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A novel class of stable monoareno-pentalenes is introduced that have an olefinic proton on each five-membered ring of the pentalene subunit. Their synthesis was accomplished via a regioselective carbopalladation cascade reaction between

The construction of a donor–acceptor Stenhouse adduct molecular layer on a gold surface is presented. To avoid the incompatibility of the thiol surface-binding group with the donor–acceptor polyene structure of the switch, an interfacial reaction approach was followed. Poly(dopamine)-supported gold nanoparticles on quartz slides were chosen as substrates, which was expected to facilitate both the interfacial reaction and the switching process by providing favorable steric conditions due to the curved particle surface. The reaction between the surface-bound donor half and the CF3-isoxazolone-based acceptor half was proved to be successful by X-ray photoelectron spectroscopy (XPS). However, UV–vis measurements suggested that a closed, cyclopentenone-containing structure of the switch formed on the surface irreversibly. Analysis of the wetting behavior of the surface revealed spontaneous water spreading that could be associated with conformational changes of the closed isomer.

Morphologically different gold nanoparticle (AuNP) aggregates were prepared on macroscopic surfaces covered with a layer of polydopamine (PDA). The extent of particle aggregation and the particle size distribution could be controlled by the Au(III) reduction times, while the reduction process was triggered solely by the redox active polymer. Shorter reaction times led to smaller particles along with lower levels of aggregation, while longer reductions resulted in larger average particle diameter and heavier aggregation. The prepared surfaces were characterized by UV-Vis, AFM and KPFM techniques. These surfaces were used as solvent-free condensed phases to probe the photochemical and thermal isomerization processes of attached azobenzenes with different spacer lengths. Fast and reversible light-induced switching was observed in each case. The thermal cis-to-trans isomerization was found to be accelerated for particle-bound azobenzenes compared to those in solution.

The synthesis and properties of a series of unsymmetrical thienopentalenes are explored, including both monoareno and diareno derivatives. For the synthesis of monoareno pentalenes, a carbopalladation cascade reaction between alkynes and

The facile preparation of dynamic interfaces is presented based on the combination of photoisomerizable azobenzenes and polydopamine (PDA)/Au nanoparticle composite materials. Azobenzenes with different spacer lengths (C3 , C6 ) and surface-binding groups (SH, NH2 ) were synthesized. The polymer layer on macroscopic quartz surface was prepared by the facile aerobic autopolymerisation of dopamine hydrochloride under basic conditions. The presence of redox-active catechol moieties meant that gold nanoparticles were formed on the polymer surface. The obtained UV-Vis spectroscopic results confirmed that following their successful assembly, the switching of azobenzenes on PDA/Au was not affected by the surface binding group and the spacer length of the azobenzene molecules under the measurement conditions. Furthermore, facilitated by the curved nature of the Au particles, the surface-bound azobenzene layer could be reconstructed by ligand-exchange processes, and the photochemical characterization of the mixed layer was performed.

Herein, the design and synthesis of a click-derived Pd-complex merged with a photoswitchable azobenzene unit is presented. While in the trans-form of the switch the complex showed limited solubility, the photogenerated cis-form rendered the molecule soluble in polar solvents. This light-controllable solubility was exploited to affect the catalytic activity in the Suzuki coupling reaction. The effect of the substrate and catalyst concentration and light intensity on the proceeding and outcome of the reaction was studied. Dehalogenation of the aryl iodide starting material was found to be a major side reaction; however, its occurrence was dependent on the applied light intensity.

In this chapter, an overview on the applications of photochromic molecular switches in catalytic transformations is given. The structure of these molecules can be reversibly controlled by light as an external stimulus, thereby not requiring any additional material that might turn to be a waste at the end of the process. The light-induced changes in molecular structure or shape can be associated with changes in function such as catalytic activity, solubility, aggregation, or selective binding. The diversity of their applications is gradually expanding and departs from the original goal of activity control (ON/OFF, high/low) in homogeneous systems towards controlling selectivity, including stereoselectivity, controlling phase transfer, facilitating catalyst recycling and reuse, and the development of heterogeneous and supported systems. These latter examples are well in line with the principles and aims of green chemistry.

