Synthesis of colorimetric sensors for isomeric dicarboxylate anions: selective discrimination between maleate and fumarate

Four new colorimetric receptors (1-4) were synthesized and characterized. Upon addition of maleate to receptor in DMSO, the appearance of the solution of receptor 1 showed a color change from dark-blue to dark-red, which can be detected by the naked eye at parts per million. Similar experiments were repeated using receptors 2-4; the solution showed a distinct color change from blue to violet for receptor 2 and from blue-green to purple for both receptors 3 and 4, when they are formed as complexes with maleate. The striking color changes are thought to be due to the deprotonation of the thiourea moiety of the 4-nitronaphthyl chromophore. Whereas, in the addition of fumarate to receptors 1-4, the color of the solution changed from dark-blue to bright yellow for receptor and did not induce any color change for receptors 2-4. Thus, for a distinct color change, receptors 1-4 can act as optical chemosensors for recognition of maleate versus fumarate. Especially, only receptor 1 has a unique color change for the recognition of fumarate, accordingly it can be used for detection of the fumarate anion. In this research it was also found that the performance of the receptor is highly dependent on the substituent group on the phenyl ring; a stronger electron-withdrawing group resulted in a receptor with a higher binding constant with the maleate anion.     

Synthesis of colorimetric receptors for dicarboxylate anions: a unique color change for malonate

Three new chromogenic receptors (1, 2, and 3) containing p-nitrophenyl or p-nitronaphthyl or methyl groups appended to the thiourea groups were synthesized and characterized. Upon addition of a series of dicarboxylate anions to receptor 1 in DMSO, only the appearance of the solution of receptor 1 with malonate showed a color change from blue to yellow which can be detected by the naked eye at parts per million. With the addition of the series of dicarboxylate anions to receptor 2, the solutions showed an indistinct intense dark-red color. Whereas the addition of the same dicarboxylate anions to receptor 3, the solutions did not induce any color change. Thus, for the unique color change, the receptor 1 can act as an optical chemosensor for the malonate anion even in the presence of other dicarboxylate anions.     

Highly selective silver nanoparticles based label free colorimetric sensor for nitrite anions

Highly selective label free colorimetric sensor based on AgNPs stabilized by phenolic chelating ligand, N,N′-bis(2-hydroxybenzyl)-1,2-diaminobenzene (1), for NO₂⁻ anions has been developed. Addition of NO₂⁻ showed selective decolourisation of brownish yellow colour of 1-AgNPs with the detection limit of 10⁻⁷ M. Absorption studies showed the complete disappearance of 1-AgNPs peak at 426 nm due to the conversion of AgNPs to silver ions. The presence silver ions were confirmed by white precipitates of AgCl formation with NaCl. The interference studies confirmed the high selectivity of NO₂⁻ sensing in presence of anions as well as cations by 1-AgNPs. A linear relationship was observed between the change of absorption and concentration of NO₂⁻. The present approach could be performed at room temperature and ambient conditions. The practical applications of 1-AgNPs for selective sensing of NO₂⁻ in different water samples such as ground, river, pond and tap water have also been demonstrated.     

Amide-nitrophenyl based colorimetric receptors for selective sensing of fluoride ions

New chromogenic receptors containing 2-nitrophenyl or 3,5-dinitrophenyl groups appended to the amide or in secondary amine positions have been synthesized and characterized. Upon addition of fluoride to two of the receptors in acetonitrile, the solution acquired a yellow colour. The third receptor showed an intense purple colour with fluoride in acetonitrile and the appearance of the purple colour can be detected by the naked eye at parts per million level. The addition of chloride, bromide and iodide to the receptors did not induce any colour. Thus the receptors can act as fluoride ion sensors even in the presence of other halide ions.     

Bis-amidocarbazolyl urea receptor for short-chain dicarboxylate anions

Urea receptor 1 based on two (1-amino-8-amido-3,6-dichloro)carbazole units shows a strong association with dicarboxylate anions such as oxalate, malonate and succinate guests through multiple hydrogen bonds from the carbazole, urea and amide NH groups. (1)H NMR complexation studies exhibit high values of association constants in DMSO-d(6). X-ray structures of the 1?:?1 complexes of 1 with oxalate and malonate as their ditetrabutylammonium salts were obtained. A modelling study of the complex of receptor 1 with succinate (as its diTBA salt) showed a more reduced geometric complementarity than its homologue malonate.     

