From Kelly Kearse: Certain non-cellulosic saccharides (for example, xylose, uronic acid derivatives) can be relatively resistant to acid hydrolysis-mentioned because these are two byproducts of saponin (if one includes saponaria as a potential surface coating of the cloth). I think the type of approach you suggested is important to help characterize the details of (specific) carbohydrate involvement.
My preference would be to start without any preconceptions as to what might or might not be there, and simply compare the sugars peaks on one’s glc trace with that of flax and modern linen v older specimens. One expects to see glucose peaks for cellulose and NCPs, and pentosan peaks that correspond to the arabinoxylans and other hemicellulose sugars, and of course those uronic acids from pectins. It’s my hunch (purely that) one will see depletion of hemicelluloses in image-bearing zones, but retention of most of the cellulose, on the assumption that the image is on the superficial PCW hemicelluloses.
Anything unusual or unexpected can be investigated using the fragmentation pattern from glc-mass spec’. Specifically looking for saponins from those “Tales of Mystery and Imagination” would come rather low down my list of priorities. As indicated earlier, the real fun is to see what happens to those sugar profiles if one takes linen that has had its surface discolored by varying degrees of carbohydrate dehydration, aka pyrolysis or caramelisation or just plain “scorching”.
I realize that this type of study, probably requiring sizeable samples for analysis, could only be done after a de-mythologizing second round of C-14 dating, with a confirmation of medieval provenance and change in perceptions by no means certain.
More later (in response to your second para’).
October 12, 2013 at 7:24 am | #62
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Comment from Piero:
Non-destructive testing (NDT) can solve the problem.
Colin wrote : “…Anything unusual or unexpected can be investigated using the fragmentation pattern from glc-mass spec’. Specifically looking for saponins from those “Tales of Mystery and Imagination” would come rather low down my list of priorities. As indicated earlier, the real fun is to see what happens to those sugar profiles if one takes linen that has had its surface discolored by varying degrees of carbohydrate dehydration…”
Using this kind of technology seems to be an old way to proceed :
a destructive analysis ! …
I prefer to wait and see the results obtained from the SPM analyses.
The non-destructive way is the right way.
Scanning probe microscopes (SPM) is a branch of microscopy that creates images of surfaces using a physical probe that scans a specimen.
I want to add :
The SPM results can see in comparison with the Raman Spectroscopy results.
Yes, Piero, but would AFM in one or other of its different variants tell us precisely what we want to know about the Shroud image – like what class of carbohydrate has been modified and in what manner (dehydration? oxidation?)? Or would it only show topological relief?
I’m broadly aware of the technique, having reported on one of its successes some years ago with pentacene:
But that particular molecule lends itself well to the technique – atypically well perhaps – it being recently acknowledged that the kind of detail revealed with a linear polycyclic hydrocarbon cannot be achieved, at least in the short term, with just any old organic molecule. Can you supply links that would suggest otherwise, or show that I’m being overly pessimistic?
Yes, conventional wet chemistry is destructive. But what if a repeat of the radiocarbon dating with a proper sampling frame were to again return that same medieval dating? It would still leave us with an unsolved mystery as to how the image had been created (and for what purpose)?
Maybe the dorsal side, or a portion thereof, could then be sacrificed for uninhibited scientific research – says he to anticipated howls of outrage… But does it not seem overly self-indulgent to release just enough science over many decades to much fanfare, whetting everyone’s appetite, only – in an admittedly hypothetical scenario- to stomp off with a de-mythologized shroud if or when the science had been unable to vouch for its authenticity? So what say we repeat the radiocarbon dating, and then review again the state of AFM. If still considered unfit- or sufficiently undeveloped for-purpose, then we should think about reaching for those scissors a second or third time.
October 12, 2013 at 9:45 am | #64
Reply to Kelly Kearse (Part 2)
“If an image fiber was subjected to diamide reduction & then subsequently treated with a reducing agent (to oxidize), do you think the “image” would be reformed, i.e. do you think the process is reversible?”
