Characterization of Hydrogen-Bonded Supramolecular Assemblies by MALDI-TOF Mass Spectrometry after Ag+ Labeling

The high affinity of Ag ⁺ ions for aromatic π donors and cyano groups is exploited in a novel MALDI-TOF mass spectrometric method for the identification of hydrogen-bonded assemblies. The interaction with the Ag⁺ ions—which, for example, can be complexed by two phenyl groups in a sandwich-type manner (see drawing on the right)—provides positively charged assemblies in a nondestructive way.     

C-H?Br, C-Br?Br, and C-Br?π interactions in the crystal structures of mesitylene- and dimesitylmethane-derived compounds bearing bromomethyl units

X-ray structure determinations of mesitylene- and dimesitylmethane-derived compounds bearing bromomethyl units (compounds 1-3) show that the crystal packing of the molecules is characterized by the presence of C-H?Br interactions, such as BrCH₂?Br, CH₃?Br, and C_PhH?Br. In addition, C-Br?Br and C-Br?π interactions determine the crystal packing. The bromomethyl groups play a major role in the packing of 1-3.     

Controlled Formation of Thiol‐Thiolate Hydrogen versus Disulfide Bonds between Two Iridium(III) Centers

Here, we report an iridium(III) coordination system with 2‐aminoethanethiolate (aet), which shows the formation of S?H???S hydrogen and S?S disulfide bonds in a controlled manner. Treatment of fac‐[Ir(aet)₃] with aqueous HBF₄ under aerobic conditions gave dinuclear [Ir₂(aet)₄(cysta)]²⁺ ([ 1 ]²⁺; cysta=cystamine) with a single S?S disulfide bond, while dimeric [Ir₂(aet)₃(Haet)₃](BF₄)₃ ([ 2 ](BF₄)₃) with a triple S?H???S hydrogen bond was formed by similar treatment under anaerobic conditions. Upon exposure to air, [ 2 ]³⁺ was converted to dinuclear [Ir₂(aet)₂(Haet)₂(cysta)]⁴⁺ ([ 3 ]⁴⁺), in which two Ir^III centers are spanned by a double S?H???S hydrogen bond and a single S?S disulfide bond. Complex [ 3 ]⁴⁺ was interconvertible with [ 1 ]²⁺ via the removal/addition of protons on S donors, accompanied by the intermolecular exchange of the fac‐[Ir(aet)₃] units. Complexes [ 1 ]²⁺, [ 2 ]³⁺, and [ 3 ]⁴⁺, isolated as BF₄^? salts, were fully characterized by single‐crystal X‐ray crystallography.     

Guest-Controlled Formation of a Hydrogen-Bonded Molecular Capsule

The dimerization of the self-complementary resorcarene tetraesters is triggered by the entrapment of a tropylium cation in the π-basic cavity. Eight intermolecular OH⋅⋅⋅OC hydrogen bonds together with host–guest interactions such as charge transfer and C−H⋅⋅⋅π bonding are responsible for the high stability of this assembly (see picture). Hereby neither the host–guest interaction nor the interaction of two resorcarene molecules through hydrogen bonds is sufficient by itself to form the complex.     

Noncovalent associations in fluorous fluids

Perfluorocarbons (PFCs) are emerging as a new type of liquid phase in which molecular recognition processes can effectively take place. The combination of perfluorocarbons (PFCs) and noncovalent associations, mostly hydrogen bonds, ion pairing, halogen bonds or coordination bonds, has already been successfully exploited for applications in organic synthesis (catalyst recycling, by-product removal), electrochemical sensing, selective extraction/titration processes or to prepare gels. Due to the extreme solvophobic effect in PFCs, the least polar existing fluids, noncovalent associations tend to be enhanced. For instance, quantitative data on the increase in association strength occurring in PFCs have recently been reported for ion-pairing interactions or encapsulation processes. Moreover, several examples show that confining a receptor in a fluorous phase leads to recognition processes with improved selectivity.     

Cross-Section Molecular Imaging of Supramolecular Microtubes with Contact Atomic Force Microscopy

Bent molecules, distorted layers, columnar domains, and tube membranes (shown schematically in the picture): These hierarchical layers were directly visualized by contact atomic force microscopy along the long axes of the molecules aligned within microtubes made up of bolaamphiphile 1 by self-assembly.     

Electrospray Mass Spectrometry of Biomacromolecular Complexes with Noncovalent Interactions—New Analytical Perspectives for Supramolecular Chemistry and Molecular Recognition Processes

