Backbone Moieties Research Articles

Dual-functional adsorptive membranes for PFAS removal: Mechanism, CFD simulation, and selective enrichment

The remediation of emerging water contaminants, particularly per- and polyfluoroalkyl substances (PFAS), presents challenges due to their refractory nature and the presence of competing substances. Dual-functional adsorptive membranes, with hydrophobic backbone and quaternary ammonium moieties, were thereby designed to selectively intercept organic competitors while enrich PFAS. A 96.8 % removal of perfluorooctanoic acid (PFOA) was achieved and this effective removal (>90 %) maintained across five reuse cycles with a total treatment capacity of 650 L m−2. Rather than the rejection mechanism of nanofiltration process, these adsorptive membranes utilize synergistic electrostatic attraction and hydrophobic interactions, leading to a greater enrichment factor of 18.5 (PFOA over humic acid) and a permeability of 34.6 L m-2h−1 bar−1 (1.9- and 4.5-fold higher than reported NF 270 membranes, respectively). Furthermore, computational fluid dynamics (CFD) modeling revealed that the sponge-like matrix effectively prevents channeling flow and enhance access to adsorption sites. Sensitivity analysis and the high Damkohler number indicated that the adsorption process is mass transfer-controlled, with the key parameters ranked in order of significance: residence time > fluid viscosity > intrinsic adsorption rate. With consistent removal performance with co-existing competitors, efficient regeneration, and reusability, the dual-functional adsorptive membranes offer promising practical efficacy for PFAS remediation.

Developing double-crosslinking 3D printed hydrogels for bone tissue engineering

Bone defects are one of the main causes of disability worldwide. Due to the disadvantages associated with autografts, the latest advances have been focused on tissue regeneration approaches that use injectable hydrogels or 3D printed hydrogel-based structures that could refill appropriately the bone gap area without the need for external fixatives, leading to bone formation in the long term. Injectable hydrogels could be applied in extrusion-based 3D printing as inks; in this sense, double-crosslinking hydrogels appear as ideal candidates. In this work, injectable and printable double crosslinkable hydrogels based on oxidized xanthan gum (XGox) and methacrylate polyaspartylhydrazide (PAHy-MA) were produced. The formation of dynamic hydrazone bonds, occurring between aldehyde groups on the polysaccharide backbone and hydrazine moieties of PAHy-MA, induced an instant gelation, conferring, also, injectability and self-healing properties to the hydrogels. The presence of methacrylic moieties on the synthetic polymer allowed further crosslinking upon UV irradiation that stabilized the hydrogel shape and mitigated its susceptibility to hydrolytic degradation. Obtained hydrogels showed pseudoplastic behaviour and good recovery of viscoelastic properties over time. The physicochemical and rheological characterization highlighted increased stability and higher viscoelastic moduli after photo-crosslinking. The hydrogels also showed good printability, cytocompatibility and the early formation of a bone-like matrix when osteosarcoma-derived cells (MG-63) were cultured in the scaffolds for 21 days, with an increased collagen I deposition, mineralization and the expression of characteristic osteogenic markers.

The rise of FTIR spectroscopy in the characterization of asymmetric lipid membranes

In contrast to symmetric unilamellar liposomes (sLUVs) prepared from a mixture of different lipids, asymmetric ones (aLUVs) with different lipid composition in the inner and outer membrane leaflets are more suitable model systems of eukaryotic plasma membranes. However, apart from the challenging preparation of asymmetric liposomes and small amounts of obtained asymmetric unilamellar liposomes (aLUVs), a major drawback is the qualitative characterization of asymmetry, as each of the techniques used so far has certain limitations. In this regard, we prepared aLUVs composed dominantly of DPPC(out)/DPPS(in) lipids and, along with 1H NMR and DSC characterization, we showed for the first time how FTIR spectroscopy can be used in the presence of (a)symmetry between DPPC/DPPS lipid bilayers. Using second derivative FTIR spectra we demonstrated not only that the hydration of lipids glycerol backbone and choline moiety of DPPC differs in s/aLUVs, but in addition that the lateral interactions between hydrocarbon chains during the phase change display different trend in s/aLUVs. Molecular dynamics simulations confirmed different chain ordering and packing between s/a bilayers, with a significant influence of temperature, i.e. membrane phase.

