Predicting Pt-195 NMR chemical shift using new relativistic all-electron basis set

Predicting NMR properties is a valuable tool to assist the experimentalists in the characterization of molecular structure. For heavy metals, such as Pt-195, only a few computational protocols are available. In the present contribution, all-electron Gaussian basis sets, suitable to calculate the Pt-195 NMR chemical shift, are presented for Pt and all elements commonly found as Pt-ligands. The new basis sets identified as NMR-DKH were partially contracted as a triple-zeta doubly polarized scheme with all coefficients obtained from a Douglas–Kroll–Hess (DKH) second-order scalar relativistic calculation. The Pt-195 chemical shift was predicted through empirical models fitted to reproduce experimental data for a set of 183 Pt(II) complexes which NMR sign ranges from −1000 to −6000 ppm. Furthermore, the models were validated using a new set of 75 Pt(II) complexes, not included in the descriptive set. The models were constructed using non-relativistic Hamiltonian at density functional theory (DFT-PBEPBE) level with NMR-DKH basis set for all atoms. For the best model, the mean absolute deviation (MAD) and the mean relative deviation (MRD) were 150 ppm and 6%, respectively, for the validation set (75 Pt-complexes) and 168 ppm (MAD) and 5% (MRD) for all 258 Pt(II) complexes. These results were comparable with relativistic DFT calculation, 200 ppm (MAD) and 6% (MRD)

NMR-DKH basis set analysis for calculation of 1j(195pt15n) in platinum(ii) complexes

The Nuclear Magnetic Resonance is a widely used technique and plays a key role in many different areas, especially in elucidation of reaction mechanisms and designing of new drugs. In this context, the use of Quantum Chemistry methods is an important tool in NMR study. However, theoretical calculations of NMR parameters are, most of the times, expensive and imprecise. Therefore, one of the greatest challenges in Computational Chemistry is developing protocols with low computational cost that yield satisfactory results. In this work, the 1 J(195Pt15N) coupling constant was studied in Pt(II) complexes in order to develop a computational protocol for the calculation of the constant with affordable cost and satisfactory results using the all-electron relativistic basis set NMR-DKH, previously proposed for calculation of 195Pt chemical shift. Several topics were tested and analyzed in order to develop the protocol, such as DFT functionals and modifications to the basis set. The final computational protocol for predicting the 1 J(195Pt15N) coupling constant in Pt(II) complexes included a working set of 82 coupling constants for 57 Pt(II) complexes. Furthermore, it was applied for a testing set of 16 coupling constants in 14 Pt(II) complexes. The protocol was based on nonrelativistic calculations at PBEPBE/NMR-DKH level. The MAD was 36 Hz corresponding to the MRD of 10.4%, considering all 98 coupling constants for 71 Pt(II) complexes.A Ressonância Magnética Nuclear é uma técnica amplamente utilizada e tem um papel fundamental em diferentes áreas, especialmente na elucidação de mecanismos reacionais e desenvolvimento de novos fármacos. Neste contexto, o uso de métodos de Química Quântica é uma importante ferramenta no auxílio aos estudos de RMN. No entanto, os cálculos teóricos dos parâmetros de RMN são muitas vezes custosos e imprecisos. Assim, um dos maiores desafios na Química Computacional é desenvolver protocolos com baixo custo computacional que levem a bons resultados. Neste trabalho, a constante de acoplamento 1 J(195Pt15N) foi estudada em complexos de platina(II) a fim de desenvolver um protocolo para o cálculo da constante com custo computacional acessível e resultados satisfatórios, usando a função de base relativística all-electron NMR-DKH, previamente desenvolvida para o cálculo do deslocamento químico de 195Pt. Diversos tópicos foram testados e analizados no desenvolvimento do protocolo, como funcionais DFT e modificações na função de base. O protocolo computacional final para o cálculo da constante de acoplamento 1 J(195Pt15N) incluiu um conjunto de 82 constantes de acoplamento para 57 complexos de Pt(II). Ademais, o protocol foi aplicado a um conjunto teste de 16 constantes de acoplamento para 14 complexos de Pt(II). O protocolo foi baseado em cálculos não-relativísticos no nivel PBEPBE/NMR-DKH. O desvio absoluto médio foi de 36 Hz, que corresponde a um desvio relativo médio de 10.4% considerando todas as 98 constantes de acoplamento para os 71 complexos de Pt(II)