Life Sciences Commons^™

Induction Of Crystallization Of Calcium Oxalate Dihydrate In Micellar Solutions Of Anionic Surfactants, H. Füredi-Milhofer, L. Tunik, N. Filipovic-Vincekovic, D. Skrtic, V. Babic-Ivancic, N. Garti

Scanning Microscopy

Calcium oxalate dihydrate (CaC₂O₄.(2+x)H₂O; COD; x ≤ 0.5) does not readily crystallize from electrolytic solutions but appears as a component in crystalluria. In this paper, we review in vitro studies on the factors responsible for its nucleation and growth with special attention given to the role of surfactants. The following surfactants were tested: dodecyl ammonium chloride (cationic), octaethylene monohexadecylether (non-ionic), sodium dodecyl sulfate (SOS, anionic), dioctyl sulphosuccinate (AOT, anionic), and sodium cholate (NaC, anionic). The cationic and some of the anionic surfactants (SOS, AOT) induced different habit modifications of growing calcium oxalate crystals by …

Adsorption Of Fibrinogen On Thin Oriented Poly(Tetrafluoroethylene) (Ptfe) Fibres Studied By Scanning Force Microscopy, J. R. Rasmusson, R. Erlandsson, W. R. Salaneck, M. Schott, D. T. Clark, I. Lundström

Scanning Microscopy

We have investigated fibrinogen adsorption on ordered poly(tetrafluoroethylene), PTFE, fibres deposited on hydrophilic and hydrophobic silicon substrates. Fibrinogen molecules appear to adsorb with their long axis perpendicular to the fibre direction for PTFE fibres having widths of less than 100 nm. On these thin fibres, fibrinogen apparently forms close packed bands or clusters, consisting of small integer numbers of molecules arranged parallel to each other. On broader (> 100 nm) PTFE fibres, the fibrinogen forms two dimensional networks. The orientation of the molecules in these networks is random in the central flat part of the fibres but perpendicular to the …

Caesium On Si(100) Studied By Biassed Secondary Electron Microscopy, M. Azim, C. J. Harland, T. J. Martin, R. H. Milne, J. A. Venables

Scanning Microscopy

An ultra-high vacuum scanning electron microscope (UHV-SEM) has been used to study sub-monolayers of Cs on Si(100) surface. Cs adsorption on the surface causes a considerable change in the work function. Coverages below 1/2 monolayer (ML) have been estimated by correlating the work function changes with the secondary electron (SE) signal. It has been found that this signal is sensitive down to ~ 0.005 ML when the sample is biassed to a few hundred volts.

Electron trajectories from a biassed sample have been simulated for electrons originating from different areas with different work functions across the sample. This indicates that …

Atomic Force Microscopy Study Of Human Tooth Enamel Surfaces, Ph. Schaad, E. Paris, F. J. G. Cuisinier, J. -C. Voegel

Scanning Microscopy

Human enamel features from individual crystals up to prisms were observed by atomic force microscopy (AFM). Low magnification images of vestibular tooth surfaces show the existence of enamel prisms appearing as deep holes. Individual, parallel enamel crystals show lateral faces elongated and formed by the (100) planes of hydroxyapatite (HA). Height differences between (001) faces create the roughness of enamel surface. Individual (001) crystal faces can be observed clearly at higher magnification and show the characteristic hexagonal shape with 60° angles between (100) faces. This study confirms the applicability of AFM for studying biological hydroxyapatite crystals.

Can We See Living Structure In A Cell?, Gilbert N. Ling

Scanning Microscopy

Colloid chemistry (κολλα: glue, or gelatin) was introduced in 1861 after the discovery of protoplasm which exhibits gelatin-like properties. Some 80 years later, colloid chemistry (and with it, the concept of protoplasm) was largely abandoned. The membrane (pump) theory, according to which cell water and cell solute like K⁺ are free as in a dilute KCl solution, became dominant. Later studies revealed that rejecting the protoplasmic approach to cell physiology was not justified. Evidence against the membrane (pump) theory, on the other hand, has stood the test of time. In a new theory of the living cell called the …

