Analysis of oxidized glycerophosphocholine lipids using electrospray ionization mass spectrometry and microderivatization techniques

Oxidized low-density lipoprotein (LDL) is thought to play an important role in atherogenesis and cardiovascular disease in humans. Oxidized LDL is a complex mixture of many oxidized species, including numerous oxidized glycerophospholipids. Electrospray ionization and tandem mass spectrometry as well as microchemical derivatization of high-performance liquid chromatographically purified fractions derived from oxidized LDL were investigated as means to determine the structure of individual components present in oxidized LDL. One major oxidized phosphocholine lipid had an [M + H](+) ion at m/z 650. Derivatization to the trimethylsilyl ether and methoxime caused shifts in mass which, along with negative ion collision-induced dissociation mass spectra, were consistent with the presence of three species, 1-palmitoyl-2-(9-oxononanoyl)glycerophosphocholine and two isomeric 1-octadecanoyl-2-(hydroxyheptenoyl)glycerophosphocholines. These species were chemically synthesized. Trimethylsilylation of free hydroxyl groups increased the mass of the phospholipid acyl chains containing hydroxyl groups by 72 u. Conversion of carbonyl groups to the methoxylamine derivative increased the mass by 29 u. Ozonolysis of those products which contained double bonds proved to be a facile technique to determine the position and number of double bonds present. The use of these techniques was illustrated in the structural characterization of one major component (m/z 650, positive ions) in oxidized LDL as 1-octadecanoyl-2-(7-hydroxyhepta-5-enoyl)glycerophosphocholi ne. A possible mechanism for the formation of this unique chain-shortened glycerophospholipid is proposed.     

Use of cluster expansion techniques in quantum chemistry. A linear response model for calculating energy differences

In this paper we have reviewed the theoretical framework of the coupled-cluster (cc) based linear response model as a tool for directly calculating energy differences of spectroscopic interest like excitation energy (ee), ionisation potential (ip) or electron affinity (ea). In this model, the ground state of a many-electron system is described as in a coupled cluster theory for closed shells. The electronic ground state is supposed to interact with an external photon field of frequencyw, and the poles of the linear response function as a function ofw furnish with the elementary excitations of the system. Depending on the general form of the coupling term chosen, appropriate difference energies like ee, ip or EA may be generated. Pertinent derivations of the general working equations are reviewed, and specific details as well as approximations for ee, ip or ea are indicated. It is shown that the theory bears a close resemblance to the equation of motion (eom) method but is superior to the latter in that the ground state correlation is taken to all orders and may be looked upon as essentially a variant of renormalisedtda. A perturbative analysis elucidating the underlying perturbative structure of the formulation is also given which reveals that the theory has a hybrid structure: the correlation terms are treated akin to an open shellmbpt, while the relaxation terms are treated akin to a Green function theory. A critique of the methodvis-a-vis other cc-based approaches for difference energies forms the concluding part of our review.     

Synthesis of 3‐(substituted)‐2,4,8,15‐tetroxa‐3‐phosphadispiro[5.2.5]hexadecane‐3‐oxides

Novel 3‐(substituted)‐2,4,8,15‐tetroxa‐3‐phosphadispiro[5.2.5]hexadecane‐3‐oxides (3‐12) have been synthesized by cyclization of 1,5‐dioxaspiro[5.5]undecande‐3,3‐dimethanol (1) with various substituted aryl phosphorus dichloridates (2) in dry toluene‐THF in the presence of triethylamine at 40‐60 ^oC. Their molecular structures were determined by ir, nmr and mass spectral studies and were screened for antifungal activity against Curvularia lunata and Aspergillus niger, and antibacterial activity on Staphylococcus aureus and Escherichia coli. Most of them possess significant activity.     

A novel one-pot conversion of amines to homologated esters in poly(ethylene glycol)

The first deaminative homologation of amines (-CH₂NH₂) to esters (-CH₂CH₂COOEt) in one-pot is reported. The reaction proceeds through, formation of an aldehyde from an amine in the presence of Pd/C as catalyst followed by Wittig reaction and catalytic hydrogenation using poly(ethylene glycol) as the solvent in one-pot.     

Counterions of BINAP-Pt(II) and -Pd(II) complexes: novel catalysts for highly enantioselective Diels-Alder reaction

[formula: see text] Platinum and palladium chiral bisphosphine complexes and their counterion effects in asymmetric Diels-Alder reactions have been investigated. The reaction of cyclopentadiene and various bidentate dienophiles in the presence of a catalytic amount of Pt(II)- or Pd(II)-BINAP complex proceeds with excellent endo/exo selectivity as well as endo enantioselectivity (up to 99% ee).     

