Amorphous structures of iron obtained by quenching of the liquid state

The frozen-in structure of liquid iron was relaxed under periodic boundary conditions, where the potential of Pak and Doyama was used. The pair distribution functions of the final quenched structures resemble that of the amorphous structure, but depend on the details of the initial atomic arrangement.     

Studies on the Antisense Oligonucleotide Conjugate

Four oligonucleotides (15 mer) 13–16 and their conjugates 17–20 in which psoralen was covalently linked to 5′ end were synthesized. Compounds 16 and 20 contain the sequence which is complementary to the sense strand covering the first four codons and the upstream sequence close to the ribosome binding site of c-Ha-ras mRNA. It was found that compounds 16 and 20 inhibited the growth of cells that had been transformed by the c-Ha- ras plasmid activated c-Ha- ras oncogene. Compound 20 that carried psoralen was more efficient in inhibiting the growth of transformed cells than compound 16 without psoralen, suggesting that the psoralen might have increased permeability of oligodeoxynucleotides. A model experiment of duplex formation was pertinent to the idea that the inhibitory effect was caused by RNase H activity.     

Prediction of glycyrrhizin disposition in rat and man by a physiologically based pharmacokinetic model

Three physiologically based pharmacokinetic models A--C, incorporating enterohepatic recycling, were developed to predict glycyrrhizin (GLZ) disposition in rat plasma and tissues, and human serum. Model A, which included fourteen compartments (artery, vein, tissues except brain, and gut lumen) with the assumption of direct excretion of GLZ from the liver into the gut lumen gave fairly good agreement between the observed and predicted disposition profiles in rat, but was unsuitable in man, where elimination is very rapid. Models B and C for man were obtained by adding a gallbladder compartment (drug storage organ) for the excretion from the liver into the gut lumen and by assuming continuous transfer from the storage compartment or instantaneous emptying from it during meal ingestion as the excretion process from the gallbladder into the gut lumen, respectively. The agreement between the observed and predicted serum concentration time-course profiles was better with model C than model B, especially in the terminal elimination phase, where secondary peaks appeared. However, it was thought that the observed serum disposition can be sufficiently well predicted by model B. In conclusion, prediction in rat was successful in all compartments except the brain, which shows a negligible distribution. Scale-up of the disposition kinetics of GLZ from rat to man was also successful.     

Direct measurement of proton dissociation in thhe excited state of protonated 1-aminopyrene with picosecond pulses

Direct measurement of proton dissociation in the excited singlet state of protonated I-aminopyrene in a mixture of H₂O (or D₂O) and acetonitrile (1:1) has been carried out by means of picosecond time-resolved spectroscopy. The proton dissociation retes k¹₁ and k^D+₁ at about 300 K were determined tobe 3.7 (±0.6) * 10⁹ s^-1, respectively. These rates are in very good agreement with those obtained by nanosecond time-resolved spectroscopy with fluorometry. The excited singlet state ;K^*₂ value of l-aminopyrene was also determined by dynamic analyses.     

Ion/molecule reactions in the orifice-skimmer region of an atmospheric pressure Penning ionization mass spectrometer

Atmospheric pressure Penning ionization mass spectra of methanol were measured as functions of Ar or He gas pressure in the first vacuum chamber, the position of the skimmer, and the voltage applied between the orifice and the skimmer. When the orifice and the skimmer were coaxial with a distance of 4 mm, the distribution of CH3OH2+(CH3OH)n clusters was only weakly dependent on both Ar pressure (in the range of 19-220 Pa) and orifice-skimmer voltage (in the range of 1-45 V). The ion/molecule reaction CH3OH2+ + CH3OH --> CH3+(CH3OH) + H2O was observed in the free jet expansion, especially at high orifice-skimmer voltage values. When the orifice and the skimmer were off-centered and the distance between them was increased to 18 mm, the formation of large CH3OH2+(CH3OH)n clusters, as well as their dissociation, were seen. The endothermic proton transfer reaction, CH3+(CH3OH) + CH3OH --> CH3OH2+ + CH3OCH3, occurred at high orifice-skimmer voltage. The collision-induced dissociation of cluster ions by He gas in the first vacuum chamber was much more efficient than by Ar. These results demonstrated that the mass spectra are highly dependent on skimmer position and on orifice-skimmer voltage and that ions observed by mass spectrometry do not necessarily reflect the abundance of ions produced in the atmospheric pressure ion source.     

