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1.
We characterize six new fluorescent probes that show both intensity and lifetime changes in the presence of free uncomplexed aqueous cyanide, allowing for fluorescence based cyanide sensing up to physiological safeguard levels, i.e. <30 μM. One of the probes, m-BMQBA, shows a ≈15-fold reduction in intensity and a ≈10% change in mean lifetime at this level.The response of the new probes is based on their ability to bind the cyanide anion through a boronic acid functional group, changing from the neutral form of the boronic acid group R-B(OH)2 to the anionic R-B(CN)3 form, a new cyanide binding mechanism which we have recently reported. The presence of an electron deficient quaternary heterocyclic nitrogen nucleus, and the electron rich cyanide bound form, provides for the intensity changes observed. We have determined the disassociation constants of the probes to be in the range ≈15-84 μM3. In addition we have synthesized control compounds which do not contain the boronic acid moiety, allowing for a rationale of the cyanide responses between the probe isomers to be made.The lifetime of the cyanide bound probes are significantly shorter than the free R-B(OH)2 probe forms, providing for the opportunity of lifetime based cyanide sensing up to physiologically lethal levels.Finally, while fluorescent probes containing the boronic acid moiety have earned a well-deserved reputation for monosaccharide sensing, we show that strong bases such as CN and OH preferentially bind as compared to glucose, enabling the potential use of these probes for cyanide safeguard and determination in physiological fluids, especially given that physiologies do not experience any notable changes in pH.  相似文献   

2.
Badugu R  Lakowicz JR  Geddes CD 《Talanta》2005,66(3):569-574
We describe the pH response of a set of isomeric water-soluble fluorescent probes based on both the 6-aminoquinolinium and boronic acid moieties. These probes show spectral shifts and intensity changes with pH, in a wavelength-ratiometric and colorimetric manner. Subsequently, changes in pH can readily be determined around the physiological level.Although boronic acid containing probes are known to exhibit pH sensitivity along with an ability for saccharide binding/chelating, the new probes reported here are considered to be unique and show an unperturbed pH response, even in the presence of high concentrations of background saccharide, such as with glucose and fructose, allowing for the predominant pH sensitivity. The response of the probes is based on the ability of the boronic acid group to interact with strong bases like OH, changing from the neutral form of the boronic acid group, R-B(OH)2, to the anionic ester, R-B(OH)3, form, which is an electron donating group. The presence of an electron deficient quaternary heterocyclic nitrogen center and a strong electron donating amino group in the 6-position of the quinolinium backbone, provides for the spectral changes observed upon OH complexation. In addition, by comparing the results obtained with systems separately incorporating 6-methoxy or 6-methyl substituents, the suppressed response towards monosaccharides, such as with glucose and fructose, can clearly be observed for these systems. Finally we compare our results to those of a control compound, BAQ, which does not contain the boronic acid group, allowing a rationale of the spectral changes to be made.  相似文献   

3.
A two-component saccharide sensing system using the fluorescent dye, hydroxypyrene trisulfonic acid, combined with a boronic acid functional viologen as a receptor/quencher in pH 7.4 buffer solution has been further investigated. The effect of substituents on the acidity of the boronic acid was measured. The boronic acid pKa changed in the expected manner when electron donating or withdrawing groups were present. The glucose binding constants were dependent on pKa, but no simple correlation was observed for the Stern-Volmer quenching constants and the fluorescence signal modulation.  相似文献   

4.
A new dicationic diboronic acid structure, DBA2+ , was designed to exhibit good affinity (Kd≈1 mm ) and selectivity toward glucose. Binding of DBA2+ to glucose changes the pKa of DBA2+ from 9.4 to 6.3, enabling opportunities for detection of glucose at physiological pH. Proton release from DBA2+ is firmly related to glucose concentrations within the physiologically relevant range (0–30 mm ), as verified by conductimetric monitoring. Negligible interference from other sugars (for example, maltose, fructose, sucrose, lactose, and galactose) was observed. These results demonstrate the potential of DBA2+ for selective, quantitative glucose sensing. The nonenzymatic strategy based on electrohydrodynamic effects may enable the development of stable, accurate, and continuous glucose monitoring platforms.  相似文献   