Efficient Ion-Selective Transport in Sulfonated Diels-Alder Poly(phenylene) Membrane Enables Aqueous Organic Flow Batteries with Undetectable Crossover

In most aqueous redox flow batteries (RFBs), ion exchange membranes are used to suppress crossover of redox active species while enabling conductivity of charge carrying ions. Many aqueous RFB chemistries, such as the all-vanadium RFB, involve metal cations dissolved in acid. In such systems, high proton conductivity affords low ohmic resistance from the membrane, but crossover rates are also high. Organic and metalorganic reactants with extreme chemical stability are an emerging direction for the development of RFB electrolytes, and may enable batteries with long calendar life composed of earth-abundant elements. Moreover, the size and charge numbers of these reactants enable much lower crossover than observed for systems like vanadium RFBs. However, the most stable chemistries use neutral or alkaline electrolytes where protons are not abundant enough to carry the ionic current. Currently, this presents a drawback: the incumbent cation exchange membrane, Nafion, exhibits a factor-of-ten lower conductivity of potassium compared to protons. The present work introduces a new membrane cast from sulfonated Diels-Alder poly(phenylene) to enable improved area-specific resistance while suppressing crossover.Nafion contains a perflourinated hydrophobic backbone with intervals of a flexible side chain that terminates in hydrophilic sulfonic acid moieties. This structure of a hydrophobic backbone with hydrophilic side chains is common to most ion exchange membranes. When a membrane with this polymer structure is hydrated and ion exchanged to an alkali metal cation form, the cations promote aggregation of the ionic groups via rearrangement of the flexible side chains, giving a configuration that is not optimal for ion conductivity. In contrast, the new membrane has a sulfonated hydrophilic backbone and external hydrophobic moieties, which we hypothesize prevents the aggregation effects seen in Nafion to enable efficient ion-selective transport. In the present work, we show that the new membrane affords negligible ferricyanide permeability (< 2 × 10−13 cm2/s) and promising area-specific resistances (< 1 Ω cm2) for a variety of cations. The conductivity of the new membrane in 1 M KCl electrolyte is 3.6 mS cm-1, more than double that of Nafion NR212 measured in the same flow battery cell. We demonstrate the use of this membrane in an alkaline organic RFB, with a ferri-/ferrocyanide posolyte and a 4,4’-((9,10-anthraquinone-2,6-diyl)dioxy)dibutyrate (2,6-DBEAQ) negolyte. Three-electrode voltametric methods for post-cycling detection of crossed-over species will be discussed and their sensitivities compared, in an effort to quantify crossover fluxes during cycling and their possible contributions to capacity fade. We conclude that in this flow battery, the new membrane suppresses crossover of both iron hexacyanide and 2,6-DBEAQ to the extent that any crossed over compounds cannot be detected by our methods, and we assign an upper limit of 2 × 10−7 μmol cm−2 s−1 on the possible crossover flux, amounting to a projected < 1 %/year capacity fade from crossover in the lab-scale cell.

A novel organic anode with 14 electrons participating in redox reactions prepared under mild conditions

Covalent organic frameworks (COFs) have been widely used in various fields due to their abundant elemental resources, easy structure control, and abundant tunable porous structures. COFs containing electroactive organic groups with reversible redox behavior are potential electrode materials for next-generation high-performance lithium-ion batteries (LIBs). However, the aromatic conjugated structure of the backbone moiety in most reported COFs cannot participate in redox reactions, resulting in low capacity of COFs. At the same time, the synthesis processes of COFs are usually complicated and generally requires high temperature and high pressure. On this basis, an imine bond-rich COF (TAACOF) with reversible Li-ion bonding is developed, which has the advantages of facile preparation and low energy consumption. In particular, the lone pair electrons of the N atom in the imine bond can induce lithium ions to combine with the aromatic conjugated structure, which greatly improves the capacity of the TAACOF electrode. After 800 cycles, the active sites of the TAACOF are fully activated, and after a 14-electron redox reaction, the specific capacity can reach as high as 1035.7 mAh/g.

