Molecular Rods Research Articles

Fucoidan from brown seaweed Tubinaria decurrens: Structure and structure - anticancer activity relationship

The aims of this study are to determine the structure of a fucoidan from brown seaweed Turbinaria decurrens, to investigate its anticancer activity and structure–activity relationship. SEC-MALLS, IR, ESI-MS and NMR spectra analysis indicated that dominant structure of the fucoidan, with a Mw 122.6 KDa, has a backbone of (1 → 3)– and (1 → 4)–α–L–Fucp residues, branched at C–4, sulfate groups are attached at C–2, C–3 and C–4; branches are (1 → 4)–β–D–Galp residues and sulfated at C–2. The fucoidan was hydrolyzed by HCl aqueous solution to obtain hydrolyzed fucoidans. It is assumed that native and hydrolyzed fucoidans have a rod-like conformation in solution with cross–sectional radius of gyration (Rgc) ranged from 0.53 to 1.52 nm as estimated from SAXS measurements. The fucoidans show great anticancer activity against HT29 human colon cancer cell line with IC50 ranging from 5.41 ± 0.36 to 73.52 ± 2.54 μg/mL. Anticancer activity of the fucoidan could be significantly improved by lowering molecular weight, furthermore, fucoidan required small molecular weight, small molecular weight distribution and rod–like structure with a short branch length for high anticancer activity.

Initial Stages of the Formation of the Supramolecular Structure of Ca and Mg Oxides

The optimal geometries of (CaO)n and (MgO)n clusters at n = 2–30 have been found and the enthalpies of formation of 1D, 2D, and 3D structures have been determined using quantum-chemical DFT calculations. The calculation demonstrates that the formation of linear chains of Ca and Mg oxides practically does not occur, while the formation of two-dimensional (tiled) and three-dimensional (cubic) structures proceeds with a large release of energy. The competing process of formation of molecular rods consisting of planar six-membered rings (MO)3 has been considered, and it has been shown to proceed not through the stage of preliminary formation of six-membered rings, but directly from monomer units.

Electrospun Conducting Polymers: Approaches and Applications.

Inherently conductive polymers (CPs) can generally be switched between two or more stable oxidation states, giving rise to changes in properties including conductivity, color, and volume. The ability to prepare CP nanofibers could lead to applications including water purification, sensors, separations, nerve regeneration, wound healing, wearable electronic devices, and flexible energy storage. Electrospinning is a relatively inexpensive, simple process that is used to produce polymer nanofibers from solution. The nanofibers have many desirable qualities including high surface area per unit mass, high porosity, and low weight. Unfortunately, the low molecular weight and rigid rod nature of most CPs cannot yield enough chain entanglement for electrospinning, instead yielding polymer nanoparticles via an electrospraying process. Common workarounds include co-extruding with an insulating carrier polymer, coaxial electrospinning, and coating insulating electrospun polymer nanofibers with CPs. This review explores the benefits and drawbacks of these methods, as well as the use of these materials in sensing, biomedical, electronic, separation, purification, and energy conversion and storage applications.

Front Cover: Molecular Metallocorrole–Nanorod Photocatalytic System for Sustainable Hydrogen Production (ChemSusChem 17/2022)

The Front Cover shows the solar-driven photocatalytic generation of hydrogen from water. It is accomplished via a successful combination of nanorod photocatalysts that have proven record activity for the water reduction half-reaction, with molecular metallocorroles suitable for catalyzing the accompanying oxidation reactions. The utilization of redox species as charge transfer shuttle between freely mixed molecular catalysts and rods afford a simple and elegant alternative to a chemical linkage, which results in high quantum efficiency for hydrogen production. In place of a sacrificial scavenger capable of extracting but a single hole, the molecular metallocorrole catalyst is found to successfully handle nearly 300,000 holes during its lifespan. More information can be found in the Research Article by K. Dong, T.-A. Le et al.

