Efficiency consideration of generalized age replacement policy

Under the generalized age replacement policy, the system is replaced either at the predetermined age or upon failure if its corresponding repair time exceeds the threshold, whichever comes first. In this paper, we investigate the optimal choice of the pre‐determined preventive replacement age for a nonwarranted system, which minimizes the expected cost rate during the life cycle of the system from the customer's perspective under certain cost structures. Furthermore, we discuss several properties of such a generalized age replacement policy in comparison with the traditional age replacement policy. An efficiency, which represents the fractional time that the system is on, is defined under the proposed generalized age replacement policy and its monotonicity properties are investigated as well. The main objective of this study is to investigate the advantageous features of the generalized age replacement policy over the traditional age replacement policy with regard to the availability of the repairable system. Assuming that the system deteriorates with age, we illustrate our proposed optimal policies numerically and observe the impact of relevant parameters on the optimal preventive replacement age.     

Cu(ii)-BODIPY photosensitizer for CAIX overexpressed cancer stem cell therapy

Chemoresistance originating from cancer stem cells (CSCs) is a major cause of cancer treatment failure and highlights the need to develop CSC-targeting therapies. Although enormous progress in both photodynamic therapy (PDT) and chemodynamic therapy (CDT) has been made in recent decades, the efficacy of these modalities against CSC remains limited. Here, we report a new generation photosensitizer, CA9-BPS-Cu(ii), a system that combines three subunits within a single molecule, namely a copper catalyst for CDT, a boron dipyrromethene photosensitizer for PDT, and acetazolamide for CSC targeting via carbonic anhydrase-9 (CA9) binding. A therapeutic effect in MDA-MB-231 cells was observed that is ascribed to elevated oxidative stress mediated by a combined CDT/PDT effect, as well as through copper-catalysed glutathione oxidation. The CSC targeting ability of CA9-BPS-Cu(ii) was evident from the enhanced affinity of CA9-BPS-Cu(ii) towards CD133-positive MDA-MB-231 cells where CA9 is overexpressed vs. CD133-negative cells. Moreover, the efficacy of CA9-BPS-Cu(ii) was successfully demonstrated in a xenograft mouse tumour model.

Chemoresistance originating from cancer stem cells (CSCs) is a major cause of cancer treatment failure and highlights the need to develop CSC-targeting therapies.     

Spectrophotometric determination of periodate and glycerol with 5,5-dimethyl-1,3-cyclohexanedione bisthiosemicarbazone monohydrochloride

A direct spectrophotometric method for the determination of periodate (1—10 ppm) is based on the formation of a yellow oxidation product of 5,5-dimethyl-1,3-cyclohexanedione bisthiosemicarbazone monohydrochloride in aqueous solution at pH 0.5—1.2. The molar absorptivity at 415 nm is 1.72 × 10⁴ l mol^-1 cm^-1. The relative standard deviation is 0.8% for 8.0 ppm periodate. A modification to this procedure is used for the indirect spectrophotometric determination of glycerol (2–10 ppm), via the Malaprade reaction.     

Antidiabetic properties and mechanism of action of Gynura procumbens water extract in streptozotocin-induced diabetic rats

Gynura procumbens (Lour.) Merr (family Compositae) is cultivated in Southeast Asia, especially Indonesia, Malaysia and Thailand, for medicinal purposes. This study evaluated the in vivo hypoglycemic properties of the water extract of G. procumbens following 14 days of treatment and in vitro in RIN-5F cells. Glucose absorption from the intestines and its glucose uptake in abdominal skeletal muscle were assessed. The antidiabetic effect of water extract of G. procumbens leaves was investigated in streptozotocin-induced diabetic rats. The intraperitoneal glucose tolerance test (IPGTT) was performed in diabetic rats treated with G. procumbens water extract for 14 days. In the IPGTT, blood was collected for insulin and blood glucose measurement. After the IPGTT, the pancreases were collected for immunohistochemical study of β-cells of the islets of Langerhans. The possible antidiabetic mechanisms of G. procumbens were assessed through in vitro RIN-5F cell study, intestinal glucose absorption and glucose uptake by muscle. The results showed that G. procumbens significantly decreased blood glucose levels after 14 days of treatment and improved outcome of the IPGTT. However, G. procumbens did not show a significant effect on insulin level either in the in vivo test or the in vitro RIN-5F cell culture study. G. procumbens also showed minimal effects on β-cells of the islets of Langerhans in the pancreas. However, G. procumbens only significantly increased glucose uptake by muscle tissues. From the findings we can conclude that G. procumbens water extract exerted its hypoglycemic effect by promoting glucose uptake by muscles.     

