Tollens Reaction Research Articles

Time-domain Tollens reaction: synthesising silver nanoparticles with the formaldehyde clock.

The addition of silver(i) ions to the methylene glycol-sulphite (MGS) clock reaction results in the sudden formation of metallic silver nanoparticles. Stable suspensions are obtained in the presence of poly(vinylpyrrolidone). The time delay before the appearance of the particles, as well as their size, decreases with the initial methylene glycol concentration while their monodispersity increases.

Tollens Reaction‐Based Integration of Thin Film Wall Electrodes into Microfluidic PDMS Devices

AbstractThe integration of electrodes into microfluidic devices is a prerequisite for several key technologies such as electrophoresis, dielectrophoresis, electrowetting, or analysis and manipulation of biological cells in organ‐on‐a‐chip applications. However, conventional sputtering or metal deposition methods result in electrodes on the top or the bottom of the microfluidic device leading to either an inhomogeneous electrical field or considerable restrictions regarding optical analysis methods. Here, a novel method for integrating electrodes into microfluidic devices based on the deposition of silver films on the sidewalls of microfluidic channels by Tollens reaction is presented. Aldehydes diffuse readily through polydimethylsiloxane walls and reduce noble metal ions such as silver, which in turn precipitate and deposit on the phase border as homogeneous thin layers. The process results in sidewall electrodes that adopt the channel's geometry and offer a highly homogeneous electrical field in the case of a rectangular channel. The electrodes were analyzed by dissipative X‐ray (EDX) and electrical impedance spectroscopy, while the electrical field was visualized by particle image velocimetry. The method can fabricate electrodes in different shapes rendering the process highly promising for a wide range of different electrochemical applications in the field of microfluidics, while simultaneously enable optical analysis methods.

New application of atraditional method: colorimetric sensor array for reducing sugars based on the in-situ formation of core-shell gold nanorod-coated silver nanoparticles by the traditional Tollens reaction.

An effective and robust colorimetric sensor array for simultaneous detection and discrimination of five reducing sugars (i.e., glyceraldehyde (Gly), fructose (Fru), glucose (Glu), maltose (Mal), and ribose (Rib)) has been proposed. In the sensor array, two negatively charged polydielectrics (sodium polystyrenesulfonate (NaPSS) and sodium polymethacrylate (NaPMAA)), which served as the sensing elements, were individually absorbed on the surface of the cetyltrimethylammonium bromide (CTAB)-coated gold nanorods (AuNR) with positive charges through electrostatic action, forming the designed sensor units (NaPSS-AuNR and NaPMAA-AuNR). In the presence of Tollens reagent (Ag(NH3)2OH), Ag+ was absorbed on the surface of negatively charged NaPSS-AuNR and NaPMAA-AuNRs. When confronted with differential reducing sugars, different reducing sugars exhibited differential levels of deoxidizing abilities toward Ag+, thus Ag+ was reduced to diverse amounts of silver nanoparticles (AgNPs) in situ to form core-shell AuNR@AgNP by the traditional Tollens reaction method, leading to distinct colorimetric response patterns (value of AS/AL (the ratio of absorbance at 360nm to that at 760nm in Ag+-NaPMAA-AuNR, and the ratio of absorbance at 360nm to that at 740nm in Ag+-NaPSS-AuNR)). These response patterns are characteristic for each reducing sugar, and can be quantitatively distinguished by linear discriminant analysis (LDA) atconcentrations as low as 10nM with relative standard deviation (RSD) of 4.11% (n = 3). The practicability of this sensor array has been validated by recognition of reducing sugars in serum and urine samples. A colorimetric sensor array for reducing sugar discrimination based on the reduction of Ag+ and in situ formation of AuNR@AgNP.

Synthesis of silver nanoplates on electrospun fibers via tollens reaction for SERS sensing of pesticide residues.

Silver nanoplates were for the first time synthesized on electrospun chitosan/polyethylene oxide (CS/PEO) fibers via tollens reaction. Ag nanoplates/CS/PEO fibers were used as the SERS-active substrates for quantitative evaluation of 2-naphthylthiol, with an enhancement factor (1.41± 0.07)× 106. The SERS-active substrates are flexible, stable, and easy for transportion and preservation, and act as the SERS platform for sensitive detection of the target. Thiram and thiabendazole as the representatives of pesticide residues were identified and detected by the Ag nanoplates/CS/PEO fibers, exhibiting linear response ranges from 10-11 to 10-7M with a detection limit of 10-11 M. The Ag nanoplates/CS/PEO fibers meet the requirement of thiram detection in practical samples, such as apple, pear, tomato, and cucumber juices. The strategy revealed the feasibility of fabrication of Ag nanoplates on electrospun fibers via tollens reaction and SERS sensing of pesticides in real samples. Ag nanoplates/CS/PEO fibers were fabricated by tollens reaction and electrospinning for SERS sensing of pesticide residues with high sensitivity.

