Arthur Lindo Patterson, his function and element preferences in early crystal structures

In 1934, Arthur Lindo Patterson showed that a map of interatomic vectors is obtainable from measured X-ray diffraction data without phase information. Such maps were interpretable for simple crystal structures, but proliferation and overlapping of peaks caused confusion as the number of atoms increased. Since the peak height of a vector between two particular atoms is related to the product of their atomic numbers, a complicated structure could effectively be reduced to a simple one by including just a few heavy atoms (of high atomic number) since their interatomic vectors would stand out from the general clutter. Once located, these atoms provide approximate phases for Fourier syntheses that reveal the locations of additional atoms. Surveys of small-molecule structures in the Cambridge Structural Database during the periods 1936-1969, when Patterson methods were commonly used, and 1980-2013, dominated by direct methods, demonstrate large differences in the abundance of certain elements. The moderately heavy elements K, Rb, As and Br are the heaviest elements in the structure more than 3 times as often in the early period than in the recent period. Examples are given of three triumphs of the heavy atom method and two initial failures that had to be overcome

2-(3-Hydroxy-propyl)isoindoline-1,3-dione:Competition among hydrogen-bond acceptors

The title compound, C11H11NO3, has two mol-ecules in the asymmetric unit, which differ in the orientation of their side-chain OH groups, allowing them to form inter-molecular O - H⋯O hydrogen bonds to different acceptors. In one case, the acceptor is the OH group of the other mol-ecule, and in the other case it is an imide O=C group. This is the first example in the N-substituted phthalimide series in which independent mol-ecules have different types of acceptor. Mol-ecular-orbital calculations place the greatest negative charge on the OH group. © 2008 International Union of Crystallography

19F-labeling of the adenine H2-site to study large RNAs by NMR spectroscopy

In comparison to proteins and protein complexes, the size of RNA amenable to NMR studies is limited despite the development of new isotopic labeling strategies including deuteration and ligation of differentially labeled RNAs. Due to the restricted chemical shift dispersion in only four different nucleotides spectral resolution remains limited in larger RNAs. Labeling RNAs with the NMR-active nucleus [superscript 19]F has previously been introduced for small RNAs up to 40 nucleotides (nt). In the presented work, we study the natural occurring RNA aptamer domain of the guanine-sensing riboswitch comprising 73 nucleotides from Bacillus subtilis. The work includes protocols for improved in vitro transcription of 2-fluoroadenosine-5′-triphosphat (2F-ATP) using the mutant P266L of the T7 RNA polymerase. Our NMR analysis shows that the secondary and tertiary structure of the riboswitch is fully maintained and that the specific binding of the cognate ligand hypoxanthine is not impaired by the introduction of the [superscript 19]F isotope. The thermal stability of the [superscript 19]F-labeled riboswitch is not altered compared to the unmodified sequence, but local base pair stabilities, as measured by hydrogen exchange experiments, are modulated. The characteristic change in the chemical shift of the imino resonances detected in a 1H,15N-HSQC allow the identification of Watson–Crick base paired uridine signals and the [superscript 19]F resonances can be used as reporters for tertiary and secondary structure transitions, confirming the potential of [superscript 19]F-labeling even for sizeable RNAs in the range of 70 nucleotides.Deutsche Forschungsgemeinschaft (collaborative research center: SFB902

Caesium bis­(5-bromo­salicyl­aldehyde thio­semicarbazonato-κ3O,N,S)ferrate(III): supramolecular arrangement of low-spin FeIII complex anions mediated by Cs+ cations

The synthesis and crystal structure determination (at 293 K) of the title complex, Cs[Fe(C8H6BrN3OS)2], are reported. The compound is composed of two dianionic O,N,S-tridentate 5-bromo­salicyl­aldehyde thio­semicarbazonate(2-) ligands coord­inated to an FeIII cation, displaying a distorted octa­hedral geometry. The ligands are orientated in two perpendicular planes, with the O- and S-donor atoms in cis positions and the N-donor atoms in trans positions. The complex displays inter­molecular N-H...O and N-H...Br hydrogen bonds, creating R44(18) rings, which link the FeIII units in the a and b directions. The FeIII cation is in the low-spin state at 293 K

Synonymous codons direct cotranslational folding toward different protein conformations.

In all genomes, most amino acids are encoded by more than one codon. Synonymous codons can modulate protein production and folding, but the mechanism connecting codon usage to protein homeostasis is not known. Here we show that synonymous codon variants in the gene encoding gamma-B crystallin, a mammalian eye-lens protein, modulate the rates of translation and cotranslational folding of protein domains monitored in real time by Forster resonance energy transfer and fluorescence-intensity changes. Gamma-B crystallins produced from mRNAs with changed codon bias have the same amino acid sequence but attain different conformations, as indicated by altered invivo stability and invitro protease resistance. 2D NMR spectroscopic data suggest that structural differences are associated with different cysteine oxidation states of the purified proteins, providing a link between translation, folding, and the structures of isolated proteins. Thus, synonymous codons provide a secondary code for protein folding in the cell

Lars Vegard:key communicator and pioneer crystallographer

The Norwegian physicist Lars Vegard studied with William H. Bragg in Leeds and then with Wilhelm Wien in Würzburg. There, in 1912, he heard a lecture by Max Laue describing the first X-ray diffraction experiments and took accurate notes which he promptly sent to Bragg. Although now remembered mainly for his work on the physics of the aurora borealis, Vegard also did important pioneering work in three areas of crystallography. He derived chemical insight from a series of related crystal structures that he determined, Vegard's Law relates the unit-cell dimensions of mixed crystals to those of the pure components, and he determined some of the first crystal structures of gases solidified at cryogenic temperatures