4-Chloro-2,6-bis(hydroxymethyl)pyridinium Chloride and 4-Dimethylamino-2,6-bis(hydroxymethyl)pyridinium Chloride Hemihydrate

Abstract  Two substituted pyridinium chloride salts, namely 4-chloro-2,6-bis(hydroxymethyl)pyridinium chloride (triclinic, P-1, a = 6.0651(8) ?, b = 8.4393(8) ?, c = 8.6554(9) ?, α = 78.845(1)°, β = 83.156(1)°, γ = 89.047(1)°; V = 431.55(8) ?³; Z = 2) and 4-dimethylamino-2,6-bis(hydroxymethyl)pyridinium chloride hemihydrate (orthorhombic, Aba2, a = 17.2179(14) ?, b = 17.6332(15) ?, c = 7.2068(6) ?; V = 2188.0(3) ?³; Z = 4), have been structurally characterized. Hydrogen bonding and van der Waals contacts are evident in both structures. Furthermore, the 4-dimethylamino derivative features a trigonal planar dimethylamino group with some π interaction between the nitrogen atom and the pyridine ring. Graphical Abstract  Two compounds, namely 4-chloro-2,6-bis(hydroxymethyl)pyridinium chloride and 4-dimethylamino-2,6-bis(hydroxymethyl)pyridinium chloride hemihydrate, have been spectroscopically and structurally characterized.      

Spin-dependent electronic states of the ferromagnetic semimetal EuB6

The spin polarization of EuB6 has been measured by using Andreev reflection spectroscopy. Analyses of the conductance spectra of the EuB6/Pb junctions yield a spin polarization of about 56%. The results demonstrate that the ferromagnetic EuB6 is not half-metallic. Combined with the Hall effect and magnetoresistivity data, the results indicate a semimetallic band structure with a fully spin-polarized hole band and an unpolarized electron band. The values and the spread of the measured spin polarization are quantitatively consistent with the experimentally determined Fermi surface and carrier densities.     

The synthesis of 2-amino-4(3H)-quinazolinones and related heterocycles via a mild electrocyclization of aryl guanidines

A new method for the preparation of 2-amino-4(3H)-quinazolinones and similar fused heterocycles is described. Simply warming a mixture of an aryl guanidine and carbonyl diimidazole in acetonitrile results in formation of a putative N-amidinoisocyanate intermediate which undergoes a 6π-electron electrocyclic reaction with the aryl ring to generate the quinazolinone ring system. The mild conditions are compatible with a variety of functional groups, and the reaction is shown to be successful on multigram scale.     

Ruthenium-Catalyzed C−C Coupling of Terminal Alkynes with Primary Alcohols or Aldehydes: α,β-Acetylenic Ketones (Ynones) via Oxidative Alkynylation

The first metal-catalyzed oxidative alkynylations of primary alcohols or aldehydes to form α,β-acetylenic ketones (ynones) are described. Deuterium labelling studies corroborate a novel reaction mechanism in which alkyne hydroruthenation forms a transient vinylruthenium complex that deprotonates the terminal alkyne to form the active alkynylruthenium nucleophile.     

In situ Observation of Evolving H2 and Solid Electrolyte Interphase Development at Potassium Insertion Materials within Highly Concentrated Aqueous Electrolytes

The solid-electrolyte interphase (SEI) is key to stable, high voltage lithium-ion batteries (LIBs) as a protective barrier that prevents electrolyte decomposition. The SEI is thought to play a similar role in highly concentrated water-in-salt electrolytes (WISEs) for emerging aqueous batteries, but its properties remain unknown. In this work, we utilized advanced scanning electrochemical microscopy (SECM) and operando electrochemical mass spectrometry (OEMS) techniques to gain deeper insight into the SEI that occurs within highly concentrated WISEs. As a model, we focus on a 55 mol/kg K(FSA)_0.6(OTf)_0.4 electrolyte and a 3,4,9,10-perylenetetracarboxylic diimide negative electrode. For the first time, our work showed distinctly passivating structures with slow apparent electron transfer rates alike to the SEI found in LIBs. In situ analyses indicated stable passivating structures when PTCDI was stepped to low potentials (≈−1.3 V vs. Ag/AgCl). However, the observed SEI was discontinuous at the surface and H₂ evolution occurred as the electrode reached more extreme potentials. OEMS measurements further confirmed a shift in the evolution of detectable H₂ from −0.9 V to <−1.4 V vs. Ag/AgCl when changing from dilute to concentrated electrolytes. In all, our work shows a combined approach of traditional battery measurements with in situ analyses for improving characterization of other unknown SEI structures.     

Exploiting an inherent neighboring group effect of alpha-amino acids to synthesize extremely hindered dipeptides

The creation of highly hindered peptides that contain combinations of non-natural N-alkyl amino acids and N-alkyl-alpha,alpha-disubstituted amino acids presents a formidable challenge. Hindered, non-natural amino acids are of interest because they import resistance to proteolysis and unusual conformational properties to peptides that contain them. Toward a solution to this problem, we describe a new approach to creating extremely hindered dipeptides that is operationally simple and uses mild conditions and commercially available amino acids. The approach reduces the need for protecting groups and yields urethane-protected dipeptide acids that can be used as building blocks in the synthesis of larger peptides. We propose that the reaction proceeds through a previously unexploited intramolecular O,N-acyl transfer pathway.     

Direct observation of the preference of hole transfer over electron transfer for radical ion pair recombination in donor-bridge-acceptor molecules

Understanding how the electronic structures of electron donor-bridge-acceptor (D-B-A) molecules influence the lifetimes of radical ion pairs (RPs) photogenerated within them (D+*-B-A-*) is critical to designing and developing molecular systems for solar energy conversion. A general question that often arises is whether the HOMOs or LUMOs of D, B, and A within D+*-B-A-* are primarily involved in charge recombination. We have developed a new series of D-B-A molecules consisting of a 3,5-dimethyl-4-(9-anthracenyl)julolidine (DMJ-An) electron donor linked to a naphthalene-1,8:4,5-bis(dicarboximide) (NI) acceptor via a series of Phn oligomers, where n = 1-4, to give DMJ-An-Phn-NI. The photoexcited charge transfer state of DMJ-An acts as a high-potential photoreductant to rapidly and nearly quantitatively transfer an electron across the Phn bridge to produce a spin-coherent singlet RP 1(DMJ+*-An-Phn-NI-*). Subsequent radical pair intersystem crossing yields 3(DMJ+*-An-Phn-NI-*). Charge recombination within the triplet RP then gives the neutral triplet state. Time-resolved EPR spectroscopy shows directly that charge recombination of the RP initially produces a spin-polarized triplet state, DMJ-An-Phn-3*NI, that can only be produced by hole transfer involving the HOMOs of D, B, and A within the D-B-A system. After the initial formation of DMJ-An-Phn-3*NI, triplet-triplet energy transfer occurs to produce DMJ-3*An-Phn-NI with rate constants that show a distance dependence consistent with those determined for charge separation and recombination.