Sodium hydroxide as pretreatment and fluorosurfactant-capped gold nanoparticles as sensor for the highly selective detection of cysteine

A sensor for detecting cysteine (Cys) in a solution of fluorosurfactant (FSN)-capped gold nanoparticles (AuNPs) has been developed. Under acidic conditions, FSN-capped AuNPs are aggregated in the presence of homocysteine (HCys) and Cys but not in the presence of cysteinylglycine, glutathione, and gamma-glutamycysteine. When adding NaOH to a solution of HCys, the five-membered ring transition state is formed through intramolecular hydrogen abstraction. By contrast, it is difficult for Cys to form a four-membered ring transition state after Cys has been pretreated with NaOH. As a result, the HCys-induced aggregation of the FSN-capped AuNPs is suppressed because the five-membered ring transition state exhibits relatively larger steric hindrance and has stronger interaction with the FSN molecules. Thus, we can discriminate between Cys and HCys on the basis of different aggregation kinetics. Under the optimum condition, the selectivity of the probe for Cys in aqueous solutions is remarkably high over the other aminthiols. Note that HCys and Cys have very similar structure and pK(a) value. We have validated the applicability of our method through the analyses of Cys in urine samples. It is believed that this approach has great potential for the detection of Cys in biological samples.     

On-line concentration of proteins by SDS-CGE with LIF detection

We present a simple approach for on-line concentration of SDS-protein complexes by using poly(vinyl alcohol) (PVA) solution in CGE. In comparison to the coated capillary, the presence of EOF in CGE omitted the need to fill the capillaries with polymer solutions prior to the analysis. More importantly, we found that highly reproducible separation of eight proteins by 3.5% PVA was achieved between runs and without the regeneration of high bulk EOF; the RSD of migration times was less than 0.7%. To further improve the concentration sensitivity, neutral PVA was introduced into the capillary with the help of EOF to act as sieving matrix. The occurrence of stacking at the boundary between the PVA and the sample zone is mainly due to the retardation of proteins by PVA. As a result, the LODs at an S/N of 3 for SDS-protein complexes are of the order of sub-nM to several nM. For example, the LOD for BSA is 0.78 nM, which is a 91-fold sensitivity enhancement over the normal injection. In addition, our stacking method has been applied to the analyses of proteins in Escherichia coli cells. The peak for beta-galactosidase (E. coli) was observed after 0.1 microM beta-galactosidase was spiked into the E. coli samples.     

Infinite Polyiodide Chains in the Pyrroloperylene–Iodine Complex: Insights into the Starch–Iodine and Perylene–Iodine Complexes

We report the preparation and X‐ray crystallographic characterization of the first crystalline homoatomic polymer chain, which is part of a semiconducting pyrroloperylene–iodine complex. The crystal structure contains infinite polyiodide I_∞^δ?. Interestingly, the structure of iodine within the insoluble, blue starch–iodine complex has long remained elusive, but has been speculated as having infinite chains of iodine. Close similarities in the low‐wavenumber Raman spectra of the title compound and starch–iodine point to such infinite polyiodide chains in the latter as well.     

Phosphate-modified TiO2 nanoparticles for selective detection of dopamine, levodopa, adrenaline, and catechol based on fluorescence quenching

For the first time, an aqueous solution, comprising 6-nm phosphate-modified titanium dioxide (P-TiO2) nanoparticles (NPs) and fluorescein, has been used for sensing dopamine (DA), levodopa (L-DOPA), adrenaline, and catechol. The complexes obtained by means of chelation of surface Ti(IV) ions with an enediol group exhibit strong absorption at 428 nm; thus, they can be designed as efficient quenchers for fluorescein. The fluorescence of a fluorescein solution containing 1.4 mM P-TiO2 NPs at pH 8.0 decreases if the solution comprises DA, L-DOPA, adrenaline, and catechol, but not noradrenaline, ascorbic acid, and salicylic acid. We consider that P-TiO2 NPs have a number of advantages over bare TiO2 NPs, such as ease of preparation, high selectivity, and high stability. By measuring fluorescence quenching, the limits of detection at a signal-to-noise ratio of 3 are calculated as 33.5, 81.8, 20.3, and 92.1 nM for DA, L-DOPA, adrenaline, and catechol, respectively. In contrast, UV-vis absorption reveals the relatively poor sensitivity of these compounds. We have validated the applicability of our method by means of analyses of DA in urine samples. High-performance liquid chromatography in combination with an electrochemical cell has been used to further confirm our results. We believe that this approach has great potential for diagnostic purposes.     

