國科會邀請訪問演講 講員：陳 守 信 教授 (Prof. Sow-Hsin Chen) 美國麻省理工學院 核子科學與工程系 國立清華大學傑出校友 第一場演講 暨 國立清華大學傑出校友 頒獎 講題： Observation of Pressure Dependence of Fragile-to-Strong Dynamic Crossover and Its Relation to the Second Critical Point of Water 時間： 2006 年 5 月 16 日 ( 星期二 ) 11 AM 地點：國立清華大學 物理館 019 室 We investigated, using quasi-elastic and inelastic neutron scattering, the slow single-particle dynamics of water confined in lab synthesized nanoporous silica matrices, MCM-41- S, with pore diameters ranging from 10 Å to 18 Å. Inside the pores of these matrices, the freezing process of water is strongly inhibited. We analyzed the neutron scattering spectra with a relaxing-cage model (RCM) and determined the temperature and pressure dependencies of the Q-dependent transnational relaxation time and the stretch exponent. The calculated Q-independent average relaxation time shows a fragile-to-strong (FS) dynamic crossover for pressures lower than 1600 bar. Above this pressure, it is no longer possible to discern the characteristic feature of the FS crossover. Identification of this end point with the predicted second low-temperature critical point of water is discussed. A subsequent inelastic neutron scattering experiment identifies appearance of a low-energy Boson peak below the crossover temperature. In addition, the investigation of librational density of states of water indicates that the FS crossover is a generalized mode-coupling dynamic transition, which is associated with a structural change of the hydrogen-bond cage surrounding a typical water molecule from a denser liquid-like configuration to a less-dense ice-like open structure. 第二場演講 講題： Observation of Fragile-to-Strong Dynamic Crossover in Protein Hydration Water and Its Relation to the Glass Transition of Protein 時間： 2006 年 5 月 22 日 ( 星期一 ) 2 PM 地點：中央研究院物理所 Without water, a biological system would not function. Dehydrated enzymes are not active, but a single layer of water surrounding them restores their activity. It has been shown that the enzymatic activity of proteins depends crucially on the presence of at least a minimum amount of solvent water. It is believed that about 0.3 g of water per g of protein is sufficient to cover most of the protein surface with one single layer of water molecules and to fully activate the protein functionality. Thus, biological functions, such as enzyme catalysis, can only be understood with a precise knowledge of the behavior of this single layer of water and how that water affects conformation and dynamics of the protein. The knowledge of the structure and dynamics of water molecules in the so-called hydration layer surrounding proteins is, therefore, of utmost relevance to the understanding of the protein functionality. It is well documented that at low temperature proteins exist in a glassy state, which has no conformational flexibility. As the temperature is increased, the atomic motional amplitude increases linearly initially, as in a harmonic solid. In hydrated proteins, at approximately 220 K, the rate of the amplitude increase suddenly becomes enhanced, signaling the onset of additional anharmonic and diffusive motion. This ‘dynamical’ transition of proteins is believed to be triggered by its strong coupling through hydrogen bonding with the hydration water, which also shows some kind of dynamic transition at the similar temperature. In this lecture, I shall show, using a high-resolution quasi-elastic neutron scattering (QENS) experiment, that this dynamic transition of hydration water on lysozyme protein is in fact the Fragile-to-Strong (FS) dynamic crossover at 220 K. This crossover signals a transition of water structure from predominantly high-density liquid (HDL, more fluid) to low-density liquid (LDL, less fluid), emanating from existence of the second low-temperature critical point at an elevated pressure, similar to that recently observed in confined water in cylindrical nanopores of silica material. More recent experiment further shows that the hydration water around DNA molecules exhibits the same crossover transition. 第三場演講 講題： Observation of Fragile-to-Strong Dynamic Crossover in Protein Hydration Water and Its Relation to the Glass Transition of Protein 時間： 2006 年 5 月 24 日 ( 星期三 ) 11 AM 地點：國立台灣大學凝態科學研究中心, Room 212, CCMS/Phys Building 主辦單位：國立清華大學 原子科學院 暨 工程與系統科學系 ( 聯絡人 : 林滄浪， ) 協辦單位：國立清華大學 物理系，國家理論科學研究中心，中研院物理所，中研院原分所