OPTIMIZATION OF THE TECHNOLOGY FOR PRODUCING A MAGNETO CONTROLLABLE NANOCOMPOSITE Ag@Fe3O4 USING MATHEMATICAL DESIGN

Objective: The purpose of the research was to optimize technology for producing a magneto controllable nanocomposite Ag@Fe3O4 with modern physicochemical and therapeutic requirements using methods of mathematical design of the experiment.
 Methods: To optimize the synthesis process of the nanocomposite Ag@Fe3O4, the method of factor experiment was used. Mathematical calculations were performed using the STATISTICA 10 StatSoft Inc. system and Excel spreadsheet processor of MS Office 2019 Professional Plus.
 Results: Based on the study of technological parameters of nanocomposite synthesis Ag@Fe3O4 (16 experiments) a regression equation was obtained: Y = 106.415+0.038X1+4.448Х2+1.806Х3–1.593Х4–18.945Х5–109.980Х6. By the use of this equation the synthesis parameters were optimized with the help of steepest ascent method. It was found that the maximum yield of Ag@Fe3O4 can be achieved under the following conditions: X1 (magnetite synthesis time, min)–40; X2 (glucose content in solution,%)–10; X3 (temperature of the Tollens reaction, °С)–65; X4 (magnetite silver coating time, min)–30; X5 (pH, units)–8.5; X6 (rate of addition of ammonia, mol/min)–0.36.
 Conclusion: Using mathematical design of the experiment, a technology was developed for producing Ag@Fe3O4 with modern physicochemical and therapeutic requirements.

Enhanced photocatalytic activity of novel TiO2/Ag/MoS2/Ag nanocomposites for water-treatment

MoS2/TiO2 based nanocomposites exhibit great prospect in the area of photocatalysis and rechargeable batteries. However, many efforts have to be made to avoid the agglomeration of MoS2 on TiO2 nanobelts, to increase the interfacial bonding between MoS2 and TiO2, and to utilize the inert basal surface of 2H–MoS2. Herein, we report the TiO2/Ag/MoS2/Ag nanocomposites with double Ag loadings by hydrothermal method combined with the Tollen reaction. The as-obtained nanocomposites possess excellent photocatalytic performance to Cr (Ⅵ) and RhB, which is ascribed to the fast transfer and effective separation of charge carriers due to the formation of heterojunction between TiO2/Ag/MoS2 and MoS2/Ag. The present study illustrates the potential application of these analogous multiphase nanocomposites for water purification.

A Study of 3D-Printable Reinforced Composite Resin: PMMA Modified with Silver Nanoparticles Loaded Cellulose Nanocrystal.

With the rapid application of light-curing 3D printing technology, the demand for high-performance polymer resins is increasing. Existing light-curable resins often have drawbacks limiting their clinical applications. This study aims to develop a new type of polymethyl methacrylate (PMMA) composite resins with enhanced mechanical properties, high antibacterial activities and excellent biocompatibilities. A series of reinforced composite resins were prepared by mechanically mixing PMMA with modified cellulose nanocrystals (CNCs), which were coated with polydopamine and decorated by silver nanoparticles (AgNPs) via Tollen reaction. The morphology of CNCs-Ag was observed by transmission electron microscopy and the formation of AgNPs on CNCs was confirmed by X-Ray photoelectron spectroscopy analyses. Functional groups in PMMA-CNCs-Ag composites were verified by Fourier Transform infrared spectroscopy (FTIR) spectroscopy. The mechanical assessment and scanning electron microscopy analysis suggested that the evenly distributed CNCs-AgNPs composite effectively improve mechanical properties of PMMA resin. Cytotoxicity assay and antibacterial activity tests indicated excellent biocompatibility and high antibacterial activities. Furthermore, PMMA with CNCs-AgNPs of 0.1 wt.% (PMMA-CNCs-AgNPs-0.1) possessed the most desirable mechanical properties owing to the homogeneous distribution of AgNPs throughout the resin matrix. This specific composite resin can be used as a functional dental restoration material with potential of other medical applications.

Total Synthesis of the Norhasubanan Alkaloid Stephadiamine.

