Ab Initio Molecular Dynamics Simulations of the Interaction between Organic Phosphates and Goethite

Deciphering competitive interactions: Phosphate and organic matter binding on goethite through experimental and theoretical insights

The adsorption of phosphorus (P) onto active soil surfaces plays a pivotal role in immobilizing P, thereby influencing soil fertility and the filter function of soil to protect freshwater systems from eutrophication. Competitive anions, such as organic matter (OM), significantly affect the strength of this P-binding, eventually controlling P mobility and release, but surprisingly, these processes are insufficiently understood at the molecular level. In this study, we provide a molecular-level perspective on the influence of OM on P binding at the goethite-water interface using a combined experimental-theoretical approach. By examining the impact of citric acid (CIT) and histidine (HIS) on the adsorption of orthophosphate (OP), glycerol phosphate (GP), and inositol hexaphosphate (IHP) through adsorption experiments and molecular dynamics simulations, we address fundamental questions regarding P binding trends, OM interaction with the goethite surface, and the effect of OM on P adsorption. Our findings reveal the complex nature of P adsorption on goethite surfaces, where the specific OM, treatment conditions (covering the surface with OM or simultaneous co-adsorption), and initial concentrations collectively shape these interactions. P adsorption on goethite exhibits a binding strength increasing in the order of GP < OP < IHP. Crucially, this trend remains consistent across all adsorption experiments, regardless of the presence or absence of OM, CIT, or HIS, and irrespective of the specific treatment method. Notably, OP is particularly susceptible to inhibition by OM, while adsorption of GP depends on specific OM treatments. Despite being less sensitive to OM, IHP shows reduced adsorption, especially at higher initial P concentrations. Of significance is the strong inhibitory effect of CIT, particularly evident when the surface is pre-covered, resulting in a substantial 70 % reduction in OP adsorption compared to bare goethite. The sequence of goethite binding affinity to P and OM underscores a higher affinity of CIT and HIS compared to OP and GP, suggesting that OM can effectively compete with both OP and GP and replace them at the surface. In contrast, the impact of OM on IHP adsorption appears insignificant, as IHP exhibits a higher affinity than both CIT and HIS towards the goethite surface. The coverage of goethite surfaces with OM results in the blocking of active sites and the generation of an unfavorable electric potential and field, inhibiting anion adsorption and consequently reducing P binding. It is noteworthy that electrostatic interactions predominantly contribute more to the binding of P and OM to the surface compared to dispersion interactions.

Expatiating the impact of anthropogenic aspects and climatic factors on long-term soil monitoring and management

This article is an extensive collection of scientific literature related to the impact of fertilizers on soil microbial and enzymatic activity. Due to the significance of technology in quantitative and qualitative evaluation of agricultural production, this is a basic problem for the present and future of mankind, where the scientific data being of utmost importance related to the topic. The comparison, including pedo-enzymological evaluation of minerals along with organic fertilization, highlights significant differences between mineral and organic fertilizers, confirming the superiority of complex mineral-organic fertilization. Enzymatic indicators that describe and define the soil quality resulted from enzymatic activities value and provide valuable information regarding the soil fertility status. Moreover, soil enzyme responds to soil management as well as to environmental pollutants. Changes of environmental conditions and pollutants like heavy metals and other toxic substances result in a shift in the biological activity of the soil. These changes can destabilize the soil system and cause a decrease in the nutrient pools. To ensure the improvement of fertilization techniques, the properties of nanoparticles are exploited that can efficiently release nutrients to plant cells. Numerous researches were performed in order to follow the long-term effects of incorporating nanofertilizers into the soil, obtaining an exhaustive overview of this new technology over the development of sustainable agriculture.

The Binding of Phosphorus Species at Goethite: A Joint Experimental and Theoretical Study

Knowledge of the interaction between inorganic and organic phosphates with soil minerals is vital for improving soil P-fertility. To achieve an in-depth understanding, we combined adsorption experiments and hybrid ab initio molecular dynamics simulations to analyze the adsorption of common phosphates, i.e., orthophosphate (OP), glycerolphosphate (GP) and inositolhexaphosphate (IHP), onto the 100 surface plane of goethite. Experimental adsorption data per mol P-molecule basis fitted to the Freundlich model show the adsorption strength increases in the order GP < OP < IHP, and IHP adsorption being saturated faster followed by GP and OP. Modeling results show that OP and GP form stable monodentate (M) and binuclear bidentate (B) motifs, with B being more stable than M, whereas IHP forms stable M and 3M motifs. Interfacial water plays an important role through hydrogen bonds and proton transfers with OP/GP/IHP and goethite. It also controls the binding motifs of phosphates with goethite. Combining both experimental and modeling results, we propose that the B motif dominates for OP, whereas GP forms M and IHP forms a combination of M and 3M motifs. The joint approach plausibly explains why IHP is the predominant organically bound P form in soil. This study could be considered as a preliminary step for further studies for understanding the mechanisms of how microbes and plants overcome strong IHP–mineral binding to implement the phosphate groups into their metabolism.