| 1. |
- Erdelyi, Mate, 1975, et al.
(författare)
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Dynamics of the Glycosidic Linkage: Conformational Space of Lactose
- 2011
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Ingår i: Chemistry - A European Journal. - : Wiley. - 1521-3765 .- 0947-6539. ; 17:34, s. 9280-9282
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Tidskriftsartikel (refereegranskat)abstract
- Abstract: The dynamics of the glycosidic bond of lactose was studied by a paramagnetic tagging-based NMR technique, which allowed the collection of an unusually large series of NMR data for a single compound. By the use of distance- and orientation-dependent residual dipolar couplings and pseudocontact shifts, the simultaneous fitting of the probabilities of computed conformations and the orientation of the magnetic susceptibility tensor of a series of lanthanide complexes of lactose show that its glycosidic bond samples syn/syn, anti/syn and syn/anti f/y regions of the conformational space in water. The analysis indicates a higher reliability of pseudocontact shift data as compared to residual dipolar couplings with the presently available weakly orienting paramagnetic tagging technique. The method presented herein allows for an improved understanding of the dynamic behaviour of oligosaccharides.
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| 2. |
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| 3. |
- Afewerki, Samson, et al.
(författare)
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Direct Regiospecific and Highly Enantioselective Intermolecular α-Allylic Alkylation of Aldehydes by a Combination of Transition-Metal and Chiral Amine Catalysts
- 2012
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 18:10, s. 2972-2977
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Tidskriftsartikel (refereegranskat)abstract
- The first direct intermolecular regiospecific and highly enantioselective a-allylic alkylation of linear aldehydes by a combination of achiral bench-stable Pd0 complexes and simple chiral amines as co-catalysts is disclosed. The co-catalytic asymmetric chemoselective and regiospecific a-allylic alkylation reaction is linked in tandem with in situ reduction to give the corresponding 2-alkyl alcohols with high enantiomeric ratios (up to 98:2 e.r.; e.r.=enantiomeric ratio). It is also an expeditious entry to valuable 2-alkyl substituted hemiacetals, 2-alkyl-butane-1,4-diols, and amines. The concise co-catalytic asymmetric total syntheses of biologically active natural products (e.g., Arundic acid) are disclosed.
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| 4. |
- Agarwala, Hemlata
(författare)
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Correspondence of RuIIIRuII and RuIVRuIII Mixed Valent States in a SmallDinuclear Complex
- 2012
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 18, s. 5667-5675
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Tidskriftsartikel (refereegranskat)abstract
- The dirutheniumACHTUNGTRENUNG(III) compound[(m-oxa){RuACHTUNGTRENUNG(acac)2}2] [1, oxa2=oxamidato(2), acac=2,4-pentanedionato]exhibits an S=1 ground statewith antiferromagnetic spin-spin coupling(J=40 cm1). The molecularstructure in the crystal of 1·2C7H8 revealedan intramolecular metal–metaldistance of 5.433 and a notableasymmetry within the bridging ligand.Cyclic voltammetry and spectroelectrochemistry(EPR, UV/Vis/NIR) of thetwo-step reduction and of the two-stepoxidation (irreversible second step)produced monocation and monoanionintermediates (Kc=105.9) with broadNIR absorption bands (e ca.2000m1cm1) and maxima at 1800 (1)and 1500 nm (1+). TD-DFT calculationssupport a RuIIIRuII formulationfor 1 with a doublet ground state. The1+ ion (RuIVRuIII) was calculated withan S=3/2 ground state and the doubletstate higher in energy (DE=694.6 cm1). The Mulliken spin densitycalculations showed little participationof the ligand bridge in the spin accommodationfor all paramagnetic species[(m-oxa){RuACHTUNGTRENUNG(acac)2}2]n, n=+1, 0, 1,and, accordingly, the NIR absorptionswere identified as metal-to-metal (intervalence)charge transfers. Whereasonly one such NIR band was observedfor the RuIIIRuII (4d5/4d6) system 1,the RuIVRuIII (4d4/4d5) form 1+ exhibitedextended absorbance over the UV/Vis/NIR range.
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| 5. |
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| 6. |
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| 7. |
- Amorati, Riccardo, et al.
(författare)
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Multi-faceted reactivity of alkyltellurophenols towards peroxyl radicals : Catalytic antioxidant versus thiol-depletion effect
- 2013
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 19:23, s. 7510-7522
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Tidskriftsartikel (refereegranskat)abstract
- Hydroxyaryl alkyl tellurides are effective antioxidants both in organic solution and aqueous biphasic systems. They react by an unconventional mechanism with ROO. radicals with rate constants as high as 107M1s1 at 303K, outperforming common phenols. The reactions proceed by oxygen atom transfer to tellurium followed by hydrogen atom transfer to the resulting RO. radical from the phenolic OH. The reaction rates do not reflect the electronic properties of the ring substituents and, because the reactions occur in a solvent cage, quenching is more efficient when the OH and TeR groups have an ortho arrangement. In the presence of thiols, hydroxyaryl alkyl tellurides act as catalytic antioxidants towards both hydroperoxides (mimicking the glutathione peroxidases) and peroxyl radicals. The high efficiency of the quenching of the peroxyl radicals and hydroperoxides could be advantageous under normal cellular conditions, but pro-oxidative (thiol depletion) when thiol concentrations are low.
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| 8. |
- Andersson, Johanna, 1983, et al.
(författare)
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AT-Specific DNA Binding of Binuclear Ruthenium Complexes at the Border of Threading Intercalation
- 2010
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Ingår i: Chemistry - A European Journal. - : Wiley. - 1521-3765 .- 0947-6539. ; 16:36, s. 11037-11046
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Tidskriftsartikel (refereegranskat)abstract
- The binuclear ruthenium complex [mu-bidppz(phen)(4)Ru-2](4+) has been extensively studied since the discover}, of its unusual threading intercalation interaction with DNA, a binding mode with extremely slow binding and dissociation kinetics. The complex has been shown to be selective towards long stretches of alternating AT base pairs, which makes it interesting, for example, as a model compound for anti-malaria drugs due to the high AT content of the genome of the malaria parasite P falciparum. We have investigated the effect of bridging ligand structure on threading intercalation ability and found that length and rigidity as well as the size of the intercalated ring system are all factors that affect the rate and selectivity of the threading intercalation. In particular, we discovered a new DNA-threading compound, [mu-dppzip(phen)(4)Ru-2](4+) which appears to be just at the border of being capable of threading intercalation and displays even greater selectivity for AT-DNA than the parent compound, [mu-bidppz(phen)(4)Ru-2](4+).
