Collision-induced dissociation pathways of H1-antihistamines by electrospray ionization quadrupole time-of-flight mass spectrometry.

Over the past decades, mass spectrometry technologies have been developed to obtain mass accuracies of one ppm or less. Of the newly developed technologies, quadrupole time-of-flight mass spectrometry (Q-TOF-MS) has emerged as being well suited to routine and high-throughput analyses of pharmaceuticals. Dietary supplements and functional foods have frequently been found to be contaminated with pharmaceuticals. In our continuous efforts to develop methodologies to protect public health against adulterated dietary supplements, we have constructed a mass spectral database for 21 H1-antihistamines encountered as adulterants by using liquid chromatography-electrospray ionization (LC-ESI)/Q-TOF-MS, and have proposed their possible collision-induced dissociation pathways. This database will be very useful for the rapid and accurate detection of H1-antihistamines (known) and their analogues (unknown) illegally added to dietary supplements as well as in other sample matrices.

Synthesis and transistor properties of asymmetric oligothiophenes: relationship between molecular structure and device performance.

A series of three thiophene-naphthalene-based asymmetric oligomers-5-decyl-2,2':5',2'':5'',2'''-quaterthiophene (DtT), 5-decyl-5''-(naphthalen-2-yl)-2,2':5',2''-terthiophene (D3TN), and 5-(4-decylphenyl)-5'-(naphthalen-2-yl)-2,2'-bithiophene (DP2TN)-was synthesized by Suzuki cross-coupling reactions. The long alkyl side chains improved both the solubility of the oligomers in solvents and their tendency to self-assemble. UV/Vis absorption measurements suggested that DtT, D3TN, and DP2TN form H-type aggregates with a face-to-face packing structure. In addition, the three oligomers were found to adopt vertically aligned crystalline structures in films deposited on substrates, as revealed by grazing-incidence wide-angle X-ray scattering. These oligomers were used as the active layers of p-type organic field-effect transistors, and the resulting devices showed field-effect mobilities of 3.3×10(-3)  cm(2) V(-1) s(-1) for DtT, 1.6×10(-2)  cm(2) V(-1) s(-1) for D3TN, and 3.7×10(-2)  cm(2) V(-1) s(-1) for DP2TN. The differences in transistor performances were attributed to the degree of π overlap and the morphological differences determined by the molecular structures.