X2 system

The ESI-MS experiments were all performed on a LCMS-9030 qTOF Shimadzu (Shimadzu, Kyoto, Japan) device, equipped with a standard ESI source and the Nexera X2 system. The analysis was performed in the positive ion mode between 50 and 2000 m/z. The LCMS-9030 parameters were as follows: nebulizing gas, nitrogen; nebulizing gas flow, 3.0 L/min; drying gas flow, 10 L/min; heating gas flow, 10 L/min; interface temperature, 300 °C; desolvation line temperature, 400 °C; detector voltage, 2.02 kV; interface voltage, 4.0 kV; collision gas, argon; collision energy was optimized between 10 and 30 eV. The injection volume was 5 μL. The obtained signals all had a mass accuracy error in the range of 1 ppm. The used solvents were all of LC-MS grade. The chromatographic module was operated as follows: eluent (A) water + 0.1% HCOOH, eluent (B) acetonitrile + 0.1% HCOOH. The obtained data were analyzed by LabSolutions software (Shimadzu, Kyoto, Japan).

ESI-MS experiments were performed on the LCMS-9030 qTOF Shimadzu (Shimadzu, Kyoto, Japan) device, equipped with a standard ESI source and the Nexera X2 system. Analysis was performed in the positive ion mode between 100 and 3000 m/z. The LCMS-9030 parameters were: nebulizing gas—nitrogen, nebulizing gas flow—3.0 L/min, drying gas flow—10 L/min, heating gas flow—10 L/min, interface temperature 300 °C, desolvation line temperature—400 °C, detector voltage—2.02 kV, interface voltage 4.0 kV, collision gas-argon, mobile phase 50% A in B (where A is water + 0.1% acetic acid and B is acetonitrile + 0.1% acetic acid), mobile phase total flow—0.3 mL/min. The injection volume was within the range of 0.1 to 1 μL, depending on the intensity of the signals observed on the mass spectrum. All obtained signals had mass accuracy errors in the range of 1 ppm. The concentration of peptide was 1 10⁻⁴ M with a M/L molar ratio of 1:1. Samples were prepared in the water/acetonitrile (50/50 v/v) mixture at pH 7. All of the used solvents were of LC-MS grade. The obtained data were analyzed and simulated using an ACD/Spectrus processor (ACD/Labs, Toronto, ON, Canada).

Electrospray
ionization-mass spectrometry (ESI-MS) experiments were performed on
the LCMS-9030 qTOF Shimadzu (Shimadzu, Kyoto, Japan) device equipped
with a standard ESI source and the Nexera X2 system. Analysis was
performed in the positive ion mode, between 100 and 3000 m/z. LCMS-9030 parameters: nebulizing gas–nitrogen,
nebulizing gas flow 3.0 L/min, drying gas flow—10 L/min, heating
gas flow—10 L/min, interface temperature 300 °C, desolvation
line temperature −400 °C, detector voltage −2.02
kV, interface voltage 4.0 kV, collision gas–argon, mobile phase
(A) H2O +0.1% HCOOH and (B) MeCN +0.1% HCOOH, and mobile phase total
flow −0.3 mL/min. The injection volume was optimized depending
on the intensity of the signals observed on the mass spectrum within
the range of 0.1–1 μL. Obtained signals had a mass accuracy
error in the range of 1 ppm. The concentration of peptide was 0.1
mM, and M/L molar ratio was 1:1. Samples were prepared in a mixture
of water/methanol (50/50 v/v) at pH 7.40. All used solvents were of
LC–MS grade. The obtained data were analyzed by LabSolutions
software (Shimadzu, Kyoto, Japan).

High-resolution mass spectra were obtained on an LCMS-9030 qTOF Shimadzu (Shimadzu, Kyoto, Japan) device, equipped with a standard ESI source and the Nexera X2 system. The mass spectrometer was operated in the positive and negative ion modes. The instrumental parameters were as follows: scan range m/z 100–2000, nebulizing gas nitrogen, nebulizing gas flow 3.0 L/min, drying gas flow 10 L/min, heating gas flow 10 L/min, interface temperature 300 °C, desolvation line temperature 400 °C, detector voltage 2.02 kV, interface voltage 4.0 kV, collision gas argon, mobile phase (A) H₂O + 0.1% HCOOH, (B) MeCN + 0.1% HCOOH, mobile phase total flow 0.3 mL/min. The injection volume was optimized depending on the intensity of the signals observed on the mass spectrum within the range of 0.1 to 3 μL. The samples were prepared in a 1:1 methanol-water mixture at a pH value of 7.4. The sample concentration was [ligand]_tot = 0.1 M, and M:L molar ratio was 1:1. Data were processed using the ACDLabs Spectrus Processor v2021.1.3 program. A comparison between the obtained experimental signals and the true isotopic pattern calculated using Bruker Compass DataAnalysis 3.4 program enabled an unambiguous confirmation of the elemental composition of the obtained complex (Table S2, Figures S15–S17, Supplementary Materials).