Excitation relaxation dynamics and energy transfer in fucoxanthin–chlorophyll a/c-protein complexes,probed by time-resolved fluorescence

In algae, light-harvesting complexes contain specific chlorophylls (Chls) and keto-carotenoids; Chl a, Chl c, and fucoxanthin (Fx) in diatoms and brown algae; Chl a, Chl c, and peridinin in photosynthetic dinoflagellates; and Chl a, Chl b, and siphonaxanthin in green algae. The Fx–Chl a/c-protein (FCP) complex from the diatom Chaetoceros gracilis contains Chl c₁, Chl c₂, and the keto-carotenoid, Fx, as antenna pigments, in addition to Chl a. In the present study, we investigated energy transfer in the FCP complex associated with photosystem II (FCPII) of C. gracilis. For these investigations, we analyzed time-resolved fluorescence spectra, fluorescence rise and decay curves, and time-resolved fluorescence anisotropy data. Chl a exhibited different energy forms with fluorescence peaks ranging from 677 nm to 688 nm. Fx transferred excitation energy to lower-energy Chl a with a time constant of 300 fs. Chl c transferred excitation energy to Chl a with time constants of 500–600 fs (intra-complex transfer), 600–700 fs (intra-complex transfer), and 4–6 ps (inter-complex transfer). The latter process made a greater contribution to total Chl c-to-Chl a transfer in intact cells of C. gracilis than in the isolated FCPII complexes. The lower-energy Chl a received excitation energy from Fx and transferred the energy to higher-energy Chl a. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: Keys to Produce Clean Energy.     

Dopamine release and molecular modeling study of some coumarin derivatives

4-aryl-2-amino-6-(4-hydroxy-2-oxo-2H-chromen-3-yl)-pyridin-3-carbonitrile (1), 4-aryl-2-oxo-6-(4-hydroxy-2-oxo-2H-chromen-3-yl)-pyridin-3-carbonitriles (2a-2c), 3-(6-aryl-1,2,5,6- tetrahydro-2-thioxopyrimidin-4-yl)-4-hydroxy-2H-chromen-2-one (3a, 3b) and pyrazol-3-yl-4-hydroxycoumarin derivatives (4a-4c, 5, 6a, 6b, 7a, 7b, and 8a-8c) were prepared in order to measure their % change dopamine release in comparison to amphetamine as reference, using PC-12 cells in different concentrations. In addition, the molecular modeling study of the compounds into 3BHH receptor was also demonstrated. The calculated inhibition constant (k_i) implemented in the AutoDock program revealed identical correlation with the experimental results to that obtained binding free energy (ΔG_b) as both parameters revealed reasonable correlation coefficients (R²) being 0.51 involving 10 compounds; (1, 2b, 2c, 3a, 3b, 4a, 4b, 6a, and 8c).     

Thiazolyl-pyrazole derivatives as potential antimycobacterial agents

Mycobacterium tuberculosis (Mtb) is an obligate aerobe that is capable of long-term persistence under conditions of low oxygen tension. A series of thiazolyl-pyrazole derivatives (6a–f, 7a–f, 8c, 8e) were screened for antimycobacterial activity against dormant M. tuberculosis H37Ra (D-MTB) and M. bovis BCG (D-BCG). Nine thiazolyl-pyrazole analogs, 6c, 6e, 7a, 7b, 7c, 7e, 7f, 8c and 8e exhibited promissing minimum inhibitory concentration (MIC) values (0.20–28.25?µg/mL) against D-MTB and D-BCG strains of Mtb. Importantly, six compounds (7a, 7b, 7e, 7f, 8c and 8e) exhibited excellent antimycobacterial activity and low cytotoxicity at the maximum evaluated concentration of >250?µg/mL. Finally, the promising antimycobacterial activity and lower cytotoxicity profile suggested that, these compounds could be further subjected for optimization and development as a lead, which could have the potential to treat tuberculosis.     

