抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

J. Appl. Cryst.の発刊に際して

The long-standing challenge of designing and constructing new crystalline solid-state materials from molecular building blocks is just beginning to be addressed with success. A conceptual approach that requires the use of secondary building units to direct the assembly of ordered frameworks epitomizes this process: we call this approach reticular synthesis. This chemistry has yielded materials designed to have predetermined structures, compositions and properties. In particular, highly porous frameworks held together by strong metal-oxygen-carbon bonds and with exceptionally large surface area and capacity for gas storage have been prepared and their pore metrics systematically varied and functionalized.

/pdf/reticular-synthesis-and-the-design-of-new-materials-lazbx7tdux.pdf

Reticular synthesis and the design of new materials

Self-assembly is the autonomous organization of components into patterns or structures without human intervention. Self-assembling processes are common throughout nature and technology. They involve components from the molecular (crystals) to the planetary (weather systems) scale and many different kinds of interactions. The concept of self-assembly is used increasingly in many disciplines, with a different flavor and emphasis in each.

http://science.sciencemag.org/content/sci/295/5564/2418.full.pdf

Self-assembly at all scales.

From molecules to crystal engineering: supramolecular isomerism and polymorphism in network solids.

A crystal of an organic compound is the ultimate supermolecule, and its assembly, governed by chemical and geometrical factors, from individual molecules is the perfect example of solid-state molecular recognition. Implicit in the supramolecular description of a crystal structure is the fact that molecules in a crystal are held together by noncovalent interactions. The need for rational approaches towards solid-state structures of fundamental and practical importance has led to the emergence of crystal engineering, which seeks to understand intermolecular interactions and recognition phenomena in the context of crystal packing. The aim of crystal engineering is to establish reliable connections between molecular and supramolecular structure on the basis of intermolecular interactions. Ideally one would like to identify substructural units in a target supermolecule that can be assembled from logically chosen precursor molecules. Indeed, crystal engineering is a new organic synthesis, and the aim of this article is to show that rather than being only nominally relevant to organic chemistry, this subject is well within the mainstream, being surprisingly similar to traditional organic synthesis in concept. The details vary because one is dealing here with intermolecular interactions rather than with covalent bonds; so this article is divided into two parts. The first is concerned with strategy, highlighting the conceptual relationship between crystal engineering and organic synthesis and introduces the term supramolecular synthon. The second part emphasizes methodology, that is, the chemical and geometrical properties of specific intermolecular interactions.

Supramolecular Synthons in Crystal Engineering—A New Organic Synthesis

1. Introduction 2. Archetypes of the weak hydrogen bond 3. Other weak and non-conventional hydrogen bonds 4. The weak hydrogen bond in supramolecular chemistry 5. The weak hydrogen bond in biological structures 6. Conclusions Appendix

The weak hydrogen bond : in structural chemistry and biology

A hydrogen bond, X-H...A, is an interaction wherein a hydrogen atom is attracted to two atoms, X and A, rather than just one and so acts like a bridge between them. This attraction always increases with increasing electronegativity of X and A, and in the classical view all hydrogen bonds are highly electrostatic and sometimes even partly covalent. Gradually, the concept of a hydrogen bond became more relaxed to include weaker interactions, provided some electrostatic character remains. In the limit, these weak hydrogen bonds have considerable dispersive-repulsive character and merge into van der Waals interactions. A great variety of hydrogen bonds are observed in the solid state and the aim of this article is to highlight some features common to all these bonds and further to suggest that the term hydrogen bridge is perhaps a better descriptor for them. Such a description recognizes an interaction without borders and one that admits of much variation in its relative covalent, electrostatic, and van der Waals content.

Hydrogen bridges in crystal engineering: interactions without borders.

The C-H‚‚‚O hydrogen bond is so well-established in structural chemistry that it seems difficult now to believe that when Sutor proposed the existence of this type of hydrogen bond in the early 1960s,1,2 her suggestion was drowned in scepticism, if not outright hostility.3 It was only two decades later, with Taylor and Kennard’s paper, that the subject was properly revived.4 Shortly thereafter, an Account appeared from this laboratory describing the role of the C-H‚‚‚O interaction in crystal engineering.5 Subsequently, one felt confident enough to term these erstwhile “interactions” hydrogen bonds, in a second Account.6 A recent invitation to contribute another Account and the many recent efforts in this direction by my students and postdoctorals have led to the present paper. It is clearly no longer necessary to justify the relevance of C-H‚‚‚O hydrogen bonds, so widely invoked are they in small-molecule and biological crystallography. The presence of O-atoms in a large majority of organic molecules means that this hydrogen bond is widespread, even if not identified in many cases. However, other questions concerning these weak hydrogen bonds could be posed: (1) What is their upper distance limit? (2) Are very short, bent bonds significant? (3) Why do C-H‚‚‚O bonds sometimes disturb the strong O-H‚‚‚O and N-H‚‚‚O network? Alternatively, why do hydrogen bond donors and acceptors not always pair in descending order of strength? (4) How important is cooperativity for weak hydrogen bonds? (5) Are C-H‚‚‚O hydrogen bonds responsible for crystal packing, or are they the forced consequences of packing? (6) Are weak hydrogen bonds robust enough for supramolecular synthesis and crystal engineering? (7) Does the C-H‚‚‚O hydrogen bond have any biological significance? These difficult questions cannot be answered fully. This Account attempts to address some of them, but better answers can only follow from further work.

The C-h···o hydrogen bond: structural implications and supramolecular design.

1 Molecular Crystals and Crystal Engineering Crystal engineering Why design crystal structures of organic molecules? Some extensions Conclusions 2 The Atom-Atom Potential Method and the Close-Packing Model for Molecular Crystals Intermolecular forces in crystals The atom-atom potential method The close-packing model of Kitaigorodskii Crystal structure prediction Conclusions 3 Crystallographic Databases and the Recognition of Intermolecular Patterns The nature and growth of crystallographic information The Cambridge structural database Intermolecular patterns in crystals Conclusions 4 Structures Based Mostly on van der Waals Forces Non-bonded interactions involving carbon and hydrogen atoms Effects of van der Waals forces on crystal packing Occupied and unoccupied volumes in crystals Conclusions 5 Some Structures Based on Hydrogen Bonding Introduction Rationalisation of hydrogen bonding patterns The role of C-HO interactions in determining crystal structures Other types of hydrogen bonding in crystals Conclusions 6 Structures Based on Intermolecular Contacts to Halogen Atoms The nature of halogenhalogen forces The geometry of halogenhalogen interactions Design of halogenhalogen stabilised crystal structures Contacts between halogen and non-halogen atoms Conclusions 7 Structures Based on Intermolecular Contacts to Sulphur The nature of sulphurheteroatom contacts Crystal design and engineering Conclusion 8 Designing Non-Centrosymmetric Crystals Introduction Some properties and applications of non-centrosymmetric crystals Methods of crystal design Non-centrosymmetry in other organised media Conclusions 9 Structures Based on Interactions Between Distinct Molecular Species: Solid Solutions, Donor-Acceptor Complexes and Clathrates Design of crystal structures of molecular complexes 10 Polymorphism - The Nemesis of Crystal Design? Polymorphism and crystal structure design 11 Conclusions Index

Gautam R. Desiraju

Papers

Supramolecular Synthons in Crystal Engineering—A New Organic Synthesis

The weak hydrogen bond : in structural chemistry and biology

Hydrogen bridges in crystal engineering: interactions without borders.

The C-h···o hydrogen bond: structural implications and supramolecular design.

Crystal engineering : the design of organic solids