Study of CH/π Interactions in the Molecular Recognition between Acetyl Galactopyranoside and 6-substituted 2-Methoxypyridines and 2(1H)-Pyridones

A series of 6-substituted 2-methoxypyridine and 2(1<em>H</em>)-pyridones was designed and synthesized for its evaluation in the molecular recognition of acetyl 2,3,4,6-tetra-<em>O</em>-methyl-b-D-galactopyranoside substrate. ¹H-NMR titration (affinity constant <em>K</em>_a determination) and chemical shift perturbation experiments were performed to evaluate the capacity of these receptors to form CH/π interactions with the substrate. The addition of 2-methoxypyridines to the substrate effected up-field shift for the H³, H⁴ and H⁵ proton signals and down-field shift for the H² proton signal of galactopyranoside substrate. The determined affinity constant <em>K</em>_a values for the association between 2(1<em>H</em>)-pyridones and galactopyranoside showed that molecular recognition was weak. These results have demonstrated the existence of weak CH/π interactions and have reflected their weak intermolecular nature. Finally DFT calculations were performed to illustrate the geometry of the molecular recognition between 2(1<em>H</em>)-pyridones and galactopyranoside.

INVESTIGATION ON THE INFLUENCE OF BACK SCATTERED PROTONS IN PIXE SPECTRUM

The pre-amplifier with an active reset system was examined to carry out PIXE analysis under the condition that X-rays and back scattered protons are detected simultaneously. Rejection of false signals produced by back scattered protons is discussed, and it is confirmed that false signals can be completely rejected by using an inhibit signal of the preamplifier. Energy resolution of an X-ray detector and a live-time of measurement system were measured as a function of counting rate. As a result, energy resolution did not change and the live-time was 70 % at the high counting rate over 3kcps. The pile-up effect on the X-ray signal with the proton signal tail is also discussed.

Coupling constants nitrogen-15-nitrogen-15 and nitrogen-15-hydrogen in phenylhydrazones forming hydrogen bond

Absolute values of the coupling constants 1J(15N15N), 1J(15NH) of six phenylhydrazones forming hydrogen bond, 2J(15N15NH) of four, and 4J(15NH) of two phenylhydrazones have been determined. Three coupling constants 1J(15N15N) have been obtained from the nitrogen-15 monolabelled compounds by measuring the other nitrogen at natural abundance. The coupling constants 2J(15N15NH) have been measured with the nitrogen-15 doubly labelled compounds, because in the arrangement 15N14NH there exists a broadening of the proton signal due to nitrogen-14. Absolute values of the coupling constants 1J(15N15N) of the phenylhydrazones forming hydrogen bond to the ester group are smaller ( 10.8 Hz) than those of the phenylhydrazones having hydrogen bond to carbonyl group ( 11.1 Hz). The coupling constants 2J(15N15NH) have a value 2.4 ± 0.2 Hz. The value of 1J(15N15N) of 1-phenylazo-2-naphthalenol decreases with increasing content of hydrazone form. The values of 2J(15N15NH) of this compound are within 1.2 to 1.6 Hz.