Synthesis and Characterization of the First Pyrrolidine‐Based Chiral Ionic Liquids

The first example of pyrrolidine‐based room‐temperature chiral ionic liquids using 2‐aminobutanol as chiral auxiliary is described.     

Flow Through Diffusion Cell Method: A Better Approach to Study Drug Release Behavior as Compared to Traditional Dissolution Test Method

Co‐polymeric hydrogels consisting of N‐vinyl‐2‐pyrrolidone (NVP) and acrylic acid (AAc) were synthesized and evaluated for release of a model drug, i.e., vitamin B₁₂. Release studies in simulated gastric fluid (pH 1.2) and intestinal fluid (pH 7.4), at 37°C, showed the hydrogels to be pH sensitive. An in vitro release study by ‘traditional dissolution test’ (TDT) showed that percent drug released from the hydrogel was nearly 8.6±2.1 and 83.2±4.8 in the media of pH 1.2 and 6.8, respectively. However, in order to incorporate in vivo GI conditions such as acidic pH and high water content in the stomach, low water content and the presence of a semi–solid mass in the large intestine, a new test model, called flow through diffusion cell (FTDC) was also used. The two approaches yielded almost different release profiles. The gels were characterized by thermogravimetric analysis and FTIR spectroscopy.     

Supramolecular heterogeneity in β-turn forming synthetic tripeptides nucleated by isomers of fluorinated phenylalanine and aib as corner residues

The influences of fluorines in chemistry have emerged as a breakthrough in various arenas of bio-organic and medicinal chemistry. But its incorporation in β-turn design and its implications for supramolecular chemistry remains in a rudimentary stage. Inspired by the diversity displayed by the isomers of mono-fluorinated phenylalanine in biological sciences, here our effort is to modulate the solid state conformational analysis of three terminally protected synthetic tripeptides Boc-(Y)-F-Phe-Aib-Xaa-OMe, where (Y is (2)-F-Phe, Xaa; Leu in peptide I, (3)-F-Phe, Xaa; Leu in peptide II and (4)-F-Phe, Xaa; Ile in peptide III). Interestingly, all the three peptides display a conformational preference for β-turns, stabilized by 4→1 intramolecular hydrogen bonding. Our investigation further demonstrates that mere interchange of positions of fluorines in mono-fluorinated phenylalanine in peptides I–III introduces significant diversity in supramolecular chemistry. X-ray crystallography sheds some light at atomic resolution. Furthermore, this supramolecular heterogeneous behavior is evident from the morphologies obtained from the materials of all the three peptides grown from acetone to petroleum ether solution, studied by field emission scanning electron microscopy. Thus, these monofluorinated peptides I–III may serve as prominent candidates in understanding the structure and function of misfolded disease causing peptides like prion and Alzheimer's amyloid.     

Efficient and Green Syntheses of 12-Aryl-2,3,4,12-tetrahydrobenzo[b]xanthene-1,6,11-triones in Water and Task-Specific Ionic Liquid

Facile and convenient one-pot cascade/tandem approaches for the syntheses of privileged medicinal scaffolds, 12-aryl-2,3,4,12-tetrahydrobenzo[b]xanthene-1,6,11-trione derivatives, have been reported under extremely mild reaction conditions using a catalytic amount of H₂SO₄ in water or in the presence of the acidic ionic liquid bmim[HSO₄], which could be recycled.

Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file.     

Trichloroisocyanuric Acid–KF as an Efficient Reagent for One-Pot Synthesis of Dialkylfluorophosphates from Dialkylphosphites

Trichloroisocyanuric acid–KF afforded dialkylfluorophosphates from dialkylphosphites at room temperature through a facile electrophilic–nucleophilic metathesis.     

Thermoluminescence studies of UV-irradiated Y2O3:Eu3+ doped phosphor

The present paper reports thermoluminescence (TL) glow curves of Eu³⁺-doped Y₂O₃ phosphor with different ultraviolet (UV) exposure times. The glow peak shows second-order kinetics of Eu³⁺-doped Y₂O₃, and corresponding kinetic parameters were evaluated using the peak shape method. Calculations of trap depth were carried out using different methods. The kinetics order, activation energy, and frequency factor were calculated. The recorded glow curve shifts towards higher intensity with longer UV exposure. The heating rate used for recording TL was 3.0 °C s^?1. Particle size and structure were verified by X-ray diffraction (XRD) pattern and morphology by scanning electron microscopy (SEM) imaging.     

Direct Evidence of Significantly Different Chemical Behavior and Excited‐State Dynamics of 1,7‐ and 1,6‐Regioisomers of Pyrrolidinyl‐Substituted Perylene Diimide

Novel bay‐functionalized perylene diimides with additional substitution sites close to the perylene core have been prepared by the reaction between 1,7(6)‐dibromoperylene diimide 6 (dibromo‐PDI) and 2‐(benzyloxymethyl)pyrrolidine 5 . Distinct differences in the chemical behaviors of the 1,7‐ and 1,6‐regioisomers have been discerned. While the 1,6‐dibromo‐PDI produced the corresponding 1,6‐bis‐substituted derivative more efficiently, the 1,7‐dibromo‐PDI underwent predominant mono‐debromination, yielding a mono‐substituted PDI along with a small amount of the corresponding 1,7‐bis‐substituted compound. By varying the reaction conditions, a controlled stepwise bis‐substitution of the bromo substituents was also achieved, allowing the direct synthesis of asymmetrical 1,6‐ and 1,7‐PDIs. The compounds were isolated as individual regioisomers. Fullerene (C₆₀) was then covalently linked at the bay region of the newly prepared PDIs. In this way, two separate sets of perylene diimide–fullerene dyads, namely single‐bridged (SB‐1,7‐PDI‐C₆₀ and SB‐1,6‐PDI‐C₆₀) and double‐bridged (DB‐1,7‐PDI‐C₆₀ and DB‐1,6‐PDI‐C₆₀), were synthesized. The fullerene was intentionally attached at the bay region of the PDI to achieve close proximity of the two chromophores and to ensure an efficient photoinduced electron transfer. A detailed study of the photodynamics has revealed that photoinduced electron transfer from the perylene diimide chromophore to the fullerene occurs in all four dyads in polar benzonitrile, and also occurs in the single‐bridged dyads in nonpolar toluene. The process was found to be substantially faster and more efficient in the dyads containing the 1,7‐regioisomer, both for the singly‐ and double‐bridged molecules. In the case of the single‐bridged dyads, SB‐1,7‐PDI‐C₆₀ and SB‐1,6‐PDI‐C₆₀, different relaxation pathways of their charge‐separated states have been discovered. To the best of our knowledge, this is the first observation of photoinduced electron transfer in PDI‐C₆₀ dyads in a nonpolar medium.