Colorimetric Detection of Anions in Aqueous Solution Using Poly(phenylacetylene) with Sulfonamide Receptors Activated by Electron Withdrawing Group

Chromaticity sensor for discriminatory identification of aliphatic and aromatic primary amines based on conformational changes of polyacetylene

The design and construction of suitable sensors that can selectively recognize chemically similar substances such as aliphatic and aromatic amines remain challenging. In this work, we reported a poly(phenylacetylene) bearing two aldehyde pendants as the color indicator for discriminative identification of amines. Reversible Schiff-base reaction of the aldehyde group with the amine resulted in a conformational transition of the polyacetylene backbone from cis-cisoid to cis-transoid, which further achieved a colorimetric change. Thirteen aliphatic amines and aromatic amines had been studied. Compared with aromatic amines, aliphatic amines generally caused the polyene backbone to display perceivable colorimetric change. Steric and electronic effect played a significant role in the colorimetric response. In addition, external environment, including amine content, polymer concentration, and temperature, had influence on the sensitivity of this colorimetric indicator system. The amines-induced colorimetric variation was further demonstrated by the CIELAB color space. Moreover, the colorimetric sensor exhibited excellent reversibility and recyclability.

Stimuli-responsive synthetic helical polymers

Synthetic dynamic helical polymers (supramolecular and covalent) and foldamers share the helix as a structural motif. Although the materials are different, these systems also share many structural properties, such as helix induction or conformational communication mechanisms. The introduction of stimuli responsive building blocks or monomer repeating units in these materials triggers conformational or structural changes, due to the presence/absence of the external stimulus, which are transmitted to the helix resulting in different effects, such as assymetry amplification, helix inversion or even changes in the helical scaffold (elongation, J/H helical aggregates). In this review, we show through selected examples how different stimuli (e.g., temperature, solvents, cations, anions, redox, chiral additives, pH or light) can alter the helical structures of dynamic helical polymers (covalent and supramolecular) and foldamers acting on the conformational composition or molecular structure of their components, which is also transmitted to the macromolecular helical structure.

Photostability and Dynamic Helical Behavior in Chiral Poly(phenylacetylene)s with a Preferred Screw‐Sense

Helical polymers such as poly(phenylacetylene)s (PPAs) are interesting materials due to the possibility of tuning their helical scaffold (sense and elongation) once they have been prepared and by the presence of external stimuli. The main limitation in the application of PPAs is their poor photostability. These polymers degrade under visible light exposure through a photochemical electrocyclization process. In this work, it was demonstrated, through a selected example, how the photochemical degradation in PPAs is directly related to their dynamic helical behavior. Thus, while PPAs with dynamic helical structures show poor photostability under UV/Vis light exposure, poly‐(R)‐1, bearing an enantiopure sulfoxide group as pendant group and designed to have a quasi‐static helical behavior, shows a large photostability due to the restricted conformational composition at the polyene backbone, needed to orient the conjugated double bonds prior to the photochemical electrocyclization process and the subsequent degradation of the material.

Sulfonamides as Optical Chemosensors

Sulfonamides are auspicious chemosensors which are capable to bind with ionic species through various ways like complexation, charge transfer, proton transfer etc. and produce a detection signal in the form of an optical change either in visible or UV-light and for electronic as well as fluorimetric spectra. Sulfonamides have gained much attention of analytical chemists these days as these are inexpensive, robust, green in nature and some what sensitive and selective to many anionic and cationic species. Due to their promising versatility in sensing properties, these are under great consideration in forensic, environmental, analytical and biochemistry laboratories. This review narrates how sulfonamides are being used to optically sense ionic species.

The detection of multiple analytes by using visual colorimetric and fluorometric multimodal chemosensor based on the azo dye

In recent decades, researchers have conducted in-depth studies of the design and synthesis of colorimetric/fluorometric probes and the application of such probes to biological and practical samples. The multifunctional colorimetric and fluorescent azo benzene-based probe (4′-hydroxyl-2,4-diaminoazobenzene, MP) was designed to detect Al³⁺, Fe³⁺, Cu²⁺ and F¯. Based on the distinct redshift of the absorption band and a significant color change (yellow → purple), MP was utilized for both naked-eyed and quantitative detection of Al³⁺ and Fe³⁺ after formation of the 1:1 complex. Test paper coated with MP and used in conjunction with a cell phone was used for colorimetric detection of Al³⁺ and Fe³⁺ ions (20 μM–2.0 mM) in water samples through naked-eye and digital image colorimetry. The “MP-Fe³⁺” coordination shift that occurs in the presence of the competitive ligand F¯ was used in the colorimetric measurement of F¯ in toothpaste. In the presence of Cu²⁺ ion, the non-emissive MP has transformed into fluorescent benzotriazole product PMP (Φ = 0.53) through the bimolecular rate-limiting step, and the second-order rate constant k is calculated as 31 ± 2 M⁻¹ s⁻¹. MP exhibits a “turn-on” fluorescence response in the presence of Cu²⁺ that is greater than its response in the presence of competitive species such as Fe³⁺, Al³⁺, Co²⁺, Fe²⁺, Zn²⁺, Cd²⁺, Mg²⁺, Mn²⁺, Ni²⁺ and Ag⁺. MP was shown to have low toxicity to living HeLa cells and to present good imaging characteristics for tracking of Cu²⁺ in vivo.

