Qualitative Alterations of Bacterial Metabolome after Exposure to Metal Nanoparticles with Bactericidal Properties: A Comprehensive Workflow Based on ¹H NMR, UHPLC-HRMS, and Metabolic Databases

Metal nanoparticles (NPs) have proven to be more toxic than bulk analogues of the same chemical composition due to their unique physical properties. The NPs, lately, have drawn the attention of researchers because of their antibacterial and biocidal properties. In an effort to shed light on the mechanism through which the bacteria elimination is achieved and the metabolic changes they undergo, an untargeted metabolomic fingerprint study was carried out on Gram-positive (<i>Staphylococcus aureus</i>) and Gram-negative (<i>Escherichia coli</i>) bacteria species. The ¹H NMR spectroscopy, in conjunction with high resolution mass-spectrometry (HRMS) and an unsophisticated data processing workflow were implemented. The combined NMR/HRMS data, supported by an open-access metabolomic database, proved to be efficacious in the process of assigning a putative annotation to a wide range of metabolite signals and is a useful tool to appraise the metabolome alterations, as a consequence of bacterial response to NPs. Interestingly, not all the NPs diminished the intracellular metabolites; bacteria treated with iron NPs produced metabolites not present in the nonexposed bacteria sample, implying the activation of previously inactive metabolic pathways. In contrast, copper and iron–copper NPs reduced the annotated metabolites, alluding to the conclusion that the metabolic pathways (mainly alanine, aspartate, and glutamate metabolism, beta-alanine metabolism, glutathione metabolism, and arginine and proline metabolism) were hindered by the interactions of NPs with the intracellular metabolites

Stalikas, “Study of the behavior of water-soluble vitamins in HILIC on a diol column

Abstract An effort has been made to investigate the chromatographic behavior and to understand the basic mechanisms in HILIC-based separation of water-soluble vitamins with highly varied properties on a diol column. The water content of the mobile phase is of utmost importance because it directly affects the type and extent of interactions of the solutes with the stationary phase and with the buffered mobile phase. A mixed-mode partitioning-surface adsorption mechanism enables most precise description of their chromatographic retention and separation. The point at which surface adsorption becomes apparent, however, depends on the properties of the solutes on the given stationary phase, and on the presence of buffer salt ions. Adjustment of mobile phase pH and use of different buffer salts can be used to modify electrostatic interactions among the solutes, active silanols, and counter-ions. The role of hydrogen bonding was clarified by substitution of ACN by solvents with moderate to strong hydrogen bonding potential. Analytes which are neutral at the working pH start to interact with the stationary phase when the ACN content is increased to 80%. Negatively charged analytes are adsorbed on the stationary phase when the ACN content is approximately 86%, because augmentation of the counter-ions weakens electrostatic repulsion by the active silanol groups. On the other hand, the electrostatic attraction of thiamine contributes significantly to its retention even when using mobile phases with high water content

Stalikas, “Study of the behavior of water-soluble vitamins in HILIC on a diol column

Abstract An effort has been made to investigate the chromatographic behavior and to understand the basic mechanisms in HILIC-based separation of water-soluble vitamins with highly varied properties on a diol column. The water content of the mobile phase is of utmost importance because it directly affects the type and extent of interactions of the solutes with the stationary phase and with the buffered mobile phase. A mixed-mode partitioning-surface adsorption mechanism enables most precise description of their chromatographic retention and separation. The point at which surface adsorption becomes apparent, however, depends on the properties of the solutes on the given stationary phase, and on the presence of buffer salt ions. Adjustment of mobile phase pH and use of different buffer salts can be used to modify electrostatic interactions among the solutes, active silanols, and counter-ions. The role of hydrogen bonding was clarified by substitution of ACN by solvents with moderate to strong hydrogen bonding potential. Analytes which are neutral at the working pH start to interact with the stationary phase when the ACN content is increased to 80%. Negatively charged analytes are adsorbed on the stationary phase when the ACN content is approximately 86%, because augmentation of the counter-ions weakens electrostatic repulsion by the active silanol groups. On the other hand, the electrostatic attraction of thiamine contributes significantly to its retention even when using mobile phases with high water content

Qualitative Alterations of Bacterial Metabolome after Exposure to Metal Nanoparticles with Bactericidal Properties: A Comprehensive Workflow Based on ¹H NMR, UHPLC-HRMS, and Metabolic Databases

