Charge-transfer complexes and photochemistry

Dack, Michael R. J.

doi:10.1021/ed050p169

Cited by 10 publications

(2 citation statements)

References 24 publications

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“…and RS.. The rate-limiting step involves the formation of a charge-transfer complex (Mulliken, 1952;Birks and Slifkin, 1963;Foster, 1969; Dack, 1973), in which cysteine donates one of its nonbonding electrons to the excited pyrimidine across a hydrogen bridge (Riehl, 1968). A proton is then rapidly transferred before the ions can dissociate and escape their solvent cage (Lamola, 1972), resulting in a geminate pair of radicals:…”

Section: Mechanism Of Formation Of Hp-mentioning

confidence: 99%

Ultraviolet‐induced Reactions of Thymine and Uracil in the Presence of Cysteine

Fisher

Varghese

Johns

1974

Photochem & Photobiology

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Abstract—Ultraviolet‐radiation photolysis of thymine in the presence of cysteine gives rise to four isomeric dimers, dihydrothymine, and at least five cysteine addition products. Similar reactions occur for uracil but the products have not all been characterized in detail. The addition reactions arise from the triplet state of the pyrimidine. The initial step is production of a hydropyrimidine radical, which then reacts with cysteine to give the addition products. The triplet is quenched by cysteine with a rate constant of about 2 times 108 M‐1 s‐1 for thymine and 2–9 times 108 for uracil. The total yield of products gives a lower‐limit estimate of the triplet yield and hence of the intersystem‐crossing efficiency. These studies, combined with earlier determinations of dimer yields, show that 93% of the thymine triplets which interact with another thymine molecule are quenched without forming stable dimers. For uracil, the corresponding figure is 75%.

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Section: Mechanism Of Formation Of Hp-mentioning

confidence: 99%

Ultraviolet‐induced Reactions of Thymine and Uracil in the Presence of Cysteine

Fisher

Varghese

Johns

1974

Photochem & Photobiology

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“…Significant studies of charge transfer in biological systems such as DNA and bacterial photosynthesis also have been reported (10)(11)(12)(13). In spite of the intense research interest in and the importance of charge-transfer complexes, only a few articles on this topic have been published in this Journal (14)(15)(16)(17)(18)(19)(20). None of these articles describe a student experiment involving the determination of the changes in enthalpy (ΔH), entropy (ΔS), and Gibbs energy (ΔG) associated with the formation of a charge-transfer complex.…”

mentioning

confidence: 99%

Investigating the Thermodynamics of Charge-Transfer Complexes. A Physical Chemistry Experiment

Baum¹,

Marzzacco²,

Kendrow³

2009

J. Chem. Educ.

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Thermodynamic parameters for the formation of charge-transfer complexes in heptane solution are determined from UV–visible absorption measurements at different temperatures. The systems studied include complexes of molecular iodine with toluene, xylene, mesitylene, and t-butanol as well as those of chloranil with mesitylene and hexamethylbenzene. Student results are in good agreement with published values. In addition to introducing an important method for studying chemical systems at equilibrium, this experiment explores the nature of charge-transfer interactions that play a significant role in chemistry and biology.

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