115 research outputs found
Galle goes green:one million trees under Sri Lanka tourism's 'earth lung initiative, towards a carbon free Sri Lanka'
Oxidation and reduction data of four subphthalocyanines with axially coordinated ferrocenylcarboxylic acids
Fungal lignin peroxidase does not produce the veratryl alcohol cation radical as a diffusible ligninolytic oxidant
11p.-5 fig.-1 tab. + 13 p.- Supporting InformationPeroxidases are considered essential agents of lignin degradation by white-rot basidiomycetes. However, low-molecular-weight oxidants likely have a primary role in lignin breakdown because many of these fungi delignify wood before its porosity has sufficiently increased for enzymes to infiltrate. It has been proposed that lignin peroxidases (LPs, EC 1.11.1.14) fulfill this role by oxidizing the secreted fungal metabolite veratryl alcohol (VA) to its aryl cation radical (VA+•), releasing it to act as a one-electron lignin oxidant within woody plant cell walls. Here, we attached the fluorescent oxidant sensor BODIPY 581/591 throughout beads with a nominal porosity of 6 kDa and assessed whether peroxidase-generated aryl cation radical systems could oxidize the beads. As positive control, we used the 1,2,4,5-tetramethoxybenzene (TMB) cation radical, generated from TMB by horseradish peroxidase. This control oxidized the beads to depths that increased with the amount of oxidant supplied, ultimately resulting in completely oxidized beads. A reaction-diffusion computer model yielded oxidation profiles that were within the 95% confidence intervals for the data. By contrast, bead oxidation caused by VA and the LPA isozyme of Phanerochaete chrysosporium was confined to a shallow shell of LP-accessible volume at the bead surface, regardless of how much oxidant was supplied. This finding contrasted with the modeling results, which showed that if the LP/VA system were to release VA+•, it would oxidize the bead interiors. We conclude that LPA releases insignificant quantities of VA+• and that a different mechanism produces small ligninolytic oxidants during white rot.This work was supported by United States Department of Energy, Office of Biological and Environmental Research Grant DE-SC0006929 (to K. E. H.,C. J. H.,and C. G. H.)Peer reviewe
Supramolecular Complexation of Biogenic Amines by Functional Electroactive Monomers of Thiophene Derivatives for Formation of Molecularly Imprinted Polymer (MIP) Films for Biosensor Development
We synthesized electronically conducting polymers for devising selective chemical
sensors. Toward that, electroactive functional monomers were derivatized to bear
recognition sites capable of formation of complexes in solution with target analytes.
These monomers included derivatives of bis(2,2'-bithienyl)methane substituted with
either the 18-crown-6, 3,4-dihydroxyphenyl, or dioxaborinane moiety. The analytes
were selected from biogenic amines. These included adenine, dopamine, histamine, and
melamine. By DFT quantum chemistry calculations at the B3LYP/3-21G(*) level, we
modeled geometries of these complexes. Initially, the analytes played a role of
templates. Then, the complexes were electropolymerized in the presence of suitably
selected cross-linking monomers and porogenic solvents. A derivative of 3,3-
bithianaphthene and an ionic liquid suited that purpose very well. Next, the resulting
molecularly imprinted polymer (MIP) films were washed with abundance of a base
solution to extract the templates. That way, molecularly imprinted cavities were left in
the MIP film. Size and shape of these cavities were compatible to those of the analyte
molecules. In this form, the film was suitable for use as a recognition material in a
