Control of Rapid Phase Transition Induced by Supramolecular Complexation of β-Cyclodextrin-Conjugated Poly(ε-lysine) with a Specific Guest

States of Aggregation and Phase Transformation Behavior of Metallosurfactant Complexes by Hexacyanoferrate(II): Thermodynamic and Kinetic Investigation of ETR in Ionic Liquids and Liposome Vesicles

Electronic absorption spectroscopy was used to study the ETR of surfactant-cobalt(III) complexes containing imidazo[4,5-f][1,10]phenanthroline, dipyrido[3,2-d:2'-3'-f]quinoxaline and dipyrido[3,2-a:2',4'-c](6,7,8,9-tetrahydro)phenazine ligands by using ferrocyanide ions in unilamellar vesicles of dipalmitoylphosphotidylcholine (DPPC) and 1-butyl-3-methylimidazolium bromide ((BMIM)Br), at different temperatures under pseudo-first-order conditions using an excess of the reductant. The reactions were found to be second-order and the electron transfer is postulated as occurring in the outer sphere. The rate constant for the electron transfer reactions was found to increase with increasing concentrations of ionic liquids. Besides these, the effects of surfactant complex ions on liposome vesicles in these same reactions have also been studied on the basis of hydrophobicity. We observed that, below the phase transition temperature, there is an increasing amount of surfactant-cobalt(III) complexes expelled from the interior of the vesicle membrane through hydrophobic effects, while above the phase transition temperature, the surfactant-cobalt(III) complexes are expelled from the interior to the exterior surface of the vesicle. Kinetic data and activation parameters are interpreted in respect of an outer-sphere electron transfer mechanism. By assuming the existence of an outer-sphere mechanism, the results have been clarified based on the presence of hydrophobicity, and the size of the ligand increases from an ip to dpqc ligand and the reactants become oppositely charged. In all these media, the ΔS^# values are recognized as negative in their direction in all the concentrations of complexes employed, indicative of a more ordered structure of the transition state. This is compatible with a model in which these complexes and [Fe(CN)₆]^4- ions bind to the DPPC in the transition state. Thus, the results have been interpreted based on the self-aggregation, hydrophobicity, charge densities of the co-ligand and the reactants with opposite charges.

Injectable In-Situ Forming Depot of Doxycycline Hyclate/α-Cyclodextrin Complex Using PLGA for Periodontitis Treatment: Preparation, Characterization, and In-Vitro Evaluation

BACKGROUND

Doxycycline (DOX) is used in treating a bacterial infection, especially for periodontitis treatment.

OBJECTIVE

To reduce irritation of DOX for subgingival administration and increase the chemical stability and against enzymatic, the complex of α-cyclodextrin with DOX was prepared and loaded into injectable in situ forming implant based on PLGA.

METHODS

FTIR, molecular docking studies, X-ray diffraction, and differential scanning calorimetry was performed to characterize the DOX/α-cyclodextrin complex. Finally, the in-vitro drug release and modeling, morphological properties, and cellular cytotoxic effects were also evaluated.

RESULTS

The stability of DOX was improved with complex than pure DOX. The main advantage of the complex is the almost complete release (96.31 ± 2.56 %) of the drug within 14 days of the implant, whereas in the formulation containing the pure DOX and the physical mixture the DOX with α-cyclodextrin release is reached to 70.18 ± 3.61 % and 77.03 ± 3.56 %, respectively. This trend is due to elevate of DOX stability in the DOX/ α-cyclodextrin complex form within PLGA implant that confirmed by the results of stability.

CONCLUSION

Our results were indicative that the formulation containing DOX/α-cyclodextrin complex was biocompatible and sustained-release with minimum initial burst release.

Surface patterned pH-sensitive fluorescence using β-cyclodextrin functionalized poly(ethylene glycol)

This paper reports the development of a pH-responsive molecular pattern that shows specific and selective affinity for particular host-guest interactions, and its use as a pH fluorescent sensor. The pH-responsive boronate ester is formed via interactions between the diol group of β-cyclodextrin (CD) and phenylboronic acid of poly(ethylene glycol), and is strategically designed to allow reversible formation of a molecular lining pattern. Printing on a versatile substrate provides a method to monitor the positioning of different molecules by using a pH-responsive boronate ester, allowing specific host-guest interactions on any surface. Confocal laser scanning microscopy, fluorescence spectroscopy, and (1)H NMR results indicate that the assembled CD monolayer can be removed by washing with an acidic pH buffer, demonstrating the presence of a boronate ester connective bridge, which is acid labile. Therefore, visualization of the pH-responsive fluorescence sensor using a rhodamine-CD complex allows straightforward discrimination between different molecules on any substrate, thus facilitating application of this sensor in clinical diagnostics and environmental monitoring.

A comparative study on the electron transfer reaction (ETR) of surfactant cobalt(iii) complexes of aliphatic/aromatic ligands in micro heterogeneous media: a thermodynamic approach

The electron transfer reaction between different surfactant cobalt(iii) complex ions and Fe²⁺ ions in micelles as well as β-cyclodextrin was studied at different temperatures using a spectrophotometry method.

