Ultraviolet Absorption Spectrophotometry Research Articles

Poly(Lactide-co-Glycolide) Nanoparticle-Mediated Vaccine Delivery of Encapsulated Surface Antigen Protein of Hepatitis B Virus Elicits Effective Immune Response.

Hepatitis B viral infection is one of the most important infectious diseases of the liver worldwide. Chronic infection with HBV often leads to cirrhosis and hepatocellular carcinoma. The currently licensed hepatitis B vaccine consists of recombinant hepatitis B surface antigen adsorbed into aluminum adjuvant and administered in three doses over the course of 6 months. However, this vaccine requires invasive administration and requires multiple booster doses. To avoid these limitations, nanoparticle (NP)-based vaccines lent itself as efficient adjuvants and delivery systems for the development of new generation vaccines. The biodegradable synthetic polymeric NPs poly(lactide-co-glycolide) (PLGA) was used in this study to formulate PLGA NPs encapsulated with hepatitis B surface protein to evaluate immune response in human peripheral blood lymphocytes in vitro. Formulation of HBP (HBV surface protein)-encapsulated PLGA (HB-nanovaccine [HB-NV]) was conducted by using double emulsion solvent evaporation technique (water-oil-water), which resulted in 94% encapsulation efficiency and 24% protein loading capacity. The resulted HB-NV had typical characteristics of spherical shape at an average size of 71.08 nm with higher densities and high stability dispersion of negatively charged NPs as assessed by atomic force microscopy, scanning electron microscopy, ultraviolet absorption spectrophotometry, zeta potential, and Fourier-transform infrared. The immune response to HB-NV was measured in vitro in lymphocytes, showed significant increase in levels of IL-2 and IFN-γ, as well as in CD4+ and CD8+ T cell counts, with a dose-dependent effect, examined by enzyme-linked immunosorbent assay and flow cytometry, respectively.

Masking of a malodorous substance on 1,2-dioleoyl-sn-glycero-3-phosphocholine molecular layer

The performance of a trans-2-nonenal (NE)-including 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) molecular layer as a model of epithelial cellular membrane damaged by malodorous substance was investigated to understand the masking effect of odorants (benzaldehyde (BA), cyclohexanecarboxyaldehyde (CA), 4-anisaldehyde (AA), and 4-methoxycyclohexanecarbaldehyde (MA)). The surface pressure of the DOPC monolayer increased upon the addition of NE, and the surface pressure–area isotherm of the DOPC-NE mixture was characteristically responsive to the odorants (BA, CA, AA, and MA). Differential scanning calorimetry, Fourier-transform infrared spectroscopy, and ultraviolet absorption spectrophotometry were conducted to evaluate the interactions among DOPC, NE, and the odorants. The results suggested that odorants with an aromatic ring form a complex with NE and were eliminated from the DOPC membrane. We found that odorants with an aromatic ring play an important role in inducing the masking effect on the DOPC-NE mixed monolayer because of the characteristic interactions between NE and odorant.

Development of an analytical method for determination of polyphenols and total tannins from leaves of Syzygium cumini L. Skeels.

Syzygium cumini L. Skeels belongs to Myrtaceae family. This species has been recognized by its antidiabetic, anti-inflammatory, and antimicrobial activities. Despite ever-increasing scientific interest for this species there is no pharmacopeia method for characterization and standardization of S. cumini yet. So, toward this aim, the objective of this work was to develop an efficient analytical methodology able to determine polyphenols and tannins content from leaves hydroethanolic extract of S. cumini using Folin-Ciocalteu method by ultraviolet absorption spectrophotometry (UV-Vis). The analytical methodology was developed for the first time in the literature for leaves of this specie shown to be fast and low-cost with results expressed through tannic acid equivalent (TAE). Moreover, the methodology presented selectivity with maximum absorption at 706 nm wavelength, linearity with R2>0.99; limit of detection 0.275 µg TAE mL-1 and 0.102 µg TAE mL-1; limit of quantification 1.046 µg TAE mL-1 and 0.912 µg TAE mL-1 for total polyphenols and total tannins, respectively. Furthermore, the methodology was accurate with recover value greater than 98%, as well as exact, reproductive, and robust with coefficient of variation values less than 15% for both compounds. All the results are found within the fixed limits according to RDC 166/2017.

