On-line combination of monolithic immobilized pH gradient-based capillary isoelectric focusing and capillary zone electrophoresis via a partially etched porous interface for protein analysis

Isoelectric point determination by imaged CIEF of commercially available SARS-CoV-2 proteins and the hACE2 receptor

In order to contribute to the scientific research on the severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2), we have investigated the isoelectric points (pI) of several related proteins, which are commercially available: the receptor‐binding domain (RBD) with His‐ and Fc‐tag, the S1 subunit with His‐tag, the S1/S2 subunits with His‐tag and the human angiotensin‐converting enzyme 2 (hACE2) with His‐tag. First, the theoretical pI values, based on the amino acid (AA) sequences of the proteins, were calculated using the ProtParam tool from the Bioinformatics Resource Portal ExPASy. The proteins were then measured with the Maurice imaged CIEF system (native fluorescence detection), testing various measurement conditions, such as different ampholytes or ampholyte mixtures. Due to isoforms, we get sections with several peaks and not just one peak for each protein. The determined pI range for the RBD/Fc is 8.24–9.32 (theoretical pI: 8.55), for the RBD/His it is 7.36–9.88 (8.91) and for the S1/His it is 7.30–8.37 (7.80). The pI range of the S1/S2/His is 4.41–5.87 (no theoretical pI, AA sequence unknown) and for hACE2/His, the determined global range is 5.19–6.11 (5.60) for all experimental conditions chosen. All theoretically derived values were found within these ranges, usually close to the center. Therefore, we consider theoretical values as useful to make predictions about the isoelectric points of SARS‐CoV‐2 proteins. The experimental conditions had only a minor influence on the pI ranges obtained and mainly influenced the peak shapes.

Small Polar Molecules: A Challenge in Marine Chemical Ecology

Due to increasing evidence of key chemically mediated interactions in marine ecosystems, a real interest in the characterization of the metabolites involved in such intra and interspecific interactions has emerged over the past decade. Nevertheless, only a small number of studies have succeeded in identifying the chemical structure of compounds of interest. One reason for this low success rate is the small size and extremely polar features of many of these chemical compounds. Indeed, a major challenge in the search for active metabolites is the extraction of small polar compounds from seawater. Yet, a full characterization of those metabolites is necessary to understand the interactions they mediate. In this context, the study presented here aims to provide a methodology for the characterization of highly polar, low molecular weight compounds in a seawater matrix that could provide guidance for marine ecologists in their efforts to identify active metabolites. This methodology was applied to the investigation of the chemical structure of an algicidal compound secreted by the bacteria Shewanella sp. IRI-160 that was previously shown to induce programmed cell death in dinoflagellates. The results suggest that the algicidal effects may be attributed to synergistic effects of small amines (ammonium, 4-aminobutanal) derived from the catabolization of putrescine produced in large quantities (0.05–6.5 fmol/cell) by Shewanella sp. IRI-160.

Selectivity enhancement in capillary electrophoresis by means of two-dimensional separation or dual detection concepts

For the identification and quantification of analytes in complex samples, highly selective analytical strategies are required. The selectivity of single separation techniques such as gas chromatography (GC), liquid chromatography (LC), or capillary electrophoresis (CE) with common detection principles can be enhanced by hyphenating orthogonal separation techniques but also by using complementary detection systems. In this review, two-dimensional systems containing CE in at least one dimension are reviewed, namely LC-CE or 2D CE systems. Particular attention is paid to the aspect of selectivity enhancement due to the orthogonality of the different separation mechanisms. As an alternative concept, dual detection approaches are reviewed using the common detectors of CE such as UV/VIS, laser-induced fluorescence, capacitively coupled contactless conductivity (C⁴D), electrochemical detection, and mass spectrometry. Special emphasis is given to dual detection systems implementing the highly flexible C⁴D as one detection component. Selectivity enhancement can be achieved in case of complementarity of the different detection techniques.

