ETUDE DES FACTEURS DETERMINANT LA GERMINATION DES GRAINES DE LYTHRUM SALICARIA (LYTHRACEES)

Abstract— Les résultats des expériences réalisées sous différentes conditions d'éclairement et de température ont permis de définer deux processus de germination probablement indépen-dants: 1°/un processus thermosensible: à l'obscurité la germination ne se produit qu'en alternance de température. L'éfficacité de ces alternances est fonction de l'éart qui existe entre les deux températures et de la valeur de ces deux températures. L'influence des alternances de températures peut être exaItée par un certain nombre de substances: nitrates, nitrites, hydroxylamine et thiourée 2°/un processus photosensible: la lumière rouge clair (630–680 mµ) stimule le germination, par contre la lumière rouge sombre (700–730 mµ) élimine la stimulation due à la lumière rouge clair. L'acide gibbéréllique sensibilise les graines à la lumière rouge clair.     

ETUDE PAR FLUORESCENCE DE BASES DE SCHIFF DU PYRIDOXAL, COMPARAISON AVEC LA L ASPARTATE-AMINOTRANSFERASE

Abstract— –Absorption and emission spectra of Schiff bases of pyridoxal-HCI or pyridoxal-5-phosphate with L-valine, n -butylamine or N-α-acetyl-L-lysine-N-methylamide have been studied as a function of pH. We can write the complete ionization diagram and equilibria. The results of Martell[6] are confirmed: the forms analogous to the coenzyme in aspartate aminotransferase, which absorb at 410 nm and 360 nm (or 340 nm for the Schiff base with n-butyl-amine) have the phenol OH ionized; the imine nitrogen is protonated for species absorbing at 410nm (in the enzyme: inactive form and complex with aminoacid) and unprotonated for species absorbing at 360 nm (in the enzyme, active form). Their fluorescence wavelengths are respectively 500 nm and 430 nm. Protonation of the pyridine nitrogen of these forms does not shift the absorption band; the fluorescence intensity is 20-fold greater for the N-protonated forms.
The real pK of the imine nitrogen is 8.5 ±0.8 for species with pyridine N-protonated or 10.4 for the non-protonated forms. The observed pK 6.3 in the enzyme can be explained if the imine nitrogen is hydrogen bonded to an amino-acid side chain of the protein: lysine, tyrosine, serine, sulfhydryl.
The quantum yield of the coenzyme fluorescence in the enzyme has been compared to that of the analogous Schiff base (absorbing at the same wavelength). According to the results, we cannot deduce whether the pyridine nitrogen is protonated in pyridoxal form of the enzyme.
If it is protonated, as in the pyridoxamine form, the coenzyme environment is not the same in the two forms. If the pyridine nitrogen is unprotonated in the pyridoxal form and protonated in the pyridoxamine form, the environment of the coenzyme is the same in these two forms of the enzyme.     

INTERPRETATION DES MODIFICATIONS SPECTRALES SUBIES PAR LES HYDROCARBURES AROMATIQUES LORS DE LEUR INTERCALEMENT AU SEIN DES ACIDES NUCLEIQUES

Abstract— This work presents a calculation of the large bathochromic shift observed in the ultraviolet spectrum of aromatic hydrocarbons (such as pyrene and 3,4 benzopyrene) when they are stacked with nucleotides and polynucleotides. For this, an estimation of the increase of molecular polarizability in the excited states is necessary. This increase is responsible for the fact that the stabilization of the stacked hydrocarbon by dispersive interactions with base pairs becomes stronger in the excited state. The calculated increases of stabilization energies are in satisfactory agreement with the observed spectral shifts.     

ETUDE DE QUELQUES REACTIONS DE LA TRIS(TERT-BUTYL)PHENYLPHOSPHINE

Abstract

The reaction of tris(tert-butyl)phenylphosphine with some hydrogen acceptors has been investigated. Triphenylcarbenium hexafluorophosphate allows to obtain a phosphonium salt: the possibility of preliminary formation of phosphenium with a P[sbnd]H bond during this reaction is discussed. With methyltrifluoromethanesulfonate, two pentacoordinated phosphorus compounds are isolated. Diethylazodicarboxylate gives rise to a σ³, λ⁵-phosphorane. The transient formation of phosphinidene and of 1,2-bis(ethylcarboxylate) 3-tris(tert-butyl)phenyldiazaphosphirine is discussed.     

