Structurally Characterized Zn2+ Selective Ratiometric Fluorescence Probe in 100 % Water for HeLa Cell Imaging: Experimental and Computational Studies

A single probe for solvent dependent optical recognition of iron(II/III) and arsenite: discrimination between iron redox states with single crystal X-ray structure evidence

The detection and discrimination of Fe2+ and Fe3+ ions have been investigated using a simple probe (L), produced by the condensation of ethylenediamine and 3-ethoxysalicyaldehyde. Single crystal X-ray structures demonstrate that L interacts with Fe2+ and Fe3+. In aqueous-DMSO media, the L recognises AsO2- by fluorescence and colorimetry techniques. The AsO2- aided PET inhibition and H-bond assisted chelation enhanced fluorescence (CHEF) boost fluorescence by 91-fold. The L can detect 0.354 ppb Fe2+, 0.22 ppb Fe3+ and 0.235 ppt AsO2-.

A Simple Isoniazid-Based N-Acylhydrazone Derivative as Potential Fluorogenic Probe for Zn2+ Ions

This study evaluated three isoniazid-based N-acylhydrazone derivatives (HL1, HL2, and HL3) varying their substituting groups (-H, -N(CH₃)₂, and -NO₂) as potential chemosensors for Zn²⁺ ions. To this end, the absorption and emission properties of these derivatives were investigated in the presence of Zn²⁺ ions. Results point to the derivative HL2 as the best chemosensor for Zn²⁺ ions because of its comparatively higher sensitivity. The color of this derivative changed from colorless to strong yellow with zinc addition, as indicated by the shift in UV-vis spectrum. Moreover, HL2 was the only derivative to emit fluorescence in the presence of Zn²⁺ ions, attributable to PET inhibition and bond isomerization promoted by coordination with this metal. LOD, LOQ, and binding constant values for HL2 + Zn²⁺ were 0.43 μmol.l^-1, 0.93 μmol.l^-1, and 5.04 × 10¹² l.mol^-1, respectively. The fluorescence of HL2 with other metal ions (Fe³⁺, Mg²⁺, Na⁺, Cd²⁺, Cu²⁺, Co²⁺, Ni²⁺, Ca²⁺, and K⁺) was also investigated. Zn²⁺ yielded the best result without Cd²⁺ interferences. Job's Plot showed that the stoichiometric ratio of the complex formed by HL2 and Zn²⁺ ions is 2:1 (ligand:metal). The strip test with adsorbed HL2 indicated fluorescence in the presence of zinc ions under 365 nm UV irradiation.

Molecular and Genomic Characterization of PFAB2: A Non-virulent Bacillus anthracis Strain Isolated from an Indian Hot Spring

Background

Thermophilic bacilli in both aerobic or facultative anaerobic forms have been isolated for over a hundred years from different mesophilic or thermophilic environments as they are potential source of bioactive secondary metabolites. But the taxonomic resolution in the Bacillus genus at species or at strain level is very challenging for the insufficient divergence of the 16S rRNA genes. One such recurring problem is among Bacillus anthracis, B. cereus and B. thuringiensis. The disease-causing B. anthracis strains have their characteristic virulence factors coded in two well-known plasmids, namely pXO1 (toxin genes) and pXO2 (capsule genes).

Objective

The present study aimed at the molecular and genomic characterization of a recently reported thermophilic and environmental isolate of B. anthracis, strain PFAB2.

Methods

We performed comparative genomics between the PFAB2 genome and different strains of B. anthracis, along with closely related B. cereus strains.

Results

The pangenomic analysis suggests that the PFAB2 genome harbors no complete prophage genes. Cluster analysis of Bray-Kurtis similarity resemblance matrix revealed that gene content of PFAB2 is more closely related to other environmental strains of B. anthracis. The secretome analysis and the in vitro and in vivo pathogenesis experiments corroborate the avirulent phenotype of this strain. The most probable explanation for this phenotype is the apparent absence of plasmids harboring genes for capsule biosynthesis and toxins secretion in the draft genome. Additional features of PFAB2 are good spore-forming and germinating capabilities and rapid replication ability.

Conclusion

The high replication rate in a wide range of temperatures and culture media, the non-pathogenicity, the good spore forming capability and its genomic similarity to the Ames strain together make PFAB2 an interesting model strain for the study of the pathogenic evolution of B. anthracis.

