RSC Advances

Dao, Tran Cao; Luong, Truc Quynh Ngan

doi: 10.1039/d0ra08060hpmid: 35519192

Surface-Enhanced Raman Scattering (SERS) is a technique currently widely used in the identification and quantification of organic and biological molecules at low concentrations, in which an important application is the detection of pesticide residues in food. To accomplish this task, SERS substrates with high Raman enhancement factor and good reproducibility are required. One of the most commonly used SERS substrates is the SERS substrate made of silver nanoparticles immobilized on a solid substrate. In this report we first present the results of electrochemical deposition of silver nanoparticles on the silicon surface using ethanol electrolyte solution. Thanks to both factors, electrochemical deposition (instead of electroless) and ethanol electrolyte (instead of aqueous), under optimal conditions, on the surface of silicon a monolayer of silver nanoparticles grew, which are uniform in shape and size and are arranged very close to each other with nanometer separation. Next we report on the use of fabricated arrays of silver nanoparticles in the role of a SERS substrate. To test the performance of the SERS substrate, the probe molecules used were molecules of difenoconazole, a well-known fungicide. Results showed that difenoconazole could be detected with a detection limit of 0.023 ppm (5.6 × 10−8 M).

Liu, Caixia; Wang, Huijun; Bi, Yalian; Zhang, Ziyin

doi: 10.1039/d0ra06697dpmid: 35519207

A series of sulphated iron-based catalysts was prepared via an impregnation method by changing the loading content of Fe3+ and SO42− on ZrO2, and their performance in the selective catalytic reduction (SCR) of NOx by ammonia was investigated. The NOx conversion exhibited large differences among the sulphated iron-based catalysts. To explore the synergistic mechanism of iron and sulphates, XRD, BET, H2-TPR, XPS, TPD and in situ DRIFTS were used to characterize the catalysts, and it was found that among all the catalysts, the NOx conversion by Fe2SZr was greater than 90% at 350–450 °C. The results indicated that the interaction between Fe3+ and SO42− can have an effect on the redox ability, acid sites, and adsorption of NOx and NH3. With an increase in the content of Fe3+, the redox activity of the catalyst and the adsorption of ammonia improved at medium and low temperatures. However, at higher temperatures, an increase in Fe3+ led to a decrease in the conversion of NOx due to the enhanced oxidation of NH3. At medium and low temperatures, an increase in the content of SO42− decreased the concentration of Fe3+ on the surface of the catalyst and inhibited the adsorption of NOx and NH3. The addition of SO42− reduced the redox activity of the catalyst and inhibited the oxidation reaction of NH3, which follows the Eley–Rideal mechanism at high temperatures, further enhancing the SCR activity of the FexSyZr catalyst.

Melag, Leena; Sadiq, M. Munir; Konstas, Kristina; Zadehahmadi, Farnaz; Suzuki, Kiyonori; Hill, Matthew R.

doi: 10.1039/d0ra07068hpmid: 35519209

Oxygen is commonly separated from air using cryogenic liquefaction. The inherent energy penalties of phase change inspire the search for energy-efficient separation processes. Here, an alternative approach is presented, where we determine whether it is possible to utilise simpler, stable materials in the right process to achieve overall energy efficiency. Adsorption and release by Metal–Organic Frameworks (MOFs) are an attractive alternative due to their high adsorption and storage capacity at ambient conditions. Cu-BTC/MgFe2O4 composites were prepared, and magnetic induction swing adsorption (MISA) used to release adsorbed oxygen quickly and efficiently. The 3 wt% MgFe2O4 composites exhibited an oxygen uptake capacity of 0.34 mmol g−1 at 298 K and when exposed to a magnetic field of 31 mT, attained a temperature rise of 86 °C and released 100% of adsorbed oxygen. This water vapor stable pelletized system, can be filled and emptied within 10 minutes requiring around 5.6 MJ kg−1 of energy.

