Setbacks and hopes: en route to the synthesis of uncialamycin

We herein report a new approach toward the synthesis of uncialamycin, an enediyne natural product isolated from the Streptomyces uncialis, bacteria present on the surface of the lichen Cladonia uncialis. A model for the preparation of uncialamycin has been achieved through a reaction cascade, an acetylide addition to the activated quinoline moiety, and a ring closure reaction as key steps.     

Phase transitions of AlFeO3 and GaFeO3 from the chiral orthorhombic (Pna2(1)) structure to the rhombohedral (R3c) structure

AlFeO(3) and GaFeO(3), which crystallize in a chiral orthorhombic (Pna2(1)) structure, transform to a rhombohedral (R3c) structure when subjected to ball-milling. There is a distinct difference between the transformations of AlFeO(3) and GaFeO(3). AlFeO(3) first transforms to an orthorhombic P2(1)2(1)2(1) structure followed by its transformation to the R3c structure, while GaFeO(3) goes directly to the R3c structure. The transformations have been characterized by X-ray diffraction and Raman spectroscopy. Magnetic properties of Pna2(1) and the transformed phases show significant differences. It is noteworthy that partial substitution of aluminum by gallium in AlFeO(3) as in Al(0.5)Ga(0.5)FeO(3) eliminates the intermediate P2(1)2(1)2(1) phase, causing direct transformation of the Pna2(1) structure to the R3c structure. All of the transformations are thermodynamically first-order associated with significant changes in volume. We have used first-principles simulations to determine the pressure-dependent properties of AlFeO(3) and GaFeO(3) in orthorhombic and corundum structures and have estimated the critical pressures for the structural phase transition between the two structures. On the basis of this information, we also comment on the differences in the behavior of AlFeO(3) and GaFeO(3) under ball-milling.     

Hf3 cluster is triply (sigma-, pi-, and delta-) aromatic in the lowest D3h, 1A1' state

The extensive search for the global minimum structure of Hf3 at the B3LYP/LANL2DZ level of theory revealed that D3h 3A2' (1a1'(2)1a2'(2)1e'(4)2a1'(2)1e'2) and D3h 1A1' (1a1'(2)2a1'(2)1e'(4)1a2'(2)3a1'2) are the lowest triplet and singlet states, respectively, with the triplet state being the lowest one. However, at the CASSCF(10,14)/Stuttgart+2f1g level of theory these two states are degenerate, indicating that at the higher level of theory the singlet state could be in fact the global minimum structure. The triplet D3h 3A2' (1a1'21a2'(2)1e'(4)2a1'(2)1e'2) structure is doubly (sigma- and pi-) aromatic and the singlet D3h 1A1' (1a1'(2)2a1'(2)1e'(4)1a2'(2)3a1'2) structure is the first reported triply (sigma-, pi-, and delta-) aromatic system.     

Snapshots of dioxygen activation by copper: the structure of a 1:1 Cu/O(2) adduct and its use in syntheses of asymmetric Bis(mu-oxo) complexes

The X-ray structure of a 1:1 Cu/O(2) adduct revealed side-on (eta(2)) O(2) coordination. Density functional calculations corroborated the structure, indicated a significant contribution of a Cu(III)-(O(2)(2-)) resonance form, and provided insights into the key bonding interactions. Reaction of a 1:1 adduct supported by a slightly different beta-diketiminate ligand with Cu(I) reagents resulted in the formation of novel asymmetric bis(mu-oxo) complexes that were identified by EPR, UV-vis, and Raman spectroscopy, as well as by an X-ray structure in one instance.     

