[LMB] Chlorophyll

[Ruchira Mathur]

The new book by Modistte has a light green sky, Isolate, I think it's
called? A book with empaths and non-empaths.

On Sat, Dec 25, 2021, 3:07 PM Joel Polowin <jpolowin at hotmail.com> wrote:

> Markus Baur <baur at chello.at> wrote:
> > i think the colour of the ersatz-chlorophyll would not only depend on
> > the metal itself, but also what exactly the surrounding molecule is
> > doing .. but i do not know enough about organic chemistry to make
> > predictions
>
> My Ph.D. is in organometallic chemistry: structures that have at least
> one metal atom in combination with an organic structure.  I'm out of
> date, having not been able to work in the field for a couple of decades,
> and I know very little biochemistry.  So take my comments with a *bit*
> of salt.
>
> Even on Earth, there are several variations of "regular" chlorophyll,
> with differing absorption spectra.  I don't think there's any particular
> reason why a biochemical "tree of life" -- the complete set of all
> living things through history, originating with some basic organism
> and branching out through multiple evolutionary paths -- couldn't run
> to variations of chlorophyll that modify the absorption spectra to
> different ranges.
>
> Many of our plants have other pigments in addition to chlorophyll which
> change their colours from the "standard" green.  We've got blue-green
> and red algae, which are very distinctly not-green, though they're still
> using the regular chlorophyll for their photosynthesis.
>
> Chlorophyll and the heme in our blood have a common substructure,
> the porphyrin ring, which is an organic ring with a metal atom at
> its center.  Other metal atoms can go in there instead.  That affects
> the colour, as do the various other organic bits that are attached to
> the ring.  I can't think of a reason why a chlorophyll analogue couldn't
> be based on a porphyrin using some metal atom other than magnesium.
>
> There are compounds other than heme that some animals use for carrying
> oxygen around -- most commonly, hemocyanin.  That's the blue pigment
> that colours the blood of cephalopods.  It isn't porphyrin-based.  There
> isn't any particular reason why a biochemical "tree of life" couldn't
> come up with some non-porphyrin structure to do photosynthesis with.
>
> As for sky colour... the blue is caused by Rayleigh scattering.  Light
> passing through an atmosphere that's essentially transparent to it still
> undergoes some scattering, as a fundamental effect.  A photon that isn't
> passing directly from sun to eyeball can be deflected; that's why the
> entire sky is lit up.  The degree of scattering varies as the fourth
> power of the frequency of the radiation.  That is, the blue/violet end
> of the visible spectrum is much more likely to be deflected.  But our
> sun emits more blue than violet light, and our eyes are more sensitive
> to blue than to violet, so we see our sky as blue.  Any planet with a
> sun similar to ours, and an atmosphere similar to ours, without a lot of
> non-transparent stuff suspended in it, is going to look like our sky.
>
> There are several factors that could change that.  If there are coloured
> gases in the atmosphere, that would (obviously) change the appearance.
> If the local sun is much cooler or hotter than ours, and therefore
> emits a lot less violet/blue than ours or a lot more violet than blue,
> there would be different light to scatter.  If there's a lot of dust or
> aerosol suspended, that also affects the scattering.  If there's a much
> denser atmosphere than ours, too much of the blue/violet is scattered
> away, rather than reaching us.
>
> Our setting sun and its sky appear red because of the last effect.
> Mars has a very thin atmosphere with lots of suspended dust, so its sky
> is red.  When our sky has a lot of particulate pollution, such as smoke,
> we also get redder skies.
>
> Joel
>
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