Initial Fluorescence Intensity Research Articles

Exploring γ and UV irradiation responses on thermoluminescence and optical thermometry studies on Y4Al2O9:Ho3+ nanophosphor

A series of green emitting Ho3+ (1–9 mol%) doped Y4Al2O9 nanophosphors (NPs) are synthesized via solution combustion technique. Photoluminescence (PL) studies shows emission peaks recorded at ∼ 522 nm (5F3→5I8), 545 (5F4, 5S2→5I8), 659 (5F5→5I8) and 730 (5F4→5I7) upon excited at 460 nm wavelength. With a tremendous potential for application in white light-emitting diodes (w-LEDs), the phosphors show a bright green emission under 460 nm excitation. They also have a notable activation energy (0.31 eV), high color purity (98.2 %), and a remarkable quantum yield (87.1 %). Most astonishingly, even at temperatures as high as 420 K, YAO:5Ho3+nanoparticles retain 88.9 % of their initial fluorescence intensity. Using the fluorescence intensity ratio (FIR) method, the temperature sensing potential is also investigated. Thermoluminescence (TL) glow curves of γ (1 kGy) and UV (1 h) irradiated YAO:Ho3+(1–9 mol%) NPs exhibit two glow curves and highest intensity is recorded for YAO:5Ho3+NPs. TL characteristics of 5 mol% Ho3+ doped YAO NPs are subjected to γ (1 Gy-5 kGy) and UV (0.25–6 h) irradiation. Two glow curves recorded at 475 K (major peak) and 567 K (shouldered peak) for γ irradiation. However, for UV irradiation two glow curves at 478 K (major peak) and 575 K (shouldered peak) are recorded utilizing a 5 °C per minute heating rate. TL intensity varies with γ and UV exposure is recorded for optimized NPs and major glow peaks showcase linear response for both γ and UV irradiations, indicating that the prepared phosphor can be used in TL personal dosimetry. Furthermore, compared to γ-irradiated phosphor, UV-irradiated phosphor shows greater fading. The overall results clearly demonstrate that the optimized phosphor has proven to be an outstanding candidate for multifunctional applications.

Fluorescence Quenching Effect of a Highly Active Nitroxyl Radical on 7-amino-4-methylcoumarin and Glutathione Sensing.

Nitroxyl radical compounds, such as 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO), are stable radical compounds with a variety of unique characteristics, including fluorescence quenching. In this study, we investigated the fluorescence quenching effect of nortropine N-oxyl (NNO), which is a highly active nitroxyl radical that is more active than TEMPO in oxidation catalysis. The fluorescence intensity of 7-amino-4-methylcoumarin (AMC) was quenched by NNO and TEMPO to 5% and 95% of the initial fluorescence intensity, respectively, indicating highly efficient quenching by NNO. In addition, we used this reaction to measure glutathione concentration. The quenching effect of NNO was abrogated by the chemical reaction with glutathione, resulting in restoration of AMC fluorescence. This response was observed at glutathione concentrations from 10 µM to 1 mM, and good calibration curves were obtained from 10 to 250 µM.

Nb-based AxNbOFy:Mn4+ (A=Na, Cs; x=2, 3; y=5, 6) red phosphors with excellent water resistance and enhanced luminescence by W6+/Mo6+ charge compensation

Mn4+ activated fluoride red phosphors are used in warm white light emitting diodes (WLEDs). However, their inherently low moisture resistance is a major barrier to their use in high humidity conditions. In this work, the Nb-based oxyfluoride phosphors AxNbOFy:Mn4+ (A = Na, Cs; x = 2, 3; y = 5, 6) were synthesized by the co-precipitation method. The crystal structure, morphology, and luminescence properties are investigated with composition variation. The non-equivalent replacement of Nd5+ ions by Mn4+ results in bright red emission under blue light excitation. These phosphors showed very good moisture resistant luminescence. The best performance was achieved by the Na3NbOF6:0.1%Mn4+, which retained 98 % of the initial fluorescence intensity after immersion in water for 60 min. In addition, the W6+ and Mo6+ are used to compensate for the charge difference between Mn4+ and Nd5+ in Na3NbOF6:Mn4+. The compensated phosphors have shown large enhancements of 169 % (W6+) and 168 % (Mo6+) in luminescence intensity. This strategy of non-equivalent doping approach of Mn4+ into the Nb-based oxyfluoride materials and the charge compensation by W6+/Mo6+ to enhance the luminescence intensity provides a new way to realize high performance red phosphors for WLEDs.

