Complementary and Self-Complementary Hydrogen Bond Double Helical Complexes

The design of artificial or synthetic strands that self-assemble to form double-helical complexes have been of great interest to chemists and researchers since the discovery of the double helical DNA structure in 1953 by Watson and Crick. Most of the complexes were self-complementary double-helical homodimers and while few heterodimer complexes are also known. The present thesis describes the design, synthesis and characterization of complementary and self-complementary hydrogen bond arrays built from heterocycles such as pyridine, thiazine dioxide and indole connected in different sequences. The sequence-based stabilities, insolubility issues, substitution and preorganization effects in these arrays have been studied in detail. The design and syntheses of four self-complementary oligomers that contain an underlying AADD hydrogen bond Donor/Acceptor sequence are presented and their self-association examined in the solution and solid states. Substitution with electron donating and withdrawing groups and the influence of preorganization had a large effect on the overall stabilities of the complexes studied. A wide range (\u3e105 M-1) of stabilities were demonstrated and in the most extreme case, the dimerization constant measured (Kdimer ≥ 4.5 x 107 M-1) is comparable to the most stable homodimers of neutral coplanar AADD arrays reported to date. Two sets of DDD hydrogen bond arrays were synthesized that form triply hydrogen bonded double helical complexes with an AAA array when combined in CDCl3 solution. In contrast to the detrimental effect of appended alkyl chain arrays containing tethers between donor heterocycles displayed an increased stability in their association constants (Ka). The effect of introduction of a hexyl chain on the solubility of an originally insoluble (in CDCl3) DDD array based on three thiazine dioxides was studied. The association constants measured based on NMR titrations and ITC titrations demonstrate formation of a highly stable double-helical pair with a Ka valueof 1.4 x 105 M-1. A self-complementary double helical complex based on six hydrogen bond AAADDD array was also synthesized and displays very strong dimerization (Kdimer \u3e 4.5 x 107 M-1 in CDCl3) examined by NMR dilution and mixed solvent studies. These findings establish the high potential of the DDD array and the AAADDD array as monomer components to build supramolecular architectures or polymers

2,6-Diamino­pyridinium tetra­phenyl­borate–1,2-bis­(5,7-dimethyl-1,8-naphthyridin-2-yl)diazene (1/1)

In the title compound, C5H8N3 +·C24H20B−·C20H18N6, the 1,2-bis­(5,7-dimethyl-1,8-naphthyridin-2-yl)diazene mol­ecule is essentially planar (r.m.s. deviation = 0.0045 Å) and aligned in nearly coplanar manner with the 2,6-diamino­pyridinium ion, making a dihedral angle of 5.19 (5)°. The diamino­pyridine mol­ecule is protonated on the central pyridine N atom and the B atom bears the counter-charge. The amine groups of the diamino pyridinium cation form intra­molecular N—H⋯N hydrogen bonds, resulting in linear and bent inter­actions with the naphthyridine ring system

Supercritical fluid rectification of lignin pyrolysis oil methyl ether (LOME) and its use as a bio-derived aprotic solvent

Lignin can be converted by pyrolysis, supercritical rectification, and methylation, into an aromatic bio-derived solvent.</p

A rare case of dual emission in a neutral heteroleptic iridium(III) complex

Herein we describe the synthesis and characterization of a neutral heteroleptic iridium complex bearing an unusual 2-pyridyl-6-methylthiazine dioxide ligand (pythdo). X-ray crystallographic analysis reveals that in the complex, the pythdo ligand is twisted and puckered, resulting in very low photoluminescent quantum efficiency. The emission profile is structured. Excited state lifetime measurements along with oxygen quenching studies point to a rare case of dual emission from different excited states whereby the high energy bands possess significant ligand-centered ((LC)-L-3) character while the lower energy bands are predominantly characterized as a mixture of charge transfer ((CT)-C-3) states. A detailed computational analysis corroborates the unusual photophysical behavior.</p

1,2,3-Triazolium-Based Poly(ionic liquid)s with Enhanced Ion Conducting Properties Obtained through a Click Chemistry Polyaddition Strategy

1,2,3-Triazolium-based poly­(ionic liquid)­s containing a triethylene glycol spacer were synthesized from the polyaddition of an α-azide-ω-alkyne monomer by copper-catalyzed azide–alkyne cycloaddition (CuAAC) followed by quaternization reactions with alkyl halides and subsequent anion exchanges with different fluorinated salts. A detailed structure–property relationship for solubility, thermal stability, and ionic conductivity was investigated by means of ¹H NMR spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and broadband dielectric spectroscopy (BDS). One of these poly­(ionic liquid)­s with a methyl substituent and bis­(trifluoromethylsulfonyl)­imide anion exhibits an ionic conductivity of 2 × 10^–5 S cm^–1 at 30 °C, which is on par with the best PILs with side-chain charge carriers reported so far and is much higher than any previously reported ionenes. The straightforward synthesis along with the broad structural design and enhanced properties of this new class of poly­(ionic liquid)­s offer both fundamental and applicative perspectives

Enhancing Properties of Anionic Poly(ionic liquid)s with 1,2,3-Triazolium Counter Cations

A series of anionic poly­(ionic liquid)­s with 1,2,3-triazolium counter cations are prepared by cation exchange between tailormade 1,3,4-trialkylated-1,2,3-triazolium iodides and a polystyrene derivative having pendant potassium bis­(trifluoromethylsulfonyl)­imide groups. The physical and ion-conducting properties of the resulting materials are compared to the parent potassium-containing polyelectrolyte based on ¹H NMR, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and broadband dielectric spectroscopy (BDS) measurements. Substitution of the potassium counter cation by 1,2,3-triazolium charge carriers affords polyelectrolytes with improved processability (broader solubility and removal of the crystalline behavior) as well as a substantial increase in anhydrous ionic conductivity