Intrinsic anisotropy parameters of a series of lanthanoid complexes deliver new insights into the structure-magnetism relationship

•Lanthanoids display ligand-field-like effects at room temperature•Anisotropic paramagnetic susceptibility parameters are reported for all lanthanoids•Site-specific isotope labels yield assignments of up to 1,400 ppm wide 1H-NMR spectra Lanthanoid tri-cations considered be chemically indistinguishable. A general dogma on the 4 f-electrons states that they shielded by outer electrons such do not show ligand-field effects, nor contribute directional bonding, but merely play a role as isotropic Coulomb clouds. Recently, research in field single-molecule magnetism and others has questioned this demonstrated lanthanoids low temperatures. Here, we present complete series isostructural lanthanoid complexes with markedly non-symmetrical chelating ligand, designed pseudocontact shift NMR spectroscopy. Unexpectedly, orientation principal magnetic axis revealed distinct correlation ground state f-electron distribution. We thus show, first time, crucial interaction ligand prolate or oblate distribution temperature, disproving aforementioned dogma. tags (LCTs) widely used advanced biomacromolecules. The magnitude their induced shifts (PCSs) residual dipolar couplings (RDCs) depends critically anisotropy tensor, which is usually determined resonances conjugated protein, inevitably reducing effect motional averaging. intrinsic full experimentally from itself. strongly shifted proton could only assigned extensive, site-specific labeling. extremely large anisotropies obtained deliver an upper limit future PCS applications. To our great surprise, least observed unprecedented between main well size anisotropy. IntroductionLanthanoids rich structural chemistry have found wide-spread utilization last few decades.1Levason W. Chemistry applications lanthanides.Coord. Chem. Rev. 2017; 340: 1-298Crossref Scopus (5) Google Scholar peculiar electronic properties resulted ranging superconductivity2Sun Kuang X. 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Localization ligands within human carbonic anhydrase 19F 10: 5064-5072Crossref 2 decades, precise itself, i.e., without due flexible attachment never characterized so far. would like coin term “intrinsic parameters” course, “intrinsic” property function temperature nature lanthanoid, among others.PCS conveniently provides Δχrh, three Euler angles, α, β, γ, if 3D model five nuclei available14Bertini 1). crucial, especially cases challenging task, assignment paramagnetically set resonances, strong (PREs) prevent classical strategies via two- higher-dimensional experiments. While axiallyδpcs=112πr3[Δχax2z2−x2−y2r2+32Δχrhx2−y2r2]whereΔχax=χzz−χxx+χyy2andΔχrh=χxx−χyy(Equation 1) symmetric tensors often allow several data sets similar trends,24Di Pietro Piano S.L. Di Bari variable crystal parameters.Coord. 2011; 255: 2810-2820Crossref (38) Scholar,25Hiller Maier Wadepohl Enders analysis substituted Biscyclooctatetraene complexes.Organometallics. 35: 1916-1922Crossref (15) rhombic spectra. 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Cucinotta Luzon Degl’Innocenti Perfetti Bernot Calvez Caneschi Sessoli spin-parity along DOTA.Angew. 350-354Crossref (253) demonstrate sufficiently non-symmetric well.Figure 2Proton spectrum Dy-DOTA-M7FPyShow caption1H-NMR Dy-DOTA-M7FPy (20 mM) (for central region spectrum, see S28). recorded 298 K phosphate buffer (50 mM, pH = 6.0) 600.13 MHz. pieced together 10 single spectra, each sweep width 154 ppm. Abbreviations: a, axial; e, equatorial; n, near; f, far.View Large Image ViewerDownload Hi-res image Download (PPT)Results discussionStructure Ln-DOTA-M7FPyDOTA-based highest hence, largest chosen DOTA-M7FPy attempt unravel because very chelator excellent PCSs. eleven stereogenic centers defined stereochemistry (1R, 2S, 4S, 5S, 7S, 8S, 10S, 11S, 2′R, 2″R, 2″′R) adopt principle four conformers, steric bulk introduced design, solely Λ(δδδδ) square antiprism (SAP) conformer formed. safely assumed both early late NOE patterns La-, Sm-, Lu-DOTA-M7FPy (Figures S34, S51, S83) literature.20Müntener Scholar,29Opina A.C.L. Strickland Lee Y.S. Tjandra Swenson R.E. Vasalatiy O. Comparison polymethylated DOTA-like opposite chirality pendant arms.Inorg. 