Analysis of intracellular α-keto acids by HPLC with fluorescence detection

Novel cathodic and anodic dual-emitting electrochemiluminescence of Ru(bpy)32+/α-keto acid system

Novel cathodic and anodic dual-emitting electrochemiluminescence (ECL) of Ru(bpy)32+ and α-keto acids system are studied for the first time. Based on their cathodic and anodic ECL intensity, α-keto acids including oxalate, glyoxylic acid, pyruvic acid, and phenylglyoxylic acid can be directly sensitively detected. The limits of detection (LOD) of oxalate, glyoxylic acid, pyruvic acid, and phenylglyoxylic acid are 31.25 nM, 23.26 µM, 36.36 µM, and 18.52 µM, respectively. Possible mechanism of ECL produced is also proposed. Electrochemical results show that the reduction of oxygen at the cathode to produce ·OH is a vital step for cathodic and anodic dual-emitting ECL. Furthermore, using the enhancement strategy of S2O82-/Ag+ as coreactant accelerators is proposed considering that decarboxylation of α-keto acids to produce acyl radical can be achieved via S2O82- or Ag+. Using the S2O82-/Ag+ enhancement strategy, the LOD of oxalate, glyoxylic acid, pyruvic acid, and phenylglyoxylic acid are improved and are 2.12 nM, 0.37 µM, 3.23 µM, and 0.28 µM, respectively. Coreactants of Ru(bpy)32+ with dual-emitting ECL are expanded, which includes additional substances with organic carboxylic acid characterized by the keto group in α-position. It also provides an effective way to enhance ECL and improve sensitivity. More importantly, cathodic and anodic dual-emitting ECL greatly improves the selectivity.

Improvement of an Automated Sample Injection System for Pillar Array Columns to Increase Analytical Reproducibility

In our previous study, we developed an automatic sample injection system for pillar array columns for quantitative analysis. An autosampler was used to maintain a constant sample injection volume. However, the sample was diluted during injection using the autosampler, thus deteriorating the analytical reproducibility. In this study, we have substituted the autosampler with a syringe pump to overcome the abovementioned problem and improve the system. Sample dilution was avoided by filling the entire capillary with the sample at a constant rate. This improved system also increased the analytical reproducibility. In the previous system, the relative standard deviation (RSD) exceeded 17% of the peak height for coumarin dyes. In contrast, the improved system decreased the RSD to the range 1.2–1.8%. The analytical reproducibility was evaluated by using five types of amino acids. The RSD of each peak height was within 3.0%, confirming good reproducibility. These results indicate that the sample injection method developed in this study can be applied to biological sample analyses as a simple quantitative analysis method for pillar array columns.

A new visual and stable fluorescent Cu-MOF as a dual-function sensor for glyphosate and Cr2O72−

A new visual and stable Cu-MOF as a dual-function sensor with high sensitivity for the detection of glyphosate and Cr2O72−.

Fast analysis using pillar array columns: Quantification of branched-chain α-keto acids in human plasma samples

Branched-chain α-keto acids (BCKAs, namely, α-ketoisovaleric acid (KIV), α-ketoisocaproic acid (KIC), and α-keto-β-methylvaleric acid (KMV)) are related to many diseases such as myeloid leukemia, liver cancer, and diabetes mellitus. A rapid quantitative analytical method for BCKAs using pillar array columns was developed. α-Keto acids were labeled with 1,2-diamino-4,5-methylenedioxybenzene (DMB), followed by their separation on octadecylsilane-treated pillar array columns with MeOH/H₂O as the mobile phase. Five DMB-labelled α-keto acids including the internal standard were separated in 160 s. The lower limits of quantification for DMB-α-keto acids were 2-5 μM. The intra- and interday precisions were 2.9-6.6 % and 5.2-10.7 %, respectively. The developed method was applied to BCKA quantification in human plasma samples; KIV, KIC, and KMV concentrations were determined to be 13.8, 24.2, and 15.2 μM, respectively. The method realized rapid, sensitive, and precise analysis of BCKAs and can be applied for clinical diagnosis.

Identification of Core Regulatory Genes and Metabolic Pathways for the n-Propanol Synthesis in Saccharomyces cerevisiae

The n-propanol produced by Saccharomyces cerevisiae has a remarkable effect on the taste and flavor of Chinese Baijiu. The n-propanol metabolism-related genes were deleted to evaluate the role in the synthesis of n-propanol to ascertain the key genes and pathways for the production of n-propanol by S. cerevisiae. The results showed that CYS3, GLY1, ALD6, PDC1, ADH5, and YML082W were the key genes affecting the n-propanol metabolism in yeast. The n-propanol concentrations of α5ΔGLY1, α5ΔCYS3, and α5ΔALD6 increased by 121.75, 22.75, and 17.78%, respectively, compared with α5. The n-propanol content of α5ΔPDC1, α5ΔADH5, and α5ΔYML082W decreased by 24.98, 8.35, and 8.44%, respectively, compared with α5. The contents of intermediate metabolites were measured, and results showed that the mutual transformation of glycine and threonine in the threonine pathway and the formation of propanal from 2-ketobutyrate were the core pathways for the formation of n-propanol. Additionally, YML082W played important role in the synthesis of n-propanol by directly producing 2-ketobutyric acid through l-homoserine. This study provided valuable insights into the n-propanol synthesis in S. cerevisiae and the theoretical basis for future optimization of yeast strains in Baijiu making.

Liquid-Chromatographic Methods for Carboxylic Acids in Biological Samples

Carboxyl-bearing low-molecular-weight compounds such as keto acids, fatty acids, and other organic acids are involved in a myriad of metabolic pathways owing to their high polarity and solubility in biological fluids. Various disease areas such as cancer, myeloid leukemia, heart disease, liver disease, and lifestyle diseases (obesity and diabetes) were found to be related to certain metabolic pathways and changes in the concentrations of the compounds involved in those pathways. Therefore, the quantification of such compounds provides useful information pertaining to diagnosis, pathological conditions, and disease mechanisms, spurring the development of numerous analytical methods for this purpose. This review article addresses analytical methods for the quantification of carboxylic acids, which were classified into fatty acids, tricarboxylic acid cycle and glycolysis-related compounds, amino acid metabolites, perfluorinated carboxylic acids, α-keto acids and their metabolites, thiazole-containing carboxylic acids, and miscellaneous, in biological samples from 2000 to date. Methods involving liquid chromatography coupled with ultraviolet, fluorescence, mass spectrometry, and electrochemical detection were summarized.