Synthesis and characterization of new coordination polymers generated from oxadiazole-containing ligands and IIB metal ions

The coordination chemistry of the oxadiazole-containing rigid bidentate ligands 2,5-bis(4-pyridyl)-1,3,4-oxadiazole (L1) and 2,5-bis(3-pyridyl)-1,3,4-oxadiazole (L2) with inorganic IIB metal salts have been investigated. Five new coordination polymers (1-5) were prepared by solution reactions and fully characterized by infrared spectroscopy, elemental analysis, and single-crystal X-ray diffraction. Cd(L1)₂(CH₃CN)₂](ClO₄)₂ · (CH₃CN)₂ (1) crystallized in the monoclinic space group P2₁/c, a = 8.4028(5) Å, b = 21.3726(13) Å, c = 10.5617(7) Å, β = 95.1200(10)°, and Z = 2. In the solid state, it adopts an infinite two-dimensional polymeric structural motif with effective cross section of ca. 14.31 × 14.31 Å. Cd(L2)(H₂O)(NO₃)₂ (2) crystallized in the monoclinic space group Ia, a = 7.1203(5) Å, b = 22.2475(15) Å, c = 20.2652(16) Å, β = 90.6080(10)°, and Z = 8. In the solid state, the two Cd(II) centers are connected to each other by L2 ligands and bridging nitrates into a two-dimensional network. [ZnCl₂(L1)] (3) and [HgI₂(L1)] · CH₃CN (4) crystallized in the monoclinic crystal system (3: P2₁/c, a = 5.3702(3) Å, b = 20.4800(11) Å, c = 12.4093(7) Å, β = 94.7930(10)°, and Z = 4; 4: P2/n, a = 17.2733(11) Å, b = 5.2173(3) Å, c = 20.4069(13) Å, β = 102.8690(10)°, and Z = 4). In the solid state, Zn(II) and Hg(II) metal centers are connected to each other by L1 ligands into a zigzag chain motif. Compound 5 (HgBr₂(L2) is different from 3 and 4, monoclinic, P2(1)/n, a = 5.470(4) Å, b = 16.271(13) Å, c = 16.486(12) Å, β = 93.197(15)°, and Z = 4) adopts a novel one-dimensional helical chain motif which resulted from the relative different coordinated orientation of the two N-donors on L2 ligand.     

Mixed-ligand tris chelated complexes of Mo(IV) and W(IV): A comparative study

Two hitherto unknown mixed-ligand tris chelated complexes containing 2-aminothiophenolate, [Et₄N]₂[M^IV(NH-(C₆H₄)-S)(mnt)₂] (M = Mo, 1a; W, 2a) and two mixed-ligand tris chelate complex containing N,N-diethyldithiocarbamate, [Et₄N]₂[M^IV(Et₂NS₂)(mnt)₂] (M = Mo, 1b; W, 2b) have been synthesized and characterized structurally. Although these complexes are supposed to be quite similar to the well-known symmetric tris chelate complexes of maleonitriledithiolate (mnt), [Et₄N]₂[M^IV(mnt)₃] (M = Mo, 1c; W, 2c), but display both trigonal prismatic and distorted trigonal prismatic geometry in their crystal structure indicating the possibility of an equilibrium between these two structural possibilities in solution. Unlike extreme stability of 1b, 2b, 1c and 2c, both 1a and 2a are highly unstable in solution. In contrast to one reversible reduction in case of 1b and 2b, 1a and 2a exhibited no possible reduction up to −1.2 V and two sequential oxidation steps which have been further investigated with EPR study. Differences in stability and electrochemical behavior of 1a, 1b, 2a and 2b have been correlated with theoretical calculations at DFT level in comparison with long known 1c and 2c.     

Crystallographic structure of the turbine C-ring from spinach chloroplast F-ATP synthase

In eukaryotic and prokaryotic cells, F-ATP synthases provide energy through the synthesis of ATP. The chloroplast F-ATP synthase (CF₁F_O-ATP synthase) of plants is integrated into the thylakoid membrane via its F_O-domain subunits a, b, b’ and c. Subunit c with a stoichiometry of 14 and subunit a form the gate for H⁺-pumping, enabling the coupling of electrochemical energy with ATP synthesis in the F₁ sector.Here we report the crystallization and structure determination of the c14-ring of subunit c of the CF₁F_O-ATP synthase from spinach chloroplasts. The crystals belonged to space group C2, with unit-cell parameters a=144.420, b=99.295, c=123.51 Å, and β=104.34° and diffracted to 4.5 Å resolution. Each c-ring contains 14 monomers in the asymmetric unit. The length of the c-ring is 60.32 Å, with an outer ring diameter 52.30 Å and an inner ring width of 40 Å.     

