Photolysis Dynamics Laser Chemistry Lab

Palladium nanoparticles encapsulated in the carbon dots (Pd/C-dots) are demonstrated to play a role of multifunctional nanohybrid in the synergetic applications of sensor and catalysis. The photochemical method is applied to synthesize Pd/C-dots in which Pd nanoparticles (NPs) are dispersedly encapsulated by C-dots layer. The nanohybrid can function as a fluorescent sensor and reductive catalyst, due to the inherent properties of C-dots and Pd NPs, respectively. The Pd/C-dots exhibit a highly selective and sensitive detection toward the nickel (Ni2+) ion with a detection limit of 7.26 × 10−9 m. Moreover, the Ni2+ is detected in MCF-7 live cells signifying the applicability of nanohybrid as a promising sensor. On the other hand, the Pd/C-dots show an excellent catalytic performance in the reduction of 4-nitrophenol and eosin yellow. A plausible mechanism for sensing and catalysis behavior is proposed. The sensor system is designed on the basis of the fluorescence turn-on when Ni2+ interacts with functional groups of the C-dots layer. The activities of catalytic reduction are mainly governed by the Pd NPs and further enhanced when the C-dots layer is incorporated. The Pd/C-dots can serve as a new paradigm for opening a potential trend in the design of multifunctional materials to diverse applications. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

We present here a physico-mathematical picture for explaining the unexpectedly large decoherence cross-section (almost 10 times larger than its gas-kinematic cross-section) recently observed by Ureña and coworkers in their scattering experiment involving a coherent NO beam with Ar gas. The present topological picture consists of a stereographic projection and the cusp catastrophe theory of Thom, and we find that this model enables us to clarify the origin of the collisional decoherence. From the view of the stereographic projection, we can naturally introduce the wave property originating from the singular point at the “North pole” on the circumference S1 coordinate corresponding to a critical point for the collisional decoherence (condition 1). This picture also predicts the sudden changes of wave-phase collapse due to network interaction in the many-body system (condition 2). Thus it is hoped that the model proposed by Ureña et al. based on the dipole-induced dipole interaction in the NO + Ar system could be modified through this picture by including interactions with many Ar atoms in the environment. One way to fill the gap between the single-pair interaction picture and the multiple interaction one would be to employ theoretical calculations by use of the density matrix theory with and without adding the second Ar atom to the NO–Ar system. The cusp catastrophe theory reinforces the necessity of some cooperative network interaction between the coherent NO molecule and many neighboring Ar atoms and provides a qualitative scenario in which the whole system leads to a sudden change of the collisional decoherence of NO as a function of the control parameters (a, b). At this stage, the present physico-mathematical picture cannot give any specific values of the decoherence distance by the theory itself, but it clearly provides us a new topological concept for clarifying the origin of collisional decoherence which is strongly connected with the complexity of the system. Thus it gives us a global guide map toward further clarification of the collisional decoherence phenomenon with the aid of more sophisticated quantum mechanical calculations in the future. © 2016 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Competitive bond dissociation mechanisms for bromoacetyl chloride and 2- and 3-bromopropionyl chloride following the 1[n(O) →π*(Cï£O)] transition at 234-235 nm are investigated. Branching ratios for C-Br/C-Cl bond fission are found by using the (2+1) resonance-enhanced multiphoton ionization (REMPI) technique coupled with velocity ion imaging. The fragment branching ratios depend mainly on the dissociation pathways and the distances between the orbitals of Br and the Cï£O chromophore. C-Cl bond fission is anticipated to follow an adiabatic potential surface for a strong diabatic coupling between the n(O)π*(Cï£O) and np(Cl)σ*(C-Cl) bands. In contrast, C-Br bond fission is subject to much weaker coupling between n(O)π*(Cï£O) and np(Br)σ*(C-Br). Thus, a diabatic pathway is preferred for bromoacetyl chloride and 2-bromopropionyl chloride, which leads to excited-state products. For 3-bromopropionyl chloride, the available energy is not high enough to reach the excited-state products such that C-Br bond fission must proceed through an adiabatic pathway with severe suppression by nonadiabatic coupling. The fragment translational energies and anisotropy parameters for the three molecules are also analyzed and appropriately interpreted. Busted open: Insight into the mechanisms causing C-Cl and C-Br bond fission of bromoacetyl chloride and 2- and 3-bromopropionyl chloride by following the 1[n(O) →π*(Cï£O)] transition is obtained. The figure shows the center-of-mass translational energy distributions of ground-state Br formation through a diabatic pathway for the dissociation of 2-bromopropionyl chloride. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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.

