Virus Capsid Modifications Accompanying Inactivation during Iron Electrocoagulation Revealed by Proteomics, Infrared Spectroscopy, and Molecular Modeling

Society's drinking water needs are increasingly met by reusing municipal wastewater, necessitating high virus Log₁₀ Reduction Values (LRVs). Concurrently, electrified processes are gaining prominence for water/wastewater treatment. Herein, we report that electrocoagulation with a low-carbon steel anode and graphite cathode at pH 6.5 and 5.5 and iron dose of 20 mg/L reduced the MS2 coliphage below detection limits (LRVs <b>≳</b>6.7) in just 11.5 min. Matrix Assisted Laser Desorption Ionization-Time-of-Flight Mass Spectrometry (MALDI-TOF-MS) of electrocoagulated viruses revealed single, double, and triple oxygen adducts and a negative mass shift peak in its coat protein without cleavage/scission. Density functional theory calculations coupled with computational spatial interaction mapping evidenced the formation of the quintet ferryl ion-cysteine 46 cluster. Hence, inactivation appears to have been accompanied by nonproteolytic capsid damages induced by reactive oxygen species (ROS). Evidence also pointed to possible ROS interactions with arginine 49 and tryptophan 32 residues. The <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mfrac><mml:mrow><mml:mi>α</mml:mi><mml:mo>-</mml:mo><mml:mrow><mml:mi>h</mml:mi><mml:mi>e</mml:mi><mml:mi>l</mml:mi><mml:mi>i</mml:mi><mml:mi>x</mml:mi></mml:mrow></mml:mrow><mml:mrow><mml:mi>β</mml:mi><mml:mo>-</mml:mo><mml:mrow><mml:mi>s</mml:mi><mml:mi>h</mml:mi><mml:mi>e</mml:mi><mml:mi>e</mml:mi><mml:mi>t</mml:mi></mml:mrow></mml:mrow></mml:mfrac></mml:math> ratio of viral protein secondary structures quantified by deconvoluting the amide I region of infrared spectra strongly and negatively correlated with inactivation, carbonyl group content, and MALDI-TOF-MS-derived protein alterations. Hence, iron electrocoagulation achieved high virus LRVs by removal (through enmeshment) and inactivation (via specific ROS interactions with coat protein residues).