M.H. Baron

INFLUENCE OF THE ANION AND SOLVENT ON THE ION-PAIR STABILITY FOR (CH3)2CHCH=NH+CH(CH3)2...X- IMINIUM SALTS (X-=CL- OR BF4-). VIBRATIONAL STUDY

Abstract Protonation of the (CH 3 ) 2 C 2′ HC 1′ H = NC 2 H(CH 3 ) 2 non-conjugated aldimine by two different proton donors HCl and HBF 4 is extensively studied by vibrational spectroscopy. The assignments are consistent with a parallel analysis of deuterated derivatives at N, C 1′ and C 2′ sites. There is evidence for an iminium/enaminium equilibrium. Protonation influences the conformation on the C 1′ and N sides of the aldiminium depending on the anion and the physical state of the salts and, for solutions, on the polarity of the solvents. Protonation apparently yields an electronic effect on the C=N bond increasing the double bond character more for BF 4 − than for the Cl − salts, but in general less for aldiminium than for cetiminium species. These phenomena are related to the strength of the hydrogen bond in which the NH + function is involved. Depending on the anion electronegativity, organic polar functions may form alternative hydrogen bonds with the aldiminium or on the contrary strengthen the stability of the ion pair. Such programmed discrete changes on the iminium local environment may influence the structure and the stability of the protonated Schiff base in the dynamical bionatural cycles involving the rhodopsin and bacteriorhodopsin photopigments.

ALL-trans RETINAL PHOTOISOMERIZATION AND PHOTOOXIDATION FROM UV LASER RADIATION. VIBRATIONAL ASSIGNMENTS OF ALL-trans 5,8-PEROXYRETINAL

Abstract— Photoisomerization and photooxygenation of all‐trans retinal in acetonitrile, illuminated by laser radiations (λact, = 333.6 or 350.7 nm), were investigated under various experimental conditions. In deoxygenated solutions, the major photoproducts are 13‐cis and 9‐cis retinal. All‐trans and 13‐cis 5,8‐peroxyretinal are obtained in large amounts in oxygenated solutions. 11‐cis derivatives have not been detected in any of these solutions. The photoproducts were identified by UV, NMR, mass and vibrational spectroscopies and HPLC chromatography. All‐trans and 13‐cis 5,8‐peroxyretinal were isolated. Their vibrational spectra (IR and Raman) are analyzed. Most of the bands are assigned by comparison with previous studies on all‐trans and 13‐cis retinal, (E,E,E)‐3‐methyl‐2,4,6‐octatrienal and peroxides.

Etude spectroscopique de derives mercuriques d'amides-thiols: Partie III. Spectres de vibration et structure de complexes mercuriques des thiol-2N-méthylacétamide, thiol-3N-méthylpropanamide et N-thiol-2 éthyle)acétamide

Abstract Raman and IR spectra of (CH 3 NHCOCH 2 S) 2 Hg, (CH 3 CONHCH 2 CH 2 S) 2 Hg and CH 3 NHCOCH 2 CH 2 SHgCl have been recorded between 3800 and 60 cm −1 . Mercury is covalently bonded to two sulphur atoms in the first two compounds and to one sulphur atom and one chlorine atom in the third compound. (CH 3 NHCOCH 2 S) 2 Hg forms a tenatom ring by intramolecular hydrogen bonding NH⋯OC. In the two other complexes, weak interactions Hg⋯O are consistent with experimental results.

Photochemical evolution of trans-retinal and trans-N-retinylidene n-butylamine under laser beam irradiation

Abstract Trans-retinal and trans-N-retinylidene n -butylamine have been irradiated by a laser beam in their absorption band and far from the maximum. Examination by Raman and visible spectroscopy shows that isomerization occurs, accompanied by transformation which seems to involve proton tansfer from the C 5 methyl to the polyene chain.

