Chantal Garrigou-Lagrange

Carbon-13 nuclear magnetic resonance studies on thyrotropin-releasing factor and related peptides

Thyrotropin-releasing factor (TRF) is a peptide which causes the release of thyroid-stimulating hormone (TSH) from the pituitary in mammals [l] . The sequence of this hormone has recently been determined [ 1,2] to be L-pyroglutamyl-l-histidylL-prolinamide. Carbon-13 nuclear magnetic resonance (13C NMR) has proven useful in detecting cis and trans isomers of proline in peptides [3-61. The purpose of this study was to investigate cis-trans isomerism about the histidyl-prolinamide bond in TRF and to measure the spin-lattice relaxation times, Tr , of all the carbons in the hormone. TRF in water is found to have 14% of the proline present as the cis isomer the amount varies with the solvent. The proline resonances are sensitive to the nature of the group attached to the proline nitrogen. 13C NMR is shown to be sensitive to the presence of D and L forms of histidine. The presence of D or L histidine in TRF has a profound influence on the 13C chemical shifts of proline, whereas those of pyroglutamate are unaffected.

Infrared and resonance Raman spectra of κ-(BEDT-TTF)2Cu(NCS)2 organic metals. H8-, H4D4- and D8-(BEDT-TTF) Derivatives

We have investigated the partially and completely deuteriated 3,4,3′,4′-bis(ethylenedithio)-2,2′,5,5′, tetrathiafulvalene (BEDT-TTF) copper thiocyanate salts which exhibit a superconducting state at ca. 10 K. We have carried out both IR absorption spectra on polycrystalline samples and polarized reflectivity measurements on single crystals at 300 and 15 K. Resonant Raman scattering under visible excitation was also performed at room temperature for investigating the Raman excitation profiles associated with the charge-transfer bands. After a careful assignment of the vibrational spectra, we examined the electron–molecular vibration (EMV) coupling involving ag vibronic modes. These EMV interactions are tentatively compared with Yamajis model, which postulates a BCS-type model for the occurrence of a superconducting state associated with these internal molecular vibrations.

New organic-donor inorganic-acceptor salts: [(TTF)6(XMo12O40) (Et4)], X = Si and P

Abstract The preparation, X-ray crystal structure, optical and magnetic properties of two new Organic-Donor Inorganic-Acceptor (ODIA) salts: [(TTF) 6 (XMo 12 O 40 ) (Et 4 N)], X= Si ( 1 ) and ( 2 ) are presented. The two materials are isostructural. Their X-ray crystal structures are characterized by 1-D TTF chains lying inside the channels formed by the inorganic anions and isolated TTF molecules. Magnetic experiments for both salts are compared: they are different and suggest, in particular, the presence of one non-interacting electron in 2 , in contrast with the diamagnetic behaviour of 1 . The optical absorption measurements of the two compounds are essentially identical. They show the presence of both intense charge transfer bands around 4800 cm −1 and vibronic modes in the middle IR range (1300–1400 cm −1 ), characteristic of mixed valence salts.

Preparation and properties of tetrathia- and tetramethyltetraselena-fulvalene salts of [M6O19]2–(M = Mo or W)

The preparation, X-ray crystal structures, conductivity and optical properties of the salts, [ttf]3[W6O19]1, [ttf]3[Mo6O19]2(ttf = tetrathiafulvalene) and [tmtsf]3[W6O19]·2dmf 3(tmtsf = tetramethyltetraselenafulvalene) are reported. Crystal data: 1, triclinic, space group P, a= 9.965(3), b= 10.503(3), c= 10.634(3)A, α= 71.93(2), β= 78.63(2), γ= 63.38(3), Z= 1, R= 0.020; 2, triclinic, space group P, a= 9.942(3), b= 10.417(3), c= 10.601(3), α= 72.33(2), β= 78.77(2), γ= 63.52(3)°, Z= 1, R= 0.030; 3, monoclinic, space group P21/c, a= 11.589(4), b= 19.385(5), c= 13.681(3), β= 99.53(2), Z= 2 and R= 0.049. In all the salts the organic molecules form trimerized stacks. A classical ring-over-double bond overlap is observed in 3, in contrast with 1 and 2 which present an unusual intra-trimer criss-cross overlap. In compound 3 the intra-trimer Se ⋯ Se (3.73–3.81 A) contacts are shorter than those observed in [tmtsf]2X (X = PF6 or BF4) series. The inter-trimer Se ⋯ Se contacts (3.94–4.12 A) are in the range of the van der Waals separation (4 A). Short O ⋯ Se (3.17–3.30 A) contacts are observed. Both electrical and optical measurements and also electronic band-structure calculations reveal that the three salts are semiconductors.

TTF derivative salts with “lindquist” polyoxometallate anions

Abstract The preparations, X-ray crystals structures, optical, ESR and magnetic characterizations of new Organic-donor Inorganic -Acceptor salts are presented. The [BEDT-TFF]2M6O19 ( M = Mo ( 1 ) and W ( 2 )) present orthogonalized fully oxidized and diamagnetic organic dimers. The structure of (TPh-TTF)2W6O19 (3) shows isolated and fully oxidized organic molecules. Organic stacks made of phenyl-rings and central TTF parts are also observed in the latter compound.

