2-Aminophenols based Schiff bases as fluorescent probes for selective detection of cyanide and aluminium ions - Effect of substituents

Three Schiff base based probes are designed and synthesized by facile condensation of a commercially available fluorophore 2,6-diformyl-4-tert-butylphenol with 4-nitro-2-aminophenol (KP1), 2-aminophenol (KP2) and 4-tert-butyl-2-aminophenol (KP3) and are characterized using various spectral techniques. The probes exhibit high selectivity and sensitivity CN^- and Al(III) ions with striking fluorescent signaling responses in H₂O-DMSO (1:1, v/v) medium. The mechanism of the probes' detection of CN involves deprotonation of the phenolic OH group(s) followed by nucleophilic addition of CN^- onto imine C-atom. The ¹H NMR chemical shifts of the OH protons of 2-aminophenol moiety exhibits a linear correlation with the Hammett's substituent constants (σ_p), yielding a positive reaction constant (ρ). In KP1, the electron-withdrawing nitro substituent polarizes the imine bond to a larger extent than in KP2, resulting in easier addition of CN^- to imine C-atom. The electron releasing tert-Bu substituent in KP3 produces the opposite effect leading to a sluggish addition reaction. The separately populated HOMO and LUMO in KP1 and a relatively lower HOMO-LUMO energy gap indicate substantial intramolecular charge transfer (ICT) character, leading to weak fluorescence emission. The large reduction in HOMO-LUMO energy gap, in KP1, upon addition of cyanide is responsible for the greater enhancement in fluorescence with blue shift upon addition of CN^-. Formation of tetrahedral Probe-Al(III) complex prevents the isomerization of imine bond, leading to enhancement in fluorescence and contribution from chelation enhanced fluorescence. As these probes show very low limits of detection of these ions, their practical utility has also been demonstrated.

3-Hydroxy-2-naphthoic hydrazide as a probe for fluorescent detection of cyanide and aluminium ions in organic and aquo-organic media and its application in food and pharmaceutical samples

The commercially available fluorophore, 3-hydroxy-2-naphthoic hydrazide (RS2), has rationally been selected for the study, which displays a rapid fluorescent response and high sensitivity for CN^- and Al(III) ions in neat DMSO and H₂O-DMSO (1:1 v/v) media. The addition of CN^- to RS2 triggers an enhancement in fluorescence at 505 nm (green fluorescence), while the addition of Al(III) increases the fluorescence of the probe with a blue-shift of emission maximum by 25 nm (bluish-green fluorescence). The probe's action was investigated by ¹H NMR titrations that indicate deprotonation of OH and NH moieties by these ions. ²⁷Al NMR of RS2-Al(III) complex suggests an octahedral geometry for the complex. The sensitivity of the fluorescent-based assays in aq. DMSO medium, 0.8 µM for CN^- and 1.9 µM for Al(III) ions are far below the limits in the World Health Organization guidelines for drinking water. RS2 detects Al(III) by the chelation-enhanced fluorescence (CHEF) mechanism. Besides, RS2 was successfully applied to detect CN^- and Al(III) ions in food materials and pharmaceutical samples, respectively.

Mining serial positioning episode rules by natural exponent inertia weight based swallow swarm optimization algorithm with constraint based event sequences

The Frequent Episode Mining (FEM) is a challenging framework to identify frequent episodes from a sequence database. In a sequence, an ordered collection of events defines an episode, and frequent episodes are only considered by the earlier studies. Also, it doesn’t support for the serial based episode rule mining. In this work, the episode rules are mined with precise and serial based rule mining considering the temporal factor, so that, the occurrence time of the consequent is specified in contrast to the traditional episode rule mining. The proposed work has a larger number of candidates and specific time constraints to generate the fixed-gap episodes, and mining such episodes from whole sequence where the time span between any two events is a constant which is utilized to improve the proposed framework’s performance. In order to improve the efficiency, an Optimal Fixed-gap Episode Occurrence (OFEO) is performed using the Natural Exponent Inertia Weight based Swallow Swarm Optimization (NEIWSSO) algorithm. The temporal constraints significantly evaluate the effectiveness of episode mining, and a noticeable advantage of the present work is to generate optimal fixed-gap episodes for better prediction. The effective use of memory consumption and performance enhancement is achieved by developing new trie-based data structure for Mining Serial Positioning Episode Rules (MSPER) using a pruning method. The position of frequent events is updated in the precise-positioning episode rule trie instead of frequent events to reduce the memory space. The benchmark datasets Retail, Kosarak, and MSNBC is used to evaluate the proposed algorithm’s efficiency. Eventually, it is found that it outperforms the existing techniques with respect to memory consumption and execution time. On an average, the proposed algorithm achieves 28 times lesser execution time and consumes 45.5% less memory space for the highest minimum support value on the Retail dataset compared to existing methods.