Baigorri Roberto, Erro Javier, Urrutia Óscar, Martinez José Manuel, Mandado Marcos, Martín-Pastor Manuel, García-Mina José M
Innovation & Development Department, Timac Agro España S.A., Roullier Group Barrio Feculas s/n 31508 Lodosa Spain
BACh Research Group, Department of Environmental Biology, University of Navarra Irunlarrea No. 1 31008 Pamplona Spain.
RSC Adv. 2019 Aug 16;9(44):25790-25796. doi: 10.1039/c9ra04383g. eCollection 2019 Aug 13.
Phosphate-metal-humic complexes are very relevant in nature due to their crucial role in phosphate availability for plants and microorganisms. Synthetic phosphate-calcium-humic acid (HA) complexes have proven to be efficient sources of available phosphorus for crops. However, the current knowledge about their structure and molecular features is very poor. The structural implications of phosphate interaction with humic binding sites through calcium bridges, in both monocalcium phosphate and dicalcium phosphate is investigated by using molecular modeling, P-NMR, H-NMR and X-ray diffractometry. The conformational changes in the molecular configuration of the humic acid involved in the interaction resulting from the synthetic process is also studied by using HPSEC and synchronous fluorescence. The results obtained allow us to identify the phosphate type in the crystalline phase that is involved in the interaction of humic acid binding sites and the different forms of calcium phosphate. Synchronous fluorescence also shows that whereas the conformational configuration of the HA binding site is only partially affected in the monocalcium phosphate interaction, it changes in the case of dicalcium phosphate showing simpler molecular arrangements. These changes in the molecular conformation of the binding site in HA in solution may influence the biological activity of the humic acid. On the other hand, HPSEC studies show that the humic-calcium-phosphate interaction is accompanied by increases in the humic acid apparent size distribution. This effect is more intense in the case of monocalcium phosphate system probably due the influence of pH.
磷酸盐 - 金属 - 腐殖质络合物在自然界中非常重要，因为它们在植物和微生物获取磷的过程中起着关键作用。合成的磷酸钙 - 腐殖酸（HA）络合物已被证明是作物有效磷的来源。然而，目前关于它们的结构和分子特征的了解非常有限。通过分子建模、P - NMR、H - NMR和X射线衍射法研究了磷酸通过钙桥与腐殖质结合位点相互作用在磷酸一钙和磷酸二钙中的结构影响。还使用高效排阻色谱法（HPSEC）和同步荧光法研究了合成过程中参与相互作用的腐殖酸分子构型的构象变化。获得的结果使我们能够确定参与腐殖酸结合位点相互作用的晶相中的磷酸盐类型以及不同形式的磷酸钙。同步荧光还表明，在磷酸一钙相互作用中，HA结合位点的构象构型仅受到部分影响，而在磷酸二钙的情况下会发生变化，显示出更简单的分子排列。溶液中HA结合位点分子构象的这些变化可能会影响腐殖酸的生物活性。另一方面，HPSEC研究表明，腐殖质 - 钙 - 磷酸盐相互作用伴随着腐殖酸表观尺寸分布的增加。在磷酸一钙体系中这种效应更为强烈，可能是由于pH的影响。
