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1.
New armed‐monoaza‐12‐crown‐4 and armed‐monoaza‐15‐crown‐5 ethers having dual phenolic OH and pyridine nitrogen binding sites in a side arm were prepared by the Mannich reaction of N‐methoxymethyl‐monoazacrown ethers with 3‐hydroxypyridine. Complexation studies of these new hydroxypyridine‐armed ligands were carried out by liquid membrane transport, 1H nmr titration experiments, thermodynamic values (log K, ΔH and TΔS), and X‐ray crystallography of two alkali‐metal complexes. These results indicate that the oxygen atom of the phenolic OH group and pyridine nitrogen atom of the side arm are involved in complexation under basic and neutral conditions, respectively.  相似文献   

2.
o-Dihydroxy-4-(3,4-dimethoxyphenyl)-chromenones (coumarins; 3a,b) were synthesised from 1,2,3-trihydroxy- or 1,2,4-triacetoxybenzenes through a reaction with ethyl 3-(3,4-dimethoxyphenyl)-3-oxopropanoate in H2SO4 or CF3COOH. The chromenone-crown ethers (4af) were prepared from the cyclic condensation of o-dihydroxy-4-(3,4-dimethoxyphenyl)chromenones (3a,b) with poly(ethylene glycol) ditosylates, in the presence of CH3CN/alkali carbonates. The chromatographically purified original chromenone-crown ethers were identified by 1H NMR, 13C NMR, MALDI-TOF mass spectrometry and elemental analysis. The 1:1 binding constants of Li+, Na+ and K+ with the chromenone-crown ethers were estimated in acetonitrile using fluorescence emission spectroscopy. The complexing-enhanced fluorescence spectra and complexing-enhanced quenching fluorescence spectra, along with the cationic recognition rules of the crown ethers allowed the ion binding powers to be determined.  相似文献   

3.
A series of double-armed benzo-15-crown-5 lariats (3–8) have been synthesized by the reaction of 4′, 5′-bis(bromomethyl)-benzo-15-crown-5 (2) with 4-hydroxybenzaldehyde, phenol, 4-chlorophenol, 4-methoxyphenol, 2-hydroxybenzaldehyde, and 4-acetamidophenol in 43 ~ 82% yields, respectively. The complex stability constants (K S) and thermodynamic parameters for the stoichiometric 1:1 and/or 1:2 complexes of benzo-15-crown-5 1 and double-armed crown ethers 3–8 with alkali cations (Na+, K+, Rb+) have been determined in methanol–water (V/V=8:2) at 25 °C by means of microcalorimetric titrations. As compared with the parent benzo-15-crown-5 1, double-armed crown ethers 3–8 show unremarkable changes in the complex stability constants upon complexation with Na+, but present significantly enhanced binding ability toward cations larger than the crown cavity by the secondly sandwich complexation. Thermodynamically, the sandwich complexations of crown ethers 3-8 with cations are mostly enthalpy-driven processes accompanied with a moderate entropy loss. The binding ability and selectivity of cations by the double-armed crown ethers are discussed from the viewpoints of the electron density, additional binding site, softness, spatial arrangement, and especially the cooperative binding of two crown ether molecules toward one metal ion.Graphical Abstract Synthesis of Double-Armed Benzo-15-crown-5 and Their Complexation Thermodynamics with Alkali CationsYU LIU*, JIAN-RONG HAN, ZHONG-YU DUAN and HENG-YI ZHANG This revised version was published online in July 2005 with a corrected issue number.  相似文献   

