Effect of uniaxial strain on a molecule-based ferrimagnet with crystal chirality

Bimetallic ferrimagnet [Cr(CN)₆][Mn(R)-pnH(H₂O)]H₂O with crystallographical chirality of space group P2₁2₁2₁ exhibits a giant third-order harmonic susceptibility at around 38 K. This anomaly appears as precursory magnetic phenomenon of the magnetic ordering. In order to investigate the effect of lattice distortion on this giant nonlinear magnetic response (NLMR) and finally elucidate the correlation between the structural chirality and the giant NLMR, we performed the ac susceptibility measurement for the single crystal in the situation of bringing about lattice distortion along the direction parallel to the a-axis. This giant NLMR was drastically suppressed even by slight strain, whereas the traces could be confirmed in the region up to 3.7 kbar. We conclude that the appearance of the giant NLMR requires crystal chirality well-regulated over the crystal.     

Unprecedented four-way-output molecular response system based on biphenyl-2,2′-diyldiacridiniums: induction of axial chirality through intramolecular hydrogen bonds between chiral amide groups

Upon the attachment of N-(R)-2-phenylethylamide moieties to the acridinium units of the title dication, intramolecular hydrogen bonds induce a diastereomeric preference in terms of axial chirality (70% de at −40 °C in CH₂Cl₂). Thus, external stimuli induce not only UV-vis and fluorescence spectra changes but also changes in the CD and fluorescence-detected CD (FDCD) spectra, realizing unprecedented four-way-output molecular response systems.     

Synthesis and properties of a diastereopure ionic liquid with planar chirality

An imidazolium-based ionic liquid with cyclophane-type planar chirality was synthesized in an optically pure form for the first time. The resultant ionic liquid existed as a liquid at room temperature (T_g = −35 °C), and was found to be applicable as an NMR chiral shift reagent for racemic anions. Excellent robustness of the ionic liquid to a highly elevated temperature (270 °C) was proved from the viewpoints of isomerization and thermal decomposition.     

Control over the chirality of (R)-1,1'-bi-2-naphthol dibenzoate in nanoparticles

Nanoparticles of (R)-1,1′-bi-2-naphthol dibenzoate (R-BND) ranging from 40 to 170 nm were prepared by using the reprecipitation method. The nanoparticles exhibit size-dependent exciton chirality, where the coupling potential V₁₂ of ¹B_b transitions increases as nanoparticles grow and simultaneously the exciton chirality peaks exhibit the bathochromic shift. Such size-dependent optical properties can be attributed to the lattice hardening with increased particle size, which leads to a decreased dihedral angel θ between the two naphthyl planes in a R-BND molecule.     

Gold-catalyzed intramolecular hydroamination of allenes: a case of chirality transfer

The hydroamination of allenes proceeded smoothly in the presence of gold catalysts to give the corresponding 2-vinyl pyrrolidines and piperidines in high yields. The reaction is very efficient and can be carried out with only 1-5 mol % catalyst at room temperature and under extremely mild conditions. As an example of chirality transfer, it is shown that aminoallene 1a (96% ee), synthesized from (S)-(−)-1-octyn-3-ol, was converted into the corresponding pyrrolidine 2a (94% ee) in 99% yield.     

Photoinduced chirality in achiral liquid crystalline azobenzene polymers containing different polar side groups

Circular dichroism (CD) was induced in the films of two achiral liquid crystalline polymers, poly[(4′-(6-(methacryloyloxy)hexyl)oxy)-(4-X)azobenzene] (PM6X, X = C and N for cyano and nitro, respectively), by irradiation with one handed circularly polarized light (CPL) at 442 nm. The CD and UV spectra of the polymeric films suggest that left-CPL induces a left helical structure and right-CPL reverses the resulting structure into a right helix. For PM6C, the photoinduced CD values of the nematic film are much higher than in the casting and isotropic film. The photoinduced chirality of PM6C films is higher than PM6N due to a higher polarity of nitro groups in PM6N. The PM6N’s CD intensity around 450 nm is increased with the irradiation time of linearly polarized light (LPL) followed by left-CPL irradiation. The correlation between azobenzene chromophores and circularly polarized light will be discussed in the paper.     

