The excitation and emission properties of several psoralen derivatives are compared using conventional single-photon excitation and simultaneous two-photon excitation (TPE). Two-photon excitation is effected using the output of a mode-locked titanium: sapphire laser, the near infrared output of which is used to promote nonresonant TPE directly. Specifically, the excitation spectra and excited-state properties of 8-methoxypsoralen and 4'-aminomethyl-4,5,8-trimethylpsoralen are shown to be equivalent using both modes of excitation. Further, in vitro feasibility of two-photon photodynamic therapy (PDT) is demonstrated using Salmonella typhimurium. Two-photon excitation may be beneficial in the practice of PDT because it would allow replacement of visible or UV excitation light with highly penetrating, nondamaging near infrared light and could provide a means for improving localization of therapy. Comparison of possible laser excitation sources for PDT reveals the titanium: sapphire laser to be exceptionally well suited for nonlinear excitation of PDT agents in biological systems due to its extremely short pulse width and high repetition rate that together provide efficient PDT activation and greatly reduced potential for biological damage.

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3We report a mechanistic DRIFTS in-situ study of NO 2 , NO + O 2 and NO adsorption on a 4 commercial Cu-CHA catalyst for NH 3 -SCR of NOx. Both pre-reduced and pre-oxidized catalyst 5 samples were investigated with the aim to clarify mechanistic aspects of the NO oxidation to NO 2 6 as a preliminary step towards the study of the Standard SCR reaction mechanism at low 7 temperatures. Nitrosonium cations (NO + , N oxidation state = +3) were identified as key surface 8 intermediates in the process of NO (+2) oxidation to NO 2 (+4) and nitrates (+5). While NO + and 9 nitrates were formed simultaneously upon catalyst exposure to NO 2 , nitrates evolved consecutively 10 to NO + when the catalyst was exposed to NO + O 2 , suggesting that nitrite-like species, and not NO 2 , 11 are formed as the primary products of the NO oxidative activation over Cu-CHA. Upon catalyst 12 exposure to NO only, i.e. in the absence of gaseous O 2 , NO + and then nitrates were formed on a 13 preoxidized sample but not on a prereduced one, which demonstrates the red-ox nature of the NO 14 oxidation mechanism. The negative effect of H 2 O on NO + and nitrates formation was also clearly 15 established. Assuming small Cu clusters, in the form of Cu dimers, as the active sites for NO 16 oxidation to NO 2 , we propose a mechanism which reconciles all the experimental observations. In 17 particular, we show that such a mechanism also explains the observed kinetic effects of H 2 O, O 2 18 and NO 2 on the NO oxidation activity of the investigated Cu zeolite catalyst. 19 20 21

The development and optimization of catalysts and catalytic processes requires knowledge of reaction kinetics and mechanisms. In traditional catalyst kinetic characterization, the gas composition is known at the inlet, and the exit flow is measured to determine changes in concentration. As such, the progression of the chemistry within the catalyst is not known. Technological advances in electromagnetic and physical probes have made visualizing the evolution of the chemistry within catalyst samples a reality, as part of a methodology commonly known as spatial resolution. Herein, we discuss and evaluate the development of spatially resolved techniques, including the evolutions and achievements of this growing area of catalytic research. The impact of such techniques is discussed in terms of the invasiveness of physical probes on catalytic systems, as well as how experimentally obtained spatial profiles can be used in conjunction with kinetic modeling. Furthermore, some aims and aspirations for further evolution of spatially resolved techniques are considered.