4.
Two new selenacrown ethers, i.e., N,N′-dimethyl-1,11-diaza-4,8,14,18,-tetraselenacycloicosane (1) and 7,11-diseleno-2,3,15,16,-dibenzo-1,4,14,17,20,23-hexaoxacyclopentacosane (2), have been synthesized and characterized by elemental analysis and UV, and 1H-NMR spectroscopy. An X-ray crystallographic structure was obtained for 1. UV-spectrophotometric titrations have been performed in CCl4 solution at 25–50 °C to obtain the complex stability constants (Ks) and the thermodynamic parameters (ΔH0 and TΔS0) for the stoichiometric 1:1 complexation of [60]-fullerene (C60) with the crown ethers 1–4. The obtained Ks values together with that reported for dicyclohexano-24-crown-8 (5) reveal that, the more the heteroatom numbers in crown ether ring are, and the larger the cavity sizes of crown ethers are, the higher theKsvalues for complexation with C60 are. Thermodynamically, the complexation of C60 with 1–5 is absolutely enthalpy-driven in CCl4, while the complex stability is governed by the entropy term.  相似文献   

5.
Chiral aminoalcohol based Schiff bases (R or S)-2-{(E)-(2-hydroxy-1-phenylethylimino)methyl}phenol and (R/S)-2-{(E)-(2-hydroxy-2-phenylethylimino)methyl}phenol coordinate to copper(II)acetate to give enantiopure Λ/Δ- or Δ/Λ-bis[(R or S)-2-{(E)-(2-hydroxy-1-phenylethylimino)methyl}phenoxide-κ2N,O]copper(II), {Λ/Δ-Cu(R-L1)2 (1) or Δ/Λ-Cu(S-L1)2 (2)}, and racemic Δ/Λ- and Λ/Δ-bis[(R/S)-2-{(E)-(2-hydroxy-2-phenylethylimino)methyl}phenoxide-κ2N,O]copper(II), {Δ/Λ- and Λ/Δ-Cu(R/S-L2)2 (3)}, respectively. The complexes are characterized by elemental analyzes, IR, UV–Vis, polarimetry, circular dichroism (CD), differential scanning calorimeter (DSC), and mass spectroscopy. Polarimetry shows the rotation to the left at ?113.6° (1) and to the right at +106.4o (2). CD spectra show the expected mirror-image relationship with opposite sign of ellipticity maxima (Δεmax = +0.43 for 1 and ?0.42 M?1 dm3 cm?1 for 2 at 638 nm) due to the d-d transitions of the metal ion. CD spectral analyzes further reveal a diastereoselectivity or diastereomeric excess towards Λ-Cu(R-L1)2 or Δ-Cu(S-L1)2 configuration for 1 or 2 in solution. Similarly, the enantiomeric pair of Δ-Cu(R-L2)2 and Λ-Cu(S-L2)2 configurations (CD inactive) for 3 will be preferred in solution. Electronic spectra in different solvents reveal a negative solvatochromism by shifting absorption maxima of the MLCT band to higher energies in solvents of increasing polarity as well as acceptor number. DSC analyzes show an endothermic peak at 525.5 (1) or 528.7 K (2), corresponding to a thermally induced structural phase transformation from distorted square-planar to regular tetrahedral.  相似文献   

