Investigation of the potential of the dissolution dynamic nuclear polarization method for general sensitivity enhancement in small-molecule NMR spectroscopy

We report results of applying a commercial implementation of the dissolution dynamic nuclear polarization (DNP) methodology developed by K. G. Golman et al. to a range of molecular species in the mass range of 100-400 Da. The molecules are typical of those that might be encountered in natural product chemistry or pharmaceutical analysis. Using an experimental protocol previously reported, in combination with the ERETIC method for generating a reference signal for estimation of concentrations, we determine the signal enhancement and high-field, liquid-state T-1 values for many of the carbon atoms in the six species studied. The results presented in this work suggest that the measured variation in nuclear magnetic resonance enhancements within a given molecule, arising from the dissolution DNP method, is accounted for principally by relaxation of C-13 atoms towards thermal polarization values in the liquid state. We conclude that dissolution DNP will be able to be employed for a wide range of chemical species, provided that the total time taken for dissolution and transfer of solutions is comparable to, or shorter than, the high-field, liquid-state T-1 values in the species being studied

Alterações morfológicas e acúmulo de compostos fenólicos em plantas de sorgo sob estresse de alumínio Changes in morfology and phenolics accumulation in sorghum (Sorghum bicolor (L.) Moench) plants under aluminum stress

Os efeitos do alumínio (Al+3) sobre a morfologia e o acúmulo de compostos fenólicos foram avaliados em duas cultivares de sorgo (Sorghum bicolor (L.) Moench) com tolerância diferencial ao Al+3. As plantas foram mantidas em solução nutritiva durante dez dias, na presença (185 mM) ou na ausência de Al+3. Os ápices radiculares foram coloridos com hematoxilina férrica, sendo a intensidade da coloração observada na presença do Al+3 muito próxima entre as cultivares, o que inviabiliza a aplicação desse teste, isoladamente, para discriminação entre o genótipo sensível e o tolerante ao Al+3. As análises da morfologia externa e interna dos ápices radiculares de plantas tratadas com Al+3 também foram muito similares entre as duas cultivares, não permitindo a utilização dessas características para seleção entre a cultivar sensível e a tolerante. O maior acúmulo de lignina e, principalmente, a menor produção de compostos fenólicos, observados na presença do Al+3 nas raízes das plantas da cultivar tolerante (BR006R), são parâmetros que possibilitam a discriminação das cultivares quanto à tolerância ao Al+3.<br>The Al+3 effects on the morphology and on the phenolics accumulation were evaluated in two sorghum cultivars exhibiting differential tolerance to Al+3. The plants were kept in nutrient solution, for ten days, in the presence (185 mM) or Al+3 absence. The root apexes were colored with ferric hematoxylin, and because the intensity of color development is very similar among evaluated cultivars, the use of this method as a selection parameter for Al+3-tolerance is not indicated. Analyses of superficial and internal morphology from tissues treated with Al+3 also expressed very similar alterations among the two cultivars, not allowing its use for selection between sensitive and Al+3-tolerant genotype. The higher lignin accumulation and, mainly, the lower phenolics production in roots of the BR006R cultivar in Al+3's presence, demonstrated the existence of differential tolerance among cultivars