Complexes of Al(III) with d-gluconic acid

The complexation of Al(III) with d-gluconic acid was studied in solution by means of pH-potentiometry, ESI mass spectrometry and one- and two-dimensional NMR spectroscopy. Six complexes were found to form in solution from pH 2 to 10: [AlL]²⁺, [AlLH₋₁]⁺, [AlLH₋₂], [AlLH₋₃]⁻, [AlL₂H₋₁] and [AlL₂H₋₂]⁻. NMR spectroscopy indicated very complicated chemical exchange processes between the free ligand and gluconic acid molecules bound in the metal complexes, with different coordination modes resulting in changes both of the chemical shift and of the line shape of the signals. A solid complex [AlL₂H₋₁] · 2H₂O was isolated as a microcrystalline powder and characterized. The structures of the complexes are discussed on the basis of the spectroscopic results and MM force field calculations.     

Synthesis,spectral, and structural investigation of [ML(NO3)2]: M = Co,Ni, Cu; L = N-(2-pyridylethyl)pyridine-2-methylketimine

Synthesis and structural characterization of distorted pentagonal bipyramidal Co(II), pseudo-octahedral Ni(II) and Cu(II) complexes of the type [ML(NO₃)₂], {L = N-(2-pyridylethyl)pyridine-2-methylketimine} are reported. Characterization includes elemental analysis, spectral, magnetism, and X-ray crystallographic studies. In case of cobalt (1) both the nitrates coordinate in bidentate fashion resulting overall distorted pentagonal bipyramidal geometry. In nickel (2) and copper (3) complexes, bivalent metal ion is coordinated by the three nitrogen atoms of the tridentate L with two pyridine-N occupying trans positions and amongst the two nitrates one coordinates in a bidentate fashion while other adopts a monodentate fashion. All the complexes exhibit d–d transitions in the visible region. Complex 1 is high-spin in nature and the X-band EPR spectra of 1, and 3 at room temperature and 77 K are reported.     

Carbon monoxide and oxygen interaction with Ru/MgF<Subscript>2</Subscript> catalyst: IR and EPR studies

Electron paramagnetic resonance (EPR) and infrared (IR) spectroscopy were used to study the formation of ruthenium and adsorbed species appearing on the catalyst upon the adsorption of CO and O₂ on 1.37 wt% Ru/MgF₂ catalysts derived from Ru₃(CO)₁₂. The presence of Ru ^x+ sites in spite of a reductive H₂ treatment at 673 K was observed by EPR and IR spectroscopy beside metallic Ru⁰ species. Both IR and EPR results provided clear evidence for the interaction between surface ruthenium and probe molecules. The IR spectra recorded after admission of CO showed a band at approx. 2000 cm⁻¹, due to linearly adsorbed CO on Ru⁰/MgF₂ and two bands at higher frequencies (approx. 2140 and approx. 2070 cm⁻¹), related to CO on oxidized Ru ⁿ⁺ species, e.g., to Ru(CO)₃ complex with Ru in the 1+ and/or 2+ state of oxidation and Ru(CO)₂ with Ru in the 3+ and/or 4+ state of oxidation. A weak anisotropic EPR signal with g _‖ = 2.017 and g _⊥ = 2.003 is due to O ₂ ⁻ radicals and a formation of Ru⁴⁺-O ₂ ⁻ complex is postulated. The Ru³⁺ appears to oxidize to Ru⁴⁺ and the resulting dioxygen anion is coordinated to the ruthenium. The strong, isotropic EPR signal at g ₀ = 2.003 detected upon admission of CO is attributed to CO radical anion rather than to any ruthenium carbonyl complexes.     

Synthesis of l-α-phosphatidyl-d-myo-inositol 3,5-bisphosphate from d-glucose

Efficient synthesis of l-α-phosphatidyl-d-myo-inositol 3,5-bisphosphate was achieved from 1,2,5,6-diisopropylidene-d-glucose by utilizing ring-closing metathesis and catalytic OsO₄ dihydroxylation.     

Synthesis of d-glucose and l-phenylalanine substituted phenylene-thiophene oligomers

Phenylene-thiophene oligomers bearing peracetylated β-d-glucose or N-BOC-l-phenylalanine as chiral substituents were synthesized in good yields by a versatile protocol based on the Suzuki-Miyaura cross-coupling reaction. Aryl iodides bearing the chiral biomolecules as substituents efficiently reacted with pinacol boronates of bi- or terthiophenes leading to the bio-functionalized oligomers in good yields.     

