Time resolved fluorescence spectroscopy of quercetin and morin complexes with Al3+.

The association process of Al3+ with quercetin and morin in methanol was studied by electronic absorption and emission spectroscopies. The number of species in solution with different absorption spectra were determined by the method of Rank analysis of the absorbance matrix, and the stoichiometries of the complexes were evaluated using the Job method. The number of fluorescent species in solution were calculated from the Rank analysis method of the time resolved emission spectra (TRES), and compared with a global analysis of the decay surface using a proper multi-exponential decay model. The association of Al3+ with morin gives rise to two complexes with 1:1 and 2:1 (morin: Al3+) stoichiometries, but in both species the association of the cation involves the carbonyl and 3-hydroxyl groups of the pyrone ring. The fluorescence decay surface of this system is biexponential and the lifetimes of the 1:1 and 2:1 complexes are 4.3 and 2.0 ns, respectively. The association of Al3+ with quercetin forms preferentially two complexes with 1:1 and 1:2 (quercetin: Al3+) stoichiometries where the first cation binds to the site of the pyrone ring but the second one is bound to the cathecol group of the molecule. However, the multichelation character of the quercetin ligand allows larger aggregates to be formed, thereby the species Al2Q3 is also detected in methanol. The lifetime of the 1:1 complex is about 2.7 ns, while for 1:2 and 3:2 complexes the lifetimes measured are 3.5 and 1.8 ns, respectively.     

1-苯基-3-甲基-4-苯甲酰基吡唑啉酮-5与胺类缔合研究

1-苯基-3-甲基-4-苯甲酸基毗哇琳酮一5（HPMBP）是一类酸性鳌合革取剂,已广泛用于多种元素分离、分析研究［'j．它不仅在单独使用时能很好地革取金属,而且在与有机胺类共同使用时对稀土元素、过渡金属元素有明显的快同革取性能L'·'］．因此研究HPMBP与胺类的相互作用对于分析产生协同作用的原因,改善革取性能是很有必要的．1实验部分1．1试剂HPMBP,化学纯（北京试剂厂）;三千胺（TOA）,FLUKA进口分装试剂,纯度大于99％;伯胺N1923,工业级（上海有机化学研究所化学实验厂）,经减压（267～533Pa）蒸馏,收集413～459K馏…     

NMR diffusometry and conductometry study of the host-guest association between beta-cyclodextrin and dodecane 1,12-bis(trimethylammonium bromide)

Surfactants form association complexes with cyclodextrins. In the present investigation we have used NMR-diffusometry and electrical conductivity to follow the interactions which take place between beta-cyclodextrin and a bolaform surfactant: dodecane 1,12-bis(trimethylammonium bromide). Both (1)H NMR self-diffusion and conductometry data indicate the formation of a 1:1 inclusion complex. Assuming this stoichiometry, it was possible to calculate the association constant; from the analysis of the self-diffusion coefficients of free beta-cyclodextrin and the bolaform surfactant an association constant K=3x10(3)M(-1) was obtained while the analysis of conductivity data gave a comparable value of K=2.5x10(3)M(-1).     

Representation of Electrical Conductances for Polyvalent Electrolytes by the Quint-Viallard Conductivity Equation. Part 4. Symmetrical 2:2, 3:3 and Unsymmetrical 2:1, 3:1 and 1:3 Type Electrolytes in Pure Organic Solvents

Conductivities of symmetrical and unsymmetrical electrolytes of 2:2, 3:3, 2:1, 3:1 and 1:3 charge types in pure organic solvents (methanol, ethanol, 1-propanol, dimethyl sulfoxide, acetonitrile, formamide, N-methylformamide, N,N-dimethylformamide, N-methylacetamide and N,N-dimethylacetamide) were analyzed using the Quint-Viallard conductivity equation and taking into account the ion association effect. The molar limiting conductances and the ion association constants were determined for various multivalent electrolytes in these solvents using the literature conductivities. In many cases, for the first time, it was possible to obtain consistent values of the limiting ionic conductances in organic solvents.     

