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PubMed2006

Correlation between HOMO alignment and contact resistance in molecular junctions: aromatic thiols versus aromatic isocyanides.

Understanding electron transport in metal-molecule-metal (MMM) junctions is of great importance for the advancement of molecular electronics. Critical factors that determine conductivity in a MMM junction include the nature of metal-molecule contacts and the electronic structure of the molecular backbone. We have studied the electronic transport property and the valence electronic structure on rigid, conjugated oligoacenes of increasing length with either thiol (-S) or isocyanide (-CN) linkers using conducting probe atomic force microscopy (CP-AFM) and ultraviolet photoelectron spectroscopy (UPS). We find that for these conjugated systems the Au-CN contact is more resistive than Au-S. The difference in contact resistance correlates with UPS measurements that show the highest-occupied molecular orbital (HOMO) of the isocyanide series is lower in energy (relative to the Fermi level of Au) than the HOMO of the thiol series, indicating the presence of a higher tunneling barrier at the contact for the isocyanide-linked molecules. By contrast, the difference in the HOMO positions for the two series of molecules does not appear to affect the length dependence of the junction resistance (i.e., the beta value = 0.5 A-1).

Journal Article↗
PubMed1965

Anomalous contraction of invertebrate striated muscle.

The phenomenon of A band shortening or contraction has been investigated in glycerinated myofibrils of Pecten irradians, Homarus americanus, Cambarus virilis, and Limulus polyphemus through the techniques of ultraviolet microbeam inactivation and polarization microscopy. With the former method, it has been shown that these muscles, even though exhibiting the shortening effect, contract in a manner consistent with only the sliding filament model. Intrinsic birefringence studies have indicated no significant changes in mass distribution or orientation within the shortened A bands. Except in the case of Limulus muscle, the shortening effect was seen only in contraction under tension. The magnitude of this anomalous phenomenon was dependent upon glycerination time and has been duplicated in rabbit psoas muscle through brief trypsin treatment. A band shortening could not be observed in glutaraldehyde-fixed muscle or in myofibrils glycerinated for only short periods. It has been concluded that the phenomenon of A band contraction is an artifact induced by the glycerination procedure, possibly through weakening of the sarcomere structure. However, the fact that the A band shortens under tension rather than lengthens poses an interesting paradox.

Adenosine Triphosphate↗
PubMed2005

Self-assembly of a novel beta-In2S3 nanostructure exhibiting strong quantum confinement effects.

The 3D beta-In2S3 flowerlike architecture assembled from nanoflakes was prepared via a novel complex-precursor assisted (CPA) solvothermal route. The as-prepared beta-In2S3 powder was characterized by X-ray diffraction pattern (XRD), X-ray photoelectron spectra (XPS), transition electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), ultraviolet-visible light (UV-vis) spectra, and photoluminescence spectrum. The novel 3D beta-In2S3 nanostructure exhibit a strong quantum confinement effect. FT-IR spectra were used to investigate the coordinative chemical effect in the complex. A possible mechanism was discussed.

Crystallization↗
PubMed1980

Ultraviolet induced lysosome activity in corneal epithelium.

A 5,000 W Xe-Hg high pressure lamp and a double monochromator were used to produce a 3.3 nm half-bandpass ultraviolet radiation at 295 nm. Pigmented rabbit eyes were irradiated with radiant exposures from 140 Jm-2 to 10,000 Jm-2 and evaluated by slit-lamp biomicroscopy, light and electron microscopy. Corneal threshold (Hc) was 200 Jm-2 and lens threshold (HL) was 7,500 Jm-2. The most repeatable and reliable corneal response to these levels of UV was the development of corneal epithelial granules. Histological changes included a loss of superficial epithelial cells and selective UV induced autolysis of the wing cells. It is suggested that the biomicroscopically observed granules are the clinical manifestation of the secondary lysosomes revealed by light and electron microscopy. It is proposed that UV breaks down the primary lysosome membranes to release hydrolytic enzymes which in turn form the secondary lysosomes during autolysis. Extreme levels of radiant exposure at 295 nm result in indiscriminate destruction of all layers of the corneal epithelium, but the posterior cornea was spared.

Animals↗
PubMed1962

Optical and electron microscopic changes in ultraviolet irradiated chromosome segments.

Chromosome segments of urodele cells lose some substance after irradiation with about 10(-1) ergs/micro(2) of heterochromatic ultraviolet light. These segments stain faintly or negatively with the Feulgen and pyronine-methyl-green methods and weakly with the Alfert-Gesch-wind stain for basic protein. In the living cells, Perry found in these chromosome segments a decrease of 50 to 60 per cent in absorption at 2400, 2600, and 2800 A, i.e., in the region of intense chromosomal absorption that is maximal at 2600 A. Apparently the material lost contains DNA (?DNP) and we call the process DNA-steresis. In such cells, fixed in neutral formalin in Tyrode's solution and stained with phosphotungstic acid, electron microscopy shows that the unirradiated parts of the chromosomes consist of (a) a homogeneous or finely fibrillar material (component-A) filling the meshes of (b) an irregular network with bars 40 to 300 A in diameter, some of which continue into a similar interchromosomal network. DNA-steretic portions of the chromosomes consist mainly of this network and only small amounts of component-A, which presumably contains the DNA. We have not been able to demonstrate DNA-steresis with the electron microscope after primary fixation with OsO(4) or KMnO(4). Structural changes due to DNA-steresis are compared with certain nuclear changes in the mitotic cycle.

