Designer Reagents for Mass Spectrometry-Based Proteomics: Clickable Cross-Linkers for Elucidation of Protein Structures and Interactions

We present novel homobifunctional amine-reactive clickable cross-linkers (CXLs) for investigation of three-dimensional protein structures and protein–protein interactions (PPIs). CXLs afford consolidated advantages not previously available in a simple cross-linker, including (1) their small size and cationic nature at physiological pH, resulting in good water solubility and cell-permeability, (2) an alkyne group for bio-orthogonal conjugation to affinity tags via the click reaction for enrichment of cross-linked peptides, (3) a nucleophilic displacement reaction involving the 1,2,3-triazole ring formed in the click reaction, yielding a lock-mass reporter ion for only clicked peptides, and (4) higher charge states of cross-linked peptides in the gas-phase for augmented electron transfer dissociation (ETD) yields. Ubiquitin, a lysine-abundant protein, is used as a model system to demonstrate structural studies using CXLs. To validate the sensitivity of our approach, biotin-azide labeling and subsequent enrichment of cross-linked peptides are performed for cross-linked ubiquitin digests mixed with yeast cell lysates. Cross-linked peptides are detected and identified by collision induced dissociation (CID) and ETD with linear quadrupole ion trap (LTQ)-Fourier transform ion cyclotron resonance (FTICR) and LTQ-Orbitrap mass spectrometers. The application of CXLs to more complex systems (e.g., in vivo cross-linking) is illustrated by Western blot detection of Cul1 complexes including known binders, Cand1 and Skp2, in HEK 293 cells, confirming good water solubility and cell-permeability

Copper and gold cyclic (alkyl)(amino)carbene complexes with sub-microsecond photoemissions: Structure and substituent effects on redox and luminescent properties

Copper and gold halide and pseudo-halide complexes stabilized by methyl-, ethyl- and adamantyl-substituted cyclic (alkyl)(amino)¬carbene (CAAC) ligands are mostly linear monomers in the solid state, without aurophilic Au···Au interactions. (Et2L)CuCl shows the highest photoluminescence quantum yield (PLQY) in the series, 70%. The photoemissions of Me2L and Et2L copper halide complexes show S1 → S0 fluorescence on the ns time scale, in agreement with theory, as well as a minor long-lived emission. Monomeric (Me2L)CuNCS is a white emitter, while dimeric [(Et2L)Cu(µ-NCS)]2 shows intense yellow emission with a PLQY of 49%. The reaction of (AdL)MCl (M = Cu or Au) with phenols ArOH (Ar = Ph, 2,6-F2C6H3, 2,6-Me2C6H3, 3,5-But2C6H3, 2-But-5-MeC6H3, 2-pyridyl), thiophenol, or aromatic amines H2NAr' (Ar' = Ph, 3,5-(CF3)2C6H3, C6F5, 2-py) afforded the corresponding phenolato, thiophenolato and amido complexes. Whereas the emission wavelengths are only marginally affected by the ring substitution pattern, the PL intensities respond sensitively to the presence of substituents in ortho or meta position. In gold aryloxides PL is controlled by steric factors, with strong luminescence in compounds with Au-O-C-C torsion angles <50. Calculations confirm the dependence of oscillator strength on the torsion angle, as well as the inter-ligand charge transfer nature of the emission. The HOMO/LUMO energy levels were estimated based on first reduction and oxidation potentials

Peripheral halo-functionalization in [Cu(N^N)(P^P)]+ emitters: influence on the performances of light-emitting electrochemical cells

