Formation Of Ordered Structures Research Articles

Chimie Douce Synthesis of Novel Metastable Cathodes for Potassium-Ion Batteries

The quest for innovative cathode materials is crucial for advancing secondary potassium-ion batteries (KIBs). Dedicated efforts have led to the exploration of broadly four distinct classes of materials, namely layered transition metal oxides, polyanion, Prussian blue analogues and organic materials [1]. However, synthesizing cathodes for KIBs, especially those based on layered 3d-series transition metals, pose significant challenges. These include the low concentration of K-ions due to electrostatic repulsion, hygroscopic instability, and decomposition susceptibility. In our current study, we addressed these complex synthetic challenges by employing the ambient ion-exchange synthesis method to create metastable cathode materials suitable for stationary energy storage applications. Integrating diffraction and spectroscopic techniques, we have elucidated that the ion exchange reaction proceeds via an overlay ordered structure formation (Figure 1) mechanism [2-6]. Additionally, we have conducted comprehensive investigations into the structural, morphological, electronic, and electrochemical characteristics of ion-exchanged materials [4]. To analyze the K+ insertion mechanism, we employed both ex-situ and in-situ X-ray diffraction analysis, along with potentio/galvanostatic titration techniques. Synergizing experimental tools with the theoretical calculations, we have unveiled the efficacy of ambient ion-exchange reactions to prepare promising novel cathode materials. Two case studies will be presented as noted below. Chemical ion-exchange route was employed to obtain a novel P2-type KxCo1/3Mn2/3O2 cathode for KIBs. With due material optimization and usage of suitable electrolytes, this oxide can be harnessed as a high-voltage cathode for KIBs operating at ~ 2.9 V at room and high (40-50 °C) temperatures (Figure 1c) [7-8].Following, two novel compounds analogous to Na2Mn3O7 has been successfully synthesized via ambient chimie douce This discovery reveals the utilization of a cost-effective, scalable, and energy-efficient K-Mn-O ternary mixture as an extensively studied cathode material for KIBs (Figure 1d) [9]. Finally, this work provides a new dimension in obtaining targeted battery material beyond traditional synthetic route for the development of KIBs for next generation stationary energy storage system.

Chimie Douce Derived Novel P2‐Type Layered Oxide for Potassium‐Ion Batteries

AbstractThe emergence of K‐ion batteries (KIBs) heralds a promising frontier in energy storage technology, offering the potential for high specific energy density, long cycle life, and robust power capabilities, all while utilizing the abundant resources of potassium. In response to the challenges posed by synthetic intricacies related to K‐based cathodes, the effort is directed toward employing soft chemistry (chimie douce) method to unveil a hitherto‐unknown P2‐type K1/3Co1/3Mn2/3O2 (KCM) layered oxide cathode for KIBs. Comprehensive analysis using diffraction, microscopy, and spectroscopy tools reveals the ion exchange reaction proceeds through overlay ordered structure formation mechanism. The as‐prepared KCM material serves as a ≈2.9 V positive K+ insertion host. Further, it showcases an exceptional structural reversibility, robust cycling performance with ≈100% coulombic efficiency even after 100 cycles, and maintaining electrochemical stability even at elevated temperature (c.a. 40° and 50 °C). The KCM cathode exhibits in‐plane Co–Mn ordering and solid‐solution redox mechanism during (de)potassiation. Combining first‐principles calculations with experimental tools, this research demonstrates the efficacy of ambient ion‐exchange route in stabilizing promising cathode materials for KIBs. This innovative synthetic approach not only streamlines synthetic complexities, but also holds significant implications for the advancement of KIB technology for stationary energy storage.

