Effect of Orientation of the Peptide-Bridge Dipole Moment on the Properties of Fullerene–Peptide–Radical Systems (original) (raw)
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Applied Magnetic Resonance, 1997
A sedes of C60 fullerene derivatives containing a nitroxide group has been photoexcited by short LASER pulses in the microwave cavity of a cw-EPR spectrometer. Strongly spin polarized signals have been observed, in glassy matrix as well as in liquid sotution, for both the ground electronic st.ate and the excited quartet state. In the quartet state the excitation resides in the fullerene part and the molecule constitutes a triplet-radical pair with the partner covalently linked. The absorptive or emissive character of the transitions is explained in terms of the mechanism of radicaltriplet interaction producing spin polarization. Opposite initial sign and polarization pattems are observed for molecules with different spacer between nitroxide and fullerene. The time evolution of the relevant sublevel populations is fitted by a kinetic model taking into account quartet deeay constants, quartet and doublet spin-lattice relaxation rates and branching ratios.
Design, synthesis, and characterization of fullerene–peptide–steroid covalent hybrids
Tetrahedron, 2014
The present study reports the synthesis, spectral characterization, self-assembly properties, and preliminary in vitro study of antioxidant capacity of two triple covalent hybrids consisting of fullerene C 60 , peptide, and steroidal moiety. Previously synthesized fulleropyrrolidinic acid and pregnenolone were connected by peptide linker using a multistep DCC/DMAP and/or EDC/HOBT esterification/amidation procedure. The hybrids were characterized by comparative analysis of spectroscopic data obtained from FTIR, UVevis, HRMS, and extensive NMR experiments ( 1 H, 13 C, COSY, HSQC, and HMBC). The selfassembling properties and morphology of triads samples prepared by drop-drying method were examined by scanning electron microscopy (SEM). Preliminary in vitro antioxidant activity was studied by Ferrous ion Oxidation-Xylenol orange (FOX) method.
The sign of the exchange interaction between triplet excited fullerene and nitroxide free radicals
Applied Magnetic Resonance, 2000
The sign of the exchange interaction J in a series of radical triplet pairs (RTPs), formed by a nitroxide free radical and a triplet excited fullerene, has been determined from the spin polarization of time-resolved electron paramagnetic resonance spectra. Radical and fullerene are linked together by covalent bonds in different geometries. It is shown that the sign of J depends on the overlap between the orbital of nitroxide unpaired electron and the LUMO of fullerene, which is singly occupied in the excited triplet state. When the overlap does not vanish, a negative contribution to J arises from the admixing of a charge transfer structure in the wave function of the excited doublet state D of the RTP, which does not take place in the excited quartet state Q. The mixing of D* and Q' states lowers the energy of the former spin state and gives antiferromagnetic coupling.
European Journal of Organic Chemistry, 2011
Inductive and mesomeric effects of the [60]fulleropyrrolidine (Pyr=C 60) and the [60]fullerene (C 60) molecular frameworks have been investigated by linear free energy relationship analyses. The electronic effects of these moieties have been studied by expressly designing [60]fulleropyrrolidine derivative 1, which has a C-H bond α to both a carbonyl group (C-H α) and a C 60 cage. The extent of polarization of such a bond was then used to probe electron-withdrawing perturbation induced by the fullerene sphere. Thermodynamic measurements based on both theoretical and experimental approaches allowed the acidity of ketone 1 to be measured; this resulted in about a 1 ϫ 10 6-fold increase in acidity with respect to that of the structurally correlated acetophenone. Experimental and theoretical kinetic determinations were used [a] Dipartimento di Chimica e Tecnologie del Farmaco,
Chemistry - A European Journal, 2000
Two hexapeptides, each bearing one photoactive a-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 10helical 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 after one complete turn of the ternary helix. Irradiation by a light pulse from an excimer laser populates the excited states localized on the chromophores. An intramolecular interaction between the singlet (Bin) or triplet (Bin and Bpa) excited states and the doublet state of the TOAC nitroxide makes a spin-selective decay pathway possible, that produces transient spin polarization. In addition, in order to determine whether the intramolecular exchange interaction occurs throughbond or through-space, we have prepared linear and cyclic TOAC-Bin dipeptide units. A CIDEP study revealed that a through-space intramolecular interaction is operative. The observation of spin polarization makes the two helical hexapeptides suitable models to test the possibility of application of this novel technique to conformational studies of peptides in solution.
