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1.  Dichloridobis(pyridine-2-thiol­ato-κ2 N,S)tin(IV): a new polymorph 
The title compound, [SnCl2(C5H4NS)2], is the product of reaction of 2,2′-dipyridyl disulfide with tin tetra­chloride. The SnIV atom adopts a distorted octa­hedral geometry, with the two bidentate pyridine-2-thiol­ate ligands forming two planar four-membered chelate rings. The two Sn—Cl, two Sn—N and two Sn—S bonds are in cis, cis and trans configurations, respectively. The crystal grown from acetonitrile represents a new monoclinic polymorph in space group C2/c with the mol­ecule having twofold rotational symmetry, the SnIV atom lying on the twofold axis. The mol­ecular structure of the monoclinic polymorph is very close to that of the triclinic polymorph studied previously in space group P-1, the mol­ecule occupying a general position [Masaki & Matsunami (1976 ▶). Bull. Chem. Soc. Jpn, 49, 3274–3279; Masaki et al. (1978 ▶). Bull. Chem. Soc. Jpn, 51, 3298–3301]. Apparently, the formation of the two polymorphs is determined by the different systems of inter­molecular inter­actions. In the crystal of the monoclinic polymorph, mol­ecules are bound into ribbons along the c axis by C—H⋯Cl hydrogen bonds, whereas in the crystal of the triclinic polymorph, mol­ecules form chains along the a axis by attractive S⋯S inter­actions. The crystal studied was a pseudo-merohedral twin; the refined BASF value is 0.221 (1).
PMCID: PMC3393155  PMID: 22807723
2.  Imperfect pseudo-merohedral twinning in crystals of fungal fatty acid synthase 
A case of imperfect pseudo-merohedral twinning in monoclinic crystals of fungal fatty acid synthase is discussed. A space-group transition during crystal dehydration resulted in a Moiré pattern-like interference of the twinned diffraction patterns.
The recent high-resolution structures of fungal fatty acid synthase (FAS) have provided new insights into the principles of fatty acid biosynthesis by large multifunctional enzymes. The crystallographic phase problem for the 2.6 MDa fungal FAS was initially solved to 5 Å resolution using two crystal forms from Thermomyces lanuginosus. Monoclinic crystals in space group P21 were obtained from orthorhombic crystals in space group P212121 by dehydration. Here, it is shown how this space-group transition induced imperfect pseudo-merohedral twinning in the monoclinic crystal, giving rise to a Moiré pattern-like interference of the two twin-related reciprocal lattices. The strategy for processing the twinned diffraction images and obtaining a quantitative analysis is presented. The twinning is also related to the packing of the molecules in the two crystal forms, which was derived from self-rotation function analysis and molecular-replacement solutions using a low-resolution electron microscopy map as a search model.
PMCID: PMC2631638  PMID: 19171964
imperfect pseudo-merohedral twinning; fungal fatty acid synthase
3.  Pseudomerohedrally twinned monoclinic structure of unfolded ‘free’ nona­ctin: comparative analysis of its large conformational change upon encapsulation of alkali metal ions 
The title compound, C40H64O12, crystallizes in a pseudo­merohedrally twinned primitive monoclinic cell with similar contributions of the two twin components. There are two symmetry-independent half-mol­ecules of nona­ctin in the asymmetric unit. Each mol­ecule has a pseudo-S 4 symmetry and resides on a crystallographic twofold axis; the axes pass through the mol­ecular center of mass and are perpendicular to the plane of the macrocycle. The literature description of the room-temperature structure of nona­ctin as an order–disorder structure in an ortho­rhom­bic unit cell is corrected. We report a low-temperature high-precision ordered structure of ‘free’ nona­ctin that allowed for the first time precise determination of its bond distances and angles. It possesses an unfolded and more planar geometry than its complexes with encapsulated Na+, K+, Cs+, Ca2+ or NH4 + cations that exhibit more isometric overall conformations.
PMCID: PMC2816929  PMID: 19805886
4.  Tris(cyclo­hexyl­ammonium) cis-di­chlorido­bis­(oxalato-κ2 O 1,O 2)stann­ate(IV) chloride monohydrate 
The crystal structure of the title compound, (C6H14N)3[Sn(C2O4)2Cl2]Cl·H2O, contains three cyclo­hexyl­ammonium cations, one stannate(IV) dianion, one isolated chloride anion and one lattice water mol­ecule. The cyclo­hexyl­ammonium cations adopt chair conformations. In the complex anion, two bidentate oxalate ligands and two chloride anions in cis positions coordinate octa­hedrally to the central SnIV atom. The cohesion of the mol­ecular entities is ensured by the formation of N—H⋯O, O—H⋯O, O—H⋯Cl and N—H⋯Cl inter­actions involving cations, anions and the lattice water mol­ecule, giving rise to a layer-like arrangement parallel to (010).