Coordination environment friendly silicon in copper(I) chloride π-complexes with tetravinylsilane and dimethyltetravinyldisiloxane

Two crystal complexes of copper(I) chloride with tetravinylsilane (TVS) dimethyltetravinyldisiloxane (DMTVDS) were prepared and examined by IR spectroscopy and X-ray diffraction: sp. gr. P2/a, Z = 4, a = 13.428(1) Å, b = 7.9584(7) Å, c = 14.694(1) Å for [Cu₄Cl₄(TVS)]; sp. gr. P2₁/c, a = 10.505(1) Å, b = 13.487(1) Å, c = 13.870(1) Å for [Cu₄Cl₄(DMTVDS)]. The influence of the vinylsilicon ligands on the efficiency of the Cu?CC interaction is discussed. Thus, the consideration of d_Si ← π∗_CC ← d_Cu conjugate system may help to understand how the silicon π-acceptor properties influence on the degree of trigonal distortion of the Cu(I) coordination tetrahedron as well as on the inorganic part organization. The present studies are aimed at the use of the structure controlled nanoparticles supported on vinyl modified silicon (or silicone) substrate.     

Most of the homoeologous pairing at metaphase I in wheat-rye hybrids is not chiasmatic

The use of telomeric C-bands in wheat-rye hybrids has made it possible to distinguish three types of wheat-wheat (1B^L) and wheat-rye associations (a, end-to-end extremely distal; b, end-to-ed distal; and c, interstitial) between homoeologous chromosomes at different metaphase I stages (early, middle and late) and also to estimate the actual recombination frequencies for such associations at anaphase I. There was a decrease of the a and b association frequencies during the different metaphase I stages, whereas the c type remained without variation in all stages. A good fit between the frequencies of c associations at metaphase I and the number of recombinant chromosomes at anaphase I, assuming a maximum of one chiasma per bond, was found; however, there was no correspondence between metaphase I and anaphase I data when all associations (a + b + c) were considered. In addition, rye-rye homologous pairing was observed at metaphase I, but no evidence for rye-rye recombination was found at anaphase I. The results indicate that most of end-to-end (a and b) homoeologous and nonhomologous associations are actually nonchiasmatic and are a remnant of prophase pairing.     

Synthesis and molecular docking study of some 3,4-dihydrothieno[2,3-d]pyrimidine derivatives as potential antimicrobial agents

In continuation of our research program aiming at developing new potent antimicrobial agents, new series of substituted 3,4-dihydrothieno[2,3-d]pyrimidines was synthesized. The newly synthesized compounds were preliminary tested for their in vitro activity against six bacterial and three fungal strains using the agar diffusion technique. The results revealed that compounds 7, 8a, 10b, 10d and 11b exhibited half the potency of levofloxacine against the Gram-negative bacterium, Pseudomonas aeruginosa, while compounds 5a, 8b, 10c and 12 displayed half the potency of levofloxacine against Proteus Vulgaris. Whereas, compounds 7, 10b, 10d and 11b showed half the activity of ampicillin against the Gram-positive bacterium, B. subtilis. Most of the compounds showed high antifungal potency. Compounds 3, 6, 7, 9b, 10a, 11a, 11b, 15 and 16 exhibited double the potency of clotrimazole against A. fumigatus. While compounds 3, 4, 5a, 5b, 9b, 10a, 10b, 10c, 13, 15, 16 and 18 displayed double the activity of clotrimazole against R. oryazae. Molecular docking studies of the active compounds with the active site of the B. anthracis DHPS, showed good scoring for various interactions with the active site of the enzyme compared to the co-crystallized ligand.     

Synthesis of novel dihydrotriazine derivatives bearing 1,3-diaryl pyrazole moieties as potential antibacterial agents

Three novel series of dihydrotriazine derivatives bearing 1,3-diaryl pyrazole moieties were designed, synthesized and evaluated in terms of their antibacterial and antifungal activities. Most of the synthesized compounds showed potent inhibition of several Gram-positive bacterial strains (including multidrug-resistant clinical isolates) and Gram-negative bacterial strains with minimum inhibitory concentration values in the range of 1–64?µg/mL. Compounds 4b and 4c presented the most potent inhibitory activity against Gram-positive bacteria (S. aureus 4220, MRSA 3167, QRSA 3519) and Gram-negative bacteria (E. coli 1924), with minimum inhibitory concentration values of 1 or 2?µg/mL. Compared with previous studies, these compounds exhibited a broad spectrum of inhibitory activity. The cytotoxic activity of the compounds 4a, 4b, 4c and 11n were assessed in L02 cells. In vitro enzyme study implied that compound 4c exerted its antibacterial activity through DHFR inhibition.     

