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Catenanes
In macromolecular chemistry, a catenane () is a mechanically interlocked molecular architecture consisting of two or more interlocked macrocycles, i.e. a molecule containing two or more intertwined rings. The interlocked rings cannot be separated without breaking the covalent bonds of the macrocycles. They are conceptually related to other mechanically interlocked molecular architectures, such as rotaxanes, molecular knots or molecular Borromean rings. Recently the terminology "mechanical bond" has been coined that describes the connection between the macrocycles of a catenane. Catenanes have been synthesised in two different ways: statistical synthesis and template-directed synthesis. Synthesis There are two primary approaches to the organic synthesis of catenanes. The first is to simply perform a ring-closing reaction with the hope that some of the rings will form around other rings giving the desired catenane product. This so-called "statistical approach" led to the fi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Catenane Crystal Structure ChemComm Page634 1991 Commons
In macromolecular chemistry, a catenane () is a mechanically interlocked molecular architecture consisting of two or more interlocked macrocycles, i.e. a molecule containing two or more intertwined rings. The interlocked rings cannot be separated without breaking the covalent bonds of the macrocycles. They are conceptually related to other mechanically interlocked molecular architectures, such as rotaxanes, molecular knots or molecular Borromean rings. Recently the terminology "mechanical bond" has been coined that describes the connection between the macrocycles of a catenane. Catenanes have been synthesised in two different ways: statistical synthesis and template-directed synthesis. Synthesis There are two primary approaches to the organic synthesis of catenanes. The first is to simply perform a ring-closing reaction with the hope that some of the rings will form around other rings giving the desired catenane product. This so-called "statistical approach" led to the fi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Catenane ChemComm 244 1985
In macromolecular chemistry, a catenane () is a mechanically interlocked molecular architecture consisting of two or more interlocked macrocycles, i.e. a molecule containing two or more intertwined rings. The interlocked rings cannot be separated without breaking the covalent bonds of the macrocycles. They are conceptually related to other mechanically interlocked molecular architectures, such as rotaxanes, molecular knots or molecular Borromean rings. Recently the terminology " mechanical bond" has been coined that describes the connection between the macrocycles of a catenane. Catenanes have been synthesised in two different ways: statistical synthesis and template-directed synthesis. Synthesis There are two primary approaches to the organic synthesis of catenanes. The first is to simply perform a ring-closing reaction with the hope that some of the rings will form around other rings giving the desired catenane product. This so-called "statistical approach" led to the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mechanically Interlocked Molecular Architectures
In chemistry, mechanically-interlocked molecular architectures (MIMAs) are molecules that are connected as a consequence of their topology. This connection of molecules is analogous to keys on a keychain loop. The keys are not directly connected to the keychain loop but they cannot be separated without breaking the loop. On the molecular level, the interlocked molecules cannot be separated without the breaking of the covalent bonds that comprise the conjoined molecules; this is referred to as a mechanical bond. Examples of mechanically interlocked molecular architectures include catenanes, rotaxanes, molecular knots, and molecular Borromean rings. Work in this area was recognized with the 2016 Nobel Prize in Chemistry to Bernard L. Feringa, Jean-Pierre Sauvage, and J. Fraser Stoddart. The synthesis of such entangled architectures has been made efficient by combining supramolecular chemistry with traditional covalent synthesis, however mechanically interlocked molecular architectu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Molecular Switch
A molecular switch is a molecule that can be reversibly shifted between two or more stable states. The molecules may be shifted between the states in response to environmental stimuli, such as changes in pH, light, temperature, an electric current, microenvironment, or in the presence of ions and other ligands. In some cases, a combination of stimuli is required. The oldest forms of synthetic molecular switches are pH indicators, which display distinct colors as a function of pH. Currently synthetic molecular switches are of interest in the field of nanotechnology for application in molecular computers or responsive drug delivery systems. Molecular switches are also important in biology because many biological functions are based on it, for instance allosteric regulation and vision. They are also one of the simplest examples of molecular machines. Biological molecular switches In cellular biology, proteins act as intracellular signaling molecules by activating another protein i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rotaxane
In chemistry, a rotaxane () is a mechanically interlocked molecular architecture consisting of a dumbbell-shaped molecule which is threaded through a macrocycle (see graphical representation). The two components of a rotaxane are kinetically trapped since the ends of the dumbbell (often called ''stoppers'') are larger than the internal diameter of the ring and prevent dissociation (unthreading) of the components since this would require significant distortion of the covalent bonds. Much of the research concerning rotaxanes and other mechanically interlocked molecular architectures, such as catenanes, has been focused on their efficient synthesis or their utilization as artificial molecular machines. However, examples of rotaxane substructure have been found in naturally occurring peptides, including: cystine knot peptides, cyclotides or lasso-peptides such as microcin J25. Synthesis The earliest reported synthesis of a rotaxane in 1967 relied on the statistical probabili ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Azobenzene
