5 research outputs found
cryopreservation EPSR folder
This is the entire EPSR folder for the data and simulations and analysis shown in this paper
cryopreservation EPSR folder
This is the entire EPSR folder for the data and simulations and analysis shown in this paper
Microscopic Structure of Liquid Nitric Oxide
The microscopic structure
of nitric oxide is investigated
using
neutron scattering experiments. The measurements are performed at
various temperatures between 120 and 144 K and at pressures
between 1.1 and 9 bar. Using the technique of empirical potential
structure refinement (EPSR), our results show that the dimer is the
main form, around 80%, of nitric oxide in the liquid phase at 120 K,
but the degree of dissociation to monomers increases with increasing
temperature. The reported degree of dissociation of dimers, and its
trend with increasing temperature, is consistent with earlier measurements
and studies. It is also shown that nonplanar dimers are not inconsistent
with the diffraction data and that the possibility of nitric oxide
molecules forming longer oligomers, consisting of bonded nitrogen
atoms along the backbone, cannot be ruled out in the liquid. A molecular
dynamics simulation is used to compare the present EPSR simulations
with an earlier proposed intermolecular potential for the liquid
Axial Structure of the Pd(II) Aqua Ion in Solution
Solution chemistry of Pd(II) and Pt(II) complexes is relevant to many fields of chemistry given the widespread applications of their compounds in homogeneous and heterogeneous catalysis, intermediate reaction synthesis, and antitumoral drugs. The well-defined square-planar arrangement of their complexes contrasts with the rather diffuse axial environment in solution. A theoretical proposal for a characteristic hydration shell in this axial region, called the meso-shell, stimulated further experimental and theoretical studies which have led to different pictures. The present work characterizes the structure of the axial region of the Pd(II) aqua ion in solution using a combination of neutron and X-ray diffraction and extended X-ray absorption fine structure (EXAFS) spectroscopy, with empirical potential structure refinement (EPSR). The results confirm the existence of the axial region and structurally characterize the water molecules within it. An important finding not previously reported is that the counterion, in this case the perchlorate anion, competes with water molecules for the meso-shell occupancy. The important role played by the axial region in many ligand substitution reactions is therefore intimately connected with the presence of the counterion and not just hydration water. This must call the attention of the experimental community to the important role that the counterion of the precursor salt must play in the synthesis
Pronounced Microheterogeneity in a Sorbitol–Water Mixture Observed through Variable Temperature Neutron Scattering
In this study, the structure of concentrated d-sorbitol–water
mixtures is studied by wide- and small-angle neutron scattering (WANS
and SANS) as a function of temperature. The mixtures are prepared
using both deuterated and regular sorbitol and water at a molar fraction
of sorbitol of 0.19 (equivalent to 70% by weight of regular sorbitol
in water). Retention of an amorphous structure (i.e., absence of crystallinity)
is confirmed for this system over the entire temperature range, 100–298
K. The glass transition temperature, Tg, is found from differential
scanning calorimetry to be approximately 200 K. WANS data are analyzed
using empirical potential structure refinement, to obtain the site–site
radial distribution functions (RDFs) and coordination numbers. This
analysis reveals the presence of nanoscaled water clusters surrounded
by (and interacting with) sorbitol molecules. The water clusters appear
more structured compared to bulk water and, especially at the lowest
temperatures, resemble the structure of low-density amorphous ice
(LDA). Upon cooling to 100 K the peaks in the water RDFs become markedly
sharper, with increased coordination number, indicating enhanced local
(nanometer-scale) ordering, with changes taking place both above and
well below the Tg. On the mesoscopic (submicrometer) scale, although
there are no changes between 298 and 213 K, cooling the sample to
100 K results in a significant increase in the SANS signal, which
is indicative of pronounced inhomogeneities. This increase in the
scattering is partly reversed during heating, although some hysteresis
is observed. Furthermore, a power law analysis of the SANS data indicates
the existence of domains with well-defined interfaces on the submicrometer
length scale, probably as a result of the appearance and growth of
microscopic voids in the glassy matrix. Because of the unusual combination
of small and wide scattering data used here, the present results provide
new physical insight into the structure of aqueous glasses over a
broad temperature and length scale, leading to an improved understanding
of the mechanisms of temperature- and water-induced (de)stabilization
of various systems, including proteins, pharmaceuticals, and biological
objects