Colloidal CdS-induced photocatalytic reaction of 2-methylindole?mechanistic analysis of oxidation of indoles

Abstract

2-Methylindole (2-MI) is adsorbed on the surface of colloidal CdS particles with an adsorption intensity of 0.6 Â 10 3 dm 3 mol À1. A new emission band at 530 nm is produced by forming an exciplex between excited CdS and 2-MI and the red emission due to CdS is simultaneously quenched. The emission maxima of green bands for different indoles increase in the order indole`tryptophan`2-MI`3-MI and are observed at 508, 520, 530 and 540 nm, respectively. The shift in emission maxima is related to the oxidation potential of these substrates. The irradiation of an aerated reaction mixture containing CdS and 2-MI with visible light induces the oxidation of adsorbed 2-MI by photogenerated holes to produce 2-methyl-3-indolinone and 2-acetamidobenzaldehyde. The latter product is formed due to oxidative C-C bond cleavage of the pyrrole ring. The reactivity of trapped holes towards the adsorbed 2-MI is evidenced by a decrease in the lifetime of the red emission of CdS in the presence of 2-MI. In this reaction the possibility of the participation of singlet oxygen is ruled out. A general mechanism of CdS-induced oxidation of indoles is discussed.

Flavin Conjugated Polydopamine Nanoparticles Displaying Light-Driven Monooxygenase Activity

“…As shown in Figure 4A the absorption spectrum of indole (0 h) has a characteristic absorbance band at λ max = 287 nm. After 0.5 h irradiation, this peak decreases in intensity and a new band appears at λ max ~ 380 nm which is consistent with the consumption of indole and the production of 2 and 3-position hydroxylated indole species (Kumar and Kumar, 1998; Kuo and Mauk, 2012; Linhares et al, 2014). These bands increase in intensity with time and a shoulder replacing the characteristic band belonging to indole at 2 h indicates its consumption (Kuo and Mauk, 2012).…”

Electronic and photocatalytic properties of purine(s)-capped CdS nanoparticles in the presence of tryptophol

“…these particles is quite different to CdS nanoparticles stabilized by polyphosphate [24][25][26], the fluorescence of which is not quenched by the dissolved oxygen. In the present case, relatively deep among shallow trapped charge carriers are involved in the quenching of emission as is evident by the decrease in the value of long time constant component in Scheme 1. lifetime data (Table 2), whereas in the polyphosphate stabilized particles the deeply trapped charge carriers have been suggested to participate in the quenching as well as oxidation processes in the presence of donors [24,25,27].…”

“…In the present case, relatively deep among shallow trapped charge carriers are involved in the quenching of emission as is evident by the decrease in the value of long time constant component in Scheme 1. lifetime data (Table 2), whereas in the polyphosphate stabilized particles the deeply trapped charge carriers have been suggested to participate in the quenching as well as oxidation processes in the presence of donors [24,25,27]. It is likely that upon addition of tryptophol to purine(s)-capped Q-CdS, tryptophol removes the loosely bound purine from the outer shell in the ground state.…”

Photodeposition of Pt on Colloidal CdS and CdSe/CdS Semiconductor Nanostructures

“…Among the II-VI semiconductors, CdS is of particular interest because it has the correct band alignment for water photolysis [2] and has been demonstrated to be photocatalytically active. [11][12][13][14][15][16] We have found that the photoexcitation of CdS and CdSe/CdS in the presence of an organometallic Pt precursor leads to deposition of Pt nanoparticles on the semiconductor surface. Stark differences are observed in the Pt nanoparticle location on the two substrates, and the photodeposition can be completely inhibited by the modification of the semiconductor surface.…”