# What is the correct way to notate conformation preferences of polysaccharides?

In some webpages (1 or 2) are found the way to notate the conformational preferences of monosaccharides such as furanose and pyranose.

But, it lacks to give a brief description on how to do it with polysaccharides.

For a given example:

Would it be: $^4C_1\ \phi\ \psi\ \omega\ ^4C_1$ ?

Or

Would it be mixed with Newman projections (3, 4 or 5): $^4C_1\ [a,s,t,g],\ [a,s,t,g],\ [a,s,t,g]\ ^4C_1$ ?

Or

What is the proper way to notate?

If I understood the question correctly, your first notation looks correct and less ambiguous.

Common polysaccharides (glycogen, starch, and cellulose are composed of pyranoside subunits (having six-membered rings)). Such molecules can be represented as a series of rigid pyranose rings connected by an oxygen atom bridging two carbon atoms (the glycosidic bond).

There is, in principle, free rotation about both $\ce{C–O}$ bonds linking the residues , but rotation about each bond is limited by steric hindrance by substituents. The three dimensional structures of these molecules can be described in terms of the dihedral angles,ϕ and Ψ, about the glycosidic bond.

The bulkiness of the pyranose ring and its substituents, and electronic effects at the anomeric carbon, place constraints on the angles ϕ and Ψ thus certain conformations are much more stable than others, as can be shown on a map of energy as a function of ϕ and Ψ:

(a)

(a) When the relative energy (Ʃ) is plotted for each value of ϕ and Ψ with isoenergy (“same energy”) contours drawn at intervals of 1 kcal/mol above the minimum energy state, the result is a map of preferred conformations.

A map of favored conformations for oligosaccharides and polysaccharides.

The torsion angles ϕ and Ψ which define the spatial relationship between adjacent rings, can in principle have any value from 0 to 360 degrees. In fact, some of the torsion angles would give conformations that are sterically hindered, whereas others give conformations that maximize hydrogen bonding.

(b)

(b) Two energetic extremes for the disaccharide Gal(β-3)Gal; these values fall on the energy diagram (a) as shown by the red and blue dots. The red dot indicates the least favored conformation, the blue dot the most favored conformation.

Conformation at the glycosidic bonds of cellulose, amylose, and dextran.

The polymers are depicted as rigid pyranose rings joined by glycosidic bonds, with free rotation about these bonds. Note that in dextran there is also free rotation about the bond between C-5 and C-6 (torsion angle ѡ (omega)).

So the notation considering the glycosidic linkage will be $\ce{Glu(ϕ)-(β1-4)-Glu(Ψ)}$ or another detailed way of illustrating this is $\ce{C1(ϕ)-O4(Ψ)-C4}$ for cellulose.

There are other ways of illustrating polyasacharides notations, and their side groups e.g hydroxyl group (in newman projection)

For the precise specification of the orientation of a polyatomic ring substituent, it is necessary to specify the torsion angle about the exocyclic bond.

The reference atom in the ring is the carbon atom with the number one lower than that of the substituted carbon, unless substitution is on the anomeric carbon, when the ring oxygen is the reference atom. The reference atom in the exocyclic –CH2X group is X. The exocyclic torsion angle is denoted by χ(chi), followed by the atoms to which it refers e.g χ(C1-C2-O2-H).

References

• Thank you but your answer did not response the question. Along your answer, you showed the conformational space, but you did not show, in any part of your response, a treatment related to the main question, on how to notate each conformer. At least, did you read the links that I shared? Thank you again – Another.Chemist Oct 8 '17 at 16:24
• I tried to give an example from the diagrams drawn just before the underlined paragraph "So the notation will be......" Is it different from what you're looking for? It considers the anomeric form of polysaccharides with repeating Glu units – xavier_fakerat Oct 8 '17 at 16:28
• No, that notation is not related to conformational studies. It only relates the type of bond between two monosaccharides. – Another.Chemist Oct 8 '17 at 16:30
• Ok thanks I will update if I get something, along the lines – xavier_fakerat Oct 8 '17 at 16:32