Adrian Fifere

Theoretical study on β-cyclodextrin inclusion complexes with propiconazole and protonated propiconazole.

Summary The synthesis of the β-cyclodextrin/propiconazole nitrate inclusion complex and the advantages of the encapsulation of this drug were recently reported, but the experimental data only partially revealed the structure of the supramolecular complex due to the limitations in understanding the intermolecular association mechanism. The present work describes the equilibrium molecular geometries of β-cyclodextrin/propiconazole and β-cyclodextrin/protonated propiconazole, established by the AM1 and PM3 semi-empirical methods. The affinity between different parts of the guest molecule and the cyclodextrin cavity was studied considering that propiconazole possesses three residues able to be included into the host cavity through primary or secondary hydroxyl rims. The results have revealed that the most stable complex is formed when the azole residue of the propiconazole enters the cavity of the cyclodextrin through the narrow hydroxyl’s rim.

Synthesis and micellization of polydimethylsiloxane– carboxy-terminated poly(ethylene oxide) graft copolymer in aqueous and organic media and its application for the synthesis of core-shell magnetite particles

Abstract An amphiphilic graft copolymer having an average of 7-8 carboxyesterterminated poly(ethylene oxide) grafted sequences on each polydimethylsiloxane main chain was obtained by a multistep procedure. Through fluorescence, surface tension and laser diffractometry methods the graft copolymer was proved to undergo micellization in aqueous media. In water, the critical micellization concentrations (CMC) are dependent on pH. Two CMC values were established for pH = 4, i.e. CMC1 = 1.01 g/L and CMC2 = 1.73 g/L corresponding to the transition from single chain to multiple chain micelles and to intermicellar aggregation, respectively. Between CMC1 and CMC2, the dimensions of micelles increased from 18 nm to 46 nm. The graft copolymer was proved to efficiently act as surfactant in the preparation of magnetite particles with a hydrophobic siloxane shell.

Synthesis and Characterization of Polyrotaxanes based on Cyclodextrins and Viologen-modified Polydimethylsiloxanes

β-Cyclodextrin (1 -CD) and 2 -cyclodextrin (2 -CD) (hosts) formed inclusion complexes with 4,41-bipyridinium dication derivatives with long chains (guests), in which the substituents on the bipyridinium nitrogen atoms are 1,3-bis(chloromethylphenethyl)-1,1,3,3-tetramethyldisiloxane. The number of 2 -CD molecules threaded onto the polymer chain increases with the length of the guest chain. In contrast, the number of β-CD molecules threaded onto the polymer is approximately 4 corresponding to each molecular chain, due to the repulsive interaction between β-CD and the quaternary bipyridinium units. The complexes were isolated in high yield and characterized by 1H NMR, 13C NMR, X-ray diffraction, thermal and scanning electron micrographs studies. As proven by X-ray analysis, the synthesized polyrotaxanes are crystalline materials with crystalline patterns significantly different from that of native cyclic oligosaccharide. The thermal stabilities of polyrotaxanes are higher than that of the physical mixture between cyclodextrin and the alternating copolymer, denoting the formation of the inclusion complexes. Scanning electron micrographs of polyrotaxanes reveal cubic and linear shapes without a well formed shape. Shape regularity and geometrical regularities in the agglomerating forms can be observed.

Multifunctional magnetic cargo-complexes with radical scavenging properties

Core-shell magnetic nanoparticle synthesis offers the opportunity to engineering their physical properties for specific applications when the intrinsic magnetic properties can be associated with other interesting ones. The purpose of this study was to design, synthesize, and characterize core-shell magnetic nanoparticles that mimic superoxide dismutase activity offering the possibility of guidance and therapeutic action. We proposed, for the first time, the synthesis and characterization of the nanocarriers comprised of magnetite nanoparticles functionalized with branched polyethyleneimine of low molecular weight (1.8 kDa) permitting the loading of the protocatechuic acid or its inclusion complex with anionic sulfobutylether-β-cyclodextrin for active drug delivery, in order to combine the useful properties of the magnetite and the protocatechuic acid antioxidant effect. NMR and DSC analyses confirmed the formation of the inclusion complex between sulfobutylether-β-cyclodextrin and protocatechuic acid, while structural and compositional analyses (FT-IR, TEM, XRD) revealed the synthesis of the multifunctional magnetic systems. Due to the possibility of being formulated as blood system injectable suspensions, antioxidant activity (using DPPH test) and cytotoxicity (using MTS assay on normal human dermal fibroblasts cells) were also measured, showing adequate properties to be used in biomedical applications. Moreover, we proposed a nanocarrier that would be able to load unstable active principles and with very low solubility in biological fluids to increase their biological ability.

Semi‐Empirical PM3 Study On The Complexation Of α‐Cyclodextrin With 5‐Flucytosine

The paper describes the use of quantum semi‐empirical PM3 calculations to establish the equilibrium geometry of a stable inclusion complex formed of 5‐flucytosine and α‐cyclodextrin. The global minima on the potential energy surface can be obtained in several steps. Some intermolecular parameters (ex.: the distance between the two studied molecules and the orientation of 5‐flucytosine in the α‐cyclodextrin cavity) are artificially modified in each step. A stable inclusion complex was obtained when the 5‐flucytosine is partially included into the α‐cyclodextrin cavity by the primary amino group.