Stereospecific radical polymerization

Radical polymerization of N-methyl-N-(2-pyridyl)acrylamide (MPyAAm) was carried out in dichloromethane at low temperatures in the presence of trifluoroacetic acid (TFA). The m dyad contents of the polymers obtained at 0°C increased linearly from 37% to 60% with increase in the [TFA]0/[MPyAAm]0 ratio from unity to 5. NMR analysis of MPyAAm-TFA mixtures in dichloromethane-d2 revealed that the favorable conformation in terms of the pyridyl group to the carbonyl group in MPyAAm switched from s-trans to s-cis by protonation. The results suggest that controlling the conformation of MPyAAm resulted in control of the stereospecificity in radical polymerization of the monomer

STEREOSPECIFIC RADICAL POLYMERIZATION

Radical polymerization of N-methylacrylamide (NMAAm), N,N-dimethylacrylamide (DMAAm), and N-methyl-N-phenylacrylamide (MPhAAm) was investigated in toluene at low temperatures. Atactic, isotactic, and syndiotactic polymers were obtained by the polymerization of NMAAm, DMAAm, and MPhAAm, respectively, indicating that the stereospecificity of the radical polymerization of acrylamide derivatives depended on the N-substituents of the monomer used. From the viewpoint of monomer structure, the origin of the stereospecificity of radical polymerization of NMAAm derivatives is discussed

Wang-Landau molecular dynamics technique to search for low-energy conformational space of proteins

Multicanonical molecular dynamics (MD) is a powerful technique for sampling conformations on rugged potential surfaces such as protein. However, it is notoriously difficult to estimate the multicanonical temperature effectively. Wang and Landau developed a convenient method for estimating the density of states based on a multicanonical Monte Carlo method. In their method, the density of states is calculated autonomously during a simulation. In this paper we develop a set of techniques to effectively apply the Wang-Landau method to MD simulations. In the multicanonical MD, the estimation of the derivative of the density of states is critical. In order to estimate it accurately, we devise two original improvements. First, the correction for the density of states is made smooth by using the Gaussian distribution obtained by a short canonical simulation. Second, an approximation is applied to the derivative, which is based on the Gaussian distribution and the multiple weighted histogram technique. A test of this method was performed with small polypeptides, Met-enkephalin and Trp-cage, and it is demonstrated that Wang-Landau MD is consistent with replica exchange MD but can sample much larger conformational space.Comment: 8 pages, 7 figures, accepted for publication in Physical Review

Effect of a combination of hexamethylphosphoramide and alkyl alcohol on the stereospecificity of radical polymerization of N-isopropylacrylamide

Radical polymerization of N-isopropylacrylamide (NIPAAm) was investigated at low temperatures in the presence of both hexamethylphosphoramide (HMPA) and alkyl alcohols. Although HMPA and alkyl alcohols separately induced syndiotactic specificity in NIPAAm polymerization in toluene at low temperatures, a combination of HMPA and less bulky alkyl alcohols, such as methanol and ethanol, was found to induce isotactic specificity at –80°C. NMR analysis of mixtures of NIPAAm, ethanol and HMPA suggested the formation of a 1:1:1 complex through O–H•••O=C and N–H•••O=P hydrogen bonding. It is believed that the steric effect of HMPA enhanced by cooperative hydrogen bonding was responsible for the combined effect of HMPA and alkyl alcohols in inducing isotactic specificity

Replica-exchange multicanonical algorithm and multicanonical replica-exchange method for simulating systems with rough energy landscape

We propose two efficient algorithms for configurational sampling of systems with rough energy landscape. The first one is a new method for the determination of the multicanonical weight factor. In this method a short replica-exchange simulation is performed and the multicanonical weight factor is obtained by the multiple-histogram reweighting techniques. The second one is a further extension of the first in which a replica-exchange multicanonical simulation is performed with a small number of replicas. These new algorithms are particularly useful for studying the protein folding problem.Comment: 9 pages, (ReVTeX), 7 figures. Chem. Phys. Lett. (2000), in pres

Effect of acetylcholine on the highly stenotic coronary artery: Difference between the constrictor response of the infarct-related coronary artery and that of the noninfarct-related artery

AbstractTo examine the constrictor response of the infarct-related stenotic coronary artery in comparison with that of noninfarct-related stenotic arteries, acetylcholine in maximal doses of 100 μg for the left and 50 μg for the right coronary artery was injected into the 16 infarct-related coronary arteries of 16 patients with previous myocardial infarction (group 1) and into 19 stenotic coronary arteries of 16 patients with stable angina without myocardial infarction (group 2). Acetylcholine's effects on lumen diameter and area were quantitatively analyzed at the stenotic segment and its proximal segment without significant stenosis.Acetylcholine decreased lumen diameter and area at the stenotic segments from 0.72 ± 0.18 to 0.18 ± 0.33 mm and from 0.45 ± 0.22 to 0.10 ± 0.22 mm2, respectively, in group 1 (both p < 0.01) and from 0.75 ± 0.22 to 0.49 ± 0.30 mm and 0.48 ± 0.29 to 0.26 ± 0.23 mm2, respectively, in group 2 (both p < 0.01). Acetylcholine decreased the diameter and area at the proximal segment from 2.71 ± 0.75 to 2.38 ± 0.6 mm and from 6.18 ± 3.4 to 4.71 ± 2.23 mm2, respectively, in group 1 (both p < 0.01) and from 2.31 ± 0.67 to 1.95 ± 0.59 mm and from 4.5 ± 2.97 to 3.22 ± 1.96 mm2, respectively, in group 2 (both p < 0.01). The changes in diameter and area at the stenotic segment in group 1 were significantly greater than those in group 2 (both p < 0.01); there were no significant differences between groups in the changes at the proximal segment. Total or subtotal occlusion of the stenotic artery was induced in 11 (69%) patients in group 1 compared with 4 (21%) patients in group 2 (p < 0.01 group 1 vs. group 2).It is concluded that the constrictor response to acetylcholine of the stenotic segment of the infarct-related coronary artery is enhanced as compared with that of noninfarct-related arteries

The effect of self-esteem on sought infomation structure

Nishisako, Morikami and Kuwabara (1996) indicate that sought information structure consists of the information about present self, the information about future self, the information about others, the information about daily life, the information about society, the information about mystical phenomenon. The purpose of present study was to investigate the effect of self-esteem on the intensity of interest for information. Investigation is carried out by using 160 undergraduate students. The analysis and result were as follows. Firstly, the effect of self-esteem on six each factor of sought information structure was examined by analysis of variance. However, there were no significant main effect. Secondly, the effect of self-esteem on each item of seeked information structure was examined by analysis of variance. The result is that, there were several significant main effects