Intermolecular electron exchange

Hoytink, G.J.

doi:10.1021/ar50016a004

Cited by 88 publications

(53 citation statements)

References 31 publications

(9 reference statements)

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“…The relative magnitude of the quenching rate constant values for quenching of the porphyrin triplet as compared to that of singlet oxygen can be rationalized along the line of the theoretical reasoning by Hoytink [1], established later experimentally by Schwerzel and Caldwell [2]. Symmetry considerations require, in the case of EISC due to electron-exchange interactions, that the excitation energy be converted to the vibrational energy of the previously excited molecule.…”

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confidence: 79%

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Quenching of Porphyrin Triplet and Singlet Oxygen by Stable Nitroxide Radicals: Importance of Steric Hindrance

Vidóczy¹,

Baranyai²

2001

HCA

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Dedicated to Professor AndreÂ M. Braun on the occasion of his 60th birthdayTo study the nature of quenching, we used stable nitroxide radicals (most of which contain piperidine or pyrrolidine rings) as quenchers of triplet hematoporphyrin as well as of singlet molecular oxygen. A characteristic feature of quenching triplet porphyrin is a near-diffusion-limited rate constant, whereas the rate constant for quenching singlet oxygen is about three orders of magnitude lower. Accessibility of the nitroxide moiety in radicals was characterized quantitatively based on semi-empirical calculations (at AM1 level), with the use of van der Waals radii of the species. While variation in the rate constant values for quenching triplet porphyrin can be fully explained by the steric hindrance of the neighbouring groups of the nitroxide radical, no such effect can be observed in quenching singlet oxygen.

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confidence: 79%

“…± Investigations aimed at the study of quenching triplet states by doublets were initiated by the seminal paper of Hoytink [1]. ± Investigations aimed at the study of quenching triplet states by doublets were initiated by the seminal paper of Hoytink [1].…”

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confidence: 99%

Quenching of Porphyrin Triplet and Singlet Oxygen by Stable Nitroxide Radicals: Importance of Steric Hindrance

Vidóczy¹,

Baranyai²

2001

HCA

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“…This idea was originally proposed about 30 years ago according to a number of previous studies for quenching rate constants measured by laser flash photolysis. These phenomena have been understood by the spin catalytic role of paramagnetic molecules through the electron exchange of the encounter complex [18][19][20]. A study of an enhanced ISC process by CIDEP analyses provides quite different information from those by laser flash photolysis and gave us interesting pictures about the pair potentials and dynamics.…”

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Dynamic electron polarization created by the radical-triplet pair mechanism: Application to the studies on excited state deactivation processes by free radicals

Kawai

2003

Appl. Magn. Reson.

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The radical-triplet pair mechanism for chemically induced dynamic electron polarization (CIDEP) created in the quenching of excited state molecules by free radicals is explained on the basis of recent time-resolved electron spin resonance spectroscopic results and theoretical studies. The CIDEP of 2,2,6,6-tetramethylpiperidinyl-l-oxyl (TEMPO) and galvinoxyl radicals exhibir various CIDEP patterns of net and mutliplet types and CIDEP phases of absorption and emission. The CIDEP patterns are described by the quartet-doublet state mixings within the radical-triplet encounter pairs. The mixings by the spin-dipolar and the hyperfine interactions are responsible for the net and the multiplet patterns, respectively. The factors controlling the CIDEP phases are the spin multiplicity of the excited state quenched by radicals and the sign of the intermolecular exchange interaction of the radical-triplet encounter pairs. In particular, the intermolecular charge transfer effect on the exchange interaction is discussed much in detail from the viewpoints of CIDEP magnitudes and phases. A CIDEP creation in the O2(~Ag)-TEMPO system is also introduced and is described by the radical-triplet pair mechanism. Applications of this CIDEP used asa probe of O2(IAs) in condensed phase are mentioned. I IntroductionExcited state quenching by free radicals such as 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO) and galvinoxyl results in the creation of chemically induced dynamic electron polarization (CIDEP) on free radicals [1][2][3][4][5]. These CIDEPs of organic free radicals in liquid phase can be easily detected by the time-resolved (TR) electron spin resonance (ESR) spectroscopic method with enhanced absorption (Abs) or emission (Em) signals of hyperfine lines. As is well known, CIDEPs created in photochemically produced intermediate radicals have been extensively studied by the TRESR method [6]. Therefore, it is promising that CIDEP in the excited states quenching provides fruitful information on the dynamics of the quenching process.