A new approach for the determination of sunscreen levels in seawater by ultraviolet absorption spectrophotometry.

Sunscreen is released into the marine environment and is considered toxic for marine life. The current analytical methods for the quantification of sunscreen are mostly specific to individual chemical ingredients and based on complex analytical and instrumental techniques. A simple, selective, rapid, reproducible and low-cost spectrophotometric procedure for the quantification of commercial sunscreen in seawater is described here. The method is based on the inherent properties of these cosmetics to absorb in the wavelength of 300–400 nm. The absorption at 303 nm wavelength correlates with the concentration of most commercial sunscreens. This method allows the determination of sunscreens in the range of 2.5–1500 mg L-1, it requires no sample pretreatment and offers a precision of up to 0.2%. The spectrophotometric method was applied to quantify sunscreen concentrations at an Atlantic Beach with values ranging from 10 to 96.7 mg L-1 in the unfiltered fraction and from the undetectable value to 75.7 mg L-1 in the dissolved fraction. This method is suggested as a tool for sunscreen quantifications in environmental investigations and monitoring programs.

UV Spectrophotometry Applied to the Quantification of Omega-3, -6 and -9 in Fresh Tissues of Wild and Farmed Tambaqui

The demand for healthy foods has also increased the demand for wild and farmed tambaqui since it is a fish rich in omega-3, -6 and -9. To determine which of the two types of fish has the best nutritional quality and thus test the hypothesis that there are no nutritional differences between the groups of fish evaluated, the method of ultraviolet absorption spectrophotometry was used. For this, tambaqui from different environments (wild and farmed) were obtained in the states of Amazonas and Rondonia, Brazil. The fish groups showed differences in the concentrations of omega-3, -6 and -9 (ANOVA, F (8.30) = 16.213, and p < 0.01), both between states and between environments. The wild fish of the Amazonas state presented the best quality meat, and exhibited the highest concentrations of omega-3 (0.223 g ± 0.05 g) and omega-9 (0.208 g ± 0.04 g), which also implies the presence of omega-6, while the other group of fish exhibited the lowest values of omega in their composition.

Low-cost potentiometric sensor based on a molecularly imprinted polymer for the rapid determination of matrine in herbal medicines

A low-cost potentiometric sensor based on a molecularly imprinted polymer was developed for the determination of matrine in herbal medicine samples. The imprinted material was synthesized by the use of matrine as template, methacrylic acid (MAA) as the monomer, ethylene glycol dimethyl acrylate (EGDMA) as the cross linker, 2,2′-azo-bisisobutyronitrile (AIBN) as the initiator, and toluene and dodecanol as the porogenic agent. The electrode sensing membrane was fabricated by incorporating the ground imprinted particles into the polyvinyl chloride substrate that was subsequently incorporated into a laboratory constructed ion-selective electrode. The prepared imprinted sensor exhibited a rapid Nernst response across the concentration range from 1 × 10−5 to 1 × 10−1 M with a detection limit equal to 9.3 × 10−6 M. The analytical capabilities support the direct determination of matrine in herbal medicine. The analytical results were verified by a standard ultraviolet absorption spectrophotometry protocol. The proposed sensor manifested a series of advantages, including high selectivity and sensitivity, enhanced stability and low cost, that provides a wide number of potential applications for herbal analysis.

Inhibition of human glioblastoma cell invasion involves PION@E6 mediated autophagy process.

