprotonated ion ([M ? H]^?), unexpected [M + 17]^? and [M + 31]^? ions were observed in high intensity when water and methanol were used as the solvent. Chromones with different substitutes were tested. Compared with the deprotonated ion, [M + 17]^? and [M + 31]^? ions were observed with higher abundances when the C‐3 site of chromones was substituted by electron withdrawing groups. Based on high performance liquid chromatography‐mass spectrometry (LC‐MS), deuterium‐labeling and collisional‐induced dissociation experiments, a covalent gas‐phase nucleophilic addition reaction between chromone and water, and the formation of a noncovalent complex between chromone and methanol were proposed as the mechanism for the observed [M + 17]^? and [M + 31]^? ions, respectively. Understanding and using these unique gas phase reactions can avoid misannotation when analyzing chromones and their metabolites.     

Reaction between ellagic acid and an ultimate carcinogen

The reaction coordinate between a typical ultimate carcinogen benzo[a]pyrene-7,8-diol-9,10-epoxide (BPDE) and ellagic acid, a proven chemopreventive agent active against cancers caused by polycyclic aromatic hydrocarbons (PAHs), was examined by density functional theory (DFT) and semiempirical MO calculations, and activation energy was calculated. The effect of a polar environment was included using Tomasi and the Langevin dipoles methods. The calculated BPDE/ellagic acid reaction free energy of activation is found to be in decent agreement with experimental data [Sayer, J. M. et al. J. Am. Chem. Soc. 1982, 104, 5562-5564]. This work sheds light on the mechanism of action of ellagic acid. Quantum chemical calculations of this kind are valuable for the design of ellagic acid derivatives with even lower activation energy and increased reactivity toward ultimate carcinogens as well as controlled reactivity toward DNA.     

Study on the interaction between an ionic liquid and L-tryptophan by fluorescence spectroscopic technique

In this work, the interaction of an ionic liquid (IL) 1-octyl-3-methylimidazolium chloride ([Omim]Cl) and L-tryptophan was investigated with fluorescence spectroscopic method. The quenching mechanism and binding characteristics of [Omim]Cl with L-tryptophan at different temperatures were studied from fluorescence measurement. The thermodynamic parameters such as free energy change (ΔG), enthalpy change (ΔH) and entropy change (ΔS), were calculated by thermodynamic equations. The experimental results indicated that [Omim]Cl and L-tryptophan had weak interaction and the mechanism of quenching belonged to static quenching. Hydrogen bonds and van der Waals interactions played important roles in the binding of [Omim]Cl with L-tryptophan.     

Trapping a labile adduct formed between an ortho-quinone methide and 2'-deoxycytidine

Selective oxidation by bis[(trifluoroacetoxy)iodo]benzene (BTI) provides an effective trap for quenching adducts formed reversibly between dC and an ortho-quinone methide (QM) under physiological conditions. A model adduct generated by 4-methyl-o-QM and 2'-deoxycytidine is rapidly converted by intramolecular cyclization and loss of aromaticity to a characteristic product for quantifying QM alkylation. However, BTI induces a surprising rearrangement driven by overoxidation of a derivative lacking an alkyl substituent at the 4-position of the QM.     

Spontaneous phase transfer of thermosensitive hairy particles between water and an ionic liquid

This article describes the temperature-induced phase transfer behavior of a series of thermosensitive polymer brush-grafted particles between water and a hydrophobic ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]). Six samples were made by surface-initiated atom transfer radical polymerization: silica particles grafted with poly(methoxypoly(ethylene glycol) methacrylate) (PPEGMMA) with two different molecular weights, poly(methoxytri(ethylene glycol) methacrylate) (PTEGMMA), poly(methoxydi(ethylene glycol) methacrylate) (PDEGMMA), and two copolymers of PEGMMA and TEGMMA with different compositions (P(PEGMMA-co-TEGMMA)-82 and P(PEGMMA-co-TEGMMA)-74). The cloud points of free PPEGMMA with M(n,SEC) of 23 and 40 kDa, P(PEGMMA-co-TEGMMA)-82, P(PEGMMA-co-TEGMMA)-74, and PTEGMMA in [EMIM][TFSI]-saturated water were 95, 94, 80, 72, and 43 °C, respectively. PDEGMMA was not soluble in the ionic liquid-saturated water. PPEGMMA brush-grafted particles moved spontaneously and completely from water to the [EMIM][TFSI] phase upon heating at 80 °C. When cooled to 22 °C, all particles returned to the water layer. From UV-vis absorbance measurements, the transfer temperature (T(tr)) of PPEGMMA-grafted particles from water to the ionic liquid was 42 °C. Thermodynamic analysis showed that the particle transfer was an entropically driven process. P(PEGMMA-co-TEGMMA)-82, P(PEGMMA-co-TEGMMA)-74, and PTEGMMA brush-grafted particles also underwent reversible and quantitative transfer between the two phases upon heating at 70 °C and cooling at 0 °C; their transfer temperatures from water to [EMIM][TFSI] were 36, 30, and 16 °C, respectively. T(tr) was a linear function of the cloud point of the corresponding free polymer in ionic liquid-saturated water. In contrast, PDEGMMA-grafted particles moved spontaneously to the ionic liquid layer upon heating but did not return to water even after prolonged stirring at 0 °C.     

