¹³C NMR spectroscopy as a tool for the in situ characterisation of iron-supplementing preparations.

(13)C NMR spectroscopy provides insight into the chemistry of carbohydrate-based ferric preparations. Specifically, it reveals whether oxygen atoms of the carbohydrate are directly bonded to the preparations' ferric centres or whether more distant interactions are present. After having validated the method by investigating the ferric solutions of low-molecular complexes as well as polynuclear ferric samples, it is demonstrated that common constituents of medically used ferric preparations such as sucrose and other glucose-based saccharides do not support ferric carbohydrate chelates. Instead, these carbohydrates reside outside the NMR-spectroscopically 'blinded' region about the ferric centres and experience the so-called Evans effect that can be used to measure the magnetic moment of the solutions. As a result, an easily accessible physicochemical parameter is provided to characterise commercial iron(III) preparations, namely the samples' magnetism in terms of the in situ-measured spin-normalised effective Bohr magneton number µ(eff)(2)/35. The procedure can, moreover, be combined with a facile NMR-spectroscopic iron assay.

Sugar-alcohol complexes of palladium(II): on the variable rigidity of open-chain carbohydrate ligands.

The C4, C5, and C6 sugar alcohols erythritol (Eryt), D-threitol (D-Thre), D-arabitol (D-Arab), ribitol (Ribt), xylitol (Xylt), dulcitol (Dulc), and D-mannitol (D-Mann) form chelate complexes upon dissolution in Pd-en, an aqueous solution of [Pd(II)(en)(OH)2]. Stability rules are derived from the proportion of a respective species in the solution equilibrium. Crystal-structure analysis supports the NMR spectroscopic results for a series of binuclear compounds that contain the sugar alcohols as tetraanionic polyolato ligands: [Pd2(en)2(ErytH(-4))] x 10 H2O, [Pd2(en)2(D-Arab1,2;3,4H(-4))] x 7 H2O, [Pd2(en)2(Xylt1,2;3,4H(-4))] x 4 H2O, [Pd2(en)2(D-Mann1,2;3,4H(-4))] x 5 H2O, and [Pd2(en)2(Dulc2,3;4,5H(-4))] x 6 H2O. In the case of the pentitols and hexitols, the metalated tetraanions are stabilized by intramolecular hydrogen bonds. The hydrogen bonds uniformly connect an alkoxide acceptor to the hydroxy donor group located at the delta carbon atom. As a consequence of hydrogen bonding, the open-chain carbohydrate ligands become rigid. Crystal-structure analysis provides information on the configurational requirements for rigidity. According to these rules, the hydrogen-bond-supported Dulc2,3;4,5H(-4) tetraanion provides a geometrically persistent ligating pattern. Intramolecular hydrogen bonding seems to be the most-competitive variable to metalation of a polyol. [Pd2(tm-2,1:3,2-tet)(OH)3]OH (tm-2,1:3,2-tet = 1,3-bis(2'-dimethylaminoethyl)hexahydropyrimidine) is a metallizing agent that can force full metalation even in a case as intractable as that of dulcitol. Accordingly, [Pd4(tm-2,1:3,2-tet)2-(DulcH(-6))]Cl2 x 16 H2O contains the fully deprotonated hexitol as the ligand.

Silicon chelation in aqueous and nonaqueous media: the furanoidic diol approach.

Anhydroerythritol (AnEryt) shares some of its ligand properties with furanosides and furanoses. Its bonding to silicon centers of coordination number four, five, and six was studied by X-ray and NMR methods, and compared to silicon bonding of related compounds. Diphenyl(cycloalkylenedioxy)silanes show various degrees of oligomerization depending on the diol component involved. For example, Ph(2)Si(cis-ChxdH(-2)) (1) and Ph(2)Si[(R,R)-trans-ChxdH(-2))] (2; Chxd = cyclohexanediol) are dimeric, Ph(2)Si(AnErytH(-2)) (3) is monomeric, and Ph(2)Si(L-AnThreH(-2)) (4; AnThre = anhydrothreitol) is trimeric both in the solid state and in solution. Ph(2)Si(cis-CptdH(-2)) (5) (Cptd = cyclopentanediol) is monomeric in solution but dimerizes on crystallization. Si(AnErytH(-2))(2) (6) and Si(cis-CptdH(-2))(2) (7) are monomeric spiro compounds in solution but are pentacoordinate dimers in the crystalline state. Pentacoordinate silicate ions are found in A[Si(OH)(AnErytH(-2))(2)] (A = Na, 8 a; Rb, 8 b; Cs, 8 c). Related compounds are formed by substitution of the hydroxo by a phenyl ligand. K[SiPh(AnErytH(-2))(2)]1/2 MeOH (9) is a prototypical example as it shows the two most significant isomers in one crystal structure: the syn/anti and the anti/anti form (syn and anti define the oxolane ring orientation close to, or apart from, the monodentate ligand, respectively). syn/anti Isomerism generally rules the appearance of the NMR spectra of pentacoordinate silicates of furanos(id)e ligands. NMR spectroscopic data are presented for various pentacoordinate bis(diolato)silicates of adenosine, cytidine, methyl-beta-D-ribofuranoside, and ribose. In even more basic solutions, hexacoordinate silicates are enriched. Preliminary X-ray analyses are presented for Cs(2)[Si(CydH(-2))(3)] 21.5 H(2)O (10) and Cs(2)[Si(cis-InsH(-3))] cis-Ins8 H(2)O (11) (Cyd = cytidine, Ins = inositol).