We present the IR absorption and surface-enhanced Raman scattering (SERS) spectra of the isoquinoline alkaloid berberine adsorbed on a silver hydrosol and on the surface of a silver electrode for different potentials. Based on quantum chemical calculations, for the first time we have assigned the vibrations in the berberine molecule according to vibrational mode. The effect of the potential of the silver electrode on the geometry of sorption of the molecule on the surface is considered, assuming a short-range mechanism for enhancement of Raman scattering.

We have studied the absorption, fluorescence, and surface-enhanced Raman scattering (SERS) spectra of sanguinarine using a silver hydrosol and an electrochemical cell with a silver working electrode for different pH values in the medium. We carried out quantum chemical calculations in order to interpret the electronic and vibrational spectra and to establish their correlations with the structure of the molecules. We optimized the structure and determined the spectral characteristics of the cationic and neutral forms of the sanguinarine molecules in solution and adsorbed on the surface of an anodized Ag electrode for different potentials.Introduction. Sanguinarine belongs to the class of quaternary benzophenanthridine alkaloids. It is encountered in many plant species in the family Papaveraceae (Sanguinaria Canadensis, Dicranostigma lactucoides, Macleaya microcarpa, etc.) [1]. A large amount of sanguinarine is found in the roots of greater celandine (Chelidonium majus). Medicinal drugs have been created on the basis of sanguinarine. Thus the drug Chelivag (Poland) is used to treat trichomonas vaginitis. This alkaloid is also a component of such anti-tumor drugs as UKRAIN [2], which has pronounced immunostimulating properties [3,4].Since besides having antimicrobial and fungicidal action [5], sanguinarine also has a narcotic effect, inducing excitation of the central nervous system, its detection in different substances and study of the structure/function states are important for forensics and biomedicine. One of the methods sensitive to a change in molecular structure and making it possible to study aqueous media is Raman light scattering. However, rather large amounts and high (up to molar) concentrations of the original solutions are needed to record the Raman spectra, which considerably limits the analytical possibilities for this method. Surface-enhanced Raman scattering (SERS) spectroscopy with its inherent high sensitivity and selectivity, making it possible to determine the presence of a specific compound in trace amounts [6,7], is devoid of this disadvantage. An important advantage of SERS spectroscopy is the possibility of studying the structural transformations of molecules on a phase interface and under conditions of varying potential during their sorption.In this work, we have studied the UV absorption, fluorescence, and SERS spectra of sanguinarine using a silver hydrosol and an electrochemical cell in aqueous salt solutions at different pH values. We carried out quantum chemical calculations in order to interpret the electronic and vibrational spectra and their correlation with the structure of the molecules.Objects of Investigation, Study Methods, and Calculation Methods. As the test object, we used the drug sanguinarine (SIGMA), a bright orange powder.The sanguinarine molecules are characterized by the sensitivity of the polar C=N + bond to nucleophilic attack, as a result of which adducts at the carbon atom at the 4 position are rather easily formed [8,9]. Depending on the pH of the medium, the sa...

The absorption spectra and stationary and time resolved fluorescence spectra of the isoquinoline alkaloid sanguinarine are studied in aqueous media and during interactions with synthetic polyelectrolytes (polystyrene sulfonate and polyallylamine) and a natural polyelectrolyte (DNA).