Chloramphenicol-imprinted polychitosan bounded with carbon dots as fluorescent sensor, dispersive sorbent, and drug carrier.

Chitosan, an abundant natural polysaccharide, was conjugated with carbon dots (CDs) and self-polymerized with chloramphenicol (CAP) templates to synthesize CD-incorporated and molecularly CAP-imprinted polychitosan (CD-MIC). The CD-MIC was used for fluorescent sensing, dispersive sorption, and dosage release of CAP at different pH levels. The sphere of action mechanism, approved by emission and excitation fluorescence, UV-Vis absorption, and fluorescence lifetime measurements, regulated the fluorescence static quenching. By the Perrin model, the quenching extent was linearly correlated to CAP within 0.17 - 33.2 µM (LOD = 37 nM) at pH 7.0. With an imprinting factor of 3.1, the CD-MIC was more selective for CAP than CD, although it was less sensitive to CAP. The recoveries of 5.0 µM CAP from milk matrix were 95% (RSD = 2.3%) for CD-MIC probes and 62% (RSD = 4.5%) for CD. The Langmuir and pseudo-second-order models preferably described the isothermal and kinetic sorptions of CAP into the imprinted cavities in CD-MICs, respectively. The Weber - Morris kinetic model showed three stages involved in intraparticle diffusion, which was pH-dependent and gradually arduous at the later stage, and showed external diffusion partly engaged in the diffusion mechanism. The 20 - 70% of CAP formulated in CAP-embedded CD-MICs were released in 8 - 48 h. The release percentage was lower at pH 7.0 than at pH 5.0 and 9.0, but the equilibrium time was shorter. At pH 7.0, the release percentage reached 45% at 10 min and slowly increased to 51% at 24 h.

Fluorescence determination of tannic acid imprinted in conjugated hypercrosslinked polymers by Friedel-Crafts acylation.

A molecularly imprinted hypercrosslinked polymer (HCP) was synthesized from the polymerization of mesitylene monomer, terephthaloyl chloride crosslinker, and tannic acid (TA) template through FeCl3-catalyzed Friedel-Crafts acylation. The TA-imprinted HCP (TAHCP) was capable of IUPAC Type I mesoporosity, with specific surface area of 1258 m2 g-1, monolayer adsorption capacity of 289 cm2 g-1, pore sizes ranging from 4.4 to 12.6 Å, amorphous morphology, and characteristic absorption and emission bands. The extended π-conjugation framework of TAHCP was endowed with 385-nm fluorescent emission at 310-nm excitation. The fluorescence intensity of TAHCP could be dynamically quenched by TA and was linearly correlated with 20-1000 nM TA concentrations on the Stern-Volmer plot in the optimized conditions of pH 5.5 buffer, 100 µg mL-1 TAHCP, and 3.5 min equilibrium. The relative standard deviation (RSD) for 50 nM TA was 3.4% (n = 5), and the limit of detection was 6.2 nM based on the 3σ of the TA blanks). For 50nM TA, the imprinted factor was calculated to be 7.8, and the selectivity for 250 nM interferents, including ions, organic acids, saccharides, amino acids, and caffeine, which are commonly found in beverages, was 7.5-9.5, except for gallic acid (1.2). The recoveries of TA spiked in tea and juice beverages at three levels (10-150 nM) were 93.6-101.9% (RSD = 3.6-4.3%).

Imprinted ß-ketoenamine-linked covalent organic frameworks as dispersive sorbents for the fluorometric determination of timolol.

Timolol accompanied the formation of fluorescent ß-ketoenamine-linked covalent organic frameworks (COFs) via the Sc(Tof)3-catalyzed condensation of derivated carbaldehyde and hydrazide in a 1,4-dioxane/mesitylene porogen to construct timolol-imprinted COFs (TICOFs). With high imprinting factors, the synthesis-optimized TICOFs were characterized by fluorescence, UV-Vis spectrometry, X-ray diffraction, N2 adsorption/desorption analyses, scanning electron microscopy, and FTIR spectrometry. The TICOF fluorescence measured at 390 nm/510 nm is dynamically quenched by timolol and was thus utilized to quantify timolol in a linear range of 25-500 nM with a LOD of 8 nM. The TICOF recovered 99.4% of 0.5% timolol maleate in a commercial eye drop (RSD = 1.1%, n = 5). In addition, TICOF was used as a dispersive sorbent to recover 95% of 2.0 nM timolol from 20 mg of TICOF in 25 mL phosphate buffer. Dilution factors of 25 and 75 were the maximum tolerated proportions of the urine and serum matrix spiked with 2.0 nM timolol to reach recoveries of 92.4% and 90.3%, respectively.

