title: The pH dependent Raman spectroscopic study of caffeine.
abstract: First of all the surface enhanced Raman spectroscopy (SERS) and normal Raman spectra of caffeine aqueous solution were obtained at different pH values. In order to obtain the detailed vibrational assignments of the Raman spectroscopy, the geometry of caffeine molecule was optimized by density functional theory (DFT) calculation. By comparing the SERS of caffeine with its normal spectra at different pH values; it is concluded that pH value can dramatically affect the SERS of caffeine, but barely affect the normal Raman spectrum of caffeine aqueous solution. It can essentially affect the reorientation of caffeine molecule to the Ag colloid surface, but cannot impact the vibration of functional groups and chemical bonds in caffeine molecule.
authors.affiliation: Institute of Laser Life Science, College of Biophotonics, South China Normal University, 510631 Guangzhou, China.
authors.forename: Jian
authors.initials: J
authors.lastname: Kang
authors.forename: Huaimin
authors.initials: H
authors.lastname: Gu
authors.forename: Liang
authors.initials: L
authors.lastname: Zhong
authors.forename: Yongjun
authors.initials: Y
authors.lastname: Hu
authors.forename: Fang
authors.initials: F
authors.lastname: Liu
mesh_terms: D000143:Acids / Q000737:chemistry; D000468:Alkalies / Q000737:chemistry; D002110:Caffeine / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008958:Models, Molecular; D012996:Solutions; D013059:Spectrum Analysis, Raman / Q000379:methods*; D013499:Surface Properties; D014732:Vibration
chemical_list: D000143:Acids; D000468:Alkalies; D012996:Solutions; D002110:Caffeine