Validation of climate model-inferred regional temperature change for late-glacial Europe

Comparisons of climate model hindcasts with independent proxy data are essential for assessing model performance in non-analogue situations. However, standardized palaeoclimate data sets for assessing the spatial pattern of past climatic change across continents are lacking for some of the most dynamic episodes of Earth’s recent past. Here we present a new chironomid-based palaeotemperature dataset designed to assess climate model hindcasts of regional summer temperature change in Europe during the late-glacial and early Holocene. Latitudinal and longitudinal patterns of inferred temperature change are in excellent agreement with simulations by the ECHAM-4 model, implying that atmospheric general circulation models like ECHAM-4 can successfully predict regionally diverging temperature trends in Europe, even when conditions differ significantly from present. However, ECHAM-4 infers larger amplitudes of change and higher temperatures during warm phases than our palaeotemperature estimates, suggesting that this and similar models may overestimate past and potentially also future summer temperature changes in Europe.

Watson-Crick base-pairing properties of tricyclo-DNA

Tricyclo-DNA belongs to the family of conformationally restricted oligodeoxynucleotide analogues. It differs structurally from DNA by an additional ethylene bridge between the centers C(3') and C(5') of the nucleosides, to which a cyclopropane unit is fused for further enhancement of structural rigidity. The synthesis of the hitherto unknown tricyclodeoxynucleosides containing the bases cytosine and guanine and of the corresponding phosphoramidite building blocks is described, as well as a structural description of a representative of an alpha- and a beta-tricyclodeoxynucleoside by X-ray analysis. Tricyclodeoxynucleoside building blocks of all four bases were used for the synthesis of fully modified mixed-base oligonucleotides. Their Watson-Crick pairing properties with complementary DNA, RNA, and with itself were investigated by UV melting curves, CD spectroscopy, and molecular modeling. Tricyclo-DNA was found to be a very stable Watson-Crick base-pairing system. A UV melting curve analysis of the decamers tcd(pcgtgacagtt) and tcd(paactgtcacg) showed increased thermal stabilities of up to DeltaT(m)/mod. = +1.2 degrees C with complementary DNA and +2.4 degrees C with complementary RNA. With itself, tricyclo-DNA showed an increase in stability of +3.1 degrees C/base pair relative to DNA. Investigations into the thermodynamic properties of these decamers revealed an entropic stabilization and an enthalpic destabilization for the tricyclo-DNA/DNA duplexes. CD spectroscopic structural investigations indicated that tricyclo-DNA containing duplexes preferrably exist in an A-conformation, a fact which is in agreement with results from molecular modeling