Hydroxy Oximes as Organophosphorus Nerve Agent Sensors

Reactivators of butyrylcholinesterase inhibited by organophosphorus compounds

In this review, the current progress in the research and development of butyrylcholinesterase (BChE) reactivators is summarised and the advantages or disadvantages of these reactivators are critically discussed. Organophosphorus compounds such as nerve agents (sarin, tabun, VX) or pesticides (chlorpyrifos, diazinon) cause irreversible inhibition of acetylcholinesterase (AChE) and BChE in the human body. While AChE inhibition can be life threatening due to cholinergic overstimulation and crisis, selective BChE inhibition has presumably no adverse effects. Because BChE is mostly found in plasma, its activity is important for the scavenging of organophosphates before they can reach AChE in the central nervous system. Therefore, this enzyme in combination with its reactivator can be used as a pseudo-catalytic scavenger of organophosphates. Three structural types of BChE reactivators were found, i.e. bisquaternary salts, monoquaternary salts and uncharged compounds. Although the reviewed reactivators have certain limitations, the promising candidates for BChE reactivation were found in each structural group.

A review on oxime functionality: an ordinary functional group with significant impacts in supramolecular chemistry

The oxime functional group is pivotal in chemistry, finding extensive applications in medical science, catalysis, organic functional group transformations, and the recognition of essential and toxic analytes. While the coordination chemistry of oxime derivatives has been thoroughly explored and several reviews have been published on this topic in reputable journals, a comprehensive review encompassing various aspects such as crystal engineering, cation and anion recognition, as well as coordination chemistry activities, is still in demand. This feature article highlights the diverse applications of oxime derivatives across multiple domains of chemistry, including medicine, agriculture, crystal engineering, coordination chemistry, and molecular recognition studies. Each of the oxime derivatives in this feature article are meticulously described in terms of their medicinal applications, crop protection, crystal engineering attributes, analyte recognition capabilities, and coordination chemistry aspects. By providing a comprehensive overview of their versatile applications, this article aims to inspire researchers to explore and develop novel oxime-based derivatives for future applications.

Coherent Modulation of the Aggregation Behavior and Intramolecular Charge Transfer in Small Molecule Probes for Sensitive and Long-term Nerve Agent Monitoring

Aggregation-induced emission (AIE) shows promising performance in chemical sensing relying on the change of the emission behavior of the probe molecule monomers to the aggregated product. However, whether the response contrast could be further boosted by utilizing the emission property of the aggregated probe and the aggregated product remains a big challenge. Here, an exciting AIE probe regulation strategy was proposed by coherently modulating the aggregation behavior and the intramolecular charge transfer (ICT) property of the probes and thus an aggregated-to-aggregated colorimetric-fluorescent dual-mode detection was achieved. The blue emissive film obtained with the optimal AIE probe has been proven to be effective to recognize the vapor of nerve agent analog DCP in air by emitting a sharp green fluorescence. In addition, a porous polymer-based wet sensing chip loaded with the probe enables the immediate response to DCP vapor with a limit of detection (LOD) of 1.7 ppb, and it was further integrated into a wearable watch device for long-term monitoring of DCP vapor up to two weeks. We expect the present probe design strategy would greatly deepen the AIE-based science and provide new insights for long-term monitoring sensors toward trace hazardous substances.

A benzoxazole-triphenylamine conjugated fluorogenic probe for specific detection of sarin gas mimic diethylchlorophosphate

In this study, an excellent chromo-fluorogenic PMPA probe, (E)-4-(((4-(benzoxazole-2-yl)phenyl)imino)methyl)-N,N-diphenylamine, is introduced for the detection of sarin gas mimic diethyl chlorophosphate (DCP) in solution and gaseous phases. On adding DCP into PMPA solution in a pure DMSO and water-DMSO (4 : 1) medium, it exhibits a hypsochromic shift from yellow to colorless and from no fluorescence to highly intense blue-violet photoluminescence via the formation of a phosphorylated PMPA-DCP product due to the inhibition of intramolecular charge transfer (ICT) and photoinduced electron transfer (PET) mechanism. The sensor could detect DCP in the presence of several other notorious guest analytes with a detection limit in the μM range. Moreover, to accomplish the on-spot detection of DCP and explore the practical applicability of the probe, a paper strip-based test kit, "dip-stick" method, and, more interestingly, a real sample analysis was demonstrated in spiked soil samples.

