PhD Scientific Days 2021

Budapest, 7-8 July 2021

PH_II_P: Pharmaceutical Sciences II. Posters

Selenate – an Internal Chemical Shift Standard for Aqueous 77Se NMR Spectroscopy

Tamás Pálla1, Laura Herbath1, Arash Mirzahosseini1, Károly Mazák1, Béla Noszál1

1 Semmelweis University, Department of Pharmaceutical Chemistry, Budapest

Text of the abstract

Introduction
In the 77Se NMR literature chemical shifts are given relative to various references with limited accuracy and consistency, however, precise chemical shifts are needed, especially for methods making further conclusions based on chemical shift data.

Aims
In order to obtain precise chemical shift data our aim was to introduce an internal chemical shift reference for aqueous 77Se NMR measurements.

Method
The 77Se NMR spectrum of selenate was studied at various concentrations, pH media, temperatures, ionic strengths, and D2O:H2O ratios in order to examine its potential as a water-soluble internal chemical shift standard. The performance of selenate as a chemical shift reference and that of other widely accepted ones (dimethyl selenide, tetramethylsilane/TMS and 3-(trimethylsilyl)propane-1-sulfonate/DSS) was also explored.

Results
The uncertainty in the resulting chemical shift relative to the effective spectral width is comparable to that of DSS. Compared to the currently prevalent water-soluble external chemical shift reference, selenic acid solution, the properties of internal selenate are much more favorable in terms of ease of use. We have also demonstrated that selenate can be used in reducing media required for the analysis of selenol compounds. In summary it can be stated that sodium selenate can be used as a robust internal chemical shift reference in aqueous media for 77Se NMR measurements; the chemical shift of this reference in a solution containing 5 V/V% D2O at 25 °C and 0.15 mol∙dm-3 ionic strength is 1048.65 ppm relative to 60 V/V% dimethyl selenide in CDCl3 and 1046.40 ppm relative to the 1H signal of 0.03 V/V% TMS in CDCl3.

Conclusion
A water-soluble, selenium-containing internal chemical shift reference compound was introduced for 77Se NMR measurements for the first time in the literature, and with the aforementioned results all previous 77Se measurements can be converted to a unified scale defined by the International Union of Pure and Applied Chemistry.

Funding
Supported by FIKP 2020 and the ÚNKP-20-4-I-SE-2 and ÚNKP-20-4-II-SE-3 New National Excellence Program of the Ministry for Innovation and Technology from the source of the National Research, Development and Innovation Fund.

University and Doctoral School

Semmelweis University, Doctoral School of Pharmaceutical Sciences