Intermolecular hydrogen-bonding as a robust tool toward significantly improving the photothermal conversion efficiency of a NIR-II squaraine dye

The photothermal therapy (PTT) has come across as a promising noninvasive therapeutic strategy for tumor treatment. However, low photothermal conversion efficiency (PCE) and hydrophobicity may impede the therapeutic efficacy of organic photothermal agents and an efficient PTT-agent must overcome these two major challenges. In this work, we developed a new strategy to promote higher PCE wherein the intermolecular hydrogen-bonding interaction between the single dye molecule and water facilitated the transformation of the absorbed energy into the heat. A hydrophilic squaraine dye (SCy1) with the second near-infrared region (NIR-II) absorption and extremely low emission were designed to exhibit much higher PCE than that of the analogues of pentamethine-dyes (PCy1, PCy2). The presence of the ‘–O−’ at middle of squaric cycle enabled the intermolecular H-bonding formation between the SCy1 and water to promote the energy dissipation channel. Moreover, the introduction of long-chain phenylsulfonate groups helped in to improve the water solubility apart from serving as an additional means of further enhancing PCE through fluorescence quenching. Therefore, SCy1 with a squaraine backbone and long-chain sulfonate moieties revealed outstanding photothermal stability and anti-aggregation activity apart from showing exceptionally high PCE (74%) in water. SCy1 demonstrated excellent therapeutic efficacy when applied in the PTT treatment of tumor-bearing mice under a laser irradiation of 915 nm.

Exposure to dithiocarbamate fungicide Ziram results in hepatic and renal toxicity in Long Evan rats

Ziram is a dimethyldithiocarbamate fungicide that is complexed to the metal zinc. The focus of this study is to examine the effects of dimethyldithiocarbamate exposure on metal homeostasis, glutathione levels, and the physiological parameters of the kidney and liver in Long-Evan rats. Our results indicate significant accumulation of copper or zinc, and changes in total GSH or GSH/GSSG ratio in the liver and kidneys of animals treated with Ziram only. Histopathological examination of liver and kidney sections indicate the presence of infiltrates in the liver of animals treated with Ziram only, whereas protein aggregates, sloughing of cells and increased KIM-1 positive cells, an indicator of tubule deterioration, are seen in the kidneys of animals treated with Ziram and sodium-dimethyldithiocarbamate, the salt form of the dimethyldithiocarbmate backbone. These findings suggest that the overall toxicological effect of Ziram is mediated by an intrinsic property rather than to dimethyldithiocarbamate backbone or metal moiety.

Extended Conjugation Acceptors Increase Specific Energy Densities in π-Conjugated Redox Polymers

Organic materials are a sustainable alternative to replace inorganic transition metal-based cathodes in rechargeable intercalation batteries. Among the possible redox active organic materials, conjugated polymers with multiple redox sites per repeat unit are expected to afford high energy and power densities while being resistant to dissolution when in contact with battery electrolytes. However, accessing the full capacity of polymeric electrodes while ensuring electrochemical reversibility has been challenging. Using diketopyrrolopyrrole (DPP)-based donor–acceptor (D–A) polymers as model systems and complementary electrochemical experiments and first-principles calculations, we show that conjugated backbone moieties that minimize charge localization on the electron accepting repeat units lead to near theoretical discharge capacities. Further, the capacity enhancement is associated with better rate performance and improved electrochemical stability of the polymer over prolonged cycling. Our work suggests that charge density on the electron accepting moiety is a potential descriptor for rationally designing redox-active polymer electrodes that afford high discharge capacities along with a long cycle life.

The effect of solvent on determining highest occupied molecular orbital energies of semiconducting organic molecules: Insight from a combined computational approach.