Gelation of gellan induced by trivalent cations and coexisting trivalent with monovalent cations studied by rheological and DSC measurements

The effect of trivalent cation Fe3+ on the gelation process of a sodium salt form of gellan (DG, deacylated gellan gum) was investigated by rheology and DSC studies. On addition of a fairly low concentration of Fe3+ (1 mM), both the complex modulus (G*) of a 1.0 % DG solution in gel state and the sol-gel transition temperature (Tgel) slightly decreased. At higher Fe3+ concentrations (2 and 3 mM), however, a slight increase in the G* and Tgel was observed. In the coexisting monovalent cation (K+) solutions, addition of Fe3+ always improved the G* in gel state and the Tgel in a concentration-dependent manner. Moreover, for all Fe3+ DG solutions, the ordered structure formation temperature (Torder) was always lower than Tgel and increased with increasing Fe3+ concentration. This finding indicates that the network formation in the DG solutions should occur in advance of the ordered structure formation of the DG chains and that the presence of Fe3+ unfavorably affected the conformational transition of DG. In coexisting cation solution, the presence of K+ ion made a favorable contribution to the binding of Fe3+ to the disordered DG chains and to the subsequent ordered structure formation of the DG chains.

The Multiscale Structural Properties and In‐Vitro Digestibility of High Amylose Corn Starch During Autoclaving‐Cooling Treatment

AbstractThis work investigates the relationship between multiscale structural properties in high amylose corn starch (HACS) and its in‐vitro digestibility by analyzing the effects of autoclaving‐cooling treatment (ACT). Differential scanning calorimetry (DSC) shows that HACS displays a higher gelatinization temperature, wider endothermic gelatinization range, and higher enthalpy. Autoclaved corn starch exhibits enhanced thermal stability than the raw corn starch. X‐ray diffraction (XRD) shows that ACT does not change the crystalline type but increases the relative crystallinity (RC). Fourier transform infrared spectroscopy (FTIR) indicates that HACS exhibits a higher degree of order (DO) and double helixes (DHs) than normal corn starch (NCS), which are reduced by ACT. Scanning electron microscopy (SEM) reveals that HACS displays denser structures and smaller particle morphologies than NCS. After ACT, the granular of autoclaved corn starch shows a rough fiber network structure. Digestibility analysis reveals a positive correlation between the amylose content and resistant starch (RS) level in raw starch, while ACT promotes significant RS formation. This suggests that amylose promotes ordered structure formation, while autoclaving increased digestive resistance.

Reversible Selbstassemblierung von Nukleinsäuren in einer diffusiophoretischen Falle

AbstractDie Bildung und Dissoziation von Duplexen oder komplexeren Strukturen aus Nukleinsäuresträngen ist ein fundamentaler Prozess mit vielfältigen Anwendungen in Biochemie und Nanotechnologie. Hier führen wir ein einfaches experimentelles System – eine diffusiophoretische Falle – für die Nichtgleichgewichts‐Selbstassemblierung von Nukleinsäurestrukturen ein, das einen Elektrolytgradienten als Antrieb nutzt. DNA‐Stränge können durch Diffusiophorese im elektrischen Feld eines Elektrolytgradienten bis zu hundertfach konzentriert werden. Geeignete Elektrolyte für diese diffusiophoretische Falle können mit Hilfe einer einfachen Gleichung bestimmt werden. Experimente mit carboxylierten Siliziumdioxidpartikeln zeigen, dass die diffusiophoretische Kraft langreichweitig und über hunderte von Mikrometern wirksam ist. Als Anwendung untersuchen wir die reversible Selbstassemblierung verzweigter DNA‐Nanostrukturen in der Falle zu einem makroskopischen Gel. Die Strukturen assemblieren in Anwesenheit eines Elektrolytgradienten und lösen sich bei dessen Entfernung wieder auf, was eine prototypische adaptive Reaktion auf einen makroskopischen Nichtgleichgewichtszustand darstellt.DiffusiophoreseDNA‐NanosterneSelbstorganisationDNA‐StrukturenNichtgleichgewichtsprozesse

Reversible Self-Assembly of Nucleic Acids in a Diffusiophoretic Trap.

