241 research outputs found
A challenge to the Delta G~0 interpretation of hydrogen evolution
Platinum is a nearly perfect catalyst for the hydrogen evolution reaction,
and its high activity has conventionally been explained by its
close-to-thermoneutral hydrogen binding energy (G~0). However, many candidate
non-precious metal catalysts bind hydrogen with similar strengths, but exhibit
orders-of-magnitude lower activity for this reaction. In this study, we employ
electronic structure methods that allow fully potential-dependent reaction
barriers to be calculated, in order to develop a complete working picture of
hydrogen evolution on platinum. Through the resulting ab initio microkinetic
models, we assess the mechanistic origins of Pt's high activity. Surprisingly,
we find that the G~0 hydrogen atoms are kinetically inert, and that the
kinetically active hydrogen atoms have G's much weaker, similar to that of
gold. These on-top hydrogens have particularly low barriers, which we compare
to those of gold, explaining the high reaction rates, and the exponential
variations in coverages can uniquely explain Pt's strong kinetic response to
the applied potential. This explains the unique reactivity of Pt that is missed
by conventional Sabatier analyses, and suggests true design criteria for
non-precious alternatives
Scaled and Dynamic Optimizations of Nudged Elastic Bands
We present a modified nudged elastic band routine that can reduce the number
of force calls by more than 50% for bands with non-uniform convergence. The
method, which we call "dyNEB", dynamically and selectively optimizes states
based on the perpendicular forces and parallel spring forces acting on that
region of the band. The convergence criteria are scaled to focus on the region
of interest, i.e., the saddle point, while maintaining continuity of the band
and avoiding truncation. We show that this method works well for solid state
reaction barriers---non-electrochemical in general and electrochemical in
particular---and that the number of force calls can be significantly reduced
without loss of resolution at the saddle point
EXPRESSION OF A FUNCTIONAL CHIMERIC lg-MHC CLASS II PROTEIN
composed of the a- and ß-chains of the MHC class I1
I-E molecule fused to antibody V regions derived
from anti-human CD4 mAb MT310. Expression vectors
were constructed containing the functional,
rearranged gene segments coding for the V region
domains of the antibody H and L chains in place of
the first domains of the complete structural genes
of the I-E a- and ß-chains, respectively. Celltsr ansfected
with both hybrid genes expressed a stable
protein product on the cell surface. The chimeric
molecule exhibited the idiotype of the antibody
MT310 as shown by binding to the anti-idiotypic
mAb 20-46. A protein of the anticipated molecular
mass was immunoprecipitated witha nti-mouse IgG
antiserum. Furthermore, human soluble CD4 did
bind to thetr ansfected cell line, demonstrating that
the chimeric protein possessed the binding capacity
of the original mAb. Thus, the hybrid molecule retained:
1) the properties of a MHC class I1 protein
with regardt o correct chain assembly and transport
to the cell surface: as well as 2) the Ag binding
capacity of the antibody genes used. Thgee neration
of hybrid MHC class I1 molecules with highly specific,
non-MHC-restricted bindingc apacities will be
useful for studying MHC class 11-mediated effector
functions such as selection of the T cell repertoire
in thymus of transgenic mice
Nonclassical binding of formylated peptide in crystal structure of the MHC class lb molecule H2-M3
AbstractH2-M3 is a class Ib MHC molecule of the mouse with a 104-fold preference for binding N-fonmylated peptides. To elucidate the basis of this unusual specificity, we expressed and crystallized a soluble form of M3 with a fonnylated nonamer peptide, fMYFINILTL, and determined the structure by X-ray crystallography. M3, refined at 2.1A˚resolution, resembles class la MHC molecules in its overall structure, but differs in the peptide-binding groove. The A pocket, which usually accommodates the free N-terminus of a bound peptide, is closed, and the peptide Is shifted one residue, such that the P1 side chain is lodged in the B pocket. The formyl group Is coordinated by His-9 and a bound water on the floor of the groove
Present and past ecological niche models for the Great Tit (Parus major)
This presentation was given as part of the GIS Day@KU symposium on November 14, 2018. For more information about GIS Day@KU activities, please see http://gis.ku.edu/gisday/2018/PLATINUM SPONSORS:
KU Department of Geography and Atmospheric Science
KU Institute for Policy & Social Research
GOLD SPONSORS:
KU Libraries
State of Kansas Data Access & Support Center (DASC)
SILVER SPONSORS:
Bartlett & West
Kansas Applied Remote Sensing Program
KU Center for Global and International Studies
BRONZE SPONSORS:
Boundles
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