1,374 research outputs found
Green synthesis based X-type Ba–Zn Hexaferrites: Their structural, Hysteresis, Mӧssbauer, dielectric and electrical properties
No full textBa2Zn2Fe28O46 hexaferrite was prepared using green synthesis with different quantities of ginger root extract (obtained from 0.0, 17.5, 35, 52.5 and 70 g of ginger root) as a natural antioxidant reducing agent. The dried precipitates were preheated at 550 °C/4 h and finally heated at 1200 °C/5 h. The effect of ginger root extract on structural, phase purity, magnetic, Mӧssbauer and low frequency (10 Hz–2 MHz) dielectric properties were investigated. XRD analysis of samples prepared with extracts from 35, 52.5, and 70 g of ginger depicted pure X-phase, while the other samples (0.0, 17.5 g) showed the secondary phase of M-type (BaM, BaFe12O19) along with hematite (12% α-Fe2O3). Hence, samples with greater amounts of ginger extract formed single-phase X-type hexaferrite. Saturation magnetization (MS) varied from 40.8 A m2/kg without ginger extract to 69.8 A m2/kg with extract from 52.5 g ginger, and was <65 A m2/kg for all samples made with the ginger extract. All synthesized samples were relatively soft ferrites, and coercivity increased with amount of ginger extract used. The Mӧssbauer spectra explored six sextets of five magnetic sub-lattices, and the presence of Fe3+ (99.4–97.3 %) and Fe2+ (0.6–2.7 %) ions, with more Fe2+ present in the extract-derived samples. The variations in MS based on hysteresis loops were in agreement by Mössbauer spectroscopy. The use of the extract also significantly reduced the grain size, from 3.3 μm without ginger extract to 0.7–1.7 μm with the extract, with a corresponding increase in coercivity from 16 to 40–80 kA/m. The samples prepared with extracts from 35 g to 52.5 g ginger root possessed considerable real dielectric constant compared to the others, but the extract also increased conductivity in the high-frequency region. Complex impedance displayed low values in the high-frequency region, and Cole-Cole plots revealed that the main contribution to conductivity in extract-based samples was from the grains. The reducing action of the green extract not only produced single phase X ferrite, but it also reduced grain size to ∿1–2 μm and greatly increased MS
Comparison of seropositivity of human immunodeficiency virus, hepatitis B virus, hepatitis C virus, and syphilis among Hospital Cornea Retrieval Programme-Donors versus voluntary cornea donors at a large eye bank in Eastern India
No full textPurpose: To compare the serology profile of donors from Hospital Cornea Retrieval Programme-donors (HCRP-D) and voluntary cornea donors (VC-D) from a large eye bank in Eastern India. Methods: This is a retrospective analysis of donor details from January 2011 to December 2016. Donor demographics, cause of death, and serology reports were compiled. Postmortem blood was tested for human immunodeficiency virus 1 and 2 (HIV), hepatitis B virus (HBV), hepatitis C virus (HCV), and syphilis using government-approved kits as per the National Programme for Control of Blindness Standards of Eye Banking. Donors for whom serology was not possible were excluded. Results: A total of 4300 of 4353 donors were included of which 74.3% were hospital donors and 25.7% were voluntary donors. A total of 93 (2.2%) donors with 94 seropositive reports were noted: 79 (84.9%) from HCRP-D and 14 (15.1%) from VC-D which was statistically significantly higher (P = 0.02). Among seropositive reports, HIV, HBV, HCV, and syphilis accounted for 12 (12.8%), 38 (40.4%), 36 (38.3%), and eight (8.5%), respectively. There was no correlation between the cause of death and seropositivity. A statistically significant decreasing trend in seroprevalence among hospital donors was observed over the years (5.3% in 2011 to 1.4% in 2016; P = 0.004). Two (0.47%) of 421 hospital donors with prior negative serology were found to be seropositive. Conclusion: Seropositive rates are significantly higher among hospital donors in spite of medical prescreening compared to nonscreened voluntary donors. Serology should be repeated even when prior reports are available
Gamma-D crystallin gene (CRYGD) mutation causes autosomal dominant congenital cerulean cataracts
No full textCongenital cataracts are a major cause of bilateral visual impairment in childhood. We mapped the gene responsible for autosomal congenital cerulean cataracts to chromosome 2q33-35 in a four generation family of Moroccan descent. The maximum lod score (7.19 at recombination fraction theta=0) was obtained for marker D2S2208 near the g-crystallin gene (CRYG) cluster. Sequencing of the coding regions of the CRYGA, B, C, and D genes showed the presence of a heterozygous C>A transversion in exon 2 of CRYGD that is associated with cataracts in this family. This mutation resulted in a proline to threonine substitution at amino acid 23 of the protein in the first of the four Greek key motifs that characterise this protein. We show that although the x ray crystallography modelling does not indicate any change of the backbone conformation, the mutation affects a region of the Greek key motif that is important for determining the topology of this protein fold. Our data suggest strongly that the proline to threonine substitution may alter the protein folding or decrease the thermodynamic stability or solubility of the protein. Furthermore, this is the first report of a mutation in this gene resulting in autosomal dominant congenital cerulean cataracts
New avenues in nitrenium ion and carbenen chemistry: Total synthesis of TAN1251A, cinatrin B, C(1), and C(3).