Synthesis and antitumor activity of novel 1-substituted phenyl 3-(2-oxo-1,3,4-oxadiazol-5-yl) β-carbolines and their Mannich bases

A series of novel 1-(substituted phenyl)-3-(2-oxo-1,3,4-oxadiazol-5-yl) β-carbolines (4a–e) and the corresponding Mannich bases 5–9(a–c) were synthesized and evaluated for their in vitro antitumor activity against seven human cancer cell lines. Compounds of 4a–e series showed a broad spectrum of antitumor activity, with GI₅₀ values lower than 15 μM for five cell lines. The derivative 4b, having the N,N-dimethylaminophenyl group at C-1, displayed the highest activity with GI₅₀ in the range of 0.67–3.20 μM. A high selectivity and potent activity were observed for some Mannich bases, particularly towards resistant ovarian (NCI-ADR/RES) cell lines (5a, 5b, 6a, 6c and 9b), and ovarian (OVCAR-03) cell lines (5b, 6a, 6c, 9a, 9b and 9c). In addition, the interaction of compound 4b with DNA was investigated by using UV and fluorescence spectroscopic analysis. These studies indicated that 4b interact with ctDNA by intercalation binding.     

Action Spectra for the Inhibition of Hypocotyl Growth by Continuous Irradiation in Light and Dark-Grown Sinapis alba L. Seedlings

Action spectra for the inhibition by continuous (24-hour) irradiation of hypocotyl growth in 54-hour-old Sinapis alba L. seedlings were measured using seedlings which had had four different pretreatments. These seedlings were either (a) dark-grown with a high total phytochrome level, (b) dark-grown with a low total phytochrome level, (c) light-grown with chlorophyll, or (d) light-grown with no chlorophyll [treated with 4-chloro-5-(methylamino)-2-(α,α,α-trifluoro-m-tolyl)-3(2H) -pyridazinone (San 9789)].     

Letter: X-ray data for four crystalline forms of serum albumin

Cell dimensions, space groups and crystal densities are reported for a monoclinic form of human serum albumin (a = 126.5, b = 39.2, c = 135.2Å, β = 93.3 °, C2, Z = 4), tetragonal human serum albumin (a = 84.0, c = 276Å, P4₁2₁2, Z = 8), a mercury dimer of human serum albumin (a = 155, b = 83, c = 122Å, P2₁2₁2₁, Z = 4) and a hexagonal form of equine serum albumin (a = 96.6, c = 144.5Å, P6₁, Z = 6).     

Radiation-induced human chromosome aberrations. II. Human in vitro irradiation compared to in vitro and in vivo irradiation of marmoset leukocytes

Whole blood cultures from humans and from the New World primate, Saguinus fuscicollis, were irradiated with various doses of 250 kV X-rays. The resulting centric ring plus dicentric aberration yields were fitted to the three models, Y = a+bD, Y = a+bD+cD², and Y = a+cD², by least squares regression. In both instances the best fit was to the model Y = a+bD+cD², with coefficients of the one- and two-track components for human and marmoset being: b = (0.78 ± 0.09)·10⁻³, c = (5.92 ± 0.31)·10⁻⁶, and b = (1.11 ± 0.36)·⁻³, c = (7.7 ± 1.7)·10⁻⁶, respectively.     

The Cytochromes of Prototheca zopfii

The respiratory pigments of Prototheca zopfii include seven cytochromes: two c-type cytochromes, a soluble c(549) and a membrane bound c(551); three b-type cytochromes, b(555), b(559) and b(564); and cytochromes a and a₃. Cytochromes a and a₃ could be resolved spectrally in the α-band region by reducing the cells in the presence of methanol and cyanide. Methanol shifted the absorption maximum of cytochrome a from 598 to 603 nanometers and permitted dithionite (or substrate) to reduce the cyanide-cytochrome a₃ complex to give a well defined 595-nanometer absorption band. Methanol did not interfere with CO binding by cytochrome a₃, and CO did not alter the methanol effect on cytochrome a. Azide and cyanide, which partially inhibited exogenous respiration, stimulated endogenous respiration. Frozen steady states of the electron transport chain in the presence of cyanide and azide indicated that the stimulation by these inhibitors was due to an increased autooxidation of one of the b-type cytochromes, possibly b(564).     