58: 15788-15800Crossref (7) Scholar,30Joss Walliser R.M. Zimmermann Conformationally locked convenient spectroscopy.J. Biomol. NMR. 72: 29-38Crossref (17) C1-symmetry turned out (see below). Even though C1-symmetry, contain C4-pseudosymmetric axis. C4-pseudosymmetry normal cyclen-N4-plane going lanthanoid. rough estimation assigning strongest PCS, reliable requires careful less vary tremendously lanthanoids. It was, therefore, utmost importance obtain trustworthy peak complexes. structures (Data S1) required fit calculated DFT geometry optimization details, procedures). As unclear whether water molecule occupies ninth site, implicit explicit apical position. best coefficients 8-fold water.NMR isotopically labeled Ln-DOTA-M7FPyLn-DOTA-M7FPy shows 29 1D From signals, 26 (Figure 2). phenyl sulfone excluded process rotation PCS. previously shown significantly affected contact shifts.26Suturina Without restrictions, 4∗1026 shifts. order restrict manageable number, signals classified spectroscopic data. diamagnetic (La, Lu) complexes, weakly (Sm, Eu) compounds 2D (HSQC, HMBC, COSY, NOESY, ROESY) stronger PREs Ce, Pr, Nd recording COSY still observable signal intensity profited contribution dampening PRE.31Bertini Piccioli Tarchi macromolecules: observability, scalar cross-correlation relaxation-allowed coherence transfer.Concepts 1994; 6: 307-335Crossref (42) Scholar,32Bertini Are true proton–proton connectivities ever measured macromolecules?.Chem. Phys. Lett. 203: 445-449Crossref (91) Based correlations, Ce-, Pr-, Nd-DOTA-M7FPy (supplemental information) (Tables S1–S3).For no magnetization lifetimes shortened much PRE did polarization interactions. Therefore, two employed classification directly adapted known synthetic strategies.20Müntener Scholar,33Müntener Thommen Prescimone Synthesis chiral nine twelve-membered cyclic polyamines natural building blocks.Chem. 55: 4715-4718Crossref 34Häussinger Huang Grzesiek DOTA-M8: 2009; 131: 14761-14767Crossref (131) 35Müntener Protein under physiological conditions: high cyclization rigidified DOTA-based sulfhydryl-reactive activators forming reductively linkage. Phd Thesis (University Basel, Faculty Science, 2019Google cyclen ring either elongating alanine trimer 12 enriched 7 (2H) 3B) 27 (13C) S2) macrocycle 47 LiAlD4 S4). alkylation M4-cyclen (16, 34, 49 3B S2–S4) twice alkylated 54 3B, S2, S4) leads scrambling over positions, respectively. If isotopes 6 24 50% 25% respective positions achieved (1–3 3A). introduction label later step 44 100% (4 5 3A), depending again debenzylation steps. (1) synthesized (NMR Figures S30–S85) apart Pm; Tb Yb. Surprisingly, dissociated <3, rate dissociation La lowest Nd, following trend ionic radii.Figure 3Synthesis complexesShow caption(A) All throughout study. Blue dots mark deuterium 2H. Red carbon 13C.(B) Exemplary route towards (2 3) 1–5: (i) LiAlH4, THF, 0°–5°C; (2) Cbz-Cl, H2O, EtOAc, Na2CO3; (3) IBX, 77°C. (ii) T3P, DIPEA, EtOAc; NaBH4, MeOH, MeCN, 80°C. (iii) NaBH(CH3COO)3, DCM; Pd/C H2, MeOH. (iv) BnBr, 45°C. (v) HBr, AcOH, 40°C; HATU, MeCN. (vi) DCM, −78°C. (vii) TFA, (viii) OTf-Lac-O-t-Bu, K2CO3, (ix) (x) Pd(OH)2/C, NH4(HCOO), EtOH. (xi) (xii) MeCN; HCl, 80°C; aq. NH4(CH3COO), Ln(III), Below molecule, percentage noted.View (PPT)Carbon combination selectively 1H decoupled S105–S109) classify methyl signals. Attempts extend decoupling other successful gain longer PRE. Deuterium (spectra S113–S166) hand, sensitive PRE, supplemental S4–S7). Four space. Due stage labels, amount material effort greatly reduced. Careful control mM buffer, 6.0, Table S15) trifluoro acetic (TFA) HPLC purification necessary reproducible S86).Intrinsic parametersClassification reduced number. therefore fitted remaining S13–S25). Sm Eu, able correct ones correlate structure. However, simulations, one yielding coefficient. For nonetheless conserved correlated Er, Tm, Yb, unambiguously since found, while Tb, Dy, Ho, had rhombicity slightly differing orientation. further discussion, appears overall higher latter S7, S8). final free (final Tables S9 S10, S13) depicted 4. Uncertainties Monte Carlo simulations most ubiquitin, uncertainty estimated simulation generated defining orientations. avoid ambiguities, represented unique representation (UTR).36Schmitz Stanton-Cook M.J. Numbat: interactive software tool deltachi-tensors molecular coordinates shifts.J. 41: 179-189Crossref striking result Δχrh—the exceed far typical recently published DOTA-M7-Nitro LCT,37Joss Winter novel, rationally delivers restraints NMR.Chem. 12861-12864Crossref LCT, 5%–10% values. comparison about 80% lost tether.38Suturina Garbuio Model-free extraction spin position distributions data.Chem. 8: 2751-2757Crossref Scholar,39Shishmarev mobile ? modelling study.J. 203-216Crossref (58) loss increasing Ce There likely reasons trend: small makes them susceptible errors, overestimation parameters, probability coordinate additional donor site reduces noteworthy coupling (RDC)-derived values independently potential rigidifying observation significant easy-to-detect range 0.01 spins 175 Å, opening perspective long-range work. principle, d