Effective and Efficient Pretreatment of Polyimide Substrates by Capacitively Coupled Plasma for Coating the Composites of Tetracycline-Imprinted Polymers and Quantum Dots: Comparison with Chemical Pretreatment.

Composites of tetracycline (Tc)-imprinted polymethacrylates and quantum dots have been coated on chemically pretreated polyimide substrates (PIs) as fluorescent sensors. In this study, PIs were pretreated by capacitively coupled plasma (CCP) before coating the same composites on them. For the first time, to fabricate sensors by plasma modification of PIs, the CCP conditions, including plasma gas, flow rate, radio frequency generation power, and duration time, the fabrication details, including coating, baking, and stripping steps, and the sample loading process were optimized to perform a linear decrease in fluorescent intensity with Tc concentrations in the range of 5.0-3000 µM (R2 = 0.9995) with a limit of detection of 0.2 µM (S/N = 3, relative standard deviation (RSD) = 2.2%). The selectivity of the stripped PIs was evaluated by the imprinting factors (IFs) for Tc (IF = 7.2), other Tc analogues (IF = 3.4-5.3), and steroids (IF ≈ 1) and by the recoveries of 5.0 µM Tc from bovine serum albumin at 300 µg∙mL-1 (98%, RSD = 3.2%), fetal bovine serum at 1.5 ppt (98%, RSD = 2.8%), and liquid milk (94.5%, RSD = 5.3%). The superiority of the present plasma-treated-based sensor over the previous chemically-treated one in fabrication efficiency and detection effectiveness was clear.

Excitation-independent dual emissions of carbon dots synthesized by plasma irradiation of ionic liquids: Ratiometric fluorometric determination of norfloxacin and mercury(II).

The capacitively coupled plasma (CCP) discharge of an ionic liquid solution of citric acid produces carbon dots (CDs) with excitation-independent fluorescent dual-emissions peaking at 410 nm and 480 nm. The intensity of the purple photoluminescence at 410 nm increases with (a) the flow rate of O2 plasma gas supply from 2.0 to 30 standard cubic centimeters per minute (sccm), (b) the 2-h exposure of the CDs to 254 nm light, and (c) the 8-h immersion of the CDs in a solution of NaBH4. The UV exposure and the hydride immersion reduce the fluorescence intensity peaking at 480 nm, which is highest at 5.0 and 10 sccm. The two emissive states were revealed by UV-vis absorption, XPS spectra, and time-resolved fluorescence. Control of the O2 flow rate can simply tune the ratiometric fluorescence of the CCP-CDs. The CDs obtained from 5 and 30 sccm O2 supplies present a high-intensity ratio (I480 nm/I410 nm ≈ 3.35) and a low one (≈ 0.48), respectively. The 480 nm fluorescence of the former CDs is quenched by mercury(II) ions in the 0.2 to 50 µM concentration range. The 410 nm fluorescence of the latter CDs is enhanced by norfloxacin in the 25 nM to 1.0 µM concentration range. The detection limits are 75 nM for Hg(II) and 7.3 nM for norfloxacin. Graphical abstract Schematic presentation of the effect of the oxygen flow rate in capacitively coupled radio frequency (RF) plasma on the formed CDs. The emission can be quenched by Hg2+ or enhanced by norfloxacin.

Sensitive Detection of 8-Nitroguanine in DNA by Chemical Derivatization Coupled with Online Solid-Phase Extraction LC-MS/MS.

