Half-width scaling of electric field autocorrelation functions of light scattered from bull spermatozoa.

The half-width scaling of experimental and model electric field autocorrelation functions of light scattered from normally swimming, defectively swimming, and immotile bull spermatozoa is examined. It is found that a scatter of size 9.0 x 2.3 x 0.45 micrometers is most appropriate for this Rayleigh-Gans-Debye ellipsoid model. In the case of the immotile cells, this model correctly predicts the features seen in the scaling data as well as the absolute value of the data. For the normally swimming and defective populations the model proves to predict correctly the features seen in experimental scaling curves, but not the absolute value of the data. This discrepancy appears to be related to a lack of detail in the model, since the agreement is poorest at large scattering angles.     

Quasielastic light scattering from long rigid rods

The purpose of this work was to improve our understanding of quasielastic light scattering from long rigid rods (QL >> 1). For these scatterers, only small angular displacements are required to produce dephasing of the scattering light. This plus the fact that only rods lying perpendicular to Q contribute to the scattered light allow one to simplify the intermediate scattering function to an analytic form. This form is shown to be nonexponential, exhibiting (t)^?½ behavior at long delay times. This new scattering function can then be fit to experimental functions using standard methods.     

Rayleigh linewidths of laser light inelastically scattered from neural membranes

Laser light is scattered off the surface of nerve from the walking legs ofHomarus Americanus and the spectral power density of the Rayleigh line is obtained. The data is interpreted in terms of a relaxation time of a scattering unit. The experimental results are consistent with a scattering unit having a molecular weight of the order of 30,000 in a medium of several poise viscosity. The relaxation time for scattering is calculated to be 16±2μsec in the resting state and 10±2μsec in the depolarized state.     

Photon correlation spectroscopy of light scattered by eye lenses in in vivo conditions.

The application of photon correlation spectroscopy on mammalian eye lenses in vivo is revisited. It is shown that the use of a short wavelength laser type and a logarithmic correlator improves the signal-to-noise ratio to such an extent that shorter measurement times are possible without impairing the information content of the correlation function. Experimental correlation functions obtained in vivo on a rabbit eye lens, are analyzed with several techniques. The histogram approach is most successful for the determination of the distribution function of relaxation processes in the correlation function and proposes four different populations of components in the lens. This result is comparable to that from in vitro measurements on highly concentrated solutions of alpha-crystallins and of fiber cell cytoplasm, the former proteins being the main scattering components both in vivo and in vitro in the eye lens system. Our results indicate that the application of photon correlation spectroscopy on eye lenses in vivo offers new perspectives to use this technique as a fast, noninvasive tool to study relaxation phenomena in normal and cataractous lenses. The sensitivity of the method allows it to be used as an important analytical technique in the study of prevention and treatment of cataract.     

Intramolecular interference effects in dynamic light scattering from rigid rings

A formula for the apparent diffusion coefficient [D_app(κ)] of a rigid ring is derived from the exact first cumulant of its dynamic structure factor. D_app(κ) is expressed in terms of the ring radius, the diffusion coefficients (D_zz and D_xx) for translation parallel and perpendicular, respectively, to the symmetry axis, and the diffusion coefficients (D and D) for rotation around the symmetry and transverse axes, respectively. D_app(κ) exhibits oscillations as a function of the scattering vector k , which depend on D and the anisotropy of translational diffusion (D_zz ? D_xx). The maxima in D_app(κ) are associated with minima in the static structure factor S(κ, 0), which are due to destructive intramolecular interference. The oscillations in D_app(κ) result from periodic variations in the relative intensities of scattered light from different orientations of the ring, which manifest the various motions to different extents. The orientations contributing most to the scattered intensity are those that exhibit the least destructive interference and consequently contribute most to the decay of the dynamic structure factor. © 1993 John Wiley & Sons, Inc.     

The three-dimensional structure of supercoiled deoxyribonucleic acid in solution. Evidence obtained from the angular distribution of scattered light

1. The size and shape of superhelical double-stranded circular DNA from bacteriophage ØX174 were investigated by light-scattering. The molecular weight of the DNA is 3.17×10⁶ and the root-mean-square radius is 103.5nm. 2. The light-scattering envelopes of various theoretical three-dimensional models for such DNA molecules were calculated by repetitive computational techniques, and the results were compared with the experimental findings. 3. It is concluded that the structure of supercoiled DNA containing −12 superhelical turns in buffer of I0.2 corresponds best to one of the more compact models for superhelix structure such as the branched model, and the commonly employed straight interwound superhelix model is incompatible with the experimental results, at the superhelix density found.     

