Omni flex

¹H and ¹³C NMR spectra were recorded on a Varian Unity-300 MHz with tetramethylsilane (TMS) as an internal reference. Infrared (IR) spectra were measured on a Nicolet FT-SSX spectrophotometer (Bruker, Billerica, MA, USA). Elemental analysis was determined by Galbraith Laboratories, INC Knoxville (Sycamore, MO, USA). FAB+ mass spectra were taken on a JEOL JMS AX505 HA instrument (JEOL manufacturers, Tokyo, Japan). Electrospray mass spectra were taken on a Bruker Daltonic, Esquire 6000 (Bruker, Billerica, MA, USA). Matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectra were taken on a Bruker Omni FLEX using 9-nitroanthracene (9NA) as a matrix. The ultraviolet–visible (UV-Vis) absorption spectra were obtained at room temperature with a Shimadzu 2401 PC spectrophotometer (Shimadzu, Kyoto, Japan).

PNA-a9 and PNA-sc9 were synthesized by manual solid-phase synthesis using Boc/Z chemistry [57 ]. The commercially available Boc/Z-protected PNA monomers were purchased from ASM Research Chemicals GmbH (Hannover, Germany). The MBHA resin was purchased from VWR International (Milan, Italy), and it was loaded manually to 0.2 mmol/g with Boc/Z-adenine PNA monomer for PNA-a9 and with Boc-thymine PNA monomer for PNA-sc9, following the previous procedure [58 (link)]. The PNA purification was performed by reverse-phase RP-HPLC with an Agilent 1200 Series system, equipped with a diode array detector (UV detection at 260 nm). The purity of PNA-a9 and PNA-sc9 was checked by RP-HPLC analyses, and their identities were confirmed by MALDI-TOF mass spectra, which were recorded with a Bruker Daltonics Omniflex (Milan, Italy), equipped with a 337 nm pulsed nitrogen laser (sinapinic acid as matrix). PNA-a9 calculated MW for C₂₁₆H₂₆₆N₁₂₄O₅₃: 5447.2; MALDI-TOF MS found m/z 5448.6 [M+H]⁺. PNA-sc9 calculated MW for C₂₁₆H₂₆₆N₁₂₄O₅₃: 5447.2; MALDI-TOF MS found m/z 5448.4 [M+H]⁺.