(+)-Stephadiamine is an unusual alkaloid isolated from the vine Stephania japonica. It features a norhasubanan skeleton, and contains two adjacent α-tertiary amines, which renders it an attractive synthetic target. Here, we present the first total synthesis of stephadiamine, which hinges on an efficient cascade reaction to implement the aza[4.3.3]propellane core of the alkaloid. The α-aminolactone moiety in a highly hindered position was installed via Tollens reaction and Curtius rearrangement. Useful building blocks for the asymmetric synthesis of morphine and (nor)hasubanan alkaloids are introduced.

Yeast cells carrying metal nanoparticles

Yeast cells can be used as carriers for hosting metal nanoparticles via in situ metal ion reduction methods. We synthesized Ag and Pd nanoparticles (NPs) located in different positions of yeast cells, either in yeast cell envelope or inside yeast cells. Ag NPs were able to grow at the cell wall and inside the cells depending on the preparation methods. Glucans at the cell wall functioned as reductive reagents in Tollens's reaction and Ag NPs with average size of about 9 nm (measured with Scherrer equation) were formed covering yeast cells. By UV illumination on yeast cells with AgNO3 solution imported in cytoplasm in advance, Ag nanoparticles with size of about 4 nm were produced inside yeast cells. UV illumination in the presence of Ag ions could carbonize the yeast cells as indicated by Raman spectroscopic analysis, which may be conducive to establishing new sterilization mechanism. Yeast cells carrying palladium nanoparticles were also synthesized by hydrazine hydrate reduction inside cells. It was found that Pd nanoparticles with size of about 11 nm were almost evenly distributed in every parts of yeast cells, in the envelope and inside cells. Ag NPs and Pd NPs on yeast cells were observed with optical microscopy, scanning electronic microscopy (SEM), and transmission electron microscopy (TEM). Crystal structures of Ag NPs and Pd NPs were confirmed by X-ray powder diffraction (XRD). The sizes of the NPs were calculated based on XRD results and Scherrer equation. The size distribution of NPs was obtained by counting the sizes of NPs on TEM images. Those results showed that easily affordable yeast cells are good bio-carriers for synthesis and stabilization of metal nanoparticles in aqueous environments, and no other chemical stabilizers were needed. The yeast carrying metal nanoparticles structures may find applications in medical or environmental treatment fields.

In vitro studies of nanosilver-doped titanium implants for oral and maxillofacial surgery.

The addition of an antibacterial agent to dental implants may provide the opportunity to decrease the percentage of implant failures due to peri-implantitis. For this purpose, in this study, the potential efficacy of nanosilver-doped titanium biomaterials was determined. Titanium disks were incorporated with silver nanoparticles over different time periods by Tollens reaction, which is considered to be an eco-friendly, cheap, and easy-to-perform method. The surface roughness, wettability, and silver release profile of each disc were measured. In addition, the antibacterial activity was also evaluated by using disk diffusion tests for bacteria frequently isolated from the peri-implant biofilm: Streptococcus mutans, Streptococcus mitis, Streptococcus oralis, Streptococcus sanguis, Porphyromonas gingivalis, Staphylococcus aureus, and Escherichia coli. Cytotoxicity was evaluated in vitro in a natural human osteoblasts cell culture. The addition of nanosilver significantly increased the surface roughness and decreased the wettability in a dose-dependent manner. These surfaces were significantly toxic to all the tested bacteria following a 48-hour exposure, regardless of silver doping duration. A concentration of 0.05 ppm was sufficient to inhibit Gram-positive and Gram-negative species, with the latter being significantly more susceptible to silver ions. However, after the exposure of human osteoblasts to 0.1 ppm of silver ions, a significant decrease in cell viability was observed by using ToxiLight™ BioAssay Kit after 72 hours. Data from the present study indicated that the incorporation of nanosilver may influence the surface properties that are important in the implant healing process. The presence of nanosilver on the titanium provides an antibacterial activity related to the bacteria involved in peri-implantitis. Finally, the potential toxicological considerations of nanosilver should further be investigated, as both the antibacterial and cytotoxic properties may be observed at similar concentration ranges.

Mesquite Gum as a Novel Reducing and Stabilizing Agent for Modified Tollens Synthesis of Highly Concentrated Ag Nanoparticles.

