Adsorbate-induced chiral reconstructions studied by surface X-ray diffraction

通过表面 X 射线衍射研究吸附物诱导的手性重建

• 批准号: EP/G068593/1
• 负责人: Georg Held
• 金额: $ 22.59万
• 依托单位: University of Reading
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2009
• 资助国家: 英国
• 起止时间: 2009 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FG068593%2F1
• 关键词: Adsorbate; induced; chiral; reconstructions; studied

Fundamental research related to heterogeneous catalysis is often hampered by the so-called pressure gap , i.e. the fact that most experimental surface science techniques that are able to elucidate the atomic details of reactions at the catalyst surface can only be applied in vacuum, whereas the actual catalytic reactions usually take place at high reactant pressures or even in solution. This gap is bridged to some extent by surface X-ray diffraction (SXRD), an experimental technique that provides exact geometric information about the arrangement of surface atoms. The advantage of X-rays over most other surface-sensitive methods is that they can penetrate a gas atmosphere or even a thin film of liquid. Thus they are ideal for the study of heterogeneous catalytic processes, in particular those that take place in solution. At the interface between solution and catalyst, reactant and solvent molecules interact very closely and it is important to study their interaction at or near the reaction temperature, which is not possible in vacuum where all the solvent evaporates.Crystallographers have used X-ray diffraction for over a century to determine the exact positions of atoms in the bulk of crystalline material, which has been crucial for our understanding of chemical and biological processes, as complicated as information transfer in DNA. Modern synchrotron light sources, such as Diamond, which became available over the last decade, deliver very intense X-ray radiation and make it now possible to detect also the weak diffraction signal due to atoms at the surfaces of crystals and determine their positions. We plan to use SXRD to study the arrangement of atoms at the surfaces of 'enantioselective' heterogeneous catalysts, which are of particular importance to the synthesis of drugs. Most molecules that play an important role in biology are chiral, meaning that their mirror images cannot be matched with the original by any rotation in space - just as our left and right hands. These molecules exist as 'left-handed' or 'right-handed' versions ('enantiomers'). Although both versions are identical in their physical properties, all living organisms on earth only use or produce one of each biomolecule. This poses a challenge for drug manufacturing because normally only one enantiomer of a drug molecule has the desired effect, whereas the 'wrong' enantiomer often causes unwanted side effects. When chiral molecules are synthesized in the laboratory both enantiomers are created in equal amounts unless 'enantioselective catalysts' are used. Such catalysts provide 'stereoselective sites', which are shaped in a way that only allows one type of molecule to form stable chemical bonds, similar to gloves that either fit the left or the right hand.Unlike nature's enantioselective catalysts, enzymes, heterogeneous catalysts that are preferred in industrial processes are usually made of inorganic material, metals or oxides. Currently, the only way of introducing stereoselective sites in these materials in large enough quantities is by adsorbing chiral modifier molecules on their surfaces (e.g. Ni catalysts modified by tartaric acid or alanine show significant enantiomeric excess in the asymmetric hydrogenation of beta-ketoesters). Since all this takes place in solution, however, we know very little about the exact nature of the modification they cause, the involvement of solvents or the exact reaction mechanisms. This makes it difficult to further improve such catalysts and to find new chiral modifiers that could catalyse other reactions. We therefore propose to study the geometrical modifications of Ni surfaces under reaction conditions using the new surface X-ray diffraction beamline I07 at Diamond and related experiments. The aim is a microscopic understanding of the interactions between modifiers, metal surfaces and reactant molecules, which could eventually lower the costs of the production of vital drugs.