New Mn-CP as a multi-responsive fluorescent probe for ratiometric sensing toward ascorbic acid and turn-off sensing toward nitrofurazone and acetylacetone

The abuse of environmental and biological related molecules, such as small biomolecules, pharmaceutical antibiotics and volatile organic chemicals has become a hotspot issue of global concern. Thus, exploring accurate and effective techniques for monitoring these species remains a major challenge. Here, by employing semi-rigid tetracarboxylate ligand H4edda, one new 2D Mn-based coordination polymer with formula of [Mn2(edda)(phen)2(H2O)2]n (Mn-CP; H4edda = 5,5′-(ethane-1,2-diylbis(oxy)) diisophthalic acid); phen = 1,10-phenanthroline) has been hydrothermally fabricated. The prepared Mn-CP possesses a sql topology with Schläfli symbol of (44·62). Stability research for Mn-CP reveals that it maintains structural stability and initial fluorescence intensity after soaking in water for one week. Moreover, Mn-CP also displays high structural stability in acidic-basic aqueous solution of broad pH scope (1–13) for 48 h. Importantly, photoluminescence measurements indicate that it shows ratiometric fluorescence response to ascorbic acid (AA) as well as turn-off response toward nitrofurazone (NFZ) and acetylacetone (ACAC). The developed fluorescence probe based on Mn-CP shows merits of high selectivity and low detection limits (33.67 nM, 1.43 nM and 2.29 μM for AA, NFZ and ACAC, respectively). The possible mechanisms have been thoroughly explored through exhaustive experimental surveys and theories calculations. The CP-based multi-responsive fluorescent probe designed in this work extends the application of such materials in environmental and biological related fields.

Pb2+/Mn2+ co-doped Cs2ZnBr4 microcrystals with dual-band tunable white light emission

The photoelectric properties of lead halide perovskite have been extensively investigated. However, its application in the field is greatly limited due to its poor instability and high lead content. With the aim of addressing these problems, in this study, Cs2ZnBr4:Pb2+/Mn2+ microcrystals were initially synthesized using a simple precipitation method. By manipulating the lead concentration, the emission ranging from cyan to green could be adjusted in Cs2ZnBr4:Pb2+. Co-doped Cs2ZnBr4:Pb2+/Mn2+ microcrystals with the precise regulation of the doping concentration of Pb2+ and Mn2+ were obtained through precipitation. The dual-mode emission of cyan and orange-red is successfully obtained. It is important that single white light emission is achieved in Cs2ZnBr4:Pb2+/Mn2+ microcrystals, exhibiting tunability from cold white to warm white. Moreover, Cs2ZnBr4:Pb2+/Mn2+ microcrystals are demonstrated remarkable air stability: it retains 86.27 % of the initial fluorescence intensity after 45 days in ambient conditions; it exhibits excellent UV stability, with 88.3 % of the initial fluorescence intensity maintained even after nearly 30 h of ultraviolet irradiation. Therefore, this research is anticipated to have broad applications not only in the field of solid-state lighting as UV-excited white LEDs but also in serving as a valuable reference for the exploration of low-lead halide luminescent materials.

