Entropic Interactions Research Articles

Emergent hybrid mesophases in ternary mixtures of cellulose nanocrystals ‐ Pluronic micelles‐water

AbstractMixtures of nanometric rods and spherical micelles that are dominated by excluded volume (entropic) interactions tend to de‐mix into sphere‐ and rod‐rich mesophases. Here we report the observation of hybrid mesophases formed by mixtures of polymer‐decorated sulfuric‐acid‐hydrolyzed cellulose nanocrystals (CNCs, rod‐like particles), at high CNCs concentrations (7 wt%) where the native CNCs suspensions are at the bi‐phasic (isotropic‐chiral nematic) regime, and spherical micelles of the tri‐block‐copolymers Pluronic F127 (and F108) in aqueous suspension. The polymers adsorb onto the CNCs particles, and at F127 concentrations above (10–18 wt%) the macroscopic phases of the hybrid mixture are transformed into mesoscopic droplets with a nanostructure that differs from that of the CNCs or the native Pluronics, as indicated by small‐angle X‐ray scattering. The observed phases preserve the chiral nematic nature of the CNCs phases with a shortened pitch, suggesting that co‐assembly of CNCs and self‐assembling polymers may be used for engineering of emergent phases with emergent structures and properties.

Magnetic Field-Induced Self-Assembly of Conjugated Block Copolymers and Nanoparticles at the Air-Water Interface.

Here, we report the magnetic field-induced self-assembly of a conjugated block copolymer, poly(3-hexylthiopene)-block-poly(ethylene glycol) (P3HT-b-PEG), and iron oxide nanoparticles (IONPs) at the air-water interface. Binary self-assembly of P3HT-b-PEG and IONPs at the interface results in nanoparticle-embedded P3HT-b-PEG nanowire arrays with a micrometer-scale domain size. Under the magnetic field, the field-induced magnetic interaction significantly improves the degree of order, generating long-range ordered, direction-controlled nanoarrays of P3HT-b-PEG and IONPs, where IONPs are aligned in the direction of the magnetic field over a sub-millimeter scale. The size of IONPs is an important factor for the formation of an ordered assembly structure at the nanometer scale, as it dictates the magnetic dipole interaction and the entropic interaction between nanoparticles and polymers. The consideration of magnetic dipole interactions suggests that the field-induced self-assembly occurs through the formation of intermediate magnetic subunits composed of short IONP strings along the semirigid P3HT nanowires, which can be aligned through the magnetic interactions, ultimately driving the long-range ordered self-assembly. This study demonstrates for the first time that the magnetic field-induced self-assembly can be used to generate macroscopically ordered polymer films with a nanometer-scale order in low fields.

To Be or Not To Be? that is the Entropic, Enthalpic, and Molecular Interaction Dilemma in the Formation of (Water)20 Clusters and Methane Clathrate.

A detailed analysis under a comprehensive set of theoretical and computational tools of the thermodynamical factors and of the intermolecular interactions behind the stabilization of a well known set of (water)20 cavities and of the methane clathrate is offered in this work. Beyond the available reports of experimental characterization at extreme conditions of most of the systems studied here, all clusters should be amenable to experimental detection at 1 atm and moderate temperatures since 280 K marks the boundary at which, ignoring reaction paths, formation of all clusters is no longer spontaneous from the 20H2 O→(H2 O)20 and CH4 +20H2 O→CH4 @512 processes. As a function of temperature, a complex interplay leading to the free energy of formation occurs between the destabilizing entropic contributions, mostly due to cluster vibrations, and the stabilizing enthalpic contributions, due to intermolecular interactions and the PV term, is best illustrated by the highly symmetric 512 cage consistently showing signs of stronger intermolecular bonding despite having smaller binding energy than the other clusters. A fluxional wall of attractive non-covalent interactions, arising because of the cumulative effect of a large number of tiny individual charge transfers to the interstitial region, plays a pivotal role stabilizing the CH4 @512 clathrate.

Unravelling the polyethylenimine mediated non-monotonic stability behaviour of silica colloids: the role of competing electrostatic and entropic interactions.

