Stretching a polymer brush by making in situ cyclodextrin inclusion complexes

The interaction between poly(ethylene oxide) (PEO) chains grafted onto polystyrene latex particles and alpha-, beta-, and gamma-cyclodextrins (CD) was studied by small-angle neutron scattering. The particles were contrast-matched to the solvent in order that only the scattering from the polymer layers was detected. The signal from the layers was fitted to a double-exponential volume fraction profile. The effects of adding cyclodextrin on the polymer profile are shown as a function of cyclodextrin concentration. The polymer layers are seen to extend on addition of CD, which is consistent with a complexation between the grafted PEO and the CD molecules. The effect is the strongest with alpha-CD.     

Intimate blending of binary polymer systems from their common cyclodextrin inclusion compounds

A procedure for the formation of intimate blends of three binary polymer systems polycarbonate (PC)/poly(methyl methacrylate) (PMMA), PC/poly(vinyl acetate) (PVAc) and PMMA/PVAc is described. PC/PMMA, PC/PVAc, and PMMA/PVAc pairs were included in γ‐cyclodextrin (γ‐CD) channels and were then simultaneously coalesced from their common γ‐CD inclusion compounds (ICs) to obtain intimately mixed blends. The formation of ICs between polymer pairs and γ‐CD were confirmed by wide‐angle X‐ray diffraction (WAXD), fourier transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC). It was observed [solution ¹H nuclear magnetic resonance (NMR)] that the ratios of polymers in coalesced PC/PMMA and PC/PVAc binary blends are significantly different than the starting ratios, and PC was found to be preferentially included in γ‐CD channels when compared with PMMA or PVAc. Physical mixtures of polymer pairs were also prepared by coprecipitation and solution casting methods for comparison. DSC, solid‐state ¹H NMR, thermogravimetric analysis (TGA), and direct insertion probe pyrolysis mass spectrometry (DIP‐MS) data indicated that the PC/PMMA, PC/PVAc, and PMMA/PVAc binary polymer blends were homogeneously mixed when they were coalesced from their ICs. A single, common glass transition temperature (T_g) recorded by DSC heating scans strongly suggested the presence of a homogeneous amorphous phase in the coalesced binary polymer blends, which is retained after thermal cycling to 270 °C. The physical mixture samples showed two distinct T_gs and ¹H T_1ρ values for the polymer components, which indicated phase‐separated blends with domain sizes above 5 nm, while the coalesced blends exhibited uniform ¹H spin‐lattice relaxation values, indicating intimate blending in the coalesced samples. The TGA results of coalesced and physical binary blends of PC/PMMA and PC/PVAc reveal that in the presence of PC, the thermal stability of both PMMA and PVAc increases. Yet, the presence of PMMA and PVAc decreases the thermal stability of PC itself. DIP‐MS observations suggested that the degradation mechanisms of the polymers changed in the coalesced blends, which was attributed to the presence of molecular interactions between the well‐mixed polymer components in the coalesced samples. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2578–2593, 2005     

Physicochemical characterization of cholesterol-beta cyclodextrin inclusion complexes

Study and characterization of molecular complexes between cholesterol and beta cyclodextrin has been done using X-ray diffraction, thermogravimetric analysis (TG), differential scanning calorimetry (DSC) and nuclear magnetic resonance spectroscopy (¹³C NMR). Whatever the value of the molar ratio cholesterol/βCD used during the preparation, the same compound is always obtained. Corresponding to a molar ratio 1/3 (cholesterol/βCD), this compound is a stable hydrate which, contrary toβCD, contains at room temperature a large amount of molecules of water. It can be dehydrated under low pressure but the thermal degradation occurs at 200°C (250°C forβCD). This implies that cholesterol is strongly bounded toβCD.     