Fast photochromic and fluorescent switchable organohydrogels based on photoinduced electron transfer for display and storage

The current research on viologen-based photochromic hydrogels is limited due to the significant hindrance of water on the photochromic behavior of viologens. However, there is considerable potential for applying viologen-based hydrogels that exhibit a rapid response to ultraviolet light in various applications. In this study, organohydrogels (OGHs) with excellent photochromic properties and fluorescence switchability were prepared by introducing zinc oxide (ZnO) and viologens into the PVA hydrogel system that used glycerol as a multifunctional co-solvent. Under the irradiation of a UV lamp (6 W, 365 nm), the photogenerated electrons efficiently transferred from ZnO to viologen dications, resulting in visible color change within 1 s. Meanwhile, the electron transfer achieved the quenching of yellow fluorescence from ZnO, enabling the fluorescence switchability of the OGHs. In addition, the fading process of the photochromic OGHs could be adjusted according to different temperature environments. Compared to traditional photochromic hydrogels, the OGHs demonstrated good freeze resistance and dry resistance, thus maintaining better photochromic repeatability and stability of initial fluorescence intensity under long-term storage conditions. These qualities give the OGHs high potential for applications in displays, optical information storage and anti-counterfeiting.

Gallium Sulfide Quantum Dots with Zinc Sulfide and Alumina Shells Showing Efficient Deep Blue Emission.

Solution-processed quantum dot (QD) based blue emitters are of paramount importance in the field of optoelectronics. Despite large research efforts, examples of efficient deep blue/near UV-emitting QDs remain rare due to lack of luminescent wide band gap materials and high defect densities in the existing ones. Here, we introduce a novel type of QDs based on heavy metal free gallium sulfide (Ga2 S3 ) and their core/shell heterostructures Ga2 S3 /ZnS as well as Ga2 S3 /ZnS/Al2 O3 . The photoluminescence (PL) properties of core Ga2 S3 QDs exhibit various decay pathways due to intrinsic defects, resulting in a broad overall PL spectrum. We show that the overgrowth of the Ga2 S3 core QDs with a ZnS shell results in the suppression of the intrinsic defect-mediated states leading to efficient deep-blue emission at 400 nm. Passivation of the core/shell structure with amorphous alumina yields a further enhancement of the PL quantum yield approaching 50 % and leads to an excellent optical and colloidal stability. Finally, we develop a strategy for the aqueous phase transfer of the obtained QDs retaining 80 % of the initial fluorescence intensity.

Comparison of Fluorescence of Tooth Enamel, Resin Composite, Lithium Disilicate and Monolithic Zirconia Under Thermocyclic Ageing

The aim was to compare the fluorescence intensity of tooth enamel, resin composite, lithium disilicate, and monolithic zirconia before and after thermocyclic aging. Lithium disilicate (LD) and monolithic Zirconia ceramic samples were fabricated with the CAD-CAM method. Resin composite specimens, of shades A1, A2, and A3, were prepared with photo-polymerization and putty mold. Extracted second molar teeth were obtained and sectioned to produce enamel specimens. Fluorescence assessment prior to thermocycling was performed using flurolog-Qm system before and after thermocycling. Samples were exposed to thermocycling (TC) for 30,000 cycles in distilled water at 5 °C and 55 °C for 30 s each, with 5 s between the baths. The means and standard deviations were compared using, t-test, analysis of variance, and Tukey–Kramer multiple comparisons test. The initial fluorescence intensities before thermocyclic ageing were highest in LD ceramic specimens (42579±817.1). The lowest fluorescence was observed in monolithic Zr specimen 14750±584.7. The reduction in fluorescence intensity after thermocyclic ageing was highest in LD specimens, however, the lowest difference was noted in composite A3 specimens. LD ceramic showed significantly high fluorescence among all materials before and after ageing. The fluorescence of the tested materials reduced with ageing and is expected to decrease intraorally with time.

Orange LED and cell fluorescence imaging of Mn2+ doped CsPbCl3 water-soluble nanocrystals with improved stability and optimized luminescence

