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02/09/2005

Sunburn and Spinach

Last week we talked about a dimming of sunlight due to
pollution of our atmosphere. I could have used some dimming of
sunlight in my youth; applying sunscreen before going out in the
sun never occurred to me. As a result, like millions of others,
I’ve paid the price in the form of a number of skin cancers. In
fact, I’ve just had a little chunk taken from my ear by a doctor
skilled in Moh’s surgery. It was my first experience with this
type of surgery, named after a Dr. Moh. The surgeon removes a
slice, does a frozen section and examines it microscopically and
decides whether another slice has to be taken.

The waiting room was filled with patients awaiting the word as
to whether they needed another slicing. I felt thankful that my
problem was with my ear when one woman said she was having
slices from her eyelid. Yuk! I asked the surgeon how many
slices are typical and he mentioned his personal record of 17
slices! That particular case involved a growth on the patient’s
forehead that he successively tracked down her nose onto her
cheek. Thankfully, two slices sufficed in my case.

So, my ear suitably bandaged, I’m posting this column from
sunny Marco Island in Florida. Unfortunately for my skin,
Florida is one of the few states where the air quality meets EPA
standards so the sunlight is relatively undimmed. Accordingly, I
start my morning walks on the beach well before sunrise and
slather on the sunscreen very liberally if I golf. Yet, there was a
report on a local TV news program saying that people with skin
cancer should not shun the sun completely. It seems we older
folks risk getting too little vitamin D because of insufficient
exposure to the sun. Nothing is simple!

It’s tough for us humans, but what about spinach, or most other
green plants? Before spinach shows up on your salad plate, it
has spent days in the hot sun with no sunscreen. Wouldn’t you
think it would get sunburned? OK, like me, you probably never
gave it a thought. After all, spinach and other green plants
depend on photosynthesis for their growth and photosynthesis
depends on light from the sun. Chemically, a primary
photosynthesis reaction is quite simple: 6 CO2 + 6 H2O =
C6(H2O)6 + 6 O2 [stocksandnews doesn’t support subscripts].
For those not familiar with chemistry, this translates into: 6
molecules of carbon dioxide react with 6 molecules of water to
give glucose (a carbohydrate) and 6 molecules of oxygen.

A case could be made that this simple reaction is the most
important chemical reaction for us humans. Without it, we
would have no oxygen to breathe and no food to eat. The plant
takes in light from the sun, carbon dioxide from the air and water
through its roots and stems. In the plant, other sugars, starches
and other compounds vital to life are formed. Although the
primary reaction is quite simple, it’s a different story if you look
into how the plant manages to accomplish this and all the other
reactions in the plant. Frankly, the complexity of what goes on
in a plant leads me to say to myself, “Hey, you’re on vacation,
don’t burden yourself or your readers.”

However, I do think that most of us are aware that chlorophyll
plays a role in photosynthesis. Chlorophyll is a pigment that
absorbs certain colors of light from the sunlight (it does not
absorb green light but reflects it; hence, the green color). The
photons of light provide the energy to get the photosynthesis
going. One way a photon can get things going is to “excite” a
molecule such as chlorophyll. In “exciting’ the molecule the
photon can kick an electron to a higher energy state. A simple
way to look at this is to think of an atom as a nucleus with
electrons orbiting it like the planets orbit the Sun. If the closest
planet is Mercury, we might excite it by kicking it out to the orbit
of Venus. Not likely, of course, but if Mercury were an electron,
a photon might kick it out to a higher orbit in that manner.

Let’s get back to why spinach should worry about getting
sunburned. If we look at our photosynthesis reaction, we see that
it can only happen when both the water and carbon dioxide are
available to react. The carbon dioxide comes from the air and
the water comes mainly up through the roots and stems of the
spinach. Well, it takes time for the water to get to the leaf and
for the carbon dioxide to come in from the air. Meanwhile, the
Sun keeps shining and those photons keep coming.

So, we have an excess of light and we have a lot of excited
chlorophyll molecules. This isn’t good because they are all
hyped up and, unless that excess energy is dissipated, bad things
happen. Specifically, oxidative damage would result. Sunburn,
as with burning of wood or coal, is an oxidation type of reaction.
We’re continually being told to eat foods containing antioxidants
to protect ourselves from oxidative damage. In the case of
spinach and other plants, it’s obvious that plants solved the
problem of avoiding oxidative damage eons ago. Otherwise,
how does spinach grow those big, healthy green leaves?

