Noncovalent interactions between cytosine and SWCNT: curvature dependence of complexes via pi...pi stacking and cooperative CH...pi/NH...pi

Fragments of C24H12, adapted from a variety of armchair [(n,n), (n = 5, 7, and 8)] and zigzag [(m,0) (m = 8, 10, and 12)] single-walled carbon nanotube (SWCNT), are used to model corresponding SWCNTs with different diameters and electronic structures. The parallel binding mainly through pi...pi stacking interaction, as well as the perpendicular binding via cooperative NH...pi and CH...pi between cytosine and the fragments of SWCNT have been extensively investigated with a GGA type of DFT, PW91LYP/6-311++G(d,p). The eclipsed tangential (ET) conformation with respect to the six-membered ring of cytosine and the central ring of SWCNT fragments is less stable than the slipped tangential (ST) conformation for the given fragment; perpendicular conformations with NH2 and CH ends have higher negative binding energy than those with NH and CH ends. At PW91LYP/6-311++G(d,p) level, two tangential complexes are less bound than perpendicular complexes. However, as electron correlation is treated with MP2/6-311G(d,p) for PW91LYP/6-311++G(d,p) optimized complexes, it turns out there is an opposite trend that two tangential complexes become more stable than three perpendicular complexes. This result implies that electron correlation, a primary source to dispersion energy, has more significant contributions to the pi...pi stacking complexes than to the complexes via cooperative NH...pi and CH...pi interactions. In addition, it was found for the first time that binding energies for two tangential complexes become more negative with increasing nanotube diameter, while those for three perpendicular complexes have a weaker dependence on the curvature; i.e., binding energies are slightly less and less negative. The performance of a novel hybrid DFT, MPWB1K, was also discussed.     

Half-rotation in a kinetically locked [2]catenane induced by transition metal ion substitution

We report on a heterocircuit [2]catenane in which a reversible half-rotation of one ring about the other can be induced, and locked in place, by switching the coordination of the interlocked rings between Pd(II) and Co(III).     

Coordination molecular hats binding acetonitrile via C-H...pi interactions

The [M(3)L(3)](3+) metallo-macrocycles with syn, syn, syn conformation, self-assembled from crown ether functionalized 1,10-phenanthroline Pd(II) nitrates with naphthanoimidazole, bind a solvent CH(3)CN within the naphthanoimidazolate-built cavity through C-H...pi interactions in the crystalline state.     

Two classes of alongside charge-transfer interactions defined in one [2]catenane

A [2]catenane, which incorporates hydroquinone (HQ) and a sterically bulky tetrathiafulvalene (TTF) into a bismacrocycle, has been designed to probe the alongside charge-transfer (CT) interactions taking place between a TTF unit and one of the bipyridinium moieties in the tetracationic cyclophane cyclobis(paraquat-p-phenylene) (CBPQT4+). A template-directed strategy employs the HQ unit as the primary template for formation of the tetracationic cyclophane CBPQT4+, affording the desired [2]catenane structure but as an uncharacteristic green solid. The X-ray crystal structure and detailed 13C NMR assignments have identified a stereoselective preference for catenation about the cis isomer. The 1H NMR spectroscopy, electrochemistry, and X-ray crystallography all confirm that the CBPQT4+ cyclophane encircles the HQ unit, thereby defining a structure which would normally determine a red color. The visible-NIR region of the absorption spectrum displays a band at approximately 740 nm that is unambiguously assigned to a TTF --> CBPQT4+ CT transition on the basis of resonance Raman spectroscopy using 785 nm excitation. The profile of the CT band changes depending on the ratio of the cis- to trans-TTF isomers in the [2]catenane for which the molar absorptivity of each isomer is estimated to be significantly different at epsilon max = 380 and 3690 M-1 cm-1, respectively. Molecular modeling studies confirmed that the observed difference in the absorption spectroscopic profile can be accounted for by both a better overlap of the HOMO(TTF) and LUMO+1(CBPQT4+) as well as a more stable face-to-face (pi...pi) conformation in the trans isomer compared to the edge-to-face cis isomer of the [2]catenane. The latter is arranged for pi-orbital overlap through the sulfur atoms of the TTF unit, thereby defining an [Spi...pi] interaction.     

Solvent-induced aggregation through metal...metal/pi...pi interactions: large solvatochromism of luminescent organoplatinum(II) terpyridyl complexes

A dramatic color change and tremendous emission enhancement have been "switched on" upon increasing diethyl ether ratio in acetonitrile or acetone solution of [Pt(tpy)(CC-CCH)]OTf, attributed to the formation of Pt...Pt and pi-pi interactions. Two crystal forms (dark-green and red) of [Pt(tpy)(CC-CCH)]OTf, together with [Pt(tBu3-tpy)(CC-CCH)]OTf, show different crystal-packing modes as revealed by X-ray crystallography.     

Construction of a hetero pseudo[2]rota[2]catenane

A novel ammonium template containing three ammonium sites was synthesized. Two ammoniums located on the linear component served as template for cucurbit[6]uril to form the CB-based pseudo[2]rotacane while another one located on the macrocyclic component played a role of template for clipping reaction. As a result of a ‘‘threading-followed-by-clipping' approach, a novel hetero pseudo[2]rota[2]catenane was successfully constructed.     

