Enantioselective Organo‐Photocatalysis Mediated by Atropisomeric Thiourea Derivatives

Can photocatalysis be performed without electron or energy transfer? To address this, organo‐photocatalysts that are based on atropisomeric thioureas and display lower excited‐state energies than the reactive substrates have been developed. These photocatalysts were found to be efficient in promoting the [2+2] photocycloaddition of 4‐alkenyl‐substituted coumarins, which led to the corresponding products with high enantioselectivity (77–96 % ee) at low catalyst loading (1–10 mol %). The photocatalytic cycle proceeds by energy sharing via the formation of both static and dynamic complexes (exciplex formation), which is aided by hydrogen bonding.     

Titanocene-catalyzed coupling of aromatic amides in the presence of organosilanes: a novel route to vicinal diamines and a new class of amine-substituted oligomers

The title reaction has been surveyed for a number of substrates with differing substitution patterns. With a few exceptions, the methodology provides a one-pot synthesis of the 1,2-diamines from widely available and inexpensive starting materials, and in high yields. In addition, the coupling of 1,4- and 1,3-bis-(N,N,N',N'-tetraalkyl)arylenediamides is shown, under the same experimental conditions, to yield oligomers: R2NC(O)C6H4CH(NR2)-[CH(NR2)C6H4CH(NR2)]n-CH(NR2)C6H4C(O)-NR2 (R = methyl and ethyl; n = 0 to ca. 5). The chemical structures of these unprecedented oligomers are determined by comparison of NMR and MS spectra to those of vicinal diamines, prepared from the analogous N,N-dialkylbenzamides. The origin of the limitation of oligomer chain length is probably due to a specific effect of the internal benzylic amine group, since the substrate 4-Me2NCH2C6H4C(O)NMe2 was found to be uniquely unreactive compared to the other 4-substituted N,N-dialkylbenzamides investigated. N-Methylphthalimide was briefly studied as a monomer and analysis by MS showed that oligomers are formed. Attempts to fully characterize these polymers were unsuccessful.     

Fabrication of Silver Nanoparticles Decorated on Activated Screen Printed Carbon Electrode and Its Application for Ultrasensitive Detection of Dopamine

In the present study, we report the fabrication of silver nanoparticles (AgNPs) decorated on activated screen printed carbon electrode (ASPCE). The AgNPs were prepared by using Justicia glauca leaf extract as a reducing and stabilizing agent and the ASPCE was prepared by a simple electrochemical activation of screen printed carbon electrode (SPCE). The ASPCE/AgNPs shows a reversible electrochemical behaviour with enhanced response for DA than that of other modified SPCEs. Under optimum conditions, the electrochemical oxidation current response of DA is linear over the concentration range from 0.05 to 45.35 µM. The limit of detection is found as 0.017 µM with a high sensitivity of 7.85 µA µM^?1 cm^?2.     

Synthesis and Crystal Structure of Some Macrocyclic Ring Compounds

A bola-shaped diester–dicarboxylic acid (L1H₂) synthesized with ethanediol spacer and phthalic anhydride head group is demonstrated to form various macrocyclic ring compounds such as M₁, M₂, and M₃. Compound M₁, containing both lactam [-C(=O)-N-H)] and lactone [-C(=O)-O-] functional groups, has a [16]-membered macrocyclic ring, while compound M₂, composed of only lactones [-C(=O)-O-], exists with a [19]-membered macrocyclic ring. Similarly, compound M₃, composed of Cu(II) metal ions, exists with a macrocycle-like [15]-membered chelate ring. In addition to the ¹H NMR spectra, the single crystals obtained for M₁ and M₃ thoroughly established, the formation of the ring structures. This article demonstrates the versatile capability of diester-dicarboxylic acid for forming various types of ring compounds, such as bis-chelate rings in M₃ and lactam cum lactone-type macrocyclic rings in M₁ and M_2.

Material stability investigation of polyamide material before and after laser sintering

Abstract

Polymers are the long chain organic materials that are held together by directional covalent bonds. These kind of organic materials are either synthesized or naturally obtained and they have wide range of application in the medical field due to its physical properties, chemical properties and multifarious processing technique. For the past two decade, these polymers were used to produce variety of medical devices and implants by laser sintering. Since laser based additive manufacturing technique was a thermal process, there may be a change in the material property after sintering and which may affect the usage of the polymer in medical field. This work presented here aims to investigate the material property of biocompatible eos PA12 polymer powder and a laser sintered part. The Scanning Electron Microscope (SEM) with Energy Dispersive Spectroscopy (EDAX), Fourier Transform Infrared Spectroscopy (FT-IR), X-Ray Diffraction (XRD) and Differential Scanning Calorimeter (DSC) analysis were carried out to investigate the properties. The experimental investigation carried out in order to get insight into laser-material interaction and the corresponding results indicated that the laser energy influences the material properties of polyamide powder.     