Polymer-mediated interactions play an important role in the stability of colloids and are therefore paramount for both fundamental as well as scientific interests. The stability of colloids in the presence of neutral polymers depends on several parameters such as the adsorbing/non-adsorbing nature, molecular weight, concentration and temperature, and such systems are well studied. However, the stability behaviour of charged colloids in the presence of charged polyelectrolyte involves complex interaction mechanisms and hence needs attention. The present work reports the study of the stability behaviour of negatively charged silica colloids in the presence of cationic polyethylenimine (PEI) polyelectrolyte using small-angle neutron and X-ray scattering. The intriguing non-monotonic stability behaviour of silica colloids is observed with varying concentrations of PEI. In the low and intermediate PEI concentration regimes, electrosorption of PEI on the silica colloids causes partial screening of charges, leading to aggregation of colloids. The DLVO interaction potential at low and intermediate concentrations of PEI exhibit a reduced repulsion barrier which is responsible for aggregation. In the high concentration regime, the entropic interaction between the free PEI molecules and PEI decorated silica colloids leads to depletion re-stabilization. The combination of DLVO potential and adsorbed PEI mediated enhanced depletion repulsion in the presence of free PEI gives rise to an increased repulsion barrier responsible for the re-stabilization at high PEI concentrations.

Insights from computational analysis: how does the SARS-CoV-2 Delta (B.1.617.2) variant hijack ACE2 more effectively?

The SARS-CoV-2 Delta (B.1.617.2) variant was identified in India in October 2020, and it has quickly become the mainstream strain with strong toxicity and spread, posing great challenges to epidemic control. However, the molecular mechanism of its powerful infectivity remains unclear. It is meaningful to investigate the process of Delta variant's receptor-binding domain (RBD) binding to angiotensin-converting enzyme 2 (ACE2). Here, we performed three repeated molecular dynamics simulations for each system to avoid accidents, and the alanine scanning combined with the interaction entropy (ASIE) method was utilized to evaluate the binding free energy. Through the detailed energy and conformational analysis, the binding mechanism of the Delta variant was illustrated. The results showed that the existence of L452R and T478K mutations can trigger the effective hijacking of ACE2 by the Delta variant through the following three ways: (i) these two mutations can significantly enhance the electrostatic energy of the system by the introduction of two positively charged amino acids (Arg and Lys), thereby increasing the binding affinity of RBD and ACE2, (ii) the Loops 1, 3, and 4 in the receptor-binding motif (RBM) of RBD form a tighter conformation under the dominance of the T478K mutation, allowing ACE2 to be captured more effectively than the wild-type system, and (iii) these conformational changes lead to a more stable hydrogen bond in the Delta variant, which further ensures the stability of the binding. In addition, to explore the effect of mutations on the antibody, the key residues contributing to the changes in the binding ability of RBD in the Delta variant with the existing 42 neutralizing monoclonal antibodies (mAbs) have been preliminarily evaluated. The present study reveals the molecular mechanism for the increased infectivity of SARS-CoV-2 caused by mutations, and the key sites that cause antigenic changes were screened. It provides important theoretical insights for the development of novel targeted RBD drugs and antibodies.

Directing the Diffusion of Public Opinions in Incidents with Not‐in‐My‐Back‐Yard Projects: An Evolutionary Perspective

How should the public administrative department direct the diffusion of public opinions in a not‐in‐my‐backyard (NIMBY) crisis? This paper first analyzes the macroevolutionary characteristics of the public opinion associated with a NIMBY crisis. We then examine the perceptive interactions among individuals towards NIMBY projects from a microscopic perspective and develop an evolutionary game model (i.e., replicator dynamics) to describe the interactions among individuals. We also use information entropy and dynamic equations to construct an interaction entropy model and a dynamic equation to capture administrative‐department‐led public opinion. Through examining the existence and stability of the evolutionary equilibrium of these models, we analyze the evolution of NIMBY public opinion.

Molecular investigation of the dual inhibition mechanism for targeted P53 regulator MDM2/MDMX inhibitors.

