40 research outputs found
A new bernissartiid crocodyliform from the Lower Cretaceous Wessex Formation (Wealden Group, Barremian) of the Isle of Wight, southern England
Concentration-dependent Ac4GalNAz incorporation (24Â h incubation). (DOCX 322Â kb
Простір публічних комунікацій сучасних релігійних організацій
Porous aluminum oxide (PAO) is a
nanoporous material used for various
(bio)technological applications, and tailoring its surface properties
via covalent modification is a way to expand and refine its application.
Specific and complex chemical modification of the PAO surface requires
a stepwise approach in which a secondary reaction on a stable initial
modification is necessary to achieve the desired terminal molecular
architecture and reactivity. We here show that the straightforward
initial modification of the bare PAO surface with bromo-terminated
phosphonic acid allows for the subsequent preparation of PAO with
a wide scope of terminal reactive groups, making it suitable for (bio)functionalization.
Starting from the initial bromo-terminated PAO, we prepared PAO surfaces
presenting various terminal functional groups, such as azide, alkyne,
alkene, thiol, isothiocyanate, and <i>N</i>-hydroxysuccinimide
(NHS). We also show that this wide scope of easily accessible tailored
reactive PAO surfaces can be used for subsequent modification with
(bio)molecules, including carbohydrate derivatives and fluorescently
labeled proteins
Photochemical Grafting and Patterning of Organic Monolayers on Indium Tin Oxide Substrates
Covalently attached organic layers on indium tin oxide
(ITO) surfaces
were prepared by the photochemical grafting with 1-alkenes. The surface
modification was monitored with static water contact angle, X-ray
photoelectron spectroscopy (XPS), and atomic force microscopy (AFM)
measurements. Hydrophobic methyl-terminated ITO surfaces can be obtained
via the grafting of tetradec-1-ene, whereas the attachment of ω-functionalized
1-alkenes leads to functionalized ITO surfaces. The use of a CCGe(CH<sub>3</sub>)<sub>3</sub> terminus allows for facile tagging of the surface
with an azido group via a one-pot deprotection/click reaction, resulting
in bio/electronically active interfaces. The combination of nonaggressive
chemicals (alkenes), mild reaction conditions (room temperature),
and a light-induced grafting that facilitates the direct patterning
of organic layers makes this simple approach highly promising for
the development of ITO-based (bio)electronic devices
Sulfur-Phenolate Exchange as a Mild, Fast, and High-Yielding Method toward the Synthesis of Sulfonamides
Sulfonamides have
many important biological applications, yet their
synthesis often involves long reaction times under dry and non-ambient
conditions. Here we report the synthesis of a large range of sulfonamides
at room temperature using 4-nitrophenyl benzylsulfonate as a starting
material. Sulfonamides were prepared from a wide range of aliphatic,
linear, and cyclic amines, anilines, and N-methylanilines.
The yields and reaction times observed here were comparable to or
better than those reported previously, establishing sulfur-phenolate
exchange as a viable alternative
Simulation of XPS C1s Spectra of Organic Monolayers by Quantum Chemical Methods
Several
simple methods are presented and evaluated to simulate
the X-ray photoelectron spectra (XPS) of organic monolayers and polymeric
layers by density functional theory (DFT) and second-order Møller–Plesset
theory (MP2) in combination with a series of basis sets. The simulated
carbon (C1s) XPS spectra as obtained via B3LYP/6-311G(d,p) or M11/6-311G(d,p)
calculations are in good agreement (average mean error <0.3 eV)
with the experimental spectra, and good estimates of C1s spectra can
be obtained via <i>E</i><sub>C1s</sub>(exp) = 0.9698<i>E</i><sub>C1s</sub>(theory) + 20.34 (in eV) (B3LYP/6-311G(d,p)).
As a result, the simulated C1s XPS spectra can elucidate the binding
energies of the different carbon species within an organic layer and,
in this way, greatly aid the assignment of complicated C1s XPS spectra.
The paper gives a wide range of examples, including haloalkanes, esters,
(thio-)ethers, leaving groups, clickable functionalities, and bioactive
moieties
Structure and Long-Term Stability of Alkylphosphonic Acid Monolayers on SS316L Stainless Steel
Surface
modification of stainless steel (SS316L) to improve surface
properties or durability is an important avenue of research, as SS316L
is widely used in industry and science. We studied, therefore, the
formation and stability of a series of organic monolayers on SS316L
under industrially relevant conditions. These included acidic (pH
3), basic (pH 11), neutral (Milli-Q water), and physiological conditions
[10 mM phosphate-buffered saline (PBS)], as well as dry heating (120
°C). SS316L was modified with alkylphosphonic acids of chain
length (CH<sub>2</sub>)<sub><i>n</i></sub> with <i>n</i> varying between 3 and 18. While alkylphosphonic acids
of all chain lengths formed self-assembled monolayers with hydrophobic
properties, only monolayers of chain lengths 12–18 formed ordered
monolayers, as evidenced by static water contact angle (SCA), X-ray
photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and
infrared reflection absorption spectroscopy (IRRAS). A long-term stability
study revealed the excellent stability of monolayers with chain lengths
12–18 for up to 30 days in acid, neutral, and physiological
solutions, and for up to 7 days under dry heating. Under strong basic
conditions a partial breakdown of the monolayer was observed, especially
for the shorter chain lengths. Finally, the effect of multivalent
surface attachment on monolayer stability was explored by means of
a series of divalent bisphosphonic acids
Clickable Polylactic Acids by Fast Organocatalytic Ring-Opening Polymerization in Continuous Flow
The
use of microreactor technology for the ring-opening polymerization
of l-lactide catalyzed by 1,5,7-triazabicyclo[4.4.0]dec-5-ene
allows for rapid optimization of reaction parameters (reaction temperature
and residence time). At moderate catalyst loading, good control over
the polymerization is demonstrated by high conversion of monomer (>95%)
and low polydispersity (<1.3) at residence times as low as 2 s.