PMCID: PMC3884246  PMID: 24454022
5.  Chlorido{4,4′,6,6′-tetra-tert-butyl-2,2′-[o-phenyl­enebis(nitrilo­methyl­idyne)]diphenolato-κ4 O,N,N′,O′}manganese(III) 
The asymmetric unit of the title Schiff base complex, [Mn(C36H46N2O2)Cl], comprises two crystallographically independent mol­ecules. The MnIII centre in each mol­ecule adopts a distorted square-pyramidal geometry. Each MnIII ion is coordinated by the N2O2 atoms of the tetra­dentate Schiff base ligand forming the basal plane and the coordinated chloride anion occupies the apical position. Four bifurcated intra­molecular C—H⋯O contacts stabilize the mol­ecular structure. In the crystal packing, mol­ecules are linked into dimers via inter­molecular C—H⋯Cl contacts and further stabilized by C—H⋯π inter­actions. The crystal studied was a non-merohedral twin, the refined ratio of the twin components being 0.441 (1):0.559 (1).
PMCID: PMC2971881  PMID: 21578697
6.  Monohalogenated ferrocenes C5H5FeC5H4 X (X = Cl, Br and I) and a second polymorph of C5H5FeC5H4I 
The structures of the three title monosubstituted ferrocenes, namely 1-chloro­ferrocene, [Fe(C5H5)(C5H4Cl)], (I), 1-bromo­ferrocene, [Fe(C5H5)(C5H4Br)], (II), and 1-iodo­ferrocene, [Fe(C5H5)(C5H4I)], (III), were determined at 100 K. The chloro- and bromo­ferrocenes are isomorphous crystals. The new triclinic polymorph [space group P , Z = 4, T = 100 K, V = 943.8 (4) Å3] of iodo­ferrocene, (III), and the previously reported monoclinic polymorph of (III) [Laus, Wurst & Schottenberger (2005 ▶). Z. Kristallogr. New Cryst. Struct. 220, 229–230; space group Pc, Z = 4, T = 100 K, V = 924.9 Å3] were obtained by crystallization from ethanolic solutions at 253 and 303 K, respectively. All four phases contain two independent mol­ecules in the unit cell. The relative orientations of the cyclo­penta­dienyl (Cp) rings are eclipsed and staggered in the independent mol­ecules of (I) and (II), while (III) demonstrates only an eclipsed conformation. The triclinic and monoclinic polymorphs of (III) contain nonbonded inter­molecular I⋯I contacts, causing different packing modes. In the triclinic form of (III), the mol­ecules are arranged in zigzag tetra­mers, while in the monoclinic form the mol­ecules are arranged in zigzag chains along the a axis. Crystallographic data for (III), along with the computed lattice energies of the two polymorphs, suggest that the monoclinic form is more stable.
PMCID: PMC2773730  PMID: 19893225
7.  Crystal structure of μ-1κC:2(η2)-carbonyl-carbonyl-1κC-chlorido-2κCl-μ-chlorido­borylene-1:2κ2 B:B-[1(η5)-penta­methyl­cyclo­penta­dien­yl](tri­cyclo­hexyl­phosphane-2κP)iron(II)platinum(II) benzene monosolvate 
The title compound [η5-(C5(CH3)5)(CO)Fe{(μ-BCl)(μ-CO)}PtCl(P(C6H11)3)]·C6H6 shows a piano-stool coordination geometry at the FeII atom and a distorted square-planar coordination geometry at the Pt atom. Both metals are bridged by one carbonyl and one chlorido­borylene unit. Additionally, one benzene solvent mol­ecule aligns in a staggered position relative to the (penta­meth­yl)cyclo­penta­dienyl ligand of the FeII centre.
