Structural Effect of Thioureas on the Detection of Chemical Warfare Agent Simulants

Abstract

The ability to rapidly detect, identify, and monitor chemical warfare agents (CWAs) is imperative for both military and civilian defense. Since most CWAs and their simulants have an organophosphonate group, which is a hydrogen (H)-bond acceptor, many H-bond donors have been developed to effectively bind to the organophosphonate group. Although thioureas have been actively studied as an organocatalyst, they are relatively less investigated in CWA detection. In addition, there is a lack of studies on the structure-property relationship for gas phase detection. In this study, we synthesized various thioureas of different chemical structures, and tested them for sensing dimethylmethylphosphonate (DMMP), a CWA simulant. Molecular interaction between DMMP and thiourea was measured by H NMR titration and supported by density functional theory (DFT) calculations. Strong H-bond donor ability of thiourea may cause self-aggregation, and CH-π interaction can play an important role in the DMMP detection. Gas-phase adsorption of DMMP was also measured using a quartz crystal microbalance (QCM) and analyzed using the simple Langmuir isotherm, showing the importance of structure-induced morphology of thioureas on the surface.

Binding thiourea derivatives with dimethyl methylphosphonate for sensing nerve agents

“…In this work, we rst compared the binding energies of TUn (n ¼ 1-9) calculated from the DFT method with the sensing efficiencies obtained from the previous work. 14 The results from the DFT calculation and the QCM experiment matched excellently, as shown in a later section. This motivated us to test new thiourea derivatives, TUn (n ¼ 10-13, shown in Scheme 1), both computationally and experimentally.…”

“…[18][19][20]. As shown in the previous reports, 14 the QCM test can detect a trace amount of mass change by frequency shi of the crystal oscillator upon adsorption and desorption of a target molecule (i.e., DMMP). Prior to the QCM measurements, a drop (4 mL) of TUn (n ¼ 10-13) solution in DMF (2 mg mL À1 ) was casted for coating on the surface of a quartz crystal (8 MHz, AT cut).…”

“…More recently, some of us synthesized a different list of thiourea derivatives and tested their coated lms for sensing DMMP. 14 The synthesized thiourea derivatives in the previous work, namely TUn (n ¼ 1-9) series, are shown in Scheme 1. The test results employing quartz crystal microbalance (QCM) and 1 H-NMR spectroscopy can be summarized as follows: (1) Nbenzyl substitution (as in TU4) induced the higher sensing efficiency than N-phenyl (TU1), N-n-butyl (TU2), or N-cyclohexyl substitutions (TU3); (2) introducing electron-withdrawing uoro group (as in TU5) or electron-donating methoxy group (as in TU6) to para position of the N-benzyl group did not change the sensing efficiency signicantly; and (3) the symmetric thiourea derivative with N-benzyl substitutions at both branches (as in TU7) reduced the sensing efficiency probably because of increased self-aggregation.…”

Superhydrophobic Polymerized n-Octadecylsilane Surface for BTEX Sensing and Stable Toluene/Water Selective Detection Based on QCM Sensor

“…13−17 QCM is used as a transducer for detecting different gases via coating various materials. 18 Although these BTEX sensors possess good sensing ability, most of them have not focused on eliminating the interference of water, which can badly weaken the selectivity of gas sensors. The BTEX detection performance under different relative humidities (RHs) is also unstable.…”

Chromo-Fluorogenic Detection of Soman and Its Simulant by Thiourea-Based Rhodamine Probe

“…A typical chromo-fluorogenic probe is usually formed by two moieties: (1) a chromo-fluorogenic reporter group, which translates the binding event into the change of color and fluorescence, mainly containing rhodamine [22], fluorescein [15], boron dipyrromethene (BODIPY) [16,17], azo [14,20], and cyanine dye [18]; (2) a selective reactive group, which provides a reactive binding site for nucleophilic attack, mainly containing hydroxyl [15,25], oxime [19], and amino groups [26]. Recently, thiourea has been proved to be capable of reacting with nerve agents through hydrogen-bond interaction between N-H protons of thiourea and phosphonate oxygen or hydrolyzed products [27,28]. It has been also proven that the reaction of thiosemicarbazide group can induce opening of the spirolactam ring in rhodamine B accompanied with color change and enhanced fluorescence [29].…”