5.
Gurpreet Kaur 《Tetrahedron》2006,62(11):2583-2589
Earlier we communicated an anthracene-based bisboronic acid sensor for glucose. Aimed at understanding the substituent effect, we have introduced various functional groups, such as the cyano, nitro, and fluoro group on the boronic acid moiety of this glucose sensor. Fluorescent binding studies indicated that the cyano-substituted sensor (4a) has the highest affinity (K 2540 M−1) for glucose, but the lowest selectivity (three-fold over fructose); the fluoro-substituted compound (4c) shows the lowest affinity (630 M−1) and a modest selectivity (15-fold over fructose); and the unsubstituted one (1a) shows the highest selectivity over fructose (43-fold) and a modest affinity (1472 M−1).  相似文献   

6.
An accurate estimation of pKa values in methanol-water binary mixtures is very important for several separation techniques such as liquid chromatography and capillary electrophoresis that use these solvent mixtures. In this study, the pKa values of 11 polyphenolic acids have been determined in methanol-water binary mixtures (10%, 20% and 30% (v/v)) by potentiometry, liquid chromatography (LC) and LC-DAD methodology.The results show a similar trend for the pKa values of all the studied compounds, as they increase with increasing concentration of organic modifier, which allows a linear relationship between pKa values and mole fraction of methanol to be obtained. The pKa values obtained in aqueous medium have been compared with those given in the literature, and also with the values predicted by the SPARC on-line pKa calculator. The data obtained have been used to test the feasibility of an estimation of dissociation constants in a methanol-water medium from the relationship between pKa values and the organic cosolvent fraction in the mixtures.  相似文献   

7.
A new chiral fluorescent BINOL boronic acid 1 has been synthesized. The chiral recognition properties of 1 are drastically different from BINOL boronic acid c. Sensor 1 shows improved enantioselectivity as well as chemoselectivity toward sugar alcohols, such as d-sorbitol and d-mannitol.The enantioselectivity of sensor 1 toward d-sorbitol (KR/KS) is 1:35 (pH 9.0), and the chemoselectivity for d-sorbitol/d-mannitol is 20:1.  相似文献   

8.
4-Amino-3-fluorophenyl boronic acid has been synthesized from 4-bromo-2-fluoroaniline by protecting the amine group and then carrying out a lithium-bromine exchange, followed by addition of trimethyl borate and then acidic hydrolysis. We obtained a 47% yield. We also measured the X-ray crystal structure. This derivative has a relatively low boronic acid pKa value of 7.8 when acetylated or attached to acrylamide hydrogels. It also contains a pendant amine which facilitates attachment to polymers, for example. We are using this compound to construct glucose sensing materials that operates at the physiological pH of bodily fluids.  相似文献   

9.
The polarographic reduction of the tree sets of compounds, i.e. organomercury salts, symmetrical organomercury compounds and σ-derivatives of π-cyclopentadienyliron dicarbonyl, have been investigated. The polarographic parameters obtained have been correlated with the pKa values of RH. A least squares treatment of the results and a comparison of the accuracy of the determination for the new pKa values of RH obtained for the three sets of reactions investigated show that the best correlation is obtained for a plot of the half-wave reduction potentials E12 of π-C5H5Fe(CO)2-σ-R and the pKa values of RH. The pKa values for ferrocene, cyclopentadienylmanganese and rhenium tricarbonyls as CH acids have been determined.  相似文献   

10.
Omeprazole is a potent anti-acid drug. Its absorption and mode of action are closely related to its prototropic behavior. In the present study, omeprazole samples from different sources and in different forms were studied spectrophotometrically to obtain pKa values. In the neutral to alkaline pH region, two consistent pKa values of 7.1 and 14.7 were obtained from various samples. The assignment of these pKa values was realized by comparison with the prototropic properties of N(1)-methylated omeprazole substituted on the nitrogen at the 1-position of the benzimidazole ring, which was found to have a pKa of 7.5. The omeprazole pKa of 14.7 is assigned to the dissociation of the hydrogen from the 1-position of the benzimidazole ring and the pKa of 7.1 is assigned to the dissociation from the protonated pyridine nitrogen of omeprazole. The results presented are at variance with those of earlier work.  相似文献   

