An electron paramagnetic resonance study of conformational substate distribution in high spin heme-proteins

The electron paramagnetic resonance spectra of high spin ferric horse myoglobin and human hemoglobin have been analyzed by computer simulation in terms of a distribution of the metal ion crystal field energies Δ₁ and Δ₂. The widths of these distributions have been put into relation 0 to the distribution of the conformational substates which may be sampled by the biomolecules during their physiological activity and become eventually arrested at low temperature. These distributions are found to be dependent upon both the solvent used and the cooling history to which the samples were submitted. The results are discussed in connection with the physical analogies displayed by these biomolecules and the glassy systems in general.     

Ladder oligophenothiazines by direct thionation of N-Arylanilino Derivatives

Ladder oligophenothiazines were synthesized by direct catalyzed insertion of elemental sulfur in anilino-substituted phenothiazines and para-oligoanilines. The starting 3- and 3,7-anilino derivatives of phenothiazine were prepared with improved selectivities and yields by new syntheses. The oxidability of the oligomers is discussed.     

Comparison of the reaction pp → K0K0 at rest in hydrogen and deuterium. A test of S-state annihilation dominance

From the comparison of the frequency of antiproton annihilation at rest in two mesons in H₂ and D₂, the dominance of S-wave in $\text{p}\text{p}$ annihilation at rest is confirmed, the P-wave contribution being less than 6% at the 95% confidence level. The apparent discrepancy between the channels $\text{p}\text{p}\text{→}\text{K}{}^0\text{K}{}^0$ and $\text{p}\text{p}\text{→ππ}$ is due to the strong dependence of the annihilation dynamics from the angular momentum.     

Cis-trans photoisomerization of fluorescent-protein chromophores

Photochromic variants of fluorescent proteins are opening the way to a number of opportunities for high-sensitivity regioselective studies in the cellular environment and may even lead to applications in information and communication technology. Yet, the detailed photophysical processes at the basis of photoswitching have not been fully clarified. In this paper, we used synthetic FP chromophores to clarify the photophysical processes associated with the photochromic behavior. In particular, we investigated the spectral modification of synthetic chromophore analogues of wild-type green fluorescent protein (GFP), Y66F GFP (BFPF), and Y66W GFP (CFP) upon irradiation in solutions of different polarities. We found that the cis-trans photoisomerization mechanism can be induced in all the chromophores. The structural assignments were carried out both by NMR measurements and DFT calculations. Remarkably, we determined for the first time the spectra of neutral trans isomers in different solvents. Finally, we calculated the photoconversion quantum yields by absorption measurements under continuous illumination at different times and by a nanosecond laser-flash photolysis method. Our results indicate that cis-trans photoisomerization is a general mechanism of FP chromophores whose efficiency is modulated by the detailed mutant-specific protein environment.     

New 1,3-Disubstituted Benzo[h]Isoquinoline Cyclen-Based Ligand Platform: Synthesis,Eu3+ Multiphoton Sensitization and Imaging Applications

The development of lanthanide-based luminescent probes with a long emission lifetime has the potential to revolutionize imaging-based diagnostic techniques. By a rational design strategy taking advantage of computational predictions, a novel, water-soluble Eu³⁺ complex from a cyclen-based ligand bearing 1,3-disubstituted benzo[h]isoquinoline arms was realized. The ligand has been obtained overcoming the lack of reactivity of position 3 of the isoquinoline moiety. Notably, steric hindrance of the heteroaromatic chromophore allowed selective and stoichiometry-controlled insertion of two or three antennas on the cyclen platform without any protection strategy. The complex bears a fourth heptanoic arm for easy conjugation to biomolecules. This new chromophore allowed the sensitization of the metal center either with one or two photons excitation. The suitability as a luminescent bioprobe was validated by imaging BMI1 oncomarker in lung carcinoma cells following an established immunofluorescence approach. The use of a conventional epifluorescence microscope equipped with a linear structured illumination module disclosed a simple and inexpensive way to image confocally Ln-bioprobes by single photon excitation in the 350–400 nm window, where ordinary confocal systems have no excitation sources.     

