1,721,028 research outputs found
Dinuclear Metal Complexes Based on all cis 2,4,6-triamino-1,3,5-trihydroxycyclohexane as Catalysts of Phosphate Esters Cleavage
No full textTwo dimetallic ligands 2 and 3 for transition metal ions were obtained by connecting two all-cis- 2,4,6-triamino-cyclohexane-1,3,5-triol (TACI, 1) subunits via 1,3- or 1,4-xylyl linkers. Their dimetallic Cu-II and Zn-II complexes were investigated as catalysts for the cleavage of the phosphate diesters 2,4-dinitrophenyl ethyl phosphate (DNPEP) and 2-hydroxypropyl p-nitrophenyl phosphate (HPNP) and the triester 2,4-dinitrophenyl diethyl phosphate (DNPDEP). The results of a comparative kinetic study using the monometallic complexes of TACI as a reference indicate that the Cu-II complexes of 2 and 3 are virtually inert; this finding is ascribed to the formation of intra-complex p-hydroxo bridges that prevent the required interactions with the substrate. On the other hand, the dimetallic Zn-II complexes produce remarkable accelerations, particularly in the case of the HPNP transesterification. The dimetallic systems are more efficient than the TACI.Zn-II complex in promoting the hydrolysis of HPNP at pH values close to neutrality (7.0-7.8). In this case, the effects of cooperativity between the two metal centers were highlighted in a detailed kinetic study; the catalytic efficiency seems to be related to the stronger binding of the substrate to the dimetallic Zn-II complexes. Additionally, in this case, although to a much lesser extent than in the case of the Cu-II counterparts, the formation of p-hydroxo bridges apparently hampers the catalytic efficiency, as indicated also by the observation that the activity of the dimetallic complexes increases as the distance between the two metal centers increases, which, thus, thwarts the formation of intermetallic bridges
Synthesis and characterization of a hydrophilic conjugated 4+4 Re(I)-porphyrin metallacycle
No full textThe preparation and the full characterization, including the X-ray structure determination, of a polar trans-dipyridylporphyrin functionalized with two short polyoxyethylene chains is reported. Reaction of the porphyrin with a Re(I) complex yielded a 4+4 metallacycle showing an improved solubility and a lower tendency to aggregate with respect to analogous porphyrin cyclic derivatives. These properties allowed a full NMR characterization of the metallacycle including VT1H DOSY-NMR experiments and, for the first time, the recording of a13C-NMR spectrum giving further insight into the structural definition of these type of metallacycles. Spray deposition of the metallacycle on a heated mica substrate shows the formation of regular ring-like nano-structures which are not formed by the parent porphyrin
Configurational Selection in Azobenzene-Based Supramolecular Systems Through Dual-Stimuli Processes
Full text linkAzobenzene is one of the most studied light-controlled molecular switches and it has been incorporated in a large variety of supramolecular systems to control their structural and functional properties. Given the peculiar isomeric distribution at the photoexcited state (PSS), azobenzene derivatives have been used as photoactive framework to build metastable supramolecular systems that are out of the thermodynamic equilibrium. This could be achieved exploiting the peculiar E/Z photoisomerization process that can lead to isomeric ratios that are unreachable in thermal equilibrium conditions. The challenge in the field is to find molecular architectures that, under given external circumstances, lead to a given isomeric ratio in a reversible and predictable manner, ensuring an ultimate control of the configurational distribution and system composition. By reviewing early and recent works in the field, this review aims at describing photoswitchable systems that, containing an azobenzene dye, display a controlled configurational equilibrium by means of a molecular recognition event. Specifically, examples include programmed photoactive molecular architectures binding cations, anions and H-bonded neutral guests. In these systems the non-covalent molecular recognition adds onto the thermal and light stimuli, equipping the supramolecular architecture with an additional external trigger to select the desired configuration composition
A fluorescence nanosensor for Cu2+ on silica particles
No full textA fluorescence nanosensor for Cu2+ ions has been obtained by surface functionalization of silica particles with trialkoxysilane derivatized ligand and fluorescent dye
Self-assembling in surfactant aggregates: An alternative way to the realization of fluorescence chemosensors for Cu(II) ions
No full textThe self-assembling of the proper subunits of fluorescence chemosensors within surfactant aggregates in water allows the easy design, realization, and testing of new effective sensing systems. It was shown that a proper ligand and a fluorescent dye, once transferred from bulk water into an inert surfactant aggregate, are kept in such a close proximity that communication between the binding site and the signaling unit effectively occurs, thus avoiding the need for a covalent connection between the sensor's two units. To further simplify the sensing system and get rid of the inert surfactant which somehow implies the dilution of the sensor's active components in the aggregate, we have synthesized a series of lipophilic ligands for Cu(II) based on dipeptides GlyLys and GlyGlu functionalized with n-alkyl chains of different lengths at the N-terminus. These ligands are soluble in water and can form homoaggregates in the absence and in the presence of Cu(II) ions. Lipophilic fluorophores, like 8-anilino-naphthalensulfonic acid or Rhodamine 6G, are effectively bound into the aggregate pseudophase, and the binding of Cu(II) ions to the dipeptide units causes a strong fluorescence quenching. The sensor system is very sensitive to Cu(II) (concentrations in the submicromolar range are detected), is promptly reversible, and no interference is observed due to the presence of many metal ions. The sensitivity of the systems improves by decreasing the ligand concentration and (up to a point) the ligand's cmc
Amphiphilic Cu(II) Complexes Modeled After the Metal-Complexation Subunit of Bleomycin Antibiotics
No full textAnion-selective macromolecular artificial ionophores with steroid and fatty acid pendants
No full textSynthetic anion transporters are potential therapeutics for a plethora of cellular ailments including cystic fibrosis, cancer resistance, epilepsy, etc. In this context, cationic macromolecular amphiphiles are gaining revived interest because of their easy synthesis and ample ion channelization through the membrane barrier. Herein, side chain alanine containing cationic polymer amphiphiles with steroid/fatty acid decoration was established to be an efficient anion-selective artificial ionophore. The facile amphiphilicity-assisted assembly makeover of cholic acid containing copolymers channelized the better transmembrane anion transport and efficiency with the maximum selectivity found with NO2- ion
Ln(III)-catalyzed Cleavage of Phosphate-functionalyzed Synthetic Lipids: Real Time Monitoring of Vesicle Decapsulation
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