Variation in the intensity of scattered light by solutions of DNA subjected to an electric field

Preliminary experiments have been carried out which measure the variation in the intensity of the light scattered by DNA solutions under the influence of an electric field. Data have been collected on the length of DNA molecules, their electric polarizability, and their dispersion behavior.     

Molecular operational taxonomic units as approximations of species in the light of evolutionary models and empirical data from Fungi

During the last couple of decades, an increasing number of studies use sequence clusters as units for taxonomic diversity. It is well known that such molecular operational taxonomic units (MOTUs) do not necessarily correspond to species, but they are treated as such when measuring diversity and testing theories. Here, I show that data from studies of molecular evolution and species diversification of fungi indicate that commonly used cut‐offs are likely to lump species in many cases. At the same time, empirical studies show that the mean within‐species variation is close to these cut‐offs. That the within‐species variation estimates are plausible is supported by coalescence modelling under a range of parameter settings. In addition, studies using crossing tests to delimit species show that there often is an overlap in within‐ and between‐species distances. The available data therefore indicate that sequence clusters are likely to misrepresent species. However, to keep a biological relevance, MOTUs should be kept in close agreement with species. Studies using them should therefore asses how sensitive the results are to differences between MOTUs and species – something that is rarely done. An even better solution is to directly include the uncertainty in species delimitation in the analyses, but in many cases, we need to increase our knowledge of taxonomy and evolution to do this accurately. Even if the empirical data referred to here pertain to the “barcoding” region of rDNA in fungi, there is nothing indicating that the situation is substantially better for other taxa or genes.     

Dynamic light scattering from thin rigid rods: Anisotropy of translational diffusion of tobacco mosaic virus

An Exact theoretical expression for the apparent diffusion coefficient D_app(K) of a thin rigid rod with arbitrary anisotropy of its translational diffusion diffusion coefficient is derived from the first cumulant of its dynamic structure factor. D_app(K) is predicted to reach a limiting plateau value at extermely large values of KL, where K is the scattering vector and L the rod length. Howerver, that limiting plateau value is approached only very slowly along a quasi-plateau with a very gradual slope. Dynamic light-scattering studies have been performed on tobacco mosaic virus from K² = (0.4–20) × 10¹⁰ cm^?2 using 632-8-nm laser radiation. The present data yield D₀ = (4.19 ± 0.10) × 10^?8 cm²/s (corrected to 20,w conditions) and, with literature data to establish L = 2980 Å and the rotational diffusion coefficient D_R = 318s^?1, yield also Δ ≡ D_∥ ? D_⊥ = (1.79 ± 0.38) × 10^?8 cm²/s. The experimental data closely follow the curve of D_app(K) vs K² calcuated for these parameters. The present value of D₀ substantially exceeds all previous dynamic light-scattering values, but is in good aggreement with previous sedimentation data, which were confirmed for the presemt sample. The anisotropy ratio Δ/D₀ = 0.43 ± 0.09 is in accord with theoretical predictions based on the modified Kirkwood algorithm, despite the fact the D₀ lies significantly below its corresponding theoretical value. The present data largely predlude the possibility that both D₀ and Δ/D₀ could simultaneously match their theoretical predictions. We present a detailed comparison of the experimental data with the calculations of Tirado and Garcia de la Torre based on the modified Kirkwood algorithm and with the Broersma formulas.     

Structure and properties of cobalt ortho-phenylenediacetate coordination polymers with rigid dipyridyl ligands

Divalent cobalt coordination polymers containing both ortho-phenylenediacetate (ophda) and rigid dipyridyl ligands 4,4′-bipyridine (bpy) or 1,2-bis(4-pyridyl)ethylene (dpee) display different topologies depending on carboxylate binding mode, tether length, and inclusion of charged species. [Co(ophda)(H₂O)(dpee)]_n (1) displays a common (4,4) grid layer motif. Use of the shorter bpy tether afforded {[Co₂(ophda)₂(bpy)₃(H₂O)₂][Co(bpy)₂(H₂O)₄](NO₃)₂·2bpy·7H₂O}_n (2) or [Co(ophda)(bpy)]_n (3) depending on cobalt precursor. Compound 2 manifests 5-connected [Co₂(ophda)₂(bpy)₃(H₂O)₂]_n pillared bilayer slabs with rare 4⁸6² SnS topology and entrained [Co(bpy)₂(H₂O)₄]²⁺ complex cations. The 3-D coordination polymer 3 has an uncommon 4,6-connected binodal (4⁴6²)(4⁴6¹⁰8) fsc topology, and shows ferromagnetic coupling (J = +1.5(2) cm⁻¹) along 1-D spiro-fused [Co(OCO)₂]_n chain submotifs.     

