Hexapole helicenes 1, which contain six [5]helicene substructures, were synthesized by Pd-catalyzed [2+2+2]cycloadditions of aryne precursor 6. Among the possible 20 stereoisomers, which include ten pairs of enantiomers, HH-1 was obtained selectively. Density functional theory (DFT) calculations identified HH-1 as the second most stable isomer that quantitatively isomerizes under thermal conditions into the most stable isomer (HH-2). Both enantiomers of HH-2 can be separated by chiral HPLC. Single-crystal X-ray diffraction analyses revealed a saddle-like structure for (P,M,P,P,M,P) HH-1 and a propeller-like structure for (P,M,P,M,P,M) HH-2. Because of the helical assembly and the resulting steric repulsion, the structure of HH-1 is significantly distorted and exhibits the largest twisting angle reported so far (up to 35.7° per benzene unit). Electrochemical studies and DFT calculations indicated a narrow HOMO-LUMO gap on account of the extended π-system. Kinetic studies of the isomerization from HH-1 to HH-2 and the racemization of enantiomerically pure HH-2 were conducted based on H NMR spectroscopy, HPLC analysis, and DFT calculations.

N-Phenylbenzenesulfonamides exist preferentially in (+)-or (−)-synclinal conformations, which place the aromatic rings at both ends in the same direction with a twist. We have systematically analyzed the crystal structure of secondary aromatic sulfonamides bearing methyl, ethyl, and/ or methoxy groups on the benzene rings. Intermolecular hydrogen bonding between the sulfonamide protons and sulfonyl oxygens was observed in 81 out of 85 crystals. The intermolecular hydrogen-bonding patterns could be classified into four types, i.e. Dimeric, Zigzag, Helical, and Straight patterns, with retention of the synclinal conformation of the sulfonamide moiety. We investigated the relationship between the hydrogen-bonding pattern and the proportion of the compounds that show chiral crystallization. On the basis of our classification of the intermolecular hydrogen bonds of aromatic sulfonamides, the crystals with Dimeric and Zigzag patterns, which both have enantiomeric synclinal conformers, intrinsically become achiral, except for kryptoracemates. In contrast, a high proportion of compounds with Helical or Straight patterns in the crystals showed chiral crystallization. Our classification is useful for discussion regarding the chirality of molecular assemblies, on the basis of the conformational chirality of the molecules in the crystal.

We have observed the 1-bond (199)Hg-(15)N J-coupling ((1)J((199)Hg,(15)N) = 1050 Hz) within the Hg(II)-mediated thymine-thymine base pair (T-Hg(II)-T). This strikingly large (1)J((199)Hg,(15)N) is the first one for canonical sp(2)-nitrogen atoms, which can be a sensitive structure-probe of N-mercurated compounds and a direct evidence for N-mercuration.

SUMMARYWe measured the characteristics of the decline in tension during isometric relaxation of canine papillary muscle. In the intact heart, relaxation begins with the isovolumic phase, but in experiments on papillary muscle previously reported the isotonic phase preceded the isometric phase during the course of relaxation. In our experiments, however, the isotonic bar was locked at the instant the muscle reached the end-systolic fiber length in order to hold the fiber at that length during the succeeding relaxation process. Therefore, we obtained a relaxation process similar to that occurring in an intact heart. The major re- Jewell and Wilkie 2 studied the mechanics of muscle relaxation using the skeletal muscle of a frog, and observed that tension declined exponentially when the muscle was allowed to change its length, but in the case of true isometric relaxation the tension did not decline exponentially. Parmley and Sonnenblick 3 studied an isolated cat papillary muscle, and observed that tension decayed exponentially in the isometric relaxation phase following an afterloaded contraction. They mentioned that the time constant of exponential isometric tension decay (tj) increased linearly with total load. In a true isometric relaxation following true isometric contraction, they concluded that the time required for tension to fall to one-half its peak value (T -P o /2) was altered by different inotropic agents. Under conditions in which the interventions used produced similar peak contractile force (P o ) and maximum dP/dt, there were, however, significant differences in the decline in tension, depending on the intervention. On the other hand, Cohn et al., 4 using both intact hearts in situ and isolated hearts, concluded that the primary determinants of maximum rate of pressure fall (-dP/dt max ) were the end-systolic fiber length and the contractile state of the cardiac muscle. Weisfeldt et al. 5 conducted experiments similar to those of Cohn et al. 4 and observed that -dP/ dt m ax increased with mean aortic pressure. The seemingly contradictory results of these investigations make it difficult to predict exactly how myocardial relaxation is affected by various factors.