Through-space Communication Research Articles

Synergistic activation of photoswitchable supramolecular assembly based on sulfonated crown ether and dithienylethene derivative

Conformational regulation among two or more distant sites is not only one of the main pathways to accomplish multiple tasks in complex biological systems but also represents a powerful strategy to obtain stimuli-responsive supramolecular nanoconstructs with tailored physicochemical performance. We herein report the fabrication of a photochromic supramolecular assembly, which can be synergistically activated by the conformational regulation with bis(4,8-disulfonato-1,5-naphtho)-32-crown-8 and then reversibly switched by the through-space communication between restricted stilbazolium salt and photochromic dithienylethene. This work demonstrates that the synergistic conformational modulation via intra- and intermolecular interactions can be developed as a generalizable approach to construct more advanced biomimetic nanomaterials.

Emissive Single-Crystalline Boroxine-Linked Colloidal Covalent Organic Frameworks.

The synthesis of periodic two-dimensional (2D) polymers and characterization of their optoelectronic behaviors are challenges at the forefront of polymer chemistry and materials science. Recently, we showed that layered 2D polymers known as 2D covalent organic frameworks (COFs) can be synthesized as single crystals by preparing COF particles as colloidal suspensions. Here we expand this approach from the condensation of boronic acids and catechols to the dehydrative trimerization of polyboronic acids. The resulting boroxine-linked colloids are the next class of 2D COFs to be obtained as single-crystalline particles, as demonstrated here for four 2D COFs and one 3D COF. Colloidal stabilization enables detailed structural analysis by synchrotron X-ray diffraction and high-resolution transmission electron microscopy. Solution fluorescence spectroscopy revealed that the COF crystallites are highly emissive compared to their respective monomer solutions. Excitation-emission matrix fluorescence spectroscopy indicated that the origin of this enhanced emission can be attributed to through-space communication of chromophores between COF sheets. These observations will motivate the development of colloidal COF systems as a platform to organize functional aromatic systems into precise and predictable assemblies with emergent properties.

Single-molecule correlated chemical probing reveals large-scale structural communication in the ribosome and the mechanism of the antibiotic spectinomycin in living cells.

The ribosome moves between distinct structural states and is organized into multiple functional domains. Here, we examined hundreds of occurrences of pairwise through-space communication between nucleotides in the ribosome small subunit RNA using RNA interaction groups analyzed by mutational profiling (RING-MaP) single-molecule correlated chemical probing in bacterial cells. RING-MaP revealed four structural communities in the small subunit RNA, each distinct from the organization defined by the RNA secondary structure. The head domain contains 2 structural communities: the outer-head contains the pivot for head swiveling, and an inner-head community is structurally integrated with helix 44 and spans the entire ribosome intersubunit interface. In-cell binding by the antibiotic spectinomycin (Spc) barely perturbs its local binding pocket as revealed by the per-nucleotide chemical probing signal. In contrast, Spc binding overstabilizes long-range RNA–RNA contacts that extend 95 Å across the ribosome that connect the pivot for head swiveling with the axis of intersubunit rotation. The two major motions of the small subunit—head swiveling and intersubunit rotation—are thus coordinated via long-range RNA structural communication, which is specifically modulated by Spc. Single-molecule correlated chemical probing reveals trans-domain structural communication and rationalizes the profound functional effects of binding by a low–molecular-mass antibiotic to the megadalton ribosome.

Through-Space Communication Effects on the Electrochemical Reduction of Partially Oxidized Pillar[5]arenes Containing Variable Numbers of Quinone Units.

The electrochemical reduction of five partially oxidized pillar[5]arenes containing variable numbers (1-5) of quinone units was investigated in acetonitrile and dichloromethane solutions. The cathodic voltammetric behavior of all the macrocyclic compounds containing two or more quinone units indicates the existence of detectable levels of electronic communication between them. We have also investigated these compounds and their reduced forms using DFT computations. Our computational results indicate the presence of through-space communication between quinone units.

