Horst Puschmann

OLEX2: a complete structure solution, refinement and analysis program

New software, OLEX2, has been developed for the determination, visualization and analysis of molecular crystal structures. The software has a portable mouse-driven workflow-oriented and fully comprehensive graphical user interface for structure solution, refinement and report generation, as well as novel tools for structure analysis. OLEX2 seamlessly links all aspects of the structure solution, refinement and publication process and presents them in a single workflow-driven package, with the ultimate goal of producing an application which will be useful to both chemists and crystallographers.

The anatomy of a comprehensive constrained, restrained refinement program for the modern computing environment - Olex2 dissected

An in-depth presentation is given of olex2.refine, the new refinement engine integrated in the Olex2 program.

The C-Glycosylation of Flavonoids in Cereals

Flavonoids normally accumulate in plants as O-glycosylated derivatives, but several species, including major cereal crops, predominantly synthesize flavone-C-glycosides, which are stable to hydrolysis and are biologically active both in planta and as dietary components. An enzyme (OsCGT) catalyzing the UDP-glucose-dependent C-glucosylation of 2-hydroxyflavanone precursors of flavonoids has been identified and cloned from rice (Oryza sativa ssp. indica), with a similar protein characterized in wheat (Triticum aestivum L.). OsCGT is a 49-kDa family 1 glycosyltransferase related to known O-glucosyltransferases. The recombinant enzyme C-glucosylated 2-hydroxyflavanones but had negligible O-glucosyltransferase activity with flavonoid acceptors. Enzyme chemistry studies suggested that OsCGT preferentially C-glucosylated the dibenzoylmethane tautomers formed in equilibrium with 2-hydroxyflavanones. The resulting 2-hydroxyflavanone-C-glucosides were unstable and spontaneously dehydrated in vitro to yield a mixture of 6C- and 8C-glucosyl derivatives of the respective flavones. In contrast, in planta, only the respective 6C-glucosides accumulated. Consistent with this selectivity in glycosylation product, a dehydratase activity that preferentially converted 2-hydroxyflavanone-C-glucosides to the corresponding flavone-6C-glucosides was identified in both rice and wheat. Our results demonstrate that cereal crops synthesize C-glucosylated flavones through the concerted action of a CGT and dehydratase acting on activated 2-hydroxyflavanones, as an alternative means of generating flavonoid metabolites.

Very bright europium complexes that stain cellular mitochondria

The synthesis, structure and photophysical properties of a series of highly emissive europium complexes is reported. Certain complexes enter mammalian cells by macropinocytosis and stain the mitochondria selectively, allowing observation of the Eu emission in cellulo by time-gated spectral imaging.

Structural and NMR investigations of the ternary adducts of twenty α-amino acids and selected dipeptides with a chiral, diaqua–ytterbium complex

A detailed investigation of the nature of the binding of each of the 20 common alpha-amino acids and various selected dipeptides to a chiral, diaqua-ytterbium complex in aqueous solution has been carried out. Analysis of the dipolar 1H NMR paramagnetic shifts suggests that the alpha-amino acids form a common chelated structure within a nine-coordinate mono-capped square antiprismatic coordination environment, with the amine N axially disposed. Crystal structures of nine chelated YbL1-amino acid adducts (Gly, Ala, Ser, Thr, Met) confirm this. The ternary complexes with dipeptides (e.g. Gly-Ala, Gly-Ser, Gly-Met, Gly-Asp, Gly-Asn, Gly-His, Ser-Met, Asp-Phe, His-Gly) also favour the terminal amine as the axial donor with the proximate amide group binding to generate a five-ring chelate. Evidence for chelation through side-chain functionality was found only in the case of N-terminal Asp. The chiral environment about the ytterbium ion upon amino acid binding has also been probed using near-IR circular dichroism spectroscopy.

iotbx.cif: a comprehensive CIF toolbox

iotbx.cif is a comprehensive toolbox for the development of applications that make use of the CIF format.

