Troger's base molecular scaffolds in dicarboxylic acid recognition

N-(6-Bromo-meth-yl-2-pyrid-yl)acetamide

The title acetamide compound, C₈H₉BrN₂O, crystallizes with three crystallographically independent mol­ecules (A, B and C) in the asymmetric unit. In mol­ecule A, the mean plane through the acetamide unit is inclined at a dihedral angle of 4.40 (11)° with respect to the pyridine ring [10.31 (12) and 2.27 (11)°, respectively, for mol­ecules B and C]. In the crystal structure, mol­ecules are inter­connected into sheets parallel to the ac plane by N—H⋯O, C—H⋯Br, C—H⋯O and C—H⋯N hydrogen bonds. The structure is further stabilized by weak inter­molecular C—H⋯π inter­actions.

TD-DFT study on the sensing mechanism of a fluorescent chemosensor for fluoride: excited-state proton transfer

An excited-state proton transfer (ESPT) process, induced by both intermolecular and intramolecular hydrogen-bonding interactions, is proposed to account for the fluorescence sensing mechanism of a fluoride chemosensor, phenyl-1H-anthra(1,2-d)imidazole-6,11-dione. The time-dependent density functional theory (TD-DFT) method has been applied to investigate the different electronic states. The present theoretical study of this chemosensor, as well as its anion and fluoride complex, has been conducted with a view to monitoring its structural and photophysical properties. The proton of the chemosensor can shift to fluoride in the ground state but transfers from the proton donor (NH group) to a proton acceptor (neighboring carbonyl group) in the first singlet excited state. This may explain the observed red shifts in the fluorescence spectra in the relevant fluorescent sensing mechanism.

N-[6-(Dibromo-meth-yl)-2-pyrid-yl]-2,2-dimethyl-propionamide

In the mol­ecular structure of the title compound, C₁₁H₁₄Br₂N₂O, the dimethyl­propionamide substituent is twisted slightly with respect to the pyridine ring, the inter­planar angle being 12.3 (2)°. The dibromo­methyl group is orientated in such a way that the two Br atoms are tilted away from the pyridine ring. In the crystal structure, mol­ecules are associated into supra­molecular chains by weak C—H⋯O inter­actions. The crystal is further stabilized by weak N—H⋯Br and C—H⋯N inter­actions.

3,5-Dichloro-6-methylpyridin-2-amine

In the title compound, C₆H₆Cl₂N₂, intra­molecular N–H⋯Cl and C—H⋯Cl contacts generate five-membered rings, producing S(5) ring motifs. Pairs of inter­molecular N—H⋯N hydrogen bonds link neighbouring mol­ecules into dimers with R²₂(8) ring motifs. In the crystal structure, these dimers are connected by N—H⋯Cl inter­actions and are packed into columns.

Quinoline based receptor in fluorometric discrimination of carboxylic acids

Quinoline and naphthalene-based fluororeceptors 1 and 2 have been designed and synthesized for detection of hydroxy carboxylic acids in less polar solvents. The receptor 1 shows monomer emission quenching followed by excimer emission upon hydrogen bond-mediated complexation of carboxylic acids. The excimer emission distinguishes aromatic dicarboxylic acids from aliphatic dicarboxylic acids and even long chain aliphatic dicarboxylic acids from short chain aliphatic dicarboxylic acids. The receptor 1 is found to be selective for citric acid with a strong excimer emission in CHCl₃. On the contrary, the receptor 2 exhibited less binding constant value and did not form any excimer upon complexation with the same acids under similar conditions. This established the role of quinoline ring nitrogen in binding with the acids.

Enantiomeric resolution of N,N'-dimethyldithiodianthranilide through diastereomeric silver(I) complex. Circular dichroism spectra, racemization barrier, and molecular self-assembly

Planar chiral N,N'-dimethyldithiodianthranilide (2b) was resolved to enantiomers through a diasteromeric complex with easily accessible silver(I) (1S)-camphorosulfonate (3). The (-)-2b enantiomer was assigned the R absolute configuration from the X-ray crystal structure of the silver complex. The compound is configurationally stable and its racemization occurs through boat-to-boat ring inversion (DeltaG(double dagger) = 36.5 +/- 0.2 kcal mol(-1) at 438 K). The analysis of the CD spectrum of the title compound showed that the n-pi* Cotton effect sign is determined by the helicity of the skewed thiobenzamide chromophore. The molecules of 2b are unable to achieve efficient crystal packing by themselves and easily form inclusion complexes with toluene or pentafluorophenol.

The Mechanism of Tröger's Base Formation Probed by Electrospray Ionization Mass Spectrometry

Using direct infusion electrospray ionization mass and tandem mass spectrometric experiments [ESI-MS(/MS)], we have performed on-line monitoring of some reactions used to form Tröger's bases. Key intermediates, either as cationic species or as protonated forms of neutral species, have been intercepted and characterized. The role of urotropine as the methylene source in these reactions has also been accessed. Reaction pathways shown by ESI-MS(/MS) have been probed by gas-phase ion/molecule reactions, and an expanded mechanism for Tröger's base formation based on the mass spectrometric data has been elaborated.

α-Amino acid Tröger base derivatives, possible conformationally restricted scaffolds?

The first synthesis of innovative alpha-amino acid conjugates of Tröger base is reported; their potential application as conformationally restricted scaffolds is proposed and has been investigated using high level ab initio calculations.