Search

An easily accessible experimental set-up to grow large single crystals of two sweeteners readily available in supermarkets, erythritol and xylitol, is described. The crystallization of these compounds illustrates the principles of crystallization by evaporation. As these artificial sweeteners are also known to induce a cool sensation in the mouth, the crystal-growing experiment is complemented with a simple calorimetric set-up to demonstrate the endothermic nature of the dissolution of the selected sweeteners in a more qu-anti-tative approach by measuring the heat of dissolution (ΔH diss). The choice of these two sweeteners also allows use of the freely available WebCSD and Mercury tools to visualize their three-dimensional structure, crystal packing and powder diffractograms, and to deepen stereochemical concepts such as stereoisomers and meso compounds. ispartof: ACTA CRYSTALLOGRAPHICA SECTION E-CRYSTALLOGRAPHIC COMMUNICATIONS vol:78 issue:Pt 9 pages:874-879 ispartof: location:England status: published

International audience; The effect of the protein environment on the formation and stabilization of an elusive catalytically active polyoxometalate (POM) species, K$_6$[Hf($\alpha_2$-P$_2$W$_{17}$O$_{61}$)] (1), is reported. In the co-crystal of hen egg-white lysozyme (HEWL) with 1, the catalytically active monomeric species is observed, originating from the dimeric 1:2 POM form, while it is intrinsically unstable under physiological pH conditions. The protein-assisted dissociation of the dimeric POM was rationalized by means of DFT calculations. The dissociation process is unfavorable in bulk water, but becomes favorable in the protein–POM complex due to the low dielectric response at the protein surface. The crystal structure shows that the monomeric form is stabilized by electrostatic and water-mediated hydrogen bonding interactions with the protein. It interacts at three distinct sites, close to the aspartate-containing hydrolysis sites, demonstrating high selectivity towards peptide bonds containing this residue.

Successful co-crystallization of a noncovalent complex between hen egg-white lysozyme (HEWL) and the monomeric Zr(IV) -substituted Keggin polyoxometalate (POM) (Zr1 K1), (Et2 NH2 )3 [Zr(PW11 O39 )] (1), has been achieved, and its single-crystal X-ray structure has been determined. The dimeric Zr(IV) -substituted Keggin-type polyoxometalate (Zr1 K2), (Et2 NH2 )10 [Zr(PW11 O39 )2 ] (2), has been previously shown to exhibit remarkable selectivity towards HEWL hydrolysis. The reported X-ray structure shows that the hydrolytically active Zr(IV) -substituted Keggin POM exists as a monomeric species. Prior to hydrolysis, this monomer interacts with HEWL in the vicinity of the previously identified cleavage sites found at Trp28-Val29 and Asn44-Arg45, through water-mediated H-bonding and electrostatic interactions. Three binding sites are observed at the interface of the negatively charged Keggin POM and the positively charged regions of HEWL at: 1) Gly16, Tyr20, and Arg21; 2) Asn44, Arg45, and Asn46; and 3) Arg128. ispartof: Chemistry - a European Journal vol:21 issue:33 pages:11692-5 ispartof: location:Germany status: published

The title compound, C4H8O4Te, crystallized from a solution of Te4+ in ethylene glycol. The TeIV atom is in a distorted seesaw coordination defined by four O atoms from two different ethyleneglycate ligands. The C atoms of the ethyleneglycate ligands are disorderd over two positions, with population parameters of 50.3 (6) and 49.7 (6)% indicating a statistical distribution. Due to the possibility to transform the primitive monoclinic unit cell into a metrically orthorhombic C unit cell, the data are twinned and were refined with the twin law 100/ 010/101 with the relative scale factor refining to 1.82 (4)% for the minor component. journal: Acta Crystallographica Section E: Structure Reports Online content_type: organic compounds peer_reviewed: Yes review_process: Single blind received: 5 March 2013 accepted: 5 June 2013 published_online: 12 June 2013 supplementary_materials: This article has supporting information copyright: © 2013 Brooks license: Creative Commons Attribution (CC-BY) ispartof: Acta Crystallographica E, Structure Reports Online vol:69 issue:Pt 7 pages:O1080-+ ispartof: location:United States status: published

The crystal structure of Na3[Tb(C7H3NO4)3].NaClO4.6H2O has been determined by single crystal X-ray diffraction. The compound crystallizes in the hexagonal space group P (6) over bar 2c, with a=10.442(3) Angstrom, c=18.346(7) Angstrom and Z=2. Refinement of the crystal structure on basis of 722 observed reflections led to R(1)=0.067. The coordination polyhedron around terbium is a distorted tricapped trigonal prism with D3 symmetry. ispartof: Bulletin des societes chimiques belges vol:106 issue:1 pages:25-27 status: published