Polyradical PROXYL/TEMPO‐Derived Amides: Synthesis, Physicochemical Studies, DFT Calculations, and Antimicrobial Activity

Abstract

DFT = density functional theory,P ROXYL = 2,2,5,5-tetramethyl-1-pyrrolidinyloxy,TEMPO = 2,2,6,6-tetramethyl-1-piperidinyloxy.Supporting informationfor this article can be found under: https://doi.

Polyradical PROXYL/TEMPO Conjugates Connected by Ester/Amide Bridges: Synthesis, Physicochemical Studies, and DFT Calculations

“…On the contrary, for derivative 3 with −C(O)NHCH 2 CH 2 NHC(O)− linker the EPR spectra measured in DMSO in the temperature range of 298–363 K reveal the spectral line alterations typical for the dinitroxide conformation dynamics (Figure 4a). Consequently, these were analysed and interpreted using a three conformation model for the biradicals with flexible long‐chain bridges [21–30] . Figure 4b illustrates the Arrhenius plot evaluated for 3 in DMSO; the apparent activation energy of the intramolecular dynamics calculated from the slope ( ϵ =18.4 kJ mol −1 ) and parameter τ 0 =9.8×10 −12 s (which reflects the lifetime of the activated state of 3 in DMSO solvent), are well compatible with those found previously in DMSO for dinitroxide containing two TEMPO units connected with −NHC(O)CH 2 CH 2 C(O)NH− bridge [30] …”

“…Nitroxides are generally known for their significant redox activity with corresponding Noxoammonium cations to be formed during one-electron electrochemical oxidation. [30,32,33] In our case, the voltammetric profile for all studied compounds 1-9 ( Figure S2 in Supporting Information) confirmed undergoing one-electron transfer during particular electrode reaction with half-wave potentials (E 1/2 ) ranging from À 51 mV to À 17 mV vs Ag/AgCl (3 mol L À 1 KCl) reference electrode. Table 3 summarizes the experimentally determined values of the redox parameters for the studied nitroxides.…”

“…The redox properties of studied dinitroxides 1 – 5 and trinitroxides 6 – 9 were evaluated using cyclic voltammetry (CV) with the polarization rate value of 100 mV s −1 in Britton‐Robinson (BR) buffer solution (BR, pH 7), on a glassy carbon electrode (GCE). Nitroxides are generally known for their significant redox activity with corresponding N ‐oxoammonium cations to be formed during one‐electron electrochemical oxidation [30,32,33] . In our case, the voltammetric profile for all studied compounds 1 – 9 (Figure S2 in Supporting Information) confirmed undergoing one‐electron transfer during particular electrode reaction with half‐wave potentials ( E 1/2 ) ranging from −51 mV to −17 mV vs Ag/AgCl (3 mol L −1 KCl) reference electrode.…”

“…[21][22][23][24][25][26][27][28][29][30] Figure 4b illustrates the Arrhenius plot evaluated for 3 in DMSO; the apparent activation energy of the intramolecular dynamics calculated from the slope (ɛ = 18.4 kJ mol À 1 ) and parameter τ 0 = 9.8 × 10 À 12 s (which reflects the lifetime of the activated state of 3 in DMSO solvent), are well compatible with those found previously in DMSO for dinitroxide containing two TEMPO units connected with À NHC (O)CH 2 CH 2 C(O)NHÀ bridge. [30] The interpretation of the EPR spectra of trinitroxides in fluid solutions is more complex due to the potential spin exchange of electrons determined by the three values of exchange coupling constants (J EPR12 , J EPR13 , J EPR23 ), along with the conformation interconversion of different molecular structures potentially present in solution. [31] Figure 5 depicts the EPR spectra measured for trinitroxides 6-9 in DMSO in the temperature range of 303-363 K. The EPR spectra of derivatives 6-8 under given experimental conditions represent the seven-line signals reflecting the spin-spin exchange, and the simulation analysis shows that the best fit is evaluated considering the strong spin exchange between two nitroxide units (J EPR12 = J EPR13 @ A N , J EPR23T able 1.…”

Reactions of Nitroxides, Part 17. Synthesis, Fungistatic and Bacteriostatic Activity of Novel Five- and Six-Membered Nitroxyl Selenoureas and Selenocarbamates

“…Antihypertensive effects observed for nitroxides (mainly TEMPOL) were reviewed [76]. The inhibitory effect of selected dinitroxides and polynitroxides on the growth of some species of bacteria, yeasts and fungi was described [77].…”