Statistical analysis of intensity fluctuations in single molecule SERS spectra

We have investigated the fluctuations of the intensity and the line intermittency in the surface enhanced Raman spectra of a single iron-protoporphyrin IX molecule. A statistical analysis has revealed a high correlation between the intensity of each frequency couple in the spectrum. Removal of the continuum background has led to a suppression of the correlation at those frequencies where no Raman lines are present. Conversely, we have observed the persistence of a strong correlation at the intensities corresponding to the vibrational modes of the molecule. Further evidence of correlation between the intensities and the background signal indicates that the background is involved in the enhancement mechanism. Moreover, analysis of the Raman line intermittency reveals a random activation of the different molecular vibrational modes. These results can be generally put into relationship to the presence of two different contributions to the intensity fluctuations: one, strictly related to the continuum background, and affecting the whole spectrum, and another one which selectively acts on the various vibrational modes of the molecule.     

New Photosensitizers Based on Heteroleptic CuI Complexes and CO2 Photocatalytic Reduction with [NiII(cyclam)]Cl2

Earth-abundant metal complexes have been attracting increasing attention in the field of photo(redox)catalysis. In this work, the synthesis and full characterisation of four new heteroleptic Cu^I complexes are reported, which can work as photosensitizers. The complexes bear a bulky diphosphine (DPEPhos=bis[(2-diphenylphosphino)phenyl] ether) and a diimine chelating ligand based on 1-benzyl-4-(quinol-2′yl)-1,2,3-triazole. Their absorption has a relative maximum in the visible-light region, up to 450 nm. Thus, their use in photocatalytic systems for the reduction of CO₂ with blue light in combination with the known catalyst [Ni^II(cyclam)]Cl₂ was tested. This system produced CO as the main product through visible light (λ=420 nm) with a TON up to 8 after 4 hours. This value is in line with other photocatalytic systems using the same catalyst. Nevertheless, this system is entirely noble-metal free.     

A TEM and XRD study of the SbNbSe3 misfit layer structures

Two new misfit layer structures have been synthesized within the Sb-Nb-Se system. Powder X-ray diffraction and electron microscopy techniques (electron diffraction, HREM, XEDS) have been used to determine the nature of their structure. According to TEM and XEDS data (for more than 15 crystals studied) both phases are monolayer type, i.e. (SbSe)1+delta (NbSe2). Electron microscopy reveals a composite modulated structure that consists of the periodical intergrowth of a pseudotetragonal SbSe layer, denominated as Q, and a pseudohexagonal layer NbSe2, denominated as H. Both layers fit along b, stack along c and do not fit along a (misfit) giving rise to an incommensurate modulation along this direction. The two phases differ in the symmetry of the Q layers being in one case orthorhombic (for delta = 0.17) and monoclinic in the other (for delta = 0.19). After the characterization of the sample by electron microscopy the unit cells of the basic layers could be refined for both phases by powder X-ray diffraction: aQ = 5.824(2) A, bQ = 5.962(5) A, cQ = 23.927(6) A, alpha = 90 degrees, beta = 90 degrees and gamma = 90 degrees and aH = 3.415(5) A, bH = 5.962(6) A,, cH = 11.962(1) A, alpha = 90 degrees, beta = 90 degrees and gamma = 90 degrees for the orthorhombic phase; aQ = 5.844(2) A, bQ = 5.981(1) A, cQ = 23.919(5) A, alpha = 90 degrees, beta = 90 degrees and gamma = 96.00(3)degrees and aH = 3.439(1) A, bH = 5.994(2) A, cH = 11.956(3) A, alpha = 90 degrees, beta = 90 degrees and gamma = 90 degrees for the monoclinic phase. The phase with the monoclinic Q-sublattice often appears as twinned crystals. The more abundant crystals are disordered intergrowths of both monolayer phases.