Although cyclic voltammetry (CV) measurements in solution have been widely used to determine the highest occupied molecular orbital energy (EHOMO ) of semiconducting organic molecules, an understanding of the experimentally observed discrepancies due to the solvent used is lacking. To explain these differences, we investigate the solvent effects on EHOMO by combining density functional theory and molecular dynamics calculations for four donor molecules with a common backbone moiety. We compare the experimental EHOMO values to the calculated values obtained from either implicit or first solvation shell theories. We find that the first solvation shell method can capture the EHOMO variation arising from the functional groups in solution, unlike the implicit method. We further applied the first solvation shell method to other semiconducting organic molecules measured in solutions for different solvents. We find that the EHOMO obtained using an implicit method is insensitive to solvent choice. The first solvation shell, however, produces EHOMO values that are sensitive to solvent choices and agrees with published experimental results. The solvent sensitivity arises from a hierarchy of three effects: (1) the solute electronic state within a surrounding dielectric continuum, (2) ambient temperature or solvent atoms changing the solute geometry, and (3) electronic interactions between the solute and solvents. The implicit method, on the other hand, only captures the effect of a dielectric environment. Our findings suggest that EHOMO obtained by CV measurements should account for the influence of solvent when the results are reported, interpreted, or compared to other molecules.

Accumulation and ordering of P3HT oligomers at the liquid-vapor interface with implications for thin-film morphology.

The morphology of semiconducting polymer thin films is known to have a profound effect on their opto-electronic properties. Although considerable efforts have been made to control and understand the processes which influence the structures of these systems, it remains largely unclear what physical factors determine the arrangement of polymer chains in spin-cast films. Here, we investigate the role that the liquid-vapor interfaces in chlorobenzene solutions of poly(3-hexylthiophene) [P3HT] play in the conformational geometries adopted by the polymers. Using all-atom molecular dynamics (MD), and supported by toy-model simulations, we demonstrate that, with increasing concentration, P3HT oligomers in solution exhibit a strong propensity for the liquid-vapor interface. Due to the differential solubility of the backbone and side chains of the oligomers, in the vicinity of this interface, hexyl chains and the thiophene rings, have a clear orientational preference with respect to the liquid surface. At high concentrations, we additionally establish a substantial degree of inter-oligomer alignment and thiophene ring stacking near the interface. Our results broadly concur with the limited existing experimental evidence and we suggest that the interfacial structure can act as a template for film structure. We argue that the differences in solvent affinity of the side chain and backbone moieties are the driving force for the anisotropic orientations of the polymers near the interface. This finer grained description contrasts with the usual monolithic characterization of polymer units. Since this phenomenon can be controlled by concurrent chemical design and the choice of solvents, this work establishes a fabrication principle which may be useful to develop more highly functional polymer films.

Synthesis of Dendronized Polymers on the Au(111) Surface.

Dendronized polymers (DPs) consist of a linear polymeric backbone with dendritic side chains. Fine-tuning of the functional groups in the side chains enriches the structural versatility of the DPs and imparts a variety of novel physical properties. Herein, the first on-surface synthesis of DPs is achieved via the postfunctionalization of polymers on Au(111), in which the surface-confinement-induced planar conformation and chiral configurations were unambiguously characterized. While the dendronized monomer was synthesized in situ on Au(111), the subsequent polymerization afforded only short, cross-linked DP chains owing to multiple side reactions. The postfunctionalization approach selectively produced brominated polyphenylene backbone moieties by the deiodination polymerization of 4-bromo-4″-iodo-5'-(4-iodophenyl)-1,1':3',1″-terphenyl on Au(111), which smoothly underwent divergent cross-coupling reactions with two different isocyanides to form two types of DPs as individual long chains.

Quantitative Multistate Binding Model of Silica Nanoparticle-Protein Interactions Obtained from Multinuclear Spin Relaxation.

Nanoparticle-assisted NMR spin relaxation (NASR), which makes internal protein dynamics in solution directly observable on nanosecond to microsecond time scales, has been applied to different nuclei and relaxation processes of the same protein system. A model is presented describing the transient interaction between ubiquitin and anionic silica nanoparticles for the unified interpretation of a wealth of experimental data including 2H, 13C, and 15N relaxation of methyl side chain and backbone moieties. The best model, implemented using a stochastic Liouville equation, describes the exchange process via an intermediary encounter state between free and fully nanoparticle-bound protein. The implication of the three-state binding model on the interpretation of NASR data is discussed.

