Supported lipid bilayers on biocompatible polysaccharide multilayers.

Formation of supported lipid bilayers on soft polymer cushions is a useful approach to decouple the membrane from the substrate for applications involving membrane proteins. We prepared biocompatible polymer cushions by the layer-by-layer assembly of two polysaccharide polyelectrolytes, chitosan (CHI) and hyaluronic acid, on glass and silicon substrates. (CHI/HA)(5) films were characterized by atomic force microscopy, giving an average thickness of 57 nm and roughness of 25 nm in aqueous solution at pH 6.

Cellular consequences of copper complexes used to catalyze bioorthogonal click reactions.

Copper toxicity is a critical issue in the development of copper-based catalysts for copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reactions for applications in living systems. The effects and related toxicity of copper on mammalian cells are dependent on the ligand environment. Copper complexes can be highly toxic, can induce changes in cellular metabolism, and can be rapidly taken up by cells, all of which can affect their ability to function as catalysts for CuAAC in living systems.

Time-resolved photoelectron spectroscopy: from wavepackets to observables.

Time-resolved photoelectron spectroscopy (TRPES) is a powerful tool for the study of intramolecular dynamics, particularly excited state non-adiabatic dynamics in polyatomic molecules. Depending on the problem at hand, different levels of TRPES measurements can be performed: time-resolved photoelectron yield; time- and energy-resolved photoelectron yield; time-, energy-, and angle-resolved photoelectron yield. In this pedagogical overview, a conceptual framework for time-resolved photoionization measurements is presented, together with discussion of relevant theory for the different aspects of TRPES.

Activity-based protein profiling of host-virus interactions.

Virologists have benefited from large-scale profiling methods to discover new host-virus interactions and to learn about the mechanisms of pathogenesis. One such technique, referred to as activity-based protein profiling (ABPP), uses active site-directed probes to monitor the functional state of enzymes, taking into account post-translational interactions and modifications. ABPP gives insight into the catalytic activity of enzyme families that does not necessarily correlate with protein abundance.

Pressure-induced formation of molecular B2X4(μ-X)2 (X = Cl, Br, I) species.

Boron(III) halides (BX(3), where X = F, Cl, Br, I) at ambient pressure conditions exist as strictly monomeric, trigonal-planar molecules. Using correlated ab initio calculations, the three heavier halides (X = Cl, Br, I) are shown to possess B(2)X(4)(μ-X)(2) local minima, isostructural with the diborane molecule. The calculated dissociation barrier of the B(2)I(4)(μ-I)(2) species [≈14 kJ/mol with CCSD(T)/cc-pVTZ] may be high enough to allow cryogenic isolation.

In vivo ¹H-NMR microimaging during seed imbibition, germination, and early growth.

Magnetic resonance imaging (MRI) is a superior noninvasive diagnostic tool widely used in clinical medicine, with more than 60 million MRI tests performed each year worldwide. More specialized high-resolution MRI systems capable of a resolution that is 100-1,000 times higher than standard MRI instruments are used primarily in materials science, but are used with increasing frequency in plant physiology. We have shown that high-resolution (1)H-nuclear magnetic resonance (NMR) microimaging can provide a wealth of information about the internal anatomy of plant seeds as small as 1 mm or even smaller.

In vivo nuclear magnetic resonance metabolite profiling in plant seeds.

Nuclear magnetic resonance (NMR) spectroscopy has been successfully applied to profile a variety of primary and secondary metabolites in whole intact plant seeds in vivo. The nondestructive nature of NMR spectroscopy allows direct metabolic studies to be performed on the same seed throughout a given physio-logical process or key lifecycle transition, such as dormancy breakage, germination, and early postgerminative growth. Multinuclear NMR is capable of evaluating seed quality by assessing nondestructively nutrient reserves and seed protectants at seed maturity and to further monitor reserve mobilization following germination, which is critical for seedling emergence.

Highly sensitive electrical detection of TCNE on chemically passivated silicon-on-insulator.