Water-soluble Mn2+ doped CsPbCl3 nanocrystals coating by 6-aminocaproic acid (ACA) ligand were prepared by a simple ligand assisted reprecipitation method at room temperature. The CsPbCl3:Mn2+/ACA nanocrystals were almost cubic phase and had mean size of about 10 nm. Due to the coating and passivation of ACA, the CsPbCl3:Mn2+/ACA nanocrystals retained the initial fluorescence intensity of 20% after being dispersed in deionized water for 20 days. The orange LED device based on CsPbCl3:Mn2+/ACA nanocrystals were prepared with excellent luminescence properties. In the cytotoxicity test, even if the MCF-7 cells were cultured for 24 h at the concentration of CsPbCl3:Mn2+/ACA nanocrystals as high as 160 μg·ml−1, the cell survival rate was still 70%. Confocal fluorescent cell imaging results showed that the nanocrystals had remarkable fluorescent cell imaging effect even after 24 h. The synthesized CsPbCl3:Mn2+/ACA nanocrystals have nice water solubility, good water stability, low cytotoxicity and highly luminescence properties, and have great application potential in the field of orange LED and fluorescent probes.

Granulocyte concentrate splitting does not affect phenotype and function

More granulocyte concentrates (GCs) could be produced for more patients from the same donor if apheresis bags were split and stored for longer periods of time. Hence, we tested the hypothesis that splitting and extension of storage of GCs do not impair granulocyte function or viability. Granulocyte apheresis concentrates were produced using modified fluid gelatin as a separation enhancer, split into two portions, and stored for 24 and 48 h. Granulocyte function, represented by cell migration, reactive oxygen species (ROS) production, and neutrophil extracellular trap formation (NETosis), was measured by live-cell imaging. ROS production, adhesive surface protein expression, and viability were measured by flow cytometry. Splitting had no effect on any of the tested parameters. After 24 h of storage, live-cell imaging showed no significant difference in migration, time to maximum ROS production, time to half-maximum NETosis, viability, or CD11b expression, but ROS production induced by phorbol 12-myristate 13-acetate (PMA) decreased from an initial median fluorescence intensity of 1775-590 artificial units. After 48 h, PMA-induced ROS production, viability, and migration declined, as reflected by decreases in median total distance (119 vs. 63.5 μm) and median Euclidean distance (30.75 vs. 14.3 μm). Splitting GC products has no effect on granulocyte viability or function, but extended storage >24 h does compromise granulocyte function. The findings confirm that GCs should be transfused within 24 h of collection. Longer storage cannot be recommended.

Aqueous synthesis of stable Zn alloyed manganese halides for efficient backlit display

Metal halide perovskite has been widely researched in the field of wide color gamut backlight due to its excellent luminescence properties. However, the toxicity of lead and thermal stability issue greatly hindered its practical application. In this regard, environmentally friendly manganese halide perovskites has intrigued great attention. Herein, facile yet robust preparation of highly emissive all-inorganic manganese halides is presented via a one-step pure aqueous solution-based method without using corrosive acid solution. The introduction of Zn2+ cation-alloying enables the weakly luminescent Cs3MnCl5 to exhibit exceptionally efficient green emission at 521 nm. The alloyed Cs3MnxZn(1-x)Cl5 exhibits superior optical properties as well as improved thermal stability. In particular, alloyed Cs3MnxZn(1-x)Cl5 still retained 74% of the initial fluorescence intensity when the heating temperature was raised up to 225 °C. Furthermore, within the protective encapsulation of polydimethylsiloxane (PDMS) matrix, the prepared Cs3MnxZn(1-x)Cl5@PDMS films demonstrates excellent air, water and blue-light stability, which can be readily applied as light conversion films in backlit display. The as-prepared Cs3MnxZn(1-x)Cl5@K2SiF6: Mn4+@PDMS films displayed excellent quality and the color gamut was over 113% of the NTSC 1953 standard. This work provides a simple and effective pure aqueous-based strategy for the development of environment-friendly perovskite materials for the application of wide color gamut backlit display.

Photosynthesis and chlorophyll fluorescence of Iranian licorice (Glycyrrhiza glabra l.) accessions under salinity stress.