The formation and dissociation of duplexes or higher order structures from nucleic acid strands is a fundamental process with widespread applications in biochemistry and nanotechnology. Here, we introduce a simple experimental system-a diffusiophoretic trap-for the non-equilibrium self-assembly of nucleic acid structures that uses an electrolyte gradient as the driving force. DNA strands can be concentrated up to hundredfold by a diffusiophoretic trapping force that is caused by the electric field generated by the electrolyte gradient. We present a simple equation for the field to guide selection of appropriate trapping electrolytes. Experiments with carboxylated silica particles demonstrate that the diffusiophoretic force is long-ranged, extending over hundreds of micrometers. As an application, we explore the reversible self-assembly of branched DNA nanostructures in the trap into a macroscopic gel. The structures assemble in the presence of an electrolyte gradient, and disassemble upon its removal, representing a prototypical adaptive response to a macroscopic non-equilibrium state.

The Origin of Anomalous Density Behavior of Silica Glass.

The anomalous density-temperature relationship of vitreous silica with low hydroxyl content is explained by the formation of medium-range ordering structure in the glass transition process. The ordered medium-range structure has the shape of a "nanoflake" and consists of two layers of SiO4 tetrahedra, bonded by O atoms located in the middle of the structure. The nanoflakes interact with their surrounding structures through both covalent chemical bonds and van der Waals bonds. In the formation of the van der Waals bonds, the orientation of SiO4 tetrahedra can change, which results in an increase in distance between the nanoflakes and their surrounding structures. Thus, there is a slight volume enlargement associated with the formation of nanoflakes. Since the nanoflakes' formation starts at a temperature near 1480 °C, and the population of the nanoflakes grows continuously as temperature decreases until about 950 °C, the bulk volume of silica glass increases in the temperature range from about 1480 °C to 950 °C. Therefore, the density anomaly of silica glass can be explained as a byproduct of forming of medium-range ordering structure in the silica glass transition.

Study on the Mechanism of Modified Cellulose Improve the Properties of Egg Yolk gel

Natural fiber is not suitable for modifying yolk gel as a modifier because of its large size and high compactness. In this study, two kinds of modified cellulose were selected to improve the thermal gel properties of yolk. The results showed that the two kinds of cellulose promoted the formation of ordered structure in yolk gel. The ordered gel network not only improved the texture properties and rheological properties, but also improved the water retention of yolk gel significantly. CMC and CNFC at the same concentration, the modification effect of CMC on yolk gel was better than CNFC because of its excellent dispersion. However, high concentration of CNFC (1.20–1.60%) disrupted the cross-linking and ordered structure formation of yolk protein, and the quality of gel was significantly reduced.

Square ice formation in CrOCl and graphene confinement

The structure and thermodynamic properties of water in nanoscale confinement environment are greatly involved in the research field of material science and nanotechnology. However, a complete picture of the ordered structure formation and thermodynamics behavior of the confined water inside two parallel nanosheets with different surface atomic arrangement is still lacking. In this paper, by using molecular dynamics (MD) simulations, we study the structural variation and thermodynamics behavior for water molecules confined between two parallel CrOCl with a square surface atomic arrangement and two parallel graphene nanosheets with a hexagonal surface atomic arrangement. Square ice, with a lattice constant 2.1 and 2.0 Å, is observed inside the two parallel CrOCl and graphene nanosheets, respectively. By calculating the configuration entropy of the molecular dipoles St , it is found that, in the CrOCl confinement, St reaches a peak value and then is greatly reduced due to the square ice formation. On the other hand, in the graphene confinement, St continues to grow after the square ice formation and is then reduced after reaching its peak value. Interestingly, it is found that the square ice could be stable at a higher entropy state under the external pressure than the bulk water at ambient condition. By calculating the orientational order parameters M, it shows that the conventional tetrahedral geometry of hydrogen bonding between water molecules breaks due to the square ice formation. By analyzing the average number of hydrogen bonds of water molecules Nh , it is found that the hydrogen bond interaction of the square ice relies on the confinement environment, where Nh is reduced in the CrOCl confinement and increased in the graphene confinement. Probability distribution functions of the dipole orientation angles between the x- or z-axis and the projection of the oxygen atoms of the water molecules are also calculated. It is observed that the square ice structure is paralleled with the x-axis (unit cell axis) in the CrOCl confinement and tilted with the x-axis (the zigzag direction of graphene) at an angle 30° in the graphene confinement. Furthermore, the square ice formation is found to be insensitive to temperature. Our result reveals the peculiar ordered structure and thermodynamics behavior of water in different nanoscale confinement environments.