Inclusion complexes of PBN-type nitrone spin traps and their superoxide spin adducts with cyclodextrin derivatives: parallel determination of the association constants by NMR titrations and 2D-EPR simulations

(1)H NMR and electron paramagnetic resonance (EPR) titrations were used to determine the association constants of the complexes of alpha-phenyl-N-tert-butylnitrone (PBN) analogues and their superoxide spin adducts, respectively, with methylated beta-cyclodextrins. A 1:1 stoichiometry for the nitrones with randomly methylated beta-cyclodextrin and 2,6-di-O-methyl-beta-cyclodextrin and 1:1 and 1:2 stoichiometries for the corresponding cyclodextrin-nitroxide complexes were observed. After the superoxide radical spin trapping reaction, EPR titrations afforded the association constants of the corresponding cyclodextrin-nitroxide complexes. Two-dimensional EPR simulations indicated a bimodal inclusion of the nitroxide free radical spin adducts into the cyclodextrins. For all the nitrone-cyclodextrin and nitroxide-cyclodextrin complexes, the association constants were always higher for the nitroxide complexes than for the nitrone complexes. A cooperative system concerning the complexation of the nitroxide spin adduct with a cyclodextrin was evidenced by EPR titrations. The efficiency of the cyclodextrin inclusion technique to trap superoxide and to resist bioreduction by sodium l-ascorbate was also investigated.     

非离子表面活性剂和β-环状糊精包结作用的微量热法研究

用Model-4200型恒温滴定量热系统,研究了非离子表面活性剂(TritonX-114,TritonX-100,TritonX-102,TritonX-405)和β-环状糊精的包结的热力学性质,结果表明:对所有体系,均形成1:1的包结物,ΔHⅲ和ΔSⅲ值均为负值,形成包结物的过程是焓有利而熵不利的过程,而且-ΔHⅲ和ΔSⅲ值随非离子表面活性剂环氧乙烷(EO)链长的增加而减少。另外,非离子表面活性剂环氧乙烷(EO)链越长,包结物稳定常数越小。     

阴离子表面活性剂和β-环糊精包结作用

环糊精由于其特殊结构可与众多物质(客体分子)形成包结物,这种包结物在化学理论研究、化工工业、农业及医药等领域有广阔的应用前景[1、2],因而受到人们极大的关注.人们用电导法、核磁技术、表面张力法等研究了环糊精与阴离子表面活性剂的相互作用,但这些方法得出的结果很...     

Charge transfer complexes of 9-vinyl-carbazole with pi acceptors in homogeneous and in micellar solutions

The molecular association of 9-vinyl-carbazole (CBZ) with three electron acceptors, p-chloranil (CHL), 2,7-dinitro-9-fluorenone (FL), and tetracyano-p-quinodimethane (TCNQ), is studied in acetonitrile and in micellar aqueous solution of sodium dodecyl sulfate (SDS). In both media, stable charge transfer (CT) complexes are formed with association constants in the range of 8-500 M(-1). CBZ and FL form a 1:2 complex in acetonitrile, but in SDS micelles the association is 1:1 due to size restriction and occupancy statistics in the host aggregates. The combination of absorption and fluorescence emission spectroscopy data indicates that the bimolecular CT complex of CBZ with TCNQ is stabilized in two distinct environments of the SDS micelles providing then two separated CT absorption bands.     

酚类在芳烃溶剂中的缔合溶液热力学

用凝固点降低法测量了对甲酚、间甲酚、邻甲酚、2,4-二甲酚、2,6-二甲酚以及对甲酚+间甲酚、对甲酚+邻甲酚、间甲酚+邻甲酚、2,4-二甲酚+2,6-二甲酚的1:1摩尔比混合物等为溶质, 溶剂为苯或对二甲苯的活度系数, 用Wiehe-Bagley型的连续缔合模型对数据进行了处理, 得到了各种酚的自缔合常效K_A. 在同一溶剂中, K_A依下列顺序减小: 对甲酚>间甲酚>邻甲酚; 2,4-二甲酚>2,6-二甲酚. 各混合酚的表观K_A 介于两种纯酚的K_A之间.     

Non-covalently dendronized flavins as organocatalysts for aerobic reduction of olefins

A variety of association complexes of synthetic flavin with diaminopyridine and melamine receptors are described in terms of synthesis, association properties, and catalytic activities for aerobic hydrogenation of olefins. The 1:1 association complex of lumiflavin 1 with 2,6-bis(acylamino)pyridine receptor bearing 3,4,5-trialkoxybenzyl ether dendron unit 2 acts as an efficient supramolecular organocatalyst for the aerobic reduction of styrene at ambient temperature under atmospheric air pressure.     

