Mass Determination of Entire Amyloid Fibrils by Using Mass Spectrometry

Amyloid fibrils are self‐assembled protein structures with important roles in biology (either pathogenic or physiological), and are attracting increasing interest in nanotechnology. However, because of their high aspect ratio and the presence of some polymorphism, that is, the possibility to adopt various structures, their characterization is challenging and basic information such as their mass is unknown. Here we show that charge‐detection mass spectrometry, recently developed for large self‐assembled systems such as viruses, provides such information in a straightforward manner.     

The search for a potentially prebiotic synthesis of nucleotides via arabinose-3-phosphate and its cyanamide derivative

For the RNA world hypothesis to be accepted, the constitutional self-assembly of RNA will have to be demonstrated. Conceptually, the simplest route to RNA involves nucleotide polymerisation. Activated pyrimidine nucleotides can be derived from arabinose-3-phosphate under potentially prebiotic conditions, but the prebiotic synthesis of this sugar phosphate has not hitherto been investigated. The results of synthetic approaches involving phosphorylation, phosphate migration and 2,3-C--C bond construction are described herein.     

Genotoxicity of visible light (400–800 nm) and photoprotection assessment of ectoin, l-ergothioneine and mannitol and four sunscreens

This study was designed to determine the genotoxic effects of visible (400–800 nm) and ultraviolet A (UVA)/visible (315–800 nm) lights on human keratinocytes and CHO cells. The alkaline comet assay was used to quantify DNA-damage. In addition, photo-dependent cytogenetic lesions were assessed in CHO cells by the micronucleus test. Three protective compounds [ectoin, l-ergothioneine (ERT) and mannitol] were tested with the comet assay for their effectiveness to reduce DNA single-strand breaks (SSB). Finally, the genomic photoprotections of two broad-band sunscreens and their tinted analogues were assessed by the comet assay. The WST-1 cytotoxicity assay revealed a decrease of the keratinocyte viability of 30% and 13% for the highest UVA/visible and visible irradiations (15 and 13.8 J/cm², respectively). Visible as well as UVA/visible lights induced DNA SSB and micronuclei, in a dose-dependent manner. The level of DNA breakage induced by visible light was 50% of the one generated by UVA/visible irradiation. However, UVA radiations were 10 times more effective than visible radiations to produce SSB. The DNA lesions induced by visible and UVA/visible lights were reduced after a 1-h preincubation period with the three tested compounds. The maximal protective effects were 92.7%, 97.9% and 52.0% for ectoin (0.1 mM), ERT (0.5 mM) and mannitol (1.5 mM), respectively, against visible light and 68.9%, 59.8% and 62.7% for ectoin (0.1 mM), ERT (0.5 mM) and mannitol (1.5 mM), respectively, against UVA/visible light. Thus, visible light was genotoxic on human keratinocytes and CHO cells through oxidative stress mechanisms similar to the ones induced by UVA radiations. The four tested sunscreens efficiently prevented DNA lesions that were induced by both visible and UVA/visible irradiations. The tinted sunscreens were slightly more effective that their colorless analogues. There is a need to complement sunscreen formulations with additional molecules to obtain a complete internal and external photoprotection against both UVA and visible lights.     

Self-assembly of nucleoamphiphiles: investigating nucleosides effect and the mechanism of micrometric helix formation

A new family of self-assembling systems based on nucleoamphiphiles is described. Nano to micrometric left-handed helix formation in aqueous solution was induced simply by complexing a GMP or an AMP with a nonchiral monocationic amphiphile. The assembling behavior such as micellar formation, monolayer at air-water interface, as well as the aggregates in solution of these nucleoamphiphiles are strongly influenced by the presence of nucleosides in solution. The observed effects depend on the properties of complexed nucleotides and nucleosides with a complex mixture of pi stacking, hydrophobicity of the bases, and hydrogen bonding.     

Novel porphyrin-incorporated hydrogels for photoactive intraocular lens biomaterials

