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Deprotonation and protonation of humic acids as a strategy for the technological development of pH-responsive nanoparticles with fungicidal potential

机译：腐殖酸的去质子化和质子化作为具有杀真菌潜力的pH响应纳米颗粒技术开发的策略

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Humic acids (HAs) are macromolecules of undefined compositions that vary with origin, the process by which they are obtained and functional groups present in their structure, such as quinones, phenols, and carboxylic acids. In addition to agriculture, there is an increased interest in HAs due to their important pharmacological effects. However, HAs are not readily soluble in water at physiological pH, which may limit their bioavailability. Although primary aggregation forms non-uniform pseudo-micelles, the presence of ionisable groups in the HA molecule makes pH an environmental stimulus for controlled aggregation and precipitation. The aim of this work was to induce HA deprotonation and protonation, without compromising their colloidal dispersion, by means of pH changes as a strategy to produce nanoparticles. Deprotonation and protonation were achieved by treating HAs with sodium hydroxide and acetic acid, respectively, at various concentrations. Non pH-treated HAs at the same concentrations were used as control. The evolution of the treatments was monitored by pH changes in bulk solutions as a function of time. At equilibrium, the conformation of the colloidal structures was characterised by the predominant mean diameter, polydispersity index and absorbance of the solutions. The zeta potential was also measured in protonation assays. Moreover, the fungicidal activity of the nanoparticles was evaluated on the mycelial growth of three fungal genera. The results showed the pH decrease or increment as a function of the balance between hydroxyl and carboxyl groups and of the diffusion rate inside the structures. Deprotonation followed by protonation produced nanosized (100-200 nm), electrostatically stable (-30 mV) and pH-responsive particles with a polydispersity index <0.5. The protonated nanoparticles significantly inhibited (P <= 0.05) the mycelial growth of Candida albicans in vitro, when compared with control, and the fungicidal activity was dose-dependent. No activity was observed for the deprotonated HAs nanoparticles. These results show that deprotonation followed by protonation is an easy and useful strategy for the controlled production of HA nanoparticles, which exhibit a tendency to elicit fungicidal effects, with potential to develop new classes of cosmetics and pharmaceuticals. (C) 2016 Elsevier B.V. All rights reserved.
机译：腐殖酸（HAs）是不确定成分的大分子，其随来源，获得它们的过程以及结构中存在的官能团（例如醌，苯酚和羧酸）而异。除农业外，由于HA具有重要的药理作用，因此人们对其也越来越感兴趣。但是，HA在生理pH值下不易溶于水，这可能会限制其生物利用度。尽管初级聚集形成不均匀的假胶束，但HA分子中可电离基团的存在使pH成为控制聚集和沉淀的环境刺激。这项工作的目的是通过改变pH值来诱导HA去质子化和质子化，而不会损害其胶体分散性，以此作为生产纳米颗粒的策略。通过分别用不同浓度的氢氧化钠和乙酸处理HA，可以实现去质子化和质子化。相同浓度的未经pH处理的HA用作对照。通过本体溶液中pH随时间的变化来监测处理的演变。在平衡时，胶体结构的构象以溶液的主要平均直径，多分散指数和吸光度为特征。在质子化测定中也测量了ζ电势。此外，对三种真菌属的菌丝体生长评估了纳米颗粒的杀真菌活性。结果表明，pH降低或升高是羟基和羧基之间的平衡以及结构内部扩散速率的函数。去质子化然后质子化产生了纳米级（100-200 nm），静电稳定（-30 mV）和多分散指数<0.5的pH响应颗粒。与对照相比，质子化的纳米颗粒在体外显着抑制（P <= 0.05）白色念珠菌的菌丝体生长，并且杀真菌活性是剂量依赖性的。对于去质子化的HAs纳米颗粒没有观察到活性。这些结果表明，去质子化然后质子化是控制HA纳米粒子生产的一种简单而有用的策略，HA纳米粒子具有引起杀菌作用的趋势，并有可能开发新型化妆品和药物。 （C）2016 Elsevier B.V.保留所有权利。

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