Ruthenium-catalyzed [2 + 2] cycloadditions between 7-substituted norbornadienes and alkynes: an experimental and theoretical study

The ruthenium-catalyzed [2 + 2] cycloadditions of 7-substituted norbornadienes with an alkyne have been investigated. The cycloadditions were found to be highly regio- and stereoselective, giving only the anti-exo cycloadducts as the single regio- and stereoisomers in good yields. The results on the relative rate of different 7-substituted norbornadienes in the Ru-catalyzed [2 + 2] cycloadditions with an alkyne indicated that the reactivity of the alkene component decreases dramatically as the alkene becomes more electron deficient. Ab initio computational studies on the ruthenium-catalyzed [2 + 2] cycloadditions provided important information about the geometries and the arrangements of the four different groups on the Ru in the initial Ru-alkene-alkyne pi-complex, 14, and in the metallacyclopentene 15. Based on our computational studies, we also found that the first carbon-carbon bond formed in the [2 + 2] cycloaddition is between the C(5) of the alkene and the C(b) (the acetylenic carbon attached to the ester group) of the alkyne 8. Our computational studies on the potential energy profiles of the cycloadditions showed that the activation energy relative to the reactants for the oxidative addition step is in the range of 9.3-9.8 kcal/mol. The activation energy relative to the metallacyclopentene for the reductive elimination step is much higher than for the oxidative addition step (in the range of 25.9-27.6 kcal/mol).     

A Pauson-Khand-type reaction between alkynes and olefinic aldehydes catalyzed by rhodium/cobalt heterobimetallic nanoparticles: an olefinic aldehyde as an olefin and CO source

Co/Rh (Co:Rh = 2:2) heterobimetallic nanoparticles derived from Co(2)Rh(2)(CO)(12) react with alkynes and alpha,beta-unsaturated aldehydes such as acrolein, crotonaldehyde, and cinnamic aldehyde and release products resulting from [2 + 2 + 1]cycloaddition of alkyne, carbon monoxide, and alkene. alpha,beta-Unsaturated aldehydes act as a CO and alkene source. These reactions produce 2-substituted cyclopentenones.     

Competition between micro-segregation and anti-parallel alignment of an amphiphilic rod-like liquid crystal

Recently, we reported that a rod-like molecule, 4-[4-(7-hydroxyheptyloxy)phenyl]-1-(4-hexylphenyl)-2,3-difluorobenzene, exhibited a nematic phase with a layered structure and smectic C phases consisting of three states. We prepared a homologous series of the rod-like molecules in which a 2,3-difluoro-1,4-diphenylbenzene unit and a hydroxyl unit are connected via a flexible methylene spacer. We investigated their physical properties using polarised optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). Although they showed nematic, smectic A and smectic C phases, the phase structures were found to depend on the flexible spacer length. Those compounds possessing a shorter spacer length than a heptyl unit exhibited bilayered smectic A and smectic C phases, whereas those possessing a longer spacer length than a heptyl unit showed conventional monolayered smectic A and smectic C phases. A nematic phase with a smectic-like layer ordering was observed for the compound possessing an octyl unit. The structure–property relations of the amphiphilic compounds are discussed.     

Study on the reactivity of the alkyne component in ruthenium-catalyzed [2 + 2] cycloadditions between an alkene and an alkyne

The ruthenium-catalyzed [2 + 2] cycloadditions of norbornadiene with a variety of alkynes have been investigated. Electronic effect of the alkyne component has shown to play an important role on the rate of the cycloaddition, and the reactivity of the alkyne component increases dramatically as the alkyne becomes more electron deficient. Increase in the steric bulk of the alkyne component decreases the reactivity of the alkyne component. It was also found that chelation effect of propargylic alcohols greatly enhanced the reactivity of the alkyne component in the ruthenium-catalyzed [2 + 2] cycloadditions.     

