Institut de Chimie de Toulouse

The global estimation of microplastic afloat in the ocean is only approximately 1% of annual global plastic inputs. This reflects fundamental knowledge gaps in the transformation, fragmentation, and fates of microplastics in the ocean. In order to better understand microplastic fragmentation we proceeded to a thorough physicochemical characterization of samples collected from the North Artlantic subtropical gyre during the sea campaign Expedition seventh Continent in May 2014. The results were confronted with a mathematical approach. The introduction of mass distribution in opposition to the size distribution commonly proposed in this area clarify the fragmentation pattern. The mathematical analysis of the mass distribution points out a lack of debris with mass lighter than 1 mg. Characterization by means of microscopy, microtomography, and infrared microscopy gives a better understanding of the behavior of microplastic at sea. Flat pieces of debris (2 to 5 mm in length) typically have one face that is more photodegraded (due to exposure to the sun) and the other with more biofilm, suggesting that they float in a preferred orientation. Smaller debris, with a cubic shape (below 2 mm), seems to roll at sea. All faces are evenly photodegraded and they are less colonized. The breakpoint in the mathematical model and the experimental observation around 2 mm leads to the conclusion that there is a discontinuity in the rate of fragmentation: we hypothesized that the smaller microplastics, the cubic ones mostly, are fragmented much faster than the parallelepipeds.

-H auration and reductive elimination, allowing a gold-catalyzed direct arylation of arenes with aryl halides. Key to this discovery is the use of Me-Dalphos, a simple ancillary (P,N) ligand, that allows the bottleneck oxidative addition of aryl iodides and bromides to readily proceed under mild conditions. The hemilabile character of the amino group plays a crucial role in this transformation, as substantiated by density functional theory calculations.Catalysis involving Au(I)/Au(III) cycles are notoriously hampered by the reluctance of Au(I) towards oxidative addition. Here, the authors show that an hemilabile bidentate ligand promotes oxidative addition of aryl halides to Au(I) and the catalytic formation of biaryl coupling products.

Metals are found associated with beta-pleated sheets of Abeta42 in vivo and may be involved in their formation. Metal chelation has been proposed as a therapy for Alzheimer's disease on the basis that it may safely dissolve precipitated Abeta peptides. We have followed fibrillisation of Abeta42 in the presence of an additional metal ion (Al(III), Fe(III), Zn(II), Cu(II)) over a period of 32 weeks and we have investigated the dissolution of these aged peptide aggregates in the presence of both desferrioxamine (DFO) and ethylenediaminetetraacetic acid (EDTA). Abeta42 either alone or in the presence of Al(III) or Fe(III) formed beta-pleated sheets of plaque-like amyloids which were dissolved upon incubation with either chelator. Zn(II) inhibited whilst Cu(II) prevented the formation of beta-pleated sheets of Abeta42and neither of these influences were affected by incubation of the aged peptide aggregates with either DFO or EDTA. Freshly prepared solutions of Abeta42 either alone or in the presence of added Al(III) or Fe(III) did not form beta-pleated amyloid in the presence of DFO when incubated for up to 8 weeks. EDTA did not prevent beta-pleated amyloid formation in the same treatments and promoted beta-pleated amyloid formation in the presence of either Zn(II) or Cu(II). The presence of significant concentrations of Al(III) and Fe(III) as contaminants of 'Abeta42 only' preparations suggested that both of these metals were involved in either triggering the formation or stabilising the structure of beta-pleated amyloid. If the formation of such amyloid is critical to the aetiology of AD then the chelation of Al(III) and Fe(III) may prove to be a protective mechanism whilst the chelation of Cu(II) and Zn(II) without also chelating Al(III) and Fe(III) might actually exacerbate the condition.

Thanks to rational ligand design, the first gold(I) complexes to undergo oxidative addition of aryl iodides were discovered. The reaction proceeds under mild conditions and is general. The ensuing aryl gold(III) complexes have been characterized by spectroscopic and crystallographic means. DFT calculations indicate that the bending induced by the diphosphine ligand plays a key role in this process.

The value of gold: The coordination of ambiphilic diphosphanylborane ligands to AuCl provides unusual square-planar gold(I) complexes. Insight is gained on the nature of the gold→borane interactions in these complexes through natural bond orbital (NBO) analysis and 197Au Mössbauer spectroscopy.

The ambiphilic triphosphine-borane ligand 1 {TPB = [o-iPr2P-(C6H4)3B} readily coordinates to all group 10 and 11 metals to afford a complete series of metal boratranes (TPB)[M] 2-8 (2: M = Ni, 3: M = Pd, 4: M = Pt, 5: M = CuCl, 6: M = AgCl, 7: M = AuCl, 8: M = Au+). Spectroscopic and structural characterization unambiguously establishes the presence of M-B interactions in all of these complexes. The first evidence for borane coordination to copper and silver is provided, and the Au-->B interaction is shown to persist upon chloride abstraction. Experimental and theoretical considerations indicate that the M-->B interaction is strongest in the Pt and Au complexes. The influence of the oxidation state and charge of the metal is substantiated, and the consequences of relativistic effects are discussed. The coordination of the sigma-acceptor borane ligand is found to induce a significant bathochromic shift of the UV-vis spectra, the Ni, Pd, and Pt complex presenting strong absorptions in the visible range. In addition, all of the group 10 and 11 metal boratranes adopt C3 symmetry both in the solid state and in solution. The central M-->B interaction is found to moderately influence the degree of helicity and configurational stability of these three-bladed propellers, and DFT calculations support a dissociative pathway for the inversion process.