Predictability of the polymorphs of small organic compounds: crystal structure predictions of four benchmark blind test molecules

Predicting the crystal structure of an organic molecule from first principles has been a major challenge in physical chemistry. Recently, the application of Density Functional Theory including a dispersive energy correction (the DFT(d) method) has been shown to be a reliable method for predicting experimental structures based purely on their ranking according to lattice energy. Further validation results of the application of the DFT(d) method to four organic molecules are presented here. The compounds were targets (labelled molecule II, VI, VII and XI) in previous blind tests of crystal structure prediction, and their structures proved difficult to predict. However, this study shows that the DFT(d) approach is capable of predicting the solid state structures of these small molecules. For molecule VII, the most stable (rank 1) predicted crystal structure corresponds to the experimentally observed structure. For molecule VI, the rank 1, 2 and 3 predicted structures correspond to the three experimental polymorphs, forms I, III and II, respectively. For molecules II and XI, their rank 1 predicted structures are energetically more stable than those corresponding to the experimental crystal structures, and were not found amongst the structures submitted by the participants in the blind tests. The rank 1 structure of molecule II is predicted to exist under high pressure, whilst the rank 1 structure predicted for molecule XI has the same space group and hydrogen bonding pattern as observed in the crystal of 1-amino-1-methyl-cyclopropane, which is structurally related to molecule XI. The experimental crystal structure of molecule II corresponds to the rank 4 prediction, 0.8 kJ mol(-1) above the global minimum structure, and the experimental structure of molecule XI corresponds to the rank 2 prediction, 0.4 kJ mol(-1) above the global minimum.     

Hydrothermal synthesis, structures, and luminescent properties of zinc(II) and cadmium(II) phosphonates with a 3D framework structure using terephthalate as second linkers

By introduction of 1,4-benzenedicarboxylic acid as a second organic ligand, two new divalent metal(II) phosphonates with a 3D framework structure, namely, [Zn(HL1)(bdc)(0.5)] (1) and [Cd(1.5)(HL2)(bdc)(0.5)] (2) (H(2)L1 = H(2)O(3)PCH(NH(2))C(6)H(5), H(3)L2 = H(2)O(3)PCH(2)-NC(5)H(9)-COOH, H(2)bdc = HOOCC(6)H(4)COOH), have been synthesized under hydrothermal conditions. The two compounds show three-dimensional (3D) framework structure with infinite two-dimensional (2D) networks pillared by H(2)bdc. For compound 1, the {ZnO(4)} polyhedra are interconnected by phosphonate groups into a 2D layer, and the adjacent layers are further cross-linked via the bdc(2-) anions to generate a three-dimensional framework structure with two types of channel system along the c-axis. A notable feature of compound 1 is the presence of alternate left- and right-handed helical chains in the structure. In compound 2, the inorganic chains, composed of {Cd(1)O(7)}, {Cd(2)O(4)} and {CPO(3)} polyhedra, are linked by HL2(2-) ligands to form a double layer structure in the ab plane, and the adjacent layers are further linked by the bdc(2-) anions to form a 3D framework structure with one-dimensional channel systems along the a-axis. Luminescence properties of compounds 1 and 2 have also been studied.     

Theoretical prediction of the S1-S0 internal conversion of 6-cyanoazulene

Ab initio complete active-space self-consistent field (CASSCF) and second-order Multireference M?ller-Plesset perturbation (MRMP2) calculations were performed to examine the S1-S0 internal conversion of 6-cyanoazulene (6CNAZ). The azulene skeletons of 6CNAZ in S0 and S1 have features that resemble those of azulene. The stable geometry in S0 is characterized by (i) a C2v structure, (ii) an aromatic bond-equalized structure in which all the peripheral skeletal bond distances resemble an aromatic CC bond distance, and (iii) a single bond character of the transannular bond. The stable geometry in S1 is characterized by a nonaromatic C2v structure. Contrary to similarities of the stable geometries in S0 and S1 between 6CNAZ and azulene, the conical intersection (S1/S0-CIX) of 6CNAZ is different from that of azulene. The S1/S0-CIX of 6CNAZ takes a planar structure, whereas that of azulene takes a nonplanar structure in the seven-membered ring (Amatatsu, Y.; Komura, K. J. Chem. Phys. 2006, 125, 174311/1-8). On the basis of those computational findings, we predict the photochemical behavior of 6CNAZ in the S1-S0 internal conversion.     