Crystal packing patterns of cyclodextrin inclusion complexes

Cyclodextrin inclusion complexes crystallize in two basically different patterns, the cage and the channel type. The cage type occurs when cyclodextrins are packed crosswise (fishbone) or, if they are packed side-by-side, in layers and adjacent layers are displaced by about one half molecule. In each case, the internal cavity of one cyclodextrin is closed on both sides by neighbouring cyclodextrins. On the other hand, channel complexes are formed if cyclodextrins are stacked like coins in a roll so that cavities line up to produce long channels. In these crystal structures, cyclodextrins can be arranged in head-to-head or head-to-tail mode. In the smaller -cyclodextrin, cage type structures are formed with small, molecular guests whereas long molecular guests and ionic guest molecules induce channel type structures. The latter are generally preferred with the - and -cyclodextrin series which is probably due to the higher tendency for self aggregation in these two members of the cyclodextrin family.Part XXII of the series Topography of Cyclodextrin Inclusion Complexes. For part XXI, see ref. 6.     

人参皂苷与环糊精包合物的研究进展

人参皂苷是从人参、西洋参和三七中提取的主要活性成分,其药效价值相当高,但因其在水中几乎不溶,生物利用度极低,因此极大的限制了其在临床上的应用.环糊精具有独特的性质,其"腔内疏水、腔外亲水",可以选择性的包合人参皂苷等客体分子.环糊精与人参皂苷形成包合物后可以改变客体分子的某些物理化学性能,如水溶性、稳定性以及光学性质等,以此来提高其生物利用度.     

Structure and spectroscopic properties of cyclodextrin inclusion complexes

We compare spectroscopic properties of higher order complexes of organic guests (e.g. naphthalene, phenols, indole, C₆₀ fullerene) with cyclodextrins (CDx) to results of molecular modeling investigations. Naphthalene 1:2 complexes with -CDx show high spectral resolution and peculiar triplet properties. Molecular simulations and calculation of the experimentally measured induced circular dichroism (ICD) provide detailed structural information.     

Electrospinning of polymer-free nanofibers from cyclodextrin inclusion complexes

The electrospinning of polymer-free nanofibers from highly concentrated (160%, w/v) aqueous solutions of hydroxypropyl-β-cyclodextrin (HPβCD) and its inclusion complexes with triclosan (HPβCD/triclosan-IC) was achieved successfully. The dynamic light scattering (DLS) and rheology measurements indicated that the presence of considerable HPβCD aggregates and the high solution viscosity were the key factors in obtaining electrospun HPβCD and HPβCD/triclosan-IC nanofibers without the use of any polymeric carrier. The HPβCD and HPβCD/triclosan-IC solutions containing 20% (w/w) urea yielded no fibers but only beads and splashes because of the depression of the self-aggregation of the HPβCD. The inclusion complexation of triclosan with HPβCD was studied by isothermal titration calorimetry (ITC) and turbidity measurements. The characteristics of the HPβCD and HPβCD/triclosan-IC nanofibers were investigated by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and differential scanning calorimetry (DSC). It was found that the electrospinning of HPβCD/triclosan-IC solution having a 1:1 molar ratio was optimal for obtaining nanofibers without any uncomplexed guest molecules.     

Prostaglandins and their cyclodextrin complexes

Generally, prostaglandins (PG) are unstable and insoluble in water, though they exhibit strong biological activities in minute amount. The most difficult problem in developing PG preparations is how to stabilize and solubilize PG without loss of their activities. We have successfully developed the pharmaceutical preparations contaning PG complexes with cyclodextrins (CD). These preparations are already on the market, namely PGE₂ ·-CD Tablet and PGE₁ ·-CD Injection. Moreover, PG and PGI₂ derivatives are now under development as a form of CD complex.     

Photoproduction of remarkably stable benzylic radicals in cyclodextrin inclusion complexes

Photolysis of cyclodextrin inclusion complexes of diastereomers of ,′-dimethyldibenzyl ketone in the solid state resulted in stable benzylic radicals at room temperature. These radicals were characterized by their electron spin resonance (ESR) signals, emission and excitation spectra.     

