Synthesis of oligonucleotides containing an O-G-alkyl-O-G interstrand cross-link

A methodology to synthesize oligonucleotides containing an alkyl interstrand cross-link between the two O6 atoms of deoxyguanosine has been developed. This cross-link is designed to serve as a stable structural mimic of the lesion formed in duplex DNA with the bifunctional alkylating agent hepsulfam. The O6-alkyl coupling is performed via a Mitsunobu reaction between a nucleoside and mono-protected 1,7-heptanediol. Solid-phase oligonucleotide synthesis using a nucleoside bis-phosphoramidite allows for the assembly of the cross-linked duplex. Sufficient quantities of this cross-linked duplex were obtained for various structural and biological investigations.     

Chiral recognition in NMR spectroscopy using crown ethers and their ytterbium(III) complexes

Chiral crown ethers 1 and 5 are useful enantiomeric discriminating agents in ¹H NMR spectroscopy for neutral and protonated primary amines, amino acids, and amino alcohols. The presence of the carboxylic acid groups in 1 and 5 provide sites at which ytterbium(III) can bind. Adding ytterbium(III) nitrate to crown–substrate mixtures in methanol-d₄ causes shifts in the spectra of substrates and often enhances the chiral discrimination in the ¹H NMR spectrum. The enhancement in enantiomeric discrimination that occurs in the presence of ytterbium(III) allows lower concentrations of the crown ether to be used in chiral recognition studies. Several amide derivatives of 1 were prepared and evaluated as chiral NMR discriminating agents, although except for 1e, these were less effective than 1.     

High-performance liquid chromatographic determination of xanthohumol in rat plasma, urine, and fecal samples

Xanthohumol (XN) is the major prenylated flavonoid in hop plants and as such a constituent of beer. Pharmacological studies have shown that XN possesses marked antioxidant and antiproliferative effects. In order to study the resorption and metabolism of this compound, reversed-phase high-performance liquid chromatography is used for the determination of XN in rat plasma, urine, and feces. In session one, rats receive either oral or intravenous (iv) administration (20 mg/kg body weight) of XN. In session two, rats receive oral administration of 50, 100, 200, 400, and 500 mg/kg body weight XN for bioavailability studies at various dose levels. Plasma, urine, and feces are collected at varying time points and assayed for their XN content. Plasma levels of XN fell rapidly within 60 min after iv administration; no XN is detected in plasma after oral administration in either session. XN and its metabolites are excreted mainly in feces within 24 h of administration. The method is a reliable tool for performing studies of XN in different biological material.     

First row divalent transition metal complexes of aryl-appended tris((pyridyl)methyl)amine ligands: syntheses, structures, electrochemistry, and hydroxamate binding properties