ETUDE DE LA FRAGMENTATION DE N-ARYL ET DE N-ALKYL AMINOCETONES EN SPECTROMETRIE DE MASSE

A Comparison of the chemical ionisation and elctron-impact mass spectra of alkyl and aryl aminoketones has bee carried out. This has revealed the particular stabilization of the N-aryl grops in all cases.     

CINETIQUE DES ECHANGES D'OXYGENE ET DE LA FLUORESCENCE DES CHLOROPLASTES ISOLES

Abstract Oxygen evolution and fluorescence have been studied with isolated chloroplasts illuminated, in the absence of Hill reagents, by flashes or continuous light. As in whole cells, at least two substances are involved in the primary process leading to the oxygen evolution. The first, called E, probably is the photochemical “complex” of System II. After a long period of darkness, E is not active. It is activated in two steps. Step one is a photochemical reaction, induced by a quantum of light absorbed by pigment-system II, which results in the production of E in a reduced state. Step two is a dark oxidation of the reduced E by the second substance, A. The oxidized E can then enter the normal photochemical cycle of system II. Reduced E might alternatively be oxidized by oxygen, this reaction being responsible for a very rapid and brief light-induced oxygen uptake. Substance A is measured by the oxygen burst and is present in the chloroplasts at the approximate ratio of 1 molecule for 70 molecules of total chlorophyll while E is at the ratio of about 1/2800. This gives a E over A value of 1/35 which is much smaller than the one found in whoe cells (ca. 1/10). This independent behavior of E and A suggests that chloroplast extraction destroys some photochemical centers without having a direct impact on A, which might diffuse from one center to another. Besides the brief light-induced oxygen uptake above mentioned, there is another one which is related to System I functioning. The kinetics of the oxygen evolution and of the fluorescence have been compared. During the activation process of the oxygen evolving ability, rate of oxygen evolution and fluorescence yield increase in a parallel way. After the maximum velocity of the oxygen burst is reached (i.e. after activation), the fluorescence yield keeps growing up until the steady-state is attained (with an intermediary plateau), whereas the rate of oxygen emission slows down. The time-course curves of fluorescence obtained with inactivated or activated chloroplasts are essentially different in that the initial yield is higher in the latter case.     

ACTION DE LA LUMIÈRE SUR LA CROISSANCE DES TIGES PRINCIPALES DE L'ASPARAGUS MEDEOLOIDES

Abstract— Studies of the influence of light upon the growth of Asparagus medeoloides main stems show that the stem-length and the time-growth increase when the intensity of illumination decreases. There is no direct proportionality between growth and illumination intensity; a maximum is found at 660 lx.     

PHOTOCHIMIE DES ACIDES AMINES AROMATIQUES EN SOLUTION - I. dl-PHENYLALANINE, dl-TYROSINE ET l-DOPA

Abstract— The action of ultraviolet radiation on dl -phenyldanine, dl -tyrosine and l -dopa has been studied in dilute aqueous solutions (10^-2M–5 × 10^-3M). Irradiation was performed in nitrogen or in air, at a wavelength of 254nm. The photoproducts of low molecular weight (amino acids, carboxylic acids, amines) were isolated either by chromatography on an ion exchange column or by thin-layer chromatography and identified mainly by ultraviolet absorption and staining with ninhydrin. The isolation of photopolymers was carried out by chromatography on a Biogel column; identification of these photoproducts was mainly achieved by ultraviolet and infrared spectroscopy. With phenylalanine, which is the most photosensitive amino acid, the principal reaction results in splitting of the side chain, giving alanine, glycine, and four other amine compounds whose structure has not been determined. In air, additional minor products resulting from photooxydation are obtained: ortho, meta and paratyrosine. Traces of phenylethylamine were isolated after irradiation in an inert atmosphere. The polymers produced under air and nitrogen are similar. They probably result from rearrangement of aromatic radicals formed by splitting of the side chain. Tyrosine and dopa, irradiated in air, yield mainly melanin; before polymerization, tyrosine is first converted into dopa. In a inert atmosphere, these aromatic aminoacids also polymerize, giving monophenolic and biphenolic compounds with structure close to that of melanin. The biphenolic polymer (thus obtained from dopa) shows the properties of a leuco derivative of melanin. The monophenolic polymer can be converted into melanin by the combined action of oxygen and ultraviolet radiation. Other reactions give only minor products: parahydroxy-phenyllactic acid and 3,4-dihydroxyphenyllactic acid by deamination-hydroxylation of tyrosine and dopa (in air): meta and paratyrosine by dehydroxylation of dopa, either in air or in nitrogen.     