6.
The molecular clefts (R)- and (S)- 3 , incorporating 9,9′-spirobi[9H-fluorene] as a spacer and two N-(5,7-dimethyl-1,8-naphthyridin-2-yl)carboxamide (CONH(naphthy)) units as H-bonding sites were prepared via the bis(succinimid-N-yl esters) of (R)-and (S)-9,9′-spirobi[9H-fluorene]-2,2′-dicarboxylic acid ( 5 ). Derivative 6 , with one CONH(naphthy) unit and one succinimid-N-yl ester residue allowed easy access to spirobifluorene clefts with two different H-bonding sites, as exemplified by the synthesis of 4 . Binding studies with (R)- and (S)- 3 and optically active dicarboxylic acids in CDCl3 exhibited differences in free energy of the formed diastereoisomeric complexes (Δ(ΔGº)) between 0.5 and 1.6 kcal mol?1 (T 300 K). Similar enantioselectivities were observed with the spirobifluorene clefts (R)- and (S)- 1 , bearing two N-(6-methylpyridin-2-yl)carboxamide (CONH(py)) H-bonding sites. The thermodynamic quantities ΔHº and ΔSº for the recognition processes with (R)- and (S)- 1 were determined by variable-temperature 1H-NMR titrations and compared to those with (R)- and (S)- 2 , which have two CONH(py) moieties attached to the 6,6′-positions of a conformationally more flexible 1,1′-binaphthyl cleft. All association processes showed high enthalpic driving forces which are partially compensated by unfavorable changes in entropy. Pyranosides bind to the optically active clefts 1 and 3 in CDCl3 with ?ΔGº = 3.0–4.3 kcal mol?1. Diastereoisomeric selectivities up to 1.2 kcal mol?1 and enantioselectivities up to 0.4 kcal mol?1 were observed. Cleft 4 and N-(5,7-dimethyl-1,8-naphthyridin-2-yl)acetamide ( 25 ) complexed pyranosides 22–24 as effectively as 3 indicating that only one CONH(naphthy) site in 3 associates strongly with the sugar derivatives. Based on the X-ray crystal structure of 3 , a computer model for the complex between (S)- 3 and pyranoside 22 was constructed. Molecular-dynamics (MD) simulations showed that differential geometrical constraints are at the origin of the high enantioselectivity in the complexation of dicarboxylic acid (S)- 7 by (R)- and (S)- 1 and (R)- and (S)- 3 .  相似文献   

7.
Complex stability constants (K S), standard molar enthalpy changes (ΔH 0) and entropy changes (ΔS 0) for the inclusion complexation of two cyclodextrin dimers, 6,6′-{2,2′-diselenobis[2-(benzoylamino)ethylamino]}-bridged bis(β-cyclodextrin) (1) and o-phenylenediseleno bridged bis(β-cyclodextrin)s (3), and their monomer analogs, 6-deoxy-6-{[2-(2,3-dihydro-3-oxo-1,2-benzisoselenazol-2-yl)ethyl]amino}-β-cyclodextrin (2) and mono[6-(phenylseleno)-6-deoxy]-β-cyclodextrin (4), with two bile salt guests, sodium cholate (CA) and sodium deoxycholate (DCA), were determined at 25°C in Tris buffer solutions (pH 7.4) at 298.15?K by means of isothermal titration microcalorimetry (ITC). The interactions and binding modes between the host cyclodextrins and the guest bile salts were further studied by ROESY spectroscopy. The thermodynamic parameters obtained, together with the ROESY spectra, were used to examine the correlations between thermodynamic behavior and binding modes of the host–guest complexation. The results indicate that the length, structure and conformation of the tethers linked to the cyclodextrins determine the binding modes and the binding abilities between hosts and guests to a great extent, leading to a reversion in binding ability when comparing the corresponding dimer and its monomer analog.  相似文献   

8.
A series of double-armed benzo-15-crown-5 lariats (3–8) have been synthesized by the reaction of 4′, 5′-bis(bromomethyl)-benzo-15-crown-5 (2) with 4-hydroxybenzaldehyde, phenol, 4-chlorophenol, 4-methoxyphenol, 2-hydroxybenzaldehyde, and 4-acetamidophenol in 43 ~ 82% yields, respectively. The complex stability constants (K S) and thermodynamic parameters for the stoichiometric 1:1 and/or 1:2 complexes of benzo-15-crown-5 1 and double-armed crown ethers 3–8 with alkali cations (Na+, K+, Rb+) have been determined in methanol–water (V/V=8:2) at 25 °C by means of microcalorimetric titrations. As compared with the parent benzo-15-crown-5 1, double-armed crown ethers 3–8 show unremarkable changes in the complex stability constants upon complexation with Na+, but present significantly enhanced binding ability toward cations larger than the crown cavity by the secondly sandwich complexation. Thermodynamically, the sandwich complexations of crown ethers 3-8 with cations are mostly enthalpy-driven processes accompanied with a moderate entropy loss. The binding ability and selectivity of cations by the double-armed crown ethers are discussed from the viewpoints of the electron density, additional binding site, softness, spatial arrangement, and especially the cooperative binding of two crown ether molecules toward one metal ion.  相似文献   

