Crystal structures of cyclodextrin complexes with chiral molecules

The chiral recognition by cyclodextrins and permethylated cyclodextrins have been investigated on the basis of the X-ray data of crystalline inclusion complexes. The macrocyclic ring of - and -cyclodextrin shows a round and symmetrical structure. -Cyclodextrin includes racemic 1-phenylethanol with the statistical disorder of the hydroxyl group. A pair of the R- and S-isomers of flurbiprofen are included within the cylindrical cavity formed by dimeric -cyclodextrin molecules with a head-to-head arrangement. The macrocyclic ring of permethylated cyclodextrins is remarkably distorted from the regular polygonal symmetry and has more flexibility in the conformational change than cyclodextrins. Owing to the distorted conformation and steric hindrance involving methyl groups, permethylated cyclodextrins do not equally include both isomers, as demonstrated by the permethylated -cyclodextrin complexes with mandelic acids. Permethylated -cyclodextrin binds D-mandelic acid more tightlyvia a host-guest hydrogen bond and induced-fit conformational change. Permethylated -cyclodextrin forms a hydrated crystalline complex with R-flurbiprofen, but S-flurbiprofen forms a non-hydrated crystalline complex. Significant differences between the two complexes are found in the orientation of the phenyl group and hydrogen-bond formation involving the carboxyl group.     

Crystal packing in the structures of diethanolamine derivatives

Four distinct hydrogen‐bonding topologies were observed in the structures of six diethanolamine ligands. These compounds are (1R*,2R*)‐2‐[(2‐hydroxyethyl)(methyl)amino]‐1,2‐diphenylethanol, C₁₇H₂₁NO₂, (I), 1‐[(2S)‐2‐(hydroxydiphenylmethyl)pyrrolidin‐1‐yl]‐2‐methylpropan‐2‐ol, C₂₁H₂₇NO₂, (II), 2‐[(2‐hydroxyethyl)(methyl)amino]‐1,1‐diphenylethanol, C₁₇H₂₁NO₂, (III), 1‐{(2‐hydroxy‐2‐methylpropyl)[(1S)‐1‐phenylethyl]amino}‐2‐methylpropan‐2‐ol, C₁₆H₂₇NO₂, (IV), 1‐{[(2R)‐2‐hydroxy‐2‐phenylethyl][(1S)‐1‐phenylethyl]amino}‐2‐methylpropan‐2‐ol, C₂₀H₂₇NO₂, (V), and (1R*,2S*)‐2‐[(2‐hydroxyethyl)(methyl)amino]‐1,2‐diphenylethanol, C₁₇H₂₁NO₂, (VI). In each compound, all `active' hydroxy H atoms are engaged in hydrogen bonding, but the N atoms are not involved in intermolecular hydrogen bonding. In the structures of (I), (II) and (IV)–(VI), molecules are linked into chains by intermolecular O—H...O interactions. These chains are organized in such a way as to hide the hydrophilic groups inside, and so the outer surfaces of the chains are hydrophobic. The structure of (VI) contains two distinct non‐equivalent systems of intermolecular O—H...O hydrogen bonds formed by disordered hydroxy H atoms.     

On the irrelevance of electrostatics for the crystal structures and polymorphism of long even n-alkanes

It is known that the experimental triclinic crystal structures of even n-alkanes are not well reproduced upon energy minimization with current force fields. The inclusion of electrostatics does not solve this, and, moreover, some charge schemes show unphysical features such as positively charged carbon atoms or charge alternation. The effect of the electrostatics on the energies of the crystal structures of the even n-alkanes, and thereby on their polymorphism, has never been established. A new charge scheme is introduced that yields physically sensible charges without constraints. It will also be shown, however, that electrostatics are relevant neither for the structures of the crystals, nor for their energies.     