A series of heteroleptic [Cu(N^N)(P^P)][PF6] complexes is described in which P^P = bis(2-(diphenylphosphino)phenyl)ether (POP) or 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (xantphos) and N^N = 4,4′-diphenyl-6,6′-dimethyl-2,2′-bipyridine substituted in the 4-position of the phenyl groups with atom X (N^N = 1 has X = F, 2 has X = Cl, 3 has X = Br, 4 has X = I; the benchmark N^N ligand with X = H is 5). These complexes have been characterized by multinuclear NMR spectroscopy, mass spectrometry, elemental analyses and cyclic voltammetry; representative single crystal structures are also reported. The solution absorption spectra are characterized by high energy bands (arising from ligand-centred transitions) which are red-shifted on going from X = H to X = I, and a broad metal-to-ligand charge transfer band with λmax in the range 387–395 nm. The ten complexes are yellow emitters in solution and yellow or yellow-orange emitters in the solid-state. For a given N^N ligand, the solution photoluminescence (PL) spectra show no significant change on going from [Cu(N^N)(POP)]+ to [Cu(N^N)(xantphos)]+; introducing the iodo-functionality into the N^N domain leads to a red-shift in λmaxem compared to the complexes with the benchmark N^N ligand 5. In the solid state, [Cu(1)(POP)][PF6] and [Cu(1)(xantphos)][PF6] (fluoro-substituent) exhibit the highest PL quantum yields (74 and 25%, respectively) with values of τ1/2 = 11.1 and 5.8 μs, respectively. Light-emitting electrochemical cells (LECs) with [Cu(N^N)(P^P)][PF6] complexes in the emissive layer have been tested. Using a block-wave pulsed current driving mode, the best performing device employed [Cu(1)(xantphos)]+ and this showed a maximum luminance (Lummax) of 129 cd m−2 and a device lifetime (t1/2) of 54 h; however, the turn-on time (time to reach Lummax) was 4.1 h. Trends in performance data reveal that the introduction of fluoro-groups is beneficial, but that the incorporation of heavier halo-substituents leads to poor devices, probably due to a detrimental effect on charge transport; LECs with the iodo-functionalized N^N ligand 4 failed to show any electroluminescence after 50 h

Synthesis and (spectro)electrochemistry of mixedvalent diferrocenyl–dihydrothiopyran derivatives

Three novel diferrocenyl complexes were prepared and characterised. 2,2-Diferrocenyl-4,5-dimethyl- 3,6-dihydro-2H-thiopyran (1, sulphide) was accessible by the hetero-Diels–Alder reaction of diferrocenyl thioketone with 2,3-dimethyl-1,3-butadiene. Stepwise oxidation of 1 gave the respective oxides 2,2- diferrocenyl-4,5-dimethyl-3,6-dihydro-2H-thiopyran-1-oxide (2, sulfoxide) and 2,2-diferrocenyl-4,5- dimethyl-3,6-dihydro-2H-thiopyran-1,1-dioxide (3, sulfone), respectively. The molecular structures of 1 and 3 in the solid state were determined by single crystal X-ray crystallography. The oxidation of sulphide 1 to sulfone 3, plays only a minor role on the overall structure of the two compounds. Electrochemical (cyclic voltammetry (= CV), square wave voltammetry (= SWV)) and spectroelectrochemical (in situ UV-Vis/NIR spectroscopy) studies were carried out. The CV and SWV measurements showed that an increase of the sulphur atom oxidation from −2 in 1 to +2 in 3 causes an anodic shift of the ferrocenylbased oxidation potentials of about 100 mV. The electrochemical oxidation of 1–3 generates mixedvalent cations 1+–3+. These monooxidised species display low-energy electronic absorption bands between 1000 and 3000 nm assigned to IVCT (= Inter-Valence Charge Transfer) electronic transitions. Accordingly, the mixed-valent cations 1+–3+ are classified as weakly coupled class II systems according to Robin and Day.Authors (K. K. and G. M.) thank the National Science Centre (Poland) for financial support (Project Maestro-3; Dec-2012/06/ A/ST5/00219) and R. C. thanks the German Federal Ministry of Education and Research (BMBF) for support. The support from the German Academic Exchange Service (DAAD) in the framework of the exchange program “Ostpartnerschaften” is highly appreciated

Highly efficient thermally activated fluorescence of a new rigid Cu(I) complex [Cu(dmp)(phanephos)]+

