Amberly spectroscopy

From a structural point of view the OPLS results for liquids have also shown to be in accord with available experimental data, including vibrational spectroscopy and diffraction data on, for Instance, formamide, dimethylformamide, methanol, ethanol, 1-propanol, 2-methyl-2-propanol, methane, ethane and neopentane. The hydrogen bonding in alcohols, thiols and amides is well represented by the OPLS potential functions. The average root-mean-square deviation from the X-ray structures of the crystals for four cyclic hexapeptides and a cyclic pentapeptide optimized with the OPLS/AMBER model, was only 0.17 A for the atomic positions and 3% for the unit cell volumes. 

Beck, C.W. (1986). Spectroscopic studies of amber. Applied Spectroscopy Reviews 22 57-110. 

Lambert, J.B., Beck, C.W. and Frye, J.S. (1988). Analysis of European amber by carbon-13 nuclear magnetic resonance spectroscopy. Archaeometry 30 248-263. 

Amber is a fossilized form of terpenoid resin found in many parts of the world and used by people of many different cultures. The scientific analysis of amber began as early as the 16th century (1), and the analysis of its chemical composition has been going on for over 100 years (2). Because the material is nearly insoluble, modern analysis is primarily by infrared spectroscopy (3). Additional structural information about amber is now avail-... 

On the basis of these comparisons, 13C NMR spectroscopy can easily distinguish the two New World ambers from Baltic amber. Normally, Mexican and Dominican ambers are distinguishable on the basis of the exometh-... 

Laboratory tests. There are one or two further tests that can be carried out in a laboratory using specialised equipment. The test most commonly used for amber is infirared spectroscopy, which detects the chemical components of a given specimen. It can, for example, discern the differences between ambers fiom different localities, and is especially good at distinguishing between succinites and retinites (those ambers that contain succinic acid and those that contain none). It can also distinguish between various man-made polymers. 

A step forward along the route to the correct modelling of the spectroscopy and photochemical reactivity of photoreactive proteins is represented by the implementation of a Quantum Mechanics/Molecular Mechanics (QM/MM) computational strategy based on a suitable QM part coupled with a protein force field such as AMBER [34] (or CHARMM [35]). Very recently a CASPT2//CASSCF/AMBER method for rhodopsin has been implemented in our laboratory [36,37] within the QM/MM hnk-atom scheme [38]. Special care has been taken in the parametrization of the protonated Schiff base linkage region that describes the dehcate border region between the MM (the protein)... 

In light of the recently developed high interest in ambers, we decided to discuss these fossilized natural resins as a separate topic. For this reason, even information about fake ambers (mostly synthetic polymers) will be included in this discussion. Ambers have long proved difficult to examine. IR and FTIR spectroscopy provided useful tools in the determination of amber origins, but in a comprehensive review of the subject, Becld stated ... 

FTIR-VAR is a reliable tool for non-destructive investigating of amber. The spectra are more complex than FTIR-transmittance spectra, the obtained signal are rather highly difficult to ascribe and the variability of results is high, but coupled with statistical analysis and corroborated with other techniques (Raman spectroscopy. X-rays fluorescence) is a consistent method to diagnose the origin of amber in archaeological artifacts. 

HGM Edwards, DW Farwell. FT-Raman spectroscopy of amber. Spectrochim Acta A 52 1119-1125, 1996. 

RH Brody, HGM Edwards, AM Pollard. Characteristics used in the identification of ambers using Raman spectroscopy, to be published. 

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