Planar Chromatography of Cholic Acid-Derived cis—trans Isomeric bis-Steroidal Tetraoxanes

JPC – Journal of Planar Chromatography – Modern TLC - Seven pairs of cis—trans isomers of bis-steroidal tetraoxanes have been examined by both normal-phase (NP) and reversed-phase...     

Purity assessment problem in quantitative NMR—impurity resonance overlaps with monitor signal multiplets from stereoisomers

This paper describes the situation that can emerge when the signals to be evaluated in quantitative NMR measurements—so-called “monitor signals”—consist of several resonance lines from the stereoisomers of the analyte in addition to an impurity signal underneath. The monitor signal problem is demonstrated in the purity assessment of two samples of 2-(isopropylamino)-4-(ethylamino)-6-chloro-1,3,5-triazine (atrazine), a common herbizide which served as analyte in a CCQM intercomparison. It is shown that, in DMSO-d₆ solution, a mixture of stereoisomers leads to several individual overlapping singlets, which are further split by spin–spin coupling. A measurement protocol was developed for finding and identifying an impurity that has a signal that is positioned precisely beneath the methyl signal chosen as the monitor signal in one of the samples. Quantitative NMR purity assessment is still possible in this special case, but with higher uncertainty. Electronic Supplementary Material Supplementary material is available for this article at     

Iron oxide/tantalum oxide core–shell magnetic nanoparticle-based microwave-assisted extraction for phosphopeptide enrichment from complex samples for MALDI MS analysis

A new type of metal-oxide-coated magnetic nanoparticles (NPs)—tantalum-oxide-coated magnetic iron oxide (Fe₃O₄@Ta₂O₅) NPs—which are used as affinity probes for selectively trapping phosphopeptides from complex samples, is demonstrated in this study. In this approach, phosphopeptide enrichment was achieved by incubating the NPs with sample solutions under microwave heating within 1 min. The NP–target species conjugates were readily isolated from samples by magnetic separation followed by matrix-assisted laser desorption/ionization (MALDI) mass spectrometric analysis. When using human serum as the sample, phosphorylated fibrinopeptide-A-derived ions are the only ions observed in the MALDI mass spectra after enrichment by the Fe₃O₄@Ta₂O₅ NPs. Furthermore, only phosphopeptides appear in the MALDI mass spectra after using the affinity probes to selectively trap target species from the tryptic digest of a cell lysate and milk sample. The results demonstrated that the Fe₃O₄@Ta₂O₅ NPs have the capability of selectively trapping phosphorylated peptides from complex samples. The detection limit of this approach for a phosphopeptide (FQpSEEQQQTEDELQDK) was ~10 fmol. Figure For the first time, tantalum oxide-coated magnetic iron oxide (Fe₃O₄@Ta₂O₅) NPs were demonstrated as suitable affinity-probes for selectively trapping phosphopeptides from complex samples. To shorten the analysis time, phosphopeptide enrichment was achieved by incubating the NPs with sample solutions under microwave-heating within 1 min. MALDI MS was employed for characterization of the species trapped by the NPs.     

Spectral elucidation of the acid metabolites of the four geometric isomers of trifloxystrobin

Four geometric isomers of trifloxystrobin (TFS)—namely EE, EZ, ZE, and ZZ—were hydrolyzed by 0.05 M NaOH, resulting in four corresponding acid metabolites. These compounds—namely EE-, EZ-, ZE-, and ZZ-acids—were purified by preparative HPLC and authentically characterized by a combination of infrared, Raman, GC–MS, LC–MS/MS, and NMR spectroscopies. The spectra were found to be very characteristic of the individual isomers, and so they could be used to distinguish the isomers from each other. The detailed spectral features of the individual isomers are presented and compared. EE-acid was identified as being the major metabolite of TFS in soil, which indicates that hydrolysis is the principal route of degradation of TFS. This finding further justifies the importance of the present study in relation to assessing the risk associated with the release of TFS into the environment.     

