Chemically Induced Dynamic Nuclear Polarization Effects Research Articles

Chemically induced dynamic nuclear polarization studies of guanosine in nucleotides, dinucleotides, and oligonucleotides

The nuclear magnetic resonance (NMR) technique of chemically induced dynamic nuclear polarization (CIDNP) has been used to study the reactions between photoexcited flavins and a wide variety of nucleotides, dinucleotides, and oligonucleotides. The greatest emphasis is placed on the purine nucleosides adenosine (A), inosine (I), and guanosine (G), particularly guanosine. The presence of G suppresses the CIDNP effect for A, although A by itself shows very strong CIDNP. Very intense CIDNP signals are observed for the H8 proton in G-containing mononucleotides, but no nuclear polarization is detected for the sugar H1' proton. In contrast, both H8 and H1' protons exhibit CIDNP for G in a wide range of dinucleotides and higher oligonucleotides. Several possible mechanisms are analyzed to explain the H1' polarization, and it is concluded that the sugar H1' proton probably obtains spin density through interaction with guanine nitrogen 3. The proximity of the H1' proton to N3 depends explicity on the glycosidic torsion angle, chi. CIDNP studies of several model compounds in which chi is fixed are consistent with this suggestion. CIDNP for the self-complementary tetramer ApGpCpU was studied as a function of temperature. Strong CIDNP from G is only observed at temperatures above the double-strand melting temperature,more » suggesting that CIDNP is only detected in single-stranded regions, where the base is accessible to solvent. The use of brominated riboflavin as the photoreagent in place of riboflavin is shown to selectively invert the sign of A, I, and 1-methylguanosine polarization, providing a convenient method for distinguishing the NMR spectra of these residues in complex oligonucleotides.« less

An investigation of the mechanism of the reation of allyltriethylstannane with bromotrichloromethane by radiofrequency probing and chemically induced dynamic nuclear polarization (CIDNP)

The methods of radiofrequency probing (RFP) and chemically induced dynamic nuclear polarization (CIDNP) have been used to study the mechanism of the reaction of allyltriethylstannane with bromotrichloromethane. The CIDNP effects which have been detected prove the presence of radical stages in this reaction. An assumption has been made about a possible radical pathway for the β-decomposition of elementorganic compounds.

CIDNP studies of photoinitiated electron-transfer reactions. Sensitized isomerization of an electron-acceptor norbornadiene

Chemically induced dynamic nuclear polarization (CIDNP) has been observed on irradiation of dimethylbicyclolhepta-2,5-diene-2,3-dicarboxylate (3) in the presence of aromatic electron-donor sensitizers in acetonitrile. Nuclear polarization is detected for selected protons of 3 (emission) and its quadricyclene valence isomer 4 (enhanced absorption). The complementary CIDNP effects are rationalized in terms of the quenching of hydrocarbon singlets via electron transfer, intersystem crossing between resultant singlet and triplet radical-ion pairs, and competition between singlet and triplet ion recombination. The energetics of recombination allow that triplet level is above or below that of 3. The CIDNP effects are discussed in terms of other photochemical results regarding the electron-transfer photosensitized isomerization, 3 ..-->.. 4.

Photochemical Reactions of Acridan Studied by CIDNP

AbstractThe method of chemically induced dynamic nuclear polarization (CIDNP) is applied to investigate the photochemical reactions of acridan and some substituted acridans in alcoholic solutions at room temperature. It is shown that the CIDNP effect is due to the radical pair N‐radical ‐ H. which is formed from a triplet precursor. In the presence of CCl4 or CHCl3, the pair N‐radical, ·CCl3 (or ·CHCl2) is formed by direct reaction from the singlet state.