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| 9. |
- Ankner, Tobias, et al.
(författare)
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Palladium- and Nickel-Catalyzed Alkenylation of Enolates
- 2013
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 19:6, s. 1858-1871
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Forskningsöversikt (refereegranskat)abstract
- Transition-metal-catalyzed alkenylation of enolates provides a direct method to synthesize broadly useful ,-unsaturated carbonyl compounds from the corresponding carbonyl compound and alkenyl halides. Despite being reported in the early seventies, this reaction class saw little development for many years. In the past decade, however, efforts to develop this reaction further have increased considerably, and many research groups have reported efficient coupling protocols, including enantioselective versions. These reactions most commonly employ palladium catalysts, but there are also some important reports using nickel. There are many examples of this powerful transformation being used in the synthesis of complex natural products.
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| 10. |
- Aramburo, Luis R., et al.
(författare)
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The Porosity, Acidity, and Reactivity of Dealuminated Zeolite ZSM-5 at the Single Particle Level : The Influence of the Zeolite Architecture
- 2011
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 17:49, s. 13773-13781
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Tidskriftsartikel (refereegranskat)abstract
- A combination of atomic force microscopy (AFM), high-resolution scanning electron microscopy (HR-SEM), focused-ion-beam scanning electron microscopy (FIB-SEM), X-ray photoelectron spectroscopy (XPS), confocal fluorescence microscopy (CFM), and UV/Vis and synchrotron-based IR microspectroscopy was used to investigate the dealumination processes of zeolite ZSM-5 at the individual crystal level. It was shown that steaming has a significant impact on the porosity, acidity, and reactivity of the zeolite materials. The catalytic performance, tested by the styrene oligomerization and methanol-to-olefin reactions, led to the conclusion that mild steaming conditions resulted in greatly enhanced acidity and reactivity of dealuminated zeolite ZSM-5. Interestingly, only residual surface mesoporosity was generated in the mildly steamed ZSM-5 zeolite, leading to rapid crystal coloration and coking upon catalytic testing and indicating an enhanced deactivation of the zeolites. In contrast, harsh steaming conditions generated 550 nm mesopores, extensively improving the accessibility of the zeolites. However, severe dealumination decreased the strength of the Bronsted acid sites, causing a depletion of the overall acidity, which resulted in a major drop in catalytic activity.
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| 11. |
- Arkhypchuk, Anna I., et al.
(författare)
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Oxaphospholes and Bisphospholes from Phosphinophosphonates and alpha,beta-Unsaturated Ketones
- 2013
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 19:41, s. 13692-13704
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Tidskriftsartikel (refereegranskat)abstract
- The reaction of a {W(CO)(5)}-stabilized phosphinophosphonate 1, (CO)(5)WPH(Ph)P(O)(OEt)(2), with ethynyl- (2a-f) and diethynylketones (7-11, 18, and 19) in the presence of lithium diisopropylamide (LDA) is examined. Lithiated 1 undergoes nucleophilic attack in the Michael position of the acetylenic ketones, as long as this position is not sterically encumbered by bulky (iPr)(3)Si substituents. Reaction of all other monoacetylenic ketones with lithiated 1 results in the formation of 2,5-dihydro-1,2-oxaphospholes 3 and 4. When diacetylenic ketones are employed in the reaction, two very different product types can be isolated. If at least one (Me)(3)Si or (Et)(3)Si acetylene terminus is present, as in 7, 8, and 19, an anionic oxaphosphole intermediate can react further with a second equivalent of ketone to give cumulene-decorated oxaphospholes 14, 15, 24, and 25. Diacetylenic ketones 10 and 11, with two aromatic acetylene substituents, react with lithitated 1 to form exclusively ethenyl-bridged bisphospholes 16 and 17. Mechanisms that rationalize the formation of all heterocycles are presented and are supported by DFT calculations. Computational studies suggest that thermodynamic, as well as kinetic, considerations dictate the observed reactivity. The calculated reaction pathways reveal a number of almost isoenergetic intermediates that follow after ring opening of the initially formed oxadiphosphetane. Bisphosphole formation through a carbene intermediate G is greatly favored in the presence of phenyl substituents, whereas the formation of cumulene-decorated oxaphospholes is more exothermic for the trimethylsilyl-containing substrates. The pathway to the latter compounds contains a 1,3-shift of the group that stems from the acetylene terminus of the ketone substrates. For silyl substituents, the 1,3-shift proceeds along a smooth potential energy surface through a transition state that is characterized by a pentacoordinated silicon center. In contrast, a high-lying transition state TS(E-F)(R=Ph) of 37kcalmol(-1) is found when the substituent is a phenyl group, thus explaining the experimental observation that aryl-terminated diethynylketones 10 and 11 exclusively form bisphospholes 16 and 17.
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| 12. |
- Arkhypchuk, Anna I., et al.
(författare)
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Redox Switching in Ethenyl- Bridged Bisphospholes
- 2014
-
Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 20:49, s. 16083-16087
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Tidskriftsartikel (refereegranskat)abstract
- A 2e(-)/2H(+) redox platform has been implemented in the ethenyl-bridged bisphosphol-3-ol 1 to afford the first phospholes that feature chemically reversible oxidations. Oxidation of the title compounds to the corresponding bisphosphol-3-one 2 leads to a change in conjugation topology and a concomitant hypsochromic shift of the lowest-energy absorption maximum by 100nm. Electrochemical oxidation proceeds without any detectable intermediates, whereas the deprotonated form of 1 can be observed in an aprotic medium during the reduction of 2. This dianionic intermediate 3 is characterized by end absorptions that are bathochromically shifted by circa 200nm compared to those of 2.
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| 13. |
- Artacho Ruiz, Josep, et al.
(författare)
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Twisted Amide Analogues of Tröger's Base.
- 2012
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Ingår i: Chemistry: A European Journal. - : Wiley. - 1521-3765 .- 0947-6539. ; 18:4, s. 1038-1042
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Tidskriftsartikel (refereegranskat)abstract
- Let's do the twist: The first twisted bis-amide is obtained by the benzylic oxidation of Tröger's base (TB). Kinetic studies of its acidic hydrolysis reveal that the hydrolysis is to a large extent funneled through doubly protonated species.
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| 14. |
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| 15. |
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| 16. |
- Bah, Juho, et al.
