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The 2016 Nobel Prize in Chemistry highlighted another spectacular achievement in structural chemistry and supramolecular chemistry. The three awardees built molecular machines based on their intimate knowledge of molecular properties and behavior. One of the three laureates, J. Fraser Stoddart, with two co-authors, published an invited paper in 1999 in our journal in which they surveyed the interplay between the synthesis of functioning supramolecular systems and their X-ray crystallographic investigation. Structural Chemistry congratulates Stoddart and his co-laureates on this momentous occasion. [ABSTRACT FROM AUTHOR]

The evaluation of the Z/E photoisomerization efficiency is an essential task to design photoactive molecular devices. Nevertheless, this photoreactivity can be correctly described only by applying extensive and expensive computational methods. In this study, a predictive tool to screen the photoinduced Z/E isomerization efficiency of molecular switches is presented, based on three key properties: the structure of the ground state minimum, the nature of the electronic transition populating the optically bright state, and the presence of crossings between the optically bright state and the one lower in energy. Our methodology allows evaluating these properties by few and affordable calculations, potentially enabling the screening of large sets of photoswitches. After presenting the formal aspects, the tool is applied to model systems of paradigmatic classes of photoswitches (retinal, green fluorescent protein, hemithioindigo, chiroptical, and stilbene compounds) including derivatives. A comparison with the available experimental data is performed to validate our approach. Cis-trans photoisomerization is a key process for many processes in biology and materials science, but only careful and time-consuming quantum chemistry methods can describe such reaction in detail. Here, a predictive tool is presented requiring few and affordable calculations, evaluating the efficiency of paradigmatic and modified photoswitches. [ABSTRACT FROM AUTHOR]

Highlights: Recent advances and design strategies for molecular machines working as collectives in building smart responsive materials and micro/nanoscale operations are summarized in this review. The modulation of collective behaviors characteristics and properties is summarized in focus, including reversibility, amplification, anisotropy and reconfigurability of smart materials, as well as reconfigurability, orthogonality and logical control of swarming. Experiences and paradigms in the field of micro/nanorobotics in collective construction, control strategies, and model transformations are expected to provide guidance for molecular machines to build reconfigurable, multi-dimensional, and multi-modularity advanced collectives. Molecular machines are key to cellular activity where they are involved in converting chemical and light energy into efficient mechanical work. During the last 60 years, designing molecular structures capable of generating unidirectional mechanical motion at the nanoscale has been the topic of intense research. Effective progress has been made, attributed to advances in various fields such as supramolecular chemistry, biology and nanotechnology, and informatics. However, individual molecular machines are only capable of producing nanometer work and generally have only a single functionality. In order to address these problems, collective behaviors realized by integrating several or more of these individual mechanical units in space and time have become a new paradigm. In this review, we comprehensively discuss recent developments in the collective behaviors of molecular machines. In particular, collective behavior is divided into two paradigms. One is the appropriate integration of molecular machines to efficiently amplify molecular motions and deformations to construct novel functional materials. The other is the construction of swarming modes at the supramolecular level to perform nanoscale or microscale operations. We discuss design strategies for both modes and focus on the modulation of features and properties. Subsequently, in order to address existing challenges, the idea of transferring experience gained in the field of micro/nano robotics is presented, offering prospects for future developments in the collective behavior of molecular machines. [ABSTRACT FROM AUTHOR]

The article announces some of the winners of the 2016 Nobel Prizes including Yoshinori Ohsumi for physiology or medicine, David J. Thouless, F. Duncan M. Haldane and J. Michael Kosterlitz for physics and Jean-Pierre Savauge, J. Fraser Stoddart and Bernard L. Feringa for chemistry.

