bacteriochlorophylls and chlorin

Zinc 3-hydroxymethyl-13

Topics: Alkylation; Bacterial Proteins; Bacteriochlorophylls; Chlorophyll; Circular Dichroism; Isomerism; Micelles; Models, Molecular; Porphyrins; Solutions; Water; Zinc

(Bacterio)Chlorophyll ((B)Chl) molecules play a major role in photosynthetic light-harvesting proteins, and the knowledge of their triplet state energies is essential to understand the mechanisms of photodamage and photoprotection, as the triplet excitation energy of (B)Chl molecules can readily generate highly reactive singlet oxygen. The triplet state energies of 10 natural chlorophyll (Chl a, b, c2, d) and bacteriochlorophyll (BChl a, b, c, d, e, g) molecules and one bacteriopheophytin (BPheo g) have been directly determined via their phosphorescence spectra. Phosphorescence of four molecules (Chl c2, BChl e and g, BPheo g) was characterized for the first time. Additionally, the relative phosphorescence to fluorescence quantum yield for each molecule was determined. The measurements were performed at 77K using solvents providing a six-coordinate environment of the Mg(2+) ion, which allows direct comparison of these (B)Chls. Density functional calculations of the triplet state energies show good correlation with the experimentally determined energies. The correlation determined computationally was used to predict the triplet energies of three additional (B)Chl molecules: Chl c1, Chl f, and BChl f.

Topics: Bacteria; Bacteriochlorophylls; Electron Spin Resonance Spectroscopy; Energy Transfer; Photosynthesis; Porphyrins; Quantum Theory; Rhodobacter sphaeroides; Singlet Oxygen; Spectrometry, Fluorescence

A chlorophyll derivative with a central zinc ion, a methoxy functionality at its 3(1)-position, and functionalized with a second-generation dendron (3,4-3,4,5)12G2-CH(2)OH at its 17(2)-position was synthesized starting from natural chlorophyll a (Chl a). This compound exhibits liquid crystalline (LC) behavior and its mesomorphic properties have been characterized by differential scanning calorimetry (DSC), polarisation optical microscopy (POM), powder X-ray diffraction (XRD), and scanning probe microscopy (SPM). A combination of powder XRD, high resolution scanning tunneling microscopy (STM), and atomic force microscopy (AFM) experiments revealed the formation of nano-segregated well-ordered columnar tubular superstructures consisting of about five molecules in the column stratum. These self-assembled columns are further self-organized into a two-dimensional oblique unit cell lattice. Semiconducting behavior of this compound has been studied by pulse-radiolysis time-resolved microwave conductivity (PR-TRMC) method and charge carrier mobility values of ∼10(-2) cm(2) V(-1) s(-1) are observed. Such organized columnar superstructures constructed from semisynthetic zinc chlorins are reminiscent of the tubular organization of the bacteriochlorophyll dyes in the light-harvesting chlorosomal antennae of green sulphur bacteria.

Topics: Bacteriochlorophylls; Chlorophyll; Chlorophyll A; Metalloporphyrins; Microscopy, Polarization; Microscopy, Scanning Tunneling; Molecular Structure; Pigments, Biological; Porphyrins; X-Ray Diffraction; Zinc

Zinc 3(1)-hydroxy-13(1)-oxo-chlorophyll derivatives 3 and 4 having a B-ring reduced chlorin pi-system (C7-C8, C17=C18) were prepared as models of self-aggregative bacteriochlorophyll-d, which are regioisomers of 1 and 2 possessing a natural-type D-ring reduced chlorin pi-system (C7=C8, C17-C18). 3(1)-Epimerically pure forms of secondary alcohol 3 (3-CH(OH)CH(3)) as well as primary alcohol 4 (3-CH(2)OH) were effectively synthesized by modifying naturally available bacteriochlorophyll-a. Self-aggregation of 3 and 4 in an aqueous micellar solution was examined by UV-vis and CD spectroscopies and compared with that of their regioisomeric 1 and 2.