高选择性比色识别碘离子的氨基硫脲类阴离子受体

设计合成了一系列基于氨基硫脲的阴离子受体（M1～M4）.此类受体以氨基硫脲基团为识别位点,以硝基苯基为信号报告基团,其中受体M1和M3可在乙腈溶液中高选择性的比色识别碘离子.在受体M1或M3的乙腈溶液中加入I^–时,溶液的颜色由浅红色变成无色,而加入其他离子如F^–,Cl^–,Br^–,AcO^–,HSO4^–,H2PO4^–,ClO4^–等阴离子时,受体溶液不会褪色.通过紫外滴定和核磁滴定等方法研究了受体选择性比色识别碘离子的机理.结果表明,受体通过其氨基硫脲基团上的三个NH质子与碘离子形成的三重氢键选择性的结合碘离子.在此过程中,受体构型发生转变,从而导致了颜色变化,产生了比色识别的效果.此类阴离子受体具有合成方法简便,产率高,识别效果好等优点.     

Development of colorimetric sensor array for discrimination of herbal medicine

Today, traditional systems of medicines (such as herbal distillates) become important resources for providing healthcare benefits. The ability to discriminate among closely similar herbal products is critical to ensure their efficacy. This article proposes a pattern-based recognition approach for the rapid discrimination of herbal distillates using a low-cost and sensitive colorimetric sensor array composed of 25 indicators. The color changes of the sensor exposed to the vapor of the herbal distillates can be monitored easily with an ordinary flatbed scanner. The digital representation of the array response was analyzed with hierarchical clustering analysis (HCA) and principal component analysis (PCA). Using new variable selection strategy, 6 indicators among the 25 employed indicators were selected as discriminant elements of the array. So, a complete discrimination (with 100% accuracy) of 46 herbal distillates was achieved. The proposed sensor represented a better resolution when analytes were placed in an oven at 85 °C for 45 min. This colorimetric sensor array demonstrates excellent potential for quality assurance/control applications of herbal distillates.     

A ferrocenyl-guanidine derivative as a highly selective electrochemical and colorimetric chemosensor molecule for acetate anions

A highly preorganized chemosensor molecule 1 based on a ferrocenyl-guanidine decorated with a chromogenic aryl azo moiety recognizes the acetate anion in acetonitrile solution. At first, receptor 1 underwent two-step oxidation events. Initially, oxidation of 1 occurs at the Fe(II) centre (E(p) = 440 mV) to form a ferrocenium species, followed by fast electron transfer from the guanidine moiety of the receptor to the Fe(III) centre with concomitant generation of an Fe(II) species with a radical cation centred at the nitrogen atom. In the second step, the radical cation species formed should undergo electrochemical oxidation at higher potential (E(p) = 830 mV). This assumption is supported by spectroelectrochemical studies. A remarkable cathodic shift (182 mV) of the ferrocene/ferrocenium oxidation peak (E(p) = 440 mV) and a progressive red-shift (Δλ = 30 nm) of the low energy band are observed in its absorption spectrum upon complexation of receptor 1 with the acetate anion. This change in the absorption spectrum is accompanied by a colour change from yellow to orange, which can be used for the "naked-eye" detection of this anion. Its monoprotonated form is able to selectively sense the less basic Cl(-), Br(-), NO(3)(-), and HSO(4)(-) anions: the oxidation redox peak at E(p) = 865 mV is cathodically shifted (107-182 mV).     

Simple bis-thiocarbono-hydrazones as sensitive, selective, colorimetric, and switch-on fluorescent chemosensors for fluoride anions

Bis-thiocarbono-hydrazones are found to be a class of sensitive, selective, ratiometric, and colorimetric chemosensors for anions such as fluoride (F(-)) or acetate (Ac(-)). The sensitivities, or the binding constants of the sensors with anions, were found to be strongly dependent on the substituents appended on the pi-conjugation framework, the delocalization bridge CH==N, the aromatic moiety, and the hetero atom in the C==X group (X=O, S) of the sensors. Single-crystal structures and (1)H NMR titration analysis shows that the --CH==N-- moiety is a hydrogen-bond donor, and it is proposed that an additional CHF hydrogen bond is formed for the sensors in the presence F(-). A sensor bearing anthracenyl groups is demonstrated as a switch-on fluorescent chemosensor for F(-) and Ac(-). The recognition of F(-) in acetonitrile (MeCN) by a sensor with nitrophenyl substituents is tolerant to MeOH (MeCN/MeOH=10:1, v/v) and water (MeCN/H(2)O=30:1, v/v); at these solvent ratios the absorption intensity of the sensor-F(-) complex solution at maximal absorption wavelength was attenuated to half of the original value in pure MeCN.     

Vitamin B6 cofactor derived chemosensor for the selective colorimetric detection of acetate anions

A novel vitamin B₆ cofactor derived anion sensor L for the selective colorimetric detection of acetate has been developed by the condensation of pyridoxal and 2-aminothiophenol. The sensor L showed a noteworthy change in the visible region of the spectrum and was detected by the ‘naked-eye’ for both acetate and fluoride anions in DMSO but selectively for acetate in DMSO/H₂O (88:12, v/v). The anion recognition ability of L was investigated by spectroscopic (UV–vis and ¹H NMR) and DFT methods.     