Developing an eco-friendly, efficient, and highly selective gold-recovery technology is urgently needed in order to maintain sustainable environments and improve the utilization of resources. Here we report an additive-induced gold recovery paradigm based on precisely controlling the reciprocal transformation and instantaneous assembly of the second-sphere coordinated adducts formed between β-cyclodextrin and tetrabromoaurate anions. The additives initiate a rapid assembly process by co-occupying the binding cavity of β-cyclodextrin along with the tetrabromoaurate anions, leading to the formation of supramolecular polymers that precipitate from aqueous solutions as cocrystals. The efficiency of gold recovery reaches 99.8% when dibutyl carbitol is deployed as the additive. This cocrystallization is highly selective for square-planar tetrabromoaurate anions. In a laboratory-scale gold-recovery protocol, over 94% of gold in electronic waste was recovered at gold concentrations as low as 9.3 ppm. This simple protocol constitutes a promising paradigm for the sustainable recovery of gold, featuring reduced energy consumption, low cost inputs, and the avoidance of environmental pollution. Eco-friendly, efficient, and selective gold recovery technologies are urgently desired to satisfy the increasing demand for gold. Here, the authors report one such technology based on the supramolecular polymerization of second-sphere coordinated adducts formed between β-cyclodextrin and tetrabromoaurate anions. [ABSTRACT FROM AUTHOR]

The incorporation of aryl substituents at the meso-positions of calix[4]pyrrole (C4P) scaffolds produces aryl-extended (AE) and super-aryl-extended (SAE) calix[4]pyrroles. The cone conformation of the all-α isomers of “multi-wall” AE-C4Ps and SAE-C4Ps displays deep aromatic clefts or cavities. In particular, “four-wall” receptors feature an aromatic polar cavity closed at one end with four convergent pyrrole rings and fully open at the opposite end. This makes AE- and SAE-C4P scaffolds effective receptors for the molecular recognition of negatively charged ions and neutral guest molecules with donor–acceptor and hydrogen bonding motifs. In addition, adequately functionalized all-α isomers of multi wall AE- and SAE-C4P scaffolds self-assemble into uni-molecular and supra-molecular aggregates displaying capsular and cage-like structures. The self-assembly process requires the presence of template ions or molecules that lock the C4P cone conformation and complementing the inner polar functions and volumes of their cavities. We envisioned performing an in-depth revision of AE- and SAE-C4P scaffolds owing to their importance in different domains such as supramolecular chemistry, biology, material sciences and pharmaceutical chemistry. Herewith, besides the synthetic details on the elaboration of their structures, we also draw attention to their diverse applications. The organization of this review is mainly based on the number of “walls” present in the AE-C4P derivatives and their structural modifications. The sections are further divided based on the C4P functions and applications. The authors are convinced that this review will be of interest to researchers working in the general area of supramolecular chemistry as well as those involved in the study of the binding properties and applications of C4P derivatives. [ABSTRACT FROM AUTHOR]

The study of biological molecular machines, their design, and their principle of operation provoked a healthy interest in methods for reproduction of such nanoscale compounds - synthetic molecular machines with similar physical and chemical properties for performing mechanical work at the molecular level. In addition, the existence of stable redox isomers capable of controlled interconversions related to reversible intramolecular electron transfer between a metal center ion and a ligand itself may be of considerable interest for molecular electronics, since such reversible redox transformations of tetrapyrrole compounds may be followed by changes not only in the optical characteristics, but also in other properties (for example, electrical and/or magnetic), of a material based on them [[56]] and by changes in the linear dimensions of complexes. For example, the process of complexation with metals in crown-ether fragments of phthalocyanine or porphyrin molecules can be easily observed on the electronic and/or fluorescence spectra by the pronounced responses of tetrapyrrole components, due to which it is possible to use such compounds as molecular optical sensors. One should note that these requirements are met not only by metal complexes, in which electron transfer is carried out from a multivalent metal ion to a ligand and vice versa, but also by a number of compounds in which redox isomerization takes place by means of intramolecular ligand-ligand [[43]] or metal-metal transfer [[42]]. Note that, in the UV-vis spectroscopy of molecules, along with electronic transitions between the orbitals of one atom, transitions with charge transfer are also distinguished [[163]], these consisting in the transition of an electron from an orbital localized in one part of the molecule to an orbital localized in another part of the molecule. [Extracted from the article]