N-甲基甲酰胺与醇的氢键相互作用

The hydrogen bonding interactions between N-methylformamide and primary, secondary, and tertiary alcohols have been studied using the FT1R spectroscopic method. The most likely association complex between alcohol and N-methylformamide is the 1:1 stoichiometric complex formed between the hydroxyl group of alcohol and the carbonyl group of N-methylformamide. The formation constant of the 1:1 complexes has been calculated using the Nash method. It appears that the primary alcohols have larger formation constant compared with the secondary and tertiary alcohols. The results showed that the proton-donating ability of the alcohols decreased in the order: primary＞secondary＞tertiary, and that the association constant increased with the increase in carbon chain of the alkyl group of alcohols.     

Hydrogen bonding interaction between acrylic esters and monohydric alcohols in non-polar solvents: An FTIR study

The association between acrylic esters (methyl methacrylate, ethyl methacrylate and butyl methacrylate) and some monohydric (primary, secondary and tertiary) alcohols in non-polar solvents, viz. n-heptane, CCl4 and benzene has been investigated by means of FTIR spectroscopy. The most likely association complex between alcohol and acrylic ester is 1:1 stoichiometric complex through the hydroxyl group of alcohol and the carbonyl group of acrylic ester. The formation constant of the 1:1 complexes has been calculated using Nash method. It appears that the primary alcohols have larger formation constant than the secondary and tertiary alcohols. The results show that the proton donating power of the alcohols decreases in the order primary>secondary>tertiary and the association constant increases with the increase in carbon chain of the alkyl group of acrylic esters and alcohols. Also the results show a significant dependence of the association constant upon the solvents used. The solvent effect on the formation of hydrogen bond equilibria is discussed in terms of specific interaction between the solute and solvent.     

Associations between DRDs and schizophrenia in a Korean population: multi-stage association analyses

The dysregulation of the dopaminergic system has been implicated in the pathophysiology of major psychosis, including schizophrenia, with dopamine receptor genes (DRDs) presently targeted as the most promising candidate genes. We investigated DRD1-5 for association with schizophrenia using a multi-stage approach in a Korean sample. One hundred forty-two SNPs in DRD1-5 were selected from the dbSNP, and the associations of each SNP were then screened and typed by MALDI-TOF mass spectrometry using pooled DNA samples from 150 patients with major psychosis and 150 controls. Each of the suggested SNPs was then genotyped and tested for an association within the individual samples comprising each pool. Finally, the positively associated SNPs were genotyped in an extended sample of 270 patients with schizophrenia and 350 controls. Among the 142 SNPs, 88 (62%) SNPs in our Korean population were polymorphic. At the pooling stage, 10 SNPs (DRD1: 2, DRD2: 3, and DRD4: 5) were identified (P<0.05). SNPs rs1799914 of DRD1 (P=0.046) and rs752306 of DRD4 (P=0.017) had significantly different allele frequencies in the individually genotyped samples comprising the pool. In the final stage, with the extended sample, the suggestive association of DRD4 with rs752306 was lost, but the association of DRD1 with rs1799914 gained greater significance (P=0.017). In these large-scale multi-stage analyses, we were able to find a possible association between DRD1 and schizophrenia. These findings suggested the potential contribution of a multi-step strategy for finding genes related to schizophrenia.     

The cavity elongation effect. Calorimetric studies of the complexes of long-chain carboxylic acids with methyl-α-cyclodextrin in aqueous solutions

The formation of complexes between methyl-α-cyclodextrin (MαCD) and monocarboxylic acids from C₅ to C₁₂ or cycloalkanols has been studied calorimetrically at 298 K in aqueous phosphate buffer, pH 11.3. The forces involved in the association process are discussed according to the signs and values of the thermodynamic parameters obtained: association enthalpy, constant, Gibbs energy and entropy. Methyl-α-cyclodextrin forms 1:1 inclusion complexes with monocarboxylic acids, characterized by a monotonous increase in the values of enthalpies and association constants at increasing alkyl chain length. Association is characterized by negative enthalpies and by positive entropies: that determines large association constants. That behaviour is compared to the unusual trend in the values of the association constants shown by the parent α-cyclodextrin interacting␣with the same monocarboxylic acids. The model proposed to rationalize the present data provides a cavity elongation effect. Namely, because of the presence of the methyl groups on the outside, the cavity behaves as it were deeper than that of the parent cyclodextrin. The association with cycloalkanols—cyclohexanol, cycloheptanol, cyclooctanol and 1-cylohexyl-ethanol—is characterized by lower entropies, as determined by the␣enhanced negative contribution originating from the␣tighter fit of the guest into the cavity.     