In the mol­ecular structure of the dinuclear title compound [η5-(C5(CH3)5)(CO)Fe{(μ-BCl)(μ-CO)}PtCl(P(C6H11)3)]·C6H6, the two metal atoms, iron(II) and platinum(II), are bridged by one carbonyl (μ-CO) and one chlorido­borylene ligand (μ-BCl). The PtII atom is additionally bound to a chloride ligand situated trans to the bridging borylene, and a tri­cyclo­hexyl­phosphane ligand (PCy3) trans to the carbonyl ligand, forming a distorted square-planar structural motif at the PtII atom. The FeII atom is bound to a penta­methyl­cyclo­penta­dienyl ligand [η5-C5(CH3)5] and one carbonyl ligand (CO), forming a piano-stool structure. Additionally, one benzene solvent mol­ecule is incorporated into the crystal structure, positioned staggered relative to the penta­methyl­cyclo­penta­dienyl ligand at the FeII atom, with a centroid–centroid separation of 3.630 (2) Å.
PMCID: PMC4257242  PMID: 25484763
crystal structure; heterodinuclear compound; borylene; platinum; oxidative addition
8.  Chlorido[1-(diphenyl­phosphan­yl)cobaltocenium]gold(I) hexa­fluoridophosphate 
In the cobaltocenium group of the title compound, [AuCo(C5H5)(C17H14P)Cl]PF6, the substituted cyclo­penta­dienyl (Cps) and the unsubstituted cyclo­penta­dienyl (Cp) ring planes are almost parallel, making a dihedral angle of 3.1 (3)°. The C atoms in Cp and Cps are in an eclipsed conformation. The AuI atom is coordinated by a P atom from the diphenyl­phosphanyl group and a Cl atom in an almost linear arrangement [P—Au—Cl = 178.15–(7)°]. Two hexa­fluorido­phosphate anions are each located on a twofold rotation axis. In the crystal, the complex cations and hexa­fluorido­phosphate anions are linked via inter­molecular C—H⋯F hydrogen bonds.
PMCID: PMC3120450  PMID: 21754675
9.  Di-μ-chlorido-bis­[diacetonitrile­chlorido­oxidovanadium(IV)] 
The title compound, [V2Cl4O2(CH3CN)4], is a centrosymmetric dinuclear VIV complex associated with four mol­ecules of acetonitrile. The coordination around both VIV atoms is essentially square-planar, involving three Cl atoms and one O atom [maximum deviation = 0.017 (3) Å for the O atom]. The augmented octahedral coordination of the metal atom is completed by the N atoms of acetonitrile ligands. The VIV atoms are linked by two Cl atoms, acting as bridging atoms. The crystal studied was a non-merohedral twin with a ratio of the two twin components of 0.8200 (3):0.1800 (3). Although Cl and O atoms are present as potential acceptors in the title compound, no hydrogen bonds were observed in the crystal structure.
PMCID: PMC3201240  PMID: 22058702
10.  Bis(cyclo­hexyl­ammonium) tetra­chlorido­diphenyl­stannate(IV) 
The title compound, (C6H14N)2[Sn(C6H5)2Cl4], contains cyclo­hexyl­ammonium cations in general positions and a stannate(IV) anion that is located on a twofold rotation axis. The SnIV atom in the complex anion is surrounded by four Cl− ligands and two trans-phenyl groups in a distorted octa­hedral configuration. The anions are connected with the cations through N—H⋯Cl hydrogen bonds. Every cation is involved in three N—H⋯Cl bonds to the chloride ligands of three different anions, and each chloride ligand is linked to two cations. This arrangement leads to a layered structure parallel to (010).
PMCID: PMC4051057  PMID: 24940206
11.  Crystal structure of di­chlorido­bis­(1,3-diisopropyl-4,5-dimethyl-2H-imidazole-2-thione-κS)zinc(II) 
The mol­ecular structure of the title compound, [ZnCl2(C11H20N2S)2], shows tetra­hedral Zn coordination from two Cl ligands and two thione groups. The Zn—Cl bond lengths differ sligthly at 2.2310 (10) and 2.2396 (11) Å while the Zn—S bond lengths are equal at 2.3663 (9) and 2.3701 (10) Å. The Cl—Zn—Cl angle is 116.04 (4) and S—Zn—S is 101.98 (3)°. All other angles at the central Zn atom range from 108.108 (3) to 110.21 (4)°. The C—S—Zn angles are 100.75 (10) and 103.68 (11)°, the difference most probably resulting from packing effects, as both the C—S and both the S—Zn bonds are equal in each case. The two imidazole ring planes make a dihedral angle of 67.9 (1)°. The CH3 groups of one isopropyl moiety are disordered over two sets of sites with occupation factors of 0.567 (15) and 0.433 (15). It may be noteworthy that the isomolecular Cu complex shows a different crystal packing (group–subgroup relation) with the Cu atom lying on a twofold rotation axis. In the crystal, the shortest non-bonding contact is a C—H⋯Cl inter­action. This leads to the formation of centrosymmetric dimers that are stacked along the c-axis.
