Heavy metal adsorbents prepared from the modification of cellulose : A review

CHAPTER 3 – Photosensitized Oxidation and Singlet Oxygen: Consequences in Biological Systems

Publisher Summary This chapter focuses on protein–protein interaction. The unique characteristics of different proteins are developed in the interactions of proteins with each other, with ions, and with nonprotein materials such as lipids, nucleic acids, and carbohydrates. These range from covalent bonds and electrostatic interactions to the weaker electronic van der Waals' attractive forces characteristic of all atoms and groups of atoms. The interactions of proteins with each other in an aqueous environment may be divided into two categories: (1) those which take place at such distances that the average properties of the protein or its surface may be used in calculating interaction energies, and (2) those in which the interacting molecules approach closely and thus bring into play local forces, the total of which depends to a major extension specific groups and group configurations. Interactions at distances may be further subdivided into those interactions, which lead to a concentration dependence of osmotic pressure, sedimentation coefficient, and those long-range interactions which lead to more complex phenomena such as the separation of phases in suspensions of tobacco mosaic virus and bentonite. An interaction is observed only when the protein molecule is subject to a structural change which brings bonding groups into positions which allow them to interact. Structural changes of this type may be reversible or irreversible. Certain ephemeral interactions, particularly enzymatic reactions, generally lead to chemical or physical changes in one of the interactants to a much greater extent than the other.

Protein-protein interactions.

Pyrolysis behavior and kinetics of biomass derived materials

Degradation of cellulose under alkaline conditions

Two series of samples of purified cotton were irradiated in oxygen and nitrogen atmospheres with gamma rays at six dosage levels ranging from 100.000 to 100.000.000 roentgens. Some of the chemical ...

The Effects of Gamma Radiation on Cotton: Part I: Some of the Properties of Purified Cotton Irradiated in Oxygen and Nitrogen Atmospheres

Cotton cellulose of the Deltapine variety, spun into 7s/3 yarns, was purified hy extraction with hot ethanol. followed 1Iy hoilÍ11,g in dilute sodium hydroxide solution. precautions being takcn to minimi7(’ oxidation hy air. The sodium, hydroxide sulution was remoBed hy washing thycc·llnlc~~e with distilled water; tills was followed 1~)~ souring with dilute acetic acid. neutralizing with dilute ammonium hydroxide, and again washing with di.,tjJ1cd, water ,’1151., ., After conditioning the cellulose ut 21 °C and fji~/ ’ kl 1, the resulting product had a moisture content of’ahout ~r/ and a viscosity-average molecu.lar. weight of about 700.000 ( 12 ~ : ’

Photochemical Initiation of Free Radicals in Cotton Cellulose

The ESR spectra of microcrystalline cellulose and purified cotton cellulose reacted with ceric ammonium nitrate in nitric acid were determined. The effects of the concentration of ceric ion, atmosphere, temperature, and graft copolymerization with acrylonitrile on the rates of formation and decay of radicals in the cellulose molecule were determined under both static and dynamic conditions. Under static conditions, after the desired conditions of reaction, the samples were frozen at –100 or –160°C., and then the concentration of free radicals was determined. Under dynamic conditions ceric ion solution was continuously flowed through the celluloses while these determinations were being made at 25°C. In the presence of oxygen the rate of decay of free radicals was decreased. On initiation of copolymerization reactions with acrylonitrile, there was an increase in radical concentration, then a decrease. Apparently, during graft copolymerization the radical site initially on the cellulose molecule was retained on the end of the growing polymer chain. Then additional ceric ion coordinated with the hydroxyl groups of the cellulose, leading to the formation of additional radical sites. An Arrhenius interpretation of the effect of temperature on the formation of these additional radical sites gave apparent activation energies for radical formation on cotton cellulose as 34 kcal./mole and on microcrystalline cellulose as 29 kcal./mole.

ESR study of reactions of cellulose initiated by the ceric ion method

An ESR study of the free-radical mechanisms of the post-irradiation reactions of cotton cellulose with acrylonitrile is reported. The effects of atmosphere, moisture content, and solutions of acrylonitrile on the yield and stability of free-radical sites in irradiated cellulose were determined. On interaction of γ-radiation from a 60Co source with cotton cellulose, long-lived free-radical sites were found within the molecular lattice. Short-lived free-radical sites were apparently also formed on chain cleavage, gave strong singlet spectra, and were readily accessible to interaction with water. Other free-radical sites were formed within regions of the cellulosic fiber which were inaccessible to moisture or aqueous solutions even after contact times as long as three days. It was suggested that long-lived free-radical sites in cellulose I (containing regain moisture) resulted from dehydrogenation at C5, and in cellulose II (containing regain moisture) resulted from dehydrogenation at C5 and dehydrogenation of the OH group or dehydroxylation at C6. When irradiated cellulose was contacted with a solution of acrylonitrile (15%) in 75% aqueous zinc chloride, the initial rate of decrease in spin concentration was higher than the rate of decrease as the time of contact increased. The ESR spectrum of the reacted cellulose, observed at −100°C., as compared with the spectrum for the irradiated cellulose, had decreased in signal strength with increase in time of contact and changed from a three-line spectrum to an ill-defined spectrum. The free radical being observed was probably due to unreacted sites in the cellulose. The extent of the graft copolymerization reaction was directly related to the initial spin concentration in the irradiated cellulose.

ESR study of post‐irradiation reactions of cellulose and acrylonitrile

Irradiation of purified fibrous cotton cellulose I and cotton cellulose II (mercerized) with γ-radiation from Co"" gave products containing relatively stable free radicals, easily shown in electron...

Jett C. Arthur

Papers

The Effects of Gamma Radiation on Cotton: Part I: Some of the Properties of Purified Cotton Irradiated in Oxygen and Nitrogen Atmospheres

Photochemical Initiation of Free Radicals in Cotton Cellulose

ESR study of reactions of cellulose initiated by the ceric ion method

ESR study of post‐irradiation reactions of cellulose and acrylonitrile

Esr spectra of gamma-irradiated cotton cellulose i and ii.