No full textNew avenues in nitrenium ion and carbenen chemistry: Total synthesis of TAN1251A, cinatrin B, C(1), and C(3)
Use of Graph Invariants in Quantitative Structure-Activity Relationship Studies
No full textThis chapter reviews results of research carried out by Basak and collaborators during the past four decades or so in the development of novel mathematical chemodescriptors and their applications in quantitative structure-activity relationship (QSAR) studies related to the prediction of toxicities and bioactivities of chemicals. For chemodescriptors based QSAR studies, we have used graph theoretical, three dimensional (3-D), and quantum chemical indices. The graph theoretic chemodescriptors fall into two major categories: (a) Numerical invariants defined on simple molecular graphs representing only the adjacency and distance relationship of atoms and bonds; such invariants are called topostructural (TS) indices; (b) Topological indices derived from weighted molecular graphs, called topochemical (TC) indices. Collectively, the TS and TC descriptors are known as topological indices (TIs). The set of independent variables used for modeling also includes a group of three-dimensional (3-D) molecular descriptors. Semi-empirical and various levels of ab initio quantum chemical indices have also been used for hierarchical QSAR (HiQSAR) modeling. Results indicate that in many cases of property / activity / toxicity analyzed by us, a TS + TC combination explains most of the variance in the data.
This work is licensed under a Creative Commons Attribution 4.0 International License
Structural insights into Clostridium perfringens delta toxin pore formation
No full textClostridium perfringens Delta toxin is one of the three hemolysin-like proteins produced by C. perfringens type C and possibly type B strains. One of the others, NetB, has been shown to be the major cause of Avian Nectrotic Enteritis, which following the reduction in use of antibiotics as growth promoters, has become an emerging disease of industrial poultry. Delta toxin itself is cytotoxic to the wide range of human and animal macrophages and platelets that present GM2 ganglioside on their membranes. It has sequence similarity with Staphylococcus aureus β-pore forming toxins and is expected to heptamerize and form pores in the lipid bilayer of host cell membranes. Nevertheless, its exact mode of action remains undetermined. Here we report the 2.4 Å crystal structure of monomeric Delta toxin. The superposition of this structure with the structure of the phospholipid-bound F component of S. aureus leucocidin (LukF) revealed that the glycerol molecules bound to Delta toxin and the phospholipids in LukF are accommodated in the same hydrophobic clefts, corresponding to where the toxin is expected to latch onto the membrane, though the binding sites show significant differences. From structure-based sequence alignment with the known structure of staphylococcal α-hemolysin, a model of the Delta toxin pore form has been built. Using electron microscopy, we have validated our model and characterized the Delta toxin pore on liposomes. These results highlight both similarities and differences in the mechanism of Delta toxin (and by extension NetB) cytotoxicity from that of the staphylococcal pore-forming toxins
Investigation of structural, magnetic and dielectric properties of gallium substituted Z-type Sr3Co2-xGaxFe24O41 hexaferrites for microwave absorbers
No full textGallium substituted Z-type hexagonal ferrites with chemical composition Sr3Co2-xGaxFe24O41 (x = 0.0,0.4, 0.8, 1.2, 1.6, and 2.0) were successfully synthesised in air at 1200 °C for 5 h using the sol-gel auto-combustion technique, in order to investigate the effect of gallium substitution on structural, magnetic and dielectric properties. X-ray Diffraction (XRD) analysis of all samples reveals the formation of mixed hexaferrite phases, with Z ferrite as the major phase (72–90%).The average crystallite size of heated powders was found to be in the range of 21–40 nm. The saturation magnetisation decreases after gallium substitution, with the lowest values of 64 Am2 kg−1 for composition x = 1.6, which also hasthe highest value of coercivity (28.3 kA m−1). Nevertheless, all were soft ferrites, with Hc between 3.4 and 28.3 kA m−1.The Mr/MS ratio of all samples was found to be less than 0.5, suggesting that all the compositions possess multi-domain microstructures. Mössbauer spectroscopic analysis confirmed that the Fe ions were found in the 3 + high spin state for compositions below x ≤ 0.4, whereas ∼1.5% of the Fe ions were converted into Fe2+ high spin state beyond x ≥ 0.8 compositions, as Ga3+ began to substitute for Fe3+, forming Fe2+ in the cobalt positions. The average hyperfine magnetic field () was found to be decreased with Ga-substitution. Dielectric parameters such as dielectric constant and loss factor were studied as a function of frequency, and their results show normal behaviour for ferrimagnetic materials. In complex measurements at microwave frequencies (8 GHz–12.5 GHz, the X-band), all samples had a real permittivity of around 8–14. For sample x = 2.0, a dielectric resonance peak was observed around 12.15 GHz. All showed a real permeability of around 1.0–1.4 over the frequency of 8 GHz–12.5 GHz range, and ferromagnetic resonance (FMR) was observed in x = 0.0 and 2.0 samples, at around 11 and 12 GHz, respectively. This suggests that the prepared samples can be used as microwave absorbers/EMI shielding at specific microwave frequencies. The co-existence of FMR and dielectric resonance at the same frequency of 12.15 GHz for x = 2.0 could lead to the coupling of these resonances and the development of potential metamaterials
