An Investigation of the Effect of pH on Micelle Formation by a Glutamic Acid-Based Biosurfactant

Jacob D. Mayer, Robert M. Rauscher, Shayden R. Fritz, Yayin Fang, E. Billiot, F. Billiot, Kevin F. Morris
{"title":"An Investigation of the Effect of pH on Micelle Formation by a Glutamic Acid-Based Biosurfactant","authors":"Jacob D. Mayer, Robert M. Rauscher, Shayden R. Fritz, Yayin Fang, E. Billiot, F. Billiot, Kevin F. Morris","doi":"10.3390/colloids8030038","DOIUrl":null,"url":null,"abstract":"NMR spectroscopy, molecular modeling, and conductivity experiments were used to investigate micelle formation by the amino acid-based surfactant tridecanoic L-glutamic acid. Amino acid-based biosurfactants are green alternatives to surfactants derived from petroleum. NMR titrations were used to measure the monomeric surfactant’s primary and gamma (γ) carboxylic acid pKa values. Intramolecular hydrogen bonding within the surfactant’s headgroup caused the primary carboxylic acid to be less acidic than the corresponding functional group in free L-glutamic acid. Likewise, intermolecular hydrogen bonding caused the micellar surfactant’s γ carboxylic functional group to be less acidic than the corresponding monomer value. The binding of four positive counterions to the anionic micelles was also investigated. At pH levels below 7.0 when the surfactant headgroup charge was −1, the micelle hydrodynamic radii were larger (~30 Å) and the mole fraction of micelle-bound counterions was in the 0.4–0.7 range. In the pH range of 7.0–10.5, the micelle radii decreased with increasing pH and the mole fraction of micelle bound counterions increased. These observations were attributed to changes in the surfactant headgroup charge with pH. Above pH 10.5, the counterions deprotonated and the mole fraction of micelle-bound counterions decreased further. Finally, critical micelle concentration measurements showed that the micelles formed at lower concentrations at pH 6 when the headgroup charge was predominately −1 and at higher concentrations at pH 7 where headgroups had a mixture of −1 and −2 charges in solution.","PeriodicalId":504814,"journal":{"name":"Colloids and Interfaces","volume":null,"pages":null},"PeriodicalIF":0.0000,"publicationDate":"2024-06-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Colloids and Interfaces","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/10.3390/colloids8030038","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
引用次数: 0

Abstract

NMR spectroscopy, molecular modeling, and conductivity experiments were used to investigate micelle formation by the amino acid-based surfactant tridecanoic L-glutamic acid. Amino acid-based biosurfactants are green alternatives to surfactants derived from petroleum. NMR titrations were used to measure the monomeric surfactant’s primary and gamma (γ) carboxylic acid pKa values. Intramolecular hydrogen bonding within the surfactant’s headgroup caused the primary carboxylic acid to be less acidic than the corresponding functional group in free L-glutamic acid. Likewise, intermolecular hydrogen bonding caused the micellar surfactant’s γ carboxylic functional group to be less acidic than the corresponding monomer value. The binding of four positive counterions to the anionic micelles was also investigated. At pH levels below 7.0 when the surfactant headgroup charge was −1, the micelle hydrodynamic radii were larger (~30 Å) and the mole fraction of micelle-bound counterions was in the 0.4–0.7 range. In the pH range of 7.0–10.5, the micelle radii decreased with increasing pH and the mole fraction of micelle bound counterions increased. These observations were attributed to changes in the surfactant headgroup charge with pH. Above pH 10.5, the counterions deprotonated and the mole fraction of micelle-bound counterions decreased further. Finally, critical micelle concentration measurements showed that the micelles formed at lower concentrations at pH 6 when the headgroup charge was predominately −1 and at higher concentrations at pH 7 where headgroups had a mixture of −1 and −2 charges in solution.
研究 pH 值对谷氨酸类生物表面活性剂形成胶束的影响
利用核磁共振光谱、分子建模和电导率实验研究了以氨基酸为基础的表面活性剂十三烷酸-L-谷氨酸的胶束形成。氨基酸基生物表面活性剂是石油表面活性剂的绿色替代品。核磁共振滴定法用于测量单体表面活性剂的伯羧酸和γ (γ) 羧酸 pKa 值。表面活性剂头组中的分子内氢键导致初级羧酸的酸性低于游离 L-谷氨酸中相应官能团的酸性。同样,分子间氢键使胶束表面活性剂的 γ 羧酸官能团的酸性低于相应的单体值。我们还研究了四种阳性反离子与阴离子胶束的结合情况。在 pH 值低于 7.0 时,当表面活性剂头基电荷为-1 时,胶束的流体力学半径较大(约 30 Å),胶束结合的反离子的摩尔分数在 0.4-0.7 之间。在 pH 值为 7.0-10.5 的范围内,胶束半径随着 pH 值的增加而减小,胶束结合反离子的摩尔分数则增加。这些观察结果归因于表面活性剂头组电荷随 pH 值的变化。当 pH 值超过 10.5 时,反离子去质子化,胶束结合反离子的摩尔分数进一步降低。最后,临界胶束浓度测量结果表明,在 pH 值为 6 时,胶束形成的浓度较低,此时头基团的电荷主要为-1;而在 pH 值为 7 时,胶束形成的浓度较高,此时溶液中头基团的电荷混合为-1 和-2。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
求助全文
约1分钟内获得全文 求助全文
来源期刊
自引率
0.00%
发文量
0
×
引用
GB/T 7714-2015
复制
MLA
复制
APA
复制
导出至
BibTeX EndNote RefMan NoteFirst NoteExpress
×
提示
您的信息不完整,为了账户安全,请先补充。
现在去补充
×
提示
您因"违规操作"
具体请查看互助需知
我知道了
×
提示
确定
请完成安全验证×
copy
已复制链接
快去分享给好友吧!
我知道了
右上角分享
点击右上角分享
0
联系我们:info@booksci.cn Book学术提供免费学术资源搜索服务,方便国内外学者检索中英文文献。致力于提供最便捷和优质的服务体验。 Copyright © 2023 布克学术 All rights reserved.
京ICP备2023020795号-1
ghs 京公网安备 11010802042870号
Book学术文献互助
Book学术文献互助群
群 号:481959085
Book学术官方微信