Bhai, Surjit; Ganguly, Bishwajit

doi: 10.1039/d0ra07526dpmid: 35519218

Metal-mediated base pairs have attracted attention in nucleic acid research and molecular devices. Herein, we report a systematic computational study on Hg2+-mediated base pairs with canonical and TT mispair dimers. The computed results revealed that the model DTTD (thymine–thymine with DNA backbone) mispair is more energetically favored than the canonical base pairs. The DTTTTD mispair dimer is more energetically stable by ∼36.0 kcal mol−1 than the corresponding canonical DATGCD base pairs. The Hg⋯Hg metallophilic interaction was observed with the DTTTTD mispair and not the canonical base pairs. The DATGCD (adenine: thymine, guanine: cytosine) base pairs were significantly perturbed upon interaction with the mercury ion; however, the TTTT mispairs were aligned upon interaction with the Hg2+ ion. The DTTTTD mispair adopts a B-type conformation with proper alignment of its nucleobases along the axis. The MESP calculations showed a larger Vmin value for the interacting nitrogen centers of the thymine nucleobase, supporting its stronger binding with the Hg2+ ion compared to the other nucleobases. The role of the backbone is crucial in nucleic acids to determine many useful properties, and PNAs have been exploited extensively in the literature. Thus, this study was further extended to metal-mediated PNA-containing dimer mispairs such as DTTTTP (thymine–thymine dimer model with hybrid DNA and PNA backbone) and PTTTTP (thymine–thymine dimer model with PNA backbone). The calculated results showed that the PTTTTP PNA mispair is thermodynamically more stable than the canonical dimers. The enthalpy calculated for DTTTTD and PTTTTP at the B3LYP-D3/6-31G* level of theory showed that PTTTTP is ∼3.0 kcal mol−1 more stable than DTTTTD. The metallophilic interaction of Hg2+ ions in the PTTTTP mispair was not observed; however, the metal ions interact with the nitrogen of the thymine bases, presumably enhancing the stability of this mispair by strong electrostatic interactions. These interactions arise due to the P-type conformations of PNAs, which lack metallophilic interactions between the metal ions and can adopt a wider and more unwounded helix. The interaction of the mispair dimers with the explicit water molecules also showed a similar stability trend to that observed with the implicit solvation model. The metallophilic interaction (Hg⋯Hg) was found to be conserved in DTTTTD. The AIM analysis performed for these dimers revealed that the interactions are primarily electrostatic in nature. The UV-vis absorption spectra of the mispair systems calculated at the B3LYP-D3/6-31G* level of theory using the TD-DFT method in the aqueous phase suggested that the absorption maximum is located at a longer wavelength in the case of PTTTTP compared to the corresponding DTTTTD and can be a signature to identify the formation of metal-mediated nucleic acid systems.

Zhao, Qian; Peng, Cheng; Zhan, Gu; Han, Bo

doi: 10.1039/d0ra08068cpmid: 35519191

Polysubstituted arenes serve as ubiquitous structural cores of aromatic compounds with significant applications in chemistry, biological science, and materials science. Among all the synthetic approaches toward these highly functionalized arenes, organocatalytic benzannulation represents one of the most efficient and versatile transformations in the assembly of structurally diverse arene architectures under mild conditions with exceptional chemo-, regio- or stereoselectivities. Thus, the development of new benzannulation reactions through organocatalysis has attracted much attention in the past ten years. This review systemically presents recent advances in the organocatalytic benzannulation strategies, categorized as follows: (1) Brønsted acid-catalysis, (2) secondary amine catalysis, (3) primary amine catalysis, (4) tertiary amine catalysis, (5) tertiary phosphine catalysis, and (6) N-heterocyclic carbene catalysis. Each part is further classified into several types according to the number of carbon atoms contributed by different synthons participating in the cyclization reaction. The reaction mechanisms involved in different benzannulation strategies were highlighted.

Zhang, Yan; Gao, Zelin; Li, Yue; Pun, Edwin Yue Bun; Lin, Hai

doi: 10.1039/d0ra08696gpmid: 35519182

Na(Y1−x−yHoxYby)F4/PAN (NYF-HY/PAN) composite fibers were synthesized using an electrospinning method, and the sub-micron crystals embedded in the fibers had complete hexagonal crystal structures. Under 977 nm laser excitation, strong green and red up-conversion (UC) emission that originated from flexible fibers were due to the radiative transitions (5F4, 5S2) → 5I8 and 5F5 → 5I8 of Ho3+, respectively. The effective green fluorescence emission (539 and 548 nm) can be applied to micro-domain non-contact temperature measurements, realizing rapid and dynamic temperature acquisition in a complex environment without destroying the temperature field. In the temperature range of 313–393 K, the absolute and relative sensitivity of the fibers are 0.00373 K−1 and 0.723% K−1, respectively, which indicates that the NYF-HY/PAN composite fibers have good thermal sensitivity. Composite fibers in which crystallites are embedded have superior properties, with great stability, high sensitivity, and excellent flexibility, providing a reliable reference for developing temperature-sensing materials for the biomedical field.

