Über Trimethylsilylderivate von Uronsäuren

Henglein, F. A.; Kösters, Bernhard

doi:10.1002/cber.19590920724

Cited by 11 publications

(6 citation statements)

References 5 publications

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“…The changes in the rate constants of the reactions with triplet pyrene are not very dramatic. It should be pointed out that the bimolecular rate constant depends strongly o n the time required for the tunneling of a n electron only when this time is substantially longer than the duration of an encounter in solution [5]. This latter time is relatively long in the present studies as the encounters take place between a negatively charged particle and a large particle of high positive charge.…”

Section: E) Concluding Remarksmentioning

confidence: 93%

See 1 more Smart Citation

Electron Transfer Reactions of Singlet and Triplet Pyrene in Micelles with Various Radical Anions in Aqueous Solution

Frank¹,

Grätzel²,

Henglein³

et al. 1976

Ber Bunsenges Phys Chem

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The radicals COT. CH,O-, CH,CHO-, and CH,COCH; were pulse radiolytically produced in aqueous solutions of pH 13 containing 5.5. lo-' to 1 . lo-, M pyrene in cationic micelles. The pyrene reacted in either its singlet ground state or its lowest triplet state, the latter being produced by UV pre-irradiation before formation of the radicals. The electron transfer reactions were monitored by measuring either the optical absorption of the pyrene anion at 495 nm or that of triplet pyrene at 414nm. COY and CH,O-were found to be unreactive towards singlet pyrene. The anion of pyrene transfers its electron to CO, with k = 1 . lo7 M-' s -' and to CO; with k = 1.8.10'" M-' . . s-CH,CHO-transfers its charge to singlet pyrene with k = 1.7' 1 0 8 M -' s -' . The back reaction was also observed ( k = 7.4. 10' M -' s -') and the heterogeneous equilibrium constant (corrected for ionic effects) CH,CHOa; + Pmi, e CH,CHO,, + Pii, was determined (K = 1.3). CH,COCH; transfers its electron to singlet pyrene with k = 2.3. lo9 M -' s -' . The triplet state of pyrene was found to be reduced by these radicals, the rate becoming larger with increasing redox potential of the system aldehyde (or ketone)/radical anion, although the reduction power of these radicals increases in the reverse order. These results are explained in terms of electron tunneling through the electrical double layer separating the lipoidic part of the micelle where the pyrene molecule resides and the aqueous phase where the hydrophilic radical anions exist. The rate of tunneling is dependent on the relative positions of occupied and unoccupied electronic redox levels of the redox systems involved in the two phases.Die Radikale COY, CH,O-, CH,CHO-und CH,COCH; wurden pulsradiolytisch in waBrigen Losungen erzeugt, die 5.5. bis 1 10-' M Pyren in kationischen Mizellen be; pH 13 enthielten. Das Pyren reagierte entweder im Singlett-Grundzustand oder im niedrigsten Triplcttzustand, wobei der letztere durch Vorbestrahlung rnit UV-Licht erzeugt wurde. Die Elektroneniibertragungsreaktionen wurden am zeitlichen Verlauf der Absorption des Pyren-Anions bei 495 nm oder des Pyren-Tripletts bei 414 nm verfolgt. CO; und CH,O reagieren nicht mit Singulett-Pyren. Das Pyren-Anion iibertragt sein Elektron an CO, mit k = 1 . lo7 M -' s-' und an CO; mit k = 1.8.10'0 M ~ ' sC1. CH,CHO-iibertragt an Singulett-Pyren rnit k = 1,7. lo8 M -' s -' ; die Riickreaktion konnte auch beobachtet ( k = 7,4. lo-' M -' s--I ) und die Konstante des heterogenen Gleichgewichts CHACHO, + Pmic + CH,CHO,, + Pij, bestimmt werden ( K = 1,3; korrigiert fur ionische Effekte). CH,COCH; iibertragt sein Elektron an Singulett-Pyren rnit k = 2,3. lo9 M-' s -' . Der Triplett-Zustand des Pyrens wurde durch alle Radikale reduziert; dabei war die Geschwindigkeit um so grol3er. je positiver das Redoxpotential des Systems Aldehydjoder Keton)/Radikalanion, obgleich das Reduktionsvermogen dieser Radikale im allgemeinen in umgekehrter Reihenfolge steigt. Diese Ergebnisse werden durch das Tunneln des Elektrons durch die elektrische D...