(författare)
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Carbocations as Lewis Acid Catalysts in Diels-Alder and Michael Addition Reactions
- 2014
-
Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 20:4, s. 1066-1072
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Tidskriftsartikel (refereegranskat)abstract
- In general, Lewis acid catalysts are metal-based compounds that owe their reactivity to a low-lying empty orbital. However, one potential Lewis acid that has received negligible attention as a catalyst is the carbocation. We have demonstrated the potential of the carbocation as a highly powerful Lewis acid catalyst for organic reactions. The stable and easily available triphenylmethyl (trityl) cation was found to be a highly efficient catalyst for the Diels-Alder reaction for a range of substrates. Catalyst loadings as low as 500ppm, excellent yields, and good endo/exo selectivities were achieved. Furthermore, by changing the electronic properties of the substituents on the tritylium ion, the Lewis acidity of the catalyst could be tuned to control the outcome of the reaction. The ability of this carbocation as a Lewis acid catalyst was also further extended to the Michael reaction.
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| 17. |
- Bai, Linyi, et al.
(författare)
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Iron( III)-Quantity-Dependent Aggregation-Dispersion Conversion of Functionalized Gold Nanoparticles
- 2014
-
Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 20:14, s. 4032-4037
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Tidskriftsartikel (refereegranskat)abstract
- Developing gold nanoparticles (AuNPs) with well-designed functionality is highly desirable for boosting the performance and versatility of inorganic-organic hybrid materials. In an attempt to achieve ion recognition with specific signal expressions, we present here 4-piperazinyl-1,8-naphthalimide-functionalized AuNPs for the realization of quantitative recognition of Fe-III ions with dual (colorimetric and fluorescent) output. The research takes advantage of 1)quantity-controlled chelation-mode transformation of the piperazinyl moiety on the AuNPs towards Fe-III, thereby resulting in an aggregation-dispersion conversion of the AuNPs in solution, and 2)photoinduced electron transfer of a naphthaimide fluorophore on the AuNPs, thus leading to reversible absorption and emission changes. The functional AuNPs are also responsive to pH variations. This strategy for realizing the aggregation-dispersion conversion of AuNPs with returnable signal output might exhibit application potential for advanced nanoscale chemosensors.
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| 18. |
- Bantreil, Xavier, et al.
(författare)
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γ- and δ-lactams through palladium-catalyzed intramolecular allylic alkylation: enantioselective synthesis, NMR Investigation, and DFT rationalization.
- 2011
-
Ingår i: Chemistry - A European Journal. - : Wiley. - 1521-3765 .- 0947-6539. ; 17:10, s. 2885-96
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Tidskriftsartikel (refereegranskat)abstract
- The Pd-catalyzed intramolecular allylic alkylation of unsaturated amides to give γ- and δ-lactams has been studied in the presence of chiral ligands. Ligand (R)-3,5-tBu-MeOBIPHEP (MeOBIPHEP = 6,6'-dimethoxybiphenyl-2,2-diyl)bis(diphenylphosphine)) afforded the best results and allowed the cyclization reactions to take place in up to 94:6 enantiomeric ratio. A model Pd-allyl complex has been prepared and studied through NMR spectroscopic analysis, which provided insight into the processes responsible for the observed enantiomeric ratios. DFT studies were used to characterize the diastereomeric reaction pathways. The calculated energy differences were in good agreement with the experimentally observed enantiomeric ratios.
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| 19. |
- Bartoszewicz, Agnieszka, 1983-, et al.
(författare)
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A Highly Active Bifunctional Iridium Complex with an Alcohol/Alkoxide-Tethered N-Heterocyclic Carbene for Alkylation of Amines with Alcohols
- 2012
-
Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 18:45, s. 14510-14519
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Forskningsöversikt (refereegranskat)abstract
- A series of new iridium(III) complexes containing bidentate N-heterocyclic carbenes (NHC) functionalized with an alcohol or ether group (NHC?OR, R=H, Me) were prepared. The complexes catalyzed the alkylation of anilines with alcohols as latent electrophiles. In particular, biscationic IrIII complexes of the type [Cp*(NHC-OH)Ir(MeCN)]2+2[BF4-] afforded higher-order amine products with very high efficiency; up to >99?% yield using a 1:1 ratio of reactants and 12.5 mol?% of Ir, in short reaction times (216 h) and under base-free conditions. Quantitative yields were also obtained at 50?degrees C, although longer reaction times (4860 h) were needed. A large variety of aromatic amines have been alkylated with primary and secondary alcohols. The reactivity of structurally related iridium(III) complexes was also compared to obtain insights into the mechanism and into the structure of possible catalytic intermediates. The IrIII complexes were stable towards oxygen and moisture, and were characterized by NMR, HRMS, single-crystal X-ray diffraction, and elemental analyses.
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| 20. |
- Bartoszewicz, Agnieszka, et al.
(författare)
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Enantioselective Synthesis of Alcohols and Amines by Iridium-Catalyzed Hydrogenation, Transfer Hydrogenation, and Related Processes
- 2013
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 19:23, s. 7274-7302
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Forskningsöversikt (refereegranskat)abstract
- The preparation of chiral alcohols and amines by using iridium catalysis is reviewed. The methods presented include the reduction of ketones or imines by using hydrogen (hydrogenations), isopropanol, formic acid, or formate (transfer hydrogenations). Also dynamic and oxidative kinetic resolutions leading to chiral alcohols and amines are included. Selected literature reports from early contributions to December 2012 are discussed.
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| 21. |
- Bazzicalupi, Carla, et al.
(författare)
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Multimodal Use of New Coumarin-Based Fluorescent Chemosensors: Towards Highly Selective Optical Sensors for Hg2+ Probing
- 2013
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Ingår i: Chemistry - A European Journal. - : Wiley-VCH Verlag. - 0947-6539 .- 1521-3765. ; 19:43, s. 14639-14653
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Tidskriftsartikel (refereegranskat)abstract
- Despite several types of fluorescent sensing molecules have been proposed and examined to signal Hg2+ ion binding, the development of fluorescence-based devices for in-field Hg2+ detection and screening in environmental and industrial samples is still a challenging task. Herein, we report the synthesis and characterization of three new coumarin-based fluorescent chemosensors featuring mixed thia/aza macrocyclic framework as receptors units, that is, ligands L1-L3. These probes revealed an OFF-ON selective response to the presence of Hg2+ ions in MeCN/H2O 4:1 (v/v), which allowed imaging of this metal ion in Cos-7 cells in vitro. Once included in silica core-polyethylene glycol (PEG) shell nanoparticles or supported on polyvinyl chloride (PVC)-based polymeric membranes, ligands L1-L3 can also selectively sense Hg2+ ions in pure water. In particular we have developed an optical sensing array tacking advantage of the fluorescent properties of ligand L3 and based on the computer screen photo assisted technique (CSPT). In the device ligand L3 is dispersed into PVC membranes and it quantitatively responds to Hg2+ ions in natural water samples.