We report the application of polydopamine (PDA) supported Pd nanoparticles in the cyanation of aryl halides with inexpensive and non-toxic K4[Fe(CN)6]. We found that Pd/PDA is an efficient catalyst in the reaction of electron poor aryl halides, however, in other cases the addition of tetrabutyl ammonium bromide was necessary for conversion. The main limitation of the system is suggested to be catalyst deactivation due to Pd aggregation, polymer degradation/functionalization under the high temperature required for catalysis. In several cases we found the formation of magnetite upon reaction, suggesting that K4[Fe(CN)6] is giving away all its six CN groups in cyanation reaction.

Polydopamine, a ‘mussel-inspired’ polymer, has been explored extensively in materials science as a universal coating. However, as an easily available, stable and environmentally benign material, it has recently been discovered to demonstrate catalytic applications. In this short review, we briefly discuss the main approaches employing polydopamine in the catalysis of organic transformations. These include metal/polydopamine-type systems and metal-free approaches that exploit the acid/base properties of this versatile polymer.1 Introduction2 PDA and Metal Catalysis2.1 Reduction of Nitroaryl Compounds to Anilines2.2 Reduction of Carbonyl Compounds to Alcohols2.3 Suzuki and Heck Coupling Reactions2.4 Other Reactions Catalyzed by M/PDA-Type Systems3 PDA as a Catalyst Itself4 Conclusion

The application of an easily prepared and highly active polydopamine-supported Pd nanoparticles catalyst in Suzuki cross-couplings and tandem Suzuki cross-coupling/catalytic transfer hydrogenation sequences under green reaction conditions is described. In Suzuki cross-couplings between aryl bromides and arylboronic acids Pd concentrations down to ppm levels could be used, while reactions were completed within minutes. Heteroaryl bromides needed somewhat longer reaction times but could be transformed under otherwise identical conditions. The efficiency of the Suzuki cross-couplings made them compatible with the mechanistically different catalytic nitroarene transfer hydrogenations, yielding valuable biphenyl aniline products in a mild, one-pot tandem fashion. The influence of reaction time, temperature and Pd particle size on the catalyst efficiency and recyclability is also examined.

The application of Pd–polydopamine and magnetic Fe3O4@Pd–polydopamine catalysts in catalytic transfer hydrogenation reactions and the Heck arylation is reported. The reduction of a wide range of aromatic nitro-compounds bearing both electron-donating and -withdrawing substituents to the corresponding anilines could be efficiently performed, although the reduction of carbonyl compounds was found to be less general. In the latter case, only aromatic ketones could be reduced to the corresponding alcohols, whereas aldehyde substrates were unaffected, which may be owing to their reaction with the catalyst support leading to catalyst deactivation. By using magnetic Fe3O4@Pd–polydopamine system, facilitated catalyst recovery and reuse for five consecutive cycles without considerable loss of activity in nitro-group reduction. The efficiency of the catalyst in Heck reactions was comparable to that in transfer hydrogenation, however, no catalytic activity was observed upon reuse in this case, likely as a result of metal leaching. We also explored tandem Heck reaction/catalytic transfer hydrogenation sequences, however, the two reactions showed limited compatibility under the applied conditions.

According to the currently accepted structure-property relationships, aceno-pentalenes with angular shape (fused to the 1,2-bond of the acene) exhibit higher antiaromaticity than those with linear shape (fused to the 2,3-bond of the acene). To explore and expand the current view, we designed and synthesized molecules where two isomeric, yet, different, 8π antiaromatic subunits, a benzocyclobutadiene (BCB) and a pentalene are combined into, respectively, an angular and a linear topology via an unsaturated 6-membered ring. The antiaromatic character of the molecules are supported experimentally by 1H NMR, UV-Vis and cyclic voltammetry measurements and X-ray crystallography. The experimental results are further confirmed by theoretical studies including the calculation of several aromaticity indices (NICS, ACID, HOMA, FLU, MCI). In the case of the angular molecule, double bond-localization within the connecting 6-membered ring resulted in reduced antiaromaticity of both the BCB and pentalene subunits, while the linear structure provided a competitive situation for the two unequal [4n]π subunits. We found that in the latter case pentalene drew the shorter straw. The BCB unit alleviated its unfavorable antiaromaticity more efficiently, leaving the pentalene with enhanced antiaromaticity. Thus, a reversed structure-antiaromaticity relationship when compared to aceno-pentalenes was achieved.

