key: cord-0879341-djdn5kp7 authors: Joonaki, Edris; Hassanpouryouzband, Aliakbar; Heldt, Caryn L.; Areo, Oluwatoyin title: Surface Chemistry Can Unlock Drivers of Surface Stability of SARS-CoV-2 in Variety of Environmental Conditions date: 2020-08-06 journal: Chem DOI: 10.1016/j.chempr.2020.08.001 sha: 1df06d8f8e8b4b7292a570158c6481fa1ff0ed8b doc_id: 879341 cord_uid: djdn5kp7 Summary The surface stability and resulting transmission of the SARS-CoV-2, specifically in indoor environments, have been identified as a potential pandemic challenge requiring investigation. This novel virus can be found on various surfaces in contaminated sites such as clinical places, however, the behaviour and molecular interactions of the virus with respect to the surfaces are poorly understood. Regarding this, the virus adsorption onto solid surfaces can play a critical role in transmission and survival in various environments. In this article, firstly an overview of existing knowledge concerning viral spread, molecular structure of SARS-CoV-2, and the virus surface stability is presented. Then, we highlight potential drivers of the SARS-CoV-2 surface adsorption and stability in various environmental conditions. This theoretical analysis shows that different surface and environmental conditions including temperature, humidity, and pH are crucial considerations in building fundamental understanding of the virus transmission and thereby improving safety practices. glycoprotein exhibits ~76% amino acid sequence identity with the SARS-CoV S (Urbani strain) and ~80% identity with S proteins of bat SARSr-CoV ZXC21 and ZC45 1, 2 . CoV S glycoproteins form club-shaped trimers and decorate the viral membrane 3 Investigations of the stability of both SARS-CoV-2 and SARS-CoV-1 in air and on different solid surfaces including stainless steel, plastic, copper, and cardboard have calculated their persistence kinetics utilising a Bayesian regression model 5 . It has been shown that SARS-CoV-2 was more stable on plastic and stainless-steel surfaces compared to copper and cardboard pieces, and the presence of virus was detected up to ~72 hours on certain solid surfaces. The longest persistence of viability for SARS-CoV-2 was found to be on stainless steel and plastic, which showed low level viability after 72 hours. No viable SARS-CoV-2 was detected after ~4 and ~24 hours on copper and cardboard, respectively. After 3 hours, viable virus was still detected in aerosols. These experimental data imply J o u r n a l P r e -p r o o f that fomite transmission of SARS-CoV-2 is likely, as the virus can stay viable and infectious for hours up to several days on solid surfaces. Generally, some viruses can retain their activities and transmission in the environment for a long period of time, possibly owing to the adsorption process on surfaces 6, 7 . It can be inferred that building a fundamental understanding of the molecular interactions between viruses, i.e. the outer surface of proteins, and solid surfaces is crucial for controlling environmental transmission and designing removal processes and treatment strategies. The quantity of adsorbed virus is influenced by multiple factors, including characteristics of the virus outer surface proteins such as surface charge, size, stability and steric conformation 8 . These are properties of the amino acid composition and posttranslational modifications such as addition of carbohydrate moieties 9 . Likewise, substrate surface chemistry and environmental conditions are also key. Therefore, to determine the ability of the virus to adsorb to a surface, both the virus and the surface need to be well characterised and an understanding of how these change with environmental conditions is key. Viruses adsorb to surfaces through two main mechanisms, van der Waals (mainly mineral surfaces 10 ) and more importantly electrostatic interactions (charged surfaces in the presence of ions/not neutral pH [11] [12] [13] ). These two forces dictate the adsorption of viruses to surfaces. While the interplay between these two forces is difficult to separate, indications of the interactions can be determined from past data. Viruses tend to be more hydrophobic than proteins 14 , thus they are attracted to metal surfaces due to mainly van der Waals interactions as well as hydrophobic effects 15 . However, their ability to maintain the virus viability and remain infectious is more of a function of the humidity and temperature 16 , thus the surface energy of the water molecules plays a large role in the interaction between a virus particle and a surface. SARS-CoV-2 virions can be adsorbed onto metal surfaces (e.g. gold, stainless steel) in addition to hydroxyl functional group-and oxygen-containing substrates (e.g. wood, cotton, paper, glass) depending on the surface chemistry and environmental conditions (e.g. bulk fluid pH, surface charge, The functionality of viruses is not only based on their host cell but also on the different environments faced before and during the transmission process 26 . Coronaviruses have been shown to have different inactivation kinetics at different humidities 27 . Therefore, an understanding of the effect of humidity on surface stability and adsorption of this novel virus