准轮烷和轮烷研究新进展

准轮烷和轮烷是一个在超分子化学中非常活跃的新领域.它们具有的特殊结构决定了准轮烷和轮烷在纳米功能材料和分子机器等方面有很大的应用潜力,因此倍受化学家们的关注.根据形成轮烷和准轮烷时主要驱动力的不同,可将轮烷和准轮烷的制备方法分为统计学缠绕、化学转移、受氢键驱动、受亲水-疏水相互作用驱动、受金属配位作用驱动、和受π-π堆积相互作用以及电荷转移驱动等.本文分别从上述几种驱动力的角度综述了近年来准轮烷和轮烷在合成和应用方面的最新研究进展.     

Electrostatic barriers in rotaxanes and pseudorotaxanes

The ability to control the kinetic barriers governing the relative motions of the components in mechanically interlocked molecules is important for future applications of these compounds in molecular electronic devices. In this Full Paper, we demonstrate that bipyridinium (BIPY²⁺) dications fulfill the role as effective electrostatic barriers for controlling the shuttling and threading behavior for rotaxanes and pseudorotaxanes in aqueous environments. A degenerate [2]rotaxane, composed of two 1,5‐dioxynaphthalene (DNP) units flanking a central BIPY²⁺ unit in the dumbbell component and encircled by the cyclobis(paraquat‐p‐phenylene) (CBPQT⁴⁺) tetracationic cyclophane, has been synthesized employing a threading‐followed‐by‐stoppering approach. Variable‐temperature ¹H NMR spectroscopy reveals that the barrier to shuttling of the CBPQT⁴⁺ ring over the central BIPY²⁺ unit is in excess of 17 kcal mol^?1 at 343 K. Further information about the nature of the BIPY²⁺ unit as an electrostatic barrier was gleaned from related supramolecular systems, utilizing two threads composed of either two DNP units flanking a central BIPY²⁺ moiety or a central DNP unit flanked by a BIPY²⁺ moiety. The threading and dethreading processes of the CBPQT⁴⁺ ring with these compounds, which were investigated by spectrophotometric techniques, reveal that the BIPY²⁺ unit is responsible for affecting both the thermodynamics and kinetics of pseudorotaxane formation by means of an intramolecular self‐folding (through donor–acceptor interactions with the DNP unit), in addition to Coulombic repulsion. In particular, the free energy barrier to threading (Δ${G{{{\ne}\hfill \atop {\rm f}\hfill}}}The ability to control the kinetic barriers governing the relative motions of the components in mechanically interlocked molecules is important for future applications of these compounds in molecular electronic devices. In this Full Paper, we demonstrate that bipyridinium (BIPY(2+)) dications fulfill the role as effective electrostatic barriers for controlling the shuttling and threading behavior for rotaxanes and pseudorotaxanes in aqueous environments. A degenerate [2]rotaxane, composed of two 1,5-dioxynaphthalene (DNP) units flanking a central BIPY(2+) unit in the dumbbell component and encircled by the cyclobis(paraquat-p-phenylene) (CBPQT(4+)) tetracationic cyclophane, has been synthesized employing a threading-followed-by-stoppering approach. Variable-temperature (1)H?NMR spectroscopy reveals that the barrier to shuttling of the CBPQT(4+) ring over the central BIPY(2+) unit is in excess of 17 kcal mol(-1) at 343 K. Further information about the nature of the BIPY(2+) unit as an electrostatic barrier was gleaned from related supramolecular systems, utilizing two threads composed of either two DNP units flanking a central BIPY(2+) moiety or a central DNP unit flanked by a BIPY(2+) moiety. The threading and dethreading processes of the CBPQT(4+) ring with these compounds, which were investigated by spectrophotometric techniques, reveal that the BIPY(2+) unit is responsible for affecting both the thermodynamics and kinetics of pseudorotaxane formation by means of an intramolecular self-folding (through donor-acceptor interactions with the DNP unit), in addition to Coulombic repulsion. In particular, the free energy barrier to threading (ΔG(f)(++)) of the CBPQT(4+) for the case of the thread composed of a DNP flanked by two BIPY(2+) units was found to be as high as 21.7 kcal mol(-1) at room temperature. These results demonstrate that we can effectively employ the BIPY(2+) unit to serve as electrostatic barriers in water in order to gain control over the motions of the CBPQT(4+) ring in both mechanically interlocked and supramolecular systems.     

