Spectral deconvolution for overlapping GC/MS components

The use of mass chromatogram peak centroids has been investigated as a means of deconvoluting the spectra of overlapping gas chromatography/mass spectrometry components. The peak centroids have been calculated with a precision of 0.04 scans (sd). This proved sufficient to allow deconvolution of the mass spectra belonging to two chemical components which were eluted 0.48 scans apart. For a more complex chromatography peak, it was possible to deconvolute the spectra of six components which were eluted within a 9 scan window. All the spectra produced by using this deconvolution mechanism agreed well with National Institute of Standards and Technology database spectra.     

Fluorine profiles in Antarctic meteorites by nuclear reaction analysis (NRA)

Terrestrial fluorine enrichment on Antarctic meteorites can be measured by detection of γ-rays from the nuclear reaction ¹⁹F(p,αγ)¹⁶O, which is induced by a scanning proton beam. The technique (Nuclear Reaction Analysis by Proton Induced Gamma Emission: PIGME-NRA) allows simultaneous measurement of distribution and concentration without any chemical sample treatment and is not destructive. By using two detectors (HPGe and NaI) and taking into account the background contribution of the main interfering elements, the detection limit is below 10 μg/g. The information obtained allows to estimate the maximum exposure duration of meteorites on the Antarctic ice surface. Received: 15 July 1997 / Accepted: 11 December 1997     

Mass spectrometric fragmentations of hexafluoroacetone ketals derived from N-alkenes

The mass spectrometric fragmentation behavior of the cyclic hexafluoroacetone ketals derived from eighteen n-alkenes is discussed with emphasis on locating the original olefinic bond. The major analytically useful fragments result from loss of CF₃, loss of an alkyl side chain or loss of an aldehyde moiety from the ring. Influences of geometric isomerism on the spectra are examined by intensity ratios and ratios of competing fragmentations.     

Methodology for translocating the carboxy group in gibberellins: the partial synthesis of 7(6→15βH)abeo-GA4

The carboxylic acid group has been excised from phytohormone gibberellin A₄ and relocated on the D-ring, thereby generating a new clas of gibberellin derivatives related structurally to helminthosporic acid.     

Ion-Pair Charge Transfer Photochemistry in Rhenium(I) Borate Salts

The photophysics and photochemistry of the salt [(bpy)Re(CO)(3)(py)(+)][BzBPh(3)(-)] (ReBo, where bpy = 2,2'-bipyridine, py = pyridine, Bz = C(6)H(5)CH(2) and Ph = C(6)H(5)) has been investigated in THF and CH(3)CN solutions. UV-visible absorption and steady-state emission spectroscopy indicates that in THF ReBo exists primairly as an ion-pair. A weak absorption band is observed for the salt in THF solution that is assigned to an optical ion-pair charge transfer transition. Stern-Volmer emission quenching studies indicate that BzBPh(3)(-) quenches the luminescent dpi (Re) --> pi (bpy) metal-to-ligand charge transfer excited state of the (bpy)Re(CO)(3)(py)(+) chromophore. The quenching is attributed to electron transfer from the benzylborate anion to the photoexcited Re(I) complex, (bpy(-)(*))Re(II)(CO)(3)(py)(+) + BzBPh(3)(-) --> (bpy(-)(*))Re(I)(CO)(3)(py) + BzBPh(3)(*). Laser flash photolysis studies reveal that electron transfer quenching leads to irreversible reduction of the Re(I) cation to (bpy(-)(*))Re(I)(CO)(3)(py). Photoinduced electron transfer is irreversible owing to rapid C-B bond fragmentation in the benzylboranyl radical, PhCH(2)BPh(3)(*) --> PhCH(2)(*) + BPh(3)(*). Quantitative laser flash photolysis experiments show that the quantum efficiency for production of the reduced complex (bpy(-)(*))Re(I)(CO)(3)(py) is unity, suggesting that C-B bond fragmentation in the benzylboranyl radical occurs more rapidly than return electron transfer within the geminate radical pair that is formed by photoinduced electron transfer.     

Mussel adhesive protein mimetic polymers for the preparation of nonfouling surfaces

A new biomimetic strategy for modification of biomaterial surfaces with poly(ethylene glycol) (PEG) was developed. The strategy exploits the adhesive characteristics of 3,4-dihydroxyphenylalanine (DOPA), an important component of mussel adhesive proteins, to anchor PEG onto surfaces, rendering the surfaces resistant to cell attachment. Linear monomethoxy-terminated PEGs were conjugated either to a single DOPA residue (mPEG-DOPA) or to the N-terminus of Ala-Lys-Pro-Ser-Tyr-Hyp-Hyp-Thr-DOPA-Lys (mPEG-MAPD), a decapeptide analogue of a protein found in Mytilus edulis adhesive plaques. Gold and titanium surfaces were modified by adsorption of mPEG-DOPA and mPEG-MAPD from solution, after which surface analysis by X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectroscopy confirmed the presence of immobilized PEG on the surface. The ability of modified surfaces to resist cell attachment was examined by culturing 3T3 fibroblasts on the surfaces for up to 14 days. Quantitative image analysis revealed that cell adhesion to mPEG-DOPA and mPEG-MAPD modified surfaces decreased by as much as 98% compared to control surfaces. Modified Ti surfaces exhibited low cell adhesion for up to 2 weeks in culture, indicating that the nonfouling properties of mPEG-DOPA and mPEG-MAPD treated surfaces persist for extended periods of time. This strategy paradoxically exploits the strong fouling characteristics of MAP analogues for antifouling purposes and may be broadly applied to medical implants and diagnostics, as well as numerous nonmedical applications in which the minimization of surface fouling is desired.     

Proton-ionizable crown compounds. 3. Synthesis and structural studies of macrocyclic polyether ligands containing a 4-pyridone subcyclic unit

New proton-ionizable macrocyclic polyether ligands containing the 4-pyridone subcyclic unit have been prepared by reacting 4-THP blocked-2,6-pyridinedimethanol with various oligoethylene glycol ditosylates. The 18-crown-6 ligand containing the 4-pyridone subcyclic unit, 4 , forms stable complexes with alkali metal and organic ammonium cations. The crystal structure of 4 proves the 4-pyridone structural unit. The crystal structure of the potassium thiocyanate complex of 4 is also reported and shows the complex to contain the 4-hydroxypyridine unit.     

The Design and Synthesis of Highly Branched and Spherically Symmetric Fluorinated Oils and Amphiles

A new surfactant design principle, based on concepts borrowed from protein science, is proposed. Using this principle, a class of highly branched and spherically symmetric fluorinated oils and amphiles has been designed and synthesized, for potential applications in the construction of fluorocarbon nanoparticles. The Mitsunobu reaction was employed as the key step for introducing three perfluoro-tert-butoxyl groups into pentaerythritol derivatives with excellent yields and extremely simple isolation procedures. Due to the symmetric arrangement of the fluorine atoms, each fluorinated oil or amphile molecule gives one sharp singlet ¹⁹F NMR signal.