Binding of Sulfamethazine to β-cyclodextrin and Methyl-β-cyclodextrin

β-cyclodextrin (βCD) and methyl-β-cyclodextrin (MβCD) complexes with sulfamethazine (SMT) were prepared and characterized by different experimental techniques, and the effects of βCD and MβCD on drug solubility were assessed via phase-solubility analysis. The phase-solubility diagram for the drug showed an increase in water solubility, with the following affinity constants calculated: 40.4 ± 0.4 (pH 2.0) and 29.4 ± 0.4 (pH 8.0) M⁻¹ with βCD and 56 ± 1 (water), 39 ± 3 (pH 2.0) and 39 ± 5 (pH 8.0) M⁻¹ with MβCD. According to ¹H NMR and 2D NMR spectroscopy, the complexation mode involved the aromatic ring of SMT included in the MβCD cavity. The complexes obtained in solid state by freeze drying were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, and thermal analysis. The amorphous complexes obtained in this study may be useful in the preparation of pharmaceutical dosage forms of SMT.     

A novel preparation of methyl-β-cyclodextrin from dimethyl carbonate and β-cyclodextrin

A novel green synthesis process about methyl-β-cyclodextrin has been investigated through the reaction between β-cyclodextrin and dimethyl carbonate by anhydrous potassium carbonate as catalyst in DMF. The influence of experimental factors including the molar ratio of dimethyl carbonate to β-cyclodextrin, reaction temperature, and reaction time on the average degree of substitution of methyl-β-cyclodextrin was studied. The results show that the average degree of substitution of methyl-β-cyclodextrin can be dependent on the reaction temperature and the molar ratio of raw material primarily. The structures of methyl-β-cyclodextrin were characterized by TLC, IR, MS, ¹H NMR, and ¹³C NMR.     

Preparation and Enzymatic Hydrolysis of Maltosyl-α-cyclodextrin

Maltosyl-α-cyclodextrin (6-α-maltosylcyclomaltohexaose, M-CD) was prepared from maltose and α-cyclodextrin by the reverse action of Bacillus pullulanase, and the action of α-amylases on this dextrin was examined. Among α-amylases tested, Thermoactinomyces vulgaris α-amylase (TVA) and Taka-amylase A (TAA) were found to attack the M-CD. Their action pattern on M-CD was studied. These α-amylases cleaved, first the cyclodextrin ring of M-CD, and the branched octasaccharides formed were immediately degraded to form glucose, branched tetraose, or pentaose, though the action pattern was different for TVA and TAA. In addition, TAA also split M-CD into glucose and glucosyl-α-cyclodextrin. Fission products at various stages of the reaction were separated and analyzed by paper chromatography and high performance liquid chromatography, their structures were analyzed, and the degradation pattern of M-CD was found.     

Preparation and Physicochemical Characterization of Amoxicillin β-cyclodextrin Complexes

Amoxicillin (AMOX), a penicillin A, belongs to the β-lactam family It is usually the drug of choice within the class because it is better absorbed, following oral administration, than other β-lactam antibiotics. Its β-lactamase degradation might be prevented by using a molecular [AMOX:β-CD] complex. The aim of this work was to prepare complexes using two methods and then characterize interactions between AMOX and the native β-CD. The extent of complexation in solution has been evaluated by high-performance liquid chromatography (HPLC), nuclear magnetic resonance (NMR), and 2D rotating-frame Overhauser enhancement spectroscopy (2D ROESY). Mass changes (TG), calorimetric effects (DSC), and mass spectrometry (MS) were determined on the same sample under identical conditions using the Skimmer coupling system. Skimmer and infrared spectroscopy (FT-IR) were used to characterize the solid state of the binary system. Complexation of AMOX with β-CD was proven by FT-IR, NMR, DSC, and HPLC. The 2D ROESY spectra did not show any dipolar proton interaction of the AMOX with cyclodextrin. The 1:1 stoichiometry of the complex was obtained by HPLC. The stability constant for AMOX with β-CD was determined to be 1,878 M⁻¹. In the [AMOX:β-CD] complex, the phenyl group is included inside the β-CD, and the ionized carboxyl group on the penam ring forms hydrogen bonds with the secondary hydroxyl groups of another β-CD to keep the complex stable. Preparation methods allowed exactly the same complex.     