Oligomeric pseudorotaxanes adopting infinite-chain lattice superstructures

It's just an illusion: Above a critical chain length, where oligomers contain five or more recognition units, apparently infinite donor-acceptor polypseudorotaxanes are formed in the solid state (see picture). X-ray crystallographic analyses of three different examples have shown that although the oligomeric chains are undoubtedly discrete and monodisperse, they nevertheless appear to be infinite in the crystal.     

A chromophoric switch based on pseudorotaxanes

In a three-component system containing dibenzo-24-crown-8 (1), diamino-dibenzo-24-crown-8 (2), and 1,2-bis(4,4(')-dipyridyl)ethane (3(2+)), axle 3(2+) can shuttle between wheels 1 and 2 by acid-base control, accompanying color changes from yellow to red. This system could not only be taken as a chromophoric supramolecular switch, but also exhibit a function as INHIBIT logic gate.     

Kinetically controlled self-assembly of pseudorotaxanes on crystallization

[reaction: see text] Mixing of equimolar amounts of cyclobis(paraquat-p-phenylene) (CBPQT(4+)) with a bis-4-methylphenyl ether (MPE twice) of a 1,5-dioxynaphthalene (DNP) derivative in MeCN/CH(2)Cl(2) (3:1) results in the formation of a [2]pseudorotaxane which, on crystallization, yields a [4]pseudorotaxane in the solid state that is stabilized by multiple [C-H...F] interactions: a mixture of the same components in a 1:3 ratio affords a crystalline [2]pseudorotaxane after vapor diffusion of methyl-tert-butyl ether into a solution of these components in MeCN/CH(2)Cl(2) (3:1).     

Halide anion directed assembly of luminescent pseudorotaxanes

A series of new photo-active rhenium(i) bipyridyl based pseudorotaxane complexes is assembled via halide anion templation.     

Towards the stereoselective synthesis of inherently chiral pseudorotaxanes

Herein is reported an investigation towards the stereoselective synthesis of inherently chiral pseudorotaxanes. Chiral ammonium threads were readily prepared in five steps from racemic or enantiopure (M or P) salts of di-n-propyl-1,13-dimethoxyquinacridinium cation. Their self-assembly with DB24C8 or disymmetrically oriented DB24C8F6 rings formed pseudorotaxanes as shown by 1H and 19F NMR spectroscopy as well as MS measurements. A determination of the association constants (Ka) was afforded. The crucial role played by the ammonium counter-ion in the threading process was further demonstrated as salts of TRISPHAT (tris(tetrachlorobenzenediolato)phosphate(V)) anion were quite more effective than their PF6- analogues (x 7.3). A general lack of diastereoselectivity (de 相似文献   

Low temperature carbene-to-carbene homologations

Since alkynes have higher symmetry than olefins, it is not easy to infer the mechanism of a triplet carbene’s addition to an alkyne by traditional product analysis studies. Specifically, no stereochemical information which might offer insight into the carbene’s spin state can be extracted from the cyclopropene products. In 1971, Hendrick, Baron, and Jones showed that diphenylcarbene reacts with terminal alkynes in solution to produce indenes via a “self-trapping” vinylcarbene. They also examined the diphenylcarbene reaction with disubstituted alkynes and found at most trace amounts of the “self-trapping” indene product. In this work, we report the direct observation by organic matrix EPR of the vinylcarbenes generated from triplet fluorenylidene and terminal alkynes. Our efforts to confirm the identities of these intermediates by independent synthesis, intermolecular trapping, and an intramolecular “self-trapping” method-halogen-migration-are also recounted. These findings are among the few instances in which fluorenylidene undergoes carbon-carbon bond formation rather than atom abstraction reactions in a low-temperature matrix, and in which the biradical adduct of a triplet carbene and a π-bonded substrate can be directly observed.     