A highly sensitive fluorescence probe for on-site detection of nerve agent mimic diethylchlorophosphonate DCP

Nerve agents are the most toxic chemical warfare agents that pose severe threat to human health and public security. In this work, we developed a novel fluorescent probe NZNN based on naphthylimide and o-phenylenediamine to detect nerve agent mimic diethylchlorophosphonate (DCP). DCP underwent a specific nucleophilic reaction with the o-phenylenediamine group of NZNN to produce a significant fluorescence turn-on response with high selectivity, exceptional linearity, bright fluorescence, rapid response (<6 s) and a low detection limit (30.1 nM). Furthermore, a portable sensing device was fabricated for real-time detection of DCP vapor with excellent performance. This portable and sensitive device is favorable for monitoring environmental pollution and defense against chemical warfare agents.

Synthesis and evaluation of small organic molecule as reactivator of organophosphorus inhibited acetylcholinesterase

A series of uncharged salicylaldehyde oximes were synthesized and evaluated for the reactivation of organophosphorus (OP) nerve agents simulants Diethylchlorophosphonate (DCP) & Diethylcyanophosphonate (DCNP) and pesticides (paraoxon & malaoxon) inhibited electric eel Acetylcholinesterase (AChE). The computational software Swiss ADME and molinspiration were used to unfold the probability of drug-likeness properties of the oximes derivatives. Substituted aromatic oximes with diethylamino or bromo group with free hydroxyl group ortho to oxime moiety were found efficient to regenerate the enzymatic activity in in-vitro AChE assay. The alkylation of the ortho hydroxyl group of derivatives led to the loss of reactivation potential. The derivatives with a hydroxyl group and without oxime group and vice versa did not show significant reactivation potency against tested OP toxicants. Further, we also evaluated the reactivation potential of these selected molecules on the rat brain homogenate against different OPs inhibited ChE and found maximum reactivation potency of oxime 2e. The in-vitro results were further validated by molecular docking and dynamic studies which showed that the hydroxyl group interacted with serine amino acids in the catalytic anionic site of AChE enzyme and was stable up to 200 ns consequently providing proper orientation to oxime moiety for reactivating the OP inhibited enzyme. It has thus been proved by the structure-activity relationship of oximes derivatives that hydroxyl group ortho to oxime is essential for reactivating OP inhibited electric eel AChE. Amongst the twenty-one oximes derivatives, 2e was found to be most active in regenerating the paraoxon, malaoxon, DCP and DCNP inhibited AChE enzyme.

Fluorescent probes for the detection of chemical warfare agents

Chemical warfare agents (CWAs) are toxic chemicals that have been intentionally developed for targeted and deadly use on humans. Although intended for military targets, the use of CWAs more often than not results in mass civilian casualties. To prevent further atrocities from occurring during conflicts, a global ban was implemented through the chemical weapons convention, with the aim of eliminating the development, stockpiling, and use of CWAs. Unfortunately, because of their relatively low cost, ease of manufacture and effectiveness on mass populations, CWAs still exist in today's world. CWAs have been used in several recent terrorist-related incidents and conflicts (e.g., Syria). Therefore, they continue to remain serious threats to public health and safety and to global peace and stability. Analytical methods that can accurately detect CWAs are essential to global security measures and for forensic analysis. Small molecule fluorescent probes have emerged as attractive chemical tools for CWA detection, due to their simplicity, ease of use, excellent selectivity and high sensitivity, as well as their ability to be translated into handheld devices. This includes the ability to non-invasively image CWA distribution within living systems (in vitro and in vivo) to permit in-depth evaluation of their biological interactions and allow potential identification of therapeutic countermeasures. In this review, we provide an overview of the various reported fluorescent probes that have been designed for the detection of CWAs. The mechanism for CWA detection, change in optical output and application for each fluorescent probe are described in detail. The limitations and challenges of currently developed fluorescent probes are discussed providing insight into the future development of this research area. We hope the information provided in this review will give readers a clear understanding of how to design a fluorescent probe for the detection of a specific CWA. We anticipate that this will advance our security systems and provide new tools for environmental and toxicology monitoring.

