Molecular Analogues Research Articles

Iridates from the molecular side.

New exotic phenomena have recently been discovered in oxides of paramagnetic Ir4+ ions, widely known as ‘iridates'. Their remarkable properties originate from concerted effects of the crystal field, magnetic interactions and strong spin-orbit coupling, characteristic of 5d metal ions. Despite numerous experimental reports, the electronic structure of these materials is still challenging to elucidate, and not attainable in the isolated, but chemically inaccessible, [IrO6]8– species (the simplest molecular analogue of the elementary {IrO6}8− fragment present in all iridates). Here, we introduce an alternative approach to circumvent this problem by substituting the oxide ions in [IrO6]8− by isoelectronic fluorides to form the fluorido-iridate: [IrF6]2−. This molecular species has the same electronic ground state as the {IrO6}8− fragment, and thus emerges as an ideal model for iridates. These results may open perspectives for using fluorido-iridates as building-blocks for electronic and magnetic quantum materials synthesized by soft chemistry routes.

Self-assembled molecular p/n junctions for applications in dye-sensitized solar energy conversion.

The achievement of long-lived photoinduced redox separation lifetimes has long been a central goal of molecular-based solar energy conversion strategies. The longer the redox-separation lifetime, the more time available for useful work to be extracted from the absorbed photon energy. Here we describe a novel strategy for dye-sensitized solar energy applications in which redox-separated lifetimes on the order of milliseconds to seconds can be achieved based on a simple toolkit of molecular components. Specifically, molecular chromophores (C), electron acceptors (A) and electron donors (D) were self-assembled on the surfaces of mesoporous, transparent conducting indium tin oxide nanoparticle (nanoITO) electrodes to prepare both photoanode (nanoITO|-A-C-D) and photocathode (nanoITO|-D-C-A) assemblies. Nanosecond transient-absorption and steady-state photolysis measurements show that the electrodes function microscopically as molecular analogues of semiconductor p/n junctions. These results point to a new chemical strategy for dye-sensitized solar energy conversion based on molecular excited states and electron acceptors/donors on the surfaces of transparent conducting oxide nanoparticle electrodes.

A dual molecular analogue tuner for dissecting protein function in mammalian cells.

Loss-of-function studies are fundamental for dissecting gene function. Yet, methods to rapidly and effectively perturb genes in mammalian cells, and particularly in stem cells, are scarce. Here we present a system for simultaneous conditional regulation of two different proteins in the same mammalian cell. This system harnesses the plant auxin and jasmonate hormone-induced degradation pathways, and is deliverable with only two lentiviral vectors. It combines RNAi-mediated silencing of two endogenous proteins with the expression of two exogenous proteins whose degradation is induced by external ligands in a rapid, reversible, titratable and independent manner. By engineering molecular tuners for NANOG, CHK1, p53 and NOTCH1 in mammalian stem cells, we have validated the applicability of the system and demonstrated its potential to unravel complex biological processes.

Controlled Generation of Singlet Oxygen in Living Cells with Tunable Ratios of the Photochromic Switch in Metal–Organic Frameworks

AbstractDevelopment of a photosensitizing system that can reversibly control the generation of singlet oxygen (1O2) is of great interest for photodynamic therapy (PDT). Recently several photosensitizer–photochromic‐switch dyads were reported as a potential means of the 1O2 control in PDT. However, the delivery of such a homogeneous molecular dyad as designed (e.g., optimal molar ratio) is extremely challenging in living systems. Herein we show a Zr‐MOF nanoplatform, demonstrating energy transfer‐based 1O2 controlled PDT. Our strategy allows for tuning the ratios between photosensitizer and the switch molecule, enabling maximum control of 1O2 generation. Meanwhile, the MOF provides proximal placement of the functional entities for efficient intermolecular energy transfer. As a result, the MOF nanoparticle formulation showed enhanced PDT efficacy with superior 1O2 control compared to that of homogeneous molecular analogues.

Controlled Generation of Singlet Oxygen in Living Cells with Tunable Ratios of the Photochromic Switch in Metal-Organic Frameworks.

