Self-Assembly of Natural Light-Harvesting Bacteriochlorophylls of Green Sulfur Photosynthetic Bacteria in Silicate Capsules as Stable Models of Chlorosomes

In Situ Monitoring Intracellular Structural Change of Nanovehicles through Photoacoustic Signals Based on Phenylboronate-Linked RGD-Dextran/Purpurin 18 Conjugates

The stimuli-responsive polymeric nanocarriers have been studied extensively, and their structural changes in cells are important for the controlled intracellular drug release. The present work reported RGD-dextran/purpurin 18 conjugates with pH-responsive phenylboronate as spacer for monitoring the structural change of nanovehicles through ratiometric photoacoustic (PA) signal. Phenylboronic acid modified purpurin 18 (NPBA-P18) could attach onto the RGD-decorated dextran (RGD-Dex), and the resulting RGD-Dex/NPBA-P18 (RDNP) conjugates with different molar ratios of RGD-Dex and NPBA-P18 were prepared. When the moles of NPBA-P18 were equivalent to more than triple of RGD-Dex, the single-stranded RDNP conjugates could self-assemble into nanoparticles in aqueous solution due to the fairly strong hydrophobicity of NPBA-P18. The pH-responsive aggregations of NPBA-P18 were investigated by UV-vis, fluorescence, and circular dichroism spectra, as well as transmission electron microscope. Based on distinct PA signals between monomeric and aggregated state, ratiometric PA signal of I₇₅₀/I₇₁₀ could be presented to trace the structural change progress. Compared with RDNP single chains, the nanoparticles exhibited effective cellular internalization through endocytosis pathway. Furthermore, the nanoparticles could form well-ordered aggregates responding to intracellular acidic environment, and the resulting structural change was also monitored by ratiometric PA signal. Therefore, the noninvasive PA approach could provide a deep insight into monitoring the intracellular structural change process of stimuli-responsive nanocarriers.

Introduction of perfluoroalkyl chain into the esterifying moiety of bacteriochlorophyll c in the green sulfur photosynthetic bacterium Chlorobaculum tepidum by pigment biosynthesis

The green sulfur photosynthetic bacterium Chlorobaculum (Cba.) tepidum was grown in liquid cultures containing perfluoro-1-decanol, 1H,1H,2H,2H-heptadecafluoro-1-decanol [CF3(CF2)7(CH2)2OH] or 1H,1H-nonadecafluoro-1-decanol [CF3(CF2)8CH2OH], to introduce rigid and fluorophilic chains into the esterifying moiety of light-harvesting bacteriochlorophyll (BChl) c. Exogenous 1H,1H,2H,2H-heptadecafluoro-1-decanol was successfully attached to the 17(2)-carboxy group of bacteriochlorophyllide (BChlide) c in vivo: the relative ratio of the unnatural BChl c esterified with this perfluoroalcohol over the total BChl c was 10.3%. Heat treatment of the liquid medium containing 1H,1H,2H,2H-heptadecafluoro-1-decanol with β-cyclodextrin before inoculation increased the relative ratio of the BChl c derivative esterified with this alcohol in the total BChl c in Cba. tepidum. In a while, 1H,1H-nonadecafluoro-1-decanol was not attached to BChlide c in Cba. tepidum, which was grown by its supplementation. These results suggest that the rigidity close to the hydroxy group of the esterifying alcohol is not suitable for the recognition by the BChl c synthase called BchK in Cba. tepidum. The unnatural BChl c esterified with 1H,1H,2H,2H-heptadecafluoro-1-decanol participated in BChl c self-aggregates in chlorosomes.