A monoclonal antibody to cyclomaltoheptaose (β-cyclodextrin): Characterization and use for immunoassay of β-cyclodextrin and its derivatives

Cyclomaltoheptaose (β-cyclodextrin, β-CD) is a promising compound for application in various industrial fields because of its ability to entrap various compounds into its hydrophobic cavity. A monoclonal antibody (A7) to β-CD was generated by using a conjugate of glucosaminylmaltosyl-β-CD and bovine serum albumin as an antigen. The A7 monoclonal antibody was IgM/κ and reacted with β-CD with high specificity. The epitope recognized by the A7 monoclonal antibody seemed to be located on the secondary hydroxyl groups of the rim side of the β-CD molecule. The dissociation constant of the complex of β-CD and the immobilized A7 monoclonal antibody was determined to be 1.2 × 10^-4 M. A competitive ELISA using the A7 monoclonal antibody enabled determination of β-CD and its derivatives with a detection limit of 0.05 μM. This immunoassay was useful to determine β-CD in biological fluids such as human plasma and urine after appropriate pretreatment of the samples. This revised version was published online in August 2006 with corrections to the Cover Date.     

Tablet formulation containing meloxicam and β-cyclodextrin: Mechanical characterization and bioavailability evaluation

The purpose of this research was to evaluate β-cyclodextrin (β-CD) as a vehicle, either singly or in blends with lactose (spray-dried or monohydrate), for preparing a meloxicam tablet. Aqueous solubility of meloxicam in presence of β-CD was investigated. The tablets were prepared by direct compression and wet granulation techniques. The powder blends and the granules were evaluated for angle of repose, bulk density, compressibility index, total porosity, and drug content. The tablets were subjected to thickness, diameter, weight variation test, drug content, hardness, friability, disintegration time, and in vitro dissolution studies. The effect of β-CD on the bioavailability of meloxicam was also investigated in human volunteers using a balanced 2-way crossover study. Phase-solubility studies indicated an A_L-type diagram with inclusion complex of 1∶1 molar ratio. The powder blends and granules of all formulations showed satisfactory flow properties, compressibility, and drug content. All tablet formations prepared by direct compression or wet granulation showed acceptable mechanical properties. The dissolution rate of meloxicam was significantly enhanced by inclusion of β-CD in the formulations up to 30%. The mean pharmacokinetic parameters (C_max, K_e, and area under the curve [AUC]_0−∞) were significantly increased in presence of β-CD. These results suggest that β-CD would facilitate the preparation of meloxicam tablets with acceptable mechanical properties using the direct compression technique as there is no important difference between tablets prepared by direct compression and those prepared by wet granulation. Also, β-CD is particularly useful for improving the oral bioavailablity of meloxicam.     

Selective degradation of β- and γ-cyclodextrin by co-digestion using a CGTase fromBacillus ohbensis and α-glucosidase for efficient α-cyclodextrin recovery

A simple and specific recovery method for α-cyclodextrin (α-CD) was developed by employing co-digestion of CD reaction mixtures with CGTase fromBacillus ohbensis and α-glucosidase. The combination of CGTase fromB. ohbensis and α-glucosidase, such as α-amylase, β-amylase, or glucoamylase was examined for the selective degradation of β-and γ-CD in the CD reaction mixture formed by CGTase fromB. macerans. The co-digestion of the CD mixture with Taka-amylase and the CGTase resulted in α-CD and maltodextrins, the combination with β-amylase resulted in α-CD and maltose, and that with glucoamylase resulted in α-CD and glucose. The conditions of selective degradation of β- and γ-CD by co-digestion with the CGTase and glucoamylase were optimized as follows: the incubation pH, 5.5; incubation temperature, 50°C; CGTase concentration, 15 u/g of substrate; glucoamylase, 10 u/g of substrate; substrate concentration, 10% (w/v); the incubation time was fixed for 18 hr from the stand point of operation convenience. Most part of the content was presented in poster session at the 7th International Cyclodextrin Symposium, Tokyo, April 1994.     