9.
Abstract

Calorimetric titrations have been performed for the first time in anhydrous acetonitrile at 25°C to give the complex stability constant (K S) and thermodynamic quantities for the complexation of light lanthanoid(III) nitrates (La-Gd) with 5,11,17,23-tetra-tert-butyl-26,28-bis(cyanomethoxy)-25,27-dihydroxy-calix[4]arene (1) and 5,11,17,23-tetra-tert-butyl-26, 28-bis(2-aminoethoxy)-25,27-dihydroxycalix[4]arene (2). X-ray crystallographic structures of 1 and 2 were also determined and compared. Possessing the cyanomethoxy and aminoethyl substituents, 1 and 2 displayed strikingly different cation binding abilities and selectivity profiles with much higher K S values for La3+ and Ce3+, which may be related to the original structures in the solid state. Thus, the binding profile for 2 showed a rapid decrease in K S with decreasing ionic diameter from La3+ to Pr3+ and then became flat up to Gd3+, while 1 gave a very flat profile which is superimposable with that for 2 between Pr3+-Gd3+. Thermodynamically, the complexation is driven absolutely by enthalpy which compensates the entropic loss arising from the structural freezing of the calix[4]arene derivatives upon simultaneous binding of lanthanoid ion by the phenolic oxygen and acetonitrile molecule in the cavity. The general validity and the meaning of the compensative enthalpy-entropy relationship observed are discussed.  相似文献   

10.
Abstract

The complexation of tetramethylammonium (TEMA), benzyltrimethylammonium (BTMA), p-nitrobenzyltrimethylammonium (BTMAN) and N, N, N-trimethylanilinium (TMA) by the tetrasulphonate derivative of the resorcinol cyclic tetramer (1), was studied in aqueous solution by 1H NMR and calorimetry. Host 1 specifically recognizes the—N+ (CH3)3 group of TEMA, BTMA and BTMAN, whereas it binds TMA unselectively; TMA is included both via the charged group and the aromatic moiety. The binding constants of all four guests with 1, as determined by both 1H NMR and calorimetric titrations, show that all inclusion processes are almost equally stabilised.

ΔHΔ and ΔSΔ values, determined by direct calorimetry, reveal specific interactions that are not expressed in the ΔGΔ terms and indicate that we are dealing with “non-classical hydrophobic effects”. The effects of the structural, conformational and electronic properties of the guests on the forces driving the inclusion processes are discussed.  相似文献   

11.
The relative reactivities of α-monosubstituted cyclic ethers having rings of three to six members toward a cation were estimated from their copolymerizations with 3,3-bis-(chloromethyl)oxetane (M1) catalyzed by boron trifluoride etherate in methylene chloride at 0°C. It was found that the reactivity of these cyclic ethers was dominated by both the ring strain and the basicity. The following empirical equation was derived to represent the relative reactivity of cyclic ethers: log (1/r1) = ?0.086ΔRS ? 0.31ΔB + 0.57, where ΔRS and ΔB are constants, characteristic of ring strain and basicity of the cyclic ethers and determined from the differences in free energy of polymerization of the corresponding cycloalkanes and in basicity between M1 and M2 monomers, respectively. A good linear correlation was observed between the reactivities calculated from this equation and those obtained from the experiments.  相似文献   