The clinical drug candidate anle138b binds in a cavity of lipidic α-synuclein fibrils

Aggregation of amyloidogenic proteins is a characteristic of multiple neurodegenerative diseases. Atomic resolution of small molecule binding to such pathological protein aggregates is of interest for the development of therapeutics and diagnostics. Here we investigate the interaction between α-synuclein fibrils and anle138b, a clinical drug candidate for disease modifying therapy in neurodegeneration and a promising scaffold for positron emission tomography tracer design. We used nuclear magnetic resonance spectroscopy and the cryogenic electron microscopy structure of α-synuclein fibrils grown in the presence of lipids to locate anle138b within a cavity formed between two β-strands. We explored and quantified multiple binding modes of the compound in detail using molecular dynamics simulations. Our results reveal stable polar interactions between anle138b and backbone moieties inside the tubular cavity of the fibrils. Such cavities are common in other fibril structures as well.

Unique and redundant spectral fingerprints of docosahexaenoic, alpha-linolenic and gamma-linolenic acids in binary mixtures

The polyunsaturated fatty acids docosahexaenoic acid (DHA; 22:6n-3), docosapentaenoic acid (n-3DPA; 22:5n-3), and eicosapentaenoic acid (EPA; 20:5n-3) contain nearly identical structural moieties, but differ vastly in their biological activities and in their utilization in mammalian tissues. Most importantly, DHA cannot be substituted for in fast signal processing tissues such as neural retinal, cardiac and spermatogenic. Over 600 million years of evolution the difference of just a single double bond has not been overcome—DHA reigns supreme. These dramatic differences among polyunsaturated fatty acids are at least in part conformational. Binary 3:1 mixtures of DHA with either alpha-linolenic acid (18:3n-3; ALA) or gamma linolenic acid (18:3n-6; γ-LN) and both Nuclear Magnetic Resonance and Gradient Temperature Raman Spectroscopy were utilized to probe DHA in the liquid state. Raman modes at 1970, 1778 and 1578 cm−1 definitively demonstrate DHA, since absent in γ-LN and ALA. However, the latter two modes are also absent in 3:1 mixtures. This is evidence for a conformational change in DHA and of the capacity of structural analogs to disrupt the packing of DHA at the molecular level. NMR confirms chemical shifts in the middle of the DHA double bond region in the mixtures are not the same as the pure DHA chemical shifts.We propose asymmetry in torsion among =C-C-Ha, =C-C-Hb, Ha-C-C= and Hb-C-C= sites in each six carbon atom backbone moiety in =C″-C-C=C-C-C′= results in the observed non-uniformity of twisting observed spectroscopically. The distance C″-C′ is minimum when the six atom moiety is fully planar, and maximum when twisting involving C″ and C′ is in opposite directions from the double bond. For DHA -(H-C=C-H)-CH2- and -CH2-(H-C=C-H)- peaks are conformationally identical only at C17=C16: C19″ and C14′ both twist C″ and C′ to the same side of C17=C16. At C14=C13 and C8=C7, torsion is similar to that at C16=C15 in ALA. Torsion related to C″-C′ distances stepwise from C2 to C22 results in planar structure more “O” shaped then “U” shaped. In 3 + 1 mixtures, γ-LN predominantly disrupts peaks at the C′ half of DHA; ALA alters the conformation of the C″ half of DHA.

Polyglyoxylamides with a pH-Mediated Solubility and Depolymerization Switch

Self-immolative polymers (SIPs) are characterized by their ability to depolymerize in response to the cleavage of a single end-cap or backbone moiety, making them attractive for numerous applicatio...

Cation competition and recruitment around the c-kit1 G-quadruplex using polarizable simulations