Response of microbial adhesives and biofilm matrix polymers to chemical treatments as determined by interference reflection microscopy and light section microscopy.

The polymers involved in the adhesion of Pseudomonas fluorescens H2S to solid surfaces were investigated to determine whether differences between cell surface adhesives and biofilm matrix polymers could be detected. Two optical techniques, i.e., interference reflection microscopy (IRM) and light section microscopy (LSM), were used to compare the responses of the two types of polymer to treatment with electrolytes, dimethyl sulfoxide (DMSO), and Tween 20. To evaluate initial adhesive polymers, P. fluorescens H2S cells were allowed to attach to glass cover slip surfaces and were immediately examined with IRM, and their response to chemical solutions was tested. With IRM, changes in cell-substratum separation distance between 0 and ca. 100 nm are detectable as changes in relative light intensity of the image; a contraction of the polymer would be detected as a darkening of the image, whereas expansion would appear as image brightening. To evaluate the intercellular polymer matrix in biofilms, 3-day-old biofilms were exposed to similar solutions, and the resultant change in biofilm thickness was measured with LSM, which measures film thicknesses between 10 and 1,000 microns. The initial adhesive and biofilm polymers were similar in that both appeared to contract when treated with electrolytes and to expand when treated with Tween 20. However, with DMSO treatment, the initial adhesive polymer appeared to contract, whereas there was no change in thickness of the biofilm polymer. These results indicate that both polymers bear acidic groups and thus act electrostatically with cations and are able to enter into hydrophobic interactions.(ABSTRACT TRUNCATED AT 250 WORDS)     

A system for imaging transverse distribution of scattered light and chlorophyll fluorescence in intact rice leaves

In order to examine the transverse distribution of scattered light and chlorophyll fluorescence in intact rice leaves, a micro-fluorescence imaging system was devised using a microscope, a CCD camera with an image intensifier, an Ar and a He-Ne laser light source, an image processor, and a microcomputer. A laser light was projected vertically on to the surface of a rice leaf segment at a cut-edge, and scattered light and induced fluorescence were observed at the cut-section from a 90° angle to the axis of the laser beam. The intensity of scattered light showed a maximum at several micrometres depth from the leaf surface and a steep gradient afterwards. Fluorescence reached a maximum crossing with the decline curve of the scattered light. The maximum of fluorescence measured at 741 nm was observed at a greater depth from the leaf surface than that at 687 nm, suggesting that part of the fluorescence of the longer wavelength was emitted due to absorption of fluorescence of the shorter wavelength. Profiles of the scattered light and the chlorophyll fluorescence depended on leaf anatomy.     

Combined light and electron microscope immunocytochemical localization of scattered peptidergic neurons in the central nervous system

A pre-embedding immunocytochemical technique is described for combined light and electron microscope study of peptidergic neurons in the central nervous system. The protocol is especially designed to overcome the sampling problems inherent in electron microscope study of structures, such as luteinizing hormone-releasing hormone (LHRH) neurons, that are scattered individually across large brain regions. The fixation methods outlined for several mammalian species include immersion and vascular perfusion with acrolein. Fine-structural preservation and LHRH immunoreactivity obtained with this fixative are compared to results with more conventional fixatives. Vibratome sectioning and a "pretreatment" regime, which prepare the tissues for immunocytochemistry, are described. Immunocytochemical labeling is done with free-floating sections and the peroxidase-antiperoxidase unlabeled antibody enzyme technique. Techniques are also described for the subsequent processing of immunoreacted sections for electron microscopy. These methods ensure that the processed sections are readily scanned by light microscopy, so that regions containing immunoreactive structures can be specifically chosen for electron microscope analysis. Sample electron micrographs are shown that illustrate some fine structural features of LHRH neurons in rats, bats, ferrets, and monkeys, as revealed with the techniques described.