A General Catalytic Hydroamidation of 1,3‐Dienes: Atom‐Efficient Synthesis of N‐Allyl Heterocycles,Amides, and Sulfonamides

Transition‐metal‐catalyzed hydroamination reactions are sustainable and atom‐economical C N bond‐forming processes. Although remarkable progress has been made in the inter‐ and intramolecular amination of olefins and 1,3‐dienes, related intermolecular reactions of amides are still much less known. Control of the regioselectivity without analogous telomerization is the particular challenge in the catalytic hydroamidation of alkenes and 1,3‐dienes. Herein, we report a general protocol for the hydroamidation of electron‐deficient N‐heterocyclic amides and sulfonamides with 1,3‐dienes and vinyl pyridines in the presence of a catalyst derived from [{Pd(π‐cinnamyl)Cl}₂] and ligand L7 or L10 . The reactions proceeded in good to excellent yield with high regioselectivity. The practical utility of our method is demonstrated by the hydroamidation of functionalized biologically active substrates. The high regioselectivity for linear amide products makes the procedure useful for the synthesis of a variety of allylic amides.     

A mechanistic and kinetic study of the formation of metal nanoparticles by using synthetic tyrosine-based oligopeptides

Synthetic oligopeptides containing redox-active tyrosine residues have been employed to prepare gold and silver nanoparticles. In this reduction process an electron from the tyrosinate ion of the peptide is transferred to the metal ion at basic pH through the formation of a tyrosyl radical, which is eventually converted to its dityrosine form during the reaction. This reaction mechanism was confirmed from UV-visible, fluorescence, and EPR spectroscopy and was found to be pH-dependent. Transmission electron microscopy measurement shows that the average size and the monodispersity of gold nanoparticles increase as the number of tyrosine residues in the peptide increases. The kinetic study, based on spectrophotometric measurements of the surface plasmon resonance optical property, shows that the rate of formation of gold nanoparticles was much faster at higher pH than at lower pH and was also dependent on the number of tyrosine residues present in the peptide. The dityrosine form of the peptide was found to retain reducing properties like those of tyrosine in basic medium.     

Room temperature phosphorescence from organic luminogens in“non-crystalline” state

ABSTRACT

The field of room temperature phosphorescence (RTP) from purely organic materials has made rapid strides in recent years primarily due to its tremendous promise in the areas of photovoltaics, photocatalysis, bioimaging, sensing, etc. Although, the RTP properties, at one time, were considered to be exclusive features of organometallic and inorganic phosphors, a great progress in the molecular design coupled with a much better understanding of the triplet state stabilisation has led to the creation of a plethora of organic RTP materials in the current decade. In this focussed review, a special category of organic luminogens which, rather remarkably, exhibit efficient RTP emission in amorphous or fluidic state is discussed. A few selected examples of such ‘non-crystalline’ organic RTP luminogens are highlighted with an emphasis on the basic design principles and the strategies to increment the phosphorescence efficiency.     

Treatment of Baylis-Hillman adducts with triethyl orthoacetate in the presence of heterogeneous catalysts: a method for the stereoselective synthesis of two different types of trisubstituted alkenes

Baylis-Hillman adducts on treatment with triethyl orthoacetate in the presence of HClO₄-SiO₂ afford the corresponding allyl ethyl ethers while in the presence of NaHSO₄-SiO₂ undergo the Johnson-Claisen rearrangement to form ethyl alk-4-enoates. Thus two different types of trisubstituted alkenes are produced in a stereoselective manner using two different hetereogeneous catalysts.     

Catalysis by ionic liquids: cyclopropyl carbinyl rearrangements catalyzed by [pmim]Br under organic solvent free conditions

Aryl substituted cyclopropyl carbinol derivatives undergo stereoselective rearrangements catalyzed by the ionic liquid, 1-methyl-3-pentylimidazolium bromide, under sonication, without any organic solvent, to produce the substituted conjugated all-trans-butadienes.     

Novel radioassay for anti-thyroperoxidase autoantibodies using protein A coupled magnetizable cellulose particles as an immunoadsorbent

Journal of Radioanalytical and Nuclear Chemistry - Autoantibodies against thyroid peroxidase (TPO); described initially as thyroid microsomal antigen, are found in most of the patients with...     