Benzamidinium d-glucuronate: Spectroscopic and structural elucidation

Benzamidinium d-glucuronate (1) crystallizes in the orthorhombic space group P2₁2₁2₁ and exhibits a 3 D network with molecules linked by moderate intermolecular hydrogen bonds (HNH…O_(solvent) 2.993 Å, HNH…OCO 2.894 Å, HNH…O_(cycle) 2.844 Å, OH…NH₂ 2.931 Å, OH…O_(solvent) 2.894, 2.924 and 2.715 Å (stronger)) with participation of cations, anions and solvent molecules. The IR-band assignment of carbohydrate moieties is elucidated by a comparison between the types and bond lengths of intermolecular interactions with participation of OH groups in d-glucuronate and linear polarized IR-(IR-LD) spectroscopic data. Experimental results are supported by theoretical ab initio calculations of benzamidinium cation and d-glucuronate anion.     

Magnetic properties of the Fe spin crossover complex in emulsion polymerization of trifluoroethylmethacrylate using poly(vinyl alcohol)

Influence of chemical substitution in the Fe^II spin crossover complex on magnetic properties in emulsion polymerization of trifluoroethylmethacrylate using poly(vinyl alcohol) as a protective colloid was investigated near its high spin/low spin (HS/LS) phase transition. The obvious bi-stability of the HS/LS phase transition was considered by the identification of multiple spin states between the quintet (S=2) states to single state (S=0) across the excited triplet state (S=1). Magnetic parameters of gradual shifts of anisotropy g-tensor supported by the molecular distortion of the spin crossover complex would arise from a Jahn-Teller effect regarding ligand field theory on the basis of a B3LYP density functional theory using electron spin resonance (ESR) spectrum and X-ray powder diffraction.     

Fragmentation of deprotonated d-ribose and d-fructose in MALDI—Comparison with dissociative electron attachment

We present a detailed, collaborative study on the fragmentation of deprotonated native d-ribose and d-fructose and the isotopically labelled 1-¹³C-d-ribose, 5-¹³C-d-ribose and C-1-d-d-ribose. The fragmentation is studied in a matrix assisted laser desorption/ionization time of flight mass spectrometer (MALDI ToF MS), both in in-source decay (ISD) and post-source decay (PSD) mode and compared with fragmentation through dissociative electron attachment (DEA). Fragmentation of deprotonated monosaccharides formed in the MALDI process, as well as their transient molecular anions formed upon electron attachment are characterized by loss of different numbers of H₂O and CH₂O units. Two different fragmentation pathways leading to cross-ring cleavage are identified. Metastable decay of deprotonated d-ribose proceeds either via an X-type cleavage yielding fragment anions at m/z = 119, 100 and 89, or via an A-type cleavage resulting in m/z = 89, 77 and 71. A fast and early metastable cross-ring cleavage of deprotonated d-ribose observed in in-source decay is dominated by X-type cleavage leading mainly to m/z = 100 and 71. For dissociative electron attachment to d-ribose a sequential dissociation was identified that includes metastable decay of the dehydrogenated molecular anion leading to m/z = 89. All other fragmentation reactions in DEA to d-ribose are likely to proceed directly and on a faster timescale (below 400 ns).     

Syntheses and structural comparisons of two copper(II) complexes with the same formula having d-(+)- and d,l-1,2,2-trimethylcyclopentane-1,3-diamine ligands

Two five-coordinate copper(II) complexes, formulated as [Cu(L_a)₂Cl]BF₄ (1) and [Cu(L_b)₂Cl]BF₄ (2) having d-(+)-1,2,2-trimethylcyclopentane-1,3-diamine (L_a) and d,l-1,2,2-trimethylcyclopentane-1,3-diamine (L_b) ligands, have been synthesized and characterized. X-ray diffraction studies of 1 and 2 demonstrate that they crystallize in the different space groups (P2₁2₁2₁ for 1 and Pnma for 2), although they have identical unit cell volumes, due to the use of enantiomeric and racemic diamine ligands. One dimensional (1D) hydrogen-bond-sustained dimeric zigzag chains are formed by means of eight-membered N₂H₂CuBF₂ as well as 10-membered N₂H₄ClBF₂ hydrogen-bonded cycles. Thermal analyses for 1 and 2 are also described herein.     