Fluorimetric Recognition of Nerve Agent Mimic Diethylchlorophosphate Along with Cu2+/Hg2+ Ions Using Imidazole Possessing Sensor

An imidazole possessing sensor (1) has been designed and developed by simple one step reaction and characterization was done by using common spectroscopic methods. The fluorimetric sensing of nerve agent mimic, DCP, was carried out by observing blue shift in spectra accompanied with quenching in semi-aqueous solvent. The sensor was found proficient for the detection of DCP amongst other phosphates with detection limit of 69 nM. Furthermore, upon incorporation of various metal ions to CH₃CN:H₂O (4:1, v/v) solution of 1 (λ_ex 340 nm), the fluorescent probe turned non-fluorescent only in presence of Cu²⁺/Hg²⁺ ions. This was accompanied by fluorescent color change from light blue to yellow in case of Hg²⁺ and colorless in case of Cu²⁺ ions. Moreover, practical applications of sensor 1 were investigated for recognition of Cu²⁺ and Hg²⁺ ions in real water samples along with the detection of DCP in soil samples from different areas. Differential emission changes observed with addition of Hg²⁺ ions and DCP led to observation of "NOR" and an "INHIBIT" molecular photonic logic operations at 446 and 385 nm, respectively.

Enantiopure chiroptical probes for circular dichroism and absorbance based detection of nerve gas simulants

A series of oxovanadium(V) compounds 1-4 were prepared and explored as stereodynamic chiroptical probes to detect a simulant of sarin known as diethyl chlorophosphate (DCP) without any interference from the competing analytes. Simultaneous CD cum UV/vis based bimodal instant recognition of DCP using optically active probes is unprecedented. Upon fabricating the vanadium compound with a polymer has yielded a chiroptical membrane, which showed a change in its dichroic as well as colorimetric signals on interaction with DCP vapour at 1 ppm. EPR and UV/vis studies revealed an irreversible change of the CD-active V(V) to the CD-silent ternary V(V) species in presence of DCP via a transient V(IV) species. Nucleophilic attack of the alkoxo oxygen of 1-4 to the electrophilic P atom of DCP resulted in the formation of ternary V(V) compounds as confirmed by ⁵¹V/³¹P NMR.

Utilizing Experiment and Theory to Evaluate Rhodamine B ethylenediamine as a Fluorescent Sensor for G-type Nerve Agents

Nerve gas mimic binding with Rhodamine B ethylenediamine (1) was studied in organic media. Binding of the nerve gas mimic, diethyl chlorophosphate (DCP), with the probe generated a non-fluorescent intermediate and a fluorescent product. Fluorescent and non-fluorescent products generated were identified using mass spectrometry and X-ray crystallography. Time-dependent density functional theory calculations were also used to investigate the electronic structure of the fluorescent probe in the ground and lowest lying π → π* singlet excited state. Though good agreement between theory and experiment can be obtained for the intense peak in the experimental spectrum using non-hybrid functionals, care must be taken when modelling these complexes due to the appearance of an n → π* transition that is too low in energy and appears to fall in the shoulders of the π → π* transitions.