Temperature shift effect on the Chlorobaculum tepidum chlorosomes

Chlorobaculum [Cba.] tepidum is known to grow optimally at 48-52 °C and can also be cultured at ambient temperatures. In this paper, we prepared constant temperature, temperature shift, and temperature shift followed by backshift cultures and investigated the intrinsic properties and spectral features of chlorosomes from those cultures using various approaches, including temperature-dependent measurements on circular dichroism (CD), UV-visible, and dynamic light scattering. Our studies indicate that (1) chlorosomes from constant temperature cultures at 50 and 30 °C exhibited more resistance to heat relative to temperature shift cultures; (2) as temperature increases bacteriochlorophyll c (BChl c) in chlorosomes is prone to demetalation, which forms bacteriopheophytin c, and degradation under aerobic conditions. Some BChl c aggregates inside reduced chlorosomes prepared in low-oxygen environments can reform after heat treatments; (3) temperature shift cultures synthesize and incorporate more BChl c homologs with a smaller substituent at C-8 on the chlorin ring and less BChl c homologs with a larger long-chain alcohol at C-17(3) versus constant-temperature cultures. We hypothesize that the long-chain alcohol at C-17(3) (and perhaps together with the substituent at C-8) may account for thermal stability of chlorosomes and the substituent at C-8 may assist self-assembling BChls; and (4) while almost identical absorption spectra are detected, chlorosomes from different growth conditions exhibited differences in the rotational length of the CD signal, and aerobic and reduced chlorosomes also display different Qy CD intensities. Further, chlorosomes exhibited changes of CD features in response to temperature increases. Additionally, we compare temperature-dependent studies for the Cba. tepidum chlorosomes and previous studies for the Chloroflexus aurantiacus chlorosomes. Together, our work provides useful and novel insights on the properties and organization of chlorosomes.

Nanostructured aggregates of meso-tetramesitylporphyrin on solid substrate

We report aggregated nanostructure formation of water insoluble meso-tetramesitylporphyrin (MTMP) induced by hydrogen chloride (HCl) vapor on a glass plate. The formation of aggregated nanostructures of MTMP was confirmed by UV-vis, time-resolved emission spectral techniques, atomic force microscopy (AFM), and high resolution transmission electron microscopy (HR-TEM). Exposure of HCl vapor to a thin film of MTMP coated on a glass plate resulted in a 35 nm red shift of the Soret band in contrast to the case of MTMP thin film. AFM images showed the formation of MTMP aggregates induced by HCl vapor with the size of 50-170 nm in height and an average width of 120 nm. Protonation of MTMP coated on the glass plate by HCl molecules triggered the formation of aggregated nanostructures on the glass plate. Interestingly, it was found that the aggregates were not reverted back to the original morphology of MTMP thin film when it was deprotonated by exposure to ammonia vapor. The fluorescent lifetime of the MTMP thin film was decreased from 11.48 to 0.78 ns when it was exposed to HCl vapor, indicating the formation of MTMP aggregates on the glass surface.

Investigation on chlorosomal antenna geometries: tube, lamella and spiral-type self-aggregates

Molecular mechanics calculations and exciton theory have been used to study pigment organization in chlorosomes of green bacteria. Single and double rod, multiple concentric rod, lamella, and Archimedean spiral macrostructures of bacteriochlorophyll c molecules were created and their spectral properties evaluated. The effects of length, width, diameter, and curvature of the macrostructures as well as orientations of monomeric transition dipole moment vectors on the spectral properties of the aggregates were studied. Calculated absorption, linear dichroism, and polarization dependent fluorescence-excitation spectra of the studied long macrostructures were practically identical, but circular dichroism spectra turned out to be very sensitive to geometry and monomeric transition dipole moment orientations of the aggregates. The simulations for long multiple rod and spiral-type macrostructures, observed in recent high-resolution electron microscopy images (Oostergetel et al., FEBS Lett 581:5435-5439, 2007) gave shapes of circular dichroism spectra observed experimentally for chlorosomes. It was shown that the ratio of total circular dichroism intensity to integrated absorption of the Q(y) transition is a good measure of degree of tubular structures in the chlorosomes. Calculations suggest that the broad Q(y) line width of chlorosomes of sulfur bacteria could be due to (1) different orientations of the transition moment vectors in multi-walled rod structures or (2) a variety of Bchl-aggregate structures in the chlorosomes.

Energy from photobioreactors: Bioencapsulation of photosynthetically active molecules, organelles, and whole cells within biologically inert matrices

Photosynthesis is a highly efficient solar energy transformation process. Exploiting this natural phenomenon is one way to overcome the shortage in the Earth’s fuel resources. This review summarizes the work carried out in the field of photobioreactor design via the immobilization of photosynthetically active matter within biologically inert matrices and the potential biotechnological applications of the obtained hybrid materials within the domain of solar energy to chemical energy transformation. The first part deals with the design of artificial photosynthetic reaction centers (RCs) by the encapsulation of pigments, proteins, and complexes. The action of thylakoids, chloroplasts, and whole plant cells, immobilized in biocompatible supports, in the conversion of CO2 into chemical energy, is also addressed. Finally, the latest advances in the exploitation of the bioactivity of photosynthetically active micro-organisms are explored in terms of the production of secondary metabolites and hydrogen.

