van der Wel Patrick C A, Hu Kan-Nian, Lewandowski Józef, Griffin Robert G
Francis Bitter Magnet Laboratory and Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
J Am Chem Soc. 2006 Aug 23;128(33):10840-6. doi: 10.1021/ja0626685.
Dynamic nuclear polarization (DNP) permits a approximately 10(2)-10(3) enhancement of the nuclear spin polarization and therefore increases sensitivity in nuclear magnetic resonance (NMR) experiments. Here, we demonstrate the efficient transfer of DNP-enhanced (1)H polarization from an aqueous, radical-containing solvent matrix into peptide crystals via (1)H-(1)H spin diffusion across the matrix-crystal interface. The samples consist of nanocrystals of the amyloid-forming peptide GNNQQNY(7-13), derived from the yeast prion protein Sup35p, dispersed in a glycerol-water matrix containing a biradical polarizing agent, TOTAPOL. These crystals have an average width of 100-200 nm, and their known crystal structure suggests that the size of the biradical precludes its penetration into the crystal lattice; therefore, intimate contact of the molecules in the nanocrystal core with the polarizing agent is unlikely. This is supported by the observed differences between the time-dependent growth of the enhanced polarization in the solvent versus the nanocrystals. Nevertheless, DNP-enhanced magic-angle spinning (MAS) spectra recorded at 5 T and 90 K exhibit an average signal enhancement epsilon approximately 120. This is slightly lower than the DNP enhancement of the solvent mixture surrounding the crystals (epsilon approximately 160), and we show that it is consistent with spin diffusion across the solvent-matrix interface. In particular, we correlate the expected DNP enhancement to several properties of the sample, such as crystal size, the nuclear T(1), and the average (1)H-(1)H spin diffusion constant. The enhanced (1)H polarization was subsequently transferred to (13)C and (15)N via cross-polarization, and allowed rapid acquisition of two-dimensional (13)C-(13)C correlation data.
动态核极化（DNP）可使核自旋极化增强约10² - 10³倍，从而提高核磁共振（NMR）实验的灵敏度。在此，我们展示了通过（1）H - （1）H自旋扩散穿过基质 - 晶体界面，将DNP增强的（1）H极化从含自由基的水性溶剂基质有效转移到肽晶体中。样品由源自酵母朊病毒蛋白Sup35p的淀粉样形成肽GNNQQNY(7 - 13)的纳米晶体组成，分散在含有双自由基极化剂TOTAPOL的甘油 - 水基质中。这些晶体的平均宽度为100 - 200 nm，其已知晶体结构表明双自由基的尺寸使其无法穿透晶格；因此，纳米晶体核心中的分子与极化剂不太可能紧密接触。这一点得到了溶剂与纳米晶体中增强极化随时间增长差异的支持。尽管如此，在5 T和90 K下记录的DNP增强魔角旋转（MAS）光谱显示平均信号增强ε约为120。这略低于晶体周围溶剂混合物的DNP增强（ε约为160），并且我们表明这与自旋扩散穿过溶剂 - 基质界面是一致的。特别是，我们将预期的DNP增强与样品的几个性质相关联，如晶体尺寸、核T(1)以及平均（1）H - （1）H自旋扩散常数。随后，增强的（1）H极化通过交叉极化转移到（13）C和（15）N，并允许快速采集二维（13）C - （13）C相关数据。
