Ž . Vibrational Spectroscopy 19 1999 329–334 Vibrational studies of B vitamin 6 S. Cinta a, ) , C. Morari b , E. Vogel c , D. Maniu a , M. Aluas a , T. Iliescu a , O. Cozar a , W. Kiefer c a Babes-Bolyai UniÕersity, Physics Faculty, Kogalniceanu 1, RO-3400 Cluj-Napoca, Romania b Institute of Isotopic and Molecular Technology, P.O. Box 700, RO-3400 Cluj-Napoca, Romania c Institut fur Physikalische Chemie, UniÕersitat Wurzburg, Am Hubland, D-97074 Wurzburg, Germany ¨ ¨ ¨ ¨ Received 20 July 1998; received in revised form 3 November 1998; accepted 6 November 1998 Abstract Ž . Ž . Ž . Theoretical ab initio 3-STO and semiempiric PM3 IR spectra of isolated B vitamin pyridoxine hydrochloride 6 molecule have been obtained and found in good agreement with the experimental IR spectrum. FT-Raman spectrum of the B vitamin in solid polycrystalline state, polarised Raman as well as the Raman and SERS spectra on Ag colloidal surface at 6 different pH have been recorded and discussed. The protonated or deprotonated form of the B molecule was evidenced 6 from the pH dependence Raman spectra. SERS bands associated to the chemical interaction between the deprotonated N ring atom and Ag colloidal particles were absent. Compared to related polysubstituted pyridine molecules, a different SERS behaviour of B molecule was concluded. q 1999 Elsevier Science B.V. All rights reserved. 6 Keywords: B vitamin; Raman spectra; SERS bands 6 1. Introduction A vital compound with important activity at the Ž human body metabolism level, B vitamin pyrido- 6 . xine hydrochloride assists the red blood cell regen- eration, helping regulate protein, fat and carbo- hydrate use needed as co-factor for neurotransmitters Ž . wx dopamine, serotonin, norepinephrine 1 . In spite of its importance, vibrational Raman and SERS investi- gations of this compound are completely absent in this field. The vitamin absorption processes at the human body level take place at different pH values. ) Corresponding author. Tel.: q40-64-194315; Fax: q40-64- 191-906; E-mail: scinta@phys.ubbcluj.ro The B molecular structure can virtually present at 6 Ž . least two distinguished forms, as protonated B hcl 6 or deprotonated pyridoxine form. Raman and SERS spectroscopy can provide informations about the changes of molecular identity with the pH value w x 2–4 . This paper presents the pH dependence of the Raman and SERS spectra of B vitamin. In order to 6 assign the vibrational modes, two theoretical spectra were obtained and compared to the experimental IR and FT-Raman spectra. 1.1. Computation details Ab initio and semiempirical calculation have been Ž . performed for the isolated B hcl molecule with the 6 0924-2031r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. Ž . PII: S0924-2031 99 00019-3