Molecular weight parity predicted from the parity values of mass spectral peaks

The fact that an unknown mass spectrum originates from a compound of even (or odd) numbered molecular weight can be predicted for 43% (13%) of unknowns with 95% (80%) reliability.     

Morphological Evolution of Single-Crystal Ag Nanospheres during the Galvanic Replacement Reaction with HAuCl(4)

This paper presents a systematic study of the galvanic replacement reaction between 23.5 nm single-crystal Ag nanospheres and HAuCl(4) in an aqueous medium. We have monitored both morphological and spectral changes as the molar ratio of HAuCl(4) to Ag is increased. The replacement reaction on single-crystal Ag nanospheres results in the formation of a series of hollow and porous nanostructures composed of Au-Ag alloys. By varying the molar ratio of HAuCl(4) to Ag, we are able to control the size and density of the pores. In addition, the localized surface plasmon resonance peaks of these nanostructures can be readily tuned from 408 to 791 nm as the product becomes increasingly more hollow and porous.     

One step derivatization with British Anti-Lewsite in combination with gas chromatography coupled to triple-quadrupole tandem mass spectrometry for the fast and selective analysis of inorganic arsenic in rice

We developed a new fast and selective analytical method for the determination of inorganic arsenic (iAs) in rice by a gas chromatography – tandem mass spectrometry (GC-MS/MS) in combination with one step derivatization of inorganic arsenic (iAs) with British Anti-Lewsite (BAL). Two step derivatization of iAs with BAL has been previously performed for the GC-MS analysis. In this paper, the quantitative one step derivatization condition was successfully established. The GC-MS/MS was carried out with a short nonpolar capillary column (0.25 mm × 10 m) under the conditions of fast oven temperature ramp rate (4 °C/s) and high linear velocity (108.8 cm/s) of the carrier gas. The established GC-MS/MS method showed an excellent linearity (r² > 0.999) in a tested range (0.2–100.0 μg L⁻¹), ultra-low limit of detection (LOD, 0.08 pg), and high precision and accuracy. The GC-MS/MS technique showed far greater selectivity (22.5 fold higher signal to noise ratio in rice sample) on iAs than GC-MS method. The gas chromatographic running time was only 2.5 min with the iAs retention time of 1.98 min. The established method was successfully applied to quantify the iAs contents in polished rice. The mean iAs content in the Korean polished rice (n = 27) was 66.1 μg kg⁻¹ with the range of 37.5–125.0 μg kg⁻¹. This represents the first report on the GC-tandem mass spectrometry in combination with the one step derivatization with BAL for the iAs speciation in rice. This GC-MS/MS method would be a simple, useful and reliable measure for the iAs analysis in rice in the laboratories in which the expensive and element specific HPLC-ICP-MS is not available.     

Influence of Electronic Environment on the Radiative Efficiency of 9-Phenyl-9H-carbazole-Based ortho-Carboranyl Luminophores

