An Approach to Paracyclophane-Based Tetrathiafulvalenes: Synthesis and Characterization of a Pseudo-Geminal [2.2]Paracyclophane 1,3-Dithia-2-Thione

The synthesis of paracyclophane-based tetrathiafulvalene precursors is described in the context of the importance of these compounds in the field of material chemistry. Pseudo-geminal bis(1,3-dithia-2-thione) was synthesized via the corresponding 1,3-dithiol-2-ylium salt. The latter was obtained by a synthetic procedure that involves 4,15-bis(acetyl)[2.2]paracyclophane, a new compound of interest for many researchers.     

Photo-crosslink analysis in nonribosomal peptide synthetases reveals aberrant gel migration of branched crosslink isomers and spatial proximity between non-neighboring domains

Nonribosomal peptide synthetases (NRPSs) are large, multi-modular enzyme templates for the biosynthesis of important peptide natural products. Modules are composed of a set of semi-autonomous domains that facilitate the individual reaction steps. Only little is known about the existence and relevance of a higher-order architecture in these mega-enzymes, for which contacts between non-neighboring domains in three-dimensional space would be characteristic. Similarly poorly understood is the structure of communication-mediating (COM) domains that facilitate NRPS subunit docking at the boundaries between epimerization and condensation domains. We investigated a COM domain pair in a minimal two module NRPS using genetically encoded photo-crosslinking moieties in the N-terminal acceptor COM domain. Crosslinks into the C-terminal donor COM domain of the partner module resulted in protein products with the expected migration behavior on SDS-PAGE gels corresponding to the added molecular weight of the proteins. Additionally, an unexpected apparent high-molecular weight crosslink product was revealed by mass spectrometric analysis to represent a T-form isomer with branched connectivity of the two polypeptide chains. Synthesis of the linear L-form and branched T-form isomers by click chemistry confirmed this designation. Our data revealed a surprising spatial proximity between the acceptor COM domain and the functionally unrelated small subdomain of the preceding adenylation domain. These findings provide an insight into three-dimensional domain arrangements in NRPSs in solution and suggest the described photo-crosslinking approach as a promising tool for the systematic investigation of their higher-order architecture.

Photo-crosslink analysis reveals unexpected insights into the higher-order architecture of NRPS and the nature of crosslink isomers.     

Aryl Triflates in On-Surface Chemistry

The reactivity of aryl triflates in on-surface C−C coupling is reported. It is shown that the triflate group in aryl triflates enables regioselective homo coupling with preceding or concomitant hydrodetriflation on Cu(111). Three different symmetrical π-systems with two and three triflate functionalities were used as monomers leading to oligomeric conjugated π-systems. The cascade, comprising different intermediates at different reaction temperatures as observed for one of the molecules, proceeds via initial removal of the trifluoromethyl sulfonyl group to give an aryloxy radical which in turn is deoxygenated to the corresponding aryl radical. Thermodynamically driven regioselective 1,2-hydrogen atom transfer leads to a translocated aryl radical which in turn undergoes coupling. For a sterically more hindered bistriflate, where one ortho position was blocked, dehydrogenative coupling occurred at remote position with good regioselectivity. Starting materials, intermediates as well as products were analyzed by scanning tunneling microscopy. Structures and suggested mechanism were further supported by DFT calculations.     

Blocking the Hype-Hypocrisy-Falsification-Fakery Pathway is Needed to Safeguard Science

In chemistry and other sciences, hype has become commonplace, compounded by the hypocrisy of those who tolerate or encourage it while disapproving of the consequences. This reduces the credibility and trust upon which all science depends for support. Hype and hypocrisy are but first steps down a slippery slope towards falsification of results and dissemination of fake science. Systemic drivers in the contemporary structure of the science establishment encourage exaggeration and may lure the individual into further steps along the hype-hypocrisy-falsification-fakery continuum. Collective, concerted intervention is required to effectively discourage entry to this dangerous pathway and to restore and protect the probity and reputation of the science system. Chemists must play and active role in this effort.     

Location-domination in line graphs

A set $D$ of vertices of a graph $G$ is locating if every two distinct vertices outside $D$ have distinct neighbors in $D$; that is, for distinct vertices $u$ and $v$ outside $D$, $N\left(u\right)\cap D\ne N\left(v\right)\cap D$, where $N\left(u\right)$ denotes the open neighborhood of $u$. If $D$ is also a dominating set (total dominating set), it is called a locating-dominating set (respectively, locating-total dominating set) of $G$. A graph $G$ is twin-free if every two distinct vertices of $G$ have distinct open and closed neighborhoods. It is conjectured (Garijo et al., 2014 [15]) and (Foucaud and Henning, 2016 [12]) respectively, that any twin-free graph $G$ without isolated vertices has a locating-dominating set of size at most one-half its order and a locating-total dominating set of size at most two-thirds its order. In this paper, we prove these two conjectures for the class of line graphs. Both bounds are tight for this class, in the sense that there are infinitely many connected line graphs for which equality holds in the bounds.     

On martingale tail sums for the path length in random trees

For a martingale (X_n) converging almost surely to a random variable X, the sequence (X_n– X) is called martingale tail sum. Recently, Neininger (Random Structures Algorithms 46 (2015), 346–361) proved a central limit theorem for the martingale tail sum of Régnier's martingale for the path length in random binary search trees. Grübel and Kabluchko (in press) gave an alternative proof also conjecturing a corresponding law of the iterated logarithm. We prove the central limit theorem with convergence of higher moments and the law of the iterated logarithm for a family of trees containing binary search trees, recursive trees and plane‐oriented recursive trees. © 2016 Wiley Periodicals, Inc. Random Struct. Alg., 50, 493–508, 2017     

General Coorbit Space Theory for Quasi-Banach Spaces and Inhomogeneous Function Spaces with Variable Smoothness and Integrability

In this paper we propose a general coorbit space theory suitable to define coorbits of quasi-Banach spaces using an abstract continuous frame, indexed by a locally compact Hausdorff space, and an associated generalized voice transform. The proposed theory realizes a further step in the development of a universal abstract theory towards various function spaces and their atomic decompositions which has been initiated by Feichtinger and Gröchenig in the late 1980s. We combine the recent approaches in Rauhut and Ullrich (J Funct Anal 260(11):3299–3362, 2011) and Rauhut (Stud Math 180(3):237–253, 2007) to identify, in particular, various inhomogeneous (quasi-Banach) spaces of Besov–Lizorkin–Triebel type. To prove the potential of our new theory we apply it to spaces with variable smoothness and integrability which have attracted significant interest in the last 10 years. From the abstract discretization machinery we obtain atomic decompositions as well as wavelet frame isomorphisms for these spaces.