Role of Aromatic Moiety in the Probe Property toward Picric Acid: Synthesis, Crystal Structure, Spectroscopy, Microscopy, and Computational Modeling of a Knoevenagel Condensation Product of d-Glucose.

Molecular probes for picric acid (PA) in both solution and solid states are important owing to their wide usage in industry. This paper deals with the design and development of a glucosyl conjugate of pyrene (L 1 ) along with control molecular systems, possessing anthracenyl (L 2 ), naphtyl (L 3 ), and phenyl (L 4 ) moieties, via Knoevenagel condensation of 2,4-pentanedione with d-glucose. The selectivity of L 1 toward PA has been demonstrated on the basis of fluorescence and absorption spectroscopy, and the species of recognition by electrospray ionization mass spectrometry. The role of the aromatic group in the selective receptor property has been addressed among L 1 , L 2 , L 3 , and L 4 . The structural features of the {L 1 + PA} complex were established by density functional theory computations. L 1 was demonstrated to detect PA in solid state selectively over other nitroaromatic compounds (NACs). To study the utility of L 1 in film, cellulose paper strips coated with L 1 were used and demonstrated the selective detection of PA. The observed microstructural features of L 1 and its complex {L 1 + PA} differ distinctly in both atomic force microscopy and scanning electron microscopy, all in the support of the complex formation. Thus, L 1 was demonstrated as a sensitive, selective, and inexpensive probe for PA over several NACs by visual, spectral, and microscopy methods.

Selenocysteine vs Cysteine: Tuning the Derivatization on Benzenesulfonyl Moiety of a Triazole Linked Dansyl Connected Glycoconjugate for Selective Recognition of Selenocysteine and the Applicability of the Conjugate in Buffer, in Serum, on Silica Gel, and in HepG2 Cells.

A dansyl derivatized triazole linked glucopyranosyl conjugate ((NO2)L) has been synthesized and characterized and was used in the present study. The conjugate (NO2)L releases a fluorescent product upon reaction by Cys-SeH in aqueous PBS buffer by exhibiting a ∼210-fold fluorescence enhancement even in the presence of 20 other amino acids with a minimum detection limit of (1.5 ± 0.2) × 10(-7) M. The selectivity of the Cys-SeH to (NO2)L was further proven by extending the fluorescence study to different other selenium compounds. The role of para-nitrobenzenesulfonyl (pNBS) center in (NO2)L in the selective recognition of Cys-SeH was confirmed when the fluorescence emission studies were carried out using five different derivatizations possessing two NO2, five fluoro, two fluoro, one fluoro, and no fluoro groups. The nucleophilic substitution reaction of Cys-SeH on (NO2)L has been clearly demonstrated on the basis of (1)H NMR, ESI-MS, and absorption spectroscopy, and the heat changes were monitored by isothermal titration calorimetry. The application potential of (NO2)L has been demonstrated by studying its selectivity toward Cys-SeH in aqueous PBS buffer, in bovine serum, and on the silica gel surface that lead to minimum detection limits of (25 ± 2), (80 ± 5), and (168 ± 16) ppb, respectively. The biological applicability of (NO2)L for Cys-SeH was further demonstrated in HepG2 cells by fluorescence microscopy. Thus, (NO2)L is aqueous soluble and a biologically acceptable probe for Cys-SeH.

Triazole-Linked Quinoline Conjugate of Glucopyranose: Selectivity Comparison among Zn2+, Cd2+, and Hg2+ Based on Spectroscopy, Thermodynamics, and Microscopy, and Reversible Sensing of Zn2+ and the Structure of the Complex Using DFT.

