Steric Forces Research Articles

Auricularia Auricula Polysaccharide-Mediated Green Synthesis of Highly Stable Au NPs

Polysaccharide-functionalized gold nanoparticles (Au NPs) exhibit a promising application in biomedical fields due to their excellent stability and functional properties. The Au NPs from Auricularia auricula polysaccharide (AAP) were successfully synthesized using a straightforward method. By controlling the mass fraction of AAP, pH, reaction temperature, reaction time, and concentration of gold precursor, the highly dispersed spherical AAP-functionalized Au NPs (AAP-Au NPs) were prepared. The Fourier transform infrared spectrometer (FT-IR) and X-ray photoelectron spectroscopy (XPS) indicated that the synthesis mechanism of AAP-Au NPs was as follows: the molecular chain of AAP undergoes a glycosidic bond breakage to expose the reduction terminus in the presence of gold precursor, which reduced Au(III) to Au(0), and itself was oxidized to carboxylate compounds for maintaining the stability of AAP-Au NPs. Additionally, based on the electrostatic interactions and steric forces, as-prepared AAP-Au NPs exhibit excellent stability at various pH (5–11), temperature (25–60 °C), 5 mmol/L glutathione, and 0.1 mol/L Na+ and K+ solutions. Furthermore, AAP-Au NPs retained the ability to scavenge DDPH and ABTS radicals, which is expected to expand the application of Au NPs in biomedical fields.

Rheological Behavior of Clay Tailings in the Presence of Divalent Cations and Sodium Polyacrylate: Insights from Molecular Dynamics Simulations.

This study analyzes the behavior of sodium polyacrylate (NaPA) as a rheological modifier for clay-based tailings. Special emphasis is placed on the impact of calcium and magnesium ions in industrial water, which are analyzed through rheograms, zeta potential measurements, and molecular dynamics simulations. The results are interpreted as electrostatic interactions, steric phenomena, and cation solvation. This interpretation integrates experimental studies with microscopic analyses, employing molecular dynamics simulations to elucidate the underlying mechanisms. In all cases, a decrease in the yield stress of synthetic slurries is observed as the dosing of NaPA increases due to greater repulsion between tailings particles through an increase in electrostatic repulsion and larger steric forces that hinder agglomeration. However, efficiency is reduced in the presence of divalent cations as zeta potential measurements suggest a reduction in the electrical charges of the particles and the polymer, making its application more challenging. The differences obtained in the presence of calcium compared to magnesium are explained in terms of the solvation of these ions and their impact on the polymer conformation in solution and adsorption on the mineral surfaces. This explanation is reinforced by molecular dynamics studies, which indicate that polymer adsorption on minerals depends on the type of mineral and type of ion. Particularly for quartz, the highest adsorption of NaPA occurs in the presence of calcium, whereas for a kaolinite surface, the highest polymer adsorption is obtained in the presence of magnesium. The competitive effect of these phenomena leads to the rheological behavior of the tailings being dominated by the effects originating in the clay.

The role of hydrogen bonding in the conformational stability of 2-methoxyresorcinol: Insights from theoretical calculations, SERS spectroscopy, and solvent effect

Resorcinol derivatives exhibit unique structural and electronic features. The presence of two hydroxyl groups, along with other substituents, can greatly impact these molecules’ conformational profile and vibrational characteristics. This work investigates molecular and electronic properties of 2-methoxyresorcinol (2-MR) by combining quantum-chemical and spectroscopic techniques. The molecule of 2-MR can exist in the syn, anti, and anti–syn configurations, depending on the orientation of the hydroxyl groups. The syn and anti–syn forms have been verified from DFT, MP2 and MP4 (SDQ) calculations and from infrared/Raman spectroscopy to be stabilized by intramolecular hydrogen bonding that takes place between the hydrogen atoms of the OH groups and the methoxy moiety’s oxygen atom. Such an interaction results in 6–7 kcal/mol more stable states than the corresponding anti-configuration, where only steric forces control the molecule stability. The effect of different solvents on the Raman features has also been accessed. Unlike other solutions, aqueous 2-MR facilitated a split in the OH stretching peak, which can be attributed to the pronounced solute–solvent intermolecular forces through the OH groups. Surface-enhanced Raman scattering (SERS) spectroscopic analysis of trace 2-MR utilizing as-synthesized silver nanoparticles shows a remarkable boost in the Raman signal intensities of several vibrational modes. The SERS detection exhibits a wide dynamic range and a detection limit of 1 × 10−8 M.