While salinity is increasingly becoming a prominent concern in arable farms around the globe, various treatments can be used for the mitigation of salt stress. Here, the effective presence of Azotobacter sp. inoculation (A1) and absence of inoculation (A0) was evaluated on Iranian licorice plants under NaCl stress (0 and 200 mM) (S0 and S1, respectively). In this regard, 16 Iranian licorice (Glycyrrhiza glabra L.) accessions were evaluated for the effects on photosynthesis and chlorophyll fluorescence. Leaf samples were measured for photosynthetic pigments (via a spectrophotometer), stomatal and trichome-related features (via SEM), along with several other morphological and biochemical features. The results revealed an increase in the amount of carotenoids that was caused by bacterial inoculation, which was 28.3% higher than the non-inoculated treatment. Maximum initial fluorescence intensity (F0) (86.7) was observed in the ‘Bardsir’ accession. Meanwhile, the highest variable fluorescence (Fv), maximal fluorescence intensity (Fm), and maximum quantum yield (Fv/Fm) (0.3, 0.4, and 0.8, respectively) were observed in the ‘Eghlid’ accession. Regarding anatomical observations of the leaf structure, salinity reduced stomatal density but increased trichome density. Under the effect of bacterial inoculation, salinity stress was mitigated. With the effect of bacterial inoculation under salinity stress, stomatal length and width increased, compared to the condition of no bacterial inoculation. Minimum malondialdehyde content was observed in ‘Mahabad’ accession (17.8 μmol/g FW). Principle component analysis (PCA) showed that ‘Kashmar’, ‘Sepidan’, ‘Bajgah’, ‘Kermanshah’, and ‘Taft’ accessions were categorized in the same group while being characterized by better performance in the aerial parts of plants. Taken together, the present results generally indicated that selecting the best genotypes, along with exogenous applications of Azotobacter, can improve the outcomes of licorice cultivation for industrial purposes under harsh environments.

Peroxyl radical scavenging activity measurement of antioxidants using histidine-stabilized and glutathione-capped fluorescent gold nanoclusters

A fluorescent gold nanocluster was used for determining peroxyl radical scavenging activity of antioxidants. Histidine was used as a green reducing and protective agent, and glutathione (GSH) enhanced the fluorescence intensity of histidine-stabilized gold nanoclusters (AuNCs) by ligand exchange process. When AAPH-induced oxidation of GSH occurred, the initial fluorescence intensity of GSH-capped AuNCs (λex = 450 nm λem = 502 nm) was decreased with static quenching. The decline of fluorescence intensity of the GSH-capped AuNCs upon peroxyl radical attack is diminished with the addition of antioxidants to the reaction medium, the difference in fluorescence intensity being related to peroxyl radical scavenging activity of antioxidants. The 50 % inhibitive concentration of related antioxidant compounds were determined and compared to those of crocin bleaching assay. Inhibition % of sage (Salvia officinalis L.) and green tea (Camellia sinensis) infusions against peroxyl radicals were investigated. The proposed assay can be used for simple and selective estimation of the peroxyl radical scavenging activity in complex matrices, as histidine-stabilized GSH-capped AuNCs were selective toward peroxyl radicals, not affected by other ROS at the studied concentrations.

Blue‐green emission of pepsin‐stabilized copper nanoclusters ultrafast detection of hemoglobin in human urine

AbstractThis work proposed a straightforward synthesis of copper nanoclusters (CuNCs) with an emission wavelength of 496 nm and a quantum yield of 2.2% by directly using pepsin as a template with low toxicity NaBH4 and ascorbic acid as reducing agents. The chemical composition and optical properties of the pepsin‐stabilized CuNCs (pepsin‐CuNCs) were well‐characterized by spectroscopy‐related techniques. The pepsin‐CuNCs retained the fluorescence intensity at neutral pH, at 37°C, and in high salinity, proving their suitability in biological systems. Although the pepsin‐CuNCs remained only half of the initial fluorescence intensity after 24 days due to air oxidation, their storage stability was comparable to that of CuNCs reported in the literature. Given that the absorption peaks of hemoglobin overlap the excitation and emission wavelengths of pepsin‐CuNCs, this feature allowed pepsin‐CuNCs to serve as a luminescence turn‐off sensor for sensing hemoglobin through the inner‐filter effect process. The pepsin‐CuNC probe provided a fast (within 1 min) platform for hemoglobin detection with a dynamic quantitative range of 0.1–10 μM and a detection limit of 70 nM. Importantly, the proposed probe was well‐suited to detect hemoglobin in nearly undiluted human urine, demonstrating its great potential for the clinical diagnosis of trace hemoglobin in urine.

