Aryltriazene photopolymer thin films as sacrificial release layers for laser-assisted forward transfer systems: study of photoablative decomposition and transfer behavior

Thin films of a tailor-made photodecomposible aryltriazene polymer were applied in a modified laser-induced forward transfer (LIFT) process as sacrificial release layers. The photopolymer film acts as an intermediate energy-absorbing dynamic release layer (DRL) that decomposes efficiently into small volatile fragments upon UV laser irradiation. A fast-expanding pressure jet is generated which is used to propel an overlying transfer material from the source target onto a receiver. This DRL-assisted laser direct-write process allows the precise deposition of intact material pixels with micrometer resolution and by single laser pulses. Triazene-based photopolymer DRL donor systems were studied to derive optimum conditions for film thickness and laser fluences necessary for a defined transfer process at the emission wavelength of a XeCl excimer laser (308 nm). Photoablation, surface detachment, delamination and transfer behavior of aryltriazene polymer films with a thickness from 25 nm to ∼400 nm were investigated in order to improve the process control parameters for the fabrication of functional thin-film devices of microdeposited heat- and UV-sensitive materials.     

Structure and Biosynthesis of Xenoamicins from Entomopathogenic Xenorhabdus

During the search for novel natural products from entomopathogenic Xenorhabdus doucetiae DSM17909 and X. mauleonii DSM17908 novel peptides named xenoamicins were identified in addition to the already known antibiotics xenocoumacin and xenorhabdin. Xenoamicins are acylated tridecadepsipeptides consisting of mainly hydrophobic amino acids. The main derivative xenoamicin A ( 1 ) was isolated from X. mauleonii DSM17908, and its structure elucidated by detailed 1 D and 2 D NMR experiments. Detailed MS experiments, also in combination with labeling experiments, confirmed the determined structure and allowed structure elucidation of additional derivatives. Moreover, the xenoamicin biosynthesis gene cluster was identified and analyzed in X. doucetiae DSM17909, and its participation in xenoamicin biosynthesis was confirmed by mutagenesis. Advanced Marfey’s analysis of 1 showed that the absolute configuration of the amino acids is in agreement with the predicted stereochemistry deduced from the nonribosomal peptide synthetase XabABCD. Biological testing revealed activity of 1 against Plasmodium falciparum and other neglected tropical diseases but no antibacterial activity.     

Mechanism of Copper(I)‐Catalyzed Allylic Alkylation of Phosphorothioate Esters: Influence of the Leaving Group on α Regioselectivity

The mechanism of Cu^I‐catalyzed allylic alkylation and the influence of the leaving groups (OPiv, SPiv, Cl, SPO(OiPr)₂; Piv: pivavloyl) on the regioselectivity of the reaction have been explored by using density functional theory (DFT). A comprehensive comparison of many possible reaction pathways shows that [(iPr)₂Cu]^? prefers to bind first oxidatively to the double bond of the allylic substrate at the anti position with respect to the leaving group, and this is followed by dissociation of the leaving group. If the leaving group is not taken into account, the reaction then undergoes an isomerization and a reductive elimination process to give the α‐ or γ‐selective product. If OPiv, SPiv, Cl, or SPO(OiPr)₂ groups are present, the optimal route for the formation of both α‐ and γ‐substituted products changes from the stepwise elimination to the direct process, in which the leaving group plays a stabilizing role for the reactant and destabilizes the transition state. The differences to the energy barrier for the α‐ and γ‐substituted products are 2.75 kcal mol^?1 with SPO(OiPr)₂, 2.44 kcal mol^?1 with SPiv, 2.33 kcal mol^?1 with OPiv, and 1.98 kcal mol^?1 with Cl, respectively; these values show that α regioselectivity in the allylic alkylation follows a SPO(OiPr)₂>SPiv>OPiv>Cl trend, which is in satisfactory agreement with the experimental findings. This trend mainly originates in the differences between the attractive electrostatic forces and the repelling steric interactions of the SPO(OiPr)₂, SPiv, OPiv, and Cl groups on the Cu group.     

Iridium‐Catalyzed Regioselective Silylation of Aromatic and Benzylic C?H Bonds Directed by a Secondary Amine

Reported herein is an iridium‐catalyzed, regioselective silylation of the aromatic C H bonds of benzylamines and the benzylic C H bonds of 2,N‐dialkylanilines. In this process, (hydrido)silyl amines, generated in situ by dehydrogenative coupling of benzylamine or aniline with diethylsilane, undergo selective silylation at the C H bond γ to the amino group. The products of this silylation are suitable for subsequent oxidation, halogenation, and cross‐coupling reactions to deliver benzylamine and arylamine derivatives.     

Optical spectroscopic methods for intraoperative diagnosis

Molecular analytical methods are increasingly needed for a quick and reliable analysis of tissue in an operating room to provide more information during operations. In this Trends article, we highlight the current state and the developments of optical spectroscopic methods as intra operative tools. The clinical problem and challenges are illustrated on the example of brain tumor surgery. While fluorescence microscopy is already used, vibrational spectroscopy techniques will complement the standard method for brain tissue diagnostics. New portable instruments are currently available and can be stationed in the operating room for quick evaluation of tissue. The promise and limitations of fluorescence and vibrational spectroscopy as intraoperative tools are surveyed in this report.     

Enhanced in vitro anticancer activity of quercetin mediated by functionalized CdTe QDs

We report in this study the effects of red-emitting CdTe QDs capped with cysteamine(Cys-CdTe) on the in vitro anticancer activity of the well-known flavenoid quercetin(Qu). Various techniques, including the methylthiazolyldiphenyl-tetrazolium bromide assay, the real-time cell electronic sensing system, the optical and fluorescence imaging, and electrochemical methods have been utilized to study the potential interactions of Cys-CdTe QDs with Qu. The observations demonstrate that the safe-dosage Cys-CdTe QDs can greatly improve the drug uptake and enhance the inhibition efficiency of Qu towards the proliferation of cancer cells such as HepG2 cells. This study implies that Cys-CdTe QDs may be used for cancer therapy and that they exert a synergic anticancer effect when bound to drug molecules.     

Switch From Pauli-Lowering to LUMO-Lowering Catalysis in Brønsted Acid-Catalyzed Aza-Diels-Alder Reactions

Brønsted acid-catalyzed inverse-electron demand (IED) aza-Diels-Alder reactions between 2-aza-dienes and ethylene were studied using quantum chemical calculations. The computed activation energy systematically decreases as the basic sites of the diene progressively become protonated. Our activation strain and Kohn-Sham molecular orbital analyses traced the origin of this enhanced reactivity to i) “Pauli-lowering catalysis” for mono-protonated 2-aza-dienes due to the induction of an asynchronous, but still concerted, reaction pathway that reduces the Pauli repulsion between the reactants; and ii) “LUMO-lowering catalysis” for multi-protonated 2-aza-dienes due to their highly stabilized LUMO(s) and more concerted synchronous reaction path that facilitates more efficient orbital overlaps in IED interactions. In all, we illustrate how the novel concept of “Pauli-lowering catalysis” can be overruled by the traditional concept of “LUMO-lowering catalysis” when the degree of LUMO stabilization is extreme as in the case of multi-protonated 2-aza-dienes.