Modulation Of Electrostatic Interactions Research Articles

Controlled Bio-Orthogonal Catalysis Using Nanozyme-Protein Complexes via Modulation of Electrostatic Interactions.

Bio-orthogonal chemistry provides a powerful tool for drug delivery systems due to its ability to generate therapeutic agents in situ, minimizing off-target effects. Bio-orthogonal transition metal catalysts (TMCs) with stimuli-responsive properties offer possibilities for controllable catalysis due to their spatial-, temporal-, and dosage-controllable properties. In this paper, we fabricated a stimuli-responsive bio-orthogonal catalysis system based on an enhanced green fluorescent protein (EGFP)-nanozyme (NZ) complex (EGFP-NZ). Regulation of the catalytic properties of the EGFP-NZ complex was directly achieved by modulating the ionic strength of the solution. The dielectric screening introduced by salt ions allows the dissociation of the EGFP-NZ complex, increasing the access of substrate to the active site of the NZs and concomitantly increasing nanozyme activity. The change in catalytic rate of the NZ/EGFP = 1:1 complex was positively correlated with salt concentration from 0 mM to 150 mM.

The dimerization mechanism of the N-terminal domain of spider silk proteins is conserved despite extensive sequence divergence

The N-terminal (NT) domain of spider silk proteins (spidroins) is crucial for their storage at high concentrations and also regulates silk assembly. NTs from the major ampullate spidroin (MaSp) and the minor ampullate spidroin are monomeric at neutral pH and confer solubility to spidroins, whereas at lower pH, they dimerize to interconnect spidroins in a fiber. This dimerization is known to result from modulation of electrostatic interactions by protonation of well-conserved glutamates, although it is undetermined if this mechanism applies to other spidroin types as well. Here, we determine the solution and crystal structures of the flagelliform spidroin NT, which shares only 35% identity with MaSp NT, and investigate the mechanisms of its dimerization. We show that flagelliform spidroin NT is structurally similar to MaSp NT and that the electrostatic intermolecular interaction between Asp 40 and Lys 65 residues is conserved. However, the protonation events involve a different set of residues than in MaSp, indicating that an overall mechanism of pH-dependent dimerization is conserved but can be mediated by different pathways in different silk types.

Enhanced physical and antimicrobial properties of alginate/chitosan composite aerogels based on electrostatic interactions and noncovalent crosslinking

In this study, the alginate/chitosan composite aerogels based on electrostatic interactions and noncovalent crosslinking were fabricated using sol-gel method followed by freeze-drying process. The solution property results showed that with the addition of chitosan in alginate solution, a tighter network was induced by the more entangled molecular chains. The aerogel morphology observations showed that the pore diameter decreased with the increasing weight ratio of chitosan in the aerogels, but was even much lower after the crosslinking of excess alginate with calcium ions. After crosslinking, the aerogels presented the improved thermal stability and higher mechanical properties, as well as stronger antibacterial activities against Staphylococcus aureus and Escherichia coli. Therefore, the enhanced physical and antimicrobial properties of the alginate/chitosan aerogels may be achieved by modulation of electrostatic interactions and noncovalent crosslinking, suggesting the promising applications of these composite aerogels as active food packaging materials for antimicrobial purpose.

Reversible changes in the orientation of gold nanorod arrays on polymer brushes.

Nanoparticles exhibit a number of unique properties such as localized surface plasmon resonance (LSPR). As this LSPR is sensitive to geometrical or spatial conditions, the arrangement of nanoparticles, in particular the active arrangement of plasmonic structures, is an important issue. In this study, gold nanorod (GNR) arrays were prepared by GNR attachment on anionic polymer (DNA) brushes via electrostatic interactions and their stimuli-responsive changes in orientation were investigated. As a result, the orientation of GNR arrays on DNA brushes reversibly changed by the modulation of electrostatic interactions between GNRs and polymers via changes in the solution pH. As these extensive GNR arrays are prepared via easy bottom-up processes, GNR surface properties are easily tuned by simple modification, and DNAs could be replaced with various synthetic polymers, we believe that this study will lead to the development of next-generation materials and devices with actively tunable structures.

Nanoparticle–nanobubble interactions: Charge inversion and re-entrant condensation of amidine latex nanoparticles driven by bulk nanobubbles

HypothesisThe stability of colloidal suspensions can be influenced by supersaturation of the supporting electrolyte with gas. It has been proposed that this effect can be attributed to the formation of nanobubbles on the surface of the colloidal particles, in turn influencing DLVO forces. While previous interpretations have focused primarily on van der Waals interactions, probing positively charged particles can provide complementary insight into electrostatic interactions. ExperimentsHigh-power water electrolysis creates an aqueous solution supersaturated with oxygen and hydrogen. We study the ability of this solution to influence the electrophoretic properties of positive nanoparticles as a function of the particle-gas ratio. Both the ζ-potential and the effective hydrodynamic diameter of the resulting nanoentities were studied using dynamic light scattering for a range of nanoparticle sizes. FindingsGas-saturated solution interacts strongly with positive nanoparticles by decreasing and ultimately reversing the sign of their ζ-potential, which we attribute to the nucleation of negatively charged bubbles at the solid-liquid interface. This leads to re-entrant condensation of the particles near their point of zero charge, as directly observed via an increase in hydrodynamic diameter and macroscopic aggregation. These results indicate that modulation of electrostatic interactions can be the dominant mechanism for gas-particle interactions in these systems.