This metal-free, organocatalytic route yields well-defined poly(lactic
acid) in continuous flow and by using bicyclononyne- and tetrazine-containing
initiators gives access to poly(lactic acid) amenable to click chemistry
Generic Top-Functionalization of Patterned Antifouling Zwitterionic Polymers on Indium Tin Oxide
This paper presents a novel surface engineering approach
that combines photochemical grafting and surface-initiated atom transfer
radical polymerization (SI-ATRP) to attach zwitterionic polymer brushes
onto indium tin oxide (ITO) substrates. The photochemically grafted
hydroxyl-terminated organic layer serves as an excellent platform
for initiator attachment, and the zwitterionic polymer generated via
subsequent SI-ATRP exhibits very good antifouling properties. Patterned
polymer coatings can be obtained when the surface with covalently
attached initiator was subjected to photomasked UV-irradiation, in
which the C–Br bond that is present in the initiator was broken
upon exposure to UV light. A further, highly versatile top-functionalization
of the zwitterionic polymer brush was achieved by a strain-promoted
alkyne–azide cycloaddition, without compromising its antifouling
property. The attached bioligand (here: biotin) enables the specific
immobilization of target proteins in a spatially confined fashion,
pointing to future applications of this approach in the design of
micropatterned sensing platforms on ITO substrates
Toward the Rational Design of More Efficient Mo<sub>2</sub>C Catalysts for Hydrodeoxygenation–Mechanism and Descriptor Identification
Viable alternatives
to scarce and expensive noble-metal-based catalysts
are transition-metal carbides such as Mo and W carbides. It has been
shown that these are active and selective catalysts in the hydrodeoxygenation
of renewable lipid-based feedstocks. However, the reaction mechanism
and the structure–activity relationship of these transition-metal
carbides have not yet been fully clarified. In this work, the reaction
mechanism of butyric acid hydrodeoxygenation (HDO) over molybdenum
carbide (Mo2C) has been studied comprehensively by means
of density functional theory coupled with microkinetic modeling. We
identified the rate-determining step to be butanol dissociation: C4H9*OH + * → C4H9*
+ *OH. Then we further explored the possibility to facilitate this
step upon heteroatom doping and found that Zr- and Nb-doped Mo2C are the most promising catalysts with enhanced HDO catalytic
activity. Linear-scaling relationships were established between the
electronic and geometrical descriptors of the dopants and the catalytic
performance of various doped Mo2C catalysts. It was demonstrated
that descriptors such as dopants’ d-band filling and atomic radius play key roles in governing the catalytic
activity. This fundamental understanding delivers practical strategies
for the rational design of Mo2C-based transition-metal
carbide catalysts with improved HDO performance
High-Density Modification of H‑Terminated Si(111) Surfaces Using Short-Chain Alkynes
H–Si(111)-terminated
surfaces were alkenylated via two routes:
through a novel one-step gas-phase hydrosilylation reaction with short
alkynes (C<sub>3</sub> to C<sub>6</sub>) and for comparison via a
two-step chlorination and Grignard alkenylation process. All modified
surfaces were characterized by static water contact angles and X-ray
photoelectron spectroscopy (XPS). Propenyl- and butenyl-coated Si(111)
surfaces display a significantly higher packing density than conventional
C<sub>10</sub>–C<sub>18</sub> alkyne-derived monolayers, showing
the potential of this approach. In addition, propyne chemisorption
proceeds via either of two approaches: the standard hydrosilylation
at the terminal carbon (<i>lin</i>) at temperatures above
90 °C and an unprecedented reaction at the second carbon (<i>iso</i>) at temperatures below 90 °C. Molecular modeling
revealed that the packing energy of a monolayer bonded at the second
carbon is significantly more favorable, which drives <i>iso</i>-attachment, with a dense packing of surface-bound <i>iso</i>-propenyl chains at 40% surface coverage, in line with the experiments
at <90 °C. The highest density monolayers are obtained at
130 °C and show a linear attachment of 1-propenyl chains with
92% surface coverage