The Journal of Physical Chemistry A, 2003
A series of heptapeptides and one dodecapeptide doubly labeled with a triplet precursor (4′-benzoylphenylalanine) and a nitroxide (4-amino-1-oxyl-2,2,6,6-tetramethylpiperidine-4-carboxylic acid) have been synthesized by solution methods and studied through their FT-IR absorption and time-resolved EPR spectra with UV laser pulse excitation. All of the oligopeptides show EPR nitroxide lines strongly polarized in emission because of the intramolecular interaction between the free radical and the photoexcited triplet. The kinetics of the time evolution of the EPR lines is analyzed to study the radical-triplet interaction in the series of heptapeptides characterized by diverging radical and triplet relative positions in the amino acid sequence.
Bulletin of the Chemical Society of Japan, 2007
Photoinduced intramolecular events of the newly synthesized fullerene-triphenylamine-fullerene (C 60-TPA-C 60) triad, in which the TPA entity was substituted with an electron-donating CH 3 O-group to increase electron-donating ability, were investigated in relation to a C 60-TPA dyad. The molecular orbital calculations showed that the radical cation is located on the TPA entity, whereas the radical anion is located on two C 60 entities in the radical ion pair. The fluorescence intensity of the singlet excited state of C 60 was efficiently quenched by the attached TPA moiety in polar solvents. The quenching pathway involves a charge-separation process from the TPA to the singlet excited state C 60. The lifetimes of the radical ion-pairs for C 60-TPA-C 60 evaluated from nanosecond transient absorption measurements were found to be 600 and 454 ns in benzonitrile and dimethylformamide, respectively. These lifetimes of radical ion-pairs of C 60-TPA-C 60 are longer than those of the C 60-TPA dyad, which reflects the effect of the second C 60 moiety in stabilizing the radical ion-pairs.
International Journal of the Physical Sciences
C 36 is the most important fullerene cage. In this paper, the structural properties of C 36 fullerene interacting with glycine radicals are analyzed through the density functional theory. The radical adsorptions result in modifications on the structural properties of the original fullerene. It was found out that the binding of glycine to C 36 generated a slightly unstable complex. This indicates that fullerene cages might be unable to form stable bindings to glycine radicals. These results are extremely relevant in order to identify the potential applications of functionalized C 36 as drug delivery systems.
The Radical Ion Chemistry of S-Nitrosylated Peptides
2012
The radical ion chemistry of a suite of S-nitrosopeptides has been investigated. Doubly and triply-protonated ions of peptides NYCGLPGEYWLGNDK, NYCGLPGEYWLGNDR, NYCGLP-GERWLGNDR, NACGAPGEKWAGNDK, NYCGLPGEKYLGNDK, NYGLPGCEKWYGNDK and NYGLPGEKWYGCNDK were subjected to electron capture dissociation (ECD), and collisioninduced dissociation (CID). The peptide sequences were selected such that the effect of the site of S-nitrosylation, the nature and position of the basic amino acid residues, and the nature of the other amino acid side chains, could be interrogated. The ECD mass spectra were dominated by a peak corresponding to loss of • NO from the charge-reduced precursor, which can be explained by a modified Utah-Washington mechanism. Some backbone fragmentation in which the nitrosyl modification was preserved was also observed in the ECD of some peptides. Molecular dynamics simulations of peptide ion structure suggest that the ECD behavior was dependent on the surface accessibility of the protonated residue. CID of the S-nitrosylated peptides resulted in homolysis of the S-N bond to form a long-lived radical with loss of • NO. The radical peptide ions were isolated and subjected to ECD and CID. ECD of the radical peptide ions provided an interesting comparison to ECD of the unmodified peptides. The dominant process was electron capture without further dissociation (ECnoD). CID of the radical peptide ions resulted in cysteine, leucine, and asparagine side chain losses, and radical-induced backbone fragmentation at tryptophan, tyrosine, and asparagine residues, in addition to charge-directed backbone fragmentation.
The Journal of Physical Chemistry A, 2001
Nitroxide free radical/[60]fullerene derivative liquid solutions photoexcited by visible laser pulses are investigated by time-resolved EPR. Both radical and triplet excited fullerene spin-polarized EPR signals are observed. Their time evolution is examined in terms of CIDEP effects due to electron spin polarization transfer from the initially polarized triplet to the nitroxide and to spin polarization generated by the radical triplet pair mechanism. Radical and triplet spin relaxation times and rate constants for the processes of polarization transfer and radical triplet pair mechanism are obtained.