SI_video.mp4 from Pseudo-bistability of viscoelastic shells

Viscoelastic shells subjected to a pressure loading exhibit rich and complex time-dependent responses. Here we focus on the phenomenon of pseudo-bistability, i.e. a viscoelastic shell can stay inverted when pressure is removed, and snap to its natural shape after a delay time. We model and explain the mechanism of pseudo-bistability with a viscoelastic shell model. It combines the small strain, moderate rotation shell theory with the standard linear solid as the viscoelastic constitutive law, and is applicable to shells with arbitrary axisymmetric shapes. As a case study, we investigate the pseudo-bistable behaviour of viscoelastic ellipsoidal shells. Using the proposed model, we successfully predict buckling of a viscoelastic ellipsoidal shell into its inverted configuration when subjected to an instantaneous pressure, creeping when the pressure is held, staying inverted after the pressure is removed, and eventually snapping back after a delay time. The stability transition of the shell from a monostable, temporarily bistable and eventually back to the monostable state is captured by examining the evolution of the instantaneous pressure–volume change relation at different time of the holding and releasing process. A systematic parametric study is conducted to investigate the effect of geometry, viscoelastic properties and loading history on the pseudo-bistable behaviour.This article is part of the theme issue 'Probing and dynamics of shock sensitive shells'

20230112_supplementary_Yuzhen.docx from Pseudo-bistability of viscoelastic shells

Viscoelastic shells subjected to a pressure loading exhibit rich and complex time-dependent responses. Here we focus on the phenomenon of pseudo-bistability, i.e. a viscoelastic shell can stay inverted when pressure is removed, and snap to its natural shape after a delay time. We model and explain the mechanism of pseudo-bistability with a viscoelastic shell model. It combines the small strain, moderate rotation shell theory with the standard linear solid as the viscoelastic constitutive law, and is applicable to shells with arbitrary axisymmetric shapes. As a case study, we investigate the pseudo-bistable behaviour of viscoelastic ellipsoidal shells. Using the proposed model, we successfully predict buckling of a viscoelastic ellipsoidal shell into its inverted configuration when subjected to an instantaneous pressure, creeping when the pressure is held, staying inverted after the pressure is removed, and eventually snapping back after a delay time. The stability transition of the shell from a monostable, temporarily bistable and eventually back to the monostable state is captured by examining the evolution of the instantaneous pressure–volume change relation at different time of the holding and releasing process. A systematic parametric study is conducted to investigate the effect of geometry, viscoelastic properties and loading history on the pseudo-bistable behaviour.This article is part of the theme issue 'Probing and dynamics of shock sensitive shells'

SI_Matlab codes.zip from Pseudo-bistability of viscoelastic shells

Viscoelastic shells subjected to a pressure loading exhibit rich and complex time-dependent responses. Here we focus on the phenomenon of pseudo-bistability, i.e. a viscoelastic shell can stay inverted when pressure is removed, and snap to its natural shape after a delay time. We model and explain the mechanism of pseudo-bistability with a viscoelastic shell model. It combines the small strain, moderate rotation shell theory with the standard linear solid as the viscoelastic constitutive law, and is applicable to shells with arbitrary axisymmetric shapes. As a case study, we investigate the pseudo-bistable behaviour of viscoelastic ellipsoidal shells. Using the proposed model, we successfully predict buckling of a viscoelastic ellipsoidal shell into its inverted configuration when subjected to an instantaneous pressure, creeping when the pressure is held, staying inverted after the pressure is removed, and eventually snapping back after a delay time. The stability transition of the shell from a monostable, temporarily bistable and eventually back to the monostable state is captured by examining the evolution of the instantaneous pressure–volume change relation at different time of the holding and releasing process. A systematic parametric study is conducted to investigate the effect of geometry, viscoelastic properties and loading history on the pseudo-bistable behaviour.This article is part of the theme issue 'Probing and dynamics of shock sensitive shells'

Structure-Thermodynamics-Antioxidant Activity Relationships of Selected Natural Phenolic Acids and Derivatives: An Experimental and Theoretical Evaluation

