Relation between the Δ2 effect and the solution conformational entropy of aldohexoses and select methyl glycosides

Does the “C3 effect” offset the Δ2 effect, as regards the solution flexibility of aldoses?

“…As the system temperature was changed from 37 to 50°C in aqueous eluent, the solute distribution coefficient K SEC changed less than ±3% for these analytes (see Table ; similarly small changes were previously noted for gulose, talose, and allose in Ref. ). This strongly supports the conclusion that separation of the monosaccharides examined here is chiefly entropic in nature (characteristic of “near‐ideal” SEC behavior), as enthalpic interactions with the column packing material would lead to highly temperature‐dependent values of the distribution coefficient.…”

“…As described by Angyal as early as 1968, “It is thought that axial hydroxyl groups on each of C 2 and C 3 would cancel each other's effect.” Here, we systematically investigate how the C 3 and Δ2 effects affect the solution conformational entropy −Δ S (for an explanation of the use of the minus sign, see Calculation of the solution conformational entropy −Δ S ) of equilibrium solutions of aldopentoses and aldohexoses. The particular experimental method employed is size‐exclusion chromatography (SEC), an entropically‐controlled separation technique, which has previously been applied successfully to determining the solution conformational entropy of a variety of mono‐, di‐, and oligosaccharides . As will be seen for aldohexoses, while the Δ2 effect is greater than the C 3 effect (in semiquantitative agreement with Reeves's original results), in aqueous solution at quasi‐physiological conditions to a large extent these effects do compensate for one another with respect to their influence on solution conformational entropy.…”

“…The role of the solvent is thus paramount (and implicit), as the −Δ S values given will change when any/all of the analytes are dissolved in a different solvent (see e.g., Ref. for a comparison among −Δ S values of select sugars in aqueous solvent to results in N,N‐ dimethyl acetamine, both neat and with added LiCl). The importance of including the solvent in calculations of the energies of glucose and its epimers has been demonstrated by, among others, Hansen and Hünenberger, who extensively validated the GROMOS 56A CARBO force field against available experimental data in solution, and by Schnupf et al, who showed that an implicit solvent method (COSMO) needs to be included in high‐level DFTMD simulations to properly account for rotamer and anomer populations in aqueous solution .…”

“…Calculation of the standard conformational entropy difference between the mobile and stationary phases for the monosaccharides in solution was based on the retention times of peak maxima ( V R ), as measured by SEC, as well as the solute distribution coefficient ( K SEC ). These two parameters are related via: where V 0 is the void volume of the columns and V i is the total column volume. The internal pore volume of the system is defined as the difference between V i and V 0 .…”

The obstruction factor in size-exclusion chromatography. 1. The intraparticle obstruction factor

“…This conclusion was arrived at by determining the K SEC of the various PS and PMMA standards used at two different temperatures, 30 and 50 • C. With this 20 • C change in temperature, the biggest change in K SEC observed was only 2% and, in most cases, the change was <1%. Had there been a substantial enthalpic contribution to the separation, we would have expected a much larger change in K SEC (on the order of 10-20% or more) with a 20 • C change in temperature [6,25,26]. Tables 1-3 and Figs.…”