Retention of enzymatic activity of alpha-amylase in the reductive synthesis of gold nanoparticles

In this paper, we report the generation of Au nanoparticles (NPs), using a pure enzyme for the reduction of AuCl4(-), with the retention of enzymatic activity in the complex. As a model system, alpha-amylase was used to readily synthesize and stabilize Au NPs in aqueous solution. Although several other enzymes were also pursued for the synthesis, it was interesting to observe that only alpha-amylase and EcoRI could produce Au NPs. Following NP synthesis, the activity of the enzyme was retained in the Au NP-alpha-amylase complex. The presence of Au NPs and alpha-amylase in the complex was established by UV-visible and FT-IR spectroscopy, X-ray diffraction (XRD) and transmission electron microscopic (TEM) measurements. Our observations suggest that the presence of free and exposed S-H groups is essential in the reduction of AuCl4(-) to Au NPs. Structural analysis of the enzymes showed that both alpha-amylase and EcoRI enzymes have free and exposed S-H groups in their native form and thus are suitable for the generation of NPs, whereas the other ones used here do not have such groups. Fortuitously, the enzymatic functional group of alpha-amylase is positioned opposite to that of the free and exposed S-H group, which makes it ideal for the production of Au NPs; binding of the enzyme to Au NPs via Au-S bond and also retention of the biological activity of the enzyme.     

Separation of isomers of nonylphenol and select nonylphenol polyethoxylates by high-performance liquid chromatography on a graphitic carbon column

p-Nonylphenol (NP) is a ubiquitous degradation product of nonylphenol polyethoxylate (NPE) surfactants and has been reported to be an endocrine disrupter. It is composed of numerous structural isomers resulting from the various branching patterns of the C-9 group. Twenty-two isomers in a technical mix of NP have been identified with high-resolution capillary GC-MS. In most HPLC analyses, nonylphenol elutes as a single, broad peak. In the method described here, HPLC using a graphite carbon column resulted in the resolution of a technical mixture of NP into 12 peaks or groups of isomers. This method was also applied to select NPEs with one to 10 ethoxy units with similar results. Separation was achieved by gradient elution with 1% acetic acid in water and acetonitrile. Elution of individual isomers 4-butylphenol and 4-propylphenol under the same gradient conditions indicate that increased branching of an alkyl group results in shorter retention times than for the less substituted alkyl groups. This method can be used to fractionate NP based on structure and assess the potential for different isomers (or groups of structurally similar isomers) to act as endocrine disrupters.     

Isomers in the chemistry of iron coordination compounds

The coordination chemistry of iron covers a wide field, as shown by a survey covering the crystallographic and structural data of almost one thousand and three hundred coordination complexes. About 6.7% of these complexes exist as isomers and are summarized in this review. Included are distortion (96.6%) and cis — trans (3.4%) isomers. These are discussed in terms of the coordination about the iron atom, bond length and interbond angles. Distortion isomers, differing only by degree of distortion in Fe-L, Fe-L-Fe and L-Fe-L parameters, are the most common. Iron is found in the oxidation states zero, +2 and +3 of which +3 is most common. The stereochemistry around iron centers are tetrahedral, five — coordinated (mostly trigonal — bipyramid) and six — coordinated. The most common ligands have O and N donor sites.     

Metallogel Template Fabrication of pH‐Responsive Copolymer Nanowires Loaded with Silver Nanoparticles and Their Photocatalytic Degradation of Methylene Blue

Poly(N,N′‐methylenebisacrylamide–4‐vinylpyridine) (P(MBA‐4VP)) nanowires loaded with silver nanoparticles (Ag NPs) have been fabricated by silver metallogel template copolymerization, and subsequently, silver ions are reduced instead of the template being removed. Ag NPs with a diameter of 5–15 nm were dispersed throughout the core of P(MBA‐4VP) nanowires. The size and distribution of the formed Ag NPs could be finely controlled by reduction time. The pH sensitivity of P(MBA‐4VP) nanowires offers the possibility of Ag NP release from the nanowires under acidic conditions. The photocatalytic performance of the P(MBA‐4VP) nanowires loaded with Ag NPs was evaluated for the degradation of methylene blue (MB) under UV light irradiation. Their rate of degradation is dependent on the content and size of the Ag NPs, as well as the pH values of the MB solution. Moreover, the P(MBA‐4VP) nanowires loaded with Ag NPs exhibited high photostability, and the photocatalytic efficiency reduced by only 1.81 % after being used three times.     