Quantitative and Qualitative Assessment of Fluorescence in Aesthetic Direct Restorations.

Currently available direct restoration materials have been developed to have improved optical properties to interact with light in the same manner as the natural tooth. The objective of this study was to investigate the fluorescence of different enamel resin composites. In the present study, nine brands of enamel composites were tested in vitro, some of which are cited by manufacturers as having color adjustment potential. Fluorescence spectra of the composite specimens and the human natural enamel were measured with a fluorescence spectrophotometer immediately after preparation and after 6 months. Qualitative data of the specimens were also collected. Statistical analyses were conducted by Kruskal–Wallis and Mann–Whitney U nonparametric tests (p < 0.05). Almost all tested resin composites presented a significant decrease in the fluorescence values after a period of 6 months. There was no significant decrease in fluorescence in the case of Harmonize™ resin composite samples, which presented the lowest initial fluorescence values. The highest value in the reduction of the initial fluorescence intensity after 6 months (22.95%) was observed for the Charisma® specimens. Composites with a color adjustment did not perform significantly better than other composites in terms of reduction in fluorescence intensity.

Rational design of MoS2 QDs and Eu3+ as a ratiometric fluorescent probe for point-of-care visual quantitative detection of tetracycline via smartphone-based portable platform

The abuse of the antibiotic tetracycline (TC) has resulted in its residues in the environment and animals, which has caused irreversible damage to public health safety and environments. Therefore, it is urgently needed to develop alternative sensitive and low-cost for quickly and accurately detection the TC residues in the environments. We innovatively rational design of MoS2 QDs and Eu3+ to construct ratiometric fluorescent probe to detect TC. In general, TC coordinates Eu3+ to form Eu-TC coordination compound with weak luminescence. However, MoS2 QDs with exceptional fluorescence characteristics are a good energy donors and acceptors, MoS2 QDs can transfer energy with Eu-TC coordination compound, which can greatly enhance the luminous ability of Eu-TC coordination compound while accompanied by a decline of its initial fluorescence intensity. MoS2 QDs can be used as an indicator and enhancer in the MoS2-Eu3+ ratiometric probe, which can greatly improve limit of detection and accuracy of quantitation for TC. The detection of TC by fluorescent intensity ratio (F620/F470) of MoS2 QDs-Eu3+ shows a good linear response in the range of 10 nM–60 μM TC, with the limit of detection (LOD) toward TC is calculated to be 2 nM (3σ/slope), the recovery is 94.4–108.4%, and the RSD is less than 5.36. The smartphone-based portable platform with the RGB color recognition software is designed for point-of-care visual quantitative detection of TC. The portable detection system shows a low detection limit (0.05 μM) and excellent reproducibility in the range of 1–40 μM TC. This work has provided a sensitive, rapid, real-time detection of environmental pollutants.

Photoswitch-Based Fluorescence Encoding of Microspheres in a Limited Spectral Window for Multiplexed Detection.

Fluorescence barcoding with multicolor fluorophores is limited by spectral crowding. Herein, we propose a fluorescence encoding method in a single-color channel with photoswitches. The photochromic naphthopyran was used to mediate the fluorescence of polystyrene microspheres through resonance energy transfer. The initial fluorescence intensity (F0) and the fluorescence after UV light activation (F/F0) were combined to generate hundreds of 2-dimensional barcodes. The coding capacity was further expanded with the different chemical kinetics of the photoswitches. The photoswitch-based fluorescence barcodes were applied to simultaneously and selectively detect the DNA sequences of COVID-19 (with related mutations) as a proof-of-concept for real applications. The compatibility with the state-of-the-art fluorescence microscopes and simple encoding and decoding make the method very attractive for multiplexed and high-throughput analyses.

One-pot synthesis of stable and functional hydrophilic CsPbBr3 perovskite quantum dots for "turn-on" fluorescence detection of Mycobacterium tuberculosis.