Inhibitors that competitively bind MDM2/MDMX can block the inhibition of P53 by MDM2/MDMX and restart its tumor-suppressive effect. Molecular studies targeting MDM2/MDMX inhibitors have always been a hot topic in anticancer drug design. Although numerous inhibitors have been designed previously against MDM2/MDMX, their dual inhibition efficacy has not been demonstrated, and few studies assessed the general causes affecting the dual inhibition of MDM2/MDMX by these inhibitors. Here, molecular dynamics simulations and alanine scanning combined with the interaction entropy method were employed to precisely investigate whether 16 inhibitors could dually inhibit MDM2/MDMX and the similarities and differences in the interaction modes. Thereby addressing the key residue sites affecting dual inhibition. Residues L54/M53, I61/60, M62/61, Y67/66, and V93/92 of MDM2/MDMX, which are in corresponding positions in both protein structures, provide significant conditions for these inhibitors to bind to MDM2/MDMX tightly. In addition, most of these inhibitors prefer to bind MDM2 than MDMX, and residues H96 and I99 in MDM2 are attractive targets for inhibitors, resulting in inhibitors binding to MDM2/MDMX with different affinity. These key residues should be considered in the development of dual inhibitors. For these 16 inhibitors, most have dual inhibitory potential for MDM2/MDMX based on the binding affinity of the complexes. Still, it is questionable whether they can exert excellent dual inhibition considering the assessment of the hot-spots. At least their binding affinity for MDMX is not superior to that for MDM2 due to the difference in energy of the van der Waals interactions at the key sites. Furthermore, based on the analysis of three representative inhibitors (TUZ/HRH and HRQ with different binding preferences for MDM2/MDMX), 3-chloropyridine in TUZ leads to the differential binding affinity between the inhibitor and MDM2/MDMX. It readily forms hydrophobic interactions with the surrounding residues H96 and I99. But this phenomenon does not occur in the TUZ-MDMX system, implying the critical role of residues H96/P95 and I99/L98. And the completely different binding mechanism of HRQ binding to MDM2/MDMX explains its inability to inhibit MDM2 well. Thus, we are cautious about its dual inhibitory ability. Besides, HRH is more prone to strong van der Waals interactions with MDM2 than MDMX whereas its 2-chlorofluorobenzene is detrimental to this. We hope that these findings will provide reliable molecular insights for the screening and optimization of targeting MDM2/MDMX dual inhibitors.

Altering the Double-Stranded DNA Specificity of the bZIP Domain of Zta with Site-Directed Mutagenesis at N182.

Zta, the Epstein–Barr virus bZIP transcription factor (TF), binds both unmethylated and methylated double-stranded DNA (dsDNA) in a sequence-specific manner. We studied the contribution of a conserved asparagine (N182) to sequence-specific dsDNA binding to four types of dsDNA: (i) dsDNA with cytosine in both strands ((DNA(C|C)), (ii, iii) dsDNA with 5-methylcytosine (5mC, M) or 5-hydroxymethylcytosine (5hmC, H) in one strand and cytosine in the second strand ((DNA(5mC|C) and DNA(5hmC|C)), and (iv) dsDNA with methylated cytosine in both strands in all CG dinucleotides ((DNA(5mCG)). We replaced asparagine with five similarly sized amino acids (glutamine (Q), serine (S), threonine (T), isoleucine (I), or valine (V)) and used protein binding microarrays to evaluate sequence-specific dsDNA binding. Zta preferentially binds the pseudo-palindrome TRE (AP1) motif (T–4G–3A-2G/C0T2C3A4). Zta (N182Q) changes binding to A3 in only one half-site. Zta(N182S) changes binding to G3 in one or both halves of the motif. Zta(N182S) and Zta(N182Q) have 34- and 17-fold weaker median dsDNA binding, respectively. Zta(N182V) and Zta(N182I) have increased binding to dsDNA(5mC|C). Molecular dynamics simulations rationalize some of these results, identifying hydrogen bonds between glutamine and A3, but do not reveal why serine preferentially binds G3, suggesting that entropic interactions may mediate this new binding specificity.

Computational Alanine Scanning Reveals Common Features of TCR/pMHC Recognition in HLA-DQ8-Associated Celiac Disease.