Low temperature pyrolysis of carboxymethylcellulose

Unlike the common high temperature pyrolysis of carboxymethylcellulose (CMC) targeting activated carbon, this study investigates the pyrolytic behaviour of plain CMC at low temperatures ranging between 260 and 300 °C. Preliminary experiments were conducted using differential scanning calorimetry to define the temperature range necessary for the process. Low-temperature pyrolysis was then simulated using thermogravimetric analysis under inert atmosphere. Investigations reveal that a minimum holding temperature of 260 °C is required for an isothermal process, at which pyrolysis is terminated after around 26 min. Increasing exposure temperature reduces pyrolysis time. Within the range of the investigated sample and CMC particle size, no significant effects could be measured regarding the decomposition behaviour. The resulting char was further analysed using X-ray diffraction and Fourier transform infrared spectroscopy. Visual inspection was conducted using scanning electron microscopy. Upon pyrolysis, originally longitudinally shaped CMC was found to be converted into spherical particles of functionalised amorphous carbon with an average particle size of 41 µm.     

Rotaxanes and biofunctionalized pseudorotaxanes via thiol-maleimide click chemistry

Base-catalyzed thiol-maleimide click chemistry has been applied to the synthesis of neutral donor-acceptor [2]rotaxanes in good yield. This method is extended further to the synthesis of a glutathione-functionalized [2]pseudorotaxane, a precursor to integrated conjugates of interlocked molecules with proteins and enzymes.     

Low temperature capture of open shell dipolar molecules by ions: the capture of rotationally selected NO((2)Pi(1/2), j) by C(+)

The low-energy capture of dipolar diatomic molecules in an open electronic state by ions is usually considered to be induced by the first-order charge-permanent dipole interaction with other terms of the long-range potential playing a minor role. If the molecular dipole moment is anomalously small (as is the case for slightly asymmetrical molecules), however, the situation changes, and the capture dynamics is strongly affected by higher orders of the charge-permanent dipole, charge-permanent quadrupole, and charge-induced dipole interactions. The interplay of different terms in the interaction potential manifests itself in complicated temperature dependence of the rotationally state-specific capture rate coefficients. These features of the capture are studied by way of example for NO(X (2)Pi(1/2), j) + C(+) collisions in the temperature range 10(-2)-20 K where the dynamics is adiabatic with respect to rotational and fine-structure transitions and sudden with respect to transitions between Lambda doubling and hyperfine states. The theoretical rate coefficient, which depends on the translational and rotational temperature, agrees with the experimental one measured at T(tr) = 0.6 K and T(rot) = 20 K.     

Low temperature dielectric relaxation spectroscopy

It has been found during the last 2$\text{1}\text{2}$ years that dielectric relaxations associated with many organic compounds could be observed by dissolving or dispersing them in hydrocarbon solvents or matrices and cooling them to 4.2 K. Such relaxations were nearly always attributable to conformational changes of independent solute or dopant molecules and could be used as a means of spectroscopic investigation. Two ways of using such data are outlined and the advantages and limitations are discussed using ROH, RSH and R₁R₂NH compounds as examples.     

