Hans Engelkamp - Academia.edu (original) (raw)

Papers by Hans Engelkamp

Abstracts of Papers of The American Chemical Society, 2006

Science, 2006

The use of bottom-up approaches to construct patterned surfaces for technological applications is... more The use of bottom-up approaches to construct patterned surfaces for technological applications is appealing, but to date is applicable to only relatively small areas (approximately 10 square micrometers). We constructed highly periodic patterns at macroscopic length scales, in the range of square millimeters, by combining self-assembly of disk-like porphyrin dyes with physical dewetting phenomena. The patterns consisted of equidistant 5-nanometer-wide lines spaced 0.5 to 1 micrometers apart, forming single porphyrin stacks containing millions of molecules, and were formed spontaneously upon drop-casting a solution of the molecules onto a mica surface. On glass, thicker lines are formed, which can be used to align liquid crystals in large domains of square millimeter size.

Science, 1999

A disk-shaped molecule with chiral tails is shown to form long fibers of molecular diameter and m... more A disk-shaped molecule with chiral tails is shown to form long fibers of molecular diameter and micrometer length by self-assembly in chloroform. The molecules are derived from crown ethers and contain a phthalocyanine ring. In the fibers, they have a clockwise, staggered orientation that leads to an overall right-handed helical structure. These structures, in turn, self-assemble t o form coiled-coil aggregates with left-handed helicity. Addition of potassium ions to the fibers leaves their structure intact but blocks the transfer of the chirality from the tails to the cores, leading t o loss of the helicity of the fibers. These tunable chiral materials have potential in optoelectronic applications and as components in sensor devices.

Proceedings of the National Academy of Sciences, 2008

A generic method is described for the fluorescence ''readout'' of the activity of single redox en... more A generic method is described for the fluorescence ''readout'' of the activity of single redox enzyme molecules based on Fö rster resonance energy transfer from a fluorescent label to the enzyme cofactor. The method is applied to the study of copper-containing nitrite reductase from Alcaligenes faecalis S-6 immobilized on a glass surface. The parameters extracted from the single-molecule fluorescence time traces can be connected to and agree with the macroscopic ensemble averaged kinetic constants. The rates of the electron transfer from the type 1 to the type 2 center and back during turnover exhibit a distribution related to disorder in the catalytic site. The described approach opens the door to singlemolecule mechanistic studies of a wide range of redox enzymes and the precise investigation of their internal workings. electron transfer ͉ redox enzyme ͉ Fö rster transfer ͉ nitric oxide ͉ fluorescent label Fig. 1. Sequence of events during the turnover of NiR labeled on the N terminus with ATTO 655. (Left) In the resting enzyme, both types 1 (blue) and

Nature Nanotechnology, 2007

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Journal of the American Chemical Society, 1997

The ability of clip shaped molecules based on the building block diphenylglycoluril to form compl... more The ability of clip shaped molecules based on the building block diphenylglycoluril to form complexes with dihydroxybenzene guest molecules has been studied in detail. The binding strength of these complexes can be varied over a wide range (K a ≈ 0-10 5 M -1 ), by applying small modifications in the host or the guest molecule. It is found that the complexation is a combination of different effects, viz., hydrogen bonding, π-π stacking interactions, and a cavity effect. Shi, J.-P.; Knill-Jones, J.; Lowe, D. M.; Wilkinson, A. J.; Blow, D. M.; Brick, P.; Carter, C.; Waye, M. M. Y.; Winter, G. Nature 1985, 314, 235. (d) Schweitzer, B. A.; Kool, E. T.

Journal of the American Chemical Society, 2008

JA807218E Figure 2. (A, B) WF images of two drop-cast NWs. (C) Line profiles along the NWs long a... more JA807218E Figure 2. (A, B) WF images of two drop-cast NWs. (C) Line profiles along the NWs long axis in panels A and B. (D) A set of snapshots of the WF image of a drop-cast NW after (from left) 0, 1.5, 2.5, 6.5, 7.5, and 9.5 s.

Chemistry - A European Journal, 1998

The conformational behavior and binding properties of various clipshaped receptor molecules, base... more The conformational behavior and binding properties of various clipshaped receptor molecules, based on the building block diphenylglycoluril, were studied by NMR, X-ray analysis, and computational techniques. The conformation and the binding properties of these clips are dependent on the number and type of side walls. Host molecules with two naphthalene side walls and with methoxy groups at the 2-and 7-position are able to bind aromatic guests and silver ions by an inducedfit mechanism.

Chemical Communications, 1998

Chemical Communications, 2006

Single-enzyme studies suggest that dynamic disorder is a general characteristic of enzyme catalysis.

