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3-Bromopyruvic acid (3BP) is a potential anticancer drug, the action of which on cellular metabolism is not yet entirely clear. The presence of a bromine atom suggests that it is also reactive towards low-energy electrons, which are produced in large quantities during tumour radiation therapy. Detailed knowledge of the interaction of 3BP with secondary electrons is a prerequisite to gain a complete picture of the effects of 3BP in different forms of cancer therapy. Herein, dissociative electron attachment (DEA) to 3BP in the gas phase has been studied both experimentally by using a crossed-beam setup and theoretically through scattering and quantum chemical calculations. These results are complemented by a vacuum ultraviolet absorption spectrum. The main fragmentation channel is the formation of Br- close to 0 eV and within several resonant features at 1.9 and 3-8 eV. At low electron energies, Br- formation proceeds through sigma* and pi* shape resonances, and at higher energies through core-excited resonances. It is found that the electron-capture cross-section is clearly increased compared with that of non-brominated pyruvic acid, but, at the same time, fragmentation reactions through DEA are significantly altered as well. The 3BP transient negative ion is subject to a lower number of fragmentation reactions than those of pyruvic acid, which indicates that 3BP could indeed act by modifying the electron-transport chains within oxidative phosphorylation. It could also act as a radio-sensitiser.
DNA is effectively damaged by radiation, which can on the one hand lead to cancer and is on the other hand directly exploited in the treatment of tumor tissue. DNA strand breaks are already induced by photons having an energy below the ionization energy of DNA. At high photon energies, most of the DNA strand breaks are induced by low-energy secondary electrons. In the present study we quantified photon and electron induced DNA strand breaks in four different 12mer oligonucleotides. They are irradiated directly with 8.44 eV vacuum ultraviolet (VUV) photons and 8.8 eV low energy electrons (LEE). By using Si instead of VUV transparent CaF2 as a substrate the VUV exposure leads to an additional release of LEEs, which have a maximum energy of 3.6 eV and can significantly enhance strand break cross sections. Atomic force microscopy is used to visualize strand breaks on DNA origami platforms and to determine absolute values for the strand break cross sections. Upon irradiation with 8.44 eV photons all the investigated sequences show very similar strand break cross sections in the range of 1.7-2.3x10(-16) cm(2). The strand break cross sections for LEE irradiation at 8.8 eV are one to two orders of magnitude larger than the ones for VUV photons, and a slight sequence dependence is observed. The sequence dependence is even more pronounced for LEEs with energies <3.6 eV. The present results help to assess DNA damage by photons and electrons close to the ionization threshold.
We studied morphological changes in a quasi-two-dimensional Langmuir film of low molar mass poly(L-lactide) upon increasing the surface density, starting from randomly distributed molecules to a homogeneous monolayer of closely packed molecules, followed by nucleation and growth of mesoscopic, three-dimensional clusters from an overcompressed monolayer. The corresponding nucleation density of mesoscopic clusters within the monolayer can be tailored through variation of the rate of compression. For a given surface density and temperature, the nucleation probability was found to increase linearly with the rate of compression, allowing to adjust the density of mesoscopic clusters over nearly 2 orders magnitude.
Cystine was used as a platform chemical to prepare cyclic and acyclic monomers for entropy-driven ringopening polymerization (ED-ROMP) via olefin or disulfide metathesis and for step-growth polymerization. The olefin ED-ROMP of an olefin/disulfide containing 16-atom macrocycle using the 3rd generation Grubbs catalyst was examined in greater detail. Kinetic studies revealed that the catalyst turned inactive during the polymerization, which limited the achievable (apparent) polymer molar mass to similar to 70 kg mol(-1). Such limitation could be overcome with the disulfide ED-ROMP of the same macrocycle to yield polymers with molar masses of up to 180 kg mol(-1). The step-growth polymerizations of acyclic diene and dithiol monomers via olefin metathesis or oxidation were far less effective and yielded just low molar mass polymers or oligomers; photopolymerization of a thiol-ene monomer produced a polyester with a molar mass of 35 kg mol(-1).
A series of phenolic-acid-based 2-oxazoline monomers with methoxy-substituted phenyl and cinnamyl side chains is synthesized and polymerized in a microwave reactor at 140 °C using methyl tosylate as the initiator. The obtained poly(2-oxazoline)s are characterized by NMR spectroscopy, MALDI-TOF mass spectrometry, and size-exclusion chromatography (SEC). Kinetic studies reveal that the microwave-assisted polymerization is fast and completed within less than ≈10 min for low monomer-to-initiator ratios of ≤25. Polymers with number-average molar masses of up to 6500 g mol−1 and low dispersity (1.2–1.3) are produced. The aryl methyl ethers are successfully cleaved with aluminum triiodide/N,N′-diisopropylcarbodiimide to give a poly(2-oxazoline) with pendent catechol groups.