羟基功能化离子液体与溶菌酶相互作用的研究

采用荧光光谱和紫外吸收光谱研究了羟基功能化离子液体1-(1,2-二羟基丙基)-3-甲基咪唑氯盐([2,3-dhpmim]Cl)、1-(1,2-二羟基丙基)-3-甲基咪唑四氟硼酸盐([2,3-dhpmim]BF4)、1-(1,2-二羟基丙基)-3-甲基咪唑六氟磷酸盐([2,3-dhpmim]PF6)与溶菌酶的相互作用。研究发现此3种离子液体对溶菌酶的荧光猝灭均为静态猝灭;同步荧光显示离子液体与溶菌酶肽链上的色氨酸残基作用,色氨酸残基微环境发生改变;结合常数和结合位点数按照[2,3-dhpmim]Cl、[2,3-dhpmim]BF4、[2,3-dhpmim]PF6顺序依次增大,并随温度的升高而增大。     

Isotopic exchange reactions between iron-sulphur-nitrosyl clusters and nitrite

The anion [Fe₄S₃(NO)₇]⁻ undergoes slow exchange with labelled nitrite [¹⁵NO₂]⁻ to yield a product [Fe₄S₃(¹⁴NO)(¹⁵NO)₆]⁻ in which complete isotopic exchange has occurred at the basal Fe(NO)₂ groups, but with no exchange at the apical Fe(NO) group. The neutral Fe₄S₄(NO)₄ reacts rapidly with [¹⁵NO₂⁻ to give fully exchanged [Fe₄S₃(¹⁵NO)₇]⁻, and it is proposed that the conversion proceeds by fragmentation, followed by complete isotopic exchange and rapid reassembly. The binuclear anion [Fe₂S₂(NO)₄]²⁻ also yields, with [¹⁵NO₂]²⁻ in CD₂Cl₂ solution, the fully exchanged [Fe₄S₃(¹⁵NO)₇]⁻, and a mechanism involving successive fragmentation, exchange and reassembly steps is proposed; however in aqueous solution, a clean exchange reaction occurs to give [Fe₂S₂(¹⁵NO)₄]²⁻. Neutral binuclear esters Fe₂(SR)₂(NO)₄ (R = Me, Et, or Ph) with [¹⁴NO₂]⁻ yield the mononuclear paramagnetic [Fe(¹⁴NO)₂(¹⁴NO₂)₂]⁻, and with [¹⁵NO₂]⁻ the analogous [Fe(¹⁵NO)₂(₁₅NO₂)₂]⁻.     

Interactions between divalent metal ions and an octacoordinate macrocyclic ligand

A dinucleating hexaazadiphenol macrocyclic ligand, 15,31-dimethyl-3,11,19,27,33,35-hexaazapentacyclo[27.3.1.1.(5,9)1.(13,17)1. (21,25)]hexatriaconta-5,7,9(33),13,15,17(34),21,23,25(35),29,31,1(36)- dodecaene-34,36-diol (H2L), forms a number of protonated, neutral, and/or hydroxo mononuclear, homodinuclear, and heterodinuclear complexes with the divalent metal ions Cu2+, Cd2+, Mn2+, and Zn2+, controlled by the stoichiometry of the metal ion and ligand as well as the pH values of the solution. Their stability constants and species distribution as a function of p[H] are determined. The pH potentiometric studies show that the dinuclear complexes are formed via the mononuclear chelates in which two kinds of coordination patterns are observed. One is that the metal ions are complexed by exactly half of coordination sites of the dinucleating macrocycle (N3O-), and the other is that the metal ions occupy salen-like sites of the macrocycle (N3O(2)2-). In the 2:1 systems (2:1 molar ratio of metal ion to ligand), the mononuclear species predominate in acidic solutions while the dinuclear species predominate in basic solutions, except for the case of copper. The protonated mononuclear complex [H2LZn](NO3)(2).5H2O forms triclinic crystals, of space group P1, with a = 10.7797(12) A, b = 10.9047(12) A, c = 17.0176(15) A, alpha = 106.857(9) degrees, beta = 95.822(8) degrees, gamma = 100.191(9) degrees, and Z = 2; the neutral heterodinuclear complex [LZnCdCl2].6H2O forms monoclinic crystals, of space group C2/c, with a = 16.234(5) A, b = 15.976(9) A, c = 29.829(11) A, alpha = 90 degrees, beta = 90.28(2) degrees, gamma = 90 degrees, and Z = 8.     

