Photoredox reactivity of copper(II)-3,5-diisopropylsalicylate induced by ligand-to-metal charge transfer excitation of the copper-phenolate chromophore

The electronic spectrum of Cu^II(dps)₂ in CH₃CN with dps=3,5-diisopropylsalicylate shows a ligand field absorption at λ_max=711 nm (ε=140 M⁻¹ cm⁻¹), and a phenolate to Cu(II) ligand-to-metal charge transfer (LMCT) band at λ_max=428 nm (ε=950). LMCT excitation of Cu^II(dps)₂ leads to the reduction of Cu(II) to Cu(I). Copper(II) disappears with φ=2.8×10⁻³ at λ_irr=436 nm.     

Synthesis, structure and magnetic properties of lanthanide(III) complexes with new imidazole-substituted imino nitroxide radical

Synthesis, characterization and magnetic properties of new lanthanide-radical complexes, [Ln^III(hfac)₃(IM2imH)] (Ln = Gd, Tb; IM2imH = 2-(2-pyridyl)-4,5-dihydro-4,4,5,5-tetramethyl-1H-imidazolyl-1-oxy), are described. The molecular structure of the [Tb(hfac)₃(IM2imH)] has been determined by the X-ray diffraction. The magnetic susceptibility data for [Gd(hfac)₃(IM2imH)] show that the Gd-IM2imH magnetic interaction is antiferromagnetic with an exchange coupling constant J = −2.59 cm⁻¹ in contrast to the ferromagnetic interaction in most of Gd(III) complexes containing paramagnetic center, which will be examined in connection with planarity of the IM2imH chelate.     

The synthesis of triethylphosphine gold(I) 4-nitrobenzenethiolate and solvent dependent visible absorption spectra of 4-nitrobenzenethiolate

The synthesis of triethylphosphine gold(I) 4-nitrobenzenethiolate, Et₃PAu(SC₆H₄NO₂-4), is reported. Et₃PAu(SC₆H₄NO₂-4) displays a low energy visible electronic absorption band which is solvent dependent: EtOH (λ_max = 385 nm), acetonitrile (λ_max = 391 nm), THF (λ_max = 395 nm), and DMSO (λ_max = 402 nm). The corresponding low energy visible electronic absorption band of 4-nitrobenzenethiolate, 4-NO₂C₆H₄S⁻ also shows solvent dependency: acetonitrile, (λ_max = 484 nm), DMSO (λ_max = 502 nm), dimethylformamide (λ_max = 505 nm). The positive solvatochromic shifts for Et₃PAu(SC₆H₄NO₂-4) and 4-NO₂C₆H₄S⁻ are consistent with an intraligand (IL) charge transfer transition, i.e. π(S) → ∗π (C₆H₄NO₂-4) or n(S) → ∗π (C₆H₄NO₂-4). Assignment of 4-NO₂C₆H₄S⁻ was aided by a DFT calculation.     

Photolysis of the ion pair triphenylsulfonium thiophenolate induced by outersphere charge transfer excitation

The ion pair Ph₃S⁺PhS⁻ can be viewed as a sulfur-based mixed-valence system which is characterized by a PhS⁻ to Ph₃S⁺ outersphere charge transfer (OSCT) absorption at λ_max=390 nm (in CHCl₃). OSCT excitation leads to the radical pair Ph₃S/PhS which undergoes subsequent elimination and radical coupling processes with the final formation of Ph₂S. The photolysis proceeds with a quantum yield of φ=0.23 at λ_irr=436 nm.     