Photochemical Electrocyclization of Poly(phenylacetylene)s: Unwinding Helices to Elucidate their 3D Structure in Solution

Photochemical electrocyclization of poly(phenylacetylene)s (PPAs) is used for the structural elucidation of a polyene backbone. This method not only allows classification of PPAs in cis-cisoidal (ω₁ <90°) or cis-transoidal structures (ω₁ >90°), but also approximating ω₁ . A PPA solution is illuminated with visible light and monitoring the photochemical electrocyclization of the PPA helix by measuring the ECD spectra at different times. PPAs with a cis-cisoidal structure show a reduction of the ECD signal of at least 50 % before 30 min of irradiation, while cis-transoidal helices need much longer time because the transoidal bond must be isomerized. The different cis-cisoidal and cis-transoidal helices require different times to decrease their ECD signal by 50 % (t_1/2 ), depending on the degree of compression or stretching of the helix, establishing a relationship between the secondary structure adopted by PPA (ω₁ ) and the time required to lose the ECD vinylic signal by light irradiation.

Exploring the Effects of Various Polymeric Backbones on the Performance of a Hydroxyaromatic 1,2,3-Triazole Anion Sensor

Polymeric chemosensors are vital sensing tools because of higher sensitivity compared to their monomeric counterparts and tunable mechanical properties. This study focuses on the incorporation of a hydroxyaromatic 1,2,3-triazole sensor, 2-(4-phenyl 1H-1,2,3-triazol-1-yl)phenol (PTP), into polymers. By itself, the triazole has a selective, fluorometric response to the fluoride, acetate, and dihydrogen phosphate anions, and is most responsive to fluoride. Current investigations probe the suitability of various polymeric backbones for the retention and enhancement of the triazole’s sensing capabilities. Backbones derived from acrylic acid, methyl methacrylate, divinylbenzene, and styrene were explored. UV-illumination, Nuclear Magnetic Resonance (NMR) titration, and ultraviolet-visible (UV-Vis) absorption and fluorescence spectroscopy studies are used to investigate the performance of newly synthesized polymers and the derivatives of PTP that serve as the polymers’ precursors. Among the polymers investigated, copolymers with styrene proved best; these systems retained the sensing capabilities and were amenable to tuning for sensitivity.

Synthesis of Magnetite-Based Polymers as Mercury and Anion Sensors Using Single Electron Transfer-Living Radical Polymerization

In this work, hydrophilic polymers modified with iron oxide nanoparticles, such as iron oxide-poly(2-dimethylaminoethyl methacrylate) [P(DMAEMA)] magnetite-based and iron oxide-poly(acrylamide) [P(AAm)] magnetite-based polymers, were prepared via a single electron transfer-living radical polymerization approach. Bile acid and 2-bromo-2-methylpropionic acid were covalently attached onto the surface of Fe3O4 nanoparticles, and these immobilized magnetite nanoparticles were used as an initiator for the polymerization. The binding capabilities of different ions, such as Hg2+, CN-, Cl-, F-, and NO3 -, were tested using these polymeric sensors monitored by UV-vis spectroscopy. Magnetite-based P(DMAEMA) showed enhanced binding capability due to the presence of tertiary amine groups. In addition, it was possible to easily separate the bound ions from aqueous media using an external magnetic field.

Design and synthesis new colorimetric receptors for naked-eye detection of biologically important fluoride and acetate anions in organic and arsenite in aqueous medium based on ICT mechanism: DFT study and test strip application

Novel three colorimetric anion receptors R1, R2 and R3 have been designed and synthesized via condensation reaction and characterized using IR, MS, and NMR spectroscopic techniques. Anion sensing properties were studied using colorimetric, UV-vis titration, ¹H NMR titration, and Cyclic Voltammetric Studies. Comparing the UV-visible titration data of the receptors R1 and R2, R2 showed high redshift (∆λ_max) in the mixed competitive solution (DMSO: H₂O, 9: 1; v/v) of about 155 nm, 157 nm, 169 nm for Na⁺F^-, Na⁺AcO^-, and Na⁺AsO₂^- ions with LOD of 0.23 ppm, 0.18 ppm, and 0.30 ppm, respectively. The observed spectral change of receptor R2 is due to the anion-induced deprotonation of the OH proton, which is confirmed by UV-vis titration, ¹HNMR titration, and cyclic voltammetric studies. Theoretical studies via DFT calculation were carried for R1 and R2 to optimize the structure and to explain the anion-binding mechanism. The application of designed receptor R2 was successfully demonstrated for the detection of F^- and AsO₂^- ions using a test strip. The receptors R1 and R2 proved itself to be potentially useful for real-life application by sensing F^- and AcO^- ions in real samples like toothpaste, mouthwash, vinegar and seawater in a complete aqueous medium.

