Spectroelectrochemical detection of phenothiazine and phenoxazine derivatives covalently bound to self-assembled cystamine monolayers

The phenothiazine derivatives, Toluidine Blue O and Azur A, and the phenoxazine derivative Nile Blue were bound covalently to self-assembled cystamine monolayers chemisorbed on gold electrodes by derivatization of the surface amino groups with two different bifunctional spacers: terephthaloyl chloride and 1,6-hexamethylene-diisocyanate.The formation of the amido- and urea-derivatives of the parent compounds after covalent immobilization induces a shift of their redox potentials towards more positive values which can easily be detected by cyclic voltammetry.UV-Vis difference spectroelectrochemistry has been used to characterize the electroactive species immobilized onto transparent gold electrode surfaces in both oxidation states. In every case, the oxidized-minus-reduced (and reduced-minus-oxidized) difference spectra of the immobilized redox species show a shift of the UV maxima towards longer wavelengths and a shift of the Vis maximum towards shorter wavelengths when compared with their parent compounds. Each redox species showed different optical characteristics depending on the spacer used for immobilization.For phenothiazine derivatives immobilized with 1,6-hexamethylene di-isocyanate the total surface coverages obtained by optical methods were close to those obtained by cyclic voltammetry. However, for the same derivatives immobilized with terephthaloyl chloride, and for Nile Blue, independently of the spacer used, higher surface coverages were found by optical methods than by cyclic voltammetry.     

Gear effect—10 : Conformational aspects of the positive or negative buttressing effects of methyl groups: polymethylpyridines

The effect of the shape of a methyl group on reactivity, which cannot be accounted for by considering a methyl group as a spherical substituent with the appropriate van der Waals radius, was considered in kinetics of alkylalion of substituted pyridines and barriers to rotation and ground state conformations of an isopropyl group attached to a planar framework. The perturbation of a methyl group by an o-methyl group is accounted for by a unique conformational explanation which involves the polyhedral shape of the methyl group.     

Metal Catalyzed Polymerization: From Stereoregular Poly(α-olefins) to Tailor-Made Biodegradable/Biorenewable Polymers and Copolymers

Metal catalyzed polymerizations are among the most important chemical reactions, accounting for the production of about 400 million tons per year of polymeric materials, 50 % of which are polyolefins. The CIRCC research units at the University of Salerno, founded by the late Professor Adolfo Zambelli, a coworker of Giulio Natta and a pioneer in the studies of stereospecific polymerization catalysts, has a consolidated expertise in this field. Although often considered a “mature” area of research, olefin polymerization catalysis continues to drive great interest of both industrial and academic scientists. On the other hand, strong political and economic pressure toward the development of “green” and possibly biodegradable alternatives to olefin-based polymers stimulated our group to direct increasing research efforts in the area of sustainable polymers. In this perspective, we focus on the most recent work from the CIRCC research units involved in homogeneous catalysis for polymerization of a variety of monomers, with the aim to address how the concepts and the expertise developed for olefin polymerization can be applied to the development of different metal-catalyzed polymerizations and copolymerizations. Of course, although the results are discussed in the frame of the most important literature contributions, a comprehensive review of such a wide and diversified topic is out of the scope of the paper. References to reviews covering the different types of metal catalyzed polymerizations are provided in each chapter.     

Mediterranean diet in a Sicilian student population. Second part: breakfast and its nutritional profile

Abstract

Breakfast habits affect the nutritional status and health of people, in particular children and adolescents. This is the second part a previous study about the adherence to the Mediterranean diet in a Sicilian (Italy) student population. The investigation analysed both normal weight and overweight subjects in order to understand how eating habits, number of meals and daily calorie intakes could affect their body mass indexes (BMI). The aim of this second part was to analyse the breakfast nutritional profiles of this student population. The results highlighted that breakfast was regularly consumed by a percentage ranging from a maximum of 84% (in normal subjects) to a minimum value of 57.4% (in overweight/obese students). Milk, yoghurt, sugar, bread/rusk and tea contributed as main foods to the breakfast composition. The results highlighted that subjects who consumed breakfast showed lower BMI values with significant differences between normal and overweight/obese students.     