An acid/base responsive amphiphilic [2]rotaxane switch containing a hydrophilic macrocycle component and a hydrophobic terminal bulky group was prepared and characterized. The morphology of the supramolecular assemblies formed by the rotaxanes could be switched between spherical vesicles and worm-like micelles using acid/base stimuli, as confirmed by transmission electron microscopy (TEM).

Supported Pd catalysts were investigated in the Heck coupling reactions: Pd/C; Pd/BaSO4; Pd EnCat. We optimized the experimental conditions of the Heck reaction of bromobenzene and styrene by using various bases in the presence of quaternary ammonium salts. It was found that the examined catalysts work as a reservoir of the catalytically active Pd species during the reaction. However, they have a different activity and recyclability under the investigated reaction conditions. Pd EnCat displayed the highest activity and selectivity in NMP with Na2CO3 as a base and Bu4NCl as an additive. By using this catalytic system, the reactions of para-substituted aryl halides with styrene and methyl methacrylate afforded excellent conversions and selectivities.

The effect of catalyst restructuring on the polydopamine-supported Pd catalyzed transfer hydrogenation of ethyl 4-nitrobenzoate and the catalytic hydrogenation of (E)-2-methyl-2-butenoic acid is reported. Transmission electron microscopy investigation of different catalyst pre-treatment and reaction conditions revealed high catalytic activity in both reactions unless drastic aggregation of the active metal occurred. In the transfer hydrogenation reaction aggregation was primarily dependent on the H-source used, while in the catalytic hydrogenation additives in combination with the reductive environment led to extensive Pd aggregation and thus decreased catalytic activity. The enantioselective hydrogenation of (E)-2-methyl-2-butenoic acid showed increased enantioselectivity and decreased conversion with increased particle size.

Three series of stable, neutral, π-extended bispentalene derivatives, with two pentalenes fused to a central benzene or naphthalene moiety, have been prepared through a modified double carbopalladation cascade reaction. While these chromophores feature skeletons with [4n+2] π-electron perimeters, the two 8 π-electron pentalene subunits strongly influence bonding and spectral properties. (1)H NMR spectra showed large upfield shifts of the protons in the pentalene moieties, comparable to antiaromatic monobenzopentalenes. Further investigations on magnetic ring currents through NICS-XY-scans suggest a global paratropic current and a local diatropic current at the central benzene ring in two of the series, while the third series, with a central naphthalene ring, showed more localized ring currents, with stronger paratropic ring currents on the pentalene moieties. X-ray diffraction analyses revealed planar bispentalene cores with large double- and single-bond alternation in the pentalene units, characteristic for antiaromaticity, and small alternation in the central aromatic rings. In agreement with TD-DFT calculations, both optical and electrochemical data showed much smaller HOMO-LUMO energy gaps compared to other neutral, acene-like hydrocarbons with the same number of fused rings. Both experimental and computational results suggest that the molecular properties of the presented bispentalenes are dominated by the antiaromatic pentalene-subunits despite the [4n+2] π-electron perimeter of the skeletons.

Pt nanoparticles with controlled sizes between 1.6–7.0 nm were anchored onto the surface and pores of SBA-15 silica support. The catalysts were characterized by TEM-ED, BET, XRD, and ICP-MS techniques and were tested in liquid phase hydrosilylation of phenylacetylene with triethylsilane. The activity of the 7.0 nm Pt nanoparticles anchored onto the surface of SBA-15 in hydrosilylation (TOF = 0.107 molecules·site−1·s−1) was ~2 times higher compared to the 5.0 nm Pt/SBA-15 (TOF = 0.049 molecules·site−1·s−1) catalyst and ~10 times higher compared to the 1.6 nm Pt/SBA-15 (TOF = 0.017 molecules·site−1·s−1) catalyst. Regarding the selectivity, bigger nanoparticles produced more vinylsilane-type products (α- and β-(E)-products) and less side products (mainly ditriethylsilane, triethyl(1-phenylethyl)silane and triethyl(phenethyl)silane derived likely from the reduction of the vinylsilane products). However, the selectivity towards the β-(E)-triethyl(styryl)silane was higher in the case of 1.6 nm Pt/SBA-15 catalyst compared to 5.0 nm Pt/SBA-15 and 7.0 nm Pt/SBA-15, respectively, which can be attributed to the beneficial effect of the size differences of the Pt nanoparticles as well as the differences of the quality and quantity of Pt/SiO2 interfaces.