Pebax/NC-PCL membrane containing well-distributed PCL grafted biodegradable nano-chitosan particles for CO2 separation

This study presents a novel method to improve carbon dioxide (CO2) separation performance in mixed-matrix membranes (MMMs) by incorporating polycaprolactone (PCL) grafted biodegradable nano-chitosan (NC) particles into a Pebax membrane matrix. Adding NC particles strengthens the interaction between the polymer mixed-matrix and CO2 molecules through functional groups on the NC particles via a facilitated transport mechanism. Grafting NC particles with PCL prevents the aggregation of particles by introducing steric repulsive forces between them, ensuring a well-dispersion of NC particles within the polymer matrix. Gas separation tests revealed that the membrane containing NC-PCL particles at a 1:1 ratio achieved a superior CO2 permeability of 99.8 Barrer and a CO2/N2 selectivity of 234.9. This performance marks a moderate increment of 20.7% in CO2 permeability and a substantial 413% increase in CO2/N2 selectivity compared to the neat Pebax membrane. Overall, the membranes managed to exceed the Robeson upper bound line by enhancing both CO2 permeability and CO2/N2 selectivity simultaneously, thereby better balancing the trade-off effect between selectivity and permeability.

Impact of dissolved organic matter characteristics and inorganic species on the stability and removal by coagulation of nanoplastics in aqueous media

The aggregation of rough, raspberry-type polystyrene nanoparticles (PS-NPs) was investigated in the presence of six hydrophobic and hydrophilic dissolved organic matter (DOM) isolates and biopolymers (effluent OM) in NaCl and CaCl2 solutions using time-resolved dynamic light scattering. Results showed that the stability of PS-NPs mainly depends on OM characteristics and ionic composition. Due to cation bridging, the aggregation rate of PS-NPs in Ca2+-containing solutions was significantly higher than at similar Na+-ionic strength. Biopolymers rich in protein and carbohydrate moieties showed higher affinity to the surface of PS-NPs than the other DOM isolates in the absence of both Ca2+ and Na+. Overall, the stability of PS-NPs followed the order of biopolymers > hydrophobic isolates > hydrophilic isolates in the presence of Na+ and biopolymers > hydrophilic isolates > hydrophobic isolates in Ca2+-containing solutions. In the presence of high MW structures (biopolymers), PS-NPs aggregation in both NaCl and CaCl2 solutions was attributed to steric repulsive forces. The impact of hydrophilic and hydrophobic isolates on PS-NPs aggregation highly relied on the ionic composition. Coagulation was an effective pretreatment for PS-NPs removal. Using inductively coupled plasma-mass spectrometry, higher removals were recorded with Al2(SO4)3 in the absence of DOM, while PACl more efficiently coagulated PS-NPs in the presence of DOM isolates.

DFT, Structure Activity Relationship, Fukui, Wave Function, NBO, NLO, Spectral and Hole-Electron Analyses of Dexmethylphenidate

Dexmethylphenidate (DMP) is used to treat attention deficit hyperactivity disorder (ADHD) and belongs to the central nervous system (CNS) stimulant group of medicines. The physical properties of DMP were analyzed under the DFT/B3LYP/6-311++G(d,p) basis set. The ESP study reveals the electrophilic attack is possible, while FMO analysis shows that the molecule is hard, stable and an electron donor. The non-covalent interaction (NCI) study explains that van der Waals and steric repulsion forces are observed. The HEI studies indicated that this molecule has CT excitation in the S0→S5 state. The shaded surface map analysis reveals the presence of electron depletion regions in this molecule. The UV-Vis spectral analysis was carried out in various solvents. The Fukui function analysis conveys that 7C is the best domain for electrophilic attack. Theoretical IR determinations and NLO properties were also performed. The structure-activity relationship findings were performed in order to improve the docking score.

