Statistical and epidemiological data imply temperature sensitivity of the SARS-CoV-2 coronavirus. However, the molecular level understanding of the virus structure at different temperature is still not clear. Spike protein is the outermost structural protein of the SARS-CoV-2 virus which interacts with the Angiotensin Converting Enzyme 2 (ACE2), a human receptor, and enters the respiratory system. In this study, we performed an all atom molecular dynamics simulation to study the effect of temperature on the structure of the Spike protein. After 200 ns of simulation at different temperatures, we came across some interesting phenomena exhibited by the protein. We found that the solvent exposed domain of Spike protein, namely S1, is more mobile than the transmembrane domain, S2. Structural studies implied the presence of several charged residues on the surface of N-terminal Domain of S1 which are optimally oriented at 10-30 • C. Bioinformatics analyses indicated that it is capable of binding to other human receptors and should not be disregarded. Additionally, we found that receptor binding motif (RBM), present on the receptor binding domain (RBD) of S1, begins to close around temperature of 40 • C and attains a completely closed conformation at 50 • C. We also found that the presence of glycan moieties did not influence the observed protein dynamics. Nevertheless, the closed conformation disables its ability to bind to ACE2, due to the burying of its receptor binding residues. Our results clearly show that there are active and inactive states of the protein at different temperatures. This would not only prove beneficial for understanding the fundamental nature of the virus, but would be also useful in the development of vaccines and therapeutics.

Statistical and epidemiological data imply temperature sensitivity of the SARS-CoV-2 coronavirus. However, the molecular level understanding of the virus structure at different temperature is still not clear. Spike protein is the outermost structural protein of the SARS-CoV-2 virus which interacts with the Angiotensin Converting Enzyme 2 (ACE2), a human receptor, and enters the respiratory system. In this study, we performed an all atom molecular dynamics simulation to study the effect of temperature on the structure of the Spike protein. After 200ns of simulation at different temperatures, we came across some interesting phenomena exhibited by the protein. We found that the solvent exposed domain of Spike protein, namely S1, is more mobile than the transmembrane domain, S2. Structural studies implied the presence of several charged residues on the surface of N-terminal Domain of S1 which are optimally oriented at 10-C. Bioinformatics analyses indicated that it is capable of binding to other human receptors and should not be disregarded. Additionally, we found that receptor binding motif (RBM), present on the receptor binding domain (RBD) of S1, begins to close around temperature of 40 C and attains a completely closed conformation at 50 C. The closed conformation disables its ability to bind to ACE2, due to the burying of its receptor binding residues. Our results clearly show that there are active and inactive states of the protein at different temperatures. This would not only prove beneficial for understanding the fundamental nature of the virus, but would be also useful in the development of vaccines and therapeutics.3 Graphical Abstract Highlights: Statistical and epidemiological evidence show that external climatic conditions influence the SARS-CoV infectivity, but we still lack a molecular level understanding of the same. Here, we study the influence of temperature on the structure of the Spike glycoprotein, the outermost structural protein, of the virus which binds to the human receptor ACE2. Results show that the Spike's S1 domain is very sensitive to external atmospheric conditions compared to the S2 transmembrane domain. The N-terminal domain comprises of several solvent exposed charged residues that are capable of binding to human proteins. The region is specifically stable at temperatures ranging around 10-30 C.  The Receptor Binding Motif adopts a closed conformation at 40 C and completely closes at higher temperatures making it unsuitable of binding to human receptors Abbreviations: RBD -receptor binding domain; NTD -N -Terminal Domain; RBMreceptor binding motif; ACE2-Angiotensin Converting enzyme 2

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Separation of CO 2 from gas mixtures is of importance in CO 2 capture from flue gas and in natural gas sweetening. In this paper, we have conducted grand canonical Monte Carlo (GCMC) simulations to study the adsorption of CO 2 , N 2 , and CH 4 and separation of their binary mixtures in mesoporous silica MCM-41 modified by incorporation of the pyrrolidinium-based ionic liquid 1methyl-1-butyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide ([C4PYR] + [TF2N] − ) at two different loadings: ∼21 and 42% by weight, hereinafter referred to as MCM-41-IL1 and MCM-41-IL2, respectively. Although MCM-41-IL1 showed significantly higher adsorption of pure CO 2 than pristine MCM-41, the amounts of pure N 2 and CH 4 adsorbed on MCM-41-IL1 were only slightly higher. Molecular dynamics simulation of pure CO 2 in ionic liquid-loaded MCM-41 models revealed that CO 2 molecules prefer locations near the pore walls as well as in the pore interior around ionic liquid molecules. GCMC simulations of gas mixture adsorption (CO 2 / N 2 and CO 2 /CH 4 ) showed that CO 2 adsorption is highest in MCM-41-IL1 and least in pure MCM-41. The CO 2 /N 2 and CO 2 / CH 4 selectivities at 298.15 K and 1 bar followed the trend MCM-41-IL2 > MCM-41-IL1 > MCM-41 with values for MCM-41-IL2 almost twice those for pure MCM-41. Thus, modifying the mesopores of MCM-41 with ionic liquid can result in significant enhancement in CO 2 adsorption and selectivity.

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