Éditeur(s) : HAL CCSD
Résumé : International audience
In this work, an alkaloids extract from Annona squamosa plant have been studied as possible corrosion inhibitor for C38 steel in molar hydrochloric acid (1 M HCl). Potentiodynamic polarization and AC impedance methods have been used. The corrosion inhibition efficiency increases on increasing plant extract concentration. Polarisation studies showed that Annona squamosa extract was mixed-type inhibitor in 1 M HCl. The inhibition efficiency of Annona squamosa extract was temperaturedependent and its addition led to an increase of the activation corrosion energy revealing a physical adsorption between the extract and the metal surface. The adsorption of the Annona squamosa extractfollowed Langmuir’s adsorption isotherm. The inhibitive effect of Annona squamosa is ascribed to the presence of organic compounds in the extract. The examined extract is considered as non-cytotoxic substance.
International journal of electrochemical science

hal-01094042
https://hal-agroparistech.archives-ouvertes.fr/hal-01094042

Éditeur(s) : HAL CCSD
Résumé : International audience
Alkaloids extract of Aspidosperma album was tested as corrosion inhibitor for C38 steel in 1 M HCl by using polarization and electrochemical impedance spectroscopy (EIS). Potentiodynamic polarization curves indicated that the plant extract behaves as mixed-type inhibitors. Impedance measurements showed that the double-layer capacitance decreased and charge-transfer resistance increased with increase in the inhibitors concentration and hence increasing in inhibition efficiency. The effect of temperature on the corrosion behavior of C38 steel in 1 M HCl with and without addition of plant extract was studied in the temperature range 25 – 55 °C. The adsorption of the inhibitor molecules was in accordance with the Langmuir adsorption isotherm. The results obtained show that this plant extract could serve as an effective inhibitor for the corrosion of C38 steel in hydrochloric acid.
International journal of electrochemical science

hal-01097107
https://hal-agroparistech.archives-ouvertes.fr/hal-01097107

Résumé : Ce travail porte sur l'inhibition de l'acier C38 en milieu acide HC1 1M par les extraits alcaloïdes issus de 2 plantes : aspidosperma album et geissospermum laeve. Biodégradables et respectueux de l'environnement, les alcaloïdes pourraient être utilisés temporairement pour prévenir la corrosion de l'acier C39 avec des taux d'inhibition supérieurs à ceux décrits dans la littérature. Dans la première partie du travail, l'influence de la concentration, du temps d'immersion et de la température sur le processus de corrosion de l'acier C38 en milieu HC1 1M en absence de polarisation et spectroscopie d'impédance électrochimique. Les analyses de surface effectuées par microscopie électronique a balayage montrent la présence d'une couche constituée d'un mélange d'oxyde de fer incorporant les alcaloïdes et qui conduit à la diminution de la vitesse de corrosion. La deuxième partie de ce travail a été consacrée à l'isolement des alcaloïdes des deux extraits afin de déterminer le ou les alcaloïdes responsables de l'activité inhibitrice et ainsi remonter aux mécanismes d’adsorption. Il a été montré que l'alcaloïde majoritaire des extraits est responsable de l'inhibition
This work is devoted to the corrosion inhibition of C38 steel in 1M HCL acid medium by alkaloids extracts from two plants : aspidosperma album and geissospermum laeve. Biodegradable and environmentally friendly, alkaloids could be used temporarily to prevent the corrosion of C38 steel with inhibition rates higher than those described in the literature. The first part of this work studies the influence of concentration, immersion time and temperature on the corrosion inhibitor by electrochemical measurements : polarization curves and electrochemical impedance spectroscopy. The surface analyses conducted by scanning electron microscopy showed the presence of a layer composed of an iron oxide mixture incorporating alkaloids extracts and which leads to the decrease of the corrosion rate. The second part of this work was devoted to the isolation of alkaloids of two extracts in order to determine the alkaloids responsible of the inhibitory activity and thus to determine the adsorption mechanisms. It was showed that the major alkaloids of two extracts is responsible of the inhibition activity

http://www.theses.fr/2013AGUY0578/document

Éditeur(s) : HAL CCSD American Chemical Society
Résumé : Three new monoterpene indole alkaloids (13) have been isolated from the bark of Geissospermum laeve-, together with the known alkaloids (-)-leuconolam (4), geissolosimine (5), and geissospermine (6). The structures of 1-3 were elucidated by analysis of their HRMS and NMR spectroscopic data. The absolute configuration of geissolaevine (I). was deduced from the comparison of experimental and theoretically calculated ECD spectra. The isolation workflow was guided by a molecular networking-based dereplication strategy using an in-house database of monoterpene indole alkaloids. In addition, five known compounds previously undescribed in the Geissospermum genus were dereplicated from the G. laeve alkaloid extract network and were assigned with various levels of identification confidence. The antiparasitic activities against Plasmodium falciparum and Leishmania donovani as well as the Ortotoxic activity against the MRC-5 cell line were determined for compounds 1-5.
ISSN: 0163-3864

hal-01605065
https://hal.archives-ouvertes.fr/hal-01605065
DOI : 10.1021/acs.jnatprod.6b01013
PRODINRA : 402605
PUBMED : 28282127

