Influence of the phonon-bottleneck effect and low-energy vibrational modes on the slow spin-phonon relaxation in Kramers-ions-based Cu(II) and Co(II) complexes with 4-amino-3,5-bis-(pyridin-2-yl)-1,2,4-triazole and dicyanamide.

Two new complexes, bis-[4-amino-3,5-bis-(pyridin-2-yl)-1,2,4-triazole-κ2N2,N6]bis-(dicyanamide-κN8)copper(II), [Cu(abpt)2(dca)2] (1) and bis-[4-amino-3,5-bis-(pyridin-2-yl)-1,2,4-triazole-κ2N2,N6]bis-(dicyanamide-κN8)cobalt(II), [Co(abpt)2(dca)2] (2), have been prepared and magneto-structurally characterised. Single crystal studies of both complexes have shown that their crystal structures are molecular, in which the central atoms are six-coordinated in the form of a distorted octahedron by two bidentate abpt and two monodentate dca ligands. Even if both complexes have the same composition and crystallize in the same P1̄ space group, they are not isostructural. Both structures contain strong intermolecular N-H⋯N hydrogen bonds and π-π stacking interactions. IR spectra are consistent with the solved structures of both complexes and confirmed the terminal character of the dca ligands and the bidentate coordination of the abpt ligands. The analysis of the magnetic properties showed that both complexes exhibit field-induced slow spin-phonon relaxation. In both complexes, the slow spin-phonon relaxation is influenced by a severe phonon-bottleneck effect that affects the direct process, a dominant relaxation mechanism at low temperatures in both complexes. The phonon-bottleneck effect in 1 was suppressed by simply reducing the crystallite size, and further analysis of the field dependence of the relaxation time yielded the characteristic energy of vibrational modes of 11 cm-1 participating in the Raman process at low magnetic fields. The analysis of magnetic properties and ab initio calculations confirmed that 2 represents a system with a moderate uniaxial anisotropy yielding an average energy barrier of 82 cm-1 (from all four nonequivalent Co(II) sites in the structure of 2).

In vivo study of light-driven naproxen release from gated mesoporous silica drug delivery system.

A drug delivery system based on mesoporous particles MCM-41 was post-synthetically modified by photo-sensitive ligand, methyl-(2E)-3-(4-(triethoxysilyl)-propoxyphenyl)-2-propenoate (CA) and the pores of MCM-41 particles were loaded with Naproxen sodium salt (NAP). The CA was used as a photoactive molecule that can undergo a reversible photo-dimerization by [2π + 2π] cycloaddition when irradiated with UV light of specific wavelengths. Thus, it has a function of gate-keeper that is responsible for opening/closing the pores and minimizing premature release of NAP. The physicochemical properties of the prepared system were studied by infrared spectroscopy (IR), nitrogen adsorption measurements, thermogravimetric analysis (TGA), scanning transmission electron microscopy (STEM) and energy dispersive X-ray spectroscopy (EDX). The mechanism of the opening/closing pores was confirmed by UV measurements. In vitro and in vivo drug release experiments and the concentration of released NAP was determined by UV spectroscopy and high-performance liquid chromatography (HPLC). In vivo drug release in the blood circulatory system of rats has demonstrated the effective photo-cleavage reaction of CA molecules after UV-light stimulation. The localization and morphological changes of the particles were studied in the blood and liver of rats at different time intervals. The particles in the blood have been shown to retain their original rod-like shape, and the particles in the liver have been hydrolysed, which has resulted in spherical shape with a reduced size.

Mesoporous Silica as a Drug Delivery System for Naproxen: Influence of Surface Functionalization.

In this work we describe the relationship between surface modification of hexagonally ordered mesoporous silica SBA-15 and loading/release characteristics of nonsteroidal anti-inflammatory drug (NSAID) naproxen. Mesoporous silica (MPS) was modified with 3-aminopropyl, phenyl and cyclohexyl groups by grafting method. Naproxen was adsorbed into pores of the prepared MPS from ethanol solution using a solvent evaporation method. The release of the drug was performed in buffer medium at pH 2 and physiological solution at pH 7.4. Parent MPSs as well as naproxen loaded MPSs were characterized using physicochemical techniques such as nitrogen adsorption/desorption, thermogravimetric analysis (TG), Zeta potential analysis, Fourier transform infrared spectroscopy (FT-IR), and elemental analysis. The amount of naproxen released from the MPSs into the medium was determined by high-performance liquid chromatography (HPLC). It was shown that the adsorption and desorption characteristics of naproxen are dependent on the pH of the solution and the surface functionalization of the host.

Doxorobicin as cargo in a redox-responsive drug delivery system capped with water dispersible ZnS nanoparticles.