In HLA-DQ8-associated celiac disease, Gliadin-γ1 or Gliadin-α1 peptide is presented to the cell surface and recognized by several types of T-cell receptor (TCR), but it is still unclear how the TCR, peptide, and the major histocompatibility complex (MHC) act together to trigger celiac disease. For now, most of the analysis is based on static crystal structures. And the detailed information about these structures based on energetic interaction is still lacking. Here, we took four types of celiac disease-related MHC-peptide-TCR structures from three patients to perform computational alanine scanning calculations using the molecular mechanics generalized born surface area (MM/GBSA) approach combined with a recently developed interaction entropy (IE) method to identify the key residues on TCR, peptide, and MHC. Our study aims to shed some light on the interaction mechanism of this complex protein interaction system. Based on detailed computational analysis and mutational calculations, important binding interactions in these triple-interaction complexes are analyzed, and critical residues responsible for TCR/pMHC recognition pattern in HLA-DQ8-associated celiac disease are presented. These detailed analysis and computational result should help shed light on our understanding of the celiac disease and the development of the medical treatment.

Computational Insights into the Binding Mechanism of OxyS sRNA with Chaperone Protein Hfq.

Under the oxidative stress condition, the small RNA (sRNA) OxyS that acts as essential post-transcriptional regulators of gene expression is produced and plays a regulatory function with the assistance of the RNA chaperone Hfq protein. Interestingly, experimental studies found that the N48A mutation of Hfq protein could enhance the binding affinity with OxyS while resulting in the defection of gene regulation. However, how the Hfq protein interacts with sRNA OxyS and the origin of the stronger affinity of N48A mutation are both unclear. In this paper, molecular dynamics (MD) simulations were performed on the complex structure of Hfq and OxyS to explore their binding mechanism. The molecular mechanics generalized born surface area (MM/GBSA) and interaction entropy (IE) method were combined to calculate the binding free energy between Hfq and OxyS sRNA, and the computational result was correlated with the experimental result. Per-residue decomposition of the binding free energy revealed that the enhanced binding ability of the N48A mutation mainly came from the increased van der Waals interactions (vdW). This research explored the binding mechanism between Oxys and chaperone protein Hfq and revealed the origin of the strong binding affinity of N48A mutation. The results provided important insights into the mechanism of gene expression regulation affected by protein mutations.

Difference in the binding mechanisms of ABT-263/43b with Bcl-xL/Bcl-2: computational perspective on the accurate binding free energy analysis.

B-cell lymphoma/leukemia gene-2(Bcl-2) protein family known for regulating cell cycle arrest and subsequent cell death is highly expressed in a variety of cancers. Among them, the Bcl-xL and Bcl-2 are two essential proteins in the Bcl-2 family. In the present work, the differences in binding modes as between the two proteins and two ligands ABT-263/43b were investigated and compared. And the computational alanine scanning combined with the recently developed interaction entropy (AS-IE) method was employed for predicting their binding free energies and finding those amino acids that were more critical during the binding process. The result showed that the binding free energy calculated by the AS-IE method was more in line with experimental values than the molecular mechanics/Poisson-Boltzmann surface area (MM/PBSA) method. Besides, no significant difference was found between Bcl-xL and ABT-263/43b in the binding free energy, which Bcl-xL showed slightly weaker binding free energy to 43b because of the fewer number of key residues with interactions. Nonetheless, compared with the Bcl-2 and 43b complex, the Bcl-2 and ABT-263 system had greater number of key residues interacting with ABT-263, in particular, contribute favorably, resulting in a stronger binding ability for the Bcl-2 and ABT-263 systems. The van der Waals and hydrogen bond contributions were significant in the four protein-ligand complexes. Overall, Tyr108 was found to be the common key residues in the Bcl-xL-ligand complex, while Tyr105, Glu100, and Glu143 were established as the common key residue in the Bcl-2-ligand systems. We hope that the predicted hot spot residues and their energy distributions can guide the design of peptide and small-molecule drugs targeting Bcl-xL and Bcl-2.

