Counting the Monomers in Nanometer-Sized Oligomers by Pulsed Electron−Electron Double Resonance

Abstract

In a lot of cases active biomolecules are complexes of higher order, thus methods capable of counting the number of building blocks and elucidating their geometric arrangement are needed. Therefore, we experimentally validate here spin-counting via 4-pulse electron-electron double resonance (PELDOR) on well-defined test samples. Two biradicals, a symmetric and an asymmetric triradical, and a tetraradical were synthesized in a convergent reaction scheme via palladium-catalyzed cross-coupling reactions. PELDOR was then used to obtain geometric information and the number of spin centers per molecule in a single experiment. The measurement yielded the expected distances (2.2-3.8 nm) and showed that different spin-spin distances in one molecule can be resolved even if the difference amounts to only 5 A. The number of spins n has been determined to be 2.1 in both biradicals, to 3.1 and 3.0 in the symmetric and asymmetric triradicals, respectively, and to 3.9 in the tetraradical. The overall error of PELDOR spin-counting was found to be 5% for up to four spins. Thus, this method is a valuable tool to determine the number of constituting spin-bearing monomers in biologically relevant homo- and heterooligomers and how their oligomerization state and geometric arrangement changes during function.

Accurate Extraction of Nanometer Distances in Multimers by Pulse EPR

“…While a regularization artifact and improper amplitudes in the distance distribution of a tetraradical were attributed to multi‐spin effects,9 Jeschke et al. provided the first systematic study using three‐spin model systems and relieving the problem by reducing the probability of multiple excitation 7.…”

Synthesis of New Pyrroline Nitroxides with Ethynyl Functional Group

“…in dimethylsulfoxide (DMSO) yielded 3,4-bis (triazolyl)pyrroline nitroxide 5. Sonogashira coupling of compound 2b with paramagnetic vinyl iodide 6 in triethylamine-piperidine-dimethylformamide 75 (DMF) mixture [8] in the presence of CuI, PPh 3 , and Pd(PhCN) 2 Cl 2 furnished triradical 7, giving seven bands in EPR (see supplementary material) but with poor yield (9%) (Scheme 2). This compound was prepared for further EPR studies, Q1 but its utilization as molecular magnet also can be considered.…”

“…1 H NMR (of compounds 2c, 2d, 5, 9, 11), 13 C NMR (of compound 9), EPR (of compound 7), UV-vis (of compound 12), MS (of compounds 2c, 2d, 2e, 5,7,8,9,10,11,12), and IR (of compounds 2c, 170 2d, 2e, 5, 7, 8, 9, 10, 11, 12) data can be accessed on the publisher's website.…”

“…[6b] The importance of ethynyl substituent containing nitroxides has also emerged in recent decades; they have been used for spin labeling of nucleic acids by Sonogashira coupling, [7] synthesis of nanometer-sized paramagnetic oligomers, [8] modification of biomolecules…”

Probing of chain conformations in conjugated polymer nanoparticles by electron spin resonance spectroscopy

“…14, [24][25][26][27] The commonly used nitroxides 28 as spin labels 29,30 are also smaller than fluorophores, and thus interfere less with the system of interest. 31,32 On a molecular basis, p-conjugated oligomers are referred to as rigid rods, 33 which makes them desirable as building blocks for (supra-)molecular architectures.…”