Trying to find the precise chemistry of carbohydrate dehydration is proving a real trial. Most of the literature where plant material is concerned is to do with cellulose, and with high temperature treatment (with a view to making semi-synthetic fuel oils).
So it’s back to first principles in trying to guess what kind of products one might be dealing with where discoloration of linen is concerned, especially if as seems likely it is hemicelluloses that are the more susceptible to chemical change.
If one were to take as one’s model a fairly mainstream, uncontroversial model, it would be the pyrolysis of xylans to furfural (an aldehyde). First the xylan polymer de-polymerises, releasing free xylose sugar. That then loses three molecules of water to form furfural.
C5H10O5 → C5H4O2 + 3 H2O
But there’s a problem. Pure furfural is colourless. However, it does yellow quickly on exposure to air (not surprising, given that aldehydes are reactive, and tend to polymerise etc). So when they speak of carbohydrate dehydration it may in fact be dehydration plus simultaneous aerial oxidation. That would then account for the ability to bleach the product with diimide – by reversing the secondary oxidation – but presumably leaving the initial dehydration step(s) intact.
So what are the products of furfural oxidation that are yellow?
From a quick literature search:
“A problem associated with the use of furfural, however, is its tendency to oxidize in the presence of atmospheric oxygen to form oxidation products such as furoic acid or formyl acrylic acid or formic acid which further, upon heating, forms furfural acidic polymers.”
So where does that leave us? It’s possible that diimide reduction will return us to furfural, or a related aldehyde, and given its volatility, it should not be difficult to detect on glc. But if the yellow product is a polymer, formed with one or more oxidation steps, then it’s possible that while it could be bleached, it would still remain polymeric, and fail to reveal itself on glc.
Answer: Approach the task with a completely open mind. Attempt to spot patterns in the data. Or as an Australian boss of mine used to say: “Just suck it and see”.
Comments 7&8 (mine, followed by Kelly Kearse’s reply)
October 13, 2013 at 9:33 am | #67
Enzymatic action? Glycosidases? I like the idea in principle, Kelly (me being a biochemist by training) to say nothing of fewer losses as by-products of acid hydrolysis. But would it be feasible in practice? To reduce a complex heteropolymer such as hemicellulose(s) down to its constituent hexose and pentose sugars on a realistic time scale you would presumably need a cleverly-contrived mix of endo- and exoglycosidases, the first to act at particular links within the polymer chains to effect a quick reduction to smaller more manageable fragments, and then the second, working inwards from the new terminals, to release the individual sugars. Sounds a tall order to me, if you don’t mind my saying.
I don’t mind you saying at all, it could be a tall order-was actually referring to using these in combination with the previously mentioned approach, particularly to help define any species that may be resistant to acid hydrolysis or a more end-stage purification-not necessarily chopping away at the entire structure from the beginning. Labeled sugar nucleotides used in conjunction with glycosyltransferases to identify particular terminal or individual saccharides might also prove helpful-just a thought-[I myself, used the latter technique years ago in my first postdoc in Gerald Hart’s lab who studied nuclear glycosylation, O-GlcNAc. I also used this in my own lab to look at trimming & readdition of Glc residues on newly synthesized proteins in the ER-I have photos!]. Plant carbohydrates are certainly more involved, but if there’s a linkage there is a glycosyltransferase to make it & a glycosidase to break it; many of these have now been purified & cloned. I think considering the specifics of exactly what carbohydrate(s) are being modified and how are central questions in Shroud science.
Comment 9 (reply to Kelly’s comment above):
October 13, 2013 at 1:05 pm | #68
I’m not sure how relevant the zoological/medical context is to plant chemistry, especially where cell walls are concerned. In the first one has sialo-and other glycoproteins that are cell-surface associated and critical for cell-cell recognition, as well as binding water at the cell surface. Sooner of later those cells die and the detritus has to be digested by endogenous lysosomal enzymes, using those glycosidase enzymes.Otherwise the organism would get clogged up with its own cast-offs.