Organic-Molecule-Based Fluorescent Chemosensor for Nerve Agents and Organophosphorus Pesticides

Organophosphorus (OP) compounds are typically a broad class of compounds that possess various uses such as insecticides, pesticides, etc. One of the most evil utilizations of these compounds is as chemical warfare agents, which pose a greater threat than biological weapons because of their ease of access. OP compounds are highly toxic compounds that cause irreversible inhibition of enzyme acetylcholinesterase, which is essential for hydrolysis of neurotransmitter acetylcholine, leading to series of neurological disorders and even death. Due to the extensive use of these organophosphorus compounds in agriculture, there is an increase in the environmental burden of these toxic chemicals, with severe environmental consequences. Hence, the rapid and sensitive, selective, real-time detection of OP compounds is very much required in terms of environmental protection, health, and survival. Several techniques have been developed over a few decades to easily detect them, but still, numerous challenges and problems remain to be solved. Major advancement has been observed in the development of sensors using the spectroscopic technique over recent years because of the advantages offered over other techniques, which we focus on in the presented review.

Synthesis, Fabrication, and Characterization of Functionalized Polydiacetylene Containing Cellulose Nanofibrous Composites for Colorimetric Sensing of Organophosphate Compounds

Organophosphate (OP) compounds, a family of highly hazardous chemical compounds included in nerve agents and pesticides, have been linked to more than 250,000 annual deaths connected to various chronic diseases. However, a solid-state sensing system that is able to be integrated into a clothing system is rare in the literature. This study aims to develop a nanofiber-based solid-state polymeric material as a soft sensor to detect OP compounds present in the environment. Esters of polydiacetylene were synthesized and incorporated into a cellulose acetate nanocomposite fibrous assembly developed with an electrospinning technique, which was then hydrolyzed to generate more hydroxyl groups for OP binding. Scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FT-IR), Instron^® tensile tester, contact angle analyzer, and UV–Vis spectroscopy were employed for characterizations. Upon hydrolysis, polydiacetylene esters in the cellulosic fiber matrix were found unaffected by hydrolysis treatment, which made the composites suitable for OP sensing. Furthermore, the nanofibrous (NF) composites exhibited tensile properties suitable to be used as a textile material. Finally, the NF composites exhibited colorimetric sensing of OP, which is visible to the naked eye. This research is a landmark study toward the development of OP sensing in a protective clothing system.

A dual-channel optical chemical sensing system for selective detection of nerve agent simulant DFP

This paper reports a novel optical chemical sensing system for selective detection of diisopropylfluorophosphate (DFP), a simulant of fluorine-containing nerve agents (Sarin and Soman). Contrary to the reported methods involving only single sensing probe, this sensing system is comprised of two molecular sensing probes (1 and 2) having intrinsic affinities for reactive subunits of DFP (electrophilic phosphorus and fluoride ion). On exposure to DFP, two molecular probes react in tandem with electrophilic phosphorus and fluoride ion (by-product of the initial phosphorylation reaction) to induce a unique modulation in the optical properties of the sensing system which leads to selective detection of DFP in solution as interferents like phosphorus-containing compounds, acids, and anions were unable to induce similar optical modulation due to lack of both electrophilic phosphorus and fluorine in the same molecule. Calibration curve between the amount of DFP added and the absorption intensity revealed the colorimetric detection limit of the system to be 4.50 μM which was further lowered to 2.22 μM by making use of a self-immolative fluoride sensing probe 5.

Chromo-fluorogenic sensors for chemical warfare agents in real-time analysis: journey towards accurate detection and differentiation

