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- Cotton, L. J., et al.
(författare)
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Chemical relationships of ambers using attenuated total reflectance Fourier transform infrared spectroscopy
- 2017. - 1
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Ingår i: Geological Society Special Publication. - 0305-8719. ; 448:1, s. 413-424
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Bokkapitel (refereegranskat)abstract
- Amber is known for its remarkably well-preserved fossils, but the chemical complexity of amber and its history are less well known. Amber is highly variable in both its physical and chemical properties, which are dependent on factors such as the source tree and the diagenetic history. Amber from a given locality therefore has a unique chemical composition. Fourier transform infrared (FTIR) spectroscopy is often used to determine the chemical composition of amber and to provide a fingerprint for amber samples. We used FTIR spectroscopy to analyse samples spanning the time period from the Early Cretaceous to the Oligo-Miocene from 17 localities in the Americas, Europe and Asia. We then used cluster analysis to examine the trends in amber chemistry and to increase our understanding of its formation through time. A detailed analysis of the clustering followed by modelling of the variables of importance suggested that the exocyclic methylene group content and conformation play a major part in explaining the clustering. Other variables, such as the ester and alkyl contents, contribute to identification. Placed in a broader perspective, our study indicates that the dominant factor in clustering is the age of the amber, followed by the locality.
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- Dicko, Cedric, et al.
(författare)
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Differential scanning fluorimetry illuminates silk feedstock stability and processability.
- 2016
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-6848 .- 1744-683X. ; 12:1, s. 255-262
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Tidskriftsartikel (refereegranskat)abstract
- The ability to design and implement silk feedstock formulations for tailored spinning has so far eluded the bioengineers. Recently, the high throughput screening technique of differential scanning fluorimetry (DSF) demonstrated the link between the instability transition temperature (Ti) and the processability of the silk feedstock. Using DSF we screened a large set of chemicals known to affect solvent quality. A multivariate analysis of the results shows that, regardless of the diversity of chemicals, three groupings are significantly distinguishable: G1 = similar to native silk; G2 = largely dominated by electrostatic interactions; and G3 = dominated by chelating interactions. We propose a thermodynamic analysis based on a pre- and post-transition fit to estimate the van't Hoff enthalpies (ΔHv) and the instability temperature (Ti). Our analysis shows that the ΔTi and ΔHv values were distinct: G1 (ΔTi = 0.23 ± 0.2; ΔHv = -159.1 ± 5.6 kcal mol(-1)), G2 (ΔTi = -7.3 ± 0.7; ΔHv = -191.4 ± 5.5 kcal mol(-1)), and G3 (ΔTi = -19.9 ± 3.3; ΔHv = -68.8 ± 6.0 kcal mol(-1)). Our analysis further combined the ΔTi value and the ΔHv value using stability ΔΔG to find that G1 only marginally stabilizes native silks (ΔΔG = -0.15 ± 0.04 kcal mol(-1)), whereas G2 and G3 destabilize native silk (ΔΔG = 3.8 ± 0.11 and ΔΔG = 3.8 ± 0.3 kcal mol(-1), respectively). Here our analysis shows that native silk has a complex multistep transition that is possibly non-cooperative. However, all three groupings also show a direct and cooperative transition with varied stabilization effects. This analysis suggests that native silks are able to sample multiple substates prior to undergoing (or to delay) the final transition. We conclude by hypothesizing that the observed energetic plasticity may be mediated by a fragile packaging of the silk tertiary structure that is readily lost when the solvent quality changes.
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