PMCID: PMC4257301  PMID: 25484787
crystal structure; imidazoline­thio­nes; zinc(II) complex,
12.  A second polymorph of chlorido(hydroxy­diphenyl­phosphane)gold(I) 
The title complex, [AuCl{(C6H5)2P(OH)-κP}] or [AuCl(C12H11OP)], contains two independent mol­ecules in the asymmetric unit and is a polymorph of a previously reported structure [Hollatz et al. (1999 ▶) J. Chem. Soc. Dalton Trans. pp. 111–114]. The crystal structure exhibits inter­molecular Au⋯Au inter­actions with alternate distances of 3.0112 (3) Å and 3.0375 (2) Å. The Cl—Au—P bond angle varies between different mol­ecular units, depending on the degree of influence of the intra­molecular the O—H⋯Cl hydrogen bond; the angle thus varies between negligible distortion from linearity at 179.23 (3)° and more significant distortion at 170.39 (4)°, which differs from the previously reported polymorph in which both these angles are approximately 170°. The Au—Cl [2.3366 (9) and 2.3131 (10)Å] and Au—P [2.2304 (10) and 2.2254 (10) Å] bond lengths vary slightly between the two independent mol­ecules but overall, the bond lengths are in good agreement with those in the previously reported polymorph.
PMCID: PMC3201275  PMID: 22058683
13.  Pseudo-merohedral twinning and noncrystallographic symmetry in orthorhombic crystals of SIVmac239 Nef core domain bound to different-length TCRζ fragments 
P212121 crystals of SIV Nef core domain bound to a peptide fragment of the T-cell receptor ζ subunit exhibited noncrystallographic symmetry and nearly perfect pseudo-merohedral twinning simulating tetragonal symmetry. For a different peptide fragment, nontwinned tetragonal crystals were observed but diffracted to lower resolution. The structure was determined after assignment of the top molecular-replacement solutions to various twin or NCS domains followed by refinement under the appropriate twin law.
HIV/SIV Nef mediates many cellular processes through interactions with various cytoplasmic and membrane-associated host proteins, including the signalling ζ subunit of the T-­cell receptor (TCRζ). Here, the crystallization strategy, methods and refinement procedures used to solve the structures of the core domain of the SIVmac239 isolate of Nef (Nefcore) in complex with two different TCRζ fragments are described. The structure of SIVmac239 Nefcore bound to the longer TCRζ polypeptide (Leu51–Asp93) was determined to 3.7 Å resolution (R work = 28.7%) in the tetragonal space group P43212. The structure of SIVmac239 Nefcore in complex with the shorter TCRζ polypeptide (Ala63–Arg80) was determined to 2.05 Å resolution (R work = 17.0%), but only after the detection of nearly perfect pseudo-merohedral crystal twinning and proper assignment of the orthorhombic space group P212121. The reduction in crystal space-group symmetry induced by the truncated TCRζ polypeptide appears to be caused by the rearrangement of crystal-contact hydrogen-bonding networks and the substitution of crystallographic symmetry operations by similar noncrystallographic symmetry (NCS) operations. The combination of NCS rotations that were nearly parallel to the twin operation (k, h, −l) and a and b unit-cell parameters that were nearly identical predisposed the P212121 crystal form to pseudo-merohedral twinning.
PMCID: PMC2815668  PMID: 20124696
pseudo-merohedral twinning; noncrystallographic symmetry; pseudosymmetry; human immunodeficiency virus; Nef; T-cell receptor
14.  [μ-Bis(diphenyl­arsino)methane-1:2κ2 As:As’]nona­carbonyl-1κ3 C,2κ3 C,3κ3 C-(triphenyl phosphite-3κP)-triangulo-triruthenium(0) 
The asymmetric unit of the title triangulo-triruthenium compound, [Ru3(C25H22As2)(C18H15O3P)(CO)9], contains two crystallographically independent but similar mol­ecules. The bis­(diphenyl­arsino)methane ligand bridges an Ru—Ru bond and the monodentate phosphite ligand bonds to the third Ru atom. Both the phosphite and arsine ligands are equatorial with respect to the Ru3 triangle. In addition, each Ru atom carries one equatorial and two axial terminal carbonyl ligands. One of the triphenyl­phosphite benzene rings in one of the mol­ecules is disordered over two positions with refined site occupancies of 0.60 (3) and 0.40 (3). In the crystal packing, the mol­ecules are stacked along a axis. Intra­molecular C—H⋯O hydrogen bonds stabilize the mol­ecular structure and weak inter­molecular C—H⋯π inter­actions further stabilize the crystal structure. The crystal studied was a non-merohedral twin, the refined ratio of the twin components being 0.618 (1):0.382 (1).
