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Self-assembly of monodisperse graphene nanoribbons into submicron architectures with long-range order and uniform orientation
No full textFabricating organic semi-conducting materials into large-scale well-organized architectures is critical for building high performance molecular electronics. While graphene nanoribbons (GNRs) hold enormous promise for various device applications, their assembly into a well-structured monolayer or multilayer architecture poses a substantial challenge. Here we report the preparation of length-defined monodisperse GNRs and their self-assembly into submicron-architectures with long-range order, uniform orientation as well as regular layers. The use of short alkyl side chains benefits forming stable multi-layers through interlocking structures. By changing the length and backbone shapes of these monodisperse GNRs, various three-dimensional assemblies including multilayer stripes, monolayer stripes, and nanowires, can be achieved, leading to different photophysical properties and band gaps. The discovery of these intriguing self-assembly behaviors of length-defined GNRs is expected to open the door for various future applications
Basis-set limit CCSD(T) energies for large molecules with local natural orbitals and reduced-scaling basis-set corrections
No full textThe calculation of density-based basis-set correction (DBBSC), which remedies the basis-set incompleteness (BSI) error of the correlation energy, is combined with local approximations. Aiming at large-scale applications, the procedure is implemented in our efficient local natural orbital-based coupled-cluster singles and doubles with per- turbative triples [LNO-CCSD(T)] scheme. To this end, the range-separation function, which characterizes the one-electron BSI in space, is decomposed into the sum of con- tributions from individual localized molecular orbitals (LMOs). A compact domain is constructed around each LMO, and the corresponding contributions are evaluated only within these restricted domains. Furthermore, for the calculation of the com- plementary auxiliary basis set (CABS) correction, which significantly improves the Hartree–Fock (HF) energy, the local density fitting approximation is utilized. The er- rors arising from the local approximations are examined in detail, efficient prescreening techniques are introduced to compress the numerical quadrature used for DBBSC, and conservative default thresholds are selected for the truncation parameters. The effi- ciency of the DBBSC-LNO-CCSD(T) method is demonstrated through representative examples of up to 1000 atoms. Based on the numerical results, we conclude that the corrections drastically reduce the BSI error using double-ζ basis sets, often to below 1 kcal/mol compared to the reliable LNO-CCSD(T) complete basis set references, while significant improvements are also achieved with triple-ζ basis sets. Considering that the calculation of the DBBSC and CABS corrections only moderately increases the wall-clock time required for the post-HF steps in practical applications, the proposed DBBSC-LNO-CCSD(T) method offers a highly efficient and robust tool for large-scale calculations
Enhancing the Thermoelectric Figure of Merit of BiN via Polymorphism, Pressure, and Nanostructuring
No full textMaterials discovery extends beyond the synthesis of new compounds. Detailed characterization is essential to understand the potential applications of novel materials. However, experimental characterization can be challenging due to the vast chemical and physical spaces, as well as the specific conditions required for certain techniques. Computational high-throughput methods can overcome these challenges. In this work, the transport and thermoelectric properties of the recently synthesized bulk BiN are explored, including the effects of temperature, pressure, carrier concentration, polymorphism and polycrystalline grain size. We find that the band structure is strongly dependent on pressure and the polymorph studied. Both polymorphs exhibit low thermal conductivity at 0 GPa, which rapidly increases when pressure is applied. Electronic transport properties can be finely tuned based on the effects of pressure and polymorph type on the band gap, carrier mobilities, and presence of secondary pockets. The thermoelectric figure of merit can reach values around 0.85 for both p- and n-type BiN if the power factor and lattice thermal conductivity are optimized at 600 K, making this material competitive with other well-known thermoelectric families, such as Bi2Te3 or PbX, in the low-to-medium temperature range
Machine learning-assisted c-RASAR modeling of a curated set of orally active nephrotoxic drugs: Similarity-based predictions from close source neighbors
