Asymmetric polymerization via cycloaddition reactions

The reaction of N‐phthaloyl‐L ‐leucine acid chloride (1) with isoeugenol (2) was carried out in chloroform, and novel optically active isoeugenol ester derivative 3 as a chiral monomer was obtained in high yield. Compound 3 was characterized by ¹H‐NMR, IR, and mass and elemental analysis and then was used for the preparation of model compound 5 and polymerization reactions. 4‐Phenyl‐1,2,4‐triazoline‐3,5‐dione, PhTD (4), was allowed to react with compound 3. The reaction is very fast and gives only one diastereomer of 5 via Diels–Alder and ene pathways in quantitative yield. In order to explain this diastereoselectivity, a nonconcerted two‐step mechanism involving benzylic cation (BC) and aziridinium (AI) have been proposed for the Diels–Alder and ene reactions, respectively. The polymerization reactions of novel monomer 3 with bis(triazolinedione)s [bis(p‐3,5‐dioxo‐1,2,4‐triazolin‐4‐ylphenyl)methane (8) and 1,6‐bis(3,5‐dioxo‐1,2,4‐triazolin‐4‐yl)hexane] (9)] were performed in N,N‐dimethylacetamide (DMAc) at room temperature. The reactions are exothermic, fast, and gave novel optically active polymers 10 and 11 via repetitive Diels–Alder–ene polyaddition reactions. These polymers have inherent viscosities in a range about 0.18–0.22 dL/g. Some physical properties and structural characterizations of these new polymers have been studied and are reported. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1211–1219, 1999     

Synthesis,Crystal Structure,Spectral and Thermal Studies of (<Emphasis Type="Italic">E</Emphasis>)-4-Dimethamino[(1-phenylethyl)iminomethyl]benzyne

Abstract  

Schiff-base compound (E)-4-dimethamino[(1-phenylethyl)iminomethyl]benzyne was synthesized and characterized by elemental analyses (CHN), FT-IR and ¹H-NMR spectroscopic techniques and thermogravimetric analyses (TG). Crystal structure of the title compound was obtained by single crystal X-ray diffraction. The title compound crystallizes in the monoclinic space group P2₁ with unit cell parameters: a = 8.5283(2), b = 6.0699(2), c = 13.6997(4) Ǻ, β = 91.471(2)°, V = 708.94(4) Ǻ³ and Z = 2.     

DNA implementation for optical waveguide as a switchable transmission line and memristor

In this paper, an optical waveguide has been developed based on the (Deoxyribonucleic acid) DNA core as a multi-slab structure by switching characteristic at 300 THz. We show that how the DNA with various electrical characteristics can be considered as a reconfigurable material which is placed between two optical metal layers. Therefore, we can control the current and voltage density values based on the divergence of the DNA types as an optical switch. Moreover, we can select the Au and Ag for the metal coat. In this research, we demonstrate that the Ag/DNA/Ag and Au/DNA/Ag have better performance in switching qualification than Au/DNA/Au model as a conventional structure. This DNA core waveguide has a switchable feature which cannot be found at any conventional plasmonic waveguide. The FDTD time domain is used for simulating the waveguide and the current density is considered as an ON/OFF switch. We carry out parametric studies for the physical dimensions of the waveguide and illustrate that how we can improve the switching characteristic. Moreover, we have checked the coupling effect between the transmission lines and defined the figure of merit for switching quality. This structure can be considered as an optical memristor and optical “YES” gate which couldn’t be obtained by other graphene waveguide while it became feasible based on DNA switching feature.     

Design and enhanced gene silencing activity of spherical 2′-fluoroarabinose nucleic acids (FANA-SNAs)

Drug delivery vectors for nucleic acid therapeutics (NATs) face significant barriers for translation into the clinic. Spherical nucleic acids (SNAs) – nanoparticles with an exterior shell made up of DNA strands and a hydrophobic interior – have recently shown great potential as vehicles to improve the biodistribution and efficacy of NATs. To date, SNA design has not taken advantage of the powerful chemical modifications available to NATs. Here, we modify SNAs with 2′-deoxy-2′-fluoro-d-arabinonucleic acid (FANA-SNA), and show increased stability, enhanced gene silencing potency and unaided uptake (gymnosis) as compared to free FANA. By varying the spacer region between the nucleic acid strand and the attached hydrophobic polymer, we show that a cleavable DNA based spacer is essential for maximum activity. This design feature will be important when implementing functionalized nucleic acids into nanostructures for gene silencing. The modularity of the FANA-SNA was demonstrated by silencing two different targets. Transfection-free delivery was superior for the modified SNA compared to the free FANA oligonucleotide.

Optimizing FANA modified spherical nucleic acids (FANA-SNAs) for highly efficient delivery of nucleic acid therapeutics.     

