A search for losses of chemical elements during freeze-drying of biological materials

Possible losses of seven chemical elements were investigated in biological tissues during freeze-drying in vacuum. Thyroid glands were taken during post-mortem examination of 23 people died of different diseases. Instrumental neutron activation analysis (INAA) was used to estimate contents of Br, Ca, Cl, I, K, Mg, and Na. The nuclear reator vertical channel with flux density of 1.2·10¹³n·cm^–2·s^–1 was used for neutron irradiation. The analysis was carried out using short-lived radionuclides induced in samples after neutron irradiation. Then thyroids were freeze-dried at below 0 °C in vaccum up to the constant mass (lyophilisation) and then homogenized. Samples of lyophilised and homogenized tissues were again studied by INAA. The lack of difference between the results of the analysis before and after lyophilisation is an evedence of no loss of Br, Ca, Cl, I, K, Mg and Na during freeze-drying of biotissues in vaccum.     

Recombination of nanometric vesicles during freeze-drying

Concentrated dispersions of nanometric lipid vesicles (mean diameter 20 nm) in water/maltose solutions have been freeze-dried and then redispersed in water, yielding again dispersions of lipid vesicles. At each stage of the freeze-drying process, the organization of the vesicles in the dispersion and their size distribution were examined through small-angle neutron scattering and gel permeation chromatography. It was found that the osmotic deswelling of the vesicles caused them to recombine into larger vesicles. A single burst of recombination events occurred when the maltose concentration in the aqueous phase rose above 100 g/L. The final vesicle population was monopopulated, with a central diameter about twice as large as that of the original dispersion.     

Structural evolution during pyrolysis of sol-gel derived hybrid materials

Siloxane-titania materials have been prepared starting from diethoxydimethylsilane and titanium isopropoxide. The transparent starting gels can be described as nanocomposites formed with siloxane chains and TiO₂-based particles. The pyrolysis process under argon atmosphere up to 1600°C has been followed by various techniques such as infrared and solid state NMR spectroscopies, X-ray diffraction and Ti K-edge X-ray Absorption. Si-C bond cleavage begins at low temperature leading to redistribution reactions with the formation of new Si-O bonds. Crystallization of TiO₂ at low temperature is prevented and titanium carbide starts to form around 800°C. Samples pyrolyzed at 1600°C show the presence of SiO₂ and TiC crystalline phases.     

The freeze-drying of orange juice for the preparation of reference materials

Summary The possibility of producing fruit juice reference materials is conditioned by the availability of a method which allows the transformation of the original juice or concentrate into a better physically stable form. Therefore a feasibility study of the transformation of orange juice by freeze-drying was carried out. In general, the obtained powder is hygroscopic, and tends to agglomerate into large solid lumps. Under optimal conditions of freeze-drying combined with redrying of the powder before closing the bottles, a slightly cohesive but physically stable yellow orange powder can however be obtained. Compared to the original juice, this shows no loss of reducing sugars and has a normal glucose-fructose ratio. Moreover, most aminoacids e.g. asparagine, methionine, lysine and arginine are not affected by freeze-drying. Based on the study of a limited number of important fruit juice parameters, it may be concluded that freeze-drying seems very promising in order to obtain an orange juice reference material, which after redissolution in water keeps the original chemical orange juice properties.

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Gefriertrocknung von Orangensaft für die Herstellung von Referenzmaterialien

     

Determination of rhenium in plant materials

Methods for rhenium extraction from plant materials were studied using model systems and the ¹⁸⁶Re isotope. Conditions are described for the quantitative extraction of rhenium with acid and alkali solutions from plant ash and with ethanol and salt solutions from fresh green matter. Procedures for the analysis of real plant materials based on a combination of rhenium extraction with high-sensitive methods of its determination (catalytic, neutron activation, and solid-phase spectroscopy) were developed. Laboratory and field versions of the method are proposed. Analytical results for plant samples taken in different regions are presented.Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 1, 2005, pp. 97–103.Original Russian Text Copyright © 2005 by Borisova, Demin, Gatinskaya, Ermakov, Ryabukhin, Bozhkov.     