Density-based quantification of steric effects: validation by Taft steric parameters from acid-catalyzed hydrolysis of esters.

The steric effect is one of the most widely used concepts for chemical understanding in publications and textbooks, yet a well-accepted formulation of this effect is still elusive. Experimentally, this concept was quantified by the acid-catalyzed hydrolysis of esters, yielding the so-called Taft steric parameter. Theoretically, we recently proposed a density-based scheme to quantify the effect from density functional theory. In this work, we directly compare these two schemes, one from theory and the other from experiment. To this end, we first establish the ester hydrolysis mechanism with multiple water molecules explicitly considered and then apply the energetic span model to represent the hydrolysis barrier height between the two schemes. Our results show that the barrier height of the reaction series is strongly correlated with both Taft steric parameters from experiment and steric quantification from theory. We also obtained strong correlations with steric potential, steric force, and steric charge from our theoretical scheme. Strong correlations with a few information-theoretic quantities are additionally unveiled. To the best of our knowledge, this is the first time in the literature that such a direct comparison between theoretical and experimental results is made. These results also suggest that our proposed two-water three-step mechanism for ester hydrolysis is effective, and our theoretical quantification of the steric effect is valid, robust, and experimentally comparable. In our view, this work should have satisfactorily addressed the issue of how the steric effect can be formulated and quantified, and thus it lays the groundwork for future applications.

Evaluating the operational properties of concrete admixtures containing molecularly modified polycarboxylate superplasticizers

The objective of this study focused on the design and preparation of a molecularly modified polycarboxylate superplasticizer to develop concretes with enhanced engineering features. For this purpose, polyethylene glycol was chemically modified with maleic anhydride to give the mono polyethylene glycol maleate (MPEGM). Then, polycarboxylate superplasticizer comprising of isoprenyl oxy polyethylene glycol (TPEG) and acrylic acid (AA, PCE-1), and the synthesized MPEGM with TPEG and AA (PCE-2) were prepared through solution radical polymerization. Subsequently, concrete mixtures with different dosages (0, 0.1, 0.15, 0.2, 0.25, 0.3 wt%) of PCE-1 and PCE-2 were prepared. Chemical structure of the synthesized MPEGM and superplasticizers together with their copolymer composition were identified by FTIR and 1HNMR analyses. The molecular weights (Mw) and molecular weight distributions (PDI) of PCE-1 (8.74 × 104, 1.36) and PCE-2 (8.74 × 104, 2.19) were studied by GPC analysis, respectively. The zeta potential of cement particles (2.8 mV) becomes negative in the presence of 0.6 g/L of PCE-1 (− 7.8) and PCE-2 (− 9.5). This implies that electrostatic and steric hindrance forces of adsorbed superplasticizers synergistically provide a situation for appropriate dispersion of cement particles. The results of water-reducing percentage, fluidity, air content, bleeding water rate, initial and final setting times, wet density, flexural and compressive properties, and ultrasonic pulse velocity analyses exhibit significant enhancement on the features of concrete mixtures made of polycarboxylate superplasticizer. The superiority of PCE-2 to PCE-1 was connected to its adsorption-dispersibility potent induced by stronger electrostatic and steric repulsion forces, which result in quality and continuity enhancement in concretes.

