Varian inova 500 mhz spectrometer

NMR spectra of the isolated substances were recorded on a VARIAN INOVA 500 MHz spectrometer (Varian Inc., Palo Alto, CA, USA) working at 499.78 (¹H) and 125.68 MHz (¹³C) at the Institute of Natural Product Research (IPPN)—UFRJ/RJ; on a 400 MHz BRUKER Model: Avance II HD spectrometer equipped with a Bruker Prodigy BB0400S1 cryosonday or on a 400 MHz spectrometer at the Analytical Methodology Platform (PMA)—Farmanguinhos—Fiocruz/RJ. Bidimensional spectra (HSQC, HMBC, COSY) also proceeded. Chemical shifts (δ) were endorsed with tetramethylsilane (TMS) as internal standards (δ = 0, 1H) being expressed in ppm units and coupling constants (J) in Hertz (Hz). The pulse sequences used are all standard in the VNMRJ software, and the experiments were conducted at 25 °C. The samples were dissolved in deuterated methanol (CD₃OD).

The mPEG-b-PLA diblock copolymer was synthesized by ring-opening polymerization [22 (link),27 (link),28 (link)]. mPEG (Mw = 5000) (1 mmol) and d,l-lactide (25 mmol) was placed in a two-necked round-bottle flask with a magnetic stirrer, and toluene was added for dissolution under stirring. Afterward, the catalyst stannous octoate (Sn(Oct)₂) (1 wt %) was added dropwise to initiate the ring-opening polymerization at 130 °C for 16 h under nitrogen. Finally, the reaction was terminated by adding 0.1 N methanolic KOH, and the product was obtained via precipitation from iced diethyl ether. The product was dried in a vacuum oven. The chemical structure of mPEG-b-PLA was characterized using a proton nuclear magnetic resonance (¹H-NMR) spectrometer (Varian INOVA500 MHz spectrometer, Varian Inc., Palo Alto, CA, USA).