Single-step process to produce surface-functionalized polymeric nanoparticles

Nanoparticles (NPs) are a versatile medium for the localization of therapeutics to tumors and for cellular and tissue imaging. The ability to impart targeting capability or enhance cellular uptake is dependent in part on the presentation of relevant surface functionality, among other design parameters. Currently, the production of functionalized polymeric NPs requires the a priori synthesis of polymers bearing such functionality. Here we describe a process to produce functionalized polymeric NPs derived from nonfunctional polymers in a single step. This was achieved by tailoring the solvation of the polymer using a binary solvent system such that the addition of an aqueous phase rich in water-soluble polymer or polyelectrolytes results in the formation of NPs with the concomitant functionalization of NP surfaces with the polymeric moieties introduced into the aqueous phase. This strategy also allows for easy control over NP size independent of surface functionality. We have demonstrated that poly(lactic-co-glycolic acid) (PLGA) NPs bearing surface functionality as diverse as biological polysaccharides such as heparin, water-soluble ionic polymers, and poly(ethylene glycol) can be prepared under identical conditions in a single step, with surface coverage (mass %) ranging from 3 to >70%. We expect this novel process to enable complex surface engineering of NP chemistry that hitherto was impossible using existing approaches.     

Understanding the degradation pathway of the pesticide, chlorpyrifos by noble metal nanoparticles

Application of nanoparticles (NPs) in environmental remediation such as water purification requires a detailed understanding of the mechanistic aspects of the interaction between the species involved. Here, an attempt was made to understand the chemistry of noble metal nanoparticle-pesticide interaction, as these nanosystems are being used extensively for water purification. Our model pesticide, chlorpyrifos (CP), belonging to the organophosphorothioate group, is shown to decompose to 3,5,6-trichloro-2-pyridinol (TCP) and diethyl thiophosphate at room temperature over Ag and Au NPs, in supported and unsupported forms. The degradation products were characterized by absorption spectroscopy and electrospray ionization mass spectrometry (ESI MS). These were further confirmed by ESI tandem mass spectrometry. The interaction of CP with NP surfaces was investigated using transmission electron microscopy, energy dispersive analysis of X-rays, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). XPS reveals no change in the oxidation state of silver after the degradation of CP. It is proposed that the degradation of CP proceeds through the formation of AgNP-S surface complex, which is confirmed by Raman spectroscopy. In this complex, the P-O bond cleaves to yield a stable aromatic species, TCP. The rate of degradation of CP increases with increase of temperature and pH. Complete degradation of 10 mL of 2 ppm CP solution is achieved in 3 h using 100 mg of supported Ag@citrate NPs on neutral alumina at room temperature at a loading of ～0.5 wt %. The effect of alumina and monolayer protection of NPs on the degradation of CP is also investigated. The rate of degradation of CP by Ag NPs is greater than that of Au NPs. The results have implications to the application of noble metal NPs for drinking water purification, as pesticide contamination is prevalent in many parts of the world. Study shows that supported Ag and Au NPs may be employed in sustainable environmental remediation, as they can be used at room temperature in aqueous solutions without the use of additional stimulus such as UV light.     

预制铂纳米颗粒对质子交换膜燃料电池用铂纳米线阴极的结构影响

铂纳米线（Pt NWs）由于其独特的结构特点,比商业Pt/C具有更高的氧还原反应（ORR）比活性。在本工作中,我们将预先制备好的铂纳米颗粒（Pt NPs）引入到碳基体中,用于诱导生长Pt NWs,获得了均匀分布Pt NWs的阴极。通过改变Pt NP载量（0~0.015 mg·cm^-2）和Pt NP来源（不同Pt含量的Pt/C）研究了所制备阴极的结构和性能。用扫描电镜对阴极表面进行了表征,并用透射电镜和X射线衍射分析了Pt NW的形貌和晶体结构。在单电池中分别进行了极化曲线和循环伏安曲线测试。当Pt NP来源为40% Pt/C且其载量为0.005 mg·cm^-2时,制备的Pt NW阴极具有最佳的单电池性能和最大的电化学表面积（ECSA）。最后,提出了预制Pt NP影响Pt NWs分布的可能机制。     

Determination of potential degradation products of piroxicam by HPTLC densiometry and HPLC

Summary HPTLC densitometry and HPLC are considered for the simultaneous determination of the degradation products of piroxicam (2-aminopyridine, DP-I and DP-II). The substances were separated on silica gel with fluorescence indicator in ethylacetate — toluene — diethylamine (10∶10∶5) and toluene — absolute ethanol — glacial acetic acid (8∶1.2∶0.5) systems. The measuring absorbance (detection of reflectance) of the separated substances was carried out “in situ” at 296 nm using 4-level calibration (external standard, nonlinear regresson function) in the concentration range 600–1200 ng 2-aminopyridine/spot and 300–600 ng DP-I and DP-II/spot. The HPLC method was carried out using RP-8 stationary phase and methanol + phosphate-citrate buffer, pH 3 mobile phase with addition of sodium pentanesulfonate (40+60, v/v). 2-aminopyridine wass detected at 300 nm, DP-I at 280 nm and DP-II at 248 nm. The concentration range for 2-aminopyridine is 2–40 μg/ml, for DP-I and DP-II 2–20 μg/ml (for an injection volume of 10 μl). The results were evaluated by linear regression analysis.     