The development of “soft” ionization methods in recent years has enabled substantial progress in the mass spectrometric characterization of macromolecules, in particular important biopolymers such as proteins and nucleic acids. In contrast to the still existing limitations for the determination of molecular weights by other ionization methods such as fast atom bombardment and plasma desorption, electrospray ionization (ESI) and matrix-assisted laser desorption have provided a breakthrough to macromolecules larger than 100 kDa. Whereas these methods have been successfully applied to determine the molecular weight and primary structure of biopolymers, the recently discovered direct characterization by ESI-MS of complexes containing noncovalent interactions (“noncovalent complexes”) opens new perspectives for supramolecular chemistry and analytical biochemistry. Unlike other ionization methods ESI-MS can be performed in homogeneous solution and under nearly physiological conditions of pH, concentration, and temperature. ESI mass spectra of biopolymers, particularly proteins, exhibit series of multiply charged macromolecular ions with charge states and distributions (“charge structures”) characteristic of structural states in solution, which enable a differentiation between native and denatured tertiary structures. In the first part of this article, fundamental principles, the present knowledge about ion formation mechanism(s) of ESI-MS, the relations between tertiary structures in solution and charge structures of macro-ions in the gas phase, and experimental preconditions for the identification of noncovalent complexes are described. The hitherto successful applications to the identification of enzyme–substrate and –inhibitor complexes, supramolecular protein–and protein–nucleotide complexes, double-stranded polynucleotides, as well as synthetic self-assembled complexes demonstrate broad potential for the direct analysis of specific noncovalent interactions. The present results suggest new applications for the characterization of supramolecular structures and molecular recognition processes that previously have not been amenable to mass spectrometry; for example, the sequence-specific oligomerization of polypeptides, antigen–antibody complexes, enzyme–and receptor–ligand interactions, and the evaluation of molecular specificity in combinatorial syntheses and self-assembled systems.     

X-ray Crystallographic Studies on the Noncovalent Syntheses of Supermolecules

An approach to the supramolecular syntheses of discrete multicomponent aggregates of noncovalently bound molecules, i.e., supermolecules, is described. This approach involved the careful analysis of X-ray crystal structures so as to permit a gradual increase in superstructural complexity. Many elaborate supermolecules were synthesized noncovalently from dialkylammonium-containing cations and crown ethers, following the initial observation that the dibenzylammonium ion threads through dibenzo[24]crown-8 to generate a singly stranded, singly encircled [2]pseudorotaxane, principally as a result of and hydrogen bond formation. The scope of the fundamental recognition motif obtained from this initial observation was then broadened, through the use of thread-like ions with multiple dialkylammonium centers and/or larger crown ethers, so that multiply stranded and/or multiply encircled pseudorotaxanes could be prepared. Cations bearing both dialkylammonium and crown ether recognition sites were also used for the nocovalent synthesis of a discrete daisy chain supermacrocycle and the basic recognition motif was combined with other motifs for the production of a wide range of novel superarchitectures. As a greater understanding of the noncovalent interactions governing the self-assembly of the complex superarchitectures was acquired, new protocols for the noncovalent syntheses of doubly docked pseudorotaxanes and interwoven supramolecular bundles, including a supramolecular analogue of the photosynthetic special pair, were developed. The discovery that anions can play a prominent role in the solid-state self-assembly of some of the supermolecules was a valuable spinoff of the research.     

Self-Organization of a Heteroditopic Molecule to Linear Polymolecular Arrays in Solution

Like the proverbial monkey chain one heteroditopic self-complementary molecule, comprising a crown ether unit and a paraquat unit, catches a second such molecule in solution and thus by self-organization forms novel linear oligo- and polymolecular arrays (shown schematically; the crown ether unit is denoted by the ellipse, and the paraquat unit by the rectangle).     

Self-Assembly in Natural and Unnatural Systems

Although there are no fundamental factors hindering the development of nanoscale structures, there is a growing realization that “engineering down” approaches, in other words a reduction in the size of structures generated by lithographic techniques below the present lower limit of roughly 1 μm, may become impractical. It has, therefore, become increasingly clear that only by the development of a fundamental understanding of the self-assembly of large-scale biological structures, which exist and function at and beyond the nanoscale, downwards, and the extension of our knowledge regarding the chemical syntheses of small-scale structures upwards, can the gap between the promise and the reality of nanosystems be closed. This kind of construction of nanoscale structures and nanosystems represents the so-called “bottom up” or “engineering up” approach to device fabrication. Significant progress can be made in the development of nanoscience by transferring concepts found in the biological world into the chemical arena. Central to this mission is the development of simple chemical systems capable of instructing their own organization into large aggregates of molecules through their mutual recognition properties. The precise programming of these recognition events, and hence the correct assembly of the growing superstructure, relies on a fundamental understanding and the practical exploitation of non-covalent bonding interactions between and within molecules. The science of supramolecular chemistry—chemistry beyond the molecule in its very broadest sense—has started to bridge the yawning gap between molecular and macro-molecular structures. By utilizing inter-actions as diverse as aromatic π–π stacking and metal–ligand coordination for the information source for assembly processes, chemists have, in the last decade, begun to use biological concepts such as self-assembly to construct nanoscale structures and superstructures with a variety of forms and functions. Here, we provide a flavor of how self-assembly operates in natural systems and can be harnessed in unnatural ones.     