INFLUENCE DE LA LUMIÈRE SUR LES MOUVEMENTS DE NUTATION DES PLANTULES

Abstract— Red light can promote (a) the straightening of the curvature ( Phaseolus vulgaris, Pisum sativum ) (b) the formation of a loop ( Phacelia tanacetifolia and Picea abies ) or (c) the induction of a curvature which does not occur in the darkness ( Lactuca sativa ). Thesc red-light induced movements could be reversed by following each brief red exposure with short irradiation by far-red light. These reactions are controlled by the phytochrome system.
On the other hand, exposure to far-red and blue light during a long period can induce other movements:
(a) The light re-opens the hook which has been closed by red radiation ( Lactuca sativa ).
(b) The light induces the straightening of the dark-induced curvature ( Phacelia tanacetifolia ). These facts may be due to an unknown property of phytochrome or to the action of another photoreceptor.     

AGREGATION DES CHLOROPHYLLES IN VITRO-II. PHOTODECOLORATION DE LA CHLOROPHYLLE a ADSORBEE SUR DES PARTICULES DE LIPOPROTEINES EXTRAITES DU LAIT

Abstract— Chlorophyll a (chl a ) adsorbed on milk proteins or lipoproteins has absorption maxima at 437 ± 1 nm and 671 ± 1 nm, whatever its concentration. A 750-nm-absorbing form appears when (chl/proteins) > 2 × 10^-2 mg chl/mg proteins, in the case of lipoproteins; or 4.5 × 10^-3 mg chl/mg proteins, in the case of proteins. In both cases, the apparent molar extinction coefficient at 671 nm is the same (3 × 10⁴ liter mole^-1 cm^-1) at the highest (chl/proteins) ratio for which no 750 nm absorbancy appears. It is shown that adsorbed chl a undergoes irreversible (in the present conditions) photo-oxidation by light in the presence of oxygen. The reaction is second order, with similar rate constants for chl a adsorbed to proteins or to lipoproteins.     

SPECTROSCOPIE DE LA CHLOROPHYLLE DANS LES CHLOROPLASTES ENTIERS ET DES FRAGMENTS CHLOROPLASTIQUES

Abstract— Chloroplast fragments obtained after treatment with a non-ionic detergent (Triton X-100) are studied spectroscopically. Their absorption and fluorescence spectra show the possibility of obtaining separately, without any visible alteration, the two groups of chlorophyll holochromes corresponding to the two photochemical systems. One of the chloroplastic fractions, enriched in chlorophyll- b shows, like whole chloroplasts, an oxygen burst upon illumination.     

CONTRIBUTION A L''ETUDE DE LA LUMINESCENCE DIFFEREE DE COLORANTS EN MILIEU RIGIDE. PHOTOIONISATION DE LA FLUORESCEINE DANS L''ACIDE BORIQUE PAR UN PROCESSUS A DEUX PHOTONS

Abstract— A study of the delayed luminescence and thermoluminescence of fluorescein and others dyes in boric acid glass gives evidence of photoionisation of these compounds. To account for the energetic aspect of the photoionisation, a two photon process involving solute-solvent proton exchange is proposed. The participation of the heterogeneous structure of the glass in the mechanism of the photoionisation is confirmed.     