Construction of nanoparticle superstructures on the basis of host-guest interaction to achieve performance integration and modulation

Creation of nanoparticle (NP) architectures via a self-assembly strategy is the current means to integrate and/or modulate the functionalities of NPs. In this paper, we demonstrate the capability for constructing NP spherical superstructures through the specific interaction between host and guest molecules, for instance the model system of α-cyclodextrin (α-CD) and oleic acid (OA), which are decorated on two different NPs beforehand. Subsequently, the OA-decorated hydrophobic NPs are dispersed in hexane, whereas the α-CD-decorated NPs are dispersed in water. The blending of these two immiscible solutions produces NP binary superstructures because of the multiple linkages between the α-CD- and OA-decorated NPs. Control experiments indicate that the self-assembly of NPs occurs either at the hexane/water interface to form hybrid films or in the aqueous phase to generate spherical architectures, which strongly depends on the amount and the size of α-CD-decorated NPs. The high ratio and small size of the α-CD-decorated NPs facilitate the formation of spherical architectures. Competitive experiments with the addition of host α-CD and guest sodium oleate clearly confirm that the main driving force for the NP co-assembly is the specific interaction between α-CD and OA. In addition, the flexible decoration of α-CD and OA on the NPs makes the current strategy generally applicable for a variety of NPs, such as the superstructures of Au/Fe(3)O(4), Pt/Fe(3)O(4), and Au/NaYF(4):Yb,Tm, which is expected to promote the further application of NPs in environmental and biological sciences.     

Quantitative reversed phase HPLC analysis of L-ascorbic acid (Vitamin C) and identification of its degradation products

Summary An isocratic ion suppression reversed phase method is utilized for the qualitative and quantitative determination of L-ascorbic acid in fresh fruit juices — complex sample matrices. The selectivity of the method, when a macroreticular poly(styrene-divinylbenzene) reversed phase adsorbent is used, is sufficient to resolve the isomers L-ascorbic acid and D-erythorbic acid (isoascorbic acid) to baseline in under 8 minutes. L-Ascorbic acid solution stability is monitored using the same analytical conditions with the degradation products sufficiently well resolved not to interfere in the quantification of L-ascorbic acid. By the use of commercial materials and the preparation of the proposed products of the oxidative degradation of L-ascorbic acid the degradation sequence and identification of the products in an aged L-ascorbic acid solution is accomplished.     

Concentration–polarization effect of poly(sodium styrene sulfonate) on size distribution of colloidal silver nanoparticles during diafiltration experiments

Polyelectrolyte (PEL)-based dual systems and nanoparticles (NPs) are two topics which have generated great interest as a result of their many and novel applications. Here, PEL–NPs system which appears transitorily when a high molecular weight PEL solution is mixed with metal NP colloidal dispersions during diafiltration is studied. The aim of this paper was to analyze the concentration–polarization effect of PEL molecules on size distribution of NPs capable to pass through the ultrafiltration membrane. Poly(sodium styrene sulfonate) (PSSNa) and silver nanoparticles (AgNPs) were used as PEL and metal NP colloidal dispersion, respectively. It was seen that particle size decreased from 42.4?±?37.8 to 10.1?±?0.7 nm in the presence of PSSNa and concentration–polarization. In addition, our results indicate that polarization–concentration phenomenon can be used to modify the size distribution of NP colloidal dispersions, that by changes of polarization–concentration features is possible the modification of NP size in the permeate during diafiltration experiments and that in presence of concentration–polarization, PSSNa was only a modifier factor of medium. In addition, it was observed that exclusion size of ultrafiltration membrane is an important element for establishing of particle size in the permeate.     