Gauge-free duality in pure square spin ice: Topological currents and monopoles

We consider pure square spin ice, that is, square ice, where only nearest neighbors are coupled. The gauge-free duality between the perpendicular and collinear structure leads to a natural description in terms of topological currents and charges as the relevant degrees of freedom. That, in turn, can be expressed via a continuous field theory where the discrete spins are subsumed into entropic interactions among charges and currents. This approach produces structure factors, correlations, and susceptibilities for spins, monopoles, and currents. It also generalizes the height formalism of the disordered ground state to non-zero temperature. The framework can be applied to the zoology of recent experimental results, especially realizations on quantum annealers, and can be expanded to include longer range interactions.

Isosteric Heats and Entropy of Adsorption in Henry's Law Region for Carbon and MOFs Structures for Energy Conversion Applications

The thermodynamic property surfaces such as enthalpy and entropy of an adsorbate + adsorbent systems are essential for designing adsorption-assisted thermal compression, gas storage, separation, and other applications. This paper presents the enthalpy (∆ho) and the entropy (∆so) of the adsorbent-adsorbate system under the barrier of Henry's law region. Hence Henry's law coefficient and Gibbs analogy are applied to formulate the adsorption driving force (∆go). To justify the proposed formulation, the initial adsorption phenomena (at pressure, P → 0) of C2H5OH, CO2, CH4, N2, H2O, R125, R134a, R152a, and R1234yf on graphite/MOFs (such as Zr-MOF-801, Mg-MOF-74, and Al-Fumarate) are considered. It is found that the adsorption driving force is linked with the pore structure of adsorbent materials. We employ experimentally measured isotherms data to calculate the adsorption driving force, ∆go for various adsorbate + activated carbon/MOFs systems. The maximum adsorption driving force is found at the pore widths of 3 Å to 7 Å. The ∆go decreases with higher adsorbent-pore volume and depends on adsorbate molecule size. Employing the proposed driving force concepts, (i) the specific cooing, heating, and COP of the adsorption system, and (ii) the CO2/CH4 storage capacity in the adsorption cell can be projected and analyzed. The adsorption driving force relates to enthalpic and entropic interactions and is useful for the design of adsorbents and the selection of adsorbent-adsorbate pairs for gas storage, separation, and various energy-related applications.

Gmx_MMPBSA: A New Tool to Perform End-State Free Energy Calculations with GROMACS

Molecular mechanics/Poisson-Boltzmann (Generalized-Born) surface area is one of the most popular methods to estimate binding free energies. This method has been proven to balance accuracy and computational efficiency, especially when dealing with large systems. As a result of its popularity, several programs have been developed for performing MM/PB(GB)SA calculations within the GROMACS community. These programs, however, present several limitations. Here we present gmx_MMPBSA, a new tool to perform end-state free energy calculations from GROMACS molecular dynamics trajectories. gmx_MMPBSA provides the user with several options, including binding free energy calculations with different solvation models (PB, GB, or 3D-RISM), stability calculations, computational alanine scanning, entropy corrections, and binding free energy decomposition. Noteworthy, several promising methodologies to calculate relative binding free energies such as alanine scanning with variable dielectric constant and interaction entropy have also been implemented in gmx_MMPBSA. Two additional tools-gmx_MMPBSA_test and gmx_MMPBSA_ana-have been integrated within gmx_MMPBSA to improve its usability. Multiple illustrating examples can be accessed through gmx_MMPBSA_test, while gmx_MMPBSA_ana provides fast, easy, and efficient access to different graphics plotted from gmx_MMPBSA output files. The latest version (v1.4.3, 26/05/2021) is available free of charge (documentation, test files, and tutorials included) at https://github.com/Valdes-Tresanco-MS/gmx_MMPBSA.

Size-Selective Sub-micrometer-Particle Confinement Utilizing Ionic Entropy-Directed Trapping in Inscribed Nanovoid Patterns.