Stimuli-Directed Colorimetric Interconversion of Helical Polymers Accompanied by a Tunable Self-Assembly Process

Interconversion between extended and bent structures at the pendant groups of a chiral polyene framework [poly(phenylacetylene) with (R)-(2-methoxy-2-phenylacetyl)glycine residues linked to 4-vinylanilines] allows the reversible colorimetric transformation from stretched to compressed helical cis-transoid polyenic structures through manipulation of the flexible spacer. This transformation generates either organogels (stretched helical form) or nanoparticles (compressed helical form) under the control of polar/low polar stimuli respectively and opens the way to the development of new sensors and stimuli-sensitive materials based on these concepts.

Influence of different sequences of l-proline dipeptide derivatives in the pendants on the helix of poly(phenylacetylene)s and their enantioseparation properties

Novel helical poly(phenylacetylene)s bearing different sequences of l-proline dipeptide derivative pendants were prepared and used as CSPs in HPLC for enantioseparation.

Robust, sensitive and facile method for detection of F-, CN- and Ac- anions

Sensing of F^-, CN^- and Ac^- is important from the viewpoint of both medically and environmentally. Particularly, sensing of the anions in 100% water by a colorimetric chemical sensor is a highly difficult task as water molecules interfere the sensing mechanism. In this regard, sensor R1, having azo and nitrophenyl groups as signaling units and thiourea as a binding site was prepared. This sensor exclusively detected CN^- ion over other testing anions in 30% aq. DMSO solution by exhibiting distinct spectral and visual color changes. However, in 15% aq. DMSO solution, R1 exhibited obvious spectral and color changes in response to F^-, CN^- and Ac^-. On the other hand, we have also designed sensor, R2, having same signaling units of R1, but a different binding site of urea group. Surprisingly, in contrast to R1, R2 exhibited obvious spectral and color changes in 5% aq. DMSO solution only. Further, economically viable "test stripes" were prepared in a facile mode to detect the CN^- in 100% aqueous solution. Such stripes can serve as a practical colorimetric probe for "in the field" detection of the ions and thus avoid additional expensive equipment.

Detection of cyanide ions in aqueous solutions using cost effective colorimetric sensor

Cyanide (CN̄) is one of the most toxic material to the human and environment. It is very important to develop the diagnostic tools for the detection of CN̄ ions. Moreover, detection of the ions in an aqueous medium is a challenging task as water molecules interfere with the sensing mechanism. In this context, we prepared chemical sensor, S1, having anthraquinone as a signaling unit and thiourea as a binding site. This sensor exhibited distinct visual color and spectral changes in response to CN̄ ion over other testing anions in 50% aq. DMSO solution. However, in 20% aq. DMSO solution, S1 exhibited obvious spectral and color changes in response to CN̄, fluoride (F̄), acetate (Ac̄) and benzoate (Bz̄). Another sensor, S2, having a same signaling unit with that of S1, but a different binding site of urea group. In contrast to S1, S2 exhibited obvious spectral and color changes to F̄ in 2.5% aq. DMSO solution. NMR titration results suggested that the spectral and colorimetric responses were due to the formation of host-guest complex and deprotonation events. Finally, economically viable paper-based colorimetric "test stripes" of S1 were fabricated to detect the CN̄ ions in 100% aqueous solution.

Heck functionalization of an asymmetric aza-BODIPY core: synthesis of far-red infrared probes for bioimaging applications

Heck functionalization of azadipyrromethenes (aza-DIPY) allows the introduction of suitable functional groups to convert aza-BODIPY in bioconjugate complexes.

