Exploration of triple-helical fragments : crystallization and preliminary X-ray diffraction of d(TGGCCTTAAGG)

The nonamer d(GCGAATTCG) and decamer d(GGCCAATTGG), containing one and two overhanging guanines, respectively, form G (.) GC triplets in their crystal packing. In order to introduce a third subsequent T (.) AT triplet, the decamer was further extended by one overhanging thymine residue. Two different crystal morphologies of the sequence d(TGGCCTTAAGG) were obtained by hanging-drop vapour diffusion and diffracted to 2.5 and 2.3 angstrom resolution, respectively. However, both crystals belong to the orthorhombic space group P2(1)2(1)2(1), with similar unit-cell parameters. Therefore, the two data sets could be merged to a resolution of 2.4 angstrom with unit-cell parameters a = 26.97, b = 41.12, c = 52.72 angstrom

Tris(1-ethyl-3-methyl­imidazolium) hexa­bromidoeuropate(III)

The crystal structure of the title compound, (C6H11N2)3[EuBr6], consists of 1-ethyl-3-methyl­imidazolium cations and centrosymmetric octa­hedral hexa­bromido­europate anions. The [EuBr6]3− anions are located at the corners and face-centres of the monoclinic unit cell. Characteristic hydrogen-bonding inter­actions can be observed between the bromide anions and the acidic H atoms of the imidazolium cations

Synthesis and post-functionalization of alternate-linked-meta-para-[2(n). 1(n)]thiacyclophanes

In recent decades, considerable research attention has been devoted to new synthetic procedures for thiacyclophanes. Thiacyclophanes are widely used as host molecules for the molecular recognition of organic compounds as well as metals. Herein, we report the selective and high-yielding synthesis of novel alternate-linked-meta-para-thiacyclophanes. These novel thiacyclophanes are selectively synthesized in high-yielding procedures. Furthermore, post-functionalization of the phenolic moieties was successfully performed. The 3D structure of the alternate-linked-meta-para-[22.12]thiacyclophane was further elucidated via X-ray crystallographic analysis

trans-Chlorido[6-chloro-4-(4-methoxy­benz­yl)-3-oxo-3,4-dihydro­pyrazin-2-yl]­bis­(triphenyl­phosphine)palladium(II)

The title compound, [Pd(C12H10ClN2O2)Cl(C18H15P)2], is the inter­mediate of the reduction of a 3,5-dichloro­pyrazinone [Loosen, Tutonda, Khorasani, Compernolle & Hoornaert (1991 ▶). Tetra­hedron, 47, 9259–9268]. This species is formed by oxidative addition of coordinatively unsaturated Pd0 to the reactive 3-position of the heterocycle. The coordination around the Pd atom is square planar, with two trans PPh3 ligands. π–π inter­actions are observed between the centroid of the pyrazinone ring and planes of two adjacent phenyl rings, one from each PPh3 group (3.25 and 3.078 Å), stabilizing the inter­mediate structure. This could explain the reduced reactivity towards substitution of the Cl atom by the formate anion, resulting in poor yield of the reduced compound. 3-Substituted pyrazinones are important precursors in the synthesis of 5-amino­piperidinone-2-carboxyl­ate (APC) systems

Stereoselective Syntheses and Application of Chiral Bi- and Tridentate Ligands Derived from (+)-Sabinol

A library of bidentate diols, as well as tridentate triols and aminodiols, derived from (+)-sabinol, was synthesized in a stereoselective manner. Sabinol was transformed into allylic trichloroacetamide via Overman rearrangement of the corresponding trichloroacetimidate. After changing the protecting group to Boc, the enamine was subjected to stereospecific dihydroxylation with OsO4/NMO, resulting in the (1R,2R,3R,5R)-aminodiol diastereomer. The obtained primary aminodiol was transformed to a secondary analogue. The ring closure of the N-benzyl-substituted aminodiol with formaldehyde was investigated and regioselective formation of the spiro-oxazolidine ring was observed. Hydroboration or dihydroxylation of sabinol or its benzyl ether with OsO4/NMO resulted in the formation of sabinane-based diols and triols following a highly stereospecific reaction. Treatment of sabinol with m-CPBA afforded O-benzoyl triol as a diastereoisomer of the directly dihydroxylated product, instead of the expected epoxy alcohol. The resulting aminodiols, diol, and triols were applied as chiral catalysts in the reaction of diethylzinc and benzaldehyde from moderate to good selectivity

