Reactant concentrations from fluorescence correlation spectroscopy with tailored fluorescent probes. An example of local calibration-free pH measurement

The present account is concerned with the measurement of local reactant concentrations by observing specific fluorescent probes in fluorescence correlation spectroscopy (FCS). The Theoretical Analysis section revisits the photophysical, thermodynamic, and kinetic information that is contained in the corresponding FCS correlation curves. In particular, we examine the conditions under which FCS is revealed as a superior tool to measure concentrations of reactive species. Careful molecular engineering of the specific fluorescent probes that simultaneously integrates photophysical, thermodynamic, and kinetic constraints will be required to benefit most from FCS. We illustrate the FCS titration approach with a series of fluorescent probes that we tailored to measure pH at around 4-6 by FCS after two-photon excitation. We show that an optimal design allows one to access pH without any preliminary calibrations such as the determination of the protonation constant or the photophysical properties of the fluorescent probe.     

Influence of carbonates on the surface charge of a natural solid

Carbonates are the predominating species in natural chemical processes. Thus, understanding the reactions that occur on their surfaces is very important. The aim of this study was to determine the influence of carbonates on the surface charge of a natural soil sample. First, surface properties of a synthesized calcite were determined using a simplified surface speciation model correlated to potentiometric titrations, and then intrinsic acidity constants and pH(znpc) (pH where protonic surface charge is equal to 0) were studied for solids with different percentages of calcite. A strong influence on surface properties of the solids was evidenced even for small additional quantities of calcite.     

Asymmetric Michael reaction involving chiral imines/secondary enamines: stereocontrolled synthesis of 2,2-disubstituted tetrahydrothiophen-3-ones

[reaction: see text] The asymmetric Michael reaction involving a chiral imine derived from 2-methyltetrahydrothiophenone-3-one and enantiopure (R)-1-phenylethylamine with a variety of electrophilic alkenes furnished 2,2-disubstituted tetrahydrothiophenone-3-ones with good yields and excellent stereoselectivity.     

Synthesis of copolymer brushes endowed with adhesion to stainless steel surfaces and antibacterial properties by controlled nitroxide-mediated radical polymerization

Novel copolymer brushes have been synthesized by a two-step "grafting from" method that consists of the electrografting of poly(2-phenyl-2-(2,2,6,6-tetramethyl-piperidin-1-yloxy)-ethylacrylate) onto stainless steel, followed by the nitroxide-mediated radical polymerization of 2-(dimethylamino ethyl)acrylate and styrene or n-butyl acrylate, initiated from the electrografted polyacrylate chains. The grafted copolymers were quaternized in order to endow them with antibacterial properties. Peeling tests have confirmed the strong adhesion of the grafted copolymer onto the stainless steel substrate. Quartz crystal microbalance experiments have proven that fibrinogen adhesion is lower on the hydrophilic quaternized films compared to the nonionic counterpart. Such quaternized copolymers exhibit significant antibacterial activity against the Gram-positive bacteria S. aureus and the Gram-negative bacteria E. coli.     

Diastereoselective allylzincation of γ-oxygenated vinyllithiums bearing functionalized side-chains

Allylzincation of γ-oxygenated vinyllithiums bearing functionalized side-chains proved to be more difficult than that reported in the case of γ-oxygenated vinyllithiums with unfunctionalized side-chains. However, when allylzincation occurs it gives the corresponding linear compounds with high diastereoselection as a consequence of the zinc being coordinated by the two oxygen atoms of the methoxymethyl ether moiety.     

The Heck-type arylation of allylic alcohols with arenediazonium salts

The Heck coupling of ArN₂BF₄ with secondary allylic alcohols, carried out in methanol using Pd(dba)₂ as catalyst without extra ligands and base, leads to the corresponding β-arylated carbonyl compounds. Such conditions afford arylated acetals from primary allylic alcohols.     

