A new photoelectron-photofragment-coincidence spectrometer is described. Using a multiparticle time-and position-sensitive detector, this apparatus allows the study of dissociation processes of negative ions yielding three photofragments in coincidence with a photoelectron. The photoelectron spectrometer uses two detectors and works in time of flight mode, detecting 10% of the photoelectrons with an energy resolution of 5% at 1.3 eV as shown in studies of the photodetachment of O 2 Ϫ . A third detector is used for collection of multiple photofragments ͑up to 8͒ in coincidence. This multiparticle detector uses a crossed-delay-line anode and fast timing signals to encode the time-and position-of-arrival of multiple photofragments. The detector was demonstrated to record all three particles produced in a single three-body dissociation event, yielding an energy resolution of Ϸ15% ⌬E/E at 0.7 eV in experiments on the three-body dissociative photodetachment of O 6Ϫ .

Articles you may be interested inOxygen cluster anions revisited: Solvent-mediated dissociation of the core O4 − anion Thermal effects on energetics and dynamics in water cluster anions (H2O) n − Dissociative photodetachment dynamics of the iodide-aniline cluster Photodetachment of hydrated oxalate dianions in the gas phase, C 2 O 4 2− ( H 2 O ) n (n=3-40): From solvated clusters to nanodroplet The dissociative photodetachment of O 2Ϫ (H 2 O) nϭ1 -6 was studied at 388 and 258 nm using photoelectron-multiple-photofragment coincidence spectroscopy. Photoelectron spectra for the series indicate a significant change in the energetics of sequential solvation beyond the fourth water of hydration. Photoelectron-photofragment kinetic energy correlation spectra were also obtained for O 2Ϫ (H 2 O) 1 -2 , permitting a determination of the first and second energies of hydration for O 2 Ϫ to be 0.85Ϯ0.05 and 0.70Ϯ0.05 eV, respectively. The correlation spectra show that the peak photofragment kinetic energy release in the dissociative photodetachment of O 2Ϫ (H 2 O) and O 2Ϫ (H 2 O) 2 are 0.12 and 0.25 eV, respectively, independent of the photon and photoelectron kinetic energies. The molecular frame differential cross section for the three-body dissociative photodetachment: O 2Ϫ (H 2 O) 2 ϩh→O 2 ϩ2H 2 Oϩe Ϫ is also reported. The observed partitioning of momentum is consistent with either a sequential dissociation or dissociation from a range of initial geometries.

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Photoelectron-photofragment coincidence ͑PPC͒ spectroscopy has been used to study the dissociative photodetachment of H 2 O 2 Ϫ and D 2 O 2 Ϫ . The observed partitioning of photoelectron and photofragment translational energies provides information on the dynamics in the transition state region of the reaction between two hydroxyl radicals: OHϩOH→O( 3 P)ϩH 2 O. The data reveal vibrationally resolved product translational energy distributions for both the entrance channel OHϩOH and the exit channel O( 3 P)ϩH 2 O upon photodetachment. The total translational energy distribution shows a convoluted vibrational progression consistent with antisymmetric stretch excitation of H 2 O in the exit channel and OH stretch in the entrance channel. The photoelectron spectra are compared to two-dimensional time-dependent wave packet dynamics simulations based on an anharmonic potential in the anion and a model collinear potential energy surface for the neutral complex. The PPC spectra also yield the dissociation energies D 0 (H 2 O 2 Ϫ →H 2 OϩO Ϫ ) ϭ1.15Ϯ0.08 eV and D 0 (D 2 O 2 Ϫ →D 2 OϩO Ϫ )ϭ1.05Ϯ0.08 eV.

This paper describes the development of a new class of N-linked imidazoles as potential pH-sensitive, cleavable linkers for use in cancer drug delivery systems. Kinetic analysis of eight derivatives of N-ethoxybenzylimidazoles (NEBIs) showed that their rates of hydrolysis are accelerated in mild aqueous acidic solutions compared to in solutions at normal, physiological pH. Incorporation of electron donating or electron withdrawing substituents on the phenyl ring of the NEBI resulted in the ability to tune the rates of hydrolysis under mild acidic conditions with half-lives ranging from minutes to months. A derivative of NEBI carrying doxorubicin, a widely used anticancer agent, also showed an increased rate of hydrolysis under mild acid compared to that at normal physiological pH. The doxorubicin analogue resulting from hydrolysis from the NEBI exhibited good cytotoxic activity when exposed to human ovarian cancer cells. These results demonstrate a potentially useful, general strategy for conjugating a wide range of drugs to imidazole-containing delivery vessels via NEBI functionalities for controlled release of therapeutics for drug delivery applications.

Photodetachment and photofragmentation pathways in the [ ( C O 2 ) 2 ( H 2 O ) m ] − cluster anions

This paper presents a pH-sensitive bifunctional crosslinker that enables facile conjugation of small molecule therapeutics to macromolecular carriers for use in drug delivery systems. This N-ethoxybenzylimidazole (NEBI) bifunctional crosslinker was designed to exploit mildly acidic, subcellular environments to trigger the release of therapeutics upon internalization in cells. We demonstrate that an analog of doxorubicin (a representative example of an anticancer therapeutic) conjugated to human serum albumin (HSA, a representative example of a macromolecular carrier) via this NEBI crosslinker can internalize and localize into acidic lysosomes of ovarian cancer cells. Fluorescence imaging and cell viability studies demonstrate that the HSA-NEBI-doxorubicin conjugate exhibited improved uptake and cytotoxic activity compared to the unconjugated doxorubicin analog. The pH-sensitive NEBI group was also shown to be relatively stable to biologically-relevant metal Lewis acids and to serum proteins, supporting that these bifunctional crosslinkers may be useful for constructing drug delivery systems that will be stable in biological fluids such as blood.