Research Highlight Archive

Research Highlight: Nanoparticles of the Novel Coordination Polymer KBi(H₂O)₂[Fe(CN)₆]•H₂0 as a Potential Contrast Agent for Computed Tomography

Vindya S. Perera, Songping D. Huang, et. al.

Published online in Inorg. Chem., 2011, 50, 7910-12.

Abstract:
Computed tomography (CT) is the gold standard in diagnostic medicine for noninvasively visualizing internal organs. Because of the small X-ray attenuation differences among various soft tissues, a contrast medium is often administered to enhance the quality of X-ray images. All the current intravascular X-ray contrast agents are based on the 1,3,5-tri-iodobenzene based organic compounds. The X-ray attenuation efficiencies of iodinated contrast agents are far from optimal due to the low atomic number of iodine (Z=53). In addition, iodinated contrast agents exhibit a short blood circulation half-life, nonspecific biodistribution, and occasional renal toxicity or even anaphylaxis. In this communication, Huang et al report on a novel potassium bismuth ferrocyanide coordination polymer KBi(H₂O)₂[Fe(CN)₆]•H₂O with an extended 3D structure. The nanoparticles of this coordination polymer are extremely stable and biocompatible. They show great potential as a novel CT contrast agent.

Research Highlight: Mechanistic Studies on the Reaction between Cob(II)alamin and Peroxynitrite: Evidence for a Dual Role for Cob(II)alamin as a Scavenger of Peroxynitrous Acid and Nitrogen Dioxide

Riya Mukherjee and Nicola E. Brasch*

Published online in Chem. - Eur. J., 2011, 17, 11805-11812.  Article featured together with a second related article from the same authors on the journal cover.  Artwork designed by Frank Mueller.

Abstract:
Peroxynitrite/peroxynitrous acid (ONOO^-/ONOOH; pK_a(ONOOH) = 6.8) is implicated in multiple chronic inflammatory and neurodegenerative diseases. Both mammalian B₁₂-dependent enzymes are inactivated under oxidative stress conditions. We report studies on the kinetics of the reaction between peroxynitrite/peroxynitrous acid and a major intracellular vitamin B₁₂ form, cob(II)alamin (Cbl(II)), using stopped-flow spectroscopy. The pH dependence of the reaction is consistent with peroxynitrous acid reacting directly with cob(II)alamin to give cob(III)alamin and ^•NO₂, followed by a subsequent rapid reaction between ^•NO₂ and a second molecule of Cbl(II) to primarily form nitrocobalamin. In support of this mechanism a Cbl(II):ONOO(H) stoichiometry of 2:1 is observed at pH 7.35 and 12.0. The final major cob(III)alamin product observed (nitrocobalamin or hydroxycobalamin) depends on the solution pH. Analysis of the reaction products in the presence of tyrosine, a well established ^•NO₂ scavenger, reveals that cob(II)alamin reacts with ^•NO₂ at least an order of magnitude faster than tyrosine itself. Given that protein-bound Cbl is accessible to small molecules, it is likely that enzyme-bound and free intracellular Cbl(II) are rapidly oxidized to inactive cob(III)alamins upon exposure to peroxynitrite or ^•NO₂.

Research Highlight: Detection of Single Nucleotide Polymorphism Using Tension Dependent Stochastic Behavior of a Single-Molecule Template

Deepak Koirala, Zhongbo Yu, Soma Dhakal, and Hanbin Mao.

J. Am. Chem. Soc., 2011, 133(26), pp 9988-9991.

Abstract:
Single Nucleotide Polymorphism (SNP) is the variation in the DNA sequence when a specific gene of individuals differs by a single nucleotide A, T, G or C.  It is the most common genetic variation in human genome wiht an average occurrence of ~1 per 1000 base pairs.  SNP is associated with diseases, anthropometric characteristics, phenotype variations, gene functions, and individual's response to pathogens.  Therefore reliable detection of SNP is crucial for biological and clinical aspects.  Recent development in the personalized medicine necessitates the recognition of genetic markers to track disease genes for biomedical diagnosis and therapy, which further amplifies the importance of SNP detection.  In this work, we report a force based sensing of SNP at the single-molecule level, which presents superior sensitivity with an inherent capacity for stochastic sensing.  The on-off stochastic signals of a single DNA template that recognizes SNP are recorded by laser tweezers in a microfluidic platform.

Compared to current approaches that heavily replies of amplification steps such as PCR to generate detectable signals, our detection system exploits mechanical signals that provide little background interference and high specificity between wild type and SNP sequences which is varied either by G/C or A/T mutations.  The microfluidic setting allows multiplex sensing and in situ recycling of the SNP probe.  Although previous attempts to combine laser tweezers and lab-on-a-chip system exist, our method represents the first SNP sensing based on these two techniques.  Using this setup, we have successfully detected a SNP associated with coronary heart diseases at 100 pM in 30 minutes.  We anticipate this system can function as a highly sensitive generic biosensor after incorporation of a specific recognition element, such as an apatmer for example.