chemosensor. A 10-MHz thickness-shear-mode bulk-acoustic-wave resonator of a
quartz crystal microbalance was used as the piezoelectric transducer of the detection
signal into the mass change signal. The MIP-template interactions of the covalent bond,
hydrogen bond, and inclusion complex nature appeared to be reversible allowing for
extensive and reversible accumulation of the analyte in the film and its subsequent
removal for the analytical reuse. Due to this accumulation, detection limits reached the
nanomole concentration level. Imprinting of the adenine, dopamine, and histamine
electroactive analytes required preliminary coating of the electrode with a barrier
underlayer film. This film served to prevent electrode processes of the analytes on the
one hand and to afford efficient charge exchange with the MIP film deposited by
electrochemical polymerization on top of the barrier film on the other. The electrode
processes of the analytes were highly undesired because adsorption of products of these
processes would be imprinted instead of the analytes themselves. Moreover, products of
these processes would adsorb on the electrode surface blocking it and obstructing
adhesion of the MIP film. Selectivity of the imprinting was tested by using typical
interfering compounds structurally or functionally analogous to the analytes. This
selectivity was high being mainly governed by complementarity of the stereo geometry
of the analytes and imprinted molecular cavities of MIPs as well as affinity of the MIP
binding sites located in these cavities to the binding sites of the analytes
Initial Report on Molecular and Electronic Structure of Spherical Multiferrocenyl/tin(IV) (Hydr)oxide [(FcSn)12O14(OH)6]X2 Clusters
Two spherical organic-inorganic ferrocene-tin (hydr)oxide clusters of general formula [(FcSn)12O14(OH)6]X2 (Fc = ferrocenyl, X = nitroso-dicyanmethanide, DCO- and benzoylcyanoxime, PCO- anions) were prepared by the direct hydrolysis of Fc2SnCl2 or FcSnCl3 precursors in the presence of light- and thermally stable Ag(DCO) or Ag(PCO) salts. Molecular structures of FcSnCl3Py2 (1), Fc2SnCl2Py2 (2), [(FcSn)12O14(OH)6](DCO)2 (3), and [(FcSn)12O14(OH)6](PCO)2 (4) were investigated by X-ray crystallography. Density function theory (DFT) and time-dependent density functional theory (TDDFT) calculations were conducted on FcSnCl3Py2, Fc2SnCl2Py2, and [(FcSn)12O14(OH)6]2+ compounds in order to elaborate electronic structures and assign transitions in UV-vis spectra of these systems. The DFT and TDDFT calculations suggest that the organometallic substituents in the [(FcSn)12O14(OH)6]2+ core are rather isolated from each other
Synthesis, Redox Properties, and Electronic Coupling in the Diferrocene Aza-dipyrromethene and azaBODIPY Donor–Acceptor Dyad with Direct Ferrocene−α-Pyrrole Bond
3,3′-Diferrocenylazadipyrromethene
(<b>3</b>) and
corresponding difluoroboryl (azaBODIPY) complex (<b>4</b>) were
synthesized in several steps from ferrocenecarbaldehyde, following
the well-explored chalcone-type synthetic approach. The novel diiron
complexes, in which ferrocene groups are directly connected to the
α-pyrrolic positions were characterized by a variety of spectroscopic
techniques, electrochemistry, spectroelectrochemistry, and X-ray crystallography,
while their electronic structure, redox properties, and UV–vis
spectra were correlated with the density functional theory (DFT) and
time-dependent DFT calculations
Syntheses and Excitation Transfer Studies of Near-Orthogonal Free-Base Porphyrin–Ruthenium Phthalocyanine Dyads and Pentad
A new series of molecular dyads and pentad featuring
free-base
porphyrin and ruthenium phthalocyanine have been synthesized and characterized.