Cooperative self-assembly of dendrimers via pseudorotaxane formation from a homotritopic guest molecule and complementary monotopic host dendrons

Interaction of the homotritopic guest 1,3,5-tris[p-(benzylammoniomethyl)phenyl]benzene tris(hexafluorophosphate) (1a) with dibenzo-24-crown-8 (DB24C8) leads to the sequential self-assembly of [2]-, [3]-, and [4]-pseudorotaxanes 7a, 8a, and 9a, respectively. The self-assembly processes were studied using NMR spectroscopy. In CD(3)CN and CD(3)COCD(3) the individual association constants K(1), K(2), and K(3) for 1:1, 1:2, and 1:3 complexes were determined by several methods. Via Scatchard plots, the three NH(2)(+) sites of 1a were shown to behave independently in binding DB24C8. K values (4.4 x 10(2), 1.4 x 10(2), and 41 M(-)(1), respectively, in CD(3)CN) directly determined from signals for the individual complexes (7a, 8a, and 9a) were somewhat higher than those estimated from the Scatchard plot because of concentration dependence, but the ratios of association constants followed the expected statistical order (K(1):K(2):K(3) = 3:1:(1)/(3)). These are believed to be the first evaluations of association constants leading to a [4]-pseudorotaxane. In the less polar CDCl(3), association constants could not be determined because approximately 90% of the dissolved tritopic guest, which by itself is insoluble, was present as the fully loaded [4]pseudorotaxane 9a! Self-assembly of homotritopic guest 1a with benzyl ether dendrons of the first, second, and third generations functionalized at the "focal point" with DB24C8 moieties (3-5) produces pseudorotaxane dendrimers. The self-assembly processes were studied using (1)H NMR spectroscopy. In CD(3)COCD(3) for all three generations the individual association constants K(1), K(2), and K(3) for [2]-, [3]-, and [4]-pseudorotaxane complexes 7c-e, 8c-e, and 9c-e indicated that the self-assembly was cooperative; that is, the ratios of the individual association constants exceeded the expected statistical ratios. Scatchard plots confirmed this behavior. Self-assembly processes in the less polar CDCl(3) were kinetically slow, requiring ca. 1, 2, and 3 days, respectively, for the first, second, and third generation systems to reach equilibrium with 1a; the slow rate is attributed to the insolubility of the homotritopic guest 1a in this medium and the steric demands of the resulting dendrimers. However, only dendrimers of 1:3 stoichiometry, that is, the nanoscopic [4]pseudorotaxanes 9, were formed! Moreover, it is noteworthy that the extent of dissolution of 1a (reflective of the overall association constant which is too high to measure) increases with generation number, presumably because of the more effective screening of the ionic guest by the larger dendrons and perhaps favorable pi-pi and CH-pi interactions. Such cooperative effects suggest a number of applications that can take advantage of the pH-switchable nature of these self-assembly processes.     

N-甲基甲酰胺与醇的氢键相互作用

Amides are used as synthetic reagents and as starting mate- rials for the preparation of insecticides and pharmaceuticals products[1]. Alcohols are industrially and scientifically important organic compounds, and their physical and chemical properties are…     

Thermodynamic aspects of dicarboxylate recognition by simple artificial receptors.