Electrochemical test of flexibility of pyridine terminated molecular rods

A family of seven symmetrical molecular rods, which are sharing 4-ethynylpyridyl terminal groups and differ in the structure of the linker have been investigated. Although structurally related they show unique electrochemical behavior, which clearly correlates with their conformational flexibility. Two flexible compounds are reduced by two electrons. Their reduction yields intensive charge transfer UV-vis absorption bands and is accompanied by characteristic EPR spectra. In contrast, all conformationally rigid structures are reduced by four electrons and do not yield neither charge transfer bands nor distinct EPR signals. Simple irreversible voltammetry of all derivatives is similar to the reduction of 4-ethynylpyridine at -2.1 V. The experimental observations were supported by the extensive DFT calculations. Electrochemical techniques proved to be valuable in distinction between molecular rigidity and flexibility.

Molecular Bending: An Important Factor Affecting the Packing of Self-Assembled Monolayers of Triptycene-Based Molecular Rods on a (111) Gold Surface

Molecular Bending: An Important Factor Affecting the Packing of Self-Assembled Monolayers of Triptycene-Based Molecular Rods on a (111) Gold Surface

Triptycene-Based Molecular Rods for Langmuir-Blodgett Monolayers.

Herein we introduce fully modular synthesis leading to three representative examples of rigid molecular rods that are intended to form sturdy monolayers on various surfaces. These molecules contain two triptycene units that are designed to interlock into a compact "double-decker" structure. Two of the three final products provided suitable crystals for X-ray diffraction (analyzed on synchrotron), allowing deeper insight into packing in the 3-D crystal lattice. The acidity of all three compounds were determined by capillary electrophoresis, and the pKa values ranged between 2.06-2.53. All three rigid rods easily formed Langmuir-Blodgett monolayers (LBMs) on the water-air interfaces, with the area per molecule equal to 55-59 Å2 /molecule, suggesting tight intermolecular packing. The thickness of all three films reached ∼19 Å after transfer to a gold (111) surface, meaning that individual molecules are tilted maximally 38° from the axis perpendicular to the surface. The structure of one of these films on a gold (111) surface was visualized by AFM. These geometrically unique molecules represent promising platforms with a wide scope of applicability in the supramolecular architecture.

Thermally reconfigurable monoclinic nematic colloidal fluids.

Fundamental relationships are believed to exist between the symmetries of building blocks and the condensed matter phases that they form1. For example, constituent molecular and colloidal rods and disks impart their uniaxial symmetry onto nematic liquid crystals, such as those used in displays1,2. Low-symmetry organizations could form in mixtures of rods and disks3-5, but entropy tends to phase-separate them at the molecular and colloidal scales, whereas strong elasticity-mediated interactions drive the formation of chains and crystals in nematic colloids6-11. To have a structure with few or no symmetry operations apart from trivial ones has so far been demonstrated to be a property of solids alone1, but not of their fully fluid condensed matter counterparts, even though such symmetries have been considered theoretically12-15 and observed in magnetic colloids16. Here we show that dispersing highly anisotropic charged colloidal disks in a nematic host composed of molecular rods provides a platform for observing many low-symmetry phases. Depending on the temperature, concentration and surface charge of the disks, we find nematic, smectic and columnar organizations with symmetries ranging from uniaxial1,2 to orthorhombic17-21 and monoclinic12-15. With increasing temperature, we observe unusual transitions from less- to more-ordered states and re-entrant22 phases. Most importantly, we demonstrate the presence of reconfigurable monoclinic colloidal nematic order, as well as the possibility of thermal and magnetic control of low-symmetry self-assembly2,23,24. Our experimental findings are supported by theoretical modelling of the colloidal interactions between disks in the nematic host and may provide a route towards realizing many low-symmetry condensed matter phases in systems with building blocks of dissimilar shapes and sizes, as well as their technological applications.