BackgroundGlioblastoma (GBM) is the most severe brain cancer due to its ability to invade surrounding brain tissue. Iron oxide nanoparticles (ION) could effectively induce a decrease of cell migration/invasion. Also IONs could generate ROS stress which induces autophagy elevation. Autophagy is associated with both anti-tumorigenesis and protumorigenesis.ObjectiveTo explore the effect of PEGylated IONs (PION@E6) on the GBM cell invasion and its mechanism based on autophagy.Materials and methodsPION@E6 were prepared and characterized according to our previous study. After incubation of U251 cells with PION@E6, cellular uptake of PION@E6 and cell viability were tested by Prussian blue staining and Cell Counting Kit-8, respectively. The migration and invasive capability was assessed by transwell cell migration and invasion assay. Expressions of autophagy biomarkers were detected by Western blotting. Intracellular ROS level was determined using 2′–7′-dichlorodihydrofluorescein diacetate.ResultsAverage hydrate particle size and zeta potential of PION@E6 were 37.86±12.90 nm and –23.8 mV, respectively, and uniformly distributed nanoparticles with an average diameter of 10 nm were observed by TEM. Chlorin e6 successfully incorporated onto PION@E6 was demonstrated by ultraviolet and visible absorption spectrophotometry, and PION@E6 owning excellent water solubility and stability were showed by Colloid stability test. PION@E6 were successfully taken up by U251 cells with Prussian blue staining, and they showed in vitro cytotoxicity to glioma cells after long incubation of 72 hours. Migration/invasion of cells was significantly inhibited by PION@E6, which could be counteracted by pretreatment with 3-MA. Additionally, the expression of beclin-1, IC3I, and IC3II proteins was higher, whereas that of p62 protein was lower. Moreover, a dose dependent intracellular ROS generation of PION@E6 was detected.ConclusionInvasiveness of human GBM cells involves the PION@E6-mediated autophagy process, which may be related to the intracellular ROS induced by PION@E6.

Metal-dependent photocatalytic activity and magnetic behaviour of a series of 3D Co-Ni metal organic frameworks.

Crystalline MOF materials with adjustable properties are of great interest for multiple potential applications. In this study, a series of 3D isostructural mixed metal MOFs {[M3(L)2(4,4'-bpy)2(H2O)2]·14H2O}n (M = Co (1), Co0.7Ni0.3 (2), Ni0.5Co0.5 (3), Co0.3Ni0.7 (4), Co0.1Ni0.9 (5), and Ni (6); H3L = 1-aminobenzene-3,4,5-tricarboxylic acid) have been synthesized. The crystal color changed regularly with the increase in the Ni ion content from red to green, and a new ultraviolet absorption spectrophotometry method has been developed for the accurate determination of the metal content of Co in MOF materials. In the detection of magnetic behaviour, 1 shows antiferromagnetism. As the Ni ion component gradually increases in 2-6, the magnetic behaviour of the complexes appears to transition from antiferromagnetic to ferromagnetic. Moreover, complex 1 exhibits preeminent photocatalysis activity in the degradation of organic dyes under visible light irradiation. As the ratio of Ni ions increases gradually in the complexes, the photocatalytic activities of 1-6 decrease. This work offers controllable regulation of the photocatalytic properties and magnetic behaviour of MOFs by changing the metal ions.

Morphology control and optical properties of Bi 2 O 3 crystals prepared by low‐temperature liquid phase method

γ-Bi2O3 powders were prepared from [Bi(NO3)3·5H2O] and NaOH through low-temperature liquid phase method at <90°C. This process featured low cost, simplicity and a normal pressure. Bismuth oxides were synthesised in large quantities in water systems. Morphology, structure and optical properties were characterised by X-ray diffraction, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and ultraviolet visible absorption spectrophotometry (UV–Vis). The SEM indicated that tetrahedral Bi2O3 with the edge length of 1–5 μm was formed. The FTIR spectra show a chemical bond of Bi–O existed. Bi2O3 presents the photo absorption properties from UV light region to visible light and the band gap of the Bi2O3 is 3.0 eV.

