Lambda 35 uv visible spectrophotometer

One mL of the alcoholic extract was diluted to 50 mL with distilled water. Two mL of diluted extract was added with 4.0 mL of Folin-Ciocalteu’s reagent (1:1) and 2.0 mL of 35% sodium carbonate. The contents were further made up to 10.0 mL with distilled water and the mixture was shaken thoroughly and allowed to stand still for 30 min. Absorbance of the blue color developed was read at 700 nm against the reagent blank using PerkinElmer Lambda-35 UV–Visible spectrophotometer. Quantum of polyphenols present in tea leaves was computed using the standard calibration curve derived from known concentrations (10 to 50 ppm) of gallic acid (Sigma chemicals Private Limited, Bangalore) and the results were expressed as per cent gallic acid equivalents^{9 (link)}.

The CIE (Commission Internationale de l’Eclairage) L*, a* and b* color coordinates of the oenotannin solutions were measured according to OIV [34 ]. Visible spectra were recorded in transmittance at 400–700 nm using a 10 mm path length quartz cell and the Lambda 35 UV-Visible spectrophotometer (Perkin Elmer Inc., Shelton, CT, USA) equipped with the RSA-PE-20 Integrating Sphere accessory assembly (Labsphere, North Sutton, NH, USA). UV WinLab software was used to record the spectra (version 2.85.04, Perkin Elmer Inc., Shelton, CT, USA), and CIELab color coordinates were calculated for the CIE illuminant D65 and 10° standard observed conditions using Color software (version 3.00, 2001, Perkin Elmer Inc., Shelton, CT, USA). Color differences between the oenotannin solutions were determined using the ΔE value of the CIELab diagram, according to the following equation: $$\Delta E=\sqrt{{\left({\Delta L}^{*}\right)}^2+{\left({\Delta a}^{*}\right)}^2+{\left({\Delta b}^{*}\right)}^2}$$
When ΔE ≥ 3, the differences between oenotannin solutions are perceivable by the human eye [35 (link)].

Analysis of the synthetic products of CDs under different conditions was conducted on a 4.6 × 250 mm BDS HYPERSIL-C18 5 μm column (Thermo Scientific, USA) using an Ultimate-3000 HPLC system (Dionex, USA) equipped with an Ultimate-3000 diode arraydetector (DAD) and an Ultimate-3000 fluorescence detector. Separation of CDs was performed on a 10.0 × 250 mm YMC Pack ODS-A S-5 μm, 12 nm column (YMC Korea Co., Ltd). UV-visible absorption spectra were acquired using a Lambda-35 UV/visible spectrophotometer (PerkinElmer Company). Fluorescence spectra were recorded using an LS55 spectrofluorometer (PerkinElmer Company). Fourier transform-infrared spectra were obtained on a Nicolet 6700 (FT-IR) spectrometer (Thermo Fisher Scientific), and the sample mixed with potassium bromide powder was measured at room temperature. Hydrogen spectrum (¹H-NMR) and carbon spectrum (¹³C-NMR) were recorded on a Bruker Ascend IIITM 600 MHz NMR spectrometer (Bruker). Electrospray ionization mass spectrometry (ESI-MS) was performed using a UHPLC system and a Q Exactive HF mass spectrometer (*Q Exactivee*Q Exactive).

UV-visible absorption spectra were acquired with a Lambda-35 UV/visible spectrophotometer (PerkinElmer Company) to determine the bandgap absorption of QDs. Fluorescence spectra were recorded on a LS55 spectrofluorometer (PerkinElmer Company). All optical measurements were performed under ambient conditions. The TEM sample was prepared by dropping an aqueous ZnCdSe QDs solution onto an Agar carbon-coated copper grid (400 meshes) with the excess solvent evaporated. The TEM image was obtained at 310 K magnification with an FEI Tecnai G220 twin transmission electron microscope. X-ray diffraction (XRD) patterns were recorded on a Shimadzu XRD-2000 x-ray diffractometer. Energy-dispersive x-ray spectroscopy (EDS) measurements were performed with an FEI Quanta 200 scanning electron microscope equipped with an energy dispersive x-ray spectrometer. X-ray photoelectron spectroscopy (XPS) measurements were carried out with a Leybold Heraeus SKL 12 x-ray photoelectron spectrometer. The QY of ZnCdSe QDs was measured according to the literature [29 (link)]. Quinoline sulfate in 1 mol L⁻¹ H₂SO₄ aqueous solution was chosen as the reference standard (QY = 54.6%).

Enzyme activity was assayed spectrophotometrically using cyt c (ε₅₅₀ = 19.6 mM⁻¹ cm⁻¹) as electron acceptor for intact CDH or DCIP (ε₅₅₀ = 6.8 mM⁻¹ cm⁻¹) as an electron acceptor for both the intact holoenzyme and the dehydrogenase domain. The activities were determined by monitoring the reduction of 300 μM 2,6-dichlorophenol indophenol (DCIP) in 50 mM sodium acetate buffer (pH 5.5) containing 30 mM lactose and 4 mM of sodium fluoride (sodium fluoride was used as a laccase inhibitor). The cyt c-based assay contained 50 mM Tris–HCl buffer, pH 7.5, 20 µM cyt c and 30 mM lactose. The reaction was monitored for 180 s at 30 °C in a Lambda 35 UV–Visible spectrophotometer featuring a temperature-controlled 8-cell changer (Perkin Elmer, Massachusetts, USA). Enzyme activity was defined as the amount of enzyme that oxidizes 1 µmol of the electron acceptor per minute under the assay conditions.