We have developed a single-step, high-throughput methodology to selectively confine sub-micrometer particles of a specific size into sequentially inscribed nanovoid patterns by utilizing electrostatic and entropic particle-void interactions in an ionic solution. The nanovoid patterns can be rendered positively charged by coating with an aluminum oxide layer, which can then localize negatively charged particles of a specific size into ordered arrays defined by the nanovoid topography. On the basis of the Poisson-Boltzmann model, the size-selective localization of particles in the voids is directed by the interplay between particle-nanovoid geometry, electrostatic interactions, and ionic entropy change induced by charge regulation in the electrical double layer overlapping region. The underlying principle and developed method could potentially be extended to size-selective trapping, separation, and patterning of many other objects including biological structures.

Cefepime electronic structure, optical, spectroscopic, and the effect of water molecules on its physical properties

Cefepime is a fourth-generation antibiotic with the Stoichiometry C19H24N6O5S2. It is a 1.5 nm molecule. The electronic structure and related spectroscopic properties of cefepime are discussed in the present work. The thermodynamic interaction of the cefepime molecule with water molecules is also discussed. Density functional theory at the B3LYP/6-311G** level is used. Results show good agreement with available structural experimental results such as bond lengths. The iso-electrostatic potential energy shows the position of positive and negative potentials. The HOMO-LUMO energy gap is increased to more than 4 eV due to interaction with water molecules. The highest peak in the experimental IR spectrum (1773 cm−1) is confined between the calculated cefepime highest peak at (1694.4 cm−1) and the hydrated cefepime molecules at (1819-1823 cm−1). Many other evaluated properties such as Raman spectrum, dipole moment, Gibbs free energy, enthalpy, and entropy of interaction with water do not have experimentally measured values. The most stable Gibbs free energy is when cefepime interacts with two H2O molecules.

On the Use of Interaction Entropy and Related Methods to Estimate Binding Entropies.

Molecular mechanics combined with Poisson–Boltzmann or generalized Born and solvent-accessible area solvation energies (MM/PBSA and MM/GBSA) are popular methods to estimate the free energy for the binding of small molecules to biomacromolecules. However, the estimation of the entropy has been problematic and time-consuming. Traditionally, normal-mode analysis has been used to estimate the entropy, but more recently, alternative approaches have been suggested. In particular, it has been suggested that exponential averaging of the electrostatic and Lennard–Jones interaction energies may provide much faster and more accurate entropies, the interaction entropy (IE) approach. In this study, we show that this exponential averaging is extremely poorly conditioned. Using stochastic simulations, assuming that the interaction energies follow a Gaussian distribution, we show that if the standard deviation of the interaction energies (σIE) is larger than 15 kJ/mol, it becomes practically impossible to converge the interaction entropies (more than 10 million energies are needed, and the number increases exponentially). A cumulant approximation to the second order of the exponential average shows a better convergence, but for σIE > 25 kJ/mol, it gives entropies that are unrealistically large. Moreover, in practical applications, both methods show a steady increase in the entropy with the number of energies considered.

Abstract 83: Structural and biochemical properties of DIRAS3 N-terminal extension that permit its function as a tumor suppressor of oncogenic K-RAS