Scientists have long known there must be something that gets rid
of this excess energy, “deexcitation”, as it’s known in the trade.
Graham Fleming and Krishna Niyogi and coworkers from the
Lawrence Berkeley National Laboratory and the University of
California have the answer, detailed in an article in the January
21 issue of Science. I was tipped to this study by a brief item by
Amanda Yarnell in the January 7 issue of Chemical and
Engineering News. Otherwise, I would not have been drawn to
the Science article, dauntingly titled “Carotenoid Cation
Formation and the Regulation of Photosynthetic Light
Harvesting”! Carotenoids are another class of pigments that
absorb light of a green color as might be deduced by the orange
color of carrots. The researchers worked with spinach.

They found that in the presence of intense light a carotenoid
identified as zeaxanthin (Zea for short) forms. Put crudely, this
compound sidles up to an excited chlorophyll molecule and
hands it an electron. This pairing up of Zea and the excited
chlorophyll soothes the chlorophyll and all that energy is
dissipated as heat. The chemistry is more complicated and the
processes take place very rapidly, in only tens or hundreds of
picoseconds (a picosecond is only one trillionth of a second).
The plant needs fast reactions because those photons keep
coming. Now that we know the role of Zea as a sort of sunscreen
for green plants, the hope is that there may be practical
applications in other fields such as solar energy generation.

Finally, a personal concern that Florida may not remain as one of
the cleaner air states. We flew down and picked up our shipped
car near the Fort Myers airport. On leaving the parking lot, I had
to press the brake pedal to the floor to stop! As a result, we had
to rent a car, leaving my VW Jetta at a nearby garage overnight,
and drive to Marco. Route I75 is an interstate highway with a
speed limit of 70 mph in this area. In late afternoon and early
evening, our actual speed was zero to 5 mph. With no accidents,
only traffic volume, the road was a parking lot. The pollution
emissions from idling vehicles can only get worse with a
multitude of new developments and shopping centers under
construction. Hurricanes haven’t slowed construction here.

The brakes? The cost of master cylinder and associated work, a
mere $740! Not a good start to our Florida stay.

Allen F. Bortrum



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-02/09/2005-      
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Dr. Bortrum

02/09/2005

Sunburn and Spinach

Last week we talked about a dimming of sunlight due to
pollution of our atmosphere. I could have used some dimming of
sunlight in my youth; applying sunscreen before going out in the
sun never occurred to me. As a result, like millions of others,
I’ve paid the price in the form of a number of skin cancers. In
fact, I’ve just had a little chunk taken from my ear by a doctor
skilled in Moh’s surgery. It was my first experience with this
type of surgery, named after a Dr. Moh. The surgeon removes a
slice, does a frozen section and examines it microscopically and
decides whether another slice has to be taken.

The waiting room was filled with patients awaiting the word as
to whether they needed another slicing. I felt thankful that my
problem was with my ear when one woman said she was having
slices from her eyelid. Yuk! I asked the surgeon how many
slices are typical and he mentioned his personal record of 17
slices! That particular case involved a growth on the patient’s
forehead that he successively tracked down her nose onto her
cheek. Thankfully, two slices sufficed in my case.

So, my ear suitably bandaged, I’m posting this column from
sunny Marco Island in Florida. Unfortunately for my skin,
Florida is one of the few states where the air quality meets EPA
standards so the sunlight is relatively undimmed. Accordingly, I
start my morning walks on the beach well before sunrise and
slather on the sunscreen very liberally if I golf. Yet, there was a
report on a local TV news program saying that people with skin
cancer should not shun the sun completely. It seems we older
folks risk getting too little vitamin D because of insufficient
exposure to the sun. Nothing is simple!

It’s tough for us humans, but what about spinach, or most other
green plants? Before spinach shows up on your salad plate, it
has spent days in the hot sun with no sunscreen. Wouldn’t you
think it would get sunburned? OK, like me, you probably never
gave it a thought. After all, spinach and other green plants
depend on photosynthesis for their growth and photosynthesis
depends on light from the sun. Chemically, a primary
photosynthesis reaction is quite simple: 6 CO2 + 6 H2O =
C6(H2O)6 + 6 O2 [stocksandnews doesn’t support subscripts].
For those not familiar with chemistry, this translates into: 6
molecules of carbon dioxide react with 6 molecules of water to
give glucose (a carbohydrate) and 6 molecules of oxygen.

