Effect of surfactant phase transition on the inclusion behaviour of an amphiphilised porphyrin derivative

The macroscopic morphology of a micelle biomembrane model strongly affects the aggregation state of an included porphyrin derivative.     

Interaction of a chirally functionalised porphyrin derivative with chiral micellar aggregates

The functionalisation of a porphyrin derivative with a chiral functionality results in a selective interaction with chiral micellar aggregates.     

Spectroscopic Properties and Conformational Features of Short Linear Peptides in Solution: A Fluorescence and Molecular Mechanics Investigation

The ground- and excited-state properties of two conformationally constrained hexapeptides of general formula Boc-Bin-A₁-A₂-T-A₁-A₂-OtBu, where A₁ and A₂ are -aminoisobutyric acid (Aib) or L-alanine (Ala), Bin is an optically pure, axially chiral 1,1-binaphthyl-substituted Aib, and T (Toac) is a stable nitroxide free radical-containing Ac6c analog, were investigated in methanol solution. These peptides are denoted as (R)-Bin/Toac and (S)-Bin/Toac, depending on the chirality of the binaphthyl moiety. Electronic spectra in methanol indicate the occurrence of intramolecular exciton interaction between the naphthyl moieties of Bin, and time-resolved fluorescence measurements show a biexponential decay for both peptides examined. According to infrared (IR) absorption data in the NH stretching frequency region, and to earlier X-ray diffraction results on (S)-Bin/Toac in the crystal state, both (R)-Bin/Toac and (S)-Bin/Toac populate a 3₁₀-helix in solution with opposite screw sense, the helical handedness being determined by the chirality of binaphthyl and not by that of the Ala residues in the main chain. The combination of molecular mechanics calculations with fluorescence decay data indicate that the two observed lifetimes for each peptide arise from two conformations having different interprobe distance and orientation, in which electronic energy transfer from excited Bin to Toac takes place.     

A combined spectroscopic and theoretical study of a series of conformationally restricted hexapeptides carrying a rigid binaphthyl-nitroxide donor-acceptor pair

The structural features of a series of linear hexapeptides of general formula Boc‐B‐A_r‐T‐A_m‐OtBu, where A is L ‐Ala or Aib (α‐aminoisobutyric acid), B is (R)‐Bin, a binaphthyl‐based C^α,α‐disubstituted Gly residue, T is Toac, a nitroxide spin‐labeled C^α,α‐disubstituted Gly, and r+m=4, were investigated in methanol solution by fluorescence, transient absorption, IR and CD spectroscopic studies, and by molecular mechanics calculations. These peptides are denoted as B‐T/r‐m, to emphasize the different position of Toac with respect to that of the Bin fluorophore in the amino acid sequence. The rigidity of the B‐T donor–acceptor pair and of the Aib‐rich backbone allowed us to investigate the influence of the interchromophoric distance and orientation on the photophysics of the peptides examined. The excited state relaxation processes of binaphthyl were investigated by time‐resolved fluorescence and transient absorption experiments. Dynamic quenching of the excited singlet state of binaphthyl by Toac was successfully interpreted by the Förster energy transfer model, provided that the mutual orientation of the chromophores is taken into account. This implies that interconversion among conformational substates, which involves puckering of the Toac piperidine ring, is slow on the time scale of the transfer process, that is slower than 5 ns. By comparison of the experimental and theoretical data, the type of secondary structure (right‐handed 3₁₀ helix) from the B‐T/r‐m peptides in solution was determined; this would not have been achievable by using the CD and NMR data only, as the data are not diagnostic in this case. Static quenching was observed in all peptides examined but B‐T/1‐3, where the effect can be ascribed to a non‐fluorescent complex. Among the computed low‐energy conformers of these peptides, there is one structure exhibiting a NO ^. –naphthalene center‐to‐center distance <6 Å, which might be assigned to this complex. The overall results emphasize the versatility of fluorescence experiments in 3D‐structural studies in solution.     

Transition-Metal Complexes with Bidentate Ligands Spanning trans-Positions. III. Preparation and solution studies of complexes [MX(1)] (M = Cu,Ag and Au; X = anionic ligand; 1 = 2, 11-bis(diphenylphosphinomethyl)benzo[c]phenanthrene)

The preparation of monomeric complexes [MX( 1 )] is reported where M = Cu, Ag, Au; X = I, Cl, NO₃, BF₄ and 1 = 2,11-bis(diphenylphosphinomethyl)benzo[c]phenanthrene. The solution structure of the complexes is discussed on the basis of molecular weight, conductivity and NMR. measurements. In acetonitrile and nitromethane, the nitrate and fluoroborate complexes exist as ionic species [M( 1 )]⁺X^? whereas the halo-complexes are present as equilibrium mixtures of ‘covalent’ and ‘ionic’ forms. All the complexes are associated in CH₂Cl₂-solutions. The values of ¹J show that this association in [Ag(NO₃) ( 1 )] and [Ag(BF₄) ( 1 )] is best described in terms of ion-pairing while that for species [AgX( 1 )] (X = Cl, Br and I) is mainly ‘covalent’ in nature. Evidence is presented for the formation of the complex ion [Ag(CH₃CN)_n( 1 )]⁺ in acetonitrile solution.     

Transition metal complexes with bidentate ligands spanning trans-positions. IV. Preparation and properties of some rhodium and iridium complexes of 2,11-bis(diphenylphosphinomethyl)benzo [c]phenanthrene

The bidentate phosphine 2,11-bis(diphenylphosphinomethyl)benzo [c]phenanthrene ( 1 ) has been used to prepare the mononuclear, square planar complexes trans-[MX(CO)( 1 )] and trans-[M(CO)(CH₃CN)( 1 )][BF₄] (M = Rh, Ir; X = Cl, Br, I, NCS). It is found that the tendency of these complexes to form adducts with CO, O₂ and SO₂ is significantly lower than that of the corresponding Ph₃P complexes. The oxidative-addition reactions of complexes trans-[IrX (CO) ( 1 )] with hydrogen halides give the six-coordinate species [IrHX₂(CO) ( 1 )]. The complexes [IrH₂I (CO) ( 1 )] and [IrH₂L (CO) ( 1 )] [BF₄] (L = CO and CH₃CN) have been obtained from hydrogen and the corresponding substrates. The model compounds trans-[MCl (CO) (Ph₂PCH₂Ph)₂] (M = Rh, Ir), trans-[Ir (CO) (CH₃CN) (Ph₂PCH₂Ph)₂] [BF₄], [IrHCl₂(CO)(Ph₂PCH₂Ph)₂] and [IrH₂(CO)₂(Ph₂PCH₂Ph)₂] [BF₄] have been prepared and their special parameters are compared with those of the corresponding complexes of ligand 1 . The influence of the static requirements of this ligand on the chemistry of its rhodium and iridium complexes is discussed.