n-Type Rigid Semiconducting Polymers Bearing Oligo(Ethylene Glycol) Side Chains for High-Performance
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Chen, Xingxing↗
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2D Covalent Organic Frameworks with an Incorporated Manganese Complex for Light Driven Carbon Dioxide Reduction
Covalent organic frameworks (COFs) have emerged as a novel class of crystalline porous photocatalytic materials due to their unique properties such as large surface area, tunable porosity, and rigid structure. Here in this work, we report the direct incorporation of a manganese CO 2 molecular catalyst (MC) into COFs (Mn-TTA-COF) and the evaluation of its capability as photocatalyst for visible light driven CO 2 reduction to form CO. We found that the photocatalytic activity of Mn-TTA-COF is quite low, which mainly results from the elimination of the CO ligand in the Mn MC upon light illumination, rendering its short duration in the catalytic reaction. While this is a central concern for the further use Mn-TTA-COF as a CO 2 reduction catalyst, here we found that the stability and efficiency of Mn MC is largely enhanced after being incorporated into COFs with respect to its homogeneous version, suggesting the capability of COFs as heterogeneous platform to incorporate MC and improve the catalytic performance of MC. Moreover, transient absorption spectroscopic studies show that the intramolecular charge transfer lifetime of the Mn-incorporated COF is longer than that in the parent COF, which suggests that charge separation (CS) may occur from the parent COF to the Mn moiety. These results together suggest that COFs may show promise as a platform for creating next-generation photocatalysts with a built-in photosensitizer and MC, which can facilitate CS and enhance the stability and efficiency of the incorporated MC.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Computational design of mixed chirality peptide macrocycles with internal symmetry
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Mulligan, Vikram Khipple↗
Novel fluorinated quaternary ammonium salts and their in vitro activity as trypanocidal agents
As the impact of aromatic rings and fluorine substituents in commercial drugs is attributed to their electronic distribution and structure rigidity that determine metabolic stability and toxicity, 30 quaternary ammonium salts (QAS) of the form [X-CH{sub 2}N(CH{sub 3}){sub 2}(CH{sub 2}){sub n}CH = C(Ar{sub 2})]{sup +}I{sup −} (where X=H, Cl or I, n = 2 or 3, and Ar = m-C{sub 6}H{sub 4}CF{sub 3}, p-C{sub 6}H{sub 4}CF{sub 3}, m-C{sub 6}H{sub 4}F, p-C{sub 6}H{sub 4}F or C{sub 6}H{sub 5}) were tested as potential trypanocidal agents and assessed their cytotoxicity on U-937 cells. CF{sub 3}-substituted QASs exhibited LC{sub 50} values in the range of 0.5 to 6.4 μg/mL and trypanocidal EC{sub 50} values between 0.6 and 7.0 μg/mL, while the LC{sub 50} values for F-substituted analogs are between 7.0 and 207 μg/mL and EC{sub 50} values range from 3.8 to 40.9 μg/mL. As a general trend, the more effective are those bearing an N-iodomethyl moiety or having a longer tether, and para-substituted ones. Few drugs therapies are in use for Chagas disease, so this study becomes a promising contribution.
60 APPLIED LIFE SCIENCES↗
Alcoholysis of nylon 6 waste to ε-caprolactam promoted by phosphoric acid
Nylon 6 is widely used in high-performance materials. However, the inherent structural rigidity of nylon 6 inhibits catalytic depolymerization to its monomer, ε-caprolactam. Here, in this study, we demonstrate an acid-catalyzed alcoholysis process that depolymerizes nylon 6 to ε-caprolactam, achieving yields up to 74% using n-propanol as solvent and phosphoric acid as catalyst at 220°C for 2 h. We further applied the process to commercial nylon-containing products, demonstrating ε-caprolactam yields of 67% to 76%. Process modeling and techno-economic analysis estimated a minimum selling price of recycled nylon 6 at $\$$1.79/kg, 30% lower than the 5-year average market price of virgin nylon 6. These estimates depend on assumed costs and process performance and may vary with future conditions. Life cycle assessment indicated that nylon 6 produced via alcoholysis can reduce greenhouse gas emissions by up to 63% compared with primary production. Overall, this study demonstrates a facile, cost-effective, and environmentally beneficial process for nylon 6 chemical recycling.