8-Nitroguanine (8-nitroG) is a major mutagenic nucleobase lesion generated by peroxynitrite during inflammation and has been used as a potential biomarker to evaluate inflammation-related carcinogenesis. Here, we present an online solid-phase extraction (SPE) LC-MS/MS method with 6-methoxy-2-naphthyl glyoxal hydrate (MTNG) derivatization for a sensitive and precise measurement of 8-nitroG in DNA. Derivatization optimization revealed that an excess of MTNG is required to achieve complete derivatization in DNA hydrolysates (MTNG: 8-nitroG molar ratio of 3740:1). The use of online SPE effectively avoided ion-source contamination from derivatization reagent by washing away all unreacted MTNG before column chromatography and the ionization process in mass spectrometry. With the use of isotope-labeled internal standard, the detection limit was as low as 0.015 nM. Inter- and intraday imprecision was <5.0%. This method was compared to a previous direct LC-MS/MS method without derivatization. The comparison showed an excellent fit and consistency, suggesting that the present method has satisfactory effectiveness and reliability for 8-nitroG analysis. This method was further applied to determine the 8-nitroG in human urine. 8-NitroG was not detectable using LC-MS/MS with derivatization, whereas a significant false-positive signal was detected without derivatization. It highlights the use of MTNG derivatization in 8-nitroG analysis for increasing the method specificity.

Trace analysis of methylated and hydroxymethylated cytosines in DNA by isotope-dilution LC-MS/MS: first evidence of DNA methylation in Caenorhabditis elegans.

From 1986 to the present, the popular research model organism Caenorhabditis elegans has been thought to completely lack DNA methylation and seems to have lost DNA methylation enzymes from its genomes. In the present study, we report the development of a sensitive and selective assay based on LC-MS/MS to simultaneously measure 5-methyl-2'-deoxycytidine (5-mdC) and 5-hydroxymethyl-2'-deoxycytidine (5-hmdC) in DNA hydrolysates. With the use of isotope internal standards ([2H3]5-mdC and [2H3]5-hmdC) and online solid-phase extraction, the detection limits of 5-mdC and 5-hmdC were estimated to be 0.01 and 0.02 pg respectively, which correspond to a 0.000006% and 0.00001% methylation and hydroxymethylation level. This method was applied to investigate whether DNA methylation/hydroxymethylation exists in C. elegans. The present study for the first time demonstrates that 5-mdC is present in C. elegans genomic DNA (0.0019-0.0033% of cytosine methylated) using LC-MS/MS, whereas another epigenetic modification, 5-hmdC, is not detectable. Furthermore, we found that C. elegans DNA was hypo- or hyper-methylated in a dose-dependent manner by the DNA methyltransferase (DNMT)-inhibiting drug decitabine (5-aza-2'-deoxycytidine) or cadmium respectively. Our data support the possible existence of an active DNA-methylation mechanism in C. elegans, in which unidentified DNMTs could be involved. The present study highlights the importance of re-evaluating the evolutionary conservation of DNA-methylation machinery in nematodes which were traditionally considered to lack functional DNA methylation.

Direct analysis of tobacco-specific nitrosamine NNK and its metabolite NNAL in human urine by LC-MS/MS: evidence of linkage to methylated DNA lesions.

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and its urinary metabolite, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), are the most investigated carcinogenic biomarkers of tobacco-specific nitrosamines. Here, we report the development of a sensitive and selective assay based on liquid chromatography-tandem mass spectrometry (LC-MS/MS) to simultaneously measure urinary NNK and NNAL. With the use of isotope internal standards and online solid-phase extraction, urine samples were directly analyzed without prior sample purification. The detection limits of this method were 0.13 and 0.19 pg on column for NNK and NNAL, respectively. Inter- and intra-day imprecision was <10 %. Mean recovery of NNK and NNAL in urine was 99-100 %. This method was applied to measure urinary NNK and NNAL in 101 smokers and 40 nonsmokers to assess tobacco exposure. Urinary nicotine, cotinine, N3-methyladenine (N3-MeA), and N7-methylguanine (N7-MeG) were also measured by isotope-dilution LC-MS/MS methods. The results showed that urinary NNK was not observed in all smokers. Urinary free NNAL (0.10 ± 0.09 ng/mg creatinine) and total NNAL (0.17 ± 0.14 ng/mg creatinine) were detected in all smokers. Urinary concentrations of NNAL were significantly correlated with nicotine, cotinine, N3-MeA, and N7-MeG in smokers (P < 0.001). This method enables the direct and simultaneous measurement of NNK and NNAL in urine using only 50 µL of urine. This study first demonstrated in human that urinary tobacco-specific nitrosamines metabolite (NNAL) are highly correlated with their resulting methylated DNA lesions in urine, which may help to substantiate an increased cancer risk associated with tobacco smoke exposure.

