There are few comparative data as to whether plastic or self-expanding metallic stents are preferable for palliating malignant hilar biliary obstruction.
Thirty-day outcomes of consecutive endoscopic ...retrograde cholangiopancreatographies performed for malignant hilar obstruction at 6 private and 5 university centers were assessed prospectively.
Patients receiving plastic (N=28) and metallic stents (N=34) were similar except that metallic stent recipients more often had: Bismuth III or IV tumors (16/34 vs. 5/28 P=0.043), higher Charlson comorbidity scores (P=0.003), metastatic disease (P=0.006), and management at academic centers (P=0.018). The groups had similar rates of bilateral stent placement (4/28 vs. 5/34), and similar frequency of opacified but undrained segmental ducts (7/28 vs. 5/34). Adverse outcomes including cholangitis, stent occlusion, migration, perforation, and/or the need for unplanned endoscopic retrograde cholangiopancreatography or percutaneous transhepatic cholangiography occurred in 11/28 (39.3%) patients with plastic versus 4/34 (11.8%) with metal stents (P=0.017). By logistic regression, factors associated with adverse outcomes included plastic stent placement (odds ratio 6.32; 95% confidence interval 1.23, 32.56) and serum bilirubin (1.11/mg/dL above normal: 1.01, 1.22) but not center type or Bismuth class.
Metallic stent performance was superior to plastic for hilar tumor palliation with respect to short-term outcomes, independent of disease severity, Bismuth class, or drainage quality.
The structure of methylfluoroisocyanato silane (Me–SiHF–NCO) has been deduced by a combination of microwave (MW) spectra including data from 12,13C, 14,15N, and 28,29,30Si isotopomers, and ab initio ...calculations. The rotational constants (RC) for the most abundant isotopes are A = 6301.415(45), B = 1535.078(39), and C = 1310.485(39) MHz. The symmetric quartic centrifugal distortion constants have been identified, using the Ir representation for C 1 symmetry, which includes the 3-fold rotor. The spectra of the isotopomer combinations gave a partial substitution structure where the C2Si3, Si3N4, and N4C9 bond lengths are 1.8427(70), 1.7086(77), and 1.2120(90)Å; although the C2Si3N4 angle is close to tetrahedral (109.71° (52)), the Si3N4C9 angle is wide (157.69° (18)). The rotational constants are only consistent with a trans-orientation for each of the dihedral angles (HC2Si3N4, C2Si3N4C9, and Si3N4C9O10). The structural analysis was completed by calculations of the equilibrium structure, using MP3 in conjunction with an aug-cc-pVTZ basis set (434 Cartesian basis functions). This gave A = 6240.324, B = 1518.489, and C = 1297.819 MHz. The equilibrium structure bond lengths for C2Si3, Si3N4, and N4C9 were 1.8485, 1.7147, and 1.1947 Å, with the C2Si3N4 and Si3N4C9 angles 109.55 and 156.67°, respectively. Although the SiNC polynomial bending surface is complex, the data points can be fit to the simple form V(x) = 50.36(91)x 4 – 7.53(44)x 5, with comparatively little loss of accuracy. The A-rotational constant is strongly influenced by the Si3N4C9 angle, and smaller bases lead to this angle being nearly linear. The theoretical results suggest a very heavily polarized molecule, which is supported by the positions of the local electron density minima within the bonds and electron density calculations.
Purpose: This archival study examined the relationship between the speech sound production skill of kindergarten children and literacy outcomes in Grades 1-3 in a data set where most children's ...vocabulary skills were within normal limits, speech therapy was not provided until 2nd grade, and phonological awareness instruction was discouraged at the time data were collected. Method: Data were accessed from the Templin Archive (2004), and the speech sound production skill of 272 kindergartners were examined relative to literacy outcomes in 1st and 2nd grade (reading) and 3rd grade (spelling). Results: Kindergartners in the 7th percentile for speech sound production skill scored more poorly in 1st- and 2nd-grade reading and 3rd-grade spelling than did kindergartners with average speech sound production skill; kindergartners in the 98th percentile achieved superior literacy skills compared to the mean. Phonological awareness mediated the effects of speech sound production skill on reading and spelling; vocabulary did not account for any unique variance. Conclusion: Speech sound disorders appear to be an overt manifestation of a complex interaction among variables influencing literacy skills, including nonlanguage cognition, vocabulary, letter knowledge, and phonological awareness. These interrelationships hold across the range of speech sound production skill, as children with superior speech sound production skill experience superior literacy outcomes.