The existence of chemical weapons (blister and nerve agents) is an unfortunate reality of the modern world. The usage of these chemical agents by rogue states or terrorist groups has showcased their ugly faces in the past and even in recent years. Despite extensive and strenuous efforts by the Organization for the Prohibition of Chemical Weapons (OPCW) to eliminate chemical warfare agents (CWAs) by the prohibition of their production and the destruction of their stockpiles, many countries still possess them in enormous quantities. Given the potential threat from these lethal agents, it is imperative to have a foolproof chemical sensor and detection system, which should consist of readily deployable chemical probes that can operate with high specificity and sensitivity. Over the last decade, our group has been engaged in designing and developing novel field-deployable sensing techniques by exploring approaches based on supramolecular tools, which can result in excellent specificity, sensitivity, high speed, portability and low cost. In this article, I describe our group's journey and success stories in the development of chemical warfare detection protocols, detailing the range of unique chemical probes and methods explored to achieve the specific detection of individual agents under real environmental conditions. It is interesting to note that the combination of three molecular probes (SQ, Fc and LH2) could simply achieve the detection of all CWAs at room temperature in one go without the need for nonportable and expensive instruments. The ease and generality of these techniques/methods suggest great promise for the highly specific chemical sensing of almost the entire class of CWAs. In this paper, a brief introduction is first provided to present the basic chemistry related to CWAs and the importance of supramolecular chemistry in the design of new protocols with new insights. The manipulation of molecular probes is then debated towards the development of a system for the chromo-fluorogenic sensing of CWAs without interference from most relevant analytes. Finally, the outlook of open challenges and the future developments of this rapidly evolving field is discussed.

Bis-heteroleptic Ru(ii) polypyridine complex-based luminescent probes for nerve agent simulant and organophosphate pesticide

Two bis-heteroleptic Ru(ii) complexes of a 4,7-dihydroxy-1,10-phenanthroline ligand were synthesized for the detection of the nerve agent gas mimic, DCP, and the organophosphate pesticide, dichlorvos, through the “off–on” luminescence response.

Selective detection of chemical warfare agents VX and Sarin by the short wavelength inner filter technique (SWIFT)

A novel SWIFT-based strategy for fluorimetric detection of practical amounts (minimal effective dose or lower) of chemical warfare agents is reported. This strategy employs readily available reagents and allows distinguishing between the V and G agents, as well as their discrimination from potential interferents.

Challenges in Fluorescence Detection of Chemical Warfare Agent Vapors Using Solid-State Films

Organophosphorus (OP)-based nerve agents are extremely toxic and potent acetylcholinesterase inhibitors and recent attacks involving nerve agents highlight the need for fast detection and intervention. Fluorescence-based detection, where the sensing material undergoes a chemical reaction with the agent causing a measurable change in the luminescence, is one method for sensing and identifying nerve agents. Most studies use the simulants diethylchlorophosphate and di-iso-propylfluorophosphate to evaluate the performance of sensors due to their reduced toxicity relative to OP nerve agents. While detection of nerve agent simulants in solution is relatively widely reported, there are fewer reports on vapor detection using solid-state sensors. Herein, progress in organic semiconductor sensing materials developed for solid-state detection of OP-based nerve agent vapors is reviewed. The effect of acid impurities arising from the hydrolysis of simulants and nerve agents on the efficacy and selectivity of the reported sensing materials is also discussed. Indeed, in some cases it is unclear whether it is the simulant that is detected or the acid hydrolysis products. Finally, it is highlighted that while analyte diffusion into the sensing film is critical in the design of fast, responsive sensing systems, it is an area that is currently not well studied.

Tacroximes: novel unique compounds for the recovery of organophosphorus-inhibited acetylcholinesterase

Aim: Organophosphorus compounds are irreversible inhibitors of AChE. Without immediate countermeasure, intoxication leads quickly to death. None of the clinically-used causal antidotes can ensure a good prognosis for any poisoned patient. When fallen into the wrong hands, organophosphates represent a serious threat to mankind. Results & methodology: Herein, we describe two novel compounds as unique merged molecules built on a tacrine scaffold against organophosphorus intoxication. These reactivators of AChE have balanced physicochemical properties, and should be able to cross the blood–brain barrier with a slightly lowered cytotoxicity profile compared to reference tacrine. Conclusion: Their efficiency compared with pralidoxime and obidoxime was proved against dichlorvos.

