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[en] Recently enhanced one-color two-photon (1+1) ionization spectra of jet-cooled methylamines (CH_3NH_2 and CH_3ND_2) reveal the vibrational structures of these molecules in predissociative ∼A states. Rotational fine structure is clearly resolved for CH_3ND_2 at the origin and first wagging vibrational level in the excited state. The spectra line-width becomes homogeneously broadened to give only vibrationally resolved spectra features for the higher vibrational energy levels of CH_3ND_2 (∼A). From the spectral analysis of the ∼A-X transition of CH_3ND_2, it is found that the methylmoiety rotates freely about the C-N axis with respect to the amino group in the ∼A states, indicating that the removal of an electron from the nonbonding orbital of N is responsible for the free internal rotation. Vibrational levels are only barely resolved in the ∼A-X excitation spectrum of CH_3NH_2 due to severe homogeneous line-broad ing, indicating ultra-short lifetimes of ∼0.4 ps predissociating CH_3NH_2 molecules in the ∼A states. Spectral interpretation of the ∼A-X excitation spectrum of CH_3NH_2 is carried out by the comparison with that of CH_3HD_2, giving the confirmative vibrational assignment of methylamines in the ∼A states for the first time. The dramatic difference of (CH_3NH_2 and CH_3ND_2) in their lifetimes in ∼A states suggests that the major dissociation channel of the excited methylamine may be the N-H (or D) bond dissociation.
[en] The charge-transfer interaction between an aromatic amine (p-toluidine) and a halogen (iodine) is investigated in different solvents. The effects of the solvent dielectric constant, of the ionic strength and of the light absorbed on the transformation of the intermediate 'outer' complex into a polar 'inner' structure are studied. An overall reaction mechanism is suggested. (Author)
[en] In this work, X-ray crystallography was used to examine ligand complexes of spermidine synthase from the malaria parasite Plasmodium falciparum (PfSpdS). The enzymes of the polyamine-biosynthesis pathway have been proposed to be promising drug targets in the treatment of malaria. Spermidine synthase (SpdS; putrescine aminopropyltransferase) catalyzes the transfer of the aminopropyl moiety from decarboxylated S-adenosylmethionine to putrescine, leading to the formation of spermidine and 5′-methylthioadenosine (MTA). In this work, X-ray crystallography was used to examine ligand complexes of SpdS from the malaria parasite Plasmodium falciparum (PfSpdS). Five crystal structures were determined of PfSpdS in complex with MTA and the substrate putrescine, with MTA and spermidine, which was obtained as a result of the enzymatic reaction taking place within the crystals, with dcAdoMet and the inhibitor 4-methylaniline, with MTA and 4-aminomethylaniline, and with a compound predicted in earlier in silico screening to bind to the active site of the enzyme, benzimidazol-(2-yl)pentan-1-amine (BIPA). In contrast to the other inhibitors tested, the complex with BIPA was obtained without any ligand bound to the dcAdoMet-binding site of the enzyme. The complexes with the aniline compounds and BIPA revealed a new mode of ligand binding to PfSpdS. The observed binding mode of the ligands, and the interplay between the two substrate-binding sites and the flexible gatekeeper loop, can be used in the design of new approaches in the search for new inhibitors of SpdS
[en] A conformational analysis of the benzylidene-aniline, stilbene and azobenzene isoelectronic molecules has been carried out using the INDO and MNDO methods. The potential energy curves obtained with different geometric parameters are compared: the experimental values determined in the gas phase are only partly accounted for with the two methods. In order to understand these failures, the different terms contributing to the energy calculation are discussed (π-π and n-π conjugations, steric interactions) for the three molecules. It appears that each method is more sensitive to one term: the n-π conjugation is favoured in the INDO method, while the steric interaction is favoured in MNDO. (orig.)
[en] The multiphoton ionization and photoacoustic signals from aniline have been detected as a function of time delay between two laser pulses of different wavelength. The first pulse excited the S0 → S1 0--0 transition. The second pulse either excited S1 to a higher singlet state, or a triplet state produced by intersystem crossing to a higher triplet state, depending on the time delay between pulses. Both ionization and dissociation processes are observed. By varying the conditions of excitation it appears that a given amount of energy can be selectively channeled almost exclusively into either ionization or dissociation pathways. The results are explained using a simple Franck--Condon factor model