Robert Robergs , Bridgette O'Malley , Sam Torrens , Jason Siegler
{"title":"The missing hydrogen ion, part-1: Historical precedents vs. fundamental concepts","authors":"Robert Robergs , Bridgette O'Malley , Sam Torrens , Jason Siegler","doi":"10.1016/j.smhs.2023.10.008","DOIUrl":null,"url":null,"abstract":"<div><p>The purpose of this review and commentary was to provide an historical and evidence-based account of organic acids and the biochemical and organic chemistry evidence for why cells do not produce metabolites that are acids. The scientific study of acids has a long history dating to the 16<sup>th</sup> and 17<sup>th</sup> centuries, and the definition of an acid was proposed in 1884 as a molecule that when in an aqueous solution releases a hydrogen ion (H<sup>+</sup>). There are three common ionizable functional groups for molecules classified as acids: 1) the carboxyl group, 2) the phosphoryl group and 3) the amine group. The propensity by which a cation will associate or dissociate with a negatively charged atom is quantified by the equilibrium constant (<em>K</em><sub>eq</sub>) of the dissociation constant (<em>K</em><sub>d</sub>) of the ionization (K<sub>eq</sub> = <em>K</em><sub>d</sub>), which for lactic acid (HLa) vs. lactate (La<sup>-</sup>) is expressed as: <span><math><mrow><msub><mi>K</mi><mrow><mi>e</mi><mi>q</mi></mrow></msub><mo>=</mo><msub><mi>K</mi><mi>d</mi></msub><mo>=</mo><mfrac><mrow><mrow><mo>[</mo><msup><mi>H</mi><mo>+</mo></msup><mo>]</mo></mrow><mspace></mspace><mrow><mo>[</mo><msup><mrow><mi>L</mi><mi>a</mi></mrow><mo>−</mo></msup><mo>]</mo></mrow></mrow><mrow><mo>[</mo><mrow><mi>H</mi><mi>L</mi><mi>a</mi></mrow><mo>]</mo></mrow></mfrac><mo>=</mo></mrow></math></span> 4 677.351 4 (ionic strength = 0.01 Mol⋅L<sup>-1</sup>, T = 25 °C). The negative log<sub>10</sub> of the dissociation pK<sub>d</sub> reveals the pH at which half of the molecules are ionized, which for HLa = 3.67. Thus, knowing the pK<sub>d</sub> and the pH of the solution at question will reveal the extent of the ionization vs. acidification of molecules that are classified as acids.</p></div>","PeriodicalId":33620,"journal":{"name":"Sports Medicine and Health Science","volume":"5 4","pages":"Pages 336-343"},"PeriodicalIF":2.3000,"publicationDate":"2023-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S266633762300080X/pdfft?md5=c3708d748600204b46935ae222b653f1&pid=1-s2.0-S266633762300080X-main.pdf","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Sports Medicine and Health Science","FirstCategoryId":"1085","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S266633762300080X","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"SPORT SCIENCES","Score":null,"Total":0}
引用次数: 0
Abstract
The purpose of this review and commentary was to provide an historical and evidence-based account of organic acids and the biochemical and organic chemistry evidence for why cells do not produce metabolites that are acids. The scientific study of acids has a long history dating to the 16th and 17th centuries, and the definition of an acid was proposed in 1884 as a molecule that when in an aqueous solution releases a hydrogen ion (H+). There are three common ionizable functional groups for molecules classified as acids: 1) the carboxyl group, 2) the phosphoryl group and 3) the amine group. The propensity by which a cation will associate or dissociate with a negatively charged atom is quantified by the equilibrium constant (Keq) of the dissociation constant (Kd) of the ionization (Keq = Kd), which for lactic acid (HLa) vs. lactate (La-) is expressed as: 4 677.351 4 (ionic strength = 0.01 Mol⋅L-1, T = 25 °C). The negative log10 of the dissociation pKd reveals the pH at which half of the molecules are ionized, which for HLa = 3.67. Thus, knowing the pKd and the pH of the solution at question will reveal the extent of the ionization vs. acidification of molecules that are classified as acids.