Anders Engdahl

Water in krypton matrices

Abstract The infrared spectrum of water (H2O, HDO, D2O) in krypton matrices has been studied. Bands due to rotating monomers, non-rotating monomers, nitrogen-induced bands, dimer bands and trimer bands are assigned. The results are compared with argon data.

On the structure of the water trimer. A matrix isolation study

The infrared spectra of several isotopomers of the water trimer have been studied in argon and krypton matrices. The results show that the trimer is cyclic, with three equivalent water molecules.

On the relative stabilities of H‐ and D‐bonded water dimers

The infrared spectra of water dimers formed from H2O, D2O, and HDO in krypton matrices have been recorded. Thermal equilibria between H‐ and D‐bonded dimers have been studied. D bonding is preferred, and H‐bonded dimers are approximately 60 cm−1 less stable than D‐bonded dimers. The energy difference seems to be due to the higher value of the intermolecular out‐of‐plane H‐bond shear vibration compared to the corresponding D‐bond vibration.

The acetylene-water complex. A matrix isolation study

Abstract Infrared spectra of argon matrices containing water and acetylene show that acetylene forms a hydrogen bond to water. C 2 HD can form either a hydrogen or a deuterium bond.

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.

The water–hydroxyl radical complex: A matrix isolation study

The water–hydroxyl radical complex was prepared by irradiating peroxy radicals in hydrogen-doped argon matrices. The low water content of the matrices made it possible to observe the fundamental bands of the complexed water molecule. The experimental results are compared with the results from ab initio calculations. The complex rotates around the O–O axis in the matrix.

A matrix-isolation study of the ethylene—water interaction

Abstract Water and ethylene form a weak molecular complex in argon matrices. Water is hydrogen-bonded to the π-orbital of ethylene. For the HDO complex, only D-bonding is observed. A complex containing two water molecules and one ethylene has been observed. This complex can be described as a water dimer where the proton acceptor forms a hydrogen bond with ethylene. Both the water—ethylene interaction and the dimer hydrogen bond are significant stronger in the ternary complex than in the corresponding binary complexes.

The intramolecular vibrations of the ammonia water complex. A matrix isolation study

The infrared spectrum of the ammonia water complex has been recorded from 10 to 4000 cm−1 for complexes trapped in neon and krypton matrices. Spectra have been observed for NH3 or ND3 complexed with H2O, HDO, or D2O. The observed intramolecular fundamentals are compared with frequencies calculated from a rigid‐molecule harmonic oscillator model.

Complex formation between water and formamide

The infrared spectrum of the water–formamide complex in argon matrices has been recorded from 10 to 4000 cm−1. The interaction energy of the complex forming molecules has been calculated from a theoretical potential. One global and three different local minima have been found for this potential. Intermolecular vibration frequencies have been calculated for each minimum. The results are compared with the experimentally observed far infrared spectrum. In agreement with microwave measurements and ab initio calculations, the global minimum of the complex is found, both from calculations and experiment, to have a cyclic structure with water forming a hydrogen bond to the amide oxygen and receiving a hydrogen bond from an amide hydrogen. In addition to the cyclic complex, we observe one of the local minimum structures of the complex, where water accepts a hydrogen bond from the amide NH on the CH side of the amide.

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.