Synthesis of a Pentacene-Type Silaborin via Double Dehydrogenative Cyclization of 1,4-Diboryl-2,5-disilylbenzene.

A new pentacene-type silaborin, in which three benzene rings are bridged by silicon and boron atoms, has been synthesized and characterized by using NMR spectroscopy and X-ray crystallographic analysis. The precursor, 1,4-bis(dimesitylboryl)-2,5-bis(phenylsilyl)benzene (4), was prepared by stepwise introduction of a silyl group and a boryl group to a benzene ring starting from 1,4-dibromobenzene. Double cyclization of 4 proceeds by a H-Mes exchange and a B-H/C-H dehydrogenative condensation to afford pentacene-type silaborin 5. X-ray crystal structure analysis reveals that 5 adopts a bent structure rather than a planar one. UV/Vis spectra and DFT calculations for 5 reveal a lowering of the LUMO energy level compared with corresponding anthracene-type 3.

Quantification of Groundwater - Saline Surface Water Interaction in a Small Coastal Plain in North-East Tunisia using Multivariate Statistical Analysis and Geophysical Method.

Amultivariate statistical analysis used with geophysical investigation enabled the assessment of interaction between saline surface water and groundwater in the coastal plain of Wadi Al Ayn and Daroufa in CapBon peninsula, north-east Tunisia. The application of the Principal Component Analysis (PCA) identified the end members which contribute to groundwater recharge: the wastewater infiltrated from Wadi Al Ayn, the oilfield brine infiltrated to the aquifer through the sandy bed of Wadi Al Ayn, the intruded seawater near Wadi Daroufa in the downstream region and the fresh groundwater flowing from the upstream region. The contribution of wastewater in groundwater recharge varies from 1.4% in the upstream region of Wadi Al Ayn to 77% near its downstream part. The fraction of oilfield brine mixed with groundwater in the alluvial aquifer under Wadi Al Ayn varies from 1% to 13%; whereas the fraction of intruded seawater into the coastal part of the aquifer near Daroufa region varies from 2% to 21%.

Assessment of organic micropollutants occurrence in treated wastewater using heat shock protein 47 stress responses in Chinese hamster ovary cells and GC/MS-based non-target screening.

Combining bioassays and analytical chemistry screening is a powerful approach to assess organic micropollutants which are the main contributors to toxic potential in complex mixtures of treated wastewater (TWW). The aim of this study was to perform a comprehensive toxicity assessment of treated effluents using stress response bioassays and then to assess the occurrence of the organic micropollutants which were responsible for this biological response using gas chromatography coupled with a mass spectrometry detector (GC/MS). Results showed that TWW samples induced significant stress response on Chinese hamster ovary cells, stably transfected with heat shock protein 47 promoter, at 0.1%, 1%, 5% and 10% concentrations. The organic chemical compounds responsible for stress response potential were identified at different percentage values using non-target chemical screening. Of the compounds detected in TWW1 and TWW4, 55.09% and 74.5% respectively, fell within the class of aliphatic hydrocarbons. Aliphatic hydrocarbons were also present in TWW3 at 26.46% whereas 11.96% corresponded to 6-acetyl-1,1,2,4,4,7-hexamethyltetralin and 16.08% to triethoxysilane. Moreover, 76.73% of TWW2 was recorded as decamethylcyclopentasiloxane (D5) and 17.44% as n-hexadecanoic acid.

Effects of metal pollution on sediments in a highly saline aquatic ecosystem: case of the Moknine continental Sebkha (eastern Tunisia).

Potential contamination of the sediments in the Sebkha of Moknine (Tunisia) ecosystem was assessed by means of enrichment factors (EFs) estimated against reference sediment located ≈70 km away from the Sebkha. The use of EFs is recommended as a reliable method for heavy metal contamination assessment, provided that (1) element contents are corrected following a careful normalization procedure, and (2) the reference sediment is unaffected by anthropogenic alterations. The degree of contamination was assessed by the modified contamination degree approach. The obtained results indicated that surface sediments were enriched up to 22.9, 13.2, 5.46 and 3.19 times with Pb, Cu, Cr and Zn, respectively. Lower enrichment factors for Ni and Co suggested that anthropogenic sources were less important for these metals. The modified degree of contamination showed that the sediments in the Sebkha of Moknine have suffered significant systematic heavy metal contamination following catchment urbanization and industrialization .

Identification of 6-octadecynoic acid from a methanol extract of Marrubium vulgare L. as a peroxisome proliferator-activated receptor γ agonist.

6-Octadecynoic acid (6-ODA), a fatty acid with a triple bond, was identified in the methanol extract of Marrubium vulgare L. as an agonist of peroxisome proliferator-activated receptor γ (PPARγ). Fibrogenesis caused by hepatic stellate cells is inhibited by PPARγ whose ligands are clinically used for the treatment of diabetes. Plant extracts of Marrubium vulgare L., were screened for activity to inhibit fibrosis in the hepatic stellate cell line HSC-T6 using Oil Red-O staining, which detects lipids that typically accumulate in quiescent hepatic stellate cells. A methanol extract with activity to stimulate accumulation of lipids was obtained. This extract was found to have PPARγ agonist activity using a luciferase reporter assay. After purification using several chromatographic methods, 6-ODA, a fatty acid with a triple bond, was identified as a candidate of PPARγ agonist. Synthesized 6-ODA and its derivative 9-octadecynoic acid (9-ODA), which both have a triple bond but in different positions, activated PPARγ in a luciferase reporter assay and increased lipid accumulation in 3T3-L1 adipocytes in a PPARγ-dependent manner. There is little information about the biological activity of fatty acids with a triple bond, and to our knowledge, this is the first report that 6-ODA and 9-ODA function as PPARγ agonists.