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Section: E) Concluding Remarksmentioning

confidence: 93%

“…It can readily be calculated from the known rate constants of all the OH and e; reactions mentioned above that 70 9; of the OH radicals produced were converted into CO; via reaction (3) and practically all the hydrated electrons into CO; via reaction (5). when the solutions were saturated with C 0 2 (Concentration at 20°C: 0.035 M).…”

mentioning

confidence: 99%

Electron Transfer Reactions of Singlet and Triplet Pyrene in Micelles with Various Radical Anions in Aqueous Solution

Frank¹,

Grätzel²,

Henglein³

et al. 1976

Ber Bunsenges Phys Chem

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“…Significant deviations from bulk semiconductor properties occur when the crystal size is reduced in one or more dimensions to the diameter of the exciton radius ( Figure 2.13c) [115][116][117]. The strong influence of the reduction in size on the semiconductor properties can be understood by considering that both the electron and the hole can theoretically only exist within the semiconductor material, which means, its interface constitutes an infinite potential.…”

Section: Nanocrystalsmentioning

confidence: 99%

Fluorophores and Fluorescent Labels

Sauer

Hofkens

Enderlein

2011

Handbook of Fluorescence Spectroscopy and Imaging

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Substances that display significant fluorescence generally possess delocalized electrons, formally present in conjugated double bonds. Most proteins and all nucleic acids are colorless in the visible region of the spectrum. However, they exhibit absorption and emission in the ultraviolet (UV) region. Natural fluorophores in tissue include the reduced form of nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD), structural proteins such as collagen, elastin, and their crosslinks, and the aromatic amino acids, each of which has a characteristic wavelength for excitation with an associated characteristic emission. Within the proteins the aromatic amino acids tryptophan, tyrosine, and phenylalanine are responsible for the fluorescence signal emitted (Figure 2.1) [1].Among the three aromatic amino acids, tryptophan is the most highly fluorescent. Owing to differences in fluorescence quantum yield and resonance energy transfer from proximal phenylalanine to tyrosine or tyrosine to tryptophan, fluorescence of proteins is usually dominated by tryptophan fluorescence. The tryptophan residues of proteins generally account for about 90% of the total fluorescence of proteins. A natural fluorophore is highly sensitive to the polarity of its surrounding environment. In general, proteins absorb light at 280 nm, and fluorescence emission maxima range from 320 to 350 nm. The fluorescence quantum yield for tryptophan in different proteins is virtually unpredictable, and may lie anywhere in a range varying from <0.01 to around 0.35, with lifetimes well below 1 ns up to $7 ns. One serious limitation of native fluorescence detection of aromatic amino acids is their low photostability under one-and two-photon excitation conditions, which renders the application of native fluorescence for highly sensitive detection schemes, for example, single-molecule fluorescence spectroscopy, almost impossible [2,3]. In addition, the intrinsic fluorescence of tryptophan or tyrosine residues is generally much weaker compared with conventional fluorescent dyes.Nucleotides and nucleic acids are generally nonfluorescent at room temperature (W f < 10 À4 ) in aqueous solvents, but show a slightly increasing fluorescence yield with decreasing temperature [4,5]. However, some modified derivatives, such as j31 7-methylguanosine and 7-methylinosine are strongly fluorescent at room temperature [5]. Also deoxyadenosine derivatives bearing alkenyl side chains at C(8) are highly fluorescent upon excitation at $280 nm with emission maxima at $400 nm [6].Nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD) play important roles in the energy metabolism of cells. The reduced cofactor NADH is highly fluorescent, with absorption and emission maxima at 340 and 450 nm, respectively. On the other hand, the oxidized form NAD þ is nonfluorescent. The fluorescent group in NADH is the reduced nicotinamide ring, and its fluorescence is partially quenched by collisions with the adenine moiety. Upon binding to proteins, the qua...

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“…Optical excitation can produce dipole moments, 2 heat production, 3 fluorescent emission, 4 and electron transfer. This results in a unique mix of material properties.…”

Section: Introductionmentioning

confidence: 99%

Optimization of Quantum Dot – Nerve Cell Interfaces

2003

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Nerve cells communicate by passing electrical signals through extensions from their cell bodies. Micron-scale devices such as microelectrode arrays and field effect transistors have already been used to externally manipulate these signals. However, these devices are almost as large as the cell body of the neuron. In order to make functional electrical connections to nerve extensions or their component ion channels that propagate signals, it will be necessary to utilize increasingly smaller components. We propose the use of semiconductor quantum dots, which can be optically activated, as a potential means of perturbing the nerve membrane potentials. As a first step, we have created qdot-neuron interfaces with cadmium sulfide quantum dots. The qdots may be attached to cells either non-specifically or through selected interactions exploiting biorecognition molecules attached to the qdot particle surface. We have investigated the effect of altered synthesis conditions including pH, concentration, reactant ratio, ligand length, ligand R group, and ligand concentration on the nature and quality of qdot-cell binding. We discuss the effect of these altered synthesis conditions on particle fluorescence intensity and color. Additionally, we studied the interaction of these particles with cells and determined that larger particles are more likely to bind non-specifically than smaller particles produced with the same amount of passivating ligand. It is possible this results from reduced surface area coverage of passivating chemical. Finally, we have produced particles passivated with the biorecognition peptide CGGGRGDS in the absence of other chemical stabilizers and characterized their surfaces using NMR and IR.

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Über Trimethylsilylderivate von Uronsäuren

Cited by 11 publications

References 5 publications

Electron Transfer Reactions of Singlet and Triplet Pyrene in Micelles with Various Radical Anions in Aqueous Solution

Electron Transfer Reactions of Singlet and Triplet Pyrene in Micelles with Various Radical Anions in Aqueous Solution

Fluorophores and Fluorescent Labels

Optimization of Quantum Dot – Nerve Cell Interfaces

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