Purification of characterization of a minor form of hepatic microsomal cytochrome P-450 from rats treated with polychlorinated biphenyls

A minor form of hepatic microsomal cytochrome P-450 has been purified to apparent homogeneity from rats treated with the polychlorinated biphenyl mixture, Aroclor 1254. This newly isolated hemoprotein, cytochrome P-450_e, is inducible in rat liver by Aroclor 1254 and phenobarbital, but not by 3-methylcholanthrene. Two other hemoproteins, cytochromes P-450_b and P-450_c, have also been highly purified during the isolation of cytochrome P-450_e based on chromatographic differences among these proteins. By Ouchterlony double-diffusion analysis with antibody to cytochrome P-450_b, highly purified cytochrome P-450_e is immunochemically identical to cytochrome P-450_b but does not cross-react with antibodies prepared against other rat liver cytochromes P-450 (P-450_a, P-450_c, P-450_d) or epoxide hydrolase. Purified cytochrome P-450_e is a single protein-staining band in sodium dodecyl sulfate-polyacrylamide gels with a minimum molecular weight (52,500) slightly greater than cytochromes P-450_b or P-450_d (52,000) but clearly distinct from cytochromes P-450_a (48,000) and P-450_c (56,000). The carbon monoxide-reduced difference spectral peak of cytochrome P-450_e is at 450.6 nm, whereas the peak of cytochrome P-450_b is at 450 nm. Ethyl isocyanide binds to ferrous cytochromes P-450_e and P-450_b to yield two spectral maxima at 455 and 430 nm. At pH 7.4, the 455:430 ratio is 0.7 and 1.4 for cytochromes P-450_b and P-450_e, respectively. Metyrapone binds to reduced cytochromes P-450_e and P-450_b (absorption maximum at 445–446 nm) but not cytochromes P-450_a, P-450_c, or P-450_d. Metabolism of several substrates catalyzed by cytochrome P-450_e or P-450_b reconstituted with NADPH-cytochrome c reductase and dilauroylphosphatidylcholine was compared. The substrate specificity of cytochrome P-450_e usually paralleled that of cytochrome P-450_b except that the rate of metabolism of benzphetamine, benzo[a]pyrene, 7-ethoxycoumarin, hexobarbital, and testosterone at the 16α-position catalyzed by cytochrome P-450_e was only 15–25% that of cytochrome P-450_b. In contrast, cytochrome P-450_e catalyzed the 2-hydroxylation of estradiol-17β more efficiently (threefold) than cytochrome P-450_b. Cytochrome P-450_d, however, catalyzed the metabolism of estradiol-17β at the greatest rate compared to cytochromes P-450_a, P-450_b, P-450_c, or P-450_e. The peptide fragments of cytochromes P-450_e and P-450_b, generated by either proteolytic or chemical digestion of the hemoproteins, were very similar but not identical, indicating that these two proteins show minor structural differences.     

Crystal structures of α- and β-(1,10-phenanthroline)tetrahydroborato(triphenylphosphine)copper(I) and (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline)tetrahydroboratocopper(I)

Copper(I) is five coordinate in (1,10-phenanthroline)tetrahydroborato(triphenylphosphine)copper(I). This compound crystallizes from either toluene as the yellow, α-form, a = 16.247(8), b = 9.750(7), c = 9.322(5) Å, α = 62.92(4), β = 84.77(4), γ = 84.34(5)°, triclinic P$\text{1}$, Z = 2, or from a xylene/methylene chloride mixture as the red β-form, X-ray cell, a = 13.675(11), b = 10.115(8), c = 9.700(7) Å, α = 95.22(6), β = 96.22(6), γ = 101.02(6)°; neutron cell, as the tetradeuteroborate, a = 13.703(1), b = 10.096(8), c = 9.74(1) Å, α = 95.23(9), β = 96.51(8), γ = 101.04(2)°, triclinic, P$\text{1}$, Z = 2. For both forms, unidentate triphenylphosphine, bidentate 1,10-phenanthroline and unsymmetrical bidentate BH₄^? completes the copper(I) coordination but there are subtle differences between the two. When the ligand 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline, dmdp, replaces 1,10-phenanthroline, the compound obtained is four coordinate with no tpp in the crystal. [C(dmdp)BH₄] is monoclinic, Cc, a = 14.522(4), b = 20.07(2), c = 7.718(2) Å, β = 106.17(2)°, Z = 4.     

Maize Mitochondria: Cytochromes of Fertile and Cytoplasmic Male-sterile Lines

Cytochromes a + a₃, b, and c of mitochondria prepared from fertile and cytoplasmic male-sterile single- and double-cross maize (Zea mays L.) lines were examined by difference spectra at 25 C. The sterile lines contained the full complement of cytochromes, and absorption maxima were identical for each fertile-sterile combination. A small, but significant, increase of b cytochromes was detected in each sterile line, whereas the quantities of cytochromes a + a₃ and c were essentially unchanged. The yield of mitochondrial protein per gram of tissue was higher for the single-than for the double-cross, whereas the sterile cytoplasm did not affect ultimate mitochondrial yield.