Selective Synthesis of 6′‐Arylidene‐1‐aryl‐3‐aryl‐spiro[pyrrolizidine‐2,2′‐cyclohexanone] by Cycloaddition of Azomethine Ylides to Dibenzylidene Cyclohexanone

Azomethine ylides derived in situ from l ‐proline and aryl aldehydes underwent regioselective and stereoselective cycloadditions with diaryl cycloahexanone to form a series of spiro‐pyrrolizidine compounds. By using equimolar proportions of the reactants in DMF, only a single mono‐adduct, namely 6′‐arylidene‐1‐aryl‐3‐aryl‐spiro[pyrrolizidine‐2,2′‐cyclohexanone], was formed, the second double bond in the dipolarophile remaining unaffected. Structure elucidation was achieved by detailed spectroscopic analyses and XRD studies. Interesting solid‐state structural characteristics were revealed by XRD analysis.     

Substituent effects at nitrogen/phosphorus atoms of dialkaline earth metal complexes: Excess electron and large second-hyperpolarizability

A number of imido-, amido-, and phosphido-bridged dialkaline earth metal (M = Be, Mg, and Ca) complexes and their alkali metal (Li and Na) derivatives have been considered to study the ground state structure and the second-hyperpolarizability. The calculated ground state geometries contain four-membered M N(P) M N(P) ring having either planar or butterfly-like bent structure. The second-hyperpolarizability has been calculated at the HF and CCSD(T) levels using Sadlej's pol and aug-pc-2 basis sets, respectively. The addition of second hydrogen/alkali metal atom on nitrogen/phosphorus (N/P) atom substantially reduces the charge transfer from the alkaline earth metal atoms as the high negative charge on N/P exerts stronger push effect on the outermost electron pair in the “ns” sub-shell of M. The excess electron density on the alkaline earth metal atoms plays a crucial role in the enhancement of second-hyperpolarizability. The sum-over-state method calculated two-photon contribution of second-hyperpolarizability has been found to be significant. The variation of second-hyperpolarizability has been explained satisfactorily in terms of the TD-CAMB3LYP calculated spectroscopic properties in the light of two-state model. The calculated mean second-hyperpolarizabilities of alkali substituted amido- and phosphido-bridged complexes are in the order of 10⁷ au.     

Carbon-13 NMR spectra of Piper alkamides and related compounds

¹³C NMR spectra of Piper alkamides and related compounds have been completely assigned on the basis of splitting patterns in the coupled spectra, application of additivity relationships and internal comparison of chemical shifts.     

Nonorientable Manifolds, Complex Structures, and Holomorphic Vector Bundles

A generalization of the notion of almost complex structure is defined on a nonorientable smooth manifold M of even dimension. It is defined by giving an isomorphism J from the tangent bundle TM to the tensor product of the tangent bundle with the orientation bundle such that JJ=–Id _TM . The composition JJ is realized as an automorphism of TM using the fact that the orientation bundle is of order two. A notion of integrability of this almost complex structure is defined; also the Kähler condition has been extended. The usual notion of a complex vector bundle is generalized to the nonorientable context. It is a real vector bundle of even rank such that the almost complex structure of a fiber is given up to the sign. Such bundles have generalized Chern classes. These classes take value in the cohomology of the tensor power of the local system defined by the orientation bundle. The notion of a holomorphic vector bundle is extended to the context under consideration. Stable vector bundles and Einstein–Hermitian connections are also generalized. It is shown that a generalized holomorphic vector bundle on a compact nonorientable Kähler manifold admits an Einstein–Hermitian connection if and only if it is polystable.     