pH-induced interconversion between J-aggregates and H-aggregates of 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin in polyelectrolyte multilayer films

We fabricated a layer-by-layer (LbL) film composed of 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) and poly(allylamine) (PAA) and investigated its pH response by UV-visible spectrometry. When the (PAA/TPPS)5PAA film was immersed in a pH 1.5 solution, J-aggregate bands were observed at 484 and 691 nm. Above pH 3.0, the J-aggregates were completely dissociated and an H-aggregate band was observed at 405 nm. The interconversion between the J-aggregates and H-aggregates in the LbL film was repeatable and controllable by changing the pH of the solutions.

One-Dimensional, Cofacial Porphyrin Polymers Formed by Self-Assembly ofmeso-Tetrakis(ERE Donor) Zinc(II) Porphyrins

A series of meso-tetrakis-(ERE donor) zinc(II) porphyrins nZn (ERE donor = 4-R-3,5-bis[(E)-methyl]phenyl; 1Zn: E = NMe2, R = Br; 2Zn: E = NMe2, R = H; 3Zn: E = OMe, R = Br; 4Zn: E = OMe, R = H) have been synthesized in excellent yields. As a result of the combination of a Lewis acidic site and eight Lewis basic sites within one molecule, monomeric molecules of nZn self-assemble to form one-dimensional porphyrin polymers [nZn](infinity) in the solid state, as confirmed for 1Zn and 3Zn by X-ray crystallography. The coordination environment around the zinc(II) ions in these polymers is octahedral. They are ligated by four equatorial nitrogen atoms of the porphyrin and two apical E atoms (E = N, O) provided by the EBrE donor groups of adjacent nZn molecules. Complexes 2Zn and 4Zn did not form single crystals, but solid-state UV/Vis analysis points to the formation of similar structures. Solution UV/Vis and 1H NMR spectroscopy indicated that interactions between 1Zn and 2Zn monomers in the polymers are stronger than between 3Zn and 4Zn monomers. Interestingly, they also revealed that the presence of a neighboring bromine atom in the EBrE donor groups has a considerable influence on the coordination properties of the benzylic N or O atoms. The zinc(II) ions of the porphyrins most likely adopt only hexacoordination in the solid state, owing to the unique predisposition of Lewis acidic and basic sites in the nZn molecules. Several parameters of the aggregates, for example, the interplanar separation between porphyrins and the zinc-zinc distances, change as a function of the coordinating E groups. The high degree of modularity in their synthesis makes these zinc(II) porphyrins an interesting new entry in noncovalent multiporphyrin assemblies.

Regioisomerically Controlled Self-Aggregation of Zinc 3-Hydroxymethyl-13-formyl-chlorin/Porphyrin and Their 3,13-Inverted Pigments

Zinc 3-hydroxymethyl-13-formyl-chlorin, 1, and its 3,13-inverted (3-formyl-13-hydroxymethyl) regioisomer, 2, and their corresponding 17,18-dehydrogenated porphyrins, 3 and 4, were synthesized for models of natural bacteriochlorophylls-c/d/e possessing 3(1)-OH and 13-C=O groups which self-aggregate in main light-harvesting antenna systems of green photosynthetic bacteria. Zinc chlorins 1 and 2 were monomers in neat THF and gave an obvious difference in their visible absorption spectra, indicating that sole inversion of the 3- and 13-substituents in a chlorin chromophore controlled their optical properties. In an aqueous Triton X-100 solution (a nonionic surfactant), zinc 3(1)-OH-13-CHO-chlorin 1 and porphyrin 3 self-aggregated as do natural bacteriochlorophylls, while zinc 3-CHO-13(1)-OH chlorin 2 and porphyrin 4 (the 3,13-inverted regioisomers of 1 and 3) hardly formed such large oligomers, showing that the inversion of the peripheral 3,13-substituents made their oligomerization unfavorable. FT-IR spectra of aggregated 1-4 in the solid film and their molecular modeling calculations suggested that the 17(2)-C=O moiety in inverted 2/4 interacted with its own 13(1)-OH group to disturb further aggregation.