Antiferromagnetic coupling between rare earth ions and semiquinones in a series of 1:1 complexes

We use the strategy of diamagnetic substitution for obtaining information on the crystal field effects in paramagnetic rare earth ions using the homologous series of compounds with the diamagnetic tropolonato ligand, Ln(Trp)(HBPz(3))(2), and the paramagnetic semiquinone ligand, Ln(DTBSQ)(HBPz(3))(2), (DTBSQ = 3,5-di-tert-butylsemiquinonato, Trp = tropolonate, HBPz(3)= hydrotrispyrazolylborate) for Ln = Sm(iii), Eu(iii), Gd(iii), Tb(iii), Dy(iii), Ho(iii), Er(iii) or Yb(iii). The X-ray crystal structure of a new form of tropolonate derivative is presented, which shows, as expected, a marked similarity with the structure of the semiquinonate derivative. The Ln(Trp)(HBPz(3))(2) derivatives were then used as a reference for the qualitative determination of crystal field effects in the exchange coupled semiquinone derivatives. Through magnetisation and susceptibility measurements this empirical diamagnetic substitution method evidenced for Er(iii), Tb(iii), Dy(iii) and Yb(iii) derivatives a dominating antiferromagnetic coupling. The increased antiferromagnetic contribution compared to other radical-rare earth metal complexes formed by nitronyl nitroxide ligands may be related to the increased donor strength of the semiquinone ligand.     

Intramolecular rhodium-catalyzed activation of α-amino C-H bonds: decisive influence of conformational factors in the synthesis of bicyclic aminals from N-sulfamoyloxyacetyl azacycloalkanes

The activation of α-amino C-H bonds in azacycloalkanes by way of intramolecular rhodium-catalyzed amination is reported. In this study, the ‘activating’ sulfamoyloxy group is attached to the endocyclic nitrogen atom with an appropriate linker. The influence of various structural parameters was studied. Results obtained demonstrate the remarkable conformational control that is possible with such azacycloalkane systems. This work leads to the first example of a successful intramolecular catalyzed amination of a tertiary sulfamic ester, a substrate known to be highly prone to elimination and/or nucleophilic displacement.     

Atom-sensitive textiles as visual indicators for plasma post-discharges

The efficiency of surface treatments by plasma and post-discharge plasma processes is greatly dependent on the density of active species, such as neutral atoms in post-discharges. Therefore, many diagnostics exist to detect the presence and measure the concentrations of these species, but they often require expensive instrumentation and highly qualified personnel. These conditions are not often met when the process is industrially used and it becomes important to imagine simple indicators allowing to validate that the correct operating conditions are reached. In the present paper, we present the first results on the investigation of an inexpensive and easy to use visual indicator able to quantify the atomic species density in nitrogen post-discharge plasma processes. It is based on the differential recombination coefficients of N-atoms on metallic/textile fibres which are intrinsically bonded together in a fabric matrix which serves as support for a thermochromic ink. The specific heating of the metallic fibres by N-atom recombination heats the whole of the fabric, leading to a visible colour change of the thermochromic ink, and therefore, of the indicator. Through modelling, it was possible to estimate that the inclusion of copper fibres to a pure cotton matrix leads to a 60% increase of the global N-atom recombination coefficient of the fabric, sufficient enough to provide a clearly visible colour change.     

Synthesis and MALDI‐TOF analysis of dendritic‐linear block copolymers of lactides: Influence of architecture on stereocomplexation

Formation of a stereocomplex from polylactide copolymers can be tuned by changing the size and the chain topology of the second block in the copolymer. In particular, the use of a dendritic instead of linear architecture is expected to destabilize the cocrystallisation of polylactide blocks. With this idea in mind, dendritic‐linear block copolymers were synthesized by ring‐opening polymerization (ROP) of lactides using benzyl alcohol dendrons of generation 1–3 as macroinitiators and stannous octoate as catalyst. Polymers with controlled and narrow molar mass distribution were obtained. The MALDI‐TOF mass spectra of these dendritic‐linear block copolymers show well‐resolved signals. Remarkably, 10% or less of odd‐membered polymers are present, indicating that ester‐exchange reactions which occur classically parallel to the polymerization process, were in these conditions, very limited. Thermal analysis of polyenantiomers of generation 1–3 and the corresponding blends were examined. The blend of a pair of enantiomeric dendritic‐linear block copolymers exhibit a higher melting temperature than each copolymer, characteristic for the formation of a stereocomplex. Melting temperatures are strongly dependent on the dendron generation. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6782–6789, 2006