2-DIMENSIONAL STRUCTURES OF CRYSTALLINE SELF-AGGREGATES OF AMPHIPHILIC ALCOHOLS AT THE AIR-WATER-INTERFACE AS STUDIED BY GRAZING-INCIDENCE SYNCHROTRON X-RAY-DIFFRACTION AND LATTICE ENERGY CALCULATIONS
Jl. Wang et al., 2-DIMENSIONAL STRUCTURES OF CRYSTALLINE SELF-AGGREGATES OF AMPHIPHILIC ALCOHOLS AT THE AIR-WATER-INTERFACE AS STUDIED BY GRAZING-INCIDENCE SYNCHROTRON X-RAY-DIFFRACTION AND LATTICE ENERGY CALCULATIONS, Journal of the American Chemical Society, 116(4), 1994, pp. 1192-1204
The two-dimensional (2D) crystal structures of self-aggregated cluster
s of amphiphilic alcohols (CnH2n+1OH, n=23, 30, 31, and C19H39CO2(CH2)
(n)OH, n=9, 10) on pure water at a temperature of 5 degrees C have bee
n determined to near-atomic resolution in order to understand the rela
tive abilities of these monolayers to induce ice nucleation. The struc
tures were solved making use of grazing incidence synchrotron X-ray di
ffraction (GID) data, complemented by lattice energy calculations. The
GID data of the different monolayers within each of the two series (C
nH2n+1OH, C19H39CO2CnH2nOH) are very similar. The molecules pack in a
rectangular unit cell of average dimensions a=5.0 Angstrom, b=7.5 Angs
trom for the normal alcohols CnH2n+1OH and a=5.7 Angstrom, b=7.5 Angst
rom for C(19)H(39)CO(2)CnH(2n)OH. The plane group symmetry is essentia
lly p1g1 for the normal alcohols The two-dimensional (2D) crystal stru
ctures of self-aggregated clusters of amphiphilic alcohols (CnH2n+1OH,
n=23, 30, 31, and C19H39CO2(CH2)(n)OH, n=9, 10) on pure water at a te
mperature of 5 degrees C have been determined to near-atomic resolutio
n in order to understand the relative abilities of these monolayers to
induce ice nucleation. The structures were solved making use of grazi
ng incidence synchrotron X-ray diffraction (GID) data, complemented by
lattice energy calculations. The GID data of the different monolayers
within eech of the two series (CnH2+1OH, C19H39CO2C(n)H(2n)OH) are ve
ry similar. The molecules pack in a rectangular unit cell of average d
imensions a=5.0 Angstrom, b=7.5 Angstrom for the normal alcohols CnH2n
+1OH and a=5.7 Angstrom, b=7.5 Angstrom for C19H39CO2CnH2nOH. The plan
e group symmetry is essentially p1g1 for the normal alcohols CnH2+1OH
and essentially pllg for the other group. The molecular chains are til
ted from the vertical by an average angle of 9 degrees, in the directi
on of the b axis, for CnH2n+1OH and by 29 degrees, in the direction of
the a axis, for the other molecular type. The mclecular chains relate
d by glide (g) symmetry are arranged in a herringbone pattern. The fit
to the Bragg rod intensity data of CnH2n+1OH permitted a reliable est
imate of 0.07 Angstrom(2) for the molecular mean-squared motion parall
el to the water surface. The absolute orientations of the molecules C1
9H39CO2CnH2nOH were determined by lattice energy calculations. The ani
sotropic coherence lengths of the crystallites of C19H39CO2CnH2nOH der
ived from the widths of the two observed Bragg peaks have been correla
ted with the binding energies of molecules in different directions.CnH
2+1OH and essentially p11g for the other group. The molecular chains a
re tilted from the vertical by an average angle of 90, in the directio
n of the b axis, for CnH2n+1OH, and by 29 degrees, in the direction of
the a axis, for the other molecular type. The molecular chains relate
d by glide (g) symmetry are arranged in a herringbone pattern. The fit
to the Bragg rod intensity data of C,CnH(2+1)OH permitted a reliable
estimate of 0.07 Angstrom(2) for the molecular mean-squared motion par
allel to the water:r surface. The absolute orientations of the molecul
es C19H39CO2CnH2nOH were determined by lattice energy calculations. Th
e anisotropic coherence lengths of the crystallites of C19H39CO2CnH2nO
H derived from the widths of the two observed Bragg peaks have been co
rrelated with the binding energies of molecules in different direction
s.