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| 22. |
- Bengtsson, Christoffer, et al.
(författare)
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Asymmetric Synthesis of 2,4,5-Trisubstituted (2)-Thiazolines
- 2013
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 19:30, s. 9916-9922
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Tidskriftsartikel (refereegranskat)abstract
- (2)-Thiazolines are interesting heterocycles that display a wide variety of biological characteristics. They are also common in chiral ligands used for asymmetric syntheses and as synthetic intermediates. Herein, we present asymmetric routes to 2,4,5-trisubstituted (2)-thiazolines. These (2)-thiazolines were synthesized from readily accessible/commercially available ,-unsaturated methyl esters through a Sharpless asymmetric dihydroxylation and an ON acyl migration reaction as key steps. The final products were obtained in good yields with up to 97% enantiomeric excess.
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| 23. |
- Bermejo Gomez, Antonio, et al.
(författare)
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Iridium-Catalyzed Isomerization/Bromination of Allylic Alcohols : Synthesis of alpha-Bromocarbonyl Compounds
- 2014
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 20:34, s. 10703-10709
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Tidskriftsartikel (refereegranskat)abstract
- alpha-Brominated ketones and aldehydes, with two adjacent electrophilic carbon atoms, are highly valuable synthetic intermediates in organic synthesis, however, their synthesis from unsymmetrical ketones is very challenging, and current methods suffer from low selectivity. We present a new, reliable, and efficient method for the synthesis of alpha-bromocarbonyl compounds in excellent yields and with excellent selectivities. Starting from allylic alcohols as the carbonyl precursors, the combination of a 1,3-hydrogen shift catalyzed by iridium(III) with an electrophilic bromination gives alpha-bromoketones and aldehydes in good to excellent yields. The selectivity of the process is determined by the structure of the starting allylic alcohol; thus, alpha-bromoketones formally derived from unsymmetrical ketones can be synthesized in a straightforward and selective manner.
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| 24. |
- Biswas, Srijit, et al.
(författare)
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Atom-Efficient Gold(I)-Chloride-Catalyzed Synthesis of alpha-Sulfenylated Carbonyl Compounds from Propargylic Alcohols and Aryl Thiols : Substrate Scope and Experimental and Theoretical Mechanistic Investigation
- 2013
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 19:52, s. 17939-17950
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Tidskriftsartikel (refereegranskat)abstract
- Gold(I)-chloride-catalyzed synthesis of -sulfenylated carbonyl compounds from propargylic alcohols and aryl thiols showed a wide substrate scope with respect to both propargylic alcohols and aryl thiols. Primary and secondary aromatic propargylic alcohols generated -sulfenylated aldehydes and ketones in 60-97% yield. Secondary aliphatic propargylic alcohols generated -sulfenylated ketones in yields of 47-71%. Different gold sources and ligand effects were studied, and it was shown that gold(I) chloride gave the highest product yields. Experimental and theoretical studies demonstrated that the reaction proceeds in two separate steps. A sulfenylated allylic alcohol, generated by initial regioselective attack of the aryl thiol on the triple bond of the propargylic alcohol, was isolated, evaluated, and found to be an intermediate in the reaction. Deuterium labeling experiments showed that the protons from the propargylic alcohol and aryl thiol were transferred to the 3-position, and that the hydride from the alcohol was transferred to the 2-position of the product. Density functional theory (DFT) calculations showed that the observed regioselectivity of the aryl thiol attack towards the 2-position of propargylic alcohol was determined by a low-energy, five-membered cyclic protodeauration transition state instead of the strained, four-membered cyclic transition state found for attack at the 3-position. Experimental data and DFT calculations supported that the second step of the reaction is initiated by protonation of the double bond of the sulfenylated allylic alcohol with a proton donor coordinated to gold(I) chloride. This in turn allows for a 1,2-hydride shift, generating the final product of the reaction.
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| 25. |
- Biswas, Srijit, et al.
(författare)
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Tandem Pd/Au-Catalyzed Route to alpha-Sulfenylated Carbonyl Compounds from Terminal Propargylic Alcohols and Thiols
- 2014
-
Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 20:8, s. 2159-2163
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Tidskriftsartikel (refereegranskat)abstract
- An efficient and highly atom-economical tandem Pd/Au-catalyzed route to -sulfenylated carbonyl compounds from terminal propargylic alcohols and thiols has been developed. This one-step procedure has a wide substrate scope with respect to substituents at the -position of the alcohol. Both aromatic and aliphatic thiols generated the -sulfenylated carbonyl products in good to excellent yields. A mechanism is proposed in which the reaction proceeds through a Pd-catalyzed regioselective hydrothiolation at the terminal triple bond of the propargyl alcohol followed by an Au-catalyzed 1,2-hydride migration.
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| 26. |
- Björk, Jonas, et al.
(författare)
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Towards Design Rules for Covalent Nanostructures on Metal Surfaces
- 2014
-
Ingår i: Chemistry - A European Journal. - : Wiley-VCH Verlagsgesellschaft. - 0947-6539 .- 1521-3765. ; 20:4, s. 928-934
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Tidskriftsartikel (refereegranskat)abstract
- The covalent molecular assembly on metal surfaces is explored, outlining the different types of applicable reactions. Density functional calculations for on-surface reactions are shown to yield valuable insights into specific reaction mechanisms and trends across the periodic table. Finally, it is shown how design rules could be derived for nanostructures on metal surfaces.
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| 27. |
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| 28. |
- Börjesson, Karl, 1982, et al.
(författare)
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Exploring the Potential of Fulvalene Dimetals as Platforms for Molecular Solar Thermal Energy Storage: Computations, Syntheses, Structures, Kinetics, and Catalysis
- 2014
-
Ingår i: Chemistry - A European Journal. - : Wiley. - 1521-3765 .- 0947-6539. ; 20:47, s. 15587-15604
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Tidskriftsartikel (refereegranskat)abstract
- A study of the scope and limitations of varying the ligand framework around the dinuclear core of FvRu(2) in its function as a molecular solar thermal energy storage framework is presented. It includes DFT calculations probing the effect of substituents, other metals, and CO exchange for other ligands on Delta H-storage. Experimentally, the system is shown to be robust in as much as it tolerates a number of variations, except for the identity of the metal and certain substitution patterns. Failures include 1,1',3,3'-tetra-tert-butyl (4), 1,2,2',3'-tetraphenyl (9), diiron (28), diosmium (24), mixed iron-ruthenium (27), dimolybdenum (29), and di-tungsten (30) derivatives. An extensive screen of potential catalysts for the thermal reversal identified AgNO3-SiO2 as a good candidate, although catalyst decomposition remains a challenge.