A series of π-extended pentalenes with fused naphthyl-ring systems in different geometries were synthesised via a cascade carbopalladation reaction between alkynes and gem-dibromoolefins. This novel methodology was applied both in an intermolecular and an intramolecular fashion to access pentalenes with new topologies. The relationship between the fusion pattern and the opto-electronic properties within the synthesised series was investigated by UV/vis spectroscopy and electrochemical techniques. Novel pentalene reactivity, leading to yet unprecedented derivatives, was also uncovered.

Despite considerable progress in genome- and proteome-based high-throughput screening methods and in rational drug design, the increase in approved drugs in the past decade did not match the increase of drug development costs. Network description and analysis not only give a systems-level understanding of drug action and disease complexity, but can also help to improve the efficiency of drug design. We give a comprehensive assessment of the analytical tools of network topology and dynamics. The state-of-the-art use of chemical similarity, protein structure, protein-protein interaction, signaling, genetic interaction and metabolic networks in the discovery of drug targets is summarized. We propose that network targeting follows two basic strategies. The "central hit strategy" selectively targets central nodes/edges of the flexible networks of infectious agents or cancer cells to kill them. The "network influence strategy" works against other diseases, where an efficient reconfiguration of rigid networks needs to be achieved by targeting the neighbors of central nodes/edges. It is shown how network techniques can help in the identification of single-target, edgetic, multi-target and allo-network drug target candidates. We review the recent boom in network methods helping hit identification, lead selection optimizing drug efficacy, as well as minimizing side-effects and drug toxicity. Successful network-based drug development strategies are shown through the examples of infections, cancer, metabolic diseases, neurodegenerative diseases and aging. Summarizing >1200 references we suggest an optimized protocol of network-aided drug development, and provide a list of systems-level hallmarks of drug quality. Finally, we highlight network-related drug development trends helping to achieve these hallmarks by a cohesive, global approach.

We examined the activity of a series of L-hydroxyproline derivatives in enantioselective alpha-amination reaction between diethyl azodicarboxylate and propanal both in organic and aqueous media. In organic media most of the catalysts showed high activity and enantioselectivities comparable to that accessible with L-proline that is among the best catalysts in the reaction. The catalysts showed good activity under aqueous conditions as well; however, only low enantioselectivities were obtained in this case, primarily due to the racemisation of the product under the reaction conditions. Thus, the attempted achiral acid/base additive-driven stereocontrol was not feasible on a practical level.

A series of π-extended pentalenes with fused naphthyl-ring systems in different geometries were synthesised via a cascade carbopalladation reaction between alkynes and gem-dibromoolefins. This novel methodology was applied both in an intermolecular and an intramolecular fashion to access pentalenes with new topologies. The relationship between the fusion pattern and the opto-electronic properties within the synthesised series was investigated by UV/vis spectroscopy and electrochemical techniques. Novel pentalene reactivity, leading to yet unprecedented derivatives, was also uncovered.

Despite considerable progress in genome- and proteome-based high-throughput screening methods and in rational drug design, the increase in approved drugs in the past decade did not match the increase of drug development costs. Network description and analysis not only give a systems-level understanding of drug action and disease complexity, but can also help to improve the efficiency of drug design. We give a comprehensive assessment of the analytical tools of network topology and dynamics. The state-of-the-art use of chemical similarity, protein structure, protein-protein interaction, signaling, genetic interaction and metabolic networks in the discovery of drug targets is summarized. We propose that network targeting follows two basic strategies. The "central hit strategy" selectively targets central nodes/edges of the flexible networks of infectious agents or cancer cells to kill them. The "network influence strategy" works against other diseases, where an efficient reconfiguration of rigid networks needs to be achieved by targeting the neighbors of central nodes/edges. It is shown how network techniques can help in the identification of single-target, edgetic, multi-target and allo-network drug target candidates. We review the recent boom in network methods helping hit identification, lead selection optimizing drug efficacy, as well as minimizing side-effects and drug toxicity. Successful network-based drug development strategies are shown through the examples of infections, cancer, metabolic diseases, neurodegenerative diseases and aging. Summarizing1200 references we suggest an optimized protocol of network-aided drug development, and provide a list of systems-level hallmarks of drug quality. Finally, we highlight network-related drug development trends helping to achieve these hallmarks by a cohesive, global approach.