Etude spectroscopique de derives mercuriques d'amides-thiols: I. Spectres de vibration et structure des thiol-2 N-méthylacétamide, thiol-3 N-méthylpropanamide et N-(thiol-2 éthyle) acétamide

Abstract Raman and infrared spectra of CH3NHCOCH2SH, CH3NHCO(CH2)2SH and CH3CONH(CH2)2SH have been recorded between 3800 and 200 cm−1. Some structural information is obtained from their analysis: for pure liquids or solids, molecules form linear chains with NH ⋯ OC hydrogen bonds, the SH group being probably bound to the oxygen of an adjacent molecule. For CCl4 solutions, an intramolecular hydrogen bond NH ⋯ S is observed for the first compound only, corresponding to the formation of a five-membered ring.

Infrared evidence for the structure of salt saturated aqueous solutions

Abstract The identification, by their infrared spectra, of species formed by specific interactions between water and three salts (LiClO4, BrNBuO4, LiBr) leads to some understanding of the microscopic structure of salt saturated aqueous solutions. The concepts “structure-maker”, “structure-breaker”, are criticised.

NMR and vibrational studies of a stable carbinolaminium chloride (CH3)2CHCH(OH)NH+2CH(CH3)2Cl− in the solid state. Influence of the solvation on carbinolaminium/iminium equilibrium

Abstract A stable carbinolaminium species formed as a solid from N -methylpropyliden-propan-2-iminium chloride and water vapour is evidenced through 13 C NMR spectroscopy. The characteristic infrared and Raman modes of the CH(OH)NH + 2 Cl −  and CH(OD)ND + 2 Cl −  functional groups are identified. The carbinolaminium derivatives are stable in the solid state when the OH(D) and NH + 2 (D + 2 ) groups of the same molecule are both hydrogen bonded to a Cl − anion in an apolar environment. In organic solvents, the carbinolaminium soon reverts to water and aldiminium. In basic organic media the water is complexed to the solvent and the aldiminium is stable. In slightly acidic solvent (CHCl 3 ) the aldiminium is slowly, but in time totally, hydrolyzed. The relevance of these results to the study of rhodopsin and bacteriorhodopsin photocycles is discussed.

Photon correlation spectroscopy as a tool of characterization of SERS-active systems based on Ag sols

Abstract Photon correlation spectroscopy and microelectrophoresis are investigated as tools to characterize SERS-active systems. Mutual relations of SERS spectra, UV/vis spectra, hydrodynamic size and zeta-potential are studied for systems based on Ag sol and two different adsorbates (2,2′-bipyridine and pefloxacin).

Selective site deuteration on the sugar ring as an efficient marker of conformation in nucleosides: The CD stretching mode of the (2′-R)-[2′-2H]-2′-deoxyuridine and its 3′,5′-O-(1,1,3,3-tetraisopropyldisiloxan-1,3-diyl)-derivative

A uridine specifically deuterated on the deoxyribose ring at the C2′, and the same compound in a more rigid form, due to a chemically fused ring (between C3′ and C5′), have been synthesized. By NMR, the coupling constants J1′-2′ and J3′-4′ have been determined and the populations of the C2′-endo and C3′-endo conformers have been deduced for the two compounds. Comparison of these results with an FTIR and Raman study of the stretching mode νCD on the C2′ site allows a specific assignment of each observed band to one of the two classes of conformers. This enables us to consider the further step: the direct recognition, by IR and Raman spectroscopies, of the local conformation at a specific site of a synthetic oligonucleotide, using the νCD signals as marker bands.

Vibrational analysis of the S—trans conformation of (E,E), (Z,E) and (Z,Z)-2,4-hexadienes in the gaseous and solid states

Abstract The infrared (IR) spectra of liquid, gaseous and solid states as well as the liquid and solid phases Raman ones of the pure (Z,Z)-2, 4-hexadiene are recorded for the first time between 3100–50 cm −1 . Furthermore, the IR spectra of the gaseous and solid states and the solid Raman ones have been obtained (3100-50 cm −1 ) for the (E,E) and (Z,E) isomers. A comparison between the present and our previous results for the liquid phase have enabled us to complete and confirm our previous assignment and to conclude that the planar s-trans conformation is prevailing in the three physical states under conditions used in this work.