Dataset Information

A Calixarene Promotes Disaggregation and Sensing Performance of Carboxyphenyl Porphyrin Films.

ABSTRACT: The aggregation of a free base porphyrin, meso-tetrakis(4-carboxyphenyl)porphyrin and its Zn(II) derivative have been studied at the air/water interface in the presence of a p-tert-butylcalyx[8]arene matrix. The mixed Langmuir films were obtained either by premixing the compounds (cospreading) or by sequential addition. The negative deviation from the additivity rule of the cospread films is indicative of a comparatively good miscibility that was further confirmed by Brewster angle microscopy. The images of the cospread mixed films showed a more homogeneous morphology in comparison with those of pure porphyrin that is attributed to a deeper and earlier self-aggregation state at the interface of the latter. These results were similar for both porphyrins and revealed the disaggregating effect of the calixarene matrix. The orientation and association of the porphyrins were studied by UV-visible reflection spectroscopy at the interface. A different aggregation behavior can be inferred from the resulting spectra, and a higher orientational freedom was observed when the molecules were less aggregated in mixed cospreaded films. The disaggregating effect was retained when the films were transferred to solid supports as demonstrated by UV-visible spectroscopy. Finally, the potential use of these Langmuir-Blodgett films as optical gas sensors was tested against ammonia and amine vapors. The changes in the spectrum in the presence of the volatile compounds are higher for the Zn-porphyrin. The presence of calixarene enhances the sensor response due to the higher accessibility of volatiles to disaggregated porphyrins in the mixed films. The resulting changes were mapped into a numerical matrix that can be transformed into a color pattern to easily discriminate among these gases.

SUBMITTER: Flores-Sanchez R

PROVIDER: S-EPMC7114168 | biostudies-literature | 2020 Mar

REPOSITORIES: biostudies-literature

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A Calixarene Promotes Disaggregation and Sensing Performance of Carboxyphenyl Porphyrin Films.

Flores-Sánchez Rubén R Gámez Francisco F Lopes-Costa Tânia T Pedrosa José María JM

ACS omega 20200317 12

The aggregation of a free base porphyrin, meso-tetrakis(4-carboxyphenyl)porphyrin and its Zn(II) derivative have been studied at the air/water interface in the presence of a p-tert-butylcalyx[8]arene matrix. The mixed Langmuir films were obtained either by premixing the compounds (cospreading) or by sequential addition. The negative deviation from the additivity rule of the cospread films is indicative of a comparatively good miscibility that was further confirmed by Brewste ...[more]

PMID: 32258864

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Project description:Metal-free porphyrin-dendrimers provide a convenient platform for the construction of membrane-impermeable ratiometric probes for pH measurements in compartmentalized biological systems. In all previously reported molecules, electrostatic stabilization (shielding) of the core porphyrin by peripheral negative charges (carboxylates) was required to shift the intrinsically low porphyrin protonation pK(a)'s into the physiological pH range (pH 6-8). However, binding of metal cations (e.g., K(+), Na(+), Ca(2+), Mg(2+)) by the carboxylate groups on the dendrimer could affect the protonation behavior of such probes in biological environments. Here we present a dendritic pH nanoprobe based on a highly non-planar tetraaryltetracyclohexenoporphyrin (Ar(4)TCHP), whose intrinsic protonation pK(a)'s are significantly higher than those of regular tetraarylporphyrins, thereby eliminating the need for electrostatic core shielding. The porphyrin was modified with eight Newkome-type dendrons and PEGylated at the periphery, rendering a neutral water-soluble probe (TCHpH), suitable for measurements in the physiological pH range. The protonation of TCHpH could be followed by absorption (e.g., ?(Soret)(dication)?270,000 M(-1) cm(-1)) or by fluorescence. Unlike most tetraarylporphyrins, TCHpH is protonated in two distinct steps (pK(a)'s 7.8 and 6.0). In the region between the pK(a)'s, an intermediate species with a well-defined spectroscopic signature, presumably a TCHpH monocation, could be observed in the mixture. The performance of TCHpH was evaluated by pH gradient measurements in large unilamellar vesicles. The probe was retained inside the vesicles and did not pass through and/or interact with vesicle membranes, proving useful for quantification of proton transport across phospholipid bilayers. To interpret the protonation behavior of TCHpH we developed a model relating structural changes on the porphyrin macrocycle upon protonation to its basicity. The model was validated by density functional theory (DFT) calculations performed on a planar and non-planar porphyrin, making it possible to rationalize higher protonation pK(a)'s of non-planar porphyrins as well as the easier observation of their monocations.

Dataset Information

A Calixarene Promotes Disaggregation and Sensing Performance of Carboxyphenyl Porphyrin Films.

Publications

A Calixarene Promotes Disaggregation and Sensing Performance of Carboxyphenyl Porphyrin Films.

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