Endogenous networks and international cooperation

The rise of social network analyses in the social sciences has allowed empirical work to better account for interdependencies among actors and among their actions. However, this work has been, to a large extent, descriptive: it has treated these actions as exogenous and immutable. In many cases these networks describe actions like alliance formation or trade phenomena that are the outcome variables for programs of social scientific research. In this paper, I attempt to account for both interdependencies and the endogenous nature of networks by incorporating formal theory; helping answer the question of how these networks arise by looking at the incentives of actors to form links with each other. I discuss the appropriate solution concept for a network formation game, and present an algorithm for finding the equilibrium of these networks computationally as well as ways to compare the theoretical networks to observed ones in order to evaluate the fit of the theory. I apply these methods to the study of international cooperation a subject where both the interdependencies and purposive nature of actors must be accounted for. The theoretical network is able to reproduce a number of important observed characteristics. Still, there are more factors that must be accounted for if we want to understand how the network of international cooperation is formed

Recent advances in organic synthesis using light-mediated n-heterocyclic carbene catalysis

The combination of photocatalysis with other ground state catalytic systems have attracted much attention recently due to the enormous synthetic potential offered by a dual activation mode. The use of N-heterocyclic carbene (NHC) as organocatalysts emerged as an important synthetic tool. Its ability to harness umpolung reactivity by the formation of the Breslow intermediate has been employed in the synthesis of thousands of biologically important compounds. However, the available coupling partners are relatively restricted, and its combination with other catalytic systems might improve its synthetic versatility. Thus, merging photoredox and N-heterocyclic carbene (NHC) catalysis has emerged recently as a powerful strategy to develop new transformations and give access to a whole new branch of synthetic possibilities. This review compiles the NHC catalyzed methods mediated by light, either in the presence or absence of an external photocatalyst, that have been described so far, and aims to give an accurate overview of the potential of this activation modeL.M. acknowledges the Autonomous Community of Madrid (CAM) for the financial support (PEJD-2019-PRE/AMB-16640 and SI1/PJI/ 2019-00237) and for an “Atracción de Talento Investigador” contract (2017-T2/AMB-5037

A pH‐Triggered Polymer Degradation or Drug Delivery System by Light‐Mediated Cis / Trans Isomerization of o ‐Hydroxy Cinnamates

A new methodology for the pH-triggered degradation of polymers or for the release of drugs under visible light irradiation based on the cyclization of ortho-hydroxy-cinnamates (oHC) to coumarins is described. The key oHC structural motif can be readily incorporated into the rational design of novel photocleavable polymers via click chemistry. This main-chain moiety undergoes a fast photocleavage when irradiated with 455 nm light provided that a suitable base is added. A series of polyethylene glycol-alt-ortho-hydroxy cinnamate (polyethylene glycol (PEG)n-alt-oHC)-based polymers are synthesized and the time-dependent visible-light initiated cleavage of the photoactive monomer and polymer is investigated in solution by a variety of spectroscopic and chromatographic techniques. The photo-degradation behavior of the water-soluble poly(PEG2000-alt-oHC) is investigated within a broad pH range (pH = 2.1–11.8), demonstrating fast degradation at pH 11.8, while the stability of the polymer is greatly enhanced at pH 2.1. Moreover, the neat polymer shows long-term stability under daylight conditions, thus allowing its storage without special precautions. In addition, two water-soluble PEG-based drug-carrier molecules (mPEG2000-oHC-benzhydrol/phenol) are synthesized and used for drug delivery studies, monitoring the process by UV–vis spectroscopy in an ON/OFF intermittent manner

Application concepts for ultrafast laser induced skyrmion creation and annihilation

Magnetic skyrmions can be created and annihilated in ferromagnetic multilayers using single femtosecond infrared laser pulses above a material dependent fluence threshold. From the perspective of applications, optical control of skyrmions offers a route to a faster and, potentially, more energy efficient new class of information technology devices. Here, we investigate laser induced skyrmion generation in two different materials, mapping out the dependence of the process on the applied field and the laser fluence. We observe that sample properties like strength of the Dzyaloshinskii Moriya interaction and pinning do not considerably influence the initial step of optical creation. In contrast, the number of skyrmions created can be directly and robustly controlled via the applied field and the laser fluence. Based on our findings, we propose concepts for applications, such as all optical writing and deletion, an ultrafast skyrmion reshuffling device for probabilistic computing, and a combined optical and spin orbit torque controlled racetrac

Advanced flavin catalysts elaborated with polymers

A variety of biological redox reactions are mediated by flavoenzymes due to the unique redox activity of isoalloxazine ring systems, which are found in flavin cofactors. In the field of synthetic organic chemistry, the term “flavin” is generally used for not only isoalloxazines but also related molecules including their isomers and some analogues, and those having catalytic activity are called flavin catalyst. Flavin catalysts are typically metal-free, and their catalytic activity can be readily accessed using mild terminal oxidants such as H2O2 and O2; therefore, redox reactions with these compounds have great promise as alternatives to reactions with conventional metal catalysts for the sustainable production of important chemicals. We recently became interested in using polymers for the development of flavin catalysts, especially to improve their practicality and advance the field of catalysis. Here, we summarize our recent research on such flavin-polymer collaborations including the development of facile preparation methods for flavin catalysts using polymers, readily reusable polymer-supported flavin catalysts, and flavin-peptide-polymer hybrids that can catalyze the first flavoenzyme-mimetic aerobic oxygenation reactions

Contra-thermodynamic, photocatalytic E→Z isomerization of styrenyl boron species : vectors to facilitate exploration of two-dimensional chemical space

We acknowledge financial support from the WWU Münster, Deutsche Forschungsgemeinschaft (Excellence Cluster EXC 1003), and Fonds der Chemischen Industrie (Fellowship to JBM). JJM was supported by a PEER/PECRE award by WestChem and the Scottish Funding Council.Designing strategies to access stereodefined olefinic organoboron species is an important synthetic challenge. Despite significant advances, there is a striking paucity of routes to Z-α-substituted styrenyl organoborons. Herein, this strategic imbalance is redressed by exploiting the polarity of the C(sp2)−B bond to activate the neighboring π system, thus enabling a mild, traceless photocatalytic isomerization of readily accessible E-α-substituted styrenyl BPins to generate the corresponding Z-isomers with high fidelity. Preliminary validation of this contra-thermodynamic E→Z isomerization is demonstrated in a series of stereoretentive transformations to generate Z-configured trisubstituted alkenes, as well as in a concise synthesis of the anti-tumor agent Combretastatin A4.PostprintPeer reviewe

<i>Contra</i>-thermodynamic, photocatalytic E→Z isomerization of styrenyl boron species:vectors to facilitate exploration of two-dimensional chemical space

Designing strategies to access stereodefined olefinic organoboron species is an important synthetic challenge. Despite significant advances, there is a striking paucity of routes to Z-α-substituted styrenyl organoborons. Herein, this strategic imbalance is redressed by exploiting the polarity of the C(sp2)−B bond to activate the neighboring π system, thus enabling a mild, traceless photocatalytic isomerization of readily accessible E-α-substituted styrenyl BPins to generate the corresponding Z-isomers with high fidelity. Preliminary validation of this contra-thermodynamic E→Z isomerization is demonstrated in a series of stereoretentive transformations to generate Z-configured trisubstituted alkenes, as well as in a concise synthesis of the anti-tumor agent Combretastatin A4