Chromosomes↗
PubMed1993

Intravital and electron microscopic observation of Ito cells in rat hepatic microcirculation.

Intralobular distribution of Ito cells (fat-storing cells) in hepatic microcirculatory units was investigated through intravital fluorescence microscopy. By using a low-level ultraviolet epi-illumination and a sensitive silicon intensified target camera, the intrahepatic autofluorescence was visualized and digitally processed. In rats fed an ordinary diet, the ultraviolet-excited autofluorescence was composed of at least two different origins that could not be spectrophotometrically distinguished, namely, multiple patchy autofluorescence activities along the sinusoids and terminal hepatic venules and diffuse parenchymal autofluorescence. Multiple patchy activities showed a rapid photobleaching phenomenon under the continuous ultraviolet excitation. These fluorescent activities were completely eliminated by depleting the intrahepatic retinoid contents using a vitamin A-deficient diet for 4 weeks. Furthermore repeated administration of vitamin A significantly enhanced the patchy fluorescent activities. Electron microscopy revealed that these vitamin A fluorescent activities are colocalized with the fat droplets in Ito cells, providing evidence that Ito cells exist not only in perisinusoidal spaces but also in the perivascular spaces of the terminal hepatic and portal venules. The current intravital technique thus provides a new method to observe Ito cells in hepatic microcirculatory units in vivo.

Animals↗
PubMed1981

Spectral properties of fluorescence induced by glutaraldehyde fixation.

Following fixation with glutaraldehyde, tissues or gelatin films fluoresce. This fluorescence can be enhanced more than thirtyfold by several minutes exposure to near ultraviolet light. Longer wavelengths produce a smaller effect. The enhanced fluorescence is maximally excited at 540 nm (half-band width about 45 nm), and fluorescence emission peaks at 560 nm. The rate of photoenhancement is independent of temperature in the 12--30 degrees C range. Photoenhancement is greater at alkaline than acid pH; the pH dependence involves a single acid binding group with pK = 7.3. These effects are not observed following treatment with paraformaldehyde or prior reduction with boranedimethylamine. Schiff base linkages between the bifunctional cross-linking reagent and free amino groups therefore seem to be involved. The effects of pH and wavelength on the photoenhancement of fluorescence are best accounted for by a kinetic scheme that includes both photogeneration of fluorophore from an ultraviolet-absorbing precursor, and its subsequent photodestruction by visible light.

Aldehydes↗
PubMed2000

The antiviral activity exerted by vaccinia virus on the growth of herpes simplex virus in BS-C-1 cells.

The growth of herpes simplex virus type 2 (HSV-2) in BS-C-1 cells, was inhibited following super-infection with vaccinia virus. This inhibition was efficiently induced by both the intracellular mature virus (IMV) form of vaccinia virus and the extracellular enveloped virus (EEV), containing an additional external viral membrane. Treatment of vaccinia IMV with the detergents NP-40, Brij-58 or n-octyl-alpha-D-glucopyranoside, abolished its ability to inhibit the growth of HSV-2. Ultraviolet irradiation of vaccinia virus, that completely inactivated the infectivity of the virus, resulted in partial loss of the capability to inhibit the growth of HSV-2: 16-fold more irradiated virus was needed for the inhibition. Electron microscopy showed that the irradiated vaccinia virus adsorbed and penetrated into the HSV-infected cells but remained morphologically intact within the cells for at least 22 h. When the steps in the growth of HSV affected by the irradiated vaccinia virus were followed, it was found that while the synthesis of HSV DNA was partially decreased, the synthesis of HSV proteins was very strongly inhibited and virus particles were not formed.

Animals↗
PubMed2000

The ontogeny of ultraviolet sensitivity, cone disappearance and regeneration in the sockeye salmon Oncorhynchus nerka.

This study examines the spectral sensitivity and cone topography of the sockeye salmon Oncorhynchus nerka throughout its life history with special emphasis on ultraviolet sensitivity. Electrophysiological recordings from the optic nerve show that ultraviolet sensitivity is greatly diminished at the smolt stage but reappears in adult fish weighing about 201 g. Concomitantly, light microscopy observations of the retina show that ultraviolet cones disappear from the dorsal and temporal retina at the smolt stage but reappear at the adult stage. These changes occur for sockeye salmon raised in fresh water or salt water after smoltification. In contrast to this ultraviolet cycle, the other cone mechanisms (short-, middle- and long-wavelength-sensitive) and the rod mechanism remain present throughout ontogeny. The natural appearance and disappearance of ultraviolet cones in salmonid retinas follows surges in blood thyroxine at critical developmental periods. Their presence coincides with times of prominent feeding on zooplankton and/or small fish that may be more visible under ultraviolet light. It is proposed that the primary function of ultraviolet cones in salmonids is to improve prey contrast.

Animals↗
PubMed1982

[Spectrophotometric study of several rhodamines commonly used in microscopy (2)].

From the examination of the visible and ultraviolet spectra, together with the excitation and fluorescence spectra of the chromatographically pure samples of rhodamine B, rhodamine 6G and violamine R, it is possible to establish the nature of the chromophores in the samples we have studied. In particular there is a report on the possible structures of resonance of rhodamine B, from which it is possible to understand the spectral behaviour of the rhodamines we have studied.

Microscopy↗