One-dimensional manganese coordination polymers composed of polynuclear cluster blocks and polypyridyl linkers: structures and properties

The synthesis, crystal structures and magnetic properties of five new manganese compounds are reported. These include a linear trinuclear cluster [Mn(II)(3)(O(2)CCHMe(2))(6)(dpa)(2)].2MeCN (1) (dpa = 2,2'-dipyridylamine), a tetranuclear cluster [Mn(II)(2)Mn(III)(2)O(2)(O(2)CCMe(3))(6)(bpy)(2)] (3) (bpy = 2,2'-bipyridine), and chain coordination polymers composed of cluster blocks such as Mn(3), Mn(3)O, and Mn(4)O(2) bridged by 2,2'-bipyrimidine (bpm) or hexamethylentetramine (hmta) ligands to give ([Mn(II)(3)(O(2)CCHMe(2))(6)(bpm)].2EtOH)(n) (2), [Mn(II)(2)Mn(III)(2)O(2)(O(2)CCHMe(2))(6)(bpm)(EtOH)(4)](n) (4), and (([Mn(II)Mn(III)(2)O(O(2)CCHMe(2))(6)(hmta)(2)].EtOH)(n) (5). The magnetic analysis of the compounds was achieved using a combination of vector coupling and full-matrix diagonalization methods. Susceptibility data for compound 1 was fitted using a vector coupling model to give g = 2.02(1) and 2J/k(B) = -5.38(2) K. To model the trimer chain, we used vector coupling for initial values of J(1) and then diagonalization techniques to estimate J(2) to give g = 1.98(1), 2J(1)/k(B) = -3.3(1) K and 2J(2)/k(B) = -1.0(1) K by approximating the system to a dimer of trimers. The analysis of 3 was made difficult by the mixture of polymorphs and the difficulties of a three-J model, while for 4 an analysis was not possible because of the size of the computation and the relative magnitudes of the three couplings. Compound 5 was modeled using the same techniques as 2 to give g = 1.99(1), 2J(1)/k(B) = +32.5(2) K, 2J(2)/k(B) = -16.8(1) K, and 2J(3)/k(B) = +0.4(1) K. The combination of techniques has worked well for compounds 2 and 5 and thus opens up a method of modeling complex chains.     

Tailoring Atomoxetine Release Rate from DLP 3D-Printed Tablets Using Artificial Neural Networks: Influence of Tablet Thickness and Drug Loading

Various three-dimensional printing (3DP) technologies have been investigated so far in relation to their potential to produce customizable medicines and medical devices. The aim of this study was to examine the possibility of tailoring drug release rates from immediate to prolonged release by varying the tablet thickness and the drug loading, as well as to develop artificial neural network (ANN) predictive models for atomoxetine (ATH) release rate from DLP 3D-printed tablets. Photoreactive mixtures were comprised of poly(ethylene glycol) diacrylate (PEGDA) and poly(ethylene glycol) 400 in a constant ratio of 3:1, water, photoinitiator and ATH as a model drug whose content was varied from 5% to 20% (w/w). Designed 3D models of cylindrical shape tablets were of constant diameter, but different thickness. A series of tablets with doses ranging from 2.06 mg to 37.48 mg, exhibiting immediate- and modified-release profiles were successfully fabricated, confirming the potential of this technology in manufacturing dosage forms on demand, with the possibility to adjust the dose and release behavior by varying drug loading and dimensions of tablets. DSC (differential scanning calorimetry), XRPD (X-ray powder diffraction) and microscopic analysis showed that ATH remained in a crystalline form in tablets, while FTIR spectroscopy confirmed that no interactions occurred between ATH and polymers.     

