Microbeam synchrotron imaging of hairs from ancient Egyptian mummies.

Developments in microfocus synchrotron techniques have led to new results regarding the long-term alteration of archaeological samples of biological origin. Here, ancient hair samples from two Egyptian mummies have been analyzed using a conjunction of structural and elemental synchrotron methods. In this favored context of conservation, structural analysis revealed a remarkable preservation of keratin supramolecular organization at any observed length scale. Bulk keratin structure has therefore not been modified significantly over 2000 years. However, infrared spectroscopy indicated a partial disorganization of keratins close to the hair surface through polypeptide bond breakage. Elemental mapping showed a strongly heterogeneous distribution which can be related to mummification and cosmetic treatments.

Lead-revealed lipid organization in human hair.

Human hair lipids form a complex mixture of composition close to that of sebum. Part of these lipids appears in an organized state that has been studied by diffraction techniques in the literature. Nevertheless, information on the structure of these lipids remains very scarce due to their low contribution to global hair diffraction pattern. Here we show that appropriate lead treatment considerably enhances organized lipid features observed by microbeam synchrotron radiation diffraction experiments. We attribute these features to the formation of lead soaps of free fatty acids. Specific orientation of hair "lipid crystals" in planes parallel to the hair axis is clearly demonstrated. Inclusion of these lipids in the bulk of the hair shaft is shown by diffraction experiments following removal of the cuticular outermost layer of hair. Moreover, microfluorescence and diffraction experiments are consistent with part of the lipids being present as calcium soaps in native hair. We therefore consider lead fixation as a powerful tool to evaluate the lipid organization in human hair for medical, environmental and archaeological purposes, including lead poisoning.

The crystallographic symmetry test for the correctness of a set of phases.

One of the most important problems in the application of direct methods for large structures is to establish reliable consistency criteria for the correctness of a phasing trial. The introduction in the twin variables method [Bethanis, Tzamalis, Hountas, Mishnev & Tsoucaris (2000). Acta Cryst. A56, 105-111] of a new criterion based on the crystallographic symmetry consists of testing the phase extension and refinement algorithm by deliberately sacrificing the space-group-symmetry information in the auxiliary variable set then using its gradual re-appearance as a criterion for correctness. In the present paper, the crystallographic symmetry test has been used in the implementation of the twin algorithm in two different ways: (i) as an overall test throughout the iterations that is likely to reflect the correctness of the phasing procedure for each one of the extension trials in a macromolecular phasing environment; (ii) as a convenient criterion to determine the optimum cycle for freeing the initial phases used by the algorithm for the phase-extension procedure.

Ab initio determination of a crystal structure by means of the Schrödinger equation.

It is shown that the use of the Schrödinger equation may lead to the ab initio determination of the positions of the nuclei in a crystal, given a limited number of diffracted-beam intensities. In particular, it is shown that an extremely simplified Schrödinger equation in physical momentum space provides a sufficiently sound theoretical basis to develop an algorithm using diffraction data alone. This algorithm has been tested with a known 41 atom crystalline structure (not including hydrogen atoms) in space group P1. The extracted information is sufficient to determine the positions of all atoms. In addition, theoretical developments relevant to the connection between momentum space in quantum mechanics and diffraction theory have been formulated.

[Chemistry of cosmetics in antiquity]. / Chimie et maquillage dans l'Antiquité.

Several texts, statues and paintings denote the importance of make up and eye medicines since the earliest periods of Egyptian history. We have investigated cosmetic powders that were preserved in original alabaster and reed containers. Quantitative crystallographic and chemical analysis of the mineral and organic components revealed surprising facts. In addition to the well known galena PbS and cerussite PbCO3, two unexpected constituents have been identified: laurionite PbOHCl and phosgenite Pb2 (CO3) Cl2, which are rare halide minerals found in lead slag only in certain places where the sea water has weathered lead debris left over from silver mining operations in Antiquity. Alteration of natural lead minerals is also unlikely, given the excellent state of conservation of the reed vessels. This evidence indicates that laurionite and phosgenite were synthesised artificially. Support for this statement comes from recipes of medicinal products to be "used in ophthalmology" reported by Greco-Roman authors such as Dioscorides and Pline (1st Century B.C.): silver foam PbO is crushed and mixed with rock salt and sometimes with natron (Na2CO3). The reaction seems to be straightforward. However, our experiments in the laboratory have shown a major difficulty, arising from the concomitant production of alkali, which raises the pH and leads to different products. It follows that the Egyptians very early mastered this kind of chemical synthesis and technology, a fact of great importance in the History of Sciences. Fire-based technology had been mastered to manufacture Egyptian Blue pigments since the third millennium B.C. The present results now suggest that wet chemistry was already known 4000 years ago. This key finding provides a new insight into the chemical technology of far greater antiquity than has previously been believed. Yet, an important question remains relative to the ultimate motivation for these technological developments. If the Egyptians initially only aimed at different nuances of grey, they could use cerussite, an easily accessible mineral, crushed and mixed with galena. Thus, one should seek other motivations; we shall propose to consider a religious-ritual context, ultimately linked to a pharmaceutical aspect.

