Studying friction and shear fracture in thin confined films using a rotational shear apparatus

This paper describes the effects of the elastic modulus and sliding velocity on the friction and shear fracture of smooth silanized rigid disks rotating against thin confined films of poly(dimethylsiloxane) (PDMS) elastomers. A rigid glass disk is rotated against thin PDMS films of different thicknesses and moduli bonded to a glass plate at various speeds. While the disk rotates on the PDMS coated glass plate, a load cell measures the resulting force with a cantilever beam. One end of the cantilever beam is glued to the glass plate, while its other end presses against a load cell. From the balance of forces and torques, the friction force at a given slip velocity is determined. The friction force increases with the slip velocity sublinearly, which is consistent with the results reported previously by Vorvolakos and Chaudhury (Langmuir 2003, 19, 6778). During rotation, however, the glass disk comes off the PDMS film when the shear stress reaches a critical value. This critical shear stress increases with the modulus of the film, but it decreases with its thickness, following a square root relationship, which is similar to the adhesive fracture behavior in thin films under pull-off conditions. A simple model is presented that captures the essential physics of the fracture behavior under shear mode.     

Role of stimuli-sensitive polymers in protein refolding: alpha-amylase and CcdB (controller of cell division or death B) as model proteins

Alginate, a calcium-sensitive polymer, could carry out simultaneous purification and refolding of 8 M urea/100 mM dithiothreitol (DTT) denatured and thermally denatured alpha-amylase present in a commercial preparation. Activity recoveries of 80 and 70% in the former and the latter cases, respectively, were obtained. The fluorescence spectra showed refolding, and PAGE showed the absence of any aggregates in the refolded preparation. As another example, Eudragit S-100, a pH-sensitive poly(methyl methacrylate), was used to refold CcdB (controller of cell division or death B) protein. Initial experiments with wild-type (WT) CcdB showed that Eudragit bound and precipitated (upon lowering the pH to 4.0) CcdB quantitatively from the latter's aqueous solution. The bioconjugate showed DNA gyrase inhibition activity of CcdB and could be recycled. The inclusion bodies of CcdB mutant CcdB-17P were solubilized in 8 M urea/100 mM dithiothreitol. This preparation could be refolded by precipitation with Eudragit. The fluorescence and CD spectra showed that protein refolding has occurred.     

Synthesis of s-fac/mer bis(N2-methyldiethylenetriamine,L) nickel(II): X-ray single crystal structures of s-fac[NiL2](NO3)2 and mer[NiL2](CF3CO2)2

[NiL2](NO3)2 (1) and [NiL2](CF3CO2)2 (2) (L = N2-methyldiethylenetriamine] have been synthesized and their X-ray single crystal structures have been determined. The triamines are ligated to NiII s-facially in (1) and meridionally in (2), with a NiN6 chromophore in each complex.     

Emergence of diverse dynamical responses in a fractional-order slow–fast pest–predator model

To explore the impact of pest-control strategy on integrated pest management, a three-dimensional (3D) fractional- order slow–fast prey–predator model is introduced in this article. The prey community (assumed as pest) represents fast dynamics and two predators exhibit slow dynamical variables in the three-species interacting prey–predator model. In addition, common enemies of that pest are assumed as predators of two different species. Pest community causes serious damage to the economy. Fractional-order systems can better describe the real scenarios than classical-order dynamical systems, as they show previous history-dependent properties. We establish the ability of a fractional-order model with Caputo’s fractional derivative to capture the dynamics of this prey–predator system and analyze its qualitative properties. To investigate the importance of fractional-order dynamics on the behavior of the pest, we perform the local stability analysis of possible equilibrium points, using certain assumptions for different sets of parameters and reveal that the fractional-order exponent has an impact on the stability and the existence of Hopf bifurcations in the prey–predator model. Next, we discuss the existence, uniqueness and boundedness of the fractional-order system. We also observe diverse oscillatory behavior of different amplitude modulations including mixed mode oscillations (MMOs) for the fractional-order prey–predator model. Higher amplitude pest periods are interspersed with the outbreaks of small pest concentration. With the decrease of fractional-order exponent, small pest concentration increases with decaying long pest periods. We further notice that the reduced-order model is biologically significant and sensitive to the fractional-order exponent. Additionally, the dynamics captures adaptation that occurs over multiple timescales and we find consistent differences in the characteristics of the model for various fractional exponents.