Optimization of global DNA methylation measurement by LC-MS/MS and its application in lung cancer patients.

Global analyses of DNA methylation contribute important insights into biology and the wide-ranging role of DNA methylation. We describe the use of online solid-phase extraction and isotope-dilution liquid chromatography/tandem mass spectrometry (LC-MS/MS) for the simultaneous measurement of 5-methyl-2'-deoxycytidine (5-medC) and 2'-deoxycytidine (dC) in DNA. With the incorporation of isotope internal standards and online enrichment techniques, the detection limit of this method was estimated to be as low as 0.065 pg which enables human global DNA methylation detection using only picogram amounts of DNA. This method was applied to assess the optimal amounts of enzymes required for DNA digestion regarding an accurate global DNA methylation determination and completeness of digestion and to determine global methylation in human tumor adjacent lung tissue of 79 lung cancer patients. We further determined methylated (N7-methylguanine (N7-meG), O (6)-methylguanine (O (6)-meG), and N3-methyladenine (N3-meA)) and oxidized DNA lesions (8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG)) in lung cancer patients by LC-MS/MS. Optimization experiments revealed that dC was liberated from DNA much more readily than 5-medC by nuclease P1 and alkaline phosphatase (AP) in DNA, which could lead to an error in the global DNA methylation measurement following digestion with insufficient enzymes. Nuclease P1 showed more differential activity for 5-medC and dC than AP. Global DNA methylation levels in adenocarcinoma and squamous cell carcinoma patients were similar in the range of 3.16-4.01 %. Global DNA methylation levels were not affected by smoking and gender and were not correlated with N7-meG or 8-oxodG in lung cancer patients. Levels of O (6)-meG and N3-meA were however found to be undetectable in all lung tissue samples.

Conjugated hypercrosslinked polymers imprinted with 3,5-dinitrosalicylic acid for the fluorescent determination of α-amylase activity.

The discovery of a series of coupling reactions between various building blocks has driven the development of porous organic polymers, but the common usage of expensive and air-sensitive organometallic catalysts and complex procedures in harsh syntheses has limited their expansion. A microporous hypercrosslinked polymer (HCP) was synthesized by polymerizing a naphthalene monomer and a 1,4-dimethoxybenzene crosslinker using Friedel-Crafts alkylation over an FeCl3 catalyst and imprinted with 3,5-dinitrosalicylic acid (DNS). The DNS-molecularly-imprinted HCPs (MIHCPs) were characterized as having IUPAC Type I mesoporosity, a specific surface area of 1134 m2 g-1, a monolayer adsorption capacity of 116 cm2 g-1, pore sizes ranging from 5 to 8.5 Å, amorphous frameworks, and distinctive absorption and emission bands by N2 adsorption/desorption analyses, scanning and transmission electron microscopies, and FTIR, UV-Vis, and fluorescence spectrometries. The π-conjugated imprinted framework endowed the MIHCPs with 405-nm fluorescent emission at a 330-nm excitation and dynamic quenching, which was confirmed by changes in fluorescence lifetime and followed a linear Stern-Volmer plot against 1.0-200 µM DNS template molecules under optimized conditions of a pH 7.0 buffer, an MIHCP concentration of 125 µg mL-1, and a 3.0-min equilibration time. The MIHCPs exhibited a high imprinted factor of 8.7 against nonimprinted HCP and a selectivity of 8.63 against reduced DNS, which enabled fluorometric detection of DNS molecules produced by the hydrolysis of starch with microbial, salivary, and pancreatic α-amylases and the subsequent redox incubation with the DNS oxidant. The fluorometric measurement of α-amylase activity was higher in accuracy and precision (RSD: 2.6-2.8% vs. 3.9-4.0%) than conventional UV-Vis spectrometry because the excellent fluorescent sensitivity and imprinting selectivity of the MIHCP probes enabled the use of higher dilution factors with weaker matrix effects.

