Michel Perrot

Raman light scattering studies of the depolarized Rayleigh wing of liquids and solutions

Raman spectra of the depolarized Rayleigh wing region (10–300 cm−1) of a number of liquids and solutions have been recorded in digital form employing signal averaging techniques. The symmetrized I(?) spectra have been recast in an I(?)?2 format which transforms the Rayleigh spectra into forms directly comparable to far‐infrared absorption. The major advantage of this procedure is that it suppresses the exciting line and emphasizes the weak low frequency peaks. As a result, the basic characteristics of the ’’peaks’’ previously reported are confirmed with improved precision. Peaks have also been observed for the first time for cyclohexane, acetone, and n‐tetradecane. These peaks appear to reflect the short‐time behavior of the external coordinates of individual anisotropic molecules and should not be confused with fundamental vibrational or negative combination modes. For liquid benzene, studies of the effects of concentration change (in carbon tetrachloride), temperature change, and isotopic substitution c...

Raman light scattering studies of the depolarized low frequency region of water and aqueous solutions

Raman spectra of the depolarized Rayleigh wing (20–350 cm−1) for water and aqueous solutions have been recorded in digital form and recast in the R2(?) format as described previously. Studies of water, aqueous fluoride, and perchlorate suggest that the weak peak at 191 cm−1 has its origin in the hydrogen bonded water structure. Temperature and isotopic substitution (D2O, H2u200918O) measurements support this conclusion. Anisotropic ions and molecules such as NO3−, CN−, and acetone superimpose an intense librational peak on the water spectrum.

Cloning gene ura5 for the orotidylic acid pyrophosphorylase of the filamentous fungus Podospora anserina: transformation of protoplasts

From a genomic library of the filamentous fungus Podospora anserina, we have cloned a 4.9-kb fragment which complements an Escherichia coli mutant strain deficient for orotidylic acid pyrophosphorylase (pyrE gene). The recombinant plasmid pPAura5 also transforms to prototrophy a mutant strain of P. anserina carrying a mutation in the ura5 gene and lacking OMPppase activity.

On the vibrational T2 processes in partially ordered systems

The stretched (‘‘extended’’ or ‘‘fractional’’) exponential, exp{−(t/T)α}, where 0<α≤1 and T (ps) a time constant, is introduced as a modulation function for a vibrational T2 process in order to describe the non‐Markovian dynamics of the bath of amorphous systems in the picosecond domain. The theory simulates well published dephasing data of probe oscillators in concentrated aqueous solutions of KSCN, molten mixtures of Li and Rb nitrates, and of polycrystalline and smectic phases of the liquid crystal 4‐n‐octyloxy‐4’‐cyanobiphenyl. The temperature and phase dependence of dispersion parameter α follows an accepted model of constrained‐sequential relaxation with a scale‐invariant (‘‘fractal’’) distribution of relaxation times.

Ribosomal proteins in the fungus Podospora anserina: evidence for an electrophoretically altered 60S protein in a cycloheximide resistant mutant.

SummaryProteins of cytoplasmic ribosomes of the Podospora anserina were analyzed by two dimentional gel electrophoresis. The numbers of proteins were estimated to be 28 in the small subunit and 41 in the large subunit. The L21 protein of the large subunit was found to migrate differently in a cycloheximide resistant mutant.

Genetic and biochemical analysis of cycloheximide resistance in the fungus Podospora anserina.

Genetic analysis of cycloheximide-resistant mutants has shown that at least three genes control the resistance to cycloheximide in Podospora anserina and that the antibiotic resistance is recessive to sensitivity. In vitro and in vivo studies of protein synthesis indicated that for two mutants cycloheximide resistance is associated with the ribosomes. For one of these mutants, the elongation step in protein biosynthesis is insensitive to cycloheximide over a wide range of concentration. In this mutant the resistance to cycloheximide is a property of the 60S subunit.

Picosecond dynamics and molecular aggregation from vibrational dephasing in the fluid phases of some 4‐n‐alkyl‐4’‐cyanobiphenyl liquid crystals

We describe the temperature dependence of the inhomogeneously broadened CN Raman profile I(ω) at ωc ∼2230 cm−1 of the title compounds (n=1, 6, 8, 9, 11, 12) in their isotropic liquid phase and solutions (CHCl3, CCl4) by simulating the oscillator amplitude correlation function by a vibrational equilibrium renewal process in terms of random fluctuations of the oscillator transition frequency ω(t)=ωc +ω1(t) about its central value ωc. To this effect, the autocorrelation function of the frequency shift ω1(t) is expressed as a probability density function (PDF) F(t) of recurrence times of the stochastic motional narrowing events in the local environment of the CN oscillators. System‐related physical meaning and satisfactory data fit is obtained if F(t) is understood as an expansion in terms of parallel, independent exponential relaxation processes with characteristic times τ that are distributed by a PDF ρα(τ)=〈τ〉h(τ)/τ, where α is the dispersion parameter of the extended exponential and 〈τ〉 the expectation ...

Influence de la pression sur les profils des bandes de diffusion Raman dépolarisée et Rayleigh dépolarisée du dioxyde de carbone liquide

On analyse les profils des bandes de diffusion depolarisee Raman et Rayleigh du dioxyde de carbone liquide, obtenus a 100, 1500 et 3000 atmospheres. Lutilisation des moments de ces bandes et des fonctions de correlation calculees par transformation de Fourier, permet de comparer les resultats experimentaux avec les theories proposees par Gordon et Litovitz pour rendre compte de la dynamique moleculaire a letat liquide. On montre que les profils de diffusion depolarisee Raman associes a une transition Σ g + ont, essentiellement pour origine, la reorientation monomoleculaire de CO2 quelle que soit la pression exercee, tandis que la diffusion Rayleigh depolarisee est influencee a la fois par les dynamiques monomoleculaire et multimoleculaire; laspect cooperatif des mouvements augmentant avec la pression.

Vibrational dephasing under fractional (“stretched”) exponential modulation in a liquid crystal system

Abstract The amplitude correlation and memory functions associated with the inhomogeneous broadening of the Raman CN oscillator profile of 4- n -nonyl-4′-cyanobiphenyl (9-CB) were determined for the polycrystalline, smectic, nematic, and liquid phases and simulated using a fractional (“extended”) exponential modulation function, exp[-( t / T ) α ]. Shape parameter α ( T (ps) is a characteristic time. For mesophases and liquid, modulation of the oscillator phase depends on a sequence of relaxation steps with a scale-invariant distribution of relaxation time (“fractal time”). An effective modulation event is envisaged to occur if a favorable [CH 2 ] n configuration arises from fast group motions in the alkyl chain that induces a transition between trans/gauche forms at the CN oscillator site. For the more ordered polycrystal, memory is essentially pure-exponential, leading to damped-harmonic vibrational amplitude dephasing. The data corroborate the presence of cybotactic groups in the liquid.

Vibrational dephasing under fractional (“stretched”) exponential modulation

A fractional (or stretched) time exponential, F(t)= exp[−(t/F)α], where 0<α<1, T a time constant, is proposed as the modulation function for vibrational band-narrowing in locally structured, amorphous media. It leads to physically sounder modulation times than current, pure exponential models, yields the same superior data fit as recently proposed, two-process relaxation mechanisms and promises useful and interesting physical insight into structural-dyamical aspects of the systems.