The Physical State Of Potassium Ion In The Living Cell, G. N. Ling

Scanning Microscopy

This review summarizes more than 30 years of experimental testing (and confirmation) of a key postulate of the association-induction (AI) hypothesis: most K⁺ ions in resting cells are adsorbed on 𝛃-and 𝛄-carboxyl group of cell proteins in a close-contact one ion-one site manner. Failure of healthy, cytoplasm-free, squid axon-membrane sacs to selectively accumulate K⁺ over Na⁺ and success of muscle cells without a functional cell membrane (and postulated pumps) to achieve the same, point to the cytoplasm as the seat of selective K⁺ accumulation. Four independent techniques unanimously confirmed the predicted localization in striated muscle cells, …

Appearance Potential Spectroscopy Of Solid Surfaces, D. R. Chopra, A. R. Chourasia

Scanning Microscopy

Among the techniques utilized for the study of unfilled density of states above the Fermi level in a system, appearance potential spectroscopy (APS) has emerged as one of the simplest. Some review papers on APS have appeared in the last decade. Since then APS has been applied to several interesting systems, the studies of which have been limited by other experimental techniques available. This paper reviews some of these applications of APS. We discuss briefly the one-electron theory describing the APS process and outline the basic experimental set-ups used by workers in this field. We then survey some important applications …

Ion And Water Retention By Permeabilized Cells, Carlton F. Hazlewood, Miklos Kellermayer

Scanning Microscopy

Nonionic detergents, Triton X-100 and Brij 58, removed, within 2-5 minutes, lipid membrane of suspended thymus lymphocytes and monolayer H-50 cells grown in culture. Studies of hydration, ionic asymmetry, and ionic and protein release kinetics were conducted on these membraneless cellular preparations. The hydration of nuclei isolated by Triton X-100 procedures appears to be influenced strongly by the monovalent ionic concentration of the buffer bathing the organelles. The putative monovalent ionic concentration of the cellular aqueous phase (i.e., 150 meq/L) caused nuclei to swell and coalesce. Monovalent ionic concentrations of 30 meq/L or less caused minimal changes in volume and …

Ex Vivo Platelet Deposition On Fibronectin-Preadsorbed Surfaces, William E. Collins, Deane F. Mosher, Anil R. Diwan, Kedar D. Murthy, Scott R. Simmons, Ralph M. Albrecht, Stuart L. Cooper

Scanning Microscopy

Temporal platelet deposition profiles of canine plasma fibronectin (CPFN) adsorbed to different polymers ex vivo and the in vitro characteristics of CPFN adsorption were studied in an attempt to correlate the two. The maximum platelet deposition (𝚪_plt^max) obtained at a protein preadsorption time of 30 min was greater than that obtained using an adsorption time of 120 min for all surfaces studied. At 30 min of preadsorption, 𝚪_plt^max was 520, 560 and 1230 platelets/1000 μm² on Biomer, polyethylene (PE) and oxidized PE (OXPE), respectively. In contrast, the platelet deposition at 120 min. of fibronectin …

Utilization Of Immunogold Labeling To Compare The Adsorption Behavior Of Fibrinogen, Fibronectin And Albumin On Polymers, K. D. Murthy, A. R. Diwan, S. R. Simmons, R. M. Albrecht, S. L. Cooper

Scanning Microscopy

Immunogold labeling followed by scanning electron microscopy (SEM) was used to examine the surface distribution of adsorbed plasma proteins. Adsorption was performed under various conditions on six different polymers; [low density polyethylene (PE), chromic acid-oxidized PE (OXPE), solution grade Biomer® (SB), Teflon-(FEP)®, a laboratory synthesized polyurethane containing some zwitterions (ZW) and a polydimethylsiloxane based polyurethane (ZS) also containing zwitterions]. The proteins used were purified human and canine fibrinogen, fibronectin, and serum albumin. The immunogold staining technique was successful in the labeling of the adsorbed proteins. The adsorbed proteins were distributed differently on the polymers selected. Human and canine fibrinogen were …