Transient and stationary nutations in chemically induced dynamic nuclear polarization

Transient nutations are observed in nuclear magnetic resonance during continuous generation of magnetization at and near resonance in reactions leading to chemically induced dynamic nuclear polarization. Modulation of the reaction with the nutation frequency leads to stationary nutations. The phase-sensitive detection of the nutation signals is used to discriminate effects of chemically induced polarization from steady state resonance signals. For single line spectra the effects are quantitatively explained by Bloch-type equations containing magnetization production terms. Experimental results obtained during photochemical reactions of di-tert-butyl ketone demonstrate general applications of the method.     

The creation of off-diagonal elements in chemically induced dynamic nuclear polarization experiments

The nuclear density matrix created in pulsed CIDNP experiments contains off-diagonal elements whenever the resulting nuclear spin system is strongly coupled. These off-diagonal elements, which connect spin states with the same magnetic quantum number, are due to the mixing of nuclear state functions during the process of product formation. The observation of these elements by means of a two-pulse experiment is described.     

Intramolecular electron transfer in lysozyme studied by time-resolved chemically induced dynamic nuclear polarization

The kinetics of the chemically induced dynamic nuclear polarization (CIDNP) produced in reactions of hen lysozyme with photosensitizers have been studied for the native state of the protein at pH 3.8 and for two denatured states. The latter were generated by raising the temperature to 80 degrees C or by combining a temperature rise (to 50 degrees C) with the addition of chemical denaturant (10 M urea). Detailed analysis of the CIDNP time dependence on a microsecond time scale revealed that, in both denatured states, intramolecular electron transfer (IET) from a tyrosine residue to the cation radical of a tryptophan residue (rate constant k(f)) is highly efficient and plays a decisive role in the evolution of the nuclear polarization. To describe the observed CIDNP kinetics with a self-consistent set of parameters, IET in the reverse direction, from a tryptophan residue to a tyrosine residue radical (rate constant k(r)), has also to be taken into account. The IET rate constants determined by analysis of the CIDNP kinetics are, at 80 degrees C: k(f) = 1 x 10(5) s(-1) and k(r) = 1 x 10(4) s(-1); at 50 degrees C in the presence of 10 M urea: k(f) = 7 x 10(4) s(-1), k(r) = 1 x 10(4) s(-1). IET does not appear to influence the CIDNP kinetics of the native state.     

A violation of the magnetic equivalence of nuclei in chemically induced dynamic nuclear polarization spectroscopy

It has been shown that a correlation between the hyperfine coupling constant and the ability of a given nucleus to be abstracted in the radical reaction could cause a violation of the equality in CIDNP signals from protons constituting a group of magnetically equivalent nuclei in the radical undergoing the abstraction. The scale of the effect is analyzed and optimal conditions for its detection are found.     

Photoinitiated oxidation of NADH catalyzed by horseradish peroxidase studied by chemically induced dynamic nuclear polarization

The photoinitiated oxidation of β-NADH catalyzed by horseradish peroxidase (Per³⁺) was studied by time-resolved photoinitiated chemically induced dynamic nuclear polarization (CIDNP). The polarization observed on protons at the C(4) atom of the β-NADH molecule is evidence for the reversible one-electron transfer between the radical cation NADH^+· and the ferroperoxidase intermediate (Per²⁺). A new approach based on electron transitions in the (NADH^+· Per²⁺) pair was proposed to describe the formation of CIDNP effects in systems including quartet (Q)—doublet (D) electron transitions. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1090–1094, July, 2006.     

Mechanism of the reaction between diazonium salts and potassium nitrite based on chemically induced dynamic nuclear polarization

Theoretical and Experimental Chemistry -     

Chemically induced dynamic nuclear polarization. Decarboxylation of photochemically generated benzoyloxy radicals

CIDNP has been studied during thermal decomposition, photolysis, and sensitized photolysis of benzoyl chloroacetyl peroxide. The ratio of the CIDNP intensities for the recombination products benzyl chloride and chloromethyl benzoate is dependent on the mode of decomposition, reflecting the extent of rapid decarboxylation of the primary formed benzoyloxy radicals.     

Radical pair formation from excited states in doped aromatic crystals. II. Optical nuclear polarization (ONP) studies

The use of ONP to determine absolute signs of fine and hyperfine tensor elements in excited triplet states is developed theoretically and demonstrated experimentally. Convenient ONP-rules are formulated which relate the desired signs of the tensor elements to quantities which can be extracted from the measured ONP field dependence. Application is made to the ONP originating from the radical pair triplet state formed after photochemical hydrogen abstraction from a fluorene host molecule and hydrogen transfer to an acridine guest molecule in doped single crystals. Negative fine and hyperfine tensor elements are determined and confirm the structural model of a radical pair product inferred from EPR-data.     

Study of the reaction of the superacid HGeCl3 with olefins by the chemically induced dynamic nuclear polarization method

Conclusions In reactions of the superacid HGeCl₃ with 2-methylbutene-2,2,3-dimethyl-2-butene and styrene, leading to hydrogermylation products of the indicated olefins, we have observed chemically induced dynamic nuclear polarization effects which are clear evidence for the presence of radical stages in the reactions.Translated from Izvestiya Akademii Nauk SSSR, No. 7, pp. 1617–1620, July, 1987.