Sintesis dan Karakterisasi Sifat Optik Eosin Y@Metal- Organic Framework Zirkonium Naftalendikarboksilat

Eosin Y telah berhasil diembankan pada Metal-Organic Framework Zirkonium Naftalendikarboksilat (MOF Zr-NDC) dengan cara menambahkan Eosin Y dalam pelarut etanol (0,034 ml, 10-4 M) pada MOF Zr-NDC (0,3 g). Pengukuran Powder X-Ray Diffraction (PXRD) dilakukan untuk mengkonfirmasi pembentukan MOF Zr-NDC dengan puncak khas pada 2θ di 6.47 dan 7.45. Spektra UV-vis Diffuse Reflectance Spectra diperoleh dengan menggunakan spektrofotometer UV-vis. MOF Zr-NDC memberikan serapan pada 274 nm yang berhubungan dengan energi celah sebesar 4.32 eV, sedangkan Eosin Y menunjukkan serapan pada 524 nm. Di sisi lain, Eosin Y@MOF Zr-NDC menunjukkan puncak-puncak serapan pada 300, 357, dan 524 nm yang berkorelasi dengan energi celah masing-masing sebesar 3,65, 3,15, dan 2,19 e

Polarization control of metal-enhanced fluorescence in hybrid assemblies of photosynthetic complexes and gold nanorods

Fluorescence imaging of hybrid nanostructures composed of a bacterial light-harvesting complex LH2 and Au nanorods with controlled coupling strength is employed to study the spectral dependence of the plasmon-induced fluorescence enhancement. Perfect matching of the plasmon resonances in the nanorods with the absorption bands of the LH2 complexes facilitates a direct comparison of the enhancement factors for longitudinal and transverse plasmon frequencies of the nanorods. We find that the fluorescence enhancement due to excitation of longitudinal resonance can be up to five-fold stronger than for the transverse one. We attribute this result, which is important for designing plasmonic functional systems, to a very different distribution of the enhancement of the electric field due to the excitation of the two characteristic plasmon modes in nanorods

Absorption Enhancement in Peridinin–Chlorophyll–Protein Light-Harvesting Complexes Coupled to Semicontinuous Silver Film

We report on experimental and theoretical studies of plasmon-induced effects in a hybrid nanostructure composed of light-harvesting complexes and metallic nanoparticles in the form of semicontinuous silver film. The results of continuous-wave and time-resolved spectroscopy indicate that absorption of the light-harvesting complexes is strongly enhanced upon coupling with the metallic film spaced by 25 nm of a dielectric silica layer. This conclusion is corroborated by modeling, which confirms the morphology of the silver island film

Relative binding affinities of chlorophylls in peridinin-chlorophyll-protein reconstituted with heterochlorophyllous mixtures

Peridinin-chlorophyll-protein (PCP), containing differently absorbing chlorophyll derivatives, are good models with which to study energy transfer among monomeric chlorophylls (Chls) by both bulk and single-molecule spectroscopy. They can be obtained by reconstituting the N-terminal domain of the protein (N-PCP) with peridinin and chlorophyll mixtures. Upon dimerization of these "half-mers, homo- and heterochlorophyllous complexes are generated, that correspond structurally to monomeric protomers of native PCP from Amphidinium carterae. Heterochlorophyllous complexes contain two different Chls in the two halves of the complete structure. Here, we report reconstitution of N-PCP with binary mixtures of Chl a, Chl b, and [3-acetyl]-Chl a. The ratios of the pigments were varied in the reconstitution mixture, and relative binding constants were determined from quantification of these pigments in the reconstituted PCPs. We find higher affinities for both Chl b and [3-acetyl]-Chl a than for the native pigment, Chl a.6 page(s

Peridinin-chlorophyll-protein reconstituted with chlorophyll mixtures : preparation, bulk and single molecule spectoscopy

