[X] My Assistant

[Guest_AlexBlackwell_*]

Hunter Waite et al. have a paper ("The Process of Tholin Formation in Titan's Upper Atmosphere") to be published in the May 11, 2007, issue of Science; there is also an accompanying Perspectives piece ("Titan's Organic Factory") by Sushil Atreya.

The embargo will be lifted in a hour or two, so if do not have embargo access, the direct links to the articles probably will not be accessible until then. However, you can click here for a brief description.

Also, Opher et al. have a paper ("The Orientation of the Local Interstellar Magnetic Field") with an accompanying Perspectives piece ("A Local Wiggle in the Turbulent Interstellar Magnetic Field") by Jokipii. Again, unless you have embargo access, click here for a brief description.

[Juramike]

(I think I'm gonna have to reread these full papers as well...)

But shooting right off the cuff (and without rereading the papers), I'd interpret the brief statements in the abstract as saying that the large, complex, 8,000+ Dalton, negative ions [which may or may not be molecular, they could be a bunch of things all associated together, gotta check] could serve as a catalytic surface that would allow the absorption and construction of polyaromatic molecules (PAH's).

Reading some of the recent articles in press in Icarus regarding tholin characterization (no link to abstracts as yet), I'm still not sure if tholins are a discrete mega-molecule or a big mess of many types of molecules that holds onto discrete large molecules really well (incorporating them into pockets of the "lattice"). Either way, they are pretty insoluble, pretty intractable, and difficult to characterize. (Tholin types are very sensitive to the original gas mixture, the pressure, and the formation method - there is not yet a standard "Tholin" you can buy from Aldrich for chemists to play with. Many of the literature articles are generating and examining different sets of tholins - which makes things more difficult to cross-reference.)

Aqueous hydrolysis (acidic and basic) experiments with tholin materials seem to be able to release discrete and identifiable molecules from the mess, but then you've changed the original material.

I'm still unsure of the relationship between PAH's and tholins. I always thought of PAH's as a bunch of higher order benzenes stuck together with very few heteroatoms. Tholins appear to have things (and aromatics) derived from nitrile (CN) polymerization: things like triazine rings. I thought I read (somewhere?) that tholins do not have any aromatic C-H resonances observed by NMR experiments (DEPT? 1H-13C HETCORR? HSQC?).

Personally, I'm not going to be happy until someone can draw a structure on a white board and say "This is a tholin". I think at this point people can start to draw partial pieces and some pretty good guesses of possible pieces, but the whole elephant still is a long way from being described.

-Mike

[marsbug]

Thanks Mike! I've been doing some more research and I found this interesting paper, i hope you can access it. It gives me the impression of tholins being shards of wire mesh (PAH's) tangled into bundles of string (chains)!:

Tholins formed at low pressures contain the clusters of nitrogen-containing polycyclic aromatic compounds (N-PACs) in a matrix of carbon and nitrogen branched chain networks, which are connected tightly to each other with hydrogen bonding of N---H bonds. Tholin formed at high pressure (2300 Pa) consists of a polymer-like branched chain structure terminated with ---CH3, ---NH2, and ---CN with fewer aromatic compounds

It also mentions near the end that tholin production at lower pressures (higher altitudes) more accurately matches titans smog.