Spin-Orbit Charge-Transfer Intersystem Crossing of Compact Naphthalenediimide-Carbazole Electron-Donor-Acceptor Triads.

Compact electron donor-acceptor triads based on carbazole (Cz) and naphthalenediimide (NDI) were prepared to study the spin-orbit charge-transfer intersystem crossing (SOCT-ISC). By variation of the molecular conformation and electron-donating ability of the carbazole moieties, the electronic coupling between the two units was tuned, and as a result charge-transfer (CT) absorption bands with different magnitudes were observed (ε = 4000-18 000 M cm). Interestingly, the triads with NDI attached at the 3-C position or with a phenyl spacer at the position of the Cz moiety, thermally activated delayed fluorescence (TADF) was observed.

Insight into the drastically different triplet lifetimes of BODIPY obtained by optical/magnetic spectroscopy and theoretical computations.

The triplet state lifetimes of organic chromophores are crucial for fundamental photochemistry studies as well as applications as photosensitizers in photocatalysis, photovoltaics, photodynamic therapy and photon upconversion. It is noteworthy that the triplet state lifetime of a chromophore can vary significantly for its analogues, while the exact reason was rarely studied. Herein with a few exemplars of typical BODIPY derivatives, which show triplet lifetimes varying up to 110-fold (1.

Elucidation of the Intersystem Crossing Mechanism in a Helical BODIPY for Low-Dose Photodynamic Therapy.

Intersystem crossing (ISC) of triplet photosensitizers is a vital process for fundamental photochemistry and photodynamic therapy (PDT). Herein, we report the co-existence of efficient ISC and long triplet excited lifetime in a heavy atom-free bodipy helicene molecule. Via theoretical computation and time-resolved EPR spectroscopy, we confirmed that the ISC of the bodipy results from its twisted molecular structure and reduced symmetry.

Photo-induced spin switching in a modified anthraquinone modulated by DNA binding.

An anthraquinone modified with a nitroxide radical and able to intercalate into DNA has been synthesized to obtain a molecule the spin state of which can be manipulated by visible light and DNA binding. The doublet ground state of the molecule can be photo-switched to either a strongly coupled spin state (quartet + doublet), when isolated, or to an uncoupled spin state (triplet and doublet), when bound to DNA. The different spin state that is obtained upon photoexcitation depends on the intercalation of the quinonic core into double-stranded DNA which changes the conformation of the molecule, thereby altering the exchange interaction between the excited state localized on the quinonic core and the nitroxide radical.

Precise determination of the orientation of the transition dipole moment in a Bodipy derivative by analysis of the magnetophotoselection effect.

Magnetophotoselection effects, observed for the lowest triplet state of a boron-dipyrromethene (Bodipy) derivative by time-resolved electron paramagnetic resonance (TR-EPR) spectroscopy, have been exploited to determine with a good precision of about 5° the 3D orientation of the singlet-singlet transition dipole moment (TDM) in the molecular frame. We have shown that the TR-EPR spectrum lineshape, obtained using a polarized laser pulse, is different from that obtained by using depolarized light. We first developed a new model for the simulation of the TR-EPR spectra obtained with polarized light excitation; the model explicitly takes into account the orientation of the TDM in the molecular frame.

Synthesis of Intrinsically Blue-Colored bis-Nitronyl Nitroxide Peptidomimetic Templates and Their Conformational Preferences as Revealed by a Combined Spectroscopic Analysis.

The intrinsically blue-colored Ullman imidazolinyl nitronyl nitroxide (NN) mono-radicals have found various applications, in particular as spin probes and organic magnetic materials. Here, we present the solution-phase synthesis, extensive characterization, and conformational analysis of the first peptidomimetics with two pendant, chiral nitronyl nitroxide free radical units. Two (R)-Aic(NN) residues, where Aic(NN) is 2-amino-5-nitronylnitroxide-indan-2-carboxylic acid, have been inserted at positions i and i+3 of the pentapeptide Boc-(R)-Aic(NN)-(Ala)-(R)-Aic(NN)-Ala-OMe and the hexapeptide Boc-[Ala-(R)-Aic(NN)-Ala]-OMe as well.

Radical-Enhanced Intersystem Crossing in New Bodipy Derivatives and Application for Efficient Triplet-Triplet Annihilation Upconversion.

A long-lived triplet excited state of the well-known fluorophore boron dipyrromethene (Bodipy) was observed for the first time via efficient radical-enhanced intersystem crossing (EISC). The triplet state has been obtained in two dyads in which the Bodipy unit is linked to a nitroxide radical, 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO), with two different length spacers. The photophysical properties were studied with steady-state and time-resolved transient optical spectroscopies and electron spin resonance (cw-ESR and TR-ESR).