Electrostatic Control of Chemistry in Terpene Cyclases

Electrostatic interactions play a major role in stabilizing transition states in enzymes. A crucial question is how general this electrostatic stabilization principle is. To address this point, we study a key common C–C bond formation step in a family of enzymes that is responsible for the biosynthesis of 60% of all natural products. In these terpene cyclases, we have previously shown that the enzymes gain chemical control by raising the energy of initial carbocation intermediates along the reaction coordinate to bypass the formation of unwanted side products. Here we employ hybrid quantum mechanics–molecular mechanics free energy simulations to show that this energy tuning is achieved by modulation of electrostatic interactions. The tempering of electrostatic interactions allows enzymatically directed chemical control that slows down the reaction temporarily by introducing thermodynamic and activation barriers. We show that this electrostatic control in terpene cyclases is achieved by a unique binary act...

Controlling microstructure and physical properties of biopolymer hydrogel particles through modulation of electrostatic interactions

Foods contain varying amounts of salts and acids, which alters the electrostatic interactions between biopolymer molecules. This study therefore examined the influence of NaCl content (0–400mM) and pH (3–8) on the physical properties of hydrogel particles fabricated by mixing sodium caseinate (1.5%) and pectin (1.5%). The hydrogel particles were assembled using a biopolymer phase separation approach that involved both segregation (thermodynamic incompatibility) and aggregation (complex coacervation) mechanisms. The addition of NaCl increased hydrogel particle size and altered the shape from spherical to rod-like, which was attributed to the influence of salt on the electrostatic attraction between biopolymers. There was a reduction in the lightness and increase in the shear viscosity of the hydrogel particle suspensions with NaCl addition, which was attributed to changes in particle dimensions and morphology. Solution pH also altered particle size and shape, and therefore the lightness and viscosity of the suspensions. In particular, the lightness of the suspensions was greater at pH 3–5, than at higher pH values. This study highlighted the significant effects of salt and pH on the properties of hydrogel particles. This knowledge could be used to manipulate food formulations to achieve desirable physicochemical or sensory properties.

Controlling the charge of pH-responsive redox hydrogels by means of redox-silent biocatalytic processes. A biocatalytic off/on switch

Coupling of redox-silent biocatalytic processes for analyte detection with enzyme-catalyzed redox reactions for signal generation is proposed by the modulation of electrostatic interactions between a pH-responsive polymer and a redox enzyme to control the off–on transition for electrochemical signal generation. Glassy carbon electrodes are modified with a poly(vinyl)imidazole Os(bipyridine)2Cl redox hydrogel film entrapping urease and PQQ-dependent glucose dehydrogenase, while glucose is present in the solution. The off–on transition is based on the detection of urea as model analyte which is hydrolyzed to ammonia by urease within the hydrogel film concomitantly increasing the local pH value thus invoking deprotonation of the imidazole groups at the polymer backbone. The decrease of positive charges at the polymer decreases electrostatic repulsion between the polymer and the positively charged PQQ-dependent glucose dehydrogenase. Hence, electron transfer rates between polymer-bound Os complexes and PQQ inside the enzyme are enhanced activating electrocatalytic oxidation of glucose. This process generates the electrochemical signal for urea detection.

Unique holoenzyme dimers of the tetrameric enzyme Escherichia coli methylenetetrahydrofolate reductase: characterization of structural features associated with modulation of the enzyme's function.

Impaired functioning of methylenetetrahydrofolate reductase (MTHFR) can cause high levels of homocysteine in plasma or hyperhomocysteinemia, which is an independent risk factor for cardiovascular diseases and neural tube defects. We have studied in detail the effect of modulation of hydrophobic and electrostatic interactions of Escherichia coli MTHFR on its structure and function. Alterations in hydrophobic interactions of MTHFR, using urea, lead to dissociation of the native tetramer, resulting in stabilization of enzymatically active holoenzyme dimers followed by unfolding of the holoenzyme dimer to the denatured monomer along with dissociation of FAD from the enzyme. This is the first report of an enzymatically active dimer of E. coli MTHFR and suggests that the dimer rather than tetramer is the smallest functionally active unit of the enzyme. Furthermore, these results also demonstrate that dissociation of the FAD cofactor from the enzyme occurs only on unfolding of the dimer to denatured monomers. Modulation of electrostatic interactions, using NaCl, leads to dissociation of the native enzyme, resulting in stabilization of an enzymatically inactive partially unfolded holoenzyme dimer. Comparative analysis of loss of enzymatic activity and changes in structural features of MTHFR demonstrate a very good correlation between enhanced flexibility of the enzyme-bound FAD and loss of enzymatic activity, suggesting the importance of rigidity of the FAD cofactor in maintenance of the enzymatic activity of MTHFR.