Quantum dot on a rope

The conjugation of nanoparticles (NPs) typically yields supramolecular materials which are fairly rigid, and the electronic coupling between the NP and other structural units of these compounds is fixed by covalent bonds. Here, we report on a novel bichromophor system constructed from a quantum dot tethered to a semiconducting polymer, which demonstrates the possibility of the dynamic interunit coupling in the NP supramolecules. The NP bichromophoric system was made on the basis of the layer-by-layer assembled (LBL) films of an anionic polyelectrolyte with poly(p-phenylene ethynylene) backbone, aPPE, and poly(allylamine hydrochloride) PAH polycation. To conjugate CdTe NPs to the (aPPE/PAH)(m) LBL film, we took advantage of the reactive groups of NP stabilizer, that is, -COOH, and the aminogroups on PAH. Tethering of CdTe was accomplished by using poly(ethyleneglycole), PEG, chains with two reactive terminals such as t-BOC-NH-PEG-COO-NHS. The evidence for successful conjugation of NPs to the LBL films can be seen both in AFM images and in optical data. The latter also indicate that the light quanta emitted by the NPs originate from the light absorption of the polymer film, which proves the presence of the aPPE-->NP energy-transfer process. The average separation distance between the NPs tethered to the LBL films can be changed by altering the dielectric properties of the solvent affecting PEG tether coiling (water/alcohol mixture). The reduced emission intensity of aPPE was found to follow the extension of the PEG tether. The quenching of aPPE is reversible when the original composition of the solvent mixture is restored. Thus, CdTe-PEG-aPPE is an example of an organized NP system with tunable optical coupling. Variable electronic coupling offers a convenient structural platform for new nanotechnological devices for which spatial control translates into a higher level of sophistication. PEG molecules afford a wide variety of polymer chain configurations with different reactive terminals, which makes possible the preparation of diverse NP superstructures.     

Disruption of supported lipid bilayers by semihydrophobic nanoparticles

Understanding the interaction between functional nanoparticles and cell membranes is critical to use nanomaterials for broad biomedical applications with minimal cytotoxicity. In this work, we have investigated the effect of adsorbed semihydrophobic nanoparticles (NPs) on the dynamics and morphology of model cell membranes. We have systematically varied the degree of surface hydrophobicity of carboxyl end-functionalized polystyrene NPs of varied size in buffer solutions with varied ionic strength. It is observed that semihydrophobic NPs can readily adsorb on neutral SLBs and drag lipids from SLBs to NP surfaces. Above a critical NP concentration, the disruption of SLBs is observed, accompanied with the formation and rapid growth of lipid-poor regions on NP-adsorbed SLBs. In the study of the effect of solution ionic strength on NP surface hydrophobic degree and the growth of lipid-poor regions, we have concluded that the hydrophobic interaction enhanced by screened electrostatic interaction underlies the envelopment of NPs by lipids that are attracted from SLBs to the surface of NPs or their aggregates. Hence, the formation and growth of lipid-poor regions, or vaguely referred as "pores" or "holes" in the literature, can be controlled by NP concentration, size, and surface hydrophobicity, which is critical to design functional nanomaterials for effective nanomedicine while minimizing possible cytotoxicity.     

Hydrophobic Cysteine Poly(disulfide)‐based Redox‐Hypersensitive Nanoparticle Platform for Cancer Theranostics

Selective tumor targeting and drug delivery are critical for cancer treatment. Stimulus‐sensitive nanoparticle (NP) systems have been designed to specifically respond to significant abnormalities in the tumor microenvironment, which could dramatically improve therapeutic performance in terms of enhanced efficiency, targetability, and reduced side‐effects. We report the development of a novel L ‐cysteine‐based poly (disulfide amide) (Cys‐PDSA) family for fabricating redox‐triggered NPs, with high hydrophobic drug loading capacity (up to 25 wt % docetaxel) and tunable properties. The polymers are synthesized through one‐step rapid polycondensation of two nontoxic building blocks: L ‐cystine ester and versatile fatty diacids, which make the polymer redox responsive and give it a tunable polymer structure, respectively. Alterations to the diacid structure could rationally tune the physicochemical properties of the polymers and the corresponding NPs, leading to the control of NP size, hydrophobicity, degradation rate, redox response, and secondary self‐assembly after NP reductive dissociation. In vitro and in vivo results demonstrate these NPs’ excellent biocompatibility, high selectivity of redox‐triggered drug release, and significant anticancer performance. This system provides a promising strategy for advanced anticancer theranostic applications.     

Synthesis of copper nanoparticles stabilized by polyoxyethylenesorbitan monooleate

We studied the influence of synthesis parameters and the composition of the reaction mixture on the size and morphology of copper nanoparticles (NPs). Use of a surfactant (polyoxyethylenesorbitan monooleate) is promising for confining NP growth and stabilizing NPs. Concentration ranges of existence were determined for copper NP dispersions stable to aggregation and sedimentation. Scanning electron microscopy and dynamic light scattering were used to show that: the NP size varied from 10 to 65 nm, the average diameter was 25–35 nm, and the shape was spherical. The sizes of copper NP aggregates were determined.