Stereoselective synthesis of (+)-SCH 351448: a unique ligand system for sodium, calcium, and other cations

(+)-SCH 351448 (Na+ salt A) was synthesized employing ring-closing olefin metathesis reaction of an open diene diester intermediate for construction of the 28-membered macrodiolide structure. The open diene diester was prepared from the monomeric hydroxy carboxylic acid and two different olefin fragments. The monomeric hydroxy acid was synthesized via Julia-Julia coupling reaction of intermediates derived from the same olefinic fragments. Oxane units in these fragments were prepared by radical cyclization reactions of beta-alkoxyacrylates. Analogous SCH 351448 salts incorporating other mono- and divalent cations may be prepared. Under acidic conditions, SCH 351448 (Na+ salt A) was the most stable complex, but SCH 351448 (Ca2+ salt) and (Na+ salt B) appear to be physiologically important species.     

Synthesis and manganese complexes of pentagonal bipyramidal ligands: N,N′-disubstituted pentaaza macrocycles

Two novel heptadentate ligands, pentaaza macrocycles with two pendant xpyridyl and phenol groups, were prepared and the crystal structure of the manganese(II) complex of N,N′-bis(2-pyridylmethyl)-pentaaza macrocycle revealed a pentagonal bipyramidal geometry.     

Engineering the structure and magnetic properties of crystalline solids via the metal-directed self-assembly of a versatile molecular building unit

We report the supramolecular chemistry of several metal complexes of N-(4-pyridyl)benzamide (NPBA) with the general formula [Ma(NPBA)2AbSc], where M = Co2+, Ni2+, Zn2+, Mn2+, Cu2+, Ag+; A = NO3-, OAc-; S = MeOH, H2O; a = 0, 1, 2; b = 0, 1, 2, 4; and c = 0, 2. NPBA contains structural features that can engage in three modes of intermolecular interactions: (1) metal-ligand coordination, (2) hydrogen bonding, and (3) pi-pi stacking. NPBA forms one-dimensional (1-D) chains governed by hydrogen bonding, but when reacted with metal ions, it generates a wide variety of supramolecular scaffolds that control the arrangement of periodic nanostructures and form 1- (2-4), 2- (5), or 3-D (6-10) solid-state networks of hydrogen bonding and pi-pi stacking interactions in the crystal. Isostructural 7-9 exhibit a 2-D hydrogen bonding network that promotes topotaxial growth of single crystals of their isostructural family and generates crystal composites with two (11) and three (12) different components. Furthermore, 7-9 can also form crystalline solid solutions (M,M')(NPBA)2(NO3)2(MeOH)2 (M, M' = Co2+, Ni2+, or Zn2+, 13-16), where mixtures of Co2+, Ni2+, and Zn2+ share the same crystal lattice in different proportions to allow the formation of materials with modulated magnetic moments. Finally, we report the effects that multidimensional noncovalent networks exert on the magnetic moments between 2 and 300 K of 1-D (4), 2-D (5), and 3-D (7, 8, 10, and 13-16) paramagnetic networks.     

Evaluation of the enantiomeric resolution of 7,8-dihydroxy-7,8-dihydrobenzo[a]-pyrene and its 6-fluoro and 6-bromo derivatives on polysaccharide-derived stationary phases

The enantiomeric resolution and the elution order of (+/-)-trans-7,8-dihydrodiols of benzo[a]pyrene and its 6-fluoro and 6-bromo derivatives were analyzed on three polysaccharide-based columns: Daicel Chiralcel CA-I (cellulose triacetate), OF, and OG [cellulose tris(4-chloro- and 4-methylphenylcarbamate)]. For comparison, the separation of (+/-)-1,1'-bi-2-naphthol was evaluated on the OG and OF columns. Possibly similar interactions of (S)-1,1'-bi-2-naphthol and (7S,8S)-isomers of 6-halo-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene with the chiral sorbent are suggested.     

Disodium tetrakis(hexanoato‐O)zinc(II)

The structure of the title compound, Na₂[Zn(C₆H₁₁O₂)₄], consists of two‐dimensional polymeric sheets. The Zn²⁺ ions are approximately tetrahedrally coordinated by O atoms from different hexanoate anions. Both Na⁺ ions are six‐coordinated by carboxyl­ate O atoms. One of the hexanoate O atoms is attached to one Zn²⁺ ion and one Na⁺ ion, and the remaining O atom is attached to two Na⁺ ions.     

High precision procedure for determination of selected herbicides and their degradation products in drinking water by solid-phase extraction and gas chromatography-mass spectrometry

For target monitoring of selected herbicides in groundwater transport studies, a precise and accurate method for the determination of atrazine (ATR), desethylatrazine (DEAT) and 2,6-dichlorobenzamide (BAM) was developed. The method is based on solid-phase extraction and GC-MS analysis. Deuterated standards are used as surrogates for calibration by the overall procedure. For legal requirements the method described was validated and is regularly subject to external quality control. Typical limits of detection are 2 ng/l. Uncertainty contributions were evaluated using the GUM workbench modelling software. At the concentration level of interest (100 ng/l), an expanded uncertainty of no more than 10% was estimated. Accurate data on the distribution of ATR, DEAT and BAM in affected well fields enabled operational changes to be implemented to control the drinking water supply according to legal requirements.