The infrared and Raman spectra of 1-chloro-1-methyl-1-silacyclohexane were recorded between 293 and 78K, and a conformational equilibrium was established in the vapor, liquid, supercooled liquid and ...solid plastic phases. The a(Cl) had lower enthalpy than e(Cl); only a(Cl) was present in the crystal. DFT calculations revealed ΔH(e(Cl)–a(Cl)) to be in the range 3.2–2.4kJmol−1. The 32A′ and 25A″ modes of both conformers were assigned from the spectra and supported by B3LYP/cc-PVTZ calculations in the anharmonic approximation. Display omitted
•Infrared and Raman spectra of 1-chloro-1-methyl-1-silacyclohexane.•Attribution of equatorial (e) and axial (a) conformers from spectra of the crystal.•Assignments of the A′ and A″ modes of the e and a conformers.•Determination of the enthalpy difference ΔH between the e and a conformers from variable temperature Raman spectra.•DFT calculations of vibrational modes in the anharmonic approximation.
A 1,1-disubstituted silacyclohexane, 1-chloro-1-methyl-1-silacyclohexane, C5H10SiClCH3, was synthesized and studied by infrared and Raman spectroscopy. The infrared spectra of the vapor and liquid were recorded at ambient temperature and the solid sample investigated at 78K. Negligible spectral changes ocurred at 78K compared with the fluid state, but after annealing to ca. 165K an apparent crystal was formed.
Raman spectra of the liquid were recorded at 293K and depolarization data obtained. Additional Raman spectra were recorded at various temperatures between 293 and 143K. A supercooled liquid appeared after slow cooling, but an amorphous solid phase was observed after shock freezing to 78K. After annealing, a plastic phase was observed and an anisotropic crystal appeared after further annealing. In the crystalline phase spectral shifts and some vanishing bands were observed and only the a (Cl) conformer remained.
The compound exists in two conformers, equatorial (Cl) (e) and axial (Cl)(a) in the liquid, amorphous and plastic phases, but only the a-conformer was present in the crystal. The experimental results suggest that the a-conformer has 1.5±0.5kJmol−1 lower enthalpy than e in the liquid.
B3LYP calculations with various basis sets and the G3 model chemistry gave conformational energy difference ΔE (a–e) in the range 3.2–2.4kJmol−1. Infrared and Raman intensities, polarization ratios and vibrational frequencies for the two conformers were calculated. The 32A′ and 25A″ modes for the e(Cl) and a(Cl) conformations were assigned, supported by anharmonic B3LYP/cc-pVTZ calculations.
Bis(cyclopentadienyl) complexes (Cp2M) of the divalent first-row transition metals V−Ni have been known and used for over 50 years. For almost as long, an analogous series of compounds has been known ...with the indenyl ligand (i.e., Ind2M), with the conspicuous exception of M = Mn. Bis(indenyl) complexes of manganese(II), Ind′2MnL n , have now been synthesized by halide metathesis from MnCl2 and an appropriate potassium indenide. Depending on the indenyl ligand substituents and the presence of coordinated bases, a variety of structural motifs and bonding modes of the indenyl ligand are found in the resulting complexes. Single-crystal X-ray structures obtained for 2-(SiMe3)C9H62Mn, 1,3-(SiMe3)2C9H52Mn, and 1,3-(i-Pr)2C9H52Mn confirm that they possess classic η5-bound sandwich structures. In contrast, the unsubstituted parent complex recrystallizes from THF as a disolvate with two differently bonded indenyl ligands: i.e., (η3-C9H7)(η1-C9H7)Mn(thf)2. Without the coordinated solvent, density functional theory calculations suggest that the complex would have two slipped η5-bound ligands. When methyl groups are present on the benzo portion of the indenyl ligand, specifically in the 4,7-positions, the corresponding manganese complex is isolated as a cyclic octomer, {(4,7-Me2C9H5)2Mn}8, containing both bridging and terminal indenyl ligands. In the presence of 1,4-dioxane, however, attempted synthesis of (4,7-Me2C9H5)2Mn results in the isolation of the K(dioxane)1.5Mn(4,7-Me2C9H5)3 salt, in which each manganese atom is surrounded by a paddlewheel of three η2-bound 4,7-dimethylindenyl ligands. Cation−π bonding to the potassium and the presence of coordinated dioxane molecules generates a layered structure for the salt. Magnetic susceptibility measurements on the compounds indicate the presence of high-spin Mn(II) centers in all cases. These compounds demonstrate the high degree of conformational flexibility in the Mn(II)−indenyl bond.