New conducting radical cation salt based on BEDT-TTF and substituted polyoxometalate anions : [BEDT-TTF]5[VW5O19], 6H2O

Abstract The preparation, X-ray crystal structure, conducting and optical properties of (BEDT-TTF)5VW5O19(H2O)6 are reported. Crystal data: monoclinic, P21/c, a = 19.77(2) A , b = 11.598(6), c = 41.34(4), β = 100.90°(7), V = 9308 A 3 , Z = 4, R = 0.071 for 6746 reflections with I⩾3 σ(I). The water molecules are cheeked by TGA. The organic sublattice forms bidimensional layers along a . Short S⋯S contacts (3.40–4.62A) are observed. Electrical measurements reveal that the title compound exhibits a metallic behaviour down to 250K where a metal-insulator transition occurs.

Some new radical-cation salts based on unsymmetrical tetraheterofulvalenes : (MDTTTF)4Pt(CN)4, the first κ-phase salt, with a square planar dianion

Abstract We report the synthesis of the organic donor radical cations, methylenedithiotetrathiafulvalene (MDTTTF), ethylenedithiotetrathiafulvalene (EDTTTF) and vinylenedithiotetrathiafulvalene (VDTTTF), with the square planar dianions, Pt(CN) 4 and Ni(CN) 4 . Among these salts, the κ-(MDTTTF) 4 Pt(CN) 4 (CH 2 Cl 2 ) phase constitutes the first κ-phase, produced with a nonlinear dianion. Crystal and electronic structures, electrical and optical properties and ESR measurements have been investigated for these salts. Crystal and electronic structures of κ-(MDTTTF) 4 Pt(CN) 4 are similar to those of (MDTTTF) 2 AuI 2 , which is an ambient pressure superconductor ( T c = 4.5 K). However, d.c. conductivity measurements show a semiconducting behaviour, associated with an ESR linewidth decreasing with temperature in contrast with all other known κ salts. An explanation of the origin of these different behaviours is proposed.

Optical study of charge-transfer salts with organic donors issued from TTF and tetracyanometallate planar dianions M(CN)4, M = Pt(II), Ni(II)

Abstract The class of mixed-valence one-dimensional systems based on tetrathiafulvalene (TTF) and its derivatives and inorganic anions of tetracyanometallates such as Krogmanns salts have been two of the most extensively studied low-dimensional conducting materials. A new series of conducting radical-cation salts has been recently synthesized including both types of compounds with a general formula (D x ) 2+ C 2− (D = TTF, TMTTF, TMTSF, BEDT-TTF; C = Ni(CN) 4 , Pt(CN) 4 ). The visible and IR absorption spectra of these compounds have been examined. Two main types of results are observed and presented: (i) first, the charge-transfer bands characteristic of a mixed-valence system are observed around 3400 cm −1 for every salt (except TTF 5 [Pt(CN) 4 ] 2 [(CH 3 CN) 2 ] for which this ‘A band’ occurs at 5700 cm −1 ); (ii) secondly, vibronic lines which are a g modes, usually IR-forbidden, are detected in all compounds; besides, the temperature dependency studied for both BEDT-TTF salts seems to be representative of a phase transition occurring around 200– 250 K. These optical properties are explained in relation to the specific structural organization observed in these new materials, in particular with the presence of centrosymmetric pentamers in a TTF salt.

Metal-insulator phase transition in (BEDITTF)4M(CN)4 salts

Abstract Two isostoichiometric phases of metallocyanate salts (BEDT) 4 (M(CN) 4 ) 1 with M=Pt, Ni are isolated characterized; for each of them, phase transitions are evidenced by ESR and IR spectroscopies.

Giant analogues of tetrathiafulvalene in Langmuir and Langmuir–Blodgett films

The behaviour of new giant tetrathiafulvalene (TTF) analogues has been studied at the gas/water interface and in Langmuir–Blodgett films. These compounds, denoted G-TTFCn, have a dihydro-TTF core which bears two conjugated side-arms with various alkyl chains (from methyl to octyl). Langmuir films of these compounds are quite stable versus time and are characterized by a collapse pressure that increases as the length of the alkyl chains decreases. The ability of these compounds to form Langmuir films should then be due to their extended TTF core. Except for G-TTFC1, transfer of the monolayer onto a solid substrate is easily done at low surface pressure. Doping of the LB films by iodine vapours changes their spectroscopic (EPR, electronic and vibrational) behaviour and leads to rather poor conducting films. Conductivity of G-TTFC4 films (σRT≈ 4 × 10–7 S cm–1) is two orders of magnitude lower than for G-TTFC2(σRT≈ 4 × 10–4 S cm–1), showing the influence of the molecular packing on the electrical properties of such films. Different results are obtained upon mixing these G-TTFCn compounds with pentadecyltetracyanoquinodimethane (C15TCNQ) in various proportions, which gives rise to charge transfer complexes of adjustable stoichiometry. It is shown that these extended π-donor molecules give new insights on the redox processes that can lead to conducting films.