Carbohydrate and Trivalent Iron Ion Interactions in the Gas Phase and in Aqueous Solution - Metallic Systems: A Quantum Chemist's Perspective - page 100

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5
0
-200

-100 0
φ(O5-C1-O1-C7)/degrees

100 200

(A)

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-100 0
φ(O5-C1-O1-C7)/degrees

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(B)

FIGURE 3.6 Calculated. torsional. energy. change. of. the. glycosidic. linkage. of. methyl-α-
mannopyranoside.(solid.line).and.its.energy.change.in.the.vicinity.of.one.(dashed.line).and.
two.Fe 3+ .ions.(dotted.line).in.water,.with.the.PMF.method:.(A).CPMD.simulations,.(B).CMD.
simulations.. The.inset. plot.(B).presents. the.calculated.energy. differences. of.the.glycosidic.
linkage. of. methyl-α-mannopyranoside. with. the. perturbation. and. PMF. methods. by. CMD.
simulations..Errors.were.calculated.using.the.time-dependent.standard.deviation.method.

of.the.glycosidic.linkage.and.predict.+60°.as.the.minimum.for.M,.M-Fe 3+ ,.and.in.
water..For.the.gas.phase,.this.trend.is. g+ > t ≈ g −.as.reported.above.and.indicates.
that.water.stabilizes.the. g −.orientation.of.the.glycosidic.linkage.over.its. t .orientation.
upon.coordination.of.Fe.
According.to.the.CPMD.simulations,.the.average.intramolecular.hydrogen.bond-
ing. distances. O2-O3,. O3-O4,. and. O4-O6. of. M. in. water. vary. between. 2.1. and.
4.5.Å..In.contrast,.CMD.simulations.predict.that.these.intramolecular.distances.are.
between. 2.4. and. 3.7. Å.. The. intramolecular. hydrogen. bonds. between. O2. and. the.
H. attached. to. O3. are. shorter. than. those. for. O3-O4. and. O4-O6. according. to. the.
CPMD.simulations.(Table.3.4)..Furthermore,.the.predicted.intermolecular.hydrogen.
bonds.between.O2-water,.O3-water,.and.O4-water.indicate.a.stronger.coordination.