09 BIOMASS FUELS↗
Redox Chemistry Mediated Control of Morphology and Properties in Electrically Conductive Coordination Polymers: Opportunities and Challenges
Coordination polymers (CPs) and metal–organic frameworks (MOFs) have attracted significant research interest in the past several decades due to their reticular structures and modularity. However, realizing electrically conductive CPs or MOFs with comparable properties to classic conducting organic polymers has only been a recent development. This emerging class of materials has found wide appli-cation in many fields due to combined features of structural rigidity, chemical tunability, porosity, and charge transport. Alongside many studies revealing myriad design approaches to access these materials, the role that redox chemistry plays in both material synthesis and modulation of electronic properties has been an emerging theme. This perspective provides a brief overview of select examples where redox chemistry medi-ates control of morphology and properties in electrically conductive CPs/MOFs. Here, the challenges and limitations in this area are also discussed. Particular challenges include the characterization of redox states in these materials and measuring and understanding highly correlated elec-tronic properties and other unusual physical phenomena which may be important for potential applications.
36 MATERIALS SCIENCE↗
Tunable Optical Properties and Increased Thermal Quenching in the Blue-Emitting Phosphor Series: Ba 2 (Y 1– x Lu x ) 5 B 5 O 17 :Ce 3+ ( x = 0–1)
The preparation of cerium-substituted barium lutetium borate, Ba2Lu5B5O17:Ce3+, is achieved using high temperature solid state synthesis. This compound crystallizes in the Ba2Y5B5O17-type structure and shows an efficient blue emission (λmax = 447 nm) when excited by UV-light (λex = 340 nm) with a photoluminescent quantum yield near 90%, a fast luminescence decay time (<40 ns), and a thermal quenching temperature of 452 K. Further, preparing a solid solution following Ba2(Y1–xLux)5B5O17:Ce3+ (x = 0, 0.25, 0.50, 0.75, 1) confirms that all compounds are isostructural and follow Vegard’s law. Substituting Y3+ for Lu3+ yields a nearly constant emission spectrum that blue-shifts by only 9 nm and has a consistent luminescence lifetime across the range prepared. The photoluminescent quantum yield (PLQY) and thermal quenching (T50) of the solid solution, however, are dramatically impacted by the composition, with the PLQY decreasing to ≈70% and the T50 dropping 49 K going from x = 1 to x = 0. These significant changes in the optical properties likely stem from enhanced structural rigidity as the larger, more polarizable Y3+ is substituted for the smaller, harder Lu3+ cation. These results highlight the importance of optimizing chemical bonding to improve a phosphor’s optical properties.
36 MATERIALS SCIENCE↗
Improved Treatment of 1–4 Interactions in Force Fields for Molecular Dynamics Simulations
Traditional force fields commonly use a combination of bonded torsional terms and empirically scaled nonbonded interactions to capture 1-4 energies and forces of atoms separated by three bonds in a molecule. While this approach can yield accurate torsional energy barriers, it often leads to inaccurate forces and erroneous geometries and creates an interdependence between dihedral terms and nonbonded interactions, complicating parametrization and reducing transferability. Here, in this paper, we demonstrate that 1-4 interactions can be accurately modeled using only bonded coupling terms, eliminating the need for arbitrarily scaled nonbonded interactions altogether. Furthermore, by leveraging the automated parametrization capabilities of the Q-Force toolkit, we efficiently determine the necessary coupling terms without the need for manual adjustment. Our approach is first validated on a range of small molecule systems, encompassing both flexible and rigid structures, and shows a significant improvement in force field accuracy, obtaining subkcal/mol mean absolute error for every molecule tested. We further extend the bonded-only model for 1-4 interactions to Amber ff14sb, CHARMM36, and OPLS-AA force fields to reproduce ab initio gas and implicit solvent ϕ,ψ surfaces of alanine dipeptide.
