Guidelines for the achievement of true atomic resolution with noncontact atomic force microscopy

We investigated the conditions to achieve true atomic resolution with an atomic force microscope under noncontact mode (NC-AFM). At first, we derived the equation of vertical resolution as a function of the signal-to-noise ratio and the decay length of frequency shift by assuming an exponential tip-to-sample distance dependence of frequency shift. Next, by assuming a single atom probe, we derived the equation of lateral resolution as a function of the vertical resolution and the tip-to-sample distance, from which we clarified the guidelines to achieve true atomic resolution with NC-AFM. At last, we made clear the attainable decay length of frequency shift both for the van der Waals potential and the electrostatic (Coulomb) potential.     

Molecular interpretation for the solvation of poly(acrylamide)s. I. Solvent-dependent changes in the C=O stretching band region of poly(N,N-dialkylacrylamide)s

The solvation of poly(N,N-dimethylacrylamide) (PNdMA) and poly(N,N-diethylacrylamide) (PNdEA) in various protic and aprotic solvents has been studied by using infrared (IR) spectroscopy. Because PNdMA and PNdEA have the same polar functional group, their IR spectra show quite similar solvent effects. Unexpectedly, the solvent-dependent changes of the C=O stretching vibration (nu(C=O)) bands of the two polymers cannot be explained only by dielectric constants of the solvents. Then, infrared spectra of N,N-dimethylacetamide (NdMA) and N,N-diethylacetamide (NdEA), monomer models for PNdMA and PNdEA, respectively, in the same solvents as the polymer solutions have also been examined. Interestingly, the solvent-dependent spectra in the nu(C=O) band region of NdMA and NdEA are correlated with those of PNdMA and PNdEA, respectively, except for slight deviations, which may be ascribed to molecular mobility and/or exclusive volume. These correlations permit one to regard the solvation of the polymers as that of the corresponding monomers. As a result, we have proposed the assignments of nu(C=O) bands for the PNdMA and PNdEA solutions regarding the interactions between solvents and NdMA and NdEA as hydrogen bondings. In the IR spectra of PNdMA and PNdEA in the protic solvents, two C=O bands are mainly observed; one appears at a similar frequency to that of a C=O band observed for the monomer solution, and the other is characteristic of the polymer systems. The former band is likely to reflect the solvation behavior of PNdMA and PNdEA. The results clearly show that the solvation of a polymer can be interpreted at the molecular level using infrared spectroscopy sensitive to solvent effects.     

Lactone formation of N-acetylneuraminic acid oligomers and polymers as examined by capillary electrophoresis.

We examined lactone-formation reaction of oligomers and polymers of N-acetylneuraminic acid in diluted hydrochloric acid solution and found that the time course of the lactonization reaction was easily traced by capillary electrophoresis. The reaction proceeded more rapidly with increasing the molecular mass of oligomers because the conformation of inner units became rigid and more favorable for the formation of lactone linkage. Present results obtained using capillary electrophoresis will be useful in understanding of physical and chemical properties of oligo/polysialic acids.     

Back-Extraction of Uranium(VI) from Organophosphoric Acid with Hydrazine Carbonate

The back-extraction of uranium(VI) from di(2-ethylhexyl)phosphoric acid (HDEHP) and diisodecylphosphoric acid (DIDPA) was studied by using hydrazine carbonate as back-extractant. U(VI) was back-extracted from n-dodecane solutions of 0.5M HDEHP - 0.2M TBP and 0.5M DIDPA - 0.1M TBP by hydrazine carbonate. The distribution ratios were decreased with an increase of hydrazine carbonate concentration. The back-extraction equilibria were expressed by slope analysis in consideration of neutralization between the extractant (DIDPA, HDEHP) and hydrazine carbonate, which occurred quantitatively during the back-extraction.     

IMiCMO: a new integrated ab initio multicenter molecular orbitals method for molecular dynamics calculations in solvent cluster systems

A new computational scheme integrating ab initio multicenter molecular orbitals for determining forces of individual atoms in large cluster systems is presented. This method can be used to treat systems of many molecules, such as solvents by quantum mechanics. The geometry parameters obtained for three models of water clusters by the present method are compared with those obtained by the full ab initio MO method. The results agree very well. The scheme proposed in this article also intended for use in modeling cluster systems using parallel algorithms. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1107–1112, 2001     

Laser-induced thin film formation from a gaseous mixture of trimethylsilylacetylene and methyl acrylate

Under irradiation with N₂ laser light, gaseous trimethylsilylacetylene (TMeSiA) and a gaseous mixture of TMeSiA and methyl acrylate (MA) produced thin films on an incident optical quartz window of an irradiation vessel. The product yield decreased with increasing partial pressure of TMeSiA. From the analysis of FT-IR spectra and X-ray photoelectron spectra of the deposited films, it was shown that Si---C bond of TMeSiA was cleaved by a two-photon absorption of N₂ laser light to produce trimethylsilyl radical and the silanes, R(CH₃)Si=CH₂ (R: H₃C---, CHC---). Trimethylsilyl radical reacted with MA at C=C and C=O bonds to produce Si---C and Si---O bonds in the film deposited from the gaseous mixture. The silanes were polymerized in each other to produce a thin film from pure TMeSiA vapor. Under irradiation with a medium pressure mercury lamp, a gaseous mixture of TMeSiA and MA produced aerosol particles in addition to the film. Polymeric species of TMeSiA was more involved in the aerosol particles rather than in the film, suggesting that collisionally induced chemical reaction takes place efficiently between excited MA and TMeSiA molecules.     