Research Highlight: An RNA G-Quadruplex is Essential for Cap-Independent Transition Initiation in Human VEGF IRES

Mark J. Morris, Yoichi Negishi, Cathy Pazsint, Joseph D. Schonhoft, and Soumitra Basu.

J. Am. Chem. Soc., 2010, 132, pp 17831-17839.

Abstract:
RNA G-quadruplexes located within the 5'-UTR of mRNA are almost always known to be associated with repression of cap-dependent translation.  However, in this report we present functional as well as structural evidence that sequence redundancy in a G-rich segment within the 5'-UTR of human VEGF mRNA supports a 'switchable' RNA G-quadruplex structure that is essential for IRES-mediated translation initiation.  Additionally, utilization of a specific combination of G-tracts within this segment allows for the conformational switch that implies a tunable regulatory role of the quadruplex structure in translation initiation.  A sequence engineered from a functionally handicapped mutant moderately rescued the activity, further indicating the importance of G-quadruplex structure for VEGF IRES-A function.  This to our knowledge is the first report of a conformationally flexible RNA G-quadruplex which is essential for IRES-mediated translation initiation.

RNA quadruplexes present within the 5'-untranslated regions are known to act as repressors inhibiting translation.  In this work we show for the first time that an RNA G-quadruplex can be an essential element for translation of the human vascular endothelial growth factor (hVEGF).  Given the importance of VEHF in tumor angiogenesis, this newly discovered G-quadruplex motif can potentially be an anti-cancer therapeutic target.

Research Highlight: Superresolution Imaging of Targeted Proteins in Fixed and Living Cells Using Photoactivatable Organic Fluorophores

Hsiao-lu D. Lee, Samuel J. Lord, Shigeki Iwanaga, Ke Zhan, Hexin Xie, Jarrod C. Williams, Hui Wang, Grant R. Bowman, Erin D. Goley, Lucy Shapiro, Robert J. Twieg, Jianghong Rao, and W. E. Moerner

J. Am. Chem. Soc., 2010, 132 (43), pp 15099–15101             DOI: 10.1021/ja1044192

Research Highlight "Zooming in on Proteins", Nature, 467, 1009, 28 October 2010

Superresolution (SR) imaging techniques based on sequential imaging of sparse subsets of single molecules require fluorophores whose emission can be photoactivated or photoswitched. Because organic fluorophores can emit significantly more photons than average fluorescent proteins, organic fluorophores have a potential advantage in SR imaging schemes, but targeting to specific cellular proteins must be provided.

The design and application of HaloTag-based target-specific azido DCDHFs, a class of photoactivatable push−pull fluorogens which produce bright fluorescent labels suitable for single-molecule SR imaging in live bacterial and fixed mammalian cells, is described in this publication. The two images show localized labeling of PopZ (a pole organizing protein) at the cell poles in live Caulobacter crescentusbacteria with DCDHF fluorophores. The unresolved image at left is obtained in the conventional diffraction limited (DL) mode with a nonphotoactived amino-DCDHF fluorophore while the image at right, which reveals the distinct shape of the cap-like polymeric network, was obtained in SR mode using a photoactivated azido-DCDHF fluorogen.

This research is a result of a collaborative project between Stanford University (Departments of Chemistry, Radiology & Cellular Biology; photophysics, bioconjugation and imaging) and Kent State University (Department of Chemistry and Biochemistry; fluorogen synthesis, J.C.W and R. J. T)

Research Highlight: 1,1,3,3-Tetramethylguanidine Solvated Lanthanide Aryloxides: Pre-Catalysts for Intramolecular Hydroxylation

Janini, T. E., Rakosi, R., Durr, C. B., Bertke J. A., Bunge, S. D.* "1,1,3,3-Tetramethylguanidine solvated lanthanide aryloxides: Pre-catalysts for intramolecular hydroalkoxylation" Dalton Trans, 2009 47 10601-10608.

The development of single-site homogeneous lanthanide-catalysts for organic transformations is driven to a large degree by the quest for increased efficiency and selectivity.  In this report, we present the synthesis and characterization of 1,1,3,3-tetramethylguanidine (H-TMG) solvated lanthanide aryloxide complexes with the general formula [Ln(H-TMG)2(OAr)2(OR)].  These complexes were utilized as pre-catalysts for the intramolecular hydroalkoxylation of 4-pentyn-1-ol.  Each compound was found to be effective at converting 4-pentyn-1-ol to 2-methylenetetrahydrofuran.