Sarcoplasmic reticulum–mitochondrial through-space coupling in skeletal muscleThis paper is one of a selection of papers published in this Special Issue, entitled 14th International Biochemistry of Exercise Conference – Muscles as Molecular and Metabolic Machines, and has undergone the Journal’s usual peer review process.

The skeletal muscle contractile machine is fueled by both calcium and ATP. Calcium ions activate the contractile machinery by binding to troponin C and relieving troponin-tropomyosin inhibition of actinomyosin interaction. ATP binding to myosin during the contractile cycle results in myosin detachment from actin, and energy liberated from subsequent ATP hydrolysis is then used to drive the next contractile cycle. ATP is also used to lower myoplasmic calcium levels during muscle relaxation. Thus, muscle contractility is intimately linked to the proper control of sarcomeric Ca2+ delivery and (or) removal and ATP generation and (or) utilization. In skeletal muscle, the sarcoplasmic reticulum (SR) is the primary regulator of calcium storage, release, and reuptake, while glycolysis and the mitochondria are responsible for cellular ATP production. However, the SR and mitochondrial function in muscle are not independent, as calcium uptake into the mitochondria increases ATP production by stimulating oxidative phosphorylation and mitochondrial ATP production, and production and (or) detoxification of reactive oxygen and nitrogen species (ROS/RNS), in turn, modulates SR calcium release and reuptake. Close spatial Ca2+/ATP/ROS/RNS communication between the SR and mitochondria is facilitated by the structural attachment of mitochondria to the calcium release unit (CRU) by 10 nm of electron-dense tethers. The resultant anchoring of mitochondria to the CRU provides a structural basis for maintaining bidirectional SR-mitochondrial through-space communication during vigorous contraction. This review will consider the degree to which this structural link enables privileged or microdomain communication between the SR and mitochondria in skeletal muscle.

Intramolecular Excimer Formation and Delayed Fluorescence in Sterically Constrained Pyrene Dimers

The synthesis is described for a series of five molecular dyads comprising pyrene-based terminals covalently linked through a 1,3-disubstituted phenylene spacer. The extent of through-space communication between the pyrene units is modulated by steric interactions imposed by bulky moieties attached at the 6,8-positions of each pyrene unit. For the control compound, only hydrogen atoms occupy the 6,8 positions (DP1), whereas the remaining compounds incorporate ethynylene groups terminated with either triisopropylsilyl (DP2), 1-tert-butylbenzene (DP3), 2,6-di-tert-butylbenzene (DP4) or 1-tert-butyl-3,5-dimethylbenzene (DP5) units. Each compound shows a mixture of monomer and excimer fluorescence in fluid solution at room temperature, but only monomer emission in a glassy matrix at 77 K. The ratio of monomer to excimer fluorescence depends markedly on the molecular structure; DP1 is heavily biased in favour of the excimer and DP4 is enriched with monomer fluorescence. Photophysical properties, including laser induced and delayed fluorescence data, are reported for each compound. Delayed fluorescence occurs by both intramolecular and bimolecular steps, but these events take place on different timescales. The possibility is raised for using intramolecular triplet-triplet annihilation as a means of molecular imaging.

Electrochemistry of the metallo-bisfullerene [Mo(η2-C60)2(CO)2(dbc-bipy)] (dbc-bipy = 4,4′-di(butylcarboxyl)-2,2′-bipyridine)