Nanographenes have kindled considerable interest in the fields of materials science and supramolecular chemistry as a result of their unique self-assembling and optoelectronic properties. Encapsulating the contorted nanographenes inside artificial receptors, however, remains challenging. Herein, we report the design and synthesis of a trigonal prismatic hexacationic cage, which has a large cavity and adopts a relatively flexible conformation. It serves as a receptor, not only for planar coronene, but also for contorted nanographene derivatives with diameters of approximately 15 Å and thicknesses of 7 Å. A comprehensive investigation of the host-guest interactions in the solid, solution and gaseous states by experimentation and theoretical calculations reveals collectively an induced-fit binding mechanism with high binding affinities between the cage and the nanographenes. Notably, the photostability of the nanographenes is improved significantly by the ultrafast deactivation of their excited states within the cage. Encapsulating the contorted nanographenes inside the cage provides a noncovalent strategy for regulating their photoreactivity. Encapsulating large and contorted nanographenes inside artificial receptors remain challenging. This work reports the synthesis, characterization and binding properties of a trigonal prismatic cage compound that can serve as a receptor for contorted nanographene derivatives. [ABSTRACT FROM AUTHOR]

In order to understand the mechanism of molecular brake more clearly, the brake system (3-(9-triptycyl)-6,6′-dimethoxy-2,2′-bipyridine) was studied in computational methods using the density functional theory (DFT). The M06-2X functional is used to obtain various parameters of the molecules. The relaxed potential energy surface scans were performed to obtain the minimum energy profiles (MEPs). The ground state and transition state during rotation are accurately found, and then a lot of thermodynamic data are obtained and analyzed. For the purpose of proving the occurrence of rotation motion, the transition state theory (TST) was used to investigate the kinetic properties. The Boltzmann statistics was used to analyze the conformer populations, which can also explain some thermodynamic properties of molecular brake. Based on these results, the braking mechanism was pointed out: The rotation of triptycene (Tp) rotor was suppress by a chemical method, to terminate the motion completely, the temperature was lowered appropriately. The molecular dynamics (MD) simulations of the ground states and transition states were also carried out to further verify the rationality of the mechanism. Comparing with the experimental results, the conclusions were figured out. [ABSTRACT FROM AUTHOR]

Ionic self-assembly (ISA) is a powerful tool that has been exploited to create various functional nanomaterials through the electrostatic interactions of different building blocks. Herein, we disclose for the first time the synthesis and characterization of benzoic acid functionalized silica nanoparticles (MSNs-Bn) and its subsequent ISA with meso-tetrakis(N-methylpyridinium-4-yl)porphyrin (TMPyP) to form a pH responsive hybrid material. The resulting pH responsive conjugate is an attractive candidate as a drug delivery vehicle in which the MSNs-Bn act as a drug carrier and the TMPyP act as a capping agent for the silica nanopores. The application of these pH-responsive interactions between the negatively charged carboxylate groups on the surface of mesoporous silica nanoparticles and the positively charged porphyrin as a drug delivery system was investigated by studying the loading and release of Hoechst 33342 dye (a water-soluble biological stain with similar size to those of therapeutic drugs) in response to a pH change. The reported approach enables the delivery of a chemotherapeutic drug in addition to the TMPyP, which is also well-known as a photodynamic therapy (PDT) agent, thus paving the way for synergistic chemo-photodynamic cancer therapy. The study shows that the resulting conjugate demonstrate the drug delivery mechanism which is responsive to changing the pH values from 7.5 to 4.5, and can deliver about 2 wt% of the chemotherapeutic drug tested. [ABSTRACT FROM AUTHOR]