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| 29. |
- Carson, Fabian, et al.
(författare)
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Ruthenium Complexation in an Aluminium Metal-Organic Framework and its Application in Alcohol Oxidation Catalysis
- 2012
-
Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 18:48, s. 15337-15344
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Forskningsöversikt (refereegranskat)abstract
- A ruthenium trichloride complex has been loaded into an aluminium metalorganic framework (MOF), MOF-253, by post-synthetic modification to give MOF-253-Ru. MOF-253 contains open bipyridine sites that are available to bind with the ruthenium complex. MOF-253-Ru was characterised by elemental analysis, N2 sorption and X-ray powder diffraction. This is the first time that a Ru complex has been coordinated to a MOF through post-synthetic modification and used as a heterogeneous catalyst. MOF-253-Ru catalysed the oxidation of primary and secondary alcohols, including allylic alcohols, with PhI(OAc)2 as the oxidant under very mild reaction conditions (ambient temperature to 40 degrees C). High conversions (up to >99%) were achieved in short reaction times (13 h) by using low catalyst loadings (0.5 mol% Ru). In addition, high selectivities (>90%) for aldehydes were obtained at room temperature. MOF-253-Ru can be recycled up to six times with only a moderate decrease in substrate conversion.
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| 30. |
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| 31. |
- Chen, Shi-Lu, et al.
(författare)
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How Is Methane Formed and Oxidized Reversibly When Catalyzed by Ni-Containing Methyl-Coenzyme M Reductase?
- 2012
-
Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 18:20, s. 6309-6315
-
Tidskriftsartikel (refereegranskat)abstract
- Ni-containing methyl-coenzyme M reductase (MCR) is capable of catalyzing methane formation and has recently been observed to also be able to catalyze the reverse reaction, the anaerobic oxidation of methane. The forward reaction has been extensively studied theoretically before and was found to consist of two steps. The first step is rate-limiting and the second step was therefore treated at a lower level. For an accurate treatment of the reverse reaction, both steps have to be studied at the same level. In the present paper, the mechanisms for the reversible formation and oxidation of methane catalyzed by MCR have been investigated using hybrid density functional theory with recent developments, in particular including dispersion effects. An active-site model was constructed based on the X-ray crystal structure. The calculations indicate that the MCR reaction is indeed reversible and proceeds via a methyl radical and a Ni-S(CoM) intermediate with reasonable reaction barriers in both directions. In a competing mechanism, the formation of the crucial Ni-methyl intermediate, was found to be strongly endergonic by over 20 kcal?mol-1 (including a barrier) with dispersion and entropy effects considered, and thus would not be reachable in a reasonable time under natural conditions.
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| 32. |
- Cheng, Ming, et al.
(författare)
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Dye-Sensitized Solar Cells Based on a Donor-Acceptor System with a Pyridine Cation as an Electron-Withdrawing Anchoring Group
- 2012
-
Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 18:50, s. 16196-16202
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Tidskriftsartikel (refereegranskat)abstract
- New hemicyanine dyes (CM101, CM102, CM103, and CM104) in which tetrahydroquinoline derivatives are used as electron donors and N-(carboxymethyl)-pyridinium is used as an electron acceptor and anchoring group were designed and synthesized for dye-sensitized solar cells (DSSCs). Compared with corresponding dyes that have cyanoacetic acid as the acceptor, N-(carboxymethyl)-pyridinium has a stronger electron-withdrawing ability, which causes the absorption maximum of dyes to be redshifted. The photovoltaic performance of the DSSCs based on dyes CM101CM104 markedly depends on the molecular structures of the dyes in terms of the n-hexyl chains and methoxyl. The device sensitized by dye CM104 achieved the best conversion efficiency of 7.0?% (Jsc=13.4 mA?cm-2, Voc=704 mV, FF=74.8?%) under AM 1.5 irradiation (100 mW?cm-2). In contrast, the device sensitized by reference dye CMR104 with the same donor but the cyanoacetic acid as the acceptor gave an efficiency of 3.4?% (Jsc=6.2 mA?cm-2, Voc=730 mV, FF=74.8?%). Under the same conditions, the cell fabricated with N719 sensitized porous TiO2 exhibited an efficiency of 7.9?% (Jsc=15.4 mA?cm-2, Voc=723 mV, FF=72.3?%). The dyes CM101CM104 show a broader spectral response compared with the reference dyes CMR101CMR104 and have high IPCE exceeding 90?% from 450 to 580 nm. Considering the reflection of sunlight, the photoelectric conversion efficiency could be almost 100?% during this region.
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| 33. |
- Cheshev, Pavel, et al.
(författare)
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Synthesis and affinity evaluation of a small library of bidentate cholera toxin ligands: towards nonhydrolyzable ganglioside mimics
- 2010
-
Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 16:6, s. 1951-1967
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Tidskriftsartikel (refereegranskat)abstract
- A small library of nonhydrolyzable mimics of GM1 ganglioside, featuring galactose and sialic acid its pharmacophoric carbohydrate residues,, was synthesized and tested. All compounds were synthesized from readily available precursors using high-performance reactions, including click chemistry protocols, and avoiding O-glycosidic bonds. Sonic of the most active molecules also feature a point of further derivatization that can be used for conjugation will, polyvalent aglycons. Their affinity towards cholera toxin was assessed by weak affinity chromatography, which allowed a systematic evaluation and selection of the best candidates. Affinity could be enhanced up to one or two orders of magnitude over the affinity of the individual pharmacophoric sugar residues.
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| 34. |
- Chorell, Erik, et al.
(författare)
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Design and Synthesis of Fluorescent Pilicides and Curlicides : Bioactive Tools to Study Bacterial Virulence Mechanisms
- 2012
-
Ingår i: Chemistry - A European Journal. - Berlin : Wiley-VCH Verlagsgesellschaft. - 0947-6539 .- 1521-3765. ; 18:15, s. 4522-4532
-
Tidskriftsartikel (refereegranskat)abstract
- Pilicides and curlicides are compounds that block the formation of the virulence factors pili and curli, respectively. To facilitate studies of the interaction between these compounds and the pili and curli assembly systems, fluorescent pilicides and curlicides have been synthesized. This was achieved by using a strategy based on structure-activity knowledge, in which key pilicide and curlicide substituents on the ring-fused dihydrothiazolo 2-pyridone central fragment were replaced by fluorophores. Several of the resulting fluorescent compounds had improved activities as measured in pili- and curli-dependent biofilm assays. We created fluorescent pilicides and curlicides by introducing coumarin and 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) fluorophores at two positions on the peptidomimetic pilicide and curlicide central fragment. Fluorescence images of the uropathogenic Escherichia coli (UPEC) strain UTI89 grown in the presence of these compounds shows that the compounds are strongly associated with the bacteria with a heterogeneous distribution.
