Optically active phosphines play a most important role as the chiral ligands in various metal-catalyzed asymmetric reactions, and numerous chiral phosphines have been designed and synthesized over the past three decades. 1 Among them, some P-chiral phosphines such as (R,R)-1,2-bis[(o-methoxyphenyl)phenylphosphino]ethane (DIPAMP) were landmark discoveries at an early stage in the history of asymmetric hydrogenation reactions. 2,3 Thereafter, however, relatively less attention has been paid to P-chiral phosphine ligands in the field of asymmetric catalysis. 4 This is largely ascribed not only to the synthetic difficulty of highly enantiomerically enriched P-chiral phosphines but also to the fact that this class of phosphines, especially diaryl-and triarylphosphines, are configurationally unstable and gradually racemize at high temperatures. 5 On the other hand, optically active trialkylphosphines are known to hardly racemize even at considerably high temperature. 6 On the basis of this fact, we designed a new class of P-chiral phosphine ligands, 1,2-bis(alkylmethylphosphino)ethanes (alkyl ) tert-butyl, 1,1-diethylpropyl, 1-adamantyl, cyclopentyl, cyclohexyl) (abbreviated as BisP*) (Figure 1). 7 An important feature of these ligands is that a bulky alkyl group and the smallest alkyl S0002-7863(97)03423-9 CCC: $15.00

Time-resolved X-ray reflectivity measurements for lysozyme (LSZ) adsorbed at an air/water interface were performed to study the mechanism of adsorption-induced protein unfolding. The time dependence of the density profile at the air/water interface revealed that the molecular conformation changed significantly during adsorption. Taking into account previous work using Fourier transform infrared (FTIR) spectroscopy, we propose that the LSZ molecules initially adsorbed on the air/water interface have a flat unfolded structure, forming antiparallel beta-sheets as a result of hydrophobic interactions with the gas phase. In contrast, as adsorption continues, a second layer forms in which the molecules have a very loose structure having random coils as a result of hydrophilic interactions with the hydrophilic groups that protrude from the first layer.

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