Abstract DIRAS3 is an imprinted tumor suppressor gene that encodes a small GTPase of the RAS superfamily. In contrast to oncogenic RAS proteins, DIRAS3 inhibits tumor growth and migration, while inducing autophagy and tumor dormancy. DIRAS3 inhibits PI3K/AKT/mTOR and RAS/MAP signaling. DIRAS3 inhibits oncogenic, mutant K-RAS signaling by binding directly to mutant K-RAS and disrupting K-RAS dimers and clusters on the inner leaflet of the plasma membrane. DIRAS3 bears 60% amino acid homology to K-RAS, differing by the addition of a distinctive 34 amino acid N-terminal extension (NTE). Both the NTE and an intact C-terminal CAAX box are required for the suppressor function of DIRAS3 in breast and ovarian cancers. While prenylation of the CAAX box is thought to facilitate binding of DIRAS3 to the inner leaflet of the cell surface membrane through a lipid tail, how the NTE influences membrane association is not well understood. In this study, we apply biochemical and biophysical methods to investigate NTE structure and ligand binding activities using synthetic wild type and mutated NTE peptides. Using a lipid overlay assay and surface plasmon resonance (SPR) analysis, we found that the DIRAS3 NTE has affinity for phosphatidylinositol phosphate lipids, especially PI(3,4,5)P3 and PI(4,5)P2. SPR demonstrated a strong interaction between NTE and PIP3 (dissociation constant of ~36 nM) with a cooperative self-association of NTE on the PIP3 sensor surface. Isothermal titration calorimetry revealed that NTE-PIP3 binding is complex, involving multiple sites and cooperativity, that appeared dominated by entropic interaction. Structural analysis of NTE mutants with circular dichroism spectroscopy indicated that the NTE is mainly unstructured in solution, however PIP3-binding induces a conformational rearrangement of the NTE that involves a hydrophobic surface of an amphipathic helix region. Furthermore, mass spectrometry identified N-myrisoylation of glycine in the NTE region of DIRAS3, which is unique among RAS family proteins. In addition, SPR screening of a K-RAS peptide library and kinetic analysis of the interaction between DIRAS3 NTE and K-RAS revealed engagement of the NTE with the effector lobe of K-RAS and a conformational change in the NTE•K-RAS complex. Together, our study suggests that DIRAS3 NTE may play an important role in inhibiting K-RAS and AKT signaling by facilitating specific protein-lipid interactions at the plasma membrane. The affinity of the NTE for PIP3 could contribute to the known regulation of PI3K by DIRAS3. Moreover, functional DIRAS3 may be tethered to the inner leaflet of the cell membrane at two points, by prenylation of the CAAX box at the C-terminal and by myristoylation of the NTE. Citation Format: Xiaowen Liang, Kwangkook Lee, Sung Y. Jung, Gamze Bildik, Weiqun Mao, Joshua P. Gray, Steven W. Millward, Zhen Lu, Robert C. Bast. Structural and biochemical properties of DIRAS3 N-terminal extension that permit its function as a tumor suppressor of oncogenic K-RAS [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 83.

Interface Structure and Dynamics in Polymer‐Nanoparticle Hybrids: A Review on Molecular Mechanisms Underlying the Improved Interfaces

AbstractIn a nano‐assembly of soft polymer chains and hard filler nanoparticles (NPs), the intermolecular interactions at the polymer‐filler interface lead to variations in viscoelastic properties in the vicinity of the NP surface. However, unravelling the molecular parameters controlling the entropic and enthalpic interactions, including polymer chain conformation, dynamics, dispersion mechanisms and confinement effects across the interfacial region, has been remote and challenging. Even though the polymer‘s molecular structure and the NPs surface chemistry contribute to these interfacial interactions, the underlying mechanism behind the enhanced dynamic‐mechanical performance is still a hot topic of debate. By controlling the chemistry of NPs and polymer matrix in model nanocomposites, many efforts have been made in elucidating the physical origin of the structure and dynamics of the interfacial polymer layer with estimates varying from 1 to 10 nm around the spherical NPs. Therefore, understanding the interface structure and dynamics influenced by polymer‐NP interaction is of great technological importance. In this article, the latest polymer‐particle interface literature developments are reviewed where computational simulations, calorimetry, and dielectric spectroscopy studies have been used to examine the constraints levied by the interface structure on segmental relaxation dynamics of polymer chains in the vicinity of NP surface.

Vapor-liquid and liquid-liquid equilibria in the water + poly(propylene glycol) system

The aim of this study was to investigate phase equilibria in a water + poly(propylene glycol) [Mn = 425 g mol−1] system. Vapor-liquid equilibria (VLE) were determined ebulliometrically in the completely miscible region with higher water concentrations at isotherms 323.15, 333.15, 343.15, and 353.15 K. These data were correlated with the UNIQUAC free-volume (FV) model to be consistent with our previous studies. Liquid-liquid equilibrium (LLE) was determined using the cloud-point method at 320–350 K, and lower critical solution temperature was found at 320.2 K. LLE was correlated with the entropic FV-UNIQUAC segmental interaction model developed earlier, which is suited for correlation and calculation of LLE of polymer solutions. We estimated new binary segmental interaction parameters for interactions between propylene glycol and water segments.