Simultaneous determination of areca nut- and tobacco-specific alkaloids in saliva by LC-MS/MS: Distribution and transformation of alkaloids in oral cavity.

Areca nut and tobacco are frequently used in combination. Cigarette smoking and betel quid (BQ) chewing habits impose greater oral cancer risk than either habit alone. Saliva is a better noninvasive diagnostic material as it is in direct contact with oral mucosa and cancerous lesions. This study describes the application of isotope-dilution LC-MS/MS for simultaneous quantitation of five areca nut-specific alkaloids (ASAs) and three tobacco-specific alkaloids (TSAs) in human saliva. With this method, we demonstrate that the distribution of ASAs vary significantly in smokers who chew BQ habitually, due to the hydrolysis of ASAs and metabolic activity in the oral cavity. The alkaline condition formed due to slaked lime in BQ, plays an important role in the distribution of ASAs and TSAs, by catalyzing the hydrolysis of ester forms of ASAs to their respective carboxylic acid forms besides facilitating the TSA (i.e., nicotine) absorption in the oral cavity. Moreover, our results reveal that oral mucosa rather than saliva contributes to the metabolism of ASAs at oral cavity. Less than 2.1% of ASAs were metabolized by saliva, as determined by in vitro test. Our findings may provide a better insight into the pathobiology of oral carcinogenesis due to BQ chewing.

Elevated Nitrite/Nitrate Ratio as a Potential Biomarker for the Differential Diagnosis of Pleural Effusions.

Pleural effusions (PEs) are common in clinical practice and can be due to many different underlying diseases such as cancer, congestive heart failure, or pneumonia. An accurate differential diagnostic categorization is essential, as the treatment and prognosis of PEs largely depend on its cause. In this study, we tested the hypothesis that nitrite and nitrate concentrations in PEs are associated with the inflammation and infection conditions. We therefore measured the nitrite and nitrate levels in 143 PE samples using a sensitive liquid chromatography-tandem mass spectrometry method and investigated their diagnostic potential in differentiating PEs. The results showed that nitrite concentrations and nitrite/nitrate ratios were higher in exudates than in transudates (NO2-: 2.12 vs. 1.49 µM; NO2-/NO3-: 23.3 vs. 14.0). Both the nitrite concentrations and the nitrite/nitrate ratios were positively correlated with the three Light's criteria. Moreover, the receiver operating characteristic curve analysis revealed that the nitrite/nitrate ratio with an area under the curve of 0.71 could be a potential diagnostic biomarker in separating infectious PEs (IPEs) from other types of PEs. Taken together, the nitrite/nitrate ratio not only reflected the statuses of inflammation, but also the nitrate reduction by pathogenic bacteria infection in the pleural cavity. The nitrite/nitrate ratio could be a better biomarker in the differential diagnosis of PEs than the nitrite concentration alone.

Nanochitosan crosslinked with polyacrylamide as the chiral stationary phase for open-tubular capillary electrochromatography.

Nanoparticles exhibiting favorable surface-to-volume ratios create efficient stationary phases for electrochromatography. New nanomaterials derived from chitosan (CS) were immobilized onto modified capillaries for use as the chiral stationary phase (CSP) in open-tubular electrochromatography. This immobilization was achieved through the copolymerization of glycidyl methacrylate-modified nano-CS with methacrylamide (MAA) and bis-acrylamide crosslinkers (forming the MAA-CS capillary) rather than the attachment of nano-CS to the copolymer of glycidyl methacrylate, MAA, and bis-acrylamide (forming the MAA+CS capillary). The completed MAA-CS capillary and its precursors were examined by SEM and ATR-IR measurements. Before separating chiral samples, the MAA-CS capillary was characterized by electroosmotic flow measurements at varying pH values, concentrations, and volume percentages of organic modifiers in the running buffers. Tryptophan enantiomers were well separated by the MAA-CS capillary, whereas no enantioselectivity was observed in the MAA+CS capillary. With the addition of 80% MeOH into the phosphate buffer, the chiral separation of (±)-catechin was accomplished in a normal-phase mode. However, the new CSP has its limitations, as only two groups of α-tocopherol stereoisomers were separated.

Diltiazem-imprinted porphyrinic covalent organic frameworks as solid-phase extractants and fluorescent sensors.