Structure and siderophore activity of ferric schizokinen

Schizokinen, a citrate-containing dihydroxamate, is a siderophore produced by Bacillus megaterium and Anabaena sp. The involvement of the citrate α-hydroxycarboxylate moiety in iron chelation was investigated by comparing the iron binding behavior of schizokinen with that of acetylschizokinen, a derivative in which the citrate hydroxyl group was modified by acetylation. Ferric schizokinen was found to exhibit an absorption spectrum (λ_max = 460 nm) characteristic of a dihydroxamate below pH 2.5, with an isosbestic shift to a citrate dihydroxamate spectrum (λ_max = 395 nm) above pH 4. Ferric acetylschizokinen also had a dihydroxamate absorption spectrum (λ_max = 465 nm) at low pH. However, its spectral shift (λ_max = 420 nm) and intensity above pH 4 were more typical of a ferric trihydroxamate. The molecular weight and electrophoretic mobility of ferric acetylschizokinen are consistent with a dimeric Fe₂ (acetylschizokinen)₃ structure, whereas ferric schizokinen appears to exist as a monomeric 1:1 complex Despite the differences in molecular weight and α-hydroxycarboxylate coordination, both complexes are effective in promoting iron uptake in Anabaena.     

The redox potentials of the b-type cytochromes of higher plant chloroplasts

1. In fresh chloroplasts, three b-type cytochromes exist. These are b-559_HP (λ_max, 559 nm; E_m at pH 7, +370 mV; pH-independent E_m), b-559_LP (λ_max, 559 nm; E_m at pH 7, +20 mV; pH-independent E_m) and b-563 (λ_max, 563 nm; E_m at pH 7, ?110 mV; pH-independent E_m). b-559_HP may be converted to a lower potential form (λ_max, 559 nm; E_m at pH 7, +110 mV; pH-independent E_m).2. In catalytically active b-f particle preparations, three cytochromes exist. These are cytochrome f (λ_max, 554 nm; E_m at pH 7, +375 mV, pK on oxidised cytochrome at pH 9), b-563 (λ_max, 563 nm; E_m at pH 7, ?90 mV, small pH-dependence of E_m) and a b-559 species (λ_max, 559 nm, E_m at pH 7, +85 mV; pH-independent E_m).3. A positive method of demonstration and estimation of b-559_LP in fresh chloroplasts is described which involves the use of menadiol as a selective reductant of b-559_LP.     

Wavelength-dependent induction of UV-absorbing mycosporine-like amino acids in the red alga Chondrus crispus under natural solar radiation

Polychromatic response spectra for the induction of UV absorbing mycosporine-like amino acids (MAAs) were calculated after exposing small thalli of the red alga Chondrus crispus under various cut-off filters to natural solar radiation on the North Sea island Helgoland, Germany. The laboratory-grown specimens typically contain only traces of palythine and synthesise five different MAAs rapidly and in high concentrations after being transplanted into shallow water. The resulting qualitative and quantitative patterns of MAA induction differed markedly with respect to spectral distribution. Furthermore, the wavebands effective for MAA induction vary within the MAA. UV-B radiation had a negative effect on the accumulation of the major MAAs shinorine (λ_max=334 nm) and palythine (λ_max=320 nm), while short wavelength UV-A exhibits the highest quantum efficiency on their synthesis. In contrast, the synthesis of asterina-330 (λ_max=330 nm), palythinol (λ_max=332 nm) and palythene (λ_max=360 nm) was mainly induced by UV-B radiation. Whether the synthesis of shinorine and palythine is induced by a photoreceptor with an absorption maximum in the short wavelength UV-A and whether a second photoreceptor absorbing UV-B radiation is responsible for the induction of asterina-330, palythinol and palythene remains to be studied.Our results show that C. crispus has a high capacity to adapt flexibly the qualitative and quantitative MAA concentration to the prevailing spectral distribution of irradiance. On one hand, this is regarded as an important aspect with respect to the acclimation of algae to increasing UV-B irradiance in the context of ongoing depletion of stratospheric ozone. On the other hand, the experiment demonstrates that UV-A irradiance is more important for the induction of the major MAAs shinorine and palythine than UV-B.     