与多相催化相关的基础研究通常受到所谓的压力差距的阻碍，即大多数能够阐明催化剂表面反应原子细节的实验表面科学技术只能在真空中应用，而实际的催化反应通常在高反应物压力下甚至在溶液中进行。表面X射线衍射（SXRD）在一定程度上弥补了这一差距，这是一种实验技术，可以提供有关表面原子排列的精确几何信息。与大多数其他表面敏感方法相比，X射线的优点是它们可以穿透气体气氛甚至液体薄膜。因此，它们是研究多相催化过程的理想选择，特别是那些在溶液中发生的催化过程。在溶液和催化剂之间的界面处，反应物和溶剂分子非常紧密地相互作用，并且重要的是在反应温度下或接近反应温度下研究它们的相互作用，这在所有溶剂蒸发的真空中是不可能的。晶体学家已经使用X射线衍射超过世纪来确定晶体材料中原子的确切位置，这对我们理解化学和生物过程至关重要，就像DNA中的信息传递一样复杂。现代同步加速器光源，如钻石，在过去十年中变得可用，提供非常强烈的X射线辐射，现在可以检测晶体表面原子的微弱衍射信号并确定它们的位置。我们计划使用SXRD来研究“对映选择性”多相催化剂表面的原子排列，这对药物合成特别重要。大多数在生物学中发挥重要作用的分子都是手性的，这意味着它们的镜像不能通过空间中的任何旋转与原始分子相匹配-就像我们的左手和右手一样。这些分子以“左手”或“右手”形式（“对映体”）存在。虽然这两个版本在物理性质上是相同的，但地球上所有的生物体都只使用或生产每种生物分子中的一种。这对药物制造提出了挑战，因为通常只有一种药物分子的对映体具有所需的效果，而“错误”的对映体通常会导致不必要的副作用。当在实验室中合成手性分子时，除非使用“对映选择性催化剂”，否则两种对映异构体以相等的量产生。这种催化剂提供“立体选择性位点”，其形状只允许一种类型的分子形成稳定的化学键，类似于适合左手或右手的手套。与自然界的对映选择性催化剂不同，酶，工业过程中优选的多相催化剂通常由无机材料，金属或氧化物制成。目前，在这些材料中以足够大的量引入立体选择性位点的唯一方法是通过将手性改性剂分子吸附在它们的表面上（例如，由酒石酸或丙氨酸改性的Ni催化剂在β-酮酯的不对称氢化中显示出显著的对映体过量）。然而，由于所有这些都发生在溶液中，我们对它们引起的修饰的确切性质、溶剂的参与或确切的反应机制知之甚少。这使得难以进一步改进此类催化剂并发现可催化其它反应的新的手性改性剂。因此，我们建议使用新的表面X射线衍射光束线I 07在金刚石和相关的实验研究的反应条件下的Ni表面的几何修改。其目的是从微观上了解改性剂、金属表面和反应物分子之间的相互作用，这最终可能降低重要药物的生产成本。

项目成果

Stereochemistry and thermal stability of tartaric acid on the intrinsically chiral Cu{531} surface

• DOI: 10.1016/j.susc.2015.08.021
• 发表时间: 2016
• 期刊: Surface Science
• 影响因子: 1.9
• 作者: Silvia Baldanza;J. Ardini;A. Giglia;G. Held

Complete Experimental Structure Determination of the p(3 × 2) pg Phase of Glycine on Cu{110}

Cu{110} 上甘氨酸 p(3 × 2) pg 相的完整实验结构测定

• DOI: 10.1021/jp2057282
• 发表时间: 2011
• 期刊: The Journal of Physical Chemistry C
• 作者: Zheleva Z

Surface Chemistry of Alanine on Ni{111}

• DOI: 10.1021/acs.jpcc.5b08814
• 发表时间: 2015-11
• 期刊: Journal of Physical Chemistry C
• 影响因子: 3.7
• 作者: R. Nicklin;A. Cornish;A. Shavorskiy;Silvia Baldanza;K. Schulte;Zhi Liu;R. Bennett;G. Held

Adsorption of Methyl Acetoacetate at Ni{111}: Experiment and Theory

Ni{111} 上乙酰乙酸甲酯的吸附：实验与理论

• DOI: 10.1021/acs.jpcc.6b10023
• 发表时间: 2016
• 期刊: The Journal of Physical Chemistry C
• 作者: Ontaneda J

Structure and stress of Re(1121); chiral terraces at a racemic surface.

Re(1121)的结构和应力；

• DOI: 10.1039/c3cp53165a
• 发表时间: 2013
• 期刊: PCCP
• 作者: Etman HA