Application of electronic circular dichroism in the study of supramolecular systems

Pescitelli, Gennaro; Bari, Lorenzo Di; Berova, Nina

doi:10.1039/c4cs00104d

Cited by 258 publications

(236 citation statements)

References 43 publications

(77 reference statements)

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“…S16). Such a red shift indicates a change toward another molecular organization (J-aggregates) (37), leading us to conclude that the building blocks slide with respect to each other, within the tubules. After 5 min, when the trans/cis ratio is estimated at 93/7, the λ max reaches its maximum value and remains constant for a further 30 min of irradiation (Figs.…”

Section: Resultsmentioning

confidence: 99%

Molecular photoswitches mediating the strain-driven disassembly of supramolecular tubules

Fredy

Méndez-Ardoy

Kwangmettatam

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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Chemists have created molecular machines and switches with specific mechanical responses that were typically demonstrated in solution, where mechanically relevant motion is dissipated in the Brownian storm. The next challenge consists of designing specific mechanisms through which the action of individual molecules is transmitted to a supramolecular architecture, with a sense of directionality. Cellular microtubules are capable of meeting such a challenge. While their capacity to generate pushing forces by ratcheting growth is well known, conversely these versatile machines can also pull microscopic objects apart through a burst of their rigid tubular structure. One essential feature of this disassembling mechanism is the accumulation of strain in the tubules, which develops when tubulin dimers change shape, triggered by a hydrolysis event. We envision a strategy toward supramolecular machines generating directional pulling forces by harnessing the mechanically purposeful motion of molecular switches in supramolecular tubules. Here, we report on wholly synthetic, water-soluble, and chiral tubules that incorporate photoswitchable building blocks in their supramolecular architecture. Under illumination, these tubules display a nonlinear operation mode, by which light is transformed into units of strain by the shape changes of individual switches, until a threshold is reached and the tubules unleash the strain energy. The operation of this wholly synthetic and stripped-down system compares to the conformational wave by which cellular microtubules disassemble. Additionally, atomistic simulations provide molecular insight into how strain accumulates to induce destabilization. Our findings pave the way toward supramolecular machines that would photogenerate pulling forces, at the nanoscale and beyond.artificial molecular switches | supramolecular polymers | supramolecular machines | light

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Section: Resultsmentioning

confidence: 99%

Molecular photoswitches mediating the strain-driven disassembly of supramolecular tubules

Fredy

Méndez-Ardoy

Kwangmettatam

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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“…18 The absorption spectra of the metalloporphyrins show both slight blue-shifted (hypsochromic effect) Soret bands and new bands at longer wavelengths that might correspond to J-aggregates which are caused by the exciton coupling between porphyrins ( Figure 3). 59 The spectral patterns are different for each metalloporphyrin indicating a distinct assembly for each, leading to unique structures. The spectra for compounds Zn-(R,R,R)-1 and Zn-(R,R)-3 show a shoulder at around 435 nm that has been assigned previously to the coordination of pyridyl groups with the zinc (II) ion of the neighboring metalloporphyrin.…”

Section: Self-assembly Of Porphyrins and Metalloporphyrins In Solutionmentioning

confidence: 99%

Bottom-Up Hierarchical Self-Assembly of Chiral Porphyrins through Coordination and Hydrogen Bonds

et al. 2015

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A series of chiral synthetic compounds is reported that show intricate but specific hierarchical assembly because of varying positions of coordination and hydrogen bonds. The evolution of the aggregates (followed by absorption spectroscopy and temperature-dependent circular dichroism studies in solution) reveal the influence of the proportion of stereogenic centers in the side groups connected to the chromophore ring in their optical activity and the important role of pyridyl groups in the self-assembly of these chiral macrocycles. The optical activity spans two orders of magnitude depending on composition and constitution. Two of the aggregates show very high optical activity even though the isolated chromophores barely give a circular dichroism signal. Molecular modeling of the aggregates, starting from the pyridine-zinc(II) porphyrin interaction and working up, and calculation of the circular dichroism signal confirm the origin of this optical activity as the chiral supramolecular organization of the molecules. The aggregates show a broad absorption range, between approximately 390 and 475 nm for the transitions associated with the Soret region alone, that spans wavelengths far more than the isolated chromophore. The supramolecular assemblies of the metalloporphyrins in solution were deposited onto highly oriented pyrolitic graphite in order to study their hierarchy in assembly by atomic force microscopy. Zero and one-dimensional aggregates were observed, and a clear dependence on deposition temperature was shown, indicating that the hierarchical assembly took place largely in solution. Moreover, scanning electron microscopy images of porphyrins and metalloporphyrins precipitated under out-ofequilibrium conditions showed the dependence of the number and position of chiral amide groups in the formation of a fibrillar nanomaterial. The combination of coordination and hydrogen bonding in the complicated assembly of these molecules -where there is a clear hierarchy for zinc(II)-pyridyl interaction followed by hydrogen-bonding between amide groups, and then van der Waals interactions -paves the way for the preparation of molecular materials with multiple chromophore environments.

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“…2(B)], suggesting that poly-(S)-2 formed a homo-double helix with a slight excess of onehandedness induced by the chiral alkoxy substituents via self-association under equilibrium. 30,31 To gain insight into the structure of poly-(S)-2, the selfassociation behavior of its model dimer (S)-3 was thoroughly investigated by measuring the CD, CSI-MS, and 2D NMR spectra. The dimer (S)-3 exhibited an induced CD in CDCl 3 at a low temperature and high concentration whose Cotton effect sign at the longer wavelength (380-430 nm) was similar to that of the poly-(S)-2 [ Fig.…”

Section: Homo-double Helix Formationmentioning

confidence: 99%

Homo-double helix formation of an optically active conjugated polymer bearing carboxy groups and amplification of the helicity upon complexation with achiral and chiral amines

Makiguchi

Kobayashi

Furukawa

et al. 2015

J. Polym. Sci. Part A: Polym. Chem.

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An optically active, m-terphenyl-based p-conjugated polymer bearing carboxy groups was synthesized by the copolymerization of the diethynyl monomer bearing a carboxy group with (S,S)-2,5-bis(2-methylbutoxy)-1,4-dibromobenzene using Sonogashira reaction. The copolymer showed a weak circular dichroism (CD) in the main-chain chromophore region due to a homo-double helix formation with an excess helical handedness biased by the chiral alkoxy substituents through self-association. However, upon complexation with achiral amines, such as piperidine, the CD intensity of the polymer significantly increased resulting in the formation of a greater excess one-handed homo-double helix via hydrogen-bonded inclusion complexation with the achiral amines between each strand, leading to the amplification of the helicity. A preferredhanded homo-double helix was also induced in the polymer in the presence of nonracemic amines. The effect of the achiral and chiral amines on the homo-double helix formation was investigated by comparing the CD spectra of the polymer to those of its model dimer. V C 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 990-999

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Application of electronic circular dichroism in the study of supramolecular systems

Cited by 258 publications

References 43 publications

Molecular photoswitches mediating the strain-driven disassembly of supramolecular tubules

Molecular photoswitches mediating the strain-driven disassembly of supramolecular tubules

Bottom-Up Hierarchical Self-Assembly of Chiral Porphyrins through Coordination and Hydrogen Bonds

Homo-double helix formation of an optically active conjugated polymer bearing carboxy groups and amplification of the helicity upon complexation with achiral and chiral amines

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