Controlling structural and functional features of photosynthetic antenna

In order to gain control over the assembly and functioning of photosynthetic antenna, we have developed methods to manipulate pigment composition of bacterial LH1 complexes via their reconstitution with modified bacteriochlorophylls or carotenoids, major photoactive cofactors of these antennae. In the present work we show how the reconstitution and pigment exchange approach is applied to control structural and functional parameters of LH1 and its subunits. The size of the subunits and the energy of the first excited singlet state can be controlled via the use of detergent while the thermodynamics of LH1 formation can be modified using carotenoids and/or a co-solvent. Carotenoids affect the efficiency of the intracomplex energy transfer, while the replacement of native bacteriochlorophyll a with its Ni-substituted analog allows one to control the excited state properties of LH1. These results show that LH1 is a very promising model system applicable for the design of bio-inspired device performing solar energy conversion

Pulmonary metastases of the A549-derived lung adenocarcinoma tumors growing in nude mice : a multiple case study

Lung adenocarcinoma is a leading human malignancy with fatal prognosis. Ninety percent of the deaths, however, are caused by metastases. The model of subcutaneous tumor xenograft in nude mice was adopted to study the growth of control and photodynamically treated tumors derived from the human A549 lung adenocarcinoma cell line. As a side-result of the primary studies, observations on the metastasis of these tumors to the murine lungs were collected, and reported in the present paper. The metastasizing primary tumors were drained by a prominent number of lymphatic vessels. The metastatic tissue revealed the morphology of well-differentiated or trans-differentiated adenocarcinoma. Further histological and histochemical analyses demonstrated the presence of golden-brown granules in the metastatic tissue, similar to these found in the tumor tissue. In contrast to the primary tumors, the electron paramagnetic resonance spectroscopy revealed no nitric oxide - hemoglobin complexes (a source of intense paramagnetic signals), in the metastases. No metastases were found in other murine organs; however, white infarctions were identified in a single liver. Taken together, the A549-derived tumors growing subcutaneously in nude mice can metastasize and grow on site in the pulmonary tissue. Thus, they can represent an alternative for the model of induced metastatic nodule formation, following intravenous administration of the cancerous cells

Structural and electronic effects in the metalation of porphyrinoids : theory and experiment

The structure - reactivity relationships in metalation reactions of porphyrinoids have been studied using experimental and theoretical methods. A series of eight porphyrinoic ligands, derivatives of chlorophylls, was prepared in which both the peripheral groups and the degrees of saturation of the macrocycle were systematically varied. To reveal the solvent and structural factors which control the interactions of these macroligands with metal centers, their interactions with reactive Zn 2 þ and inert Pt 2 þ ions were investigated using absorption spectroscopy. In parallel, quantum chemical calculations ( density functional theory, DFT ) were performed for the same set of molecules to examine the influence of structural and electronic factors on the energy of the frontier orbitals, the nucleophilicity/electronegativity of the macrocycle, its hardness, and conformation. These static descriptors of chemical reactivity, relevant to metalation reactions, were verified against the results obtained in the experimental model. The experimentally obtained kinetic data clearly show that the solvent has a crucial role in the activation of the incoming metal center. In terms of chelator structure, the largest effects concern the size of the delocalized π -electron system and the presence of side groups. Both the DFT calculations and experimental results show the strong influence of the macrocycle rigidity and of the peripheral groups on the chelating ability of porphyrinoids. In particular, the peripheral functionalization of the macrocyclic system seems to drastically reduce its reactivity toward metal ions. The effect of peripheral groups is two- fold: ( i ) a lower electron density on the core nitrogens, and ( ii ) increased rigidity of the macrocycle.The outcomes of the theoretical and experimental analyses are discussed also in terms of their relevance to the mechanism of biological metal insertion in the biosynthesis of heme and chlorophyll

Molecular symmetry determines the mechanism of a very efficient ultrafast excitation-to-heat conversion in Ni-substituted chlorophylls

AbstractIn the Ni-substituted chlorophylls, an ultrafast (<60fs) deactivation channel is created, which is not present in Ni-porphyrins. This observation prompted us to investigate in detail the mechanism of excitation-to-heat conversion in Ni-substituted chlorophylls, experimentally, using time-resolved laser-induced optoacoustic spectroscopy, and theoretically, using group theory approach. The Ni-substituted chlorophylls show exceptional photostability and the optoacoustic measurements confirm the prompt and very efficient (100%) excitation-into-heat conversion in these complexes. Considering their excellent spectral properties and the loss-free excitation-into-heat conversion they are likely to become a new class of versatile photocalorimetric references. The curious features of the Ni-substituted chlorophylls originate from the symmetry of a ligand field created in the central cavity. The central NNi2+ bonds, formed via the donation of two electrons from each of the sp2 orbitals of two central nitrogens to an empty s−dx2−y2 hybrid centered on Ni2+, have a considerable covalent character. The extreme rate of excited state relaxation is then not due to a ladder of the metal centered d-states, often invoked in metalloporphyrins, but seems to result from a peculiar topology of the potential energy surface (a saddle-shaped crossing) due to the covalent character of the NNi2+ bonds. This is confirmed by a strong 0→0 character of electronic transitions in these complexes indicating a similarity of their equilibrium geometries in the ground (S0) and the excited states (both QX and QY). The excitation energy is very efficiently converted into molecular vibrations and dissipated as heat, involving the central Ni2+. These Ni-substituted pigments pose a fine exemplification of symmetry control over properties of excited states of transition metal complexes

Real-time non-invasive transdermal monitoring of photosensitizer level in vivo for pharmacokinetic studies and optimization of photodynamic therapy protocol

Efficient application of any therapeutic agent requires the knowledge of the time evolution of drug concentration in tissues. Usually, the collection of such pharmacokinetic data relies on sequential invasive measurements and sacrifice of many animals. Our aim was to establish a non-invasive analytical assay that would allow for determination of the levels of fluorescent (pro)drugs in the tissues. We have applied a portable fiber optics-based spectrophotometric setup to determine pharmacokinetic profiles of two water-soluble chlorophyll derivatives via transdermal emission measurements in vivo, in a model system consisting of DBA/2 mice bearing subcutaneous Cloudman S91 melanoma tumor. Based on their emission spectra, recorded transdermally in real-time, the in vivo peak levels and retention times of intraperitoneally and intravenously administered photosensitizers were estimated. These data served then to optimize the photodynamic therapy protocol. The effects of the treatment show a strong correlation between the efficacy of the therapy and the pharmacokinetic profiles, confirming the validity of the method. This approach has several important advantages, including (i) a maximization of therapeutic effects by indicating the optimal timing for irradiation; (ii) a non-invasive determination of the photosensitizer level in the tumor to predict the therapy outcome; (iii) an estimation of the safety dark period to minimize the side effects related to phototoxicity; (iv) a possibility of performing a whole series of non-invasive pharmacokinetic experiments in the same organism; and (v) a significant cut in the costs of pharmacokinetic studies. The measurements on human tissue indicate that this non-invasive method can be also applied in humans