Vibrational properties of the polymeric spin crossover (SCO) Fe(ii) complexes [{Fe(4-amino-1,2,4-triazole) 3}X 2] n: A nuclear inelastic scattering (NIS), Raman and DFT study

The vibrational properties of the cationic spin crossover (SCO) coordination polymers [{Fe(4-amino-1,2,4-triazole) 3} +2] n containing the anions chlorine, methanosulfonate and 1-naphthalenesulfonate have been studied via nuclear inelastic scattering of synchrotron radiation (NIS) as well as by Raman spectroscopy. Although the different anions have a strong influence on the spin crossover temperature, they have little effect on the positions of the spin marker bands in the NIS and Raman spectra. By comparing the line positions of the NIS spin marker bands with those observed by Raman spectroscopy, it has been possible to distinguish vibrations symmetry (A u or A g) because modes of A u and A g symmetries are NIS active, but only the A g modes are Raman active. The normal mode analysis of charge compensated cationic pentameric and hexameric model structures which have been obtained by density functional calculations reproduces the experimentally observed mode frequencies and the geometry optimization reproduces iron-ligand distances reported for these and related SCO coordination complexes. The effect of charge compensation appears to be independent of the choice of the functional and the basis set which shows that DFT calculations using B3LYP in conjunction with the basis set CEP-31G are a time effective approach in order to study vibrational properties of Fe(ii) SCO compounds. This journal is © 2012 the Owner Societies

Two-step spin transition in a 1D FeII 1,2,4-triazole chain compound

A thermochromic 1D spin crossover coordination (SCO) polymer [Fe(βAlatrz)3](BF4)2·2H2O (1·2H2O), whose precursor βAlatrz, (1,2,4-triazol-4-yl-propionate) has been tailored from a β-amino acid ester is investigated in detail by a set of superconducting quantum interference device (SQUID), 57Fe Mössbauer, differential scanning calorimetry, infrared, and Raman measurements. An hysteretic abrupt two-step spin crossover (T1/2 ↓=230 K and T1/2 ↑=235 K, and T1/2 ↓=172 K and T1/2 ↑=188 K, respectively) is registered for the first time for a 1,2,4-triazole-based FeII 1D coordination polymer. The two-step SCO configuration is observed in a 1:2 ratio of low-spin/high-spin in the intermediate phase for a 1D chain. The origin of the stepwise transition was attributed to a distribution of chains of different lengths in 1·2H2O after First Order Reversal Curves (FORC) analyses. A detailed DFT analysis allowed us to propose the normal mode assignment of the Raman peaks in the low-spin and high-spin states of 1·2H2O. Vibrational spectra of 1·2H2O reveal that the BF4 - anions and water molecules play no significant role on the vibrational properties of the [Fe(βAlatrz)3]2+ polymeric chains, although non-coordinated water molecules have a dramatic influence on the emergence of a step in the spin transition curve. The dehydrated material [Fe(βAlatrz)3](BF4)2 (1) reveals indeed a significantly different magnetic behavior with a one-step SCO which was also investigated. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Cardiac chymase: pathophysiological role and therapeutic potential of chymase inhibitors

On release from cardiac mast cells, alpha-chymase converts angiotensin I (Ang I) to Ang II. In addition to Ang II formation, alpha-chymase is capable of activating TGF-beta 1 and IL-1 beta, forming endothelins consisting of 31 amino acids, degrading endothelin-1, altering lipid metabolism, and degrading the extracellular matrix. Under physiological conditions the role of chymase in the mast cells of the heart is uncertain. In pathological situations, chymase may be secreted and have important effects on the heart. Thus, in animal models of cardiomyopathy, pressure overload, and myocardial infarction, there are increases in both chymase mRNA levels and chymase activity in the heart. In human diseased heart homogenates, alterations in chymase activity have also been reported. These findings have raised the possibility that inhibition of chymase may have a role in the therapy of cardiac disease. The selective chymase inhibitors developed to date include TY-51076, SUN-C8257, BCEAB, NK320, and TEI-E548. These have yet to be tested in humans, but promising results have been obtained in animal models of myocardial infarction, cardiomyopathy, and tachycardia-induced heart failure. It seems likely that orally active inhibitors of chymase could have a place in the treatment of cardiac diseases where injury-induced mast cell degranulation contributes to the pathology