Differential interactions of cyclodextrins with hydrophobic derivatives of sepharose CL-4B

The partition coefficients K_av between the solution phase and octyl- and phenyl-sepharose CL-4B were determined for three cyclodextrins (CDs), -CD, -CD and -CD in various aqueous solutions, as a measure of their interactions with the two hydrophobic ligands. K_av of the CDs increased in the order of -CD<-CD<-CD for octyl-sepharose CL-4B and -CD<-CD<-CD for phenyl-sepharose CL-4B. In all cases, K_av increased by increasing NaCl concentration in the aqueous solution phase and also by lowering temperature, but in the presence of NaBr and NaSCN, both chaotropic salts, K_av decreased markedly. The spontaneity of the transfer of the CDs from the aqueous solution phases to the gel phases was due to the enthalpy decrease. It was shown that discrete separation of the three CDs can be achieved by the hydrophobic chromatography on a short column (1×25cm) of octyl-sepharose CL-4B by adjusting the NaCl concentration and temperature.     

Inclusion of water by a crown amide. First crystal structure of a respective host-guest combination

Crown amide (1) forms a stoicheiometric 1:1 inclusion complex with water, the X-ray crystal structure of which is reported. Crystals of1 · H₂O are triclinic, space groupP1, witha=7.503(1),b=11.394(3),c=13.443(2) Å, =107.066(18), =96.627(10), =106.377(14)°, andZ=2.R _F =0.039 for 1697 MoK reflections [I>3(I)] measured at 24°C. The structure features a hydrogen bonded hostguest relationship with concrete1 · H₂O units. Hydrogen bonds are between the water oxygen and O(4), N(4), respectively. The crystal packing shows a cavity arrangement of four ligands around each water molecule. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82055 (16 pages).     

The Complexation Properties of the Water-Soluble Tetrasulfonatomethylcalix[4]resorcinarene toward α-Aminoacids

The flexible bowl-type water-soluble molecule1, consisting of a resorcinol core and fourconvergent tetrasulfonatomethylene groups, existingas a tetraanion in neutral water solution, was studiedas the host molecule for recognition of-aminoacids. Out of 12 examined guestmolecules only those possessing aromatic hydrophobicmoieties or a long hydrophobic chain with a second ionogenic groupform inclusion complexes with 1. The complex formationwas considered with the help of both ¹H NMRand pH-metric titration in a broad range of pH.The role of host and guest geometric complementarity aswell as additional – and hydrophobic interactionsis discussed. The lack of these interactions inaqueous media provides domination of the guestsolvation by water over the 1 : 1 complexformation with 1.     

Influence of ligand structure and solvent effects on complexation of neutral guests by several crown ethers

The formation of complexes between crown ethers and acetonitrile, chloroform, and nitromethane were investigated in carbon tetrachloride at 25°C. A significant influence of the ring size on the selectivity of the host is evident. The host 18-crown-6 forms complexes for which the reaction enthalpy and entropy are quite high. Host molecules with benzene side groups form complexes of lower reaction enthalpy and entropy and therefore the complexes formed are less stable than that of the analogous crown ethers without aromatic groups. Solvent effects on the stability constant K, the reaction enthalpy H, and the reaction entropy S were studied for the complexation of malonitrile by 18-crown-6. The reaction enthalpy and entropy values change in accordance with the dielectric constant of the solvent used, but no overall effect on complex stability with change in solvent dielectric constant was observed.     

Studies on molecular interactions of β-cyclodextrin and antiulcer agent

The search for the lowest energy conformation of complex {β-cyclodextrin (β-CD)+chlorambucil} were carried out by molecular mechanics method. Theoretical calculations of molecular interactions of complex were carried out using the molecular orbital method. The correlation between energy changes and molecular structures are discussed. The large interaction energies calculated by the molecular orbital method bears out the inclusion phenomenon.     

Cavitands. (Review)

The syntheses, reactivity and complexing properties of cavitands are reviewed.     