Face-selective Diels-Alder reactions between unsymmetrical cyclohexadienes and symmetric trans-dienophile: an experimental and computational investigation

A combined experimental and theoretical study of the Diels-Alder reactions between 2-trimethylsiloxy-1,3-cyclohexadienes (2-11) and (E)-1,4-diphenylbut-2-ene-1,4-dione (1) is reported. Two diastereomeric products, 5-endo-6-exo- (nx) and 5-exo-6-endo- (xn) dibenzoyl derivatives, are possible with symmetric trans-dienophile (1). While in many cases 5-endo-6-exo product is preferred over the corresponding 5-exo-6-endo product, the product ratio nx:xn is found to vary with the position of substituents on the diene. The density functional theory studies with the mPW1PW91/6-31G* as well as the B3LYP/6-31G* levels reveal that the electrostatic repulsion between the oxygen lone pairs on the diene and the dienophile is critical to the observed product selectivities. The optimized transition state geometries though appeared to involve secondary orbital interactions, careful examination of the frontier Kohn-Sham orbitals as well as calculations with the natural bond orbital (NBO) analyses confirm the absence of SOI in these transition states. In the case of methyl-substituted dienes, a cumulative effect of steric and electrostatic interactions between the diene and the dienophile is found to be the controlling element toward the observed selectivity.     

Dynamics in the DNA recognition by DAPI: exploration of the various binding modes

Two distinct modes of interaction of the fluorescent probe 4',6-diamidino-2-phenylindole (DAPI), depending on the sequence of DNA, have been reported in the literature. In the present study, the dynamics of solvation has been utilized to explore the binding interaction of DAPI to DNA oligomers of different sequences. Picosecond-resolved fluorescence and polarization-gated anisotropy have been used to characterize the binding of DAPI to the different oligomers. In the double-stranded dodecamer of sequence CGCGAATTCGCG (oligo1), the solvation relaxation dynamics of the probe reveals time constants of 0.130 ns (75%) and 2.35 ns (25%). Independent exploration of the minor-groove environment of oligo1 using another well-known minor-groove binder Hoechst 33258 (H258) shows similar timescales, further confirming minor-groove binding of DAPI to oligo1. In the double-stranded dodecamer (oligo2) having the sequence GCGCGCGCGCGC, where intercalation has been reported in the literature, no solvation is observed in our experimental window. DAPI bound to oligo2 shows quenching of fluorescence compared to that of DAPI in a buffer. The quenching of fluorescence of DAPI intercalated in DNA is also borne out by the appearance of a fast component of 30 ps in the fluorescence lifetime, revealing electron transfer to DAPI from GC base pairs, between which it intercalates. In addition to this, the excited-state lifetime of the probe in the DAPI-DNA complex also shows a time constant similar to that of the dye in a buffer, indicating that the excited-state photoprocesses associated with the free dye is also operative in this binding mode, consistent with the binding geometry of the DAPI in the DNA. The dynamics of DAPI in calf thymus DNA having a random sequence of base pairs is similar to that associated with the DNA minor groove. Our studies clearly explore the structure-dynamics correlation of the DAPI-DNA complex in the two distinct modes of interaction of DAPI with DNA.     

Synthesis and structural characterization of a novel dinuclear complex compound formed by the aerial oxidation of cobalt(II) having an interligand C-C sigma-bond

The aerial oxidation of cobalt(II) salt, in a methanolic solution, containing a hydrazone ligand, (E)-N'-(4-oxo-4-phenylbutan-2-ylidene)benzohydrazide (condensation product of benzoyl acetone and benzhydrazide, LH2) leads to the coupling of two such ligand units through the formation of a rather long C-C bond [1.601(6) A] giving rise to a dinuclear Co (III) hydrazone complex, [Co2(L)2(L')(].0.25H2O (L' = C-C coupled hydrazone ligand). The structure of the complex has been determined by X-ray crystallography and IR, UV-Vis spectroscopy and elemental analysis have characterized the complex.     

Effect of mycolic acid on surface activity of binary surfactant lipid monolayers

In pulmonary tuberculosis, Mycobacterium tuberculosis lies in close physical proximity to alveolar surfactant. Cell walls of the mycobacteria contain loosely bound, detachable surface-active lipids. In this study, the effect of mycolic acid (MA), the most abundant mycobacterial cell wall lipid, on the surface activity of phospholipid mixtures from lung surfactant was investigated using Langmuir monolayers and atomic force microscopy (AFM). In the presence of mycolic acid, all the surfactant lipid mixtures attained high minimum surface tensions (between 20 and 40 mN/m) and decreased surface compressibility moduli <50 mN/m. AFM images showed that the smooth surface topography of surfactant lipid monolayers was altered with addition of MA. Aggregates with diverse heights of at least two layer thicknesses were found in the presence of mycolic acid. Mycolic acids could aggregate within surfactant lipid monolayers and result in disturbed monolayer surface activity. The extent of the effect of mycolic acid depended on the initial state of the monolayer, with fluid films of DPPC-POPC and DPPC-CHOL being least affected. The results imply inhibitory effects of mycolic acid toward lung surfactant lipids and could be a mechanism of lung surfactant dysfunction in pulmonary tuberculosis.