Optical method for predicting the composition of self-assembled monolayers of mixed thiols on surfaces coated with silver nanoparticles

With a simple optical method, based on UV-vis absorption spectra on glass slides, it is possible to predict the composition of self-assembled monolayers of mixed thiols, grafted on monolayers of silver nanoparticles. Glass slides are modified with the layer-by-layer technique, first forming a monolayer of mercaptopropyltrimethoxysilane, then grafting a monolayer of silver nanoparticles on it. These surfaces are further coated by single or mixed thiol monolayers, by dipping the slides in toluene solutions of the chosen thiols. Exchange constants are calculated for the competitive deposition between the colorless 1-dodecanethiol or PEG5000 thiol and BDP-SH, with the latter being a thiol-bearing molecule containing the strongly absorbing BODIPY (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) moiety, synthesized on purpose. The constants are calculated by determining the fraction of BDP-SH deposited on the surface from a solution with a given molar fraction, directly measuring the absorption spectra of BDP-SH on the slides. Then, the exchange constant for the competitive deposition between 1-dodecanethiol and PEG5000 thiol is calculated by combining their exchange constants with BDP-SH. This allows to predict the fraction of the two colorless thiols coating the silver nanoparticles slides obtained from a toluene solution with a given molar fraction, for example, of PEG5000 thiol. The correctness of the calculated surface fraction is verified by studying the coating competition between 1-dodecanethiol and a PEG5000 thiol remotely modified with a strongly absorbing fluorescein fragment.     

Dimethylalkoxygallanes: monomeric versus dimeric gas-phase structures

The molecular structures of the vapors produced on heating dimethylalkoxygallanes of the type [Me(2)Ga(OR)](2) have been determined by gas electron diffraction and ab initio molecular orbital calculations. In the solid state [Me(2)Ga(OCH(2)CH(2)NMe(2))](2) (1) and [Me(2)Ga(OCH(2)CH(2)OMe)](2) (2) adopt dimeric structures, although only the monomeric forms [Me(2)Ga(OCH(2)CH(2)NMe(2))] (1a) and [Me(2)Ga(OCH(2)CH(2)OMe)] (2a) were observed in the gas phase. For comparison the structure of the vapor produced on heating [Me(2)Ga(O(t)Bu)](2) (3) was also studied by gas electron diffraction. In contrast to 1 and 2, compound 3 is dimeric in the gas phase, as well as in the solid state. The gas-phase structures of 1a and 2a exhibit five-membered rings formed by a dative bond between Ga and the donor atom (N or O) from the donor-functionalized alkoxide. In 3 there is no possibility of a monomeric structure being stabilized by the formation of such a dative bond since only a monofunctional alkoxide is present in the molecule.     

Hexylacrylate-based mixed-mode monolith,a stationary phase for the nano-HPLC separation of structurally related enkephalins

The potential of an in situ photopolymerized hexylacrylate-based monolithic stationary phase-bearing sulfonic acid groups was investigated by studying the chromatographic retention of small structurally related peptides (enkephalins) by nano-LC. Several retention mechanisms were highlighted. First, a reverse-phase chromatographic behavior toward neutral solutes due to hexylacrylate-moieties was demonstrated. Second, an evaluation of the influences of buffer pH suggested the involvement of a cation-exchange mechanism due to the presence of 2-acrylamido-2-methyl-1-propanesulfonic acid. This cation-exchange phenomenon was confirmed by the clear influence of Na⁺ concentration in the mobile phase on peptide retention.     

(13)C/(12)C isotope labelling to study leaf carbon respiration and allocation in twigs of field-grown beech trees

In situ (13)C/(12)C isotopic labelling was conducted in field-grown beech (Fagus sylvatica) twigs to study carbon respiration and allocation. This was achieved with a portable gas-exchange open system coupled to an external chamber. This method allowed us to subject leafy twigs to CO(2) with a constant carbon isotope composition (delta(13)C of -51.2 per thousand) in an open system in the field. The labelling was done during the whole light period at two different dates (in June 2002 and October 2003). The delta(13)C values of respiratory metabolites and CO(2) that is subsequently respired during the night were measured. It was found that night-respired CO(2) is not completely labelled (only ca. 58% and 27% of new carbon is found in respired CO(2) immediately after the labelling in June 2002 and October 2003, respectively) and the labelling level progressively disappeared during the next day. It is concluded that the carbon respired by beech leaves after illumination was supplied by a mixture of carbon sources in which current carbohydrates were not the only contributors. In addition, as has been found in herbaceous plants, isotopic data before labelling showed that carbon isotope discrimination favoring the (13)C isotope occurred during the night respiration of beech leaves.     