Comparative analysis of dietary pattern, anthropometry and serum ascorbate status of persons living with or without non-Hodgkin's lymphoma.

Recent upsurge of cancer cases across the globe is of concern to all and many studies shows the relationship between nutrient and the immune system and consequently cancer. This work aims to compare the dietary pattern, anthropometry and serum ascorbate status of the persons living with and those living without non-Hodgkin’s lymphoma (NHL). A case-control study was conducted using blood samples of eight patients diagnosed for NHL at the University College Hospital (UCH) Ibadan, while eight (8) volunteers were the control group. Socio-economic characteristics, medical history, food preferences, anthropometric indices were retrieved from questionnaires. Ascorbic Serum assay done with ultraviolet absorption spectrophotometry method using Klett-summerson photoelectric. Students’ t-test and Chi-square were used to test the educational levels fruit consumption. 25% of the respondents suffering from NHL skipped lunch and dinner, but none skipped breakfast. 66.67% of the cases and 100% of the control have their weight normally distributed. Cases had 11.11% slightly underweight and 11.11% obese. 25% of the population of the respondents had normal range of 0.4 mg/100 of serum ascorbate, while six had low serum ascorbate levels.

DEVELOPMENT AND VALIDATION OF UV SPECTROPHOTOMETRIC METHOD FOR QUANTITATIVE ESTIMATION OF LAFUTIDINE IN BULK AND PHARMACEUTICAL DOSAGE FORM

Objective: The objectives of the present research was to develop a simple, precise, economical, accurate, reproducible and sensitive method for the quantitative estimation of lafutidine in bulk and its pharmaceutical dosage forms by Ultra Violet (UV) absorption spectrophotometry.Methods: The method uses 0.1 N HCl, pH 1.20 as a solvent of choice for the quantitative estimation of lafutidine in bulk and its tablets dosage form by UV absorption spectrophotometry at a wavelength of 290 nm. The method was validated for parameters like linearity, range, precision, Limit of Detection (LOD), Limit of Quantification (LOQ), accuracy, recovery and stability of the analyte.Results: Lafutidine exhibited absorbance maxima at 290 nm in 0.1 N HCl, pH 1.20 solvent. The developed method was validated as per the ICH validation guidelines. Beer’s law was obeyed in range of 0-30 µg/ml with r2= 0.9997. The LOD and LOQ values of lafutidine were found to be 0.545 µg/ml and 1.654 µg/ml respectively. The mean % recovery for the developed method was found to be in the range of 99.25 to 99.45 % respectively for the marketed dosage forms. The developed method was also found to be robust.Conclusion: The developed method was found suitable for the routine quantitative analysis of lafutidinein bulk and pharmaceutical dosage form. It was also concluded that developed UV spectrophotometry method was accurate, precise, linear, reproducible, robust and sensitive.

РОЗРОБКА ТА ВАЛІДАЦІЯ СПЕКТРОФОТОМЕТРИЧНОЇ МЕТОДИКИ КІЛЬКІСНОГО ВИЗНАЧЕННЯ ЕНІСАМІУМУ ЙОДИДУ В КАПСУЛАХ

Мета роботи. Розробити методику кількісного визначення енісаміуму йодиду в капсулах із застосуванням методу абсорбційної спектрофотометрії в ультрафіолетовій області.Матеріали і методи. Використано стандартний зразок енісаміум йодиду та зразок готової лікарської форми виробництва ПАТ «Фармак». У ході роботи було встановлено оптимальну робочу концентрацію енісаміуму йодиду 0,02 мг/мл. Дослідження проводили із застосуванням спектрофотометра «Specord 250 Plus».Результати й обговорення. Продемонстровано, що оптимальна довжина хвилі при визначенні становить 267 нм. Вивчено валідаційні характеристики методики в діапазоні 0,016-0,024 мг/мл (80-120%): специфічність, правильність, прецизійність, лінійність, діапазон застосування, робасність, внутрішньолабораторна прецизійність відповідно до рекомендацій Міжнародної конференції з гармонізації. Коефіцієнт кореляції (r) між введеним та знайденим значенням для енісаміуму йодиду становить 0,99996, а відносний довірчий інтервал (Dz) 0,23 %. Підтверджено стабільність розчинів при їх зберіганні при кімнатній температурі протягом 48 годин.Висновки. Розроблено спектрофотометричну методику кількісного визначення енісаміуму йодиду в капсулах, експериментально доведено, що вона придатна для контролю якості капсул енісаміуму йодиду.

