Intramolecular metathesis of a vinyl group with vinylidene C=C double bond in Ru complexes

The cationic complex {[Ru]=C=CHCPh2CH2CH=CH2}BF4 (3a, [Ru] = (eta5-C5H5)(PPh3)2Ru) in solution transforms to {[Ru]=C=CHCH2CPh2CH=CH2}BF4 (4a) via a new metathesis process of the terminal vinyl group with the C=C of the vinylidene group which is confirmed by 13C labeling studies. This transformation is irreversible as revealed by deuteration and decomplexation studies. The cationic complex {[Ru]=C=CHCPh2CH2CMe=CH2}BF4 (3b) undergoes a cyclization process yielding 6b containing a eta2-cyclic allene ligand which is fully characterized by single-crystal X-ray diffraction analysis. Analogous complexes 4a' and 6b' ([Ru] = (eta5-C5H5)(dppe)Ru) containing dppe ligands were similarly obtained from protonation of the corresponding acetylide complexes via formation of vinylidene intermediate. Protonation of the acetylide complex containing a terminal alkynyl group [Ru]-CCCPh2CH2CCH (2c) generates the vinylidene complex {[Ru]=C=CHCPh2CH2CCH}BF4 (3c) which again undergoes an irreversible transformation to give {[Ru]=C=CHCH2CPh2CCH}BF4 (4c) possibly via a pi-coordinated alkynyl complex followed by hydrogen and metal migration. No similar transformation is observed for the analogous dppe complex 3c'. With an extra methylene group, complex {[Ru]=C=CHCPh2CH2CH2CH=CH2}BF4 (3d) and complex {[Ru]=C=CHCPh2CH2Ph}BF4 (3e) are stable. The presence of a gem-diphenylmethylene moiety at the vinylidene ligand with the appropriate terminal vinyl or alkynyl group along with the correct steric environment implements such a novel reactivity in the ruthenium vinylidene complexes.     

Effects of soluble surfactants on the deformation and breakup of stretching liquid bridges

Surfactants are routinely used to control the breakup of drops and jets in many applications such as inkjet printing, crop spraying, and DNA or protein microarraying. The breakup of surfactant-free drops and jets has been extensively studied. By contrast, little is known about the closely related problem of interface rupture when surfactants are present. Solutions of a nonionic surfactant, pentaethylene glycol monododecyl ether, or C12E5, in water and in 90 wt % glycerol/water are used to show the effects of surfactant and viscosity on the deformation and breakup dynamics of stretching liquid bridges. Equilibrium surface tensions for both solutions can be fitted with the Langmuir-Szyskowski equation. All experiments have been done at 24 degrees C. The critical micelle concentrations for C12E5 are 0.04 and 0.4 mM in water and the glycerol/water solution, respectively. With high-speed imaging, the dynamic shapes of bridges held captive between two rods of 3.15 mm diameter are captured and analyzed with a time resolution of 0.1-1 ms. The bridge lengths are 3.15 mm initially and about 5-7 mm at pinch-off. Breakup occurs after stretching for about 0.2-0.3 s, depending on the solution viscosity and the surfactant concentration. When the liquid bridges break up, the volume of the sessile drop left on the bottom rod is about 3 times larger than that of the pendant drop left on the top rod. This asymmetry is due to gravity and is influenced by the equilibrium surface tensions. Surfactant-containing low-viscosity water bridges are shown to break up faster than surfactant-free ones because of the effect of gravity. With or without surfactant, water bridges form satellite drops. Surfactant-containing high-viscosity glycerol/water bridges break up more slowly than surfactant-free ones because of strong viscous effects. Moreover, the shapes of the sessile drops close to breakup exhibit a "pear-like" tip; whether a satellite forms depends on the surface age of the bridge before stretching commences. These unexpected effects arising from the addition of surfactants are due to the capillary pressure reduction and Marangoni flows linked to dynamic surface tension.     

On the force field optimisation of $$\beta$$ β -lactam cores using the force field Toolkit

Journal of Computer-Aided Molecular Design - When employing molecular dynamics (MD) simulations for computer-aided drug design, the quality of the used force fields is highly important. Here we...     

Sequence Determination of a Tetrapeptide Using Long-Rang Heteronuclear Shift Correlation 2D NMR Spectroscopy

A tetrapeptide has been studied by means of NMR of ¹³C in natural abundance. By the combined application of various two-dimensional ¹H/¹H and ¹³C/¹H correlation techniques, the primary structure of the peptides could be unambiguously determined.     

Toward a four-toothed molecular bevel gear with C2-symmetrical rotors

The design, synthesis, conformational analysis, and variable-temperature NMR studies of pentiptycene-based molecular gears Pp(2)X, where Pp is the unlabeled (in 1H) or methoxy groups-labeled (in 1OM) pentiptycene rotor and X is the phenylene stator containing ortho-bridged ethynylene axles, are reported. The approach of using shape-persistent rotors of four teeth but C(2) symmetry for constructing four-toothed molecular gears is unprecedented. In addition, the first example of enantioresolution of chiral pentiptycene scaffolds is demonstrated. Density functional theory (DFT) and AM1 calculations on these Pp(2)X systems suggest two possible correlated torsional motions, geared rocking and four-toothed geared rotations, which compete with the uncorrelated gear slippage. The DFT-derived torsional barriers in 1H for rocking, four-toothed rotation, and gear slippage are approximately 2.9, 5.5, and 4.7 kcal mol(-1), respectively. The low energy barriers for these torsional motions result from the low energy cost of bending the ethynylene axles. Comparison of the NMR spectra of 1OM in a mixture of stereoisomers (1OM-mix) and in an enantiopure form (1OM-op) confirms a fast gear slippage in these Pp(2)X systems. The effect of the methoxy labels on rotational potential energy surface and inter-rotor dynamics is also discussed.     