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“…An estimate of the average location of the haptenic headgroup in the monolayer may be obtained by monitoring the quenching of membrane-bound fluorescent probes by nitroxide spin labels. This phenomenon is well-characterized and is known to require close contact of the fluorophore with the free electron (29,30). Therefore, quenching of chainlabeled fluorophores would arise only from those haptenic headgroups that are buried in the monolayer.…”

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confidence: 99%

Lateral diffusion of specific antibodies bound to lipid monolayers on alkylated substrates.

Subramaniam¹,

Seul²,

McConnell³

1986

Proc. Natl. Acad. Sci. U.S.A.

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We have measured the lateral mobility of fluoresceinated monoclonal IgG antibodies bound specifically to a spin label lipid hapten in phospholipid monolayers supported on alkylated silicon oxide surfaces. Dimyristoyl phosphatidylcholine and dipalmitoyl phosphatidylcholine monolayers containing 5 mol% of the lipid hapten were transferred by conventional Langmuir-Blodgett techniques onto substrates alkylated with hydrocarbon chains containing 10, 16, and 18 carbon atoms. We show that the diffusion of the bound antibodies depends on their lateral density, the composition of the lipid monolayer, and the nature of lipid coupling to hydrocarbon chains on the alkylated substrate. Antibody diffusion coefficients at low antibody densities are within a factor of 2 of those displayed by the lipid hapten in the absence of the bound antibody. High antibody densities result in reduced antibody mobility, but the lateral diffusion of unbound lipids is unaffected.There is much current interest in the design of appropriate model systems to investigate the structure and function of cellular membranes. In recent work from our laboratory, a variety of model phospholipid membranes has been used in attempts to understand the molecular mechanisms ofcell-cell communication in the immune system (1-3). The biochemical functions of some of these cells are triggered by interactions involving antibody molecules bound to suitable receptors on cell surfaces. For example, mast cells are triggered by the crosslinking of receptor-bound IgE, and macrophages can be triggered by the binding of IgG-antigen complexes to membrane-bound F, receptors (4, 5).The specific binding and subsequent interaction of antibodies bound to lipid haptens in model phospholipid membranes is representative of a general class of events involving ligands and receptors on cell surfaces. New and improved methods for reconstitution of receptors into artificial membranes have led to much progress in understanding membrane phenomena in the immune and nervous systems (6, 7). However, many fundamental questions remain unanswered due to the unavailability of suitable model systems.Epifluorescence and total internal reflection spectroscopy have been used recently to study the interaction of cells ofthe immune system with planar phospholipid membranes (3, 8, 9). Investigations using optical microscopy are much more easily carried out on substrate-supported flat membranes than on vesicles and liposomes. Planar membranes containing histocompatibility antigens have been prepared by fusion of vesicles with solid glass substrates and employed in the study of antigen recognition by T cells (10-12). Planar monolayers and bilayers, transferred onto solid substrates from the air-water interface of a Langmuir trough, have been successfully employed as target membranes in experiments involving antibody-mediated binding of macrophages and basophils. Langmuir-Blodgett techniques afford a high degree of control over the composition and packing densities of molecules in these transferred ...

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Intermolecular electron exchange

Cited by 88 publications

References 31 publications

Quenching of Porphyrin Triplet and Singlet Oxygen by Stable Nitroxide Radicals: Importance of Steric Hindrance

Quenching of Porphyrin Triplet and Singlet Oxygen by Stable Nitroxide Radicals: Importance of Steric Hindrance

Dynamic electron polarization created by the radical-triplet pair mechanism: Application to the studies on excited state deactivation processes by free radicals

Lateral diffusion of specific antibodies bound to lipid monolayers on alkylated substrates.

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