Bioinformatics Analysis of Mutations Sheds Light on the Evolution of Dengue NS1 Protein With Implications in the Identification of Potential Functional and Druggable Sites.

Non-structural protein (NS1) is a 350 amino acid long conserved protein in the dengue virus. Conservation of NS1 is expected due to its importance in dengue pathogenesis. The protein is known to exist in dimeric and hexameric states. The dimeric state is involved in its interaction with host proteins and viral replication, and the hexameric state is involved in viral invasion. In this work, we performed extensive structure and sequence analysis of NS1 protein, and uncovered the role of NS1 quaternary states in its evolution. A three-dimensional modeling of unresolved loop regions in NS1 structure is performed. "Conserved" and "Variable" regions within NS1 protein were identified from sequences obtained from patient samples and the role of compensatory mutations in selecting destabilizing mutations were identified. Molecular dynamics (MD) simulations were performed to extensively study the effect of a few mutations on NS1 structure stability and compensatory mutations. Virtual saturation mutagenesis, predicting the effect of every individual amino acid substitution on NS1 stability sequentially, revealed virtual-conserved and variable sites. The increase in number of observed and virtual-conserved regions across NS1 quaternary states suggest the role of higher order structure formation in its evolutionary conservation. Our sequence and structure analysis could enable in identifying possible protein-protein interfaces and druggable sites. Virtual screening of nearly 10,000 small molecules, including FDA-approved drugs, permitted us to recognize six drug-like molecules targeting the dimeric sites. These molecules could be promising due to their stable interactions with NS1 throughout the simulation.

Peptide-Modified Gemini Surfactants as Delivery System Building Blocks with Dual Functionalities for Glaucoma Treatment: Gene Carriers and Amyloid-Beta (Aβ) Self-Aggregation Inhibitors.

Retinal ganglion cell (RGC) neurodegeneration in glaucoma has potential links with amyloid-β (Aβ) deposition. Targeting the Aβ pathway was shown to reduce RGC apoptosis and protect RGCs from degeneration. We report exploratory studies on the amyloid Aβ40 aggregation inhibition properties of four cell adhesion peptide (CAP)-gemini surfactants that are intended as building blocks for gene carrier nanoparticles for glaucoma treatment. The CAP-gemini surfactants (18-7N(p1-4)-18) were evaluated as potential Aβ40 peptide aggregation inhibitors by a fluorescence kinetic assay and for their binding interactions with Aβ40 dimers by molecular docking studies. In vitro Aβ40 peptide aggregation inhibition studies showed that the 18-7N(p3)-18 and 18-7N(p1)-18 ligands inhibit Aβ40 peptide aggregation and prevent the formation of higher order structures. CDOCKER energies and CDOCKER interaction energies demonstrated that the CAP-gemini surfactants formed more stable complexes in the Aβ40 dimer assembly and underwent both polar and nonpolar interactions compared to CAP peptides alone. Also, 18-7N(p3)-18 showed a significantly lower CDOCKER energy compared to that of the unmodified gemini surfactant 18-7NH-18 (p < 0.0001) and 18-7N(p4)-18 (p < 0.001), 18-7N(p1)-18, and 18-7N(p2)-18. Similarly, 18-7N(p3)-18 showed a significantly lower CDOCKER interaction energy compared to that of 18-7NH-18, 18-7N(p4)-18 (p < 0.0001), and 18-7N(p2)-18 (p < 0.001), while 18-7N(p3)-18 and 18-7N(p1)-18 showed similar CDOCKER interaction energies. These studies suggest that a combination of both hydrophobic and electrostatic interactions contributes to the anti-Aβ40 aggregation activity of CAP-gemini surfactants. CAP-gemini surfactants showed 10-fold better Aβ40 peptide aggregation inhibition compared to previously reported values and could provide a new opportunity for glaucoma treatment as dual-functional gene carriers.

