Resonant-Convergent PCM Response Theory for the Calculation of Second Harmonic Generation in Makaluvamines A–V: Pyrroloiminoquinone Marine Natural Products from Poriferans of Genus Zyzzya

Theoretical Study on Second-Order Nonlinear Optical Responses of Pyrazine-carbazole Derivatives in Gas, Solution, and Crystal States

The packing fashion of an organic molecule in the crystal plays a critical role in the global nonlinear optical (NLO) responses under ambient conditions. To better understand how the crystal packing affects the first hyperpolarizability (β) and achieve efficient NLO material, herein, the three positional isomers (regioisomers) through changing the substituted position of 3-carbazole-pyrazine-based isomers were performed. The phenyl groups with different positions (ortho-, meta-, and para-) of pyrazine, named 23-B3C, 25-B3C, and 26-B3C, are theoretically studied in gas, solvent, and solid states by using the polarizable continuum model and the combined quantum mechanics and molecular mechanics method, respectively. These two regioisomers (23-B3C and 25-B3C) exhibit totally different aggregation behaviors. Through density functional theory (DFT) and time-dependent DFT (TDDFT) calculations, it has been concluded that the geometric changes of 23-B3C and 25-B3C are mainly contributed by the bond length and dihedral angle from gas to the solid phase. Herein, a lower HOMO-LUMO energy gap and a better intramolecular charge-transfer absorption are found for 25-B3C owing to a more sizable π-conjugation effect with smaller bond length alternation. Importantly, the β value of 25-B3C in the crystal with the π-π stacking with the same CT direction between the whole backbones (H-aggregate) and the end-groups (J-aggregate) commonly can substantially increase compared to that of the monomer. However, the obtained reduction of β value for 23-B3C is mainly because of V-aggregate (α > 90°) and reverse J-aggregate in crystal. Thus, our work showcases a profound understanding of the relationship between solid-state packing and macroscopic second-order NLO properties and provides a feasible molecule strategy for the development of high-efficiency NLO materials.

Dalton Project: A Python platform for molecular- and electronic-structure simulations of complex systems

The Dalton Project provides a uniform platform access to the underlying full-fledged quantum chemistry codes Dalton and LSDalton as well as the PyFraME package for automatized fragmentation and parameterization of complex molecular environments. The platform is written in Python and defines a means for library communication and interaction. Intermediate data such as integrals are exposed to the platform and made accessible to the user in the form of NumPy arrays, and the resulting data are extracted, analyzed, and visualized. Complex computational protocols that may, for instance, arise due to a need for environment fragmentation and configuration-space sampling of biochemical systems are readily assisted by the platform. The platform is designed to host additional software libraries and will serve as a hub for future modular software development efforts in the distributed Dalton community.

Optical absorption and magnetic circular dichroism spectra of thiouracils: a quantum mechanical study in solution

The excited electronic states of thiouracils, the analogues of uracil where the carbonyl oxygens are substituted by sulphur atoms, have been investigated by computing the magnetic circular dichroism (MCD) and one-photon absorption (OPA) spectra at the TD-DFT level of theory.

Recent advances and applications of experimental technologies in marine natural product research

Marine natural products are a rich source of novel and biologically active compounds. The number of identified marine natural compounds has grown 20% over the last five years from 2009 to 2013. Several challenges, including sample collection and structure elucidation, have limited the development of this research field. Nonetheless, new approaches, such as sampling strategies for organisms from extreme ocean environments, nanoscale NMR and computational chemistry for structural determination, are now available to overcome the barriers. In this review, we highlight the experimental technology innovations in the field of marine natural products, which in our view will lead to the development of many new drugs in the future.