The rigid [Cu(dmp)(phanephos)]+ complex displays a high luminescence quantum yield of 80% at ambient temperature. In contrast to the long-lived phosphorescence of 240 μs at T < 120 K with a radiative rate of kr = 3 × 103 s−1, the ambient-temperature emission represents a thermally activated delayed fluorescence (DF) with a decay time of only 14 μs and a radiative rate of kr(DF) = 6 × 104 s−1. Evidence for the involvement of the excited singlet state in the emission process is presented. This material has high potential to be applied in efficient OLEDs taking advantage of the singlet harvesting mechanism

Cytotoxic Activities of Bis-cyclometalated Iridium(III) Complexes Containing Chloro-substituted kappa N-2-terpyridines

The synthesis and characterization of two new bis-cyclometalated compounds [Ir(ptpy)(2)(kappa N-2-terpy-C6H4Cl-p)]PF6 [terpy-C6H4Cl-p=4'-(4-chlorophenyl)-2,2':6',2''-terpyridine, (1)], and [Ir(ptpy)(2)(kappa N-2-terpy-Cl)]PF6 [terpy-Cl=4'-chloro-2,2':6',2''-terpyridine, (2);ptpy=2-(p-tolyl)pyridinato)] are described. The molecular structures of compounds 1 and 2 in the crystal were determined by single-crystal X-ray diffraction. 1 crystallized from dichloromethane/methanol/iso-hexane in the monoclinic space group P2/(n) and 2 from the same mixture of solvents in the triclinic space group P(-)1. Photophysical investigations on 1 and 2 revealed broad unstructured luminescence in the red spectral region with the emission maxima in dichloromethane at 620 and 630 nm respectively. To explore cytotoxic properties of compounds 1 and 2, a colorimetric assay (MTT assay) against prominent cancer cell lines, MCF-7 and HT-29, was performed. The determined IC50 values are in the low micromolar range (2-3 mu M). In comparison to cisplatin, the tested complexes 1 and 2 exhibit up to >20-fold (MCF-7) and >40-fold (HT-29) increase in biological activity

Investigation of structure-directing interactions within copper(i)thiocyanate complexes through X-ray analyses and non-covalent interaction (NCI) theoretical approach

Herein, we reported the synthesis of copperIJI) thiocyanate complexes with ortho-pyridinyl carbohydrazones containing a thiophene (L1) or a furyl ring (L2) as a mixture of two different crystals for each compound, linkage isomers of C1N, [CuIJNCS)IJL1)PPh3] and C1S, [Cu(SCN)(L1)PPh3], for L1, whereas monomeric and polymeric structures C2N, [Cu(NCS)(L2)PPh3], and C2P, [–(NCS)Cu(L2)–]n, for L2. Crystallographic information and theoretical calculations, mainly noncovalent interaction reduced density gradient (NCI-RDG) analyses, were pursued to generate a profound understanding of the structure-directing interactions in these complexes. The supramolecular assemblies are first driven by cooperative π⋯π interactions and hydrogen bonds followed by CH⋯π, S⋯S and S⋯π linkages. In the case of the linkage isomers, intermolecular interactions may have a significant role in the formation of the less stable S-bound isomer C1S

Sandwich-Like Encapsulation of a Highly Luminescent Copper(I) Complex

A small molecular weight cationic copper(I) complex showing high luminescence quantum yield based on a thermally activated delayed fluorescence mechanism is immobilized between two 1 nm thin silicate layers. Partial ion exchange of the emitter into a synthetic layered silicate (fluorohectorite) yields an ordered heterostructure with two types of strictly alternating interlayers: a monolayer of the cationic emitter and a monolayer of hydrated Na+ cations. Osmotic swelling of the latter produces dispersions of double-stacks in which the emitter monolayer is encapsulated between two silicate layers. The electrostatic attraction of the emitter interlayer with the oppositely charged silicate layers exerts electrostatic pressure on the emitter. Compared to crystalline salt, rigid confinement for the encapsulated emitter provides improved thermal stability and increased emission quantum yield at ambient temperature. The suspension of delaminated, micrometer-sized double-stacks of 3.9 nm thickness allows for easy solution processing of low-cost optoelectronic devices, such as light-emitting electrochemical cells and organic light-emitting diodes