Spectrochemistry of Polycarbohydrate Free Radicals Generated by Argon Plasmolysis: Effect of Tertiary Structure on Free Radical Formation

Abstract

We report the first in-depth ESR study of plasma-induced polycarbohydrate radicals in powdered cellulose and amylose. On the basis of the ESR kinetics coupled with the systematic computer simulations, it was found that plasma irradiation produced preferentially the alkoxylalkyl radical at CI of the glucose units in both polycarbohydrates. However, the observed ESR spectra are largely different in pattern between the two anomeric polymers: The triplet spectrum with ca. 3.0 mT of HSC was present only in celullose, which is assignable to the hydroxylalkyl radical at CZ and/or C3 of the glucose units of cellulose. Presumably, the hydroxylalkyl radical at C3 of the glucose units of amylose which should likewise exhibit a triplet was not formed due to the suppression of hydrogen abstraction at C3 in the helical tertiary structure of amylose.However, the acylalkyl radicals which are formed by dehydration of the hydroxylalkyl radicals were observed in both polycarbohydrates. This anomaly in amylose was rationalized in terms of spontaneous dehydration of the hydroxylalkyl radical formed at C2 of the glucose units due to a special rehybridization-induced effect of the carbon-radical center on such dehydration reactions valid only in a solid state. It was also shown that the polycarbohydrate radicals were rapidly reacted with oxygen in air, unlike monocarbohydrate radicals which are stable even after prolonged standing in air at room temperature. This difference could be ascribed to the difference in the polymorphic forms between polycarbohydrates and monocarbohydrates.

Free radical kinetics on irradiated fennel

“…The spectra of cellulose have been confirmed to contain one isotropic doublet spectra (I) with ca. 1.7 mT of a hyperfine splitting constant (HSC) assigned to an alkoxyalkyl radical at the C 1 position of the glucose unit, one isotropic triplet (II) with 2.98 mT of HSC assigned to a hydroxylalkyl radical at the C 2 and/or C 3 split by two axial b-hydrogens, and an anisotropic single line (III) that may be a mixture of the ring-opened and/or conjugated structures resulting from glucoside bond cleavages, and one anisotropic doublet of doublets (IV) assigned to an acylalkyl radical at the C 2 and/or C 3 as the secondary products, which resulted from the dehydration of a hydroxyalkyl radical at C 2 and/or C 3 , respectively (Kuzuya et al, 1994). These components have been confirmed to be similar to those of a mono-or disaccharide (Yamauchi et al, 1999).…”

Nature of Mechanoradical Formation of Substituted Celluloses as Studied by Electron Spin Resonance

“…2) disaccharides (maltose and cellobiose), 3) and polysaccharides (cellulose and amylose), 4) ethyl-and hydroxyethylcellulose (EC and HEC), 5) and low-and high-substituted hydroxypropylcellulose (L-HPC and H-HPC). 6) We have further undertaken the characterization of the plasma-induced radicals of several other substituted celluloses such as carboxylmethylcellulose (CMC), 2-acetamido-2-deoxycellulose (chitin), and 2-amino-2-deoxycellulose (chitosan) 7) in response to the need for experimental design in a series of studies on novel plasma-assisted drug-delivery system (DDS) preparations.…”

A New Drug Delivery System Using Plasma-Irradiated Pharmaceutical Aids. IX. Controlled-Release of Theophylline from Double-Compressed Tablet Composed of Cellulose Derivatives as Wall Material.

“…It should be noted that these polymers are totally amorphous so that the radical can almost instantly dissipate on exposure to air. 4) We intend to perform more refined analyses of the component radicals involved in the ESR spectra of HPMC and HPMCP in the future and will be reported elsewhere dealing with only that subject. The present spectral comparisons still provide a good estimate of the surface reactions on such polymers induced by argon plasma-irradiation.…”

“…3) It is well known that derivatization of cellulose can readily change its physicochemical property and its functions of cellulose. Thus, there are a number of cellulose derivatives industrially used as pharmaceutical aids [17 derivatives in Japan Pharmacopoeia (JP) XIII] such as methylcellulose (MC, as binder, film coating materials), ethylcellulose (EC as film coating materials), hydroxypropylcellulose (HPC as binder, film coating materials), carboxymethylcellulose (CMC as disintegrants) and so on, several of which have been studied on the nature of plasma-induced radical formation, [4][5][6][7] including the mechanoradicals of cellulose and amylose. 8) It was found that plasma-irradiation can further enhance the functionality and/or add a new surface property of such cellulose derivatives, since one of the characterristics of plasma-irradiation is the fact that it is surface-limited (ca.…”

“…Hydroxypropylmethylcellulose phthalate (HPMCP), used as an enteric coating agent, would have a further functionality in addition to that of HPMC due to the presence of carboxybenzoyl groups. Based on the findings obtained from a series of ESR studies on elucidation of plasma-induced radicals of several cellulose derivatives thus far investigated, [4][5][6][7] HPMC and HPMCP are of dual reactive moieties, a plasma-degradable main chain of cellulose and a plasma-crosslinkable side chain structure including a highly plasma-crosslinkable aromatic ring in HPMCP.…”