Remotely Detected NMR for the Characterization of Flow and Fast Chromatographic Separations Using Organic Polymer Monoliths

Recent Advances about the Applications of Click Reaction in Chemical Proteomics

Despite significant advances in biological and analytical approaches, a comprehensive portrait of the proteome and its dynamic interactions and modifications remains a challenging goal. Chemical proteomics is a growing area of chemical biology that seeks to design small molecule probes to elucidate protein composition, distribution, and relevant physiological and pharmacological functions. Click chemistry focuses on the development of new combinatorial chemical methods for carbon heteroatom bond (C-X-C) synthesis, which have been utilized extensively in the field of chemical proteomics. Click reactions have various advantages including high yield, harmless by-products, and simple reaction conditions, upon which the molecular diversity can be easily and effectively obtained. This paper reviews the application of click chemistry in proteomics from four aspects: (1) activity-based protein profiling, (2) enzyme-inhibitors screening, (3) protein labeling and modifications, and (4) hybrid monolithic column in proteomic analysis.

Fast fabrication and modification of polyoctahedral silsesquioxane-containing monolithic columns via two-step photo-initiated reactions and their application in proteome analysis of tryptic digests

A fast and robust approach was developed to fabricate and modify hybrid monolithic columns via two-step photo-initiated reactions. At first, acrylopropyl polyoctahedral silsesquioxane (acryl-POSS) and 3-(triallyl silyl) propyl acrylate (TAPA) were chosen as precursors to synthesize poly (POSS-co-TAPA) monolithic column (monolith I) via photo-initiated free-radical polymerization within 10 min, which left lots of allyl groups on the surface of monolith. Secondly, two thiol-containing compounds, penicillamine and 1-octadecanethiol (ODT), were introduced to modify the prepared poly (POSS-co-TAPA) column via photo-initiated thiol-ene click reaction within 20 min. Finally, three resulting monolithic columns were applied to separate phenolic, anilines and antibiotics mixtures. These mixtures were baseline-separated on the monolith modified with penicillamine (monolith II), exhibiting better selectivity than both pristine monolith I and that modified with ODT (monolith III). Additionally, these columns were further used for separation of tryptic digest of HeLa cells by cLC-MS/MS. The 5071 unique peptides mapped to 2442 proteins were identified from HeLa cells digest on monolith II, which were superior over those on monolith III, but slightly lower than those on monolith I. These results demonstrated that these POSS-containing columns exhibited great separation ability for complex samples.

Binding Isotherms and Time Courses Readily from Magnetic Resonance

Evidence is presented that binding isotherms, simple or biphasic, can be extracted directly from noninterpreted, complex 2D NMR spectra using principal component analysis (PCA) to reveal the largest trend(s) across the series. This approach renders peak picking unnecessary for tracking population changes. In 1:1 binding, the first principal component captures the binding isotherm from NMR-detected titrations in fast, slow, and even intermediate and mixed exchange regimes, as illustrated for phospholigand associations with proteins. Although the sigmoidal shifts and line broadening of intermediate exchange distorts binding isotherms constructed conventionally, applying PCA directly to these spectra along with Pareto scaling overcomes the distortion. Applying PCA to time-domain NMR data also yields binding isotherms from titrations in fast or slow exchange. The algorithm readily extracts from magnetic resonance imaging movie time courses such as breathing and heart rate in chest imaging. Similarly, two-step binding processes detected by NMR are easily captured by principal components 1 and 2. PCA obviates the customary focus on specific peaks or regions of images. Applying it directly to a series of complex data will easily delineate binding isotherms, equilibrium shifts, and time courses of reactions or fluctuations.

Gradient-free microfluidic flow labeling using thin magnetic films and remotely detected MRI

Nuclear Magnetic Resonance (NMR) and Magnetic Resonance Imaging (MRI) may be employed as noninvasive measurements yielding detailed information about the chemical and physical parameters that define microscale flows. Despite these advantages, magnetic resonance has been difficult to combine with microfluidics, largely due to its low sensitivity when detecting small sample volumes and the difficulty of efficiently addressing individual flow pathways for parallel measurements without utilizing large electric currents to create pulsed magnetic field gradients. Here, we demonstrate that remotely-detected MRI (RD-MRI) employing static magnetic field gradients produced by thin magnetic films can be used to encode flow and overcome some of these limitations. We show how flow path and history can be selected through the use of these thin film labels and through the application of synchronized, frequency-selective pulses. This obviates the need for large electric currents to produce pulsed magnetic field gradients and may allow for further application of NMR and MRI experiments on microscale devices.

Radiofrequency microcoils for magnetic resonance imaging and spectroscopy

Small radiofrequency coils, often termed "microcoils", have found extensive use in many areas of magnetic resonance. Their advantageous properties include a very high intrinsic sensitivity, a high (several MHz) excitation and reception bandwidth, the fact that large arrays can fit within the homogeneous volume of the static magnetic field, and the very high resonance frequencies (several GHz) that can be achieved. This review concentrates on recent developments in the construction of single and multiple RF microcoil systems, and new types of experiments that can be performed using such assemblies.

Applications of optically detected MRI for enhanced contrast and penetration in metal

We report quantitative measurements using optically detected magnetic resonance imaging (MRI) for enhanced pH contrast and flow inside porous metals. Using a gadolinium chelate as the pH contrast agent, we show the response is 0.6s(-1) mM(-1) per pH unit at the ambient magnetic field for the pH range 6-8.5. A stopped flow scheme was used to directly measure T(1) relaxation time to determine the relaxivity. Flow profiles and images were obtained for a series of porous metals with different average pore sizes. The signal amplitudes and spatial distributions were compared. A clogged region in one of the samples was revealed using optically detected MRI but not optical imaging or scanning electron microscopy. These applications will significantly broaden the impact of optically detected MRI in chemical imaging and materials research.

Recent advances in the design of organic polymer monoliths for reversed-phase and hydrophilic interaction chromatography separations of small molecules

Owing to their favorable porous structure with pore size distribution shifted towards large flow-through pores, organic polymer monoliths have been mainly employed for the separation of macromolecules in gradient elution liquid chromatography. The absence of significant amounts of small pores with a stagnant mobile phase and the resulting low surface area were considered as the main reason for their poor behavior in the isocratic separation of small molecules. Several recent efforts have improved the separation power of organic polymer monoliths for small molecules offering column efficiency up to tens of thousands of plates per meter. These attempts include optimization of the composition of polymerization mixture, including the variation of functional monomer, the cross-linking monomer, and the porogen solvents mixture, adjustment of polymerization temperature, and time. Additionally, post-polymerization modifications including hypercross-linking and the use of carbon nanostructures showed significant improvement in the column properties. This review describes recent developments in the preparation of organic polymer monoliths suitable for the separation of small molecules in the isocratic mode as well as the main factors affecting the column efficiency.