The synthetic strategy involved reacting free-base porphyrin functionalized
with one or four entities of phenylimidazole at the meso position
of the porphyrin ring with ruthenium carbonyl phthalocyanine followed
by chromatographic separation and purification of the products. Excitation
transfer in these donor–acceptor polyads (dyad and pentad)
is investigated in nonpolar toluene and polar benzonitrile solvents
using both steady-state and time-resolved emission techniques. Electrochemical
and computational studies suggested that the photoinduced electron
transfer is a thermodynamically unfavorable process in nonpolar media
but may take place in a polar environment. Selective excitation of
the donor, free-base porphyrin entity, resulted in efficient excitation
transfer to the acceptor, ruthenium phthalocyanine, and the position
of imidazole linkage on the free-base porphyrin could be used to tune
the rates of excitation transfer. The singlet excited Ru phthalocyanine
thus formed instantly relaxed to the triplet state via intersystem
crossing prior to returning to the ground state. Kinetics of energy
transfer (<i>k</i><sub>ENT</sub>) was monitored by performing
transient absorption and emission measurements using pump–probe
and up-conversion techniques in toluene, respectively, and modeled
using a Förster-type energy transfer mechanism. Such studies
revealed the experimental <i>k</i><sub>ENT</sub> values
on the order of 10<sup>10</sup>–10<sup>11</sup> s<sup>–1</sup>, which readily agreed with the theoretically estimated values. Interestingly,
in polar benzonitrile solvent, additional charge transfer interactions
in the case of dyads but not in the case of pentad, presumably due
to the geometry/orientation consideration, were observed
Synthesis and Charge-Transfer Dynamics in a Ferrocene-Containing Organoboryl aza-BODIPY Donor–Acceptor Triad with Boron as the Hub
A <i>N</i>,<i>N</i>′-bis(ferroceneacetylene)boryl
complex of 3,3′-diphenylazadiisoindolylmethene was synthesized
by the reaction of an <i>N</i>,<i>N</i>′-difluoroboryl
complex of 3,3′-diphenylazadiisoindolylmethene and ferroceneacetylene
magnesium bromide. The novel diiron complex was characterized by a
variety of spectroscopic techniques, electrochemistry, and ultrafast
time-resolved methods. Spectroscopy and redox behavior was correlated
with the density functional theory (DFT) and time-dependent DFT calculations.
An unexpected degree of coupling between the two Fc ligands was observed.
Despite a lack of conjugation between the donor and acceptor, the
complex undergoes very rapid (τ = 1.7 ± 0.1 ps) photoinduced
intramolecular charge separation followed by subpicosecond charge
recombination to form a triplet state with a lifetime of 4.8 ±
0.1 μs
Redox and Photoinduced Electron-Transfer Properties in Short Distance Organoboryl Ferrocene-Subphthalocyanine Dyads
Reaction between ferrocene lithium
or ethynylferrocene magnesium bromide and (chloro)boronsubphthalocyanine
leads to formation of ferrocene- (<b>2</b>) and ethynylferrocene-
(<b>3</b>) containing subphthalocyanine dyads with a direct
organometallic B–C bond. New donor–acceptor dyads were
characterized using UV–vis and magnetic circular dichroism
(MCD) spectroscopies, NMR method, and X-ray crystallography. Redox
potentials of the rigid donor–acceptor dyads <b>2</b> and <b>3</b> were studied using the cyclic voltammetry (CV)
and differential pulse voltammetry (DPV) approaches and compared to
the parent subphthalocyanine <b>1</b> and conformationally flexible
subphthalocyanine ferrocenenylmethoxide (<b>4</b>) and ferrocenyl
carboxylate (<b>5</b>) dyads reported earlier. It was found
that the first oxidation process in dyads <b>2</b> and <b>3</b> is ferrocene-centered, while the first reduction as well
as the second oxidation are centered at the subphthalocyanine ligand.
Density functional theory-polarized continuum model (DFT-PCM) and
time-dependent (TD) DFT-PCM methods were used to probe the electronic
structures and explain the UV–vis and MCD spectra of complexes <b>1</b>–<b>5</b>. DFT-PCM calculations suggest that
the LUMO, LUMO+1, and HOMO-3 in new dyads <b>2</b> and <b>3</b> are centered at the subphthalocyanine ligand, while the
HOMO to HOMO-2 in both dyads are predominantly ferrocene-centered.
TDDFT-PCM calculations on compounds <b>1</b>–<b>5</b> are indicative of the π → π* transitions dominance
in their UV–vis spectra, which is consistent with the experimental
data. The excited state dynamics of the parent subphthalocyanine <b>1</b> and dyads <b>2</b>–<b>5</b> were investigated
using time-resolved transient spectroscopy. In the dyads <b>2</b>–<b>5</b>, the initially excited state is rapidly (<2
ps) quenched by electron transfer from the ferrocene ligand. The lifetime
of the charge transfer state demonstrates a systematic dependence
on the structure of the bridge between the subphthalocyanine and ferrocene
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