Practical synthesis of thiirene 1‐oxides that possess two bulky alkyl substituents

Acetylenes that possess two bulky alkyl substituents reacted with sulfur dichloride to furnish the corresponding 2,3‐dialkyl‐2,3‐dichlorothiiranes ( 5 ) nearly quantitatively. The alkaline hydrolysis of 5 afforded 2,3‐dialkylthiirene 1‐oxides ( 10 ) in high yields. These two reactions could be successively carried out in one flask, and 2,3‐di‐tert‐butyl‐, 2,3‐di‐(1‐adamantyl)‐, and 2‐(1‐adamantyl)‐3‐tert‐butylthiirene 1‐oxides ( 10a–c ) were obtained in 70, 80, and 90% yields, respectively, based on the starting acetylenes, thus providing the most convenient synthesis of thiirene 1‐oxides. Disulfur dichloride also reacted with acetylenes to give 5 in good yields with the elimination of one sulfur atom. Although the alkaline hydrolysis of 5 provided 10 exclusively, acid hydrolysis gave a mixture of α‐oxothioketone 9 and thiirene 1‐oxide 10 in modest yields. All thiirene 1‐oxides 10a–c isomerized to produce α‐oxothioketones 9 in high yields when heated in boiling toluene. Reactions of a bis‐acetylene ( 18 ) with disulfur dichloride and with sulfur dichloride gave a dihydropentathiepin ( 19 ) in high yields. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:424–430, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/hc.10070     

π-conjugated columnar polyacetylenes prepared with Rh complex catalysts

Highly stereospecific polymerization of monosubstituted acetylenes was carried out using the Rh complex, [Rh(norbornadiene)Cl]₂ catalysts. The resulting polyacetylenes were characterized in detail by ¹HNMR, ESR, laser Raman, diffuse reflective UV, and wide angle X-ray diffraction methods. The data showed that the Rh complex were the preferred catalyst to selectively yield the corresponding cis-transoid polymers even at room temperature when alcohol, triethylamine or water was used as the polymerization solvent. Additionally, the resulting cis polyacetylenes were found to have a helical form whose polymer is amorphous or composed of pseudohexagonal structures called π-conjugated columnar as self-assembly or super structure. Further compression of the amorphous cis polymers resulted in cis to trans isomerization at room temperature under vacuum, breaking rotationally the cis C=C bonds giving π-radicals called solitons as the origin of a polymer magnet. On the other hand, the π-conjugated columnar was also found to show an extremely longer wavelength absorption compared with that of the amorphous one, although the absorption maximum was shifted to a shorter wavelength when the columnar was destroyed by the compression. Therefore, the formation of the π-conjugated columnar can be considered as a new and quite useful control method concerning color of such conjugated polymers, i.e., a new concept concerning the color of conjugated polymers.     

Imposex in Sea Snails,Caused by Organotin (Tributyltin and Triphenyltin) Pollution in Japan: a Survey

A country-wide survey and laboratory experiments on imposex (a superimposition of male sex organs on female sea snails) in Japanese sea snails were carried out: 38 species were observed to be affected by imposex. For the rock shell, Thais clavigera , the percentage occurrence of imposex was 100% at almost all sites surveyed. The degree of imposex seemed to be positively correlated with the concentrations of tributyltin (TBT) and triphenyltin (TPT) in the species. The results of laboratory experiments showed that imposex in T. clavigera was initiated and promoted by both TBT and TPT. Many oviduct-blocked individuals, which were thought to be sterile, were observed in T. clavigera at sites near marinas and harbours. The effects of organotin pollution on the population of T. clavigera were observed at the sites near marinas. From the results of the additional country-wide survey on imposex in T. clavigera during 1993–1995, serious organotin pollution and imposex symptoms in the species are still continuing in Japan. © 1997 by John Wiley & Sons, Ltd.     

Total Synthesis of Decahydroquinoline Poison Frog Alkaloids ent-cis-195A and cis-211A

The total synthesis of two decahydroquinoline poison frog alkaloids ent-cis-195A and cis-211A were achieved in 16 steps (38% overall yield) and 19 steps (31% overall yield), respectively, starting from known compound 1. Both alkaloids were synthesized from the common key intermediate 11 in a divergent fashion, and the absolute stereochemistry of natural cis-211A was determined to be 2R, 4aR, 5R, 6S, and 8aS. Interestingly, the absolute configuration of the parent decahydroquinoline nuclei of cis-211A was the mirror image of that of cis-195A, although both alkaloids were isolated from the same poison frog species, Oophaga (Dendrobates) pumilio, from Panama.