ANNUAL REPORT - MTA SzFKI

H. METAL PHYSICS
K. Tompa, I. Bakonyi, P. Bánki, M. Bokor, Cs. Hargitai , Gy. Lasanda, L. Péter,
E. Tóth-Kádár
Metal-hydrogen systems. — We have in-situ investigated hydrogen charging
(discharging) processes in Pd x Ag 1-x H alloys by simultaneous hydrogen concentration and
nuclear spin-spin relaxation time measurements.
Hydration of intrinsically disordered proteins. — 1 H NMR signals of physiological
solutions of proteins were investigated (in cooperation with the Institute of Enzymology,
Biological Research Center, HAS). The principal aim of our work is to characterize
structural and dynamical properties of interfacial water at the protein surface by wide-line
NMR spectroscopy and nuclear relaxation time measurements for the identification and
characterization of intrinsically disordered proteins (IDPs) and to make a distinction
between IDPs and globular proteins. Our approach is to explore the structure↔interface
relations of IDPs and globular proteins. The main results are the direct determination of
the number of hydration water molecules, the elements of hydration water dynamics
(activation energy and correlation times), and the differences in dynamics as seen by the
different time windows provided by the different types of relaxation rates (R 1 , R 1ρ and R 2 ).
We have shown by several examples that IDPs (e.g. early responsive to dehydration 10,
caskin, histone chaperone Df31) are distinguished from globular proteins (e.g. bovine
serum albumin, ubiquitin) by their more extended interfacial region (hydration), the
stronger (spin diffusion- and chemical-) interactions between protein and bound water at
low temperatures and the higher relaxation rates and activation energies at high
temperatures. Proteins dissolved in distilled water are surrounded by a homogeneous
hydrate shell while in buffered solvent the hydrate shell is more complex and involves
more water molecules (Fig. 1). From the combined analysis of the DSC traces and the
amount of hydration water measured by NMR, we have determined the specific heat of the
system consisting of the protein molecule and its hydration shell. The NMR investigations
have been extended to lyophilized (solid state) protein samples (Fig. 2) to get structural
information on the protein molecules e.g. motional states of methyl and methylene groups.
Electrodeposition. — Electrochemical deposition of Pd-Cu alloys was investigated by
using voltammetric methods and an electrochemical quartz crystal microbalance (EQCM).
It was found that deposit composition changes continuously with electrode potential. The
codeposition of Cu was observed also in the potential range where Cu cannot be deposited
alone, but Cu underpotential deposition onto Pd can take place. Hence, the process of the
Pd-Cu codeposition is an accumulative underpotential deposition. The deposit weight
calculated from the frequency change of the quartz crystal microbalance during potential
sweeps is in good agreement with the elemental analysis performed on samples produced
by ex-situ potentiostatic deposition.
A new operation mode was elaborated with a potentiostat and the EQCM. While formerly
the microbalance has always been used as an additional detector of the surface weight
change, in our workstation it can now be used as a part of the regulation. This so-called
feedback mode enabled us to modify the deposition conditions in-situ and to deposit alloys
with either stabilized composition or with a predefined depth profile. The system was
tested successfully for the deposition of Pd-Cu alloys.
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