Salt‐induced Charge Separation in Photoinduced Electron Transfer Reactions. The Effect of Ion Size*

Grosso, Viviana; Previtali, Carlos M.; Chesta, Carlos A.

doi:10.1111/j.1751-1097.1998.tb02503.x

Cited by 15 publications

(10 citation statements)

References 25 publications

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“…We cannot rule out the possibility that high NaCl concentration itself may have quenched the excimer emission. However, salt-dependent fluorescence quenching is usually observed with exciplexes in nonpolar media with quaternary ammonium salts (46), conditions completely unlike those used here.…”

Section: Peptide Loading By Heat-induced Activation and In High Saltmentioning

confidence: 66%

Molecular Mechanisms of Peptide Loading by the Tumor Rejection Antigen/Heat Shock Chaperone gp96 (GRP94)

Sastry

Linderoth

1999

Journal of Biological Chemistry

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Complexes of gp96/GRP94 and peptides have been shown to elicit immunogenicity. We used fluorescence to understand peptide association with gp96. A pyrenepeptide conjugate was complexed with gp96 under a variety of conditions. At room temperature in low salt (20 mM NaCl), the peptide binds gp96 with a strong affinity (ϳ100 -150 nM) and forms pyrene excimers, suggesting that the peptides were assembled as dimers. In high salt (2.2 M NaCl), although peptide binding was stronger (K a Ϸ 55 nM) than in low salt, pyrene excimers were absent, implying that peptides were farther apart in the complex. Heat shock-activated peptide binding exhibited characteristics of both low salt and high salt modes of binding. Anisotropy and average lifetime of the bound pyrene suggested that peptides were probably located in a solvent-accessible hydrophobic binding pocket in low salt, whereas in high salt, the peptide may be buried in a less hydrophobic (more hydrophilic) environment. These results suggested that peptide-gp96 complexes were assembled in several different ways, depending on the assembly conditions. Resonance energy transfer between the intrinsic tryptophan(s) in gp96 and pyrene suggested that one or more tryptophan residues were within the critical Forster distance of 27-30 Å from the pyrene in the bound peptide. It is proposed that peptides are assembled within higher order gp96 complexes (dimers, etc.) in a hydrophobic pocket and that there may be a conformational change in gp96 leading to an open configuration for peptide loading.Heat shock proteins purified from tumor cells when injected into inbred mice bearing the same specific type of tumor elicit immune response against only that specific tumor (1-4). This paradigm, which has been extended to virus-infected cells (5-7), as well as to a variety of animal cancers (4), forms the basis for a new therapeutic strategy against human cancers using HSPs 1 as vaccines. The HSP-mediated specific immunogenicity has been attributed to endogenous peptides that are noncovalently bound to the HSPs (8). Examples of immunogenic HSP-peptide complexes include gp96 (GRP94), BiP, protein disulfide isomerase, and calreticulin. These stress proteins are abundant and are normally present in the lumen of the endoplasmic reticulum (9). Interestingly, HSPs display dual functionality. On the one hand, they act as molecular chaperones assisting in protein folding, and on the other, they appear to shunt peptides into the immune-response pathways. However, the relationship between the two functions remains unclear. From our perspective, it is the immunogenic function of HSPpeptide complexes that is the most intriguing and is of potential value to human health. The gp96 chaperone system is the most extensively studied from an immunological standpoint (10 -16). Gp96 is an abundant endoplasmic reticulum resident glycoprotein that binds a variety of peptides in vitro with no apparent amino acid sequence specificity (17). Unambiguous confirmation of the immunogenic properties of gp96-peptide complex...

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Section: Peptide Loading By Heat-induced Activation and In High Saltmentioning

confidence: 66%

Molecular Mechanisms of Peptide Loading by the Tumor Rejection Antigen/Heat Shock Chaperone gp96 (GRP94)

Sastry

Linderoth

1999

Journal of Biological Chemistry

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“…It is well known that "inert" salts drastically alter the rates and yields of many organic (thermal and photochemical) processes. [1][2][3][4][5][6][7][8] As such, this important tool for chemical-reactivity control has been a major focus of numerous experimental and theoretical studies, which are comprehensively discussed in several reviews and monographs. [1][2][3] Nonetheless, while the transient formation of ion-radical pairs from neutral reactants (and the tuning of this process by a salt) is considered a key step in a variety of chemical transformations, [1,9] very limited quantitative information is available on the electrolyte effects of the basic electron-transfer equilibrium between donor/acceptor dyads and the related ion-radicals pairs in nonaqueous solvents [Eq.…”

Section: Introductionmentioning

confidence: 99%

“…This deficiency is apparently related to the limited range of (donor/acceptor) redox potentials appropriate for the experimental measurements of both reactants and products in Equation (1), [11] as well as to the high reactivity of the radical species D + C and A À C. [10] Thus, in contrast to the plentiful reports on electrolyte modulation of acid/base equilibria, the studies of one-electron transfers with donor/acceptor and ion-radical pairs have mostly concentrated on thermal reaction kinetics and product yields, [1][2][3][4][5][6] dynamics of photochemically generated ion-radical pairs, [7,8] or redox-potential measurements. [12][13][14] For example, Fukuzumi and co-workers reported considerable changes in the redox-reaction rates of many donor/acceptor systems upon additions of salts (especially those containing a scandium cation).…”