Interaction between biphenols and anions: selective receptor for dihydrogenphosphate

Biphenol was shown to bind dihydrogenphosphate (H2PO4-) selectively over various other anions (MeCO2-, Cl-, Br-, I-, NO3-, HSO4-). The highly selectivity of biphenol toward dihydrogenphosphate is explained in terms of the basicity and shape of the guest anion.     

Amide based receptors for anions

This review article illustrates the contribution of amide based receptors to the development of anion complexing agents. Amides are incorporated into a wide variety of systems that can be divided into two broad categories; organic and inorganic. The first section is separated into cyclic and acyclic systems built on a solely organic framework. The second section is comprised of metal containing systems such as metallocenes, [Ru(bipy)₃]²⁺ based complexes, porphyrins and other metallo-based receptors. Where appropriate, the results of solution binding studies and sensing outputs are summarized.     

Anthracene-based macrocyclic fluorescent chemosensor for selective sensing of dicarboxylate

An anthracene-based macrocyclic receptor has been designed and synthesized for selective recognition of 1,4-phenylenediacetate (K_a = 3.34 × 10⁵ M^?1). The macrocycle binds 1,4-phenylenediacetate selectively at the charged sites of the receptor with a concomitant increase in fluorescence of anthracene. The interaction properties of the macrocycle were evaluated by ¹H NMR, UV–vis and fluorescence spectroscopic methods.     

Ferrocene-based imidazolium receptors for anions

Cyclic and acyclic ferrocene derivatives bearing two imidazolium rings have been synthesized and characterized by NMR, elemental analysis, mass spectra, and X-ray crystallography. Electrochemical measurements revealed that all the receptors displayed a significant anodic shift response for F⁻. In addition, for receptors 1, 2, and 4, addition of HSO₄⁻ induced quite different electrochemical behavior with dramatic cathodic peak current increase on CV. ¹H NMR titrations demonstrated that receptors 1, 2, and 4 showed selectivity for AcO⁻ while receptor 3 exhibited high affinity toward Cl⁻ among the anions investigated.     

Thiourea-based molecular clips for fluorescent discrimination of isomeric dicarboxylates

A new clip-like receptor, which comprises two thiourea-based binding groups and two naphthalene units, has been designed and synthesized as a fluorescent chemosensor for distinguishing o-phthalate from two other isomers of dicarboxylates. Upon the addition of these three ions, the emission intensity at 420 nm (excitation at 340 nm) decreases drastically through PET. When excited at 380 nm, a new emission band at 460 nm appears and develops gradually upon the addition of the o-phthalate ion and the fluorescent intensity increases markedly over time, but the presence of m-phthalate or p-phthalate do not cause this kind of change. It suggests a guest-induced "off-on" conformational switching signaling transduction. The presence of the o-phthalate anion induces a special conformation with two naphthalene units positioned close enough to exhibit a new emission.     

A colorimetric sensor for the recognition of biologically important anions

A colorimetric anion sensor 1 based on 3-phthaloyl-N-4-nitrophenylhydrozone was synthesized and characterized. The binding ability evaluated by UV?Cvis experiment reveals that 1 can selectively recognize fluoride. Further insights into the nature of interactions between sensor 1 and anions were investigated by H NMR titrations experiments. In addition, the color changes induced by fluoride can provide a way of detection by ??naked-eye??.     

A selective colorimetric chemosensor for lanthanide ions

The synthesis and complexing properties of a calix[4]arene derivate (6) carrying two spirobenzopyran moieties are described. The addition of lanthanide ions resulted in significant UV-vis spectral shifts (68-84 nm) in visible region. It indicates that the synthetic receptor can recognize lanthanide ions by naked eyes over other cations including Na⁺, K⁺, Mg²⁺, Ca²⁺, Fe³⁺, Cu²⁺ and Zn²⁺. The mechanism of recognition was studied with ¹H NMR, UV-vis spectra and emission spectra. The receptor may be applied to sense lanthanide ions.     

A selective, colorimetric, and fluorescent chemodosimeter for relay recognition of fluoride and cyanide anions based on 1,1'-binaphthyl scaffold

The reaction-based relay recognition of fluoride and cyanide anions was demonstrated for the first time, with rapid response and unique triple (fluorescence color, intensity and absorption band) output modes in either of two sequential sensing events. Ratiometric determination of these two anions by fluorescence and/or absorbance spectra is also achieved.     

Lab-on-nanoparticle as a multidimensional device for colorimetric discrimination of proteins

Microchimica Acta - We report on a method for sensitive detection and discrimination of multiple proteins. The peroxidase-like activity of gold nanoparticles (AuNPs) is employed to...