Synthesis of silicon-functionalized dibenzosilaborins by intramolecular B-H/C-H dehydrogenative cyclization and their tunable photophysical and chemical properties by silyl groups.

A bit borane: Silicon-functionalized dibenzosilaborins were prepared by intramolecular B-H/C-H dehydrogenative cyclization of o-(silyl)(hydroboryl)benzenes. The hydrosilyl derivative (X=H) can be converted into the fluorosilane (X=F) and chlorosilane (X=Cl). UV/Vis and fluorescence spectra are influenced by the functional groups X on the silicon atom through σ*-π* conjugation.

Synthesis of B/Si Bidentate Lewis Acids, o-(Fluorosilyl)borylbenzenes and o-(Difluorosilyl)borylbenzenes, and Their Fluoride Ion Affinities.

Herein, we report detailed studies on a series of o-(silyl)(boryl)benzenes (1-4), in which the two Lewis acid centers consisting of silicon and boron atoms are linked via an o-phenylene skeleton. o-(Fluorosilyl)(dimesitylboryl)benzenes 1 and 2 were prepared by the reaction of fluorodimesitylborane with [o-(fluorodimethylsilyl)phenyl]lithium (7) and [o-(fluorodiphenylsilyl)phenyl]lithium (8), respectively. o-(Difluorosilyl)(dimesitylboryl)benzenes 3 and 4 were also prepared by the reaction of fluorodimesitylborane with o-{[di(methoxy)methylsilyl]phenyl}lithium (11) and o-{[di(methoxy)phenylsilyl]phenyl}lithium (12), respectively, and their subsequent treatment with HF·pyridine. Compounds 1-4 readily capture a fluoride ion in the presence of 18-crown-6 or [2.2.2]cryptand to afford their corresponding µ-fluoro-bridged ate complexes (15-18). The structures of 15-18 were revealed by NMR spectroscopy and X-ray crystallography. DFT studies and natural bond orbital analysis of 15-18 were conducted to elucidate the nature of the Si-F and B-F bonding interactions in the µ-fluoro-bridges. The fluoride ion affinities of 1-4 were investigated by 1H NMR spectroscopy to monitor their competitive reactions. The dynamic behaviors of 15-18 at variable temperatures were monitored using 19F NMR spectroscopy.

Intramolecular Activation of C-O Bond by an o-Boryl Group in o-(Alkoxysilyl)(diarylboryl)benzenes.

Halogen-lithium exchange reaction of o-(silyl)bromobenzene 5 with tert-BuLi afforded o-(silyl)lithiobenzene 6, which was reacted with (alkoxy)diarylboranes 7 to form borate intermediates 8. Treatment of 8 with chlorotrimethylsilane formed o-(alkoxysilyl)(diarylboryl)benzenes 4. The C-O bond in 4 was activated by intramolecular interaction between the oxygen atom and the boron atom. 4a readily reacted with MeOH and EtOH to afford the corresponding alkoxysilanes 10 and 11, respectively. Treatment of 10 with 1,4-diazabicyclo[2.2.2]octane (DABCO) afforded the silyloxyborate complex 13.

Synthesis of B/Si bidentate Lewis acids, o-(Fluorosilyl)(dimesitylboryl)benzenes, and their fluoride ion affinity.

o-(Fluorosilyl)(dimesitylboryl)benzenes have been prepared as colorless crystals by reacting fluorodimesitylborane with o-(fluorodimethylsilyl)phenyllithium and o-(fluorodiphenylsilyl)phenyllithium. The o-(fluorosilyl)(dimesitylboryl)benzenes serve as B/Si bidentate Lewis acid and efficiently capture fluoride ion from potassium fluoride in the presence of [2.2.2]cryptand or 18-crown-6 in toluene, giving the corresponding mu-fluoro bridged products. The structures were characterized by X-ray crystal structure analysis and multinuclear NMR spectroscopy. Fluoride ion affinities of the o-(fluorosilyl)(dimesitylboryl)benzenes were evaluated in comparison with non-silylated triarylborane.

Intramolecular H-Ar ligand exchange between silicon and boron: functionality transfer of Si-H to B-H.

o-C(6)H(4)(SiR(3-n)H(n))(BMes(2)) (1; R=Me, Ph; n=1, 2) undergo Mes-H (Mes=mesityl) ligand exchange between the silicon atom and the boron atom to form o-C(6)H(4)(SiMesR(3-n)H(n-1))(BMesH) (6) upon heating. The resulting hydroborane intermediates (6) immediately react with benzaldehyde to afford their corresponding benzyloxyboranes (5). A DFT study of model compounds reveals the transition states of the ligand exchange. A hydride abstraction from the silicon atom by the boron center is key to reaching the transition states, which include the tricoordinate silyl-cation moiety and the tetracoordinate hydridoborate moiety.

Synthesis, structure and reactions of triarylgermyl anion with alpha,delta-ambiphilic character.

Benzosilagermacyclobutene bearing two Ar groups on the germanium atom [Ar = o-(fluorodimethylsilyl)phenyl] undergoes cleavage of the Ge-Si bond with KF in the presence of a cryptand to form Ar(3)Ge(-)[K(+)(cryptand)] with alpha,delta-ambiphilic character consisting of the germyl anion center and the fluorosilyl moieties. In the presence of LiBPh(4).3dme or BF(3).Et(2)O, the germylpotassium is converted back into the benzosilagermacyclobutene.