Extensive study of droplet dynamics with end-grafted polymer chains in Pickering emulsions: Molecular Dynamics simulation and a generic model derived from the generalized Langevin equation

This paper investigates Pickering emulsions (PEs), formed by suspending oil droplets as the dispersed phase in water as the continuous phase using uncharged particles at their interface. To prevent coalescence, the particles are grafted with polymer chains, as emulsifier, not only to provide steric repulsion forces through the excluded volume between monomers floating in water, compensating for the absence of Coulombic repulsive forces but also control emulsion stabilization/destabilization. We combined molecular dynamics (MD) simulations and a generalized Langevin equation (GLE) model to study the dynamics of hairy-droplets using two dynamic quantities: mean square displacement (MSD) and velocity autocorrelation function (VACF). The number of grafted-polymer-chains, f, was the main parameter of interest, while the other parameters of the system were kept constant. A statistical approach was used to estimate theoretical GLE-based model parameters along with their uncertainties, providing insight into the diffusion behavior of these hairy-droplets and specifically addressing the transition between different observed regimes. we capture three specific values of grafted-polymer-chains as, fb=47 and ft=185 describe the transitions of mushroom-brush conformation of grafted-polymer-chains and viscous-viscoelastic behavior of hairy-droplets, respectively, and fg=257 representing the gel-like state number.

Polymer-Assisted Graphite Exfoliation: Advancing Nanostructure Preparation and Multifunctional Composites.

Exfoliated graphite (ExG) embedded in a polymeric matrix represents an accessible, cost-effective, and sustainable method for generating nanosized graphite-based polymer composites with multifunctional properties. This review article analyzes diverse methods currently used to exfoliate graphite into graphite nanoplatelets, few-layer graphene, and polymer-assisted graphene. It also explores engineered methods for small-scale pilot production of polymer nanocomposites. It highlights the chemistry involved during the graphite intercalation and exfoliation process, particularly emphasizing the interfacial interactions related to steric repulsion forces, van der Waals forces, hydrogen bonds, π-π stacking, and covalent bonds. These interactions promote the dispersion and stabilization of the graphite derivative structures in polymeric matrices. Finally, it compares the enhanced properties of nanocomposites, such as increased thermal and electrical conductivity and electromagnetic interference (EMI) shielding applications, with those of neat polymer materials.

Natural Surfactant Stabilized Aqueous MoS2 Nano-Lubricants for Reducing Friction and Wear

From the outlook of energy saving and environmental protection, the development of eco-friendly and green lubricants without compromising their lubrication performance has become a global agenda. Nevertheless, water-based lubricants suffer from low lubricity and weak load-bearing capacity, making them unsuitable for various industrial applications. Herein, using liquid-phase exfoliation, bulk MoS2 layers are delaminated into atomically thin nanosheets and stabilized in a water medium by a natural surfactant, Sapindius Mukrossi (SM). A natural SM surfactant consisting of 10 % –12 % saponin molecules has a hydrophobic tail aglycone and hydrophilic head glycone molecules that provide steric repulsive forces against the aggregation of exfoliated MoS2 nanosheets. Optimization of the surfactant concentration in water led to highly concentrated MoS2 nanosheets (∼1.23 mg/ml in a single step) with an average lateral length (<L>) and number of layers (<N>) of ∼ 150 nm and ∼ 8 layers, respectively. Owing to its high concentration and few-layers, MoS2 nanosheets based aqueous dispersion was directly tested for aqueous lubricant applications. Compared to pure water, MoS2 nanosheets (0.1 wt%) in water led to effective reductions in the coefficient of friction and wear scar diameter of ∼ 75 % and ∼ 65 %, respectively. Wear depth ∼ 15 µm on SS ball is reduced to ∼ 1 µm when 0.1 wt% of MoS2 nanosheets-SM surfactant dispersion under similar testing conditions. Post-mortem analysis suggested that the stable formation of protective tribo-film on the worn surfaces of steel surface that were tested at different intervals (1-210-400 Days) leads to an effective sliding under load. To demonstrate the practicality of this dispersion, SM surfactant stabilized MoS2 nanosheets was used as a dielectric lubricant fluid in a wire EDM for advanced metal-cutting fluid applications.

