Most Efficient Tris(3-Aminopropyl) Amine Based Electron Deficient Tripodal Receptor for Azide.

Investigation on strength of the tris(2-amino ethyl) amine and tris (3-amino propyl) amine backboned tripodal receptors, L and L1 (incorporated with tripodal C3ν frame, thio urea-amide linkage and π-hole assisting functionality) which are premeditated to explore the prospect for a particular anion recognition are studied. UV-Vis, 1H- NMR, and IR spectroscopy studies indicates that both the receptors sensing azide anion, colorimetrically and binds azide anion stronger than any other anions such as acetate, and cyanide. In particular the receptor L1 shows the highest binding strength towards azide anion. To the best of our knowledge this is the first receptor showing highest binding ability with azide anion. We used Molecular Electrostatic Potential Surface analyses to support our spectroscopic findings. The association constant and limits of detection for receptor L1 with azide is found to be 8.4X105M-1 and 3.16X10-6 M respectively. The observed highest binding strength of L1 with azide is, could be due to the cooperative effect of extended traditional hydrogen bonding via thiourea-amide functionality, anion-π interaction and C3ν suitable framework.

Tuning the recognition properties of urea based receptor towards cyanide in aqueous medium: Effect of fluorine substitution on strength and selectivity of the anion receptor.

In this report, we have successfully tuned the selectivity and sensitivity of an anion receptor L1 by substituting electron withdrawing natured fluorine atoms directly on to the rim of the phenyl ring. Despite the fact that, we have two electron withdrawing natured nitro substituents on the other side of receptor L1; two fluorine substitutions made dramatic change in the sensing ability as well as the selectivity of the receptor L1 towards anions. The acetonitrile solution contains L1 with tetrabutyl ammonium salts of fluoride, cyanide, acetate and dihydrogen phosphate results sudden color changes from yellow to brown; almost negligible spectral/color change for azide and bifluoride, where as there is no color change observed with any other anionic guests with L1. Solution state binding studies of L1 are carried out by UV-Vis spectrometry titration in 100% acetonitrile and it is found to be the receptor L1 selectively binds cyanide, phosphate and fluoride stronger than acetate; it is also found that receptor binds fluoride 100 times stronger than that of the receptor L and L1 has almost similar efficiency in binding towards acetate ion (AcO-). The strength of the receptor L1 towards fluoride, cyanide, acetate and dihydrogen phosphate bindings are found to be in the order of 1.271 × 105 M-1 > 1.245 × 105 M-1 > 1.368 × 103 M-1, 1.23 × 103 M-1 respectively. When we used aqueous environment (10% of water in acetonitrile) as testing solvent system, the receptor L1 selectively sense cyanide ion. Over all, strength of the receptor is increased towards anions with an increasing the number of fluorine atom onto the receptors. Here in we have also prepared a reference compound L2 in which the receptor molecule is substituted with only one fluoride atom. The acetonitrile solution of reference receptor L2 with help of naked-eye colorimetric experiment and spectrometric ammonium salts of fluoride, cyanide, acetate and bifluoride results sudden color changes from faint-yellow to brown in color. Unlike receptor L1, receptor L2 does not recognize H2PO4-, but instead of H2PO4-, it recognizes bifluoride as evidenced from UV-Vis spectroscopic and naked-eye colorimetric studies.

Chiral porphyrin imine manganese complex as catalyst for asymmetric epoxidation of styrene derivatives.

New chiral porphyrin imine was synthesized from (S)-3-benzyl-2-methyl-4-phenylbutanal according to dipyrromethane method using trifluoroacetic acid, BF3 etherate, and p-chloranil. Manganese complex of this chiral porphyrin imine ligand was used as catalyst in the asymmetric epoxidation of styrene derivatives possessing different substituents. Styrene derivatives possessing electron withdrawing groups gave the corresponding chiral epoxides in high yield up to 98% and ee up to 99%. The mechanism for the catalytic asymmetric epoxidation was also discussed based on transfer of oxygen.

Stoichiometrically different inclusion complexes of 2-aminofluorene and 2-amino-9-hydroxyfluorene in beta-cyclodextrin: a spectrofluorimetric study.

Beta-cyclodextrin (beta-CDx) forms inclusion complexes with 2-aminofluorene (2AF) and 2-amino-9-hydroxyfluorene (2AHF) in different stoichiometries (Guest-host ratio 1:1 and 1:2 respectively) which is discussed on the basis of study by absorption and fluorescence spectroscopy. The ground and the excited state acidity constants for the neutral-monocation equilibrium of the two fluorophores in aqueous beta-CDx medium are determined by spectrophotometric and fluorimetric titration methods respectively. The dual fluorescence observed for 2AHF monocation in aqueous solution is due to the formation of monocation-water exciplex. This monocation-water exciplex formation is hindered in beta-CDx solution by the inclusion complexation. Based on the results obtained, the structures of the inclusion complexes are proposed.

Fluorimetric study on molecular recognition of beta-cyclodextrin with 2-amino-9-fluorenone.

The molecular recognition interaction of beta-cyclodextrin (beta-CDx) was investigated using 2-amino-9-fluorenone (2AFN) by UV, steady-state fluorescence and time-resolved fluorescence measurements in aqueous solution at various pH. The effect of acidity on the ground and excited state equilibria between the neutral and the monocationic forms of 2AFN in water and in beta-CDx environments are studied. Based on the change in the fluorescence spectrum and lifetimes of 2AFN by the addition of beta-CDx, it is found that the unsubstituted part of the 2AFN is encapsulated in the hydrophobic cavity of beta-CDx. The unusual red shift obtained for the protonation of amino group in water and beta-CDx solution is due to large solvent relaxation of the monocation. The structure of the 1:1 inclusion complex between 2AFN and beta-CDx has been proposed on the basis of ground and excited state pKa values and the bond distances obtained by MOPAC/AM 1 data.

Inclusion complexation of 2-amino-7-bromofluorene by beta-cyclodextrin: spectral characteristics and the effect of pH.

Spectral characteristics of 2-amino-7-bromofluorene (2ABF) have been studied in aqueous beta-cyclodextrin (beta-CDx) solution. Enhancement in the fluorescence intensity of the neutral from of 2ABF was observed due to the formation of 1:1 complex with beta-CDx. The formation of this complex was confirmed by time-resolved fluorescence spectroscopy. The ground state pKa value for the monocation-neutral equilibrium of 2ABF in beta-CDx shows no change with that in aqueous solution, but the excited state pKa value changes. Based on its photophysical and photoprototropic characteristics in beta-CDx, the structure of the 1:1 inclusion complex is proposed.