Our research group works mainly in the area of bioanalytical chemistry. We take a problem solving approach to analytical chemistry that involves identifying interesting problems, and applying various analytical tools to address the question at hand. Therfore, we employ a variety of analytical techniques in our research including separations (CE, HPLC, UPLC. GC) and characterization tools, especially NMR and mass spectrometry. Sometimes we find that the technology needs to be improved to allow us to fully address a question of interest.

Development and Application of Microcoil NMR Probes

One area where we are involved in technology development is in the use of microcoil NMR probes to improve the sensitivity of NMR measurements. Microcoil NMR probes constructed in our laboratory, capable of measuring volumes of 25 nL, permit on-line NMR detection with capillary isotachophoresis (cITP). An example of an NMR microcoil is shown in this photo. The coil, approximately 1 mm in length, is made by winding copper wire around a polyimide sleeve. Our group is using the on-line concentration and separation method of cITP coupled with NMR detection to study a number of problems related to structure elucidation including analysis of trace pharmaceutical impurities and characterization of heparin and heparan oligosaccharides.

Characterization and Biochemistry of Heparin and Heparan Sulfate

Analysis strategies are being developed in our laboratory to greatly reduce the quantity of heparin or heparan sulfate required for structure elucidation. Oligosaccharides are obtained by enzymatic depolymerization and are size-separated by gel permeation chromatography. The size-fractionated materials are profiled using capillary electrophoresis and fractionated further with ion-pairing UPLC. With cITP-NMR using our microcoil NMR probes, a proton NMR spectrum can be obtained during the on-line separation with as little as 1 - 2 micrograms of sample. Complete 2D NMR spectra can be recorded in static mode with 20 – 30 micrograms. Since NMR is non-destructive, samples can be collected for subsequent MS/MS characterization using our Q-TOF mass spectrometer.

Metabonomics Studies for Chemical Genomics in Arabidopsis thaliana

The goal of metabonomics studies is to collect as much chemical information as possible about the identity and relative concentrations of endogenous metabolites in samples from control and treated (perturbed) organisms. The choice of perturbation is at the discretion of the experimenter and can be designed to probe the effects of a drug, toxicant or genetic modification. In our case, we are probing the effect of chemicals (for example herbicides) applied to plants. In collaboration with Julia Bailey-Serres we are also studying the response of plants to hypoxia. Analytical methods such as 1H NMR, LC-MS and GC-MS are used in metabonomics studies because they produce data sets with high information content. Data reduction by principal components analysis (PCA) or other statistical methods is used to group samples based on their chemical similarity and to identify the compounds responsible for differences between the control and treated groups.

Understanding Ligand-Protein Interactions

Specific ligand-protein interactions are integral to the ability of proteins to carry out processes vital for human life such as enzymatic transformations, receptor and antibody recognition, and signal transduction. Therefore the study of ligand-protein interactions is important for understanding the biochemical basis of many diseases and provides an opportunity for the development of pharmaceutical compounds with agonistic or inhibitory activity. NMR is a useful analytical tool for the study of ligand-protein binding, because changes can be detected when a small ligand interacts with a macromolecular target without the need for special labels. We have developed experiments that provide improved spectral selectivity in ligand binding studies by manipulation of NMR pulse sequences to reduce the protein background or enhance specificity in cases where several ligands are studied simultaneously. In addition to providing information about the strength of the interaction, the build-up of transferred-NOEs during the diffusion experiment can provide insight into the nature of ligand-protein binding and can be used to prepare an epitope map of the ligand which is useful for the elucidation of structure activity relationships.

Selected Publications

A. K. Korir, J. F. K. Limtiaco, S. Gutierrez, C. K. Larive “Ultraperformance ion-pair liquid chromatography coupled to electrospray time-of-flight mass spectrometry for compositional profiling and quantification of heparin and heparan sulfate" Anal. Chem. 00:000-000 (2008).

K. E. Price, C. E. Lunte, C. K. Larive “Development of tissue-targeted metabonomics: Part 1. Analytical considerations” J. Pharm. Biomed. Anal. 46:737-747 (2008).

M. Rojas-Pierce, B. Titapiwatanakun, E. J. Sohn, F. Fang, C. K. Larive, J. Blakeslee, Y. Cheng, S. Cuttler, W. A. Peer, A. S. Murphy, N. V. Raikhel “Arabidopsis P-Glycoprotein19 participates in the inhibition of gravitropism by gravacin” Chem. Biol. 14:1366-1376 (2007).

B. C. Valle, K. F. Morris, K. A. Fletcher, V. Fernand, D. M. Sword, S. Eldridge, C. K. Larive, I. M. Warner “Understanding chiral molecular micellar separations using steady-state fluorescence anisotropy, capillary electrophoresis, and NMR” Langmuir 23:425-435 (2007).

A. Korir and C. K. Larive “On-line NMR detection of microgram quantities of heparin-derived oligosaccharides and their structure elucidation by microcoil NMR” Anal. Bioanl. Chem. 388:1707-1716 (2007).

Y. Zhao, T. F. Chow, R. S. Puckrin, S. E. Alfred, A. K. Korir, C. K. Larive and S. R. Cutler, “Chemical genetic interrogation of natural variation uncovers a molecule that is glyco-activated” Nature Chem. Biol. 3, 716 - 721 (2007).

S. L. Eldridge, V. K. Almeida, A. K. Korir, C. K. Larive, ”Separation and analysis of trace degradants in a pharmaceutical formulation using on-line cITP-NMR” Anal. Chem. 79:8446-8453 (2007).

A. K. Korir, V. K. Almeida, C. K. Larive, “Visualizing ion electromigration during isotachophoretic separation with cITP-NMR” Anal. Chem. 78:7078-7087 (2006).

A. Lebrón-Paler, J. E. Pemberton, B.A. Becker, W. H. Otto, C. K. Larive, R. M. Maier “Determination of the acid dissociation constant of the biosurfactant monorhamnolipid in aqueous solution by potentiometric and spectroscopic methods” Anal. Chem. 78:7649-7658 (2006).

K. F. Morris, B. A. Becker, B. C. Valle, I. M. Warner, C. K. Larive “Use of NMR binding interaction mapping techniques to examine interactions of chiral analytes with molecular micelles” J. Phys. Chem. B. 110:17359-17369 (2006).

B. A. Becker, K. F. Morris, C. K. Larive “An improved method for suppressing protein background in PFG NMR experiments to determine ligand diffusion coefficients in the presence of receptor” J. Magn. Reson. 181:327-330 (2006).