Estimates of cumulative plastic inputs into the oceans are expressed in hundred million tons, whereas the total mass of microplastics afloat at sea is 3 orders of magnitude below this. This large gap is evidence of our ignorance about the fate of plastics, as well as transformations and sinks in the oceans. One of the current challenges consists of identifying and quantifying plastic particles at the microscale, the small microplastics (SMP, 25–1000 μm). The aim of the present study is to investigate SMP concentration in count and in mass at the sea surface in the North Atlantic subtropical gyre during the sea campaign Expedition 7 th Continent. After isolation, SMP were characterized by micro-Fourier-transform infrared spectroscopy. Microplastic distribution was modeled by a wind-driven vertical mixing correction model taking into account individual particle properties (dimension, shape and density). We demonstrate that SMP buoyancy is significantly decreased compared to the large microplastics (LMP, 1–5 mm) and consequently more susceptible to vertical transport. The uncorrected LMP concentration in count was between 13 000 and 174 000 pieces km –2, and was between 5 and 170 times more abundant for SMP. With a wind-driven vertical mixing correction, we estimated that SMP were 300 to 70 000 times more abundant than LMP. When discussing this in terms of weight after correction, LMP concentrations were between 50 and 1000 g km –2, and SMP concentrations were between 5 and 14 000 g km –2 .

Reaction of the geminal PAl ligand [Mes2PC(═CHPh)AltBu2] (1) with [Pt(PPh3)2(ethylene)] affords the T-shape Pt complex [(1)Pt(PPh3)] (2). X-ray diffraction analysis and DFT calculations reveal the presence of a significant Pt→Al interaction in 2, despite the strain associated with the four-membered cyclic structure. The Pt···Al distance is short [2.561(1) Å], the Al center is in a pyramidal environment [Σ(C-Al-C) = 346.6°], and the PCAl framework is strongly bent (98.3°). Release of the ring strain and formation of X→Al interactions (X = O, S, H) impart rich reactivity. Complex 2 reacts with CO2 to give the T-shape adduct 3 stabilized by an O→Al interaction, which is a rare example of a CO2 adduct of a group 10 metal and actually the first with η(1)-CO2 coordination. Reaction of 2 with CS2 affords the crystalline complex 4, in which the PPtP framework is bent, the CS2 molecule is η(2)-coordinated to Pt, and one S atom interacts with Al. The Pt complex 2 also smoothly reacts with H2 and benzamide PhCONH2 via oxidative addition of H-H and H-N bonds, respectively. The ensuing complexes 5 and 7 are stabilized by Pt-H→Al and Pt-NH-C(Ph) = O→Al bridging interactions, resulting in 5- and 7-membered metallacycles, respectively. DFT calculations have been performed in parallel with the experimental work. In particular, the mechanism of reaction of 2 with H2 has been thoroughly analyzed, and the role of the Lewis acid moiety has been delineated. These results generalize the concept of constrained geometry TM→LA interactions and demonstrate the ability of Al-based ambiphilic ligands to participate in TM/LA cooperative reactivity. They extend the scope of small molecule substrates prone to such cooperative activation and contribute to improve our knowledge of the underlying factors.

Taking advantage of phosphine chelation, direct evidence for oxidative addition of Csp(2)-X bonds (X = I, Br) to a single gold atom is reported. NMR studies and DFT calculations provide insight into this unprecedented transformation, which gives straightforward access to stable (P,C) cyclometalated gold(III) complexes.

N,N'-linked oligoureas with proteinogenic side chains are peptide backbone mimetics belonging to the gamma-peptide lineage. In pyridine, heptamer 4 adopts a stable helical fold reminiscent of the 2.6(14) helical structure proposed for gamma-peptide foldamers. In the present study, we have used a combination of CD and NMR spectroscopies to correlate far-UV chiroptical properties and conformational preferences of oligoureas as a function of chain length from tetramer to nonamer. Both the intensity of the CD spectra and NMR chemical shift differences between alphaCH2 diastereotopic protons experienced a marked increase for oligomers between four and seven residues. No major change in CD spectra occurred between seven and nine residues, thus suggesting that seven residues could be the minimum length required for stabilizing a dominant conformation. Unexpectedly, in-depth NMR conformational investigation of heptamer 4 in CD3OH revealed that the 2.5 helix probably coexists with partially (un)folded conformations and that Z-E urea isomerization occurs, to some degree, along the backbone. Removing unfavorable electrostatic interactions at the amino terminal end of 4 and adding one H-bond acceptor by acylation with alkyl isocyanate (4 --> 7) was found to reinforce the 2.5 helical population. The stability of the 2.5 helical fold in MeOH is further discussed in light of unrestrained molecular dynamics (MD) simulation. Taken together, these new data provide additional insight into the folding propensity of oligoureas in protic solvent and should be of practical value for the design of helical bioactive oligoureas.

