The rational search for selective anticancer derivatives of the peptide Trichogin GA IV: a multi-technique biophysical approach

Peptaibols are peculiar peptides produced by fungi as weapons against other microorganisms. Previous studies showed that peptaibols are promising peptide-based drugs because they act against cell membranes rather than a specific target, thus lowering the possibility of the onset of multi-drug resistance, and they possess non-coded alpha-amino acid residues that confer proteolytic resistance. Trichogin GA IV (TG) is a short peptaibol displaying antimicrobial and cytotoxic activity. In the present work, we studied thirteen TG analogues, adopting a multidisciplinary approach. We showed that the cytotoxicity is tuneable by single amino-acids substitutions. Many analogues maintain the same level of non-selective cytotoxicity of TG and three analogues are completely non-toxic. Two promising lead compounds, characterized by the introduction of a positively charged unnatural amino-acid in the hydrophobic face of the helix, selectively kill T67 cancer cells without affecting healthy cells. To explain the determinants of the cytotoxicity, we investigated the structural parameters of the peptides, their cell-binding properties, cell localization, and dynamics in the membrane, as well as the cell membrane composition. We show that, while cytotoxicity is governed by the fine balance between the amphipathicity and hydrophobicity, the selectivity depends also on the expression of negatively charged phospholipids on the cell surface

correction an epr study of ampullosporin a a medium length peptaibiotic in bicelles and vesicles

Correction for 'An EPR study of ampullosporin A, a medium-length peptaibiotic, in bicelles and vesicles' by Marco Bortolus et al., Phys. Chem. Chem. Phys., 2016, 18, 749–760

Low Temperature Magnetic Instabilities in Triply Charged Fulleride Polymers

The electronic properties of the C603- polymer in Na2Rb0.3Cs0.7C60 were studied by X-band and high field (109.056 GHz) ESR. They are characteristic of a strongly correlated quasi-one-dimensional metal down to 45 K. On further cooling, a pseudogap of magnetic origin opens at the Fermi level below 45 K with three-dimensional magnetic ordering occurring below TN≈15K, as confirmed by the observation of an antiferromagnetic resonance mode. The Na2Rb1-xCsxC60 family of polymers offers a unique way to chemically control the electronic properties, as the opening of the gap in this system of predominantly itinerant electrons is an extremely sensitive function of the interchain separation

Modern developments and prospects in multifrequency High Field EMR: High Frequency ENDOR spectroscopy

The most detailed information on paramagnetic systems is obtained from studies in single crystals. It is quite obvious the advantage of being able to extract the same amount of information from studies in polycrystalline samples or frozen solutions. Regarding nuclear hyperfine couplings, this is made possible by using ENDOR spectroscopy at X and Q band only in the case of systems with large g tensor anisotropy. The method, based on the selective saturation of different manifolds of molecular orientations, has been and is applied with success by many authors for studying metalloproteins and metalloenzymes. Due to the enhanced orientation selection, ENDOR at much higher field/frequency than X and Q band allows applying the same experimental approach to investigate the important research field of organic and bioorganic radicals with small g tensor anisotropy, even much smaller than that of nitroxide radicals. The present study on an indolinone nitroxide provided evidence about the potential of ENDOR spectroscopy at 220 GHz. In addition to the magnitudes of the proton hyperfine tensors, the orientations of the tensor axes with respect to the g tensor principal system were determined from simulation of the high field ENDOR spectra. The tensor values obtained in this way have a great accuracy, since they represent the set which best reproduce all the ENDOR spectra recorded across the EPR spectrum. Moreover the spectra are characterized by a high degree of orientation selectivity, as proven by the low value (0.3-0.5 mT) of the parameter \uf073 (width of the saturated portion of the EPR spectrum)

Electron nuclear double resonance of the first excited triplet state of trans-stilbene in a diphenylacetylene-TCNB single crystal.

The first excited triplet state of trans-stilbene, contained as an impurity in diphenylacetylene-TCNB single crystal has been investigated by ENDOR spectroscopy. The hyperfine tensors of six pairs of equivalent protons of trans-stilbene have been measured. They show that in this host crystal the trans-stilbene has a centre of symmetry. The isotropic couplings compare well with those of the trans-stilbene radical anion. The calculated dipolar tensors agree with the experimental ones if the trans-stilbene molecule is assumed as planar and the in-plane principal direction x of the zero-field splitting tensor makes an angle of 12\ub0 with the central double bond. With such orientation the trans-stilbene is found to substitute one diphenylacetylene molecule with minimum distortion of the crystal lattice

ENDOR spectra of pyrene excited triplet state in naphtalene-TCNB crystals

none3Triplet state traps, observed on optically excited single crystals of Naphthalene-TCNB doped with Pyrene, have been studied by EPR and ENDOR spectroscopy. The magnetic resonance lines recorded at low temperature (20K) are shown to be due to triplet excitations localized almost completely on a Pyrene molecule. The complete hyperfine tensors of all the protons have been determined. The spin distribution is shown to be distorted in such a way that the triplet Pyrene molecule lacks the in-plane symmetry axes of the ground state molecule. The orientation of the triplet molecule in the crystal lattice and the relative orientation of Pyrene and TCNB are also discussed.noneC. Corvaja; A. Lodolo; A. L. ManieroC., Corvaja; A., Lodolo; Maniero, ANNA LIS

ENDOR SPECTRA OF 2-METHYL-NAPHTHALENE-TCNB TRIPLET TRAP IN NAPHTHALENE-TCNB SINGLE-CRYSTALS

Naphthalene-TCNB charge transfer crystals doped with 2-methyl naphthalene illuminated by visible light give rise to triplet traps which have been identified by EPR and ENDOR spectroscopy as 2-methyl naphthalene-TCNB CT complexes in their first excited triplet state. The complete hyperfine tensors of all the 2-methyl naphthalene protons have been obtained by analysis of the variation of the ENDOR frequencies with the crystal orientation in the magnetic field. The structure of the CT complex, the spin distribution and the CT character are discussed