Structural Investigation of DHICA Eumelanin Using Density Functional Theory and Classical Molecular Dynamics Simulations

Eumelanin is an important pigment, for example, in skin, hair, eyes, and the inner ear. It is a highly heterogeneous polymer with 5,6-dihydroxyindole-2-carboxylic acid (DHICA) and 5,6-dihydroxyindole (DHI) building blocks, of which DHICA is reported as the more abundant in natural eumelanin. The DHICA-eumelanin protomolecule consists of three building blocks, indole-2-carboxylic acid-5,6-quinone (ICAQ), DHICA and pyrrole-2,3,5-tricarboxylic acid (PTCA). Here, we focus on the self-assembly of DHICA-eumelanin using multi-microsecond molecular dynamics (MD) simulations at various concentrations in aqueous solutions. The molecule was first parameterized using density functional theory (DFT) calculations. Three types of systems were studied: (1) uncharged DHICA-eumelanin, (2) charged DHICA-eumelanin corresponding to physiological pH, and (3) a binary mixture of both of the above protomolecules. In the case of uncharged DHICA-eumelanin, spontaneous aggregation occurred and water molecules were present inside the aggregates. In the systems corresponding to physiological pH, all the carboxyl groups are negatively charged and the DHICA-eumelanin model has a net charge of −4. The effect of K+ ions as counterions was investigated. The results show high probability of binding to the deprotonated oxygens of the carboxylate anions in the PTCA moiety. Furthermore, the K+ counterions increased the solubility of DHICA-eumelanin in its charged form. A possible explanation is that the charged protomolecules favor binding to the K+ ions rather than aggregating and binding to other protomolecules. The binary mixtures show aggregation of uncharged DHICA-eumelanins; unlike the charged systems with no aggregation, a few charged DHICA-eumelanins are present on the surface of the uncharged aggregation, binding to the K+ ions.     

Probing differences in binding of methylbenzylamine enantiomers to chiral cobalt(II) salen complexes

In this work, we investigate the mode of chiral interactions between the asymmetric Co(II) salen complex, (S,S)-N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexane-diamine-Co(II) ([Co(1)]), and single enantiomers of methylbenzylamine (MBA) using different continuous-wave and pulsed electron paramagnetic resonance techniques combined with density functional theory computations. While [Co(1)] displays a large affinity for binding a single MBA molecule, it has a much weaker affinity for binding a second MBA molecule. Subtle differences are detected in the EPR spectra of the homochiral (S,S-[Co(1)](S-MBA)) and heterochiral (S,S-[Co(1)](R-MBA)) adducts using low [Co(1)] : MBA ratios. Moreover at high concentrations of racemic MBA, a strong preference (80%) is observed for the formation of the bis-ligated heterochiral adduct (S,S-[Co(1)](R-MBA)(2)) compared to the homochiral analogue (20% of S,S-[Co(1)](S-MBA)(2)). Differences in the (14)N hyperfine coupling from the diamine backbone in [Co(1)] were also evidenced by hyperfine sublevel correlation (HYSCORE), revealing magnetically equivalent N nuclei for the homochiral adducts and inequivalent N nuclei for the heterochiral adducts. Using DFT, these slight differences were reproduced, and explained based upon the different modes of alignment of the MBA molecule in the adduct. The current findings therefore reveal the appreciable enantiodiscrimination that occurs during the binding of MBA enantiomers to the chiral Co(II) salen complex.     

Palladium(II) Immobilized Onto the Glucose Functionalized Magnetic Nanoparticle as a New and Efficient Catalyst for the One‐pot Synthesis of Benzoxazoles

Palladium(II) have been immobilized into the nano magnetic Fe₃O₄ which was functionalized with glucose in order to achieve a one‐pot synthesis of 2‐substituted benzoxazole derivatives with high yields in the diverse range of organic solvents. The nano catalyst is highly dispersive in polar solvents and can be easily recovered and reused for 6 runs without significant loss of its activity. Finally, the catalyst was fully characterized by FT‐IR, TGA, CHN, SEM, EDX and atomic absorption spectroscopy.     

Mono‐ and dinuclear oxime palladacycles bearing diphosphine ligands: An unusual coordination mode for dppe

Three new oxime‐based palladacycles, namely [Pd{C,N‐C₆H₄{C(Me)?NOH}‐2}(dppm)]ClO₄ ( 1 ), [Pd₂{C,N‐C₆H₄{C(Me)?NOH}‐2}₂(dppe)₂(μ‐dppe)](ClO₄)₂ ( 2 ) and [Pd{C,N‐C₆H₄{C(Me)?NOH}‐2}(dppmS₂)]ClO₄ ( 3 ), were synthesized by the reaction of dinuclear oxime complex [Pd{C,N‐C₆H₄{C(Me)?NOH}‐2}(μ‐Cl)]₂ with different diphosphine ligands (dppm, dppe and dppmS₂). The synthesized complexes were characterized using Fourier transform infrared, ³¹P NMR, ¹H NMR and ¹³C NMR spectroscopic methods and elemental analyses, and their molecular structures were elucidated using X‐ray crystallography. The structure of 2 is worthy of note as it is the first oxime palladacycle where there are both bridging (P–) and chelating (P^P) dppe ligands, giving rise to a dinuclear complex. The palladium atom is in a five‐coordinate, square pyramidal P₃NC environment, while in 3 the palladium atom is in a distorted square planar environment, coordinated by the oxime ligand and a chelating (S^S) dppmS₂ ligand. These complexes were employed as efficient catalysts for the Suzuki–Miyaura cross‐coupling reaction of several aryl bromides with phenylboronic acid. The in vitro cytotoxicity of the compounds was also evaluated against human tumour cell lines (HT29, A549 and HeLa) using the MTT assay method. The results indicate that the dinuclear complex 2 has greater catalytic and anticancer activity in comparison with the mononuclear complexes 1 and 3 .