Photoinduced chirality in achiral liquid crystalline polymethacrylates containing bisazobenzene and azobenzene chromophores

One new liquid crystalline polymer containing bisazobenzene, poly[4-{(2-methacryloyloxyethyl)oxy}-4′-(4-nitrophenylazo)azobenzene] (PM2BAN), and two liquid crystalline polymers containing azobenzenes with spacers of two and six methylene units, poly[(4-(4′-nitrophenylazo)phenyloxy)x-methylene methacrylate] (PMxAN, x = 2, 6), were synthesized and characterized. The level and rate of photoinduced chirality were studied in films of the achiral polymers by irradiation with one handed circularly polarized light (CPL) at 442 nm. The results of circular dichroism (CD) suggest that left-CPL induces left helical arrangements of the polymers and right-CPL reverses the resulting arrangements into right helices. Photoinduced chirality in film of PM2BAN is increased with the increase of irradiation time. However, the level and rate of photoinduced chirality in film of PM2BAN are lower than those in films of PMxAN (x = 2, 6) at similar irradiation time. Compared with PM2AN, photoinduced CD values are higher in PM6AN. The results are discussed in terms of interactions between azobenzene chromophores and circularly polarized light.     

Helical secondary structures and supramolecular tilted chirality in N-terminal aryl amino acids with diversified optical activities

Helix structures at atomic/molecular level have not been found in self-assembled peptide seque nce with less than three residues.As β-sheet supramolecular secondary structures have been discovered in solidstate amino acids,we here report the conjugation of simple N-terminal aryl protecting group could give rise to helical supramolecular secondary structures in solid-state,which determines the optical activities of the adjacent aryl groups.The carboxylic acid-involved asymmetric H-bonds in N-te rminal aryl amino acids induce the emergence of super-helical structures of amino acid residues and aryl groups.In most cases,supramolecular tilted chirality of aryl groups is opposite to that of amino acid sequences,of which handedness and helical pitch are determined by the H-bond modalities.Determining correlation between supramolecular tilted chirality of aryl segments and their chiroptical activities is firstly unveiled,which was verified by the computational results based on density functional theory.Most aryl amino acids self-assembled by nanoprecipitation method via crystallization induced self-assembly into rigid one-dimensional microstructures with ultra-high Young's modulus.This study reveals the generic existence of chiral supramolecular structure s in aggregated amino acid derivatives and gives an in-depth investigation into the structural-property relationships,which could guide the rational design and screening of chiroptical supramolecular materials.     

Pressure-driven,solvation-directed planar chirality switching of cyclophano-pillar[5]arenes (molecular universal joints)

Planar chiral cyclophanopillar[5]arenes with a fused oligo(oxyethylene) or polymethylene subring (MUJs), existing as an equilibrium mixture of subring-included (in) and -excluded (out) conformers, respond to hydrostatic pressure to exhibit dynamic chiroptical property changes, leading to an unprecedented pressure-driven chirality inversion and the largest ever-reported leap of anisotropy (g) factor for the MUJ with a dodecamethylene subring. The pressure susceptivity of MUJs, assessed by the change in g per unit pressure, is a critical function of the size and nature of the subring incorporated and the solvent employed. Mechanistic elucidations reveal that the in–out equilibrium, as the origin of the MUJ''s chiroptical property changes, is on a delicate balance of the competitive inclusion of subrings versus solvent molecules as well as the solvation of the excluded subring. The present results further encourage our use of pressure as a unique tool for dynamically manipulating various supramolecular devices/machines.

Pressure switches the in/out conformation of cyclophano-pillararenes with accompanying inversion of the chiroptical properties.     

Expression of chirality in salicyloxazolinate complexes of zirconium

Treatment of chiral non-racemic salicyloxazoline proligands HL with tetrabenzylzirconium(IV) gave species [L₂Zr(CH₂Ph)₂]. Reactions of KL with ZrCl₄(THF)₂ gave similar chloro complexes. One example of a benzyl complex was shown to exist as the Λ-trans,cis,cis diastereomer by X-ray crystallography. DFT calculations showed the observed isomer to be the most stable by 35 kJ mol⁻¹, indicating that thermodynamic diastereoselection for this species is excellent. Examination of the chiral environment about the benzyl co-ligands indicates however that the degree of expression of the chirality of the structure in what would be the site of metal-based reactions is poor in comparison to related systems. Variable temperature ¹H NMR data are consistent with this in that the low temperature spectrum exhibits a very small chemical shift difference between the chemically inequivalent benzylic CH atoms, and at higher temperatures dissociation of the portion of the ligand that contains the chiral information, i.e., the oxazoline unit, leads to apparent equivalence.     