Azobenzene is a photoswitchable chemical compound composed of two phenyl rings linked by a N=N double bond. It is the simplest example of an aryl azo compound. The term 'azobenzene' or simply 'azo' is often used to refer to a wide class of similar compounds. These azo compounds are considered as derivatives of diazene (diimide), and are sometimes referred to as 'diazenes'. The diazenes absorb light strongly and are common dyes. Structure and synthesis ''trans''-Azobenzene is planar. The N-N distance is 1.189 Å. ''cis''-Azobenzene is nonplanar with a C-N=N-C dihedral angle of 173.5°. The N-N distance is 1.251 Å. Azobenzene was first described by Eilhard Mitscherlich in 1834. Yellowish-red crystalline flakes of azobenzene were obtained in 1856. Its original preparation is similar to the modern one. According to the 1856 method, nitrobenzene is reduced by iron filings in the presence of acetic acid. In the modern synthesis, zinc is the reductant in the presence of a base. I ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tetrathiafulvalene
Tetrathiafulvalene is an organosulfur compound with the formula (. Studies on this heterocyclic compound contributed to the development of molecular electronics. TTF is related to the hydrocarbon fulvalene, , by replacement of four CH groups with sulfur atoms. Over 10,000 scientific publications discuss TTF and its derivatives. Preparation The high level of interest in TTFs has spawned the development of many syntheses of TTF and its analogues. Most preparations entail the coupling of cyclic building blocks such as 1,3-dithiole-2-thion or the related 1,3-dithiole-2-ones. For TTF itself, the synthesis begins with the trithiocarbonate , which is S-methylated and then reduced to give , which is treated as follows: :H2C2S2CH(SCH3) + HBF4 -> 2C2S2CH+F4- + HSCH3 :2 2C2S2CH+F4- + 2 Et3N -> (H2C2S2C)2 + 2 Et3NHBF4 Redox properties Bulk TTF itself has unremarkable electrical properties. Distinctive properties are, however, associated with salts of its oxidized derivatives, suc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Viologen
Viologens are organic compounds with the formula (C5H4NR)2n+. In some viologens, the pyridyl groups are further modified. Viologens are called so, because these compounds produce violet color on reduction iolet + Latin ''gen'', generator of The viologen paraquat (R = methyl), is a widely used herbicide. As early as in the 1930s, paraquat was being used as an oxidation-reduction indicator, because it becomes violet on reduction. Other viologens have been commercialized because they can change color reversibly many times through reduction and oxidation. The name viologen alludes to violet, one color it can exhibit, and the radical cation (C5H4NR)2+ is colored intensely blue. Types of viologens As bipyridinium derivatives, the viologens are related to 4,4'-bipyridyl. The basic nitrogen centers in these compounds are alkylated to give viologens: :(C5H4N)2 + 2 RX → C5H4NR)2sup>2+(X−)2 The alkylation is a form of quaternization. When the alkylating agent is a small ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Entropy
Entropy is a scientific concept, as well as a measurable physical property, that is most commonly associated with a state of disorder, randomness, or uncertainty. The term and the concept are used in diverse fields, from classical thermodynamics, where it was first recognized, to the microscopic description of nature in statistical physics, and to the principles of information theory. It has found far-ranging applications in chemistry and physics, in biological systems and their relation to life, in cosmology, economics, sociology, weather science, climate change, and information systems including the transmission of information in telecommunication. The thermodynamic concept was referred to by Scottish scientist and engineer William Rankine in 1850 with the names ''thermodynamic function'' and ''heat-potential''. In 1865, German physicist Rudolf Clausius, one of the leading founders of the field of thermodynamics, defined it as the quotient of an infinitesimal amount of hea ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
NMR Spectroscopy
Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy or magnetic resonance spectroscopy (MRS), is a spectroscopic technique to observe local magnetic fields around atomic nuclei. The sample is placed in a magnetic field and the NMR signal is produced by excitation of the nuclei sample with radio waves into nuclear magnetic resonance, which is detected with sensitive radio receivers. The intramolecular magnetic field around an atom in a molecule changes the resonance frequency, thus giving access to details of the electronic structure of a molecule and its individual functional groups. As the fields are unique or highly characteristic to individual compounds, in modern organic chemistry practice, NMR spectroscopy is the definitive method to identify monomolecular organic compounds. The principle of NMR usually involves three sequential steps: # The alignment (polarization) of the magnetic nuclear spins in an applied, constant magnetic field B0. # The ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dynamic Covalent Chemistry
Dynamic covalent chemistry (DCvC) is a synthetic strategy employed by chemists to make complex supramolecular assemblies from discrete molecular building blocks. DCvC has allowed access to complex assemblies such as covalent organic frameworks, molecular knots, polymers, and novel macrocycles. Not to be confused with dynamic combinatorial chemistry, DCvC concerns only covalent bonding interactions. As such, it only encompasses a subset of supramolecular chemistries. The underlying idea is that rapid equilibration allows the coexistence of a variety of different species among which molecules can be selected with desired chemical, pharmaceutical and biological properties. For instance, the addition of a proper template will shift the equilibrium toward the component that forms the complex of higher stability (''thermodynamic template effect''). After the new equilibrium is established, the reaction conditions are modified to stop equilibration. The optimal binder for the templ ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dynamic Combinatorial Chemistry
Dynamic combinatorial chemistry (DCC); also known as constitutional dynamic chemistry (CDC) is a method to the generation of new molecules formed by reversible reaction of simple building blocks under thermodynamic control.Schaufelberger, F.; Timmer, B. J. J.; Ramström, O. Principles of Dynamic Covalent Chemistry. In ''Dynamic Covalent Chemistry: Principles, Reactions, and Applications''; Zhang, W.; Jin, Y., Eds.; John Wiley & Sons: Chichester, 2018; Chapter 1, pp 1–30. The library of these reversibly interconverting building blocks is called a dynamic combinatorial library (DCL).Komáromy, D.; Nowak, P.; Otto, S. Dynamic Combinatorial Libraries. In ''Dynamic Covalent Chemistry: Principles, Reactions, and Applications''; Zhang, W.; Jin, Y., Eds.; John Wiley & Sons: Chichester, 2018; Chapter 2, pp 31–119.Lehn, J.-M.; Ramström, O. Generation and screening of a dynamic combinatorial library. PCT. Int. Appl. WO 20010164605, 2001. All constituents in a DCL are in equilibrium, and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