Diltiazem, which is a calcium channel blocker, is involved in the formation of covalent organic frameworks (COFs) through the Schiff base reaction of tetrakis (4-aminophenyl)-porphine (TAPP) and dihydroxynaphthalene-dicarbaldehyde (DHNDC) and the next enol-to-keto tautomerization. The diltiazem-imprinted COFs (DICOFs) were optimally formed using Sc(OTf)3 as the catalyst, TAPP/DHNDC/diltiazem in a molar ratio of 2/3/4, N-methylpyrrolidone/mesitylene (v/v = 3/5) as the porogen, and a 1-h reaction with a high imprinting factor of 10.5 compared to the nonimprinted counterparts (NICOFs). The optimized DICOF exhibited a more amorphous XRD pattern, a larger surface area (1650 vs. 930 m2/g), a larger pore volume (1.33 vs. 0.75 cm3/g), and a finer porous SEM feature than NICOF. The selectivity of NICOF toward diltiazem and diazepam at 250 nM (α = 1.03, RSD = 1.3%) was smaller than the selectivity of DICOF (α = 2.94, RSD = 1.6%). The diltiazem samples (5.0-300 ng mL-1) dynamically quenched the fluorescence of 15 µg/mL DICOF in 50 mM phosphate buffer at pH 6.5 at 8.0 min equilibrium; thus, Stern-Volmer plots were linearly constructed for sensing diltiazem with an LOD of 3.4 ng mL-1 and an LOQ of 10.2 ng mL-1. According to the plots, 30 ng mL-1 diltiazem solutions that were diluted from 30 mg-specified tablets had an average measured concentration of 29.5 ng mL-1 (σ = 1.3% and n = 5). In addition to application as fluorescent sensors, DICOFs (30 mg) could be used as dispersive extractants to recover 95.2% of 0.6 ng mL-1 diltiazem from 25 mL phosphate buffer with quadruplicate uses of 0.5 mL methanol/acetic acid (v/v = 9/1) as the eluent. Langmuir and pseudo-second-order models were fitted to the isothermal and kinetic sorption mechanisms, respectively. The maximum sorption capacity of DICOF was ten times larger than that of NICOF (156 vs. 15.2 mg/g). The interday recoveries of 0.6 ng mL-1 spiked in 20-fold diluted human urine, and 60-fold diluted human serum were 93.2% and 90.6%, respectively.

Hispolon promotes MDM2 downregulation through chaperone-mediated autophagy.

Amplification and overexpression of murine double minute (MDM2) has been observed in several human cancers. Some chemotherapeutic agents cause MDM2 ubiquitination and degradation in a proteasome-dependent system. In addition to the proteasome system, chaperone-mediated autophagy (CMA) is a lysosomal pathway for selective misfolded protein degradation. Molecular chaperone heat shock cognate 70 protein (Hsc70) recognizes the misfolded proteins, which are then delivered to lysosome-associated membrane protein type 2A (LAMP2A) for lysosomal degradation. Our previous study reported that hispolon was able to induce cell apoptosis and downregulate MDM2 expression. In this study, our results showed that the proteasome inhibitor, MG132, could not inhibit hispolon-induced MDM2 downregulation. In contrast, both inhibition of lysosomes with NH(4)Cl and inhibition of LAMP2A using siRNA partially attenuated hispolon-induced MDM2 downregulation. To determine whether Hsc70 recognizes MDM2 on amino acids 135-141, SMP14 antibody was used to compete with Hsc70 for interaction with MDM2. After Hsc70 knockdown, SMP14 antibody immunoprecipitated increased MDM2. We also found that hispolon induced increased association of Hsp70, Hsc70, Hsp90 and LAMP2A with MDM2. This association was inhibited in cells pretreated with geldanamycin (GA), an Hsp90 inhibitor. GA also attenuated hispolon-induced MDM2 downregulation. Meanwhile, inhibition of Hsc70 using siRNA attenuated hispolon-induced MDM2 downregulation. Our study provides the first example of the ability of hispolon to mediate MDM2 downregulation in lysosomes through the CMA pathway.

Polyacrylamide grafted on multi-walled carbon nanotubes for open-tubular capillary electrochromatography: comparison with silica hydride and polyacrylate phase matrices.

