Pedro de Lima Neto

5-(4-pyridinyl)-1,3,4-oxadiazole-2-thiol on gold: SAM Formation and electroactivity

5-(4-pyridinyl)-1,3,4-oxadiazole-2-thiol (Hpyt) spontaneously adsorbs on gold forming SAMs (self-assembled monolayers) that, based on STM (Scanning Tunneling Microscopy) and electrochemical data, contain pinholes through which [Fe(CN)6]4- and [Ru(NH3)6]3+ probe molecules access the underlying gold electrode. For the former molecule, the dependence of the faradaic current on the electrolyte solution pH value allowed the evaluation of the surface pKa as 4.2. The thermodynamic parameters DHads and DGads for the Hpyt adsorption process could be described by the Langmuir model and were calculated as -20.01 and -39.39 kJ mol-1, respectively. Electrodic redox reaction of cytochrome c metalloprotein was accessed by using the Hpyt SAM with a heterogeneous electron transfer rate constant of 2.29 × 10-3 cm s-1.

New Alkaloids from Margaritopsis carrascoana (Rubiaceae)

Two new alkaloids containing Nb-methyl-triptamine units linked to bis-quinoline moieties, N-8”-formyl-calycosidine and N-8”-methyl-N-1’-demethyl-iso-calycosidine, were isolated from the aerial part of Margaritopsis carrascoana, along with known calycosidine and hodgkinsine. The cytotoxicity of the isolated alkaloids has been evaluated against cancer cell lines. The first two compounds showed only weak activity against HL-60 cell line, while hodgkinsine was the most active compound against HCT-116, OVCAR-8, HL-60 and SF-295 cancer cell lines. The structures of the isolated compounds were established by spectroscopic and molecular mechanical methods.