Section: Introductionmentioning

confidence: 99%

Spectroscopic and Electrochemical Evaluation of Salt Effects on Electron‐Transfer Equilibria between Donor/Acceptor and Ion‐Radical Pairs in Organic Solvents

et al. 2008

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Addition of "inert" tetrabutylammonium hexafluorophosphate (Bu(4)NPF(6)) to a solution of TMDO/DDQ in dichloromethane (where TMDO=2,2,6,6-tetramethylbenzo[1,2-d;4,5-d]bis[1,3]-dioxole, donor, and DDQ=diclorodicyano-p-benzoquinone, acceptor) is accompanied by drastic changes in the electronic spectrum, which are related to the appearance of the DDQ(-.) and TMDO(+.) ion radicals and a decrease in the concentration of the neutral molecules and the charge-transfer complex [TMDO,DDQ]. These changes point to a considerable rise (of about three orders of magnitude) in the apparent electron-transfer equilibrium constant (K(ET)) for this donor/acceptor pair upon increasing the electrolyte concentration from 0 to 0.5 M. Accordingly, the ion-radical fractions and K(ET) values are higher in dichloromethane, at high electrolyte concentrations, than in acetonitrile (where the effect of Bu(4)NPF(6) is less pronounced). Similar trends of the apparent equilibrium constants are observed for the tetramethyl-p-phenylenediamine/tetracyanoethylene pair. Electron-transfer equilibrium constants for both donor/acceptor dyads obtained from spectral measurements are related to those derived from the redox potentials of the reactants. The effects of media variations on the electron-transfer equilibria are discussed within the ion-pairing and ionic-activity frameworks.

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“…It is well known that quaternary ammonium salts dissolved in low-polarity solvents are effective quenchers of exciplex fluorescence (19)(20)(21). At the same time a redshift of the emission is observed in some cases (22). Furthermore, it is known that bulky ammonium salts form contact ion pairs in aprotic solvents of low dielectric constant (23).…”

Section: Mi-benzene Exciplex Quenching By Bhdcmentioning

confidence: 99%

Exciplex-type Behavior and Partition of 3-Substituted Indole Derivatives in Reverse Micelles Made with Benzylhexadecyldimethylammonium Chloride, Water and Benzene¶

Borsarelli

Bertolotti

Previtali

2007

Photochemistry and Photobiology

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The fluorescence properties of 3‐methylindole (MI), 3‐indoleacetic acid (IAA), 3‐indoleethyltrimethylammonium bromide (IETA), l‐tryptophan (Trp) and tryptamine hydrochloride (TA) were studied in reverse micelles solutions made with the cationic surfactant benzylhexadecyldimethylammonium chloride (BHDC) in benzene as a function of the molar ratio water/surfactant R (=[H2O]/[BHDC]). The fluorescence quenching of the model compound MI by benzene in cyclohexane solutions and by BHDC in benzene solutions were also studied in detail. The fluorescence of MI in benzene is characteristic of a charge‐transfer exciplex. The exciplex is quenched by the presence of BHDC, due to the interactions of the surfactant ion pairs with the polar exciplex. In reverse micelle solutions at low R values, all the indoles show exciplex‐type fluorescence. As R increases, the fluorescence behavior strongly depends on the nature of the indole derivative. The anionic IAA remains anchored to the cationic interface and its fluorescence is quenched upon water addition due to the increases of interface's micropolarity. For IETA, TA and Trp an initial fluorescence quenching is observed at increasing R, but a fluorescence recovery is observed at R > 5, indicating a probe partition between the micellar interface and the water pool. For the neutral MI, the fluorescence changes with R indicate the partition of the probe between the micellar interface and the bulk benzene pseudophase. A simple two‐site model is proposed for the calculation of the partition constants K as a function of R. In all cases, the calculation showed that even at the highest R value, about 90% of the indole molecules remain associated at the micellar interface.

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Salt‐induced Charge Separation in Photoinduced Electron Transfer Reactions. The Effect of Ion Size*

Cited by 15 publications

References 25 publications

Molecular Mechanisms of Peptide Loading by the Tumor Rejection Antigen/Heat Shock Chaperone gp96 (GRP94)

Molecular Mechanisms of Peptide Loading by the Tumor Rejection Antigen/Heat Shock Chaperone gp96 (GRP94)

Spectroscopic and Electrochemical Evaluation of Salt Effects on Electron‐Transfer Equilibria between Donor/Acceptor and Ion‐Radical Pairs in Organic Solvents

Exciplex-type Behavior and Partition of 3-Substituted Indole Derivatives in Reverse Micelles Made with Benzylhexadecyldimethylammonium Chloride, Water and Benzene¶

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