Online concentration and separation of basic proteins using a cationic polyelectrolyte in the presence of reversed electroosmotic flow

We report an online concentration and separation method for basic proteins using poly(diallyldimethylammonium chloride) (PDDA) solutions in the presence of reversed EOF. Using a capillary dynamically coated with 2% PDDA containing 0.1 M NaCl and filled with 1.2% PDDA under neutral conditions (10 mM phosphate, pH 7.0), we have demonstrated the separation of six basic proteins with peak efficiencies ranging from 175 000 to 616 000 plates/m and RSDs of migration time less than 0.4%. Additionally, high-speed separation of six basic proteins (<7 min) was achieved using a short capillary filled with 0.6% PDDA solutions. Under injection of the large-volume sample (210 nL), the LODs at S/N of 3 for basic proteins are down to nanomolar range. For example, the LOD for lysozyme is 1.2 nM, which is a 260-fold sensitivity enhancement compared with conventional injection method. The proposed method has been applied to the stacking of lysozyme in human saliva samples. Without any pretreatment, we also demonstrated the capability of this method to detect low amounts of peptide samples through the stacking of tryptic peptide of myoglobin. The experimental results indicate that our proposed method has great potential for use in clinical diagnosis and proteomics applications.     

Water oxidation catalyzed by a new tetracobalt-substituted polyoxometalate complex: [{Co4(μ-OH)(H2O)3}(Si2W19O70)]11-

A new polyoxometalate of earth adundant elements [{Co(4)(μ-OH)(H(2)O)(3)}(Si(2)W(19)O(70))](11-) has been synthesized, characterized and shown to be a water oxidation catalyst. The initial catalytic complex is unstable and slowly undergoes hydrolysis. The hydrolysis products have been isolated and characterized, and their catalytic water oxidation activity is assessed.     

Synthesis, spectral, electrochemical, and anion binding properties of 3,5-bis(dipyrromethanyl) boron-dipyrromethenes

Four new boron-dipyrromethenes (BODIPYs) containing dipyrromethanyl substituents at 3,5-positions, bis(3,5-dipyrromethanyl) BODIPYs 5-8, were synthesized by treating their corresponding 3,5-diformyl BODIPYs 1-4 with excess pyrrole under mild acid catalyzed reaction conditions. The compounds 5-8 are stable and freely soluble in common organic solvents. One-dimensional, two-dimensional NMR, high resolution mass spectrometry (HRMS), absorption, fluorescence, and electrochemical techniques were used to characterize the compounds. The spectral and electrochemical studies indicated that dipyrromethanyl groups at 3,5-positions of BODIPY are less electron deficient compared to formyl groups at the same positions. The anion binding studies indicated that bis(3,5-dipyrromethanyl) BODIPY compounds containing four pyrrole NH groups showed preferential binding with F(-) ion over other anions, as confirmed by using NMR, fluorescence, and electrochemical studies.     

Combining Fullerenes and Zwitterions in Non‐Conjugated Polymer Interlayers to Raise Solar Cell Efficiency

Polymer zwitterions were synthesized by nucleophilic ring‐opening of 3,3′‐(but‐2‐ene‐1,4‐diyl)bis(1,2‐oxathiolane 2,2‐dioxide) (a bis‐sultone) with functional perylene diimide (PDI) or fullerene monomers. Integration of these polymers into solar cell devices as cathode interlayers boosted efficiencies of fullerene‐based organic photovoltaics (OPVs) from 2.75 % to 10.74 %, and of non‐fullerene‐based OPVs from 4.25 % to 10.10 %, demonstrating the versatility of these interlayer materials in OPVs. The fullerene‐containing polymer zwitterion ( C₆₀‐PZ ) showed a higher interfacial dipole (Δ) value and electron mobility than its PDI counterpart ( PDI‐PZ ), affording solar cells with high efficiency. The power of PDI‐PZ and C₆₀‐PZ to improve electron injection and extraction processes when positioned between metal electrodes and organic semiconductors highlights their promise to overcome energy barriers at the hard‐soft materials interface of organic electronics.     

Gold nanoparticles as assisted matrices for the detection of biomolecules in a high-salt solution through laser desorption/ionization mass spectrometry

Citrate-capped gold nanoparticles (AuNPs) serve as matrices for the determination of biomolecules in a high-salt solution through matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). In the case of using 2,5-dihydroxybenzoic acid (2,5-DHB) as a matrix, the signal intensities of neutral steroids were severely suppressed in a high-salt solution. A high concentration of NaCl caused the formation of the sodium adduct ions during the desorption/ionization process, resulting in a decrease of the signal intensities of the protonated ions. In comparison, by applying AuNP-assisted LDI-TOF-MS, the signal intensities of neutral steroids remained almost constant when the concentration of NaCl was increased to 500 mM. Because the use of citrate-capped AuNPs as matrices primarily offers alkali metal ion adducts, AuNP matrices have a higher tolerance to high NaCl concentrations relative to that of 2,5-DHB matrices. The relevant phenomena are also discovered in the case of analysis of neutral carbohydrate, monosialoganglioside, indolamine, and angiotensin I. The quantification of small molecules in a high-salt solution has been accomplished by AuNP-assisted LDI-TOF-MS coupled to a unique sample preparation, in which samples are deposited onto the sample plate before AuNPs. The present method has been further applied to the determination of urea, creatinine, uric acid, and glucose in a urine sample.