Aqueous Protein-Polymer Bioconjugation via Photoinduced RAFT Polymerization Using High Loading Heterogeneous Catalyst

Light-driven polymerization, such as photoinduced electron/energy transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization, enables biological benign conditions and versatile functional polymer structure design, which is readily used in protein-polymer bioconjugates. However, conventional metalloporphyrinic homogeneous catalysts for PET-RAFT polymerization suffer from limited aqueous solubility and tedious purification. Here we demonstrate the design of PET-RAFT photocatalyst from the reticular assembled Zr-porphyrinic metal-organic frameworks (MOFs), along with a biomacromolecule-based chain transfer agent, as efficient bioconjugation tools in water. Our methodology offers manufacturing advantages on bioconjugates under mild conditions such that MTT (3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide) and cytotoxicity assays have shown the preservation of the protein integrity, bioactivity, and high cell viability after PET-RAFT polymerization. We find that the fast kinetics are benefiting from the ultrahigh loading of metalloporphyrins in MOF-525-Zn. This heterogeneous catalyst also allows us to maintain living characteristics to incorporate myriads of monomers into block copolymers. Other advantages like easy postreaction purification, reusability, and high oxygen tolerance even in an open system are demonstrated. This study provides a tool of highly efficient heterogeneous photocatalysts for polymer-protein bioconjugation in aqueous media and paves the road for biological applications.

Photochemical production of a highly reactive porphyrin-iron-oxo species

Oxidation of 5,10,15,20-tetramesitylporphyrinatoiron(III) perchlorate, (TMP)FeIII(ClO4), with ferric perchlorate in acetonitrile gave a metastable species identified as (TMP)FeIV(ClO4)2 that decayed within seconds to the known isomeric species (TMP*+)FeIII(ClO4)2. Irradiation of the metastable species with 355 nm laser light gave a highly reactive transient that reacts with simple organic reductants (alkenes and arylalkanes) 5 orders of magnitude faster than known Compound I analogues, (TMP*+)FeIV(O)(X-).

Theoretical Solar-to-Electrical Energy-Conversion Efficiencies of Perylene−Porphyrin Light-Harvesting Arrays

The efficiencies of organic solar cells that incorporate light-harvesting arrays of organic pigments were calculated under 1 sun of air mass 1.5 solar irradiation. In one set of calculations, photocurrent efficiencies were evaluated for porphyrin, phthalocyanine, chlorin, bacteriochlorin, and porphyrin-bis(perylene) pigment arrays of different length and packing densities under the assumption that each solar photon absorbed quantitatively yielded one electron in the external circuit. In another more realistic set of calculations, solar conversion efficiencies were evaluated for arrays comprising porphyrins or porphyrin-(perylene)2 units taking into account competitive excited-state relaxation pathways. A system of coupled differential equations for all reactions in the arrays was solved on the basis of previously published rate constants for (1) energy transfer between the perylene and porphyrin pigments, (2) excited-state relaxation of the perylene and porphyrin pigments, and (3) excited-state electron injection into the semiconductor. This formal analysis enables determination of the optimal number of pigments in an array for solar-to-electrical energy conversion. The optimal number of pigments depends on the molar absorption coefficient and the density at which the arrays can be packed on an electrode surface. Taken together, the ability to employ fundamental photophysical, kinetic, and structural parameters of modular molecular architectures in assessments of the efficiency of solar-to-electrical energy conversion should facilitate the design of molecular-based solar cells.

Efficient and selective hydrocarbon oxidation with sodium periodate under ultrasonic irradiation catalyzed by polystyrene-bound Mn (TPyP)

Rapid, efficient and selective alkene epoxidation and alkane hydroxylation with sodium periodate catalyzed by Mn (TPyP) supported on chloromethylated polystyrene, [Mn(TPyP)-CMP], under ultrasonic irradiation were reported. This catalytic system showed high selectivity in epoxidation of stilbenes and R-(+)-limonene and exhibits a particular ability to epoxidize linear alkenes such as 1-heptene. This supported catalyst can catalyze the oxidation of very inert saturated hydrocarbons as well as alkylbenzene derivatives with NaIO4 under ultrasonic irradiation. Under mild reaction conditions, this catalyst was consecutive reused five times without detectable catalyst leaching and gave over 95% epoxide yield in the epoxidation of styrene.