乙酰丙酮和1-萘甲酸甲酯加成物C17H18O4的晶体结构和分子力学计算

The structure of the product from the [2+2] photocycloaddition of acetylacetone to methyl 1-naphthoate was determined by X-ray crystallography. Crystal data. C_(17)H_(18)O_4, triclinic, P_1~-, a=0.7401(1), b=0.7656(1), c=1.3882(1) nm, α=84.75(1), β=86.49(1), γ=65.08(1)°, V=0.7102 nm, Z=2, D_c=1.339 g·cm~(-3), μ(MoK_a)=1.0 cm~(-1), F(000)=304. The structure was solved by direct methods and refined to final R=0.049 for 2442 MoKa reflections. The particular bridged structure of the product molecule indicates a [2+2+2] intramolecular cycloaddition in succession to the primary [2+2] photocycloaddition. Molecular mechanics calculations confirmed further that the molecular structure of the ultimate product takes a configuration of comparatively favourable steric energy even though the bridged structure itself is rather strained.     

三维球状液晶的模型分子（C6H5）Si（OC6H4）3N结构的PM3研究

三维球状液晶的模型分子（Ｃ６Ｈ５）Ｓｉ（ＯＣ６Ｈ４）３Ｎ结构的ＰＭ３研究＊丁涪江张良辅（中国科学院成都有机化学研究所成都６１００４１）关键词三苯并硅杂烷环状分子ＰＭ３方法液晶分子多为棒状一维结构和盘状二维结构。最近发现三维球状液晶分子，即长链烷烃取代...     

一种高可溶、高光学透明含氟聚酰亚胺的合成与表征

由自制芳香二胺单体9,9-双(3,5-二氟-4-胺基苯基)芴和商品化二酐单体4,4'-(六氟异丙基)双邻苯二甲酸酐经一步法高温缩聚制备了一种新型含氟聚酰亚胺.分别用FT-IR、1HNMR和19FNMR对所制聚酰亚胺结构进行了表征.结果证实其与所设计的结构完全一致,并且酰亚胺化反应完全.该含氟聚酰亚胺表现出高的溶解性:室温下在N-甲基-2-吡咯烷酮、N,N-二甲基乙酰胺、N,N-二甲基甲酰胺、氯仿、二氯甲烷、四氢呋喃等常规溶剂中的溶解度可达10wt%以上.由该聚酰亚胺溶液所制的薄膜无色透明,截断波长在315nm,400nm波长后的透光率在84%以上.此外该含氟聚酰亚胺还表现出良好的热学性能和机械性能:玻璃化转变温度在377℃,空气和氮气中10%热失重温度均在539℃以上;其薄膜的拉伸强度在70～80MPa,断裂伸长率在4%～8%,起始模量为2.6GPa.     

Characterization of complicated new polymorphs of chlorothalonil by X-ray diffraction and computer crystal structure prediction

A simultaneous experimental and computational search for polymorphs of chlorothalonil (2,4,5,6-tetrachloro-1,3-benzenedicarbonitrile) has been conducted, leading to the first characterization of forms 2 and 3. The crystal structure prediction study, using a specifically developed anisotropic atom-atom potential for chlorothalonil, gave as the global minimum in the lattice energy a structure that was readily refined against powder diffraction data to the known form 1 (P2(1)/a). The structure of form 2 was solved and refined from powder diffraction data, giving a disordered structure in the Rm (166) space group (Z = 3). It could also be refined against a P1 ordered model, starting from a low-energy hypothetical sheet structure found in the computational search. This shows that the disorder could be associated with the stacking of ordered sheets. The disordered structure for form 2 was later confirmed by single-crystal X-ray diffraction. The structure of form 3, determined from single-crystal diffraction, contains three independent molecules in the asymmetric unit in P2(1) (4) (Z = 6). Powder diffraction showed that this single-herringbone structure was similar to two low-energy structures found in the search. Further analysis confirmed that form 3 has a similar lattice energy and contains elements from both these predicted structures, which can be considered as good approximations to the form 3 structure.     

