Enhanced Analytic Approach for Describing pH Triggered Fast Drug Release Systems.

BACKGROUND: pH sensitive dendrimers attached to nanocarriers, as one of the drug release systems, have become quite popular due to their ease of manufacture in experimental conditions and the ability to generate fast drug release in the targeted area. This kind of fast release behavior cannot be represented properly in most of the existing kinetic mathematical models. Besides, these models have either no pH dependence or pH dependence added separately. Therefore, they remained one dimensional. OBJECTIVE: The aim of this study was to establish the proper analytic equation to describe the fast release of drugs from pH sensitive nanocarrier systems, and to combine it with the pH dependent equation for to establish a two-dimensional model for whole system. METHODS: We used four common kinetic models for the comparison and we fitted them to the release data. As a result, only Higuchi and Korsmeyer-Peppas models show acceptable suitable results. None of these models have pH dependence. To get a better description for pH triggered fast release, we observed the behavior of the slope angle of the release curve. Then we proposed a new analytic equation by using relation between the slope angle and time. RESULT: By adding a pH dependent equation, we assumed the drug release is "on" or "off" above/below specific pH value and we modified a step function to get a desired behavior. CONCLUSION: Our new analytic model shows good fitting, not only one-dimensional time dependent release, but also two-dimensional pH dependent release, that provides a useful analytic model to represent release profiles of pH sensitive fast drug release systems.

Synthesis, Characterization and DFT-Based Investigation of a Novel Trinuclear Singly-Chloro-Bridged Copper(II)-1-Vinylimidazole Complex.

A novel trinuclear copper(II) complex [Cu3(µ-Cl)2Cl4(1-Vim)6] with monodentate 1-vinylimidazole (1-Vim) and chloro ligands has been prepared and experimentally characterized by elemental analysis, thermogravimetry (TGA, DTG, DTA), X-ray single crystal diffractometry, TOF-MS and FT-IR spectroscopies. The electronic and structural properties of the complex were further investigated by DFT/TD-DFT methods. Density functional hybrid method (B3LYP) was applied throughout the calculations. The calculated UV-Vis results based on TD-DFT approach were simulated and compared with experimental spectrum. Based on the data obtained, DFT calculations have been found in reasonable accordance with experimental data.

trans-Bis(nitrato-κO)tetra-kis-(1-vinyl-1H-imidazole-κN(3))copper(II).

In the title compound, [Cu(NO(3))(2)(C(5)H(6)N(2))(4)], the Cu(II) ion is located on an inversion centre. It features a Jahn-Teller-distorted octa-hedral coordination geometry, defined by four N atoms of four 1-vinyl-imidazole ligands in the equatorial plane and two nitrate O atoms in the axial positions. The nitrate anion is disordered over two sets of sites in a 0.801 (6):0.199 (6) ratio. In the crystal, the complex mol-ecules are linked by weak inter-molecular C-H⋯O and C-H⋯π inter-actions.

Electronic structure modeling of dinuclear copper(II)-methacrylic acid complex by density functional theory.

A dinuclear centrosymmetric copper(II) complex with the formula [Cu(2)(mu-maa)(4)(maaH)(2)] has been synthesized and experimentally characterized by IR, electronic spectroscopy, and X-ray single-crystal diffractometry. Starting from experimental X-ray geometry and using antiferromagnetic singlet ground state, gas phase geometry optimization was performed by density functional hybrid (B3LYP) method with 6-31G(d) and LANL2DZ basis sets. Gas-phase vibrational frequencies and single point energy (SPE) calculations have been carried out at the geometry-optimized structure. Molecular electrostatic potential calculated at the optimized geometry and natural bond orbital analysis data have been extracted from SPE output. The gas-phase electronic transitions of the title complex were investigated by the time dependent-density functional theory (TD-DFT) approach with the same theory employing LANL2DZ basis set. Also the calculated UV-Vis based upon TD-DFT results and IR spectra were simulated for comparison with the experimental ones.

3-[2-(4,4-Dimethyl-2,6-dioxocyclo-hexyl-idene)hydrazin-yl]benzonitrile.

The title compound, C(15)H(15)N(3)O(2), contains benzonitrile and 4,4-dimethyl-2,6-dioxocyclo-hexyl-idene groups connected via a hydrazinyl group. The structure is in the hydrazone tautomeric form in the solid state. The benzonitrile and hydrazinyl groups (3-hydrazinylbenzonitrile) are essentially coplanar with an r.m.s. deviation of 0.016 Å. Intra-molecular N-H⋯O hydrogen bonding helps to stabilize the mol-ecular structure, and weak inter-molecular C-H⋯O hydrogen bonding is present in the crystal structure.

(Carbonato-κO,O')bis-(1,10-phenan-throline-κN,N')cobalt(III) nitrate monohydrate.