A flavonoid-based fluorescent test strip for sensitive and selective detection of a gaseous nerve agent simulant

Developing fluorescent sensors with ability of monitoring gaseous nerve agents in a sensitive and selective manner is of great importance due to the extreme toxicity and volatility of organophosphorus nerve agents. Herein we reported a novel oxime-modified flavonoid sensor and carefully investigated its sensing behavior towards nerve agent simulants, diethylchlorophosphate (DCP). In the presence of DCP, a remarkable fluorescence enhancement accompanied with emission color change could be observed by naked eyes in solution. The response time was less than 90 s and LOD value was calculated as 0.78 μmol/L in solution. The sensing mechanism could be ascribed to the specific reaction between halophosphate and hydroxyl group of oxime. Furthermore, sensor strips have been successfully constructed by using PEG as matrix with a simple preparation process, and also achieved the sensitive and selective detection of DCP vapor. These results in this study may provide important references for further design of dye-based sensor strips for detection of nerve agents both in solution and gas phase.

Organoiridium(III) Complexes as Luminescence Color Switching Probes for Selective Detection of Nerve Agent Simulant in Solution and Vapor Phase

In this work, cationic organoiridium(III) complex based photoluminescent (PL) probes have been developed to selectively detect the chemical warfare nerve agent mimic, diethyl chlorophosphate(DCP) at nanomolar range by distinct bright green to orange-red luminescence color switching (on-off-on) in solution as well as in the vapor phase. Interference of other chemical warfare agents (CWAs) and their mimics was not observed either by PL spectroscopy or with the naked-eye in solution and gas phase. The detection was attained via a simultaneous nucleophilic attack of two -OH groups of the 4,7-dihydroxy-1,10-phenanthroline ligand with DCP by forming bulkier phosphotriester. The detailed reaction mechanism was established through extensive ¹H NMR titration, ³¹P NMR, and ESI-MS analysis. Finally, a test paper strip and solid poly(ethylene oxide) (PEO) film with iridium(III) complex 1[PF₆] were fabricated for the vapor-phase detection of DCP. The solution and vapor-phase detection properties of these luminescent Ir(III) complexes can offer a worthy approach into the design of new metal complex based PL switching probes for chemical warfare agents.

Facile detection of organophosphorus nerve agent mimic (DCP) through a new quinoline-based ratiometric switch

Here a new quinoline-based (BIMQ) probe was developed which displayed ratiometric detection of organophosphorus chemical vapor threat, DCP.

Molecular recognition of organophosphorus compounds in water and inhibition of their toxicity to acetylcholinesterase

endo-Functionalized molecular tubes are able to recognize toxic organophosphorus compounds in water. They can be used as a fluorescent sensor and as an inhibitor to reduce the toxicity of paraoxon to acetylcholinesterase.

Simple and Efficient Chromophoric-Fluorogenic Probes for Diethylchlorophosphate Vapor

In this work, we developed two small-molecule probes for real-time and onsite detecting of diethylchlorophosphate (DCP) vapor by incorporating amine groups into Schiff base skeletons. Both probes can be easily synthesized with high yield through one-step and low-cost synthesis. They can detect DCP vapor in the chromophoric-fluorogenic dual mode, which combines both the advantages of the visualization of color sensing and the high sensitivity of the fluorescence sensing. Furthermore, its sensing is based on the "turn-on" mode which can avoid the interference arising from photobleaching or fluorescence quenching agents based on "turn-off" mode. The detection limit was quantified to be as low as 0.14 ppb.

Visual detection of a nerve agent simulant using chemically modified paper strips and dye-assembled inorganic nanocomposite

Chromogenic probe with oxidized bis-indolyl scaffold has been synthesized for the detection of a nerve gas mimicking agent, DCNP (diethyl cyanophosphonate) at pH 8.0 in water. The mechanism of interaction was proposed as the release of cyanide ion through the indole group mediating the hydrolysis of phosphorous-hetero atom bond and, thereafter, the Michael addition of the liberated CN^- ion to the electron deficient C[double bond, length as m-dash]C bond of the bis-indolyl moiety. The reaction featured a remarkable change in color from red to colorless at ambient condition. Then, low-cost and portable paper strips were designed for a rapid and on-site vapor phase detection of DCNP without involving any sophisticated instrument or skilled personnel. Finally, a dye assembled inorganic nanocomposite material was devised to achieve a more sensitive 'turn-on' detection of DCNP in water.

