Electrocatalytic oxidation of pyrrole on a quasi-reversible silver nanodumbbell particle surface for supramolecular porphyrin production.

Photoactive supramolecular porphyrin assemblies are attractive molecules for light-harvesting applications. This is due to their relatively non-toxicity, biological activities and charge and energy exchange characteristics. However, the extreme cost associated with their synthesis and requirements for toxic organic solvents during purification pose a challenge to the sustainability characteristics of their applications. This work presents the first report on the sustainable synthesis, spectroscopic and photophysical characterizations of a near-infrared (NIR) absorbing Ca(II)-meso-tetrakis (4-hydroxyphenyl)porphyrin using an electrolyzed pyrrole solution. The latter was obtained by cycling the pyrrole solution across the silver nanodumbbell particle surface at room temperature. The electrolyzed solution condensed readily with acidified p-hydroxybenzaldehyde, producing the targeted purple porphyrin. The non-electrolyzed pyrrole solution formed a green substance with significantly different optical properties. Remarkable differences were observed in the voltammograms of the silver nanodumbbell particles and those of the conventional gold electrode during the pyrrole cycling, suggesting different routes of porphyrin formation. The rationale behind these formations and the associated mechanisms were extensively discussed. Metalation with aqueous Ca2+ ion caused a Stokes shift of 38.75 eV. The current study shows the advantage of the electrochemical method towards obtaining sustainable light-harvesting porphyrin at room temperature without the need for high-energy-dependent conventional processes.

Chromametric and spectroscopic determinations of natural organic matter in water and caffeine/phosphoric acid-containing soft drink using grape (V. vinifera) extract.

Natural anthocyanin dyes are safe for human and the environment due to their biocompatibility and rapid biodegradability. In this paper, an aqueous anthocyanin extract from grapes was used as a colouring reagent for the determination of humic acid (a cancer-promoting agent) in water and caffeine/phosphoric acid-containing caramelized soft drink. Three techniques, viz: chromametry, ultraviolet-visible spectrophotometry (UV-Vis) and Fourier transform infrared spectroscopy (FTIR) were employed for comparative quantifications. The results showed that the chromametry technique exhibited better sensing performance than the spectroscopic techniques in terms of the limit of detection (LOD) and % recovery. However, both chromametry and UV-Vis techniques agreed that the presence of HA could easily be detected in the soft drink at a spiked concentration of 6.4 ppm where less interference occurred.