Supramolecular Networks: Helical Networks of π‐Conjugated Rods – A Robust Design Concept for Bicontinuous Cubic Liquid Crystalline Phases with Achiral Ia3¯d and Chiral I23 Lattice (Adv. Funct. Mater. 45/2020)

In article number 2004353, Goran Ungar, Carsten Tschierske, and co-workers present a general design concept of bicontinuous cubic liquid crystals consisting of helical networks that are stable over a broad temperature range. Increasingly bulky substituents cause increasing helical twist between the three-chain 2,2′-bithiophene based molecular rods, resulting in a sequence of three distinct phases: two ranges of achiral double network (Ia 3 ¯ d) separated by a range of spontaneously chiral triple network (I23).

Giant deformations and soft-inflation in LCE balloons

We propose that ballooning can be controlled, enriched and amplified by using rubbery networks of aligned molecular rods known as liquid crystal elastomers (LCEs). Firstly, LCEs are promising artificial muscles, showing large spontaneous deformations in response to heat and light. In LCE balloons, spontaneous deformations can trigger classic ballooning, either as phase separation (at constant volume) or a volume jump (at constant pressure), resulting in greatly magnified actuation strains. Secondly, even at constant temperature, LCEs have unusual mechanics augmented by soft modes of deformation in which the nematic director rotates within the elastomer. These soft modes enrich the mechanics of LCE balloons, which can also “balloon” between rotated and unrotated states, either during the classic instability, or as a separate pre-cursor, leading to successive instabilities during inflation.

Double in situ fabrication of PPy@MnMoO4/cellulose fibers flexible electrodes with high electrochemical performance for supercapacitor applications

Cellulose fibers (CFs) are used as a substrate to fabricate the flexible supercapacitor electrodes of PPy@MnMoO4/CFs via double in situ deposition method. The fabricated MnMoO4/CFs (MC), PPy@CFs (PMC0) and PPy@MnMoO4/CFs (PMC6) are characterized by SEM, XRD, FTIR and XPS, and the electrochemical tests are implemented to reveal the structure–property relationship of paper samples. The results show that the electrochemical performance of PPy@MnMoO4/CFs have positive correlation with the concentrations of the precursor solutions of generated MnMoO4. The PMC6 fabricated at equal molar concentration (0.06 mol L−1) of Mn(CH3COO)2 and Na2MoO4 has the best electrochemical performance, and the specific capacitance achieves 440.1 F g−1 at a current density of 0.2 A g−1, retaining about 83.0% after 1000 cycles at a current density of 2 A g−1. However, the specific capacitance of PMC0 reaches merely 236.8 F g−1 and maintains about 74.0% under the same conditions. The PMC6 electrode has excellent electrochemical performance when compared with PMC0, which is due to the interaction between PPy molecular chains and MnMoO4 submicron rods. MnMoO4 submicron rods not only act as the PPy deposition template to modify the morphology of PMC6 composite, but also create more paths for the transfer of electrolyte ions, to ensure a higher reaction rate and a specific capacitance.

High-Performance Phase-Pure SnS Photocathodes for Photoelectrochemical Water Splitting Obtained via Molecular Ink-Derived Seed-Assisted Growth of Nanoplates.

Although tin monosulfide (SnS) is one of the promising earth-abundant semiconducting materials for photoelectrochemical water splitting, the performance of SnS photocathodes remains poor. Herein, we report a stepwise approach for the fabrication of highly efficient photocathodes based on SnS nanoplates via elaborate modulation of molecular solutions. It is demonstrated that phase-pure SnS nanoplates without detrimental secondary phases (such as SnS2 and Sn2S3) can be readily obtained by adjusting the amounts of Sn and S in the precursor solution. Additionally, the orientation of SnS nanoplates is controlled by implementing different types of SnS seed layers. The orientations of the SnS seed layers are changed according to the molecular shapes of the Sn-S bonds in the molecular solutions, depending on the relative nucleophilicity of the molecular moieties formed by specific thiol-amine reactions. The molecular Sn-S sheets in the seed ink was obtained by the reaction in a solvent mixture of thiogylcolic acid and ethanolamine. By contrast, the short Sn-S molecular rods result from the reaction in a solvent mixture of 2-mercaptoethanol and ethylenediamine. Interestingly, the relatively short rodlike morphology of the SnS seed induces the growth of SnS nanostructures faceted by preferred (111) and (101) planes, leading to fast charge transport. With the formation of a proper band alignment with n-type CdS and TiO2, the preferred (111)- and (101)-oriented SnS nanoplate-based photocathode exhibited a photocurrent density of -19 mA cm-2 at 0 V versus a reversible hydrogen electrode, establishing a new benchmark for SnS photocathodes.