Temperature-Triggered Switchable Helix-Helix Inversion of Poly(phenylacetylene) Bearing l-Valine Ethyl Ester Pendants and Its Chiral Recognition Ability

A phenylacetylene containing the l-valine ethyl ester pendant (PAA-Val) was synthesized and polymerized by an organorhodium catalyst (Rh(nbd)BPh₄) to produce the corresponding one-handed helical cis-poly(phenylacetylene) (PPAA-Val). PPAA-Val showed a unique temperature-triggered switchable helix-sense in chloroform, while it was not observed in highly polar solvents, such as N,N′-dimethylformamide (DMF). By heating the solution of PPAA-Val in chloroform, the sign of the CD absorption became reversed, but recovered after cooling the solution to room temperature. Even after six cycles of the heating-cooling treatment, the helix sense of the PPAA-Val’s backbone was still switchable without loss of the CD intensity. The PPAA-Val was then coated on silica gel particles to produce novel chiral stationary phases (CSPs) for high-performance liquid chromatography (HPLC). These novel PPAA-Val based CSPs showed a high chiral recognition ability for racemic mandelonitrile (α = 2.18) and racemic trans-N,N′-diphenylcyclohexane-1,2-dicarboxamide (α = 2.60). Additionally, the one-handed helical cis-polyene backbone of PPAA-Val was irreversibly destroyed to afford PPAA-Val-H by heating in dimethyl sulfoxide (DMSO) accompanied by the complete disappearance of the Cotton effect. Although PPAA-Val-H had the same l-valine ethyl ester pendants as its cis-isomer PPAA-Val, it showed no chiral recognition. It was concluded that the one-handed helical cis-polyene backbone of PPAA-Val plays an important role in the chiral recognition ability.

Chiral Nanostructures from Helical Copolymer-Metal Complexes: Tunable Cation-π Interactions and Sergeants and Soldiers Effect

Poly(phenylacetylene) (PPA) copolymers containing (R)- or (S)-MPA as minor chiral pendant can be forced to selectively adopt the right- o left-handed helix, in the presence of small amounts of Na(+) or Ag(+) ("Sergeants and Soldiers Effect") by addition of a donor cosolvent. The helical sense depends exclusively on the chiral monomer/donor cosolvent ratio, and this allows a perfect on/off tuning of the helicity of the copolymer. When the amount of the donor cosolvent is low, the metal ion complex is stabilized by a cation-π interaction, which is selectively cleaved when the amount of cosolvent is higher. Macroscopically chiral nanospheres and nanotubes composed by helical copolymers with P or M helical sense are also described. Our results demonstrate that it is possible to obtain the two enantiomeric helical structures (P and M helicities) and the corresponding nanospheres and nanotubes from a single helical copolymer, by controlled activation/deactivation of the Sergeant and Soldiers Effect with a donor cosolvent.

Colorimetric detection of anions in aqueous media using N-monosubstituted diaminomaleonitrile-based azo-azomethine receptors: real-life applications

New N-monosubstituted diaminomaleonitrile-based azo-azomethine dyes have been synthesized in order to develop colorimetric sensors for detection of biologically important anions in aqueous media. Importantly, the reported sensor decorated with strong electron-withdrawing group can detect inorganic fluoride in water even at 0.037 ppm level, which is lower than WHO permissible level (below 1 ppm). Successfully, the prepared dyes were used for qualitative and quantitative detection of inorganic fluoride in toothpaste and mouthwash. The anion recognition mechanism was also investigated by detailed UV-Vis and (1)H NMR experiments. The detailed (1)H NMR experiments corroborated that anion recognition is based on the deprotonation phenomenon.

Selective fluorescence sensing of salicylic acids using a simple pyrenesulfonamide receptor

The highest change in relative intensity of probe 3 among the probes 2–5 with 3,5-DNSA demonstrated the significance of sulfonamide N–H and imidazole C2–H with the highest association constant and complete quenching.

Two and three input molecular logic operations mediated by a novel azo-azomethine based chromogenic probe through intramolecular charge transfer processes

A novel azo-azomethine based chromogenic receptor has been successfully designed and synthesized for the construction of multifunctional molecular logic circuits.

Naked-eye detection of biologically important anions by a new chromogenic azo-azomethine sensor

A new chromogenic azo-azomethine sensor, containing active phenolic sites, has been designed and synthesized via condensation reaction of N,N,N',N'-tetrakis(2-aminoethyl)-2,2-dimethyl propane-1,3-diamine with 1-(3-formyl-4-hydroxyphenylazo)-4-nitrobenzene. The anion recognition ability of the synthesized receptor was evaluated using UV-Vis spectroscopy and (1)H NMR technique. The anion recognition studies exhibited that the receptor acts as a sensor for biologically important anions such as F(-), AcO(-) and H2PO4(-) over other anions. The binding stoichiometry between sensor and anions was found to be 1:2. (1)H NMR experiment revealed that sensor recognizes anions via H-bonds and subsequent deprotonation to elicit a vivid color change. Interestingly, the sensory system not only let for the naked eye detection without any spectroscopic instrumentation but also helped to discriminate between anions.

A catalyst-free approach to a novel imidazo [4,5-f][1,10] phenanthroline ligand and its corresponding ruthenium(ii) complex: insights into their applications in colorimetric anion sensing

Novel imidazo[4,5-f][1,10]phenanthroline ligand and its corresponding Ru(ii) complex are synthesized from green protocol for colorimetric detection of anions in water.