4 research outputs found
Improved Virus Removal in Ceramic Depth Filters Modified with MgO
Ceramic filters, working on the depth filtration principle,
are
known to improve drinking water quality by removing human pathogenic
microorganisms from contaminated water. However, these microfilters
show no sufficient barrier for viruses having diameters down to 20
nm. Recently, it was shown that the addition of positively charged
materials, for example, iron oxyhydroxide, can improve virus removal
by adsorption mechanisms. In this work, we modified a common ceramic
filter based on diatomaceous earth by introducing a novel virus adsorbent
material, magnesium oxyhydroxide, into the filter matrix. Such filters
showed an improved removal of about 4-log in regard to bacteriophages
MS2 and PhiX174. This is explained with the electrostatic enhanced
adsorption approach that is the favorable adsorption of negatively
charged viruses onto positively charged patches in an otherwise negatively
charged filter matrix. Furthermore, we provide theoretical evidence
applying calculations according to Derjaguin–Landau–Verwey–Overbeek
theory to strengthen our experimental results. However, modified filters
showed a significant variance in virus removal efficiency over the
course of long-term filtration experiments with virus removal increasing
with filter operation time (or filter aging). This is explained by
transformational changes of MgO in the filter upon contact with water.
It also demonstrates that filter history is of great concern when
filters working on the adsorption principles are evaluated in regard
to their retention performance as their surface characteristics may
alter with use
Virus Removal in Ceramic Depth Filters Based on Diatomaceous Earth
Ceramic filter candles, based on the natural material
diatomaceous
earth, are widely used to purify water at the point-of-use. Although
such depth filters are known to improve drinking water quality by
removing human pathogenic protozoa and bacteria, their removal regarding
viruses has rarely been investigated. These filters have relatively
large pore diameters compared to the physical dimension of viruses.
However, viruses may be retained by adsorption mechanisms due to intermolecular
and surface forces. Here, we use three types of bacteriophages to
investigate their removal during filtration and batch experiments
conducted at different pH values and ionic strengths. Theoretical
models based on DLVO-theory are applied in order to verify experimental
results and assess surface forces involved in the adsorptive process.
This was done by calculation of interaction energies between the filter
surface and the viruses. For two small spherically shaped viruses
(MS2 and PhiX174), these filters showed no significant removal. In
the case of phage PhiX174, where attractive interactions were expected,
due to electrostatic attraction of oppositely charged surfaces, only
little adsorption was reported in the presence of divalent ions. Thus,
we postulate the existence of an additional repulsive force between
PhiX174 and the filter surface. It is hypothesized that such an additional
energy barrier originates from either the phage’s specific
knobs that protrude from the viral capsid, enabling steric interactions,
or hydration forces between the two hydrophilic interfaces of virus
and filter. However, a larger-sized, tailed bacteriophage of the family <i>Siphoviridae</i> was removed by log 2 to 3, which is explained
by postulating hydrophobic interactions
Orientation-Controlled Electrocatalytic Efficiency of an Adsorbed Oxygen-Tolerant Hydrogenase
<div><p>Protein immobilization on electrodes is a key concept in exploiting enzymatic processes for bioelectronic devices. For optimum performance, an in-depth understanding of the enzyme-surface interactions is required. Here, we introduce an integral approach of experimental and theoretical methods that provides detailed insights into the adsorption of an oxygen-tolerant [NiFe] hydrogenase on a biocompatible gold electrode. Using atomic force microscopy, ellipsometry, surface-enhanced IR spectroscopy, and protein film voltammetry, we explore enzyme coverage, integrity, and activity, thereby probing both structure and catalytic H<sub>2</sub> conversion of the enzyme. Electrocatalytic efficiencies can be correlated with the mode of protein adsorption on the electrode as estimated theoretically by molecular dynamics simulations. Our results reveal that pre-activation at low potentials results in increased current densities, which can be rationalized in terms of a potential-induced re-orientation of the immobilized enzyme.</p></div
Resonance Raman Spectroscopic Analysis of the [NiFe] Active Site and the Proximal [4Fe-3S] Cluster of an O<sub>2</sub>‑Tolerant Membrane-Bound Hydrogenase in the Crystalline State
We
have applied resonance Raman (RR) spectroscopy on single protein
crystals of the O<sub>2</sub>-tolerant membrane-bound [NiFe] hydrogenase
(MBH from Ralstonia eutropha) which
catalyzes the splitting of H<sub>2</sub> into protons and electrons.
RR spectra taken from 65 MBH samples in different redox states were
analyzed in terms of the respective component spectra of the active
site and the unprecedented proximal [4Fe-3S] cluster using a combination
of statistical methods and global fitting procedures. These component
spectra of the individual cofactors were compared with calculated
spectra obtained by quantum mechanics/molecular mechanics (QM/MM)
methods. Thus, the recently discovered hydroxyl-coordination of one
iron in the [4Fe-3S] cluster was confirmed. Infrared (IR) microscopy
of oxidized MBH crystals revealed the [NiFe] active site to be in
the Ni<sub>r</sub>-B [NiÂ(III)] and Ni<sub>r</sub>-S [NiÂ(II)] states,
whereas RR measurements of these crystals uncovered the Ni<sub>a</sub>-S [NiÂ(II)] state as the main spectral component, suggesting its
in situ formation via photodissociation of the assumed bridging hydroxyl
or water ligand. On the basis of QM/MM calculations, individual band
frequencies could be correlated with structural parameters for the
Ni<sub>a</sub>-S state as well as for the Ni-L state, which is formed
upon photodissociation of the bridging hydride of H<sub>2</sub>-reduced
active site states