Development of a photosensitizing system that can reversibly control the generation of singlet oxygen ((1) O2 ) is of great interest for photodynamic therapy (PDT). Recently several photosensitizer-photochromic-switch dyads were reported as a potential means of the (1) O2 control in PDT. However, the delivery of such a homogeneous molecular dyad as designed (e.g., optimal molar ratio) is extremely challenging in living systems. Herein we show a Zr-MOF nanoplatform, demonstrating energy transfer-based (1) O2 controlled PDT. Our strategy allows for tuning the ratios between photosensitizer and the switch molecule, enabling maximum control of (1) O2 generation. Meanwhile, the MOF provides proximal placement of the functional entities for efficient intermolecular energy transfer. As a result, the MOF nanoparticle formulation showed enhanced PDT efficacy with superior (1) O2 control compared to that of homogeneous molecular analogues.

Hyperpolarized [13 C]ketobutyrate, a molecular analog of pyruvate with modified specificity for LDH isoforms

Hyperpolarized [¹³ C]ketobutyrate, a molecular analog of pyruvate with modified specificity for LDH isoforms

MiR-181a Promotes Proliferation of Human Acute Myeloid Leukemia Cells by Targeting ATM

To investigate miR-181a function and regulation mechanism by identifying miR-181a target genes in acute myeloid leukemia (AML). The HL-60 cells of human AML was transfected by small molecular analog miR-181a, the cell proliferation was detected by CCK-8 method after electroporation in HL-60 cell lines. Target genes of miR-181a were predicted and analyzed by the bioinformatics software and database. Target genes were confirmed by HL-60 cell line and the patient leukemia cells. Overexpressed miR-181a in HL-60 cell line significantly enhanced cell proliferation compared with that in control (P < 0.05). Dual luciferase reporter gene assay showed that miR-181a significantly suppressed the reporter gene activity containing ATM 3'-UTR by about 56.8% (P < 0.05), but it didn't suppress the reporter gene activity containing 3'-UTR ATM mutation. Western blot showed that miR-181a significantly downregulated the expression of ATM in human leukemia cells. It is also found that miR-181a was significantly increased in AML, which showed a negative correlation with ATM expression. miR-181a promotes cell proliferation in AML by regulating the tumor suppressor ATM, thus it plays the role as oncogene in pathogenesis of AML.

The Nature of Secondary Interactions at Electrophilic Metal Sites of Molecular and Silica-Supported Organolutetium Complexes from Solid-State NMR Spectroscopy.

Lu[CH(SiMe3)2]3 reacts with [SiO2-700] to give [(≡SiO)Lu[CH(SiMe3)2]2] and CH2(SiMe3)2. [(≡SiO)Lu[CH(SiMe3)2]2] is characterized by solid-state NMR and EXAFS spectroscopy, which show that secondary Lu···C and Lu···O interactions, involving a γ-CH3 and a siloxane bridge, are present. From X-ray crystallographic analysis, the molecular analogues Lu[CH(SiMe3)2]3-x[O-2,6-tBu-C6H3]x (x = 0-2) also have secondary Lu···C interactions. The (1)H NMR spectrum of Lu[CH(SiMe3)2]3 shows that the -SiMe3 groups are equivalent to -125 °C and inequivalent below that temperature, ΔG(⧧)(Tc=148K) = 7.1 kcal mol(-1). Both -SiMe3 groups in Lu[CH(SiMe3)2]3 have (1)JCH = 117 ± 1 Hz at -140 °C. The solid-state (13)C CPMAS NMR spectrum at 20 °C shows three chemically inequivalent resonances in the area ratio of 4:1:1 (12:3:3); the J-resolved spectra for each resonance give (1)JCH = 117 ± 2 Hz. The (29)Si CPMAS NMR spectrum shows two chemically inequivalent resonances with different values of chemical shift anisotropy. Similar observations are obtained for Lu[CH(SiMe3)2]3-x[O-2,6-tBu-C6H3]x (x = 1 and 2). The spectroscopic data point to short Lu···Cγ contacts corresponding to 3c-2e Lu···Cγ-Siβ interactions, which are supported by DFT calculations. Calculated natural bond orbital (NBO) charges show that Cγ carries a negative charge, while Lu, Hγ, and Siβ carry positive charges; as the number of O-based ligands increases so does the positive charge at Lu, which in turns shortens the Lu···Cγ distance. The change in NBO charges and the resulting changes in the spectroscopic and crystallographic properties show how ligands and surface-support sites rearrange to accommodate these changes, consistent with Pauling's electroneutrality concept.