Abstract 4457: Inverse relationship between exon 8 single nucleotide polymorphism (c.1293 C&gt;T) of gigaxonin and human tumor cell growth
No full textAbstract
Gigaxonin, a product of the Giant Axonal Neuropathy (GAN) gene located on chromosome 16, is involved in intermediate filament processing of neural cells and vimentin fibers in fibroblasts. Previous studies have shown an interaction between p16 and gigaxonin in cisplatin mediated ubiquitination of NFkB. Genomic studies have indicated higher frequency (44.25%) of exon 8 single nucleotide polymorphism (SNP) (c.1293 C&gt;T) of gigaxonin in the individuals of Caucasian population compared to normal population (22%). The polymorphism frequency is much lower in individuals of other ethnicities. To determine the relationship to tumors, we analyzed exon 8 polymorphism in HPV positive and negative cervical and head and tumors. Our studies showed a 47.25% polymorphic frequency in these tumors. There was no relationship between the presence of polypmorphism and HPV status. However, there was an inverse relationship between polymorphism and tumor recurrence. Our studies have further shown higher expression of gigaxonin protein in cancer cell lines containing the polymorphic T allele. Growth assays in vitro and in soft agar have shown a direct relationship between the presence of the T allele and slower cell line growth. Our results therefore indicate that in addition to p16 expression, exon 8 SNP could also serve as a diagnostic marker of chemo sensitivity in human tumors.
Citation Format: Eri S. Srivatsan, Kimberly J. Hwang, Albert Ko, Jenna R. Chatoff, Saroj K. Basak, Natarajan Venkatesan, Fernando Palma-Diaz, Michael S. Lewis, Pascale Bomont, Marilene B. Wang. Inverse relationship between exon 8 single nucleotide polymorphism (c.1293 C&gt;T) of gigaxonin and human tumor cell growth [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4457. doi:10.1158/1538-7445.AM2017-4457</jats:p
Designing Reliable Operando TEM Experiments to Study (De)lithiation Mechanism of Battery Electrodes
No full textThe unique capability of TEM to resolve the microstructural and chemical evolution of electrode materials during battery operation at high temporal and spatial resolution makes it the method of choice for operando battery experiments. However, the widely used open-cell setup, that uses oxidized lithium as the electrolyte due to its inherent design, does not allow Li-ions to be (de)inserted from every part of the electrode particle, which imposes restrictions on the (de)intercalation process. This may lead to the formation of a mechanistic hypothesis based on incomplete information about the (de)lithiation of the electrode material under investigation. Using LiFePO4 as a model electrode material we propose here a MEMS based cell-on-a-chip design comprising of a thin coating of amorphous electrolyte, which can be utilized to overcome the said issue. (C) 2019 The Electrochemical Society
Isoamphipathic antibacterial molecules regulating activity and toxicity through positional isomerism
No full textPeptidomimetic antimicrobials exhibit a selective interaction with bacterial cells over mammalian cells once they have achieved an optimum amphiphilic balance (hydrophobicity/hydrophilicity) in the molecular architecture. To date, hydrophobicity and cationic charge have been considered the crucial parameters to attain such amphiphilic balance. However, optimization of these properties is not enough to circumvent unwanted toxicity towards mammalian cells. Hence, herein, we report new isoamphipathic antibacterial molecules (IAMs: 1–3) where positional isomerism was introduced as one of the guiding factors for molecular design. This class of molecules displayed good (MIC = 1–8 μg mL−1 or μM) to moderate [MIC = 32–64 μg mL−1 (32.2–64.4 μM)] antibacterial activity against multiple Gram-positive and Gram-negative bacteria. Positional isomerism showed a strong influence on regulating antibacterial activity and toxicity for ortho [IAM-1: MIC = 1–32 μg mL−1 (1–32.2 μM), HC50 = 650 μg mL−1 (654.6 μM)], meta [IAM-2: MIC = 1–16 μg mL−1 (1–16.1 μM), HC50 = 98 μg mL−1 (98.7 μM)] and para [IAM-3: MIC = 1–16 μg mL−1 (1–16.1 μM), HC50 = 160 μg mL−1 (161.1 μM)] isomers. Co-culture studies and investigation of membrane dynamics indicated that ortho isomer, IAM-1 exerted more selective activity towards bacterial over mammalian membranes, compared to meta and para isomers. Furthermore, the mechanism of action of the lead molecule (IAM-1) has been characterized through detailed molecular dynamics simulations. In addition, the lead molecule displayed substantial efficacy against dormant bacteria and mature biofilms, unlike conventional antibiotics. Importantly, IAM-1 exhibited moderate in vivo activity against MRSA wound infection in a murine model with no detectable dermal toxicity. Altogether, the report explored the design and development of isoamphipathic antibacterial molecules to establish the role of positional isomerism in achieving selective and potential antibacterial agents
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