Abdullah, Aalim S. [University of California, Berk↗
Competitive Binding of Ethylene, Water, and Carbon Monoxide in Metal–Organic Framework Materials with Open Cu Sites
Typically, metal–organic frameworks (MOFs) with open metal sites (OMS) are understood to have selectivity in olefin/paraffin separations because of π–π interactions between olefin double bonds and OMS. One concern associated with these separations is that other species that potentially bind to OMS may also be present in feed streams, causing competition for these sites. We used density functional theory (DFT) to assess the binding energy of ethylene, water, and carbon monoxide on a set of more than 60 MOFs with open Cu sites in the form of Cu dimers. A useful observation from our results is that the relative binding energies of pairs of molecules (e.g., ethylene and water) can be calculated accurately from calculations that hold the MOF structure rigid and only relax the positions of the adsorbing molecules. These kinds of calculations are far more numerically efficient than calculations that relax all degrees of freedom in the system, so this observation will be useful in future efforts to screen larger collections of materials. A second observation is that the binding energies of each molecule in the 60 MOFs are quite similar to the binding energies in CuBTC, an exemplar MOF with open Cu sites in the form of Cu dimers. Analysis of the variations that do exist in the binding energies among materials points to possible avenues for controlling either the absolute binding energies or the relative binding energies of species associated with OMS in these materials. The third observation is that two unusual MOFs can bind ethylene more strongly than water because of a dual-site binding mechanism in which an ethylene molecule can interact simultaneously with both dimers while the smaller water molecule interacts primarily with a single OMS. This observation suggests a possible avenue for developing other MOFs in which the binding energy of ethylene is higher than that of water.
36 MATERIALS SCIENCE↗
Predicting the Macroscopic Fracture Energy of Epoxy Resins from Atomistic Molecular Simulations
Predicting the macroscopic fracture energy of highly crosslinked glassy polymers from atomistic simulations is challenging due to the size of the process zone being large in these systems. Here, we present a scale-bridging approach that links atomistic molecular dynamics simulations to macroscopic fracture properties on the basis of a continuum fracture mechanics model for two different epoxy materials. Our approach reveals that the fracture energy of epoxy resins strongly depends on the functionality of epoxy resin and the component ratio between the curing agent (amine) and epoxide. The most intriguing part of our study is that we demonstrate that the fracture energy exhibits a maximum value within the range of conversion degrees considered (from 65% to 95%), which can be attributed to the combined effects of structural rigidity and post-yield deformability. Our study provides physical insight into the molecular mechanisms that govern the fracture characteristics of epoxy resins and demonstrates the success of utilizing atomistic molecular simulations towards predicting macroscopic material properties.
42 ENGINEERING↗
Nanoporous Polymer Films with a High Cation Transference Number Stabilize Lithium Metal Anodes in Light-Weight Batteries for Electrified Transportation
To suppress dendrite formation in lithium metal batteries, high cation transference number electrolytes that reduce electrode polarization are highly desirable, but rarely available using conventional liquid electrolytes. Here, we show that liquid electrolytes increase their cation transference numbers (e.g., ~0.2 to >0.70) when confined to a structurally rigid polymer host whose pores are on a similar length scale (0.5–2 nm) as the Debye screening length in the electrolyte, which results in a diffuse electrolyte double layer at the polymer–electrolyte interface that retains counterions and reject co-ions from the electrolyte due to their larger size. Lithium anodes coated with ~1 μm thick overlayers of the polymer host exhibit both a low area-specific resistance and clear dendrite-suppressing character, as evident from their performance in Li–Li and Li–Cu cells as well as in post-mortem analysis of the anode’s morphology after cycling. High areal capacity Li–S cells (4.9 mg cm –2 ; 8.2 mAh cm –2 ) implementing these high transference number polymer-hosted liquid electrolytes were remarkably stable, considering ~24 μm of lithium was electroreversibly deposited in each cycle at a C-rate of 0.2. In conclusion, we further identified a scalable manufacturing path for these polymer-coated lithium electrodes, which are drop-in components for lithium metal battery manufacturing.
25 ENERGY STORAGE↗
Incorporating Flexibility Effects into Metal–Organic Framework Adsorption Simulations Using Different Models
High-throughput calculations based on molecular simulations to predict the adsorption of molecules inside metal–organic frameworks (MOFs) have become a useful complement to experimental efforts to identify promising adsorbents for chemical separations and storage. For computational convenience, all existing efforts of this kind have relied on simulations in which the MOF is approximated as rigid. In this paper, we use extensive adsorption–relaxation simulations that fully include MOF flexibility effects to explore the validity of the rigid framework approximation. We also examine the accuracy of several approximate methods to incorporate framework flexibility that are more computationally efficient than adsorption–relaxation calculations. We first benchmark various models of MOF flexibility for four MOFs with well-established CO 2 experimental consensus isotherms. We then consider a range of adsorption properties, including Henry’s constants, nondilute loadings, and adsorption selectivity, for seven adsorbates in 15 MOFs randomly selected from the CoRE MOF database. Our results indicate that in many MOFs adsorption–relaxation simulations are necessary to make quantitative predictions of adsorption, particularly for adsorption at dilute concentrations, although more standard calculations based on rigid structures can provide useful information. Finally, we investigate whether a correlation exists between the elastic properties of empty MOFs and the importance of including framework flexibility in making accurate predictions of molecular adsorption. Our results did not identify a simple correlation of this type.