Aqueous stability of leuprolide acetate: effect of temperature, dissolved oxygen, pH and complexation with β-cyclodextrin

In the present research, the aqueous stability of leuprolide acetate (LA) in phosphate buffered saline (PBS) medium was studied (pH = 2.0-7.4). For this purpose, the effect of temperature, dissolved oxygen and pH on the stability of LA during 35 days was investigated. Results showed that the aqueous stability of LA was higher at low temperatures. Degassing of the PBS medium partially increased the stability of LA at 4 °C, while did not change at 37 °C. The degradation of LA was accelerated at lower pH values. In addition, complexes of LA with different portions of β-cyclodextrin (β-CD) were prepared through freeze-drying procedure and characterized by Fourier transform infrared (FTIR) and differential scanning calorimetry (DSC) analyses. Studying their aqueous stability at various pH values (2.0-7.4) showed LA/β-CD complexes exhibited higher stability when compared with LA at all pH values. The stability of complexes was also improved by increasing the portion of LA/β-CD up to 1/10.

Thermodynamics and kinetic investigation of electron transfer reactions of surfactant cobalt(iii) complexes containing diimine ligands with iron(ii) in the presence of liposome vesicles and amphiphilic salt media

The kinetics of reductions of surfactant cobalt(iii) complexes by iron(ii) in liposome vesicles (DPPC) and amphiphilic salt ((BMIM)Br) were studied at different temperatures by UV-Vis absorption spectroscopy method under pseudo first order conditions using an excess of the reductant.

Synthesis, CMC Determination, and Outer Sphere Electron Transfer Reaction of the Surfactant–Complex Ion, cis-[Co(en)2(4CNP)(DA)]3+ with [Fe(CN)6]4– in Micelles, β-cyclodextrin, and Liposome (Dipalmidoylphosphotidylcholine) Vesicles

The surfactant cobalt(iii) complex, cis-[Co(en)2(4CNP)(DA)](ClO4)3, en = ethylenediamine, 4CNP = 4-cyanopyridine, DA = dodecylamine, was synthesized and characterized by physico-chemical and spectroscopic methods. The critical micelle concentration value of this complex was obtained from the conductivity measurements at different temperatures to evaluate, ΔGm0, ΔHm0, and ΔSm0. The kinetics of outer sphere electron transfer reaction of this complex with Fe(CN)64– ion in micelles, β-cyclodextrin as well as in liposome vesicles media were studied. The rate constant increases with increase in the concentration of micelles but decreases in presence of β-cyclodextrin, which is a good structure breaker of micelles. In liposome vesicles media the rate constant is different at below and above phase transition temperature. The results have been explained based on the hydrophobic effect, the presence of pyridine ligand containing 4-cyano substituent and the reactants with opposite charge.

Cyclodextrin-based polymeric materials: synthesis, properties, and pharmaceutical/biomedical applications

This review describes the synthesis, properties, and, in particular, biomedical and pharmaceutical applications of an upcoming class of polymeric networks and assemblies based on cyclodextrins (CDs). CDs are cyclic oligosaccharides composed of alpha-1,4-coupled d-glucose units, which contain a hydrophobic internal cavity that can act as a host for various, generally lipophilic, guest molecules. Because of this unique physicochemical property, commonly referred to as inclusion complex formation, CDs have often been used to design polymeric materials, such as hydrogels and nanoparticles. Polymeric systems based on CDs exhibit unique characteristics in terms of mechanical properties, stimuli-responsiveness, and drug release characteristics. In this contribution, first, an outline is given of covalently cross-linked polymeric networks in which CD moieties were structurally incorporated to modulate the network strength as well as the complexation and release of low molecular weight drugs. Second, physically assembled polymeric systems are discussed, of which the formation is accomplished by inclusion complexes between polymer-conjugated CDs and various guest molecule-derivatized polymers. Due to their physical nature, these polymeric systems are sensitive to external stimuli, such as temperature changes, shear forces and the presence of competing CD-binding molecules, which can be exploited to use these systems as injectable, in situ gelling devices. In recent years, many interesting CD-containing polymeric systems have been described in literature. These systems have to be optimized and extensively evaluated in preclinical studies concerning their safety and efficacy, making future clinical applications of these materials in the biomedical and pharmaceutical field feasible.

One-Pot Synthesis of a Polyrotaxane via Selective Threading of a PEI-b-PEG-b-PEI Copolymer

A functional polyrotaxane of a PEI-b-PEG-b-PEI copolymer is synthesized in aqueous solution in a one-pot sequence. To obtain a polyrotaxane with PEG-block-selective inclusion complexes, the solution pH of the polypseudorotaxane is lowered to 4.4 in the presence of 9-anthraldehyde (AN), which triggers the expulsion of the alpha-cyclodextrins (alpha-CDs) from the flank PEI chains. Synthetic strategy of a block-selective polyrotaxane between a PEI-b-PEG-b-PEI copolymer and alpha-cyclodextrins.

Synthesis of Poly(ɛ-lysine)-Grafted Dextrans and Their pH- and Thermosensitive Hydrogelation with Cyclodextrins

To give pH sensitivity to a thermoreversible supramolecular-structured hydrogel system, poly(epsilon-lysine) (PL), as a cationic polymer, was grafted to dextran and used for inclusion complexation with alpha-cyclodextrins (alpha-CDs). The synthesized graft copolymer was characterized by 1H NMR spectroscopy, and the hydrogel formation was confirmed by X-ray diffraction and solid-state 13C NMR analysis. The hydrogelation was induced from a phase-separated structure of hydrated dextrans and hydrophobically aggregated inclusion complexes in buffer solution at pH 10.0. The prepared hydrogels showed thermoreversible gel-sol transitions as well as pH-sensitive phase transitions, which were recorded by the changes in UV/Vis transmittance. A rapid phase transition from gel to sol was observed upon decreasing the pH value to 4.0, which resulted from the dissociation process between the protonated guest polymer and alpha-CDs. The stimuli-responsive physical properties of the hydrogels were improved by modulating the degree of substitution of the grafted PL and the combination with alpha-CDs.