<div><p>Phenolic acids and derivatives have potential biological functions, however, little is known about the structure-activity relationships and the underlying action mechanisms of these phenolic acids to date. Herein we investigate the structure-thermodynamics-antioxidant relationships of 20 natural phenolic acids and derivatives using DPPH^• scavenging assay, density functional theory calculations at the B3LYP/6-311++G(d,p) levels of theory, and quantitative structure-activity relationship (QSAR) modeling. Three main working mechanisms (HAT, SETPT and SPLET) are explored in four micro-environments (gas-phase, benzene, water and ethanol). Computed thermodynamics parameters (BDE, IP, PDE, PA and ETE) are compared with the experimental radical scavenging activities against DPPH^•. Available theoretical and experimental investigations have demonstrated that the extended delocalization and intra-molecular hydrogen bonds are the two main contributions to the stability of the radicals. The C = O or C = C in COOH, COOR, C = CCOOH and C = CCOOR groups, and orthodiphenolic functionalities are shown to favorably stabilize the specific radical species to enhance the radical scavenging activities, while the presence of the single OH in the <i>ortho</i> position of the COOH group disfavors the activities. HAT is the thermodynamically preferred mechanism in the gas phase and benzene, whereas SPLET in water and ethanol. Furthermore, our QSAR models robustly represent the structure-activity relationships of these explored compounds in polar media.</p></div

Spin density values of phenoxy radicals of 20 investigated phenolic compounds and phenol calculated at the B3LYP/6-311++G(d,p) levels of theory in ethanol.

<p>Spin density values of phenoxy radicals of 20 investigated phenolic compounds and phenol calculated at the B3LYP/6-311++G(d,p) levels of theory in ethanol.</p

Spin density values of phenoxy radicals of 20 investigated phenolic compounds and phenol calculated at the B3LYP/6-311++G(d,p) levels of theory in ethanol.

<p>Spin density values of phenoxy radicals of 20 investigated phenolic compounds and phenol calculated at the B3LYP/6-311++G(d,p) levels of theory in ethanol.</p

HOMO of 20 investigated phenolic compounds calculated at the B3LYP/6-311++G(d,p) levels of theory in ethanol.

<p>The numbers indicates atomic polar tensor charges.</p

The energy difference (ΔE in kcal/mol) caused by the hydrogen bond between the O^• center and the <i>meta</i> OH for 7 radicals calculated at the B3LYP/6-311++G(d,p) levels of theory in 4 reaction media.

<p>The energy difference (ΔE in kcal/mol) caused by the hydrogen bond between the O^• center and the <i>meta</i> OH for 7 radicals calculated at the B3LYP/6-311++G(d,p) levels of theory in 4 reaction media.</p

Structural Insights into a Unique <em>Legionella pneumophila</em> Effector LidA Recognizing Both GDP and GTP Bound Rab1 in Their Active State

<div><p>The intracellular pathogen <em>Legionella pneumophila</em> hijacks the endoplasmic reticulum (ER)-derived vesicles to create an organelle designated <em>Legionella</em>-containing vacuole (LCV) required for bacterial replication. Maturation of the LCV involved acquisition of Rab1, which is mediated by the bacterial effector protein SidM/DrrA. SidM/DrrA is a bifunctional enzyme having the activity of both Rab1-specific GDP dissociation inhibitor (GDI) displacement factor (GDF) and guanine nucleotide exchange factor (GEF). LidA, another Rab1-interacting bacterial effector protein, was reported to promote SidM/DrrA-mediated recruitment of Rab1 to the LCV as well. Here we report the crystal structures of LidA complexes with GDP- and GTP-bound Rab1 respectively. Structural comparison revealed that GDP-Rab1 bound by LidA exhibits an active and nearly identical conformation with that of GTP-Rab1, suggesting that LidA can disrupt the switch function of Rab1 and render it persistently active. As with GTP, LidA maintains GDP-Rab1 in the active conformation through interaction with its two conserved switch regions. Consistent with the structural observations, biochemical assays showed that LidA binds to GDP- and GTP-Rab1 equally well with an affinity approximately 7.5 nM. We propose that the tight interaction with Rab1 allows LidA to facilitate SidM/DrrA-catalyzed release of Rab1 from GDIs. Taken together, our results support a unique mechanism by which a bacterial effector protein regulates Rab1 recycling.</p> </div

Measurement of binding affinity between LidA and GTP-bound or GDP-bound Rab1 by ITC.

<p>(A) Raw ITC data. Top panel: twenty injections of GTP-bound Rab1(Q70L) solutions were titrated into LidA(188-580) solution in ITC cell. The area of each injection peak corresponds to the total heat released for that injection. Bottom panel: the binding isotherm for GTP-bound Rab1(Q70L) and LidA(188-580) interaction, the integrated heat is plotted against the stoichiometry of 1∶1, data fitting revealed a binding affinity of 7.5 nM. (B) Top panel: twenty injections of GDP-bound Rab1(S25N) solutions were titrated into LidA(188-580) solution in ITC cell. The area of each injection peak corresponds to the total heat released for that injection. Bottom panel: the binding isotherm for GDP-bound Rab1(S25N) and LidA(188-580) interaction, the integrated heat is plotted against the stoichiometry of 1∶1, data fitting revealed a binding affinity of 7.6 nM. Both titrations were performed in the absence of added Mg²⁺ and GDP/GTP.</p