Low temperature relaxation in polypyromellitimide

The effect of heat treatment at temperatures above 300°C on the low temperature relaxation of poly(4,4′-oxydiphenylenepyromellitimide) (Kapton H-film) was studied by wide-line nuclear magnetic resonance (NMR), mechanical, and dielectric measurements. In the NMR line spectrum of the as-received film, a narrow component above ?60°C and a broad component which begins to narrow at about ?100°C were observed. It is proposed that the narrow component is associated with absorbed water, because it disappeared in the heat-treated film at 300°C in N₂. On the other hand, the behavior of the broad component was not influenced by heating to 300°C in N₂. Mechanical and dielectric loss peaks were observed at ?75°C (11 Hz) and ?65°C (1 kHz), respectively, in the as-received film. These loss peaks did not change in intensity with heating to 300°C in N₂. It is proposed that the mechanical and dielectric loss peaks corresponding to the narrowing of the NMR broad component are associated with the local-mode motion of the diphenylether portion of the polypyromellitimide chain. It was found that crosslinks are formed by heating to 374°C in air through coupling of the diphenylether portions of the molecular chains. With the formation of crosslinks the dielectric loss peak shifted toward higher temperature and the intensity decreased through restriction of the local-mode motion of the diphenylether portion of the molecular chain.     

Low temperature infrared measurements of NI

The products of a discharge in an N₂ and I₂ mixture are condensed at 10 K. The IR absorptions at 590 and 573 cm^?1 are assigned to ¹⁴NI and ¹⁵NI. Aggregates are found at lower wavenumber.     

Competing supramolecular assembly of amphiphiles to form micelles or pseudorotaxanes

[reaction: see text] Micelles of an amphiphile that encapsulate the added dye in water can be released, upon addition of alpha-CD, to form pseudorotaxane. The equilibrium between the micelles and the pseudorotaxanes and the absorption spectra of solution are controlled by temperature reversibly.     

Anion-templated calix[4]arene-based pseudorotaxanes and catenanes

We present the rational design and anion-binding properties of the first anion-templated pseudorotaxanes and catenanes in which the "wheel" component is provided by a calix[4]arene macrobicyclic unit. The designs and syntheses of two new calix[4]arene macrobicycles, 2 and 3, are presented, and the abilities of these new species both to bind anions and to undergo anion-dependent pseudorotaxane formation are demonstrated. Furthermore, it is shown that performing ring-closing metathesis reactions on some of these pseudorotaxane assemblies gives novel catenane species 14 and 15, in which the yield of interlocked molecule obtained is critically dependent on the presence of a suitable anion template, namely, chloride. Exchange of the chloride anion in catenane 14 a for hexafluorophosphate gives catenane 14 d, which contains a unique anion-binding domain defined by the permanently interlocked hydrogen-bond-donating calix[4]arene macrobicycle and pyridinium macrocycle fragments. The anion-binding properties of this domain are presented, and shown to differ from non-interlocked components.     

Electrochemically switchable cucurbit[7]uril-based pseudorotaxanes

[Structure: see text] The binding location of cucurbit[7]uril can be controlled via redox conversions in these novel, structurally simple pseudorotaxanes.     

Arranging pseudorotaxanes octahedrally around [60]fullerene

The formation of both [2]- and [7]pseudorotaxanes, which are obtained by mixing of a dibenzylammonium derivative with mono- and hexakis-adducts of [60]fullerene bearing malonato-benzo[25]crown-8 rings, has been monitored in dichloromethane by both 1D and 2D (1)H NMR spectroscopies.     

Structures and solution dynamics of pseudorotaxanes mediated by alkali-metal cations

Kinetic stability studies of a series of pseudorotaxanes formed from electron-rich crown ethers (hosts and ) and naphthalene diimide (guest ) in the presence of alkali salt templates MX (where M(+) = Li(+) and Na(+), and X(-) = Cl(-), Br(-), I(-), NO(3)(-) and CF(3)SO(3)(-)) were performed by (1)H NMR. The switching between the (bound) host and its linkage isomer host (free) was monitored in solution in the presence and absence of alkali salts, to establish the relative thermodynamic stabilities in the series. We also report here six new crystal structures, for pseudorotaxanes of type: [.], [M(2)..](2+) and [M(2)..](2+). Their solution-phase structures are in good agreement with the solid-state structures determined by X-ray crystallography.