Titus A. Jenny

Chlorophyll catabolism in Chlorella protothecoides Isolation and structure elucidation of a red bilin derivative

When grown in a medium rich in glucose but poor in nitrogen, the algae Chlorella protothecoides excrete a red pigment the structure of which has been proven to correspond to a product of oxydative ring cleavage of the chlorophyll‐α chromophore at the C4–C5 methine bridge.

The chemistry of polyphyrins 2. Syntheses of hexaphyrins and their metal complexes

The synthesis of eight derivatives of a 26π-electron macrocycle analogous to the porphyrins bearing six pyrrole rings and six methine bridges is described. This chromophore is named hexaphyrin. Owing to the flexibility of their chromophore, hexaphyrins are able to form two kind of binuclear coordination complexes of substantially different geometry

Ortho-lithiation of triphenylphosphonio-methylid and, also, triphenylphosphine oxide

Treating Ph3P+C-H2 with RLi (R = Me, Bu) gave mainly RPh2P+C-H2 via extensive ligand exchange whereas R1Li (R1 = MeEtCH, Me3C) reacts to give o-lithiated Ph2(o-LiC6H4)P+C-H2. Ph3PO is also o-lithiated by PhLi or Me3CLi to give Ph2(o-LiC6H4)P+O-. [on SciFinder (R)]

Solvent and deuterium isotope effects on the lifetime of singlet oxygen determined by direct emission spectroscopy at 1.27 μm

The relative lifetime of singlet molecular oxygen have been evaluated, as a function of solvent and deuterium substitution, via measurement involving the direct emission of singlet oxygen at 1.27 μm.

Yeast sphingolipids do not need to contain very long chain fatty acids

Synthesis of VLCFAs (very long chain fatty acids) and biosynthesis of DHS (dihydrosphingosine) both are of vital importance for Saccharomyces cerevisiae. The bulk of VLCFAs and DHS are used for ceramide synthesis by the Lag1p (longevity-assurance gene 1)/Lac1p (longevity-assurance gene cognate 1)/Lip1p (Lag1p/Lac1p interacting protein) ceramide synthase. LAG1 and LAC1 are redundant but LIP1 is essential. Here we show that 4Delta (lag1Deltalac1Deltaypc1Deltaydc1Delta) cells devoid of all known endogenous ceramide synthesis pathways are unviable but can be rescued by the expression of Lass5, a mouse LAG1 homologue. Ceramide synthase activity of 4Delta.Lass5 cells only utilizes C16 and C18 fatty acids and does not require the help of Lip1p, an essential cofactor of Lag1p/Lac1p. HPLC-electrospray ionization-MS/MS analysis demonstrated that in IPCs (inositolphosphorylceramides) of 4Delta.Lass5, the very long chain fatty acids (C26 and C24) account for <1% instead of the normal >97%. Notwithstanding, IPCs incorporated into glycosylphosphatidylinositol anchors of 4Delta.Lass5 show normal mobility on TLC and the ceramide- and raft-dependent traffic of Gas1p (glycophospholipid-anchored surface protein) from endoplasmic reticulum to Golgi remains almost normal. Moreover, the biosynthesis of C24:0 fatty acids remains essential. Thus, C(24:0) and dihydrosphingosine are both necessary for survival of yeast cells even if they utilize C16 and C18 fatty acids for sphingolipid biosynthesis.

Influence of linear and branched perfluoroalkylated side chains on the π–π stacking behaviour of hexa-peri-hexabenzocoronene and thermotropic properties

The thermotropic properties and self-assembly of two different series of hexa-peri-hexabenzocoronenes (HBC) bearing either linear or branched perfluoroalkylated side chains, each with a wide range of alkyl spacer and perfluorinated tail lengths, have been studied. Correlations between thermogravimetric analysis, differential scanning calorimetry, polarised optical microscopy and small-angle X-ray scattering experiments revealed, as expected, that the transition temperatures and phase stability are influenced by the determining roles of the aliphatic spacer length and odd/even nature, as well as the size and structure (linear vs. bifurcation) of the perfluorinated sections. Most of the investigated HBC derivatives showed a single-column hexagonal columnar phase, where the columns are structured by a double segregation process between HBC aromatic cores and aliphatic spacers, on the one hand, and between aliphatic spacers and fluorinated tails, on the other hand. For the derivatives with long linear spacers, cores of untilted or quasi-untilted HBC stacks are surrounded by a cylindrical aliphatic envelope segregated from the fluorinated periphery, whereas for those with shorter linear spacers, the same structure is kept, except that the aliphatic envelope deviates from cylindricality and causes a symmetry break to rectangular envelope for the first term of the series. Of the four HBC with branched spacers, two are amorphous, whereas a columnar phase is maintained for the other two derivatives, but with tilted HBC stacks. Consequently, the evolution of the polymorphism in the series could be correlated with the variation of both interface areas.

The enigmatic 1J(CH) coupling constants of allyl-type organometallic compounds

A new attempt has been made to identify the factors responsible for the abnormally small one-bond C, H coupling consts. obsd. for allyl, pentadienyl and heptatrienyl compds. of Li and K. In-plane deformations (widening of the central CCC angle) should have only a small, if not negligible effect. The out-of-plane bending of hydrogen atoms appears to contribute significantly, as probably also does accumulation or polarization of electron d. in conjugated structures. [on SciFinder (R)]

2,2-Divinyladamantane: a new substrate for the modification of silicon surfaces

Abstract 2,2-Divinyladamantane has been readily obtained in six steps from 2-adamantanone. The key steps were a Wittig-Horner-Emmons reaction, an ortho ester Claisen rearrangement using the microwave heating technique and a selenoxide elimination.

Thermoreversible photocyclization of a pyrazolotriazole to a triazasemibullvalene: a novel electrocyclic reaction.

The photochemistry of the pyrazolo[1,2-a]benzotriazole 1b and its dimethyl derivative 1c was studied in argon matrices at 12 K and in solution at 190 K. On irradiation at 365 nm, 1b and 1e undergo ring closure to yield the triazasemibullvalenes 2b and 2c, respectively, which were identified unambiguously by NMR and IR spectroscopy. This novel type of cyclization is reversed on warming or by irradiation at 313 nm. Quantum chemical calculations serve to model the observed IR and UV spectra and to rationalize the mechanism of the photocyclization and its thermal back-reaction.

Chemical vapor deposition of diamond growth using a chemical precursor

A nucleation method to form diamond on chemically pretreated silicon (111) surfaces is reported. The nucleation consisted of binding covalently 2,2-divinyladamantane molecules on the silicon substrate. Subsequently, low pressure diamond growth was performed via microwave plasma chemical vapor deposition in a tubular deposition system. The resulting diamond layers presented a good crystallinity and the Raman spectra showed a very sharp peak at 1331 cm−1.