The present study involves the synthesis, characterization, and catalytic application of ruthenium nanoparticles (Ru NPs) supported on plastic-derived carbons (PDCs) synthesized from plastic wastes (soft drink bottles) as an alternative carbon source. PDCs have been further activated with CO2 and characterized by various analytical techniques. The catalytic activity of Ru@PDC for the reduction of potassium hexacyanoferrate(III), (K3[Fe(CN)6]), and new fuchsin (NF) dye by NaBH4 was performed under mild conditions. The PDCs had spherical morphology with an average size of 0.5 μm, and the Ru NP (5 ± 0.2 nm) loading (4.01 wt %) into the PDC provided high catalytic performance for catalytic reduction of ferrocyanate(III) and NF dye. This catalyst can be recycled more than six times with only a minor loss of its catalytic activity. In addition, the stability and reusability of the Ru@PDC catalyst are also discussed. Copyright © 2018 American Chemical Society.

Recent experimental and theoretical advances in the study of the dissociation of excited molecules are revealing unexpected mechanisms, when their outcomes are tackled by combining (i) space-time ion imaging of translational features, with (ii) spectroscopic probing of rotational and vibrational distributions; crucial is the assistance of (iii) the quantum chemistry of structural investigations of rearrangements of chemical bonds, and of (iv) the simulations of molecular dynamics to follow the evolution of selective bond stretching and breaking. Here we present results of such an integrated approach to methyl formate, HCOOCH3, the simplest of esters; the main focus is on the rotovibrationally excited CO (v = 1) product and in general on the energy distribution in the fragments. Previous laser studies of dissociation into CO and CH3OH at a sequence of various wavelengths discovered signatures of a roaming mechanism by the late arrival of CO (v = 0) products in time-of-flight ion imaging. Subsequent detailed investigations as a function of excitation energy provided the assessment of the threshold, which opens for triple breakdown into CO and further fragments H and CH3O, as spectroscopically characterized by ion imaging and FTIR respectively. Accompanying quantum mechanical electronic structure calculations and classical molecular dynamics simulations clarify the origin of these fragments through "roaming" pathways involving incipient radical intermediates at energies below the triple fragmentation threshold: a specific role is played by nonadiabatic transitions at a conical intersection between ground and excited states; alternative pathways focalize our attention to regions of the potential energy surfaces other than those in the neighbourhoods of saddle points along minimum energy paths: eventually this leads us to look for avenues in reaction kinetics beyond those of venerable transition state theories. This journal is © The Royal Society of Chemistry.

The multiple sensing capabilities of molybdenum disulfide quantum dots (MoS2 QDs) towards metal ions were scrutinized by tuning their surface functional groups. The MoS2 QDs surface was individually modified with thiol-containing capping agents to form carboxylic-, amine- and thiol-functionalized MoS2 QDs (MoS2/COOH, MoS2/NH2 and MoS2/SH) by the facile hydrothermal method. Each as-prepared QDs exhibits strong excitation wavelength dependent fluorescence behavior. The design of MoS2 QDs based metal ion sensor was implemented based on the fluorescence turn-on mechanism. These MoS2/COOH, MoS2/NH2 and MoS2/SH QDs sensors exhibit superior performance towards the highly selective detection of Co2+, Cd2+ and Pb2+ ions, respectively, due to the varied association of each functional group towards metal ions. The resultant detection limit of Co2+, Cd2+ and Pb2+ was evaluated to be 54.5, 99.6 and 0.84 nM, respectively, and the related fluorescence turn-on mechanism is verified unambiguously. The binding energies were calculated for QDs with metal ions pairs and the results lent support to the determined sensitivity. The as-prepared QDs were also successfully demonstrated to detect the above metal ions in real water samples. While becoming potential candidates in the chemosensors based on the fluorescence probe, these surface modified MoS2 QDs can offer an excellent sensing capability for specific metal ions with extremely high selectivity.