36 MATERIALS SCIENCE↗
Bimetallic Metal–Organic Framework Fe/Co-MIL-88(NH 2 ) Exhibiting High Peroxidase-like Activity and Its Application in Detection of Extracellular Vesicles
Metal–organic frameworks (MOFs) have many attractive features, including tunable composition, rigid structure, controllable pore size, and large specific surface area, and thus are highly applicable in molecular analysis. Depending on the MOF structure, a high number of un-saturated metal sites can be exposed to catalyze chemical reactions. In the present work, we report that by using both Co(II) and Fe(III) to prepare the MIL-88(NH 2 ) MOF, we can produce the bimetallic MOF that can catalyze the conversion of 3,3', 5,5"-tetramethylbenzidine (TMB) to a color product through reaction with H 2 O 2 at a higher reaction rate than the monometallic Fe-MIL-88(NH 2 ). The Michaelis constants (K m ) of the catalytic reaction for TMB and H 2 O 2 are 3-5 times smaller, and the catalytic constants (k cat ) are 5-10 times higher than those of the horse-radish peroxidase (HRP), supporting ultrahigh peroxidase-like activity. These values are also much more superior to those of the HRP-mimicking MOFs reported previously. Interestingly, the bimetallic MOF can be coupled with glucose oxidase (GOx) to trigger the cascade enzymatic reaction for highly sensitive detection of extracellular vesicles (EVs), a family of important biomarkers. Through conjugation to the aptamer that recognizes the marker protein on EV surface, the MOF can help isolate the EVs from biological matrices, which are subsequently labeled by GOx via antibody recognition. The cascade enzymatic reaction between MOF and GOx enables detection of EVs at a concentration as low as 7.8 × 10 4 particles/ml. Further, the assay can be applied to monitor EV secretion by cultured cells, and also can successfully detect the different EV quantities in the sera samples collected from cancer patients and healthy controls. Overall, we prove that the bimetallic Fe/Co-MIL-88(NH 2 ) MOF, with its high peroxidase-activity and high biocompatibility, is a valuable tool deployable in clinical assays to facility disease diagnosis and prognosis.
36 MATERIALS SCIENCE↗
Bioinspired design of flexible armor based on chiton scales
Man-made armors often rely on rigid structures for mechanical protection, which typically results in a trade-off with flexibility and maneuverability. Chitons, a group of marine mollusks, evolved scaled armors that address similar challenges. Many chiton species possess hundreds of small, mineralized scales arrayed on the soft girdle that surrounds their overlapping shell plates. Ensuring both flexibility for locomotion and protection of the underlying soft body, the scaled girdle is an excellent model for multifunctional armor design. Here we conduct a systematic study of the material composition, nanomechanical properties, three-dimensional geometry, and interspecific structural diversity of chiton girdle scales. Moreover, inspired by the tessellated organization of chiton scales, we fabricate a synthetic flexible scaled armor analogue using parametric computational modeling and multi-material 3D printing. This approach allows us to conduct a quantitative evaluation of our chiton-inspired armor to assess its orientation-dependent flexibility and protection capabilities.