11.
The ionization of six compounds of bis-phenolic amides was studied spectrophotochemically in DMF-water mixture. The compounds showed two pKa values in the range of 5.97-7.32 for pKa1 and 7.61-8.44 for pKa2. The obtained values of Ka were normalized using the distribution diagrams of the different species and found to be in the range of 5.81-7.42 for pKa1 and 7.48-8.27 for pKa2.  相似文献   

12.
With the specific aim of calculating the acidity equilibrium constant (Ka) of carboxylic acids in aqueous solution we investigated the solute-solvent interactions of these acids and their corresponding anions. The pKa (−lg Ka) values have been calculated using density functional theory (DFT). The polarized continuum model (PCM) is used to describe the solvent. Using these methods, we successfully predicted the pKas of 66 carboxylic acids in aqueous with the average error of 0.5 in pKa units. Two different thermodynamic cycles have been studied. The theoretical values are in better agreement with the experimental results for those acids with moderate strength of acidity with the pKa value higher than 3.  相似文献   

13.
Jia-Ning Li  Yao Fu 《Tetrahedron》2006,62(18):4453-4462
A first-principle theoretical protocol was developed, which could successfully predict the pKa values of a number of amines and thiols in DMSO with a precision of about 1.1 pKa unit. Using this protocol we calculated the pKa values of diverse types of organophosphorus compounds in DMSO. The accuracy of these predicted values was estimated to be about 1.1 pKa because phosphorus is in the same group as nitrogen and in the same period as sulfur. The theoretical predictions were also consistent with all the available experimental data. Thus, a scale of reliable pKa values was constructed for the first time for organophosphorus. These pKa values would be helpful to synthetic chemists who need to design the experimental conditions for handling deprotonated organophosphorus. On the basis of these pKa values we also studied, for the first time, some interesting topics such as the substituent effects on the pKa values of various types of organophosphorus, and the differences between the pKa values of organophosphorus and organic amines.  相似文献   

14.
The formation of supramolecular complexes with ethonium, a cationic gemini surfactant having a broad-spectrum antimicrobial activity, is shown to significantly alter the physicochemical properties (spectral, protolytic, and adsorption properties and solubility) of a natural f lavonol, quercetin. The constant of binding between quercetin and ethonium is calculated. Apparent dissociation constants pK a1 a of quercetin in solutions of this cationic surfactant are for the first time determined within a broad concentration range. A shift in the pH dependence of quercetin adsorption by 0.5 units to the alkaline region upon the transition from a premicellar ethonium solution to a micellar one correlates with an increase in pK a1 a under these conditions. The value of quercetin adsorption from aqueous ethonium solutions depends on the concentration of the cationic surfactant, pH of a solution, and the pK a1 a value of the f lavonol bound into the supramolecular complex.  相似文献   

15.
In this paper the validation of pKa determination in MDM-water mixtures is presented. The MDM-water mixture is a new multicomponent cosolvent mixture (consisting of equal volumes of methanol, dioxane and acetonitrile, as organic solvents) that dissolves a wide range of poorly water-soluble compounds. The cosolvent dissociation constants (psKa) of 50 chemically diverse compounds (acids, bases and ampholytes) were measured in 15-56 wt% MDM-water mixtures by potentiometric or spectrophotometric titration and the aqueous pKa values obtained by extrapolation. Three different extrapolation procedures were compared in order to choose the best extrapolation in MDM-water mixture using a sub-set of 30 water-soluble compounds. The extrapolated results are in good agreement with pKa values measured in aqueous medium. No significant difference was found among these extrapolation procedures thus the widely used Yasuda-Shedlovsky plot was proposed for MDM cosolvent also. Further we also present that the single point estimation based on measurement in 20%/v MDM-mixture using a general calibration equation may be suitable for rapid pKa determination in the early phase of drug research.  相似文献   