High-Speed, Comprehensive, Two Dimensional Separations of Peptides and Small Molecule Biological Amines Using Capillary Electrophoresis Coupled with Micro Free Flow Electrophoresis

Two-dimensional (2D) separations are able to generate significantly higher peak capacities than their one-dimensional counterparts. Unfortunately, current hyphenated 2D separations are limited by the speed of the second dimension separation and the consequent loss of peak capacity due to under sampling of peaks as they elute from the first dimension separation. Continuous micro free flow electrophoresis (μFFE) separations eliminate under sampling as a limitation when incorporated as the second dimension of a 2D separation. In the current manuscript we describe the first coupling of capillary electrophoresis (CE) with μFFE to perform 2D CE × μFFE separations. The CE separation capillary was directly inserted into the μFFE separation channel using an edge on interface. Analyte peaks streamed directly into the μFFE separation channel as they migrated off the CE capillary. No complicated injection, valving, or voltage changes were necessary to couple the two separation modes. 2D CE × μFFE generated an ideal peak capacity of 2 592 in a 9 min separation of fluorescently labeled peptides (7.6 min separation window, 342 peaks/min). Data points were recorded every 250-500 ms (>8 data points/peak), effectively eliminating under sampling as a source of band broadening. CE × μFFE generated an ideal peak capacity of 1885 in a 2.7 min separation of fluorescently labeled small molecule bioamines (1.8 min separation window, 1053 peaks/min). Peaks in the 2D CE × μFFE separation of peptides covered 30% of the available separation space, resulting in a corrected peak capacity of 778 (102 peaks/min). The fractional coverage of the 2D CE × μFFE separation of small molecule bioamines was 20%, resulting in a corrected peak capacity of 377 (209 peaks/min).

Trajectory of isoelectric focusing from gels to capillaries to immobilized gradients in capillaries

This review presents the need for replacing gels in 2D separations for proteomics, where speed, high-throughput, and the ability to characterize trace level proteins or small samples are the current desires. The theme of the review is isoelectric focusing, which is a valuable tool because it pre-concentrates proteins in addition to separating with high peak capacity. The review traces the technological progress from gel IEF to CIEF to packed capillaries with immobilized gradients for CIEF. Multiple capillary techniques are progressing toward meeting the current desires, providing extremely high sensitivity with regard to concentration and to small samples, integrated automation, and high peak capacity from multiple dimensions of separation. Capillaries with immobilized pH gradients for CIEF are emerging, which will alleviate interference from ampholytes and improve reproducibility in separation times when this valuable technique can be used as one of the dimensions.

Separation technique for the determination of highly polar metabolites in biological samples

Metabolomics is a new approach that is based on the systematic study of the full complement of metabolites in a biological sample. Metabolomics has the potential to fundamentally change clinical chemistry and, by extension, the fields of nutrition, toxicology, and medicine. However, it can be difficult to separate highly polar compounds. Mass spectrometry (MS), in combination with capillary electrophoresis (CE), gas chromatography (GC), or high performance liquid chromatography (HPLC) is the key analytical technique on which emerging "omics" technologies, namely, proteomics, metabolomics, and lipidomics, are based. In this review, we introduce various methods for the separation of highly polar metabolites.

Microscale 2D separation systems for proteomic analysis

Microscale 2D separation systems have been implemented in capillaries and microfabricated channels. They offer advantages of faster analysis, higher separation efficiency and less sample consumption than the conventional methods, such as liquid chromatography (LC) in a column and slab gel electrophoresis. In this article, we review their recent advancement, focusing on three types of platforms, including 2D capillary electrophoresis (CE), CE coupling with capillary LC, and microfluidic devices. A variety of CE and LC modes have been employed to construct 2D separation systems via sophistically designed interfaces. Coupling of different separation modes has also been realized in a number of microfluidic devices. These separation systems have been applied for the proteomic analysis of various biological samples, ranging from a single cell to tumor tissues.