Compression of silver sulfide: X-ray diffraction measurements and total-energy calculations

Angle-dispersive X-ray diffraction measurements have been performed in acanthite, Ag(2)S, up to 18 GPa in order to investigate its high-pressure structural behavior. They have been complemented by ab initio electronic structure calculations. From our experimental data, we have determined that two different high-pressure phase transitions take place at 5 and 10.5 GPa. The first pressure-induced transition is from the initial anti-PbCl(2)-like monoclinic structure (space group P2(1)/n) to an orthorhombic Ag(2)Se-type structure (space group P2(1)2(1)2(1)). The compressibility of the lattice parameters and the equation of state of both phases have been determined. A second phase transition to a P2(1)/n phase has been found, which is a slight modification of the low-pressure structure (Co(2)Si-related structure). The initial monoclinic phase was fully recovered after decompression. Density functional and, in particular, GGA+U calculations present an overall good agreement with the experimental results in terms of the high-pressure sequence, cell parameters, and their evolution with pressure.     

手性二茂铁色氨酸化合物[Fc-(CO-L-Trp-OMe)2]的合成和结构表征

由色氨酸甲酯和1,1′-二茂铁二羧酸合成了化合物1[Fc-(CO-L-Trp-OMe)₂],并对化合物1在固体和溶液中的结构进行了表征。单晶结构表明,该化合物通过2个分子内氢键,形成了规则的手性构象。通过分子间的氢键,形成了二维网状结构。对化合物1的乙腈溶液进行了CD谱的测定,结果表明,该化合物在溶液中呈现P螺旋构象。¹H NMR谱和FTIR谱也证实了该化合物在固体和溶液状态中都形成了含分子内氢键的构象。     

NaCl/KCl flux single crystal growth and crystal structure of the new quaternary mixed-metal pnictide: BaCuZn3As3

Synthesis and crystal structure of a new compound, BaCuZn(3)As(3), are reported. Single crystals of BaCuZn(3)As(3) are synthesized via NaCl/KCl flux reaction in a sealed fused silica ampule. Its elemental composition has been determined to be Ba/Cu/Zn/As = 1.03(4):1(0):2.91(6):2.98(3), suggesting BaCuZn(3)As(3) as the chemical formula. The structure of BaCuZn(3)As(3) has been determined by X-ray diffraction. It crystallizes in the orthorhombic Cmcm space group with a = 4.2277(3) A, b = 12.970(1) A, and c = 12.011(1) A at T = 90.7 K, and it exhibits a columnar structure along the a-axis. This structure is isotypic to beta-BaCu(4)S(3) but highly distorted. beta-BaCu(4)S(3) is considered to be a layered structure whereas BaCuZn(3)As(3) is a three-dimensional network.     

Structure of the jet-cooled 1-naphthol dimer studied by IR dip spectroscopy: cooperation between the pi-pi interaction and the hydrogen bonding

The structure of a jet-cooled 1-naphthol (1-NpOH) dimer was investigated by using resonant-enhanced two-photon ionization (R2PI) and ion-detected infrared (IR) dip spectroscopy. A geometrical optimization and a frequency calculation in (1-NpOH)2 were also performed at the MP2/cc-pVDZ level. Stable isomers in the MP2/cc-pVDZ calculation were classified into a structure dominated only by the pi-pi interaction and structures formed by cooperation between the pi-pi interaction and hydrogen bonding. On the basis of a comparison between the observed and calculated IR spectra, the geometry of (1-NpOH)2 was concluded to be a pi-pi stacking structure supported by hydrogen bonding.     

Synthesis and crystal structure of lithium beryllium deuteride Li2BeD4

Single-phase ternary deuteride Li(2)BeD(4) was synthesized by a high-pressure high-temperature technique from LiD and BeD(2). The crystal structure of Li(2)BeD(4) was solved from X-ray and neutron powder diffraction data. The compound crystallizes in the monoclinic space group P2(1)/c with lattice parameters a = 7.06228(9) A, b = 8.3378(1) A, c = 8.3465(1) A, beta =93.577(1) degrees, and Z = 8. Its structure contains isolated BeD(4) tetrahedra and Li atoms that are located in the structure interstices. Li(2)BeD(4) does not undergo any structural phase transitions at temperatures down to 8 K.     