Thermodynamics, static properties and transport behaviour of fluids with competing interactions

Competing interaction fluids have become ideal model systems to study a large number of phenomena, for example, the formation of intermediate range order structures, condensed phases not seen in fluids driven by purely attractive or repulsive forces, the onset of particle aggregation under in- and out-of-equilibrium conditions, which results in the birth of reversible and irreversible aggregates or clusters whose topology and morphology depend additionally on the thermodynamic constrictions, and a particle dynamics that has a strong influence on the transport behaviour and rheological properties of the fluid. In this contribution, we study a system of particles interacting through a potential composed by a continuous succession of a short-ranged square-well (SW), an intermediate-ranged square-shoulder and a long-ranged SW. This potential model is chosen to systematically analyse the contribution of every component of the interaction potential on the phase behaviour, the microstructure, the morphology of the resulting aggregates and the transport phenomena of fluids described by competing interactions. Our results indicate that the inclusion of a barrier and a second well leads to new and interesting effects, which in addition result in variations of the physical properties associated to the competition among interactions.

Polar swimmers induce several phases in active nematics

Swimming bacteria in passive nematics in the form of lyotropic liquid crystals are defined as a new class of active matter known as living liquid crystals in recent studies. It has also been shown that liquid crystal solutions are promising candidates for trapping and detecting bacteria. We ask the question, can a similar class of matter be designed for background nematics which are also active? Hence, we developed a minimal model for the mixture of polar particles in active nematics. It is found that the active nematics in such a mixture are highly sensitive to the presence of polar particles and show the formation of large scale higher order structures for a relatively low polar particle density. Upon increasing the density of polar particles, different phases of active nematics are found and it is observed that the system shows two phase transitions. The first phase transition is a first order transition from quasi-long-ranged ordered active nematics to disordered active nematics with larger scale structures. On further increasing density of polar particles, the system transitions to a third phase, where polar particles form large, mutually aligned clusters. These clusters sweep the whole system and enforce local order in the nematics. The current study can be helpful for detecting the presence of very low densities of polar swimmers in active nematics and can be used to design and control different structures in active nematics.

Effects of Al replacement on glass forming ability and mechanical properties of Zr-based bulk metallic glasses

In this present study, the effects of Al substitution for Zr in Zr73-xCu12Ni12AlxNb3 (x=7.5, 10, 12.5, 15, 17.5 at.%) metallic glasses on the glass-forming ability, thermal stability, quasi-static and dynamic mechanical properties were investigated. Proper Al replacement improved the glass-forming ability, crystallization activation energy and mechanical properties of the amorphous alloys. Compared with quasi-static compression, due to the shorter loading time and more significant adiabatic temperature rise, the fracture strength decreased and no dynamic compression plasticity was observed for all alloys subjected to dynamic loading. From the aspect of atomic structure, the substitution of appropriate amount of Al not only promoted the formation of the stable short-range ordering (SRO) structure, but also changed the content and distribution of the free volume, which resulted in the improvement of GFA, strength and plasticity of the amorphous alloy.