A novel section–section potential for short-range interactions between plane beams

We derive a novel formulation for the interaction potential between deformable fibers due to short-range fields arising from intermolecular forces. The formulation improves the existing section–section interaction potential law for in-plane beams by considering an offset between interacting cross sections. The new law is asymptotically consistent, which is particularly beneficial for computationally demanding scenarios involving short-range interactions like van der Waals and steric forces. The formulation is implemented within a framework of rotation-free Bernoulli–Euler beams utilizing the isogeometric paradigm. The improved accuracy of the novel law is confirmed through thorough numerical studies. We apply the developed formulation to investigate the complex behavior observed during peeling and pull-off of elastic fibers interacting via the Lennard–Jones potential.

Zr-BTB nanosheets assist in optimizing the structure of forward osmosis membranes to enhance the lithium concentration performance

Recently, low-energy forward osmosis (FO) technology has been employed in the lithium concentration stage during the extraction of lithium from brine sources. The interlayer FO membrane is renowned for its exceptional structural characteristics; however, challenges remain in selecting suitable interlayer materials and exploring their control mechanisms on amine monomers. As interlayer materials, traditional 3D nanomaterials are prone to detachment, while traditional 2D materials without micropores can increase the transmission resistance of water molecules. This study introduces a novel FO membrane utilizing Zr-BTB nanosheets with 5.4 Å micropores as the interlayer material. Based on detection and simulation calculations, it was found that the increase in steric hindrance and interaction forces jointly slowed the diffusion of amine monomers in the presence of the Zr-BTB interlayer. This results in a thinner separation layer, facilitating water transport. The interlayer also plays crucial roles in preventing defective pore formation in the separation layer and assisting in intercepting salt ions. The Zr-BTB interlayer membrane exhibited a water flux of 29.14 L m−2 h−1 and a reverse salt flux of 0.16 g m−2 h−1, which are superior to those of many FO membranes reported in the field. The prepared membrane also has excellent performance in lithium concentration applications, and its separation mechanism was explored by MD simulations.

Impact of the reductive deiodination on the sorption of iodinated X-ray contrast media to filter sand and activated carbon

Iodinated X-ray contrast media (ICM) and their aerobic transformation products (TPs) are widespread in the aquatic environment due to their persistent and mobile character. In a previous lab study, we have shown that the reductive (partial) deiodination of selected triiodobenzene derivatives increases the sorption to aquifer sand and loam soil, since iodine affects the compounds by steric hindrance, repulsive forces, resonance and inductive effects. These results suggest that the (partial) deiodination generally occurring to ICM and aerobic ICM TPs during anoxic/anaerobic bank filtration has a potential to increase their removal by sorption to natural sorbents. To basically assess the sorption potential to technically applied materials for drinking water treatment subsequent to bank filtration, we investigated the sorption of iopromide, diatrizoate and 5-amino-2,4,6-triiodoisophtalic acid and their di, mono and deiodinated structures to used filter sand from a waterworks and different fresh powdered activated carbons in batch tests using Berlin drinking water. The filter material, coated by iron and manganese oxides as well as organic material (including biofilm), preferentially removed monoiodinated derivatives, but diffusion through the organic layer heavily slowed the sorption. Therefore, the removal potential by sorption in rapid sand filters of waterworks for (partially) deiodinated benzene derivatives is suggested to be low. The deiodination of iopromide and diatrizoate significantly increased the sorption affinity to activated carbon and the competitiveness with regard to drinking water DOC. Despite the large atom radius of iodine, no clear correlation was found between the pore characteristics of the activated carbons and the molecular size of the compounds. This study emphasises the importance of anoxic/anaerobic conditions for the removal of persistent and mobile ICM and ICM TPs during drinking water treatment.

