# Reactions of hypobromous acid with dimethyl selenide, dimethyl diselenide and other organic selenium compounds: kinetics and product formation

## TL;DR

This study examines how different organic selenium compounds react with hypobromous acid, finding that selenomethionine reacts very quickly.

## Contribution

The study reports new kinetic data on the reactivity of various organic selenium compounds with HOBr, highlighting selenomethionine's significant reactivity.

## Key findings

- Selenomethionine (SeMet) has a high reactivity with HOBr, suggesting it may act as a quencher of HOBr.
- Dimethyl selenide (DMSe) reacts with HOBr but less rapidly than dimethyl sulfide (DMS), making it less relevant for marine DMSe abatement.
- Phenyl-selenides like diphenyl diselenide (DPDSe) also show significant reactivity with HOBr.

## Abstract

Selenium (Se) is an essential micronutrient for many living organisms particularly due to its unique redox properties. We recently found that the sulfur (S) analog for dimethyl selenide (DMSe), i.e. dimethyl sulfide (DMS), reacts fast with the marine oxidant hypobromous acid (HOBr) which likely serves as a sink of marine DMS. Here we investigated the reactivity of HOBr with dimethyl selenide and dimethyl diselenide (DMDSe), which are the main volatile Se compounds biogenically produced in marine waters. In addition, the reactivity of HOBr with further organic Se compounds was tested, i.e., SeMet (as N-acetylated-SeMet), and selenocystine (SeCys2 as N-acetylated-SeCys2), as well as the phenyl-analogs of DMSe and DMDSe, respectively, diphenyl selenide (DPSe) and diphenyl diselenide (DPDSe). Apparent second-order rate constants at pH 8 for the reactions of HOBr with the studied Se compounds were (7.1 ± 0.7) × 107 M−1 s−1 for DMSe, (4.3 ± 0.4) × 107 M−1 s−1 for DMDSe, (2.8 ± 0.3) × 108 M−1 s−1 for SeMet, (3.8 ± 0.2) × 107 M−1 s−1 for SeCys2, (3.5 ± 0.1) × 107 M−1 s−1 for DPSe, and (8.0 ± 0.4) × 106 M−1 s−1 for DPDSe, indicating a very high reactivity of all selected Se compounds with HOBr. The reactivity between HOBr and DMSe is lower than for DMS and therefore this reaction is likely not relevant for marine DMSe abatement. However, the high reactivity of SeMet with HOBr suggests that SeMet may act as a relevant quencher of HOBr.

We studied reactions between a variety of organic forms of the essential element selenium (Se) and the oxidant hypobromous acid (HOBr). The studied Se compounds, especially selenomethionine, had a high reactivity with HOBr.