No full textCheminformatics and Machine Learning (ML) have seen exponential progress in the last decade, in the field of chemical risk assessment, due to their efficiency, accuracy, and reliability. The constant evolution of New Approach Methodologies (NAM) has inspired researchers around the globe to deviate from conventional approaches and adopt or develop new, “unconventional” methods. The classification Read-Across Structure-Activity Relationship (c-RASAR) is an unconventional approach that utilizes similarity and error-based information from the nearest neighboring compounds into a Machine Learning modeling framework, resulting in enhanced predictivity. Although this technique has so far been applied to molecular descriptors, we have applied this approach in the present study on molecular fingerprints along with conventional molecular descriptors for ML-based model development from a recently reported highly curated set of orally active nephrotoxic drugs. We initially developed ML models using nine different linear and non-linear algorithms separately on molecular descriptors and MACCS fingerprints, thus generating 18 different ML QSAR models. Using the chemical spaces defined by the modeling descriptors and fingerprints, the similarity and error-based RASAR descriptors were computed, and the most discriminating RASAR descriptors were used to develop another set of 18 different ML c-RASAR models. All 36 models were cross-validated 20 times with a 5-fold cross-validation strategy, and their predictivity was checked on the test set data. A multi-criteria decision-making strategy – the Sum of Ranking Differences (SRD) approach - was adopted to identify the best-performing model based on robustness and external validation parameters. This statistical analysis suggested that the c-RASAR models had an overall good performance, while the best-performing model was also a c-RASAR model. This model was used to screen a true external set data prepared from the known nephrotoxic compounds of DrugBankDB. These results also showed that our model efficiently identifies nephrotoxic compounds. The t-SNE analyses on the descriptors, fingerprints, and the RASAR descriptor spaces inferred that the RASAR descriptors efficiently encode the chemical information, as evident from the tight and distinct clustering of the data points. Additionally, the molecular descriptors and the corresponding RASAR descriptors were used to identify potential activity cliffs using the ARKA framework
Anodic Hydrogen Generation from Benzaldehyde on Au, Ag, and Cu: Rotating Ring-Disk Electrode Studies
No full textAldehydes are selectively oxidized to carboxylates on group 11 metals at low potentials (<0.4 V vs. RHE) in alkaline media. This process can occur by a pathway that generates H2 gas from the aldehyde, known as electro-oxidative dehydrogenation (EOD) or anodic hydrogen production. The EOD process occurs with transfer of only one electron per aldehyde, whereas typical oxidation with discharge of hydrogen to form water is a two-electron process. Here, we study the catalytic activity and selectivity toward H2 of Au, Ag, and Cu electrodes using benzaldehyde with rotating disk and ring-disk electrode (RDE/RRDE) techniques. The average number of electrons per benzaldehyde molecule obtained via H2 detection by RRDE agrees with that obtained via Koutecký-Levich analysis conducted at various rotation rates. We find that Au and Ag have much higher H2 and benzoate formation rates than Cu, but that Cu can perform the reaction at about 0.2 V lower overpotentials. On all three materials, benzaldehyde oxidation has high selectivity to anodic H2 (one-electron pathway) below ~0.5 V vs. RHE, but, with increasing potential, the selectivity shifts to H-oxidation forming water (two-electron pathway)
Two-photon Absorption Strengths of Small- and Medium-Sized Molecules: Reference CC3 Values and Benchmarks
No full textWe present the largest dataset of highly-accurate vertical and degenerate two-photon transition strengths (\delta^{\mbox{\tiny TPA}}) for standard small- and medium-sized organic molecules, calculated using the quadratic response implementation of the third-order coupled cluster method that includes iterative triples (Q-CC3). The aug-cc-pVTZ basis set was used for all small molecules, while medium-sized molecules were assessed with aug-cc-pVDZ and the differences due to the basis sets are discussed. This dataset, encompassing 82 singlet transitions of various characters (Rydberg, valence, and double excitations), enables a comprehensive benchmark of both small basis sets and, alternative wavefunction methods when Q-CC3 calculations become beyond reach. These methods include quadratic (Q) response and equation of motion CCSD approximations, Q-CC2, second-order algebraic diagrammatic construction in its intermediate state representation (I-ADC2), as well as time-dependent density functional theory (TD-DFT) with a set of 5 commonly used exchange-correlation functionals. This extensive analysis provides a quantitative assessment of these methods, revealing how different system sizes, response intensities, and types of transitions affect their performances
