in black and white
Main menu
Share a book About us Home
Biology Business Chemistry Computers Culture Economics Fiction Games Guide History Management Mathematical Medicine Mental Fitnes Physics Psychology Scince Sport Technics

The porphyrin handbook - Kadish K.M.

Kadish K.M. The porphyrin handbook - Academic press, 2000. - 368 p.
Download (direct link): kadishsmishgulilard2000.djvu
Previous << 1 .. 144 145 146 147 148 149 < 150 > 151 152 153 154 155 156 .. 240 >> Next

the circular disk of the exposed electrode, and because the current
(analytical signal) is directly proportional to the surface area, it is
important to make this area as large as possible for the smallest
possible diameter. The area of disk electrode is 10-20 times smaller than
the cone-shaped fibers prepared by the gradual burning process.
The carbon-fiber tip modification process consists of poly-(TMHPP)Ni
film deposition on the electrode surface and confirmation of deposition
followed by demetalation to poly-TMHPP and confirmation of
demetalation.34 Polymeric film is deposited from a 0.25 mM (TMHPP)Ni
solution in 0.1 M sodium hydroxide by constant-potential electrolysis at
0.70 V. The number of monolayers deposited is dependent on the initial
concentration of (TMHPP)Ni and the time of electrolysis. At the end of
the deposition time, the electrode is immersed in 0.1 M sodium hydroxide.
The presence of (poly-TMHPP)Ni film on the electrode surface is confirmed
by a peak at Ep = 0.55 V, attributable to the Ni(II)/Ni(III) couple, in a
differential pulse voltammetry scan. The (poly-TMHPP)Ni film is
demetalated in a chemical process by placing the electrode in 0.1 M HC1.
potential, V
The absence of the Ni(II)/Ni(III) peak in a DPV scan between 0.0 and 0.70
V in 0.1 M NaOH confirms the absence of Ni(II) in the poly-TMHPP film.
3. Nickel Determination in a Single Cell
The sharpened tip (0.5-1 ) of the fiber covered with 10-20 monolayers
of polymeric porphyrin and then demetalated can be implanted into a
single cell with help from the computer-controlled micromanipulator.
Unbound Ni(II) from the intracellular fluid is selectively chemically
incorporated by the poly-TMHPP in the microsensor. The poly-TMHPP sensor
with its re-incorporated Ni(II) is removed from analyte solution and
transferred to a 0.1 M NaOH solution for analysis. Two voltammetric peaks
can be used as an analytical signal.34 One, observed at Ep = 0.55 V,
corresponds to the Ni(II)/Ni(III) redox couple and a peak at Ep = 0.80 V
which corresponds to the catalytic oxidation of water to molecular
oxygen. The current from the Ni(II)/Ni(III) oxidation or the catalytic
oxidation of water can be determined using DPV. A linear relationship
between the current of the Ni(II)/Ni(III) reaction in the film and Ni(II)
concentration in the bulk solution is observed for the concentration
range lxlO-5 to 5x10 2 M with a detection limit of 8 x 10"6 M. The
current observed for the catalytic oxidation of water on (poly-TMHPP)Ni
is higher than the current due to the Ni(II)/Ni(III) couple. The
relationship between Ni(II) concentration and catalytic current in 0.1 M
NaOH is linear between 5 x 10"6 and
5 x 10 ~~4 M Ni(II) with a detection limit of at least 1 x 10"6 M.
Figure 6 shows a typical differential pulse voltammogram of Ni(II)
accumulated in BC3H-1 myocytes and the changes of the total concentration
of bound and unbound Ni(II) as measured by the liquid scintillation
method and unbound nickel measured by the sensor in BC3H-1 myocytes.
b Time, h
Figure 6. Differential pulse voltammogram of (TMHP)Ni with Ni(ll)
accumulated from a single BC3H-1 myocyte (a), concentration of an unbound
nickel accumulated in BC3H-1 myocytes as measured by the polymeric TMHPP
sensor (b).
1. Nitric Oxide Signaling
Endothelial cells modulate the contraction of vascular smooth-muscle
cells by releasing factors that cause relaxation and contraction.35-37
The endothelial cell layer has been referred to as a "transducing
surface." It transduces shear stress/flow and signals the presence of
many substances in the blood, and it is known to be intimately involved
in the pathophysiology of atherosclerosis, coronary vasospasm and
coronary thrombosis. The endothelium-derived relaxation factor (EDRF) was
discovered more than a decade ago and recently was confirmed to be
identical to nitric oxide (NO).20'38-40 NO has been determined to be a
unique, ubiquitous messenger of cellular signals. NO not only is involved
in the regulation of blood pressure but also has been characterized as a
neurotransmitter and plays an important role in the immune system. Its
chemical nature makes NO an excellent candidate for short-term and short-
range signaling. NO is very lipophilic (and therefore diffuses readily
through cellular membranes), is synthesized rapidly on demand, and its
short life (half-life 2-5 seconds) ensures a localized response.41
NO is synthesized from L-arginine and oxygen by a Ca2+/calmodulin-
dependent enzyme NO synthase (NOS). The oxidation of L-arginine is a
five-electron-transfer reaction involving N-hydroxlation, formation of
NG-hydroxy-L-arginine as an intermediary product and stoichiometric al
formation of NO plus L-citrulline. The molecular mechanism of NO
synthesis is complex and not completely understood. It involves the
Previous << 1 .. 144 145 146 147 148 149 < 150 > 151 152 153 154 155 156 .. 240 >> Next