The earlier chapter recounted the early history of the development of X-ray crystallography and described how the early technical problems were over)come. It is a fascinating technique because unlike the optical microscope, it required the development of a deeper understanding of the way in which the X-rays interact with the electron density in the planes of the crystal and the development of theories which were able to quantitatively model it. The following sections deal with how the use of these techniques has led to structural chemistry becoming a very important aspect of modern chemistry. In the early days, the structures of even simple organic molecules would take a PhD student several months or even years to solve the structure. Since the 1950s the development of more sophisticated equipment and the massive rise in computing power made it possible to solve the three-dimensional structure of an organic molecule within hours if not minutes. This successful trajectory has resulted in the ability to study ever more complex molecules and use smaller and smaller crystals. The structures of over a million organic and organo)metallic compounds are now archived in the most commonly used database, and this wealth of information creates a new set of problems for future generations of scientists. This chapter introduces the techniques which have developed to help the chemist use the vast amount of data and the theoretical models which have helped them make use of the data to further their research activities. [ABSTRACT FROM AUTHOR]

Organocatalysis—the branch of catalysis featuring small organic molecules as the catalysts—has, in the last decade, become of central importance in the field of asymmetric catalysis, so much that it is now comparable to metal catalysis and biocatalysis. Organocatalysis is rationalized and classified by a number of so-called activation modes, based on the formation of a covalent or not-covalent intermediate between the organocatalyst and the organic substrate. Among all the organocatalytic activation modes, enamine and iminium catalysis are widely used for the practical preparation of valuable products and intermediates, both in academic and industrial contexts. In both cases, chiral amines are employed as catalysts. Enamine activation mode is generally employed in the reaction with electrophiles, while nucleophiles require the iminium activation mode. Commonly, in both modes, the reaction occurs through well-organized transitions states. A large variety of partners can react with enamines and iminium ions, due to their sufficient nucleophilicity and electrophilicity, respectively. However, despite the success, organocatalysis still suffers from narrow scopes and applications. Multicatalysis is a possible solution for these drawbacks because the two different catalysts can synergistically activate the substrates, with a simultaneous activation of the two different reaction partners. In particular, in this review we will summarize the reported processes featuring Lewis acid catalysis and organocatalytic activation modes synergically acting and not interfering with each other. We will focus our attention on the description of processes in which good results cannot be achieved independently by organocatalysis or Lewis acid catalysis. In these examples of cooperative dual catalysis, a number of new organic transformations have been developed. The review will focus on the possible strategies, the choice of the Lewis acid and the catalytic cycles involved in the effective reported combination. Additionally, some important key points regarding the rationale for the effective combinations will be also included. π-Activation of organic substrates by Lewis acids, via formation of electrophilic intermediates, and their reaction with enamines will be also discussed in this review. [ABSTRACT FROM AUTHOR]

An artificial molecular machine consists of molecule or substituent components jointed together in a specific way so that their mutual displacements could be initiated using appropriate outside stimuli. Such an ability of performing mechanical motions by consuming external energy has endowed these tiny machines with vast fascinating potential applications in areas such as actuators, manipulating atoms/molecules, drug delivery, molecular electronic devices, etc. To date, although vast kinds of molecular machine archetypes have been synthesized in facile ways, they are inclined to be defined as switches but not true machines in most cases because no useful work has been done during a working cycle. More efforts need to be devoted on the utilization and amplification of the nanoscale mechanical motions among synthetic molecular machines to accomplish useful tasks. Here we highlight some of the recent advances relating to molecular machines that can perform work on different length scales, ranging from microscopic levels to macroscopic ones. [ABSTRACT FROM AUTHOR]

The contents of issues 3 and 4 of Structural Chemistry from the calendar year 2017 are summarized in the present review. A brief thermochemical commentary and recommendations for future research have been added to the summary of each paper. [ABSTRACT FROM AUTHOR]