Novel surface-modified hydrogel materials have been prepared by binding charged porphyrins TMPyP (tetrakis(4-N-methylpyridyl)porphyrin) and TPPS (tetrakis(4-sulfonatophenyl)porphyrin) to copolymers of HEMA (2-hydroxyethyl methacrylate) with either MAA (methacrylic acid) or DEAEMA (2-(diethylamino)ethyl methacrylate). The charged hydrogels display strong electrostatic interactions with the appropriate cationic or anionic porphyrins to give materials which are intended to be used to generate cytotoxic singlet oxygen (1O2) on photoexcitation and can therefore be used to reduce postoperative infection of the intraocular hydrogel-based replacement lenses that are used in cataract surgery. The UV/vis spectra of TMPyP in MAA:HEMA copolymers showed a small shift in the Soret band and a change from single exponential (161 micros) triplet decay lifetime in solution to a decay that could be fitted to a biexponential fit with two approximately equal components with tau = 350 and 1300 micros. O2 bubbling reduced the decay to a dominant (90%) component with a much reduced lifetime of 3 micros and a minor, longer lived (20 micros) component. With D2O solvent the 1O2 lifetime was measured by 1270 nm fluorescence as 35 micros in MAA:HEMA, compared to 67 mus in solution, although absorbance-matched samples showed similar yield of 1O2 in the polymers and in aqueous solution. In contrast to the minor perturbation in photophysical properties caused by binding TMPyP to MAA:HEMA, TPPS binding to DEAEMA:HEMA copolymers profoundly changed the 1O2 generating ability of the TPPS. In N2-bubbled samples, the polymer-bound TPPS behaved in a similar manner to TMPyP in its copolymer host; however, O2 bubbling had only a very small effect on the triplet lifetime and no 1O2 generation could be detected. The difference in behavior may be linked to differences in binding in the two systems. With TMPyP in MAA:HEMA, confocal fluorescence microscopy showed significant penetration of the porphyrin into the core of the polymer film samples (>150 microm). However, for TPPS in DEAEMA:HEMA copolymers, although the porphyrin bound much more readily to the polymer, it remained localized in the first 20 microm, even in heavily loaded samples. It is possible that the resulting high concentration of TPPS may have cross-linked the hydrogels to such an extent that it significantly reduced the solubility and/or diffusion rate of oxygen into the doped polymers. This effect is significant since it demonstrates that even simple electrostatic binding of charged porphyrins to hydrogels can have an unexpectedly large effect on the properties of the system as a whole. In this case it makes the apparently promising TPPS/DEAEMA:HEMA system a poor candidate for clinical application as a postoperative antibacterial treatment for intraocular lenses while the apparently equivalent cationic system TMPyP/MAA:HEMA displays all the required properties.     

Mixed supramolecular cation-carrier and anion-carrier facilitated transport for the selective alkali cations transport

In this paper, we describe the study of the membrane transport properties of mixed supramolecular macrocyclic cation-carriers [1·K]⁺, [2·Na]⁺ and phenylureidoarene anion-carriers [3–5·I]⁻ through bulk liquid membranes. Our efforts involve the evaluation of the transport performances of these systems designed to transport ionic salts NaI and KI and strongly depending on encoded molecular features of the anion-carrier subcomponents.     

Enantiomerically pure bicyclo[3.3.1]nona-2,6-diene as the sole source of enantioselectivity in BIPHEP-Rh asymmetric hydrogenation

In situ resolution of the rapidly racemising diphosphine BIPHEP and its relatives with the cationic Rh complex of (S,S)-bicyclonona-2,6-diene permits the asymmetric hydrogenation of dehydroamino esters.     

Thermal rearrangement of 2-bromooxazolines to 2-bromoisocyanates

A unprecedented thermally induced rearrangement of 2-bromo-4-substituted oxazolines into 2-bromoisocyanates with high selectivity has been observed. Isolated yields of 85-90% were obtained with 2-bromo-4-phenyloxazoline, 2-bromo-4-isopropyloxazoline, or 2-bromo-4,4-dimethyloxazoline. In addition, chiral aziridinecarboxamides or 2-aminooxazolines could be selectively obtained from the corresponding 2-bromo isocyanate depending on reaction conditions.     

Molecular structures of M(Bu(t))3 (M = Al, Ga, In) using gas-phase electron diffraction and ab initio calculations: experimental and computational evidence for charge-transfer processes leading to photodissociation

The gas-phase structures of AI(Bu')3 and Ga(Bu')3 have been investigated by electron diffraction and are shown to consist of monomeric units with very slightly pyramidal geometries. Salient structural parameters (r(hl)) include r(A1-C) = 2.008(2) A and r(Ga-C) = 2.032(2) A. For both compounds the ligand orientations and geometries are controlled by interligand interactions. The structures of M(Bu(t))3 (M = Al, Ga, In) have been calculated ab initio and those for the aluminium and gallium derivatives are in good agreement with the electron-diffraction structures. Comparison of the ab initio calculated structure of In(Bu')3 with those of Al(Bu(t))3 and Ga(Bu(t))3 suggests that the significantly different photochemistry exhibited by the former does not result from structural factors. In fact the compounds undergo a charge-transfer process in the UV region, with the wavelength required calculated to be slightly longer for the indium compound than for the other two.     

Tethered aminohydroxylation: dramatic improvements to the process

[reaction: see text] Changing the identity of the N leaving group on a hydroxylamine-based reoxidant gives a dramatic improvement to the tethered aminohydroxylation reaction. Using OCOC6F5 as a leaving group means that only 1 mol % of osmium is required and yields as high as 98% can be obtained. Acyclic homoallylic alcohols were substrates considered too unreactive for effective use in the tethered aminohydroxylation reaction; improved reaction conditions mean that they have now become viable substrates for oxidation.