N‐protonated and O‐protonated tautomers of 1‐azabicyclo[3.3.1]nonan‐2‐one: observation of individual 13C‐NMR carbonyl peaks and comparisons with protonated tautomers of planar and other distorted lactams

An earlier study fit calculated dynamic ¹³C‐NMR spectra in trifluoroacetic acid (TFA) (with added sulfuric acid) to slow exchange between N‐protonated and O‐protonated tautomers of 1‐azabicyclo[3.3.1]nonan‐2‐one. The present study reports simultaneous observation of both carbonyl ¹³C peaks in 40% sulfuric acid/60% TFA at ?40 °C. This furnishes the only example in which experimental carbonyl ¹³C chemical shifts may be compared with a neutral lactam (in TFA or CDCl₃) with its N‐protonated and O‐protonated derivatives. The seemingly anomalous upfield chemical shifts (experimental and computational) of the ¹³C carbonyl peaks in this N‐protonated lactam (and other twisted N‐protonated lactams) relative to the free bases are compared with data for unstrained protonated lactams and amides. The results are rationalized through conventional resonance structures. Copyright © 2012 John Wiley & Sons, Ltd.     

Vibration of Shallow Shells with Two Adjacent Edges Clamped and the Others Free∗

ABSTRACT

Considerable information is available in the published literature on the free vibration frequencies and mode shapes of rectangular flat plates having two adjacent edges clamped and the other two free. However, no results appear to have been published previously for shallow shells having such edge conditions. The present work uses the Ritz method with displacement components in the form of algebraic polynomials to obtain accurate frequencies. Frequencies are determined for the first eight modes of shallow shells having spherical, cylindrical, and hyperbolic paraboloi-dal curvatures and square planforms. Beginning with the plate, the curvatures are incrementally increased in each case to the limits of shallow     

Ba5Ti12Sb19+x, a polar intermetallic compound with a stuffed γ-brass structure

The polar intermetallic compound Ba₅Ti₁₂Sb_19+x (x0.2) has been synthesized by reaction of the elements. Single-crystal X-ray diffraction analysis revealed that it adopts a new structure type (Ba₅Ti₁₂Sb_19.102(6), space group , Z=2, a=12.4223(11) Å, V=1916.9(3) Å³). The set of Ba and Sb sites corresponds to the structure of Cu₉Al₄, a γ-brass type with a primitive cell. A complex three-dimensional framework of Ti atoms, in the form of linked planar Ti₉ clusters, is stuffed within the γ-brass-type Ba–Sb substructure. Notwithstanding its relationship to the γ-brass structure, the compound does not appear to conform to the Hume–Rothery electron concentration rules. Band structure calculations on an idealized Ba₅Ti₁₂Sb₁₉ model suggest that the availability of bonding states above the Fermi level is responsible for the partial occupation, but only to a limited degree, of an additional Sb site within the structure. Magnetic measurements indicated Pauli paramagnetic behaviour.     

Synthesis of functionalized hydroxy-thiophene motifs as amido- and sulfonamido-phenol bioisosteres

Novel highly substituted hydroxy thiophene motifs were designed and synthesized as viable amido phenol and sulfonamido phenol bioisosteres. Hydroxy group-directed regioselective bromination and palladium-catalyzed amination of thienyl bromide via Buckwald protocol are the key elements of the synthetic approach. The hydroxy thiophene-containing compounds displayed good binding inhibitions.     

Morphological and crystalline studies of isotactic polypropylene plastically deformed and evaluated by small-angle X-ray scattering, scanning electron microscopy and X-ray diffraction

Morphological and structural properties of isotactic polypropylene (i-PP) submitted to uniaxial plane strain deformation at ambient temperature with compression pressures of 3, 10 and 20 MPa, were investigated using wide angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Two kinds of samples were studied, namely: sample A: Mw = 117,400 g/mol Mn = 17,300, Mw/Mn = 6.8 and sample B: Mw = 271,000 g/mol Mn = 43,700 Mw/Mn = 6.2, both with isotactic content = 95%. Crystalline α- and β-phases are clearly identified by WAXD. The lamellar long period, as well as, the crystalline and amorphous lamellar thickness for the non-deformed samples measured by SAXS indicates the presence of a more symmetric spherulitic structure for sample A, while the sample B displays anisotropic scattering. The WAXD study of the apparent relative crystallinity and the orientation of crystallites, revealed that plastic deformation of i-PP by plane-strain compression, leads to preferred orientation of main axis of crystallites at relatively early stage of the deformation process induced a monocrystal texture and an excellent molecular alignment along the FD, in both samples. The SEM evaluation shows that a gradual change occurs in the spherulitic structure and seems to transform gradually and disappear almost for the 37% deformations. The sample with highest deformation shows thin shear bands oriented along the FD-view which originate an appearance of a layered structure. Concomitantly the crystalline lamellae were detected by TEM technique.     