A water-soluble triazole-linked quinoline conjugate of glucopyranose (L) has been synthesized and characterized, and its single-crystal X-ray diffraction (XRD) structure has been established. Binding of L toward different biologically relevant metal ions has been studied using fluorescence and absorption spectroscopy in HEPES buffer at pH 7.4. The conjugate L detects Zn2+ and Cd2+ with 30 ± 2 and 14 ± 1-fold fluorescence enhancement, respectively, but in the case of Hg2+, only a fluorescence quench was observed. The stoichiometry of the complex is 1:2 metal ion to the ligand in the case of Zn2+ and Cd2+ resulting in [Zn(L)2] and [Cd(L)2], and it is 1:1 in the case of Hg2+, as confirmed from their electrospray ionization mass spectrometry (ESIMS) spectra. Zn2+ shows greater exothermicity over Cd2+, whereas Hg2+ shows endothermicity , which supports the differences in their binding strength and the nature of the corresponding complex. L exhibits rod-shaped particles and upon complexation with Zn2+, it exhibits sphere-like morphological features in scanning electron microscopy (SEM) images. However, clustered aggregates are observed in Cd2+, whereas the [HgL] complex exhibits small fused spherical structures, and therefore the signature of these ions is seen in microscopy images. The computational studies revealed that the syn-[Zn(L)2] complex is stabilized by 9.7 kcal mol-1 more than that in the case of anti-[Zn(L)2] owing to the formation of hydrogen bonds between the two glucosyl moieties within the syn-complex. Among the anions studied, [Zn(L)2] is sensitive and selective toward the phosphate ion (H2PO4 -) with a minimum detection limit of 16 ± 2 ppb. Similarly, the [HgL] can act as a secondary sensor for CN- while also exhibiting reversibility. Based on the input-output characteristics, INHIBIT logic gate was built in the case of Zn2+ vs H2PO4 - and IMPLICATION logic gate was built in the case of Hg2+ vs CN-.

Optimizing the Electron-Withdrawing Character on Benzenesulfonyl Moiety Attached to a Glyco-Conjugate to Impart Sensitive and Selective Sensing of Cyanide in HEPES Buffer and on Cellulose Paper and Silica Gel Strips.

Dansyl-derivatized, triazole-linked, glucopyranosyl conjugates, (5F)LOH, (2F)LOH, (1F)LOH, and (0F)LOH were synthesized and characterized. While the (5F)LOH acts as a molecular probe for CN(-), (2F)LOH, (1F)LOH, and (0F)LOH acts as control molecules. The reactivity of CN(-) toward (5F)LOH has been elicited through the changes observed in NMR, ESI MS, emission, and absorption spectroscopy. The conjugate (5F)LOH releases a fluorescent product upon reaction by CN(-) in aqueous acetonitrile medium by exhibiting an ∼125-fold fluorescence enhancement even in the presence of other anions. Fluorescence switch-on behavior has been clearly demonstrated on the basis of the nucleophilic substitution reaction of CN(-) on (5F)LOH. A minimum detection limit of (2.3 ± 0.3) × 10(-7) M (6 ± 1 ppb) was shown by (5F)LOH for CN(-) in solution. All the other anions studied showed no change in the fluorescence emission. The utility of (5F)LOH has been demonstrated by showing its reactivity toward CN(-) on a thin layer of silica gel as well as on Whatman No. 1 cellulose filter paper strips. The role of glucose moiety and the penta-fluorobenzenesulfonyl reactive center present in (5F)LOH in the selectivity of CN(-) over other anions has been demonstrated by fluorescence, absorption and thermodynamics study. Similar studies carried out with the control molecules showed no selectivity for CN(-). The mechanistic aspects of the reactivity of CN(-) toward (5F)LOH were supported by DFT computational study.

Water-Soluble 8-Hydroxyquinoline Conjugate of Amino-Glucose As Receptor for La(3+) in HEPES Buffer, on Whatman Cellulose Paper and in Living Cells.

A water-soluble glucopyranosyl conjugate, L, has been synthesized and characterized by different analytical and spectral techniques. The L has been demonstrated to have switch-on fluorescence enhancement of ∼75 fold in the presence of La(3+) among the nine lanthanide ions studied in the HEPES buffer at pH 7.4. A minimum detection limit of 140 nM (16 ± 2 ppb) was shown by L for La(3+) in the buffer at physiological pH. The utility of L has been demonstrated by showing its sensitivity toward La(3+) on Whatman filter paper strips. The reversible and reusable action of L has been demonstrated by monitoring the fluorescence changes as a function of the addition of La(3+) followed by F(-) and HPO4(2-) ions. The complexation of L by La(3+) was shown by absorption spectra wherein isosbestic behavior was observed. The Job's plot suggests a 2:1 complex between L and La(3+), and the same was supported by ESI-MS. The control molecular study revealed the necessity of hydroxy quinoline and the amine group for La(3+) ion binding and the glyco-moiety to bring water solubility and biocompatibility. The structural features of the [2L+La(3+)] complex were established by DFT computational calculations. The chemo-ensemble, [2L+La(3+)], is shown responsible for providing intracellular fluorescence imaging in HepG2 cells.

A water soluble glucopyranosyl conjugate as a selective and reactive probe for cysteine in a buffer and its application to living cells.

