<div><div>Protons play a central role in many chemical reactions in living organisms. In some cases, a proton may be shared between two nearby molecular groups rather than being localized on just one. This phenomenon can strongly influence the properties and reactivity of biomolecules and is important for enzyme function.</div></div><div>Researchers led by Hanns Christian Schewe (IOCB Prague and Heyrovský Institute of the CAS) together with Lukáš Tomaník (UCT Prague and Fritz Haber Institute of the Max Planck Society) have now investigated proton sharing in a range of biologically relevant polycarboxylic acids dissolved in water, including several molecules related to the citric acid cycle (Krebs cycle).Using liquid-jet X-ray photoelectron spectroscopy (LJ-PES), a technique that reveals the chemical environment of atoms in molecules dissolved in water, the team was able to probe the position of protons on an ultrafast time scale. Unlike techniques such as NMR, which provide a time-averaged picture, photoelectron spectroscopy captures the instantaneous distribution of protons and can therefore distinguish more directly between localized and shared states.The results showed significant proton sharing only in maleic acid dissolved in water. In contrast, protons remained mostly localized at individual carboxylic groups in succinic acid, fumaric acid, malic acid, glutaric acid and citric acid. This suggests that proton sharing is not a common feature of these molecules when they are freely dissolved in water.<img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/IOCB_Prague_Cropped_part_of_the_cover_by_Schewe_et_al_with_the_use_of_Nano_Banana_2_0_2_2a408dbeb5.webp" alt="IOCB Prague: Cropped part of the cover by Schewe et al. with the use of Nano Banana 2.0: Full cover by Schewe et al. with the use of Nano Banana 2.0." srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_IOCB_Prague_Cropped_part_of_the_cover_by_Schewe_et_al_with_the_use_of_Nano_Banana_2_0_2_2a408dbeb5.webp 117w," sizes="100vw" width="1620" height="2154">The difference appears to be largely controlled by molecular geometry. In maleic acid, the two carboxylic groups are held close together, creating favorable conditions for proton sharing. More flexible molecules can adopt conformations in which the groups are farther apart, while water molecules form strong hydrogen bonds with them and favor localized protons.However, the situation may be different inside proteins. When a carboxylic acid binds in the active site of an enzyme, its shape and position can be tightly constrained. Such an environment could bring the relevant groups close enough together to promote proton sharing and thereby influence enzymatic reactions.The study highlights an important distinction: proton sharing may be rare in freely hydrated molecules but could become important when biomolecules are held in the right geometry by enzymes. It also demonstrates that LJ-PES is a powerful tool for studying proton behavior in solutions. Its ultrafast and site-specific sensitivity could in future help researchers investigate proton sharing directly in more complex chemical and biological systems.<blockquote><h4>The original article</h4><h4><a target="_blank" rel="noopener noreferrer" href="https://pubs.acs.org/jaaucr/article/6/6/3349/5084661/Proton-Sharing-in-Polycarboxylic-Acids-in-Aqueous">Proton Sharing in Polycarboxylic Acids in Aqueous Solution</a></h4>Lukáš Tomaník, Jiří Tůma, Gunnar Öhrwall, Ronny Golnak, Ngoc Lan Le Nguyen, Bruno Credidio, Harmanjot Kaur, Petr Slavíček, Bernd Winter, H. Christian Schewe<div>JACS Au, 2026, 6, 3349–3355</div><a target="_blank" rel="noopener noreferrer" href="https://doi.org/10.1021/jacsau.6c00377">https://doi.org/10.1021/jacsau.6c00377</a><h6>licenced under <a target="_blank" rel="noopener noreferrer" href="https://creativecommons.org/licenses/by/4.0/">CC-BY 4.0</a></h6></blockquote><h4>Abstract</h4>We investigate proton sharing in biologically relevant polycarboxylic acids in aqueous solutions using liquid-jet X-ray photoelectron spectroscopy. In contrast to techniques that record time-averaged proton positions, like nuclear magnetic resonance, photoelectron spectroscopy captures instantaneous proton distribution due to its ultrafast probing time scale. The method is, therefore, uniquely sensitive to the occurrence of proton sharing in an aqueous environment, as demonstrated here. We only observe significant proton sharing dynamics in maleic acid, where its monoanionic form shows a single, delocalized peak in the carbon 1s spectrum. Conversely, succinic acid, fumaric acid, malic acid, glutaric acid, and citric acid exhibit distinct peaks corresponding to separate, localized COOH and COO– groups, instead of shared protons. Our results reveal that intramolecular proton sharing in water is rather an exception for most biologically relevant polycarboxylic acids. This highlights the importance of enzyme-driven structural changes of polycarboxylic acids associated with proton sharing during metabolic processes.</div>

Proton sharing in polycarboxylic acids in aqueous solution

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Breathomics, Asthma & GC×GC: PH Stefanuto on Fighting the “Proof‑of‑Concept” Trap

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Mestrelab Mnova ElViS software

By integrating Mnova ElViS into your analytical workflows, you can enhance the efficiency and accuracy of your spectroscopic data analysis across a wide range of techniques.