Nanoarchitecture through Strained Molecules: Cubane-Derived Scaffolds and the Smallest Carbon Nanothreads.

Relative to the rich library of small-molecule organics, few examples of ordered extended (i.e., nonmolecular) hydrocarbon networks are known. In particular, sp3 bonded, diamond-like materials represent appealing targets because of their desirable mechanical, thermal, and optical properties. While many covalent organic frameworks (COFs)-extended, covalently bonded, and porous structures-have been realized through molecular architecture with exceptional control, the design and synthesis of dense, covalent extended solids has been a longstanding challenge. Here we report the preparation of a sp3-bonded, low-dimensional hydrocarbon synthesized via high-pressure, solid-state diradical polymerization of cubane (C8H8), which is a saturated, but immensely strained, cage-like molecule. Experimental measurements show that the obtained product is crystalline with three-dimensional order that appears to largely preserve the basic structural topology of the cubane molecular precursor and exhibits high hardness (comparable to fused quartz) and thermal stability up to 300 °C. Among the plausible theoretical candidate structures, one-dimensional carbon scaffolds comprising six- and four-membered rings that pack within a pseudosquare lattice provide the best agreement with experimental data. These diamond-like molecular rods with extraordinarily small thickness are among the smallest members in the carbon nanothread family, and calculations indicate one of the stiffest one-dimensional systems known. These results present opportunities for the synthesis of purely sp3-bonded extended solids formed through the strain release of saturated molecules, as opposed to only unsaturated precursors.

Electric-Field-Induced Connectivity Switching in Single-Molecule Junctions.

SummaryThe manipulation of molecule-electrode interaction is essential for the fabrication of molecular devices and determines the connectivity from electrodes to molecular components. Although the connectivity of molecular devices could be controlled by molecular design to place anchor groups in different positions of molecule backbones, the reversible switching of such connectivities remains challenging. Here, we develop an electric-field-induced strategy to switch the connectivity of single-molecule junctions reversibly, leading to the manipulation of different connectivities in the same molecular backbone. Our results offer a new concept of single-molecule manipulation and provide a feasible strategy to regulate molecule-electrode interaction.

Extension of π Conjugation System By Functionalization of the Beta Position of Porphyrin

Porphyrin is a macrocyclic light harvesting molecule that absorbs the light in visible region of the electromagnetic spectrum. Extension of π-conjugation causes the red shifting of the absorbance and adding more fused aromatic rings in to the main macrocycle is a common way to achieve that goal. Heck Coupling reaction can be used to introduce fused aromatic rings in to the β position of porphyrin. π-extended porphyrins possess different and interesting photophysical , Optoelectronic and Physicochemical properties . Aromatic ring fused porphyrins open wide range of applications including in Molecular Rods, Bio sensors, near Infra-red dyes, Photodynamic therapy etc. In here, we are reporting the use of Heck coupling reaction to synthesis β - extended porphyrin and their red shifted light absorbing properties using its UV-Vis absorption spectrum.

Lamellar Liquid Crystals of In-Plane Lying Rod-Like Mesogens with Designer Side-Chains: The Case of Sliding versus Locked Layers.