16.
We report on the development of reagentless fluorescence-based sensing films utilizing hydrolytic enzymes co-entrapped with polymers that are labelled with pH sensitive fluorophores. Aqueous solutions of a hydrophilic enzyme (urease) or a lipophilic enzyme (lipase) containing fluorescein or carboxy-seminaphtharhodafluor-1 (SNARF-1), either free or conjugated to a dextran polymer backbone, were mixed with hydrolyzed alkoxysilane solutions and cast onto planar surfaces to form thin, biologically active sol-gel derived films (ca. 500 nm thick). The films also contained various additives, such as methyltrimethoxysilane, dimethyldimethoxysilane, polyethylene glycol or polyvinyl alcohol, to optimize the activity of the entrapped enzymes. The photostability, leaching, pKa and pH response of the entrapped probes were characterized, as was the performance of the entrapped enzymes, and an optimal set of processing conditions was obtained for each different sensing film. In general, the results indicated that SNARF-labelled dextran was the most useful pH sensitive dye owing to insensitivity to leaching and photobleaching. Furthermore, it was observed that the pKa and pH response of this probe was insensitive to preparation conditions. The performance of the co-entrapped enzymes was highly dependent on the type and level of additive, but in all cases, it was possible to obtain active enzymes with good performance characteristics. Reagentless sensing films for urea and glyceryl tributyrate (GTB) are demonstrated based on the detection of enzyme-mediated pH changes from films coated onto planar substrates.  相似文献   

17.
Measurements of the acidity constants in the ground (pKa(S0)) and the lowest excited singlet (pKa(S1)) states for 2,3-, 2,4-, 2,5-, 2,6-, 3,4- and 3,5-dimethylphenols in aqueous solution have been carried out spectrophotometrically at 25°C. The pKa values in S0 have been derived from the absorption spectra and the pKa values in S1 were estimated by means of the Forster cycle. It is found that the hydroxy group is more acidic in the first excited singlet than in the ground state.  相似文献   

18.
A new Vilsmeier-type reaction is suggested for the synthesis of novel indocarbocyanine pH sensors, which are fluorescent when protonated but nonfluorescent upon proton abstraction. These sensors show significant ratiometric UV-visible as well as fluorescence spectral changes upon subtle variation of pHs with pKa values near neutral.  相似文献   

19.
[AAE]X composed of amino acid ester cations is a sort of typically “bio-based” protic ionic liquids (PILs). They possess potential Brønsted acidity due to the active hydrogens on their cations. The Brønsted acidity of [AAE]X PILs in green solvents (water and ethanol) at room temperature was systematically studied. Various frameworks of amino acid ester cations and four anions were investigated in this work from the viewpoint of structure–property relationship. Four different ways were used to study the acidity. Acid dissociation constants (pKa) of [AAE]X determined by the OIM (overlapping indicator method) were from 7.10 to 7.73 in water and from 8.54 to 9.05 in ethanol. The pKa values determined by the PTM (potential titration method) were from 7.12 to 7.82 in water. Their Hammett acidity function (H0) values (0.05 mol·L−1) were about 4.6 in water. In addition, the pKa values obtained by the DFT (proton-transfer reactions) were from 7.11 to 7.83 in water and from 8.54 to 9.34 in ethanol, respectively. The data revealed that the cationic structures of [AAE]X had little effect and the anions had no effect on the acidity of [AAE]X. At the same time, the OIM, PTM, Hammett method and DFT method were reliable for determining the acidic strength of [AAE]X in this study.  相似文献   

20.
The H-bonded complexes between 2-dimethylamino-3,3-dimethyl-1-azirine (TMAAZ) and some phenol derivatives have been studied by IR spectrometry in carbon tetrachloride. The equilibrium constants at 300, 315 and 328 K and the ? ΔH°, ? ΔνOH and ΔνCN values have been determined. The comparison with previously studied OH … N complexes shows that TMAAZ forms stronger complexes than would be expected from the pKa value. These facts are discussed in terms of steric, hybridization, solvation and charge transfer effects. From a pKa of 8, the IR spectrum shows the appearance of ion pairs N+-H …?O. A predominance of protonated species can be calculated for a pKa of 6. This can explain why 1,2-ring cleavage whose first step is probably the formation of an azirinium cation, occurs for acids characterized by pKa values lower than 5 but not for enolizable ketones having pKa values higher than 9.  相似文献   

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