PMCID: PMC2979706  PMID: 21579683
15.  Bis{μ-2-[(dimethyl­amino)­meth­yl]benzene­tellurolato}bis­[chlorido­palladium(II)] dichloro­methane hemisolvate 
The asymmetric unit of the title compound, [Pd2(C9H12NTe)2Cl2]·0.5CH2Cl2, contains two half-mol­ecules, each lying on a twofold rotation axis; each mol­ecule is chiral and of the same enanti­omer. This is only possible as the mol­ecule has a hinged cis arrangement about the Pd2+ coordination spheres. For this hinged dimeric structure, the angles between the two coordination planes in each mol­ecule are 21.59 (4) and 22.10 (4)°. This hinged cis arrangement also allows the two mol­ecules to form pairs linked by secondary inter­actions between the Pd and Te atoms of an adjoining mol­ecule, leading to a tetra­meric overall structure. C—H⋯Cl inter­actions consolidate the crystal packing.
PMCID: PMC3274876  PMID: 22346823
16.  Chlorido[tris­(3-fluoro­phen­yl)phosphine]gold(I) 
In the title gold complex, [AuCl(C18H12F3P)], the P—Au—Cl unit is nearly linear, with an angle of 178.13 (5)°. The three phosphine-substituted benzene rings make dihedral angles of 77.7 (3), 84.4 (3) and 77.4 (3)° with each other. Two of the three F atoms are disordered over two positions, with refined site occupancies of 0.591 (11):0.409 (11) and 0.730 (12):0.270 (12). In the crystal structure, mol­ecules are linked into a three-dimensional network by inter­molecular C—H⋯Cl and C—H⋯F hydrogen bonds.
PMCID: PMC2983311  PMID: 21587375
17.  A 3,5-dinitro­benzoyl derivative of a stereoisomer of glycerol menthonide 
The title compound, [(2S,5R,6S,9R)-6-isopropyl-9-methyl-1,4-dioxaspiro­[4.5]dec-2-yl]methyl 3,5-dinitro­benzoate, C20H26N2O8, was synthesized as part of a study of three-carbon stereochemical systems. The crystallographic assignment of the absolute stereochemistry is consistent with having started with (−)-menthone, the acetal carbon is R and the secondary alcohol is S. This brings the dinitro­benzoate into approximately the same plane as the menthyl ring and anti to the isopropyl group. Close inter­molecular C=O⋯NO2 contacts between neighboring mol­ecules [2.8341 (16) Å] contribute to the packing arrangement. The structure was refined as a pseudo-merohedral twin (monoclinic space group P21 emulating the ortho­rhom­bic space group C2221). Application of the twin law 100, 00, 0 gave a 2:1 ratio of twin moieties [refined BASF value = 0.3790 (7)].
PMCID: PMC2969335  PMID: 21582828
18.  Chlorido(5-formyl-2-hydroxy­phenyl-κC 1)mercury(II) 
In the planar (r.m.s. deviation = 0.027 Å) title compound, [Hg(C7H5O2)Cl], the HgII atom shows a typical linear coordination by a C atom of the benzene ring and a Cl atom. Inter­molecular O—H⋯O hydrogen bonds are present in the crystal structure, resulting in chains propagating along the b axis. The crystal studied was a non-merohedral twin, with a twin ratio of 0.802 (2):0.198 (2).