A new nanoparticle-bound polymer stationary phase was prepared by in situ polymerization of methacrylamide (MAA), bis-acrylamide crosslinker, and carboxylated multi-walled carbon nanotubes (multi-walled CNTs; MWNTs), using the abundant double bonds in the cyclopentadienyl rings in MWNT structure, on a silanized capillary. Each intermediate capillary between the synthesis steps was characterized by SEM, by ATR-IR, and by EOF measurements varying the pH, concentration, and volumetric ratios of ACN in running buffers. The resulting EOF profile was comparable to those of two other capillaries with different phase matrices, silica hydride and polybutyl methacrylate (BMA) phases. With the complex functionality of MWNTs on the hydrophilic polyacrylamide network, the MAA-CNT capillary was capable of separating diverse samples with a wide range of polarity and dissociation properties using open-tubular CEC. Besides optimizing CEC conditions, the migration times of samples were analyzed with respect to velocity and retention factors to evaluate electrophoretic and chromatographic contributions to the CEC mechanism. The migration rates of benzoic acids were determined by the electrophoretic mobilities of the various phenolate ions, while phenolic aldehydes and ketones were additionally influenced by chromatographic interactions, such as π-π, electrostatic effects, hydrogen bonding, and hydrophobic interactions. The retention factors were greater for flavonoids, which are polyphenolic, than for simple phenols, but were smaller than those obtained from the hydrophobic BMA-CNT column. A complete well-resolved separation of the cationic forms of tetracyclines was acheived either by electrophoresis or by chromatography in the MAA-CNT capillary, but not in the BMA-CNT and silica hydride-CNT capillaries.

The role of methacrylate polymerized as porous-layered and nanoparticle-bound phases for open-tubular capillary electrochromatography: substitution of a charged monomer for a bulk monomer.

The bulk monomer, butyl methacrylate (BMA), was copolymerized with an ionizable monomer (mono-(2-(methacryloyloxy)ethyl) succinate (MES)) and carbon nanotubes (CNTs) by ethylene dimethacrylate (EDMA) crosslinking to form the porous-layered and nanoparticle-bound stationary phases for open-tubular CEC. Here, two new phases were synthesized to check the role of BMA on the BMA-MES and BMA-CNT phases and the suitability of the MES monomer for concurrently acting as a bulk monomer. One phase, MES-EDMA, was simply composed of MES monomer and EDMA crosslinker and exhibited a phase construction of molecular layers, in contrast to the polymeric phases of BMA-MES. Another phase studied was MES-CNT, which SEM images showed that MES could be a good bulk monomer for a CNT-polyacrylate composite phase with embedded CNTs. For all the modified capillaries, the EOF profiles observed in phosphate buffers between pH 3.6 and 9.6 were comparable with each other and conformed to their corresponding SEM images. The residual silanols retained their influence on the EOF profiles in the MES-EDMA and BMA-MES capillaries, but diminished in the CNT-bound capillaries. In a comparison with the MES-EDMA capillary, the BMA-MES capillary afforded a stronger interaction with flavonoids and phenolic acids and still retained positive capacity factor values. Additionally, the capacity factors obtained from the BMA-CNT capillary were higher than those from the MES-CNT capillary, as the BMA-CNT phase had hydrophobic BMA units and a high surface contact area of bound CNTs.

Multi-walled carbon nanotube composites with polyacrylate prepared for open-tubular capillary electrochromatography.

