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  • Molecular Architecture and Helicity of Bacterial Amyloid Nanofibers: Implications for the Design of Nanoscale Antibiotics

    work
    Creator:
    Elvati, Paolo, Luyet, Chloe, Wang, Yichun, Liu, Changjiang, VanEpps, J. Scott, Kotov, Nicholas A., and Violi, Angela
    Description:
    Amyloid nanofibers are abundant in microorganisms and are integral components of many biofilms, serving various purposes, from virulent to structural. Nonetheless, the precise characterization of bacterial amyloid nanofibers has been elusive, with incomplete and contradicting results. The present work focuses on the molecular details and characteristics of PSMa1-derived functional amyloids present in Staphylococcus aureus biofilms, using a combination of computational and experimental techniques, to develop a model that can aid the design of compounds to control amyloid formation. Results from molecular dynamics simulations, guided and supported by spectroscopy and microscopy, show that PSMa1 amyloid nanofibers present a helical structure formed by two protofilaments, have an average diameter of about 12 nm, and adopt a left-handed helicity with a periodicity of approximately 72 nm. The chirality of the self-assembled nanofibers, an intrinsic geometric property of its constituent peptides, is central to determining the fibers' lateral growth.
    Keyword:
    molecular self-assembly, computational nanotechnology, nanobiotechnology, and structural properties
    Citation to related publication:
    Paolo Elvati, Chloe Luyet, Yichun Wang, Changjiang Liu, J. Scott VanEpps, Nicholas A. Kotov, and Angela Violi ACS Applied Nano Materials 2023 6 (8), 6594-6604 DOI: 10.1021/acsanm.3c00174
    Discipline:
    Engineering and Science

  • On the growth of Si nanoparticles in non-thermal plasma: physisorption to chemisorption conversion

    work
    Creator:
    Shi, Xuetao, Elvati, Paolo, and Violi, Angela
    Description:
    Non-thermal plasma systems offer unique opportunities in the fields of bio-imaging, drug delivery, photovoltaics, microelectronics manufacturing. Such interests are largely inspired by the fact that hot plasma electrons coexist with neutral species and ions close to room-temperature under non-thermal plasma conditions. Modeling of these systems requires a deep understanding of the atomistic processes underlying the rich chemistry of the various radicals and ions with the nascent nanoparticle surface. A key parameter for determining the contribution of a certain radical/ion species to the nanoparticle surface growth, called sticking coefficient, is computed as a weighted sum from the simulated sticking outcomes with different collision velocities drawn from a Maxwell-Boltzmann distribution at certain temperatures. In this work, the collisions of SiHx (x=1-4) fragments and silicon cluster (Si4, Si2H6, and Si29H36) surfaces, responsible for the sticking coefficients, are simulated by molecular dynamics (MD) with a reactive force field. The dependence of sticking coefficients on temperature, H coverage of both silane fragments and cluster surfaces, and the size of the cluster, are systematically examined. And the mechanism underlying the sticking events, specifically the conversion of physical aggregation to chemisorption is investigated to better understand the complex interplay between factors influencing the surface growth. The detailed and multi-parameter model of sticking coefficients, accompanied by the mechanism study of physisorption to chemisorption conversion, provides a more accurate and robust approximation of surface growth rate using sticking coefficients, and a deeper understanding of surface growth processes, for the wider non-thermal plasma simulation community.
    Keyword:
    Sticking coefficients, Silanes, Molecular Dynamics, Non-equilibrium, and Aggregation mechanisms
    Citation to related publication:
    Shi, X., Elvati, P., Violi, A. (2021). On the growth of Si nanoparticles in non-thermal plasma: physisorption to chemisorption conversion. J. Phys. D. Submitted.
    Discipline:
    Science

  • Spatial dependence of the growth of polycyclic aromatic compounds in an ethylene counterflow flame: experimental measurements and simulation results

    work
    Creator:
    Wang, Qi, Elvati, Paolo, Kim, Doohyun, Johansson, K. Olof, Schrader, Paul E., Michelsen, Hope A., and Violi, Angela
    Description:
    Datasets for article in CARBON: Spatial dependence of the growth of polycyclic aromatic compounds in an ethylene counterflow flame. The experiment VUV-AMS measurements ("VUV_AMS_C2H4_Counterflow.txt") consists aerosol mass spectra data from an atmospheric-pressure ethylene/oxygen/argon counterflow diffusion flame described in Johansson et al., Proc. Combust. Inst. 36, 799-806 (2017) doi:10.1016/j.proci.2016.07.130., The experiment VUV-MBMS measurements ("VUV_MBMS_C2H4_Counterflow.txt") consists gas-phase data from an atmospheric-pressure ethylene/oxygen/argon counterflow diffusion flame described in Johansson et al., Proc. Combust. Inst. 36, 799-806 (2017) doi:10.1016/j.proci.2016.07.130., 2D CFD simulation results by KAUST mechanism II ("CFD_KM2_results.xlsx") consists stabilized CFD gas-phase species profiles along different x,y,z coordinates. Species are given by mole fractions., The SNapS2 simulation results ("SNapS2_results.zip") consist streamline I (from fuel side), i (from oxidizer side), and middle (DFFO = 5.0mm) for producing results in Fig. 5, Fig. 6, and Table 1. Three folders under each streamline ("C5H6", "C6H5CH3", and "C6H6") represent simulations by using different seeds (cyclopentadiene, toluene, and benzene respectively). The text files inside each folder are a single trace (time-history) for one SNapS2 simulation. Text file name consists "starting time"+"."+"simulation number"+".txt". For example 0.041.25.txt meaning the 25th simulation starting at 0.041s. Four columns inside the text files represent time, molecular mass, reaction index, and SMILES (Simplified molecular-input line-entry system) of the molecule., and Data citation: Wang, Q., Elvati, P., Kim, D., Johansson, K.O., Schrader, P.E., Michelsen, H.A., Violi, A. (2019). Spatial dependence of the growth of polycyclic aromatic compounds in an ethylene counterflow flame: experimental measurements and simulation results [Data set]. University of Michigan Deep Blue Data Repository.  https://doi.org/10.7302/69e6-cd20
    Citation to related publication:
    Wang, Q., Elvati, P., Kim, D., Johansson, K.O., Schrader, P.E., Michelsen, H.A., Violi, A., 2019. Spatial dependence of the growth of polycyclic aromatic compounds in an ethylene counterflow flame. Carbon 149, 328–335.  https://doi.org/10.1016/j.carbon.2019.03.017
    Discipline:
    Science