Nucleic acid-ion interactions are fundamentally important to the physical, energetic, and conformational properties of DNA and RNA. These interactions help fold and stabilize highly ordered secondary and tertiary structures, such as G-quadruplexes (GQs), which are functionally relevant in telomeres, replication initiation sites, and promoter sequences. The c-kit proto-oncogene encodes for a receptor tyrosine kinase and is linked to gastrointestinal stromal tumors, mast cell disease, and leukemia. This gene contains three unique GQ-forming sequences that have proposed antagonistic effects on gene expression. The dominant GQ, denoted c-kit1, has been shown to decrease expression of c-kit transcripts, making the c-kit1 GQ a promising drug target. Toward disease intervention, more information is needed regarding its conformational dynamics and ion binding properties. Therefore, we performed molecular dynamics simulations of the c-kit1 GQ with K+, Na+, Li+, and mixed salt solutions using the Drude-2017 polarizable force field. We evaluated GQ structure, ion sampling, core energetics, ion dehydration and binding, and ion competition and found that each analysis supported the known GQ-ion specificity trend (K+ > Na+ > Li+). We also found that K+ ions coordinate in the tetrad core antiprismatically, whereas Na+ and Li+ align coplanar to guanine tetrads, partially because of their attraction to surrounding water. Further, we showed that K+ occupancy is higher around the c-kit1 GQ and its nucleobases than Na+ and Li+, which tend to interact with backbone and sugar moieties. Finally, we showed that K+ binding to the c-kit1 GQ is faster and more frequent than Na+ and Li+. Such descriptions of GQ-ion dynamics suggest the rate of dehydration as the dominant factor for preference of K+ by DNA GQs and provide insight into noncanonical nucleic acids for which little experimental data exist.

Synthesis of multifunctional liquid crystalline epoxy resin embedded cyclic-siloxane chain with Tg-less behavior and enhanced toughness

A novel tetrafunctional mesogenic epoxy monomer with a cyclic-siloxane chain as a central part was successfully synthesized and characterized by proton nuclear magnetic resonance, Fourier transform infrared spectroscopy, differential scanning calorimetry, and polarized optical microscopy. The transition temperature and liquid crystallinity of cyclic-siloxane type mesogenic epoxy were compared with those of linear-siloxane type mesogenic epoxy. Moreover, epoxy thermosets were prepared based on the cyclic- and linear-siloxane type mesogenic epoxy monomers and 4,4′-diaminodiphenylethane. The effects of epoxy backbone moiety on thermal and mechanical properties were investigated in detail. As a result, the cyclic-siloxane type mesogenic epoxy thermoset shows glass transition temperature-less behavior and low coefficient of linear thermal expansion without a decrease in toughness.

Toward the Prediction and Control of Glass Transition Temperature for Donor–Acceptor Polymers

AbstractSemiconducting donor–acceptor (D–A) polymers have attracted considerable attention toward the application of organic electronic and optoelectronic devices. However, a rational design rule for making semiconducting polymers with desired thermal and mechanical properties is currently lacking, which greatly limits the development of new polymers for advanced applications. Here, polydiketopyrrolopyrrole (PDPP)‐based D–A polymers with varied alkyl side‐chain lengths and backbone moieties are systematically designed, followed by investigating their thermal and thin film mechanical responses. The experimental results show a reduction in both elastic modulus and glass transition temperature (Tg) with increasing side‐chain length, which is further verified through coarse‐grained molecular dynamics simulations. Informed from experimental results, a mass‐per‐flexible bond model is developed to capture such observation through a linear correlation between Tg and polymer chain flexibility. Using this model, a wide range of backbone Tg over 80 °C and elastic modulus over 400 MPa can be predicted for PDPP‐based polymers. This study highlights the important role of side‐chain structure in influencing the thermomechanical performance of conjugated polymers, and provides an effective strategy to design and predict Tg and elastic modulus of future new D–A polymers.

Cyclic Aliphatic Hydrocarbons as Linkers in Metal-Organic Frameworks: New Frontiers for Ligand Design.

In this Minireview we outline the development of cyclic aliphatic moieties as ligands in metal-organic frameworks (MOFs), with a focus on the relationship between ligand design and synthesis and the properties of the subsequent materials. Aliphatic ligands have received considerably less attention than aromatic analogues in MOF chemistry but offer advantages in their unique combinations of geometric and electronic properties which are unattainable from conventional ligands. Here, we focus on rigid and semi-rigid backbone moieties derived from monocyclic and fused polycyclic aliphatic backbones, including cyclohexane and adamantane, cubane and bicyclo[2.2.2]octane, and discuss the synthetic chemistry of these species along with their potential importance as the next generation of building blocks for microporous materials.

Structure–Property Relationships in Sterically Congested Proton-Conducting Poly(phenylene)s: the Impact of Biphenyl Linearity

The structure–property relationship of sulfonated phenylated poly(phenylene)s possessing either angled or linear backbone moieties was investigated. Polymers were synthesized using either bent (ort...