Per Uvdal

Molecular preservation of the pigment melanin in fossil melanosomes

Fossil feathers, hairs and eyes are regularly preserved as carbonized traces comprised of masses of micrometre-sized bodies that are spherical, oblate or elongate in shape. For a long time, these minute structures were regarded as the remains of biofilms of keratinophilic bacteria, but recently they have been reinterpreted as melanosomes; that is, colour-bearing organelles. Resolving this fundamental difference in interpretation is crucial: if endogenous then the fossil microbodies would represent a significant advancement in the fields of palaeontology and evolutionary biology given, for example, the possibility to reconstruct integumentary colours and plumage colour patterns. It has previously been shown that certain trace elements occur in fossils as organometallic compounds, and hence may be used as biomarkers for melanin pigments. Here we expand this knowledge by demonstrating the presence of molecularly preserved melanin in intimate association with melanosome-like microbodies isolated from an argentinoid fish eye from the early Eocene of Denmark.

Skin pigmentation provides evidence of convergent melanism in extinct marine reptiles

Throughout the animal kingdom, adaptive colouration serves critical functions ranging from inconspicuous camouflage to ostentatious sexual display, and can provide important information about the environment and biology of a particular organism. The most ubiquitous and abundant pigment, melanin, also has a diverse range of non-visual roles, including thermoregulation in ectotherms. However, little is known about the functional evolution of this important biochrome through deep time, owing to our limited ability to unambiguously identify traces of it in the fossil record. Here we present direct chemical evidence of pigmentation in fossilized skin, from three distantly related marine reptiles: a leatherback turtle, a mosasaur and an ichthyosaur. We demonstrate that dark traces of soft tissue in these fossils are dominated by molecularly preserved eumelanin, in intimate association with fossilized melanosomes. In addition, we suggest that contrary to the countershading of many pelagic animals, at least some ichthyosaurs were uniformly dark-coloured in life. Our analyses expand current knowledge of pigmentation in fossil integument beyond that of feathers, allowing for the reconstruction of colour over much greater ranges of extinct taxa and anatomy. In turn, our results provide evidence of convergent melanism in three disparate lineages of secondarily aquatic tetrapods. Based on extant marine analogues, we propose that the benefits of thermoregulation and/or crypsis are likely to have contributed to this melanisation, with the former having implications for the ability of each group to exploit cold environments.

Water Tetramer, Pentamer, and Hexamer in Inert Matrices

The infrared spectrum of water, isolated in inert matrices, has been studied in the interval from 60 to 4000 cm(-1). Experiments with partially deuterated water combined with DFT (density functional theory) calculations have been used to investigate the structure of matrix-isolated water tetramer. A few, strong intermolecular fundamentals of the water tetramer have been observed. Mid-infrared bands due to deuterated pentamers and hexamers have been observed and are used to discuss the assignments of these water clusters.

Far-Infrared Band Strengths in the Water Dimer: Experiments and Calculations

Most fundamentals modes of the water dimer have been experimentally determined, and the frequencies have been measured in either neon or parahydrogen matrices. The band strengths of all intramolecular and most intermolecular fundamentals of the water dimer have been measured. The results are further corroborated by comparison with the corresponding data for the fully deuterated water dimer. DFT calculations of the mode frequencies and band strength are in qualitative agreement with the experimental observations.

Titanium dioxide thin-film growth on silicon (111) by chemical vapor deposition of titanium(IV) isopropoxide

Titanium dioxide thin film growth on silicon (111) by chemical vapor deposition of titanium(IV) isopropoxide

Metalorganic chemical vapor deposition of anatase titanium dioxide on Si: Modifying the interface by pre-oxidation

Metalorganic chemical vapor deposition of anatase titanium dioxide on Si: Modifying the interface by pre-oxidation

Oxygen sticking on Pd(111): double precursors, corrugation and substrate temperature effects

Abstract The initial sticking coefficient for oxygen on Pd(111) was measured as a function of O 2 translational energy, angle of incidence and substrate temperature. The results indicate that the O 2 dissociation involves sequential population of a physisorbed and a chemisorbed precursor state at low translational energies and direct molecular chemisorption at high energies. No direct dissociation was observed. A strong angular dependence in the sticking coefficient at high translational energies suggests considerable corrugation in the activation barrier for molecular chemisorption. An observed enhancement in the sticking with increasing substrate temperature is consistent with a reduction in this corrugation.

Microspectroscopic evidence of cretaceous bone proteins.

Low concentrations of the structural protein collagen have recently been reported in dinosaur fossils based primarily on mass spectrometric analyses of whole bone extracts. However, direct spectroscopic characterization of isolated fibrous bone tissues, a crucial test of hypotheses of biomolecular preservation over deep time, has not been performed. Here, we demonstrate that endogenous proteinaceous molecules are retained in a humerus from a Late Cretaceous mosasaur (an extinct giant marine lizard). In situ immunofluorescence of demineralized bone extracts shows reactivity to antibodies raised against type I collagen, and amino acid analyses of soluble proteins extracted from the bone exhibit a composition indicative of structural proteins or their breakdown products. These data are corroborated by synchrotron radiation-based infrared microspectroscopic studies demonstrating that amino acid containing matter is located in bone matrix fibrils that express imprints of the characteristic 67 nm D-periodicity typical of collagen. Moreover, the fibrils differ significantly in spectral signature from those of potential modern bacterial contaminants, such as biofilms and collagen-like proteins. Thus, the preservation of primary soft tissues and biomolecules is not limited to large-sized bones buried in fluvial sandstone environments, but also occurs in relatively small-sized skeletal elements deposited in marine sediments.

Intermolecular vibrations of different isotopologs of the water dimer: Experiments and density functional theory calculations.

Far infrared spectra of seven different isotopologs of the water dimer have been measured in neon matrices at 2.8 K. The experiments are interpreted with the aid of density functional theory calculations, in particular the calculated harmonic isotopic shifts were utilized. All six intermolecular vibrational modes of the water dimer and the fully deuterated water dimer are assigned based the isotopic shifts induced. 31 of a total of 42 intermolecular fundamental modes of the seven different H, D, and (18)O containing water dimers have been experimentally observed and assigned accordingly. The overall agreement between the calculations and the experiments of all isotopologs results in a complete and consistent description of these modes.

DECOUPLING OF VIBRATIONAL MODES AS A STRUCTURAL TOOL : COVERAGE-INDUCED REORIENTATION OF METHOXIDE ON MO(110)

The structure and reactivity of methoxide adsorbed on Mo(110) was investigated using temperature programmed reaction, x‐ray photoelectron, high resolution electron energy loss and infrared reflection absorption spectroscopies. Methanol decomposes through a methoxy surface intermediate on Mo(110), with dehydrogenation and carbon–oxygen bond scission occurring at ∼400 K. The structure of the methoxy moiety is dependent on coverage, by reference to data obtained using surface infrared spectroscopy in combination with selective isotopic labeling. We demonstrate that methoxy exhibits C3v symmetry, i.e., the C–O bond is normal to the surface, at coverages below 0.17 ML. However, the C–O axis begins to tilt towards the surface at higher coverages, so that at saturation coverage (0.25 ML), two distinct methoxy species with Cs symmetry are observed with an average tilt angle of 25°±15° from the surface normal. In addition, we conclusively show that the intense features at ∼2910 cm−1 in the infrared spectrum of ads...