The eChem project has been previously presented as an interactive platform for quantum and computational chemistry education [J. Chem. Educ. 100, 1664-1671]. However, education is only one side of the eChem project. Another aspect is that it highly accelerates method development by means of code prototyping in notebooks. Complex equations can be understood, and algorithms are examined before the actual software programming step is carried out. Here, the benefits of notebooks for code prototyping are illustrated using the example of vibrational spectroscopy-a type of spectroscopy which involves complex equations with a large number of terms.

We present a second-quantization based Liouville-space formulation of response theory for non-eigenstates of unperturbed Hamiltonian in the single-determinant self-consistent field framework, where we include a time-independent relaxation superoperator in the Liouville equation of motion. This density-based formulation uses quantities and concepts similar to those introduced in established wave function-based forms of approximate-state response theory, and we discuss how the wave function-based class of theory relates to the present more general treatment. We also discuss various aspects of the present methodology, including its opportunities and limitations/challenges, and outline future work.

Protein deposits are common hallmarks of several neurodegenerative diseases, including Alzheimer’s disease (AD), and ligands that selectively detect specific protein aggregates are crucial. Herein, we investigated the molecular requirements of a thiophene-based ligand, denoted HS-276, for selective detection of Aβ deposits in human brain tissue sections with AD pathology. The staining of Aβ deposits was altered when replacing the terminal thiophene moiety with other heterocyclic moieties. In addition, when changing the central thiophene moiety of the ligand to a phenylene, a quinoxaline, or a benzothiadiazole moiety, the staining of Aβ aggregates was completely abolished, verifying that specific molecular interactions between these ligands and the aggregates were required. The experimental observations were also verified by theoretical calculations of the ligands’ binding mode towards Aβ filaments. Our findings provide chemical insights for developing ligands that selectively target Aβ deposits and highlight the importance of certain chemical requirements for achieving a selective ligand, such as HS-276, for detecting Aβ deposits in sporadic AD. We foresee that these findings might aid in creating novel agents for clinical imaging of Aβ aggregates in AD.

An automatic code generated C++/HIP/CUDA implementation of the (auxiliary) Fock, or Kohn-Sham, matrix construction for execution in GPU-accelerated hardware environments is presented. The module is developed as part of the quantum chemistry software package VeloxChem, employing localized Gaussian atomic orbitals. The performance and scaling characteristics are analyzed in view of the specific requirements for self-consistent field optimization and response theory calculations. As an example, the electronic circular dichroism spectrum of a G-quadruplex is calculated at the level of time-dependent density functional theory in conjunction with the range-separated CAM-B3LYP exchange-correlation functional. Computational issues due to the high-density of states following the adoption of large-scale model systems are here bypassed with use of the complex polarization propagator approach. The origin of the negative Cotton effect in the long-wavelength onset of the experimental spectrum is elucidated in large-scale modeling and shown to be associated with the TTA nucleobase linkers in the G-quadruplex.

Being a program written primarily in Python that strictly adheres to modern object-oriented software engineering and parallel programming practices, VeloxChem is shown to be suitable for the development of (semi)automatized workflows that extend its scope from first-principles quantum chemical purism to hybrid quantum-classical interoperability and some degree of semiempiricism. Methods are presented for building complex systems such as metal-organic frameworks, constructing molecular mechanics and interpolation mechanics force fields, conformer searches, system solvation, determining free energies of solvation, and determining free energy profiles of reaction pathways using the empirical valence bond method. The implementations are made intuitive with opportunities for interactive plotting and 3D molecular structure illustrations through the use of Jupyter notebooks.

Molecules that can undergo reversible chemical transformations following the absorption of light, the so-called molecular photoswitches, have attracted increasing attention in technologies, such as solar energy storage. Here, the optical and thermochemical properties of the photoswitch are central to its applicability, and these properties are influenced significantly by solvation. We investigate the effects of solvation on two norbornadiene/quadricyclane photoswitches. Emphasis is put on the energy difference between the two isomers and the optical absorption as these are central to the application of the systems in solar energy storage. Using a combined classical molecular dynamics and quantum mechanical/molecular mechanical computational scheme, we showcase that the dynamic effects of solvation are important. In particular, it is found that standard implicit solvation models generally underestimate the energy difference between the two isomers and overestimate the strength of the absorption, while the explicit solvation spectra are also less red-shifted than those obtained using implicit solvation models. We also find that the absorption spectra of the two systems are strongly correlated with specific dihedral angles. Altogether, this highlights the importance of including the dynamic effects of solvation.