Four-way-output molecular response system based on the dihydrodibenzo[c,g]phenanthrene skeleton: modulation of CD and FDCD activity by acid and electron-transfer

Presence or absence of electron-accepting dye chromophores is the key function for ON/OFF switching of fluorescence from the dihydrodibenzo[c,g]phenanthrene skeleton in 2²⁺/3. The helical fluorophore in 2²⁺ could be generated stereoselectively upon electrolysis of binaphthylic donor 1 through intramolecular chirality transmission. Huge chiroptical signals are easily detected by circular dichroism (CD) and fluorescence-detected CD (FDCD) techniques to realize novel four-way-output response.     

Application of the cd homoallylic benzoate method as a chiroptical tool for determination of absolute configuration

After the conformation I was clarified to 5α-,10α,-cis-solidagolactones by ¹H NMR measurement with Eu(dpm)₃ and chemical transformations, the CD homoallylic benzoate chirality method was applied to the homoallylic alcohol system of solidagolactone IV ($\text{1a}$) for a chiroptical determination of the absolute configuration. The result agreed with absolute configuration elucidated by x-ray analysis, indicating the usefulness of the cd method.     

Chiroptical Sensing of Amino Acid Derivatives by Host–Guest Complexation with Cyclo[6]aramide

A hydrogen-bonded (H-bonded) amide macrocycle was found to serve as an effective component in the host–guest assembly for a supramolecular chirality transfer process. Circular dichroism (CD) spectroscopy studies showed that the near-planar macrocycle could produce a CD response when combined with three of the twelve L-α-amino acid esters (all cryptochiral molecules) tested as possible guests. The host–guest complexation between the macrocycle and cationic guests was explored using NMR, revealing the presence of a strong affinity involving the multi-point recognition of guests. This was further corroborated by density functional theory (DFT) calculations. The present work proposes a new strategy for amplifying the CD signals of cryptochiral molecules by means of H-bonded macrocycle-based host–guest association, and is expected to be useful in designing supramolecular chiroptical sensing materials.     

1,1'-Binaphthol annulated perylene diimides: Aggregation-induced emission enhancement and chirality inversion

Aggregation-induced emission enhancement and aggregation-induced chirality inversion are two individual phenomena for the enantiomerically pure organic dyes in the aggregates. Herein we reported for the first time that these two interesting phenomena could be observed simultaneously in the aggregated states of enantiomerically pure S/R-1,1’-binaphthol annulated perylene diimides, in which two perylene diimides moieties were bridged by S/R-1,1’-binaphthol(BINOL) at the bay positions. Owing to the...     

Synthesis, characterization and antitumor activity of 1,2-disubstituted ferrocenes and cyclodextrin inclusion complexes

Seven different ferrocene derivatives have been tested in vitro against Ehrlich ascites tumor cells. Neither ferrocene nor the monosubstituted derivative N,N-dimethylaminomethylferrocene showed cytotoxic activity (IC₅₀ > 1000 μM for 3 h treatments). Better results were obtained with 1,2-disubstituted derivatives. The IC₅₀ values ranged from 376.6 μM for 1,2-diformylferrocene to 71.2 μM for racemic 2-(N,N-dimethylaminomethyl)ferrocenecarboxamide. The latter derivative was also encapsulated in native β-cyclodextrin (CD), heptakis-2,3,6-tri-O-methyl-β-CD (TRIMEB) and 2-hydroxypropyl-β-CD (HPβCD) to give 1:1 (host:guest) inclusion compounds. The existence of true inclusion complexes in the solid state was confirmed by a combination of powder X-ray diffraction, thermogravimetric analysis, FTIR and ¹³C CP MAS NMR spectroscopy. The IC₅₀ value for the β-CD inclusion compound was identical to that obtained for the nonincluded ferrocene derivative. By contrast, the inclusion compounds comprising TRIMEB and HPβCD yielded IC₅₀ values of 25.2 and 20.0 μM, respectively. No obvious relationship could be established between the redox behavior of the compounds determined by cyclic voltammetry and the biochemical data.     