Recent Advances in the Development of Chromophore-Based Chemosensors for Nerve Agents and Phosgene

The extreme toxicity and ready accessibility of nerve agents and phosgene has caused an increase in the demand to develop effective systems for the detection of these substances. Among the traditional platforms utilized for this purpose, chemosensors including surface acoustic wave (SAW) sensors, enzymes, carbon nanotubes, nanoparticles, and chromophore based sensors have attracted increasing attention. In this review, we describe in a comprehensive manner recent progress that has been made on the development of chromophore-based chemosensors for detecting nerve agents (mimic) and phosgene. This review comprises two sections focusing on studies of the development of chemosensors for nerve agents (mimic) and phosgene. In each of the sections, the discussion follows a format which concentrates on different reaction sites/mechanisms involved in the sensing processes. Finally, chemosensors uncovered in these efforts are compared with those based on other sensing methods and challenges facing the design of more effective chemosensors for the detection of nerve agents (mimic) and phosgene are discussed.

An ESIPT fluorescent probe and a nanofiber platform for selective and sensitive detection of a nerve gas mimic

An ESIPT based fluorescent probe, containing a hydroxyphenyl-benzothiazole fluorophore and an oxime reaction site, serves as a selective probe for a nerve gas mimic, diethyl cyanophosphonate (DECP), in solutions and the gas phase.

7-Dialkylaminocoumarin Oximates: Small Molecule Fluorescent "Turn-On" Chemosensors for Low-Level Water Content in Aprotic Organic Solvents

The water sensing properties of two efficient two-component fluorescent “turn-on” chemo-sensors based on the 7-dialkylaminocoumarin oxime acid-base equilibrium were investigated. Interestingly, although simple frontier orbital analysis predicts an intramolecular photoinduced electron transfer quenching pathway in conjugated oximates, TD-DFT (Time-dependent density functional theory) quantum chemical calculations support non-radiative dark S₁ excited state deactivation as a fluorescence quenching mechanism. Due to the acid-base sensing mechanism and sensitive “turn-on” fluorescent response, both studied coumarin aldoxime chemosensors exhibit rapid response to low-level water content in polar aprotic solvents, with detection limits comparable to chemodosimeters or chemosensors based on interpolymer π-stacking aggregation.

Fluorescent Chemosensors with Varying Degrees of Intramolecular Charge Transfer for Detection of a Nerve Agent Mimic in Solutions and in Vapor

Nerve agents are highly toxic organophosphorus compounds, and their possible use in terrorist attacks has led to increasing interest in the development of reliable and accurate methods to detect these lethal chemicals. In this paper, we have prepared six 6-aminoquinolines with various N-substituents as chemosensors for a nerve-agent mimic diethylchlorophosphate (DCP). The chemosensors with the nucleophilic pyridine-N atom as the active site detect DCP via a catalytic hydrolysis approach to form the protonated sensor. The nucleophilicity of the pyridine-N atom depends on the donating ability of the 6-amine group, which affects the intramolecular charge-transfer (ICT) character of sensors and the protonated sensors, leading to different fluorescence-response modes. The effects of the ICT character on the sensing property have been clarified. Among these charge transfer sensors, the sensor 3 displays ratiometric fluorescence response to DCP and a low limit of detection (8 nM). Furthermore, a facile testing strip with 3 has been fabricated with poly(ethylene oxide) for real-time selective monitoring of DCP vapor.

New Autoinductive Cascade for the Optical Sensing of Fluoride: Application in the Detection of Phosphoryl Fluoride Nerve Agents

A new autoinductive cascade employing benzoyl fluoride as a latent source of fluoride is reported for signal amplification and optical detection of fluoride. The autoinduction leads to a maximum 4-fold signal enhancement for each fluoride generated, as well as a self-propagating cycle that generates three fluorophores for each single fluoride released. A two-step integrated protocol creates a more rapid autoinductive cascade than previously reported, as well as a highly sensitive diagnostic assay for the ultratrace quantitation of a phosphoryl fluoride nerve agent surrogate.