Excitation-Energy Migration in Self-Assembled Cyclic Zinc(II)-Porphyrin Arrays: A Close Mimicry of a Natural Light-Harvesting System

The excitation-energy-hopping (EEH) times within two-dimensional cyclic zinc(II)-porphyrin arrays 5 and 6, which were prepared by intermolecular coordination and ring-closing metathesis reaction of olefins, were deduced by modeling the EEH process based on the anisotropy depolarization as well as the exciton-exciton annihilation dynamics. Assuming the number of energy-hopping sites N = 5 and 6, the two different experimental observables, that is, anisotropy depolarization and exciton-excition annihilation times, consistently give the EEH times of 8.0 +/- 0.5 and 5.3 +/- 0.6 ps through the 1,3-phenylene linkages of 5 and 6, respectively. Accordingly, the self-assembled cyclic porphyrin arrays have proven to be well-defined two-dimensional models for natural light-harvesting complexes.

Charge-transfer Zn-porphyrin derivatives with very large two-photon absorption cross sections at 1.3–1.5 μm fundamental wavelengths

A series of charge-transfer Zn-porphyrin derivatives with large two-photon absorption cross sections at 1.3-1.5 microm fundamental wavelengths are designed using time-dependent hybrid density functional theory. The fluorescence of these chromospheres is expected to be in the region of 700-900 nm. These unique features make them suitable for a variety of biophotonic and telecommunication applications.

Quantitative determination of localized tissue oxygen concentration in vivo by two-photon excitation phosphorescence lifetime measurements

This study describes the use of two-photon excitation phosphorescence lifetime measurements for quantitative oxygen determination in vivo. Doubling the excitation wavelength of Pd-porphyrin from visible light to the infrared allows for deeper tissue penetration and a more precise and confined selection of the excitation volume due to the nonlinear two-photon effect. By using a focused laser beam from a 1,064-nm Q-switched laser, providing 10-ns pulses of 10 mJ, albumin-bound Pd-porphyrin was effectively excited and oxygen-dependent decay of phosphorescence was observed. In vitro calibration of phosphorescence lifetime vs. oxygen tension was performed. The obtained calibration constants were kq = 356 Torr(-1) x s(-1) (quenching constant) and tau0 = 550 micros (lifetime at zero-oxygen conditions) at 37 degrees C. The phosphorescence intensity showed a squared dependency to the excitation intensity, typical for two-photon excitation. In vivo demonstration of two-photon excitation phosphorescence lifetime measurements is shown by step-wise PO2 measurements through the cortex of rat kidney. It is concluded that quantitative oxygen measurements can be made, both in vitro and in vivo, using two-photon excitation oxygen-dependent quenching of phosphorescence. The use of two-photon excitation has the potential to lead to new applications of the phosphorescence lifetime technique, e.g., noninvasive oxygen scanning in tissue at high spatial resolution. To our knowledge, this is the first report in which two-photon excitation is used in the setting of oxygen-dependent quenching of phosphorescence lifetime measurements.

Bio-mimetic hydrogen production from polysaccharide using the visible light sensitization of zinc porphyrin

A biohydrogen production system coupling the polysaccharide such as sucrose and maltose degradation with invertase and glucose dehydrognase (GDH) and hydrogen production with colloidal platinum as hydrogen-evolved catalyst using the visible light-induced photosensitization of water-soluble zinc porphyrin, zinc tetraphenylporphyrin tetrasulfonate (ZnTPPS) has been investigated. Continuous hydrogen gas production was observed when the sample solution containing polysaccharide, invertase, GDH, nicotinamide adenine dinucreotide (NAD(+)), ZnTPPS, methylviologen (an electron relay reagent), and colloidal platinum was irradiated by visible light. After 240-min irradiation, the amount of hydrogen production in the system using sucrose and maltose was estimated to be 3.1 and 0.35 micromol, respectively.

