Effect of polymorphism on the C?H stretching region of the infrared spectrum of polyethylene

A complex fine structure in the C? H stretching region of the infrared spectrum of deformed polyethylene single crystals is reported. The deformed crystals are shown to be transformed from the orthorhombic crystal form to a monoclinic structure. The previously deduced C_2/m monoclinic structure does not account for the appearance of the new bands. An alternative but similar monoclinic structure is proposed. The symmetry of this structure is consistent with the Fermi resonance interactions required for the observation of these bands.     

Structural Determination and Chemical Synthesis of the N-Glycan from the Hyperthermophilic Archaeon Thermococcus kodakarensis

Asparagine-linked protein glycosylations (N-glycosylations) are one of the most abundant post-translational modifications and are essential for various biological phenomena. Herein, we describe the isolation, structural determination, and chemical synthesis of the N-glycan from the hyperthermophilic archaeon Thermococcus kodakarensis. The N-glycan from the organism possesses a unique structure including myo-inositol, which has not been found in previously characterized N-glycans. In this structure, myo-inositol is highly glycosylated and linked with a disaccharide unit through a phosphodiester. The straightforward synthesis of this glycan was accomplished through diastereoselective phosphorylation and phosphodiester construction by S_N2 coupling. Considering the early divergence of hyperthermophilic organisms in evolution, this study can be expected to open the door to approaching the primitive function of glycan modification at the molecular level.     

Mometasone furoate revisited,or how did the hydrate get in the bottle?

The redetermined structure of 9α,21‐dichloro‐11β,17α‐dihydroxy‐16α‐methyl‐3,20‐dioxopregna‐1,4‐dien‐17‐yl furan‐2‐carboxylate monohydrate, C₂₇H₃₂Cl₂O₇·H₂O, at 100 K has triclinic (P1) symmetry. The structure displays O—H...O hydrogen bonding, which gives rise to infinite sheets extending parallel to the [110] plane. The previously published structure [Chen et al. (2005). J. Pharm. Sci. 94 , 2496–2509] was determined at room temperature and no significant anomalous signal was present. Data for the structure presented in this study were collected at low temperature and the absolute configuration could be established based solely on anomalous diffraction. Another point of interest is that the structure determined in this study is that of the monohydrate, even though the crystal was harvested from a bottle of nasal spray that was supposed to contain exclusively crystals of the anhydrous form.     

Phenolic Components of Empetrum nigrum Extract and the Crystal Structure of One of Them

Four phenolic components are isolated from the CHCl ₃ extract ofEmpetrum nigrumL. Three of them are known from this plant. The fourth (6,8-dimethylpinocembrine) is isolated from crowberry for the first time. The previously proposed structure for 2'-methoxy-4'-hydroxy- ,-dihydrochalcone is confirmed by x-ray structure analysis     

The matrix-isolation IR spectrum of the o-quinonoid intermediate in the photolysis of 2-nitrobenzyl methyl ether

Photolysis of 2-nitrobenzyl methyl ether in Ar and N₂ matrices at 12 K generated an intermediate with λ_max at 430 nm, and which was itself photolabile at 430–460 nm. Matrix IR spectra, as well as the UV-visible absorption, were obtained for this species. An analogous intermediate had previously been observed in flash-photolysis studies of 2-nitrobenzyl 4-cyanophenyl ether, and had been assigned an o-quinonoid structure on the basis of its kinetic behaviour and the position of its UV-visible absorption. In the matrix studies with 2-nitrobenzyl methyl ether, the IR spectra confirmed the o-quinonoid structure.     

The Crystal Structure of YPdSi,the Isotypic Compounds LnPdSi (Ln = Gd–Lu), and their Structural Relation to some other Equiatomic Compounds of the Rare Earth and Transition Metals with Main Group Elements

The nine title compounds were prepared from the elements by arc-melting and subsequent heat treatment in resistance and high-frequency furnaces. The crystal structure of these isotypic compounds was determined for YPdSi from single-crystal X-ray diffractometer data: Pmmn, a = 430.8(1) pm, b = 1391.2(1) pm, c = 743.1(1) pm, Z = 8, R = 0.024 for 417 structure factors and 40 variable parameters. The crystal structures of the isotypic compounds GdPdSi and ErPdSi were also refined from single-crystal data. The structure is of a new type. It consists of condensed, six-membered rings of alternating palladium and silicon atoms with Pd–Si bond distances varying between 249.6 and 258.8 pm. These two-dimensionally infinite nets are connected to each other via weak Pd–Si and Si–Si bonds with bond distances of 276.3 and 259.5 pm. The rare earth atoms are situated above and below the six-membered palladium-silicon rings in a manner as it is known for the aluminum atoms in the AlB₂ type structure. The crystal-chemical similarities and topologies of several structures derived from the aristotype AlB₂ (including those of BaPtSb, EuAuGe, KHg₂, ZrBeSi, and TiNiSi) are described, emphasizing their group-subgroup relationships. The previously reported compound ”︁Er₂Pd₂Si”︁”︁ has the same structure as has been found here for ErPdSi.     