Structural characterization of nanosized CeO(2)-SiO(2), CeO(2)-TiO(2), and CeO(2)-ZrO(2) catalysts by XRD, Raman, and HREM techniques

Structural characteristics of nanosized ceria-silica, ceria-titania, and ceria-zirconia mixed oxide catalysts have been investigated using X-ray diffraction (XRD), Raman spectroscopy, BET surface area, thermogravimetry, and high-resolution transmission electron microscopy (HREM). The effect of support oxides on the crystal modification of ceria cubic lattice was mainly focused. The investigated oxides were obtained by soft chemical routes with ultrahighly dilute solutions and were subjected to thermal treatments from 773 to 1073 K. The XRD results suggest that the CeO(2)-SiO(2) sample primarily consists of nanocrystalline CeO(2) on the amorphous SiO(2) surface. Both crystalline CeO(2) and TiO(2) anatase phases were noted in the case of CeO(2)-TiO(2) sample. Formation of cubic Ce(0.75)Zr(0.25)O(2) and Ce(0.6)Zr(0.4)O(2) (at 1073 K) were observed in the case of the CeO(2)-ZrO(2) sample. Raman measurements disclose the fluorite structure of ceria and the presence of oxygen vacancies/Ce(3+). The HREM results reveal well-dispersed CeO(2) nanocrystals over the amorphous SiO(2) matrix in the cases of CeO(2)-SiO(2), isolated CeO(2), and TiO(2) (anatase) nanocrystals, some overlapping regions in the case of CeO(2)-TiO(2), and nanosized CeO(2) and Ce-Zr oxides in the case of CeO(2)-ZrO(2) sample. The exact structural features of these crystals as determined by digital diffraction analysis of HREM experimental images reveal that the CeO(2) is mainly in cubic fluorite geometry. The oxygen storage capacity (OSC) as determined by thermogravimetry reveals that the OSC of the mixed oxide systems is more than that of pure CeO(2) and is system dependent.     

Energy dispersive X-ray fluorescence (EDXRF) determination of lanthanides after preconcentration on 1-(2-pyridylazo)-2-naphthol modified naphthalene

A method is described for the simultaneous multielement determination of yttrium and lanthanides at microgram level. This is based on the preconcentration of these lanthanides on to 1-(2-pyridylazo)-2-naphthol (PAN) modified naphthalene. The optimal conditions for quantitative preconcentration viz., pH, amount of PAN modified naphthalene, time of stirring and aqueous phase volume were systematically evaluated. The quantitation of lanthanides was carried out by energy dispersive X-ray fluorescence analyzer, employing²⁴¹Am annular source, via their characteristic K X-rays. The developed procedure gave reliable results in the analysis of xenotime samples.     

Magnetic nanoparticle assemblies on denatured DNA show unusual magnetic relaxivity and potential applications for MRI

Denatured (substantially single-stranded) herring sperm DNA acts as a template for the preparation of magnetic nanowires, forming stable aqueous suspensions, which exhibit unprecedentedly high relaxivity at low field, suggesting that the material may be a potentially useful reagent for MRI.     

Zirconyl chloride promoted highly efficient solid phase synthesis of amide derivatives

An efficient solid phase route for the synthesis of amide derivatives by the reaction of carboxylic acids with urea in the presence of catalytic amount of zirconyl chloride under microwave irradiation conditions was described.In this way,a range of interesting amide derivatives was obtained in good to excellent yields.The catalyst was recycled with fresh reactants and it gave almost similar results without significant loss of activity up to the third run.     

Electrocatalytic Proton Reduction by a Cobalt Complex Containing a Proton-Responsive Bis(alkylimdazole)methane Ligand: Involvement of a C−H Bond in H2 Formation

Homogeneous electrocatalytic proton reduction is reported using cobalt complex [ 1 ](BF₄)₂. This complex comprises two bis(1-methyl-4,5-diphenyl-1H-imidazol-2-yl)methane (HBMIM ) ligands that contain an acidic methylene moiety in their backbone. Upon reduction of [ 1 ](BF₄)₂ by either electrochemical or chemical means, one of its HBMIM ligands undergoes deprotonation under the formation of dihydrogen. Addition of a mild proton source (acetic acid) to deprotonated complex [ 2 ](BF₄) regenerates protonated complex [ 1 ](BF₄)₂. In presence of acetic acid in acetonitrile solvent [ 1 ](BF₄)₂ shows electrocatalytic proton reduction with a k_obs of ≈200 s⁻¹ at an overpotential of 590 mV. Mechanistic investigations supported by DFT (BP86) suggest that dihydrogen formation takes place in an intramolecular fashion through the participation of a methylene C−H bond of the HBMIM ligand and a Co^II−H bond through formal heterolytic splitting of the latter. These findings are of interest to the development of responsive ligands for molecular (base)metal (electro)catalysis.