ChemBioChem, 2010

A mild, fast and flexible method for photoimmobilization of biomolecules based on the light-initi... more A mild, fast and flexible method for photoimmobilization of biomolecules based on the light-initiated thiol-ene reaction has been developed. After investigation and optimization of various surface materials, surface chemistries and reaction parameters, microstructures and microarrays of biotin, oligonucleotides, peptides, and MUC1 tandem repeat glycopeptides were prepared with this photoimmobilization method. Furthermore, MUC1 tandem repeat glycopeptide microarrays were successfully used to probe antibodies in mouse serum obtained from vaccinated mice. Dimensions of biomolecule microstructures were shown to be freely controllable through photolithographic techniques, and features down to 5 microm in size covering an area of up to 75x25 mm were created. Use of a confocal laser microscope with a UV laser as UV-light source enabled further reduction of biotin feature size opening access to nanostructured biochips.

Annual Review of Analytical Chemistry, 2010

The potential of single-enzyme studies to unravel the complex energy landscape of these polymeric... more The potential of single-enzyme studies to unravel the complex energy landscape of these polymeric catalysts is the next critical step in enzymology. From its inception in Rotman's emulsion experiments in the 1960s, the field of single-molecule enzymology has now advanced into the time-resolved age. Technological advances have enabled individual enzymatic turnover reactions to be observed with a millisecond time resolution. A number of initial studies have revealed the underlying static and dynamic disorder in the catalytic rates originating from conformational fluctuations. Although these experiments are still in their infancy, they may be able to relate the topography of the energy landscape to the biological function and regulation of enzymes. This review summarizes some of the experimental techniques and data-analysis methods that have been used to study individual enzyme molecules in search of a deeper understanding of their kinetics.

Angewandte Chemie International Edition, 2008

The immobilization of proteins on solid substrates while controlling the size and dimensions of t... more The immobilization of proteins on solid substrates while controlling the size and dimensions of the generated patterns is increasingly relevant in biotechnology. Site-specific immobilization and thus control over the orientation of proteins is particularly important because, as opposed to nonspecific adsorption, it generates homogeneous surface coverage and accessibility to the active site of the protein. Consequently, different types of bioorthogonal reactions have been developed to attach proteins site-specifically to surfaces and to control protein patterning. Herein, we report the photochemical coupling of olefins to thiols to generate a stable thioether bond for the covalent surface patterning of proteins and small molecules. This reaction has been applied previously in solution for carbohydrate and peptide coupling. [6] The thiol-ene photoreaction proceeds at close to visible wavelengths (l = 365-405 nm) and in buffered aqueous solutions. As a result of its specificity for olefins, this photoreaction can be considered to be bioorthogonal, unlike other photochemical methods used previously for protein immobilization. To adopt the thiol-ene reaction for the immobilization of biomolecules, surfaces functionalized with thiols and biomolecules derivatized with olefins were prepared ( ). Polyamidoamine (PAMAM) dendrimers were attached covalently to silicon oxide surfaces. An aminocaproic acid spacer was attached to the dendrimers to create distance from the surface. Cystamine was coupled to the spacer, and subsequent reduction of the disulfide yielded the desired thiolterminated surfaces. A liquid layer of terminal-olefinfunctionalized molecules dissolved in ethylene glycol was spread onto these wafers, which were then covered immediately with a photomask. Subsequent irradiation of the surfaces through the photomask led to patterning with adducts of covalently attached thioethers.

Angewandte Chemie International Edition, 2001

Angewandte Chemie International Edition, 2006

Advanced Materials, 2005

Electrodes for room-temperature and high-temperature electricalproperty measurements were fabrica... more Electrodes for room-temperature and high-temperature electricalproperty measurements were fabricated with fired-on silver paste (Johnson Matthey, E1100) and palladium paste (Gwent Electronic Materials Ltd., C2011004D5), respectively. Samples for piezoelectric measurements were poled in silicone oil at 200 C under various direct-current (DC) electric fields (15±20 kV mm ±1 ). The piezoelectric constant d 33 was measured using a quasi-static d 33 meter (CAS, ZJ-3B). The ferroelectric polarization±electric field (P±E) hysteresis loops were measured by a ferroelectric hysteresis measurement tester (NPL, UK). The temperature dependence of dielectric constant and loss were measured at 1 MHz using an Agilent 4284A LCR meter connected to a furnace. Thermal-depoling experiments were conducted by holding the poled samples with Pt electrodes for 2 h at various high temperatures, cooling to room temperature, measuring d 33 , and repeating the procedure up to 950 C.

physica status solidi (b), 2013

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