The dimensionality of self-assembled nanostructures plays an essential role for their properties and applications. Herein, an understanding of the transition from weakly to strongly coupled layers in soft matter systems is provided involving in-plane organized π-conjugated rods. For this purpose, bolaamphiphilic triblock molecules consisting of a rigid biphenyl core, polar glycerol groups at the ends, and a branched (swallow-tail) or linear alkyl or semiperfluoroalkyl chain in lateral position have been synthesized and investigated. Besides weakly coupled lamellar isotropic (LamIso ), lamellar nematic (LamN ) and sliding lamellar smectic phases (LamSm ), a sequence of three distinct types of strongly coupled (correlated) lamellar smectic phases with either centered (c2mm) or non-centered rectangular (p2mm) lattice and an intermediate oblique lattices (p2) were observed depending on chain length, chain branching and degree of chain fluorination. This new sequence is explained by the strengthening of the layer coupling and the competition between energetic packing constraints and the entropic contribution of either longitudinal or tangential fluctuations. This example of directed side chain engineering of small generic model compounds provides general clues for morphological design of two-dimensional and three-dimensionally coupled lamellar systems involving larger π-conjugated molecular rods and molecular or supramolecular polymers, being of actual interest in organic electronics and nanotechnology.

Molecular Rods: Facile Desymmetrization of 1,4‐Diethynylbicyclo[2.2.2]octane

We report a facile desymmetrization of 1,4‐diethynylbicyclo[2.2.2]octane. One of the acetylene termini was protected by TMS and the desired product was purified by sublimation. It is stable but reactive, as shown by the synthesis of a complex pyridine‐terminated molecular rod containing both a bicyclo[1.1.1]pentane and a bicyclo[2.2.2]octane cage. Six crystal structures of key intermediates are presented.

A bifunctional smart material: the synthesis of a metal-free black pigment for optoelectronic applications from an organic semiconducting molecular rod

PurposeThis paper aims to synthesise and evaluate the properties of a novel smart material consisting of a metal-free organic black pigment with a unique chromophore for bifunctional applications in optoelectronics.Design/methodology/approachA robust and highly efficient organic reaction, namely, a double [2 + 2] cycloaddition, was deployed to transform a rod-like structure for charge-transfer applications to a strongly conjugated light-absorbing molecule for both optical and electronic applications.FindingsThe synthesis and characterisation of an air-stable metal-free black pigment is reported, which contains an unconventional donor–acceptor panchromatic chromophore with an absorption window spanning 600 nm; the compound was synthetically converted from an organic semiconducting molecular rod and retains strong charge-transfer properties. The chromophore comprises tetracyanoquinodimethane adduct on either side of a dithienothiophenyl core, capped with hexyl thiophenes that ensure solubility in common organic solvents. Its propensity to form excellent thin films on different substrates such as glass and paper, with a total opacity in organic solvent, gives it the potential for wide-ranging applications in organic optoelectronics.Research limitations/implicationsThe synthetic chemistry and fundamental properties are investigated in the present study, with more detailed treatments and analysis to be soon developed. One leading smart material is presented, with further derivatives under investigation.Practical implicationsThe work presented shows the possibility of converting structures from one application to another with relative ease, but how they retain properties for both, using well-known and facile conditions.Originality/valueThe structures are novel and an enhanced air-stable organic panchromatic chromophore is reported for processing in common organic solvents.

Two-dimensional Arrays of Molecular Rods as a Precursor of Gel Fibrils

The monolayer behavior of a chiral gelator with perfluoroalkyl chains, (1R,2R)- or (1S,2S)- N,N’-diperfluoroheptanoyl 1,2-diaminocyclohexane (denoted as RR- or SS-CF7, respectively), was investigated by means of the Langmuir-Blodgett method. The AFM image of an enantiomeric film deposited onto a hydrophilic glass plate exhibited an array of rod-like aggregates with 0.05-0.8 μm in diameter, suggesting that they were a two-dimensional analogue of fibrils in a gel.

New Synthetic Approach to Molecular Rods Using Cyclophosphazene-Based Oligospiranes.

A synthetic approach was developed to prepare a new type of highly functionalized inorganic-organic heterocyclic molecular rod (3a and 3b) consisting of cyclophosphazene and carbocyclic units. Single-crystal X-ray diffraction analysis of 3a revealed that the molecular length was ca. 2.5 nm. The products of this high-yield process have the potential for derivatization via known phosphazene reactions.