Unusual low-energy phonon dynamics in the negative thermal expansion compound ZrW2O8

An infrared study of the phonon spectra of ZrW2O8 as a function of temperature which includes the low-energy (2-10 meV) region relevant to negative thermal expansion is reported and discussed in the context of specific heat and neutron density of state results. The prevalence of infrared active phonons at low energy and their observed temperature dependence are highly unusual and indicative of exotic low-energy lattice dynamics. Eigenvector calculations indicate a mixing of librational and translational motion within each low-frequency IR mode. The role of the underconstrained structure in establishing the nature of these modes and the relationship between the IR spectra and the large negative thermal expansion in ZrW2O8 are discussed.     

NMR and ion selective electrode studies of hydraphile channels correlate with biological activity in E. coli and B. subtilis

Previous sodium ion transport results obtained by NMR methods are compared with those obtained by a new ISE technique and are found to correlate well with each other and with the biological activity against E. coli and B. subtilis.     

Attenuation and coupling of far infrared surface plasmos

Far infrared surface plasmon propagation has been studied on Ge coated Au and Pb surfaces. Attenuation coefficients in reasonable agreement with Drude theory are found. Anomalously large surface plasmon attenuation coefficients for bare metal surfaces reported by earlier investigators are reinterpreted in terms of bulk wave packet spreading near the surface.     

The C-terminal ester of membrane anchored peptide ion channels affects anion transport

Five heptapeptide derivatives, [CH3(CH2)17]2NCOCH2OCH2CO-Gly-Gly-Gly-Pro-Gly-Gly-Gly-OR, in which R = ethyl, 2-propyl, heptyl, benzyl, and cyclohexylmethyl, were found to transport chloride anion through a phospholipid bilayer to varying extents dependent on the identity of R. It was concluded that the R group is a membrane anchor for the synthetic chloride channels.     

Dynamic assessment of bilayer thickness by varying phospholipid and hydraphile synthetic channel chain lengths

A library of "hydraphile" synthetic ion channel analogues that differ in overall length from approximately 28-58 A has been prepared. A new and convenient ion-selective electrode (ISE) method was used to assay Na(+) release. Liposomes were formed from three different phospholipids: 1,2-dimyristoleoyl-sn-glycero-3-phosphocholine (DMPC), 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), and 1,2-dierucoyl-sn-glycero-3-phosphocholine (DEPC). The acyl chains of the lipids comprise cis-unsaturated 14:1, 18:1, or 22:1 residues, respectively. Sodium release was measured for each liposome system with each of the synthetic channels. Peak activity was observed for shorter channels in liposomes formed from DMPC and for longer channels in DEPC. A separate study was then conducted in DMPC liposomes in the presence of the putative membrane-thickening agents cholesterol and decane. Peak activity was clearly shifted to longer channel lengths upon addition of 20 or 40 mol % cholesterol or n-decane to the liposome preparation.     

Charge-transfer biexciton annihilation in a donor–acceptor co-crystal yields high-energy long-lived charge carriers

Organic donor–acceptor (D–A) co-crystals have attracted much interest due to their important optical and electronic properties. Co-crystals having ⋯DADA⋯ π-stacked morphologies are especially interesting because photoexcitation produces a charge-transfer (CT) exciton, D˙⁺–A˙⁻, between adjacent D–A molecules. Although several studies have reported on the steady-state optical properties of this type of CT exciton, very few have measured the dynamics of its formation and decay in a single D–A co-crystal. We have co-crystallized a peri-xanthenoxanthene (PXX) donor with a N,N-bis(3-pentyl)-2,5,8,11-tetraphenylperylene-3,4:9,10-bis(dicarboximide) (Ph4PDI) acceptor to give an orthorhombic PXX–Ph4PDI ⋯DADA⋯ π-stacked co-crystal with a CT transition dipole moment that is perpendicular to the transition moments for S_n ← S₀ excitation of PXX and Ph4PDI. Using polarized, broadband, femtosecond pump–probe microscopy, we have determined that selective photoexcitation of Ph4PDI in the single co-crystal results in CT exciton formation within the 300 fs instrument response time. At early times (0.3 ≤ t ≤ 500 ps), the CT excitons decay with a t^−1/2 dependence, which is attributed to CT biexciton annihilation within the one-dimensional ⋯DADA⋯ π-stacks producing high-energy, long-lived (>8 ns) electron–hole pairs in the crystal. These energetic charge carriers may prove useful in applications ranging from photovoltaics and opto-electronics to photocatalysis.

Femtosecond transient absorption microscopy of donor–acceptor single co-crystals shows that photogenerated charge transfer excitons in one-dimensional donor–acceptor π stacks annihilate to produce high-energy, long-lived electrons and holes.     

Synthetic hydraphile channels of appropriate length kill Escherichia coli

Crown ether-based synthetic cation conducting channels called hydraphiles show clear ionophoretic activity in phospholipid vesicles. These compounds are shown to be active against the bacterium E. coli. Disk diffusion assays were performed to assess the toxicity of different hydraphile derivatives. Liquid culture tests were conducted to quantitate the dependence of bacterical activity on channel length. It is proposed that hydraphiles are toxic to bacteria as a result of channel formation in the membrane. The bactericidal activity is found to depend at least on the presence of a functional central relay and proper channel length. It is speculated that hydraphiles insert into the bilayer and disrupt the cell's osmotic balance, leading to cell death.