Indian Association for the Cultivation of Science

About: Indian Association for the Cultivation of Science is a education organization based out in Kolkata, India. It is known for research contribution in the topics: Catalysis & Excited state. The organization has 3867 authors who have published 10457 publications receiving 220098 citations.

Doping Mn2+ in Single-Crystalline Layered Perovskite Microcrystals

Abstract: While solution-processed doping of Mn ions in 3D lead halide perovskites is extensively studied, the chemistry for Mn doping in 2D layered perovskites is limited. Following a generic solution-phase colloidal approach in the presence of alkylammonium salts, formation of single-crystalline microcrystals of Mn-doped layered perovskites (L2PbX4, X = Cl, Br, I) is reported. While Mn was present in all microstructures, only L2PbBr4 led to Mn d–d emission with high quantum yield (∼61%). These doped layered structures showed robust stability and even retained the original emission in continuous thermocycling or constant heating at 200 °C in air for more than 24 h. Moreover, these materials also showed solid-state thermal annealing-induced 2D agglomeration leading to a larger structure, which was reflected from optical microscopic images and the enhanced intensity of powder XRD peaks that originated from the layered structure. Apart from the generic synthesis, these results also provided several new fundamental in...

Zn(II) metal–organic frameworks (MOFs) derived from a bis-pyridyl-bis-urea ligand: effects of crystallization solvents on the structures and anion binding properties

Abstract: The Reaction of N,N′-bis-(3-pyridyl)ethylene-bis-urea (BPEBU) with ZnSO4 in 2:1 ligand:metal ratio in various crystallization solvents afforded four metal–organic frameworks (MOFs), namely [{Zn(H2O)3(SO4)(µ-BPEBU)}·EG·2H2O]n2, [{Zn(µ-BPEBU)2(H2O)2}.SO4·2H2O.2THF}n3, [{Zn(µ-BPEBU)2(H2O)2}·SO4·2H2O.2acetone}n4 and [{Zn(µ-BPEBU)2(H2O)2}·SO4·2H2O·2(1,4-dioxane)}n5, which were mainly characterized by single cyrstal X-ray diffraction. MOFs 3–5 are found to be isomorphous. The study revealed that the crystallization solvents affected the structures; the single crystal structure of the free BPEBU was also discussed in the context of the conformation and ligating topology of the ligand found in the reported MOFs. When the MOFs syntheses were performed in a competitive environment wherein other oxo-counter anions such as NO3−, ClO4− and CF3SO3− were present, the isolated MOFs turned out to be the corresponding sulfate MOFs 2–4 indicating interesting sulfate selectivity.

Alzheimer’s Disease: A Heme–Aβ Perspective

Abstract: Redox active iron is utilized in biology for various electron transfer and catalytic reactions essential for life, yet this same chemistry mediates the formation of partially reduced oxygen species (PROS). Oxidative stress derived from the iron accumulated in the amyloid plaques originating from amyloid β (Aβ) peptides and neurofibrillary tangles derived from hyperphosphorylated tau proteins has been implicated in the pathogenesis of Alzheimer's disease (AD). Altered heme homeostasis leading to dysregulation of expression of heme proteins and heme deposits in the amyloid plaques are characteristic of the AD brain. However, the pathogenic significance of heme in neurodegeneration in AD has been unappreciated due to the lack of detailed understanding of the chemistry of the interaction of heme and Aβ peptides. As a result, the biochemistry and biophysics of heme complexes of Aβ peptides (heme-Aβ) remained largely unexplored. In this Account, we discuss the active site environment of heme bound Aβ complexes, which involves three amino acid residues unique in mammalian Aβ (Arg5, Tyr10, and His13) and missing in Aβ from rodents, which do not get affected by AD. The histidine residue binds heme, while the arginine and the tyrosine act as key second sphere residues of the heme-Aβ active site that play a crucial role in its reactivity. Generation of PROS, enhanced peroxidase activity, and oxidation of neurotransmitters such as serotonin (5-HT) are all found to be catalyzed by heme-Aβ in in vitro assays, and these reactivities can potentially be linked to the observed neuropathologies in AD brain. Association of Cu with heme-Aβ leads to the formation of heme-Cu-Aβ. The heme-Cu-Aβ complex produces a greater amount of PROS than reduced heme-Aβ or Cu-Aβ alone. Nitric oxide (NO), a signaling molecule, is found to ameliorate the detrimental effects of heme-Aβ and Cu bound heme-Aβ complexes by detaching heme from the heme-Aβ complex and releasing it into the environment solution. Heme-Aβ complexes show fast electron transfer with oxidized cytochrome c and rapid heme transfer with apomyoglobin and aponeuroglobin. NO, cytochrome c, and apoglobins can all lead to reduction in PROS generated by reduced heme-Aβ. Synthetic analogues of heme, offering a hydrophobic distal environment, have been used to trap oxygen bound intermediates, which provides insight into the mechanism of PROS generation by reduced heme-Aβ. Artificial constructs of Aβ on nonbiological platforms are used not only to stabilize metastable and physiologically relevant large and small amyloid aggregates but also to monitor the interaction of various drug candidates with heme and Cu bound Aβ aggregates, representing a tractable avenue for testing therapeutic agents targeting metals and cofactors in AD.