7 research outputs found
Biorelated Polyelectrolyte Coatings Studied by in Situ Attenuated Total Reflection–Fourier Transform Infrared Spectroscopy: Deposition Concepts, Wet Adhesiveness, and Biomedical Applications
In this conceptual contribution,
thin functional coatings consisting of either pure polyelectrolytes
(PELs) or complexes between oppositely charged PELs at model and applied
substrates are outlined. Latter PEL/PEL complexes were deposited by
two concepts. In a first well-known concept, PEL multilayers (PEM)
were consecutively deposited according to the layer-by-layer (LbL)
technique. In a second less known concept, PEL complex (PEC) nanoparticles
(NPs) preformed by mixing polycation (PC) and polyanion (PA) solutions
were deposited in one step. Both concepts based on binary oppositely
charged PELs are compared to one based on a single polycation system.
Examples shall be given on adhesiveness, nanostructure, and biomedical
applications of PEM and PEC NP coatings. In situ attenuated total
reflection (ATR) infrared (IR) spectroscopy, circular dichroism (CD),
and scanning force microscopy (SFM) were used for molecular, optical,
and microscopic characterization. At first, results on the adsorbed
amount and wet adhesiveness of pure (single-component) PEL coatings
as a function of charge density are given to motivate coatings of
mixed oppositely charged PELs. Second, the wet adhesiveness of PEM
and PEC NP coatings of identical PEL compounds in aqueous media varying
the molar charge ratio (<i>n</i>–/<i>n</i>+) and the deposition step <i>z</i>, respectively, is compared.
Upon comparing the three PEL deposition concepts, it is suggested
that the lack or absence of excess charge at the PEL/surface interface
is one of the main factors for the wet adhesiveness of all pure PEL,
PEM, and PEC NP coatings. Finally, the potential of PEM and PEC NP
coatings for biomedical applications is outlined. Concerning biopassivation,
PEM coatings excessed or terminated by PA repel proteins with low
isoelectric points. Concerning bioactivation, PEM coatings loaded
with antibiotics as well as PEC NP coatings loaded with therapeutic
bisphosphonates showed retarded, optionally temperature responsive
drug release for applications in acute surgery and bone healing, and
immunoglobulin/PEL complex coatings might open theranostic applications
Quantitative Proteomics Using Ultralow Flow Capillary Electrophoresis–Mass Spectrometry
In this work, we evaluate the incorporation
of an ultralow flow
interface for coupling capillary electrophoresis (CE) and mass spectrometry
(MS), in combination with reversed-phase high-pressure liquid chromatography
(HPLC) fractionation as an alternate workflow for quantitative proteomics.
Proteins, extracted from a SILAC (stable isotope labeling by amino
acids in cell culture) labeled and an unlabeled yeast strain were
mixed and digested enzymatically in solution. The resulting peptides
were fractionated using RP-HPLC and analyzed by CE–MS yielding
a total of 28 538 quantified peptides that correspond to 3 272
quantified proteins. CE–MS analysis was performed using a neutral
capillary coating, providing the highest separation efficiency at
ultralow flow conditions (<10 nL/min). Moreover, we were able to
demonstrate that CE–MS is a powerful method for the identification
of low-abundance modified peptides within the same sample. Without
any further enrichment strategies, we succeeded in quantifying 1 371
phosphopeptides present in the CE–MS data set and found 49
phosphopeptides to be differentially regulated in the two yeast strains.
Including acetylation, phosphorylation, deamidation, and oxidized
forms, a total of 8 106 modified peptides could be identified
in addition to 33 854 unique peptide sequences found. The work
presented here shows the first quantitative proteomics approach that
combines SILAC labeling with CE–MS analysis
Enhanced Activity of Acetyl CoA Synthetase Adsorbed on Smart Microgel: an Implication for Precursor Biosynthesis
Acetyl coenzyme A (acetyl CoA) is an essential precursor molecule
for synthesis of metabolites such as the polyketide-based drugs (tetracycline,
mitharamycin, Zocor, etc.) fats, lipids, and cholesterol. Acetyl CoA
synthetase (Acs) is one of the enzymes that catalyzes acetyl CoA synthesis,
and this enzyme is essentially employed for continuous supply of the
acetyl CoA for the production of these metabolites. To achieve reusable
and a more robust entity of the enzyme, we carried out the immobilization
of Acs on poly(<i>N</i>-isopropylacrylamide)-poly(ethylenimine)
(PNIPAm-PEI) microgels via adsorption. Cationic PNIPAm-PEI microgel
was synthesized by one-step graft copolymerization of NIPAm and <i>N</i>,<i>N</i>-methylene bis-acrylamide (MBA) from
PEI. Adsorption studies of Acs on microgel indicated high binding
of enzymes, with a maximum binding capacity of 286 μg/mg of
microgel for Acs was achieved. The immobilized enzymes showed improved
biocatalytic efficiency over free enzymes, beside this, the reaction
parameters and circular dichroism (CD) spectroscopy studies indicated
no significant changes in the enzyme structure after immobilization.