It’s an entirely different situation in plant cells walls. Cellulose provides the fibres for mechanical strength, especially in the secondary cell wall, and hemicelluloses provide a ground substance or cement. The difference is that plants do not recycle their dead and dying cell wall components. After lignification they continue to provide support after death. Finally they drop off, and the only type of organism that can then recycle the carbon are the saprophytic fungi with their invasive feeding hyphae. But fibrous strands, or even hemicelluloses within those strands, are a tough substrate, which is why it can take years or decades even for dead wood and other vegetation finally to disappear. So the enzymes for hemicellulose digestion are not indigenous to the plants that made them, but in an entirely different organism, so are unlikely to show the kind of exquisite selectivity that one might desire if seeking to use, say, purified fungal glycosidases to effect an efficient step-by-step dismantling of hemicelluloses (and let’s not forget that they they have chains that can have hundreds of sugar residues strung together.).
I did a year of botany as subsidiary subject at University (if only because the zoology course was oversubscribed!). Did you do any botany, Kelly?
Comment 10 (reply from Kelly)
No botany here, I was a bit allergic to anything with a chloroplast-I appreciate the difference in chain length & structure, but if there’s a terminal end you might find a key that fits-very well put discussion by the way. Many of the saccharides that could constitute a suggested impurity layer at the surface would be amenable to analysis by the aforementioned techniques-I’m not saying it’s there or not-that’s where one of the fundamental issues lies, on which sugars, cloth or cloth-bound does the image reside?
October 15, 2013 at 1:46 am | #71
David, was there ever any chemical testing performed on Luigi Garlaschelli’s reproduction of the Turin Shroud?
I may have mentioned it some months ago, albeit briefly: there’s a strategy that is maybe worth pursuing that is a blend (OK, mishmash) of Luigi Garlaschelli’s ideas and my own. It would start with his use of a pigment paste to imprint features from a real subject onto linen (being careful to avoid going “too far round the sides, i.e. being content with a shallow bas-relief effect. Now if you go to his papers you will see there is then a baking stage in an oven (intended partially or primarily to mimic age-related yellowing of the linen), but there is also mention of pigment subsequently flaking off, leaving a residual image, the nature of which is unspecified. Hugh Farey here has for some time been hypothesizing that the Shroud image is a ‘shadow’ or faint signature of something that was originally more prominent, prior to a flaking off (and I have said the same previously re partially or extensively flaked-off bloodstains).
Is anyone thinking what I am thinking? The oven treatment did more than just artificially age the linen. It produced a more pronounced and highly localized chemical reaction between the pigment and the underlying linen that might be described as thermochemical imprinting via temperature-assisted chemical ‘scorching’. The phenomenon is not too dissimilar to the one I described in my very first posting on the TS, referred to as thermo-stencilling:
There I used charcoal as the pigment, and radiant heat at a distance to get it hot (rather than baking in an air oven, or direct contact say with a hot iron). But the end -result is/was (or could have been) the same – localised scorching of the linen in contact with pigment. This model has similarities and differences with the direct scorching model that I later adopted using heated metal or ceramic templates like a “cattle brand” instead of a real subject. But then ideas evolve (sometimes getting side-tracked!) and I have always been impressed with Garlaschelli’s end-result, differing only with his interpretation of how the end-result was achieved, a closer scrutiny of that oven-baking step perhaps being required.
There’s more one could say about the chemistry that produces the scorch, which probably involves chemical dehydration reactions that are a sub-group of “scorching”, but that can be explored another time. The role of iron and its compounds is worth studying, especially in the light of McCrone’s (prematurely?) discredited results and interpretation thereof, recalling that Luigi used ochre – a form of iron oxide – as his imprinting pigment. Might it have had acidic impurities, producing thermochemical dehydration of linen carbohydrates, allowing scorching at lower temperatures than required for direct hot template contact?
Thanks for the reminder re Luigi G. and his fascinating experiment.