12.
Preparation of the trimethylsilyl ethers of 1-alkyl-3-azetidinols from non-hindered primary amines and epichlorohydrin by conversion of the intermediate 1-(alkylamino)-3-chloro-2-propanols to their trimethylsilyl ethers by either N-(trimethylsilyl)acetamide or by 1-(trimethylsilyl)imidazole followed by ring closure in acetonitrile is described. This sequence of reactions fails for aromatic amines, but appears to be general for all primary aliphatic amines, although the condensation of hindered amines with epichlorohydrin occurs slowly. Several novel azetidinols, in which the N-alkyl substituent itself contains a second heterocyclic system, are reported. In addition, the pKA's of several m. and p-substituted 1-benzylazetidinols correlates well with the Hammett equation.  相似文献   

13.
刘育  戚爱棣  陈荣悌  张有明 《化学学报》1997,55(11):1091-1096
本文用分光光度滴定法测定了双(苯并-15-冠-5)(1)与轻稀土(III)硝酸盐在无水乙腈溶液中, 20.0-35.0℃时分子内夹心配位作用的稳定常数, 进而计算了配位焓和配位熵, 并与母体苯并15-冠-5(2)的实验结果作了比较。化学计量法表明, 所有稀土硝酸盐均与双(苯并-15-冠-5)形成了1 : 1的配合物。从热力学的观点, 讨论了双冠醚分子结构、尺寸效应和空间构型等配位稳定性的影响。研究结果发现, 双冠醚(1)对于Eu^3^+具有较强的配位能力和配位选择性, Nd^3^+次之。配合物的稳定性主要来自于熵的贡献。  相似文献   

14.
The thermodynamic stabilities of Ag+, Ni2+ and Fe3+with diaza-crown ethers have been determinedconductometrically in acetonitrile at temperatures of 293, 298, 303 and 308 K.Both the size of the macrocyclic ring and the hard and soft acidand base (HSAB) character of the metal ions influence the relative stabilities of the complexes. For the metal ions with diazacrown ethers the values of log Kf for the 1 : 1 complexesfollow the order Ag+ > Ni2+ > Fe3+in accordance with Pearson's principle of HSAB character. The enthalpy and entropy of complexation were determined from the temperature dependence of the complexationconstants. The complexation process is entropy governed.  相似文献   

15.
《合成通讯》2013,43(4):679-686
Abstract

2-(Cyclohex-2′-enyl)-5,5-dimethyl-3-hydroxycyclohex-2-enone undergoes regioselective heterocyclization to give bridged heterocycles 5a,b and 7 on treatment with pyridine hydrotribromide or hexamethylenetetramine hydrotribromide (1 h); or elemental bromine (7 h); N-iodosuccinimide in acetonitrile at 0–5°C (1 h) and conc. H2SO4 at 0–5°C (2 h), respectively.  相似文献   

16.
The complexation reactions between 4′,4″(5″)-di-tert-butyldibenzo-18-crown-6 (DTBDB18C6) and Li+, Na+ and K+ ions were studied conductometrically in different acetonitrile–nitromethane mixtures at various temperatures. The formation constants of the resulting 1:1 complexes were calculated from the computer fitting of the molar conductance-mole ratio data at different temperatures. At 20 °C and in nitromethane solvent, the stability of the resulting complexes varied in the order K+ > Na+ > Li+. The enthalpy and entropy changes of the complexation reactions were evaluated from the temperature dependence of formation constants. It was found that the stability of the resulting complexes increased with increasing nitromethane in the solvent mixture. The TΔS° versus ΔH° plot of thermodynamic data obtained shows a fairly good linear correlation indicating the existence of enthalpy–entropy compensation in the complexation reactions. The ab initio studies calculated at B3LYP/6-31G level of theory, indicate the binding energy of complexes decreases with increasing cation size in the gas phase. In the solution phase, DTBDB18C6 preferentially forms complexes with the larger ions rather than the smaller ions because the solvation energies of the smaller ions are large enough to overcome and reverse the trends in gas phase complexation. The findings of this study suggest that the current understanding of the factors influencing the selectivity of metal ion complexation by crown ethers may be in need of revision.  相似文献   

