Ali Gelir

Elucidation of multiple-point interactions of pyranine fluoroprobe during the gelation

We have studied the multiple-point interactions of the pyranine (8-hydroxypyrene-1,3,6-trisulfonic acid, trisodium salt; 3sPyOH) fluoroprobe with polymer chains during the free-radical polymerization of acrylamide (AAm) by using the steady state fluorescence measurements. We observed a considerable blue shift from 515nm to 406nm in the emission spectra due to a C-O ether bond formation between the hydroxylic oxygen of 3sPyOH and a terminal C-atom of the growing AAm chain. Furthermore ionic (electrostatic) interactions occur between the three ionized sulfonic acid groups (SO(3)(-)) of 3sPyOH and protonated amide groups on the AAm chains. These electrostatic interactions also cause a gradual red shift in the maximum of the short-wavelength-peak, from 406nm to 430nm. The results showed that the pyranine can be used as a probe for real time monitoring of the polymerization process of AAm system since it monitors both the progression of the polymerization via chemical binding over OH group and the change in the local density of the polymerizing sample by means of the gradual red shift in the short-wavelength-peak via ionic interactions over SO(3)(-) groups.

Synthesis and photophysical properties of a porphyrin–BODIPY dyad and a porphyrin–o-carborane–BODIPY triad

A novel porphyrin–BODIPY dyad, where BODIPY acts as the central antenna, linked via the Sonogashira coupling reaction, and a novel porphyrin–o-carborane–BODIPY triad, where both porphyrin and BODIPY are covalently attached to the o-carborane, have been synthesised and characterised. X-ray crystallography confirmed a V-shaped triad molecule. Detailed studies on the photophysical properties revealed the excitation of the BODIPY dyad system, which selectively triggered an efficient resonance energy transfer to the porphyrin unit. The presence of the o-carborane group in the triad system significantly diminished the energy transfer efficiency from BODIPY to the porphyrin moiety, because of its quenching properties. Besides, the triad system displayed aggregation-enhanced emission in THF/water systems, due to the presence of the o-carborane unit. The in-depth investigation of the electrochemical properties demonstrated that o-carborane insertion extended the initial reduction potentials and shifted half waves from the anodic to the cathodic site.

How the internal structures of the imprinted and the random hydrogels change upon washing

The effect of washing with acidic and basic solutions on the internal structure (fluctuations in the density and the size of the polymer clusters through the gel) of the imprinted and the random PNIPA (polyN-isopropylacrylamide) hydrogels has been studied by using steady-state fluorescence technique, swelling kinetics and SEM images. When the gel is imprinted, fluctuations in the density and the size of the polymer clusters decrease through the gel; i.e., the gel becomes more homogeneous. Washing with acid causes no considerable change in the internal structure of the both gels, but washing with base causes a drastic change in the structure by breaking the bonds between the polymer strands. The release rate of target molecules for the imprinted gel becomes considerably higher than for the random one regardless of the washing condition since the target molecules are trapped in the dense blobs of the random gel. The change in the internal structure of the gels upon washing is modeled by a spring approximation.Graphical AbstractThe effect of washing with acidic and basic solutions on the morphology of the imprinted and the random PNIPA hydrogels was studied. When the gel is imprinted, it becomes more homogeneous. Washing with acid causes no considerable change in the morphology of the both gels, but washing with base causes a drastic change by breaking the bonds between the polymer strands.

Magnetic and fluorescence properties of cobalt implanted hydrogels

Co-doped plain gels (PAAm) were prepared with and without pyranine fluoroprobe (8-hydroxypyrene-1, 3,6-trisulfonic acid, trisodium salt; POH), which have a OH- reactive group and three SO-3 ionic groups. Magnetization and fluorescence measurements were used for characterization of the gels. It was observed that both the plain gel itself and the gel including only POH (PAAm-POH) have a diamagnetic response to the external field. When the gels were synthesized together with cobalt (PAAm-Co) and cobalt/POH (PAAm-Co-POH), both gels magnetized in the direction of the magnetic field, as expected. However, the magnitude of the magnetization was different in the gels which were synthesized in the presence of POH and the one into which POH molecules were diffused after the synthesis, even though they have the same cobalt concentration. Fluorescence measurements and SEM micrographs were used to understand this surprising difference in the magnetization of PAAm-Co-POH gels. It was proposed that the electrostatic interaction between SO-3 groups of POH and free electrons of cobalt (Co+2) atoms led to the formation of Co-POH clusters having fewer unpaired electrons, and this results in a decrease in overall magnetization. It was also observed from the SEM images that the size of clusters depends on the Co-POH composition.