Synthesis and liquid crystalline structures of poly(L-lysine) containing undecanamidobiphenyl units in the side chains

In order to obtain liquid crystalline comb-like poly(L-lysine) bearing biphenylyl mesogenic groups in their side chains, we synthesized the 11-(biphenyl-4-carboxamido)undecanamidoL-lysine (KC10φφ) from L-lysine by a five step procedure and transformed the KC10 φφ into its polymerizable cyclic derivative (the N-carboxyanhydride or NCA derivative) by the action of diphosgene. We homopolymerized the NCA of KC10 φφ to obtain the polymer pKC10 φφ and copolymerized it with the NCA of trifluoroacetyl-L-lysine (Kt) to obtain block copolymers pKt-pKC10 φφ of various compositions. X-ray diffraction studies demonstrated the existence of mesophases for our homopolymers and copolymers, resolved the structure of the mesophases and established the influence of temperature and the composition of the copolymers on the structure of the mesophases. Homopolymers pKC10 φφ exhibit, as a function of temperature, three phases (CrE_d, SmB_d and SmA_d) deriving from the β -pleated sheet structure of polypeptides and proteins. The presence of a pKt block in copolymers pKt-pKC10 φφ transforms the smectic CrE_d structure into a SmA_d structure and, when the content of pKt block increases, into a bidimensional hexagonal structure similar to that of the homopolymers pKt.     

Excitonic Emission in van der Waals Nanotubes of Transition Metal Dichalcogenides

Nanotubes (NTs) of transition metal dichalcogenides (TMDs), were first synthesized more than a quarter of a century ago; nevertheless, many of their optical properties have so far remained basically unknown. Herein, the state of the art in the knowledge of the optical properties of TMD NTs is presented. First, general properties of multilayered crystals are evaluated, and available data on related NTs are analyzed. Then, the technology for the formation and the structural characteristics of NTs are represented, focusing on the structures synthesized by chemical transport reaction. The core of this work is the presentation of the ability of synthesized TMD NTs to emit bright photoluminescence (PL), which has been discovered recently. By means of micro‐PL spectroscopy of individual tubes, we show that excitonic transitions relevant to both direct and indirect band gaps contribute to the emission spectra of the NTs despite having the dozens of monolayers in their walls. The performance of the tubes as efficient optical resonators is highlighted, where confined optical modes strongly affect the emission. Finally, a brief conclusion is presented, along with an outlook of the future studies of this novel radiative member of the NTs family, which have unique potential for different nanophotonics applications.     

Coupled structural and magnetic properties of ferric fluoride nanostructures: Part II,a Monte Carlo–Heisenberg study

We present a numerical study of the magnetic structure of nanostructured iron fluoride, using the Monte Carlo Metropolis simulated annealing technique and a classical Heisenberg Hamiltonian with superexchange angle dependent interactions. The parameters are adjusted on experimental results, and the atomic structure and topology taken from a previous atomistic model of grain boundaries in the same system. We find perfect antiferromagnetic crystalline grains and a disordered magnetic configuration (speromagnetic) at the grain boundary, in agreement with experimental features. Both the lowest magnetic energy and the rate of magnetic frustration are found to be dependent on the relative disorientation of crystalline grains, i.e. on the cationic topology. We conclude on possible extensions of the model.     

Nickel as a Lewis Base in a T‐Shaped Nickel(0) Germylene Complex Incorporating a Flexible Bis(NHC) Ligand

Flexible, chelating bis(NHC) ligand 2 , able to accommodate both cis‐ and trans‐coordination modes, was used to synthesize ( 2 )Ni(η²‐cod), 3 . In reaction with GeCl₂, it produced ( 2 )NiGeCl₂, 4 , featuring a T‐shaped Ni⁰ and a pyramidal Ge center. Complex 4 could also be prepared from [( 2 )GeCl]Cl, 5 , and Ni(cod)₂, in a reaction that formally involved Ni–Ge transmetalation, followed by coordination of the extruded GeCl₂ moiety to Ni. A computational analysis showed that 4 possesses considerable multiconfigurational character and the Ni→Ge bond is formed through σ‐donation from the Ni 4s, 4p, and 3d orbitals to Ge. (NHC)₂Ni(cod) complexes 9 and 10 , as well as (NHC)₂GeCl₂ derivative 11 , incorporating ligands that cannot accommodate a wide bite angle, failed to produce isolable Ni–Ge complexes. The isolation of ( 2 )Ni(η²‐Py), 12 , provides further evidence for the reluctance of the ( 2 )Ni⁰ fragment to act as a σ‐Lewis acid.     

On A Safe and Practical Method for The Preparation of β-Keto Phosphonates1

Acylations of the magnesium enolate derivatives of trimethyl and triethylphosphonoacetates, using a magnesium chloride-triethylamine system, lead to 2-acylphosphonoacetates which are decarbalkoxylated to give β-keto phosphonates.     

A Convenient Preparation of p-Methoxybenzyl Esters

Carboxylic acids are conveniently and efficiently protected as their p-methoxybenzyl esters under very mild conditions using the pre-formed reagent N,N-diisopropyl-O-(4-methoxybenzyl)isourea, and this method allows selective protection of carboxylic acids in the presence of other functionalities such as enolisable ketones and alcohol groups.     

Synthesis and spectroscopic characterisation of (E)-2-(2-(9-(4-(1H-1,2,4-triazol-1-yl)butyl)-9H-carbazol-3-yl)vinyl)-3-ethylbenzo[d]thiazol-3-ium, a new ligand and potential DNA intercalator

Three new compounds based on carbazole planar skeleton were synthesised. Among them there is a new ligand and a potential DNA intercalator which contains a benzothiazolium moiety connected to the carbazole ring by a vinyl bridge. The absorption and emission spectral properties of this new ligand have been studied by spectroscopic methods.     

IN-SITU SYNTHESES OF ALKYLLITHIUM COMPOUNDS UNDER ULTRASONIC IRRADIATION

Abstract

The syntheses of organometallics such as alkyllithium compounds are performed. Furan and thiophene derivatives were prepared. Parameters which influence the yield have been optimized. The more important were the physical states of lithium and its sodium content and the nature of the substrate.