pH-dependent porphyrin based receptor for bromide-ions selective binding

It was determined that the diprotonated form of 2,8,12,18-tetramethyl-3,7,13,17-tetrabutyl- H 21, H 23-porphine ( H 4III2+) acts as a bromide selective receptor. It forms stable complexes H 4III2+( CH 3 CN )( Br −) ( log K d1 = 5.50 ± 0.03), H 4III2+( Br −)2 ( log K d2 = 3.25 ± 0.03) in the system H 2III-( Et )4 NBr - HClO 4-acetonitrile at 25°C. Spectrophotometric method allows to determine the bromide ions' concentration 3 × 10−8 M−1.

Raman Spectral Studies of Aqueous Acidic Pyrazine Solutions

Raman spectra of aqueous pyrazine have been investigated in acidic media: HCl from pH = 4 up to 11 M; HCLO4 from 0.1 M to 12 M; H2SO4 form 0.1 M to 18 M. From observation of the shifts of the bands from neutral solutions, it has been possible to identify bands uniquely characteristic of unprotonated pyrazine and its two protonated forms. The diprotonated form was only observed for high concentrations of HCLO4 and H2SO4. From bandfitting of the spectral contours it has been possible to construct the species distribution diagram and estimate the pK values. Raman bands of the three species have been identified and assigned. The results are used to explain an unassigned band at 1235 cm-1, reported by several authors, in SERS from pyrazine on silver and gold electrodes.

Poly(pyrazol-1-ylmethyl)Benzenes: New Multidentate Ligands

Twelve new multidentate poly(pyrazol-1-ylmethyl)benzene ligands , (5)-(16), have been synthesized by phase-transfer-catalysed alkylations of pyrazoles with poly( bromomethyl )benzenes, and their 1H and 13C n.m.r. spectra have been fully assigned. X-Ray crystal structure determinations have been carried out on the tetrachloropalladate salt of the diprotonated form of 1,4-bis(3,5-dimethylpyrazol-1-ylmethyl)-2,3,5,6-tetramethylbenzene and on hexakis (pyrazol-1-ylmethyl)benzene.