Combined use of EPR and 23Na MAS NMR spectroscopy for assessing the properties of the mixed cobalt-nickel-manganese layers of P3-NayCo1-2xNixMnxO2.

Knowledge on the formation of mixed transition metal layers on lithium and sodium transition metal oxides, Li/Na(Co,Ni,Mn,)O2, determines the ability to control their electrochemical properties as electrode materials in alkaline ion batteries. Taking this into account, herein we combine the EPR and 23Na MAS NMR spectroscopic techniques to gain insights into the structural peculiarities of the mixed cobalt-nickel-manganese layers of NayCo1-2xNixMnxO2 with a three-layer stacking (P3-type) structure. Two types of compositions are examined where diamagnetic Co3+ and paramagnetic Ni3+ and Mn4+ are stabilized: Na2/3Co1/3Ni1/3Mn1/3O2 and Na1/2Ni1/2Mn1/2O2. EPR spectroscopy operating in the X- and Q-band region is applied with an aim to improve the spectra resolution and, on the other hand, to provide straightforward information on the coordination of the transition metal ions inside the layers. The analysis of EPR spectra is based on the reference for the Mn4+ and Ni2+ ions occurring simultaneously in oxides with two layer stacking, P2-Na2/3Ni1/3Mn2/3O2. Complementary to EPR, 23Na MAS NMR spectroscopy at high spinning rates is undertaken to assess the local structure of the Na nucleus in the layered P3-NayCo1-2xNixMnxO2 oxides. All results are discussed taking into account the EPR and NMR data for the well-known lithium analogues O3-LiCo1/3Ni1/3Mn1/3O2 and O3-LiNi1/2Mn1/2O2. Finally, the structure peculiarities of the transition metal layers extracted from the EPR and NMR methods are demonstrated by electrochemical intercalation of Li+ ions into P3-NayCo1-2xNixMnxO2.

High-frequency electron paramagnetic resonance analysis of the oxidation state and local structure of Ni and Mn ions in Ni,Mn-codoped LiCoO(2).

High-frequency electron paramagnetic resonance (HF-EPR) spectroscopy was employed to examine the oxidation state and local structure of Ni and Mn ions in Ni,Mn-codoped LiCoO(2). The assignment of EPR signals was based on Mg,Mn-codoped LiCoO(2) and Ni-doped LiCoO(2) used as Mn(4+) and low-spin Ni(3+) EPR references. Complementary information on the oxidation state of transition-metal ions was obtained by solid-state (6,7)Li NMR spectroscopy. For slightly doped oxides (LiCo(1-x)Ni(x)Mn(x)O(2) with x < 0.05), nickel and manganese substitute for cobalt in the CoO(2) layers and are stabilized as Ni(3+) and Mn(4+) ions. The local structure of Mn(4+) ions was determined by modeling of the axial zero-field-splitting parameter in the framework of the Newman superposition model. It has been found that the local trigonal distortion around Mn(4+) is smaller in comparison with that of the host site. To achieve a local compensation of Mn(4+) charge, several defect models are discussed. With an increase in the total dopant content (LiCo(1-x)Ni(x)Mn(x)O(2) and 0.05

NMR analysis of weak molecular interactions using slice-selective experiments via study of concentration gradients in agar gels.

Weak molecular interactions can be localized and quantified using a single NMR experiment analysing concentration gradients generated in agar gels. The spectra from various cross-sections along the gradient were obtained using a slice-selective pulse sequence realisable with standard NMR equipment.

Alternative NMR method for quantitative determination of acyl positional distribution in triacylglycerols and related compounds.

High-resolution 13C NMR spectroscopy has been used to analyze the positional distribution of fatty acids in model triacylglycerols. A novel method for quantitative determination of the positional distribution of unsaturated chains in triacylglycerols simultaneously with the ratio of saturated/unsaturated acyl chains has been proposed, utilizing the chemical shift differences of the aliphatic atoms C4, C5, and C6. The use of HSQC-TOCSY spectra allows unequivocal proof of the position of the unsaturated chain as well as complete assignment of the 13C NMR signals in tripalmitin.

Antibacterial diterpenic acids from Brazilian propolis.

Four labdane-type diterpenic acids and syringaldehyde were isolated and identified from Brazilian propolis. All the compounds exhibit antibacterial activity. The diterpenes, found for the first time in propolis, are typical for some Araucaria species and thus indicate a possible plant source of Brazilian propolis.

A rapid differentiation between oak honeydew honey and nectar and other honeydew honeys by NMR spectroscopy.

An NMR-based approach for rapid differentiation of oak honeydew honey from all other honey types (floral and other honeydew honeys) was proposed. It is based on the identification of the signals of the protons and the carbon of the methylene group of quercitol in the (1)H and (13)C NMR spectra of honey. The presence of quercitol was supported by TOCSY spectroscopy. Quercitol is a deoxyinositol which is regarded as a good taxonomic marker for the genus Quercus. All samples of oak honeydew honey contained quercitol, while in floral honey samples and honeydew honeys from fir and spruce it was absent. In addition, the described approach is promising with respect to quercitol quantification in honey by qNMR.

Synthesis and antibacterial activity of 7 beta-[3-(un)substituted-2-aminopropionamido]-3-vinylcephalosporin s and related compounds.

A series of new 7 beta-[3-(un)substituted-alanyl]-3-vinylcephalosporins and some related compounds, 4a-l is described. They incorporate residues of proteinogenic L-alpha-aminocarboxylic acids, their antimetabolites and enantiomers as well as a dipeptide in the 7 beta-acylamido side chain. The acylation of diphenyl-methyl 7-amino-3-vinyl-3-cephem-4-carboxylate (2: R2 = DPM) with various protected alpha-aminocarboxylic acids 1a-k and the dipeptide 1l is carried out using TBTU as coupling reagent. The compounds, except 4f, are active in vitro against S. aureus and S. lutea, but only 4a, 4k, and 4l inhibit some of the Gram-negative strains.

Autosomal dominant distal renal tubular acidosis is associated in three families with heterozygosity for the R589H mutation in the AE1 (band 3) Cl-/HCO3- exchanger.

Distal renal tubular acidosis (dRTA) is characterized by defective urinary acidification by the distal nephron. Cl-/HCO3- exchange mediated by the AE1 anion exchanger in the basolateral membrane of type A intercalated cells is thought to be an essential component of lumenal H+ secretion by collecting duct intercalated cells. We evaluated the AE1 gene as a possible candidate gene for familial dRTA. We found in three unrelated families with autosomal dominant dRTA that all clinically affected individuals were heterozygous for a single missense mutation encoding the mutant AE1 polypeptide R589H. Patient red cells showed approximately 20% reduction in sulfate influx of normal 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid sensitivity and pH dependence. Recombinant kidney AE1 R589H expressed in Xenopus oocytes showed 20-50% reduction in Cl-/Cl- and Cl-/HCO3- exchange, but did not display a dominant negative phenotype for anion transport when coexpressed with wild-type AE1. One apparently unaffected individual for whom acid-loading data were unavailable also was heterozygous for the mutation. Thus, in contrast to previously described heterozygous loss-of-function mutations in AE1 associated with red cell abnormalities and apparently normal renal acidification, the heterozygous hypomorphic AE1 mutation R589H is associated with dominant dRTA and normal red cells.