Topics: Bacteriochlorophylls; Chromatography, High Pressure Liquid; Circular Dichroism; Crystallography, X-Ray; Magnetic Resonance Spectroscopy; Molecular Structure; Porphyrins; Spectrometry, Mass, Fast Atom Bombardment

The oxidation of bacteriopyropheophorbide with ferric chloride hexahydrate or its anhydrous form produced the ring-D oxidized (ring-B reduced) chlorin in >95% yield. Replacing the five-member isocyclic ring in bacteriopyropheophorbide- a with a fused six-member N-butylimide ring system made no difference in regioselective oxidation, and the corresponding ring-B reduced chlorin was isolated in almost quantitative yield. When the oxidant was replaced by 2,3-dichloro-5,6-dicyano-p-benzoquinone, which is frequently used at the oxidizing stage of the porphyrin synthesis, the ring-B oxidized (ring-D reduced) chlorins were obtained. With both ring-B reduced and ring-D reduced chlorins in hand, their photophysical and electrochemical properties were examined and compared for the first time. The ring-B reduced chlorine 20, with a fused six-member N-butylimide ring, exhibits the most red-shifted absorption band (at lambda(max) = 746 nm), the lowest fluorescence quantum yield (4.5%), and the largest quantum yield of singlet oxygen formation (67%) among the reduced ring-B and ring-D chlorins investigated in this study. Measurements of the one-electron oxidation and reduction potentials show that compound 20 is also the easiest to oxidize among the examined compounds and the third easiest to reduce. In addition, the 1.62 eV HOMO-LUMO gap of 20 is the smallest of the examined compounds, and this agrees with values calculated using the DFT method. Spectroelectrochemical measurements afforded UV-visible absorption spectra for both the radical cations and radical anions of the examined chlorins. The ring-B reduced compound 20, with a fused six-member N-butylimide ring, is regarded as the most promising candidate in this study for photodynamic therapy because it has the longest wavelength absorption and the largest quantum yield of singlet oxygen formation among the compounds investigated.

Topics: Bacteriochlorophyll A; Chlorides; Circular Dichroism; Computer Simulation; Electrochemistry; Ferric Compounds; Imides; Magnetic Resonance Spectroscopy; Models, Chemical; Molecular Conformation; Oxidation-Reduction; Photochemistry; Porphyrins; Quantum Theory; Reference Standards; Singlet Oxygen; Spectrometry, Fluorescence; Stereoisomerism

A series of zinc 3(1)-hydroxymethyl chlorins 10 a-e and zinc 3(1)-hydroxyethyl chlorins 17 with varied structural features were synthesized by modifying naturally occurring chlorophyll a. Solvent-, temperature-, and concentration-dependent UV/Vis and CD spectroscopic methods as well as microscopic investigations were performed to explore the importance of particular functional groups and steric effects on the self-assembly behavior of these zinc chlorins. Semisynthetic zinc chlorins 10 a-e possess the three functional units relevant for self-assembly found in their natural bacteriochlorophyll (BChl) counterparts, namely, the 3(1)-OH group, a central metal ion, and the 13(1) C==O moiety along the Qy axis, and they contain various 17(2)-substituents. Depending on whether the zinc chlorins have 17(2)-hydrophobic or hydrophilic side chains, they self-assemble in nonpolar organic solvents or in aqueous media, respectively. Zinc chlorins possessing at least two long side chains provide soluble self-aggregates that are stable in solution for a prolonged time, thus facilitating elucidation of their properties by optical spectroscopy. The morphology of the zinc chlorin aggregates was elucidated by atomic force microscopy (AFM) studies, revealing well-defined nanoscale rod structures for zinc chlorin 10 b with a height of about 6 nm. It is worth noting that this size is in good accordance with a tubular arrangement of the dyes similar to that observed in their natural BChl counterparts in the light-harvesting chlorosomes of green bacteria. Furthermore, for the epimeric 3(1)-hydroxyethyl zinc chlorins 17 with hydrophobic side chains, the influence of the chirality center at the 3(1)-position on the aggregation behavior was studied in detail by UV/Vis and CD spectroscopy. Unlike zinc chlorins 10, the 3(1)-hydroxyethyl zinc chlorins 17 formed only small oligomers and not higher rod aggregate structures, which can be attributed to the steric effect imposed by the additional methyl group at the 3(1)-position.

Topics: Bacteriochlorophylls; Circular Dichroism; Light; Microscopy, Atomic Force; Molecular Structure; Polyethylene Glycols; Porphyrins; Spectrophotometry; Temperature; Zinc

Zinc 3(1)-hydroxy-13(1)-oxo-chlorins possessing various perfluorooctyl groups in the 17-propionate were prepared by modifying naturally occurring chlorophyll-a. The synthetic compound having four perfluorooctyl groups readily self-assembled to form large J-aggregates, which were dissolved in fluorous phases with more ordered supramolecular structures than in a hydrocarbon solvent.

