NMR spectra of imino protons for RNAs 1–7 in H₂O.

<p>Peaks for <b>2</b> are labeled according to assignments described in the text. Conditions were as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0108231#s4" target="_blank">Materials and Methods</a>.</p

Stereoview of a representative structure for nucleotides 8–23 of RNA 2 (PDB ID 2MNC).

<p>Stereoview of a representative structure for nucleotides 8–23 of RNA 2 (PDB ID 2MNC).</p

Portion of the NOESY spectrum showing NOEs between H8/H6/H2 (7.4–8.0 ppm) and H1′/H5 (5.2–6.0 ppm) protons.

<p>Mixing time was 400 ms and temperature was 25°C. Cross-peaks due to NOEs from a nucleotide aromatic proton to the H1′ proton of its own sugar are labeled. A. Sequential NOEs from C9 to U12. B. Sequential NOEs from G13 to U16. Crosspeaks due to H2 of A14 and A15 and the U16 H5 to U16 H6 are labeled. C. Sequential NOEs from U16 to C21.</p

Chemical Shifts (ppm) of Assigned Protons^a.

a<p>Assignments of nonexchangeable protons are at 25°C. All chemical shifts are reported relative to TSP.</p>b<p>Assignments of imino and amino protons are at 10°C.</p>c<p>NA: not applicable.</p><p>Chemical Shifts (ppm) of Assigned Protons^{<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0108231#nt101" target="_blank">a</a>}.</p

Mg²⁺-stimulated (in-line) cleavage of RNAs 1 and 2.

<p>A. Electrophoretic analysis of cleavage. Mg²⁺: RNA treated with 5 mM MgCl₂. OH: hydrolysis ladder. T1: Ribonuclease T1 digestion. Untreated RNA in lanes labeled “-“. Bands due to guanosines identified from RNAse T1 digestion are indicated. B. Mapping of cleavage onto predicted secondary structures of <b>1</b> and <b>2</b>. Cleavage after each nucleotide is indicated by a line with length proportional to band intensity.</p

Stereoviews of structural features apparent in the NMR-based model of 2.

<p>A. Stacking of consecutive purines G13–A15 and cross-strand stacking of A20. B. Orientation of U12 with respect to U18. The fourteen lowest energy structures were aligned on U18 and the pyrimidine rings of U18 and U12 are shown.</p

Structural features of pri-miRNAs.

<p>The stem and apical loop sequences of pri-miR-21 are shown. Arrows indicate sites of cleavage by Drosha and Dicer, as indicated. The sequence of nucleotides shown in large font is investigated in this work.</p

Imino proton region of NOESY spectrum of 2 in H₂O.

<p>Conditions were as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0108231#s4" target="_blank">Materials and Methods</a>. Sequential NOEs are indicated by lines to peaks due to proximal protons. Peaks are labeled according to assignments based on sequential NOEs.</p

Amplifying the Sensitivity of Zinc(II) Responsive MRI Contrast Agents by Altering Water Exchange Rates

Given the known water exchange rate limitations of a previously reported Zn­(II)-sensitive MRI contrast agent, GdDOTA-diBPEN, new structural targets were rationally designed to increase the rate of water exchange to improve MRI detection sensitivity. These new sensors exhibit fine-tuned water exchange properties and, depending on the individual structure, demonstrate significantly improved longitudinal relaxivities (<i>r</i>₁). Two sensors in particular demonstrate optimized parameters and, therefore, show exceptionally high longitudinal relaxivities of about 50 mM^–1 s^–1 upon binding to Zn­(II) and human serum albumin (HSA). This value demonstrates a 3-fold increase in <i>r</i>₁ compared to that displayed by the original sensor, GdDOTA-diBPEN. In addition, this study provides important insights into the interplay between structural modifications, water exchange rate, and kinetic stability properties of the sensors. The new high relaxivity agents were used to successfully image Zn­(II) release from the mouse pancreas <i>in vivo</i> during glucose stimulated insulin secretion