A case could be made that this simple reaction is the most
important chemical reaction for us humans. Without it, we
would have no oxygen to breathe and no food to eat. The plant
takes in light from the sun, carbon dioxide from the air and water
through its roots and stems. In the plant, other sugars, starches
and other compounds vital to life are formed. Although the
primary reaction is quite simple, it’s a different story if you look
into how the plant manages to accomplish this and all the other
reactions in the plant. Frankly, the complexity of what goes on
in a plant leads me to say to myself, “Hey, you’re on vacation,
don’t burden yourself or your readers.”

However, I do think that most of us are aware that chlorophyll
plays a role in photosynthesis. Chlorophyll is a pigment that
absorbs certain colors of light from the sunlight (it does not
absorb green light but reflects it; hence, the green color). The
photons of light provide the energy to get the photosynthesis
going. One way a photon can get things going is to “excite” a
molecule such as chlorophyll. In “exciting’ the molecule the
photon can kick an electron to a higher energy state. A simple
way to look at this is to think of an atom as a nucleus with
electrons orbiting it like the planets orbit the Sun. If the closest
planet is Mercury, we might excite it by kicking it out to the orbit
of Venus. Not likely, of course, but if Mercury were an electron,
a photon might kick it out to a higher orbit in that manner.

Let’s get back to why spinach should worry about getting
sunburned. If we look at our photosynthesis reaction, we see that
it can only happen when both the water and carbon dioxide are
available to react. The carbon dioxide comes from the air and
the water comes mainly up through the roots and stems of the
spinach. Well, it takes time for the water to get to the leaf and
for the carbon dioxide to come in from the air. Meanwhile, the
Sun keeps shining and those photons keep coming.

So, we have an excess of light and we have a lot of excited
chlorophyll molecules. This isn’t good because they are all
hyped up and, unless that excess energy is dissipated, bad things
happen. Specifically, oxidative damage would result. Sunburn,
as with burning of wood or coal, is an oxidation type of reaction.
We’re continually being told to eat foods containing antioxidants
to protect ourselves from oxidative damage. In the case of
spinach and other plants, it’s obvious that plants solved the
problem of avoiding oxidative damage eons ago. Otherwise,
how does spinach grow those big, healthy green leaves?

Scientists have long known there must be something that gets rid
of this excess energy, “deexcitation”, as it’s known in the trade.
Graham Fleming and Krishna Niyogi and coworkers from the
Lawrence Berkeley National Laboratory and the University of
California have the answer, detailed in an article in the January
21 issue of Science. I was tipped to this study by a brief item by
Amanda Yarnell in the January 7 issue of Chemical and
Engineering News. Otherwise, I would not have been drawn to
the Science article, dauntingly titled “Carotenoid Cation
Formation and the Regulation of Photosynthetic Light
Harvesting”! Carotenoids are another class of pigments that
absorb light of a green color as might be deduced by the orange
color of carrots. The researchers worked with spinach.

They found that in the presence of intense light a carotenoid
identified as zeaxanthin (Zea for short) forms. Put crudely, this
compound sidles up to an excited chlorophyll molecule and
hands it an electron. This pairing up of Zea and the excited
chlorophyll soothes the chlorophyll and all that energy is
dissipated as heat. The chemistry is more complicated and the
processes take place very rapidly, in only tens or hundreds of
picoseconds (a picosecond is only one trillionth of a second).
The plant needs fast reactions because those photons keep
coming. Now that we know the role of Zea as a sort of sunscreen
for green plants, the hope is that there may be practical
applications in other fields such as solar energy generation.

Finally, a personal concern that Florida may not remain as one of
the cleaner air states. We flew down and picked up our shipped
car near the Fort Myers airport. On leaving the parking lot, I had
to press the brake pedal to the floor to stop! As a result, we had
to rent a car, leaving my VW Jetta at a nearby garage overnight,
and drive to Marco. Route I75 is an interstate highway with a
speed limit of 70 mph in this area. In late afternoon and early
evening, our actual speed was zero to 5 mph. With no accidents,
only traffic volume, the road was a parking lot. The pollution
emissions from idling vehicles can only get worse with a
multitude of new developments and shopping centers under
construction. Hurricanes haven’t slowed construction here.

The brakes? The cost of master cylinder and associated work, a
mere $740! Not a good start to our Florida stay.

Allen F. Bortrum