Enhancing proton transport in polyvinylidenedifluoride membranes and reducing biofouling for improved hydrogen production in microbial electrolysis cells

Hydrophilic porous membranes, exemplified by polyvinylidene fluoride (PVDF) membranes, have demonstrated significant potential for replacing ion exchange membranes in microbial electrolysis cells (MECs). Membrane fouling remains a major challenge in MECs, impeding proton transport and consequently limiting hydrogen production. This study aims to investigate a synergistic antifouling strategy for PVDF membrane through the incorporation of a coating composed of polydopamine (PDA), polyethyleneimine (PEI), and silver nanoparticles (AgNPs). The PDA-PEI-Ag@PVDF membrane not only effectively mitigates fouling through steric and electrostatic repulsion forces, but also amplifies ion transport by facilitating water diffusion and electromigration. The PDA-PEI-Ag@PVDF membrane exhibited a reduced membrane resistance of 1.01 mΩ m2 and PDA-PEI-Ag modifying PVDF membrane was found to be effective in enhancing the proton transportation of PVDF membrane. Therefore, the enhanced hydrogen production rate of 2.65 ± 0.02 m3/m3/d was achieved in PDA-PEI-Ag@PVDF-MECs.

In silico analyses of solvent effects, toxicity, NBO, homo-lumo and hole-electron transfer of 7-hydroxy-2-nitrofluoranthene

7-Hydroxy-2-nitrofluoranthene (7H2NF) is a fused polynuclear aromatic molecule. A naphthalene molecule is fused with a benzene ring through a five-membered ring. Since it is aromatic, it has conjugated double bonds. In this molecule, an electron-donor and an electron-acceptor are placed in different corners. Hence, electrons can flow from electron-donor to acceptor through π-linkers. DFT/B3LYP/6-311 G method is adopted to perform the calculations. The electronic structure, Frontier energy gap, Mulliken charge analysis, stability, theoretical IR, and UV are investigated with the help of Gaussian 16W software. The NCI study reveals that it has steric and Van der Waals forces. The shaded surface with a projection of LOL indicates that it has electron depleted areas. The hole-electron transfer analysis suggests that it has a CT type excitation at the S6 level. Multiwfn 3.8 is used for these investigations. Toxicity is predicted. Solvent effects are calculated for FMO, MEP, etc.

Effects of charge and size on the coadsorption of counterionic colloids in Gibbs monolayers

This study uses a coarse-grained Monte Carlo algorithm to model and simulate the coadsorption of a binary mixture of counterionic colloids in Gibbs monolayers. These monolayers form at a idealized air-water interface, with one non-soluble species confined at the interface and the second one partially soluble in the aqueous phase. The investigation focuses on the effect of colloidal size and charge on the thermodynamics and microstructure of the monolayer. We find that the composition of the monolayer evolves non-trivially with surface coverage, depending on the balance of steric and electrostatic forces. When the electrostatic interactions are weak, the soluble species is expelled from the monolayer upon compression, yielding a phase behaviour particularly sensitive to the relative size of the soluble and non-soluble colloids. By contrast, strong electrostatic interactions favour the stabilization of the soluble particles in the monolayer and the formation of quasi-equimolar fluids, with only a weak dependence on particle size. The combination of these phenomena results in the formation of a number of two-dimensional mesoscopic arrangements in the monolayer, ranging from diluted gas-phase behaviour to domains of aggregates and percolates, and to incipient crystalline structures.