Chemiluminescence in the reaction of cytochrome c with hydrogen peroxide

(1) Aqueous solutions of 1–10 μM ferricytochrome c treated with 100 μM–100 mM H₂O₂ at pH 8.0 emit chemiluminescence with quantum yield $\text{Ф ? 10}{}^{\mathrm{?9}}$ and absolute maximum intensity $\text{I}{}_{\mathrm{<mtext>max</mtext>}}\text{? 10}{}^5\text{hv/}\text{s}$ per cm³ (λ = 440), and exhibit exponential decay with a rate constant of 0.15 s^?1. (2) The emission spectrum of the chemiluminescence covers the range 380–620 nm with the maximum at 460 ± 10 nm. (3) Neither cytochrome c nor haemin fluoresce in the spectral region of the chemiluminescence. In the reaction course with H₂O₂, a weak fluorescence in the region 400–620 nm with λ_max = 465–510 nm (λ_exc 315–430 nm) gradually arises. This originates from tryptophan oxidation products of the formylkynurenine type or from imidazole derivatives, respectively. (4) Frozen solutions (77 K) of cytochrome c exhibit phosphorescence typical of tryptophan (λ_exc = 280 nm, λ_em = 450 nm). During the peroxidation, an additional phosphorescence gradually appears in the range 480–620 nm with λ_max = 530 nm (λ_exc = 340 nm). This originates from oxidative degradation products of tryptophan. (5) There are no red bands in the chemiluminescence spectra of cytochrome c or haemin. This result suggests that singlet molecular oxygen $\text{O}{}_2\text{(}{}^1\text{Δ}{}_{\mathrm{<mtext>g</mtext>}}\text{)}$ is not involved in either peroxidation or chemiluminescence. (6) The haem Fe³⁺ group and H₂O₂ appear to be crucial for the chemiluminescence. It is suggested that the generation of electronically excited, light-emitting states is coupled to the production of conformational out-of-equilibrium states of peroxy-Fe-protoporphyrin IX compounds.     

Internally illuminated photobioreactor using a novel type of light-emitting diode (LED) bar for cultivation of <Emphasis Type="Italic">Arthrospira platensis</Emphasis>

The biochemical properties of Spirulina platensis in an internally illuminated photobioreactor (IlPBR) were investigated under different light-emitted diode (LED) wavelengths; blue (λ_max= 450 and 460 nm), green (λ_max= 525 nm), red (λ_max = 630 and 660 nm), and white (6,500K), with various light intensities (200, 500, 1,000, and 2,000 μmol/m²/sec) were examined. The highest specific growth rate, maximum biomass, and phycocyanin productivity occurred under the red LEDs (0.39/day, 0.10 g/L/day, and 0.14 g/g-cell/day, respectively) at 1,000 μmol/m²/sec; the lowest growth rate was obtained under blue LEDs. Indeed, the size of trichomes was changed into short form under blue LEDs at all light intensities or all LEDs at 2,000 μmol/m²/sec for the first 2 days after inoculation, and S. platensis did not grow in the IlPBR under the dark condition. These results provide a base for different approaches for designing the pilot scale photobioreactor and developing cost-effective light sources.     

The distribution of mycosporine-like amino acids (MAAs) and the phylogenetic identity of symbiotic dinoflagellates in cnidarian hosts from the Mexican Caribbean

A survey of 54 species of symbiotic cnidarians that included hydrozoan corals, anemones, gorgonians and scleractinian corals was conducted in the Mexican Caribbean for the presence of mycosporine-like amino acids (MAAs) in the host as well as the Symbiodinium fractions. The host fractions contained relatively simple MAA profiles, all harbouring between one and three MAAs, principally mycosporine-glycine followed by shinorine and porphyra-334 in smaller amounts. Symbiodinium populations were identified to sub-generic levels using PCR-DGGE analysis of the Internal Transcribed Spacer 2 (ITS2) region. Regardless of clade identity, all Symbiodinium extracts contained MAAs, in contrast to the pattern that has been found in cultures of Symbiodinium, where clade A symbionts produced MAAs whereas clade B, C, D, and E symbionts did not. Under natural conditions between one and four MAAs were identified in the symbiont fractions, mycosporine-glycine (λ_max = 310 nm), shinorine (λ_max = 334 nm), porphyra-334 (λ_max = 334 nm) and palythine (λ_max = 320 nm). One sample also contained mycosporine-2-glycine (λ_max = 331 nm). These data suggest that Symbiodinium is restricted to producing five MAAs and there also appears to be a defined order of appearance of these MAAs: mycosporine-glycine followed by shinorine (in one case mycosporine-2-glycine), then porphyra-334 and palythine. Overall, mycosporine-glycine was found in highest concentrations in the host and symbiont extracts. This MAA, unlike many other MAAs, absorbs within the ultraviolet-B range (UVB, 280-320 nm) and is also known for moderate antioxidant properties thus potentially providing protection against the direct and indirect effects of UVR. No depth-dependent changes could be identified due to a high variability of MAA concentrations when all species were included in the analysis. The presence of at least one MAA in all symbiont and host fractions analyzed serves to highlight the importance of MAAs, and in particular the role of mycosporine-glycine, as photoprotectants in the coral reef environment.     