Quantitative thin-layer chromatography of carbohydrates using pentavalent vanadium in sulphuric acid : Determination of mixtures of d-Fructose, d-Glucose and sucrose

Pentavalent vanadium in sulphuric acid can be used for the quantitative analysis of sugars. The yellow pentavalent vanadium is reduced by carbohydrates to the blue tetravalent form, and either the consumption of vanadium(V) or the amount of vanadium(IV) formed can be measured. For model studies, different d-fructose-d-glucose-sucrose mixtures were used. The monosaccharides were separated from the disaccharide by thin-layer chromatography. Owing to the great difference in reactivity between aldohexoses and ketohexoses, d-fructose and d-glucose can be determined separately without prior separation. The method enables 10 μg of each sugar to be determined.     

Building carbohydrates on the dioxanone scaffold: stereoselective synthesis of d-glycero-d-manno-2-octulose

The title compound has been synthesized via two proline-catalyzed aldol addition reactions of 2,2-dialkyl-1,3-dioxan-5-ones: the first addition to 1,3-dithiane-2-carboxaldehyde, followed by reduction to the corresponding diol, protection of the OH groups and dithiane hydrolysis afforded a protected d-ribose that was used in the second aldol addition reaction.     

EPR spectroscopic studies in (30 − x) Li2O-xK2O-10CdO-59B2O3-1MnO2 multi-component glass system

EPR studies were carried out in (30 - x) Li₂O-xK₂O-10CdO-59B₂O₃-1MnO₂ multi-component glass system to understand the effect of the variation in the alkali ratios on the EPR parameters. The observed EPR spectra of Mn²⁺ ion exhibits resonances at g = 2.0, 3.3 and 4.3. The resonance at g = 2.0 is due to Mn²⁺ ions in an environment close to the octahedral symmetry, where as the resonances at g = 3.3 & 4.3 are due to the rhombic surroundings of Mn²⁺ ions. Hyperfine splitting constant values at g = 2.0 and number of paramagnetic centers & paramagnetic susceptibility at different observed resonances were evaluated. These parameters show non linear variation with progressive substitution of Li⁺ ion with K⁺ ions may be due to the changes in cation field strengths and local structural variation due to the variation in mixed alkali ion ratios.     

Magnetization and EPR of a series of Cr squarate dimers

A series of Cr(III) dimers were synthesized from a parent compound [Cr₂(μ-oxo)₂(μ_1,2-C₄O₄)₂(H₂O)₄]·2H₂O (I) by ligand substitution. The compounds have been analyzed using variable frequency EPR (9–110 GHz) and magnetic susceptibility as a function of field (0–9 T) and temperature (1.9–300 K) to obtain their electronic g-values, exchange energies, and zero-field parameters. The parent compound exhibits a broad maximum around 34 K characteristic of a dimer with antiferromagnetic coupling that fit the Van Vleck susceptibility model well. It was found that the maxima could be tuned from 34 to 80 K by ligand substitution of the waters. Each compound possesses a characteristic color spanning the range of teal to pink. The g-value of each compound was found to be ∼1.98 using spectral simulation. The DMSO derivative is water soluble and has a high LC₅₀ for PC3 cancer cells, suggesting its use as a magnetic resonance imaging agent. X-ray crystal structure of the DMSO derivative [Cr₂(μ-oxo)₂(μ_1,2-C₄O₄)₂(C₂H₆SO)₄]·2H₂O (II) revealed that the DMSO ligands are equatorial, and the squarate groups bridge the two chromiums. This is in contrast to the previously proposed structure of the parent compound where the water ligands were axial and the equatorial squarate groups did not bridge the chromiums. These compounds are interesting because of their ease of synthesis, and their wide range of magnetic behavior. The compounds are good probes into antiferromagnetic dimer exchange by controlling the ligand field surrounding the superexchange pathway present in the molecule.     