Online Quantification of Criegee Intermediates of α-Pinene Ozonolysis by Stabilization with Spin Traps and Proton-Transfer Reaction Mass Spectrometry Detection.

Biogenic alkenes, which are among the most abundant volatile organic compounds in the atmosphere, are readily oxidized by ozone. Characterizing the reactivity and kinetics of the first-generation products of these reactions, carbonyl oxides (often named Criegee intermediates), is essential in defining the oxidation pathways of organic compounds in the atmosphere but is highly challenging due to the short lifetime of these zwitterions. Here, we report the development of a novel online method to quantify atmospherically relevant Criegee intermediates (CIs) in the gas phase by stabilization with spin traps and analysis with proton-transfer reaction mass spectrometry.

Evaluation of the inactivation effect of Triton X-100 on Ebola virus infectivity.

Background: The recent Ebola virus disease outbreak occurred in West Africa since December 2013 highlighted the need of appropriate virus inactivation procedures to be set up to allow the necessary processing of specimens outside BSL-4 facilities and to perform laboratory tests without affecting clinical decisions. For this purpose, international guidelines suggest the pre-treatment of the samples with Triton X-100.

Objectives: Due to the limited scientific evidence about the efficacy of Triton X-100 on enveloped-viruses, the aim of this work was to evaluate the effect of Triton X-100 on the virus infectivity and to establish the optimal conditions for its use.

Cotton functionalized with peptides: characterization and synthetic methods.

Three approaches for the chemical ligation of peptides to cotton fibers are described and compared. This investigation was encouraged by the need to create peptide-decorated natural textiles, furnished with useful properties (e.g.

Self-association of an enantiopure β-pentapeptide in nematic liquid crystals.

Herein, we report for the first time that nematic liquid-crystalline environments drive the reversible self-aggregation of an enantiopure β-pentapeptide into oligomers with a well-defined structure. The peptide contains four (1S,2S)-2-aminocyclopentane carboxylic acid (ACPC) residues and the paramagnetic β-amino acid (3R,4R)-4-amino-1-oxyl-2,2,5,5-tetramethylpyrrolidine-3-carboxylic acid (POAC). The structure of the oligomers was investigated by electron paramagnetic resonance (EPR) spectroscopy, which allowed us to obtain the intermonomer distance distribution in the aggregates as a function of peptide concentration in two nematic liquid crystals, E7 and ZLI-4792.

Time resolved EPR of [70]fullerene monoadducts in the photoexcited triplet state.

Triplet excited states of isomers α, β and γ of N-methyl-[70]fulleropyrrolidine in glassy toluene (T = 120 K) are investigated with Time Resolved EPR (TR-EPR) spectroscopy using pulsed laser photoexcitation. Both the zero field splitting (ZFS) parameters D, E and the anisotropic triplet population rates are measured. Results reveal a strong dependence of the triplet state wavefunction on the position (α, β or γ) of the pyrrolidine addend with respect to the pole of the [70]fullerene unit.

Synthesis and preliminary conformational analysis of TOAC spin-labeled analogues of the medium-length peptaibiotic tylopeptin B.

A set of analogues of the 14-residue peptaibol tylopeptin B, containing the stable free-radical 4-amino-1-oxyl-2,2,6,6,-tetramethylpiperidine-4-carboxylic acid (TOAC) at one or two selected positions, was synthesized by the solid-phase methodology. A solution conformational analysis performed by FTIR absorption and CD suggests that, in membrane-mimicking solvents, the labeled tylopeptin B analogues preserve the helical propensity of the parent peptide, with a preference for the α-helix or the 3(10) -helix type depending upon the nature of the solvent. In aqueous environment, the spin-labeled analogues present a higher content of helical conformation as a consequence of the strong helix promoter effect of the conformationally constrained TOAC residue.

Synthesis and conformational characterisation of hexameric β-peptide foldamers by using double POAC spin labelling and cw-EPR.

A selected set of terminally protected β-hexapeptides, each containing two nitroxide-based (3R,4R)-4-amino-1-oxyl-2,2,5,5-tetramethylpyrrolidine-3-carboxylic acid (POAC) residues combined with four (1S,2S)-2-aminocyclopentane-1-carboxylic acid (ACPC) residues, was synthesised by using solution methods and was fully characterised. The two POAC residues are separated in the sequences by different numbers of intervening ACPC residues. The conformational features of the doubly spin-labelled β-hexapeptides were examined in chloroform by FTIR absorption and continuous-wave electron paramagnetic resonance spectroscopic techniques.

Time-resolved EPR observation of synthetic eumelanin-superoxide radical pairs.