Calyciphylline G, a novel alkaloid with an unprecedented fused-hexacyclic skeleton from Daphniphyllum calycinum

Calyciphylline G (1), a novel Daphniphyllum alkaloid with an unprecedented fused-hexacyclic skeleton containing a 5-azatricyclo[6.2.1.0^1,5]undecane ring, has been isolated from the stem of Daphniphyllum calycinum (Daphniphyllaceae), and the structure and relative stereochemistry were elucidated on the basis of spectroscopic data.     

Mono- and di-t-butyl substituted 2,2′-bis(1,3-dithia[3]ferrocenophane-2-ylidene) derivatives: TTF-like ferrocene analogs

Mono- and di-t-butyl substituted 2,2′-bis(1,3-dithia[3]ferrocenophane-2-ylidene) derivatives were prepared. These derivatives showed the E_1/2(1) in lower potential region than that of differrocenyl-ethene and -ethyne. Also, the ΔE_1/2 value declined according to the increase of a t-butyl group.     

Sequential multi-element analysis of sediments and soils by inductively-coupled plasma/atomic emission spectrometry with a computer-controlled rapid-scanning echelle monochromator

A computer-controlled rapid-scanning echelle monochromator is used to determine the major, minor and trace elements in reference sediments and soils. The high resolving power of the echelle spectrometer effectively decreases line overlap interferences, and permits a wide selection of analytical lines to be used. The concentrations of 17 elements in five standard materials are determined by using a single set of analytical lines without any corrections for line overlap interferences. Averages of relative standard deviations and relative deviations from the certified values for the 17 elements range from 2.4 to 4.3% and from 1 to 5%, respectively.     

A reappraisal,based on (31)P NMR,of the direct coordination of a metal ion with the phosphoryl oxygen at the cleavage site of a hammerhead ribozyme

It has been generally accepted, on the basis of kinetic studies with phosphorothioate-containing substrates and analyses by NMR spectroscopy, that a divalent metal ion interacts directly with the pro-Rp oxygen at the cleavage site in reactions catalyzed by hammerhead ribozymes. However, results of our recent kinetic studies (Zhou, D.-M.; Kumar, P. K. R.; Zhang. L. H.; Taira, K. J. Am. Chem. Soc. 1996, 118, 8969-8970. Yoshinari, K.; Taira, K. Nucleic Acids Res. 2000, 28, 1730-1742) demonstrated that a Cd(2+) ion does not interact with the sulfur atom at the Rp position of the scissile phosphate (P1.1) in the ground state or in the transition state. Therefore, in the present study, we attempted to determine by (31)P NMR spectroscopy whether a Cd(2+) ion binds to the P1.1 phosphorothioate at the cleavage site in solution. In the case of the R32-S11S (ribozyme-substrate) complex, neither the Rp- nor the Sp-phosphorothioate signal from the S11S substrate at the cleavage site was perturbed (the change was less than 0.1 ppm) upon the addition of Cd(2+) ions (19 equiv) at pH 5.9 and 8.5. By contrast, we detected the significant perturbation of the P9 phosphorothioate signal from another known metal-binding site (the A9/G10.1 metal-binding motif). The Rp-phosphorothioate signal from A9/G10.1 was shifted by about 10 ppm in the higher field direction upon the addition of Cd(2+) ions. These observations support the results of our kinetic analysis and indicate that a Cd(2+) ion interacts with the sulfur atom of the phosphorothioate at the A9/G10.1 site (P9) but that a Cd(2+) ion does not interact with the sulfur atom at the Rp- or at the Sp-position of the scissile phosphate (P1.1) in the ground state.