In this work, we have prepared and investigated a redox-responsive drug delivery system (DDS) based on a porous carrier. Doxorubicin (DOX), a chemotherapy medication for treatment of different kinds of cancer, was used as a model drug in the study. DOX was loaded in ordered hexagonal mesoporous silica SBA-15, a nanoporous material with good biocompatibility, stability, large pore size and specific surface area (S BET = 908 m2 g-1, V P = 0.79 cm3 g-1, d = 5.9 nm) and easy surface modification. To prepare the redox-responsive system, cystamine derivative ligands, with redox active disulphide linkers were grafted onto the surface of SBA-15. To ensure no significant premature release of DOX from the porous system, thioglycolic acid modified ZnS nanoparticles (ZnS-COOH NPs) were used as pore capping agents. The grafted redox-responsive cystamine derivative ligand containing disulphide linkers was bonded by a peptide bond to the thioglycolic acid groups of ZnS-COOH NPs, capping the pores. Once the disulphide bond was cleaved, the ZnS-COOH NPs caps were released and pores were opened to deliver the DOX cargo. The dithiol bond was cleavable by redox active molecules such as dithiothreitol (DTT) or glutathione, the concentration of which in cancer cells is 4 times higher than in healthy cells. The redox release of DOX was studied in two different media, physiological saline solution with DTT and saline without DTT. The prepared DDS proved the concept of redox responsive release. All samples were characterised by powder X-ray diffraction (XRD), transition electron microscopy (TEM), nitrogen adsorption/desorption at 77 K, Fourier-transform infrared spectroscopy (FTIR), thermal analysis and zeta potential measurements. The presence of semiconducting ZnS nanoparticle caps on the pore openings was detected by magnetic measurements using SQUID magnetometry showing that such cargo systems could be monitored using magnetic measurements which opens up the possibilities of using such drug delivery systems as theranostic agents.

A Study of 5-Fluorouracil Desorption from Mesoporous Silica by RP-UHPLC.

In cancer treatment, the safe delivery of the drug to the target tissue is an important task. 5-fluorouracil (5-FU), the well-known anticancer drug, was encapsulated into the pores of unmodified mesoporous silica SBA-15, as well as silica modified with 3-aminopropyl and cyclohexyl groups. The drug release studies were performed in two different media, in a simulated gastric fluid (pH = 2) and in a simulated body fluid (pH = 7) by RP-UHPLC. The simple and rapid RP-UHPLC method for quantitative determination of 5-fluorouracil released from unmodified and modified mesoporous silica SBA-15 was established on ODS Hypersil C18 column (150 × 4.6 mm, 5 µm) eluted with mobile phase consisted of methanol: phosphate buffer in volume ratio of 3:97 (v/v). Separation was achieved by isocratic elution. The flow rate was kept at 1 mL/min, the injection volume was set at 20 µL and the column oven temperature was maintained at 25 °C. The effluent was monitored at 268 nm. This paper provides information about the quantitative determination of the released 5-FU from silica. It was found out that larger amount of the drug was released in neutral pH in comparison with the acidic medium. In addition, surface functionalisation of silica SBA-15 influences the release properties of the drug.

Low-dimensional compounds containing cyanido groups. Part XXXV. Structure, spectral, thermal and magnetic properties of a binuclear CuII-biquinoline complex with bridging and terminal dicyanamide ligands.

From the system CuCl2-biq-NaN(CN)2 (biq is 2,2'-biquinoline), the binuclear molecular complex bis(µ-dicyanamido-κ2N1:N5)bis[(2,2'-biquinoline-κ2N,N')(dicyanamido-κN1)copper(II)], [Cu2(C2N3)4(C18H12N2)2] or [Cu2(biq)2(dca)2(µ1,5-dca)2] (1) [dca is dicyanamide, N(CN)2-] was isolated and characterized by crystal structure analysis, and spectral, thermal and magnetic measurements. IR spectroscopy confirmed the presence of the biq and dca ligands in 1. Its solid-state structure consists of discrete centrosymmetric binuclear copper(II) units with double end-to-end dca bridges. Each CuII atom is in a distorted square-pyramidal environment with the equatorial plane formed by two nitrile N atoms from bridging dca groups, one of the two N atoms of the chelate biq molecule and one nitrile N atom from a terminal dca ligand, whereas the second biq N atom occupies the axial position. Thermal decomposition of 1 in an air atmosphere proceeds gradually, with copper(I) cyanide being the final decomposition product. Magnetic measurements revealed the formation of alternating spin chains and a relatively strong exchange interaction within the binuclear units was also confirmed by Broken Symmetry DFT (density functional theory) calculations.