TR-EPR spectra of UV irradiated synthetic eumelanin in equilibrium with air oxygen, reveal the formation of melanin-superoxide radical pairs and allow to determine both the electron dipolar interaction D and the exchange interaction J between the two radicals.

Homoleptic complexes of cobalt(0) and nickel(0,I) with 1,1'-bis(diphenylphosphino)ferrocene (dppf): synthesis and characterization.

Reduction of Co(dppf)Cl2 with 2 equiv of sodium naphthalenide in THF, in the presence of dppf, affords the homoleptic complex Co(dppf)2, 1, isolated in 65% yield as a brick red solid, extremely air sensitive. In solution, under inert atmosphere, 1 slowly decomposes into Co and dppf, following a first-order kinetic law (t1/2 = 21 h at 22 degrees C). Similarly to the Rh and Ir congeners, 1 undergoes a one-electron reversible reduction to [Co(dppf)2]-.

Interaction of 7-azatryptophan and beta-(1-azulenyl)-alanine with a nitroxyl radical.

Aal and 7-Atrp, quasi-isosteric with Trp, have been inserted together with a TOAC residue in two 3(10)-helical, model hexapeptides. The interaction of photoexcited AA1 and 7-Atrp with the nitroxide group of TOAC was investigated by time resolved EPR. Both peptides showed nitroxide spin polarized signals revealing that an intramolecular interaction takes places between the excited chromophore and the free radical moiety.

An interaction between apo C-III variants and protease inhibitors contributes to high triglyceride/low HDL levels in treated HIV patients.

Background: Long-term therapy with protease inhibitors (PI) is associated with hypertriglyceridaemia, low high-density lipoprotein (HDL) levels and accumulation of apolipoprotein (apo) E- and apo C-III-containing lipoproteins.

Objectives: To evaluate the impact, on this dyslipaemic phenotype, of three polymorphisms of the apo C-III gene: two on an insulin response element and one in the 3'-region. Apo E genotypes were evaluated also.

Interaction between TOAC free radical and photoexcited triplet chromophores linked to peptide templates.

The intramolecular quenching of photoexcited triplet states by free radicals linked to peptide templates was studied by time-resolved electron paramagnetic resonance (EPR) with pulsed laser excitation. The systems investigated are 3(10)-helix forming peptides, having in the amino acid sequence the free radical 2,2,6,6-tetramethylpiperidine-1-oxyl-4-amino-4-carboxylic acid (TOAC) and a triplet precursor, such as Bin, Bpa, or Trp, incorporated at different relative positions. Upon interaction with the excited triplet the TOAC radical spin sublevel populations assume values that differ from the Boltzmann equilibrium values.

CIDEP effects of intramolecular quenching of singlet and triplet excited states by nitroxide radicals in oligopeptides: a potentially useful new method for investigating peptide secondary structures in solution.

Two hexapeptides, each bearing one photoactive alpha-amino acid (Bin or Bpa) and one nitroxide-containing TOAC residue, have been synthesized and fully characterized. FT-IR absorption measurements indicate that a 3(10)-helical conformation is adopted by these peptides in solution. As two amino acid units separate the photoactive residue from TOAC in the peptide sequences, the two moieties face each other at a distance of about 6 A after one complete turn of the ternary helix.

Aluminum (III) induces alterations on the physical state of the erythrocytic membrane: an ESR evaluation.

The action of aluminum [Al(III)] as Al(acac)3 on erythrocytes causes biophysical effects such as osmotic fragility and echino-acanthocytes formation. In this paper, we present these effects in terms of variation of membrane fluidity, together with findings regarding conformational modifications of membrane proteins consequent to Al(III) exposure, as well as the effects on the mobility of the membrane protein bound sialic acid. To this end, we utilized ESR measurements of rabbits and humans erythrocytic ghosts after probing or labeling with suitable stable radicals used as spin probes or labels.

Synthesis and conformational studies of peptides containing TOAC, a spin-labelled C alpha, alpha-disubstituted glycine.

A variety of host L-alanine homo-peptides (to the pentamer) containing one or two spin-labelled TOAC (2,2,6,6-tetramethylpiperidine-1-oxyl-4-amino-4-carboxylic acid) residues were synthesized by solution methods and fully characterized. The conformational features of the terminally blocked, doubly spin-labelled TOAC-(Ala)2-TOAC-Ala-pentapeptide were examined in the crystal state by X-ray diffraction and in solution using a combination of techniques (Fourier transform infrared, circular dichroism, cyclic voltammetry and electron spin resonance) in comparison with singly labelled shorter peptides. The 3(10)-helical structure of the pentapeptide, promoted by the two C alpha, alpha-disubstituted glycines under favourable experimental conditions, allows an interaction to take place between the two nitroxide TOAC side chains spaced by one turn of the helix.