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Abstract Herein is reported the first asymmetric utilization of aryldiazonium cations as a source of electrophilic nitrogen. This is achieved through a chiral anion phase‐transfer pyrroloindolinization reaction that forms C3‐diazenated pyrroloindolines from simple tryptamines and aryldiazonium tetrafluoroborates. The title compounds are obtained in up to 99 % yield and 96 % ee . The air‐ and water‐tolerant reaction allows electronic and steric diversity of the aryldiazonium electrophile and the tryptamine core.
Pendent metals bound to heterocubanes are components of well-known active sites in enzymes that mediate difficult chemical transformations. Investigations into the specific role of these metal ions, sometimes referred to as "danglers", have been hindered by a paucity of rational synthetic routes to appropriate model structures. To generate pendent metal ions bonded to an oxo cubane through a carboxylate bridge, the cubane Co<sub>4</sub>(μ<sub>3</sub>-O)<sub>4</sub>(OAc)<sub>4</sub>(<i>t</i>-Bupy)<sub>4</sub> (OAc = acetate, <i>t</i>-Bupy = 4-<i>tert</i>-butylpyridine) was exposed to various metal acetate complexes. Reaction with Cu(OAc)<sub>2</sub> gave the structurally characterized (by X-ray diffraction) dicopper dangler Cu<sub>2</sub>Co<sub>4</sub>(μ<sub>4</sub>-O)<sub>2</sub>(μ<sub>3</sub>-O)<sub>2</sub>(OAc)<sub>6</sub>(Cl)<sub>2</sub>(<i>t</i>-Bupy)<sub>4</sub>. In contrast, the analogous reaction with Mn(OAc)<sub>2</sub> produced the Mn<sup>IV</sup>-containing cubane cation [MnCo<sub>3</sub>(μ<sub>3</sub>-O)<sub>4</sub>(OAc)<sub>4</sub>(<i>t</i>-Bupy)<sub>4</sub>]<sup>+</sup> by way of a metal-metal exchange that gives Co(OAc)<sub>2</sub> and [Co<sup>III</sup>(μ-OH)(OAc)]<i><sub>n</sub></i> oligomers as byproducts. Additionally, reaction of the formally Co<sup>IV</sup> cubane complex [Co<sub>4</sub>(μ<sub>3</sub>-O)<sub>4</sub>(OAc)<sub>4</sub>(<i>t</i>-Bupy)<sub>4</sub>][PF<sub>6</sub>] with Mn(OAc)<sub>2</sub> gave the corresponding Mn-containing cubane in 80% yield. A mechanistic examination of the related metal-metal exchange reaction between Co<sub>4</sub>(μ<sub>3</sub>-O)<sub>4</sub>(OBz)<sub>4</sub>(py)<sub>4</sub> (OBz = benzoate) and [Mn(acac)<sub>2</sub>(py)<sub>2</sub>][PF<sub>6</sub>] by ultraviolet-visible (UV-vis) spectroscopy provided support for a process involving rate-determining association of the reactants and electron transfer through a μ-oxo bridge in the adduct intermediate. The rates of exchange correlate with the donor strength of the cubane pyridine and benzoate ligand substituents; more electron-donating pyridine ligands accelerate metal-metal exchange, while both electron-donating and -withdrawing benzoate ligands can accelerate exchange. These experiments suggest that the basicity of the cubane oxo ligands promotes metal-metal exchange reactivity. The redox potentials of the Mn and cubane starting materials and isotopic labeling studies suggest an inner-sphere electron-transfer mechanism in a dangler intermediate.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
The rotation of the plane of polarization of light passing through a non-magnetic material is known as natural optical activity or optical gyrotropy. The behavior of this effect in thin chiral conductors is of current interest. For example, the low frequency limit of gyrotropy in chiral 3D crystals, known as the gyrotropic magnetic effect (GME), is controlled by the orbital magnetic moment of electrons, which has been proposed to be relevant to current-induced switching in twisted bilayer graphene. We show that the GME is not limited to bulk materials but also appears for quasi-2d systems with minimal structure incorporated in the third direction. Starting from multi-band Kubo formula, we derive a generic expression for GME current in quasi-2d materials induced by low-frequency light, and provide a Feynman-diagrammatic interpretation. The relations between the 2d finite layered formula and 3d bulk formula are also discussed.
No abstract available.
For the purpose of object recognition, we learn one discriminative classifier based on one prototype, using shape context distances as the feature vector. From multiple prototypes, the outputs of the classifiers are combined using the method called "error correcting output codes". The overall classifier is tested on a benchmark dataset and is shown to outperform existing methods with far fewer prototypes.
Abstract For the past 40 years, liposomal and polymeric delivery vehicles have been studied as systems capable of modulating the cytotoxicity of small molecule chemotherapeutics, increasing tumor bearing animal survival times, and improving drug targeting. Although a number of macromolecular‐drug conjugates have progressed to clinical trials, tuning drug release to maintain efficacy in conjunction with controlling drug toxicity has prevented the clinical adoption of many vehicles. In this article, we review the motivations for and approaches to polymer and liposomal delivery with regard to camptothecin and cisplatin delivery. WIREs Nanomed Nanobiotechnol 2013, 5:130–138. doi: 10.1002/wnan.1209 This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease
We measure cloth properties and create cloth animations from video of actual cloth. This work spans several domains: texture tracking and replacement, 3D shape estimation from a single view, 3D shape from multiple views and data driven cloth animation. In the first part of the thesis, the emphasis is on single view estimation of visual properties and the related problem of texture replacement. We show that screen print cloth has advantageous properties and that simple lighting estimation makes texture replacement and geometry estimation substantially better. In the second part of the thesis, we create cloth animations in a data-driven manner by recording real cloth movement. Our method involves printing custom clothing, capturing video of the clothing from multiple viewpoints and then building models of the cloth motion as frame-by-frame geometry. This problem is difficult because of occlusion: often some portion of the cloth makes it impossible to see other regions of the cloth. To overcome this challenge, we print a multi-colored pattern on the surface of the cloth to simplify identification of the surface and we use a data-driven hole filling technique to sew in observations of missing data from other frames. The resulting data can be used in several applications: we show examples of editing and modifying the data for different animation purposes.
No abstract is provided for this article.
A series of elongated dibenzopentalenes were synthesized via a Pd-catalyzed cyclization followed by an Fe-mediated cyclodehydrogenation. Structural geometries varying from linear to extremely bent are shown to drastically influence solubility properties as well as reduction potentials. Comparisons are made to monopentalenes and related diindenoindacenes. UV-vis absorption spectra and cyclic voltammetry measurements indicate a strong modulation of the electronic structure of these compounds mediated by the strength of interactions between pentalene centers.
