The terahertz time-domain spectroscopy(THz-TDS) was used for sensing and identifying illicit drugs.The absorption spectra of seven illicit drug samples(morphine and its hydrochloride,cocaine hydrochloride,codeine phosphate,papaverine hydrochloride,pethidine hydrochloride,and thebaine) were studied by THz-TDS at 0.3-2.0 THz at room temperature.The geometric structure and vibration frequencies of morphine were calculated by density functional theory.The four absorption features were dominated by intra-/inter-molecular collective or lattice vibration modes.Each illicit drug has a distinct signature in its THz spectra.The results indicate that the THz-TDS can be used to identify and discriminate illicit drugs by their characteristic fingerprints.
LIU Guifeng MA Shihua JI Te ZHAO Hongwei WANG Wenfeng
Triplet-triplet extinction coefficients for astaxanthin （I） and canthaxanthin （II） in different deaerated polarity solutions of MeCN and benzene were evaluated by laser flash photolysis at 298 K in the spectral region from 350 to 650 nm by energy transfer method, employing 2-acetonaphthone as sensitizer. The triplet-triplet extinction coeffi- cients in MeCN and benzene were different in terms of the carotenoid present. The maximum triplet-triplet extinc- tion coefficient was 0.1-1.7 ×10^5 L·mol^-1·cm^-1 in different solvents. The rate constants of triplet decay were I： 1.25×10^10 L·mol^-1·s^-1, II： 1.12×10^10 L·mol^-1·s^-1 in MeCN; and I： 1.75×10^10 L·mol^-1, II： 3.27×10^10 L·mol^-1·s^-1 in benzene. The bimolecular rate constants of energy transfer from triplet excited 2-acetonaphthone to carotenoids were determined from the linear regression of the decay rate constant of 2-acetonaphthone triplet at varying carotenoid concentrations. The triplet lifetimes of ^3AST^＊ and 3CAN^＊ in different solvents were also determined. The results indicated that triplet energy transfer was nearly diffusion-controlled.
The properties of norfloxacin(NFX)and its 4?-N-acetyl derivative(ANFX)are investigated in different pH aqueous solutions and H2O-CH3CN mixed solutions,to determine the effects of pH and polarity on their ground and excited states.The triplet states of NFX and ANFX are affected more by pH than by polarity.The pH dependence of the NFX and ANFX triplet states is likely due to the different quantum yields of different protonated forms.Steady-state fluorescence,time-resolved fluorescence,and laser flash photolysis experiments at different pH values provide clear evidence of the involvement of different intramolecular charge-transfer pathways in the singlet states of NFX and ANFX.The different electron-donating capacities of 1-N,1?-N,and 4?-N under different conditions determine the major pathway.