Éditeur(s) : HAL CCSD
Résumé : International audience
The effect of alkaloids extracted from Isertia coccinea plant (AEIC) on the corrosion of C38 steel in 1 M hydrochloric acid was investigated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques. Potentiodynamic polarization curves indicated that the extract behave as mixed-type inhibitor. The experimental data obtained from EIS method show a frequency distribution and therefore a modelling element with frequency dispersion behaviour, a constant phase element (CPE) has been used. The inhibition efficiencies of the extract calculated by three methods show the same tendency. Inhibition was found to increase with increasing concentration of the plant extract. The results obtained show that the extract solution of the plant could serve as an effective inhibitor for the corrosion of C38 steel in hydrochloric acid solution. The apparent activation energy of the process taking place in inhibitor presence was determined on the ground of four temperature values in the range from 25 °C to 55 °C using the data obtained by two independent methods. Theoretical fitting of different isotherms, Langmuir, Temkin and Frunkin, were tested to clarify the nature of adsorption.
International journal of electrochemical science

hal-01097030
https://hal-agroparistech.archives-ouvertes.fr/hal-01097030

Éditeur(s) : HAL CCSD
Résumé : International audience
Corrosion inhibition effect of alkaloids extract from Palicourea guianensis plant (AEPG) on C38 steel in 1 M HCl medium has been investigated by potentiodynamic polarization and electrochemical impedance spectroscopy. The polarization studies showed that AEPG acts as mixed-type inhibitor. The electrochemical impedance spectroscopy showed that the charge transfer resistance increases and the double layer capacitance decreases on increasing plant extract concentration. The inhibition efficiency of the extract obtained from impedance and polarization measurements was in a good agreement and was found to increase with increasing concentration of the extract. Inhibition efficiency of 89% was achieved with 100 mg L-1 of AEPG at 25 °C. The obtained results showed that, the Palicourea guianensis extract could serve as an effective inhibitor for the corrosion of steel in acid media. The adsorption of AEPG obeys the Langmuir adsorption isotherm.
International journal of electrochemical science

hal-01096655
https://hal-agroparistech.archives-ouvertes.fr/hal-01096655

Éditeur(s) : HAL CCSD Wiley-Blackwell: No OnlineOpen
Résumé : International audience
Eight chemically defined, naturally occurring compounds were extracted from the tropical flora of the Caribbean island of Guadeloupe: pilocarpine, an alkaloid from Pilocarpus racemosus; heraclenol and isomeranzin, coumarins from Triphasia trifolia; lochnerin, an indole alkaloid from Rauwolfia biauriculata; ibogaine and voacangine, indole alkaloids from Tabernaemontana citrifolia; texalin, an oxazole from Amyris elemifera; and canellal, a sesquiterpene dialdehyde from Canella winterana. An essential oil fraction from Canella winterana was also tested. The antimycobacterial activity of these substances was tested against Mycobacterium tuberculosis, M. avium and M. kansasii using the Middlebrook 7H11 agar medium, the Bactec 460-TB radiometric methodology, and determination of bacterial viable counts. Three compounds, namely ibogaine, voacangine and texalin, showed antimycobacterial activity. Investigations on the structure-modification and structure-activity relationships of these compounds may help determine new targets for future drug development.
FEMS Immunology and Medical Microbiology

pasteur-00931155
https://hal-riip.archives-ouvertes.fr/pasteur-00931155
PUBMED : 9626931

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
Sponges are a rich source for investigation of bioactive small molecules. They have been mostly investigated for the search of new pharmacological models or therapeutic agents for the treatment of human diseases. Micro-organisms can also represent a virulent pathogen for marine invertebrates such as sponges, which need to protect themselves against these microbes. Sponges' self defence mechanisms involving dialogue molecules thus represent a pertinent research track for potent anti-infective and anti-biofilm activities such as quorum sensing inhibitors (QSIs). The investigation of the QSI crude extract of Leucetta chagosensis Dendy, 1863 led to the isolation of three new alkaloids, isonaamine D, di-isonaamidine A and leucettamine D, along with the known isonaamine A and isonaamidine A. Isonaamidine A and isonaamine D were identified as inhibitors of the three quorum sensing pathways of Vibrio harveyi (CAI-1, AI-2 and harveyi auto inducer), but isonaamidine A displayed the strongest activity on AI-2 biosensor. Both compounds are new examples of natural QSIs of V. harveyi. These results outline the importance of these secondary metabolites for their producing organisms themselves in their natural environment, as well as the potential of the marine resource for aquaculture needs.
ISSN: 0266-8254

hal-01684926
https://hal.archives-ouvertes.fr/hal-01684926
DOI : 10.1111/lam.12461
PUBMED : 26138555

Éditeur(s) : HAL CCSD American Chemical Society
Résumé : Four new sesquiterpene alkaloids (1-4) with a β-dihydroagrofuran skeleton and a new triterpenoid (5) were isolated from an ethyl acetate extract of Maytenus oblongata stems. Their structures were elucidated using 1D and 2D NMR spectroscopy as well as MS and ECD experiments. The M. oblongata stem EtOAc extract and the pure compounds isolated were tested for larvicidal activity against Aedes aegypti under laboratory conditions, and compounds 2 and 3 were found to be active.
ISSN: 0163-3864

hal-01603411
https://hal.archives-ouvertes.fr/hal-01603411
DOI : 10.1021/acs.jnatprod.6b00850
PUBMED : 28186749
PRODINRA : 406747

Éditeur(s) : HAL CCSD
Résumé : International audience
International journal of electrochemical science

hal-01109736
https://hal-agroparistech.archives-ouvertes.fr/hal-01109736