Synthesis, optical and electrochemical characterization of lnter-ring bridged tetramers based on thiophene

Tetramers based on thiophene and phenylene residues in which the torsion angles between thiophene rings are locked by a chemical bridge have been synthesised by organosynthetic routes. The effect of locking on photoluminescence and absorption in solution has been studied. An enhanced tendency of doubly locked tetrathiophene to aggregate together with its facile decomposition upon light exposure greatly influence the luminescence properties.     

Extrinsic Heavy Metal Atom Effect on the Solid‐State Room Temperature Phosphorescence of Cyclic Triimidazole

Four coordination compounds [Zn₃(CH₃COO)₆(H₂O)₂](TT)₂ [Cd(H₂O)₆](ClO₄)₂(TT)₂, [Cd(H₂O)₆](BF₄)₂(TT)₂, [Zn(H₂O)₆](BF₄)₂(TT)₂ ( 1 – 4 ) accommodating the crystallization induced emissive triimidazo[1,2‐a:1′,2′‐c:1′′,2′′‐e][1,3,5]triazine ( TT ) as a guest in their crystal lattice are isolated and fully photophysically and structurally characterized. Their emission properties are compared with those of afterglow TT and interpreted taking into account the heavy atom effect and crystal packing similarities and differences. In the case of 1 , due to the closeness of the TT H‐aggregates arrangement with that of the phosphor's pure phase, the observed intensification of the phosphorescent emission at the expense of the prompt one is attributed to the extrinsic heavy atom effect of Zn. In 2 and 3 , the heavier Cd atom is responsible for a decrease in the lifetimes of the afterglow emission, despite the presence of tightly overlapped H‐dimers in the crystal structure. Finally, for 4 , isostructural with 3 , the Zn atom reveals in RTUP lifetime comparable with that of 1 .     

High Relaxivity Mn2+‐Based MRI Contrast Agents

Stable Mn²⁺ mono‐ and binuclear complexes containing pentadentate 6,6′‐((methylazanediyl)bis(methylene))dipicolinic acid coordinating units give remarkably high relaxivities due to the presence of two inner‐sphere water molecules. The mononuclear derivative binds human serum albumin (HSA) with an association constant of 3372 M ^?1, which results in the replacement of the coordinated water molecules by donor atoms of protein residues. The dinuclear analogue also binds HSA while leaving one of the Mn²⁺ centres exposed to the solvent with two coordinated water molecules. Thus, this complex shows remarkably high relaxivities upon protein binding (39.0 mM ^?1 s^?1 per Mn, at 20 MHz and 37 °C).     

6-alkyl and 5,6-dialkyl-2-methoxy-4(3H)- pyrimidinones in the transformations of pyrimidines—2: Synthesis and conversion into alkyluracils and 2-alkoxy-4(3H)-pyrimidinones

The synthesis of 6-alkyl and 5,6-dialkyl-2-methoxy-4(3H)-pyrimidinones 3 is described. Their versatility to be transformed into 6-alkyl and 5,6-dialkyluracils 4(a-h), 6-alkyl and 5,6-dialkyl-3-methyluracils 7(a,e,f) and 6-alkyl and 5,6-dialkyl-2-alkoxy-4(3H)-pyrimidinones 5(a-i) is also shown.     

Analysis and design of photobioreactors for microalgae production I: method and parameters for radiation field simulation

Having capabilities for the simulation of the radiation field in suspensions of microalgae constitutes a great asset for the analysis, optimization and scaling-up of photobioreactors. In this study, a combined experimental and computational procedure is presented, specifically devised for the assessment of the coefficients of absorption and scattering, needed for the simulation of such fields. The experimental procedure consists in measuring the radiant energy transmitted through samples of suspensions of microalgae of different biomass concentrations, as well as the forward and backward scattered light. At a microscopic level, suspensions of microalgae are complex heterogeneous media and due to this complexity, in this study they are modeled as a pseudocontinuum, with centers of absorption and scattering randomly distributed throughout its volume. This model was tested on suspensions of two algal species of dissimilar cell shapes: Chlorella sp. and Scenedesmus quadricauda. The Monte Carlo simulation algorithm developed in this study, when used as a supporting subroutine of a main optimization program based on a genetic algorithm, permits the assessment of the physical parameters of the radiation field model. The Monte Carlo algorithm simulates the experiments, reproducing the events that photons can undergo while they propagate through culture samples or at its physical boundaries.     

Non-covalent conjugates between cationic polyamino acids and GdIII chelates: a route for seeking accumulation of MRI-contrast agents at tumor targeting sites

Three novel Gd chelates containing on their external surface pendant phosphonate and carboxylate groups, which promote the interaction with the positively charged groups of polyornithine and polyarginine, have been synthesized. Their solution structures have been assessed on the basis of 1H- and 31P-NMR spectra of the Eu and Yb analogues. A thorough investigation of the relaxometric (1H and 17O) properties of the Gd chelates has been carried out and the observed relaxivities have been accounted for the sum of three contributions arising from water molecules in the first, second, and outer coordination layers, respectively. It has been found that the occurrence of a tight second coordination coating renders the dissociation of the water molecule directly coordinated to the Gd ion more difficult. The binding interactions between the negatively charged Gd chelates and the positively charged groups of polyornithine (ca. 140 residues) and polyarginine (ca. 204 residues) have been evaluated by means of the proton relaxation enhancement (PRE) method. Although the binding interaction decreases markedly in the presence of competitive anions in the solution medium, the affinity is strong enough that in blood serum it is possible to meet the conditions where most of the chelate is bound to the polyamino acid substrate. On this basis one may envisage a novel route for a MRI location of tumors as it is known that positively charged polyamino acids selectively bind to tumors having a greater negative charge than non-tumor cells.     

Construction and validation of a RET TK catalytic domain by homology modeling

RET tyrosine kinase (TK) oncoproteins are potential targets for anticancer therapy. However, the search for novel RET inhibitors has been hampered by the lack of a 3D structure of the receptor. In this study, the "open" and the "closed" structure of the RET TK catalytic domain have been built by homology modeling techniques. The structures were validated by extensive docking studies with practically all the inhibitors reported in the literature and through molecular dynamics simulations of the resulting complexes. All the expected major interactions between the active domain amino acids and the inhibitors have been reproduced in their details. Furthermore, the proposed 3D models are in agreement with the results of available mutation studies. Therefore, these models could be profitably used to filter off from large libraries new potential hit compounds able to target this enzyme.