FT-IR spectroscopic, AM1 and PM3 computational studies of conformation of natural products: cytisine

Infrared spectra were recorded for cytisine (1) and its model compounds: N-methyl-2-pyridone (2) and piperidine (3) in solution. Eight solvents of different polarity, polarizability and acid-base properties: CCl(4), CS(2), CHCl(3), CDCl(3) (for comparison with the NMR spectra), CH(2)Cl(2), MeOH, Et(2)O and Et(3)N were chosen. Experimental FT-IR spectra were analysed with the help of those calculated for isolated derivatives at the AM1 and PM3 levels. Influence of environment on the conformational preferences in solvated cytisine was discussed and compared with those in the solid state (X-ray measurements) and in the gas phase (quantum-mechanical calculations).     

Nanoscale organization of adsorbed collagen: influence of substrate hydrophobicity and adsorption time

The adsorption of collagen on polystyrene (PS) and polystyrene oxidized by oxygen plasma discharge (PSox) was studied as a function of time using radiolabeling, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). Radiolabeling and XPS indicated that the initial step of adsorption was faster on PS than on PSox. AFM imaging under water revealed very different supramolecular organization of the adsorbed films depending on time and on the nature of the substrate: PS showed patterns of collagen aggregates at all adsorption times (from 1 min to 24 h); PSox was covered with a smooth layer except at long adsorption times (24 h), for which a mesh of collagen structures was observed. After fast drying, the collagen layer remained continuous and showed a morphology which recalled that observed under water. The mechanical stability of the adsorbed films was assessed under water by scraping with the AFM probe at different loading forces: no perturbations were created on PSox; in contrast, the layer adsorbed on PS was sensitive to scraping, the minimum force required to alter the collagen layer morphology increasing with time. These differences in the film properties were correlated with force measurements upon retraction: multiple adhesion forces were observed with collagen adsorbed on PS samples, whereas such an effect was never observed on PSox. The results show that the amount adsorbed and the organization of the adsorbed film respond differently to the adsorption time and that this is influenced by surface hydrophobicity. The quick initial adsorption on PS, compared to PSox, is thought to leave dangling collagen segments that are responsible for the observed morphology, for adhesion forces, and for lower mechanical resistance of the adsorbed layer.     

Quadrupole relaxation enhancement and polarisation transfer in DMSO solution of [Bi(NO3)3(H2O)3]*18-crown-6 in solid state

ABSTRACT

¹H spin-lattice relaxation studies have been performed for pure [Bi(NO₃)₃(H₂O)₃]*18-crown-6 in powder and its solution in dimethyl sulfoxide (DMSO). The experiments have been carried out in the frequency range of 10?kHz–30?MHz and the temperature range of 240–277?K; at 277?K the solution is already frozen. The ¹H relaxation of pure [Bi(NO₃)₃(H₂O)₃]*18-crown-6 has been interpreted in terms of three dynamical processes. Quadrupole Relaxation Enhancement effects have been observed in the frozen DMSO solution of [Bi(NO₃)₃(H₂O)₃]*18-crown-6. The specific mechanisms of the ¹H spin-lattice relaxation enhancement have been discussed distinguishing between effects caused by time independent (residual) and fluctuating ¹H-²⁰⁹Bi dipole-dipole interactions.     

Pharmacokinetics of lithium in rat brain regions by spectroscopic imaging

Lithium (Li) and its salts have been demonstrated to be the most effective drug in both acute and prophylactic treatment of bipolar disorder. The exact molecular mechanisms and particular target regions accounting for its mood-stabilizing effect remain unknown. Knowledge of Li distribution and its regional pharmacokinetic properties in the living brain is of value in localizing its action in the brain. Pharmacokinetic measurements in different anatomical regions of the human brain are not yet available. Limited pharmacokinetic measurements in rat brain subvolumes have been performed using atomic absorption technique. However, a noninvasive way of estimating the pharmacokinetics in different regions of the brain where the drug exerts its beneficial effects would allow such methods to be used in the study of patients undergoing Li therapy. Earlier (7)Li MR studies on rat brain regions have provided preliminary pharmacokinetic information from the whole brain. Using (7)Li MR spectroscopic imaging (SI) technology, Li distribution in brain regions of the rat at therapeutic dosages has been recently demonstrated by us. Here we report feasibility of local pharmacokinetic measurements on brain regions obtained by magnetic resonance SI technology. Our results suggest that Li is most active in a region stretching from the anterior cingulate cortex and striatum to the caudal midbrain, with greatest activity including the preoptic area and hypothalamic region. Some activity was seen in prefrontal cortex, but only minimal amounts in the region of the cerebellum and metencephalic brainstem.     

F-Continuous Graphs

For a nontrivial connected graph F, the F-degree of a vertex in a graph G is the number of copies of F in G containing . A graph G is F-continuous (or F-degree continuous) if the F-degrees of every two adjacent vertices of G differ by at most 1. All P₃-continuous graphs are determined. It is observed that if G is a nontrivial connected graph that is F-continuous for all nontrivial connected graphs F, then either G is regular or G is a path. In the case of a 2-connected graph F, however, there always exists a regular graph that is not F-continuous. It is also shown that for every graph H and every 2-connected graph F, there exists an F-continuous graph G containing H as an induced subgraph.     

Lariat ether alcohols based on dibenzo‐16‐crown‐5

Synthetic routes to forty‐four dibenzocrown ether alcohols are reported. The new crown ether com pounds are based on a sym‐dibenzo‐16‐crown‐5 platform. Most have a hydroxy group and an alkyl, aryl, aralkyl, alkenyl, alkynyl, or perfluoroalkyl group on the central carbon of the three‐carbon bridge. Others have substituted benzene rings and either a hydroxy or ‐O(CH₂)_nOH group attached to the central carbon of the three‐carbon bridge.     

Biodegradable polycarbonates containing side carboxyl groups—synthesis,properties, and degradation study

The main objective of the presented research was to synthesise biodegradable aliphatic polycarbonates containing reactive carboxyl pendant groups and to examine the influence of the copolymer chain microstructure and composition on the process of their hydrolytic degradation and cytocompatibility. The work describes copolymerization of cyclic trimethylene carbonate derivative containing benzyl‐ester pendant group (benzyl 5‐methyl‐2‐oxo‐1,3‐dioxane‐5‐carboxylate) with trimethylene carbonate. The copolymerization was conducted with the use of zinc (II) and lanthanum (III) acetylacetonates as ring‐opening polymerization coordination initiators. Detailed NMR analysis allowed to define the microstructure of the obtained copolymers, which depended on the composition and type of used initiator. The final tapered chain microstructure of the obtained copolymers was related to huge differences in comonomers reactivity and evidenced low level of transesterification of the main copolymer backbone. Chosen copolymers, with unprotected carbonyl groups, were subjected to in vitro degradation test and cytocompatibility studies. It was found that high concentration of carboxyl groups resulted in copolymers which formed hydrogels and were very prone to hydrolytic degradation; they were also cytotoxic toward osteoblast‐like MG 63 cells. Copolymers with lower content of carboxyl groups were found less susceptible to degradation and cytocompatible with studied cells. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2756–2769