Molecule-based Systems Research Articles

Impact of Collective Electrostatic Effects on Charge Transport through Molecular Monolayers

A microscopic understanding of charge transport through molecule-based systems is essential for advancing the field of molecular electronics. In the present paper we highlight fundamental differences between devices with an individual molecule or a homogeneous monolayer as the active element. These differences arise from collective electrostatic effects that govern the electronic level alignment in monolayer-based devices, but are absent in the case of individual molecules. Employing density functional theory in conjunction with a Green’s function approach, we show that depending on the chemical nature of the employed molecules collective electrostatic effects can result in either a significant increase or a significant decrease of the current per molecule as a function of the packing density, in certain cases even resulting in a change in the transport polarity. Understanding the underlying principles also allows for designing molecules in which dipolar effects cancel, and thus, the transport characteristics of individual molecules and monolayers remain similar.

A Racemic and Enantiopure Unsymmetric Diiron(III) Complex with a Chiral o‐Carborane‐Based Pyridylalcohol Ligand: Combined Chiroptical, Magnetic, and Nonlinear Optical Properties

The design of molecule-based systems combining magnetic, chiroptical and second-order optical nonlinear properties is still very rare. We report an unusually unsymmetric diiron(III) complex 1, in which three bulky chiral carboranylpyridinealkoxide ligands (oCBhmp(-)) bridge both metal ions and the complex shows the above-mentioned properties. The introduction of o-carborane into the 2-(hydroxymethyl)pyridine (hmpH) architecture significantly alters the coordination of the simple or aryl-substituted 2-hmpH. The unusual architecture observed in 1 seems to be triggered by the poor nucleophilicity of our alkoxide ligand (oCBhmp(-)). A very rare case of spontaneous resolution takes place on precipitation or exposure to solvent vapor for the bulk compound, as confirmed by a combination of single-crystal and powder X-ray diffraction, second-harmonic generation, and circular dichroism. The corresponding enantiopure complexes (+)1 and (-)1 have also been synthesized and fully characterized. This research provides a new building block with unique geometry and electronics to construct coordination complexes with multifunctional properties.

Metallic Nanoparticles and Their Medicinal potential. Part I: Gold and Silver Colloids

The article highlights the synthesis, properties and recent advances in therapeutic possibilities of metallic nanoparticles. Nanometallic structures that behave as drug-carrying agents, gene regulators, imaging agents and photoresponsive assemblies have been discussed in the context of cells and many debilitating diseases. These structures not only act as alternatives to molecule-based systems, but also possess new physical and chemical properties, which confer substantive advantages in medicinal field.

Spin crossover or intra-molecular electron transfer in a cyanido-bridged Fe/Co dinuclear dumbbell: a matter of state

The design of molecule-based systems displaying tuneable optical and/or magnetic properties under external stimuli has received a great deal of attention in the past few years. This interest is driven by the potential applications in high-performance molecule-based electronics in the areas of recording media, switches, sensors, and displays. As an example, three-dimensional Fe/Co Prussian blue compounds exhibit a concomitant change in magnetic and optical properties due to a temperature- or light-induced metal-to-metal electron transfer. The foregoing remarkable properties in Prussian blues prompted us to design soluble molecular fragments of these coordination networks through a rational building-block approach in order to mimic their properties on a single molecule. With a judicious choice of the ligands for the iron and cobalt molecular precursors, we prepared a dinuclear cyanido-bridged Fe/Co complex that exhibits an unexpected temperature-dependent spin crossover in the solid state while an intramolecular electron transfer triggered by protonation is observed in solution.

Realizing artificial photosynthesis

Artificial photosynthesis comprises the design of systems for converting solar energy into useful forms based on the fundamental science underlying natural photosynthesis. There are many approaches to this problem. In this report, the emphasis is on molecule-based systems for photochemical production of fuels using sunlight. A few examples of typical components of artificial photosynthetic systems including antennas, reaction centres, catalysts for fuel production and water oxidation, and units for photoprotection and photoregulation are presented in order to illustrate the current state of the field and point out challenges yet to be fully addressed.

Ion Translocation in Artificial Molecule-based Systems Induced by Light, Electrons, or Chemicals

Synthetic molecules and nanodevices, like their more elaborate biological counterparts, have been shown to perform several sophisticated functions, using even fairly simple molecular architectures. One limitation to developing artificial molecular arrays and networks from these miniscule building blocks is the lack of a unifying strategy whereby they can communicate or interact together, which has been successfully developed in natural systems. Understanding and harnessing these efficient biological processes could prove key in the development of future integrated molecule-based nanodevices and networks. Herein, we give a short overview of some manifestations of intra- and intermolecular communication based on chemical messengers in artificial systems, in some ways analogous to natural systems, which are in turn controlled by light, a redox process or a chemical reaction or interaction. Some advantages, limitations, and challenges are highlighted.