PMCID: PMC2971446  PMID: 21578177
19.  [μ-Bis(diphenyl­arsino)methane-1:2κ2 As:As′]nona­carbonyl-1κ3 C,2κ3 C,3κ3 C-tricyclo­hexyl­phosphine-3κP-triangulo-triruthenium(0) 
In the title triangulo-triruthenium compound, [Ru3(C25H22As2)(C18H33P)(CO)9], the bis­(diphenyl­arsino)methane ligand bridges an Ru—Ru bond and the monodentate phosphine ligand bonds to the third Ru atom. Both the phosphine and arsine ligands are equatorial with respect to the Ru3 triangle. In addition, each Ru atom carries one equatorial and two axial terminal carbonyl ligands. All three cyclo­hexane rings are disordered over two positions with site occupancies of 0.628 (6) and 0.372 (6). The mean planes of these three phosphine-substituted cyclo­hexane rings make dihedral angles of 53.0 (8), 68.3 (6) and 89.9 (7)° (major components), and 46.7 (14), 41.3 (11) and 75.8 (10)° (minor components) with each other. The dihedral angles between the two phenyl rings are 85.0 (2) and 88.1 (2)° for the two diphenyl­arsino groups. Two cyclo­hexane rings adopt a chair conformation whereas the other adopts a slightly twisted chair conformation for the major components; these conformations are similiar for the minor components. Intra­molecular C—H⋯O hydrogen bonds stabilize the mol­ecular structure. In the crystal packing, the mol­ecules are linked together into chains via inter­molecular C—H⋯O hydrogen bonds down the a axis. Weak inter­molecular C—H⋯π inter­actions further stabilize the crystal structure.
PMCID: PMC2972057  PMID: 21578646
20.  Three crystal forms of the bifunctional enzyme proline utilization A (PutA) from Bradyrhizobium japonicum  
The first diffraction-quality crystals of a PutA protein are reported. One of the three crystal forms described here exhibits pseudo-merohedral twinning. Removal of the N-terminal histidine tag aided the crystallization of another form.
Proline utilization A proteins (PutAs) are large (1000–1300 residues) membrane-associated bifunctional flavoenzymes that catalyze the two-step oxidation of proline to glutamate by the sequential action of proline dehydrogenase and Δ1-pyrroline-5-carboxylate dehydrogenase domains. Here, the first successful crystallization efforts for a PutA protein are described. Three crystal forms of PutA from Bradyrhizobium japonicum are reported: apparent tetragonal, hexagonal and centered monoclinic. The apparent tetragonal and hexagonal crystals were grown in the presence of PEG 3350 and sodium formate near pH 7. The apparent tetragonal form diffracted to 2.7 Å resolution and exhibited pseudo-merohedral twinning such that the true space group is P212121 with four molecules in the asymmetric unit. The hexagonal form diffracted to 2.3 Å resolution and belonged to space group P6222 with one molecule in the asymmetric unit. Centered monoclinic crystals were grown in ammonium sulfate, diffracted to 2.3 Å resolution and had two molecules in the asymmetric unit. Removing the histidine tag was important in order to obtain the C2 crystal form.
PMCID: PMC2564878  PMID: 18931443
proline utilization A; PutA; proline catabolism; proline dehydrogenase; P5C dehydrogenase; pseudo-merohedral twinning
21.  Preliminary X-ray analysis of twinned crystals of sarcosine dimethylglycine methyltransferase from Halorhodospira halochoris  
The crystallization and preliminary X-ray diffraction analysis of sarcosine dimethylglycine methyltransferase from H. halochoris is reported.
Sarcosine dimethylglycine methyltransferase (EC is an enzyme from the extremely halophilic anaerobic bacterium Halorhodospira halochoris. This enzyme catalyzes the twofold methylation of sarcosine to betaine, with S-­adenosylmethionine (AdoMet) as the methyl-group donor. This study presents the crystallization and preliminary X-ray analysis of recombinant sarcosine dimethylglycine methyltransferase produced in Escherichia coli. Mass spectroscopy was used to determine the purity and homogeneity of the enzyme material. Two different crystal forms, which initially appeared to be hexagonal and tetragonal, were obtained. However, on analyzing the diffraction data it was discovered that both crystal forms were pseudo-merohedrally twinned. The true crystal systems were monoclinic and orthorhombic. The monoclinic crystal diffracted to a maximum of 2.15 Å resolution and the orthorhombic crystal diffracted to 1.8 Å resolution.
