Characterization of Fe–Leonardite Complexes as Novel Natural Iron Fertilizers

Water-soluble humic substances (denoted by LN) extracted at alkaline pH from leonardite are proposed to be used as complexing agents to overcome micronutrient deficiencies in plants such as iron chlorosis. LN presents oxidized functional groups that can bind Fe²⁺ and Fe³⁺. The knowledge of the environment of Fe in the Fe–LN complexes is a key point in the studies on their efficacy as Fe fertilizers. The aim of this work was to study the Fe²⁺/Fe³⁺ species formed in Fe–LN complexes with ⁵⁷Fe Mössbauer spectroscopy under different experimental conditions in relation to the Fe-complexing capacities, chemical characteristics, and efficiency to provide iron in hydroponics. A high oxidation rate of Fe²⁺ to Fe³⁺ was found when samples were prepared with Fe²⁺, although no well-crystalline magnetically ordered ferric oxide formation could be observed in slightly acidic or neutral media. It seems to be the case that the formation of Fe³⁺–LN compounds is favored over Fe²⁺–LN compounds, although at acidic pH no complex formation between Fe³⁺ and LN occurred. The Fe²⁺/Fe³⁺ speciation provided by the Mössbauer data showed that Fe²⁺–LN could be efficient in hydroponics while Fe³⁺–LN is suggested to be used more effectively under calcareous soil conditions. However, according to the biological assay, Fe³⁺–LN proved to be effective as a chlorosis corrector applied to iron-deficient cucumber in nutrient solution

Atrial Fibrillation: Mechanisms, Therapeutics, and Future Directions

Atrial fibrillation (AF) is the most prevalent cardiac arrhythmia, affecting 1% to 2% of the general population. It is characterized by rapid and disorganized atrial activation leading to impaired atrial function, which can be diagnosed on an EKG by lack of a P-wave and irregular QRS complexes. AF is associated with increased morbidity and mortality and is a risk factor for embolic stroke and worsening heart failure. Current research on AF support and explore the hypothesis that initiation and maintenance of AF require pathophysiological remodeling of the atria, either specifically as in lone AF or secondary to other heart disease as in heart failure-associated AF. Remodeling in AF can be grouped into three categories that include: (i) electrical remodeling, which includes modulation of L-type Ca(2+) current, various K(+) currents and gap junction function; (ii) structural remodeling, which includes changes in tissues properties, size, and ultrastructure; and (iii) autonomic remodeling, including altered sympathovagal activity and hyperinnervation. Electrical, structural, and autonomic remodeling all contribute to creating an AF-prone substrate which is able to produce AF-associated electrical phenomena including a rapidly firing focus, complex multiple reentrant circuit or rotors. Although various remodeling events occur in AF, current AF therapies focus on ventricular rate and rhythm control strategies using pharmacotherapy and surgical interventions. Recent progress in the field has started to focus on the underlying substrate that drives and maintains AF (termed upstream therapies); however, much work is needed in this area. Here, we review current knowledge of AF mechanisms, therapies, and new areas of investigation