Pyrolysis-gas chromatography/fourier-transform infrared spectrometry of poly(ester urethane) elastomers

Three types of industrial poly (ester urethane) elastomers were studied by Curie–point pyrolysis–gas chromatography/Fourier–Transform infrared spectrometry (Py–GC/FTIR) with a maximum pyrolysis temperature of 973 K. The samples chosen were the Urepans 600 and 641 from Bayer and Elastollan C 78 A from BASF/Elastogran. The poly(ester urethane) elastomers are composed of three units: a polyesterdiol, a short chain diol and a diisocyanate. Py–GC/FTIR allows a rapid and unambiguous identification of the polymer chains by key fragments.     

Aggregation induced colour change for phosphorescent iridium(III) complex-based anionic surfactants

We describe a new class of water soluble metallosurfactant molecules based on luminescent neutral iridium(III) complexes. The compounds possess an alkyl chain terminated with a negatively charged group, a sulphate. Due to their amphiphilic nature they assemble in aggregates in water and their photophysical properties, as well as the morphological characterization of the assemblies are presented. In particular, UV-Vis absorption, steady-state and time-resolved emission spectroscopy, dynamic light scattering and scanning electron microscopy techniques have been employed towards the analysis of the assemblies in different media. Comparison with the single components shows that the aggregates have very different photophysical properties. Importantly, the change in colour upon self-assembly is a remarkable feature which could be used for the design of probes which can change properties in different environments.     

Chemical basis of peptidoglycan discrimination by PrkC, a key kinase involved in bacterial resuscitation from dormancy

Bacterial Ser/Thr kinases modulate a wide number of cellular processes. In Bacillus subtilis , the Ser/Thr kinase PrkC has been shown to induce germination of bacterial spores in response to DAP-type but not Lys-type cell wall muropeptides. Muropeptides are a clear molecular signal that growing conditions are promising, since they are produced during cell wall peptidoglycan remodeling associated with cell growth and division of neighboring bacteria. However, whether muropeptides are able to bind the protein physically and how the extracellular region is able to distinguish the two types of muropeptides remains unclear. Here we tackled the important question of how the extracellular region of PrkC (EC-PrkC) senses muropeptides. By coupling NMR techniques and protein mutagenesis, we exploited the structural requirements necessary for recognition and binding and proved that muropeptides physically bind to EC-PrkC through DAP-moiety-mediated interactions with an arginine residue, Arg500, belonging to the protein C-terminal PASTA domain. Notably, mutation of this arginine completely suppresses muropeptide binding. Our data provide the first molecular clues into the mechanism of sensing of muropeptides by PrkC.     

A DFT study of substituent effects in corannulene dimers

Corannulene dimers made up of corannulene monomers with different curvature and substituents were studied using M06-2X, B97D and ωB97XD functionals and 6-31+G* basis set. Corannulene molecules were substituted with five alternating Br, Cl, CH(3), C(2)H or CN units. Geometric results showed that substituents gave rise to small changes in the curvature of corannulene bowls. So, there was not a clear relationship between the curvature of bowls and the changes on interaction energy generated by addition of substituents in the bowl. Electron withdrawing substituents gave rise to a more positive molecular electrostatic potential (MEP) of the bowl, which was able to get a strong interaction with the negative MEP at the surface of a fullerene. Substitution with CN caused the largest effect, giving rise to the most positive MEP and to a large interaction energy of -24.64 kcal mol(-1), at the ωB97XD/6-31+G* level. Dispersive effects must be taken into account to explain the catching ability of the different substituted corannulenes. For unsubstituted dimers, calculations with DFT-D methods employing ωB97XD and B97D functionals led to similar results to those previously reported at the SCS-MP2/cc-pVTZ level for corannulene dimers (A. Sygula and S. Saeb?, Int. J. Quant. Chem., 2009, 109, 65). In particular, the ωB97XD functional led to a difference of only 0.35 kcal mol(-1), regarding MP2 interaction energy for corannulene dimers. On the other hand, the M06-2X functional showed a general considerable underestimation of interaction energies. This functional worked quite well to study trends, but not to obtain absolute interaction energies.