Hydrated Materials Research Articles

Low-temperature scanning electron microscopy

More than thirteen years have passed since the first micrographs were taken of specimens maintained in a frozen state on the cold stage of a scanning electron microscope (SEM).O) The pictures which were taken showed little we did not already know about the particular cells and tissues but it did demonstrate that this was potentially a powerful technique for examining and analysing hydrated material in as near a natural state as possible. Cryofixation is, for all intents and purposes, a physical process, and as such can avoid the use of wet-chemical preparative methods. Low temperatures immobilize the liquid state, arrest physiological processes, and diminish the movement of dissolved substances. Where specimens are examined and analysed at low temperatures inside the microscope the presence of large areas of cold surfaces results in a significant reduction in contamination and in the damage to the specimen. It is therefore appropriate to examine the progress that has been made in the intervening years and for convenience this will be discussed under three separate headings: 1) Instrumentation, 2) Morphological studies, and 3) Analytical studies.

The Glen Kyllachy Granite and its bearing on the nature of the Caledonian Orogeny in Scotland

The Tomatin (Findhorn) Granite in the NW Grampian Highlands has been separated into two distinct complexes: a late-tectonic Glen Kyllachy Granite (tectonically foliated) and a post-tectonic Findhorn Granite (flow foliated). For the Glen Kyllachy complex, Rb-Sr analyses of muscovites from the granite and from an associated suite of cross-foliated pegmatites yield an emplacement age of 443 +5 −15 Ma. Whole-rock Rb-Sr data support field and textural evidence that the pegmatite and granite emplacement was late-tectonic to the last (F3) phase of Caledonian folding. Initial granite 87 Sr/ 86 Sr of 0.7176 supports field and geochemical evidence of derivation from upper crustal metasediments first metamorphosed during the Grenville event. For the Findhorn Granite, concordant Rb-Sr and K-Ar mineral data establish an age of 413± 5 Ma, and an initial 87 Sr/ 86 Sr of c. 0.706 indicates a lower crustal and/or mantle source. This age and isotopic contrast between these granites is characteristic of the whole Grampian region, in which a plutonic hiatus between c . 440 and 415 Ma coincides with the peak of sedimentary accretion in the Southern Uplands, and may be explained in terms of the lack of hydrous materials passing down the associated subduction zone. Structural, metamorphic and radiometric evidence suggests (a) that the late-F3 Glen Kyllachy pegmatites are comparable with the 442 ± 7 Ma old, syn-F3 pegmatites in the N Highlands—both pegmatite suites are situated in the axial zone of the metamorphic Caledonides displaced by the Great Glen Fault; and (b) that the Caledonian, c . 454 Ma old ‘peak’ tectonic-metamorphic event (D2) previously documented in the N Highlands coincides with a Caradocian basin closure along the Highland Boundary Fault. For Silurian events in the N Highlands we propose a separate subduction history; in this region, the peak of calc-alkaline plutonism was accompanied by continuous folding and westward thrusting at the same time as a plutonic hiatus in the Grampian Highlands. Current evidence suggests that the c . 160 km or greater sinistral movements on the Great Glen Fault were not initiated until late Silurian–early Devonian time.

Low Temperature X-Ray Microanalysis of Solid Biological Samples: Prospects and Problems

IntroductionThe advantages to be gained from using low temperatures in the preparation, examination and analysis of biological materials are well documented. The low temperature approach is particularly important in the analysis of low atomic number diffusible elements (x-ray microanalysis, electron spectroscopy and secondary ion analysis) and low molecular weight compounds (autoradiography, fluorescent microscopy and laser probe analysis). A recent paper discusses the application of these and other methods to the analysis of solid organic samples. This present discussion centres on the advantages and disadvantages of carrying out x-ray microanalysis on frozenhydrated (as distinct from frozen-dried) biological materal, with particular emphasis to solid samples. Two main methods have evolved for the analysis of frozen hydrated biological material; the use of frozen-hydrated sections and frozen-hydrated fracture faces. There are merits and short comings to both approaches and for any given tissue both methods can be complementary, neither are mutually exclusive.