PMCID: PMC2720339  PMID: 19652345
sarcosine dimethylglycine methyltransferase; Halorhodospira halochoris; twinning
22.  [1,2-Bis(di­cyclo­hexyl­phosphan­yl)-1,2-dicarba-closo-dodeca­borane-2κ2 P,P′]di-μ-chlorido-1:2κ4 Cl:Cl-di­chlorido-1κ2 Cl-dimercury(II) 
The title compound, [Hg2Cl4(C26H54B10P2)], was synthesized by the reaction of 1,2-bis­(di­cyclo­hexyl­phosphan­yl)-1,2-dicarba-closo-dodeca­borane with HgCl2. Both HgII atoms show a distorted tetra­hedral coordination geometry, provided by the two bridging chloride anions and the P atoms of the diphosphanyl ligand for one metal atom, and by two bridging and two terminal chloride anions for the other. The five-membered HgP2C2 chelate ring assumes an envelope conformation, with the HgII atom displaced by 0.1650 (5) Å from the mean plane of the other four atoms (r.m.s. deviation = 0.002 Å). In the crystal, B—H⋯Cl interactions link the molecules, forming a supramolecular chain along the a-axis direction.
PMCID: PMC3998597  PMID: 24826101
23.  Cloning, expression, purification, crystallization and preliminary X-ray diffraction analysis of succinyl-diaminopimelate desuccinylase (Rv1202, DapE) from Mycobacterium tuberculosis  
Acta Crystallographica Section F  2012;68(Pt 9):1089-1093.
M. tuberculosis succinyl-diaminopimelate desuccinylase, the enzyme which catalyzes the seventh step of the lysine-biosynthesis pathway, has been cloned, expressed, purified and crystallized. Preliminary X-ray diffraction analysis indicated the presence of pseudo-merohedral twinning in space group P21, resulting in possible emulation of space group C2221.
Succinyl-diaminopimelate desuccinylase from Mycobacterium tuberculosis (DapE, Rv1202) has been cloned, heterologously expressed in Escherichia coli and purified using standard chromatographic techniques. Diffraction-quality crystals were obtained at acidic pH from ammonium sulfate and PEG and diffraction data were collected from two crystals to resolutions of 2.40 and 2.58 Å, respectively. The crystals belonged to the monoclinic space group P21, with unit-cell parameters a = 79.7, b = 76.0, c = 82.9 Å, β = 119°. The most probable content of the asymmetric unit was two molecules of DapE, which would correspond to a solvent content of 56%. Both examined crystals turned out to be pseudo-merohedrally twinned, with twin operator −h, −k, h + l and twin fractions of approximately 0.46 and 0.16, respectively.
PMCID: PMC3433205  PMID: 22949202
succinyl-diaminopimelate desuccinylase; DapE; Rv1202; Mycobacterium tuberculosis
24.  Bis(1,4-diazo­niabi­cyclo­[2.2.2]octa­ne) di-μ-chlorido-bis­[tetra­chlorido­anti­monate(III)] dihydrate 
The title salt, (C6H14N2)2[Sb2Cl10]·2H2O, was obtained by slow evaporation of an acidic solution of 1,4-di­aza­bicyclo­[2.2.2]octane and SbCl3. The crystal structure consists of (C6H14N2)2+ cations, [Sb2Cl10]4− double octa­hedra and lattice water mol­ecules. All mol­ecular components are situated on special positions. The cation and the lattice water mol­ecule exhibit mirror symmetry, whereas the anion has site symmetry 2/m. The cations, anions and water mol­ecules are alternately arranged into columns along [010]. Individual columns are joined into layers extending along (001). Intra­layer N—H⋯O and inter­layer N—H⋯Cl hydrogen-bonding inter­actions lead to the formation of a three-dimensional network.
PMCID: PMC3684890  PMID: 23794992
25.  Bis[4-(di­methyl­amino)­pyridinium] tetra­chlorido­cuprate(II) 
The asymmetric unit of the title salt, (C7H11N2)2[CuCl4], comprises half a tetrahedral tetra­chlorido­cuprate anion, being located on a twofold axis, and a protonated 4-(di­methyl­amino)­pyridine cation. The geometry around the CuII ion is highly distorted with the range of Cl—Cu—Cl angles being 94.94 (1)–141.03 (1)°. The crystal structure is stabilized by N—H⋯Cl and C—H⋯Cl hydrogen bonds. In the three-dimensional network, cations and anions pack in the lattice so as to generate chains of [CuCl4]2− anions separated by two orientations of cation layers, which are inter­locked through π–π stacking contacts between pairs of pyridine rings, with centroid–centroid distances of 3.7874 (7) Å.
PMCID: PMC3884264  PMID: 24454040

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