Spectroelectrochemical Properties and Catalytic Activity in Cyclohexane Oxidation of the Hybrid Zr/Hf-Phthalocyaninate-Capped Nickel(II) and Iron(II) tris-Pyridineoximates and Their Precursors

The in situ spectroelectrochemical cyclic voltammetric studies of the antimony-monocapped nickel(II) and iron(II) tris-pyridineoximates with a labile triethylantimony cross-linking group and Zr(IV)/Hf(IV) phthalocyaninate complexes were performed in order to understand the nature of the redox events in the molecules of heterodinuclear zirconium(IV) and hafnium(IV) phthalocyaninate-capped derivatives. Electronic structures of their 1e-oxidized and 1e-electron-reduced forms were experimentally studied by electron paramagnetic resonance (EPR) spectroscopy and UV−vis−near-IR spectroelectrochemical experiments and supported by density functional theory (DFT) calculations. The investigated hybrid molecular systems that combine a transition metal (pseudo)clathrochelate and a Zr/Hf-phthalocyaninate moiety exhibit quite rich redox activity both in the cathodic and in the anodic region. These binuclear compounds and their precursors were tested as potential catalysts in oxidation reactions of cyclohexane and the results are discussed.     

Efficient Synthesis of a New Family of 2,6-Disulfanyl-9-selenabicyclo[3.3.1]nonanes

The efficient synthesis of a new family of 2,6-disulfanyl-9-selenabicyclo[3.3.1]nonanes in high yields has been developed based on 9-selenabicyclo[3.3.1]nonane-2,6-dithiolate anion generated from bis-isothiouronium salt of 2,6-dibromo-9-selenabicyclo[3.3.1]nonane. The derivatives of 2,6-disulfanyl-9-selenabicyclo[3.3.1]nonane containing alkyl, allyl and benzyl moieties have been prepared in 90–99% yields by nucleophilic substitution of 9-selenabicyclo[3.3.1]nonane-2,6-dithiolate anion with alkyl, allyl and benzyl halides. The reaction of nucleophilic addition of 9-selenabicyclo[3.3.1]nonane-2,6-dithiolate anion to alkyl propiolates afforded 2,6-di(vinylsulfanyl)-9-selenabicyclo[3.3.1]nonanes. The conditions for regio- and stereoselective addition of 9-selenabicyclo[3.3.1]nonane-2,6-dithiolate anion to a triple bond of alkyl propiolates have been found. To date, not a single representative of 2,6-disulfanyl-9-selenabicyclo[3.3.1]nonanes has been described in the literature.     

Volatile constituents of aerial parts of Centaurea sibthorpii (Sect. Carduiformes, Asteraceae) from Greece and their biological activity

The volatile constituents of the aerial parts of Centaurea sibthorpii [Sect. Carduiformes, Asteraceae] collected in Greece were extracted by hydrodistillation and analysed by GC and GC-MS. Altogether 63 components were identified. Fatty acids and sesquiterpenoidic compounds were the most abundant components in the oil. A study on the biological activity of the oil showed no action against Gram-positive and Gram-negative bacteria.     

First-principles-based calculations of vibrational normal modes in polyatomic materials with translational symmetry: application to PETN molecular crystal

Numerical studies of vibrational energy transport and associated (non)linear infrared and Raman response in polyatomic materials require knowledge of the multidimensional vibrational potential-energy surface and the ability to perform normal-mode analysis on that potential. The presence of translational symmetry, as in crystals, leads to the observed dispersion of the unit cell normal modes and has to be accounted for in calculations of energy transfer rates and other spectroscopic quantities. Here we report on the implementation of a computational approach that combines the generalized supercell method and density functional theory electronic structure calculations to investigate the vibrational structure in translationally symmetric materials containing relatively large numbers of atoms in the unit cell (58 atoms in the present study). The method is applied to calculate the phonon and vibron dispersion relations and the vibrational density of states in pentaerythritol tetranitrate (PETN) molecular crystal which is an important energetic material. The results set the stage for future investigations of vibrational energy transport and associated nonlinear spectroscopic signatures in this class of materials.     

Peculiarities of RBCs resistance to acid hemolysis in hibernating mammals

The binding of acids and alkalis, formed in tissues by metabolism, along with oxygen and CO(2) transport are recognise as the principal functions of red blood cells (RBCs). Decreases in internal environment pH may result in activation of potential endogenous cytotoxic metabolites, OH and oxidant formation and, as a consequence, result in oxidative damage of cell membrane leading to hemolysis. The characteristics of acid hemolysis in hibernating mammals have been determined in this study. Parameters of HCl-hemolysis, such as the average time for RBC hemolysis and the population distribution of the response, have been investigated. Measurements were performed within 40-5 degrees C temperature range. The resistance of hibernator RBCs to increased acidity, determined according to the acid hemolysis parameters, was found to reflect whether the animal was in the summer active period or in hibernation, with differences also apparent at different points with the hibernation season itself. It was demonstrated that hemolysis parameters of naturally cold-tolerant organisms are altered by decreases in temperature. We discuss a role of cytoskeletal-membrane interactions as a fast-acting switch of the structural and functional state of hibernator RBCs as an adaptation mechanism to acidosis arising from hypothermia and hypermetabolism.     

