Construction of a Highly Sensitive Thiol-Reactive AIEgen-Peptide Conjugate for Monitoring Protein Unfolding and Aggregation in Cells.

Impairment of the protein quality control network leads to the accumulation of unfolded and aggregated proteins. Direct detection of unfolded protein accumulation in the cells may provide the possibility for early diagnosis of neurodegenerative diseases. Here a new platform based on a peptide-conjugated thiol-reactive aggregation-induced emission fluorogen (AIEgen), named MI-BTD-P (or D1), for labeling and tracking unfolded proteins in cells is reported. In vitro experiments with model proteins show that the non-fluorescent D1 only becomes highly fluorescent when reacted with the thiol group of free cysteine (Cys) residues on unfolded proteins but not glutathione or folded proteins with buried or surface exposed Cys. When the labeled unfolded proteins form aggregates, D1 fluorescence intensity is further increased, and fluorescence lifetime is prolonged. D1 is then used to measure unfolded protein loads in cells by flow cytometry and track the aggregate formation of the D1 labeled unfolded proteins using confocal microscopy. In combination with fluorescence lifetime imaging technique, the proteome at different folding statuses can be better differentiated, demonstrating the versatility of this new platform. The rational design of D1 demonstrates the outlook of incorporation of diverse functional groups to achieve maximal sensitivity and selectivity in biological samples.

Near-Infrared Electrochemiluminescence from Bistridentate Ruthenium(II) Di(quinoline-8-yl)pyridine Complexes in Aqueous Media.

We report the synthesis, photophysics, electrochemistry and electrochemiluminescence (ECL) of two dqp (dqp=2,6-di(quinoline-8-yl)pyridine) based ruthenium(II) complexes, bearing either a n-butyl ester (1) or the corresponding carboxylic acid functionality (2). The complexes were prepared from [Ru(dqp)(MeCN)3 ][PF6 ]2 by reaction with the dqp precursor using microwave irradiation. In both cases, photoluminescence spectra present strong 3 MLCT-based red/near-infrared (NIR) emissions centred at about 710 nm. The photoluminescence quantum yields were 6.1 % and 1.8 % for 1 and 2 respectively while the excited state lifetimes were 3.60 µs and 2.37 µs. Both complexes are ECL active, although ECL efficiency (ΦECL ) of 1 was substantially higher than 2, due to its more favourable electrochemical properties. Importantly, 1 also gave strong ECL in aqueous media, which is rare for near-infrared emitters. The results suggest the possibility of very interesting ECL sensing applications for this class of emitter in biological media.

Metathesis Reactions between Heavy d-8 Fluorides and I(III)-Pyridine Complexes.

The reaction between trans-[AuF2(pyridine)2]+ and [PhI(pyridine)2]2+ results in the formation of PhIF2 and [Au(pyridine)4]3+. Investigation of the reaction pathway using model Pd and Pt analogues of the gold complex indicate that the most likely mechanism is attack by the Au-F onto the I(III), rather than a redox process. This demonstrates that the Au(III)-F fragment can behave in a nucleophilic manner even in a relatively electron-poor cationic complex.

Site-Specific Description of the Enhanced Recognition Between Electrogenerated Nitrobenzene Anions and Dihomooxacalix[4]arene Bidentate Ureas.

Electron transfer controlled hydrogen bonding was studied for a series of nitrobenzene derivative radical anions, working as large guest anions, and substituted ureas, including dihomooxacalix[4]arene bidentate urea derivatives, in order to estimate binding constants (Kb) for the hydrogen-bonding process. Results showed enhanced Kb values for the interaction with phenyl-substituted bidentate urea, which is significantly larger than for the remaining compounds, e.g., in the case of 4-methoxynitrobenzene a 28-fold larger Kb value was obtained for the urea bearing a phenyl (Kb ∼ 6888) vs tert-butyl (Kb ∼ 247) moieties. The respective nucleophilic and electrophilic characters of the participant anion radical and urea hosts were parametrized with global and local electrodonating (ω(-)) and electroaccepting (ω(+)) powers, derived from DFT calculations. ω(-) data were useful for describing trends in structure­activity relationships when comparing nitrobenzene radical anions. However, ω(+) for the host urea structures lead to unreliable explanations of the experimental data. For the latter case, local descriptors ωk(+)(r) were estimated for the atoms within the urea region in the hosts [∑kωk(+)(r)]. By compiling all the theoretical and experimental data, a Kb-predictive contour plot was built considering ω(-) for the studied anion radicals and ∑kωk(+)(r) which affords good estimations.

Electrochemical and theoretical analysis of the reactivity of shikonin derivatives: dissociative electron transfer in esterified compounds.

An electrochemical and theoretical analysis of a series of shikonin derivatives in aprotic media is presented. Results showed that the first electrochemical reduction signal is a reversible monoelectronic transfer, generating a stable semiquinone intermediate; the corresponding E(I)° values were correlated with calculated values of electroaccepting power (ω(+)) and adiabatic electron affinities (A(Ad)), obtained with BH and HLYP/6-311++G(2d,2p) and considering the solvent effect, revealing the influence of intramolecular hydrogen bonding and the substituting group at position C-2 in the experimental reduction potential. For the second reduction step, esterified compounds isobutyryl and isovalerylshikonin presented a coupled chemical reaction following dianion formation. Analysis of the variation of the dimensionless cathodic peak potential values (ξ(p)) as a function of the scan rate (v) functions and complementary experiments in benzonitrile suggested that this process follows a dissociative electron transfer, in which the rate of heterogeneous electron transfer is slow (~0.2 cm s(-1)), and the rate constant of the chemical process is at least 10(5) larger.

Nature of electrogenerated intermediates in nitro-substituted nor-ß-lapachones: the structure of radical species during successive electron transfer in multiredox centers.

Electrochemical, spectroelectrochemical, and theoretical studies of the reduction reactions in nor-ß-lapachone derivatives including a nitro redox center showed that reduction of the compounds involves the formation of several radical intermediates, including a biradical dianion resultant from the separate reduction of the quinone and nitro groups in the molecules. Theoretical descriptions of the corresponding Fukui functions f(αα)⁺ and f(ßß)⁺(r) and LUMO densities considering finite differences and frozen core approximations for describing the changes in electron and spin densities of the system allowed us to confirm these results. A description of the potential relationship with the obtained results and biological activity selectivity indexes suggests that both the formation of stable biradical dianion species and the stability of the semiquinone intermediates during further reduction are determining factors in the description of their biological activity.