Probing the potential energy landscape for dissociation of protonated indole via threshold collision-induced dissociation and theoretical studies

Electronic Spectra of the Protonated Indole Chromophore in the Gas Phase

“…The UV photofragmentation spectrum recorded at m/z 91 is presented in Figure 1; its first band at 359.8 nm (3.446 eV) was assigned to the 0−0 transition of the C 3 H + isomer (vide infra). Because the results of Yang et al 33 showed that, in the collisioninduced dissociation (CID) of protonated indole with xenon, a collision energy of at least 5 eV in the center-of-mass frame is required to induce fragmentation (mainly through the loss of HCN), the spectrum recorded here corresponds to two-photon absorption. The laser power dependence of the signal was recorded and it showed signs of saturation (see the Supporting Information).…”

“…The UV photo-fragmentation spectrum recorded at m/z 91 is presented in Figure 1, the first band at 359.8 nm (3.446 eV), being assigned to the 0-0 transition of the C 3 H + isomer (vide infra). Since the results of Yang et al 33 The spectrum recorded at m/z 91 in the visible region is presented in Figure 2. In this spectrum, the first band at 488 nm (2.54 eV) is assigned to the 0-0 band origin, as no transition is observed further to the red.…”

Quantum Chemical Investigation on Indole: Vibrational Force Field and Theoretical Determination of Its Aqueous pKa Value

“…However, these experimental values are significantly different from the calculated ones reported in literature. Yang et al 33 and 861.0 kJ mol −1 (corresponding to 205.8 kcal mol −1 ), respectively. Somers et al 24 gave a value of 888.7 kJ mol −1 (212.4 kcal mol −1 ) for proton affinity on the basis of B3LYP/6-31G* computations; similar values have been reported by Otero et al 25 employing B3LYP/6-311++G(2d,2p) and MP2/ 6-31++G(2d,2p) levels of theory.…”

“…However, these experimental values are significantly different from the calculated ones reported in literature. Yang et al . computed a proton affinity and gas phase basicity at T = 0 K by means of MPW1PW91/6-311+G(2d,2p) and MP2(full)/6-311+G(2d,2p) single-point energy calculations on MPW1PW91/6-31G* and MP2(full)/6-31G* optimized geometries reporting a value of 892.2 kJ mol –1 (corresponding to 213.3 kcal mol –1 ) and 861.0 kJ mol –1 (corresponding to 205.8 kcal mol –1 ), respectively.…”

[M−H]+ ions in 3-alkyl substituted indoles detected by electrospray mass spectrometry

“…An indole scaffold is an important privileged structure, and its derivatives are widely found in pharmaceuticals, agrochemicals, and natural products with a range of important biological activities [1][2][3][4][5]. Amongst various indole derivatives, optically active 3-substituted indoles containing phenolic hydroxyl groups in the substituents are important subunits found in many synthetic and natural products.…”