A new phase containing immobilized carbon nanotubes (CNTs) was synthesized by in situ polymerization of acid-treated multi-walled CNTs using butylmethacrylate (BMA) as the monomer and ethylene dimethacrylate as the crosslinker on a silanized capillary, forming a porous-layered open-tubular column for CEC. Incorporation of CNT nanomaterials into a polymer matrix could increase the phase ratio and take advantage of the easy preparation of an OT-CEC column. The completed BMA-CNT column was characterized by SEM, ATR-IR, and EOF measurements, varying the pH and the added volume organic modifier. In the multi-walled CNTs structure, carboxylate groups were the major ionizable ligands on the phase surface exerting the EOF having electroosmotic mobility, 4.0 × 10(4) cm2 V(-1)1 S(-1)1, in the phosphate buffer at pH 2.8 and RSD values (n=5), 3.2, 4.1, and 4.3%, for three replicate capillaries at pH 7.6. Application of the BMA-CNT column in CEC separations of various samples, including nucleobases, nucleosides, flavonoids, and phenolic acids, proved satisfactory upon optimization of the running buffers. Their optima were found in the borate buffers at pH 9.0/50 mM, pH 9.5/10 mM/50% v/v ACN, and pH 9.5/30 mM/10% v/v methanol, respectively. The separations could also be used to assess the relative contributions of electrophoresis and chromatography to the CEC mechanism by calculating the corresponding velocity and retention factors. Discussions about interactions between the probe solutes and the bonded phase included the π-π interactions, electrostatic repulsion, and hydrogen bonding. Furthermore, a reversed-phase mode was discovered to be involved in the chromatographic retention.

Fluorometric determination of amifostine and alkaline phosphatase on amphiprotic molecularly imprinted silica crosslinked with binary functional silanes and carbon dots.

A silica-based molecularly imprinted polymer (MIP) formed by functional silanes (basic 3-aminopropyltriethoxysilane (APTES) and acidic 2-(4-chlorosulfonylphenyl)ethyltrimethoxysilane (CSPTMS)) was crosslinked with carbon dots (CDs) to develop a fluorescent sensor toward an amphiprotic template, amifostine (AMF). The CDs were synthesized by hydrothermal carbonization of succinic acid and an ionic liquid and possessed hydroxyl and pyrrolic functional groups, which enabled the CDs to be derivatized with silanes for subsequent sol-gel polymerization. Except for the CDs derivatized with tetraethoxysilane, CD-APTES, CD-CSPTMS, and CD-APTES/CSPTMS (molar ratio = 1/1) all presented distinct fluorescence dynamic quenching when interacted with AMF. However, APTES/CSPTMS was selected as the sol-gel monomer for the formation of MIP because its quenching ratio and imprinted factor were the highest among the CD-silane-MIPs. Moreover, 0.5 mg/mL of CD-APTES/CSPTMS -MIP in pH 7.5 buffer was used to quantify AMF (0.5-200 nM, LOD = 0.15 nM) and alkaline phosphatase (ALP) (2-150 µU/mL, LOD = 0.5 µU/mL), which activates the metabolism of AMF, and the calibration curves of AMF and ALP were determined via fluorescence quenching and restoration, respectively. The recoveries of 1, 10, and 60 nM AMF from 360-fold-diluted human serum solutions were 95, 104, and 103%, respectively, with RSD values that were lower than 4.2%. The average ALP activity of the original human serum was determined to be 32.1 U/L (RSD = 5.41%).

Etched succinate-functionalized silica hydride stationary phase for open-tubular CEC.

An open-tubular (OT) CEC column was designed to anchor ionizable succinate-functionalized ligands onto a silica hydride-based stationary phase through surface etching, silanization, and hydrosilation reactions beginning from a bare fused-silica tube. The modified columns that were produced in each step were monitored by analysis of the effect of performance of EOF on the changes of pH values, concentrations, and the amount of ACN added in the running buffers. By tracking the EOF patterns between columns, the author determined that the surface composition of the final product column was a combination of silanols, silica hydrides, and succinate ligands. Furthermore, lower loading volumes of the succinate ligands prepared for the hydrosilation reaction served to complete the mixed-mode OT-CEC columns, and subsequently to carry out the separation of six phenyl alcohols. Studies on the elution order of these alcohols identified the presence of chromatographic interactions in addition to electrophoresis. Based on the employment of a solvation parameter model, these interactions likely included dispersion interactions, dipole-type interactions, and interactions arising through the polarizable electrons in the solute. The optimum buffer conditions for CEC separations of phenyl alcohols, carbonyl-substituted phenols, and a mixture of nucleosides and thymine were a phosphate buffer (50 mM, pH 10.51), a borate buffer (50 mM, pH 8.62), and a borate buffer (50 mM, pH 9.50), respectively. Overall, the hydride-based stationary phases with ionizable ligands were successfully applied to the OT-CEC separations, and these results confidently propose an ideal route to the synthesis of novel OT-CEC columns.