Dual color microscopic imagery of cells expressing the green fluorescent protein and a red-shifted variant

The green fluorescent protein (GFP) from the jellyfish, Aequorea victoria, has become a versatile reporter for monitoring gene expression and protein localization in a variety of cells and organisms. GFP emits bright green light (λ_max = 510 nm) when excited with ultraviolet (UV) or blue light (λ_max = 395 nm, minor peak at 470 nm). The chromophore in GFP is intrinsic to the primary structure of the protein, and fluorescence from GFP does not require additional gene products, substrates or other factors. GFP fluorescence is stable, species-independent and can be monitored noninvasively using the techniques of fluorescence microscopy and flow cytometry [Chalfie et al., Science 263 (1994) 802–805; Stearns, Curr. Biol. 5 (1995) 262–264]. The protein appears to undergo an autocatalytic reaction to create the fluorophore [Heim et al., Proc. Natl. Acad. Sci. USA 91 (1994) 12501–12504] in a process involving cyclization of a Tyr⁶⁶ aa residue. Recently [Delagrave et al., Bio/Technology 13 (1995) 151–154], a combinatorial mutagenic strategy was targeted at aa 64 through 69, which spans the chromophore of A. victoria GFP, yielding a number of different mutants with redshifted fluorescence excitation spectra. One of these, RSGFP4, retains the characteristic green emission spectra (λ_max = 505 nm), but has a single excitation peak (λ_max = 490 nm). The fluorescence properties of RSGFP4 are similar to those of another naturally occurring GFP from the sea pansy, Renilla reniformis [Ward and Cormier, Photobiochem. Photobiol. 27 (1978) 389–396]. In the present study, we demonstrate by fluorescence microscopy that selective excitation of A. victoria GFP and RSGFP4 allows for spectral separation of each fluorescent signal, and provides the means to image these signals independently in a mixed population of bacteria or mammalian cells.     

Photolysis of the ion pair [Pt(NH3)5Cl]S2O8: reduction of platinum(IV) induced by outer-sphere charge transfer excitation

The ion pair [Pt^IV(NH₃)₅Cl]³⁺S₂O₈²⁻ shows a S₂O₈²⁻ → [Pt(NH₃)₅Cl]³⁺ outer-sphere charge transfer (OSCT) absorption at λ_max=267 nm. OSCT excitation leads to the reduction of Pt(IV) by S₂O₈²⁻ to Pt(II) with φ=3×10⁻³ at λ_irr=280 nm.     

Heme/heme redox interaction and resolution of individual optical absorption spectra of the hemes in cytochrome bd from Escherichia coli