This thoroughly characterized enzyme bioconjugate was further immobilized
on an ultrathin membrane to assess the same reaction in flow through
condition. Bioconjugate was covalently immobilized on a thin layer
of preformed microgel support upon polyethylene terephthalate (PET)
track etched membrane. The prepared membrane was used in a dead end
filtration device to monitor the bioconversion efficiency and operational
stability of cross-linked bioconjugate. The membrane reactor showed
consistent operational stability and maintained >70% of initial
activity
after 7 consecutive operation cycles
Bienzymatic Sequential Reaction on Microgel Particles and Their Cofactor Dependent Applications
We report, the preparation
and characterization of bioconjugates,
wherein enzymes pyruvate kinase (Pk) and l-lactic dehydrogenase
(Ldh) were covalently bound to poly(<i>N</i>-isopropylacrylamide)-poly(ethylenimine)
(PNIPAm-PEI) microgel support using glutaraldehyde (GA) as the cross-linker.
The effects of different arrangements of enzymes on the microgels
were investigated for the enzymatic behavior and to obtain maximum
Pk-Ldh sequential reaction. The dual enzyme bioconjugates prepared
by simultaneous addition of both the enzymes immobilized on the same
microgel particles (PL), and PiLi, that is, dual enzyme bioconjugate
obtained by combining single-enzyme bioconjugates (immobilized pyruvate
kinase (Pi) and immobilized lactate dehydrogenase (Li)), were used
to study the effect of the assembly of dual enzymes systems on the
microgels. The kinetic parameters (<i>K</i><sub>m</sub>, <i>k</i><sub>cat</sub>), reaction parameters (temperature, pH),
stability (thermal and storage), and cofactor dependent applications
were studied for the dual enzymes conjugates. The kinetic results
indicated an improved turn over number (<i>k</i><sub>cat</sub>) for PL, while the <i>k</i><sub>cat</sub> and catalytic
efficiency was significantly decreased in case of PiLi. For cofactor
dependent application, in which the ability of ADP monitoring and
ATP synthesis by the conjugates were studied, the activity of PL was
found to be nearly 2-fold better than that of PiLi. These results
indicated that the influence of spacing between the enzymes is an
important factor in optimization of multienzyme immobilization on
the support
Facile Approach to Grafting of Poly(2-oxazoline) Brushes on Macroscopic Surfaces and Applications Thereof
This study reports on a facile and versatile approach
for modification
of macroscopic surface via grafting of multifunctional poly(2-oxazoline)
molecules in brush-like conformation. For this purpose, carboxyl-terminated
poly(2-isopropyl-2-oxazoline) molecules have been synthesized by ring-opening
cationic polymerization and subsequently grafted on underlined substrates
by exploiting the ”grafting to” approach. A systematic
variation in thickness of the grafted poly (2-isopropyl-2-oxazoline)
brushes has been demonstrated. Polymer-modified surfaces have been
characterized by means of a number of analytical tools including ellipsometry,
X-ray photoelectron spectroscopy, ultraviolate spectroscopy, attenuated
total reflection infrared spectroscopy
and atomic force microscopy. Interestingly, poly(2-isopropyl-2-oxazoline)
molecules have been found to retain their physical properties even
after grafting on macroscopic surfaces. Finally, fabricated polymer
brushes have been used as platform for stabilization of inorganic
nanoparticles on macroscopic surfaces
Biohybrid Networks of Selectively Desulfated Glycosaminoglycans for Tunable Growth Factor Delivery
Sulfation
patterns of glycosaminoglycans (GAG) govern the electrostatic
complexation of biomolecules and thus allow for modulating the release
profiles of growth factors from GAG-based hydrogels. To explore options
related to this, selectively desulfated heparin derivatives were prepared,
thoroughly characterized, and covalently converted with star-shaped
poly(ethylene glycol) into binary polymer networks. The impact of
the GAG sulfation pattern on the network characteristics of the obtained
hydrogels was theoretically evaluated by mean field methods and experimentally
analyzed by rheometry and swelling measurements. Sulfation-dependent
differences of reactivity and miscibility of the heparin derivatives
were shown to determine network formation. A theory-based design concept
for customizing growth factor affinity and physical characteristics
was introduced and validated by quantifying the release of fibroblast
growth factor 2 from a set of biohybrid gels. The resulting new class
of cell-instructive polymer matrices with tunable GAG sulfation will
be instrumental for multiple applications in biotechnology and medicine
Tunable Strain in Magnetoelectric ZnO Microrod Composite Interfaces
The
intrinsic strain at coupled components in magnetoelectric composites
plays an important role for the properties and function of these materials.
In this in situ X-ray nanodiffraction experiment, the coating-induced
as well as the magnetic-field-induced strain at the coupled interface
of complex magnetoelectric microcomposites were investigated. These
consist of piezoelectric ZnO microrods coated with an amorphous layer
of magnetostrictive (Fe<sub>90</sub>Co<sub>10</sub>)<sub>78</sub>Si<sub>12</sub>B<sub>10</sub>. While the intrinsic strain is in the range
of 10<sup>–4</sup>, the magnetic-field-induced strain is within
10<sup>–5</sup>, one order of magnitude smaller. Additionally,
the strain relaxation distance of around 5 μm for both kinds
of strain superposes indicating a correlation. The value of both intrinsic
and magnetic-field-induced strain can be manipulated by the diameter
of the rodlike composite. The intrinsic interface strain within the
ZnO increases exponentially by decreasing the rod diameter while the
magnetic-field-induced strain increases linearly within the given
range. This study shows that miniaturizing has a huge impact on magnetoelectric
composite properties, resulting in a strongly enhanced strain field
and magnetic response