Organic carbonates: experiment and ab initio calculations for prediction of thermochemical properties

This work has been undertaken in order to obtain data on thermodynamic properties of organic carbonates and to revise the group-additivity values necessary for predicting their standard enthalpies of formation and enthalpies of vaporization. The standard molar enthalpies of formation of dibenzyl carbonate, tert-butyl phenyl carbonate, and diphenyl carbonate were measured using combustion calorimetry. Molar enthalpies of vaporization of these compounds were obtained from the temperature dependence of the vapor pressure measured by the transpiration method. Molar enthalpy of sublimation of diphenyl carbonate was measured in the same way. Ab initio calculations of molar enthalpies of formation of organic carbonates have been performed using the G3MP2 method, and results are in excellent agreement with the available experiment. Then the group-contribution method has been developed to predict values of the enthalpies of formation and enthalpies of vaporization of organic carbonates.     

Role of the ancillary ligand N,N-dimethylaminoethanol in the sensitization of Eu(III) and Tb(III) luminescence in dimeric beta-diketonates

Two types of dimeric complexes [Ln2(hfa)6(mu2-O(CH2)2NHMe2)2] and [Ln(thd)2(mu2,eta2-O(CH2)2NMe2)]2 (Ln = YIII, EuIII, GdIII, TbIII, TmIII, LuIII; hfa- = hexafluoroacetylacetonato, thd- = dipivaloylmethanato) are obtained by reacting [Ln(hfa)3(H2O)2] and [Ln(thd)3], respectively, with N,N-dimethylaminoethanol in toluene and are fully characterized. X-ray single crystal analysis performed for the TbIII compounds confirms their dimeric structure. The coordination mode of N,N-dimethylaminoethanol depends on the nature of the beta-diketonate. In [Tb2(hfa)6(mu2-O(CH2)2NHMe2)2], eight-coordinate TbIII ions adopt distorted square antiprismatic coordination environments and are O-bridged by two zwitterionic N,N-dimethylaminoethanol ligands with a Tb1...Tb2 separation of 3.684(1) A. In [Tb(thd)2(mu2,eta2-O(CH2)2NMe2)]2, the N,N-dimethylaminoethanol acts as chelating-bridging O,N-donor anion and the TbIII ions are seven-coordinate; the Tb1...Tb1A separation amounts to 3.735(2) A within centrosymmetric dimers. The dimeric complexes are thermally stable up to 180 degrees C, as shown by thermogravimetric analysis, and their volatility is sufficient for quantitative sublimation under reduced pressure. The EuIII and TbIII dimers display metal-centered luminescence, particularly [Eu2(hfa)6(O(CH2)2NHMe2)2] (quantum yield Q(L)Ln = 58%) and [Tb(thd)2(O(CH2)2NMe2)]2 (32%). Consideration of energy migration paths within the dimers, based on the study of both pure and EuIII- or TbIII-doped (0.01-0.1 mol %) LuIII analogues, leads to the conclusion that both the beta-diketone and N,N-dimethylaminoethanol ligands contribute significantly to the sensitization process of the EuIII luminescence. The ancillary ligand increases considerably the luminescence of [Eu2(hfa)6(O(CH2)2NHMe2)2], compared to [Ln(hfa)3(H2O)2], through the formation of intra-ligand states while it is detrimental to TbIII luminescence in both beta-diketonates. Thin films of the most luminescent compound [Eu2(hfa)6(O(CH2)2NHMe2)2] obtained by vacuum sublimation display photophysical properties analogous to those of the solid-state sample, thus opening perspectives for applications in electroluminescent devices.