Nonconjugated hydrocarbons, like bicyclo1.1.1pentane, bicyclo2.2.2octane, triptycene, and cubane are a unique class of rigid linkers. Due to their similarity in size and shape they are useful mimics ...of classic benzene moieties in drugs, so‐called bioisosteres. Moreover, they also fulfill an important role in material sciences as linear linkers, in order to arrange various functionalities in a defined spatial manner. In this Review article, recent developments and usages of these special, rectilinear systems are discussed. Furthermore, we focus on covalently linked, nonconjugated linear arrangements and discuss the physical and chemical properties and differences of individual linkers, as well as their application in material and medicinal sciences.
Rigid, linear, versatile, and increasingly in use are attributes of nonconjugating hydrocarbons, such as bicyclo1.1.1pentane, bicyclo2.2.2octane, triptycene, and cubane. This Review article details their fundamental properties, synthetic chemistry, and use as linker systems in materials sciences and drug development (see figure).
Mucin-related carbohydrates are overexpressed on the surface of cancer cells, providing a disease-specific target for cancer immunotherapy. Here, we describe the design and construction of ...peptide-free multivalent glycosylated nanoscale constructs as potential synthetic cancer vaccines that generate significant titers of antibodies selective for aberrant mucin glycans. A polymerizable version of the Tn-antigen glycan was prepared and converted into well-defined glycopolymers by Reversible Addition–Fragmentation chain Transfer (RAFT) polymerization. The polymers were then conjugated to gold nanoparticles, yielding ‘multicopy-multivalent’ nanoscale glycoconjugates. Immunological studies indicated that these nanomaterials generated strong and long-lasting production of antibodies that are selective to the Tn-antigen glycan and cross-reactive toward mucin proteins displaying Tn. The results demonstrate proof-of-concept of a simple and modular approach toward synthetic anticancer vaccines based on multivalent glycosylated nanomaterials without the need for a typical vaccine protein component.
Previous studies by Desiraju and co‐workers have implicated the acidic hydrogen atoms of cubane as a support network for hydrogen bonding groups. Herein we report a detailed structural analysis of ...all currently available 1,4‐disubstituted cubane structures with an emphasis on how the cubane scaffold interacts in its solid‐state environment. In this regard, the interactions between the cubane hydrogen atoms and acids, ester, halogens, ethynyl, nitrogenous groups, and other cubane scaffolds were cataloged. The goal of this study was to investigate the potential of cubane as a substitute for phenyl. This could be achieved by analyzing all contacts that are directed by the cubane hydrogen atoms in the X‐ray crystal structures. As a result, we have established several new cubane interaction profiles, such as the catemer formation seen in esters, the preferences of halogen–hydrogen contacts over direct halogen bonding, and the stabilizing effects caused by the cubane hydrogen atoms interacting with ethynyl groups. These interaction profiles can then be used as a guide for designing cubane bioisosteres of known materials and drugs containing phenyl moieties.
How the dice rolls: Cubanes have been successfully used as bioisosteres for benzene rings, but most of these studies rely on the fact that the 1,4‐axis of both these compounds are of similar length. However, with its 3D geometry, cubane has a significant difference in the types of interactions that occur in comparison to benzene. Here, we highlight the differences by an in‐depth study on cubane–hydrogen interaction profiles with multiple functional groups.
Cubane Cross‐Coupling and Cubane–Porphyrin Arrays Bernhard, Stefan S. R.; Locke, Gemma M.; Plunkett, Shane ...
Chemistry : a European journal,
January 24, 2018, Volume:
24, Issue:
5
Journal Article
Peer reviewed
Open access
Herein, an improved methodology for aryl‐cubane cross‐coupling is reported. The peculiarities of the cubane core and its behavior during cross‐coupling conditions were analyzed, while the versatility ...of this adapted Baran cross‐coupling methodology was demonstrated by the synthesis of various aryl‐cubane systems, including coupling products of cubanes and porphyrins. Furthermore, arm extension of alkynyl‐cubanes by Sonogashira reactions is demonstrated, showcasing the first proof of the stability of the cubane core in the presence of palladium catalysts.
Alea Iacta Est: The compatibility of cubanes and transition metals (Ni, Pd) was explored, and a direct arylation of cubanes via a Baran‐type nickel‐catalyzed radical cross‐coupling and arm‐extended Sonogashira coupling of alkynyl‐cubanes is reported. Furthermore, the first series of cubane–porphyrins was prepared (see figure).