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| 35. |
- Debatin, Franziska, et al.
(författare)
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An Isoreticular Family of Microporous Metal-Organic Frameworks Based on Zinc and 2-Substituted Imidazolate-4-amide-5-imidate : Syntheses, Structures and Properties
- 2012
-
Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 18:37, s. 11630-11640
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Tidskriftsartikel (refereegranskat)abstract
- We report on a new series of isoreticular frameworks based on zinc and 2-substituted imidazolate-4-amide-5-imidate (IFP-14, IFP=imidazolate framework Potsdam) that form one-dimensional, microporous hexagonal channels. Varying R in the 2-substitued linker (R=Me (IFP-1), Cl (IFP-2), Br (IFP-3), Et (IFP-4)) allowed the channel diameter (4.01.7 angstrom), the polarisability and functionality of the channel walls to be tuned. Frameworks IFP-2, IFP-3 and IFP-4 are isostructural to previously reported IFP-1. The structures of IFP-2 and IFP-3 were solved by X-ray crystallographic analyses. The structure of IFP-4 was determined by a combination of PXRD and structure modelling and was confirmed by IR spectroscopy and 1H MAS and 13C CP-MAS NMR spectroscopy. All IFPs showed high thermal stability (345400?degrees C); IFP-1 and IFP-4 were stable in boiling water for 7 d. A detailed porosity analysis was performed on the basis of adsorption measurements by using various gases. The potential of the materials to undergo specific interactions with CO2 was investigated by measuring the isosteric heats of adsorption. The capacity to adsorb CH4 (at 298 K), CO2 (at 298 K) and H2 (at 77 K) at high pressure were also investigated. In situ IR spectroscopy showed that CO2 is physisorbed on IFP-14 under dry conditions and that both CO2 and H2O are physisorbed on IFP-1 under moist conditions.
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| 36. |
- Debela, Ahmed M., et al.
(författare)
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Facile Electrochemical Hydrogenation and Chlorination of Glassy Carbon to Produce Highly Reactive and Uniform Surfaces for Stable Anchoring of Thiolated Molecules
- 2014
-
Ingår i: Chemistry - A European Journal. - : Wiley-VCH Verlagsgesellschaft. - 0947-6539 .- 1521-3765. ; 20:25, s. 7646-7654
-
Tidskriftsartikel (refereegranskat)abstract
- Carbon is a highly adaptable family of materials and is one of the most chemically stable materials known, providing a remarkable platform for the development of tunable molecular interfaces. Herein, we report a two-step process for the electrochemical hydrogenation of glassy carbon followed by either chemical or electrochemical chlorination to provide a highly reactive surface for further functionalization. The carbon surface at each stage of the process is characterized by AFM, SEM, Raman, attenuated total reflectance (ATR) FTIR, X-ray photoelectron spectroscopy (XPS), and electroanalytical techniques. Electrochemical chlorination of hydrogen-terminated surfaces is achieved in just 5 min at room temperature with hydrochloric acid, and chemical chlorination is performed with phosphorus pentachloride at 50 °C over a three-hour period. A more controlled and uniform surface is obtained using the electrochemical approach, as chemical chlorination is observed to damage the glassy carbon surface. A ferrocene-labeled alkylthiol is used as a model system to demonstrate the genericity and potential application of the highly reactive chlorinated surface formed, and the methodology is optimized. This process is then applied to thiolated DNA, and the functionality of the immobilized DNA probe is demonstrated. XPS reveals the covalent bond formed to be a CS bond. The thermal stability of the thiolated molecules anchored on the glassy carbon is evaluated, and is found to be far superior to that on gold surfaces. This is the first report on the electrochemical hydrogenation and electrochemical chlorination of a glassy carbon surface, and this facile process can be applied to the highly stable functionalization of carbon surfaces with a plethora of diverse molecules, finding widespread applications.
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| 37. |
- Deiana, Luca, et al.
(författare)
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Catalytic Asymmetric Aziridination of alpha,beta-Unsaturated Aldehydes
- 2011
-
Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 17:28, s. 7904-7917
-
Tidskriftsartikel (refereegranskat)abstract
- The development, scope, and application of the highly enantioselective organocatalytic aziridination of α,β-unsaturated aldehydes is presented. The aminocatalytic azirdination of α,β-unsaturated aldehydes enables the asymmetric formation of β-formyl aziridines with up to >19:1 d.r. and 99 % ee. The aminocatalytic aziridination of α-monosubstituted enals gives access to terminal α-substituted-α-formyl aziridines in high yields and up to 99 % ee. In the case of the organocatalytic aziridination of disubstituted α,β-unsaturated aldehydes, the transformations were highly diastereo- and enantioselective and give nearly enantiomerically pure β-formyl-functionalized aziridine products (99 % ee). A highly enantioselective one-pot cascade sequence based on the combination of asymmetric amine and N-heterocyclic carbene catalysis (AHCC) is also disclosed. This one-pot three-component co-catalytic transformation between α,β-unsaturated aldehydes, hydroxylamine derivatives, and alcohols gives the corresponding N-tert-butoxycarbonyl and N-carbobenzyloxy-protected β-amino acid esters with ee values ranging from 92-99 %. The mechanisms and stereochemistry of all these catalytic transformations are also discussed.
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| 38. |
- Deiana, Luca, 1982-, et al.
(författare)
-
Catalytic asymmetric aziridination of α,β-unsaturated aldehydes
- 2011
-
Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 17:28, s. 7904-7917
-
Tidskriftsartikel (refereegranskat)abstract
- The development, scope, and application of the highly enantioselective organocatalytic aziridination of α,β-unsaturated aldehydes is presented. The aminocatalytic azirdination of α,β-unsaturated aldehydes enables the asymmetric formation of β-formyl aziridines with up to >19:1 d.r. and 99% ee. The aminocatalytic aziridination of α-monosubstituted enals gives access to terminal α-substituted-α-formyl aziridines in high yields and upto 99% ee. In the case of the organocatalytic aziridination of disubstituted α,β-unsaturated aldehydes, the transformations were highly diastereo- and enantioselective and give nearly enantiomerically pure β-formyl-functionalized aziridine products (99% ee). A highly enantioselective one-pot cascade sequence based on the combination of asymmetric amine and N-heterocycliccarbene catalysis (AHCC) is also disclosed. This one-pot three-component co-catalytic transformation between α,β-unsaturated aldehydes, hydroxylamine derivatives, and alcohols gives the corresponding N-tert-butoxycarbonyl and N-carbobenzyloxy-protected β-amino acid esters with ee values ranging from 92–99%. The mechanisms and stereochemistry of all these catalytic transformations are also discussed.