Colorimetric detection and removal of radioactive Co ions using sodium alginate-based composite beads

We demonstrate a simple method for the visual determination and removal of Co ions using a bead-shaped, capturing probe based on hybridized sodium alginate. For Co ions, the designed protocol consisted of three main constituents: an azopyridine-based Co ion-probe for visual detection; sodium alginate as an adsorbent for the Co ion and a bead construct for removal and structure; silica as a linker for the probe and the alginate, leading to a robust structure. When the composite beads were exposed to Co ions, the yellow color of the beads turned to intensive violet and the color intensity was associated with the Co ion concentration. The color variation was quantified using red-green-blue (RGB) color values that were obtained with a scanner and evaluated with Photoshop. The technique achieved both visual recognition with obvious color change of the beads and efficient removal of the radioactive ⁶⁰Co ion. The sensing and removal of any radioactive isotope could be achieved with an appropriate sensing probe, to provide a simple and universal platform for remediation.

Substrate Specificity and Leaving Group Effect in Ester Cleavage by Metal Complexes of an Oximate Nucleophile

Deprotonated zinc(II) and cadmium(II) complexes of a tridentate oxime nucleophile (1, OxH) show a very high reactivity, breaking by 2-3 orders of magnitude the previously established limiting reactivity of oximate nucleophiles in the cleavage of substituted phenyl acetates and phosphate triesters, but are unreactive with p-nitrophenyl phosphate di- and monoesters. With reactive substrates, these complexes operate as true catalysts through an acylation-deacylation mechanism. Detailed speciation and kinetic studies in a wide pH interval allowed us to establish as catalytically active forms [Cd(Ox)]⁺, [Zn(Ox)(OH)], and [Zn(Ox)(OH)₂]^- complexes. The formation of an unusual and most reactive zinc(II) oximatodihydroxo complex was confirmed by electrospray ionization mass spectrometry data and supported by density functional theory calculations, which also supported the previously noticed fact that the coordinated water in [Zn(OxH)(H₂O)₂]²⁺ deprotonates before the oxime. Analysis of the leaving group effect on the cleavage of phenyl acetates shows that the rate-determining step in the reaction with the free oximate anion is the nucleophilic attack, while with both zinc(II) and cadmium(II) oximate complexes, it changes to the expulsion of the leaving phenolate anion. The major new features of these complexes are (1) a very high esterolytic activity surpassing that of enzyme hydrolysis of aryl acetate esters and (2) an increased reactivity of coordinated oxime compared to free oxime in phosphate triester cleavage, contrary to the previously observed inhibitory effect of oxime coordination with these substrates.

Complexation of Racemic 2,6-Helic[6]arene and Its Hexamethyl-Substituted Derivative with Quaternary Ammonium Salts, N-Heterocyclic Salts, and Tetracyanoquinodimethane

Complexation of racemic 2,6-helic[6]arene 1 and its hexamethyl-substituted derivative 2 with quaternary ammonium salts, N-heterocyclic salts, and tetracyanoquinodimethane have been described in detail. It was found that host 2 could form stable complexes with acetyl choline, thiaacetyl choline, N,N,N-trimethylbenzenammonium salt, pyridinium, and 4,4'-bipyridinium salts in solution and/or in the solid state. The unsubstituted macrocycle 1 showed more significant complexation with the widely tested quaternary ammonium salts and N-heterocyclic salts, and exhibited stronger complexation towards the guests than its derivative 2. Moreover, it was found that macrocycle 1 and its derivative 2 could also complex with neutral electron-deficient tetracyanoquinodimethane (TCNQ), and the association constants were determined to be 2840±94 and 1358±46 m^-1 , respectively. These results could make this new macrocycle and its derivatives find wide applications in the design and construction of functional supramolecular assemblies.