Energy to molecular oxygen

Here, the electronically excited drug molecule (D ) transfers energy to molecular oxygen producing which then can, in some cases, react with and consume the drug. 

The mechanism by which PUVA induces photosensitivity is not known. The action spectrum for oral PUVA is between 320 and 400 nm. Two distinct photoreactions take place. Type I reactions involve the oxygen-independent formation of mono- and bifunctional adducts in DNA. Type II reactions are oxygen-dependent and involve sensitized transfer of energy to molecular oxygen. The therapeutic effects of PUVA in psoriasis may result from a decrease in DNA-dependent proliferation after adduct formation. Perhaps more importantly, PUVA can alter cytokine profiles and cause immunocyte apoptosis, thereby interrupting immunopathologic processes. 

Figure 25 An encapsulated sensitizer is excited with light and it releases the energy to molecular oxygen that oxidizes a second hydrophobic guest selectively to the corresponding hydroperoxide.

In addition to transferring excitation energy to molecular oxygen to generate singlet oxygen 2) (cf section 7.3), the photoactivated dye molecule (D )... 

The UV-A-excited (320 to 400 nm) triamterene molecule transferred its energy to molecular oxygen, with subsequent formation of Oj however, photodegradation was not observed. Triamterene itself shows a photohemolytic effect and photoinduced lipid peroxidation. 

As we have seen, the metabolic energy from oxidation of food materials—sugars, fats, and amino acids—is funneled into formation of reduced coenzymes (NADH) and reduced flavoproteins ([FADHg]). The electron transport chain reoxidizes the coenzymes, and channels the free energy obtained from these reactions into the synthesis of ATP. This reoxidation process involves the removal of both protons and electrons from the coenzymes. Electrons move from NADH and [FADHg] to molecular oxygen, Og, which is the terminal acceptor of electrons in the chain. The reoxidation of NADH,... 

Ubiquinones function within the mitochondria of cells to mediate the respiration process in which electrons are transported from the biological reducing agent NADH to molecular oxygen. Through a complex series of steps, the ultimate result is a cycle whereby NADH is oxidized to NAD+, O2 is reduced to water, and energy is produced. Ubiquinone acts only as an intermediary and is itself unchanged. 

The process occurring in plants and algae by which water is oxidized to molecular oxygen and carbon dioxide is converted to carbohydrates in the presence of light is called photosynthesis. In addition to the products oxygen and carbohydrate, light energy is stored chemically in adenosine triphosphate (ATP) for later use for a variety of purposes. The production of... 

The respiratory chain is one of the pathways involved in oxidative phosphorylation (see p. 122). It catalyzes the steps by which electrons are transported from NADH+H or reduced ubiquinone (QH2) to molecular oxygen. Due to the wide difference between the redox potentials of the donor (NADH+H or QH2) and the acceptor (O2), this reaction is strongly exergonic (see p. 18). Most of the energy released is used to establish a proton gradient across the inner mitochondrial membrane (see p. 126), which is then ultimately used to synthesize ATP with the help of ATP synthase. 

Of the reactions listed in Table II, the only process that leads to a decrease of the energy of molecular oxygen is the formation of the free superoxide ion, Oj ( — 10.15 kcal/mol). The superoxide ion would therefore be expected to be the dioxygen species most commonly formed on oxide surfaces and in fact it is the species most studied, both in the bulk of various matrices and on surfaces. The other species (Oj and Oj ) are not stable in the gas phase, although they can be stabilized in the solid state (Table I) due to the additional coulombic stabilization from the lattice. 

Looking at this summary reaction, you may wonder why it doesn t reflect the substantially greater ATP yield that is supposed to be characteristic of aerobic metabolism. The answer is that energy is stored in the reduced coenzyme molecules on the right-hand side of the reaction. Reoxidation of these compounds liberates a large amount of free energy. It is only as the electrons are transferred stepwise from the coenzymes to molecular oxygen that the coupled... 

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