Prediction of interfacial tension between an organic solvent and aqueous solutions of mixed-electrolytes

The recently proposed approach for representing and predicting surface tension of aqueous electrolyte solutions [Chem. Eng. Sci. 56 (2001) 2879] is extended to the prediction of interfacial tension between an organic solvent and aqueous multi-electrolyte solutions. The method of Meissner was adopted in all the calculations of activity coefficient of electrolytes. Model parameters were determined by correlating interfacial tensions reported in the literature for 11 single electrolytes, including 10 inorganic salts and one inorganic acid at isothermal conditions. The correlation yielded an overall average absolute percentage deviation (AAPD) of 0.42. Using these model parameters, the proposed approach was successfully applied to the prediction of interfacial tensions available in the literature for aqueous FeCl₃–HCl, NiCl₂–FeCl₃–HCl and NiCl₂–CoCl₂–FeCl₃–HCl solutions with an AAPD of 5.73.     

Topological equivalences between organic and coordination polymer crystal structures: an organic ladder formed with three-connected molecular and supramolecular synthons

[structure: see text] Crystal engineering of an organic ladder can be achieved with a T-shaped molecule, 4,4-bis(4'-hydroxyphenyl)-1-cyclohexanol, having three hydroxyl functionalities that can form O-H...O hydrogen-bonded helices. The topology of this network structure finds a parallel in three-connected coordination polymers.     

Evaluation of hydrogen bonding complementarity between a secondary sulfonamide and an alpha-amino acid residue

[structure: see text] We report an initial step toward the development of sulfonamide-based complements for extended peptide strands. A molecule containing one secondary sulfonamide unit and one valine residue linked by a turn-forming segment was found by IR and NMR to exhibit a doubly hydrogen-bonded folding pattern in chloroform.     

二苯并噻吩及其氧化物与离子液体相互作用的理论研究

采用密度泛函理论方法比较了DBT/DBTO₂和[BMIM]⁺[PF₆]^-/[BMIM]⁺[BF₄]^-的相互作用。对最稳定的[BMIM]⁺[PF₆]^-、[BMIM]⁺[PF₆]^--DBT、[BMIM]⁺[PF₆]^--DBTO₂、[BMIM]⁺[BF₄]^-、[BMIM]⁺[BF₄]^--DBT、[BMIM]⁺[BF₄]^--DBTO₂进行了NBO和AIM分析。结果表明,DBT和[BMIM]⁺[PF₆]^-/[BMIM]⁺[BF₄]^-中的咪唑环彼此相互平行,NBO和AIM分析表明它们之间发生了π-π相互作用。H1'和H9'形成的F…H氢键有利于π-π堆积作用的形成。DBTO₂倾向于趋近C2-H2和甲基基团形成O…H相互作用;DBTO₂优先吸附在[BMIM]⁺[PF₆]^-/[BMIM]⁺[BF₄]^-。在模拟油中,[BMIM]⁺[PF₆]^-和[BMIM]⁺[BF₄]^-离子液体对DBTO₂的萃取能力大于DBT,其原因是可能是DBTO₂具有较大的极性和O…H与F…H的氢键作用。     

Assembly of an allenylidene ligand, a terminal alkyne, and an acetonitrile molecule: formation of osmacyclopentapyrrole derivatives

Treatment in acetonitrile at -30 C of the hydride-alkenylcarbyne complex [OsH([triple bond]CCH=CPh2)(CH3CN)2(P(i)Pr3)2][BF4]2 (1) with (t)BuOK produces the selective deprotonation of the alkenyl substituent of the carbyne and the formation of the bis-solvento hydride-allenylidene derivative [OsH(=C=C=CPh2)(CH3CN)2(P(i)Pr3)2]BF4 (2), which under carbon monoxide atmosphere is converted into [Os(CH=C=CPh2)(CO)(CH3CN)2(P(i)Pr3)2]BF4 (3). When the treatment of 1 with (t)BuOK is carried out in dichloromethane at room temperature, the fluoro-alkenylcarbyne [OsHF([triple bond]CCH=CPh2)(CH3CN)(P(i)Pr3)2]BF4 (4) is isolated. Complex 2 reacts with terminal alkynes. The reactions with phenylacetylene and cyclohexylacetylene afford [Os[(E)-CH=CHR](=C=C=CPh2)(CH3CN)2(P(i)Pr3)2]BF4 (R = Ph (5), Cy (6)), containing an alkenyl ligand beside the allenylidene, while the reaction with acetylene in dichloromethane at -20 degrees C gives the hydride-allenylidene-pi-alkyne [OsH(=C=C=CPh2)(eta2-HC[triple bond]CH)(P(i)Pr3)2]BF4 (7), with the alkyne acting as a four-electron donor ligand. In acetonitrile under reflux, complexes 5 and 6 are transformed into the osmacyclopentapyrrole compounds [Os[C=C(CPh2CR=CH)CMe=NH](CH3CN)2]BF4 (R = Ph (8), Cy (9)), as a result of the assembly of the allenylidene ligand, the alkenyl group, and an acetonitrile molecule. The X-ray structures of 2, 5, and 8 are also reported.