Low-Dimensional Polyoxometalate Molecules/Tantalum Oxide Hybrids for Non-Volatile Capacitive Memories.

Transition-metal-oxide hybrids composed of high surface-to-volume ratio Ta2O5 matrices and a molecular analogue of transition metal oxides, tungsten polyoxometalates ([PW12O40](3-)), are introduced herein as a charge storage medium in molecular nonvolatile capacitive memory cells. The polyoxometalate molecules are electrostatically self-assembled on a low-dimensional Ta2O5 matrix, functionalized with an aminosilane molecule with primary amines as the anchoring moiety. The charge trapping sites are located onto the metal framework of the electron-accepting molecular entities as well as on the molecule/oxide interfaces which can immobilize negatively charged mobile oxygen vacancies. The memory characteristics of this novel nanocomposite were tested using no blocking oxide for extraction of structure-specific characteristics. The film was formed on top of the 3.1 nm-thick SiO2/n-Si(001) substrates and has been found to serve as both SiO2/Si interface states' reducer (i.e., quality enhancer) and electron storage medium. The device with the polyoxometalates sandwiched between two Ta2O5 films results in enhanced internal scattering of carriers. Thanks to this, it exhibits a significantly larger memory window than the one containing the plain hybrid and comparable retention time, resulting in a memory window of 4.0 V for the write state and a retention time around 10(4) s without blocking medium. Differential distance of molecular trapping centers from the cell's gate and electronic coupling to the space charge region of the underlying Si substrate were identified as critical parameters for enhanced electron trapping for the first time in such devices. Implementing a numerical electrostatic model incorporating structural and electronic characteristics of the molecular nodes derived from scanning probe and spectroscopic characterization, we are able to interpret the hybrid's electrical response and gain some insight into the electrostatics of the trapping medium.

Graphite-Conjugated Rhenium Catalysts for Carbon Dioxide Reduction.

Condensation of fac-Re(5,6-diamino-1,10-phenanthroline)(CO)3Cl to o-quinone edge defects on graphitic carbon surfaces generates graphite-conjugated rhenium (GCC-Re) catalysts that are highly active for CO2 reduction to CO in acetonitrile electrolyte. X-ray photoelectron and X-ray absorption spectroscopies establish the formation of surface-bound Re centers with well-defined coordination environments. GCC-Re species on glassy carbon surfaces display catalytic currents greater than 50 mA cm(-2) with 96 ± 3% Faradaic efficiency for CO production. Normalized for the number of Re active sites, GCC-Re catalysts exhibit higher turnover frequencies than that of a soluble molecular analogue, fac-Re(1,10-phenanthroline)(CO)3Cl, and turnover numbers greater than 12,000. In contrast to the molecular analogue, GCC-Re surfaces display a Tafel slope of 150 mV/decade, indicative of a catalytic mechanism involving rate-limiting one-electron transfer. This work establishes graphite-conjugation as a powerful strategy for generating well-defined, tunable, heterogeneous electrocatalysts on ubiquitous graphitic carbon surfaces.

Weaving organic threads

Molecular Frameworks Woven fabrics are inherently flexible. Liu et al. created a molecular fabric analog using metal-organic frameworks (see the Perspective by Gutierrez-Puebla). Phenanthroline ligands on a copper metal complex directed the addition of organic linkers via imine bonds to create

ChemInform Abstract: Switchable Fe/Co Prussian Blue Networks and Molecular Analogues

AbstractReview: 88 refs.

A multi-stimuli responsive switch as a fluorescent molecular analogue of transistors.

Although the quantum nature of molecules makes them specially suitable for mimicking the operation of digital electronic elements, molecular compounds can also be envisioned to emulate the behavior of analog devices. In this work we report a novel fluorescent three-state switch capable of reproducing the analog response of transistors, an ubiquitous device in modern electronics. Exploiting the redox and thermal sensitivity of this compound, the amplitude of its fluorescence emission can be continuously modulated, in a similar way as the output current in a transistor is amplified by the gate-to-source voltage.