Calculation of microscopic exchange interactions and modelling of macroscopic magnetic properties in molecule-based magnets

The state-of-the-art theoretical evaluation and rationalization of the magnetic interactions (J(AB)) in molecule-based magnets is discussed in this critical review, focusing first on isolated radical···radical pair interactions and afterwards on how these interactions cooperate in the solid phase. Concerning isolated radical pairwise magnetic interactions, an initial analysis is done on qualitative grounds, concentrating also on the validity of the most commonly used models to predict their size and angularity (namely, McConnell-I and McConnell-II models, overlap of magnetic orbitals,…). The failure of these models, caused by their oversimplified description of the magnetic interactions, prompted the introduction of quantitative approaches, whose basic principles and relative quality are also evaluated. Concerning the computation of magnetic interactions in solids, we resort to a sum of pairwise magnetic interactions within the Heisenberg Hamiltonian framework, and follow the First-principles Bottom-Up procedure, which allows the accurate study of the magnetic properties of any molecule-based magnet in an unbiased way. The basic principles of this approach are outlined, applied in detail to a model system, and finally demonstrated to properly describe the magnetic properties of molecule-based systems that show a variety of magnetic topologies, which range from 1D to 3D (152 references).

Origin of the Magnetic Bistability in Molecule-Based Magnets: A First-Principles Bottom-Up Study of the TTTA Crystal

The magnetic bistability present in some molecule-based magnets is investigated theoretically at the microscopic level using the purely organic system TTTA (1,3,5-trithia-2,4,6-triazapentalenyl). The TTTA crystal is selected for being one of the best-studied molecule-based systems presenting magnetic bistability. The magnetic properties of the high- and low-temperature structures (HT and LT phases, respectively) are accurately characterized by performing a First-Principles Bottom-Up study of each phase. The changes that the magnetic exchange coupling constants (J(AB)) undergo when the temperature is raised (LT → HT) or lowered (HT → LT) are also fully explored in order to unravel the reasons behind the presence of these two different pathways. The triclinic LT phase is diamagnetic due to the fact that the nearly eclipsed π dimer is effectively magnetically silent and not to formation of a covalent bond between two TTTA molecules. It is also shown that bistability in TTTA results from the coexistence of the monoclinic HT and triclinic LT phases in the temperature range studied.

ChemInform Abstract: Gold Nanoparticles for Biology and Medicine

AbstractReview: 127 refs.

Gold nanoparticles for biology and medicine.

Gold colloids have fascinated scientists for over a century and are now heavily utilized in chemistry, biology, engineering, and medicine. Today these materials can be synthesized reproducibly, modified with seemingly limitless chemical functional groups, and, in certain cases, characterized with atomic-level precision. This Review highlights recent advances in the synthesis, bioconjugation, and cellular uses of gold nanoconjugates. There are now many examples of highly sensitive and selective assays based upon gold nanoconjugates. In recent years, focus has turned to therapeutic possibilities for such materials. Structures which behave as gene-regulating agents, drug carriers, imaging agents, and photoresponsive therapeutics have been developed and studied in the context of cells and many debilitating diseases. These structures are not simply chosen as alternatives to molecule-based systems, but rather for their new physical and chemical properties, which confer substantive advantages in cellular and medical applications.

Reversible electronic energy transfer: a means to govern excited-state properties of supramolecular systems

A strategy to manage energy, following light absorption, and modulate excited-state properties, including luminescence lifetimes of multicomponent photoactive systems, is presented. The intervening mechanism, which is illustrated through the use of bi-/multi-chromophoric molecules, relies on energy shuttling between different matched chromophores under kinetic and thermodynamic control. This tutorial review is destined to show supramolecular and materials chemists, spectroscopists and nanoscientists how to harness reversible electronic energy transfer in a predictable fashion in designer molecule-based systems.

Possibilities of magnetic modifications of DNA wires, sheets and related materials

Our theoretical efforts towards molecule-based magnetic conductors and superconductors on the basis of ab initio Hamiltonians and effective model Hamiltonians are summarized in relation to recently developed DNA-based molecular materials. Guanine and adenine derivatives coupling with organic radicals (R) are investigated as possible π–R components. In order to elucidate electronic and magnetic properties of these species, effective exchange integrals (Jab) for magnetic clusters are calculated by ab initio hybrid density functional methods. Theoretical possibilities of organic magnetic conductors and the organic solenoid are elucidated on the basis of these models in self-assembled DNA wires, sheets and related materials. Implications of the calculated results are finally discussed in order to obtain a unified picture of many p–d, π–d and π–R molecule-based systems with strong electron correlations.

Theoretical studies of molecule-based magnetic conductors

Our theoretical efforts towards molecule-based magnetic conductors and superconductors on the basis of ab initio Hamiltonians and effective model Hamiltonians are summarized in relation to recently developed π–d systems, for which transition metal complexes have been used as spin sources. Organic π-electron donors or acceptors coupling with organic radicals (R) are also investigated as possible π–R interaction systems. In order to elucidate electronic and magnetic properties of these species, effective exchange integrals (Jab) for magnetic clusters are calculated by ab initio hybrid density functional (HDFT) methods. The ab initio Jab values are numerically reproduced by using model Hamitonians such as t–J, Kondo, Anderson and RKKY models. Theoretical possibilities of magnetic conductors and spin-mediated superconductors are elucidated on the basis of these models in the intermediate region for metal–insulator transitions. Interrelationships among magnetism, superconductivity and fluctuations in strongly correlated electron systems are discussed on the basis of the SO(5) and three-dimensional quantum electrodynamics (QED3) theories. External magnetic field effects such as Jaccarino–Peter effect are also examined for elucidation of magnetic field induced superconductivity. Implications of the calculated results are finally discussed in order to obtain a unified picture of many p–d, π–d and π–R molecule-based systems with strong electron correlations.