Wang, Jen-Hsuan; Chen, Hsin-Yu; Chuang, Ching-Cheng; Chen, Jung-Chih

doi: 10.1039/d0ra05385fpmid: 35519194

Clinical requirements have necessitated the development of biomedical nanomaterials that can be implanted into tissues or bodies. Physiological regulation can be achieved in these nanomaterials through external light. The combination of nanomaterials with infrared optics can be termed optogenetics. The low autofluorescence of upconversion nanoparticles (UCNPs) has several applications in the biological field. For optogenetics applications, UCNPs with high fluorescence performance and photostability can solve the penetration depth problem. NaYF4:Yb,Tm nanocrystals with controllable sizes, shapes, and compositions were synthesized using a rapid coprecipitation method in organic solvent. UCNPs using single crystal nanoparticles provide higher chemical stability than those using amorphous phase. However, because UCNPs are usually capped with hydrophobic ligands, it is particularly important to prepare biocompatible UCNPs with specific molecular recognition capabilities. Surface modification and subsequent functionalization are essential for the application of inorganic nanomaterials in the biological environment and are arousing increasing research interest. Due to the high biocompatibility and high loading of materials, mesoporous silica and amine groups were selected as the best candidates. Expression of plasmid DNA in vivo and transfection efficiency were determined by fluorescence microscopy and flow cytometry. The MTT assay was used to evaluate the particle biocompatibility; the results showed that UCNP@mSiO2 has great biocompatibility. Additionally, at neutral pH, the cell surface is negatively charged. Therefore, the surface is functionalized with amino groups and can be electrostatically bound to DNA. Finally, UCNP@mSiO2-NH2 as a vector was applied in live cells by loading DNA; according to the results, DNA-UCNPs were successfully transfected in the primary cells, and NaYF4:Yb,Tm@mSiO2-NH2-DNA were observed to have good transfection efficiency by flow cytometry. It is expected that this work will provide a different method from the traditional adenovirus method and improve the immune response and side effects caused by adenovirus.

Chen, Mingyang; Shen, Yong; Xu, Lihui; Xiang, Guanghong; Ni, Zhewei

doi: 10.1039/d0ra07074bpmid: 35519214

Superabsorbent polymers as soft materials that can absorb water have aroused great interest in the fields of agriculture and forestry. Water absorption and water retention performance of a hydrogel are important indicators to evaluate its practical application. However, few reports show that hydrogels have both excellent water absorption and water retention properties. To date, superabsorbent hydrogels with a swelling capacity of more than 3000 g g−1 have rarely been reported. In this work, a novel superabsorbent poly(acrylic acid) (PAA)-based nanocomposite hydrogel (NC gel) was prepared via free radical polymerization of acrylic acid by using vinyl hybrid silica nanospheres (VSNPs) as the cross-linking agent. The PAA NC hydrogel achieved a great swelling ratio of more than 5000 times in deionized water at 323 K, and the swollen hydrogel could hold 60% moisture when it was exposed to the air at 303 K for 42 h. Moreover, the hydrogel also obtained a good swelling ratio of 136 g g−1 in NaCl solution. The PAA NC hydrogel showed excellent repetitive swelling ability. The influences of variable factors (acrylic acid, initiator and sodium hydroxide) on the swelling ratio of the NC hydrogel were researched. It can be speculated that the PAA NC hydrogel has potential application in agriculture and forestry areas due to its excellent water absorption and water retention properties.

Kondo, Yoshifumi; Goto, Tomoyo; Sekino, Tohru

doi: 10.1039/d0ra06662apmid: 35519197

The development of new technologies for securing and recycling water resources are in high demand. A key focus of these technologies is the development of various ion exchangers or adsorbents that are used for the purification of aqueous solutions. Layered sodium titanate is one of the cation exchangers utilised in the removal of heavy metals and radionuclides from wastewater. To enhance the removal efficiency, the precise design of the crystal morphology, structure, and chemical composition is important. Herein, we synthesised a unique seaweed-like sodium titanate mat (SST) using a template-free alkaline hydrothermal process. The Co2+ sorption capacity of SST was investigated by batch testing with cobalt(ii) nitrate. SST, which was synthesised from titanium sulphate in a 10 M NaOH solution at 200 °C, had a seaweed-like structure composed of randomly distributed nanofibres of layered sodium titanate that is approximately 9 nm in diameter. The crystal shape changed from roundish crystals to fibrous crystals as the hydrothermal reaction period increased. The Co2+ sorption isotherm of SST was fitted with the Langmuir isotherm model and the maximum sorption density was 1.85 mmol g−1. The selectivity of the Co2+ sorption on SST was high in comparison to that of Ca2+ and Mg2+. Herein, the Co2+ sorption mechanisms of SST were studied in comparison with commercially available sodium titanate. Results show that controlling the crystal morphology, structure, and Na concentration of the layered titanate that can be ion-exchanged determines the cation sorption properties of sodium titanate.

Liu, Hong-Yan; Chen, Yu; Hao, Li-Qiang; Wang, Guo-Dong; Li, Hong-Shuang; Xia, Cheng-Cai

doi: 10.1039/d0ra08441gpmid: 35519175

Herein we report an oxidative coupling reaction for N–S/S–S bond formation from (E)-N′-benzylideneacetohydrazide and S8 to furnish substituted N,N′-disulfanediyl-bis(N′-((E)-benzylidene) acetohydrazide). It provides a direct approach for the synthesis of disulfides with good yields.