Topics: Bacteriochlorophylls; Chemistry, Pharmaceutical; Chlorophyll; Circular Dichroism; Drug Design; Hexanes; Macromolecular Substances; Models, Chemical; Molecular Conformation; Molecular Structure; Porphyrins; Solvents; Zinc; Zinc Compounds

Allomerization of bacteriochlorophyll a (Bchl a) was studied under various reaction conditions. Bchl a on stirring with KOH/propanol produced an "unstable bacteriochlorin", which decomposed in acidic conditions to give a complex mixture containing bacteriopurpurin a as a principal component. The yields of other compounds varied and were found to be dependent on reaction condition. The structures of the isolated porphyrins, chlorins, and bacteriochlorins, related to Bchl a, were assigned on the basis of 1D, 2D NMR (ROESY), and mass spectroscopy analyses. The presence of fused anhydride rings in porphyrin, chlorin, and bacterichlorin systems showed a significant influence on their optical properties. Compared to bacteriochlorophyll a and bacteriopheophytin, the related structurally modified analogues, e.g., the bacteriopurpurin a, 13(1)/15(1)-N-alkyl isoimide, and the imide analogues were found to be more stable with a significant difference in spectroscopic properties. Bacteriochlorins containing anhydride, imide, or isoimide cyclic rings demonstrated a significant bathochromic shift of their Q bands in their electronic absorption spectra. Under basic conditions the formation of the 12-hydroxymethyl, 12-formyl, and 12-methylene analogues as byproducts from the 12-methyl-bacteriopurpurin-N-hexylimide could be due to subsequent oxidation of the vinylogous enolate intermediates. To investigate the effect of the central metal in the electronic spectra, the stable bacteriopurpurin-18-N-hexylimide was converted to a series of metal complexes [Zn(II), Cd(II), and Pd(II)] by following the direct or transmetalation approaches. Compared to the free-base analogue, these complexes showed a remarkable shift in their electronic absorption spectra.

Topics: Anhydrides; Anthraquinones; Bacteriochlorophyll A; Imides; Mass Spectrometry; Organometallic Compounds; Porphyrins

Topics: Bacterial Proteins; Bacteriochlorophylls; Chlorobi; Chlorobium; Methylation; Methyltransferases; Porphyrins

On-line high performance liquid chromatography/atmospheric pressure chemical ionization mass spectrometry (HPLC/APCI-MS) has been applied to the identification of a number of tetrapyrrolic pigments as well as several magnesium-free analogs. Mass spectra, acquired both in positive (+) and negative (-) ionization mode, allow not only the determination of the structural features of the pigments, but also a very easy differentiation of the Mg-chelated pigments from the free bases. In the positive ionization mode, all pigments show mainly a [M + H]+ ion and a [M + H - C20H38]+ fragment ion corresponding to the loss of the phytyl chain via a hydrogen rearrangement. In the negative ionization mode, on the other hand, although all pigments give an abundant molecular anion [M]-*, only the Mg-chelated chlorin spectra show a prominent fragment [M - C20H39]- produced by a formal loss of the phytyl radical.

Topics: Bacteriochlorophylls; Chlorophyll; Chromatography, High Pressure Liquid; Magnesium; Mass Spectrometry; Molecular Structure; Porphyrins

In isolated, chlorosome-free reaction centers from Chlorobium limicola f thiosulphatophilum, a chlorin pigment exhibits a Qy absorption band at 672 nm (Feiler, U., Nitschke, W., & Michel, H. (1992) Biochemistry 31, 2608-2614). To characterize the chemical nature of this chlorin pigment and its interactions within the reaction-center protein, selective enhancement of its Raman scattering was achieved by resonant excitation within its Soret band. This is the first time that structural studies of this pigment were performed on the native reaction-center protein. The obtained resonance Raman spectra were consistent with a single population of a chlorophyll a(-like) pigment, possessing a vinyl group on ring I, but not with bacteriochlorophyll c or bacteriophaeophytin c. The stretching frequencies of the C9-keto carbonyl of this pigment indicates that it is H-bonded to the reaction-center protein. The strength of this H-bond is very close to those of the keto carbonyls of the primary electron acceptors in purple bacterial reaction centers and D1/D2 particles. Since in membranes of Chlorobiaceae a transient bleaching at 670 nm is due to the primary acceptor in the reaction center (Nuijs, A. M., Vasmel, H., Joppe, H. L. P., Duysens, L. N. M., & Amesz, J. (1985a) Biochim. Biophys. Acta 907, 24-34), we thus conclude that the primary acceptor in Chlorobium reaction centers is the characterized chlorophyll a(-like) pigment.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Bacteria; Bacteriochlorophylls; Binding Sites; Chlorophyll; Chlorophyll A; Hydrogen Bonding; Kinetics; Light-Harvesting Protein Complexes; Magnesium; Photosynthetic Reaction Center Complex Proteins; Porphyrins; Spectrum Analysis, Raman