A CuII complex with an carbamoylcyanonitrosomethanide ligand formed in situ by the nucleophilic addition of water to dicyanonitrosomethanide: structure, spectral and magnetic properties.

The complex (2,2'-biquinoline-κ2N,N')(carbamoylcyanonitrosomethanide-κ2N,O)chloridocopper(II) acetonitrile monosolvate, [Cu(C3H2N3O2)Cl(C18H12N2)]·CH3CN or [Cu(ccnm)Cl(biq)]·acn (acn is acetonitrile, biq is 2,2'-biquinoline and ccnm is carbamoylcyanonitrosomethanide), (I), was prepared as a result of nucleophilic addition of water to the dicyanonitrosomethanide ion in the presence of CuII and biq. IR spectroscopy confirmed the presence of ccnm, biq and acn in (I). The solid-state structure consists of the neutral complex containing ccnm and biq ligands, coordinated to the CuII atom in a bidendate chelating manner, and a chloride ligand, resulting in a distorted tetragonal pyramidal coordination of CuII. The asymmetric unit is supplemented by one molecule of solvated acn which, along with the nitrile group of ccnm, serves as an acceptor in intermolecular hydrogen bonding, creating infinite chains along the b axis. Magnetic measurements revealed a paramagnetic behaviour with a very small Weiss temperature Θ = -0.32 K and high anisotropy of the g tensor (gx = 2.036, gy = 2.120 and gz = 2.205).

Slow magnetic relaxation in octahedral cobalt(II) field-induced single-ion magnet with positive axial and large rhombic anisotropy.

Pseudooctahedral mononuclear cobat(II) complex [Co(abpt)2(tcm)2] (1), where abpt = 4-amino-3,5-bis(2-pyridyl)-1,2,4-triazole and tcm = tricyanomethanide anion, shows field-induced slow relaxation of magnetization with U = 86.2 K and large axial and rhombic single-ion zero-field-splitting parameters, D = +48(2) cm(-1) and E/D = 0.27(2) (D = +53.7 cm(-1) and E/D = 0.29 from ab initio CASSCF/NEVPT2 calculations), thus presenting a new example of a field-induced single-ion magnet with transversal magnetic anisotropy.

Low-dimensional compounds containing cyanide groups. XXV. Synthesis, spectroscopic properties and crystal structures of two ionic iron(II) complexes with tricyanomethanide: tris(1,10-phenanthroline-κ(2)N,N')iron(II) bis(tricyanomethanide) and tris(2,2'-bipyridine-κ(2)N,N')iron(II) bis(tricyanomethanide) sesquihydrate.

Two new diamagnetic coordination compounds, [Fe(phen)3][C(CN)3]2, (I), and [Fe(bpy)3][C(CN)3]2·1.5H2O, (II), have been synthesized and characterized by single-crystal X-ray diffraction analysis, and IR and UV-Vis spectroscopy (phen is 1,10-phenanthroline, C12H8N2, and bpy is 2,2'-bipyridine, C10H8N2). Both compounds are ionic with distorted octahedral [Fe(phen)3](2+) or [Fe(bpy)3](2+) complex cations, with average Fe-N distances of 1.977 (2) and 1.971 (3) Å, respectively, and two uncoordinated planar tricyanomethanide, or [C(CN)3](-), counter-anions balancing the positive charges of the cations. Solvent water molecules and tcm anions in (II) are linked via O-H...N hydrogen bonds into negatively charged layers and the interlayer space is filled by [Fe(bpy)3](2+) cations. The structures of (I) and (II) are stabilized by π-π interactions between the stacked aromatic rings of the phen ligands of two adjacent cations and by O-H...N hydrogen bonds, respectively, and also by π-π stacking interactions between phen and tcm units in (I).

Tris(5,6-dimethyl-1,10-phenanthroline-κ(2) N,N')iron(II) bis-(tricyano-methanide).

The title compound, [Fe(C14H12N2)3](C4N3)2, consists of one [Fe(dimephen)3](2+) complex cation (dimephen = 5,6-dimethyl-1,10-phenanthroline) and two uncoordinating tcm anions (tcm = tricyano-methanide). In the complex cation, the Fe(II) atom is coordinated by six N atoms from three chelating dimephen ligands at an average Fe-N distance of 1.963 (4) Šgiving a distorted octa-hedral geometry. The crystal structure is stabilized by weak C-H⋯N hydrogen bonds and C N⋯π inter-actions between planar [maximum deviations of 0.024 (3) and 0.015 (3) Å] tcm anions and pyridine rings of dimephen [N2⋯centroid = 3.531 (3) and 3.726 (3) Å; C N⋯centroid = 96.4 (2) and 97.1 (2)°].