Design and characterization of novel β-cyclodextrin based copolymer materials

Reported herein are the systematic design and characterization of several novel polyurethane (PU) copolymers containing a macrocyclic porogen (β-cyclodextrin; β-CD). These copolymers were synthesized from the reaction between β-CD with different types of diisocyanate linker molecules (e.g., 1,6-hexamethylene diisocyanate (HDI), 4,4′-dicyclohexylmethane diisocyanate (CDI), 4,4′-diphenylmethane diisocyanate (MDI), 1,4-phenylene diisocyanate (PDI) and 1,5-naphthalene diisocyanate (NDI)) at variable synthetic conditions. The copolymers were characterized using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), solid state ¹³C CP-MAS NMR, ¹H/¹³C solution NMR spectroscopy, thermogravimetric analysis (TGA) and elemental analyses (CHN). The PU copolymers were generally insoluble in water and the optimal preparation of copolymer materials for sorption-based applications is for β-CD/linker synthetic mole ratios from 1:1 to 1:3. The practical upper limit of the crosslink density (∼1:7, β-CD/linker) depends on the steric bulk of the cross linker units.     

Characterization of β-lapachone and methylated β-cyclodextrin solid-state systems

The purpose of this research was to explore the utility of β cyclodextrin (βCD) and β cyclodextrin derivatives (hydroxypropyl-β-cyclodextrin [HPβCD], sulfobutylether-β-CD [SB\CD], and a randomly methylated-β-CD [RMβCD]) to form inclusion complexes with the antitumoral drug, β-lapachone (βLAP), in order to overcome the problem of its poor water solubility. RMβCD presented the highest efficiency for βLAP solubilization and was selected to develop solid-state binary systems. Differential scanning calorimetry (DSC), X-ray powder diffractometry (XRPD), Fourier transform infrared (FTIR) and optical and scanning electron microscopy results suggest the formation of inclusion complexes by both freeze-drying and kneading techniques with a dramatic improvement in drug dissolution efficiency at 20-minute dissolution efficiency (DE_20-minute 67.15% and 88.22%, respectively) against the drug (DE_20-minute 27.11%) or the βCD/drug physical mixture (DE_20-minute 27.22%). However, the kneading method gives a highly crystalline material that together with the adequate drug dissolution profile make it the best procedure in obtaining inclusion complexes of RMβCD/βLAP convenient for different applications of βLAP. Published: July 27, 2007     

Inclusion complexation between baicalein and β-cyclodextrin and the influence of β-cyclodextrin on the binding of baicalein with DNA: a spectroscopic approach

This work deals with the commonly studied cyclic oligosaccharide and gains importance as it is entered on a drug delivering carbohydrate and provides insight into the oligosaccharide complex–biomolecular interaction. The binding of a flavone, baicalein, to β-cyclodextrin and calf thymus DNA is studied. The binding of baicalein to calf thymus DNA in the presence of β-cyclodextrin is analysed using the UV–vis absorption and fluorescence spectroscopy. The mode of binding and structure of the baicalein–β-cyclodextrin complex are reported. The role of the structure and the stoichiometry of the inclusion complex of baicalein–β-cyclodextrin in its influence on DNA binding are analysed.

Highlights

? This paper deals with the binding of a flavone, baicalein to β-cyclodextrin and/or DNA.