Science & Technology - Other Topics↗
Ultra-thermostable RNA nanoparticles for solubilizing and high-yield loading of paclitaxel for breast cancer therapy
Paclitaxel is widely used in cancer treatments, but poor water-solubility and toxicity raise serious concerns. Here we report an RNA four-way junction nanoparticle with ultra-thermodynamic stability to solubilize and load paclitaxel for targeted cancer therapy. Each RNA nanoparticle covalently loads twenty-four paclitaxel molecules as a prodrug. The RNA-paclitaxel complex is structurally rigid and stable, demonstrated by the sub-nanometer resolution imaging of cryo-EM. Using RNA nanoparticles as carriers increases the water-solubility of paclitaxel by 32,000-fold. Intravenous injections of RNA-paclitaxel nanoparticles with specific cancer-targeting ligand dramatically inhibit breast cancer growth, with nearly undetectable toxicity and immune responses in mice. No fatalities are observed at a paclitaxel dose equal to the reported LD 50 . The use of ultra-thermostable RNA nanoparticles to deliver chemical prodrugs addresses issues with RNA unfolding and nanoparticle dissociation after high-density drug loading. This finding provides a stable nano-platform for chemo-drug delivery as well as an efficient method to solubilize hydrophobic drugs.
60 APPLIED LIFE SCIENCES↗
Synergistic maximization of the carbohydrate output and lignin processability by combinatorial pretreatment
Lignocellulosic biorefineries have gained much attention worldwide as a potential solution to the challenges of energy demand and global climate change. However, the industrial implementation of biorefineries has been hindered by low fermentable sugar yields and low lignin processability. Combinatorial pretreatments with a low holding temperature were investigated in an effort to synergistically improve the carbohydrate output and lignin processability from corn stover. Upon combinatorial pretreatment with 1% H 2 SO 4 for 30 min followed by 1% NaOH for 60 min at 120 °C, glucan and xylan conversion increased by 11.2% and 8.3% respectively relative to single pretreatment. This combinational pretreatment removed the amorphous portion, disrupted the rigid structure, and increased the water holding capacity of corn stover, thus increasing the hydrolysis performance. With whole fractionation by combinatorial pretreatment, glucose and xylose yields were 88.4% and 72.6%, respectively, representing increases of 10.0% and 8.1%. The lignin yield was 19.7% in the solid residue and 77.6% in the liquid stream, which increased by 33.4%. When grown in fed-batch fermentation mode, a record level of polyhydroxyalkanoate (PHA) concentration (1.0 g l –1 ) was obtained using lignin as a carbon source by Pseudomonas putida KT2440. Lignin characterization results showed that combinatorial pretreatment increased the G- and H-lignin content, reduced the β–β and β-O-4 groups, and fractionated more aromatic monomers, thus facilitating lignin processability into PHA. Furthermore, these results highlighted the use of combinational pretreatment at a low holding temperature as a means to synergistically maximize the carbohydrate output and lignin processability, which provides a unique set of features to improve the biorefining performance.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Design principles for the ultimate gas deliverable capacity material: nonporous to porous deformations without volume change
Understanding the fundamental limits of gas deliverable capacity in porous materials is of critical importance as it informs whether technical targets (e.g., for on-board vehicular storage) are feasible. High-throughput screening studies of rigid materials, for example, have shown they are not able to achieve the original ARPA-E methane storage targets, yet an interesting question remains: what is the upper limit of deliverable capacity in flexible materials? In this work we develop a statistical adsorption model that specifically probes the limit of deliverable capacity in intrinsically flexible materials. The resulting adsorption thermodynamics indicate that a perfectly designed, intrinsically flexible nanoporous material could achieve higher methane deliverable capacity than the best benchmark systems known to date with little to no total volume change. Density functional theory and grand canonical Monte Carlo simulations identify a known metal–organic framework (MOF) that validates key features of the model. Therefore, this work (1) motivates a continued, extensive effort to rationally design a porous material analogous to the adsorption model and (2) calls for continued discovery of additional high deliverable capacity materials that remain hidden from rigid structure screening studies due to nominal non-porosity.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Softening by charging: how collective modes of ionic association in concentrated redoxmer/electrolyte solutions define the structural and dynamic properties in different states of charge
Understanding the physical and chemical processes occurring in concentrated electrolyte solutions is required to achieve redox flow batteries with high energy density. Highly concentrated electrolyte solutions are often studied in which collective crowded interactions between molecules and ions become predominant. In this work, experimental and computational methods were used to examine non-aqueous electrolyte solutions in two different states of charge as a function of redoxmer concentration. As the latter increases and the ionic association strengthens, the electric conductivity passes through a maximum and the solution increasingly gels, which is seen through a rapid non-linear increase in viscosity. We establish that the structural rigidity of ionic networks is closely connected with this loss of fluidity and show that charging generally yields softer ionic assemblies with weaker attractive forces and improved dynamical properties.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