The crystal structure of the title compound, [Co(CO(3))(C(12)H(8)N(2))(2)]NO(3)·H(2)O, consists of Co(III) complex cations, nitrate anions and uncoordinated water mol-ecules. The Co(III) cation is chelated by a carbonate anion and two phenanthroline ligands in a distorted octa-hedral coordination geometry. A three-dimensional supra-molecular structure is formed by O-H⋯O and C-H⋯O hydrogen bonding, C-H⋯π and aromatic π-π stacking [centroid-centroid distance = 3.995 (1)Å] inter-actions.

Bis(2-pyridylmethanol)bis(saccharinato)zinc(II) and -cadmium(II) at 120 K: three-dimensional structures containing both N-and O-coordinated ambidentate saccharinate ligands.

The title complexes [M(sac)(2)(mpy)(2)] [sac is saccharinate (C(7)H(4)NO(3)S) and mpy is 2-pyridylmethanol (C(6)H(7)NO)], with M = Zn(II) and Cd(II), are isostructural and consist of neutral molecules. The Zn(II) or Cd(II) cations are octahedrally coordinated by the two neutral mpy and two anionic sac ligands. The mpy ligand acts as a bidentate donor through the amine N and hydroxyl O atoms. The sac ligands exhibit an ambidentate coordination behaviour; one is N-coordinated and the other is O-coordinated within the same coordination octahedron. The crystal packing is determined by C-H...O-type hydrogen bonding, as well as by weak py-py and sac-sac aromatic pi-pi-stacking interactions.

N-(2-hydroxyethyl)ethylenediammonium hydrogenphosphate monohydrate.

The title compound, C(4)H(14)N(2)O(2+) x HPO(4)(2-) x H(2)O, contains alternating interleaved layers of hydrogenphosphate and N-(2-hydroxyethyl)ethylenediammonium moieties. The water molecules are associated with channel-like voids in the structure and a network of hydrogen bonds stabilizes the crystal packing.

trans-Bis(diethanolamine-N,O)bis(saccharinato-N)cadmium(II).

The structure of the title complex consists of isolated [Cd(C7H4NO3S)2(C4H11NO2)2] units. The Cd2+ cation lies on an inversion centre and is octahedrally coordinated by two N,O-bidentate diethanolamine (dea) and two N-bonded saccharinate (sac) ligands [saccharin is 1,2-benzisothiazol-3(2H)-one 1,1-dioxide]. The dea ligands constitute the equatorial plane of the octahedron, forming two five-membered chelate rings around the Cd(II) ion, while the sac ligands are localized at the axial positions. The Cd-N(sac), Cd-N(dea) and Cd-O(dea) bond distances are 2.3879 (12), 2.3544 (14) and 2.3702 (13) A, respectively. The H atoms of the free and coordinated hydroxyl groups of the dea ligands are involved in hydrogen bonding with the carbonyl and sulfonyl O atoms of the neighbouring sac ions, while the amine H atom forms a hydrogen bond with the free hydroxyl O atom. The individual molecules are held together by strong hydrogen bonds, forming an infinite three-dimensional network.

Bis(pyridine-2,6-dimethanol-N,O,O')cobalt(II) and -copper(II) disaccharinate dihydrate: three-dimensional structures with extensive hydrogen bonds and aromatic pi-pi-stacking interactions.

Bis(pyridine-2,6-dimethanol-N,O,O')cobalt(II) disaccharinate dihydrate, [Co(C7H9NO2)2](C7H4NO3S)2*2H2O, (I), and bis(pyridine-2,6-dimethanol-N,O,O')copper(II) disaccharinate dihydrate, [Cu(C7H9NO2)2](C7H4NO3S)2*2H2O, (II), collectively [M(dmpy)2](sac)2*2H2O (where M is Co(II) or Cu(II), sac is the saccharinate anion and dmpy is pyridine-2,6-dimethanol), are isostructural. The [M(dmpy)2]2+ cations exhibit distorted octahedral geometry in which the two neutral dmpy species act as tripodal N,O,O'-tridentate ligands. The crystal packing is determined by hydrogen bonding, as well as by weak pyridine-saccharinate pi-pi-stacking interactions.

Sodium p-nitrobenzoxasulfamate monohydrate.

The title compound, alternatively named sodium 6-nitro-3H-1,2,3-benzoxathiazole 2,2-dioxide monohydrate, Na+*C6H3N2O5S-*H2O, consists of chains of NaO7 units, with the seven donor-O atoms coming from two water molecules and five p-nitrobenzoxasulfamate anions. The seven-coordinate geometry around the Na+ ion is described as monocapped trigonal prismatic, but with a large distortion from ideal geometry. Each triangular face is defined by one O atom each from a water molecule, a nitro group and a sulfonyl group. An O atom from a sulfonyl group caps one of the square faces of the trigonal prism in an unsymmetrical fashion. The water molecules and one sulfonyl O atom are involved in bridging adjacent units, as is the nitro group of the anion. The sulfamate ions adopt an antiparallel alignment between the NaO7 units and are connected to each other by C-H...O and pi-pi interactions. The three-dimensional crystal structure is stabilized by a network of strong O-H...N hydrogen bonds.