The rotational orientation of cyclopentadienyl rings usually has no effect on d-orbital energy levels and splitting in transition metal complexes. With related but less symmetrical carbocyclic ...ligands, however, the magnetic properties of the associated complexes can be altered by the alignment of the ligands. Examples of this effect are found in substituted organochromium(II) bis(indenyl) complexes. The monosubstituted compounds (1-RC(9)H(6))(2)Cr (R = t-Bu, SiMe(3)) are prepared from the substituted lithium indenides and CrCl(2) in THF; they are high-spin species with four unpaired electrons. Their spin state likely reflects that in the unknown monomeric (C(9)H(7))(2)Cr, which is calculated to have a high-spin (S = 2) ground state in the staggered configuration (180 degrees rotation angle). However, the analogous bis(indenyl) complexes containing t-Bu or SiMe(3) groups in both the 1 and 3 positions on the indenyl ligands ((1,3-R(2)C(9)H(5))(2)Cr) are low-spin compounds with two unpaired electrons. X-ray diffraction results indicate that 1-(t-Bu)C(9)H(6)(2)Cr exists in a staggered conformation, with Cr-C (av) = 2.32(4) A. In contrast, the average Cr-C distances in 1,3-(t-Bu or SiMe(3))(2)C(9)H(5)(2)Cr are 2.22(2) and 2.20(2) A, respectively, and the rings are in a gauche configuration, with rotation angles of 87 degrees. The indenyl conformations are sterically imposed by the bulk of the t-Bu and SiMe(3) substituents. The change from a staggered to a gauche indenyl orientation lowers the symmetry of a (C(9)H(7))(2)M complex and allows greater mixing of metal and ligand orbitals. Calculations indicate that previously nonbonding pi orbitals of the indenyl anion are able to interact with the chromium d orbitals, producing bonding and antibonding combinations. The latter remain unpopulated, and the resulting increase in the HOMO-LUMO gap forces the complexes to adopt a low-spin configuration. The possibility of using sterically imposed ligand rotation as a means of spin-state manipulation makes indenyl compounds a potentially rich source of magnetically adjustable molecules.
The structure of methyldifluoroisocyanato silane, MeF2SiNCO (2), has been studied by molecular rotational spectroscopy. The rotational spectrum has a complicated structure from 14N nuclear quadrupole ...coupling and internal rotation of the methyl group. Cavity Fourier-transform microwave spectroscopy measurements were important for providing high spectral resolution to analyze the quadrupole and internal rotation fine structure. Broadband chirped-pulse Fourier-transform microwave spectroscopy was used to achieve high measurement sensitivity making it possible to observe the lower abundance C, N, O, and Si isotopologues in natural abundance for structure determination. Analysis of the microwave spectrum of the most abundant isotopomer of MeF2SiNCO (2) yields the rotational constants: A = 3827.347(7), B = 1264.5067(14), and C = 1240.6182(11) MHz. The spectrum has been analyzed in the I r representation for Cs symmetry, with inclusion of the 3-fold rotor (V 3 = 446(50) cm–1). A partial substitution structure was obtained for the C, Si, N, and O atoms. The analysis was assisted by calculations of the equilibrium structure, using a 6-311++G (3df, 3pd) basis set, with calculations at each of the B3LYP, MP2, and CCSD(T) levels. The calculated and experimental rotational constants are only consistent with a trans-orientation at each of the HCSiN, CSiNC, and SiNCO centers; there is relatively close agreement between the experimental and the theoretical structures, especially at the CCSD(T) level. In addition, the observed low value for the 14N quadrupole coupling term (χ bb – χ cc ) implies a wide SiNC angle, which is consistent with the calculated values: 165.3° (B3LYP), 157.6° (MP2), and 157.4° (CCSD(T)). The skeletal bending potential is discussed.