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| 39. |
- Deng, Youqian, et al.
(författare)
-
Palladium-Catalyzed Oxidative Carbocyclizations
- 2012
-
Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 18:37, s. 11498-11523
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Forskningsöversikt (refereegranskat)abstract
- Palladium-catalyzed oxidative carboncarbon bond-forming annulations, that is, carbocyclization reactions, have recently emerged as efficient and atom-economical routes to carbo- and heterocycles, whereby less functionalized substrates and fewer synthetic steps are needed to obtain a target molecule compared with traditional non-oxidative carboncarbon bond-forming reactions. In this review, the synthetic efforts in palladium-catalyzed oxidative carbocyclization reactions are summarized.
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| 40. |
- Deska, Jan, et al.
(författare)
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Chemoenzymatic dynamic kinetic resolution of axially chiral allenes
- 2010
-
Ingår i: Chemistry - A European Journal. - Weinheim : Wiley-VCH Verlag GmbH & Co. KGaA. - 0947-6539 .- 1521-3765. ; 16:15, s. 4447-4451
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Tidskriftsartikel (refereegranskat)abstract
- Dimeric palladium bromide complexes bearing monodentate N-heterocyclic carbene ligands have been identified as efficient catalysts for the chemoselective racemization of axially chiral allenyl alcohols. In combination with porcine pancreatic lipase as biocatalyst, a dynamic kinetic resolution has been developed, giving access to optically active allenes in good yield and high enantiomeric purity (
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| 41. |
- Dierckx, Anke, 1986, et al.
(författare)
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Quadracyclic Adenine: A Non-Perturbing Fluorescent Adenine Analogue
- 2012
-
Ingår i: Chemistry - A European Journal. - : Wiley. - 1521-3765 .- 0947-6539. ; 18:19, s. 5987-5997
-
Tidskriftsartikel (refereegranskat)abstract
- Fluorescent-base analogues (FBAs) comprise a group of increasingly important molecules for the investigation of nucleic acid structure and dynamics as well as of interactions between nucleic acids and other molecules. Here, we report on the synthesis, detailed spectroscopic characterisation and base-pairing properties of a new environment-sensitive fluorescent adenine analogue, quadracyclic adenine (qA). After developing an efficient route of synthesis for the phosphoramidite of qA it was incorporated into DNA in high yield by using standard solid-phase synthesis procedures. In DNA qA serves as an adenine analogue that preserves the B-form and, in contrast to most currently available FBAs, maintains or even increases the stability of the duplex. We demonstrate that, unlike fluorescent adenine analogues, such as the most commonly used one, 2-aminopurine, and the recently developed triazole adenine, qA shows highly specific base-pairing with thymine. Moreover, qA has an absorption band outside the absorption of the natural nucleobases (>300 nm) and can thus be selectively excited. Upon excitation the qA monomer displays a fluorescence quantum yield of 6.8?% with an emission maximum at 456 nm. More importantly, upon incorporation into DNA the fluorescence of qA is significantly less quenched than most FBAs. This results in quantum yields that in some sequences reach values that are up to fourfold higher than maximum values reported for 2-aminopurine. To facilitate future utilisation of qA in biochemical and biophysical studies we investigated its fluorescence properties in greater detail and resolved its absorption band outside the DNA absorption region into distinct transition dipole moments. In conclusion, the unique combination of properties of qA make it a promising alternative to current fluorescent adenine analogues for future detailed studies of nucleic acid-containing systems.
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| 42. |
- Ding, Aixiang, et al.
(författare)
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Complex-Formation-Enhanced Fluorescence Quenching Effect for Efficient Detection of Picric Acid
- 2014
-
Ingår i: Chemistry - A European Journal. - : Wiley-VCH Verlag. - 0947-6539 .- 1521-3765. ; 20:38, s. 12215-12222
-
Tidskriftsartikel (refereegranskat)abstract
- Amine-functionalized alpha-cyanostilbene derivatives (Z)-2-(4-aminophenyl)-3-(4-butoxyphenyl) acrylonitrile (ABA) and (Z)-3-(4-butoxyphenyl)-2-[4-(butylamino) phenyl] acrylonitrile (BBA) were designed for specific recognition of picric acid (PA), an environmental and biological pollutant. The 1:1 host-guest complexes formed between the chemosensors and PA enhanced fluorescence quenching, thus leading to sensitive and selective detection in aqueous media and the solid phase.
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| 43. |
- Ding, Yubin, et al.
(författare)
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Acid/Base Switching of the Tautomerism and Conformation of a Dioxoporphyrin for Integrated Binary Subtraction
- 2014
-
Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 20:40, s. 12910-12916
-
Tidskriftsartikel (refereegranskat)abstract
- Compared with most of the reported logic devices based on the supramolecular approach, systems based on individual molecules can avoid challenging construction requirements. Herein, a novel dioxoporphyrin DPH22 was synthesized and two of its tautomers were characterized by single-crystal X-ray diffraction studies. Compound DPH22 exhibits multichannel controllable stepwise tautomerization, protonation, and deprotonation processes through interactions with H and F- ions. By using the addition of H+ and F- ions as inputs and UVNis absorption values at.1=412, 510, 562, and 603 nm as outputs, the controlled tautomerism of DPH22 has been successfully used for the construction of an integrated molecular level half-subtractor and comparator. In addition, this acid/base-switched tautomerism is reversible, thus endowing the system with ease of reset and recycling; consequently, there is no need to modulate complicated intermolecular interactions and electron-/chargetransfer processes.
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| 44. |
- Donovan, P., et al.