Cytochrome bd is a terminal component of the respiratory chain of Escherichia coli catalyzing reduction of molecular oxygen to water. It contains three hemes, b₅₅₈, b₅₉₅, and d. The detailed spectroelectrochemical redox titration and numerical modeling of the data reveal significant redox interaction between the low-spin heme b₅₅₈ and high-spin heme b₅₉₅, whereas the interaction between heme d and either hemes b appears to be rather weak. However, the presence of heme d itself decreases much larger interaction between the two hemes b. Fitting the titration data with a model where redox interaction between the hemes is explicitly included makes it possible to extract individual absorption spectra of all hemes. The α- and β-band reduced-minus-oxidized difference spectra agree with the data published earlier ([22] J.G. Koland, M.J. Miller, R.B. Gennis, Potentiometric analysis of the purified cytochrome d terminal oxidase complex from Escherichia coli, Biochemistry 23 (1984) 1051-1056., and [23] R.M. Lorence, J.G. Koland, R.B. Gennis, Coulometric and spectroscopic analysis of the purified cytochrome d complex of Escherichia coli: evidence for the identification of “cytochrome a₁” as cytochrome b₅₉₅, Biochemistry 25 (1986) 2314-2321.). The Soret band spectra show λ_max = 429.5 nm, λ_min ≈ 413 nm (heme b₅₅₈), λ_max = 439 nm, λ_min ≈ 400 ± 1 nm (heme b₅₉₅), and λ_max = 430 nm, λ_min = 405 nm (heme d). The spectral contribution of heme d to the complex Soret band is much smaller than those of either hemes b; the Soret/α (ΔA₄₃₀:ΔA₆₂₉) ratio for heme d is 1.6.     

Cyclam cored luminescent dendrimers as ligands for Co(II), Ni(II) and Cu(II) ions

We have investigated the photophysical properties of two dendrimers containing a cyclam core decorated with 4 naphthyl units (G0), 12 dimethoxybenzene and 16 naphthyl units (G2). These dendrimers show fluorescence bands that can be assigned to naphthyl localized excited states (λ_max = 337 nm), naphthyl-amine exciplexes (λ_max = 470 nm) and, for G2, naphthyl excimers (λ_max ca. 400 nm). Cyclam is a very good ligand for transition metal ions and we have investigated complex formation between these dendritic ligands and Ni(II), Co(II) and Cu(II), added as nitrate salts. This process can be monitored by the strong changes, both in shape and intensity, observed in the emission spectra of these dendrimers. Complexation with Cu(II) causes not only changes in the relative intensities of the fluorescence bands, but also the appearance of a new absorption band in the near UV spectral region. An analysis of the titration curves has allowed us to obtain clear evidence for the formation of not only 1:1 species, but also 1:2 metal to ligand species. G2 shows a clear preference, compared to G0, in forming complexes with a 1:2 metal-to-ligand stoichiometry, although it possesses very bulky dendrons appended to the cyclam central unit.     

Synthesis and structural characterization of copper(II) bishexafluoroacetylacetonate complexes with N-donor ligands

The reactions of Cu(hfac)₂ with different N-donor ligands such as 2-ethynylpyridine and imidazole give copper complexes Cu(hfac)₂(ethynylpyridine) (1) and Cu(hfac)₂(ImH)₂ (2), respectively. The reaction of Cu(hfac)₂ · (ethynylpyridine) (1) and ethynylpyridine with oxygen in tmeda (tmeda = N,N,N′,N′-tetramethylethylenediamine) in the presence of copper(I) chloride gives Cu(hfac)₂(tmeda) (3). Finally, [Cu(hfac)₂(H₂O)]₂(μ-TCNE) (4) was prepared by reaction of Cu₂O on the free acid β-diketone in the presence of TCNE (TCNE = tetracyanoethylene) (ratio 1.5:1:1), under an atmosphere of oxygen-free Ar. The previously synthesized Cu(hfac)TCNE proceeded further reaction by disproportionation, yielding [Cu(hfac)₂(H₂O)]₂(μ-TCNE). All new compounds have been structurally characterized and their thermal properties were examined by thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC).     

Optical properties of Ag(tripod)X with tripod = 1,1,1-tris(diphenyl-phosphinomethyl)ethane and X = Cl and I: Intraligand and ligand-to-ligand charge transfer

The complexes Ag^I(tripod)X with tripod = 1,1,1-tris(diphenylphosphinomethyl)ethane and X⁻ = Cl⁻ and I⁻ are luminescent in solution at r.t. It is suggested that the emission is a phosphorescence which originates from a tripod intraligand state for X = Cl (λ_max = 464 nm) and a X⁻ → tripod ligand-to-ligand charge transfer state for X = I (λ_max = 482 nm).     