Anionische Antimon(III)-Fluorokomplexe mit protonierten Azakronenethern als Gegenionen. Strukturen und Mößbauerspektren von [H2cyclam]2[Sb4F16] · 2 H2O, [H4cyclam][Sb2F10] · 2 HF und [H4(tetramethyl)cyclam]2[Sb4F15][HF2][F]4 (cyclam = 1,4,7,11-Tetraazacyclotetradecan)

Anionic Antimony(III) Fluoro Complexes with protonated Azacrownethers as Counterions. Crystal Structures and Mößbauer Spectra of [H₂cyclam]₂[Sb₄F₁₆] · 2H₂O, [H₄cyclam][Sb₂F₁₀] · 2 HF, and [H₄(tetramethyl)cyclam]₂[Sb₄F₁₅][HF₂][F]₄ (cyclam = 1,4,7,11-Tetraazacyclotetradecane) The title compounds are formed by reaction of SbF₃ with the respective azacrownether. [H₂cyclam]₂[Sb₄F₁₆] · 2 H₂O contains tetrameric anions which weakly associate to chains. The [H₂cyclam]²⁺ ions possess an unusual conformation due to intramolecular hydrogen bonds. [H₄cyclam][Sb₂F₁₀] · 2HF contains the dimeric hitherto unknown [Sb₂F₁₀]^4? ion; two HF molecules are attached to it by hydrogen bonds. The structure of [H₄(tetramethyl)cyclam]₂[Sb₄F₁₅][HF₂][F]₄ is made up of the two dimensional polymeric [HSb₄F₁₇]^4? anion. The tetra-protonated tetramethylcyclam ions form host-guest complexes with fluoride ions.     

Polymorphism of Crystalline Inclusion Complexes and Unsolvated Hosts. Part 8

Crystallization of cyclotriveratrylene (CTV) from solutions in acetone at 40°C gave a new 4:1 host-guest complex instead of the conventional 2:1 clathrate (-phase) whose X-ray crystal structure was determined. Data for 2(C₂₇H₃₀O₆) · 0.5(CO(CH₃)₂): monoclinic, P2₁/c, a = 18.942(4), b = 24.697(5), c = 10.508(2) Å, = 91.10(2)°, V = 4915(2) ų, Z = 8, D _x = 1.257 g/cm³, T = 293 K, R = 0.077 (for 2694 reflections). One of the two crystallographically independent CTV molecules (molecule A) is stacked into columns characteristic of the CTV - or -phase complexes. Molecules B face each other enclathrating inside around the inversion center disordered acetone molecules giving rise to the molecular capsule. The acetone molecule is H-bonded simultaneously to both host molecules by C(H₂)--H ··· O type bonds forming centrosymmetric dimers. Dimers are incorporated together with two A molecules into centrosymmetric units also by C(H₂)--H ··· O type H-bonds. Packing of these units gives rise to the crystal structure of the clathrate.     

β-卤素取代对杯[4]吡咯构象及主-客体相互作用的影响II. 密度泛函理论研究

应用密度泛函理论对杯[4]吡咯及卤素取代杯[4]吡咯模型分子的自由主体以及其卤素离子复合物体系进行计算研究. 结果表明, 杯[4]吡咯β位被卤素拉电子基团取代后, 主体分子的构象特征受吡咯单元的偶极影响; β-卤素取代导致了杯[4]吡咯对卤素离子的结合作用增强, 且当β位为氯取代时, 杯[4]吡咯对卤素离子的结合能力最强. 并从振动光谱、NBO电荷布居、相互作用的前线轨道、“活性”构象的偶极矩和Mulliken成键布居等方面阐述β-卤素取代对杯[4]吡咯与卤素离子之间的主-客体相互作用的影响.     

Enantiomeric Recognition of d- and l-Amino Acid Methyl Ester Hydrochlorides by New Chiral Bis-pyridino-18-crown-6 Substituted with Urea, and Diphenyl Groups

The article reports the synthesis and chiral recognition properties of a new chiral bis-pyridino-18-crown-6 (7), having urea, diphenyl, and allyloxy groups. The chiral bis-pyridino-18-crown-6 was prepared by a thirteen-steps procedure from the commercially available (S)-(+)-mandelic acid and chelidamic acid. The association constants (K _a) (1.33 × 10³–3.20 × 10³) for enantiomeric recognition of d- and l-amino acid methyl ester hydrochlorides using the chiral bis-pyridino-18-crown-6 have been examined by ¹H-NMR titration method in CDCl₃ at 25 °C. The chiral bis-pyridino-18-crown-6 showed higher association constants for the d-series amino acid methyl ester (d-AlaOMe, d-LeuOMe, d-MetOMe) hydrochlorides as compared to the corresponding l-series (l-AlaOMe, l-LeuOMe, l-MetOMe) hydrochlorides.