In this Letter, we present a pioneering analysis of the density functional approximations (DFAs) beyond the generalized gradient approximation (GGA) for predicting two-photon absorption (2PA) strengths of a set of push-pull π-conjugated molecules. In more detail, we have employed a variety of meta-generalized gradient approximation (meta-GGA) functionals, including SCAN, MN15, and M06-2X, to assess their accuracy in describing the 2PA properties of a chosen set of 48 organic molecules. Analytic quadratic response theory is employed for these functionals, and their performance is compared against the previously studied DFAs and reference data obtained at the coupled-cluster CC2 level combined with the resolution-of-identity approximation (RI-CC2). A detailed analysis of the meta-GGA functional performance is provided, demonstrating that they improve upon their predecessors in capturing the key electronic features of the π-conjugated two-photon absorbers. In particular, the Minnesota functional MN15 shows very promising results as it delivers pleasingly accurate chemical rankings for two-photon transition strengths and excited-state dipole moments.

Chiral and enantiopure perfluorinated sulfonimidamides act as low-molecular weight gelators at low critical gelation concentration (<1 mg mL-1) via supramolecular polymerization in nonpolar organic solvents and more heterogenic mixtures, such as biodiesel and oil. Freeze-drying of the organogel leads to ultralight aerogel with extremely low density (1 mg mL-1). The gelation is driven by hydrogen bonding resulting in a helical molecular ordering and unique fibre assemblies as confirmed by scanning electron microscopy, CD spectroscopy, and computational modeling of the supramolecular structure.

Misfolding and aggregation of transthyretin (TTR) causeseveralamyloid diseases. Besides being an amyloidogenic protein, TTR hasan affinity for bicyclic small-molecule ligands in its thyroxine (T4)binding site. One class of TTR ligands are trans-stilbenes. The trans-stilbenescaffold is also widely applied for amyloid fibril-specific ligandsused as fluorescence probes and as positron emission tomography tracersfor amyloid detection and diagnosis of amyloidosis. We have shownthat native tetrameric TTR binds to amyloid ligands based on the trans-stilbenescaffold providing a platform for the determination of high-resolutionstructures of these important molecules bound to protein. In thisstudy, we provide spectroscopic evidence of binding and X-ray crystallographicstructure data on tetrameric TTR complex with the fluorescent salicylicacid-based pyrene amyloid ligand (Py1SA), an analogue of the Congored analogue X-34. The ambiguous electron density from the X-ray diffraction,however, did not permit Py1SA placement with enough confidence likelydue to partial ligand occupancy. Instead, the preferred orientationof the Py1SA ligand in the binding pocket was determined by moleculardynamics and umbrella sampling approaches. We find a distinct preferencefor the binding modes with the salicylic acid group pointing intothe pocket and the pyrene moiety outward to the opening of the T4binding site. Our work provides insight into TTR binding mode preferencefor trans-stilbene salicylic acid derivatives as well as a frameworkfor determining structures of TTR-ligand complexes.

Distinct aggregated proteins are correlated with numerous neurodegenerative diseases and the development of ligands that selectively detect these pathological hallmarks is vital. Recently, the synthesis of thiophene-based optical ligands, denoted bi-thiophene-vinyl-benzothiazoles (bTVBTs), that could be utilized for selective assignment of tau pathology in brain tissue with Alzheimer's disease (AD) pathology, was reported. Herein, we investigate the ability of these ligands to selectively distinguish tau deposits from aggregated amyloid-β (Aβ), the second AD associated pathological hallmark, when replacing the terminal thiophene moiety with other heterocyclic motifs. The selectivity for tau pathology was reduced when introducing specific heterocyclic motifs, verifying that specific molecular interactions between the ligands and the aggregates are necessary for selective detection of tau deposits. In addition, ligands having certain heterocyclic moieties attached to the central thiophene-vinylene building block displayed selectivity to aggregated Aβ pathology. Our findings provide chemical insights for the development of ligands that can distinguish between aggregated proteinaceous species consisting of different proteins and might also aid in creating novel agents for clinical imaging of tau pathology in AD.