? The inclusion complexation between baicalein and β-cyclodextrin is analysed.

? The stoichiometry and the binding strength of the inclusion complex is reported.

? The role of β-cyclodextrin in tuning the binding of baicalein to DNA is emphasized.

? Spectroscopic and docking analysis are used to articulate the results.     

Diclofenac-β-cyclodextrin binary systems: Physicochemical characterization and in vitro dissolution and diffusion studies

The aim of this work was to study the influence of β-cyclodextrin (β-CD) on the biopharmaceutic properties of diclofenac (DCF). To this purpose the physicochemical characterization of diclofenac-β-cyclodextrin binary systems was performed both in solution and solid state. Solid phase characterization was performed using differential scanning calorimetry (DSC), powder x-ray diffractometry (XRD), and Fourier transform infrared spectroscopy (FTIR). Phase solubility analyses, and in vitro permeation experiments through a synthetic membrane were performed in solution. Moreover, DCF/β-CD interactions were studied in DMSO by¹H nuclear magnetic resonance (NMR) spectroscopy. The effects of different preparation methods and drug-to-β-CD molar ratios were also evaluated. Phase solubility studies revealed 1∶1 M complexation of DCF when the freeze-drying method was used for the preparation of the binary system. The true inclusion for the freeze-dried binary system was confirmed by¹H NMR spectroscopy, DSC, powder XRD, and IR studies. The dissolution study revealed that the drug dissolution rate was improved by the presence of CDs and the highest and promptest release was obtained with the freeze-dried binary system. Diffusion experiments through a silicone membrane showed that DCF diffusion was higher from the saturated drug solution (control) than the freeze-dried inclusion complexes, prepared using different DCF-β-CD molar ratios. However, the presence of the inclusion complex was able to stabilize the system giving rise to a more regular diffusion profile. Published: October 22, 2005     

Molecular recognition and enhancement of aqueous solubility and bioactivity of CD437 by β-cyclodextrin

CD437 (6-[3-(1-adamantyl)-4-hydroxyphenyl]-2-naphthalene carboxylic acid) is a novel synthetic retinoic acid derivative that has been shown to selectively induce apoptosis in human lung cancer cells. This compound, however, is limited in its application due to its low solubility in aqueous solutions. One technique for increasing the solubility and bioavailability of a cytotoxic agent is the formation of inclusion complexes with cyclodextrins. Herein, we report the formation and characterization of a 2:1 complex between β-cyclodextrin (β-CD) and CD437. It is shown that CD437 is a tight binder of β-CD with an overall association constant of 2.6 ± 0.6 × 10⁷ M⁻². In addition, we demonstrate (a) that β-CD-derived complexation enhances the aqueous solubility of CD437, and (b) that a significant increase in the toxicity of CD437 against a human lung adenocarcinoma cell line can be achieved by co-treatment with β-CD.     

Triamterene-β-cyclodextrin systems: Preparation,characterization and in vivo evaluation

The purpose of this research was to improve the solubility and therefore dissolution and bioavailability of triamterene, a poorly water soluble diuretic, by complexation with β-cyclodextrin. Triamterene has been reported to show low bioavailability after oral administration, with wide intersubject variation. This study presents the formulation of solid dispersions of triamterene with β-cyclodextrin—by cogrinding, kneading, and coevaporation, using low pH conditions—and their characterizations, evaluation of improvement in dissolution profiles, and in vivo advantage. Phase solubility studies indicated complex with possible stoichiometry of 1∶1 and a stability constant of 167.67M⁻¹. The solid dispersions were characterized by Fourier transform infrared spectroscopy, nuclear magnetic resonance, x-ray diffraction, and differential scanning calorimetry studies. The characterization studies confirmed inclusion of the phenyl ring of triamterene within the nonpolar cavity of β-cyclodextrin in the coevaporate. Remarkable improvement in in vitro drug release profiles in 0.1 N HCl and pH 6.8 phosphate buffer was observed with all dispersions, especially the coevaporate. The coevaporate, when administered orally in rats, also exhibited improved in vivo activity, as measured by net sodium ion excretion, as compared with triamterene powder. Thus, coevaporation of the drug and β-cyclodextrin from acidified alcohol provide the optimum condition for inclusion complexation to give a binary system with remarkable improvement in in vitro drug release profile and in vivo performance.     