The ability of the MeDalphos ligand to trigger oxidative addition of iodoarenes preferentially electron-rich, to gold has been thoroughly studied and exploited to develop an efficient Au( i )/Au( iii )-catalysed C3-arylation of indoles.

Two P or not two P: The synthesis of the first stable disilyne bisphosphine adduct is reported. Its X-ray structure, showing a short SiSi bond with a certain multiple-bond character, illustrates the peculiar ligand effect of phosphine towards SiI compared to other ligands. The disilyne derivative rapidly reacts with CO2 at room temperature, thus allowing the non-metal-mediated direct reduction of CO2 to CO (see picture).

Gallant exchange: Upon coordination of phosphanyl gallane ligands to AuCl, both neutral and zwitterionic complexes coexist. NMR spectroscopy provides direct evidence for the transfer of the chloride between gold and gallium in diphosphanyl gallane. The introduction of a third phosphanyl buttress allows the separation and structural characterization of the two coordination isomers (see picture; Au yellow, P red, Cl green, Ga blue).

Tuberculosis, HIV coinfection with TB, emergence of multidrug-resistant TB, and extensively drug-resistant TB are the major causes of death from infectious diseases worldwide. Because no new drug has been introduced in the last several decades, new classes of molecules as anti-TB drugs are urgently needed. Herein, we report the synthesis and structure-activity relationships of a series of thioester, amide, hydrazide, and triazolophthalazine derivatives of 4-alkoxy cinnamic acid. Many compounds exhibited submicromolar minimum inhibitory concentrations against Mycobacterium tuberculosis strain (H(37)Rv). Interestingly, compound 13e, a 4-isopentenyloxycinnamyl triazolophthalazine derivative, was found to be 100-1800 times more active than isoniazid (INH) when tested for its ability to inhibit the growth of INH-resistant M. tuberculosis strains. The results also revealed that 13e does not interfere with mycolic acid biosynthesis, thereby pointing to a different mode of action and representing an attractive lead compound for the development of new anti-TB agents.

Cycling between Au(i) and Au(iii) is challenging, so gold-catalyzed cross-couplings are rare. The (MeDalphos)AuCl complex, which we showed was prone to undergo oxidative addition, is reported here to efficiently catalyze the C-N coupling of aryl iodides and amines. The transformation does not require an external oxidant or a directing group. It is robust and works with a wide scope of aryl iodides and N-nucleophiles under mild conditions. Mechanistic studies, including the NMR and MS characterization of a key aryl amido Au(iii) complex, strongly support a 2e redox cycle in which oxidative addition precedes transmetalation and reductive elimination is the rate-determining step.

A homogeneous system which is able to yield silylamine from N2 and bis(silane) in one pot is reported. Mechanistically a {(triphosphine)molybdenum(I)} fragment, generated in situ, splits N2 into the corresponding nitrido complex at room temperature. Then, functionalization of the molybdenum nitrido is achieved by double Si-H addition under mild reaction conditions. Moreover, the bis(silyl)amine product is decoordinated from the metal center.

The ambiphilic phosphino-borane i-Pr2P(o-C6H4)BMes2 affords stable versions of key zwitterionic intermediates by reactions with diethyl azodicarboxylate or PhNCO.

The specific electronic properties of bent o-carborane diphosphine gold(I) fragments were exploited to obtain the first classical carbonyl complex of gold [(DPCb)AuCO](+) (ν(CO)=2143 cm(-1) ) and the diphenylcarbene complex [(DPCb)Au(CPh2 )](+) , which is stabilized by the gold fragment rather than the carbene substituents. These two complexes were characterized by spectroscopic and crystallographic means. The [(DPCb)Au](+) fragment plays a major role in their stability, as substantiated by DFT calculations. The bending induced by the diphosphine ligand substantially enhances π-backdonation and thereby allows the isolation of carbonyl and carbene complexes featuring significant π-bond character.

Experimental NMR diffusion measure on polymers and on globular proteins are presented. These results, complemented with results found in the literature, enable a general description of effective fractal dimension for objects such as small organic molecules, sugars, polymers, DNA, and proteins. Results are compared to computational simulations as well as to theoretical values. A global picture of the diffusion phenomenon emerges from this description. A power law relating molecular mass with diffusion coefficients is described and found to be valid over 4 orders of magnitude. From this law, the fractal dimension of the molecular family can be measured, with experimental values ranging from 1.41 to 2.56 in full agreement with theoretical approaches. Finally, a method for evaluating the molecular mass of unknown solutes is described and implemented as a Web page.

A new stable heterocyclic germylene, in which the divalent germanium atom lies between a nitrogen atom and a phosphanylidene phosphorane group, was synthesized. Experimental and theoretical studies revealed the peculiar effect of phosphanylidene phosphorane substituent, which is a stronger π-donor towards germanium than an amino group is. Because of the weak phosphorus-germanium π-bond, this new germylene compound shows an enhanced reactivity compared to classical N-heterocyclic germylenes.