Revisiting the planarity of nucleic acid bases: Pyramidilization at glycosidic nitrogen in purine bases is modulated by orientation of glycosidic torsion

We describe a novel, fundamental property of nucleobase structure, namely, pyramidilization at the N1/9 sites of purine and pyrimidine bases. Through a combined analyses of ultra-high-resolution X-ray structures of both oligonucleotides extracted from the Nucleic Acid Database and isolated nucleotides and nucleosides from the Cambridge Structural Database, together with a series of quantum chemical calculations, molecular dynamics (MD) simulations, and published solution nuclear magnetic resonance (NMR) data, we show that pyramidilization at the glycosidic nitrogen is an intrinsic property. This property is common to isolated nucleosides and nucleotides as well as oligonucleotides—it is also common to both RNA and DNA. Our analysis suggests that pyramidilization at N1/9 sites depends in a systematic way on the local structure of the nucleoside. Of note, the pyramidilization undergoes stereo-inversion upon reorientation of the glycosidic bond. The extent of the pyramidilization is further modulated by the conformation of the sugar ring. The observed pyramidilization is more pronounced for purine bases, while for pyrimidines it is negligible. We discuss how the assumption of nucleic acid base planarity can lead to systematic errors in determining the conformation of nucleotides from experimental data and from unconstrained MD simulations

Can participative coach behavior be perceived as controlling? The role of athletes’ expectations

Study on the importance of an alignment between athletes' expectations for participation and coach-rated participative behaviors in developing domineering perceptions in athletes

Refinement of the crystal structure of dichloro-bis(pyridine-N)-copper(II), C10H10Cl2CuN2, at 100 K

C10H10Cl2CuN2, monoclinic, P12(1)/n1 (No. 14), a = 3.7911(2) Angstrom, b = 8.5205(3) Angstrom, c = 16.9910(7) Angstrom, beta = 91.973(3)degrees, V = 548.5 Angstrom(3), Z = 2, R-gt(F) = 0.033, wR(ref)(F-2) = 0.086, T = 100 K.status: publishe

Direct observation of two cyclohexenyl (CeNA) ring conformations in duplex DNA

Cyclohexene Nucleic Acids (CeNA), in which the 2′-deoxyribofuranose ring of the DNA building blocks is substituted by a cyclohexenyl ring, were designed as potential mimics of natural nucleic acids for antisense and, later, for siRNA applications. CeNA units, in contrast to HNA (hexitol nucleic acid) building blocks, show more flexibility at the level of the C2′–C3′ bond due to the possibility of the cyclohexenyl moiety to adopt different conformations. In order to analyze the influence of CeNA residues onto the helix conformation and hydration of natural nucleic acid structures and to verify the cyclohexenyl ring conformation, a cyclohexenyl-thymine building block was incorporated into the non-self-complementary sequence d(GCG(xT)GCG)/d(CGCACGC) with (xT) a cyclohexene residue. The crystal structure of this sequence has been determined to a resolution of 1.17 Å and contains two duplexes in the asymmetric unit. The global helices belong to the B-type family and the conformations of the cyclohexenyl rings in both duplexes are different. The cyclohexene ring adopts as well the 2H3-conformation (similar to C2′-endo) as the 3H2-conformation (similar to C3′-endo). The crystal packing is stabilized by cobalt hexamine residues and triplet formation

Crystal structure of tris(N-(n-butyl)-4-methoxy-2-hydroxybenzaldimine)tris(nitrato)europium(III), Eu(LH)(3)(NO3)(3)

C36H51EuN6O15, triclinic, P (1) over bar (No. 2), a = 11.426(3) Angstrom, b = 13.842(3) Angstrom, c = 14.080(3) Angstrom, alpha = 98.58(1)degrees, beta = 98.46(1)degrees, gamma = 92.52(2)degrees, V = 2173.1 Angstrom(3), Z = 2, R-gt(F) = 0.047, wR(ref)(F-2) = 0.113, T = 289 K.status: publishe