Recent experimental results confirm the previous finding that ionic solute species locally form ordered structures in macroscopically homogeneous, dilute solutions. Ionic dendrimers with univalent counterions are found to show a Bragg diffraction peak in the small-angle X-ray profiles, as has been reported for other ionic polymers and colloidal particles. The Bragg spacing is smaller than the average spacing expected from concentration, suggesting the localized ordered arrangements in solutions. The localization testifies to a weak, but undeniable attraction between like-charged dendrimer ions, which is generated through the intermediary of unlikely charged counterions. The like-like attraction is shown to disappear for bivalent counterions, however; The diffraction peak is not observed, because the charge number of the dendrimers is lowered more strongly by the bivalent ions than the univalent ones. Neutron scattering profiles for polystyrenesulfonate (PSS) solutions demonstrate diffraction peaks, sustaining the existence of the like-like attraction. The transfer from univalent counterions to bivalent ones increases the Bragg spacing, suggesting weakening of the attraction. Dynamic light scattering indicates the presence of two diffusive (fast and slow) modes for homogeneous PSS solutions, which correspond to the Brownian motion of free macroions and the motion of the localized structures, respectively. With increasing counterion valency, the fast mode becomes smaller while the slow mode is increased. A strong attraction is detected by a direct measurement of the interaction potential using colloidal particles of a high charge density while no attraction but only repulsion is found for low charge particles. This is reasonable in light of the nature of the counterion -mediated attraction. Recent computer simulation works substantiate qualitatively the existence of the like-like attraction. Quantitatively, however, they fail to reproduce the observed fact that the attraction is more intense for univalent counterions than for bivalent ones. The size of the local structure is found to depend on the diameter of filter pores employed in purification process, while the Bragg spacing is not influenced. It is concluded that the structures are ruptured by filtration and thereafter regenerated rather rapidly, suggesting that they are not filtrable aggregates but loose assemblies of macroions containing solvent. The likewise local structure is inferred to exist in simple ionic solution and in“dust”plasma as well, albeit with largely different time and length scales. The structural inhomogeneity (and hence the like-like attraction) thus appears to be one of basic features of dilute ionic systems in general.
In an attempt to find the link between excessive sodium intake and high blood pressure, we established the identity of renin and the presence of tissue renin. We isolated renin in a pure and stable form for the first time, and established a novel concept that a specific hormone producing peptidase exists that is not a digestive protease. We determined the complete amino acid sequence, and identified a catalytically essential pair of aspartyl residues by two specific inhibitors. These studies showed that renin is an aspartyl protease with a highly stringent substrate specificity limited to the cleavage of one specific leucyl-leucyl (or leucyl-valyl in humans) peptide bond in angiotensinogen. We showed that renin is not isorenin, pseudo-renin or a renin-like enzyme but is a unique enzyme. By preparing specific antibodies to pure renin, and affinity separation from cathepsin, we found the presence of non-secreted renin in the brain, pituitary, adrenal, testis and other tissues in which it produces angiotensins by an intracellular mechanism that later was extended to the heart, vasculature and kidney. The presence of tissue bound renin was also suggested. These results can explain local effects of angiotensin II, particularly when plasma renin concentration and its pathophysiological effects are not proportional.
New40Ar-39Ar total fusion ages have been obtained on sanidine from tuffs in the zone of Mantelliceras saxbii (equivalent to the same subzone of the European ammonite zonation) and the zone of Graysonites wooldridgei (equivalent to the European subzone of Neostlingoceras carcitanense). Ages of 98.98±0.38 Ma and 99.16±0.37 Ma, for these zones, respectively, place new constraints on the age of the AlbianlCenomanian boundary. If the base of the Cenomanian is to be defined, as currently proposed, as the FAD of the planktonic foraminifera Rotalipora globotruncanoides then the Albian/Cenomanian boundary will be at least as old as 99.2±0.4 Ma. Some 50±10m of undated sediments lie below the lowest find of R. globotruncanoides and above bono fide uppermost Albian strata.
Alkenyldimethyl (2-thienyl) silanes underwent the cross-coupling reaction with organic halides mediated by tetrabutylammonium fluoride and a palladium catalyst under extremely mild conditions to afford alkenyl-coupled products in good to excellent yields. Starting from 1, 2-bissilylated alkenes, 1, 2-disubstituted olefins were also synthesized and successfully applied to the cross-coupling reaction.
In genomes of higher eukaryotes, the numbers of clusters of 10 or more thymine nucleotides are much larger than what are expected for random combinations. The T bases in clusters occupy increasing percentages of the genomes with increasing the genome size, reaching 0.7% in human. The frequencies of these clusters in introns and intergenic regions are higher than that in exons, although the average lengths of clusters are similar in the three regions. Possible functions of T clusters for stabilizing chromatin and chromosome structures are discussed.