17.
The complexation reaction between uranyl (II) nitrate, and N-methyliminobis(methylenephosphonic acid) (MIDPH) was investigated in two different binary solvent mixtures of D2O-DMSO-d6 at various temperatures using 31P NMR spectroscopy. The exchange between the free ligand and the 1:1 complexed ligand was slow on the NMR timescale and two 31P NMR signals were observed. The formation constant of the resulting complex was evaluated from integration of the two 31P NMR signals. The values of thermodynamic parameters of the resulting complex (ΔH, ΔS and ΔG) were determined from the temperature dependence of the formation constants. In the two solvent mixtures studied, the resulting complex is enthalpy stabilized but entropy destabilized.  相似文献   

18.
The density and the viscosity data have been used to determine the thermodynamic activation parameters, free energies (ΔG ?), enthalpies (ΔH ?) and entropies (ΔS ?), for viscous flow of the systems; water (W) + ethylenediamine (ED), W + trimethylenediamine (TMD) and W + N,N-dimethyltrimethylenediamine (DMTMD) in the temperature range of 303.15–323.15 K over the composition range of 0 ≤ X 2 ≤ 0.45, where X 2 is the mole fraction of diamines. On addition of diamines to water, ΔG ?, ΔH ? and ΔS ? values increase sharply, pass through a maximum and then decline. The heights of maximum in the ΔG ? versus X 2 curve vary as, W + DMTMD > W + TMD > W + ED. For all systems, the excess properties, ΔG ? E , ΔH ? E and ΔS ? E are positive. The observed increase in thermodynamic values may be due to combined effect of hydrophobic hydration of diamines and water–diamine interaction as a result of hydrophilic effect.  相似文献   

19.
Abstract

The Cs+ selectivity of some calix-crown ligands makes them excellent candidates for use in separation systems such as liquid membranes. Separation performance can be understood and predicted from thermodynamic data for cation complexation. We have therefore determined the log K, ΔH and ΔS for the interaction of Na+, K+, Rb+, Cs+ and NH4 + with didodecyl-calix[4]arene-crown-6 in acetonitrile at 25°C by titration calorimetry. The ligand is strongly selective for Cs+, and the selectivity trend results entirely from the enthalpy contribution, with entropy effects opposing the trend. These results are discussed in light of some corresponding data obtained by other researchers with similar ligands.  相似文献   

20.
张洪林  孔哲  闫咏梅  李干佐  于丽  李真 《化学学报》2007,65(10):906-912
N,N-二甲基乙酰胺(DMA)/长链醇非水溶液体系中, 利用微量量热仪, 研究阴离子表面活性剂十二烷基羧酸钠(SLA)、十二烷基硫酸钠(SDS)的临界胶束浓度(CMC)和热力学函数. 本文在十二烷基羧酸钠, 十二烷基硫酸钠的N,N-二甲基乙酰胺溶液中, 分别加入长链醇(庚醇、辛醇、壬醇、癸醇), 测定体系的热功率-时间曲线. 借助热力学理论, 由测得曲线, 进一步得到临界胶束浓度和热力学函数(ΔHm0, ΔGm0和ΔSm0). 讨论了温度、醇的碳原子数目、醇的浓度与热力学参数之间的关系. 结果表明, 对十二烷基羧酸钠或十二烷基硫酸钠的DMA溶液, 在含有相同浓度的各种醇的体系中, CMC, ΔHm0和ΔSm0的值随着温度的升高而增加, 而ΔGm0的值随着温度的升高而降低. 在相同温度及相同浓度的醇体系中, CMC, ΔHm0Gm0和ΔSm0的值都随着醇中碳原子数目的增加而降低. 在相同温度及相同醇的体系中, CMC, ΔGm0的值随着醇的浓度的增加而增大, 而ΔHm0, ΔSm0的值随着醇的浓度的增加而减少.  相似文献   

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