Sequential Fluorescence Recognition of Molybdenum(VI), Arsenite, and Phosphate Ions in a Ratiometric Manner: A Facile Approach for Discrimination of AsO2 - and H2PO4. ACS OMEGA 2019;4:10877-10890. [PMID: 31460185 PMCID: PMC6648501 DOI: 10.1021/acsomega.9b00377]

An amide-based smart probe (L) is explored for nanomolar detection of Mo(VI) ion in a ratiometric manner, involving hydrogen-bond-assisted chelation-enhanced fluorescence process through inhibition of photoinduced electron transfer process. The recognition of Mo(VI) is associated with a 17-fold fluorescence enhancement and confirmed by single-crystal X-ray diffraction of the resulting Mo(VI) complex (M1). Further, M1 selectively recognizes arsenite through green emission of their adduct (C1) with an 81-fold fluorescence enhancement. Interestingly, dihydrogen phosphate causes dissociation of C1 back to free L having weak fluorescence. The methods are fast, highly selective, and allow their bare eye visualization at physiological pH. All of the interactions have been substantiated by time-dependent density functional theory calculations to rationalize their spectroscopic properties. The corresponding lowest detection limits are 1.5 × 10-8 M for Mo(VI), 1.2 × 10-10 M for AsO2 -, and 3.2 × 10-6 M for H2PO4 -, whereas the respective association constants are 4.21 × 105 M-1 for Mo(VI), 6.49 × 104 M-1 for AsO2 -, and 2.11 × 105 M-1 for H2PO4 -. The L is useful for efficient enrichment of Mo(VI) from aqueous solution, while M1 efficiently removes AsO2 - from environmental samples by solid-phase extraction.

Subtle structural variation in azine/imine derivatives controls Zn2+ sensitivity: ESIPT-CHEF combination for nano-molar detection of Zn2+ with DFT support

Excited-state intra-molecular proton transfer (ESIPT)-active imine and azine derivatives, structurally characterised by XRD, and denoted L1, L2, L3 and L4, possess weak fluorescence. The interaction of these probes with Zn²⁺ turns ON the fluorescence to allow its nano-molar detection. Among the four ESIPT-active molecules, L2, L3 and L4 are bis-imine derivatives while L1 is a mono-imine derivative. Among the three bis-imine derivatives, one is symmetric (L3) while L2 and L4 are unsymmetrical. The lowest detection limits (DL) of L1, L2, L3 and L4 for Zn²⁺ are 32.66 nM, 36.16 nM, 15.20 nM and 33.50 nM respectively. All the probes bind Zn²⁺ (10⁵ M⁻¹ order) strongly. Computational studies explore the orbital level interactions responsible for the associated photo-physical processes.

Single crystal X-ray structurally characterised ESIPT-active weakly fluorescent imine and azine derivatives undergo Zn²⁺ assisted turn ON fluorescence.

Metal-Ion Displacement Approach for Optical Recognition of Thorium: Application of a Molybdenum(VI) Complex for Nanomolar Determination and Enrichment of Th(IV)

An azine-based molybdenum (Mo(VI)) complex (M1) is exploited for selective detection of thorium (Th(IV)) ions through a metal-ion displacement protocol. Th(IV) displaces Mo(VI) from M1 instantly leading to the formation of the Th(IV) complex, having orange-red emission. Consequently, a red shift of the emission wavelength along with 41-fold fluorescence enhancement is observed. This unique method allows detection of Th(IV) as low as 1.5 × 10^-9 M. The displacement of Mo(VI) from M1 by Th(IV) is established by spectroscopic studies and kinetically followed by the stopped-flow technique. The displacement binding constant for Th(IV) is notably strong, 4.59 × 10⁶ M^-1. Extraction of Th(IV) from aqueous solution to the ethyl acetate medium using M1 has been achieved. The silica-immobilized M1 efficiently enriches Th(IV) from its reservoir through solid-phase extraction. Computational studies (density functional theory) support experimental findings.

Exploring the Scope of Photo-Induced Electron Transfer-Chelation-Enhanced Fluorescence-Fluorescence Resonance Energy Transfer Processes for Recognition and Discrimination of Zn2+, Cd2+, Hg2+, and Al3+ in a Ratiometric Manner: Application to Sea Fish Analysis

A rhodamine-based smart probe (RHES) has been developed for trace-level detection and discrimination of multiple cations, viz. Al³⁺, Zn²⁺, Cd²⁺, and Hg²⁺ in a ratiometric manner involving photo-induced electron transfer-chelation-enhanced fluorescence-fluorescence resonance energy transfer processes. The method being very fast and highly selective allows their bare eye visualization at a physiological pH. The optimized geometry and spectral properties of RHES and its cation adducts have been analyzed by time-dependent density functional theory calculations. RHES detects as low as 1.5 × 10^-9 M Al³⁺, 1.2 × 10^-9 M Zn²⁺, 6.7 × 10^-9 M Cd²⁺, and 1.7 × 10^-10 M Hg²⁺, whereas the respective association constants are 1.33 × 10⁵ M^-1, 2.11 × 10⁴ M^-1, 1.35 × 10⁵ M^-1, and 4.09 × 10⁵ M^-1. The other common ions do not interfere. The probe is useful for intracellular imaging of Zn²⁺, Cd²⁺, and Hg²⁺ in squamous epithelial cells. RHES is useful for the determination of the ions in sea fish and real samples.