Crystal structures of rhodacyclopentane derivatives

Two complexes containing a rhodacyclopentane ring, viz. (acac)Rh(C₆H₈)(py)₂ and (acac)₂Rh₂(C₆H₈)(PPh₃) have been studied by X-ray diffraction. The ring forms through oxidative coupling of two allene molecules giving the structure A with trivalent, octahedrally-coordinated rhodium. In the second complex the unsaturated hydrocarbon part is also π-bonded to another Rh atom, and one acac group acts as a five-electron donor.     

Crystal and molecular structures of the alkaloid verdine

An x-ray structural analysis has been made with the object of reliably determining the structure of the alkaloid verdine. The position of the hydroxy group, not determined by other methods has been found and it has been established that the alkaloid verdine has the structure and configuration of 1,3,6-trihydroxy-5-jervanin-12-en-11-one.Institute of the Chemistry of Plant Substances, Academy of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 753–758, November–December, 1984.     

Crystal and molecular structures of the copper dichloride complex with 1-isopropenylimidazole

Crystal and molecular structures of the [CuL₂Cl₂] complex (L is 1-isopropenylimidazole) (I) are determined (R = 0.038, (wR ₂ = 0.092 for 2026 reflections with F _o ≥ 4σ(F _o); R ₁ = 0.123, wR ₂ = 0.117 for all reflections)) and compared with the structure of the known cobalt complex of analogous composition [CoL₂Cl₂] (II). Unlike complex II with the usual tetrahedral environment of the cobalt atom, the structure of the coordination polyhedron of the copper atom in compound I is intermediate between tetrahedron and square (the average dihedral angle between the ClCuN planes is 35.9°, and the ClCuCl (147.5°) and NCuN (163.1°) angles are much larger than the ClCuN angle of 90.1°–93.1°). The Cu-N (1.975(3), 1.959(3) Å) and Cu-Cl bonds (2.291(1), 2.278(1) Å) in complex I are typical of the copper(II) compounds. Different spatial structures of the 1-alkenylimidazole cycles in complexes I and II are found. Different short intermolecular contacts in crystals of compounds I (Cu…Cl, Cu…H) and II (Cl…C) result in the formation of chains with different mutual arrangements of molecules of the complexes.     

Crystal and molecular structures of the alkaloid verdine

An x-ray structural analysis has been made with the object of reliably determining the structure of the alkaloid verdine. The position of the hydroxy group, not determined by other methods has been found and it has been established that the alkaloid verdine has the structure and configuration of 1β,3α,6α-trihydroxy-5β-jervanin-12-en-11-one.     

Crystal structures of three intermetallic phases in the Mo-Pt-Si system

The crystal structures of three ternary Mo-Pt-Si intermetallic compounds have been determined ab initio from powder X-ray diffraction data. All three structures are representative of new structure types. Both the X (MoPt₂Si₃, Pmc2₁, oP12, a=3.48438(6), b=9.1511(2), c=5.48253(8) Å) and Y (MoPt₃Si₄, Pnma, oP32, a=5.51210(9), b=3.49474(7), c=24.3090(4) Å) phases derive from PtSi (FeAs type) structure while the Z phase (ideal composition Mo₃₂Pt₂₀Si₁₆, refined composition Mo_29.9(2)Pt_21.0(3)Si_17.1(1), Cc, mC68, a=13.8868(3), b=8.0769(2), c=9.6110(2) Å, β=100.898(1)°) present similarities with the group of Frank-Kasper phases.     

Crystal structures of Candida albicans N-myristoyltransferase with two distinct inhibitors

Myristoyl-CoA:protein N-myristoyltransferase (Nmt) is a monomeric enzyme that catalyzes the transfer of the fatty acid myristate from myristoyl-CoA to the N-terminal glycine residue of a variety of eukaryotic and viral proteins. Genetic and biochemical studies have established that Nmt is an attractive target for antifungal drugs. We present here crystal structures of C. albicans Nmt complexed with two classes of inhibitor competitive for peptide substrates. One is a peptidic inhibitor designed from the peptide substrate; the other is a nonpeptidic inhibitor having a benzofuran core. Both inhibitors are bound into the same binding groove, generated by some structural rearrangements of the enzyme, with the peptidic inhibitor showing a substrate-like binding mode and the nonpeptidic inhibitor binding differently. Further, site-directed mutagenesis for C. albicans Nmt has been utilized in order to define explicitly which amino acids are critical for inhibitor binding. The results suggest that the enzyme has some degree of flexibility for substrate binding and provide valuable information for inhibitor design.     