Symplectic Structures on Moduli Spaces of Parabolic Higgs Bundles and Hilbert Scheme

Parabolic triples of the form (E_*,,) are considered, where (E_*,) is a parabolic Higgs bundle on a given compact Riemann surface X with parabolic structure on a fixed divisor S, and is a nonzero section of the underlying vector bundle. Sending such a triple to the Higgs bundle (E_*,) a map from the moduli space of stable parabolic triples to the moduli space of stable parabolic Higgs bundles is obtained. The pull back, by this map, of the symplectic form on the moduli space of stable parabolic Higgs bundles will be denoted by d. On the other hand, there is a map from the moduli space of stable parabolic triples to a Hilbert scheme Hilb(Z), where Z denotes the total space of the line bundle K_{X X}(S), that sends a triple (E_*,,) to the divisor defined by the section on the spectral curve corresponding to the parabolic Higgs bundle (E_*,). Using this map and a meromorphic one–form on Hilb(Z), a natural two–form on the moduli space of stable parabolic triples is constructed. It is shown here that this form coincides with the above mentioned form d.     

Dimerization of the transmembrane domain of amyloid precursor proteins and familial Alzheimer's disease mutants

Background  

Amyloid precursor protein (APP) is enzymatically cleaved by γ-secretase to form two peptide products, either Aβ40 or the more neurotoxic Aβ42. The Aβ42/40 ratio is increased in many cases of familial Alzheimer's disease (FAD). The transmembrane domain (TM) of APP contains the known dimerization motif GXXXA. We have investigated the dimerization of both wild type and FAD mutant APP transmembrane domains.     

13C NMR Studies: Effect of steric compression on chemical shifts of carbons in diastereoisomers

¹³C NMR of diastereoisomeric pairs of 2,3-diaryl-2-methylbutyronitriles revealed a difference in the chemical shift of the carbon atoms between the diastereoisomers and the observed shifts were greatly influenced by the presence of an ortho substituent in the 3-phenyl ring.     

Design of a Waste Paper-Derived Chemically ‘Reactive’ and Durable Functional Material with Tailorable Mechanical Property Following an Ambient and Sustainable Chemical Approach

Controlled tailoring of mechanical property and wettability is important for designing various functional materials. The integration of these characteristics with waste materials is immensely challenging to achieve, however, it can provide sustainable solutions to combat relevant environmental pollutions and other relevant challenges. Here, the strategic conversion of discarded and valueless waste paper into functional products has been introduced following a catalyst-free chemical approach to tailor both the mechanical property and water wettability at ambient conditions for sustainable waste management and controlling the relevant environmental pollution. In the current design, the controlled and appropriate silanization of waste paper allowed to modulate both the a) porosity and b) compressive modulus of the paper-derived sponges. Further, the association of 1,4-conjugate addition reaction between amine and acrylate groups allowed to obtain an unconventional waste paper-derived chemically ‘reactive’ sponge. The appropriate covalent modification of the residual reactive acrylate groups with selected alkylamines at ambient conditions provided a facile basis to tailor the water wettability from moderate hydrophobicity, adhesive superhydrophobicity to non-adhesive superhydrophobicity. The embedded superhydrophobicity in the waste paper-derived sponge was capable of sustaining large physical deformations, severe physical abrasions, prolonged exposure to harsh aqueous conditions, etc. Further, the waste paper-derived, extremely water-repellent sponges and membranes were successfully extended for proof-of-concept demonstration of a practically relevant outdoor application, where the repetitive remediation of oil spillages has been demonstrated following both selective absorption (25 times) of oils and gravity-driven filtration-based (50 times) separation of oils from oil/water mixtures at different harsh aqueous scenarios.     

A quinoline based bis-urea receptor for anions: a selective receptor for hydrogen sulfate

A dipodal bis-urea receptor has been synthesized from the reaction of 8-amino quinoline and 1,4-phenylene diisocyanate in dichloromethane, and the anion binding ability of the receptor has been studied using fluoride, chloride, bromide, iodide, perchlorate, nitrate, dihydrogen phosphate and hydrogen sulfate by UV-Vis titrations in DMSO. The results show that the receptor binds each of the anions with a 1:1 stoichiometry, showing high affinity and moderate selectivity for hydrogen sulfate among the anions studied. Ab initio calculations based on density functional theory (DFT) suggest that an anion (X(-)) is bonded within the cleft formed by the two arms of the receptor through two NH...X(-) and two aromatic CH...X(-) interactions. The results from solution and theoretical studies suggest that binding is predominantly influenced by hydrogen bonding interactions and the basicity of anions.