New developments of the TWIN algorithm for phase extension and refinement in disordered supramolecular structures.

A new development of the TWIN algorithm is described and used for phase extension/refinement in supramolecular complexes. A small number of phased reflections at low resolution are sufficient for the quasi-automated determination of all atomic coordinates, including disordered atoms.

Upgrading the twin variables algorithm for large structures.

Phase extension from lower to higher resolution by using an upgraded TWIN variables algorithm [Hountas & Tsoucaris (1995). Acta Cryst. A51, 754-763] in protein molecules with close to 1,000 non-H atoms is presented. Three points of this procedure are of particular interest. (i) The use of a set of auxiliary variables providing a satisfactory fit for many kinds of constraints: the new algorithm works efficiently despite the extreme 'dilution' of very limited initial phase information into a much larger set of auxiliary variables. (ii) The extension of this auxiliary variables set beyond the resolution of the observed data, which enhances the phase extension in a so-called 'super-resolution' sphere. (iii) The use of the crystallographic symmetry as a new figure of merit and as a reliable test for the correctness of the phase-extension process allows an efficient screening.

Inclusion of the main pheromone component of Dacus oleae, 1,7-dioxaspiro[5,5]undecane, in beta-cyclodextrin.

The complex beta-cyclodextrin-1,7-dioxaspiro[5,5]undecane nonahydrate, C42H70O35.C9H16O2.9H2O, belongs to the class of beta-cyclodextrin dimeric-type complexes. The racemic guest molecule is present in a disordered position. Both enantiomers are located in two different regions inside the channel formed by the host dimers.

The crystal structure of the inclusion complex of cyclo-maltoheptaose (beta-cyclodextrin) with 3,3-dimethylbutylamine.

The crystal of the 1:1 complex of 3,3-dimethylbutylamine with cyclomaltoheptaose (beta CD, beta-cyclodextrin) is monoclinic C2 with a = 19.187(9), b = 24.56(1), c = 15.893(7) A, beta = 108.77(4) degrees, V = 7091 A3, and Z = 4. Two beta CD molecules, held together by intermolecular hydrogen bonds involving HO-3, form dimers, in the cavities of which two 3,3-dimethylbutylamine and two water molecules are accommodated. The guest molecule is completely enclosed in the cavity. The amino group is located at the secondary-hydroxyl-group side, and is hydrogen-bonded to the entrapped water molecules. The dimers form channels along the c axis. The inter-dimer space is filled with 10.7 water molecules that are distributed over 14 sites, and there is a dense network of hydrogen bonds involving the water molecules and the beta CD hydroxyl groups.

Oriented structure in human stratum corneum revealed by X-ray diffraction.

Various types of human stratum corneum (sheets or callus) were exposed, in parallel and perpendicular geometry, to the high flux of X rays produced by a synchrotron radiation source. Under these conditions, very clear and rich diffraction patterns, corresponding to the supramolecular organization of stratum corneum proteins and lipids, were obtained. The comparative study of normal or delipidized stratum corneum sheets and membrane couplets allows one to attribute certain diffraction features to lipids. Our results in the 3-7-nm range show two different distances for lipid bilayers. Concerning the protein nature of normal stratum corneum, the results show that keratin would occur in the beta form, whereas for callus it is in the alpha form. Indeed, normal stratum corneum sheets never display the 0.514-nm characteristic of alpha keratin. This result means that the supramolecular organization of keratin could depend on the keratinization process. Finally, our studies also confirm the presence of a still-unknown protein component existing in the beta form that would be located either inside the corneocytes or in some dilatated zones of the intercellular spaces.