Nano pyramid array on Si by concurrent growth of parallel and perpendicular spatial wave and local angle-dependent sputtering

I report simultaneous growth of the Si nano-structures with wave vectors parallel and perpendicular to the projection of obliquely bombarding O2+ ions. At the initial stage of growth, finite length parallel and long length perpendicular nano-patterns are observed. Following the linear model of ion induced nanopatterning, the fast growth of amplitude of the developed structures as a function of ion fluence is observed. However, for further ion bombardment, change of local ion incidence angle leads to slope dependent nonlinear effects. At very high ion fluence when the amplitude is comparable to the wavelength of the structures, local angle-dependent sputtering and ion shadowing effect transforms the sinusoidal ripple to a triangular terraced structure. For further ion bombardment, the correlation length along ion beam direction increases faster than the parallel direction, which results in rotation of the initial nano-pattern and formation of the nano-pyramidal array structure. While nonlinear continuum Kuramoto-Sivashinsky equation predicts a disordered structure at such high fluence, we find pyramidal ordered structure formation by oxygen ion bombardment. Such nano-pyramidal structures could be used as a template for mask and resistless large area nano-dot lithography.

LAP2alpha maintains a mobile and low assembly state of A-type lamins in the nuclear interior.

Lamins form stable filaments at the nuclear periphery in metazoans. Unlike B-type lamins, lamins A and C localize also in the nuclear interior, where they interact with lamin-associated polypeptide 2 alpha (LAP2α). Using antibody labeling, we previously observed a depletion of nucleoplasmic A-type lamins in mouse cells lacking LAP2α. Here, we show that loss of LAP2α actually causes formation of larger, biochemically stable lamin A/C structures in the nuclear interior that are inaccessible to lamin A/C antibodies. While nucleoplasmic lamin A forms from newly expressed pre-lamin A during processing and from soluble mitotic lamins in a LAP2α-independent manner, binding of LAP2α to lamin A/C during interphase inhibits formation of higher order structures, keeping nucleoplasmic lamin A/C in a mobile state independent of lamin A/C S22 phosphorylation. We propose that LAP2α is essential to maintain a mobile lamin A/C pool in the nuclear interior, which is required for proper nuclear functions.

Mycobacterial STAND adenylyl cyclases: The HTH domain binds DNA to form biocrystallized nucleoids

Mycobacteria harbor a unique class of adenylyl cyclases with a complex domain organization consisting of an N-terminal putative adenylyl cyclase domain fused to a nucleotide-binding adaptor shared by apoptotic protease-activating factor-1, plant resistance proteins, and CED-4 (NB-ARC) domain, a tetratricopeptide repeat (TPR) domain, and a C-terminal helix-turn-helix (HTH) domain. The products of the rv0891c-rv0890c genes represent a split gene pair, where Rv0891c has sequence similarity to adenylyl cyclases, and Rv0890c harbors the NB-ARC-TPR-HTH domains. Rv0891c had very low adenylyl cyclase activity so it could represent a pseudoenzyme. By analyzing the genomic locus, we could express and purify Rv0890c and find that the NB-ARC domain binds ATP and ADP, but does not hydrolyze these nucleotides. Using systematic evolution of ligands by exponential enrichment (SELEX), we identified DNA sequences that bound to the HTH domain of Rv0890c. Uniquely, the HTH domain could also bind RNA. Atomic force microscopy revealed that binding of Rv0890c to DNA was sequence independent, and binding of adenine nucleotides to the protein induced the formation of higher order structures that may represent biocrystalline nucleoids. This represents the first characterization of this group of proteins and their unusual biochemical properties warrant further studies into their physiological roles in future.

Biophysical Characterization of Interaction between E. coli Alanyl-tRNA Synethase with its Promoter DNA.