Reaction of (TMEDA)Pd(CH3)2 (TMEDA = tetramethylethylenediamine) with primary perfluoroalkyl iodides gives a mixture of products that depend markedly on the choice of solvent. In hexanes, ...(TMEDA)PdMe(RF) RF = n-C3F7 (1); n-C4F9 (2) is afforded in about 50% yield, with (TMEDA)Pd(CH3)I (3) formed concurrently. In hexanes 3 precipitates from solution and does not react further, but with THF as the solvent 3 remains in solution and reacts with RFI in the presence of light to give (TMEDA)PdI(RF) RF = n-C3F7 (4); n-C4F9 (5) and (TMEDA)PdI2, as well as 1 and 2, respectively. Treatment of either 1 or 2 with I2 yields the corresponding iodide compounds 4 and 5, with elimination of CH3I, while an analogous reaction of 2 with concentrated HCl produces the chloride compound (TMEDA)PdCl(C4F9) (8). In contrast, reaction of (TMEDA)Pd(CH3)2 with the secondary iodide ICF(CF3)2 gives only one fluoroalkyl product, (TMEDA)Pd(CH3)(i-C3F7) (6), in either hexanes or THF. Reaction of 6 with I2 occurs with selective cleavage of the Pd−CH3 bond to give the iodide product (TMEDA)PdI(i-C3F7) (7). The solid-state structures of 1−5, 7, and 8 have been confirmed by X-ray crystallography. Examination of bond distances illustrates that fluoroalkyl ligands have smaller trans-influences than methyl ligands, but larger trans-influences than iodide or chloride ligands toward the N-donor TMEDA ligand. This results in a shorter, presumably stronger Pd−fluoroalkyl bond being trans to a shorter, presumably stronger Pd−N bond. The principal steric effect of the perfluoroisopropyl group in the solid state is to generate an almost planar TMEDA ring. The solution NMR data for 1, 2, 4, 5, and 8 show resonances due to diastereotopic CF2 groups below room temperature, with the CF2 group acting as a remote sensor for formation of a stereocenter at the metal due to slowing of the inversion of the puckered five-membered metallacycle formed by the TMEDA ligand and Pd. The other TMEDA complexes show the same behavior below room temperature, with the exception of (TMEDA)PdI(i-C3F7) (7), in which the TMEDA ring is presumably almost planar in the ground state.
Select C(α), N‐carbo‐tert‐butoxyhydrazones were dilithiated with excess lithium diisopropylamide followed by condensation with methyl 2‐(aminosulfonyl)benzoate, acid cyclization, hydrolysis, and ...decarboxylation to afford new 2‐(1H‐pyrazol‐5‐yl)benzenesulfonamides, NH‐pyrazolyl‐ortho‐benzene‐sulfonamides.
Reaction of 2 equiv of potassium indenide (KInd) with AeI2 (Ae = Ca, Sr, Ba) in THF produces the bis(indenyl) complexes (Ind)2Ae(thf) n (n = 1 for Sr, Ba; n = 2 for Ca) in high yields. The use of ...potassium 1,3-diisopropylindenide (KInd2i) with the same diiodides produces the analogous complexes (Ind2i)2Ae(thf) n (n = 1 for Ca; n = 2 for Sr and Ba). All the complexes are air-sensitive solids. Single-crystal X-ray diffraction studies were completed for (Ind)2Ca(thf)2, (Ind2i)2Ca(thf), (Ind2i)2Ba(thf)2, and (Ind)2Sr(thf); these represent the first structurally characterized indenyl complexes of the heavier alkaline-earth metals. The calcium and barium compounds are monomeric, with bent metallocene geometries and average Ae−C distances of 2.73(3), 2.69(2), and 3.03(4) Å for (Ind)2Ca(thf)2, (Ind2i)2Ca(thf), and (Ind2i)2Ba(thf)2, respectively. The strontium complex is an infinite coordination polymer, (Ind)2Sr(thf)∞, with both terminal (Sr−C = 2.94 Å (av)) and bridging (Sr−C = 3.07 Å (av)) indenyl ligands. Although the individual Sr−C bond distances differ as much as 0.25 Å, there is no clear indication of slippage toward an η3-configuration. The presence of the two isopropyl substituents on the indenyl ligands makes them effectively as bulky as triisopropylcyclopentadienyl rings.
