Third-order nonlinear optical studies of newly synthesized polyoxadiazoles containing 3,4-dialkoxythiophenes

The third-order nonlinear optical properties of newly synthesized soluble polyoxadiazoles containing 3,4-dialkoxythiophenes were investigated by using Z-scan and degenerate four-wave mixing (DFWM) techniques. The measurements were performed at 532 nm with 7 ns pulses from a Nd:YAG laser. We found a good agreement between the values of χ⁽³⁾ determined from both the experiments. Z-scan results indicate a negative nonlinear refractive index, n₂, whose magnitude is of the order of 10⁻¹⁰ esu for all the copolymers. The variation of nonlinear response among the copolymers clearly indicates the dependence of χ⁽³⁾ on donor and acceptor type of units present in these copolymers. The copolymers exhibit strong reverse saturable absorption and good optical limiting properties at 532 nm.     

Synthesis of bulgecinine: a new amino acid in bulgecins

Bulgecinine, a new proline type amino acid in bulgecins, was synthesized stereospecifically by use of D-glucose as a chiral precursor.     

Lithium isotope separation by laser

A lithium isotope separation was performed using a laser isotope separation method. It was found that the lithium atoms with a natural isotopic abundance enhanced its⁶Li concentration up to over 90% by tuning the laser wavelength to the² P _1/2 of⁶Li. Too high power, however, leads to a loss of enrichment due to the power broadening effect which was analysed by the equation of motion of density matrices.     

Absence of Cooper-type bound states in three- and few-electron systems

It is shown that the appearance of a fixed-point singularity in the kernel of the two-electron Cooper problem is responsible for the formation of the Cooper pair for an arbitrarily weak attractive interaction between two electrons. This singularity is absent in the problem of three and few superconducting electrons at zero temperature on the full Fermi sea. Consequently, such three- and few-electron systems on the full Fermi sea do not form Cooper-type bound states for an arbitrarily weak attractive pair interaction. Received: 9 February 1998 / Revised and Accepted: 13 May 1998     

Specificity and biomineralization activities of Ti-binding peptide-1 (TBP-1)

Numerous peptide aptamers that recognize inorganic materials have been isolated using in vitro peptide evolution systems. However, it remains unknown how peptides interact with inorganic materials or how specific those interactions are. We, therefore, assessed the target specificities of the peptide aptamer TBP-1 (RKLPDAPGMHTW) by monitoring its ability to bind 10 different metals. We found that phages displaying TBP-1 bound to Ti, Si, and Ag surfaces but not to Au, Cr, Pt, Sn, Zn, Cu, or Fe. As previously seen with Ti, binding to Si and Ag was diminished by R1A, P4A, or D5A mutation, suggesting that the same molecular mechanism underlies TBP-1 binding to all three materials. We also observed that a synthetic TBP-1 peptide mediated mineralization of both silica and Ag. It, thus, appears that although the overall chemical characteristics of Ti, Si, and Ag surfaces are dissimilar, they share a common subnanometric structure that is recognized by TBP-1.     

Structural determination of carnosadine,a new cyclopropyl amino acid,from red alga Grateloupia carnosa

A new cyclopropyl amino acid, carnosadine, was isolated from red alga Grateloupia carnosa and the structure was determined to be 1-amino-2-guanidino-methylcylopropane-1-carboxylic acid from the results of NMR, mass spectrometry and coloring tests.