Synthesis and axial chirality of an enantiopure aminodibenzazepinone

A route for the synthesis of (S,S)-7-amino-5-methyl-5H-dibenzo[b,d]azepin-6(7H)-one hydrochloride is disclosed. The synthesis includes a Friedel–Crafts alkylation to form the seven-membered ring and a highly efficient classical resolution. Additional studies on the enantiopure material showed the amine to be highly resistant to racemization, which led us to investigate the unexpected stability. We propose that the inherent axial chirality contained in the dibenzazepinone works to produce an interesting chirality transfer mechanism, which accounts for the observed robustness of the stereocenter. This previously unrecognized stereochemical element exists within this specific class of molecules, and they should be drawn in a manner which displays the axial chirality.     

Supramolecular chirality and reversible chiroptical switching in new chiral liquid-crystal azopolymers

The synthesis of chiral liquid-crystalline polymers of well-controlled structure (linear and three-armed star-shaped) with distinct average chain lengths and low polydispersity was achieved by atom transfer radical polymerisation (ATRP) of a new optically active monomer (S)-4-[6-(2-methacryloyloxypropanoyloxy)hexyloxy)]-4'-ethoxyazobenzene [(S)-ML6A], containing the L-lactic residue of one absolute configuration in the side-chain. All the obtained polymeric samples, characterised by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and polarised optical microscopy (POM), exhibit a smectic A(1/2) (fully interdigitated) liquid-crystalline phase and high cleaning points, with transition temperatures dependent on the average polymerisation degree and the macromolecular structure. The chirality originated at the molecular level by the asymmetric functionality of the L-lactic acid residue provides the polymers, in the smectic phase, of highly homogeneous conformations with a prevailing chirality related to the presence of H-aggregates having conformational dissymmetry of one prevailing screw-sense. By irradiating with circularly polarised light (CPL), it is possible to photomodulate the chiroptical properties of these intrinsically chiral polymeric thin films. Upon irradiation with left-handed CPL (l-CPL), the circular dichroism (CD) spectra of the films show enhancement of ellipticity and a net inversion of sign. The effect is reversible and the mirror image of the CD spectrum can be restored by pumping with right-handed CPL radiation (r-CPL). The results show the ability of l-CPL to invert the supramolecular chirality of the materials and demonstrate the essential role of azoaromatic aggregates.     

Bistabercarpamines A and B,first vobasinyl-chippiine-type bisindole alkaloid from Tabernaemontana corymbosa

Two novel dimeric monoterpene indole alkaloids, bistabercarpamines A (1) and B (2) possessing unprecedented bis-vobasinyl-chippiine-type skeleton, were isolated from the leaves of Tabernaemontana corymbosa. The structures were elucidated on the basis of spectroscopic data, and the absolute configurations of these isolates were determined by CD excition chirality method. Bistabercarpamine A (1) exhibited moderate cell growth inhibitory activity against HepG-2 cells with IC₅₀ of 38.14 ± 1.1 μM.     

Single stranded helical supramolecular architecture with a left handed helical water chain in ternary copper(II) tryptophan/diamine complexes

The ternary copper(II) complexes [Cu(l-trp)(bpy)](ClO₄) (1) and [Cu(l-trp)(phen)] (ClO₄) · 3H₂O (2) (where l-trp = l-tryptophan, bpy = bipridyl, phen = phenanthroline) have been synthesized. The single crystal X-ray structures for these complexes revealed that the monocationic Cu^II-units are interlinked through Cu–OCO–Cu connectivity and exist as helical coordination polymers. The two different helical strands composed with Cu1 and Cu2 independently, possess a similar pitch distance of 7.713 Å in complex 1. For complex 2, existing in the hydrated form, the Cu(II) polymeric strand and the hydrated water molecules have gained a supramolecular helical architecture with a similar pitch distance of 8.133 Å. The two helical strands in complex 1 are associated with right handed (PP) supramolecular chirality, while the helical water chain and the Cu^II-strand in 2 are self assembled into left handed (MM) helicity in the solid state. The solid state CD recorded for 1 and the dehydrated form of 2 exhibit a positive optical sign at their respective d–d band [λ_max = 667 nm, 1; λ_max = 630 nm, 2], the solution state CD for both these complexes are found to be inverted into a negative optical sign, which could be attributed to inversion of their associated supramolecular helicity. The TGA curve illustrates two distinct weight losses at 60 °C and 87 °C, equivalent to one and two water molecules, respectively. The PXRD pattern for the hydrated and dehydrated forms of 2 indicated a change, on comparison with the simulated diffractograph. The fluorescence properties of both these complexes, possessing tryptophan and bipy/phen, were investigated.