is crucial. Water molecules in the liquid phase condense from its vapor phase on various surfaces (e.g. between virus particles and solid substrates) and create liquid bridges with a curvature which is related to the relative humidity "h" expressed by the Kelvin equation 28 (eq. 1). When the solid surfaces are fixed in one dimension, as for structures with a high aspect ratio, the interface curvature radii "r" is determined by: where γ is the water surface tension, V m is the water molar volume, R is the gas constant, T is the temperature. The water roundel radius |r| increments with h and would be infinite at full hydration with relative humidity of 100%. On the water-coated surfaces, the virus particles would establish strong interactions with the hydrophilic surface in the presence of a thin film water layer, mainly through hydrogen bonding 29 between water and the virus outer surface protein molecules. Water molecules can also fill the gaps between the virus particles that are spaced closer than the |r| value defined by the relative humidity. On hydrophobic surfaces, the roundel expands less. Therefore, a thin layer of water can be created According to eq. 1, the water roundel radii |r| decreases as temperature increases, which means that at higher temperatures the described complexes and molecular interactions are disturbed, lower water bridging would occur, and a reduced quantity of virus would be adsorbed onto solid surfaces. This theoretical analysis may explain previous observations 27 that higher temperature inactivates coronaviruses on stainless steel. In low temperature environments, the enveloped virions stay infectious for number of days as denoted in laboratory experiments 27 . Humans lungs acting as reservoirs of respiratory viral infections can disperse microdroplets through sneezing and coughing, and the virions can even be exhaled during the speaking and breathing [40] [41] [42] . The bigger virus-laden microdroplets precipitate and adsorb onto the solid surface, however, the water contained within these virus-laden microdroplets can vaporise and form residues as solid phase or droplet nuclei at higher temperature conditions 16, 43 (Figure 3c ). It is worth noting that conditions of too high humidity can create a greater water network around the virus 44 , thus providing interactions with the proteins and the lipid bilayer that promote degradation. As the temperature increases, the movement of the water molecules increase and therefore also promote interaction and degradation. Atomic Force Microscopy (AFM) and AFM-based methods including AFM-infrared-spectroscopy (AFM-IR) are powerful techniques for characterisation of a wide range of biological species and can help us to understand molecular interactions that occur at viral interfaces 45 . They can monitor the molecular interactions among the biomolecules including protein-protein interaction, antibodyantigen interaction 46 , and ligand-receptor interactions 47 without disrupting the virion. Nanoindentation measures the rupture force of a virus capsid under force and gives information on the chemical bond strength between viral capsid proteins 48 . To understand the chemical force between a virus particle and a cell, AFM tips have been functionalized with a single viral particle and then used to probe the interaction of the probe and a cell 49 . AFM can also be used to measure how viral chemistry changes in different liquid environments 45 . A practical example of using AFM technique for studying of interactions of an enveloped virus with a solid surface is presented in Figure 4 . In this perspective article, we have highlighted the adsorption characteristics and molecular interactions of the SARS-CoV-2 outer surface proteins on solid surfaces from different points of view which is critical to understanding the virus transmission process and taking necessary actions to tackle it. As discussed, some important factors influencing the virus adsorption phenomenon include: surface active moieties of the viral proteins, hydrophilic/hydrophobic characteristics of the solid surface, pH of the bulk fluid, relative humidity, and temperature of the environment. Our theoretical analysis throughout this study has demonstrated that the SARS-CoV-2 can be adsorbed onto surfaces and remain stable within a range of pH values from acidic to basic environments at moderate temperature. Based on the Kelvin equation, it is expected that the SARS-CoV-2 would be less stable in higher temperature conditions. Accordingly, it is anticipated that the rate of transmission and infection will be lower during the summer months. Further experimental research studies on this topic are required to confirm our hypothesis and propositions we have made. The preservation of the virus shape and structure after condensation/evaporation processes in the air and/or water and the viral electrostatic surface properties of this new virus should also be explored. Moreover The authors declare no competing interests. Structure, function, and antigenicity of the SARS-CoV-2 spike glycoprotein Structural basis for human coronavirus attachment to sialic acid receptors Chemistry and Biology of SARS-CoV-2. 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