Conspectus The exponential growth in published studies on phosphorescent metal complexes has been triggered by their utilization in optoelectronics, solar energy conversion, and biological labeling ...applications. Very recent breakthroughs in organic photoredox transformations have further increased the research efforts dedicated to discerning the inner workings and structure–property relationships of these chromophores. Initially, the principal focus was on the Ru(II)-tris-diimine complex family. However, the limited photostability and lack of luminescence tunability discovered in these complexes prompted a broadening of the research to include 5d transition metal ions. The resulting increase in ligand field splitting prevents the population of antibonding eg* orbitals and widens the energy range available for color tuning. Particular attention was given to Ir(III), and its cyclometalated, cationic complexes have now replaced Ru(II) in the vast majority of applications. At the start, this Account documents the initial efforts dedicated to the color tuning of these complexes for their application in light emitting electrochemical cells, an easy to fabricate single-layer organic light emitting device (OLED). Systematic modifications of the ligand sphere of Ir(ppy)2bpy+ (ppy: 2-phenylpyridine, bpy: 2,2′-bipyridine) with electron withdrawing and donating substituents allowed access to complexes with luminescence emission maxima throughout the visible spectrum exhibiting room temperature excited state lifetimes ranging from nanoseconds to dozens of microseconds and quantum yields up to 15 times that of Ru(bpy)32+. The diverse photophysical properties were also beneficial when using these Ir(III) complexes for driving solar fuel-producing reactions. For instance, photocatalytic water-reduction systems were explored to gain access to efficient water splitting systems. For this purpose, a variety of water reduction catalysts were paired with libraries of Ir(III) photosensitizers in high-throughput photoreactors. This parallelized approach allowed exploration of the interplay between the diverse photophysical properties of the Ir compounds and the electron-accepting catalysts. Further work enhanced and simplified the critical electron transfer processes between these two species through the use of bridging functional groups installed on the photosensitizer. Later, a novel approach summarized in this Account explores the possibility of using Zn metal as a solar fuel. Structure–activity relationships of the light-driven reduction of Zn2+ to Zn metal are described. DFT calculations along with cyclic voltammetry were utilized to gain clear insights into the complexes’ electronic structures responsible for the effective photochemical properties observed in these dyes. While Ir(ppy)2bpy+ and its derivatives were found to be much more photostable than the Ru(II)-tris-diimine complex family, mass spectrometry indicated that the bpy ligand still photodissociated under extensive illumination. An interesting new approach involved the substitution of the bidentate 2,2′-bipyridine with a stronger chelating terpyridine ligand. This approach leaves room for one 2-phenylpyridine ligand and a third, anionic ligand, either Cl– or CN–. This Account reviews the effect of structural modifications on the photophysical properties of these Ir(tpy)(ppy)X+ complexes and corroborates the findings with the results obtained through DFT modeling. These complexes found application in photocatalytic CO2 reductions as well as a solvent tolerant light-absorber for the photogeneration of hydrogen. It was also documented that the robustness of these dyes in photoredox processes supersedes those of the commercially available Ir(ppy)2(dtbbpy)PF6 and Ir(dF(CF3)ppy)2(dtbbpy)PF6 complexes pioneered in the Bernhard laboratory.
How to understand meaning-making in social relations has long been a key issue in sociological network thinking and research and has been addressed by an impressive body of research, most with either ...a theory-oriented or a method-oriented focus. This article argues for the value of strengthening the links between both approaches to meaning-making in networks. From an empirical perspective, this article draws on small story research and combines it with recent advances in network theory led by Harrison C. White. People relate to one another by telling small stories that engage positioned identities in story lines. Meaning-making in social relations builds on and continues this shared storytelling history. I suggest two basic analytical operations to reconstruct meaning-making in social ties from textual data. The first basic operation disentangles small story sequences from a text and investigates their identity positionings (small story level). The second basic operation integrates all small stories about a tie and teases out varieties of identity positionings, their patterning, and their inner logic (tie level). This article presents a practical procedure to analyze meaning-making in network ties that is simultaneously combined with qualitative research principles and consistent with recent developments in sociological network thinking.
A series of novel Ir(III) luminophores containing pendant pyridyl moieties that allow for adsorption onto metal surfaces has been synthesized. These new photosensitizer compounds have been evaluated ...for their efficacy in hydrogen-producing photoreactions. The new complexes are shown to significantly outperform the control photosensitizers without adsorbing moieties.
Steady state emission spectra and excited state lifetimes were measured for 1440 distinct heteroleptic Ir(C^N)2(N^N)+ complexes prepared via combinatorial parallelized synthesis; 72% of the ...complexes were found to be luminescent, and the emission maxima of the library spanned the visible spectrum (652–459 nm). Spectral profiles ranged from broad structureless bands to narrow emissions exhibiting vibrational substructure. Measured excited state lifetimes ranged between ∼0.1–14 μs. Automated emission spectral fitting with successive Gaussian functions revealed four distinct measured classes of excited states; in addition to well understood metal–ligand to ligand-charge transfer (3MLLCT) and ligand-centered (3LC) excited states, our classification also identified photophysical characteristics of less explored mixed 3MLLCT/3LC states. Electronic structure features obtained from DFT calculations performed on a large subset of these Ir(III) chromophores offered clear insights into the excited state properties and allowed the prediction of structure/luminescence relationships in this class of commonly used photocatalysts. Models with high prediction accuracy (R2 = 0.89) for emission color were developed on the basis of experimental data. Furthermore, different degrees of nuclear reorganization in the excited state were shown to significantly impact emission energy and excited state lifetimes.
Think oxygen: Iridium(III) complexes containing an unusually bound chelating triazolylidene ligand (see picture) show excellent activity towards water oxidation, producing hundreds of milliliters or ...O2 per milligram of iridium. The active catalysts include either an ylide or an unusually bound pyridylidene as the chelating L group and are readily accessible by click chemistry.
Gold-based materials hold promise in electrocatalytic reduction of CO2 to fuels. However, the polydispersity of conventional gold nanostructures limits mechanistic studies. Here, we report two types ...of atomically precise Au25 nanoclusters (1 nm) with distinct morphology (i.e., nanosphere and nanorod) for CO2 reduction catalysis. The Au25 nanosphere exhibits higher Faradaic efficiency for CO with higher formation rates compared to the Au25 nanorod. First-principles calculations reveal that the negative charge and the energetically favorable removal of one ligand to generate an active site on the nanosphere can better stabilize the important *COOH intermediate in CO2 electroreduction.
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