The estimation of vanadium in plant materials

A method has been proposed whereby microgram quantities of vanadium may be determined in plant materials. The procedure involves the removal of iron by means of a mercury cathode electrolysis, and the separation of manganese with cupferron and titanium with sodium diethyl dithiocarbamate. The final estimation is made with a polarograph whereby quantities of vanadium down to 0.006μg may be measured. Although the process involves several steps, it eliminates all of the interfering metals and achieves considerable sensitivity.     

Si/C nanocomposite anode materials by freeze-drying with enhanced electrochemical performance in lithium-ion batteries

The nanostructured Si/graphite composites embedded with the pyrolyzed polyethylene glycol was synthesized from coarse silicon and natural graphite by a facile and cost-effective approach. The Si/C nanocomposite showed the fluffy carbon-coated structure, which was confirmed by the SEM and TEM measurements. The as-obtained Si/C nanocomposite, employed as anode material in lithium-ion batteries, exhibited significantly enhanced rate capability and cycling stability. The improved electrochemical stability of the composite was evaluated by EIS and galvanostatically charge/discharge test. A reversible capacities as high as 85% and 91% of the initial charge capacities, could be maintained for the Si/C nanocomposite electrode after 40 cycles under the high current densities of 500 and 1,000?mA?g^?1, respectively. The relatively low cost and excellent electrochemical capability of the Si/C nanocomposite would well meet the challenge in rapid charge and discharge for large-size lithium-ion rechargeable batteries.     

Development of knotting during the collapse transition of polymers

A dynamic Monte Carlo simulation of the collapse transition of polymer chains is presented. The chains are represented as self-avoiding walks on the simple cubic lattice with a nearest-neighbor contact potential to model the effect of solvent quality. The knot state of the chains is determined using the knot group procedure presented in the accompanying paper. The equilibrium knot spectrum and the equilibrium rms radius of gyration as functions of the chain length and the contact potential are reported. The collapse transition was studied following quenches from good-to poor-solvent conditions. Our results confirm the prediction that the newly formed globule is not yet at equilibrium, since it has not yet achieved its equilibrium knot spectrum. For our model system, the relaxation of the knot spectrum is about an order of magnitude slower than that of the radius of gyration. The collapse transition is also studied for a model in which both ends of the chain remain in good-solvent conditions. Over the time scale of these simulations, knot formation is frustrated in this inhomogeneous model, verifying that the mechanism of knotting is the tunneling of chain ends in and out of the globule.     

Protection of protein secondary structure by saccharides of different molecular weights during freeze-drying

The protective effects of saccharides with various molecular weights (glucose, maltose, maltotriose, maltotetraose, maltopentaose, maltoheptaose, dextran 1060, dextran 4900, and dextran 10200) against lyophilization-induced structural perturbation of model proteins (BSA, ovalbumin) were studied. Fourier transform infrared (FT-IR) analysis of the proteins in initial solutions and freeze-dried solids indicated that maltose conferred the greatest protection against secondary structure change. The structure-stabilizing effect of maltooligosaccharides decreased in increasing the number of saccharide units. Larger molecules of dextran also showed a smaller structure-stabilizing effect. Increasing the effective saccharide molecular size by a borate-saccharide complexation reduced the protein structure-stabilizing effect of all of the saccharides except glucose. The results indicate that the larger saccharide molecules, and/or the complex formation with borate ion, reduce the free and accessible hydroxyl groups to interact with and stabilize the protein structure by a water-substitution mechanism.     

Immobilization of plant cells in hybrid sol-gel materials

Cells of three different plant species were immobilized on a glass fiber fabric by sol-gel deposition. The process involved the following steps: (1) reinforcement of glass-fiber supports by coating with a gelling solution of hybrid-SiO₂ precursors, (2) entrapment of cells by stuffing the voids of the support with a suspension cell culture, (3) achievement of a definite immobilization by a primary treatment with SiO₂-sol, followed by gas phase reaction of tetraethoxysilane and diethoxymethylsilane with OH groups of cell wall and of surface silica. Immobilized cells maintained their viability as tested by the positive reaction to TTC and by the development of calli from stretched samples. The samples did not release cells in solution over a time period of four months, at least. The biosynthetic capability of one of immobilized species, Coronilla vaginalis, was studied by periodically monitoring the production of umbelliferone and marmesin which constituted the major secondary metabolites produced by in vitro cultured cells of this species. The results were evaluated in order to determine the versatility of the method and its potential for exploitation in continuous industrial-scale production of rare and fine chemicals.Abbreviations 2,4-D = 2,4-dichlorophenoxyacetic acid - K = kinetin - IAA = indol-3-acetic acid - NAA = naphthalenacetic acid - B5 = Gamborg's medium - MS = Murashige and Skoog medium - TEOS = tetraethoxysilane - DEMS = diethoxymethylsilane - DEDMS = diethoxydimethylsilane - TTC = tetrazolium salt     