Reconstitution of the 16kDa N-terminal domain of the peridinin–chlorophyll–protein, N-PCP, with mixtures of chlorophyll a (Chl a) and Chl b, resulted in 32kDa complexes containing two pigment clusters, each bound to one N-PCP. Besides homo-chlorophyllous complexes, hetero-chlorophyllous ones were obtained that contain Chl a in one pigment cluster, and Chl b in the other. Binding of Chl b is stronger than that of the native pigment, Chl a. Energy transfer from Chl b to Chl a is efficient, but there are only weak interactions between the two pigments. Individual homo- and hetero-chlorophyllous complexes were investigated by single molecule spectroscopy using excitation into the peridinin absorption band and scanning of the Chl fluorescence, the latter show frequently well resolved emissions of the two pigments.6 page(s

Energy transfer from conjugated polymer to bacterial light-harvesting complex

Energy transfer from a conjugated polymer blend (poly(9,9-dioctylfluorenyl-2,7-diyl):poly (2-methoxy-5-(2-ethylhexyloxy)-1, 4-phenylenevinylene) to a light-harvesting complex 2 from purple bacteria has been demonstrated using time-resolved fluorescence spectroscopy. For our hybrid nanostructure, we observe a 30% reduction of the fluorescence lifetime of the polymer emission as compared to the pure polymer layer. This result is an important step towards integrating naturally evolved biomolecules with synthetic materials into biohybrid organic electronic systems

Tracking energy transfer between light harvesting complex 2 and 1 in photosynthetic membranes grown under high and low illumination

Energy transfer (ET) between B850 and B875 molecules in light harvesting complexes LH2 and LH1/RC (reaction center) complexes has been investigated in membranes of Rhodopseudomonas palustris grown under high- and low-light conditions. In these bacteria, illumination intensity during growth strongly affects the type of LH2 complexes synthesized, their optical spectra, and their amount of energetic disorder. We used a specially built femtosecond spectrometer, combining tunable narrowband pump with broadband white-light probe pulses, together with an analytical method based on derivative spectroscopy for disentangling the congested transient absorption spectra of LH1 and LH2 complexes. This procedure allows real-time tracking of the forward (LH2 → LH1) and backward (LH2←LH1) ET processes and unambiguous determination of the corresponding rate constants. In low-light grown samples, we measured lower ET rates in both directions with respect to high-light ones, which is explained by reduced spectral overlap between B850 and B875 due to partial redistribution of oscillator strength into a higher energetic exciton transition. We find that the low-light adaptation in R. palustris leads to a reduced elementary backward ET rate, in accordance with the low probability of two simultaneous excitations reaching the same LH1/RC complex under weak illumination. Our study suggests that backward ET is not just an inevitable consequence of vectorial ET with small energetic offsets, but is in fact actively managed by photosynthetic bacteria

Conservation of spin polarization during triplet-triplet energy transfer in reconstituted peridinin-chlorophyll-protein complexes

Peridinin-chlorophyll-protein (PCP) complexes, where the N-terminal domain of native PCP from Amphidinium carterae has been reconstituted with different chlorophyll (Chl) species, have been investigated by time-resolved EPR in order to elucidate the details of the triplet-triplet energy transfer (TTET) mechanism. This spectroscopic approach exploits the concept of spin conservation during TTET, which leads to recognizable spin-polarization effects in the observed time-resolved EPR spectra. The spin polarization produced at the acceptor site (peridinin) depends on the initial polarization of the donor (chlorophyll) and on the relative geometric arrangement of the donor-acceptor spin axes. A variation of the donor triplet state properties in terms of population probabilities or triplet spin axis directions, as produced by replacement of chlorophyll a (Chl a) with non-native chlorophyll species (ZnChl a and BacterioChl a) in the reconstituted complexes, is unambiguously reflected in the polarization pattern of the carotenoid triplet state. For the first time, in the present investigation spin-polarization conservation has been shown to occur among natural cofactors in protein complexes during the TTET process. Proving the validity of the assumption of spin conservation adopted in the EPR spectral analysis, the results reinforce the hypothesis that in PCP proteins peridinin 614, according to X-ray nomenclature (Hofmann, E.; et al. Science1996, 272, 1788-1791), is the carotenoid of election in the photoprotection mechanism based on TTET.10 page(s