Development of a single‐cell X‐ray fluorescence flow cytometer

An X‐ray fluorescence flow cytometer that can determine the total metal content of single cells has been developed. Capillary action or pressure was used to load cells into hydrophilic or hydrophobic capillaries, respectively. Once loaded, the cells were transported at a fixed vertical velocity past a focused X‐ray beam. X‐ray fluorescence was then used to determine the mass of metal in each cell. By making single‐cell measurements, the population heterogeneity for metals in the µM to mM concentration range on fL sample volumes can be directly measured, a measurement that is difficult using most analytical methods. This approach has been used to determine the metal composition of 936 individual bovine red blood cells (bRBC), 31 individual 3T3 mouse fibroblasts (NIH3T3) and 18 Saccharomyces cerevisiae (yeast) cells with an average measurement frequency of ～4 cells min^?1. These data show evidence for surprisingly broad metal distributions. Details of the device design, data analysis and opportunities for further sensitivity improvement are described.     

A Coculture Based, 3D Bioprinted Ovarian Tumor Model Combining Cancer Cells and Cancer Associated Fibroblasts

Ovarian cancer remains a major public health issue due to its poor prognosis. To develop more effective therapies, it is crucial to set-up reliable models that closely mimic the complexity of the ovarian tumor's microenvironment. 3D bioprinting is currently a promising approach to build heterogenous and reproducible cancer models with controlled shape and architecture. However, this technology is still poorly investigated to model ovarian tumors. In this study, a 3D bioprinted ovarian tumor model combining cancer cells (SKOV-3) and cancer associated fibroblasts (CAFs) are described. The resulting tumor models show their ability to maintain cell viability and proliferation. Cells are observed to self-assemble in heterotypic aggregates. Moreover, CAFs are observed to be recruited and to circle cancer cells reproducing an in vivo process taking place in the tumor microenvironment. Interestingly, this approach also shows its ability to rapidly generate a high number of reproducible tumor models that can be subjected to usual characterizations (cell viability and metabolic activity; histology and immunological studies; and real-time imaging). Therefore, these ovarian tumor models can be an interesting tool for high throughput drug screening applications.     

Synthesis of Polyanionic C5-Modified 2′-Deoxyuridine and 2′-Deoxycytidine-5′-Triphosphates and Their Properties as Substrates for DNA Polymerases

Modified 2′-deoxyribonucleotide triphosphates (dNTPs) have widespread applications in both existing and emerging biomolecular technologies. For such applications it is an essential requirement that the modified dNTPs be substrates for DNA polymerases. To date very few examples of C5-modified dNTPs bearing negatively charged functionality have been described, despite the fact that such nucleotides might potentially be valuable in diagnostic applications using Si-nanowire-based detection systems. Herein we have synthesised C5-modified dUTP and dCTP nucleotides each of which are labelled with an dianionic reporter group. The reporter group is tethered to the nucleobase via a polyethylene glycol (PEG)-based linkers of varying length. The substrate properties of these modified dNTPs with a variety of DNA polymerases have been investigated to study the effects of varying the length and mode of attachment of the PEG linker to the nucleobase. In general, nucleotides containing the PEG linker tethered to the nucleobase via an amide rather than an ether linkage proved to be the best substrates, whilst nucleotides containing PEG linkers from PEG₆ to PEG₂₄ could all be incorporated by one or more DNA polymerase. The polymerases most able to incorporate these modified nucleotides included Klentaq, Vent(exo-) and therminator, with incorporation by Klenow(exo-) generally being very poor.     