Ge Pairs and Sb Ribbons in Rare‐Earth Germanium Antimonides RE12Ge7−xSb21 (RE=La–Pr)

The ternary rare‐earth germanium antimonides RE₁₂Ge_7?xSb₂₁ (RE=La–Pr; x=0.4–0.5) are synthesized by direct reactions of the elements. Single‐crystal X‐ray diffraction studies indicate that they adopt a new structure type (space group Immm, Z=2, a=4.3165(4)–4.2578(2) Å, b=15.2050(12)–14.9777(7) Å, c=34.443(3)–33.9376(16) Å in the progression from RE=La to Pr), integrating complex features found in RE₆Ge_5?xSb_11+x and RE₁₂Ga₄Sb₂₃. A three‐dimensional polyanionic framework, consisting of Ge pairs and Sb ribbons, outlines large channels occupied by columns of face‐sharing RE₆ trigonal prisms. These trigonal prisms are centered by additional Ge and Sb atoms to form GeSb₃ trigonal‐planar units. A bonding analysis attempted through a Zintl–Klemm approach suggests that full electron transfer from the RE atoms to the anionic substructure cannot be assumed. This is confirmed by band‐structure calculations, which also reveal the importance of Ge? Sb and Sb? Sb bonding. Magnetic measurements on Ce₁₂Ge_6.5Sb₂₁ indicate antiferromagnetic coupling but no long‐range ordering down to 2 K.     

The highly regiospecific synthesis and crystal structure determination of 1,1′-2,5′ substituted ring-locked ferrocenes

1,1′-Ferrocene biscarboxaldehyde (1) has been prepared and the aldehyde groups were subsequently protected with acetal groups to produce 1,1′-bisacetalferrocene (2). A ring-locked ferrocene was synthesised by further derivatisation of the cyclopentadiene rings at the 2,2′ positions with phosphine substituents to produce 2,2′-bis-(acetal)-1,1′-diphenylphosphinoferrocene (3), which was subsequently coordinated to either a nickel chloride (5) or nickel bromide (6) metal centre. The ring-locked ferrocene complexes produced 2,5′-bis-(acetal)-1,1′-diphenylphosphinoferrocene substitution patterns. The acetal protecting groups of 2,2′-bis-(acetal)-1,1′-diphenylphosphinoferrocene were removed to produce 1,1′-bis-carboxaldehyde-2,2′-diphenylphosphinoferrocene (4). The Cp rings of 1,1′-bisacetalferrocene were also further derivatised at the 2,2′ positions with a silane to produce the ring-locked 1,1′-siloxane-2,5′-bisacetalferrocenophane (7). The acetal protecting groups were removed from this to produce 1,1′-siloxane-2,5′-ferrocenophanecarboxaldehyde (8). For both the phosphine and siloxane electrophiles, the substitution on the Cp rings gives chiral products (obtained as racemic mixtures). Due to the highly regioselective nature of the reaction and diastereoselectivity in the products only C₂-symmetric compounds were observed without the presence of meso diastereoisomers. Subsequent ring-locking forced the Cp rings to rotate, leading to 1,1′-ring-locked ferrocenes with 2,5′-arrangement of the acetal groups (i.e. on opposite faces of the ferrocene unit).     

Synthesis of Stable Aminoacyl‐tRNA Analogues Containing Triazole as a Bioisoster of Esters

Stable analogues : An effective synthetic route involving cycloaddition between alkynes and azidonucleosides to afford a new class of stable aminoacyl‐tRNA analogues such as depicted is presented. Biological evaluation showed that theses new compounds act as potent inhibitors of FemX_Wv aminoacyl transferase, a novel drug target.

     

Sensitive femtosecond coherent anti-Stokes Raman spectroscopy discrimination between dipicolinic acid and dinicotinic acid

We demonstrate that femtosecond ultraviolet and visible coherent anti-Stokes Raman spectroscopy provides the sensitivity and specificity needed to distinguish between two similar molecules of pyridinedicarboxylic acid. The Fourier transforms of the temporal measurements provide the energy difference between the ground state vibrational modes. Quantum chemical calculations provide theoretical predictions that agree well with the measurements. The present technique allows us to distinguish 10 cm(-1) frequency shifts by using pulses ten times broader than the shifts.     

Impact of local diffusion on macroscopic dispersion in three-dimensional porous media

While macroscopic longitudinal and transverse dispersion in three-dimensional porous media has been simulated previously mostly under purely advective conditions, the impact of diffusion on macroscopic dispersion in 3D remains an open question. Furthermore, both in 2D and 3D, recurring difficulties have been encountered due to computer limitation or analytical approximation. In this work, we use the Lagrangian velocity covariance function and the temporal derivative of second-order moments to study the influence of diffusion on dispersion in highly heterogeneous 2D and 3D porous media. The first approach characterizes the correlation between the values of Eulerian velocity components sampled by particles undergoing diffusion at two times. The second approach allows the estimation of dispersion coefficients and the analysis of their behaviours as functions of diffusion. These two approaches allowed us to reach new results. The influence of diffusion on dispersion seems to be globally similar between highly heterogeneous 2D and 3D porous media. Diffusion induces a decrease in the dispersion in the direction parallel to the flow direction and an increase in the dispersion in the direction perpendicular to the flow direction. However, the amplification of these two effects with the permeability variance is clearly different between 2D and 3D. For the direction parallel to the flow direction, the amplification is more important in 3D than in 2D. It is reversed in the direction perpendicular to the flow direction.