Characterisation of uniformly ¹³C, ¹⁵N labelled bacteriochlorophyll a and bacteriopheophytin a in solution and in solid state: complete assignment of the ¹³C, ¹H and ¹⁵N chemical shifts

Abstract

In this investigation we report a complete assignment of (13)C, (1)H and (15)N solution and solid state chemical shifts of two bacterial photosynthetic pigments, bacteriochlorophyll (BChl) a and bacteriopheophytin (BPheo) a. Uniform stable-isotope labelling strategies were developed and applied to biosynthetic preparation of photosynthetic pigments, namely uniformly (13)C, (15)N labelled BChl a and BPheo a. Uniform stable-isotope labelling with (13)C, (15)N allowed performing the assignment of the (13)C, (15)N and (1)H resonances. The photosynthetic pigments were isolated from the biomass of photosynthetic bacteria Rhodopseudomonas palustris 17001 grown in uniformly (13)C (99%) and (15)N (98%) enriched medium. Both pigments were characterised by NMR in solution (acetone-d(6)) and by MAS NMR in solid state and their NMR resonances were recorded and assigned through standard liquid 2D (13)C-(13)C COSY, (1)H-(13)C HMQC, (1)H-(15)N HMBC and solid 2D (13)C-(13)C RFDR, (1)H-(13)C FSLG HETCOR and (1)H-(15)N HETCOR correlation techniques at 600 MHz and 750 MHz. The characterisation of pigments is of interest from biochemical to pharmaceutical industries, photosynthesis and food research.

Nanosecond-Flash 15N Photo-CIDNP MAS NMR on Reaction Centers of Rhodobacter sphaeroides R26

“…Intensity simulations show that the stronger signal is caused by N-IV, while the weaker originates from N-II. Such assignment is also in line with the chemical shift data of the isolated cofactors [32] showing for N-IV a higher ppm value as for N-II.…”

“…All signals have rather similar intensities, unfortunately also the ppm values coincide in the model compound study [32].…”

“…sphaeroides R26 has been performed using Igor Pro v. 6.01 (Lake Oswego, OR, USA). As starting parameters for the fitting procedure, the chemical shifts have been taken from the literature [32]. During the fitting procedures, the chemical shifts have been kept fixed for all the spectra collected at different evolution times.…”

“…Furthermore, under continuous illumination spin diffusion and relaxation effects may establish steadystate polarizations that do not follow such simple rules. In the present paper, we reinvestigate these assignments on basis of new 15 N data from model compounds [32] and of simulations of the local nuclear polarization occurring transiently from the singlet state of the radical pair. As shown in Sect.…”

“…2). Table 2 contains the chemical shift assignments from isolated cofactors [32] as well as the new assignments obtained on RCs from Rb. sphaeroides.…”