Evidences for temperature-dependent mechanism of host-guest complexation

Summary High-performance liquid chromatography and ultraviolet spectroscopy methods were applied to the studies on the influence of temperature on the complexation of β-cyclodextrin with naphthalene and its derivatives. The strong nonlinearity of Van't Hoff plots suggests, that the retention mechanism of hydrocarbons investigated might be different in high and low temperature region. The total lack of correlation (r=−0.230) between chromatographic data (capacity factors ratio:k _PAH/k _PAH×CD) and spectrophotometric data (ΔA) at high temperature (60°) as well as a significant correlation (r=0.922) at subambient temperature (15°C) suggest, that the inclusion mechanism starts to be important at low temperature region and the predominant mechanism for chromatographic retention is the formation of an inclusion complexes in the mobile phase.     

Syntheses and Structural Aspects of Cyclodextrin/Dialkylamine Inclusion Compounds

We report the syntheses and structural aspects of cyclodextrin host–guest inclusion compounds containing linear secondary alkylamines (dipropyl, dibutyl, dipentyl, dihexyl, and dioctyl) at 25 °C. Elemental analysis, ¹³C CP-MAS NMR spectroscopy, and powder X-ray diffraction analysis confirm the inclusion process. The basic host structure of the products is similar to that of typical cyclodextrin inclusion systems. ¹³C MAS NMR experiments show a different resonance pattern for the confined guest molecules with respect to the amine in the liquid phase. The presence of different resonance signals for the homologous carbon atoms of both dialkylamine branches is evidence for the non-symmetric location of the amine in the cyclodextrin channels.     

Structural and Magnetic Study of N2, NO,NO2, and SO2 Adsorbed within a Flexible Single‐Crystal Adsorbent of [Rh2(bza)4(pyz)]n

The crystalline one‐dimensional compound, [Rh^II₂(bza)₄(pyz)]_n ( 1 ) (bza=benzoate, pyz=pyrazine) demonstrates gas adsorbency for N₂, NO, NO₂, and SO₂. These gas‐inclusion crystal structures were characterized by single‐crystal X‐ray crystallography as 1 ?1.5 N₂ (298 K), 1 ?2.5 N₂ (90 K), and 1 ?1.95 NO (90 K) under forcible adsorption conditions and 1 ?2 NO₂ (90 K) and 1 ?3 SO₂ (90 K) under ambient pressure. Crystal‐phase transition to the P space group that correlates with gas adsorption was observed under N₂, NO, and SO₂ conditions. The C2/c space group was observed under NO₂ conditions without phase transition. All adsorbed gases were stabilized by the host lattice. In the N₂, NO, and SO₂ inclusion crystals at 90 K, short interatomic distances within van der Waals contacts were found among the neighboring guest molecules along the channel. The adsorbed NO molecules generated the trans‐NO???NO associated dimer with short intermolecular contacts but without the conventional chemical bond. The magnetic susceptibility of the NO inclusion crystal indicated antiferromagnetic interaction between the NO molecules and paramagnetism arising from the NO monomer. The NO₂ inclusion crystal structure revealed that the gas molecules were adsorbed in the crystal in dimeric form, N₂O₄.     

Improvement of some pharmaceutical properties of nocloprost by β- and γ-Cyclodextrin Complexation

Inclusion complexation of nocloprost, a potent antiulcer prostaglandin derivative, with -, -, and -cyclodextrins (CyDs) in aqueous solutions has been studied by the solubility method and¹³C-NMR spectroscopy. The steric requirement of host-guest interaction was reflected in the magnitude of the stability constants and the thermodynamic parameters of the inclusion complexes. Solid complexes of nocloprost with - and -CyDs in a molar ratio of 1 : 2 were obtained on the basis of aBs-type phase solubility diagram. The X-ray diffraction data suggested that nocloprost is included in the cylindrical channel formed by coaxial alignment of -CyD molecules to give a channel type structure. Release and thermal behavior of the solid complexes was examined and compared with nocloprost itself. The results indicated that the -CyD complex may have great utility among the three CyDs, being a rapid dissolving form of nocloprost with improved thermal stability.     

Selective transport of cesium ion in polymeric CTA membrane containing calixcrown ethers

A series of calixcrown ethers for which the cavity size of the crown ring is varied from crown-6 to crown-7 to crown-8 were examined for the transport abilities toward alkali metal ions. These ligands were incorporated into supported liquid membranes (SLMs) and into polymer inclusion membranes (PIMs) composed of cellulose triacetate (CTA) as a support and 2-nitrophenyl octyl ether (NPOE) and tris(2-butoxyethyl) phosphate (TBEP) as a plasticizer. In both membrane systems, calixcrown-6 showed the best selectivity toward a cesium ion over other alkali metal ions. The polymeric CTA membrane showed more rapid transport rate as well as higher durability than did the SLMs.     