Solid-state NMR and EPR study of fluorinated carbon nanofibers

Carbon nanofibers were fluorinated in two manners, in pure fluorine gas (direct fluorination) and with a fluorinating agent (TbF₄ during the so-called controlled fluorination). The resulting fluorinated nanofibers have been investigated by solid-state nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR). This underlines that the fluorination mechanisms differ since a (CF)_n structural type is obtained, whatever the temperature, with the controlled reaction, whereas, during the direct process, a (C₂F)_n type is formed over a wide temperature range. Through a careful characterization of the products, i.e. density of dangling bonds (as internal paramagnetic centers), structural type (acting on molecular motion) and specific surface area (related to the amount of physisorbed O₂), the effect of atmospheric oxygen molecules on the spin-lattice nuclear relaxation has been underlined.     

新型荧光/EPR双功能次氯酸探针的构建及性能

构建了一种新型香豆素-萘酰亚胺荧光/电子顺磁共振双功能探针CNNOH,并结合荧光光谱、电子顺磁共振(EPR)波谱和紫外-可见吸收光谱对其性能进行了研究.结果表明,该探针可结合荧光光谱的灵敏性和EPR波谱的特异性进行次氯酸的检测;由于香豆素与萘酰亚胺之间存在荧光共振能量转移(FRET)效应,探针分子具有较大的Stokes位移(135 nm),可有效避免由激发光导致的杂散光对检测的干扰.该双功能探针具有检出限低(0.214μmol/L)、反应速度快(~10 s)、检测范围宽(0~5 mmol/L)、选择性好及在生理条件下稳定的特点,预期在活体细胞检测方面有良好的应用前景.     

An efficient synthesis of d-ribo- and l-lyxo-phytosphingosine from d-tartaric acid

The preparations of d-ribo- and l-lyxo-phytosphingosines (1, 2) are described. Chelation-controlled addition of tetradecylmagnesium bromide to pentylidene-protected d-threitol aldehyde 6 afforded the key intermediate tetrol 7, providing the desired l-lyxo stereochemistry of phytosphingosine. Inversion at C4 of intermediate 7 provided the d-ribo stereochemistry.     

New entry to pyrrolidine homoazasugars: conversion of d-arabinose into 2,5-anhydro-2,5-imino-d-glucitol via aminohomologation

The title homoazasugar, also referred as (2R,5S)-bis(hydroxymethyl)-(3R,4R)-dihydroxypyrrolidine, has been synthesized by addition of 2-lithiothiazole to the 2,3,5-tri-O-benzyl-d-arabinofuranose-derived nitrone---hydroxylamine mixture followed by reductive N-dehydroxylation and conversion of the thiazole ring into the hydroxymethyl group.     

Cyclic oligomers (macroaldonolactones) from a protected d-galactonic acid monomer

Dicyclohexylcarbodiimide-promoted self-condensation of 2,3:4,5-di-O-isopropylidene-d-galactonic acid (3) led to the macrocyclic oligomeric cyclo[(2,3:4,5-di-O-isopropylidene-(1→6)-d-galactonate)₂] (4) and cyclo[(2,3:4,5-di-O-isopropylidene-(1→6)-d-galactonate)₃] (5), having, respectively, 14- and 21-membered rings. The macrocycles 4 and 5 were also synthesized by cyclization of the respective linear dimer 11 and trimer 14 ω-hydroxy acids precursors prepared by stepwise additions of 3. Compounds 4 and 5 are biomaterials that may be described as macrolactone-cyclodextrins.     

Asymmetric syntheses of the methyl glycosides of 2-deoxy-2-aminohexoses: d-allosamine, d-mannosamine, d-idosamine and d-talosamine

A range of the methyl glycosides of 2-deoxy-2-aminohexoses, comprising d-allosamine, d-mannosamine, d-idosamine and d-talosamine, were prepared from the corresponding d-aldopentoses via a seven step synthetic sequence. The doubly diastereoselective conjugate addition of the requisite antipode of lithium N-benzyl-N-(α-methylbenzyl)amide and in situ enolate oxidation with the requisite antipode of camphorsulfonyloxaziridine (CSO) was used as the key, stereodefining step. Sequential reduction of the resultant α-hydroxy-β-amino esters and oxidative cleavage of the C(1)–C(2) diol unit furnished the corresponding α-amino aldehydes. Subsequent N- and O-deprotection gave the target compounds (as mixtures of anomers) in good yield and high diastereoisomeric purity.