Divalent manganese, cobalt, nickel, and zinc complexes of 6-Ph(2)TPA (N,N-bis((6-phenyl-2-pyridyl)methyl)-N-((2-pyridyl)methyl)amine; [(6-Ph(2)TPA)Mn(CH(3)OH)(3)](ClO(4))(2) (1), [(6-Ph(2)TPA)Co(CH(3)CN)](ClO(4))(2) (2), [(6-Ph(2)TPA)Ni(CH(3)CN)(CH(3)OH)](ClO(4))(2) (3), [(6-Ph(2)TPA)Zn(CH(3)CN)](ClO(4))(2) (4)) and 6-(Me(2)Ph)(2)TPA (N,N-bis((6-(3,5-dimethyl)phenyl-2-pyridyl)methyl)-N-((2-pyridyl)methyl)amine; [(6-(Me(2)Ph)(2)TPA)Ni(CH(3)CN)(2)](ClO(4))(2) (5) and [(6-(Me(2)Ph)(2)TPA)Zn(CH(3)CN)](ClO(4))(2) (6)) have been prepared and characterized. X-ray crystallographic characterization of 1A.CH(3)()OH and 1B.2CH(3)()OH (differing solvates of 1), 2.2CH(3)()CN, 3.CH(3)()OH, 4.2CH(3)()CN, and 6.2.5CH(3)()CN revealed mononuclear cations with one to three coordinated solvent molecules. In 1A.CH(3)()OH and 1B.2CH(3)()OH, one phenyl-substituted pyridyl arm is not coordinated and forms a secondary hydrogen-bonding interaction with a manganese bound methanol molecule. In 2.2CH(3)()CN, 3.CH(3)()OH, 4.2CH(3)()CN, and 6.2.5CH(3)()CN, all pyridyl donors of the 6-Ph(2)TPA and 6-(Me(2)Ph)(2)TPA ligands are coordinated to the divalent metal center. In the cobalt, nickel, and zinc derivatives, CH/pi interactions are found between a bound acetonitrile molecule and the aryl appendages of the 6-Ph(2)TPA and 6-(Me(2)Ph)(2)TPA ligands. (1)H NMR spectra of 4 and 6 in CD(3)NO(2) solution indicate the presence of CH/pi interactions, as an upfield-shifted methyl resonance for a bound acetonitrile molecule is present. Examination of the cyclic voltammetry of 1-3 and 5 revealed no oxidative (M(II)/M(III)) couples. Admixture of equimolar amounts of 6-Ph(2)TPA, M(ClO(4))(2).6H(2)O, and Me(4)NOH.5H(2)O, followed by the addition of an equimolar amount of acetohydroxamic acid, yielded the acetohydroxamate complexes [((6-Ph(2)TPA)Mn)(2)(micro-ONHC(O)CH(3))(2)](ClO(4))(2) (8), [(6-Ph(2)TPA)Co(ONHC(O)CH(3))](ClO(4))(2) (9), [(6-Ph(2)TPA)Ni(ONHC(O)CH(3))](ClO(4))(2) (10), and [(6-Ph(2)TPA)Zn(ONHC(O)CH(3))](ClO(4))(2) (11), all of which were characterized by X-ray crystallography. The Mn(II) complex 8.0.75CH(3)()CN.0.75Et(2)()O exhibits a dinuclear structure with bridging hydroxamate ligands, whereas the Co(II), Ni(II), and Zn(II) derivatives all exhibit mononuclear six-coordinate structures with a chelating hydroxamate ligand.     

New phosphate fluorosurfactants for carbon dioxide

Anionic phosphate fluorosurfactants were shown to self-assemble into water-in-carbon dioxide microemulsions. The surfactants, having either two fluorinated chains or one fluorinated chain and one hydrocarbon chain, facilitated significant water uptake in CO2. Small angle neutron scattering (SANS) measurements of surfactant/water/CO2 solutions confirmed the presence of nanometer-scale aggregates, indicative of microemulsion formation.     

Polymer-assisted dispersion of single-walled carbon nanotubes in alcohols and applicability toward carbon nanotube/sol-gel composite formation

Single-walled carbon nanotubes (SWCNTs) were directly dispersed into various alcohols by sonicating the nanotubes in the presence of poly(4-vinylpyridine) (P4VP). Depending upon the alcohol, it was possible to disperse up to 0.3 g of SWCNTs per liter of alcohol using only 0.6 g of P4VP, and with solution stability greater than 6 weeks. Scanning electron microscopy of "bucky" paper prepared from the polymer-treated nanotubes revealed reduced bundle size compared to the corresponding untreated nanotube paper. Additionally, the applicability of the dispersion system in the formation of SWCNT/silica composites is demonstrated.     

Flow-injection liposome immunoanalysis (FILIA) for alachlor

An automated Flow-Injection Liposome ImmunoAnalysis (FILIA) system has been modified from a previous design, using a specific environmental contaminant, the herbicide alachlor, as a model analyte. Signal amplification by means of fluorescent marker-loaded, analyte-tagged liposomes provides high sensitivity. The computer controlled system is composed of commercially available components, with the exception of the column packing material, which has to be prepared for each specific analyte to be determined. The use of such components means that the system is easily modified. The relationships between antibody concentration and assay speed and sensitivity are explored, and the possibilities of using the system for determination of multiple analytes is discussed.     

The potential of composite pyrolysis gas chromatographic mass spectra in the study of lignocellulosics

The objective of this work was to evaluate the use of composite mass spectral (CMS) data from pyrolysis gas chromatography/mass spectrometry (PY–GC/MS) for lignocellulosic materials. Various forages, by-products and fiber fractions derived from them were examined as CMS by PY–GC/MS. The PY–GC/MS system consisted of a heated platinum filament, a capillary gas chromatograph and an ion trap detector (ITD) mass spectrometer operated under electron impact conditions. Mass spectra were then composited in several ways by summing all the mass spectra acquired within retention times corresponding to major product classes. CMS data were entered in a dedicated library and compared using the ITD library editor software. The usefulness of such a simple procedure for studies related to lignocellulose analysis, such as forage recognition, development of analytical methods and digestibility/maturity correlation, is discussed.