14 research outputs found
Laserowa fotoliza błyskowa : wyznaczanie wpływu tlenu na kinetykę dezaktywacji wzbudzonych cząsteczek chlorofilu
Mechanism of photochemical reduction of chromium(VI) by alcohols and its environmental aspects
Electron transfer and intersystem crossing processes in new dyes based on 1H-pyrazolo[3,4-b]quinoxaline : effect of temperature and solvent polarity on the CT fluorescence
Effect of co-ligands on photoredox pathways in Cr(III) oxalate complexes
The
photochemical
behaviour
of
some
mixed
ligand
chromium(III)
complexes
with
amino
acids,
[Cr(C
2
O
4
)
2
(Aa)]
n
−
(where
Aa
=
alanine,
valine,
serine,
cysteine,
asparagine,
aspartic
acid)
was
studied.
The
attention
was
focused
on
the
photoredox
mode,
which
proceeded
via
inner-
or
intramolecular
path-
way
yielding
Cr(II)
species
and
hydrated
electrons,
respectively.
The
secondary
thermal
processes
were
dependent
on
the
O
2
presence
and
solution
pH:
(i)
in
oxygen-free
media
the
regeneration
of
substrate
and
photoaquation
induced
by
the
Cr(III)
→
Cr(II)
reduction
were
observed,
(ii)
in
the
presence
of
O
2
both
Cr(II)
and
ligands
were
oxidized
and
the
former
was
transformed
not
only
into
Cr(III)
but
also
to
Cr(VI)
(provided
that
pH
>
7).
Prolonged
irradiation
resulted
in
photoreduction
of
Cr(VI)
accompanied
by
pho-
todegradation
of
oxalate
and/or
amino-acid
ligands.
The
photoreaction
modes
were
independent
of
the
co-ligand
nature,
but
the
secondary
reaction
rates
and
efficiencies
were
sensitive
both
to
the
co-ligand
nature
and
its
side
substituent.
Environmental
consequences
of
the
chromium
photoreduction
are
dis-
cussed
in
the
paper:
the
parameters
affecting
production
and
consumption
of
Cr(VI)
are
analysed,
and
the
tools
of
controlling
the
photoredox
behaviour
of
the
Cr(III)
and
Cr(VI)
compounds
are
suggested
Effects of heavy central metal on the ground and excited states of chlorophyll
Chlorophylls, owing to their adjustable p-electron system and intense, well-separated electronic transitions, can serve as convenient intrinsic spectroscopic probes of ligand–metal center interactions. They are also interesting for their photosensitizing properties.
In order to examine the heavy-atom effects on the chlorophyll triplet state, a key intermediate in chlorophyll–photosensitized reactions, the synthesis of a novel Pt(II)-substituted chlorophyll a was carried out, and the effects of the substitution on steady-state and transient photophysical properties of chlorophyll were studied by absorption and fluorescence spectroscopies, and by laser flash photolysis. The presence of highly electronegative platinum as the central ion increases the energies of the chlorophyll main absorption transitions. As laser flash photolysis experiments show, in air-equilibrated solutions, chlorophyll triplets are efficiently quenched by molecular oxygen. Interestingly, this quenching by oxygen is more effective with metal-containing pigments, in spite of the increased spin–orbit coupling, introduced with the central metals. This points to occurrence of nonspecific interactions of molecular oxygen with metallochlorophylls. The differences in the effects exerted on the pigment triplet by the central metal become distinct after the removal of oxygen. The lifetime of a Ptchlorophyll triplet remains very short, in the range of only a few microseconds, unlike in the free-base and Mg- and Zn-substituted chlorophylls. Such drastic shortening of the triplet lifetime can be attributed to a large heavy-atom effect, implying that strong interactions must occur between the central Pt(II) ion and the chlorophyll macrocycle, which lead to a more efficient spin–orbit coupling in Pt-chlorophyll than in Pt-porphyrins
Thermodynamics and kinetics of as an efficient scavenger for nitric oxide in aqueous solution
The edta complex of Ru
III
reacts very rapidly with NO in aqueous solution at pH
=
5 to form a stable nitrosyl
complex. The results from FT-IR (ATR) and
15
N-NMR studies clearly support the NO
character of coordinated
NO, such that the nitrosyl product can be formulated as [Ru
II
(edta)NO]
. A combination of UV-Vis spectroscopy
and electrochemical detection of NO was used to determine the overall equilibrium constant
K
NO
as (9.1 ± 1.2) ×
10
7
M
1
at 25
C and pH
=
5.0. Stopped-
fl
ow kinetic studies on the reaction of acetate-bu
ff
ered solutions of
[Ru
III
(edta)H
2
O]
with NO gave
k
on
values two orders of magnitude lower than that reported in the literature as
a result of bu
ff
er e
ff
ects. The values of
k
on
determined at low and high pH,
viz
. 3.8 × 10
4
and 1.2 × 10
5
M
1
s
1
,
respectively, are signi
fi
cantly smaller than that found at pH
=
5.0, and in agreement with that observed for the
substitution reactions of Ru
III
(edta) with other entering nucleophiles. Attempts to determine
k
on
for the binding
of NO to [Ru
III
(edta)H
2
O]
using laser
fl
ash photolysis failed due to the occurrence of side reactions. Under speci
fi
c
conditions (NO in excess and NO
2
as impurity), the formation of the disubstituted [Ru
II
(edta)(NO
)(NO
2
)]
2
species was detected using
15
N-NMR spectroscopy. Laser
fl
ash photolysis of this complex leads to multiple chemical
reaction steps as a result of the formation of two primary photoproducts, which decay with di
ff
erent rate constants to
the starting complex. Possible mechanisms for these photoinduced reactions are proposed and compared to related
systems reported in the literature
Verteporfin, photofrin II, and merocyanine 540 as PDT photosensitizers against melanoma cells
The efficiency of photodynamic effect (PDE) for Photofrin II (PfII), Verteporfin, and Merocyanine 540 (MC540) was compared against neoplastic cells. Triplet state lifetimes and singlet molecular oxygen quantum yields were correlated with biological effect. PfII triplet lifetime was two times longer than that of Verteporfin, however, its singlet molecular oxygen quantum yield was two times lower in comparison with Verteporfin. High singlet molecular oxygen quantum yield of Verteporfin resulted in high biological efficacy. To achieve 50% mortality of cells four times lower light dose and five times lower concentration of Verteporfin were applied in comparison with PfII. The same level of cell damage was reached using 10 times higher light dose and two times higher concentration of MC540 in comparison with PfII. Our results confirm that singlet molecular oxygen based mechanism, prevalent for Verteporfin and PfII, was highly effective against melanoma cells. Verteporfin can be used at small doses with high cellular damage efficiency