Triplet radical ion pair state of the Zn-porphyrin-viologen dyad as a magnetic field sensitive probe of phase transitions in small unilamellar vesicles

The magnetic field effect on the recombination kinetics of the triplet radical ion pair state (RIPS) of the Zn-porphyrin-viologen dyad (P-Ph-Vi2+) in the small unilamellar vesicles (SUV) of D,L-dipalmitoyl-alpha-phosphatidylcholine has been studied by the nanosecond laser flash photolysis technique at 5-60 degrees C. The increase in temperature from 25 to 40 degrees C enhances the rate constant (kr) of the RIPS recombination in zero magnetic field from 0.9 x 10(6) to 1.6 x 10(6) s-1, while kr is temperature insensitive at 5-25 and 40-60 degrees C. The typical break in the kr temperature dependence is observed in the temperature range of the phase transition of the SUV bilayers from the solid to the fluid state. The kr value in a strong magnetic field (B = 0.24 T) is equal to 2.7 x 10(5) s-1 and it is independent of temperature at 5-60 degrees C. The shape of the magnetic field dependence of kr is unaffected by the phase transition of the SUV bilayers and is characterized by the existence of an initial plateau of kr at B = 0 to 0.5 mT.

Comparative photoactivity of tin and zinc porphyrin inhibitors of heme oxygenase: pronounced photolability of the zinc compounds

Metalloporphyrin inhibitors of heme oxygenase may also have photosensitizing properties in vivo. To assess photoactivity in serum, the relative ability to mediate photooxidation of tryptophan or other oxidizable targets, presumably by singlet oxygen production, was measured for tin mesoporphyrin, zinc mesoporphyrin, and zinc deuteroporphyrin bisglycol in aqueous solution and when bound to human serum albumin. While tin mesoporphyrin sensitized at the greatest initial rate in aqueous solution, the zinc compounds sensitized at a greater initial rate in detergent micelles or when bound to albumin. There was minimal alteration of the tin mesoporphyrin during the time course of illumination in the Soret or visible absorption regions. The zinc compounds, however, proved to be extremely photolabile and were extensively destroyed by light; the photooxidized forms were found to be ineffective as inhibitors of heme oxygenase.

Metalloporphyrin phototoxicity

The phototoxicities of six metalloporphyrin dimethylesters (i.e. cobalt (Co), copper (Cu), manganese (Mn), nickel (Ni), tin (Sn) and zinc (Zn) were investigated. Hemolysis of human erythrocytes and inactivation of two enzymes (acetylcholinesterase and beta-galactosidase) were used to assess the phototoxic efficacy of these metal chelates. Tin protoporphyrin (SnPP), the only porphyrin found to hemolyze erythrocytes at a concentration of 40 microM (radiation dose, 230 kJ m-2), was much less efficient than either free protoporphyrin IX or hematoporphyrin. SnPP completely inactivated beta-galactosidase at concentrations above 15 microM (radiation dose, 75 kJ m-2) and drastically interfered with acetylcholinesterase activity at a concentration of 150 microM (radiation dose, 75 kJ m-2). CoPP, CuPP, MnPP, NiPP and ZnPP were ineffective photohemolytic agents at 40 microM (radiation dose, 230 kJ m-2), but inactivated acetylcholinesterase and beta-galactosidase activity to varying degrees. These results suggest that (i) metal ions reduce the phototoxicity of protoporphyrin IX, (ii) different metal ions reduce the phototoxic activity of protoporphyrin IX to different degrees and (iii) the biological activities of the various metal complexes vary in different assay systems.

Laser flash photolysis of purpurins: novel potential photosensitizers of interest in photodynamic therapy

Purpurins, a new class of photosensitizers of potential use in the photodynamic therapy of cancer, have been studied by laser spectroscopy to determine the properties of their excited states. For the two molecules studied, generation of triplet states and singlet oxygen (1O2) is very efficient. Singlet oxygen yields are presented for red and blue excitation though no significant wavelength effect is apparent. The promise these sensitizers have shown merits further investigation of other derivatives.

[Impulse photoconductivity of chlorophyll and its analogs]

Impute photoconductivity of pyridine solutions of chlorophyll a and pheophytin a in the presence of phenylhydrasin was studied, as well as that of tetraphenylporphin, zinc-tetraphenylporphin, mezoporphyrin, zinc-mezoporphyrin, and palladium-mezoporphyrin in the presence of hydrasin hydrate depending on flash intensity and temperature (20--30 degrees C). The lifetimes of anion-radicals and monoprotonated dianions of the studied pigments were estimated, as well as activation energies of some intermediate stages of photoreduction. From the data obtained the ratio between the constant of the death rate of anion-radicals and the total mobility of negative and positive ion-radical was found.