The platinum-catalyzed hydroamination of ethylene with aniline is reported for the first
time. Using PtBr2 as a catalyst precursor in n-Bu4PBr under 25 bar of ethylene pressure
affords N-ethylaniline with 80 turnovers after 10 h at 150 °C. The reaction simultaneously
produces 2-methylquinoline in ca. 10 cycles. The catalytic activity is slightly improved by
increasing the reaction temperature or the ethylene pressure and strongly depends on the
aniline/platinum ratio. The beneficial effects of added P(OMe)3 (2 equiv/PtBr2) or of a proton
source (3 equiv/PtBr2) have also been pointed out. A gradual poisoning by N-ethylaniline
has been observed, which could be minimized by using biphasic systems. The best result for
the hydroamination with aniline (TON = 145 after 10 h at 150 °C) has been obtained in a
biphasic system (n-Bu4PBr/decane) in the presence of C6H5NH3
+ (3 equiv/PtBr2). The basicity
of the arylamine has been shown to play an important role: the lower the basicity, the higher
the TON. Thus, the hydroamination of ethylene with the weakly basic 2-chloroaniline in
the presence of the PtBr2/H+ catalytic system (0.3% mol) for 72 h at 150 °C yields N-ethyl-2-chloroaniline as the sole reaction product (70% yield based on the amine charged) with
TON = 250. When conducted with 1% of the above catalytic system, the reaction resulted in
nearly quantitative conversion of 2-chloroaniline.
Human serum albumin (HSA) is the most abundant protein in the blood plasma and is involved in the transport of metal ions. Four metal-binding sites with different specificities have been described in HSA: (i) the N-terminal site provided by Asp1, Ala2, and His3, (ii) the site at the reduced Cys34, (iii) site A, including His67 as a ligand, and (iv) the nonlocalized site B. HSA can bind CoII, and HSA was proposed to be involved in CoII transport. Recently, binding of CoII to HSA has attracted much interest due to the so-called albumin cobalt binding (ACB) test approved by the Food and Drug Administration for evaluation of myocardial ischemia. Although the binding of CoII to HSA is important, the binding of CoII to HSA is not well-characterized. Here the binding of CoII to HSA was studied under anaerobic conditions to prevent CoII oxidation. Electronic absorption, EPR, and NMR spectroscopies indicate three specific and well-separated binding sites for CoII in HSA. CoII ions in all three sites are in a high-spin state and coordinated in a distorted octahedral geometry. Competition experiments with CdII (known to bind to sites A and B) and CuII (known to bind to the N-terminal site) were used to identify the sites of binding of CoII to HSA. They revealed that the first two equivalents of CoII bind to sites A and B. Only the third may be bound to the N-terminal site. The repercussions of these results on the understanding of the ACB test and hence the myocardial ischemia are discussed.
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