Inhibition of cyclodextrin acid hydrolysis by some inclusion complexes

Acidic hydrolysis of ??-cyclodextrin in the solution of hydrochloric acid containing some aliphatic alcohols was investigated. The reaction was carried out at 90 °C. It was observed that the rate of the reaction has decreased with the increase in concentration of a guest.     

Influence oftert-butyl alcohol on cyclodextrin inclusion complexes of pyrene

The effect oftert-butyl alcohol on complexes of pyrene and various cyclodextrins is investigated. The equilibrium constant for the complexation is derived from the fluorescence decay parameters. A greater than twofold enhancement of pyrene lifetime is observed in the presence oftert-butyl alcohol and -cyclodextrin or -cyclodextrin. As the number of hydroxyl groups decreases, substituted -cyclodextrins show smaller enhancements to both the fluorescence lifetime and the formation constant. These observations are explained by proposing that alcohol molecules are associated with the inclusion complex. This association increases the apparent hydrophobicity of the cyclodextrin cavity, protects the molecule from collisional quenching and deactivation, and provides additional rigidity to the system.     

Study of inclusion complexes of cyclodextrin by cyclic voltammetry

The inclusion complexes of a series of organometallic compound-cyclodextrin and aromatic compound-cyclodextrin have been studied by cyclic voltammetry using glassy carbon electrode. The variations of peak potential and peak current are showed on cyclic voltammogram when the electroactive guest molecules are complexed by cyclodextrins. Dissociation constants of cyclodextrin inclusion complexes have been calculated on the basis of this variation by both potential and current methods. According to the magnitude of dissociation constants the relationship between the stability of cyclodextrin inclusion complex and the degree of matching host molecule with guest molecule has been discussed.     

Potentiometric characterisation of cyclodextrin inclusion complexes of local anaesthetics

The complexation of several local anaesthetics by β and γ-cyclodextrins was studied by potentiometry with glass electrode. Tetracaine and dibucaine complexation constants were determined at 25°C in the presence of 0.1 M of NaCl. It was found that prilocaine and lidocaine complexes cannot be detected.     

Ability of the acetotoluides to form cyclodextrin inclusion complexes

Conclusion These series of experiments have shown that the -CD cavity was too small to allow stable inclusion complex formation. p-ACT is the isomer within this series that is best able to form inclusion complexes with -CD, then m-ACT and finally o-ACT. This would seem to indicate that the benzene ring of the molecule is the part of the structure most likely to penetrate the cavity since (a) -CD could not form stable complexes with any of the guest molecules and (b) less effective entry into the -CD cavity is the results of the acetamido group moving from p^–m^–o^– positions. Benzene ring penetration of the CD cavity is therefore required for stable inclusion complex formations in this group of compounds.     

Thermoanalytical method for studying the guest content in cyclodextrin inclusion complexes

The interaction of cypermethrin with β-cyclodextrin was investigated using different (coprecipitation, suspension, kneading and ‘melting in solution’) complexation methods and qualifying the resulted complexes by UV-spectrophotometry, thermal methods (TG, DTG and DSC) and X-ray powder diffraction. The total guest content of complexes can be measured by UV-spectrophotometry in aqueous ethanol solution, while the uncomplexed guest fraction of samples can be determined by DSC based on a previous calibration curve, which was found between the melting enthalpy change of cypermethrin and the guest content of physical mixture samples. The combination of both analytical methods enables the determination of really complexed guest content.     

环糊精包络物的循环伏安法研究

本文采用玻碳电极以循环伏安法研究了水溶液体系中二茂铁衍生物及芳香族衍生物与环糊精(α-CD, α-CD)的包络行为. 当电活性客体分子被包络时, 在循环伏安图上表现为峰电流和峰电位的变化, 用电流和电位法测定了包络物的解离常数, 并根据解离常数的大小次序探讨了主体分子与客体分子之间的匹配情况同包络物稳定性之间的关系.     