Metal nanoparticles (NPs) have proven to be more toxic than bulk analogues of the same chemical composition due to their unique physical properties. The NPs, lately, have drawn the attention of researchers because of their antibacterial and biocidal properties. In an effort to shed light on the mechanism through which the bacteria elimination is achieved and the metabolic changes they undergo, an untargeted metabolomic fingerprint study was carried out on Gram-positive (<i>Staphylococcus aureus</i>) and Gram-negative (<i>Escherichia coli</i>) bacteria species. The ¹H NMR spectroscopy, in conjunction with high resolution mass-spectrometry (HRMS) and an unsophisticated data processing workflow were implemented. The combined NMR/HRMS data, supported by an open-access metabolomic database, proved to be efficacious in the process of assigning a putative annotation to a wide range of metabolite signals and is a useful tool to appraise the metabolome alterations, as a consequence of bacterial response to NPs. Interestingly, not all the NPs diminished the intracellular metabolites; bacteria treated with iron NPs produced metabolites not present in the nonexposed bacteria sample, implying the activation of previously inactive metabolic pathways. In contrast, copper and iron–copper NPs reduced the annotated metabolites, alluding to the conclusion that the metabolic pathways (mainly alanine, aspartate, and glutamate metabolism, beta-alanine metabolism, glutathione metabolism, and arginine and proline metabolism) were hindered by the interactions of NPs with the intracellular metabolites

Metabolomic Profiling Unveils the Impact of Non-Doped and Heteroatom-Doped Carbon Nanodots on Zebrafish (<i>Danio rerio</i>) Embryos

Recently, concern has been raised over the transport, transformation, and fate of carbon nanodots (CNDs) after their release into the environment. Their toxicity towards organisms and humans has recently been addressed as an important issue. In this study, a metabolomic approach was employed to obtain an insight into the effect of CNDs (either pristine or doped with nitrogen and nitrogen/sulfur) on zebrafish. Embryos were exposed to concentrations corresponding to lethal concentration (LC) LC50 (550, 400, and 150 μg mL−1), LC50/2 (275, 200, and 75 μg mL−1), and LC50/4 (138, 100, and 38 μg mL−1) of the three CNDs (non-doped, N-doped, and N,S-codoped, respectively) to scrutinize the interactions of the CNDs with the larvae. Numerous differences in the metabolic pathways were recorded in all cases. Seven metabolic pathways were detected in the control larvae. When the larvae were exposed to concentrations equal to LC50, LC50/2, and LC50/4 of non-doped CNDs, 12, 12, and 3 metabolic pathways were detected, respectively. In the case of N-doped CNDs, 4, 7, and 4 pathways were detected, while in the case of N,S-codoped CNDs, 8, 5, and 5 pathways were detected when exposed to concentrations of LC50, LC50/2, and LC50/4, respectively. In all cases, certain metabolic pathways were altered while others were either down-regulated or up-regulated. Some of these changes include the activation of alanine, aspartate, and glutamate metabolism, aminoacyl-tRNA biosynthesis, butanoate metabolism, D-glutamine, and D-glutamate metabolism, glutathione metabolism, selenoamino acid metabolism, valine, leucine, and isoleucine degradation pathways. Moreover, the deactivation of starch and sucrose metabolism, the glycine, serine, and threonine metabolism, among others, were recorded. Our findings underline the importance to further study the impact of CNDs on marine organisms. As zebrafish has been shown to share many similarities with humans in bioprocesses and genome, it can be assumed that CNDs may also pose a threat to human health

Melamine Sponge Functionalized with Urea-Formaldehyde Co-Oligomers as a Sorbent for the Solid-Phase Extraction of Hydrophobic Analytes

A new procedure for the functionalization of melamine sponge (MeS) with urea-formaldehyde (UF) co-oligomers is put forward. The procedure differs from the typical synthesis of the UF co-polymer, as it employs a base-catalyzed condensation step at certain concentrations of urea and formaldehyde. The produced melamine-urea-formaldehyde (MUF) sponge cubes are hydrophobic, despite the presence of hydrophilic groups in the oligomers. The MUF sponge developed herein is used as a sorbent for the solid-phase extraction of 10 analytes, from 6 different classes (i.e., non-steroidal anti-inflammatory drugs, benzophenones, parabens, phenols, pesticides and musks) and an analytical method is developed for their liquid chromatographic separation and detection. Low limits of quantification (0.03 and 1.0 &mu;g L&minus;1), wide linear ranges and excellent recoveries (92&ndash;100%) are some of the benefits of the proposed procedure. The study of the synthesis conditions of MUF cubes reveals that by altering them the hydrophilic/lipophilic balance of the MUF cubes can be tuned, hinting towards a strong potential for many other applications