(författare)
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Unexpected Deformations Induced by Surface Interaction and Chiral Self-Assembly of Co-II-Tetraphenylporphyrin (Co-TPP) Adsorbed on Cu(110): A Combined STM and Periodic DFT Study
- 2010
-
Ingår i: Chemistry - A European Journal. - : Wiley. - 1521-3765 .- 0947-6539. ; 16:38, s. 11641-11652
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Tidskriftsartikel (refereegranskat)abstract
- In a combined scanning tunnelling microscopy (STM) and periodic density functional theory (DFT) study, we present the first comprehensive picture of the energy costs and gains that drive the adsorption and chiral self-assembly of highly distorted Co-II-tetraphenylporphyrin (Co-TPP) conformers on the Cu(110) surface. Periodic, semi-local DFT calculations reveal a strong energetic preference for Co-TPP molecules to adsorb at the short-bridge site when organised within a domain. At this adsorption site, a substantial chemical interaction between the molecular core and the surface causes the porphyrin macrocycle to accommodate close to the surface and in a flat geometry, which induces considerable tilting distortions in the phenyl groups. Experimental STM images can be explained in terms of these conformational changes and adsorption-induced electronic effects. For the ordered structure we unambiguously show that the substantial energy gain from the molecule surface interaction recuperates the high cost of the induced molecular and surface deformations as compared with gas phase molecules. Conversely, singly adsorbed molecules prefer a long-bridge adsorption site and adopt a non-planar, saddle-shape conformation. By using a van der Waals density functional correction scheme, we found that the intermolecular pi-pi interactions make the distorted conformer more stable than the saddle conformer within the organic assembly. These interactions drive supramolecular assembly and also generate chiral expression in the system, pinning individual molecules in a propeller-like conformation and directing their assembly along non-symmetric directions that lead to the coexistence of mirror-image chiral domains. Our observations reveal that a strong macrocycle surface interaction can trigger and stabilise highly unexpected deformations of the molecular structure and thus substantially extend the range of chemistries possible within these systems.
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| 45. |
- Dreiser, Jan, et al.
(författare)
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The Metallofullerene Field-Induced Single-Ion Magnet HoSc2N@C-80
- 2014
-
Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 20:42, s. 13536-13540
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Tidskriftsartikel (refereegranskat)abstract
- The low-temperature magnetic properties of the endohedral metallofullerene HoSc2N@C-80 have been studied by superconducting quantum interference device (SQUID) magnetometry. Alternating current (ac) susceptibility measurements reveal that this molecule exhibits slow relaxation of magnetization in a small applied field with timescales in the order of milliseconds. The equilibrium magnetic properties of HoSc2N@C-80 indicate strong magnetic anisotropy. The large differences in magnetization relaxation times between the present compound and the previously investigated DySc2N@C-80 are discussed.
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| 46. |
- Duan, Lele, et al.
(författare)
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Chemical and Photochemical Water Oxidation Catalyzed by Mononuclear Ruthenium Complexes with a Negatively Charged Tridentate Ligand
- 2010
-
Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 16:15, s. 4659-4668
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Tidskriftsartikel (refereegranskat)abstract
- Two mononuclear ruthenium complexes [RuL(pic)(3)] (1) and [RuL(bpy)(pic)] (2) (H2L = 2,6-pyridinedicarboxylic acid, pic=4-picoline, bpy = 2,2'-bipyridine) have been synthesized and fully characterized. Both complexes could promote water oxidation chemically and photochemically. Compared with other known ruthenium-based water oxidation catalysts using [Ce(NH4)(2)(NO3)(6)] (Ce-IV) as the oxidant in solution at pH 1.0, complex 1 is one of the most active catalysts yet reported with an initial rate of 0.23 turnovers(-1). Under acidic conditions, the equatorial 4-picoline in complex 1 dissociates first. In addition, ligand exchange in 1 occurs when the Rum state is reached. Based on the above observations and MS measurements of the intermediates during water oxidation by 1 using Ce-IV as oxidant, [RuL(pic)(2)(H2O)](+) is proposed as the real water oxidation catalyst.
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| 47. |
- Emanuelsson, Rikard, et al.
(författare)
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Configuration- and Conformation-Dependent Electronic-Structure Variations in 1,4-Disubstituted Cyclohexanes Enabled by a Carbon-to-Silicon Exchange
- 2014
-
Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 20:30, s. 9304-9311
-
Tidskriftsartikel (refereegranskat)abstract
- Cyclohexane, with its well-defined conformers, could be an ideal force-controlled molecular switch if it were to display substantial differences in electronic and optical properties between its conformers. We utilize sigma conjugation in heavier analogues of cyclohexanes (i.e. cyclohexasilanes) and show that 1,4-disubstituted cyclohexasilanes display configuration-and conformation-dependent variations in these properties. Cis- and trans-1,4-bis(trimethylsilylethynyl)-cyclohexasilanes display a 0.11 V difference in their oxidation potentials (computed 0.11 V) and a 0.34 eV difference in their lowest UV absorption (computed difference between first excitations 0.07 eV). This is in stark contrast to differences in the corresponding properties of analogous all-carbon cyclohexanes (computed 0.02 V and 0.03 eV, respectively). Moreover, the two chair conformers of the cyclohexasilane trans isomer display large differences in electronic-structure-related properties. This enables computational design of a mechanically force-controlled conductance switch with a calculated single-molecule ON/OFF ratio of 213 at zero-bias voltage.
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| 48. |
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| 49. |
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| 50. |
- Erdem, Özlen F, et al.
(författare)
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Effect of cyanide ligands on the electronic structure of [FeFe] hydrogenase active-site model complexes with an azadithiolate cofactor
- 2013
-
Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 19:43, s. 14566-14572
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Tidskriftsartikel (refereegranskat)abstract
- A detailed characterization of a close synthetic model of the [2 Fe]H subcluster in the [FeFe] hydrogenase active site is presented. It contains the full primary coordination sphere of the CO-inhibited oxidized state of the enzyme including the CN(-) ligands and the azadithiolate (adt) bridge, [((μ-SCH2 )2 NR)Fe2 (CO)4 (CN)2 ](2-) , R=CH2 CH2 SCH3 . The electronic structure of the model complex in its Fe(I) Fe(II) state was investigated by means of density functional theory (DFT) calculations and Fourier transform infrared (FTIR) spectroscopy. By using a combination of continuous-wave (CW) electron paramagnetic resonance (EPR) and hyperfine sublevel correlation (HYSCORE) experiments as well as DFT calculations, it is shown that, for this complex, the spin density is delocalized over both iron atoms. Interestingly, we found that the nitrogen hyperfine coupling, which represents the interaction between the unpaired electron and the nitrogen at the dithiolate bridge, is slightly larger than that in the analogous complex in which the CN(-) ligands are replaced with PMe3 ligands. This reveals, first, that the CN(-) /PMe3 ligands coordinated to the iron core are electronically coupled to the amine in the adt bridge. Second, the CN(-) ligands in this complex are somewhat stronger σ-donor ligands than the PMe3 ligand, and thereby enable more spin density to be transferred from the Fe core to the adt unit, which might in turn affect the reactivity of the bridging amine.
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