Photolysis Dynamics Laser Chemistry Lab

The fluorogenic aptamer sensing of interferon-gamma (IFN-γ) was scrutinized using two-dimensional (2D) ReS2 and TiS2 nanosheets (NSs) as a platform. The IFN-γ an important cytokine, functions as a bio-indicator to detect infectious diseases such as tuberculosis and human immunodeficiency virus. This 2D NSs based aptamer sensor was implemented to induce the fluorescence off/on resulting from an aptamer, in the absence or presence of a target to be probed. The fluorescence emitting from the aptamer is quenched by interacting with NSs, while the ensuing fluorescence is recovered upon addition of target. Such a fluorescence off/on mechanism was proposed based on the behavior of fluorescence resonance energy transfer (FRET) between the aptamer and NSs. The fluorescence response exhibits linearity as a function of target, and the detection limit of IFN-γ was evaluated to be 57.6 and 82.7 pM for ReS2 and TiS2 NSs, respectively, being comparable to or even better than those methods adopted for probing IFN-γ. The selectivity property was also characterized with various targets, exhibiting a very specific selectivity for IFN-γ. The findings reveal that the aptamer-transition metal dichalcogenides (TMD) NSs will be a great sensing pair to the development of aptamer-based biosensors. Moreover, the biocompatibility and sensing capability of IFN-γ was implemented in human embryonic kidney 293T (HEK) live cells. This is the first report to emerging fluorogenic sensing of IFN-γ aptamer with 2D TMD, showing a promising trend for future design of biosensors. © 2017 Elsevier B.V.

Atmospheric halogen chemistry has drawn much attention, because the halogen atom (X) playing a catalytic role may cause severe stratospheric ozone depletion. Atomic X elimination from X-containing hydrocarbons is recognized as the major primary dissociation process upon UV-light irradiation, whereas direct elimination of the X2 product has been seldom discussed or remained a controversial issue. This account is intended to review the detection of X2 primary products using cavity ring-down absorption spectroscopy in the photolysis at 248 nm of a variety of X-containing compounds, focusing on bromomethanes (CH2Br2, CF2Br2, CHBr2Cl, and CHBr3), dibromoethanes (1,1-C 2H4Br2 and 1,2-C2H 4Br2) and dibromoethylenes (1,1-C2H 2Br2 and 1,2-C2H2Br2), diiodomethane (CH2I2), thionyl chloride (SOCl 2), and sulfuryl chloride (SO2Cl2), along with a brief discussion on acyl bromides (BrCOCOBr and CH2BrCOBr). The optical spectra, quantum yields, and vibrational population distributions of the X2 fragments have been characterized, especially for Br2 and I2. With the aid of ab initio calculations of potential energies and rate constants, the detailed photodissociation mechanisms may be comprehended. Such studies are fundamentally important to gain insight into the dissociation dynamics and may also practically help to assess the halogen-related environmental variation. This journal is © the Partner Organisations 2014.

Rotational energy transfer (RET) by Ar collisions within the v′ = 0 level of the SH A2Σ+ state is probed using a laser-induced dispersed fluorescence technique, following photodissociation of H2S at 248 nm. The Ar pressure is adjusted appropriately to allow for significant observation of the single-collision induced RET process. The spin-resolved and spin-averaged rate constants are then evaluated with the aid of a kinetic model under single-collision conditions. The theoretical counterparts are calculated using a quantum scattering method, in which a newly fitted potential energy function is based on ab initio potential energy surface reported previously. The experimental and theoretical kinetic data are essentially consistent in the trend of N and ΔN dependence. Several propensity rules are found in the RET collisions. For instance, for ΔN = 1, 2, and 3, the rate constants decrease with increasing N or ΔN. Given a fixed ΔN, the rate constants of the same initial N in the downward transition appear to be larger than those in the upward transitions. In ΔN = 0, the F2 → F1 transitions prevail over the F 1 → F2 transitions (F1 = N + 1/2, F 2 = N - 1/2), whereas in ΔN ≠ 0, the fine-structure- conserving collisions are more favored than the fine-structure-changing collisions. The principle of microscopic reversibility is also examined for both experimental and theoretical kinetic data, showing that translational energies of the RET collisions are close to thermal equilibrium at room temperature. The propensity rules may be rationalized according to this principle. © 2010 the Owner Societies.

This perspective focuses on the mechanistic insights and complexity, which are difficult to acquire from pure experimental techniques, of the computational studies of Pd-catalyzed Suzuki, Heck, and Sonogashira carbon-carbon bond-forming reactions. These reactions consist of three fundamental steps including oxidative addition (OA), transmetalation (TM), and reductive elimination (RE) for the generation of carbon-carbon bonds from the bond-forming reactions of aryl halides (R1X) and organometallic species (R2M). Computational studies of these coupling reactions allow us to understand specific reaction pathways in the analysis of OA (resolving the linkage between coordination number and selectivity in Suzuki reaction), TM (the function of the base in the Suzuki reaction and various mechanistic options in the Sonogashira reaction), and RE (way of efficient β-hydride elimination in the Heck reaction). In addition, the reaction pathways and complexities in the full catalytic cycle of each reaction along with the future perspective are also discussed. © 2017 American Chemical Society.

Ion imaging coupled with (2 + 1) resonance-enhanced multiphoton ionization (REMPI) technique is employed to probe CO(v″ = 0) fragments at different rotational levels following photodissociation of methyl formate (HCOOCH 3) at 234 nm. When the rotational level, J″CO, is larger than 24, only a broad translational energy distribution extending beyond 70 kcal mol-1 with an average energy of about 23 kcal mol -1 appears. The dissociation process is initiated on the energetic ground state HCOOCH3 that surpasses a tight transition state along the reaction coordinate prior to breaking into CO + CH3OH. This molecular dissociation pathway accounts for the CO fragment with larger rotational energy and large translational energy. As J″CO decreases, a bimodal distribution arises with one broad component and the other sharp component carrying the average energy of only 1-2 kcal mol-1. The branching ratio of the sharp component increases with a decrease of J″CO; (7.3 ± 0.6)% is reached as the image is probed at J″CO = 10. The production of a sharp component is ascribed to a roaming mechanism that has the following features: a small total translational energy, a low rotational energy partitioning in CO, but a large internal energy in the CH3OH co-product. The internal energy deposition in the fragments shows distinct difference from those via the conventional transition state. © the Owner Societies 2011.