Adsorption of tetracyanoethylene (TCNE) onto hydrogen terminated, n-type silicon-on-insulator is shown to cause significant depletion of majority carriers. Employing an ambient pseudo-MOSFET, ppm levels of TCNE vapour rapidly decrease the n-channel saturation current by at least two orders of magnitude. Covalent passivation with a decyl monolayer improves the reversibility of the response while only slightly decreasing the sensitivity.

Metallization of solid hydrogen: the challenge and possible solutions.

The search for the means to convert molecular hydrogen to a metal under static conditions at high pressure is reviewed with emphasis on selected recent developments in both experimental studies and theoretical approaches. One approach suggested recently makes use of mixtures of hydrogen and suitable impurities. In these materials hydrogen is perturbed by impurities with the goal of obtaining the metallization of hydrogen at moderate pressures.

Through-bond interactions and the localization of excited-state dynamics.

The influence of through-bond interactions on nonadiabatic excited-state dynamics is investigated by time-resolved photoelectron spectroscopy (TRPES) and ab initio computation. We compare the dynamics of cyclohexa-1,4-diene, which exhibits a through-bond interaction known as homoconjugation (the electronic correlation between nonconjugated double bonds), with the nonconjugated cyclohexene. Each molecule was initially excited to a 3s Rydberg state using a 200 nm femtosecond pump pulse.

Strain-promoted cycloadditions of cyclic nitrones with cyclooctynes for labeling human cancer cells.

Strain-promoted cycloadditions of cyclic nitrones with cyclooctynes proceed with rate constants up to 3.38 ± 0.31 M(-1) s(-1) in CD(3)CN, or 59 times faster than the analogous reaction of azides.

Enhanced specificity of the viral suppressor of RNA silencing protein p19 toward sequestering of human microRNA-122.

Tombusviruses express a 19 kDa protein (p19) that, as a dimeric protein, suppresses the RNAs silencing pathway during infection by binding short-interfering RNA (siRNA) and preventing their association with the RNA-induced silencing complex (RISC). The p19 protein can bind to both endogenous and synthetic siRNAs with a high degree of size selectivity but with little sequence dependence. It also binds to other endogenous small RNAs such as microRNAs (miRNAs) but with lower affinity than to canonical siRNAs.

Single-domain antibody bioconjugated near-IR quantum dots for targeted cellular imaging of pancreatic cancer.

Successful targeted imaging of BxPC3 human pancreatic cancer cells is feasible with near-IR CdTeSe/CdS quantum dots (QDs) functionalized with single-domain antibody (sdAb) 2A3. For specific targeting, sdAbs are superior to conventional antibodies, especially in terms of stability, aggregation, and production cost. The bright CdTeSe/CdS QDs were synthesized to emit in the diagnostic window of 650-900 nm with a narrow emission band.

Highly-photoluminescent ZnSe nanocrystals via a non-injection-based approach with precursor reactivity elevated by a secondary phosphine.

Highly-photoluminescent ZnSe quantum dots with 72% quantum yield and 22 nm full width at half maximum were synthesized with more reactive precursors via a non-injection approach with high synthetic reproducibility; (31)P NMR provided insight into the formation mechanisms of ZnSe monomers.

In-situ observation of nucleation and growth of PbSe magic-sized nanoclusters and regular nanocrystals.

In-situ observation of the temporal evolution of the absorption of PbSe nanocrystals (NCs) via a low-temperature noninjection approach is presented. Based on a model reaction of lead oleate (Pb(OA)(2) ) and n-trioctylphosphine selenide (TOPSe) in 1-octadecene at 35-80 °C, the use of commercially available TOP (90 or 97%) in affecting the formation of the NCs is explored. TOPSe solutions made from TOP 90% exhibited higher reactivity than those made from TOP 97%.

Toughening of epoxy matrices with reduced single-walled carbon nanotubes.