Spectroscopic Study of Cu(II) Ion Doped in Bis-Glycine Sodium Nitrate

Single-crystal Electron Paramagnetic Resonance (EPR) and optical absorption studies were performed at room temperature on Cu(II)-ion–doped bis-glycine sodium nitrate, a semiorganic nonlinear optical material (NLO). Spin-Hamiltonian parameters, obtained from single-crystal EPR spectra, recorded in three mutually orthogonal planes, revealed the presence of two magnetically inequivalent Cu(II) sites. Molecular orbital parameters were also evaluated. The optical absorption spectrum at room temperature exhibits the lowering of octahedral symmetry to an axially elongated tetragonal of Cu(II) ion in NLO.     

Picking Out Logic Operations in a Naphthalene β-Diketone Derivative by Using Molecular Encapsulation,Controlled Protonation,and DNA Binding

On–off switching and molecular logic in fluorescent molecules are associated with what chemical inputs can do to the structure and dynamics of these molecules. Herein, we report the structure of a naphthalene derivative, the fashion of its binding to β-cyclodextrin and DNA, and the operation of logic possible using protons, cyclodextrin, and DNA as chemical inputs. The compound crystallizes out in a keto-amine form, with intramolecular N−H⋅⋅⋅O bonding. It shows stepwise formation of 1:1 and 1:2 inclusion complexes with β-cyclodextrin. The aminopentenone substituents are encapsulated by β-cyclodextrin, leaving out the naphthalene rings free. The binding constant of the β-cyclodextrin complex is 512 m⁻¹. The pK_a value of the guest molecule is not greatly affected by the complexation. Dual input logic operations, based on various chemical inputs, lead to the possibility of several molecular logic gates, namely NOR, XOR, NAND, and Buffer. Such chemical inputs on the naphthalene derivative are examples of how variable signal outputs based on binding can be derived, which, in turn, are dependent on the size and shape of the molecule.     

Crystal growth,optical, mechanical and electrical properties of organic NLO material γ‐glycine

Single crystals of organic non‐linear optical material, γ‐glycine have been grown by gel method for the first time. The γ‐phase is confirmed by single crystal XRD. The presence of various functional groups of γ‐glycine are confirmed by FTIR. The UV‐Vis‐NIR spectrum reveals the high percentage of transmission of the sample in the entire visible region. The SHG of γ‐glycine is confirmed by Kurtz powder technique. TGA‐DTA studies indicate that the crystal is structurally stable upto 170 °C. Microhardness investigations are conducted on the grown crystals. The dielectric constant measurements are carried out and the nature of variation of dielectric constant ε′ and dielectric loss D in the frequency range of 50 Hz to 5 MHz is studied and reported. Photoconductivity studies of γ‐glycine crystals revealed the negative photoconducting nature. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Bismuth(III) dication trapped on a chlorobismuthate

Abstract

Metal cations observed with tetrachloroaluminate anion provide insights into the structure and stability of reactive cations. Addition of tris(3,5-dimethylpyrazolyl)borate anion (Tp^Me2) to [BiCl₂][AlCl₄] traps a bismuth(III) dication, [Tp^Me2Bi]²⁺, possessing a highly electrophilic bismuth center with short coordinate Bi―N bonds. [Tp^Me2Bi]²⁺ has weak interactions with the chlorides of [Bi₃Cl₁₃]_∞. Strong affinity of [Tp^Me2Bi]²⁺ with the triflate (OTf) observed in [Tp^Me2Bi(OTf)₃]^- demonstrates the high electrophilicity at bismuth.     

Ru- and Fe-based N,N′-bis(2-pyridylmethyl)-N-methyl-(1S,2S)-1,2-cyclohexanediamine complexes immobilised on mesoporous MCM-41: Synthesis, characterization and catalytic applications

Protected mesoporous MCM-41 phases were synthesized by grafting of the ligand, (1S,2S)-N,N′-bis-pyridin-2-ylmethyl-cyclohexane-1,2-diamine (L₂Me), through the reactive 3-chloropropyltrimethoxysilane (3-CPTMS) group and designated as L₂Me-MCM-41. Subsequently, RuCl₃ and Fe(BF₄)₂ or Fe(CF₃SO₃)₂ were added to the heterogenized L₂Me-MCM-41 for complexation and designated as M-L₂Me-MCM-41 (M = Ru and Fe). All samples were characterized in detail using XRD, N₂ sorption isotherm, FT-IR, TGA-DTA, XPS, UV–vis, solid state ¹³C NMR, EPR and elemental analysis, etc. The XRD and sorption measurements of the catalyst confirmed the structural integrity of the mesoporous hosts and the spectroscopic characterization techniques proved the successful anchoring of the metal complexes over the modified mesoporous support. The screening of catalyst M-L₂Me-MCM-41 was done for the oxidation reaction of thioanisole (methyl phenyl sulphide) using H₂O₂ as an oxidant. The Ru-L₂Me-MCM-41 and Fe-L₂Me-MCM-41 catalysts show higher activities and turnover numbers and exhibit enantiomeric excess comparable to the homogeneous catalysts, Ru-L₂(Me)₂ and Fe-L₂(Me)₂. Furthermore, Fe-L₂Me-MCM-41 and Fe-L₂(Me)₂ were also found active in the epoxidation of styrene. These results indicate that metal complexes are confined into the pore of the material which play a major role in the reaction.