Molecular Gears: From Solution to Surfaces

This review highlights the major efforts devoted to the development of molecular gears over the past 40 years, from pioneering covalent bis-triptycyl systems undergoing intramolecular correlated rotation in solution, to the most recent examples of gearing systems anchored on a surface, which allow intermolecular transmission of mechanical power. Emphasis is laid on the different strategies devised progressively to control the architectures of molecular bevel and spur gears, as intramolecular systems in solution or intermolecular systems on surfaces, while aiming at increased efficiency, complexity and functionality.     

The synthesis, structure and reactivity of aldehyde substituted η-allylic complexes of molybdenum

Reaction of cis-[Mo(NCMe)₂(CO)₂(η⁵-L)][BF₄] (L=C₅H₅ or C₅Me₅) with 1-acetoxybuta-1,3-diene gives the cationic complexes [Mo{η⁴-syn-s-cis-CH₂CHCHCH(OAc)}(CO)₂(η⁵-L)][BF₄], which, on reaction with aqueous NaHCO₃/CH₂Cl₂, afford good yields of the anti-aldehyde substituted complexes [Mo{η³-exo-anti-CH₂CHCH(CHO)}(CO)₂(η⁵-L)] 2 (L=C₅Me₅), 4 (L=C₅H₅)]. The corresponding η⁵-indenyl substituted complex 5 was prepared by protonation (HBF₄·OEt₂) of [Mo(η³-C₃H₅)(CO)₂(η⁵-C₉H₇)] followed by addition of CH₂=CHCH=CH(OAc) and hydrolysis (aq. NaHCO₃/CH₂Cl₂). An X-ray crystallographic study of complex 2 confirmed the structure and showed that there is a contribution from a zwitterionic form involving donation of electron density from the molybdenum to the aldehyde carbonyl group. Treatment of 2 and 4, in methanol solution, with NaBH₄ afforded the alcohols [Mo{η³-exo-anti-CH₂CHCHCH₂(OH)}(CO)₂(η⁵-L)] [6 (L=C₅H₅), 8 (L=C₅Me₅)]; however, prolonged (30 h) reaction with NaBH₄/MeOH surprisingly gave good yields of the methoxy-substituted complexes [Mo{η³-exo-anti-CH₂CHCHCH₂(OMe)}(CO)₂(η⁵-L)] [7 (L=C₅H₅), 9 (L=C₅Me₅)], the structure of 7 being confirmed by single crystal X-ray crystallography. This methoxylation reaction can be explained by coordination of the hydroxyl group present in 6 and 8 onto B₂H₆ to form the potential leaving group HOBH₃⁻, which on ionisation affords [Mo(η⁴-exo-buta-1-3-diene)(CO)₂(η⁵-L)]⁺ which is captured by reaction with OMe⁻. Complex 8 is also formed in good yield on reaction of 2 with HBF₄·OEt₂ followed by treatment of the resulting cation [Mo{η⁴-exo-s-cis-syn-CH₂CHCHCH(OH)}(CO)₂(η⁵-C₅Me₅)][BF₄] with Na[BH₃CN]. Reaction of 4 with the Grignard reagents MeMgI, EtMgBr or PhMgCl afforded moderate yields of the alcohols [Mo{η³-exo-anti-CH₂CHCHCH(OH)R}(CO)₂(η⁵-C₅H₅)] [11 (R=Me), 12 (R=Et), 13 (R=Ph)]. Similarly, treatment of 2 with MeLi gave the corresponding alcohol 14. An attempt to carry out the Oppenauer oxidation [Al(OPr′)₃/Me₂CO] of 11 resulted in an elimination reaction and the formation of the η³-s-pentadienyl complex [Mo{η³-exo-anti-CH₂CHCH(CHCH₂)}(CO)₂(η⁵-C₅H₅)], which was structurally identified by X-ray crystallography. Interestingly, oxidation of 6 with [Bu₄ⁿN][RuO₄]/morpholine-N-oxide affords the aldehyde complex, 4 in good yield. Finally, reaction of 11 with [NO][BF₄] followed by addition of Na₂CO₃ affords the fur-3-ene complex [Mo{η²-

(H)Me}(CO)(NO)(η⁵-C₅H₅)].