Reduced single-walled carbon nanotubes (r-SWCNT) are shown to react readily at room temperature under inert atmosphere conditions with epoxide moieties, such as those in triglycidyl p-amino phenol (TGAP), to produce a soft covalently bonded interface around the SWCNT. The soft interface is compatible with the SWCNT-free cross-linked cured matrix and acts as a toughener for the composite. Incorporation of 0.

Analysis of kinetic isotope effects in enzymatic carbon-hydrogen cleavage reactions.

The instanton approach, as previously applied to proton tunneling in molecular systems, is adapted to carbon-hydrogen bond cleavage catalyzed by enzymes. To compensate for the complexity of enzymatic reactions, simplifications are introduced based on the observation in numerous X-ray measurements that enzymes tend to form compact structures, which is assumed to have led toward optimization of specific parameters that govern the tunneling rate in the instanton formalism. On this basis, semiempirical equations are derived that link observed kinetic data directly to these parameters.

Photochrome that was not: 2-hydroxynaphtylidene-(8-aminoquinoline).

We report the results of quantum-chemical calculations, which show that the keto form of 2-hydroxynaphtylidene-(8-aminoquinoline) (HNAQ) is slightly more stable than the enol form both in the ground and first excited ππ* electronic states. The barrier for proton transfer between the enol and the ketone in the ground state is ca. 3300 cm(-1) (HF), and 770 cm(-1) (B3LYP), indicating a very fast (ps scale) exchange of protons between the two tautomeric forms.

Low-temperature noninjection approach to homogeneously-alloyed PbSe(x)S(1-x) colloidal nanocrystals for photovoltaic applications.

Homogeneously alloyed PbSe(x)S(1-x) nanocrystals (NCs) with their excitonic absorption peaks in wavelength shorter than 1200 nm were developed for photovoltaic (PV) applications. Schottky-type solar cells fabricated with our PbSe₀.₃S₀.

Communication: Single crystal x-ray diffraction observation of hydrogen bonding between 1-propanol and water in a structure II clathrate hydrate.

Single crystal x-ray crystallography is used to detect guest-host hydrogen bonding in structure II (sII) binary clathrate hydrate of 1-propanol and methane. X-ray structural analysis shows that the 1-propanol oxygen atom is at a distance of 2.749 and 2.

Clusters of superparamagnetic iron oxide nanoparticles encapsulated in a hydrogel: a particle architecture generating a synergistic enhancement of the T2 relaxation.

Clusters of iron oxide nanoparticles encapsulated in a pH-responsive hydrogel are synthesized and studied for their ability to alter the T(2)-relaxivity of protons. Encapsulation of the clusters with the hydrophilic coating is shown to enhance the transverse relaxation rate by up to 85% compared to clusters with no coating. With the use of pH-sensitive hydrogel, difficulties inherent in comparing particle samples are eliminated and a clear increase in relaxivity as the coating swells is demonstrated.

Pseudo-bimolecular [2+2] cycloaddition studied by time-resolved photoelectron spectroscopy.

The first study of pseudo-bimolecular cycloaddition reaction dynamics in the gas phase is presented. We used femtosecond time-resolved photoelectron spectroscopy (TRPES) to study the [2+2] photocycloaddition in the model system pseudo-gem-divinyl[2.2]paracyclophane.

Forward-collected simultaneous fluorescence lifetime imaging and coherent anti-Stokes Raman scattering microscopy.

We demonstrate the simultaneous collection and separation of femtosecond-laser-based forward-collected coherent anti-Stokes Raman scattering (F-CARS) and two-photon-excitation-induced fluorescence lifetime images (FLIM) using time-correlated single photon counting (TCSPC). We achieve this in a nondescanned geometry using a single multimode fiber without significant loss of light, field of view, and most importantly, TCSPC timing fidelity. In addition to showing the ability to separate CARS images from FLIM images using time gating, we also demonstrate composite multimodal epicollected FLIM imaging with fiber-collected F-CARS imaging in live cells.