Biomedical subjects
Publications and source records attributed to Jaiwook Park.
An efficient oxidant-free oxidation for a wide range of alcohols was achieved by a recyclable ruthenium catalyst. The catalyst was prepared from readily available reagents by a one-pot synthesis through nanoparticle generation and gelation. [structure: see text]
The effects of the number of anchoring groups (carboxylate vs phosphonate) in Ru-bipyridyl complexes on their binding to TiO(2) surface and the photoelectrochemical performance of the sensitized TiO(2) electrodes were systematically investigated. Six derivatives of Ru-bipyridyl complexes having di-, tetra-, or hexacarboxylate (C2, C4, and C6) and di-, tetra-, or hexaphosphonate (P2, P4, and P6) as the anchoring group were synthesized. The properties and efficiencies of C- and P-complexes as a sensitizer depended on the number of anchoring groups in very different ways. Although C4 exhibited the lowest visible light absorption, C4-TiO(2) electrode showed the best cell performance and stability among C-TiO(2) electrodes. However, P6, which has the highest visible light absorption, was more efficient than P2 and P4 as a sensitizer of TiO(2). The surface binding (strength and stability) of C-complexes on TiO(2) is highly influenced by the number of carboxylate groups and is the most decisive factor in controlling the sensitization efficiency. A phosphonate anchor, however, can provide a stronger chemical linkage to TiO(2) surface, and the overall sensitization performance was less influenced by the adsorption capability of P-complexes. The apparent effect of the anchoring group number on the P-complex sensitization seems to be mainly related with the visible light absorption efficiency of each P-complex.
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A new recyclable rhodium catalyst was synthesized by a simple procedure from readily available reagents, which showed high activities in the hydrogenation of various arenes under 1 atm H2 at room temperature.
[reaction: see text] A novel racemization catalyst was synthesized for the dynamic kinetic resolution (DKR) of alcohols with a lipase at room temperature in the air. Furthermore, a polymer-supported derivative was also synthesized and tested as a recyclable catalyst for the aerobic DKR of alcohols.
[reaction: see text] A new aluminum hydroxide-supported palladium catalyst (1) made by a one-pot synthesis through nanoparticle generation and gelation shows a dual catalytic activity for olefinic hydrogenation and aerobic alcohol oxidation.
Aminocyclopentadienyl ruthenium complexes, which can be used as room-temperature racemization catalysts with lipases in the dynamic kinetic resolution (DKR) of secondary alcohols, were synthesized from cyclopenta-2,4-dienimines, Ru(3)(CO)(12), and CHCl(3): [2,3,4,5-Ph(4)(eta(5)-C(4)CNHR)]Ru(CO)(2)Cl (4: R = i-Pr; 5: R = n-Pr; 6: R = t-Bu), [2,5-Me(2)-3,4-Ph(2)(eta(5)-C(4)CNHR)]Ru(CO)(2)Cl (7: R = i-Pr; 8: R = Ph), and [2,3,4,5-Ph(4)(eta(5)-C(4)CNHAr)]Ru(CO)(2)Cl (9: Ar = p-NO(2)C(6)H(4); 10: Ar = p-ClC(6)H(4); 11: Ar = Ph; 12: Ar = p-OMeC(6)H(4); 13: Ar = p-NMe(2)C(6)H(4)). The tests in the racemization of (S)-4-phenyl-2-butanol showed that 7 is the most active catalyst, although the difference decreased in the DKR. Complex 4 was used in the DKR of various alcohols; at room temperature, not only simple alcohols but also functionalized ones such as allylic alcohols, alkynyl alcohols, diols, hydroxyl esters, and chlorohydrins were successfully transformed to chiral acetates. In mechanistic studies for the catalytic racemization, ruthenium hydride 14 appeared to be a key species. It was the major organometallic species in the racemization of (S)-1-phenylethanol with 4 and potassium tert-butoxide. In a separate experiment, (S)-1-phenylethanol was racemized catalytically by 14 in the presence of acetophenone.
A new procedure for the dynamic kinetic resolution (DKR) of racemic alcohols into single enantiomers is described. This procedure employs surfactant-treated subtilisin as an (S)-selective resolving catalyst and an aminocyclopentadienylruthenium complex as a racemizing catalyst. The DKR is performed best in the presence of an acyl donor such as trifluoroethyl butyrate in THF at room temperature. Eight simple secondary alcohols have been efficiently resolved with high optical purities and good yields. The subtilisin-based DKR is complementary in stereoselectivity to its lipase-based counterpart. For an acyl-carrying alcohol, both subtilisin- and lipase-based DKRs have proceeded equally well to give a pair of enantiomeric products (>99.5% ee each) with opposite optical rotations in high yields (94-95%).
A multipathway process comprising several enzyme- and metal-catalyzed reactions has been explored for the asymmetric transformations of acyloxyphenyl ketones to optically active hydroxyphenyl alcohols in the ester forms. The process comprises nine component reactions in three pathways, all of which take place by the catalytic actions of only two catalysts, a lipase and a ruthenium complex. The synthetic reactions were carried out on 0.2-0.6 mmol scales for eight different substrates under an atmosphere of hydrogen (1 atm) in toluene at 70 degrees C for 3 days. In most cases, the yields were high (92-96%) and the optical purities were excellent (96-98% ee), This work thus has demonstrated that enzyme-metal multicatalysis has great potential as a new methodology for asymmetric transformations.
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The reaction products of polystyryllithium with air were characterized by size-exclusion chromatography, temperature gradient interaction chromatography and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Polystyryllithium was prepared by anionic polymerization of styrene initiated with sec-butyllithium in cyclohexane under an Ar atmosphere. It was confirmed that polystyryl ketone, polystyryl alcohol, and directly coupled polystyrene were the major products in addition to the normally terminated polystyrene, which is consistent with the results in the literature. We could also identify the presence of methoxy and carboxylic acid end capped polystyrenes as well as dipolystyryl ether as minor products. Among the minor products, dipolystyryl ether has not been reported yet.
The combination of enzyme and metal catalysis is described as a useful method for the synthesis of optically active compounds. A key feature of this new methodology is the use of metal catalysts for the in situ racemization of enzymatically unreactive enantiomers in the enzymatic resolution of racemic substrates. So far, two combinations - lipase-ruthenium and lipase-palladium - have been developed for the efficient dynamic kinetic resolution of alcohols and amines. The use of these combinations has also been extended to catalysis of the asymmetric transformation of ketones, their enol acetates, and ketoximes. In most cases, enzyme-metal combination catalysis has provided good yields and high optical purities.