Interactions of poly(amidoamine) dendrimers with Survanta lung surfactant: the importance of lipid domains

The interaction of generation 5 (G5) and 7 (G7) poly(amidoamine) (PAMAM) dendrimers with mica-supported Survanta bilayers is studied with atomic force microscopy (AFM). In these experiments, Survanta forms distinct gel and fluid domains with differing lipid composition. Nanoscale defects are induced by the PAMAM dendrimers. The positively charged dendrimers remove lipid from the fluid domains at a significantly greater rate than for the gel domains. Dendrimer accumulation on lipid edges and terraces preceding lipid removal has been directly imaged. Immediately following lipid removal, the mica surface is clean, indicating that lipid defects are not induced by dendrimers binding to the mica substrate and displacing the lipid.     

Poly(amidoamine) dendrimers on lipid bilayers I: Free energy and conformation of binding

Third-generation (G3) poly(amidoamine) (PAMAM) dendrimers are simulated approaching 1,2-dimyristoyl- sn-glycero-3-phosphocholine (DMPC) bilayers with fully atomistic molecular dynamics, which enables the calculation of a free energy profile along the approach coordinate. Three different dendrimer terminations are examined: protonated primary amine, uncharged acetamide, and deprotonated carboxylic acid. As the dendrimer and lipids become closer, their attractive force increases (up to 240 pN) and the dendrimer becomes deformed as it interacts with the lipids. The total energy release upon binding of a G3-NH3+, G3-Ac, or G3-COO- dendrimer to a DMPC bilayer is, respectively, 36, 26, or 47 kcal/mol or, equivalently, 5.2, 3.2, or 4.7x10(-3) kcal/g. These results are analyzed in terms of the dendrimers' size, shape, and atomic distributions as well as proximity of individual lipid molecules and particular lipid atoms to the dendrimer. For example, an area of 9.6, 8.2, or 7.9 nm2 is covered on the bilayer for the G3-NH3+, G3-Ac, or G3-COO- dendrimers, respectively, while interacting strongly with 18-13 individual lipid molecules.     

Rovibrational energy transfer in the 4nuCH manifold of acetylene, viewed by IR-UV double resonance spectroscopy. 5. Detailed kinetic model

Time-resolved infrared-ultraviolet double resonance (IR-UV DR) spectroscopy provides a distinctive way to examine collision-induced state-to-state energy transfer between rotational J-levels in vibrational manifolds of small polyatomic molecules, such as acetylene (C2H2) in its electronic ground state X. We consider the 4nuCH rovibrational manifold of C2H2 at approximately 12,700 cm(-1), where the principal source of IR-brightness is the (nu1+3nu3) or (1 0 3 0 0)0 Sigma+u vibrational combination level. In this highly congested manifold, anharmonic, l-resonance, and Coriolis couplings affect the J-levels of interest, implicating them in a complicated variety of intramolecular dynamics. Previous papers of this series have reported several seemingly anomalous J-resolved phenomena induced by collisions in C2H2 gas at room temperature with pressures and IR-UV pump-probe delay intervals corresponding to remarkably high Lennard-Jones collisional efficiencies P: odd-DeltaJ rotational energy transfer (10(-3)相似文献   

Above threshold dissociation of vibrationally cold HD+ molecules

The experimental study of molecular dissociation of H2+ by intense laser pulses is complicated by the fact that the ions are initially produced in a wide range of vibrational states, each of which responds differently to the laser field. An electrostatic storage device has been used to radiatively cool HD+ ions enabling the observation of above threshold dissociation from the ground vibrational state by 40 fs laser pulses at 800 nm. At the highest intensities used, dissociation through the absorption of at least four photons is found to be the dominant process.     

Collapse of the N=28 shell closure in (42)Si

The energies of the excited states in very neutron-rich (42)Si and (41,43)P have been measured using in-beam gamma-ray spectroscopy from the fragmentation of secondary beams of (42,44)S at 39A MeV. The low 2(+) energy of (42)Si, 770(19) keV, together with the level schemes of (41,43)P, provides evidence for the disappearance of the Z=14 and N=28 spherical shell closures, which is ascribed mainly to the action of proton-neutron tensor forces. New shell model calculations indicate that (42)Si is best described as a well-deformed oblate rotor.     

Novel approach to the lundurine alkaloids: synthesis of the tetracyclic core

The tetracyclic core of the lundurine family of alkaloids has been synthesized by a novel approach that features a double ring-closing olefin metathesis to form the five-and eight-membered rings.     

Remote functionalisation via sodium alkylamidozincate intermediates: access to unusual fluorenone and pyridyl ketone reactivity patterns

Treating fluorenone or 2-benzoylpyridine with the sodium zincate [(TMEDA)·Na(μ-(t)Bu)(μ-TMP)Zn((t)Bu)] in hexane solution, gives efficient (t)Bu addition across the respective organic substrate in a highly unusual 1,6-fashion, producing isolable organometallic intermediates which can be quenched and aerobically oxidised to give 3-tert-butyl-9H-fluoren-9-one and 2-benzoyl-5-tert-butylpyridine respectively.