Geir Kildahl-Andersen

Isolation and characterization of marine pigmented bacteria from Norwegian coastal waters and screening for carotenoids with UVA-blue light absorbing properties

Microbial culture collections are important resources for isolation of natural compounds with novel properties. In this study, a culture collection of around 1,500 pigmented heterotrophic bacteria was established. The bacteria were isolated from the sea surface microlayer at different sampling sites along the mid-part of the Norwegian coast. The bacterial isolates produced pigments of various coloration (e.g. golden, yellow, red, pink and orange). Methanol extracts of sixteen isolates were characterized with LC-Diodearray-TOF mass spectrometry analysis. The number of pigments per isolate varied considerably, and a tentative identification of the pigments was performed based on UV-absorbance profile and molecular formula assignation based on the accurate mass determination. The LC-MS analyses revealed that most of the pigments probably were carotenoids. Furthermore, we developed a high throughput LC-MS method for characterization and screening of a larger sub-fraction (300 isolates) of the culture collection. The aim was to screen and identify bacterial isolates producing carotenoids that absorb light in the UVA-Blue light. Six of the bacterial strains were selected for detailed investigation, including 16s rRNA sequencing, preparative HPLC for purification of major carotenoids and subsequent structural elucidation with NMR. Among the identified carotenoids were zeaxanthin, nostoxanthin and sarcinaxanthin, some with novel glycosylation patterns.

Studies on the mechanism of the Carr–Price blue colour reaction

The reaction of retinoids (retinol, retinyl acetate and anhydroretinol) with Brønsted acids was studied as a model system for the Carr-Price reaction. The anhydroretinylic cation was characterised by VIS and 2D NMR spectroscopy, including an estimate of the charge distribution and region of bond inversion, observed in a mixture of identified E/Z isomers. Products obtained by quenching with NaOMe-MeOH were identified by HPLC and MS. The classical Carr-Price reaction between retinol (vitamin A) and the Lewis acid SbCl(3) in saturated chloroform solution was reinvestigated by VIS, NMR, EPR, dynamic light scattering and chemical quenching. Whereas product instability and failure to provide informative NMR spectra indicated a radical cation, EPR results excluded free-radical species. Dynamic light scattering experiments, in comparison with model systems, revealed strong aggregation for the Carr-Price complex, rationalizing the low stability, NMR problems and dimerisation observed by chemical quenching. The VIS data support structural similarity of the blue Carr-Price product with the delocalized anhydroretinylic cation, and a detailed structure of the antimony complex is evaluated.

NMR spectral assignment of 2α- and 3β-methylhopanes and evidence for boat conformation in D ring of 17α(H),21α(H)-hopanes

The full 1H and 13C NMR chemical shift assignment of 2α‐methyl‐17α(H),21β(H)‐hopane is presented. This compound is formed in mature sediments from biogenic sources of 2β‐methyl‐17β(H),21β(H)‐hopanoids, which include several cyanobacteria. In addition, full 1H and 13C NMR chemical shift data of all four 17,21 isomers of 3β‐methylhopane have been assigned. The thermodynamically most stable 3β‐configuration corresponds to that found in bacterial sources. The data presented here suggest minor corrections to the 13C chemical assignments reported earlier for 17α(H)‐hopanes. Moreover, spectral evidence indicates an unexpected ring‐D boat conformation of 17α(H),21α(H)‐hopanes, which may serve to explain the steric strain reported for this isomer. Copyright

Longer polyenyl cations in relation to soliton theory

The carotene-like polyenes decapreno-beta-carotene (C50), C54-beta-carotene (C54, first synthesis) and dodecapreno-beta-carotene (C60) with 15, 17 and 19 conjugated double bonds, respectively, were synthesized by double Wittig reactions. Introduction of a leaving group in allylic position failed, and cations were obtained by hydride elimination effected by i) triphenylcarbenium tetrafluoroborate-d15, prepared by a new method, or ii) treatment with trifluoroacetic acid-d. Deuterated reagents were employed for product analysis by 1H NMR. Parallel experiments were performed with beta,beta-carotene (C40). NIR spectra at room temperature and at -15 degrees C were employed for characterisation and stability studies of the cationic products. In CH2Cl2lambdamax in the 900-1350 nm region was recorded. NMR data for the cationic product of beta,beta-carotene obtained by the two new preparation methods were consistent with the two monocations previously characterised. The cationic products of the longer polyenes provided downfield-shifted, broadened signals, compatible with C50-monocation, mixed C54-mono- and dication and C60-dication. Combined NIR and NMR data suggest that the extent of charge delocalisation is limited by the maximum soliton width for cations obtained from linear polyenes with more than ca. 20 sp2-hybridized carbon atoms.