     

Why intermolecular nitric oxide (NO) transfer? Exploring the factors and mechanistic aspects of NO transfer reaction

Small molecule activation and their transfer reactions in biological or catalytic reactions are greatly influenced by the metal-centers and the ligand frameworks. Here, we report the metal-directed nitric oxide (NO) transfer chemistry in low-spin mononuclear {Co(NO)}⁸, [(12-TMC)Co^III(NO⁻)]²⁺ (1-CoNO, S = 0), and {Cr(NO)}⁵, ([(BPMEN)Cr(NO)(Cl)]⁺) (4-CrNO, S = 1/2) complexes. 1-CoNO transfers its bound NO moiety to a high-spin [(BPMEN)Cr^II(Cl₂)] (2-Cr, S = 2) and generates 4-CrNOvia an associative pathway; however, we did not observe the reverse reaction, i.e., NO transfer from 4-CrNO to low-spin [(12-TMC)Co^II]²⁺ (3-Co, S = 1/2). Spectral titration for NO transfer reaction between 1-CoNO and 2-Cr confirmed 1 : 1 reaction stoichiometry. The NO transfer rate was found to be independent of 2-Cr, suggesting the presence of an intermediate species, which was further supported experimentally and theoretically. The experimental and theoretical observations support the formation of μ-NO bridged intermediate species ({Cr–NO–Co}⁴⁺). Mechanistic investigations using ¹⁵N-labeled-¹⁵NO and tracking the ¹⁵N-atom established that the NO moiety in 4-CrNO is derived from 1-CoNO. Further, to investigate the factors deciding the NO transfer reactivity, we explored the NO transfer reaction between another high-spin Cr^II-complex, [(12-TMC)Cr^II(Cl)]⁺ (5-Cr, S = 2), and 1-CoNO, showing the generation of the low-spin [(12-TMC)Cr(NO)(Cl)]⁺ (6-CrNO, S = 1/2); however, again there was no opposite reaction, i.e., from Cr-center to Co-center. The above results advocate clearly that the NO transfer from Co-center generates thermally stable and low-spin and inert {Cr(NO)}⁵ complexes (4-CrNO & 6-CrNO) from high-spin and labile Cr-complexes (2-Cr & 5-Cr), suggesting a metal-directed NO transfer (cobalt to chromium, not chromium to cobalt). These results explicitly highlight that the NO transfer is strongly influenced by the labile/inert behavior of the metal-centers and/or thermal stability rather than the ligand architecture.

Nitric oxide activation and parameters influencing intermolecular transfer of nitric oxide.     

Natural Product-Based Potential Therapeutic Interventions of Pulmonary Fibrosis

Pulmonary fibrosis (PF) is a disease-refractive lung condition with an increased rate of mortality. The potential factors causing PF include viral infections, radiation exposure, and toxic airborne chemicals. Idiopathic PF (IPF) is related to pneumonia affecting the elderly and is characterized by recurring scar formation in the lungs. An impaired wound healing process, defined by the dysregulated aggregation of extracellular matrix components, triggers fibrotic scar formation in the lungs. The potential pathogenesis includes oxidative stress, altered cell signaling, inflammation, etc. Nintedanib and pirfenidone have been approved with a conditional endorsement for the management of IPF. In addition, natural product-based treatment strategies have shown promising results in treating PF. In this study, we reviewed the recently published literature and discussed the potential uses of natural products, classified into three types—isolated active compounds, crude extracts of plants, and traditional medicine, consisting of mixtures of different plant products—in treating PF. These natural products are promising in the treatment of PF via inhibiting inflammation, oxidative stress, and endothelial mesenchymal transition, as well as affecting TGF-β-mediated cell signaling, etc. Based on the current review, we have revealed the signaling mechanisms of PF pathogenesis and the potential opportunities offered by natural product-based medicine in treating PF.     

Electron temperature (T e) measurements by Thomson scattering system

Thomson scattering technique based on high power laser has already proved its superoirity in measuring the electron temperature (T _e and density (n _e) in fusion plasma devices like tokamaks. The method is a direct and unambiguous one, widely used for the localised and simultaneous measurements of the above parameters. In Thomson scattering experiment, the light scattered by the plasma electrons is used for the measurements. The plasma electron temperature is measured from the Doppler shifted scattered spectrum and density from the total scattered intensity. A single point Thomson scattering system involving a Q-switched ruby laser and PMTs as the detector is deployed in ADITYA tokamak to give the plasma electron parameters. The system is capable of providing the parameters T _e from 30 eV to 1 keV and n _e from 5 × 10¹²cm⁻³−5 × 10¹³cm⁻³. The system is also able to give the parameter profile from the plasma center (Z=0 cm) to a vertical position of Z=+22 cm to Z=−14 cm, with a spatial resolution of 1 cm on shot to shot basis. This paper discusses the initial measurements of the plasma temperature from ADITYA.     

An investigation of basis set effects in the characterization of electron – atom scattering resonances using the dilated electron propagator method

 The effects of basis set variations on resonance attributes are investigated using systematically augmented basis sets by correlating the resulting changes in resonance energy and width with the alterations induced in the radial probability density profile of the resonant orbital. Applications to ²P Be⁻ and ²P Mg⁻ shape resonances reveal that basis sets capable of describing both electron density accumulation near the target nucleus to facilitate resonance formation and sufficiently large electron density away from the target nucleus to provide for its decay are necessary for effective characterization of these resonances. A comparison of radial probability density profiles from the bivariational self-consistent field, the second-order, the diagonal two particle–one hole Tamm–Dancoff approximation and quasiparticle decouplings reveals that relaxation effects dominate in resonance formation. Received: 3 January 2000 / Accepted: 5 March 2000 / Published online: 21 June 2000