Chain conformation in polyretropeptides: Quantum mechanical and empirical force field calculations on 2,6,8-trioxo-3,5,9-triazadecane,a model compound for poly(retro-glycine)

We report here our results on semiempirical AM1 calculations for the conformational preferences of 2,6,8-trioxo-3,5,9-triazadecane, a model compound for polymers made of retropeptide units. We have evaluated the effect of applying symmetry constraints between chemically equivalent torsion angles. These results suggest that preferred conformations around the ? NH? CH₂? NH? group are quite independent from those on the ? CO? CH₂? CO? unit, so all possible combinations generate the complete set of energy minima for the model compound. We have analyzed the implications of the different minimum energy conformation in an infinite chain model and we have explored the conformational space of regular polyretropeptides. This shows a close relation to that of regular polypeptides but with significant differences arising from the change of orientation of the peptide units along the polymer molecule. The energy calculations also support previously proposed models for the crystal structure of the simplest polyretropeptide, poly(retro-glycine). Finally, we discuss the consequences of retropeptide-peptide copolymerization as well as the expected conformations for regular alternate terpolymers. © 1995 John Wiley & Sons, Inc.     

The action of melatonin (MLT) on platelet metabolism in vitro.-II-

Melatonin induces an apparent platelets emission by rat's megakaryocytes in vitro.     

Ferrylmyoglobin formation induced by acute magnesium deficiency in perfused rat heart causes cardiac failure

The oxidation states in intracellular myoglobin and cytochrome oxidase aa₃ were monitored by reflectatnce spectrophotometry in isoltaed perfused rat hearts subjected to an acutely magnesium deficient environment. After exposure to low extracellular [Mg²⁺]_o (i.e., 0.3 mM) for 30 min, more than 80% of the oxymyoglobin converted to its deoxygenated form. The level of reduced cytochrome oxidase aa₃ also increased about 80% in low [Mg²⁺]_o. the deoxymyoglobin was converted further to a species identified as ferrymyoglobin by its reaction with Na₂S to form ferrous sulfmyoglobin which was optically visible. This process, set into motion by acute Mg deficiency, resulted from a direct accessibility of the exogenous peroxide to the cytosolic protein. The results suggest that a pathway leading to cardiac tissue damage, induced magnesium deficiency, is probably involved in the generation of a ferrylmyoglobin radical which could be prevented by addition of ascorbate, which is known to be a one-electron reductant of this hypervalent form of myglobin. In further studies, we also investigated whether addition of different concentrations of ascorbic acid (AA) to the perfusate could enhance myocardial function after exposure to log [Mg²⁺]_o perfusion. Four concentrations of AA (0.5, 1, 5, 10 mM) were tested, indicate that they exert their effects in a concentration-dependent manner; 1 mM AA was the most effective dose in improving aortic output in a Mg-deficient heart. Ferrylmyoglobin formation was found to be formed considerably before intracellylar release of either creatine phosphokinase or lactic dehydrogenase. These studies may have wide implications as a new mechanisms by which extracellular Mg²⁺ can induce myocardial injury and subsequent cardiac failure.     

Comparison of the physical properties of the nuclear progesterone receptor, bound to antiprogestin RU 486 or progestin ORG 2058, following limited proteolysis

The susceptibility of the progesterone receptor, liganded either by the antiprogestin RU 486 or by the progestin ORG 2058, to chymotrypsin and trypsin degradation was investigated. The nuclear fraction was isolated from T47D cells previously exposed either to 0.1 microM [3H]RU 486 or to 0.1 microM [3H]ORG 2058. The proteolytic digestion was performed on the micrococcal nuclease hydrolysate. The molecular weights of the receptor fragments were calculated, in high salt buffer, from the sedimentation coefficients determined on a sucrose gradient and from the Stokes radii estimated by gel filtration on an Agarose A-0.5 m column. Micrococcal nuclease solubilized receptor forms with molecular weights of 80,000 and 75,000 for the antiprogestin- or progestin-liganded receptor, respectively. Chymotrypsin degraded these receptor forms to fragments with molecular weights of 23,000 either for the antiprogestin- or progestin-liganded receptor. Similar molecular weights of 23,000 were calculated for the progesterone receptor liganded either by the antiprogestin RU 436 or the progestin ORG 2058 following trypsin cleavage. We conclude that the degradation pattern of the progesterone receptor liganded either by the antiprogestin RU 486 or the progestin ORG 2058 following chymotrypsin or trypsin digestion seems to be similar.     

Heterogeneous bone-marrow stromal progenitors drive myelofibrosis via a druggable alarmin axis

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Self-assembled monolayers of bis(salicylaldiminato)nickel(II) Schiff-base complexes: synthesis and structure

The synthesis of two derivatized Ni^II Schiff-base complexes is reported. Self-assembled monolayers (SAMs) have been obtained by reaction of coupling layers, functionalized glass substrates and the derivatized complex precursors. The self-assembled films have been characterized by contact angle measurements, X-ray photoelectron spectroscopy, and UV-Vis absorption spectroscopy. A structure of these SAMs is proposed on the basis of spectroscopic data and molecular metrical parameters.     

Decolorization of Direct Red 28 by mixed bacterial culture in an up-flow immobilized bioreactor

Aerobic mixed bacterial culture comprised of five isolates (Bacillus vallismortis, B. pumilus, B. cereus, B. subtilis and B. megaterium) identified by 16srDNA analysis was developed from wastewater samples from the aeration tank of an effluent treatment plant of a textile and dyeing industry and evaluated for its ability to decolorize azo dye Direct Red 28 in an up-flow immobilized packed bed bioreactor using marble chips as support matrix. The bioreactor was operated under two parameters: an aeration rate of 0.4 and 0.6 mmol/min at a flow rate of 60, 90 and 120 ml/h, respectively. At a constant aeration rate of 0.4 mmol/min and with flow rates of 60, 90 and 120 ml/h, optimum decolorization of 91, 75 and 72% was observed, while at an aeration rate of 0.6 mmol/min and flow rates of 60, 90 and 120 ml/h, optimum decolorization of 93, 78 and 72% was observed over 10 days. The study concluded that across the two aeration rates and the respective flow rates, the higher aeration rate of 0.6 mmol/min along with a flow rate of 60 ml/h was best suited to decolorize Direct Red 28 in the packed bed bioreactor. Spectral changes of the input and output of the bioreactor by UV–visible spectroscopy indicated decolorization of the dye solution by degradation in addition to the visual observation of the biosorption process.     

Synthesis, crystal structure, and second-order nonlinear optical properties of [N,N-bis(1H-pyrrol-2-ylmethylene)-1,2-benzenediaminato]nickel(II) Schiff base complexes

The synthesis, characterization, crystal structure, thermal stability, optical spectroscopic, electronic structure, and second-order nonlinear optical (NLO) properties of a novel class of materials, based on planar [N₄]Ni(II) complexes, are reported. The single-crystal X-ray structure of the dichloro derivative indicates a planar structure of the molecule. The Ni(II) ion is tetracoordinated in a square planar environment, with the four nitrogen atoms as donors. The unsubstituted derivative exhibits efficiency 1.2 times that of urea in second-harmonic generation at 1.9 μm. INDO/SCI-SOS quantum-chemical calculations predict a sizeable molecular response and a significant octupolar contribution to optical nonlinearity.