Mechanism and Kinetics of Thermal Dissociation of Inclusion Complex of Benzaldehyde with β-Cyclodextrin

The inclusion complex of benzaldehyde (BA) with β-cyclodextrin (β-CD) was prepared and was studied by thermal analysis and X-ray diffractometry. The composition of the complex was identified by TG and elemental analysis as β-CD·BA·9H₂O. TG and DSC studies showed that the thermal dissociation of β-CD·BA·9H₂O took place in three stages: dehydration in the range 70-120°C; dissociation of β-CD·BA in the range 235-270°C; and decomposition of β-CD above 280°C. The kinetics of dissociation of β-CD·BA in flowing dry nitrogen was studied by means of TG both at constant temperature and at linearly increasing temperature. The results showed that the dissociation of β-CD·BA was dominated by a one-dimensional random nucleation and subsequent growth process (A₂). The activation energy E was 124. 8 kJ mol^-1, and the pre-exponential factor A 5.04·10¹¹ min^-1. This revised version was published online in July 2006 with corrections to the Cover Date.     

Solubility enhancement of triflumizole by host-guest interaction with β-cyclodextrin

Summary The solubility enhancement of triflumizole, a systemic fungicide, by -cyclodextrin inclusion complexation was investigated by electron absorption spectroscopy. The respective association constant determined by different methods was estimated to 470±20M ^–1 in aqueous solution. A model for the host-guest complexation was deduced by molecular calculations.

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Löslichkeitsverbesserung von Triflumizole durchHost-Guest-Complexierung mit -Cyclodextrin

Zusammenfassung Die Löslichkeitsverbesserung des systemischen Fungizids Triflumizole durch Komplexierung mit -Cyclodextrin wurde mittels Elektronenabsorptionsspektroskopie untersucht. Die entsprechende Stabilitätskonstante wurde durch verschiedene Methoden erfaßt und betrug im wäßrigen Medium 470±20M ^–1. Ein Model für denHost-Guest-Complex wurde durch Molekülrechnungen erstellt.

     

Molecular Recognition Study on a Supramolecular System. Part 21. Inclusion Complexation Thermodynamics of Aliphatic Alcohols by Organoselenium Modified β-Cyclodextrins

The spectrophotometric titrations have beenperformed at 25–40 °C in aqueous solution to give the complexstability constants and the thermodynamic parametersfor the stoichiometric 1 : 1 inclusion complexation ofvarious aliphatic alcohols withmono[6-(phenylseleno)-6-deoxy]--cyclodextrin (2),mono[6-(o-, m-,p-tolylseleno)-6-deoxy]--cyclodextrin (3–5),mono[6-(p-chloro-phenyl-seleno)-6-deoxy]--cyclodextrin(6), mono[6-(benzylseleno)-6-deoxy]--cyclodextrin (7) and mono[6-(naphthaleneseleno)-6-deoxy]--cyclodextrin(8). On thebasis of the present and previous results, themolecular binding abilities and selectivities forguest aliphatic alcohols of the host -cyclodextrinderivatives (2–8) are discussed comparatively and globallyfrom the thermodynamic point of view. Thethermodynamic parameters obtained are criticalfunctions of the size/shape of aliphatic alcohols, andthe position and type of the substituent introduced tothe aromatic ring of -cyclodextrin's sidearm,which are elucidatedin terms of the conformational, electrostatic,hydrogen-bonding, and hydrophobic effects.     

An improved enzymatic assay for glucose determination in blood serum using a l,1′-dimethylferricinium dye

l,l′-dimethylferricinium (DMFe⁺),a stable and pH-insensitive blue dye, was prepared via enzymatic oxidation of a 1,1′-dimethylferrocene (DMFe):2-hydroxypropyl-β-cyclodextrin (HPCD) watersoluble inclusion complex, using bilirubin oxidase immobilized onto porous aminopropyl glass beads via glutaraldehyde activation. In the presence of glucose, DMFe⁺ was reduced to DMFe by reacting with the reduced glucose oxidase (FADH₂), and the absorbance decrease was followed at 650 nm. In acetate pH 5.2 buffer, the response to glucose in blood serum was nonlinear, especially in the low concentration range, because of a competition for the reduced glucose oxidase between the DMFe⁺ dye and oxygen. At this pH, endogenous ceruloplasmin was also observed to oxidize residual DMFe (16%) in the dye preparation, causing an increase in absorbance at 650 nm. An assay protocol was then developed using maleate buffer, pH 6.5, to overcome these interferences as well as mutarotation of α-D-glucose. The results obtained for glucose in the blood serum samples agreed well with those of the reference hexokinase/glucose-6-phosphate dehydrogenase method.     

Optimisation of Supercritical Carbon Dioxide Systems for Complexation of Naproxen : Beta-Cyclodextrin

Supercritical carbon dioxide (scCO₂)offers several attractive scenarios for thepharmaceutical processing as an alternativeto aqueous and organic solvents. In thiswork naproxen, a widely used non steroidalanti-inflammatory drug with analgesic andanti-inflammatory properties, was chosenas a model drug. Its complexation with cyclodextrinsimproves the rate and extent of dissolutionof the drug, increase its rate of absorption and mayreduce the unpleasant side-effects of the drug.The interest in using this supercritical technologyled us to develop an experimental unit for the useof supercritical CO₂ as a processing medium forthe complexation of naproxen with beta cyclodextrin (CD).