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Melatonin is a potent defensive molecule against oxidative damage. The knowledge of the interaction between melatonin and reactive oxygen species (ROS) is important for understanding antioxidant mechanisms. However, direct observation of reaction products of melatonin with ozone (a reactive oxygen species) in vitro is absent. In this paper, a simple and rapid method using a laser-induced acoustic desorption time-of-flight mass spectrometer (LIAD-TOFMS) is reported to characterize the reaction products of melatonin with ozone at the gas-solid interface. The advantage of this approach is the direct analysis of the products without secondary treatment. A series of oxidation products were observed, including primary hydroxymelatonin (HO-MLT), N1-acetyl-N2-formyl-5-methoxykynurenin (AFMK), and secondary (N1-acetyl-5-methoxykynurenin, AMK). Another significant finding is two pathways for the reaction of melatonin with ozone in vitro. These results demonstrate a novel strategy for the direct determination of reaction products at the gas-solid interface. [ABSTRACT FROM AUTHOR]

As is well-known, the S2 molecule is a ubiquitous intermediate in the combustion, atmosphere, and interstellar space. The six low-lying bound states of S2 have been characterized via photoelectron velocity map imaging and a high-level multi-reference configuration interaction method with the Davidson correction. Spectroscopic constants have been extracted by fitting the potential energy curves extrapolated to the complete basis set limit with a series of Dunning's correlation-consistent basis sets: aug-cc-pV(Q, 5)Z. The calculated spectroscopic parameters well reproduce the experimental results in this work. On the basis of the theoretical calculations, Franck-Condon simulations are performed to assign six adjacent electronic states, especially for three higher overlapping electronic states (c1Σu−, A′3Δu, and A3Σu+). The dissociation energy De of the S2− is evaluated to be 4.111 (4) eV in this work, in agreement with the theoretical prediction (4.056 eV). [ABSTRACT FROM AUTHOR]

L-cysteine S-sulfate, Cys-SSO3H, and their derivatives play essential roles in biological chemistry and pharmaceutical synthesis, yet their intrinsic molecular properties have not been studied to date. In this contribution, the deprotonated anion [cysS-SO3]− was introduced in the gas phase by electrospray and characterized by size-selected, cryogenic, negative ion photoelectron spectroscopy. The electron affinity of the [cysS-SO3]• radical was determined to be 4.95 ± 0.10 eV. In combination with theoretical calculations, it was found that the most stable structure of [cysS-SO3]− (S1) is stabilized via three intramolecular hydrogen bonds (HBs); i.e., one O−H⋯⋯N between the –COOH and –NH2 groups, and two N−H⋯⋯O HBs between –NH2 and –SO3, in which the amino group serves as both HB acceptor and donor. In addition, a nearly iso-energetic conformer (S2) with the formation of an O−H⋯⋯N−H⋯⋯O−S chain-type binding motif competes with S1 in the source. The most reactive site of the molecule susceptible for electrophilic attacks is the linkage S atom. Theoretically predicted infrared spectra indicate that O−H and N−H stretching modes are the fingerprint region (2800 to 3600 cm−1) to distinguish different isomers. The obtained information lays out a foundation to better understand the transformation and structure–reactivity correlation of Cys-SSO3H in biologic settings. [ABSTRACT FROM AUTHOR]

Covalent and noncovalent interactions dominate most compounds in the condensed phase and gas phase. For a classical diatomic molecule CO, it is usually regarded as a triple-bond system with one dative bond. In this work, the photoelectron velocity-map imaging spectra of the CS and PbS anions were first measured. The two interactions have been intuitively understood by a comparative investigation of electrostatic potential (ESP) and bond features in CO, CS, and PbS. It is suggested that both electrostatic and dative covalent interactions compete in CO molecules, while dative covalent interaction prevails in CS molecules and electrostatic interaction dominates in PbS molecules. As a consequence, CO has a very small dipole moment (∼0.1 D) compared to the large dipole moment in CS (>1.8 D) and PbS (>4 D). It is indicated that the electron affinity value increases with the increasing dipole moment in the order of CO < CS < PbS. In addition, intriguing ESP with negative bond-ends and positive bond-cylindrical-surface in CO is also revealed by comparing with that in CS and PbS. In the latter, the two molecules present opposite ESP maps. Molecular orbital analyses indicate surprising participation of Pb 5d orbitals in the Pb–S chemical bonding although Pb belongs to main-group elements. Further bond analyses using electron localization function, natural resonance theory, and bond order methods suggest that covalence is dominant in CS and ionicity is a major component in PbS, but somewhere in between for CO molecules. By a comparative study in this work, the CS molecule is also revealed as a promising ligand molecule for the transition-metal coordination chemical synthesis. [ABSTRACT FROM AUTHOR]

We investigate the feasibility of laser-induced breakdown spectroscopy for determination of heavy metal Pb in a Pb[(N[O.sub.3]).sub.2] aqueous solution by using a simple homemade vertical jet device and nanosecond laser pulses. Key experimental parameters that affect the analytical performance, such as delay of the time of observation, laser pulse energy, and liquid flow rate are optimized for the best limit of detection (LOD). The LOD was determined using Pb I emission at 405.781 nm, and after optimization, the 3[sigma] LOD was found to be at the level of 60ppm. [c] 2010 Optical Society of America OCIS codes: 300.6365, 140.3440, 120.1880.