Carteraol E, a potent polyhydroxyl ichthyotoxin from the dinoflagellate Amphidinium carterae

Carteraol E (1), C₇₄H₁₂₆O₂₄, a polyhydroxyl ichthyotoxin, was isolated from the lab-cultured marine dinoflagellate Amphidinium carterae. Carteraol E possessed three tetrahydropyrans, and 19 hydroxyl groups on a C69-linear aliphatic chain with a ketone moiety, an exo-methylene, and three methyl branches. The structure was elucidated by extensive analyses of 2D NMR spectra. Cateraol E exhibited potent ichthyotoxicity with LD₅₀ value of 0.28 μM, and antifungal activity against Aspergillus niger.     

Synthesis of photo-luminescent Zn(II) Schiff base complexes and its derivative containing Pd(II) moiety

An efficient method was developed for the preparation of a series of zinc Schiff base complexes. Introduction of a pyridyl group as a bridging unit as well as incorporation of ethynyl and electron-donating groups into the salicylidene moiety of these complexes moderately enhances the photoluminescence intensity and quantum yield. Electron-rich palladium groups possibly influence the photophysical character through the bridging C[triple bond]C bond. The crystal structure of the pyridine adduct of a salen Zn complex is determined by X-ray diffraction analysis.     

Synthesis of alkynylated photo-luminescent Zn(II) and Mg(II) Schiff base complexes

A new series of photo-luminescent Zn(II) and Mg(II) Schiff base complexes were prepared by treatment of the arylethynyl-substituted salicylaldehydes obtained from the Sonogashira reaction with the metal salt followed by addition of the different diamines. Most square-planar Zn(II) complexes exhibited good quantum efficiencies. The Mg(II) complexes displayed even higher quantum yields than the corresponding Zn-complexes. Unsymmetrical Zn(II) Schiff base complexes were also successfully prepared from organic monoimines obtained as intermediates in the formation of the Mg metal Schiff base complex. The monoimine can also be prepared from the reaction of salicylaldehydes with excess diaminoarene. Two crystal structures featuring the zinc atom are reported, one with a rare four-coordinate square planar geometry and the other with a five-coordinate square pyramidal geometry.     

Dynamic adsorption and surface tension of aqueous dilauroylphosphatidylcholine dispersions under physiological conditions

The dynamic surface tension and equilibrium adsorption behavior of DLPC dispersions in phosphate buffer saline at 37 and 25 degrees C was studied with tensiometry, infrared reflection--absorption spectroscopy (IRRAS), and ellipsometry. The results are compared with those in water (Pinazo et al. Langmuir 2002, 18, 8888). Even though the pH and salinity have no apparent effect on the equilibrium surface tension and the surface pressure--area isotherm, they affect the dynamic surface tension by decreasing the adsorption rate and increasing the dynamic tension minima at a pulsating area of 20 or 80 cycles per minute. Moreover, IRRAS and ellipsometry results show that the adsorbed layers and the spread monolayers have larger area per molecule, or looser packing, in buffer than in water. A new hypothesis is proposed to elucidate the effect of pH/salinity on this zwitterionic surfactant: there is some specific interaction or binding between the ions from the buffer saline with the polar headgroups of DLPC. This interaction induces stronger intermolecular repulsions of the surfactant layer in buffer than that in water, despite the expected electrostatic screening effect, and causes higher dynamic surface tensions. The results have implications in designing lung surfactant replacement formulations.     

Syntheses and Reactions of Rhenium Carbamoyl Complexes of the Type (CO)4Re(NH2R)(CONHR) (R = Ethyl,Allyl or Isopropyl)

Carbamoyl complexes, (CO)₄Re(NH₂R)(CONHR)(R = ethyl, 1; R = allyl, 2; R = isopropyl, 3) were prepared by reactions of (CO)₅ReBr (or (CO)₅ReCH₂SiMe₃) with appropriate amines. Complexes 1, 2 and 3 reacted with CH₃CH₂COCl to give Re(CO)₅(NH₂R)⁺Cl^? (R = ethyl, 4; R = allyl, 5; R - isopropyl, 6). Complex 5 undergoes nucleophilic attack by KOMe to give the alkoxycarbonyl complexes (CO)₄Re(NH₂-Allyl)(COOMe), 7. Complexes 4, 5, 6 and 7 were transformed to the corresponding carbamoyl complexes by reacting with appropriate amines. The reactions between the carbamoyl complexes and R″OH/CHCl₃ in air at room temperature gave the proposed products [(CO)₄Re(NH₂R)]₂O (R = allyl, 8; R = isopropyl, 9), respectively. Complex 8 can also be prepared by heating 7 in CDCl₃ at 63–68°C for several days. The structure of 1 was confirmed by a X-ray crystallographic study. Crystallographic data: space group P2₁/c, a = 8.193 (3) Å, b = 19.273 (3) Å, c = 9.348 (8) Å, β = 110.37 (4)°, V = 1383.68 ų, Z = 4; R(F) = 0.027, R_w(F) = 0.030, based on 1888 reflections with I > 2.5σ(I). The other complexes were characterized by ¹H NMR, ¹³CNMR, IR and mass spectra.