Structure determination of homoleptic AuI, AgI, and CuI aryl/alkylethynyl coordination polymers by X-ray powder diffraction

This article describes the structure determination of five homoleptic d(10) metal-aryl/alkylacetylides [RC triple bond CM] (M=Cu, R=tBu 1, nPr 2, Ph 3; R=Ph, M=Ag 4; Au 5) by using X-ray single-crystal and powder diffraction. Complex 1.C6H6 reveals an unusual Cu20 catenane cluster structure that has various types of tBuC triple bond C-->Cu coordination modes. By using this single-crystal structure as a starting model for subsequent Rietveld refinement of X-ray powder diffraction data, the structure of the powder synthesized from CuI and tBuC triple bond CH was found to have the same structure as 1. Complex 2 has an extended sheet structure consisting of discrete zig-zag Cu4 subunits connected through bridging nPrC triple bond C groups. Complex 3 forms an infinite chain structure with extended Cu-Cu ladders (Cu-Cu=2.49(4)-2.83(2) A). The silver(I) congener 4 is iso-structural to 3 (average Ag-Ag distance 3.11 A), whereas the gold(I) analogue 5 forms a Au...Au honeycomb network with PhC triple bond C pillars (Au-Au=2.98(1)-3.26(1) A). Solid-state properties including photoluminescence, nu(C triple bond C) stretching frequencies and thermal stability of these polymeric systems are discussed in the context of the determined structures.     

Confirmation of the Structures of Lutein and Zeaxanthin

A series of new esters of lutein ( 1a ) have been prepared with the aim of confirming the structure of lutein via an X‐ray crystal‐structure analysis. Although well crystallized, only one of the derivatives, the (?)‐(1R)‐menthyl carbonate ( 1i ) proved to be useful for a complete structure analysis. The same derivative of zeaxanthin ( 2a ) also allowed its crystal structure to be determined. Both analyses represent the first successful X‐ray crystal structure analyses of the most important xanthophylls. At the same time, they confirm both the constitution and absolute configuration of 1a and 2a that had been deduced earlier by classical methods.     

Non-centrosymmetric coordination polymer with a highly hindered octahedral copper center bridged by mandelate

A novel chiral coordination polymer, [Cu(C(6)H(5)CH(OH)COO)(μ-C(6)H(5)CH(OH)COO)] (1-L and 1-D), was synthesized through a reaction of copper acetate with L-mandelic acid at room temperature. Although previously reported copper mandelate prepared by hydrothermal reaction was a centrosymmetric coordination polymer because of the racemization of mandelic acid, the current coordination polymer shows noncentrosymmetry and a completely different structure from that previously reported. The X-ray crystallography for 1-L revealed that the copper center of the compound showed a highly distorted octahedral structure bridged by a chiral mandelate ligand in the unusual coordination mode to construct a one-dimensional (1D) zigzag chain structure. These 1D chains interdigitated each other to give a layered structure as a result of the formation of multiple aromatic interactions and hydrogen bonds between hydroxyl and carboxylate moieties at mandelate ligands. The coordination polymer 1-L belongs to the noncentrosymmetric space group of C2 to show piezoelectric properties and second harmonic generation (SHG) activity.     

Lanthanide-binding peptides with two pendant aminodiacetate arms: impact of the sequence on chelation

Lanthanide complexes with a series of hexapeptides-incorporating two unnatural chelating amino acids with aminodiacetate groups, Ada(1) and Ada(2)-have been examined in terms of their speciation, structure, stability and luminescence properties. Whereas Ada(2) acts as a tridentate donor in all cases, Ada(1) may act as a tetradentate donor thanks to the coordination of the amide carbonyl function assisted by the formation of a six-membered chelate ring. The position of the Ada(1) residue in the sequence is demonstrated to be critical for the lanthanide complex speciation and structure. Ada(1) promotes the coordination of the backbone amide function to afford a highly dehydrated Ln complex and an S-shape structure of the peptide backbone, only when found in position 2.