STRUCTURE STERIQUE DES COMPOSES CYCLIQUES DU PHOSPHORE. XIII. ETUDE PAR MOMENT DIPOLAIRE DES OXO-2 ET THIO-2 PERHYDRO OXAZAPHOSPHORINES-1,3,2

Abstract

L'étude par moment dipolaire de la conformation de huit perhydro oxazaphosphorines-1,3,2 est décrite. The conformation of eight perhydro 1,3,2-oxazaphosphorines is studied by means of dipole moments.     

POST-LUMINESCENCE DES CHLOROPLASTES INTACTS ET ALTERES PAR DENATURATION PARTIELLE: ETUDE EXPERIMENTALE, INTERPRETATION THEORIQUE ET CALCUL D'ENERGIES D'ACTIVATION

Abstract— The authors have studied the temperature effect on the luminescence of spinach chloroplast suspension after illumination at 675 nm.
The decay of the luminescence has been followed at constant temperature (from 0°C to 40°C) or after sudden temperature jumps (0°C ≤Δ T ≤ 47°C).
They have compared the results obtained with intact chloroplasts and those after mild thermal denaturation.
From these experimentally found values they have calculated the activation energies related to the radiative and non-radiative ways of disappearence of the entity which is at the origin of the luminescence.
On the basis of the values found for these energies (0·9 eV and 0·43 eV respectively), the authors evolve the hypothesis that this entity may be an electron self-trapped in the chloroplast structure (small polaron).     

SEPARATION ET CARACTERISATION SPECTROSCOPIQUE DU MONOMERE ET DES POLYMERES DE LA C. PHYCOCYANINE.*

Abstract— Monomer, trimer and hexamer states of C. Phycocyanin chromophore protein have been isolated. Owing to a very slow approach to equilibrium mixing, it has been possible to estimate the number of each type of the two chromophores ‘s’; and ‘f’ present, using a fluoros-cence polorization method. It is found that there is one s chromophore and one f chromophore per protein monomer of molecular weight 30,000, a value in agreement with the monomer mol. wt. determined by Berns et al and by thermodynamic measurements in this laboratory. Absorption and fluorescence spectra of hexamer and monomer solutions have been compared. The hexamer solution shows greater fluorescence than the monomer solution, a phenomenon that may be attributable to a change in environment of chromophore following polymerization, with consequent change of fluorescence yield of each chromophore type and/or variation in energy transfer between them.     

ACTION DE LA LUMIÈRE SUR LE DÉVELOPPEMENT DES TISSUS DE FEUILLES D'ENDIVE CULTIVÉS IN VITRO

Abstract— Light is not necessary for the formation of buds by tissues of chicory roots. However, in darkness, their number is reduced and the development of leaves is slowed down considerably. Absence of light also reduces the proliferative capacity of leaf explants as well as the number of buds formed on them. The number of buds is greater and their growth more rapid for longer periods of illumination. Also, the photoperiod conditions the formation of flowers in vitro .     

TELOMERISATION PAR CATALYSE REDOX IX ADDITION DE TELOGENES PHOSPHORES SUR DES COMPOSES POSSEDANT DEUX DOUBLES LIAISONS NON CONJUGUEES

Abstract

The synthesis of telechelic oligomers with phosphorated end groups was realized by redox catalysis telomerization reaction by addition of phosphorated telogens containing a trichloromethyl group on monomers with two non-conjugated double bonds.

Nous effectuons la synthèse d'oligoméres téléchéliques à extrémités phosphorées en additionnant au moyen de la réaction de télomerisation par catalyse Redox des télogènes phosphorés renfernant le groupement trichlorométhyle, sur des monomères à deux doubles liaisons non conjuguées.     

SPECTROMETRIE DE MASSE DES AMINO-4 STEROIDES

The mass spectrometric fragmentation of the 4-amino steroids has been studied and interpretations are proposed for the formation of the principal fragments. The loss of a primary radical in the principal fragmentations explains the low rate constant of these reactions, as shown by the occurrence of important intramolecular H-D scrambling in the case of the deuterated derivative in positions 3 and 5.