<h4>Visualize, process, analyze and report various electronic and vibrational spectroscopic techniques</h4>Carry out the analysis of various optical spectroscopy data including ultraviolet and visible (UV/Vis), near and mid infrared (NIR/MIR), Raman, fluorescence, and other spectroscopic methods operating in the whole region of wavelength from 100 nm to 100 µm.<h4>Benefits:</h4><ul><li>Spectroscopic processing and analysis of ultraviolet and visible (UV/Vis), near and mid infrared (NIR/MIR), Raman, fluorescence methods.</li><li>Vendor and Operating System agnostic, supports most data file formats.</li><li>Wide range of processing functions, including a dynamic processing template.</li><li>Manual and automatic peak picking analysis.</li><li>Data Analysis of stacked/arrayed spectra.&nbsp;</li></ul><h4>Features:</h4><h5>PLS-Based Baseline Correction Tool (IarPLS)</h5>To improve the processing of electronic and vibrational spectroscopy data, Mnova 15 introduces an enhanced PLS-based baseline correction tool, IarPLS (penalized-least-squares based). It now features an automatic button to compute the near-optimal asymmetry parameter.&nbsp;<img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/Mestrelab_Research_Mnova_EI_Vis_PLS_Based_Baseline_Correction_Tool_Iar_PLS_f3180f6927.webp" alt="Mestrelab Research: Mnova EIVis - PLS-Based Baseline Correction Tool (IarPLS)." srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_Mestrelab_Research_Mnova_EI_Vis_PLS_Based_Baseline_Correction_Tool_Iar_PLS_f3180f6927.webp 245w," sizes="100vw" width="1500" height="845"><h5>Normalization Processing Modes</h5>Three Normalization Processing modes, namely Largest Peak, Integral and Vector Length are available in Mnova 15. These three features aim to simplify the baseline correction process, streamline your workflow, and provide a rapid method for normalizing data to address quantitative issues.&nbsp;<img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/Mestrelab_Research_Mnova_EI_Vis_Normalization_Processing_Modes_675cb7c407.webp" alt="Mestrelab Research: Mnova EIVis - Normalization Processing Modes" srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_Mestrelab_Research_Mnova_EI_Vis_Normalization_Processing_Modes_675cb7c407.webp 245w," sizes="100vw" width="1500" height="844"><h5>Electronic and Vibrational Spectroscopies supported file formats</h5>Mnova ElViS supports the most frequently used data file formats for these analytical techniques, including import and export of single and multi-column matrix-like spectra (i.e., ASCII XY and XYY, as .txt or .csv files). Supported formats include SPC (Galactic), JCAMP-DX, OPUS (Bruker), SPA and SPG (Omnic), Perkin Elmer's .sp files, and ASCII (XY and XYY).<img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/Mestrelab_Research_Mnova_EI_Vis_Electronic_and_Vibrational_Spectroscopies_supported_file_formats_bb6afc3eab.webp" alt="Mestrelab Research: Mnova EIVis - Electronic and Vibrational Spectroscopies supported file formats" srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_Mestrelab_Research_Mnova_EI_Vis_Electronic_and_Vibrational_Spectroscopies_supported_file_formats_bb6afc3eab.webp 245w," sizes="100vw" width="1500" height="910"><h5>Manual &amp; automatic spectral analysis</h5>Mnova ElViS provides both manual and automatic peak picking, offering flexibility and convenience in your spectral analysis. It also features advanced tools for the analysis of stacked or arrayed spectra, ensuring thorough data evaluation and interpretation for all your spectral needs.&nbsp;<img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/Mestrelab_Research_Mnova_EI_Vis_Manual_and_automatic_spectral_analysis_e24a19a151.webp" alt="Mestrelab Research: Mnova EIVis - Manual &amp; automatic spectral analysis" srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_Mestrelab_Research_Mnova_EI_Vis_Manual_and_automatic_spectral_analysis_e24a19a151.webp 240w," sizes="100vw" width="940" height="611"><h5>Main processing features</h5>Mnova ElViS comes with a range of useful processing features, including Multiplicative Scatter Correction, Probabilistic Quotient Normalization, Baseline correction (both automatic IarPLS and tailored Multipoint Baseline Correction), several smoothing techniques (such as Savitzky-Golay, Nonlocal Means, Exponential), normalization and Standard Normal Variate (SNV), derivatives, and units conversion between absorbance and transmittance. <img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/Mestrelab_Research_Mnova_EI_Vis_Main_processing_features_bc6eb64b99.webp" alt="Mestrelab Research: Mnova EIVis - Main processing features" srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_Mestrelab_Research_Mnova_EI_Vis_Main_processing_features_bc6eb64b99.webp 245w," sizes="100vw" width="1074" height="581">

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Proton sharing in polycarboxylic acids in aqueous solution

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