Diarylethene-dihydroazulene multimode photochrome: a theoretical spectroscopic investigation

Using Time-Dependent Density Functional Theory, we have assessed the structural, energetic and spectroscopic properties of a hybrid diarylethene-dihydroazulene multi-addressable switch synthesized by Mrozek et al. [Chem. Commun., 1999, 1487-1488]. All possible closed/open structures have been considered and the different activation barriers along each reaction path have been evaluated. The determination of the energetic profiles allowed us to pinpoint the thermally possible reactions. To simulate the electronic absorption spectra of this compact two-way four-state hybrid compound, we relied on a PCM-TD-DFT approach combined with a molecular orbital analysis. Key insights are reached and the experimental photochromic properties of this multi-component switch are rationalised. From a more methodological point of view, this work also shows that range-separated hybrid functionals (CAM-B3LYP and ωB97XD) allow to reproduce the measured spectroscopic features with a remarkable accuracy.     

How to control the scaling of CaCO3: a "fingerprinting technique" to classify additives

A titration set-up coupling ion selective electrodes with pH adjustment was used to analyze the effects of additives present during precipitation of calcium carbonate. Besides industrially well-established antiscalants (sodium triphosphate, citrate, polyacrylate and poly(aspartic acid)), also functional polymers being active in morphosynthesis (polystyrene sulfonate and poly(styrene-alt-maleic acid)) were analyzed. Interestingly each additive acts in its specific way, suggesting the notation "fingerprinting" for a complex interplay of up to five "solution modes" of influencing CaCO(3) precipitation and crystallisation. The results provide new insights into the modes of additive controlled crystallisation, and in the long run, the insights may facilitate the design of precipitation systems that yield complex and tailor-made crystals.     

On the physisorption of water on graphene: a CCSD(T) study

The electronic structure of the zero-gap two-dimensional graphene has a charge neutrality point exactly at the Fermi level that limits the practical application of this material. There are several ways to modify the Fermi-level-region of graphene, e.g. adsorption of graphene on different substrates or different molecules on its surface. In all cases the so-called dispersion or van der Waals interactions can play a crucial role in the mechanism, which describes the modification of electronic structure of graphene. The adsorption of water on graphene is not very accurately reproduced in the standard density functional theory (DFT) calculations and highly-accurate quantum-chemical treatments are required. A possibility to apply wavefunction-based methods to extended systems is the use of local correlation schemes. The adsorption energies obtained in the present work by means of CCSD(T) are much higher in magnitude than the values calculated with standard DFT functional although they agree that physisorption is observed. The obtained results are compared with the values available in the literature for binding of water on the graphene-like substrates.     

Surface properties of hydrogenated nanodiamonds: a chemical investigation

Hydrogen terminations (C-H) confer to diamond layers specific surface properties such as a negative electron affinity and a superficial conductive layer, opening the way to specific functionalization routes. For example, efficient covalent bonding of diazonium salts or of alkene moieties can be performed on hydrogenated diamond thin films, owing to electronic exchanges at the interface. Here, we report on the chemical reactivity of fully hydrogenated High Pressure High Temperature (HPHT) nanodiamonds (H-NDs) towards such grafting, with respect to the reactivity of as-received NDs. Chemical characterizations such as FTIR, XPS analysis and Zeta potential measurements reveal a clear selectivity of such couplings on H-NDs, suggesting that C-H related surface properties remain dominant even on particles at the nanoscale. These results on hydrogenated NDs open up the route to a broad range of new functionalizations for innovative NDs applications development.     

Chemoenzymatic synthesis of biotin-appended analogues of gangliosides GM2, GM1, GD1a and GalNAc-GD1a for solid-phase applications and improved ELISA tests

Biotinylated analogues of gangliosides GM2, GM1, GD1a and GalNAc-GD1a were synthesized in high yields using glycosyltransferases from Campylobacter jejuni. The presence of a biotin moiety in the aglycone part of these mimics allows for attachment of these materials onto various streptavidin-coated surfaces. Analysis of the interaction of biotin-appended GM1 with the B subunit of Escherichia coli heat-labile enterotoxin performed in a modified ELISA procedure shows the potential of this compound to replace the natural GM1 in toxin detection.     

Optical excitations in star-shaped fluorene molecules

A detailed study of the low-energy optical transitions in two families of star-shaped molecules is presented. Both families have 3-fold rotational symmetry with oligofluorene arms attached to a central core. In one family, the core of the molecule is a rigid meta-linked truxene, while the other is a meta-linked benzene moiety. The low-energy transitions were studied both experimentally and using time-dependent density functional theory (TD-DFT). The optical transitions of these new star-shaped molecules were compared with corresponding linear oligofluorenes. Both families of star-shaped molecules showed higher absorption and fluorescence dipoles and photoluminescence quantum yields than straight chain oligofluorenes. TD-DFT calculations show that absorption takes place across the entire molecule, and after excited state relaxation, the emission results from a single arm. In both theory and experiment the transition dipole moments show an approximate n(0.5) dependence on the number of fluorene units in each arm.     

First and biomimetic total synthesis of a member of the C-glucosidic subclass of ellagitannins, 5-O-desgalloylepipunicacortein A

The first total synthesis of a member of the C-glucosidic subclass of ellagitannins, 5-O-desgalloylepipunicacortein A, was accomplished by relying on a biomimetic aldol-type formation of its characteristic C-aryl glucosidic bond through the exploitation of the inherent chemical reactivity of a glucopyranosic hemiacetal precursor.     

Ab initio modeling of optical spectra in pH‐sensitive diarylethenes

The photochromic and acidochromic shifts undergone by recently synthesized diarylethene photochromes have been simulated using a Time‐Dependent Density Functional Theory approach relying on a range‐separated functional, namely CAM‐B3LYP. The selected approach is generally accurate for reproducing the variations of the spectral features, though acidochromic shifts are clearly more challenging than their photochromic counterparts. More importantly, an analyzis of the shapes of the relevant molecular orbitals grants insights into the electro‐cyclization of several diarylethenes, therefore partly allowing to understand the presence of experimental deadlocks. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Non-equilibrium umbrella sampling applied to force spectroscopy of soft matter

Physical systems often respond on a timescale which is longer than that of the measurement. This is particularly true in soft matter where direct experimental measurement, for example in force spectroscopy, drives the soft system out of equilibrium and provides a non-equilibrium measure. Here we demonstrate experimentally for the first time that equilibrium physical quantities (such as the mean square displacement) can be obtained from non-equilibrium measurements via umbrella sampling. Our model experimental system is a bead fluctuating in a time-varying optical trap. We also show this for simulated force spectroscopy on a complex soft molecule--a piston-rotaxane.