Interactions of Guanine and Guanosine Hydrates with Quinones: A Laser Flash Photolysis and Magnetic Field Effect Study

Abstract

Laser flash photolysis and an external magnetic field have been used to study the interaction of two quinone molecules, namely, 9,10-anthraquinone (AQ) and 2-methyl 1,4-naphthoquinone, commonly known as menadione (MQ), with one of the DNA bases, guanine (G) and its nucleoside guanosine hydrate (dG). In organic homogeneous medium, it has been observed that G undergoes a predominant hydrogen (H) abstraction reaction with both the quinones while dG supports photoinduced electron transfer (PET) along with H abstraction. On the other hand, in SDS medium, G supports PET with AQ but not with MQ. However, behavior of dG remains unperturbed toward AQ and MQ with the change in medium. All of these observations have been explained on the basis of stabilization of radical ion pair and difference in size of the quinones, which can affect the distance of approach among the interacting molecules.

Role of sugar in controlling reaction pathways: A study with thymine and thymidine

“…Addition of Thy (curve 2) has resulted in a sharp increase in intensity at 370 nm with a hump at 400 nm and another small peak at 500 nm. Earlier we had mentioned that peaks at 370 and 400 nm are combined effect of MQ dÀ and MQH d and MQ dÀ also exhibits a second peak around 490 nm [5,19]. Observation of a 400 nm hump is attributed to a facile H abstraction from Thy to MQ.…”

“…Curve 1 depicts absorption due to MQ alone while curve 2 exhibits its field effect. The 370 nm peak is seen to increase in presence of an external MF thus associating it to a radical species, which can be assigned to MQH d [5,19]. The peak due to MQ and Thy (curve 3) presents broad maxima around 370 nm with appreciable absorption around 400 and 500 nm.…”

“…Our main focus is to detect any change in the reactivity of these molecules on changing their immediate surroundings. Earlier purine bases adenine (A) and guanine (G) had revealed a change in their reaction pattern with a change in medium [5][6][7], so this time we have endeavored with pyrimidine base, thymine (Thy) and its nucleoside thymidine (dThd) to investigate their behavior towards the quinones.…”

Hydrogen Bonding on Photoexcitation

“…It was observed that more or less all the DNA and RNA bases, i.e. adenine, thymine, guanine, cytosine and uracil, and their corresponding nucleosides, adenosine, thymidine, guanosine, cytidine and uridine, undergo hydrogen atom transfer in micellar media and electron transfer in polar homogeneous media while interacting with a model quinone drug, 2-methyl 1,4-naphthoquinone or menadione (MQ), used in cancer chemotherapy [78][79][80][81]. This implies that DNA bases enhance hydrogen atom transfer more in the hydrophobic interior of a micellar medium.…”

“…Among all the DNA bases, guanine and its nucleoside guanosine are the most easily oxidizable bases and play a crucial role in charge transport in DNA. However, guanine undergoes hydrogen abstraction instead of electron transfer with both the quinones, which could be attributed to the absence of hydration owing to its low solubility in aqueous phase of the micellar medium [81]. Amada et al reported that, for naphthoquinone (NPQ), a small amount of hydrogen atom transfer is possible from the solvent acetonitrile, which is known as an inert solvent for a substrate like benzophenone [82].…”