Purely rotational coherence effect and time-resolved sub-Doppler spectroscopy of large molecules I: Theoretical

Studies of ultrafast relaxation of molecular chromophores are complicated by the fact that most chromophores of biological and technological importance are rather large molecules and are strongly affected by their...

Download Full-text

High Resolution Laser Spectroscopy of Small Molecules and Clusters

Laser Chemistry ◽

10.1155/lc.11.209 ◽

1991 ◽

Vol 11 (3-4) ◽

pp. 209-223 ◽

Cited By ~ 2

Author(s):

V. Beutel ◽

H.-J. Böhm ◽

W. Demtröder ◽

H.-A. Eckel ◽

J. Gress ◽

...

Keyword(s):

High Resolution ◽

Small Molecules ◽

Excited States ◽

Laser Spectroscopy ◽

Molecular Species ◽

Molecular Beams ◽

Molecular Spectra ◽

Selective Detection ◽

Time Resolved ◽

Doppler Spectroscopy

The combination of high resolution laser spectroscopy in collimated cold molecular beams with mass selective detection allows investigations of rotationally resolved molecular spectra of selected molecular species in the presence of molecules with overlapping absorption spectra. This is illustrated by some examples, such as the isotope selective spectroscopy of Ag2–dimers or the sub-Doppler spectroscopy of Na3 in supersonic beam with a broad mass distribution of different clusters. Time resolved laser spectroscopy of excited states of alkali molecules, perturbed by bound dark states or by repulsive states, yields information about singlet–triplet mixing and predissociation rates.

Download Full-text

Microtubule nucleation sequence studied by time-resolved x-ray scattering and electron microscopy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100077402 ◽

1983 ◽

Vol 41 ◽

pp. 766-767

Author(s):

Eva-Maria Mandelkow ◽

Eckhard Mandelkow ◽

Joan Bordas

Keyword(s):

Electron Microscopy ◽

Dynamic Equilibrium ◽

Time Resolved ◽

X Ray ◽

Additional Information ◽

X Ray Scattering ◽

Low Concentrations ◽

Microtubule Growth ◽

Ray Patterns ◽

Ray Scattering

When a solution of microtubule protein is changed from non-polymerising to polymerising conditions (e.g. by temperature jump or mixing with GTP) there is a series of structural transitions preceding microtubule growth. These have been detected by time-resolved X-ray scattering using synchrotron radiation, and they may be classified into pre-nucleation and nucleation events. X-ray patterns are good indicators for the average behavior of the particles in solution, but they are difficult to interpret unless additional information on their structure is available. We therefore studied the assembly process by electron microscopy under conditions approaching those of the X-ray experiment. There are two difficulties in the EM approach: One is that the particles important for assembly are usually small and not very regular and therefore tend to be overlooked. Secondly EM specimens require low concentrations which favor disassembly of the particles one wants to observe since there is a dynamic equilibrium between polymers and subunits.

Download Full-text

Electron Channeling Patterns

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100077700 ◽

1977 ◽

Vol 35 ◽

pp. 12-13

Author(s):

David C. Joy

Keyword(s):

Electron Diffraction ◽

Incidence Angle ◽

Photographic Plate ◽

Diffraction Effect ◽

Angle Of Incidence ◽

Bulk Single Crystal ◽

Time Resolved ◽

Electron Channeling ◽

Spatially Resolved ◽

Large Bulk

Electron channeling patterns (ECP) were first found by Coates (1967) while observing a large bulk, single crystal of silicon in a scanning electron microscope. The geometric pattern visible was shown to be produced as a result of the changes in the angle of incidence, between the beam and the specimen surface normal, which occur when the sample is examined at low magnification (Booker, Shaw, Whelan and Hirsch 1967).A conventional electron diffraction pattern consists of an angularly resolved intensity distribution in space which may be directly viewed on a fluorescent screen or recorded on a photographic plate. An ECP, on the other hand, is produced as the result of changes in the signal collected by a suitable electron detector as the incidence angle is varied. If an integrating detector is used, or if the beam traverses the surface at a fixed angle, then no channeling contrast will be observed. The ECP is thus a time resolved electron diffraction effect. It can therefore be related to spatially resolved diffraction phenomena by an application of the concepts of reciprocity (Cowley 1969).

Download Full-text

The low-resolution 3D-structure of porin, a channel-forming protein in E. coliouter membranes

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100075932 ◽

1983 ◽

Vol 41 ◽

pp. 440-441

Author(s):

A. Engel ◽

D.L. Dorset ◽

A. Massalski ◽

J.P. Rosenbusch

Keyword(s):

Crystal Packing ◽

3D Structure ◽

Gram Negative Bacteria ◽

Protein Ratio ◽

Crystal Forms ◽

Large Molecules ◽

Functional Studies ◽

Voltage Dependent ◽

Planar Membranes ◽

Hexagonal Arrays

Porins represent a group of channel forming proteins that facilitate diffusion of small solutes across the outer membrane of Gram-negative bacteria, while excluding large molecules (>650 Da). Planar membranes reconstituted from purified matrix porin (OmpF protein) trimers and phospholipids have allowed quantitative functional studies of the voltage-dependent channels and revealed concerted activation of triplets. Under the same reconstitution conditions but using high protein concentrations porin aggregated to 2D lattices suitable for electron microscopy and image processing. Depending on the lipid-to- protein ratio three different crystal packing arrangements were observed: a large (a = 93 Å) and a small (a = 79 Å) hexagonal and a rectangular (a = 79 Å b = 139 Å) form with p3 symmetry for the hexagonal arrays. In all crystal forms distinct stain filled triplet indentations could be seen and were found to be morphologically identical within a resolution of (22 Å). It is tempting to correlate stain triplets with triple channels, but the proof of this hypothesis requires an analysis of the structure in 3 dimensions.

Download Full-text

Time-resolved high-resolution electron microscopy of structural stability in mgo clusters

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100165823 ◽

1996 ◽

Vol 54 ◽

pp. 672-673

Author(s):

T. Kizuka ◽

N. Tanaka

Keyword(s):

Electron Microscopy ◽

High Resolution ◽

Magnesium Oxide ◽

Structural Stability ◽

High Resolution Electron Microscopy ◽

Video Tape ◽

Solid State Physics ◽

Time Resolved ◽

Resolution Electron ◽

Structural And Functional Properties

Structure and stability of atomic clusters have been studied by time-resolved high-resolution electron microscopy (TRHREM). Typical examples are observations of structural fluctuation in gold (Au) clusters supported on silicon oxide films, graphtized carbon films and magnesium oxide (MgO) films. All the observations have been performed on the clusters consisted of single metal element. Structural stability of ceramics clusters, such as metal-oxide, metal-nitride and metal-carbide clusters, has not been observed by TRHREM although the clusters show anomalous structural and functional properties concerning to solid state physics and materials science.In the present study, the behavior of ceramic, magnesium oxide (MgO) clusters is for the first time observed by TRHREM at 1/60 s time resolution and at atomic resolution down to 0.2 nm.MgO and gold were subsequently deposited on sodium chloride (001) substrates. The specimens, single crystalline MgO films on which Au particles were dispersed were separated in distilled water and observed by using a 200-kV high-resolution electron microscope (JEOL, JEM2010) equipped with a high sensitive TV camera and a video tape recorder system.

Download Full-text