Aminoacyl-tRNA Synthetases (aaRSs) are well known for their role in the translation process. Lately investigators have discovered that this family of enzymes are also capable of executing a broad repertoire of functions that not only impact protein synthesis, but extend to a number of other activities. Till date, transcriptional regulation has so far only been described in E. coli Alanyl-tRNA synthetase and it was demonstrated that alaRS binds specifically to the palindromic DNA sequence flanking the gene's transcriptional start site and thereby regulating its own transcription. In the present study, we have characterized some of the features of the alaRS-DNA binding using various biophysical techniques. To understand the role of full length protein and oligomerization of alaRS in promoter DNA binding, two mutants were constructed, namely, N700 (a monomer, containing the N-terminal aminoacylation domain but without the C-terminal part) and G674D (previously demonstrated to form full-length monomer). Protein-DNA binding study using fluorescence spectroscopy, analytical ultracentrifugation, Isothermal Titration Calorimetry was conducted. Sedimentation equilibrium studies clearly demonstrated that monomeric variants were unable to bind promoter DNA. Isothermal Calorimetry (ITC) experiment was employed for further characterization of wild type alaRS-DNA interaction. It was observed that full length E. coli Alanyl-tRNA synthetase binds specifically with its promoter DNA and forms a dimer of dimers. On the other hand the two mutant variants were unable to bind with the DNA. In this study it was concluded that full length E. coli Alanyl-tRNA synthetase undergoes a conformational change in presence of its promoter DNA leading to formation of higher order structures. However, the exact mechanism behind this binding is currently unknown and beyond the scope of this study.

Aggregate formation in fluids with bounded repulsive core and competing interactions

Soft matter systems often exhibit an intriguing morphology, related to the formation of intermediate range order structures. A rationale proposed for this behavior is the presence of competing short-range attraction and long-range repulsion. On the basis that effective interactions among the centers of mass of soft macromolecules often result in a finite short-range repulsion, we here consider a model fluid in which competing interactions supplement a repulsive core that, at difference from the models investigated up to now, has a bounded nature. We study the structural and phase behavior of this model through a theoretical approach and by computer simulation. We find that the structure factor exhibits a low-k peak, which is particularly relevant at low densities, where our system is formed by polydisperse clusters. A distinctive feature characterizing our model fluid is the presence of a peak situated between the low-k peak and the first diffraction peak. We show that this second pre-peak is associated with the enhancement of the relative population of the second coordination shell with respect to the first one, generated at intermediate densities by the long-range repulsion. As it concerns the phase behavior, the system investigated undergoes, for weak long-range repulsion, a liquid-gas phase transition. Upon increasing the strength of the long-range repulsion, such transition becomes less evident and eventually disappears. At high densities, the system undergoes freezing into a clustered solid, with multiply occupied crystal sites.

Sequence–Structure–Binding Relationships Reveal Adhesion Behavior of the Car9 Solid-Binding Peptide: An Integrated Experimental and Simulation Study

Solid-binding peptides (SBPs) recognizing inorganic and synthetic interfaces have enabled a broad range of materials science applications and hold promise as adhesive or morphogenetic control units that can be genetically encoded within desirable or designed protein frameworks. To date, the underlying relationships governing both SBP-surface and SBP-SBP interactions and how they give rise to different adsorption mechanisms remain unclear. Here, we combine protein engineering, SPR characterization, and molecular dynamics (MD) simulations initiated from Rosetta predictions to gain insights on the interplay of amino acid composition, structure, self-association and adhesion modality in a panel of variants of the Car9 silica-binding peptide (DSARGFKKPGKR) fused to the C-terminus of superfolder green fluorescent protein (sfGFP). Analysis of kinetics, energetics and MD-predicted structures shows that the high affinity binding of Car9 to the silanol-rich surface of silica is dominated by electrostatic contributions and a spectrum of several persistent interactions that, along with a high surface population of bound molecules, promote cooperative interactions between neighboring SBPs and higher order structure formation. Transition from cooperative to Langmuir adhesion in sfGFP-Car9 variants occurs in concert with a reduction of stable surface interactions and self-association, as confirmed by AFM imaging of proteins exhibiting the two different binding behaviors. We discuss the implications of these results for the de novo design of SBP-surface binding systems.