Azobenzene derivatives due to their photo- and electroactive properties are an important group of compounds finding applications in diverse fields. Due to the possibility of controlling the trans-cis isomerization, azo-bearing structures are ideal building blocks for development of e.g. nanomaterials, smart polymers, molecular containers, photoswitches, and sensors. Important role play also macrocyclic compounds well known for their interesting binding properties. In this article selected macrocyclic compounds bearing azo group(s) are comprehensively described. Here, the relationship between compounds’ structure and their properties (as e.g. ability to guest complexation, supramolecular structure formation, switching and motion) is reviewed. [ABSTRACT FROM AUTHOR]

Macroscopic supramolecular assembly (MSA) has been a recent progress in supramolecular chemistry. MSA mainly focuses on studies of the building blocks with a size beyond ten micrometers and the non-covalent interactions between these interactive building blocks to form ordered structures. MSA is essential to realize the concept of 'self-assembly at all scales' by bridging most supramolecular researches at molecular level and at macroscopic scale. This review summaries the development of MSA, the basic design principle and related strategies to achieve MSA and potential applications. Correspondingly, we try to elucidate the correlations and differences between 'macroscopic assembly' and MSA based on intermolecular interactions; the design principle and the underlying assembly mechanism of MSA are proposed to understand the reported MSA behaviors; to demonstrate further applications of MSA, we introduce some methods to improve the ordered degree of the assembled structures from the point of precise assembly and thus envision some possible fields for the use of MSA. [ABSTRACT FROM AUTHOR]

Supramolecular chemistry as de-ned by Lehn ‘chemistry beyond the molecule’ focuses on the development of functional complex architectures through non-covalent interactions. The year 2017, marked the fiftieth anniversary of the serendipitous discovery of crown ethers. Since then, the field is growing, and due to the efforts of various researchers now it is possible to have some control over the arrangement of things on a small scale. In this review article, the concept of supramolecular chemistry, cooperativity responsible for interactions, techniques for determination of thermodynamic parameters of cooperativity, and the contribution of supramolecular chemistry to nanotechnology is described. [ABSTRACT FROM AUTHOR]

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The two current reigning paradigms enabling nanotechnology are scanning probe microscopy and molecular machine devices that date back to seminal experiments by Eigler and visionary work by Drexler, respectively. The nanoscience and nanotechnology community is seeing the emergence of a third paradigm—the use of the atomically focused beam of a scanning transmission electron microscope (STEM) to control and direct matter on the atomic scale. Beam-induced modifications involving one atom or a small group of atoms can be induced and monitored in real time with atomic resolution. Combined with the development of beam-control electronics, big data acquisition, and analytical tools such as artificial intelligence-based feedback systems, electron and ion microscopies are at the brink of a transition from purely imaging tools to tools capable of creating structures with atomic precision and high throughput. In this issue of MRS Bulletin, we present recent advances in electron- and ion-beam-based atomic fabrication on surfaces, in layered materials, and finally in three dimensions—the ultimate dream and possibly the final frontier of nanoscience. [ABSTRACT FROM PUBLISHER]

In this review, pseudorotaxanes and rotaxanes structured out of simple crown ethers and linear organic molecules with positively charged nitrogen centres (i.e., quaternary pyridinium groups, viologens like paraquat and also extended viologens, imidazolium groups, benzimidazolium groups, bis-benzimidazolium groups and their derivatives) are described. Some selected examples of such systems are assembled here with respect to their properties and applications. [ABSTRACT FROM AUTHOR]

The contributions of leading scientists, such as Nobel Prize winners often play an important role in the progress of mankind. In this article, we propose new indices to recognize foundational work in science. Based on case studies of publications by 2016 Nobel Prize winners we make a distinction between two types of fundamental contributions. In a metaphoric way we refer to them as directly igniting or sparking. Our work contains an important message for research evaluation. Besides short-term evaluations it is also important to perform longer term evaluations, otherwise work of Nobel class may fall under the radar and is not rewarded according to its scientific value. It is further suggested that scientometric investigations should not overlook transitional characteristics of scientific progress. [ABSTRACT FROM AUTHOR]