All-inorganic CsPbBr3 perovskite quantum dots (QDs) are widely studied owing to their excellent optoelectronic properties; however, they are usually hydrophobic and unstable in water and thus their biomedical applications are seriously limited. In this study, stable and hydrophilic CsPbBr3 QDs functionalized with carboxyl groups (CsPbBr3-COOH QDs) were prepared in one-pot with the aid of new ligands amino-poly(ethylene glycol)-carboxyl and perfluorooctyltriethoxylsilane. The aqueous solution of CsPbBr3-COOH QDs maintained the initial fluorescence intensity after 8 days of storage; the free carboxyl groups on the surface of CsPbBr3-COOH QDs were covalently conjugated with amino-terminal DNA to construct CsPbBr3 QDs-DNA probes for subsequent application. Then, a biosensing platform utilizing fluorescence resonance energy transfer between hydrophilic CsPbBr3 QDs-DNA and MoS2 nanosheets was developed for the sensitive and selective detection of the Mycobacterium tuberculosis DNA with a low limit of detection of 51.9 pM and the identification of drug-resistant clinical strains. This study advances the preparation of hydrophilic carboxyl-functionalized CsPbBr3 QDs with enhanced stability and extends their application in biomolecule detection.

Syntheses, structures, surface analysis, DFT and fluorescence properties of three new Cd(II)-MOFs assembled with semi-rigid polycarboxylate

Three Cd(II)-based metal-organic frameworks (MOFs), namely, [Cd(HL1)(4,4′-bipb)]n(1), [Cd2(L2)(4,4′-bipb)2(H2O)3]n (2), {[Cd2(L3)(4,4′-bipb)(H2O)2]·(4,4′-bipb)0.5}n (3), where H3L1, H4L2, H4L3, and 4,4′-bipb are semi-rigid 2-(4-carboxyphenoxy) terephthalic acid, 3-(2,4-dicarboxyphenoxy)phthalic acid, 3,3′-(1,3- phenylenebis(oxy))diphthalic acid, and 1,4-bis(pyridin-4-yl)benzene, respectively, are synthesized in the presence of 4,4′-bipb and Cd(II) ions by hydrothermal method. 1 displays a 2,6-connected 3D topological structure. 2 features a 3D framework with 4,5,5-connected topology. 3 shows a 4,4,4-connected 3D topology. The fluorescence properties of 1–3 were determined in a dilute aqueous suspension at room temperature. The initial fluorescence intensity of 1 and 2 was almost completely quenched after the addition of Fe(NO3)3 solution. It is confirmed that after the addition of AgNO3 solution, the fluorescence intensity of 3 was quenched significantly, but the fluorescence intensity is increased after the Al(NO3)3 and Fe(NO3)3 solutions are added.

Antibacterial activities and mechanisms of vine tea extract and 2R, 3R-Dihydromyricetin on Escherichia coli

In this study, the antibacterial mechanisms of vine tea aqueous extract (VTE) and 2R, 3R-Dihydromyricetin (DMY) against Escherichia coli (E. coli) were investigated. The results showed they had good antibacterial activities on E. coli, and affected cell membrane and nucleoid. The minimum bactericidal concentrations of VTE and DMY were 3.2 and 1.25 mg/mL, respectively. The constituent leakage tests showed VTE and DMY caused significant increases of extracellular alkaline phosphatase (24.4 ± 0.4% and 5.3 ± 0.1%) and β-Galactosidase (27.6 ± 1.0% and 13.6 ± 0.5%), indicating the membrane integrity might be damaged. The lipids studies showed the ratio of unsaturated fatty acids to saturated fatty acids in treated groups were significant decrease (P < 0.05), indicating the membrane liquidity might be affected. Moreover, fluorescence experiments showed they could cause reduction of more than 82% of the DAPI-DNA and EB-DNA initial fluorescence intensity, indicating VTE and DMY could interacted with DNA through intercalate and grooving bindings. Furthermore, they showed good antibacterial activities in cabbage food model system. All over, the results suggested VTE and DMY might be applied as candidates of food preservatives for their good antibacterial activities and multiple targets.