Preparation and Physicochemical Properties of Catechin/β-cyclodextrin Inclusion Complex Nanoparticles

Nano-size catechin/β-cyclodextrin inclusion complex (CA/β-CD IC) with 1:1 molar ratio was obtained by cooling precipitation at 4 °C. Physicochemical properties of the CA/β-CD IC nanoparticles were characterized. Results of dynamic light scattering and SEM observation showed that CA/β-CD IC molecules underwent a process of assembling and shaping nano-size particles. In the range of 10–14 mM, the higher the concentration of β-CD aqueous solution, the faster the CA/β-CD IC nanoparticles form and the larger the size of the nanoparticles (195.2–438.6 nm). The total recovery, inclusion ratio and loading capacity of the CA/β-CD IC nanoparticles were determined. Results of FT-IR and DSC indicated that stability of CA was enhanced after it was embedded into β-CD cavity. XRD results showed that the strongest three diffraction peaks (located at 2θ = 10.6°, 12.4° and 19.6°) of the CA/β-CD IC nanoparticles was different from that (located at 2θ = 6.6°, 11.7° and 17.7°) of micro-size CA/β-CD IC and the nanoparticles obtained from higher concentration solution possessed higher crystallinity.

     

Studies on trimethoprim:hydroxypropyl-β-cyclodextrin: aggregate and complex formation

The present study is focused on the characterization of the interaction between trimethoprim, a dihydropteroate synthesase inhibitor, and hydroxypropyl-β-cyclodextrin (HP-β-CD) in aqueous solution and solid state. The freeze-drying method was used to prepare solid complexes, while simple blending was employed to obtain physical mixtures. The phase solubility was AN type, and demonstrated that trimethoprim solubility was significantly increased upon complexation with HP-β-CD. Conductivity experiments showed the presence of aggregates that explains the type profile for the solubility isotherm. The critical concentration for the aggregate formation was determined to be 69.3 mg/ml for pure HP-β-CD and 117.7 mg/ml in the presence of trimethoprim. Nuclear magnetic resonance spectroscopy provided evidence of trimethoprim:HP-β-CD molecular interaction in solution. Moreover, the complex was characterized in solid stated using Fourier-transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). The use of differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) showed that the thermal stability of the drug is enhanced in the presence of HP-β-CD.     

Enhancement of rhubarb extract solubility and bioactivity by 2-hydroxypropyl-β-cyclodextrin

Rhubarb is a traditional Chinese medicinal herb, and the ethanolic extract of rhubarb consists of active anthraquinones, which are hydrophobic and have antiproliferative effects on hepatoma cell lines. To increase the aqueous solubility of rhubarb and study the consequent bioavailability, the ethanolic extract of rhubarb was complexed with 2-hydroxypropyl-β-cyclodextrin (HP-β-CD), a cyclic oligosaccharide that has a hydrophilic outer surface and a hydrophobic central cavity, to form a rhubarb–HP-β-CD complex. This complex was characterized by performing nuclear magnetic resonance spectroscopy, two-dimensional rotating frame spectroscopy and thin layer chromatography to confirm the inclusion of anthraquinones from rhubarb extract in HP-β-CD (weight ratio of rhubarb extract:HP-β-CD = 1:9). We investigated the effects of complexing rhubarb extract with HP-β-CD on the growth of Huh7 and HepG2 cells by performing cytotoxicity analysis, cellular uptake test, and colony formation assay. Our results showed that complexation of rhubarb extract with HP-β-CD increased the aqueous solubility and bioavailability of rhubarb and thus enhanced its effect on hepatoma cells.     