Probing the molecular character of periodic mesoporous organosilicates via photoluminescence of Lewis acid-base adducts.

Photoluminescence decay was used as a structure-sensitive method to compare the distribution of emitting sites in periodic mesoporous organosilicates (PMOs) to their respective molecular analogs. The observed close similarity of PL decays confirms the molecular nature of PMOs and high homogeneity of emitting sites.

Switchable Fe/Co Prussian blue networks and molecular analogues.

With the long term objective to build the next generation of devices from the molecular scale, scientists have explored extensively in the past two decades the Prussian blue derivatives and their remarkable physico-chemical properties. In particular, the exquisite Fe/Co system displays tuneable optical and magnetic behaviours associated with thermally and photo-induced metal-to-metal electron transfer processes. Recently, numerous research groups have been involved in the transfer of these electronic properties to new Fe/Co coordination networks of lower dimensionality as well as soluble molecular analogues in order to facilitate their manipulation and integration into devices. In this review, the most representative examples of tridimensional Fe/Co Prussian blue compounds are described, focusing on the techniques used to understand their photomagnetic properties. Subsequently, the different strategies employed toward the design of new low dimensional Prussian blue analogues based on a rational molecular building block approach are discussed emphasizing the advantages of these functional molecular systems.

Carving a 1D Co(II)-carboranylcarboxylate system by using organic solvents to create stable trinuclear molecular analogues: complete structural and magnetic studies.

This work presents a straightforward methodology to achieve small linear trinuclear molecules based on the Co(II)-carboranylcarboxylate system obtained by carving a 1D polynuclear analogous system with the use of diethylether. The reaction of the carboranylcarboxylic ligand, 1-CH3-2-CO2H-1,2-closo-C2B10H10 (LH) with different cobalt salts leads to the polynuclear compound [Co2(μ-H2O)(1-CH3-2-CO2-1,2-closo-C2B10H10)4(THF)4], and the polymeric [Co(μ-H2O)(1-CH3-2-CO2-1,2-closo-C2B10H10)2]n(H2O)n. This latter 1D chain has been obtained by an unprecedented synthetic strategy for the isolation of cobalt(ii) compounds. [Co3(μ-H2O)2(1-CH3-2-CO2-1,2-closo-C2B10H10)6(H2O)2(C4H10O)2], is formed by the dissociation of the polymeric structure that forms when a mild coordinating solvent such as diethylether is added. These compounds have been characterized by analytical and spectroscopic techniques. X-ray analysis of and revealed that presents a dinuclear structure whereas is trinuclear; in both cases a six-coordinated Co(II) compound with water molecules bridging each of the two Co(II) centres has been observed. The magnetic properties of and show a weak antiferromagnetic behaviour, respectively, between the Co(II) centres mediated by two carboxylate ligands and a molecule of water.

A macromolecular N-bromosulphonamide as a heterogeneous oxidant in acidic media

Styrene–divinylbenzene copolymer containing N-bromosulphonamide groups as sodium salt, [P]–SO2NBrNa, can be viewed as a high molecular weight redox polymer mimicking its low molecular weight analogue: Bromamine-T. The stability of this copolymer in acidic media has not been studied in detail to date. This paper reports on studies of the reaction between the copolymer and aqueous FeSO4 solution conducted in a series of batch and column experiments. It was found that pH 3.0, active bromine remains bound to the functional groups, facilitating application of this copolymer as an effective oxidant in column processes running in weakly acidic reaction media. Results of the present work provide evidence that –SO2NBr− functional groups of the copolymer can stably exist in acidic form which is in contrast to the behaviour of the low molecular weight analogue (N-bromo-p-toluenesulphonic acid does not occur as a pure chemical compound).