Determination of lead in environmental reference materials (plant materials) by slurry-ETA-AAS

Slurry-ETA-AAS is used to determine lead in plant materials. The stability of the slurry was studied and it was shown that, when NH₄H₂PO₄ modifier is added, the shape of the time resolved absorbance signal for the sample and the standards is similar and the calibration line obtained using aqueous standards is parallel to the standard addition line. Results obtained for several reference materials (lead contents between 6.1 and 64.4 g/g) were in good agreement with the certified value, the relative standard deviation being 3–9%.     

Determination of zinc in plant materials using ion-exchange chromatography

The objective of this investigation was to develop a rapid and accurate method for the determination of zinc in plant materials. An ion-exchange separation technique to eliminate interferences in the Zincon procedure for zinc is described. Comparison with the A.O.A.C. method and evaluation of zinc recovery studies show the proposed method to be satisfactory for the analysis of microgram amounts of zinc in plant materials.     

Microcalorimetric techniques for the investigation of living plant materials

Microcalorimetric investigations of living cellular systems have been conducted on small animals, cells and tissues from animals and plants and on microbial systems, but it is only recently that more systematic work has begun on plant materials. Isothermal experiments together with temperature scanning experiments have been performed. In most cases simple static ampoules have been used as calorimetric vessels and practically all calorimetric investigations reported on plant systems have been conducted under dark conditions. It is felt that some microcalorimetric techniques currently used in studies of microbial and animal systems, and in other areas, could be usefully applied more generally in the plant field: stirred injection (titration) vessels, gas and liquid perfusion vessels and different photocalorimetric methods.     

Structural characterisation of micro- and mesoporous materials by electron microscopy

Zeolites are one of the most important materials currently used in the petroleum industry for a wide variety of catalytic transformations. However, they are increasingly being considered for other applications such as for designing quantum-confined materials in their spaces. With such applications in mind, precise characterisation of zeolites and related porous materials has never been more necessary. Here we show how electron diffraction coupled with high-resolution imaging can reveal the detailed fine structure in both the bulk and at the surface of these materials. A variety of case studies are considered which include ETS-10, FAU, LTL and FSM-16.     

Cadmium losses on wet and dry ashing of plant materials

Cadmium losses on wet and dry ashing were studied using tomato leaves with metabolized¹⁰⁹Cd radiotracer. The most appreciable Cd losses (up to 35%) occured when sulphuric acid was used on wet ashing due to Cd retention in the CaSO₄ precipitate formed. Only trace amounts of Cd were retained in a silicaceous precipitate resulting from wet ashing in the absence of sulphuric and hydrofluoric acids in the decomposition mixtures employed. Small Cd losses (up to 7%) were observed on dry ashing in the air in open systems at temperatures not exceeding 500°C. Cd losses increased, however, to 30% when the final ashing temperature was raised to 900°C. Incorporation of the¹⁰⁹Cd radiotracer into various parts of tomato plants and its distribution between soil and the plants are also briefly reported.     

Determination of amorphous silica and total silica in plant materials

Amorphous silica in plant material was dissolved with potassium carbonate solution, after nitric acid/hydrogen peroxide digestion. Total silica in plant material and some minerals was obtained after ashing and fusing in nickel crucibles with potassium hydroxide containing potassium tetraborate/nitrate. The relative standard deviation for determinations of silicon by these methods in plant material was <2% for plant material containing 2–2100 μmol Si g^?1 (dry weight).     

The polarograph1c estimation of molybdenum in plant materials

A method has been developed whereby molybdenum is extracted from digests of plant materials by means of a-benzomoxime and chloroform from a medium of 1 % sulphuric acid solution, Following the decomposition of the extract, the molybdenum is estimated polarographically by measuring the catalytic wave in a sulphuric acid-pcrchloratc supporting electrolyte in which the sensitivity is increased tenfold over the normal wave. The method provides a selective, highly sensitive procedure, capable of determining very small quantities of molybdenum.