Nickel(II) complexes of the isomeric tetraazamacrocyclic ligands 1,11- and 1,8-bis(2-pyridylmethyl)-cyclam and of a structurally constrained N4,N8-methylene bridged analogue

Abstract The nickel(II) complexes of 1,8-bis(2′-pyridylmethyl)-1,4,8,11-tetraazacyclotetradecane (L1) and of the isomeric ligand 1,11-bis(2′-pyridylmethyl)-1,4,8,11-tetraazacyclotetradecane (L2) have been isolated. The X-ray crystal structure of a mixed acetate/chloride salt of [NiL1]2+ revealed an octahedral Ni coordination by two N atoms of the pyridine groups (in cis-related positions) and four of the macrocycle, which is folded along the 1,8-direction and bound in the cis-V configuration. The results of UV–Visible absorption spectroscopy and cyclic voltammetry in solution and the effective magnetic moments in the solid state are also consistent with octahedral N6-coordination of high-spin nickel(II). The intermediate in the synthesis of ligand L2, a bis-(2-pyridylmethyl) substituted formamidinium cation (L3)+, reacted with nickel(II) perchlorate to form a [Ni(H2L3)Cl]2+ complex incorporating a methylene bridge between the non-pyridylmethylated N atoms (N4 and N8) of the macrocycle, which was characterised by X-ray crystallography. The Ni atom has a fac-octahedral coordination by the two pyridine and three macrocyclic nitrogens (the fourth one, N4, is protonated) and one Cl atom.

Structure, resolution and chiroptical analysis of stable lanthanide complexes of a pyridylphenylphosphinate triazacyclononane ligand

Lanthanide complexes of a pyridylphenylphosphinate ligand based on triazacyclononane form an isostructural series. The C(3)-symmetric Δ and Λ complexes of Eu and Tb are strongly emissive and can be resolved by chiral HPLC; the absolute configuration of each complex has been assigned using CD and CPL measurements.

Synthesis and structure of 4,4′-bis(2,3,4,5,6-pentafluorostyryl)stilbene, a self-assembling J aggregate based on aryl–fluoroaryl interactions

The synthesis and characterisation of 4,4′-bis(2,3,4,5,6-pentafluorostyryl)stilbene is described; this molecule forms a J aggregate by self-assembly based on aryl–fluoroaryl interactions.

Some nickel(II) β-amino-ketone and β-amino-imine compounds; the structures of mer-bis(7-amino-4,4-dimethyl-5-azaheptan-2-one)nickel(II) perchlorate, (2,7,9,9-tetramethyl-3,6,10-triazadodeca-2,6-diene-12-amine)nickel(II) tetrachlorozincate water and (4,6,6-trimethyl-3,7-diazanon-3-ene-1,9-diamine)(nitrito-O,O′)nickel(II) perchlorate

Abstract Reactions of ethane-1,2-diamine compounds of nickel(II) with acetone can yield a variety of products, depending upon conditions. Reaction of [Ni(en) 2 ](ClO 4 ) 2 with acetone forms [Ni(amket) 2 ](ClO 4 ) 2 , which has nickel(II) in octahedral mer -coordination by two tridentate 7-amino-4,4-dimethyl-5-azaheptan-2-one ligands. The secondary amine groups are coordinated trans [NiN mean =2.104(8) A, NNiN=173.1(2)°] and the ketone [NiO mean =2.077(7) A, ONiO=86.6(2)°] and primary amine [NiN mean =2.100(8) A, NNiN=92.3(2)°] groups are coordinated cis . Compounds with the tetradentate ligand 2,7,9,9-tetramethyl-3,6,10-triazadodeca-2,6-diene-12-amine, enacim, which incorporates two diamine and three acetone residues, are formed by the same reactants in the presence of coordinating anions or solvents. The salt [Ni(enacim)][ZnCl 4 ]·H 2 O, formed by refluxing [Ni(en) 3 ][ZnCl 4 ] in acetone/methanol, has a square-planar cation, with distances: NiN(3) (terminal imine)=1.894(4), NiN(6) (internal imine)=1.922(4), NiN(10) (secondary amine)=1.912(4) and NiN(13) (primary amine)=1.915(4) A. The N -isopropylidene imine function of [Ni(enacim)] 2+ is slowly hydrolysed to form [Ni(enac)] 2+ with the tetradentate ligand 4,6,6-trimethyl-3,7-diazanon-3-ene-1,9-diamine, which incorporates two acetone and two diamine residues. A nitrito compound of this cation, [Ni(enac)(NO 2 )]ClO 4 , has two independent but similar cations with the enac ligand in folded coordination with asymmetric O , O ′-chelate nitrito ions completing distorted octahedral coordination [mean dimensions: NiN amine =2.116(4), NiN imine =2.053(4), NiO=2.113(4) and 2.237(4) A, ONiO=57.2(2)°]. Preparations of [Ni(enac)(NO 2 )]ClO 4 , [Ni(enacim)][ZnCl 4 ]·H 2 O, [Ni(enac)](NCS) 2 and [Ni(enacim)(NCS) 2 ] and improved preparations of [Ni(enac)](ClO 4 ) 2 and [Ni(enacim)](ClO 4 ) 2 are reported.