A water soluble and biocompatible glucopyranosyl conjugate (L) has been synthesized and characterized by various techniques. The L has been employed to recognize Cys selectively among the naturally occurring amino acids in HEPES buffer at physiological pH. A minimum detection limit of 2.5 × 10(-7) M was shown by L for Cys in the buffer at pH = 7.4. The reactivity of L towards biological thiols as demonstrated by emission and absorption is supported by the observed increase in the fluorescence intensity; however, Cys shows a maximum increase owing to its better nucleophilicity. The reactivity of Cys on L is demonstrated by (1)H NMR, ESI MS, emission and absorption spectroscopy, and the formation of the binary complex was supported by ESI MS. The control molecular study revealed the necessity of the glyco-moiety to bring water solubility and biological adaptability. The cellular studies support that the conjugate L is biologically adaptable and shows effective intracellular fluorescence emission upon reacting with intracellular thiols.

Coumarine-imino-C2-glucosyl conjugate as receptor for Cu(2+) in blood serum milieu, on silica gel sheet and in Hep G2 cells and the characterization of the species of recognition.

A coumarine-imino-C2-glucosyl conjugate (L) was synthesized and characterized. The conjugate L is found to recognize Cu(2+) in aqueous HEPES buffer by exhibiting a 95% fluorescence quenching in pH range 7-10 even in the presence of several biologically and ecologically relevant metal ions. Fluorescence on-off behavior has been clearly demonstrated on the basis of the binding variability of Cu(2+) to L. The binding has been elicited through the changes observed in fluorescence, absorption, ESI-MS and (1)H NMR titrations. All the other thirteen metal ions studied did not show any change in the fluorescence emission. These ions do not interfere with the recognition of Cu(2+) by L. The structural features of [CuL]2 complex in both the isomeric forms were established by DFT computational calculations. The utility of L has been demonstrated by showing its sensitivity toward Cu(2+) on a thin layer of silica gel. The L gives sensitive fluorescence signals for Cu(2+) even in blood serum and exhibits appropriate fluorescence responses in living cells.

Synthesis, structure, and Hg(2+)-ion-sensing properties of stable calixazasmaragdyrins.

The first stable calixazasmaragdyrins containing two meso-sp(2) and one meso-sp(3) carbon atoms were synthesized by [3 + 2] condensation of 2,2'-(1-methylethylidene)bis(pyrrole) and 5,10-diaryltripyrromethane under trifluoroacetic acid catalyzed conditions. The macrocycles were confirmed by high-resolution mass spectrometry, and the molecular structures were deduced by detailed 1D and 2D NMR spectroscopy. The single-crystal structural analysis showed the highly strained and distorted nature of a calixazasmaragdyrin macrocycle. The presence of the one meso-sp(3) carbon center induces sufficient flexibility into the macrocycle, which, in turn, helps with the stability of the calixazasmaragdyrin macrocycle. The calixazasmargdyrins showed one broad absorption band at ∼425 nm and an ill-defined band at ∼685 nm. The electrochemical studies revealed that the calixazasmaragdyrins are not stable under redox conditions. Because the calixazasmargdyrin macrocycle possesses five pyrrole rings with three ionizable inner NH protons, we investigated anion and cation sensing properties of calixazasmargdyrins. Our studies revealed that the calixazasmaragdyrins do not show any sensing behavior toward anions but exhibited specific sensing behavior toward Hg(2+) ions as verified by spectral and electrochemical studies.

Pyrenyl-imino-C2-glucosyl conjugate: synthesis, characterization, and ratiometric and reversible OFF-ON receptor for Hg(2+).

A pyrenyl-imino-C2-glucosyl conjugate, L, has been synthesized and characterized. The L exhibits selective chromogenic as well as fluorescent property towards Hg(2+) in a ratiometric manner by showing ∼30 fold enhanced fluorescence emission intensity. The fluorescence enhancement continues to be there even in the presence of thirteen other competitive metal ions studied. The sensing of Hg(2+) is well demonstrated using various techniques, such as, fluorescence, absorption, visual color under UV light and ESI MS. A minimum detection limit of 18±2ppb was shown by L for Hg(2+) in ethanol. All the experimental studies carried out supported the formation of 2:1 complex between L and Hg(2+). The structure of the 2:1 complex was modeled at ab initio using HF and found a structure where Hg(2+) is sandwiched between the two pyrenyl moieties. The reversibility and reusability of L has been demonstrated using fluoride ion.