Arsenic metabolism in cyanobacteria

Environmental context Cyanobacteria are ecologically important, photosynthetic organisms that are widely distributed throughout the environment. They play a central role in arsenic transformations in terms of both mineralisation and formation of organoarsenic species as the primary producers in aquatic ecosystems. In this review, arsenic resistance, transport and biotransformation in cyanobacteria are reviewed and compared with those in other organisms. Abstract Arsenic is a toxic element that is widely distributed in the lithosphere, hydrosphere and biosphere. Some species of cyanobacteria can grow in high concentrations of arsenate (pentavalent inorganic arsenic compound) (100mM) and in low-millimolar concentrations of arsenite (trivalent inorganic arsenic compound). Arsenate, which is a molecular analogue of phosphate, is taken up by cells through phosphate transporters, and inhibits oxidative phosphorylation and photophosphorylation. Arsenite, which enters the cell through a concentration gradient, shows higher toxicity than arsenate by binding to sulfhydryl groups and impairing the functions of many proteins. Detoxification mechanisms for arsenic in cyanobacterial cells include efflux of intracellular inorganic arsenic compounds, and biosynthesis of methylarsonic acid and dimethylarsinic acid through methylation of intracellular inorganic arsenic compounds. In some cyanobacteria, ars genes coding for an arsenate reductase (arsC), a membrane-bound protein involved in arsenic efflux (arsB) and an arsenite S-adenosylmethionine methyltransferase (arsM) have been found. Furthermore, cyanobacteria can produce more complex arsenic species such as arsenosugars. In this review, arsenic metabolism in cyanobacteria is reviewed, compared with that in other organisms. Knowledge gaps remain regarding both arsenic transport (e.g. uptake of methylated arsenicals and excretion of arsenate) and biotransformation (especially production of lipid-soluble arsenicals). Further studies in these areas are required, not only for a better understanding of the role of cyanobacteria in the circulation of arsenic in aquatic environments, but also for their application to arsenic bioremediation.

Dimeric [Mo2 S12 ](2-) Cluster: A Molecular Analogue of MoS2 Edges for Superior Hydrogen-Evolution Electrocatalysis.

Proton reduction is one of the most fundamental and important reactions in nature. MoS2 edges have been identified as the active sites for hydrogen evolution reaction (HER) electrocatalysis. Designing molecular mimics of MoS2 edge sites is an attractive strategy to understand the underlying catalytic mechanism of different edge sites and improve their activities. Herein we report a dimeric molecular analogue [Mo2 S12 ](2-) , as the smallest unit possessing both the terminal and bridging disulfide ligands. Our electrochemical tests show that [Mo2 S12 ](2-) is a superior heterogeneous HER catalyst under acidic conditions. Computations suggest that the bridging disulfide ligand of [Mo2 S12 ](2-) exhibits a hydrogen adsorption free energy near zero (-0.05 eV). This work helps shed light on the rational design of HER catalysts and biomimetics of hydrogen-evolving enzymes.

An insight into the complexation of UO22+ with diglycolamide-functionalized task specific ionic liquid: Kinetic, cyclic voltammetric, extraction and spectroscopic investigations

A systematic study was carried out to understand the complexation of a diglycolamide functionalized task-specific ionic liquid (DGA-TSIL) and its molecular analogue, (tetraoctyldiglycolamide) TODGA with uranyl ion by cyclic voltammetry, solvent extraction and UV–Vis spectroscopy. Significant shifts of cathodic peak potential towards more positive values as compared to the uranyl ion in a room temperature ionic liquid-diluent, [C8mim][Br] were attributed to the complexation of it with the ligands. The order of diffusion coefficient values determined gave the idea of the bulkiness of the U bearing species. In the case of DGA-TSIL, the measurable, relatively slower kinetics in ionic liquid observed by both electrochemical and biphasic extraction techniques was attributed to high viscosity coefficient of the ionic liquid. The complexation reaction with U(VI) was found to follow the first order kinetics with a rate constant of 4.8×10−4s−1. Titration data from cyclic voltammograms for a series of additions of the ligand to a fixed concentration of uranyl ion indicated that uranyl ion forms 1:1 complexed species with DGA-TSIL with the formation constant of 1.0×103M−1 which agreed well with that obtained by slope analysis from biphasic extraction results. Difference in the UV–Vis spectra in terms of shifts of peak positions and relative peak intensities could possibly indicate the presence of different species of the uranyl ion in the RTIL with and without the ligand. It was also proposed that the bond (OUO) becomes weaker on complexation due to the approach of the ligand towards the metal ion, partially neutralizing the charge on the uranyl moiety. The symmetric stretching frequency calculated from UV–Vis spectra was in conformity of the above fact.