Radiation therapy is a basic part of cancer treatment. To increase the DNA damage in carcinogenic cells and preserve healthy tissue at the same time, radiosensitizing molecules such as halogenated nucleobase analogs can be incorporated into the DNA during the cell reproduction cycle. In the present study 8.44 eV photon irradiation induced single strand breaks (SSB) in DNA sequences modified with the radiosensitizer 5-bromouracil (U-5Br) and 8-bromoadenine ((8Br)A) are investigated. U-5Br was incorporated in the 13mer oligonucleotide flanked by different nucleobases. It was demonstrated that the highest SSB cross sections were reached, when cytosine and thymine were adjacent to U-5Br, whereas guanine as a neighboring nucleobase decreases the activity of U-5Br indicating that competing reaction mechanisms are active. This was further investigated with respect to the distance of guanine to U-5Br separated by an increasing number of adenine nucleotides. It was observed that the SSB cross sections were decreasing with an increasing number of adenine spacers between guanine and U-5Br until the SSB cross sections almost reached the level of a non-modified DNA sequence, which demonstrates the high sequence dependence of the sensitizing effect of U-5Br. (8Br)A was incorporated in a 13mer oligonucleotide as well and the strand breaks were quantified upon 8.44 eV photon irradiation in direct comparison to a non-modified DNA sequence of the same composition. No clear enhancement of the SSB yield of the modified in comparison to the non-modified DNA sequence could be observed. Additionally, secondary electrons with a maximum energy of 3.6 eV were generated when using Si as a substrate giving rise to further DNA damage. A clear enhancement in the SSB yield can be ascertained, but to the same degree for both the non-modified DNA sequence and the DNA sequence modified with (8Br)A.
A one-step moderate energy vibrational emulsification method was successfully employed to produce thermo-responsive olive/silicone-based Janus emulsions stabilized by poly(N,N-diethylacrylamide) carrying 0.7 mol% oleoyl side chains. Completely engulfed emulsion droplets remained stable at room temperature and could be destabilized on demand upon heating to the transition temperature of the polymeric stabilizer. Time-dependent light micrographs demonstrate the temperature-induced breakdown of the Janus droplets, which opens new aspects of application, for instance in biocatalysis.
Hydroxyl terminated oligo(epsilon-caprolactone) (OCL) monolayers were reversibly cross-linked forming two dimensional networks (2D) at the air-water interface. The equilibrium reaction with glyoxal as the cross-linker is pH-sensitive. Pronounced contraction in the area of the prepared 2DOCL films in dependence of surface pressure and time revealed the process of the reaction. Cross-linking inhibited crystallization and retarded enzymatic degradation of the OCLfilm. Altering the subphase pH led to a cleavage of the covalent acetal cross-links. The reversibility of the covalent acetal cross-links was proved by observing an identical isotherm as non-cross-linked sample. Besides as model systems, these customizable reversible OCL2D networks are intended for use as pHresponsive drug delivery systems or functionalized cell culture substrates.
Sequentially coupling two material functions requires matching the output from the first with the input of the second function. Here, magnetic heating controls thermal actuation of a hybrid composite in a challenging system environment causing an elevated level of heat loss. The concept is a hierarchical design consisting of an inner actuator of nanocomposite material, which can be remotely heated by exposure to an alternating magnetic field (AMF) and outer layers of a porous composite system with a closed pore morphology. These porous layers act as heat insulators and as barriers to the surrounding water. By exposure to the AMF, a local bulk temperature of 71 degrees C enables the magnetic actuation of the device, while the temperature of the surrounding water is kept below 50 degrees C. Interestingly, the heat loss during magnetic heating leads to an increase of the water phase (small volume) temperature. The temperature increase is able to sequentially trigger an adjacent thermal actuator attached to the actuator composite. In this way it could be demonstrated how the AMF is able to initiate two kinds of independent actuations, which might be interesting for robotics operating in aqueous environments.
Chemoresponsive polymers are of technological significance for smart sensors or systems capable of molecular recognition. An important key requirement for these applications is the material’s structural integrity after stimulation. We explored whether covalently cross-linked metal ion–phosphine coordination polymers (MPN) can be shaped into any temporary shape and are capable of recovering from this upon chemoresponsive exposure to triphenylphosphine (Ph3P) ligands, whereas the MPN provide structural integrity. Depending on the metal-ion concentration used during synthesis of the MPN, the degree of swelling of the coordination polymer networks could be adjusted. Once the MPN was immersed into Ph3P solution, the reversible ligand-exchange reaction between the metal ions and the free Ph3P in solution causes a decrease of the coordination cross-link density in MPN again. The Ph3P-treated MPN was able to maintain its original shape, indicating a certain stability of shape even after stimulation. In this way, chemoresponsive control of the elastic properties (increase in volume and decrease of mechanical strength) of the MPN was demonstrated. This remarkable behavior motivated us to explore whether the MPN are capable of a chemoresponsive shape-memory effect. In initial experiments, shape fixity of around 60% and shape recovery of almost 90% were achieved when the MPN was exposed to Ph3P in case of rhodium. Potential applications for chemoresponsive shape-memory systems could be shapable semiconductors, e.g., for lighting or catalysts, which provide catalytic activity on demand.