The photophysical properties of closo-ortho-carboranyl-based donor–acceptor dyads are known to be affected by the electronic environment of the carborane cage but the influence of the electronic environment of the donor moiety remains unclear. Herein, four 9-phenyl-9H-carbazole-based closo-ortho-carboranyl compounds (1F, 2P, 3M, and 4T), in which an o-carborane cage was appended at the C3-position of a 9-phenyl-9H-carbazole moiety bearing various functional groups, were synthesized and fully characterized using multinuclear nuclear magnetic resonance spectroscopy and elemental analysis. Furthermore, the solid-state molecular structures of 1F and 4T were determined by X-ray diffraction crystallography. For all the compounds, the lowest-energy absorption band exhibited a tail extending to 350 nm, attributable to the spin-allowed π–π* transition of the 9-phenyl-9H-carbazole moiety and weak intramolecular charge transfer (ICT) between the o-carborane and the carbazole group. These compounds showed intense yellowish emission (λ_em = ~540 nm) in rigid states (in tetrahydrofuran (THF) at 77 K and in films), whereas considerably weak emission was observed in THF at 298 K. Theoretical calculations on the first excited states (S₁) of the compounds suggested that the strong emission bands can be assigned to the ICT transition involving the o-carborane. Furthermore, photoluminescence experiments in THF‒water mixtures demonstrated that aggregation-induced emission was responsible for the emission in rigid states. Intriguingly, the quantum yields and radiative decay constants in the film state were gradually enhanced with the increasing electron-donating ability of the substituent on the 9-phenyl group (‒F for 1F < ‒H for 2P < ‒CH₃ for 3M < ‒C(CH₃)₃ for 4T). These features indicate that the ICT-based radiative decay process in rigid states is affected by the electronic environment of the 9-phenyl-9H-carbazole group. Consequently, the efficient ICT-based radiative decay of o-carboranyl compounds can be achieved by appending the o-carborane cage with electron-rich aromatic systems.     

Deboronation-induced ratiometric emission sensing of fluoride by 1,3,5-tris-(o-carboranyl-methyl)benzene

1,3,5-Tris-(o-carboranyl-methyl)benzene (closo-1) and its nido-form (nido-1) were synthesized and fully characterized. The solid-state molecular structure of closo-1 was determined by single-crystal X-ray diffraction analysis. Compound closo-1 exhibited an intense single emission in various organic solvents that was red-shifted with increasing solvent polarity. The positive solvatochromic effect and theoretical calculation results at the first excited (S₁) optimized structure of closo-1 strongly suggest that this emissive band can be assigned to an intramolecular charge transfer. Meanwhile, nido-1 showed a pronounced red-shift of the emissive band compared to that of closo-1 and aroused low-energy emission. The specific emissive features of nido-1 were attributed to the elevation of its HOMO level, estimated by cyclic voltammetry. The photophysical changes by conversion from closo-1 to nido-1 allowed the emissive color-tunable sensing of fluoride. Thus, the tris-o-carboranyl compound showed great potential as a chemodosimeter for fluoride anion sensing, detectable by the naked-eye.     

Efficient Rhodium‐Catalyzed Multicomponent Reaction for the Synthesis of Novel Propargylamines

[{Rh(μ‐Cl)(H)₂(IPr)}₂] (IPr = 1,3‐bis‐(2,6‐diisopropylphenyl)imidazole‐2‐ylidene) was found to be an efficient catalyst for the synthesis of novel propargylamines by a one‐pot three‐component reaction between primary arylamines, aliphatic aldehydes, and triisopropylsilylacetylene. This methodology offers an efficient synthetic pathway for the preparation of secondary propargylamines derived from aliphatic aldehydes. The reactivity of [{Rh(μ‐Cl)(H)₂(IPr)}₂] with amines and aldehydes was studied, leading to the identification of complexes [RhCl(CO)IPr(MesNH₂)] (MesNH₂ = 2,4,6‐trimethylaniline) and [RhCl(CO)₂IPr]. The latter shows a very low catalytic activity while the former brought about reaction rates similar to those obtained with [{Rh(μ‐Cl)(H)₂(IPr)}₂]. Besides, complex [RhCl(CO)IPr(MesNH₂)] reacts with an excess of amine and aldehyde to give [RhCl(CO)IPr{MesN?CHCH₂CH(CH₃)₂}], which was postulated as the active species. A mechanism that clarifies the scarcely studied catalytic cycle of A₃‐coupling reactions is proposed based on reactivity studies and DFT calculations.