The synthesis that is described in this study is for the preparation of silver nanoparticles of sizes ranging from 10 nm to 30 nm with a defined shape (globular), confirmed by UV-vis, SEM, STEM and DLS analysis. This simple and favorable one-step modified Tollens reaction does not require any special equipment or other stabilizing or reducing agent except for a solution of purified mesquite gum, and it produces aqueous colloidal dispersions of silver nanoparticles with a stability that exceeds three months, a relatively narrow size distribution, a low tendency to aggregate and a yield of at least 95% for all cases. Reaction times are between 15 min and 60 min to obtain silver nanoparticles in concentrations ranging from 0.1 g to 3 g of Ag per 100 g of reaction mixture. The proposed synthetic method presents a high potential for scale-up, since its production capacity is rather high and the methodology is simple.

In situ development of nanosilver-impregnated bacterial cellulose for sustainable released antimicrobial wound dressing.

Bacterial cellulose (BC) is an interesting biomaterial found application in various fields due to its novel characteristics like purity, water holding capacity, degree of polymerization and mechanical strength. BC as wound dressing material has limitation because it has no antimicrobial activity. To circumvent this problem, the present study was carried out by impregnation of silver on bacterial cellulose surface. Bacterial cellulose was produced by Gluconoacetobacter hansenii (strain NCIM 2529) by shaking culture method. The sodium borohydride and classical Tollens reaction was used for silver nanoparticle synthesis. The effectiveness of sodium borohydride method compared with Tollens reaction was evaluated on the basis of silver nanoparticle formation and its impregnation on BC as evidenced by UV-Vis spectrum analysis, FE-SEM-EDS analysis and FT-IR spectrum. The potential of nano silver impregnated BC was determined for sustained release antimicrobial wound dressing material by swelling ratio, mechanical properties and antimicrobial activity against Staphylococcus aureus. Thus the nanosilver impregnated bacterial cellulose as promising antimicrobial wound dressing material was evidenced.

On the manufacture of silver-BaCe0.5Zr0.3Y0.16Zn0.04O3−δ composites for hydrogen separation membranes

Silver- BaCe0.5Zr0.3Y0.16Zn0.04O3−δ (Ag/BCZYZ) composites were investigated due to their potential application as hydrogen separation membranes, with emphasis on their fabrication and characterization. A precursor powder of BCZYZ was prepared via a wet chemical route and characterized by XRD, SEM and dilatometry. The precursor powder was coated with silver using Tollens reaction and then sintered under a variety of conditions. It was possible to obtain dense samples with a low level of non-percolating silver (2 vol%). Silver was present even if sintered at 1300 °C as it remained trapped in the ceramic matrix. The overall conductivity of a dense sample with 2 vol% of silver increased when compared to pure BCZYZ, and in particular the grain boundary resistance decreased considerably. A measurement of the open circuit voltage in fuel cell mode indicates the presence of mixed electronic-protonic conductivity in the composite.

Green synthesis of silver nanoparticles in xylan solution via Tollens reaction and their detection for Hg(2+).

This work reported a facile and green method to prepare highly stable and uniformly distributed Ag nanoparticles (AgNPs), in which a biopolymer xylan was used as the stabilizing and reducing agent via the Tollens reaction under microwave irradiation. Different variables were evaluated to optimize the reaction conditions. Complete characterization was performed using UV-Vis, XRD, TEM, size distribution analysis and XPS. The results revealed that AgNPs were well dispersed with diameters of 20-35 nm due to the packing of xylan. The optimal conditions were as follows: microwave irradiation temperature was 60-70 °C, microwave power was 800 W, microwave time was 30 min, the ratio of xylan to AgNO3 was 50 mg: 0.13 mmol, and ammonia concentration was 2%. In addition, the AgNPs were collected via high-speed centrifugal separation, and the supernatant was tested by HPAEC, GPC, FT-IR, and NMR. By comparing the structure of xylan before and after the reaction, the reaction mechanism was discussed. It was noted that the xylan-AgNPs composites showed high selectivity and sensitivity for Hg(2+) detection. The other 15 metal ions used had no obvious effect on the detection of Hg(2+), and the limit of detection (LOD) was 4.6 nM, which is lower than the allowed maximum level of 30 nM for drinking water by WHO. In addition, the xylan-AgNPs composites can be applied for Hg(2+) detection in real water samples. This study provides a novel way for the high-value utilization of a rich biomass resource, and a green method for the synthesis of AgNPs for the selective and sensitive detection of harmful heavy metals.

