Substituent Effect on Porphyrin Film-Gas Interaction by Optical Waveguide: Spectrum Analysis and Molecular Dynamic Simulation

Substituent effect on optical gas sensing performance in porphyrin-based optical waveguide detection system was studied by molecular dynamics simulation (MDS), absorption/emission spectrum analysis, and optical waveguide (OWG) detection. The affinities of porphyrin with seven types of substituents (-H, -OH, -tBu, -COOH, -NH2, -OCH3, -SO3-) on para position of meso-phenyl porphyrin toward gas molecules in adsorption process were studied in different size of boxes with the same pressure and concentration. Analyte gases (CO2, H2S, HCl, NO2) were exposed to porphyrin film in absorption spectrophotometer, and in OWG with evanescent field excited by a guiding laser light with 670 nm wavelength. The extent of interaction between host molecule and the guest analytes was analyzed by the number of gas molecules in vicinity of 0.3 nm around substituents of porphyrin molecules. Optical waveguide results reveal that sulfonate porphyrin is mostly responsive to hydrochloride, hydrosulfide gas and nitrogen dioxide gases with strong response intensity. Molecular dynamics and spectral analysis provide objective information about the molecular state and sensing properties. Molecular rearrangements induced by gas exposure was studied by spectral analysis and surface morphology before and after gas exposure taking hydrosulfide gas as an example. Film-gas interaction mechanism was discussed in terms of each gas and substituent group characters.

Encapsulation of Gold Nanorods with Porphyrins for the Potential Treatment of Cancer and Bacterial Diseases: A Critical Review

Cancer and bacterial diseases have been the most incidental diseases to date. According to the World Health Report 2018, at least every family is affected by cancer around the world. In 2012, 14.1 million people were affected by cancer, and that figure is bound to increase to 21.6 million in 2030. Medicine therefore sorts out ways of treatment using conventional methods which have been proven to have many side effects. Researchers developed photothermal and photodynamic methods to treat both cancer and bacterial diseases. These methods pose fewer effects on the biological systems but still no perfect method has been synthesized. The review serves to explore porphyrin and gold nanorods to be used in the treatment of cancer and bacterial diseases: porphyrins as photosensitizers and gold nanorods as delivery agents. In addition, the review delves into ways of incorporating photothermal and photodynamic therapy aimed at producing a less toxic, more efficacious, and specific compound for the treatment.

Distance-Dependent Measurements of the Conductance of Porphyrin Nanorods Studied with Conductive Probe Atomic Force Microscopy

Protocols for nanopatterning porphyrins on Au(111) were developed based on immersion particle lithography. Porphyrins with and without a central metal ion, 5,10,15,20-tetraphenyl-21H,23H-porphyrin (TPP) and 5,10,15,20-tetraphenyl-21H,23H-porphyrin cobalt(II) (CoTPP), were selected for study, which spontaneously formed nanorod geometries depending on concentration parameters. The elongated shapes of the nanorods offers an opportunity for successive distance-dependent conductive probe atomic force microscopy (CP-AFM) measurements along the length of the nanorods. To prepare patterns of TPP and CoTPP nanorods, a mask of silica mesospheres was placed on gold substrates to generate nanoholes within an alkanethiol matrix film. The nanoholes prepared by particle lithography with an immersion step were backfilled with porphyrins by a second immersion step. By controlling the concentration and immersion interval, nanorods of porphyrins were generated with one end of the nanostructure attached to gold within a nanohole. The porphyrin nanorods exhibited slight differences in dimensions at the nanoscale to enable size-dependent measurements of conductive properties. The conductivity along the horizontal direction of the nanorods was evaluated with CP-AFM studies. Changes in conductivity were measured along the long axis of TPP and CoTPP nanorods. The TPP nanorods exhibited conductive profiles of an insulating material, and the CoTPP nanorods exhibited profiles of a semiconductor. The experiments demonstrate the applicability of particle lithography for preparing unique and functional surface platforms of porphyrins to measure distance-dependent conductive properties on gold.

Aggregation behavior of the template-removed 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin chiral array directed by poly(ethylene glycol)-block-poly(L-lysine)

Complexation between 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) and poly(ethylene glycol)-block-poly(L-lysine) (PEG-b-PLL) was performed via electrostatic interaction. Two kinds of primary arrays of TPPS with different supramolecular chirality induced by PLL were obtained in the resultant complex by inverting the mixing procedure of the two components. These arrays could be displaced by poly(sodium-p-styrenesulfonate) (PSS) from the chiral PLL template through competitive electrostatic complexation, and then PSS formed a polyion complex micelle with PEG-b-PLL. The template-removed TPPS arrays preserved their induced chirality and served as primary subunits for the secondary aggregation of TPPS. The morphology of the secondary aggregates was strongly dependent upon the asymmetric primary supramolecular arrangement of TPPS. The rodlike nanostructure that was ∼200 nm in length was composed of the primary arrays that showed opposite exciton chirality between the J- and H-bands. In contrast, the micrometer-sized fibrils observed were composed of the arrays with the same exciton chirality at the J- and H-bands.

Significantly enhanced adsorption of bulk self-assembling porphyrins at solid/liquid interfaces through the self-assembly process

Controlling the adsorption behavior of bulk-phase self-assembling dye molecules at solid/liquid interfaces is of importance for application to various devices. Herein, we report an unexpected phenomenon on the adsorption behaviors of bulk J-aggregating water-soluble porphyrin diacids. A comparative study on the adsorption amounts of J-aggregated meso-tetrakis(4-sulfonatophenyl)porphyrin diacid from freshly prepared and pre-aged solutions revealed enhanced adsorption through the self-assembly process (EASAP). The aggregate structure formed by EASAP is almost identical to the one from preformed J-aggregate solutions. The generation ratio of J-aggregates at an interface and in bulk strongly depends on the interface-to-volume ratio of the solutions. The surface property of cuvettes and coexisting inorganic ions has no significant effects on EASAP. While EASAP occurs in the J-aggregations of the other water-soluble porphyrin diacids, it is suggested that self-assembly properties play an important role in the adsorption proportion. These results will provide new insight into the adsorption equilibrium of bulk self-assembling molecules at solid/liquid interfaces.