Changes in the Microstructure and Components of Eulaliopsis binata Treated by Continuous Screw Extrusion Steam Explosion

Eulaliopsis binata (EB) was pretreated by continuous screw extrusion steam explosion (SESE), with the aim of converting EB into useful materials on an industrial scale. The three main chemical components were characterized by component analysis using the Van Soest fiber detergent system, ultraviolet (UV) absorption spectrophotometry, gel permeation chromatography (GPC), and carbon-13 nuclear magnetic resonance (13C-NMR) spectroscopy. Changes in the contents of detergent soluble species in the Van Soest process revealed the partial degradation of hemicellulose and cellulose, and the partial removal of lignin. GPC indicated that the molecular weight of lignin decreased from 4194 to 3710 g/mol over the first three SESE pretreatment cycles, but then increased to 4592 g/mol following the fourth SESE pretreatment cycle. UV absorption and 13C-NMR results indicated the partial removal of lignin and the depolymerization and repolymerization of lignin during SESE pretreatment. Scanning electron microscopy (SEM) showed that the epidermis and parenchyma of EB were almost completely desquamated. X-ray diffraction (XRD) revealed that the crystallinity of EB initially increased and then subsequently decreased slightly, with increasing number of SESE pretreatment cycles. The varying physicochemical properties of EB resulting from different numbers of pretreatment cycles may find use in more diverse applications.

Kinetics of oxygen adsorption on ZnS nanoparticles synthesized by precipitation process

AbstractZnS nanoparticles were synthesized through a one-step precipitation process. Effect of time and temperature on the formation reaction was investigated. The synthesized samples were characterized by X-ray diffraction (XRD), ultraviolet (UV) visible absorption and photoluminescence (PL) spectrophotometry. Based on XRD and UV-Vis data, the particles produced at 70 °C had a mean particle size of about 5 nm. Increasing time and temperature of the synthesis reaction resulted in photoluminescence intensification. PL spectroscopy helped understanding the adsorption kinetics of oxygen on ZnS nanoparticles during the precipitation synthesis process. Fabrication of ZnS structures with appropriate oxygen adsorption capacity was suggested as a means of PL emission intensity control.

Determination of phosphate concentration in glaucoma eye drops commercially available in Spain

ObjectivesTo identify and analyze the phosphate concentration in glaucoma eye drops available in Spain. Material and methodsGlaucoma medications containing phosphates were identified according to the 2013 Vademecum and the website of the Spanish Agency for Medicines and Medical Devices. Phosphate concentration was determined in these eye drops using ultraviolet molecular absorption spectrophotometry, and pH was determined using scan image analysis algorithms of pH strips. ResultsA total of 37 phosphate containing glaucoma eye drops were identified. The mean phosphate concentration was 97.72±75.52mM. The group with higher concentration of active substance was timolol (204.85±42.38mM) followed by brimonidine/timolol (200.9mM). No statistically significant difference was found between brand name (95.65±71.11mM) and generic eye drops (99.14±80mM, p=0.892). Although no statistically significant difference was found between products containing preservatives (99.24±76.78mM) and those without preservatives (85.17±72.86mM) (p=0.730), a lower phosphate concentration was observed in the preservative-free Timolol and Latanoprost. Single dose samples showed a lower phosphate concentration than multi-dose ones (102.04±75.39 vs. 22.24±2.98mM, p<0.001). The mean pH was 7.13±0.63. No statistical correlation was found between phosphate concentration and pH (r: 0.07). ConclusionThe phosphate concentration in glaucoma eye drops exceeded the tear film physiological level (1.45mM). No difference was observed between brand names and generic eye drops. Lower phosphate concentration was observed in preservative-free single dose eye drops.