A Study on How Conformation Entropy of Attached Macromolecules Drives Polymeric Collapse and Protein Folding

AbstractThe conformation of macromolecules attached to a surface is influenced by both their excluded volume and steric forces. Here, self‐avoiding random walk simulations are used to evaluate the occurrence of various conformations as a function of the number of monomeric units to estimate the effect of conformational entropy of a tethered chain. Then, a more realistic scenario is assessed, which can more accurately reproduce the shape of a tethered macromolecule. The simulations presented here confirm that it is more likely for a polymer to undergo a collapse conformation rather than a stretched one, as a collapse conformation can be realized in more different ways. Also, they confirm the “mushroom” shape of polymers close to a surface. From this simple approach, the conformation entropy of a model 100‐unit polymer close to a surface is estimated to contribute with over 129 toward its collapse. This conformation entropy is higher than that of typical hydrogen bonds and even barriers that keep proteins folded. As such, entropic collapse of macromolecules plays an important role in realizing the mushroom shape of attached polymers and can be the driving force in protein folding, while the polypeptide chain emerges from the ribosome.

Attractive and repulsive forces in a crystal of [Rb(18-crown-6)][SbCl6] under high pressure.

The compression behavior of [Rb(18-crown-6)][SbCl6] crystal under pressure up to 2.16 (3) GPa was investigated in a diamond anvil cell (DAC) using a mixture of pentane-isopentane (1:4) as the pressure-transmitting fluid. The compound crystallizes in trigonal space group R3 and no phase transition was observed in the indicated pressure range. The low value of pressure bulk modulus [9.1 (5) GPa] found in this crystal is a characteristic of soft materials with predominant dispersive and electrostatic interaction forces. The nonlinear relationship between unit-cell parameters under high pressure is attributed to the influence of reduced intermolecular H...Cl contacts under pressure over 0.73 GPa. It also explains the high compression efficiency of [Rb(18-crown-6)][SbCl6] crystals at relatively low pressures, resulting in a significant shift of the Rb atom to the center of the crown ether cavity. At pressures above 0.9 GPa, steric repulsion forces begin to play a remarkable role, since an increasing number of interatomic H...Cl and H...H contacts become shorter than the sum of their van der Waals (vdW) radii. Below 0.9 GPa, both unit-cell parameter dependences (P-a and P-c) exhibit hysteresis upon pressure release, demonstrating their influence on the disordered model of Rb atoms. The void reduction under pressure also demonstrates two linear sections with the inflection point at 0.9 GPa. Compression of the crystal is accompanied by a significant decrease in the volume of the voids, leading to the rapid approach of Rb atoms to the center of the crown ether cavity. For the Rb atom to penetrate into the center of the crown ether cavity in [Rb(18-crown-6)][SbCl6], it is necessary to apply a pressure of about 2.5 GPa to disrupt the balance of atomic forces in the crystal. This sample serves as a compression model demonstrating the influence of both attractive and repulsive forces on the change in unit-cell parameters under pressure.

A mechanistic insight on how Compromised Hydrolysis of Triacylglycerol 7 (CHT7) restrains the involvement of it's CXC domain from quiescence repression

CHT7 is a regulator of quiescence repression in Chlamydomonas reinhardtii. Initially, CHT7's repression activity was thought to be managed by its DNA-binding CXC domain. Later, it was found that the CHT7-CXC domain is dispensable for CHT7's activities. Rather, CHT7's predicted protein domains were proposed to be involved in regulation activities by binding to other repressors in the cell. Yet, it remains unclear why and how CHT7 refrains its CXC domain from participating in any transcriptional activities. The question becomes more intriguing, since CXC binding regions are available in promoter regions of some of the misregulated genes in CHT7 mutant (cht7). Through biophysical experiments and molecular dynamics approaches, we studied the DNA recognition behavior of CHT7-CXC. The results indicate that this domain possesses sequence selectivity due to the differential binding abilities of its subdomains. Further, to understand if the case is that CXC loses its DNA binding capabilities in the vicinity of other repressors, we examined CHT7-CXC's DNA binding stability under the spatial constraint conditions created through fusing CHT7-CXC with AsLOV2. The results show limited ability of CHT7-CXC to withstand steric forces and provide insights to why and how algal cells may hold back CHT7-CXC's indulgence in quiescence repression. ClassificationsBiological Sciences, Biophysics and Computational Biology.