Recognition of dicarboxylates by bis-functional hydrogen-bonding receptors displays divergent thermodynamics in different solvent systems. NMR titration and isothermal titration calorimetry indicated that neutral bis-urea and bis-thiourea receptors form exothermic complexes with dicarboxylates in DMSO, with a near zero entropic contribution to binding. The increased binding strength of bis-guanidinium receptors precluded quantitative measurement of binding constants in DMSO, but titration calorimetry offered a qualitative picture of the association. Formation of these 1:1 complexes was also exothermic, but additional endothermic events occurred at both lower and higher host-guest ratios. These events indicated multiple binding equilibria but did not always occur at a discrete 2:1 or 1:2 host-guest molar ratio, suggesting higher aggregates. With increasing amounts of methanol as solvent, bis-guanidinium receptors form more endothermic complexes with dicarboxylates, with a favorable entropy of association. This switch from association driven by enthalpy to one driven by entropy may reflect a change from complexation involving the formation of hydrogen bonds to that promoted by solvent liberation from binding sites.     

Study of the Inclusion Complexes of β-Cyclodextrin with the Sodium Salt of Trisulfonated Triphenylphosphine

The formation of inclusion complexesbetween the sodium salt of trisulfonatedtriphenylphosphine and -cyclodextrin has beeninvestigated at two temperatures by high field nuclearmagnetic resonance, electrospray mass and UV-visspectroscopies. At 268 K, titration experiments andJob's method suggest that the major species insolution is a 1 : 1 inclusion complex. The moleculargeometry of this inclusion complex was studied usingthe ROESY NMR technique complemented by molecularmodelling. All these methods converged towards thestructure attained by inserting one aromatic ring intothe hydrophobic cavity of the host from the side ofthe secondary hydroxyls. At 298 K, a higher proportionof 2 : 1 and 3 : 1 complexes induces strong alterations ofthe NMR signals, preventing an easy and reliabledetermination of association constants. Nevertheless,an apparent association constant can be determinedfrom UV-vis data by assuming a 1 : 1 equilibrium. Thegeometry of the 2 : 1 and 3 : 1 complexes is also brieflydiscussed from ROESY NMR experiments.     

Spectrofluorimetric determination of stoichiometry and association constants of the complexes of harmane and harmine with beta-cyclodextrin and chemically modified beta-cyclodextrins

The association characteristics of the inclusion complexes of the beta-carboline alkaloids harmane and harmine with beta-cyclodextrin (beta-CD) and chemically modified beta-cyclodextrins such as hydroxypropyl-beta-cyclodextrin (HPbeta-CD), 2,3-di-O-methyl-beta-cyclodextrin (DMbeta-CD) and 2,3,6-tri-O-methyl-beta-cyclodextrin (TMbeta-CD) are described. The association constants vary from 112 for harmine/DMbeta-CD to 418 for harmane/HPbeta-CD. The magnitude of the interactions between the host and the guest molecules depends on the chemical and geometrical characteristics of the guest molecules and therefore the association constants vary for the different cyclodextrin complexes. The steric hindrance is higher in the case of harmine due to the presence of methoxy group on the beta-carboline ring. The association obtained for the harmane complexes is stronger than the one observed for harmine complexes except in the case of harmine/TMbeta-CD. Important differences in the association constants were observed depending on the experimental variable used in the calculations (absolute value of fluorescence intensity or the ratio between the fluorescence intensities corresponding to the neutral and cationic forms). When fluorescence intensity values were considered, the association constants were higher than when the ratio of the emission intensity for the cationic and neutral species was used. These differences are a consequence of the co-existence of acid-base equilibria in the ground and in excited states together with the complexation equilibria. The existence of a proton transfer reaction in the excited states of harmane or harmine implies the need for the experimental dialysis procedure for separation of the complexes from free harmane or harmine. Such methodology allows quantitative results for stoichiometry determinations to be obtained, which show the existence of both 1:1 and 1:2 beta-carboline alkaloid:CD complexes with different solubility properties.     

Gas chromatographic study of the hydrogen bonding of aliphatic alcohols to tri-n-octylphosphine oxide

Retention volumes of 21 aliphatic alcohols were measured at five temperatures between 30 and 60 degrees C in columns packed with different percentages of squalane or with solutions of tri-n-octylphosphine oxide (TOPO) in squalane coated on previously deactivated Chromosorb W. Experimental data fit to a 1:1 alcohol-TOPO association model, with association constants ranging from 26 to 59 dm3 mol(-1) at 45 degrees C. Association constants follow the trend primary alcohols>secondary alcohols>tertiary alcohols, with minor differences between the members of each of these three groups. The association enthalpy for the 21 alcohols averages -21.8 kJ mol(-1), with a standard deviation of -1.3 kJ mol(-1).