Barium picrate

Barium Picrate. [C6H3(N02)30] 2Ba, mw 594.64, N 14.14%, yel powd which explds with moderate violence at 333—37°. Can be obtained... 

The crystal structure of a barium picrate complex of (139) reveals a 2 2 dimeric structure of the form [(139)Ba(picrate)3Ba(139)]+(picrate) (148), 47 which is unique as three picrate anions are held in the space between the ligated cations. The cations are not sited within the macrocyclic cavities but are displaced towards the centre of the dimer. This situation is reminiscent of the Cs+-polyether dimer structure (Figure 15d). The outer surface of the (139)Ba(picrate)2 complex is highly lipophilic, and the bulky phenyl residues provide screening for the enclosed anions. 

Fig. 4.5. Extraction of barium picrate with the all-homocalixarene 1 in CHCI3... 

Fig. 32. Conformation of the crystalline 2 2 complex of beauvericin with barium picrate [Reproduced from Hamilton, J. A., et al Biochem. Biophys. Res. Comm. 64, 151 (1975). ...

Figure 10 The isomers G 5 and isoG 6 self-sort in the presence of barium picrate to give discrete complexes, namely [G 5Jig 2Ba 4Pic and [isoG (>] 10 Ba 2Pic (Adapted from ref 22 with permission).

Figure 15. Beauvericin, cvc/o(LMePhe-DHyv)3, forms a sandwich complex with barium picrate, (BvBa picrate3 Ba Bv) there is threefold symmetry around the axis of the complex, and there are nine Ba " —O ligands (Hamilton et a/., 1975).

These most unusual findings could be well explained after elucidation of the crystal structure of the beauvericin complex with barium picrate This adduct turned out to be a 2 2 dimer structure of the form (Bv Ba Picj Ba Bv) Pic" (Fig. 8) which is very unique inasmuch as three of the four picrate anions are incorporated into the space between the antibiotic molecules. Both the Ba ions... 

Fig. 8. Sandwich structure of the 2 2 complex between beauvericin and barium picrate shown from a 30 A distance. From top to "bottom 1) the "upper beauvericin molecule (strong < n lines), 2) one Ba ion (dark sphere), 3) three picrate anions (full bonds), 4) the other Ba ion, 5) the "lower beauvericin molecule (weak open lines). For clarity, hydrogen atoms have been omitted...

The outer surface of the beauvericin-barium picrate complex is highly hydrophobic due to the orientation of the isopropyl, N-methyl, and phenyl groups toward the... 

The intriguing power of X-ray crystallography as a method of explaining the structure-activity relationships of biomolecules It was only the X-ray structure of the barium picrate complex of beauvericin that provided an understanding of the anion-dependent activity of the antibiotic. All spectroscopic approaches failed to do so. 

A somewhat similar situation has been found in the dibenzo-24-crown-8 complex with barium picrate The Ba does only fill one compartment of the ring whilst the other is occupied by a water molecule which is hydrogen-bonded to the receptor and simultaneously coordinated to the Ba ion. Interestingly, the situation is completely changed when CIO4 is employed as anion instead of picrate. In this complex, the polyether wraps about the Ba ion which is coordinated to all the ether oxygens and to the two perchlorate anions This is another example for the structurally decisive influence of the anion. 

CgyHgiBaN9023 2 CyHer Beauvericin-barium picrate toluene solvate (form B), 46B, 522... 

Qian, X., J. Wang, Z. Hu, Nonionic surfactants in water barium picrate complex extraction spectrophotometric method (in Chinese), Fenxi Huaxue, 1987,15,97-100. 

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