17-ß-Estradiol-ß-Cyclodextrin Complex as Solid: Synthesis, Structural and Physicochemical Characterization.

17-ß-estradiol (EST) is the most potent form of naturally occurring estrogens; therefore, it has found a wide pharmaceutical application. The major problem associated with the use of EST is its very low water solubility, resulting in poor oral bioavailability. To overcome this drawback, a complexation with cyclodextrins (CD) has been suggested as a solution. In this work, the host-guest inclusion complex between the ß-CD and EST has been prepared using four different methods. The obtained samples have been deeply characterized using 13C CP MAS solid state NMR, PXRD, FT-IR, TGA, DSC, and SEM. Using SCXRD, the crystal structure of the complex has been determined, being to the best of our knowledge the first solved crystal structure of an estrogen/CD complex. The periodic DFT calculations of NMR properties using GIPAW were found to be particularly helpful in the analysis of disorder in the solid state and interpretation of experimental NMR results. This work highlights the importance of a combined ssNMR/SCXRD approach to studying the structure of the inclusion complexes formed by cyclodextrins.

Structural Studies of Piperine Inclusion Complexes in Native and Derivative ß-Cyclodextrins.

Piperine (PN), the primary pungent alkaloid in black pepper shows several biological activities such as antioxidant, antimicrobial and anti-cancerogenic effects. Similar to other alkaloids, PN is characterized by poor water solubility. One way to improve its solubility and thus its biological activities is by forming inclusion complexes with suitable cyclodextrins. In this work PN inclusion complexes in native ß-cyclodextrin (ß-CD), its methylated (randomly methylated (RM-ß-CD), heptakis-(2,6-di-O-methyl)-ß-CD (DM-ß-CD) and heptakis-(2,3,6-tri-O-methyl)-ß-CD (TM-ß-CD)) and 2-hydroxypropylated (HP-ß-CD) derivatives are investigated using physicochemical methods, such as phase solubility study and X-ray crystallography complemented by theoretical (molecular dynamics simulations) studies. The determination of the crystal structure of the PN inclusion complexes in ß-CD, DM-ß-CD and TM-ß-CD, reveals the formation of 1:2 guest:host inclusion complexes in the crystalline state. The guest PN molecule threads the hydrophobic cavities of the hosts which are arranged as couples in a tail-to-tail mode in the case of PN/ß-CD and in a head-to-tail mode in the cases of PN/DM-ß-CD and PN/TM-ß-CD. MD studies based on the crystallographically determined structures and docked models show the stability of the examined complexes in an aqueous environment whereas the binding affinity of PN for the host molecules is calculated by the MM/GBSA method. Finally, phase-solubility studies of PN with ß-CD, RM-ß-CD and HP-ß-CD are presented, indicating a Bs-type for the PN/ß-CD complex and an AL-type for the PN/RM-ß-CD and PN/HP-ß-CD complexes with 1:1 guest:host stoichiometry.

Biophysical Studies and In Vitro Effects of Tumor Cell Lines of Cannabidiol and Its Cyclodextrin Inclusion Complexes.

Phytocannabinoids possess anticancer properties, as established in vitro and in vivo. However, they are characterized by high lipophilicity. To improve the properties of cannabidiol (CBD), such as solubility, stability, and bioavailability, CBD inclusion complexes with cyclodextrins (CDs) might be employed, offering targeted, faster, and prolonged CBD release. The aim of the present study is to investigate the in vitro effects of CBD and its inclusion complexes in randomly methylated ß-CD (RM-ß-CD) and 2-hyroxypropyl-ß-CD (HP-ß-CD). The enhanced solubility of CBD upon complexation with CDs was examined by phase solubility study, and the structure of the inclusion complexes of CBD in 2,6-di-O-methyl-ß-CD (DM-ß-CD) and 2,3,6-tri-O-methyl-ß-CD (TM-ß-CD) was determined by X-ray crystallography. The structural investigation was complemented by molecular dynamics simulations. The cytotoxicity of CBD and its complexes with RM-ß-CD and HP-ß-CD was tested on two cell lines, the A172 glioblastoma and TE671 rhabdomyosarcoma cell lines. Methylated ß-CDs exhibited the best inclusion ability for CBD. A dose-dependent effect of CBD on both cancer cell lines and improved efficacy of the CBD-CDs complexes were verified. Thus, cannabinoids may be considered in future clinical trials beyond their palliative use as possible inhibitors of cancer growth.

Structural and Evolutionary Insights within the Polysaccharide Deacetylase Gene Family of Bacillus anthracis and Bacillus cereus.

Functional and folding constraints impose interdependence between interacting sites along the protein chain that are envisaged through protein sequence evolution. Studying the influence of structure in phylogenetic models requires detailed and reliable structural models. Polysaccharide deacetylases (PDAs), members of the carbohydrate esterase family 4, perform mainly metal-dependent deacetylation of O- or N-acetylated polysaccharides such as peptidoglycan, chitin and acetylxylan through a conserved catalytic core termed the NodB homology domain. Genomes of Bacillus anthracis and its relative Bacillus cereus contain multiple genes of putative or known PDAs. A comparison of the functional domains of the recently determined PDAs from B. anthracis and B. cereus and multiple amino acid and nucleotide sequence alignments and phylogenetic analysis performed on these closely related species showed that there were distinct differences in binding site formation, despite the high conservation on the protein sequence, the folding level and the active site assembly. This may indicate that, subject to biochemical verification, the binding site-forming sequence fragments are under functionally driven evolutionary pressure to accommodate and recognize distinct polysaccharide residues according to cell location, use, or environment. Finally, we discuss the suggestion of the paralogous nature of at least two genes of B. anthracis, ba0330 and ba0331, via specific differences in gene sequence, protein structure, selection pressure and available localization patterns. This study may contribute to understanding the mechanisms under which sequences evolve in their structures and how evolutionary processes enable structural variations.

Crystal structure of the inclusion complex of cholesterol in ß-cyclodextrin and molecular dynamics studies.

The role of beta-cyclodextrin (ß-CD) in cholesterol removal primarily from mammalian cells and secondly from dairy products has been studied thoroughly in recent years. Although the physicochemical characterization of the inclusion compound of cholesterol in ß-CD has been achieved by various methods, no crystal structure has been determined so far. We report here the crystal structure of the inclusion compound of cholesterol in ß-CD. The inclusion complex crystallizes in the triclinic space group P1 forming head-to-head dimers which are stacked along the c-axis. One well-defined cholesterol molecule 'axially' encapsulated inside the ß-CD dimer and 22 water molecules that stabilize the complexes in the crystalline state comprise the asymmetric unit of the structure. The dimers are arranged in an intermediate (IM) channel packing mode in the crystal. Moreover, MD simulations, at 300 and 340 K, based on the crystallographically determined coordinates of the complex show that the formed cholesterol/ß-CD inclusion compound remains very stable in aqueous solution at both temperatures.

Structure of a bacterial cytoplasmic cyclophilin A in complex with a tetrapeptide.

Cyclophilins constitute a class of peptidyl-prolyl isomerases which participate in processes related to protein folding, signalling and chaperoning. The crystal structure of the cytoplasmic cyclophilin A (CyPA) from the bacterium Azotobacter vinelandii complexed with a synthetic tetrapeptide was determined by molecular replacement at 2 resolution. The proline in the tetrapeptide is observed to adopt the cis-isomer conformation. Comparisons of this structure with other CyPA structures provide insights into the conformational variability, effects of peptide binding and structure-function relationships of this enzyme.