Crystal structure and Hirshfeld surface analysis of the anhydrous form of the nucleoside analogue entecavir

The nucleoside analogue entecavir {systematic name: 2‐amino‐9‐[(1S,3R,4S)‐4‐hydroxy‐3‐hydroxymethyl‐2‐methylenecyclopentyl]‐1,9‐dihydro‐6H‐purin‐6‐one}, C₁₂H₁₅N₅O₃, is an antihepatitis B virus drug that has been approved in the US, EU and several countries worldwide. We report here the single‐crystal structure of the anhydrous form and compare it with that of the previously reported monohydrate form [Jiang & Liu (2009). Acta Cryst. E 65 , o2232]. Hirshfeld surface analysis has been employed to understand and visualize the subtle packing differences between the two crystalline forms. The results show that, compared to the previously reported hydrated form, the anhydrous crystal has significantly different intermolecular interactions and packing patterns.     

Novel Sesquiterpenes from the Mycelial Cultures of Dichomitus squalens

Four novel sesquiterpenes, 5‐hydroxydichomitol ( 1 ), dichomilludol ( 2 ), 3β,13‐dihydroxyledol ( 3 ), and 2β,3β,13‐trihydroxyledol ( 4 ), were isolated along with 2β,13‐dihydroxyledol ( 5 ) from the AcOEt‐soluble fraction of the mycelial solid cultures of Dichomitus squalens. Their structures were determined on the basis of spectroscopic analyses. The previously assigned structure of dichomitol was revised.     

Synthesis and structure of the PdII complex with 3,3-dinitropropylamine

The reaction of 3,3-dinitropropylamine with PdCl₂ gave the previously unknown complex, bis(3,3-dinitropropylaminato-N,C ³)palladium(II). The structure of the complex was established by X-ray diffraction analysis. Translated fromIzvestiy Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1704–1705, September, 1997.     

Defense Allomones of the Nudibranch Phyllidia varicosa Lamarck 1801

The defensive secretion of the nudibranch Phyllidia varicosa consists of two isocyanosesquiterpenes: the previously described 9-isocyanopupukeanane ( 1 ), and its 2-isomer ( 4 ), for which we report the structure and properties. The mixture originates with a sponge, Hymeniacidon sp., where it is produced in varying proportions. CD. measurements and X-ray diffraction data establish the absolute configuration of the two metabolites.     

Two cubic polymorphs of AlGeLi

Aluminium germanium lithium, AlGeLi, crystallizes in two cubic dimorphs. The structure of the F3m form, already inferred from powder data, has been confirmed by both powder and single‐crystal X‐ray diffraction studies. The second dimorph, not previously identified, adopts a disordered centrosymmetric structure with space group Fmm.     

The reaction of trans-2-aminocyclohexanol with formaldehyde

From a study of the geminal coupling constants for -O-CH₂-N- protons structure II has been assigned to the product of the reaction between trans-2-aminocyclohexanol and formaldehyde. The previously proposed structure I is shown to be incorrect.     

Reaction of β-arylidennaphthylamines with 4-hydroxycoumarin. A correction in structural assignment of the product. III

The reaction of 4-hydroxycoumarin with β-arylidennaphthylamines constitutes a convenient synthetic route to the hitherto unknown 2H-benzo[f][1]benzopyrano[4,3-b]quinolin-2-one, VI . The X-ray crystallography data conform with the present benzopyrano[4,3-b]quinolin-2-one ring system and disprove the benzopyrano[3,4-c]quinolin-2-one structure previously assigned for such reaction products.     

New mesoionic systems of the azolopyridine series. 1. Synthesis and structures of thiazolo[3,2-a]pyridinium 2-thiolates

A procedure was developed for the synthesis of representatives of the previously unknown bicyclic mesoionic thiazolo[3,2-a]pyridinium 2-thiolate system by the reaction of 2-X-N-phenacylpyridinium salts (X = Cl, SMe) with CS₂ in the presence of Et₃N. The three-dimensional structure of 3-(p-nitrobenzoyl)thiazolo[3,2-a]pyridinium 2-thiolate was established by X-ray diffraction analysis.     