Crystal structures of alkaloid peganine and its cocrystal with peganol

X-ray diffraction (XRD) is used to investigate the crystal structures of the alkaloid peganine, its hemihydrate and nitrate. It is shown that (±)-peganine forms a cocrystal with the alkaloid peganol. It is typical of the alkaloid (−)-peganine crystal structures to form a closed dimer pair because of reciprocal O-H⋯N1 hydrogen bonds. Analogous H-bonds are also observed in the (±)-peganine-(±)-peganol cocrystal, where the center of symmetry binds together similar molecules to form associates. In (±)-peganine nitrate crystals, the NH⁺ and OH groups of the alkaloid form H-bonds simultaneously with two oxygen atoms of nitric acid anions.     

Crystal structures of monohalogenated benzoic acids

Crystal structures resulting from a combination of different types of specific intermolecular interactions have been analysed using examples of 12 monohalogenated benzoic acids (HBA). These have been compared with structures known for corresponding monofunctional compounds, namely benzoic acid, fluorobenzene, chlorobenzene and iodobenzene. It is found that common for carboxylic acids centrosymmetric hydrogen-bonded dimers exist in all HBA, and at the same time a degree of halogen atoms aggregation is rather high in the most part of HBA, similarly to chlorobenzene and iodobenzene crystals. Previously reported tendency to increasing degree of Hal-aggregation in the sequence F < Cl ≤ Br ≤ I is confirmed. It is remarkable that a stacking motif of benzene rings is realised in all HBA crystals though it is absent in all considered monofunctional substances.     

Crystal structures of two 4-phenylbenzophenones

Two 4-phenylbenzophenones (I) and (II) are synthesized via Friedel-Crafts reactions. There are four crystallographically independent molecules with different conformations in the crystal structure of [1,1′-biphenyl]-4-yl(2-chlorophenyl)methanone (I). Crystals are orthorhombic, Pca2₁, C₁₉H₁₃ClO, a = 13.699(3) Å, b = 8.9385(17) Å, c = 46.836(9) Å; V = 5735(2) ų, Z = 16, d _x = 1.356 g/cm³. Torsion angles between the biphenyl rings are between 28.5° and 30.8°. Several C-H…O and C-H…Cl hydrogen bonds and weak π-π stacking contacts consolidate the crystal. Crystals of [1,1′-biphenyl]-4-yl(3-methoxyphenyl)methanone (II) are orthorhombic, Pbca, C₂₀H₁₆O₂, a = 7.8179(15) Å, b = 16.003(3) Å, c = 23.345(5) Å; V = 2920.7(10) ų, Z = 8, d _x = 1.311 g/cm³. The torsion angle between the biphenyl rings is 28.1° and C-H…O hydrogen bonds are observed in compound (II).     

Crystal structures of Cr-based magnetic pyroxenes

Crystal structures of the Cr-based germanates: ACrGe₂O₆ (A = Li and Na) which show the specific magnetic properties, are solved using synchrotron powder-diffraction data at room temperature. Both compounds have isostructure which belongs to monoclinic C2/c with pyroxene-type structure. In both ACrGe₂O₆ structures, chromium atom forms the magnetic one-dimensional edge-shared CrO₆ chain. In the NaCrGe₂O₆ structure, the shortest Cr?Cr distance and Cr–O–Cr angle are both longer and wider compared to those in the LiCrGe₂O₆ structure. This behavior may give strong influence to the difference of their magnetic properties.