Determination of phosphate concentration and pH in artificial tear drops

ObjectiveTo determine phosphate concentration and pH in artificial tear eye drops commercially available in Spain. Materials and methodsA total of 71 examples of artificial tear preparations were identified in a search of Vademecum 2014 and the Spanish Medicines Agency website. In the 24 artificial tear products containing phosphates, quantification of these was performed by ultraviolet molecular absorption spectrophotometry, and the determination of pH was performed using scan image analysis algorithms of pH strips. ResultsOf the 71 artificial tears tested, 24 contained phosphate among their excipients in the data sheet, three of which had a concentration level below detection limit (<0.1mM). The mean phosphate concentration was 17.91±23.87mM. The artificial tear sample containing a higher concentration was Colircusi Humectante (87.1mM). Lubricants based on hypromellose showed the highest phosphate concentration (41.59±32.1mM), showing statistically significant differences compared to povidone (p=0.0196) and hyaluronate (p=0.0067). Statistically significant differences were found between products containing preservatives (32.39±20.91mM), and preservative free ones (8.49±11.98mM) (p=0.0498). However, no difference was found between multidose (20.21±26.91mM) and unidose (9.31±14.39mM) samples, or between brand name (15.44±23.3mM) and generic eye drops (20.81mM). The mean pH was 6.93±0.26 (6.2–7.22). No statistical correlation was detected between phosphate concentration and pH (Spearman's Rho −0.1089 and p=0.6125). ConclusionA total of 24 (33.8%) of the 71 artificial tears contained phosphate. We believe identifying the phosphate concentration of artificial tears is useful information in order to avoid complications in high-risk patients.

Determinación de la concentración de fosfatos en los colirios antiglaucomatosos comercializados en España

ObjectivesTo identify and analyze the phosphate concentration in glaucoma eye drops available in Spain. Material and methodsGlaucoma medications containing phosphates were identified according to the 2013 Vademecum and the website of the Spanish Agency for Medicines and Medical Devices. Phosphate concentration was determined in these eye drops using ultraviolet molecular absorption spectrophotometry, and pH was determined using scan image analysis algorithms of pH strips. ResultsA total of 37 phosphate containing glaucoma eye drops were identified. The mean phosphate concentration was 97.72±75.52mM. The group with higher concentration of active substance was timolol (204.85±42.38mM) followed by brimonidine/timolol (200.9mM). No statistically significant difference was found between brand name (95.65±71.11mM) and generic eye drops (99.14±80mM, P=.892). Although no statistically significant difference was found between products containing preservatives (99.24±76.78mM) and those without preservatives (85.17±72.86mM) (P=.730), a lower phosphate concentration was observed in the preservative-free Timolol and Latanoprost. Single dose samples showed a lower phosphate concentration than multi-dose ones (102.04±75.39 vs. 22.24±2.98mM, P<.001). The mean pH was 7.13±0.63. No statistical correlation was found between phosphate concentration and pH (r: 0.07). ConclusionThe phosphate concentration in glaucoma eye drops exceeded the tear film physiological level (1.45mM). No difference was observed between brand names and generic eye drops. Lower phosphate concentration was observed in preservative-free single dose eye drops.