Absorption spectra of intermediates of bacteriorhodopsin measured by laser photolysis at room temperatures

Picosecond laser spectroscopic analysis was applied to determine how many intermediates existed in the primary photochemical process of trans-bacteriorhodopsin (light-adapted bacteriorhodopsin) at room temperature (18°C) and to calculate their absorption spectra. Irradiation of bacteriorhodopsin with a laser pulse (wavelength, 532 nm; pulse width, 25 ps) yielded the K intermediate (K) which was produced through a precursor, having an absorption maximum (λ_max) longer than that of K. K was stable during a picosecond time range (50–900 ps). The λ_max was located at 610 nm and the extinction coefficient (?_max) was 0.92-times that of bacteriorhodopsin. The same K intermediate was produced from bacteriorhodopsin even when it was excited with a high-energy pulse by which a saturation effect was induced. A transient difference spectrum measured at 150 ns after the excitation of bacteriorhodopsin was different in shape from that of the K intermediate, suggesting that an intermediate was formed by thermal decay of K. This intermediate, tentatively called the KL intermediate (KL), had a λ_max at 596 nm and an ?_max 0.80-times that of bacteriorhodopsin. KL decayed to the L intermediate (L) with a time constant of 2.2 μs. L has a λ_max at 543 nm and an ?_max 0.66-times that of bacteriorhodopsin.     

Is o-carborane photoluminescent?

At 77 K in the solid state and in ethanol glasses, o-carborane (1,2-C₂B₁₀H₁₂) shows a relatively intense (? ∼ 10⁻³ at λ_exc = 260 nm) structured photoluminescence (λ_max = 441 nm).In agreement with the rather slow decay of this emission (τ ∼ 4 s) it is suggested to be a phosphorescence. While it appears to be a genuine property of o-carborane an unknown impurity as origin of this luminescence is not completely excluded.     

Adducts of europium β-diketonates with nitrogen p,p′-disubstituted bipyridine and phenanthroline ligands: Synthesis, structural characterization, and luminescence studies

Europium complexes featuring fluorinated β-diketonate ligands [thenoyltrifluoroacetone (tta), 4,4,4-trifluoro-1-phenyl-1,3-butanedione (btfac), and 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate (hfac)] and nitrogen p,p′-disubstituted bipyridine and phenanthroline ligands [4,4′-dimethoxy-2,2′-bipyridine (dmbipy) and 4,7-dimethyl-1,10-phenanthroline (dmphen)] were synthesized. Their structures were determined by single crystal X-ray diffraction. Octacoordinate complexes were obtained using trifluorinated tta and btfac, while nonacoordinated complexes were produced using hexafluorinated hfac. The differences in coordination number and bond lengths of these complexes are rationalized in terms of the electronic and steric features of the ligands. UV excitation of the complexes led to red luminescence characteristic of trivalent europium ion. The high overall quantum yields observed for the europium complexes bearing hfac and dmbipy or dmphen ligands are rationalized in terms of the relatively high ligand-to-metal energy transfer efficiencies.     

Unexpected diversity of bioluminescence in planktonic worms

The vast majority of pelagic bioluminescent organisms emit a blue light with emission maxima (λ_max) ranging from 450 to 490 nm. Among the known outliers, the tomopterids (Annelida: Polychaeta) are usually described as yellow‐emitters (λ_max = 565–570 nm) for which bioluminescence functions as a specific recognition signal. Here, we report the first data regarding the colours emitted by four different tomopterid species, Tomopteris pacifica, T. carpenteri, T. septentrionalis and T. planktonis. Surprisingly, T. planktonis is a blue‐emitter (λ_max = 450 nm). Our pharmacological results on T. planktonis support cholinergic control, as recently demonstrated in the yellow‐emitter, T. helgolandica. Moreover, as revealed by epifluorescence microscopy, the light seems to be produced in both species from the same yellow‐pigmented parapodial glands. Despite these similarities, tomopterids express an unexpected diversity of bioluminescent colour patterns. This leads us to reassess the ecological value of bioluminescence within this group.