Anion-templated assembly of a [2]catenane

The first example of a [2]catenane structure to be synthesized using anion templation is described. The nature of the anion template is demonstrated to be crucial to the assembly process, with only chloride anion producing the [2]catenane in acceptable yield. Anion binding studies reveal a dramatic catenation effect on anion selectivity properties as compared to a noncatenated acyclic receptor.     

A reverse donor-acceptor bistable [2]catenane

A [2]catenane, composed of a pi-electron-rich bis-1,5-dioxynaphthalene[38]crown10 (BDNP38C10) ring, mechanically interlocked with a large macrocycle containing two disubstituted tetraarylmethane "speed bumps" and two different pi-electron-deficient units--namely, naphthalene dimide (NpI) and bipyridinium (BIPY(2+)) units--has been synthesized from a [2]rotaxane, containing the former recognition unit, after performing two sequential Cu(I)-catalyzed azide-alkyne cycloadditions with a linker containing the latter recognition unit. The product, which exists as a single co-conformer, wherein the BDNP38C10 ring encircles the NpI unit, undergoes equilibration to give approximately equal amounts of the other co-conformer in which the BDNP38C10 ring encircles the BIPY(2+) unit.     

Quantitative formation of a tetraporphyrin [2]catenane via copper and zinc coordination

A [2]catenane is formed quantitatively by mixing substituted 1,10-phenanthroline-based chelates with copper(I) acting as central template, the ring-forming reaction being based on the coordination of pyridinic bidentate ligands onto the zinc atoms of the four porphyrins surrounding the core of the molecule.     

The diatropic sigma ring currents of [pi2s + pi2s + pi2s] pericyclic transition states

Ab initio current-density maps for the (4n + 2)-electron transition states of two thermally allowed [pi2s + pi2s + pi2s] trimerisations, of ethyne to benzene (1), and of ethene to cyclohexane (2), show that both support sigma diatropic ring currents, dominated by four-electron sigma --> sigma* virtual excitation of HOMO electrons.     

Versatile formation of [2]catenane and [2]pseudorotaxane structures; threading and noncovalent stoppering by a self-assembled macrocycle

A self-assembled dimeric macrocycle between 4,4'-bis(4-pyridylmethoxy)biphenyl (L) and (en)Pd(NO(3))(2) was constructed, and its interactions with cyclodextrins of different cavity size resulted in the formation of [2]catenane and [2]pseudorotaxane systems, respectively. The structures were identified by 1D and 2D NMR spectroscopy and cold spray ionization mass (CSI-MS) spectrometry.     

Host-guest interactions template: the synthesis of a [3]catenane

Formation of a [3]catenane containing dibenzo-24-crown ether wheels and a large dipyridiniumethane ring is templated by formation of a host-guest adduct between the [3]catenane and the external crown ether.     

Discovery of an all-donor aromatic [2]catenane

We report herein the first all-donor aromatic [2]catenane formed through dynamic combinatorial chemistry, using single component libraries. The building block is a benzo[1,2-b:4,5-b′]dithiophene derivative, a π-donor molecule, with cysteine appendages that allow for disulfide exchange. The hydrophobic effect plays an essential role in the formation of the all-donor [2]catenane. The design of the building block allows the formation of a quasi-fused pentacyclic core, which enhances the stacking interactions between the cores. The [2]catenane has chiro-optical and fluorescent properties, being also the first known DCC-disulphide-based interlocked molecule to be fluorescent.

An all-donor [2]catenane has been synthesised via dynamic combinatorial chemistry. It features stacked benzodithiophenes which are quasi-pentacyclic through hydrogen bonding.     

A Bistable Poly[2]catenane Forms Nanosuperstructures

Side‐chain poly[2]catenanes at the click of a switch! A bistable side‐chain poly[2]catenane has been synthesized and found to form hierarchical self‐assembled hollow superstructures of nanoscale dimensions in solution. Molecular electromechanical switching (see picture) of the material is demonstrated, and the ground‐state equilibrium thermodynamics and switching kinetics are examined as the initial steps towards processible molecular‐based electronic devices and nanoelectromechanical systems.

     

Sulfate anion-templated assembly of a [2]catenane

The sulfate anion's templating role in catenane formation is demonstrated for the first time; a novel bis-pyridinium nicotinamide [2]catenane is prepared in a remarkable high yield and is shown to exhibit selectivity for sulfate, the templating anion.     

Half-rotation in a [2]catenane via interconvertible Pd(II) coordination modes

Reaction of a [2]catenane with Pd(OAc)2 binds both macrocycles to the metal, locking them in position; treatment with PdCl2, however, results in coordination of only one ring, producing a half-turn in the relative orientation of the [2]catenane components in both solution and the solid state.     

The microscopic switching mechanism of a [2]catenane

We apply numerical simulations at an all-atom level to investigate the switching mechanism of a [2]catenane, a prototype of a molecular machine. This system is able to switch reversibly between two different stable states, upon external stimuli, with a time scale ranging from microseconds up to milliseconds, well over the typical domain of molecular dynamics (MD) computer simulations. However, combining a strategy recently developed for investigating rare events with ordinary MD, we are able to unravel the microscopic mechanism of the conformational rearrangements involved in the switching process, including dynamical effects. Along the path that connects the product and reactant state, we find several intermediate states characterized by pi-pi stacking interactions and hydrogen bonds. Moreover, counterions interact strongly with the system in a correlated way, in agreement with recent static calculations performed on [2]rotaxanes.