Low-friction, anhydrous, low- to high-temperature furnace sample assembly for piston-cylinder apparatus

A newly designed furnace assembly for piston-cylinder, high-pressure apparatus uses NaCl or KBr rather than hydrous materials such as talc or pyrophyllite. Unlike previous designs, our cell can be used hundreds of degrees above the melting temperatures of the salts. This cell requires little or no pressure correction and provides conditions that are free of H2 and H2O. The electrical power requirements are only about 60% of that for talc furnace assemblies, resulting in cooler operation and longer life for the steel and carbide in the pistons and pressure vessels.

Electron diffraction studies of biological membrane and lipids

IN diffraction studies of biological membranes, X-ray diffraction has been used more frequently than electron diffraction in spite of certain advantages inherent in the latter technique. Electron diffraction enables the study of a small area (about 1 µm2) of a very thin specimen, and the collection of experimental data within a short time. Moreover, the morphology and degree of purity of the specimen can often be investigated. It seems possible to overcome the main problems arising from the application of the electron diffraction technique to biological materials, namely the difficulty of studying hydrated materials and the damage caused to the specimen by the electron beam, and a study of wet biological membranes has been reported1. In this investigation dry specimens have been studied. Radiation damage was largely overcome by using minimum beam current, by maximally overfocusing the first condenser of the electron microscope, and by moderately overfocusing the second condenser. To minimise the temperature rise of the specimen, caused by inellastically scattered electrons, a cooled specimen holder was used. To facilitate heat transport, the specimen grids were covered with aluminium instead of carbon. A Philips 301 G electron microscope equipped with an anti-contamination device was used and the diffraction patterns were recorded at 100 kV on a highly sensitive X-ray film, Kodirex. All diffractograms were recorded at a specimen holder temperature of about −60 °C, which was regarded as a fair estimate of the temperature of the specimen itself.

Modification of cellulose hydrate materials with diglycidyl ether as a method of increasing their resistance to oxidation by atmospheric oxygen in an alkaline medium

Modification of cellulose hydrate materials with diglycidyl ether as a method of increasing their resistance to oxidation by atmospheric oxygen in an alkaline medium

Chemical Aspects of Coagulation

This article presents a comprehensive review of the chemistry underlying the hydrolysis of ferric and aluminum salts, the probable composition of the various hydrolysis products, and suggests the possibility that these highly hydrated materials may very likely have a polymeric structure. It is emphasized throughout the paper that the effect of the multivalent ferric and aluminum ions upon coagulation is not brought about by the ions themselves but by their hydrolysis products. A discussion by A.P. Black follows the article.

THE EFFECT OF PETIOLE TEMPERATURE ON THE TRANSLOCATION OF CARBOHYDRATES FROM BEAN LEAVES

hydrate materials through petioles, will be influenced by temperature effects on numerous other processes occurring in various parts of the plant, such as respiration and assimilation, and the effect these processes have on concentration gradients between regions of export and import. Studies, therefore, in which the entire plant is subjected to different temperatures (4), although contributing much data of value, do not permit a clear analysis of the temperature effect on the process of translocation per se. In the present experiments, therefore, only the petiole temperature was varied, the rest of the plant in all treatments being maintained at a temperature of 20 ? Io C. Materials and methods The report by Weintraub and Brown (?) that stem elongation of ??aseolus vulgaris var. Black Valentine was directly proportional, within the range of 0 to .75 M, to the concentration of sugar supplied to the leaves suggested that this relationship could be used as a basis of approach for studying the effect of temperature on translocation of carbohydrates. If temperature has an effect on the rate of movement of sugar through the petiole then the amount of sugar reaching the growing tip will vary with temperature and the rate of elongation should vary accordingly. Stem elongation may then be used as an index to the effect of temperature on translocation of sugar. The basic features of the method, therefore, consisted of jacketing the petiole of one primary leaf, immersing the blade in sugar solution and measuring the subsequent elongation of the plant occurring in the dark. Seeds of Phaseolus vulgaris, variety Burpee's Stringless Greenpod (in