Catalysts Catechin

Superoxide anion scavenging activity of the enzymatically synthesized poly(catechin) was evaluated. Poly(catechin), synthesized by HRP catalyst, greatly scavenged superoxide anion in a concentration-dependent manner, and almost completely scavenged at 200 p.M of a catechin unit concentration. The laccase-catalyzed synthesized poly(catechin) also showed excellent antioxidant property. Catechin showed pro-oxidant property in concentrations lower than 300 jlM. These results demonstrated that the enzymatically synthesized poly(catechin) possessed much higher potential for superoxide anion scavenging, compared with intact catechin. 

Mutans streptococci are the major pathogenic organisms of dental caries in humans. The pathogenicity is closely related to production of extracellular, water-insoluble glucans from sucrose by glucosyltransferase and acid release from various fermentable sugars. Poly(catechin) obtained by HRP catalyst in a phosphate buffer (pH 6) markedly inhibited glucosyltransferase from Streptococcus sorbrinus 6715, whereas the inhibitory effect of catechin for this enzyme was very low. 

The conjugation of catechin on poly(allylamine) using ML as catalyst was examined under air. During the conjugation, the reaction mixture turned brown and a new peak at 430 nm was observed in the UV-vis spectrum. At pH 7, the reaction rate was the highest. The conjugation hardly occurred in the absence of laccase, indicating that the reaction proceeded via enzyme catalysis. 

In the polymerization of catechin by using laccase (ML) as catalyst, the reaction conditions were examined in detail [112], A mixture of acetone and acetate buffer (pH 5) was suitable for the efficient synthesis of soluble poly(catechin) with high molecular weight. The mixed ratio of acetone greatly affected the yield, molecular weight, and solubility of the polymer. The polymer synthesized in 20% acetone showed low solubility toward DMF, whereas the polymer obtained in the acetone content less than 5% was completely soluble in DMF. In the UV-Vis spectrum of poly(catechin) in methanol, a broad peak centered at 370 nm was observed. In alkaline solution, this peak was red-shifted and the peak intensity became larger than that in methanol. In the ESR spectrum of the enzymatically synthesized poly (catechin), a singlet peak at g= 1.982 was detected, whereas the catechin monomer possessed no ESR peak. 

Superoxide anion scavenging activity of the enzymatically synthesized poly(catechin) was evaluated. Poly(catechin), synthesized by HRP catalyst, greatly... 

Catechins can chelate metal ions, mainly Fe and Cu, which are catalysts of free radical reactions, because of their vicinal dihydroxy or trihydroxy structures, and thus prevent the generation of free radicals. Green and black tea polyphenols reduced cell-mediated low-density lipoprotein oxidation induced by Cu + in vitro, which is proposed to contribute to the prevention of atherosclerosis and other cardiovascular diseases. ... 

Fig. 3. Hydrogenation of the ring of dihydroxy-substituted aromatic compounds using 5% Rh on AI2O3 as catalyst in 100 ml. water. 1) 500 mg. catalyst, 600 mg. hydro-quinone 2) 500 mg. catalyst, 500 mg. resorcinol 3) 500 mg. catalyst, 500 mg, pyro-catechin.

Alternative interesting applications for porous carbon materials have been recently reported. For example, porous carbons prepared from the large mesopore Fniim silica (KlT-5) demonstrated a superior ability to separate the tea components catechin and tannic add, compared to other p>orous materials, such as activated carbons and mesoporous silica [23]. Porous carbon nitride with a large surface area has been prepared using well-ordered mesoporous silica as a template for the polymerization between ethylenediamine and carbon tetrachloride [24]. In this case, the metal-free carbon nitride was able to function as an efficient basic catalyst for transesterification reactions. 

The situation is more complex in defining the regioselectivity of procyanidin synthesis. Here differences between kinetic control and thermodynamic equilibrium ratios become particularly important because of the lability of the in-terflavanoid bond in these compounds and because of differences in both the relative rate of acid-catalyzed cleavage and rate of condensation for the C-6 and C-8 substituted isomers (148). Work of Haslam s group indicated that the C-8 substituted procyanidins predominated over their C-6 linked pairs by a factor of 8 to 9 to 1 (177, 352). However, Botha et al. (28) obtained catechin-(4a- 8)-catechin and catechin-(4a- 6)-catechin in relative yields of 3.2 to 1 from a 2-hour bio-mimetic synthesis with 0.1 M HCl at ambient temperature. Similarly, Hemingway et al. (143) obtained epicatechin-(4)ff- 8)-catechin and epicatechin-(4)ff- 6)-cate-chin in relative yields of about 2.5 to 1 through synthesis by reaction of Pinus taeda proanthocyanidins with excess catechin for 48 hours at 25 °C using HCl as a catalyst. This ratio was similar to the yield of the two isomers isolated from the phloem of Pinus taeda. The extreme lability of the interflavanoid bond in the procyanidins causes one to wonder if true kinetic control ratios can be obtained from acid-catalyzed reactions of the procyanidins. 

Comparative study on the products obtained by the peroxidase-catalyzed and PPO-catalyzed oxidative couphng of catechin was reported [43]. Both enzymes produced the similar products. In the PPO-catalyzed oxidation, catechin was almost consumed, and the ohgomers were mainly formed. On the other hand, a significant amount of catechin remained, and the amount of oligomer fractions was small when peroxidase was used as a catalyst. The low catalytic activity of peroxidase may be due to the inhibition of the enzyme by the resulting products. 

A new inhibitor against disease-related enzymes, collagenase, hyaluronidase, and xanthine oxidase was developed by the conjugation of catechin on poly( -lysine) using ML as a catalyst (Fig. 9) [63]. 

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