Metal chelating activity

Two new norditerpene alkaloids linearilobin and linearilin were isolated from Delphinium linearilobum (Trautv.) N. Busch. The antioxidant activity was established by using DPPH and metal chelating activity tests. 

The antioxidant activity of the alkaloids (linearilobin, lycoctonine, 14-acetyl-talatizamine, browniine, cammaconine, talatizamine and cochlearenine) of D. linearilobum was performed by DPPH [21] and by metal chelating activity [22] assays cochlearenine and lycoctonine showed high activity (Figs. 4.3 and 4.4). 

B. Following oral administration, peak blood concentrations occur in approximately 3 hours. Distribution is predominantly extracellular, and in the blood it is extensively bound (>90%) to plasma proteins. Succimer is eliminated primarily in the urine, where 80-90% appears as mixed disulfides, mainly 2 1 or 1 1 cysteine-succimer adducts. Studies suggest that these adducts, rather than the parent dmg, may be responsible for metal chelating activity in vivo. The elimination half-life of transformed succimer is approximately 2-4 hours. Renal clearance may be diminished In the setting of pediatric lead intoxication. 

Chromatographic tests of the properties of chemically bonded phases usually are intended to determine the hydro-phobic selectivity (relative retention of two hydrocarbons), hydrogen-bonding acceptor and donor selectivity (e.g, relative retention of butyl paraben and dipropyl phthalate) and silanol activity (relative retention of basic vs. neutral compounds) metal chelating activity can be measured, e.g., as the relative retention of 2,2 dipyridyl to 4,4 dipyridyl. 

The metal chelating activity of model MRPs was determined by the combined use of atomic absorption spectroscopy and tetramethyl murexide (TMM) method (Terasawa et... 

The significance of metal chelating activity of MRPs to human health has two different aspects. On one hand, low bioavailability of trace metal ions could occur in vivo and on the otherhand, MRPs could be an effective antioxidant in retarding metal catalyzed lipid oxidations reactions. 

Several studies indicate that catechins and procyanidins are powerful scavengers of ROS. Some findings regarding the antioxidant activity of proanthocyanidins are listed in Ref. [100]. Other antioxidant mechanisms are the chelation of transition metals, as well as the mediation and inhibition of enzymes. The metal-chelating activity of proanthocyanidins is thought to be due to their capacity to reduce the concentration, and thus the oxidative activity, of hydroxyl radicals formed by Fenton reaction catalyzed by iron or copper. Flavanols also influence oxidative stress via enzyme modification and modulation of cell signaling pathways the extent of the effect relies greatly on flavanol structure-related protein reactivity [101]. 

Structural modification of the propionate type of phenolics optimizes or enhances the activity. Esters I and II are antioxidants for polyolefins and styrenics, amide XI is suitable for aliphatic polyamides, ester XII for polyesters. Incorporation of oxalamide or hydrazide moieties in bridges connecting phenolic nuclei in XIII and XIV, respectively, results in antioxidants with metal chelating activity. 

Since no difference was observed when using different types of pectin, the physical properties of the interfacial film and modified oxygen barrier properties in the spray-dried particles may be excluded to explain the data. Future research may focus on the role of the trace-metal-chelating activity of pectin [112-114] and... 

The Knorr pyrazole synthesis has been extensively utilized in the preparation of a number of pyrazoles as metal chelators, photographic dyes, herbicides, and biologically active... 

Metal deactivators (MD) act, primarily, by retarding metal-catalyzed oxidation of polymers they are, therefore, important under conditions where polymers are in contact with metals, e.g., wires and power cables. Metal deactivators are normally polyfunctional metal chelating compounds (e.g.. Table la, AO 19-22) that can chelate with metals and decrease their catalytic activity [21]. 

Metal chelates are known to decompose upon heating to generate free radicals, which can abstract hydrogen atoms from the polymeric backbone producing an active site where grafting can take place. 

Finally, there is active interest in developing catalyst systems, both ballistic and polymerization, that would promote combustion stability at high pressures (especially in metal-free systems for smokeless applications) and allow processing lattitude for relatively large motors. The ferric-based systems currently being used fall short of these performance measures. Compounds that form complex structures with the metal chelate to reduce its activity to acceptable levels seem to be most promising. Interestingly, the use of an antibiotic has been cited in this context [19],... 

The action of a peptidase can be neutralized by an inhibitor. Some inhibitors are very broad in their action and are capable of inhibiting many different peptidases, including peptidases of different catalytic types. Some inhibitors are assumed to be specific for a particular catalytic type, but can inhibit peptidases of different types. Leupeptin, for example, is widely used as an inhibitor of serine peptidases from family SI, but it is also known to inhibit cysteine peptidases from family Cl. Cysteine pqrtidase inhibitors such as iodoacetic acid interact with the thiol of the catalytic cysteine. However, this reduction can occur on any thiol group and can affect other, predominantly intracellular, peptidases with a thiol dependency. One example is thimet oligopepti-dase. Metal chelators such as EDTA can inhibit meta-llopeptidases, but can also affect peptidases that have a requirement for metal ions that is indq>endent of their catalytic activity, such as the calcium-dependent cysteine endopqrtidase calpain 1. 

Metal deactivators—Organic compounds capable of forming coordination complexes with metals are known to be useful in inhibiting metal-activated oxidation. These compounds have multiple coordination sites and are capable of forming cyclic strucmres, which cage the pro-oxidant metal ions. EDTA and its various salts are examples of this type of metal chelating compounds. 

RSS 2 was mixed with N-234 carbon black without additive or in the presence of quinonedihne, or with a peptizer (dibenzamidodiphenyl disulfide, activated with a metal chelate). In the case of the peptizer, rubber and carbon black were mixed for 30 s before the addition of carbon black. In the case of the quinone diimine, carbon black and QDI were added 15 s after addition of rubber to the mixer. 

In contrast to a, -ethylenic ketones or even a, -ethylenic sulfones, a, ) -ethylenic sulfoxides generally are not sufficiently electrophilic to undergo successful nucleophilic j8-addition . a-Carbonyl-a, j8-ethylenic sulfoxides, however, are potent, doubly activated alkenes which undergo rapid and complete -addition of various types of nucleophiles even at — 78 °C. A brief account summarizing this area is available . The stereochemical outcome of such asymmetric conjugate additions to enantiomerically pure 2-sulfmyl 2-cycloalkenones and 2-sulfinyl-2-alkenolides has been rationalized in terms of a metal-chelated intermediate in which a metal ion locks the -carbonyl sulfoxide into a rigid conformation (36 cf. 33). In this fixed conformation, one diastereoface of the cyclic n... 

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