Anthraquinone‐2,6‐disulfonate as Versatile Ligand for the Synthesis of Hydrogen‐Bonded Supramolecules

The reactions of anthraquinone‐2,6‐disulfonic acid disodium salt (Na₂a‐2,6‐dad) with Cu^II, Mn^II, and Zn^II with 1,10‐phenanthroline (phen) or 2,2′‐dipyridyl (bipy) under hydrothermal conditions formed two or three‐dimensional supramolecules of stoichiometries [Cu(a‐2,6‐dad)(phen)(H₂O)₃](H₂O)₄ ( 1 ), [Mn(a‐2,6‐dad)(bipy)₂(H₂O)](H₂O)₂ ( 2 ), and [Zn(a‐2,6‐dad)(bipy)₂(H₂O)](H₂O)₂ ( 3 ), which were synthesized and characterized. The arrangement around each metal atom is distorted octahedral. The ligands in all the compounds are engaged in intermolecular hydrogen bonding leading to the formation of hydrogen‐bonded networks, the compounds show novel π–π stacking interactions. Photoluminescence measurements indicate that the compound [Zn(a‐2,6‐dad)(bipy)₂(H₂O)](H₂O)₂ ( 3 ) shows strong blue luminescence in the solid state at room temperature.     

Sapphyrin Supramolecules through C−H⋅⋅⋅S and C−H⋅⋅⋅Se Hydrogen Bonds—First Structural Characterization of meso- Arylsapphyrins Bearing Heteroatoms

An unprecedented coupling reaction of heteroatom-containing tripyrranes leads to the formation of core-modified sapphyrins 1 and 2 , which self-assemble in the solid state to form supramolecular ladders. Weak C−H⋅⋅⋅S and C−H⋅⋅⋅Se hydrogen-bonding interactions in addition to C−H⋅⋅⋅N hydrogen bonds are responsible for the observed structures.     

A Model of Hydrogen-Bonded Liquids

The orientation defect model can be used for quantitative estimates and for understanding the properties of H-bonded liquids, such as water and alcohol. The defect concentrations can be determined by vibrational spectroscopy, and the applicability of the approximation procedure derives from considering H-bonds as chemical equilibria. Possible extensions of the simple model are critically discussed.     

以苝酰亚胺为构筑单元的氢键型超分子聚合物的组装与应用

以苝酰亚胺为构筑单元的氢键型超分子聚合物具有动态可逆的特征和独特的聚集体结构,呈现出许多新颖的光电功能特性,在有机太阳能电池,场效应晶体管和光收集材料等高新技术领域有着广阔的应用前景。本文在介绍苝酰亚胺衍生物的化学结构及其氢键组装特点的基础上,主要综述了近年来以苝酰亚胺为构筑单元,采用三重氢键,多重氢键以及其他形式氢键引导构筑的超分子聚合物的研究动态,这类超分子聚合物展示了丰富的组装体形貌结构,独特的性质功能以及在光电功能器件上的广阔的应用前景。最后,对其发展前景作了展望。     

Structural Classification and General Principles for the Design of Spherical Molecular Hosts

Cryptands, carcerands, polyoxometalates, and molecular capsules are cagelike hosts that complex guests through encapsulation. Following the discovery of a nanometer scale supramolecular shell-like spheroid, these and other shell-like hosts were structurally classified. Their frameworks may be catalogued according to principles of solid geometry. This has led to the identification of hosts that have not yet been synthesized or discovered (such as the cuboctahedron shown; X=O, S) and should lead to the design of additional container assemblies.     

A Molecular Chameleon: Chromophoric Sensing by a Self-Complexing Molecular Assembly

A color change from purple to green takes place on addition of tetrathiafulvalene (TTF) to the macrobicyclic receptor 1 ⁴⁺, which is composed of a cyclobis(paraquat-p-phenylene) tetracation that shares one of its paraphenylene rings with a 1,5-naphthoparaphenylene-[36]crown-10 macrocycle. The TTF molecule forces the macrobicycle to turn inside out (see schematic drawing below) and displaces the self-complexed 1,5-dioxynaphthalene ring system from the center of the tetracationic cyclophane.     

基于氢键作用结合的超分子聚合物

非共价键结合的超分子聚合物由于其特殊的结构及性能引起了广泛的关注。本文在介绍超分子化学、氢键及超分子聚合物的基础上,主要综述了以氢键为结合力的多重氢键作用、羧基（D）与吡啶基（A）作用以及氢键与其它非共价键协同作用形成的超分子聚合物体系,并对超分子聚合物的研究现状及前景进行了评述。     

基于氢键作用结合的超分子聚合物

非共价键结合的超分子聚合物由于其特殊的结构及性能引起了广泛的关注。本文在介绍超分子化学、氢键及超分子聚合物的基础上,主要综述了以氢键为结合力的多重氢键作用、羧基(D)与吡啶基(A)作用以及氢键与其它非共价键协同作用形成的超分子聚合物体系,并对超分子聚合物的研究现状及前景进行了评述。     

Resolution of Racemic 1,2-Dibromohexafluoropropane through Halogen-Bonded Supramolecular Helices

Halogen bonds , attractive intermolecular interactions between perfluoroalkyl bromides and bromide ions, are present in cocrystals of (−)-sparteinium hydrobromide ( 1 ) and (S)-1,2-dibromohexafluoropropane ( 2 ; shown schematically), and result in enantiopure and infinite supramolecular helices. The perfluorocarbon–hydrocarbon self-assembly allows the resolution of racemic 2 .