Electrochemical investigations on the dumb-bell like [Mo(η2-C60)2(CO)2(dbc-bipy)] show that the two fullerene subunits undergo a sequence of slightly separated stepwise reductions. The mutual electronic interaction of the two cages, which is responsible for the separation of the sequential electron additions, is comparable with that of C120, C121, C120O, C122H4 and C120SiPh2, which actually are the only symmetric bis-fullerenes able to display intramolecular electronic interactions. Changing the solvent (from CH2Cl2 to THF) causes a slight increase in the stepwise reductions exhibited by [Mo(η2-C60)2(CO)2(dbc-bipy)], thus supporting a Mo-mediated through-space communication between the two fullerene moieties. To cite this article: Piero Zanello et al., C. R. Chimie (8) 2005. Des investigations électrochimiques sur le complexe en forme de cloche [Mo(η2-C60)2(CO)2(dbc-bipy)] montrent que les deux sous-unités fullerènes subissent des réductions par étapes légèrement séparées. L'intéraction électronique des deux cages, qui est responsable de la séparation des additions éléctroniques séquentielles, est comparable à celle de C120, C121, C120O, C122H4 et C120SiPh2, qui, à l'heure actuelle, sont les seuls bis-fullerènes symmétriques capable de donner des interactions électroniques intramoléculaires. Le changement de solvent (CH2Cl2 en THF) provoque un léger accroissement dans la séparation des réductions par étapes de [Mo(η2-C60)2(CO)2(dbc-bipy)], ce qui sous-tend une communication par l'intermédiaire du Mo à travers l'espace entre les deux unités de fullerène. Pour citer cet article : Piero Zanello et al., C. R. Chimie (8) 2005.

Absorption spectra of the mono-adduct and eight bis-adduct regioisomers of pyrrolidine derivatives of C60

Absorption spectra of the pyrrolidine N-mTEG (mTEG=CH2CH2OCH2CH2OCH2CH2OCH3) mono-adduct and eight bis-adducts of C60 were studied in the 230–800 nm spectral range. The five-membered ring adducts contain an apex nitrogen atom. A theoretical discussion in terms of the effective electronic structures and transitions of these species shows that a filiation between spectra of C60, and its pyrrolidine mono- and bis-adduct derivatives can be expected and rationalised. Allowed transitions in the ultraviolet are related to fullerene core electronic transitions and are observed to be little affected in energy and in transition strength by the mono-adduct, apart from band splitting or broadening associated with the lowered molecular symmetry with respect to C60, whereas in the visible region, the transitions related to C60 forbidden transitions are significantly modified by the adduct. The bis-adducts have similar general spectral behaviour to that of the mono-adduct, with differences that reflect the relative position of the two addends but are found to be not dependent on membership of any of the three formal symmetry groups into which the bis-adducts can be classified. The second pyrrolidine adduct reinforces the perturbation of the forbidden and, to a lesser extent, the allowed transitions of the fullerene core. From a comparison with the spectra of C60[C(COOEt)2] and its bis-adducts, it was concluded that the N atom in the pyrrolidine five-membered ring adduct is a less efficient blocker of through-bond and/or through-space communication than the sp3 carbon atom in Bingel–Hirsch methanofullerenes.

Modulation of the electronic communication between two equivalent ferrocene centers by proton transfer, solvent effects and structural modifications

A series of six new dinuclear ferrocene compounds with the bridging fragment CH 2–N(R)–CH 2 were prepared and characterized. Bis(ferrocenylmethyl)- t-butylamine ( 1), bis(ferrocenylmethyl)-isopropylamine ( 2), bis(ferrocenylmethyl)-hexylamine ( 3), bis(ferrocenylmethyl)- p-methoxyaniline ( 4), bis(ferrocenylmethyl)aniline ( 5) and bis(ferrocenylmethyl)- p-nitroaniline ( 6), as well as the quaternized amine bis(ferrocenylmethyl)hexylmethylammonium hexaflurophosphate ( 3 +·PF 6 −), were investigated using electrochemical techniques, 1H NMR spectroscopy and single crystal X-ray diffraction analysis. The voltammetric data indicate that the extent of electronic communication between the equivalent ferrocene centers increases in low polarity solvents and when bulky aliphatic groups are covalently attached to the central tertiary nitrogen. The observed experimental data are consistent with through-space communication effects, essentially electrostatic in nature. The extent of electronic communication can be modulated by reversible and irreversible reactions in the solution phase. Protonation or methylation of the tertiary nitrogen in the middle of the bridge disrupts the electronic communication between the ferrocene residues.

Coupling of acid–base and redox functions in mixed sulfide monolayers on gold

A mixed acid-ferrocene self-assembled sulfide monolayer on gold shows a pH-dependent electrochemical response by through-space communication between the receptor and ferrocene readout unit.