Determinación de la concentración de fosfatos y pH en los colirios de lágrima artificial

ObjectiveTo determine phosphate concentration and pH in artificial tear eye drops commercially available in Spain. Materials and methodsA total of 71 examples of artificial tear preparations were identified in a search of Vademecum 2014 and the Spanish Medicines Agency website. In the 24 artificial tear products containing phosphates, quantification of these was performed by ultraviolet molecular absorption spectrophotometry, and the determination of pH was performed using scan image analysis algorithms of pH strips. ResultsOf the 71 artificial tears tested, 24 contained phosphate among their excipients in the data sheet, three of which had a concentration level below detection limit (<0.1mM). The mean phosphate concentration was 17.91±23.87mM. The artificial tear sample containing a higher concentration was Colircusi Humectante (87.1mM). Lubricants based on hypromellose showed the highest phosphate concentration (41.59±32.1mM), showing statistically significant differences compared to povidone (P=.0196) and hyaluronate (P=.0067). Statistically significant differences were found between products containing preservatives (32.39±20.91mM), and preservative free ones (8.49±11.98mM) (P=.0498). However, no difference was found between multidose (20.21±26.91mM) and unidose (9.31±14.39mM) samples, or between brand name (15.44±23.3mM) and generic eye drops (20.81mM). The mean pH was 6.93±0.26 (6.2-7.22). No statistical correlation was detected between phosphate concentration and pH (Spearman's Rho −0.1089 and P=.6125). ConclusionA total of 24 (33.8%) of the 71 artificial tears contained phosphate. We believe identifying the phosphate concentration of artificial tears is useful information in order to avoid complications in high-risk patients.

Influence of Ag nanoparticles on luminescent performance of SiO2:Tb3 + nanomaterials

Tb3+ single-doped SiO2 (SiO2:Tb3+) and Tb3+, Ag co-doped SiO2 (SiO2:Tb3+–Ag) nanostructured luminescent materials were prepared by a modified Stöber method. Their microstructure and optical property were investigated using scanning electron microscopy, ultraviolet visible absorption and photoluminescence spectrophotometry. Results show that the samples are composed of well-dispersed near-spherical particles with a diameter about 50nm, the highest fluorescence intensity is obtained when the doping concentration of Tb3+ is 4.86mol%, the corresponding internal quantum efficiency is 13.6% and the external quantum efficiency is 8.2%. The experimental results indicate that Ag nanoparticles can greatly enhance the light absorption at 226nm and the light emission at 543nm of SiO2:Tb3+–Ag, and the fluorescence lifetime reduces with increasing Ag concentration in SiO2:Tb3+–Ag. Additionally, the present results indicate that fluorescence enhancement is attributed to the local field enhancement and the increased radiative decay rates induced by Ag nanoparticles.

Thermal and Spectrophotometric Analysis of Liquid Crystal 8CB/8OCB Mixtures

The binary system of 4-octyl-4′-cyanobiphenyl (8CB) and 4-octyloxy-4′-cyanobiphenyl (8OCB) has been studied by means of differential scanning calorimetry (DSC) and ultraviolet absorption spectrophotometry (UV). The phase-transition temperatures, enthalpies, and entropies have been determined by using calorimetric methods on DSC. The results indicate clearly the existence of three-phase regions across the crystalline-to-smectic A, smectic A-to-nematic, and nematic-to-isotropic transitions in the 8CB/8OCB mixtures. The obtained phase-transition temperatures of the 8CB/8OCB mixtures are between the data for 8CB and 8OCB. A few of the phase transitions cannot be observed at high heating rates. The phase-transition temperatures of the 8CB/8OCB mixtures rise with the heating rate between 2°C/min and 15°C/min. The activation energies were calculated by the Ozawa method for the phase transitions of 25% 8CB and 75% 8OCB liquid crystal mixtures. UV experiments were carried out to characterize the absorptivity constants of liquid crystal and their mixtures. The molar absorptivity and maximum absorption wavelengths were measured in chloroform solution by UV spectrophotometry. The maximum absorption wavelength of the 8CB/8OCB mixtures increases with decreasing percent weight of 8CB in 8OCB, a result associated with the different lengths of the alkyl chain.