Self-aggregates formation and mucoadhesive property of water-soluble β-cyclodextrin grafted with chitosan

Water-soluble β-cyclodextrin grafted with chitosan (CD-g-CS) was carried out by quaternizing the CD-g-CS with glycidyltrimethyl ammonium chloride (GTMAC) under mild acidic condition, corresponding to the quaternized CD-g-CS (QCD-g-CS). The degrees of substitution (DS) and quaternization (DQ), ranging from 5% to 23% and 66% to 80%, respectively, were determined by (1)H NMR spectroscopy. Self-aggregates formation of all QCD-g-CSs were investigated in water using dynamic light scattering (DLS), atomic force microscopy (AFM), and transmission electron microscopy (TEM) techniques. The result revealed that all QCD-g-CSs are able to form self-aggregates in water. Large particle sizes ranged from 800 to 3000nm were obtained by DLS while zeta-potentials were ranging from 25 to 40mV. AFM and TEM depicted a spherical shape with particle sizes ranging from 100 to 900nm. Mucoadhesive and cytotoxic properties of all QCD-g-CSs were evaluated using a mucin particle method and MTT assay compared to quaternized chitosan (QCS). It was found that the mucoadhesive property increased with decreasing DS due to less quaternary ammonium moiety into the chitosan backbone. On the other hand, the cytotoxicity increased with increasing DS even though the DQ is decreased.     

Azaadamantyl nitroxide spin label: complexation with β-cyclodextrin and electron spin relaxation

Abstract

An iodoacetamide azaadamantyl spin label was studied in fluid solution and in 9:1 trehalose:sucrose glass. In 9:1 toluene:CH₂Cl₂ solution at 293 K, the isotropic nitrogen hyperfine coupling is 19.2?G, T₁ is 0.37 µs and T₂ is 0.30–0.35 µs. Between about 80 and 150 K 1/T_m in 9:1 trehalose:sucrose is approximately independent of temperature demonstrating that the absence of methyl groups decreases 1/T_m relative to that which is observed in spin labels with methyl groups on the alpha carbons. Spin lattice relaxation rates between about 80 and 293 K in 9:1 trehalose:sucrose are similar to those observed for other nitroxide spin labels, consistent with the expectation that relaxation is dominated by Raman and local mode processes. Although complexation of the azaadamantyl spin label with β-cyclodextrin slows tumbling in aqueous solution by about a factor of 10, it has little impact on 1/T₁ or 1/T_m in 9:1 trehalose:sucrose between 80 and 293 K.     

High-performance liquid chromatographic assay for methyl-β-cyclodextrin in plasma and cell lysate

This paper describes a high-performance liquid chromatographic method with fluorescence detection for the analysis of methyl-β-cyclodextrin (MEBCD) in plasma and cell lysate, after in situ complexation with 1-naphthol. The size-exclusion HPLC column packed with TSK 3000 SW gel, was equilibrated with an eluent mixture composed of methanol and purified water (2:98, v/v) containing 10⁻⁴ M 1-naphthol as a fluorophore. The detection is based on fluorescence enhancement caused by the formation of inclusion complexes and was performed at 290 and 360 nm for excitation and emission, respectively. The method involved a simple treatment of the samples with chloroform. Daunorubicin was used as internal standard. Limits of quantitation were 0.8 μM in plasma and 0.5 μM in cell lysate. Detection limits of 0.5 μM (50 pmol) and 0.3 μM (30 pmol) were obtained for MEBCD in the two media, respectively. Linear detection response was obtained for concentrations ranging from 1 to 100 μM in plasma and cell lysate. Recovery from plasma proved to be more than 40%. Precision, expressed as C.V. was in the range of 4 to 11%. Accuracy ranged from 89 to 105%.