International audienceCarbonated apatites represent an important class of compounds encountered in many fields including anthropology, archeology, geology, medicine and biomaterials engineering. They constitute, in particular, the mineral part of bones and teeth, are found in sedimentary settings, and are used as biomimetic compounds for the development of bone tissue engineering scaffolds. Whether for assessing the degree of biomimetism of synthetic apatites or for better understanding diagenetic events, their thorough physico-chemical characterization is essential, and includes, in particular, the evaluation of their carbonate content. FTIR is especially well-suited for such a goal, as this spectroscopy technique requires only a low amount of specimen to analyze, and carbonate ions exhibit a clear vibrational signature. In this contribution, we critically discuss several FTIR-approaches that may be (or have been) considered in view of carbonation quantification. The best methodology appears to be based on the analysis of the n3(CO3)and n1n3(PO4) modes. The area ratio rc/p between these two contributions was found to be directly correlated to the carbonate content of the samples (R2 ¼ 0.985), with the relation wt.% CO3 ¼ 28.62*rc/ p þ 0.0843. The method was validated thanks to titrations by coulometry assays for various synthetic reference samples exhibiting carbonate contents between 3 and 7 wt.%. The FTIR carbonate quantification methodology that we propose here was also tested with success on three skeletal specimens (two bones/one tooth), after elimination of the collagen contribution. Comparative data analysis is also presented,showing that the use of other vibration bands, or only peak heights (instead of peak areas), leads to significantly lower correlation agreement. This FTIR data treatment methodology is recommended so as to limit errors on the evaluation of carbonate contents in apatite substrates

International audienceIn order to shed some light on DNA preservation over time in skeletal remains from a physicochemicalviewpoint, adsorption and desorption of DNA on a well characterized synthetic apatite mimicking boneand dentin biominerals were studied. Batch adsorption experiments have been carried out to determinethe effect of contact time (kinetics), DNA concentration (isotherms) and environmentally relevant factorssuch as temperature, ionic strength and pH on the adsorption behavior. The analogy of the nanocrystallinecarbonated apatite used in this work with biological apatite was first demonstrated by XRD, FTIR, andchemical analyses. Then, DNA adsorption kinetics was fitted with the pseudo-first order, pseudo-secondorder, Elovich, Ritchie and double exponential models. The best results were achieved with the Elovichkinetic model. The adsorption isotherms of partially sheared calf thymus DNA conformed satisfacto-rily to Temkin's equation which is often used to describe heterogeneous adsorption behavior involvingpolyelectrolytes. For the first time, the irreversibility of DNA adsorption toward dilution and significantphosphate-promoted DNA desorption were evidenced, suggesting that a concomitant ion exchange pro-cess between phosphate anionic groups of DNA backbone and labile non-apatitic hydrogenphosphateions potentially released from the hydrated layer of apatite crystals. This work should prove helpful fora better understanding of diagenetic processes related to DNA preservation in calcified tissues

The extraction of DNA from skeletal remains is a major step in archeological or forensic contexts. However, diagenesis of mineralized tissues often compromises this task although bones and teeth may represent preservation niches allowing DNA to persist over a wide timescale. This exceptional persistence is not only explained on the basis of complex organo-mineral interactions through DNA adsorption on apatite crystals composing the mineral part of bones and teeth but is also linked to environmental factors such as low temperatures and/or a dry environment. The preservation of the apatite phase itself, as an adsorption substrate, is another crucial factor susceptible to significantly impact the retrieval of DNA. With the view to bring physicochemical evidence of the preservation or alteration of diagenetic biominerals, we developed here an analytical approach on various skeletal specimens (ranging from ancient archeological samples to recent forensic specimens), allowing us to highlight several diagenetic indices so as to better apprehend the complexity of bone diagenesis. Based on complementary techniques (X-ray diffraction (XRD), Fourier transform infrared (FTIR), calcium and phosphate titrations, SEM-EDX, and gravimetry), we have identified specific indices that allow differentiating 11 biological samples, primarily according to the crystallinity and maturation state of the apatite phase. A good correlation was found between FTIR results from the analysis of the v3(PO4) and v4(PO4) vibrational domains and XRD-based crystallinity features. A maximal amount of information has been sought from this analytical approach, by way of optimized posttreatment of the data (spectral subtraction and enhancement of curve-fitting parameters). The good overall agreement found between all techniques leads to a rather complete picture of the diagenetic changes undergone by these 11 skeletal specimens. Although the heterogeneity and scarcity of the studied samples did not allow us to seek direct correlations with DNA persistence, the physicochemical parameters described in this work permit a fine differentiation of key properties of apatite crystals among post mortem samples. As a perspective, this analytical approach could be extended to more numerous sets of specimens so as to draw statistical relationships between mineral and molecular conservation.