Expedited Aminoglutarimide C-N Cross-Coupling Enabled by High-Throughput Experimentation
No full textA simple protocol for the direct Buchwald-Hartwig cross-coupling of (hetero)aryl halides with unprotected aminoglutarimide to afford diverse Cereblon Binding Motifs is disclosed. This C-N cross-coupling method development was enabled by high throughput combinatory screening of key reaction parameters namely solvents, temperatures and ligands. Scope studies revealed generality across various heteroaryl and aryl halides, with the reaction proceeding under mild conditions. In comparison, this method demonstrated strategic superiority over previously reported approaches, as evidenced by a significant step count reduction from known syntheses in the patent literature
Mapping In Situ the Internal Structure and Dynamics of Supramolecular Homopolymers and Copolymers
No full textSupramolecular polymers are assemblies of monomers bonded non-covalently, thereby having potential to emulate the dynamic nature of biological ones such as those in the cytoskeleton, muscle, and extracellular matrices. Understanding the nature of dynamics in synthetic analogues of these assemblies is crucial to develop adaptive and functional biomaterials. Using three positively charged peptide amphiphiles, we introduce here a general base-titration methodology to systematically decrease electrostatic repulsion among monomers and probe in situ polymerization. In one-component systems, we demonstrate that weaker cohesive hydrogen bonding and stronger electrostatic repulsion enhance supramolecular dynamics and shift the assembly equilibrium from elongated polymers to spheroidal micelles. In binary systems, we find a tendency to form blocky copolymers but a reduced level of internal phase separation within the assembly is observed with less mismatch in peptide sequence. Well-mixed systems acquire different dynamics but interestingly mismatched ones retain their characteristic supramolecular motion as homopolymers. These findings provide strategies to tailor dynamics and internal structure in the assemblies of supramolecular materials, factors that can strongly impact on their useful functions.
Rational Design of Transition Metal Based Molecular Spin State Switches: Tuning the High Spin to Low Spin Transition Rate by Ligand Substitution
No full textThe effect of substitution in the axial 4\u27 position by electron withdrawing (EW) and donating (ED) groups on the ground and excited state properties of the \feterpy complex is investigated in a systematic study. DFT calculations are used to determine the geometric and electronic structures of the substituted complexes, and these calculated results were compared to experimental results from stationary and time-resolved spectroscopy. The question how this interplay of theory and experiment can be used in the context of ligand engineering is also considered
Optimizing continuous monitoring sensor placement on oil and gas sites
No full textWe propose a generic, modular framework to optimize the placement of continuous monitoring sensors on oil and gas sites aiming to maximize the methane emissions detection efficiency. Our proposed framework substantially expands the problem scale compared to previous related studies and can be adapted for different objectives in sensor placement. This optimization framework is comprised of five steps: (1) simulate emission scenarios using site-specific wind and emission information; (2) set possible sensor locations under consideration of the site layout and any site-specific constraints; (3) simulate methane concentrations for each pair of emission scenario and possible sensor location; (4) determine emissions detection based on the site-specific simulated concentrations; and (5) select the best subset of sensor locations, under a given sensor budget, using genetic algorithms combined with Pareto optimization. We demonstrate the practicality and effectiveness of our framework through its application to an oil and gas emission testing facility with a large search space of possible sensor locations; a setting which is computationally infeasible to solve with commonly used mixed-integer linear programming formulations. Additionally, a case study illustrates the successful application of our algorithm to a real oil and gas site, showcasing its real-world applicability and effectiveness