Is Second Harmonic Generation a reliable tool for studying solid-solid phase transition and structural purity?

International audienceThe second harmonic generation (SHG) is a nonlinear optical effect occurring only in noncentrosymmetric space groups. Two photons (at the fundamental angular frequency ω) can interact in a noncentric crystal structure to give a new photon at twice the fundamental frequency (2ω). In previous studies, we demonstrated that the measurement of the intensity of the signal at 2ω (SHG signal) is a very sensitive probe to detect the noncentrosymmetry of crystal arrangements such as conglomerates [1]. This technique was also used, in rare occasions, to follow centrosymmetric to noncentrosymmetric solid-solid phase transitions [2], [3]. Because of the origin of the SHG signal, only centric to noncentric or noncentric to noncentric phase transitions can be investigated via SHG. However, SHG has proved to be highly sensitive even to a slight deviation from centrosymmetric conditions and could be used to detect noncentric nuclei and as a consequence to follow the nucleation of new phases. This could give great information about the order of the transition (as defined by Ehrenfest classification). Indeed, if the transition is of the first-order kind the signal should be discontinuous at the temperature transition but continuous in the case of a second order transition.In this study, we present the results obtained using a device developed to perform SHG measurements versus temperature for the solid-solid phase transition (from centrosymmetric to noncentrosymmetric structures) of several compounds. The case of 3-Hydroxybenzoic Acid is particularly considered. MHBA is an intermediate in the production of germicides, plasticizer and pharmaceuticals and exhibits two polymorphic forms [4] one of which is noncentrosymmetric. Finally, we evaluate the potential of the SHG signal measurements to follow phase transitions by comparison with other usual techniques such as Differential Scanning Calorimetry (DSC), X-Ray Diffraction or Raman Spectroscopy.REFERENCES[1] A. Galland, V.Dupray, B.Berton, S. Morin-Grognet, M. Sanselme, H. Atmani and G.Coquerel, “Spotting Conglomerates by Second Harmonic Generation,” Crystal Growth & Design, vol. 9, no. 6, pp. 2713–2718, Jun. 2009.[2] J. P. Dougherty and S. K. Kurtz, “A second harmonic analyzer for the detection of non- centrosymmetry,” Journal of Applied Crystallography, vol. 9, no. 2, pp. 145–158, Apr. 1976.[3] L. Smilowitz, B. F. Henson, and J. J. Romero, “Intercomparison of Calorimetry, Raman Spectroscopy, and Second Harmonic Generation Applied to Solid−Solid Phase Transitions,” The Journal of Physical Chemistry A, vol. 113, no. 35, pp. 9650–9657, Sep. 2009. [4] F. L. Nordström and Å. C. Rasmuson, “Polymorphism and thermodynamics of m- hydroxybenzoic acid,” European Journal of Pharmaceutical Sciences, vol. 28, no. 5, pp. 377– 384, Aug. 2006

New guidance for the use of concrete in maritime engineering

This paper presents an overview of project that aims to deliver an up-to-date, self-supported and decision aiding guidance on the use of concrete for design / construction / repair and maintenance of maritime structures. Some of the key findings relevant to navigation structures are detailed

Second harmonic generation: applications in phase diagram investigations

International audienceThe influence of water (in its gaseous state) on the stability of crystallized organic compounds was investigated. Through two examples of solid/vapour equilibria, several behaviours were highlighted (stoichiometric or non stoichiometric hydrates, hydration/dehydration mechanisms, stability domains of multi-hydrates as a function of relative humidity). Phase diagrams (as a function of partial water pressure) and stability diagrams have been proposed for each example. This study illustrates that solid/vapour equilibrium knowledge is a crucial step during the complete characterization of solid organic compounds

Antibiotic Resistance Genes in the Bacteriophage DNA Fraction of Environmental Samples

Antibiotic resistance is an increasing global problem resulting from the pressure of antibiotic usage, greater mobility of the population, and industrialization. Many antibiotic resistance genes are believed to have originated in microorganisms in the environment, and to have been transferred to other bacteria through mobile genetic elements. Among others, β-lactam antibiotics show clinical efficacy and low toxicity, and they are thus widely used as antimicrobials. Resistance to β-lactam antibiotics is conferred by β-lactamase genes and penicillin-binding proteins, which are chromosomal- or plasmid-encoded, although there is little information available on the contribution of other mobile genetic elements, such as phages. This study is focused on three genes that confer resistance to β-lactam antibiotics, namely two β-lactamase genes (blaTEM and blaCTX-M9) and one encoding a penicillin-binding protein (mecA) in bacteriophage DNA isolated from environmental water samples. The three genes were quantified in the DNA isolated from bacteriophages collected from 30 urban sewage and river water samples, using quantitative PCR amplification. All three genes were detected in the DNA of phages from all the samples tested, in some cases reaching 104 gene copies (GC) of blaTEM or 102 GC of blaCTX-M and mecA. These values are consistent with the amount of fecal pollution in the sample, except for mecA, which showed a higher number of copies in river water samples than in urban sewage. The bla genes from phage DNA were transferred by electroporation to sensitive host bacteria, which became resistant to ampicillin. blaTEM and blaCTX were detected in the DNA of the resistant clones after transfection. This study indicates that phages are reservoirs of resistance genes in the environment

Generation and characterization of standardized forms of trehalose dihydrate and their associated solid-state behavior

Trehalose dihydrate is a nonreducing disaccharide which has generated great interest in the food and pharmaceutical industries. However, it is well recognized that considerable batch to batch variation exists for supposedly identical samples, particularly in terms of the thermal response. In this investigation, two standardized forms of trehalose dihydrate were generated using two distinct crystallization pathways. The two batches were characterized using scanning electron microscopy, X-ray powder diffraction, and FTIR. The thermal responses of the two forms were then studied using modulated temperature differential scanning calorimetry (MTDSC) and thermogravimetric analysis (TGA). In particular, we describe the technique of quasi-isothermal MTDSC as a means of studying the change in equilibrium heat capacity as a function of temperature. Finally, variable temperature FTIR was utilized to assess the change in bonding configuration as a function of temperature. SEM revealed significant differences in the continuity and grain structure of the two batches. The TGA, MTDSC, and quasi-isothermal MTDSC studies all indicated significant differences in the thermal response and water loss profile. This was confirmed using variable temperature FTIR which indicated differences in bond reconfiguration as a function of temperature. We ascribe these differences to variations in the route by which water may leave the structure, possibly associated with grain size. The study has therefore demonstrated that chemically identical dihydrate forms may show significant differences in thermal response. We believe that this may assist in interpreting and hence controlling interbatch variation for this material

Temperature resolved second harmonic generation (TR-SHG) to investigate desolvation processes among organic solvates

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Temperature resolved second harmonic generation to probe the structural purity of m-hydroxybenzoic acid

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Is Second Harmonic Generation a reliable tool for studying solid-solid phase transition and structural purity?

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Temperature-resolved second harmonic generation A tool designed to study solid-solid transitions

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