环糊精与丹参酮IIA包合作用的研究

通过荧光光谱方法分别研究了丹参酮IIA在溶液的pH为7．5时与β—CD和γ—CD的包合常数,对客体的包结能力β-CD〉γ-CD;并利用热力学方法研究了温度对包合反应的影响,计算了包合过程的熵变、焓变及自由能变化;分子模拟方法进一步证实了该包合物的形成;采用超声波法制备了环糊精与丹参酮IIA的固体包合物,并用红外光谱对固体包合物进行了表征．     

Preparation and properties of cyclodextrin inclusion compounds of organometallic complexes. Ferrocene inclusion compounds

Inclusion compounds of ferrocene(FcH) and its derivatives with cyclodextrins(CDs; -CD, -CD, and -CD) were prepared. CD-ferrocene inclusion compounds were obtained in a crystalline state in high yield. -CD and -CD formed 11 stoichiometric inclusion compounds with ferrocene and its derivatives. -CD formed 21 (CD:guest) complexes with ferrocene and the monosubstituted derivatives, but did not form complexes with 1,1-disubstituted derivatives, -CD-FcH and -CD-FcH complexes are thermally stable and do not liberate ferrocene on heating at 100°C in vacuo. The cyclodextrin inclusion compounds were characterized by¹H-NMR, IR, UV, and CD spectra. A large positive induced Cotton effect was observed in the case of -CD-FcH complex, while the -CD-FcH complex showed a negative spectrum. The binding mode is discussed. -Cyclodextrin was found to form inclusion complexes in ethylene glycol, diethylene glycol, triethylene glycol, methyl cellosolve, ethyl cellosolve, methyl alcohol, and glycerine solutions. -CD also formed complexes in ethylene glycol solution. The binding of ferrocene by -CD is stronger in ethylene glycol than in dimethyl sulfoxide and dimethyl formamide.     

Application of combined thermoanalytical techniques in the investigation of cyclodextrin inclusion complexes

Citronellol and citronellyl acetate have been entrapped with α-, β- and γ-cyclodextrin (CD). Evolved gas detection and TG-MS coupling was applied to prove the actual inclusion complex formation between monoterpens and CDs. The terpene content was determined by UV-VIS specrophotometry and RP-HPLC and the effect of storage time on the terpene content was also investigated. The α- and γ-cyclodextrin inclusion complexes showed higher thermal stabilities vs. dynamic heating compared to the β-CD complexes. On the contray, the retention of guest using β-cyclodextrin even after 10 years of storage was much more pronounced. Experimental data other than 1:1 complex compositions are assumed. Molecular modeling experiments also suggested multiple complex compositions.     

Angiotensin converting enzyme inhibitors/cyclodextrin inclusion complexes: solution and solid-state characterizations and their thermal stability

Angiotensin converting enzyme (ACE) inhibitors have recently gained attention as a new class of drug in the therapeutic management of glaucoma. However, the application of eye drops is limited because of their chemical instability in aqueous solutions. To overcome such a problem, cyclodextrins (CDs) were introduced to form inclusion complexes. Three ACE inhibitors, namely, captopril, quinapril and fosinopril (FOS), were chosen and the effect of CDs on their thermal stability in aqueous solutions was investigated. All three drugs formed inclusion complexes of 1:1 stoichiometry with all three natural CDs and the FOS/γCD inclusion complex possessed the highest stability constant, resulting in thermal stability enhancement. Furthermore, the addition of antioxidants could greatly enhance the thermal stability of FOS in the presence of γCD in aqueous solutions. The inclusion complex formation of FOS/γCD was further examined by computational and experimental characterizations. All these characterization results confirmed that FOS and γCD formed a true inclusion complex that provided drug stabilization in the aqueous eye drop medium.