We present an electronic sensor in the molecular scale, which is very sensitive for detection and sensing of DNA characteristics and DNA activities in particular activities between DNA duplex and any protein. Here, the device shows that DNA is electronically inserted to be on the same time as an electrical device transducer and as a biological target in a carbon nanotube-DNA-carbon nanotube electronic sensor. We have performed a DNA binding through an amide group by the electron transfer through amide group. The presented device has shown an efficient and rapid procedure to bind the electrical vulnerability of DNA with the detection of enzymatic effectiveness leading to high efficient biosensor. [ABSTRACT FROM AUTHOR]

A reaction of the protonated form of 7,8-dicarba- nido-undecaborate anion 7,8-CBH with thiourea leads to the formation of a mixture of 9- and 10-thiuronium derivatives, the alkaline hydrolysis of which gives a mixture of the corresponding mercapto derivatives of nido-carborane. The alkylation of the latter with benzyl bromide led to a mixture of dibenzylsulfonium derivatives 9-BnS-7,8-CBH and 10-BnS-7,8-CBH, which were separated by column chromatography on silica. [ABSTRACT FROM AUTHOR]

Carrier proteins consume fuel in order to pump ions or molecules across cell membranes, creating concentration gradients. Their control over diffusion pathways, effected entirely through noncovalent bonding interactions, has inspired chemists to devise artificial systems that mimic their function. Here, we report a wholly artificial compound that acts on small molecules to create a gradient in their local concentration. It does so by using redox energy and precisely organized noncovalent bonding interactions to pump positively charged rings from solution and ensnare them around an oligomethylene chain, as part of a kinetically trapped entanglement. A redox-active viologen unit at the heart of a dumbbell-shaped molecular pump plays a dual role, first attracting and then repelling the rings during redox cycling, thereby enacting a flashing energy ratchet mechanism with a minimalistic design. Our artificial molecular pump performs work repetitively for two cycles of operation and drives rings away from equilibrium toward a higher local concentration. [ABSTRACT FROM AUTHOR]

The emergence of a class of organic oligomers and polymers that lie at the intersection of the fields of mechanically interlocked molecules (MIMs) and synthetic foldamers is described in this review. These macromolecules are based on 4,4′-bipyridinium (BIPY2+) and 1,5-dioxynaphthalene (DNP) recognition units incorporated into linear oligo- or polymeric chains (threads) and macrocycles (rings), where the threads fold their way through a series of rings in a serpentine-like fashion. The well-defined geometries of these polyelectrolytes are rendered by the [C–H … O] hydrogen bonding interactions that transpire between the polyether chains appended to DNP and the acidic protons of BIPY2+, as well as the Π–Π and donor–acceptor (D–A) charge transfer interactions that cause DNP and BIPY2+ units to pack into extended mixed stacks. The unique folding motif of these pseudorotaxanes and rotaxanes makes them attractive candidates for novel multiferroic and mechanically tunable materials. [ABSTRACT FROM AUTHOR]

Applications of semiconductor nanocrystals such as biomarkers and light-emitting optoelectronic devices require that their fluorescence quantum yield be close to 100%. However, such quantum yields have not been obtained yet, in part, because non-radiative Auger recombination in charged nanocrystals could not be suppressed completely. Here, we synthesize colloidal core/thick-shell CdSe/CdS nanocrystals with 100% quantum yield and completely quenched Auger processes at low temperatures, although the nanocrystals are negatively photocharged. Single particle and ensemble spectroscopy in the temperature range 30-300 K shows that the non-radiative Auger recombination is thermally activated around 200 K. Experimental results are well described by a model suggesting a temperature-dependent delocalization of one of the trion electrons from the CdSe core and enhanced Auger recombination at the abrupt CdS outer surface. These results point to a route for the design of core/shell structures with 100% quantum yield at room temperature. [ABSTRACT FROM AUTHOR]