New Lignans from the Roots of Taiwania cryptomerioides Hayata

The five new lignans designated 3′,4′‐de‐O‐methylenehinokinin ( 1 ), taiwaninolide ( 2 ), 8′‐hydroxysavinin ( 3 ), isoguamarol ( 4 ), and 4′‐O‐methylsalicifolin ( 5 ), as well as the new 4‐(3,4‐dimethoxybenzyl)dihydro‐3‐(4‐hydroxybenzyl)furan‐2(3H)‐one ( 6 ) were isolated from the roots of Taiwania cryptomerioides, besides the three known compounds hinokinin ( 8 ), savinin ( 9 ), and 3,4‐de‐O‐methylenehinokinin ( 7 ). The structures of the new constituents were elucidated through chemical and spectral studies. A compound previously isolated from the heartwood of Chamaecyparis obtusa var. formosana was assigned structure 1 ; however, this structure has now been revised to be 3,4‐de‐O‐methylenehinokinin ( 7 ).     

Thermodynamic consideration on the interface formation of water and ethylene glycol isobutyl ether mixture

The interfacial tension of the binary two-phase mixture of water and ethylene glycol isobutyl ether (EIB) was measured as a function of temperature in the vicinity of the lower critical solution temperatureT _c under atmospheric pressure. The interfacial tension decreased with decreasing temperature and approached zero atT _c . The thermodynamic quantities of interface formation were evaluated by applying equations developed previously to the interfacial tension vs temperature curves. The results were compared with those of the water and diethylene glycol diethyl ether system examined previously, and the effect of the molecular structure of the ether molecule on its interfacial behavior was discussed. It was suggested that the hydration of the ethylene oxide groups of ether molecules was an important factor in the interface formation as well as in the mixing of component molecules of the systems investigated here.     

The structure of Mo4Cl8(PEt3)4: How unrecognized disorder previously reduced the quality of the refinement

The preparation and structure of the title compound were reported several years ago by McCarly and co-workers ((1978).J. Am. Chem. Soc. 100, 7900). Curiously, it was reported that refinement of the structure converged at exceptionally high figures of merit (R=0.126;R _w =0.158), but no reason was given. In view of a recent observation in this laboratory (Chen and Cotton (1991).J. Am. Chem. Soc. 113, 5857) that a similar type of compound, [Re₄Cl₈(-O)₂(-OMe)₂]^2– exhibited a subtle but elegant disorder, we reexamined the crystal structure of the title compound. It is found to have 92% of the Mo₄ rectangles in one orientation (the only one previously included in the refinement) and 8% in an orientation perpendicular to the main one. In both orientations the ligand positions are approximately the same. The figures of merit are nowR=0.041;R _w =0.064. The three structure parameters previously reported are now only slightly different: Mo-Mo=2.210(1) vs. 2.211(3) Å; Mo-Mo'=2.897(1) vs. 2.901(2) Å; angle Mo-Cl_b-Mo=74.2[8]° vs. 74.4(2)°. We report here the complete structure.     

Superstructure and stacking faults in hydrothermal-grown KBe2BO3F2 crystals

The structure of the hydrothermal-grown nonlinear optical crystal KBe₂BO₃F₂ was investigated. A new structure of the R3?c space group with cell parameters of a=4.422(1) Å and c=37.524(3) Å was obtained by powder X-ray diffraction and Rietveld refinement. The new structure is a 1×1×2 superstructure of the previously reported R32 structure with a different stacking sequence of (Be₂BO₃F₂)_∞ layers along the c axis. The relationship between the refined structure and the experimental results is discussed. A stacking fault mechanism is proposed for the formation of the superstructure as well as the nonuniformity of the hydrothermal-grown KBBF crystals.     

Isolation and elucidation of the structure of homocryptolepinone

The structure of a new indolobenzazepine alkaloid, homocryptolepinone, isolated from extracts of the roots of the indigenous Ghanaian medicinal plant Cryptolepis sanguinolenta, is reported. The structure was determined using mass spectrometric, one-dimensional nOe difference nmr, and inverse-detected two-dimensional nmr experiments which included HMQC, IDR-(Inverted Direct Response)-HMQC-TOCSY, and HMBC experiments. The structure of homocryptolepinone is significant in that it may provide insight into the biogenesis of the benzpyrrolizinobenzazepine portion of the structure of the complex spiro nona-cyclic alkaloid cryptospirolepine previously isolated in these laboratories from C. sanguinolenta, and which has no precedent in alkaloid chemistry.