Enhancement of enzymatic colorimetric response by silver island films on high throughput screening microplates

In this study, we report the use of an enzyme-based hybrid platform, which is comprised of silver island films, enzymes (HRP and AP) and high-throughput screening (HTS) microplates, to enhance the colorimetric response of enzymatic reactions. The hybrid platform was designed in a two-step process: (i) deposition of SIFs onto HTS microplates with low, medium, and high loading (refers to the extent of the surface plasmon resonance peak of SIFs at 460nm) using Tollen's reaction scheme; and (ii) attachment of b-BSA or BEA as linkers for the immobilization of enzymes. The presence of SIFs within the wells of the HTS microplates was confirmed using an optical spectrophotometer and real-color photography. Control experiments, where SIFs were omitted from the surfaces were carried out to confirm the effect of SIFs on the enzymatic colorimetric response. Significant colorimetric signal enhancement was observed for HRP or AP on SIFs (high loading) deposited HTS microplates using b-BSA (up to ~3-fold for AP and ~6-fold HRP) or BEA (up to ~7-fold for both HRP and AP), as compared to our control samples. The observed increase in colorimetric response can be attributed to the nature of BEA, which exposes surface-bound enzymes to the substrate present in bulk more efficiently than b-BSA. This study proves that SIFs can serve as a valuable tool to improve the signal output of existing bioassays carried out in HTS microplates, which can be applicable to the field biosensors and plasmonics.

Green fabrication of quaternized chitosan/rectorite/Ag NP nanocomposites with antimicrobial activity

Silver nanoparticles (Ag NPs) were synthesized rapidly in one pot via the Tollens reaction, in which quaternized chitosan (QCS) and rectorite (REC) acted as the reducing and stabilizing agent, while other chemical reducing and stabilizing agents and the surfactant were not included. X-ray diffraction, scanning electron microscopy and transmission electron microscopy results showed that spherical Ag NPs with uniform sizes were obtained, the layers of clay were peeled and thus exfoliated QCS/REC/Ag NP (QCRAg) nanocomposite was achieved. Moreover, Ag NPs dispersed well in the exfoliated nanocomposite matrix, some Ag NPs even entered into the interlayer of REC. QCRAg nanocomposites showed strong antimicrobial activity; the lowest minimum inhibitory concentration against Staphyloccocus aureus was only 0.0001% (w/v). The study reveals that the obtained QCRAg nanocomposites have great potential for biomedical applications.

Au@Ag core/shell nanoparticles as colorimetric probes for cyanide sensing.

We synthesize Au@Ag core/shell nanoparticles (NPs) using a Au NP assisted Tollens reaction. The as-synthesized NPs are used for the colorimetric cyanide sensing with a detection limit of 0.4 μM. The bimetallic NPs are immobilized into agarose gels as portable "test strips".

A colorimetric agarose gel for formaldehyde measurement based on nanotechnology involving Tollens reaction.

Gold nanoparticles (Au NPs) coupled with Tollens reagent were used for measuring formaldehyde. Au@Ag core-shell NPs were formed along with distinct color changes from pink to deep yellow. This colorimetric system was further immobilized into an agarose gel, which was used for monitoring of gaseous formaldehyde.

Facile and green synthesis of silver nanoparticles in quaternized carboxymethyl chitosan solution

A facile and green method to synthesize stable Ag nanoparticles (Ag NPs) with a narrow size distribution in water is reported. Water-soluble quaternized carboxymethyl chitosan (QCMC) with a surfactant-like structure was used as both a reducing and stabilizing agent under microwave irradiation via the modified Tollens reaction. In order to study the preparation mechanism, carboxymethyl chitosan (CMC) and quaternized chitosan (QCS) were compared as both reducing and stabilizing agents. Full characterization was performed using UV–vis, XRD, TEM, AAS, FT-IR, NMR and TGA. The results revealed that the prepared Ag NPs were mostly spherical with a small proportion being cylinders or cuboids; they were stable due to the package of the macromolecules; the diameters were 10.24 ± 3.13 nm. The Tollens reaction followed first order kinetics, and the Ea was 102.4 kJ mol−1 for QCMC/Ag NP composite. During the growth of the Ag NPs, some quaternary ammonium groups and carboxymethyl groups were respectively oxidized to −CH2COCH3 and −CH3 groups, and the quaternary ammonium groups were more helpful for the growth of Ag NPs than the carboxymethyl groups. In addition, QCMC/Ag NP composite had much higher thermal stability than QCMC.

Ethylent-15α-[(2-nitrobenzyloxy)methyl]-16-oxobeyeran-20-oate

In the title compound, C30H41NO6, the three six-membered rings adopt chair conformations and the stereochemistry of the A/B and B/C ring junctions are trans. The five-membered ring D adopts an envelope conformation, with the methyl­ene C atom as the flap. The title compound was synthesized via esterification, Tollens reaction, 1,5-hydride shift from the natural tetracyclic diterpenoid isosteviol