Theoretical chemistry Theoretical chemistry Z 0350 PARACEST Agents: Modulating MRI Contrast via Water Proton Exchange -[53 refs.]. -(ZHANG, S.; MERRITT, M.; WOESSNER, D. E.; LENKINSKI, R. E.; SHERRY, A. D.; Acc. Chem. Res. 36 (2003) 10, 783-790; Dep. Chem., Univ. Tex., Dallas, Richardson, TX 75083, USA; Eng.) -Lindner 03-276

No abstract

The yttrium complex of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetra(1 0 -13 C-acetic acid) [ 13 C]DOTA was synthesized. Fast dissolution dynamic nuclear polarization (DNP) nuclear magnetic resonance (NMR) studies revealed that the 89 Y, 13 C, and 15 N nuclei present in the complex could be co-polarized at the same optimum microwave irradiation frequency. The liquid-state spin-lattice relaxation time T 1 of these nuclei were found to be reasonably long to preserve some or most of the DNP-enhanced polarization after dissolution. The hyperpolarized 13 C and 89 Y NMR signals were optimized in different glassing mixtures. The overall results are discussed in light of the thermal mixing model of DNP.

Solid-state NMR has been used to detect an intercatechol covalent bond in sclerotized cuticle of the tobacco hornworm (Manduca sexta). Rotational-echo, double-resonance (REDOR) 13C and 15N NMR, in combination with 1H−13C dipolar modulation and 15N−15N dipolar restoration at the magic angle, were used to examine hornworm pupal exuviae labeled with β-[15N]alanine and either [β-13C]dopamine or [α-13C,15N]dopamine. The REDOR spectra showed the incorporation of N-β-alanyldopamine into insect cuticle by the formation of a variety of covalent bonds. One of these bonds links the terminal nitrogen of one N-β-alanyldopamine molecule to the β carbon of another to form an intercatechol covalent bond. This result is interpreted in terms of a novel structure for stabilized cuticle that postulates protein−catechol−catechol−protein cross-links. REDOR spectra also showed oxygen substitution at both α and β carbons of N-β-alanyldopamine, consistent with the possibility of intercatechol oxygen bridges in dimeric or oligomeric forms of catecholamines in the cuticle.