Unsolved mysteries in molecule-based magnets — a personal view

Over a decade has passed since the first International Conference on Molecule-based Magnets (ICMM) was convened, with the topic attracting an increasing number of participants, and the focus of the meeting has evolved to include aspects of magnetic ordering found in single-molecule magnets and spin-crossover materials in addition to those found in molecule-based systems. Although many aspects of the observed magnetic behaviors of molecule-based magnets are understandable in terms of the models and mechanisms first used for conventional atom-based magnets, some aspects need further study to elucidate details not well understood; a few are discussed herein. In time some mysteries will be resolved, as one already has, but new ones will undoubtedly be identified and added.

Interplay of conductivity, magnetism (and nonlinear optics) in organic-inorganic compounds

The preparation and characterization of organic-inorganic molecule-based systems in which conduction electrons coexist with localized moments is reported. These systems comprise (i) charge transfer salts of organic donors, such as BETS (bis(ethylenedithio)tetraselena-fulvalene), and paramagnetic inorganic anions, such as [MX 4] −, [M 2X 6] 2− with M = Fe, Cu, etc., and X = Cl, Br, etc., or (ii) charge transfer salts of inorganic acceptor bisdithiolato metal complexes, such as M(dmit) 2 (dmit 2− = 2-thioxo-1,3-dithiole-4,5-dithiolato), and paramagnetic organometallic cations, such as [MCp 2] n+ (Cp = cyclopentadienyl-like ligands). In some favorable cases, such as λ-(BETS) 2(FeCl 4), new experimental evidence for interaction between the conduction electrons (of BETS) and magnetic moments (localized on [FeCl 4) is discussed. Current research towards the coupling of electrical and nonlinear optical properties in molecule-based compounds is reported. Additional evidence for the oxidation-induced symmetry breakdown in [bis-TTF] + radical cations is given.

Characterization of intercellular adhesion molecule-1 ectodomain (sICAM-1) as an inhibitor of lymphocyte function-associated molecule-1 interaction with ICAM-1.

Intercellular adhesion molecule-1 (ICAM-1) is a member of the Ig superfamily, contains five Ig-like domains comprising the extracellular portion of the molecule, and interacts with lymphocyte function-associated molecule-1 (LFA-1), a member of the beta 2-integrin family. LFA-1/ICAM-1 interaction is important in a variety of cellular events including Ag-specific T cell activation and leukocyte transendothelial migration. Recently, a soluble circulating form of ICAM-1 has been detected in human serum that appears to result from the proteolytic cleavage of membrane ICAM-1. Native and recombinant soluble forms of ICAM-1 have been reported to inhibit LFA-1/ICAM-mediated adhesion in vitro, and it is conceivable that circulating forms of soluble ICAM-1 are regulators of LFA-1/ICAM-1-mediated cell-cell interaction in vivo. We have investigated the properties of the ICAM-1 ectodomain (sICAM453) as an inhibitor of LFA-1 interaction with ICAM-1 in cell- and molecule-based systems. The results show clearly that recombinant sICAM453 can inhibit LFA-1/ICAM-1 interaction. Soluble ICAM-1 inhibited LFA-1-mediated cell adhesion to immobilized sICAM453 and homotypic T-cell aggregation with IC50 in the 20 to 40 microM range. Definitive evidence that sICAM-1 can inhibit LFA-1 interaction with ICAM-1 was obtained by showing that the sICAM-1 inhibited the interaction between LFA-1 protein micelles and ICAM-1 immobilized on plastic. These results clearly show that sICAM453 can bind to LFA-1 and competitively inhibit ICAM-1/LFA-1-mediated cell-cell interaction, albeit at concentrations much greater than found in plasma. As a consequence, it is unlikely that sICAM-1 would antagonize ICAM-1/LFA-1-mediated cellular events in vivo.

Intermolecular and intramolecular excited-state electron transfer involving electrode-confined rhenium carbonyl complexes: toward molecule-based systems for light absorption, charge separation, and optical energy conversion

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTIntermolecular and intramolecular excited-state electron transfer involving electrode-confined rhenium carbonyl complexes: toward molecule-based systems for light absorption, charge separation, and optical energy conversionCharles S. Christ Jr., Jie Yu, Xiaohong Zhao, G. Tayhas R. Palmore, and Mark S. WrightonCite this: Inorg. Chem. 1992, 31, 22, 4439–4440Publication Date (Print):October 1, 1992Publication History Published online1 May 2002Published inissue 1 October 1992https://doi.org/10.1021/ic00048a003RIGHTS & PERMISSIONSArticle Views177Altmetric-Citations26LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (292 KB) Get e-Alerts Get e-Alerts