A comparison of experimental and DFT calculations of ¹⁹⁵Pt NMR shielding trends for [PtX(n)Y(6-n)](2-) (X, Y = Cl, Br, F and I) anions

Taming the Biological Activity of Pd(II) and Pt(II) Complexes with Triazolato "Protective" Groups: 1H, 77Se Nuclear Magnetic Resonance and X-ray Crystallographic Model Studies with Selenocysteine to Elucidate Differential Thioredoxin Reductase Inhibition

The biological activity of Pd(II) and Pt(II) complexes toward three different cancer cell lines as well as inhibition of selenoenzyme thioredoxin reductase (TrxR) was modulated in an unexpected way by the introduction of triazolate as a "protective group" to the inner metal coordination sphere using the iClick reaction of [M(N3)(terpy)]PF6 [M = Pd(II) or Pt(II) and terpy = 2,2':6',2″-terpyridine] with an electron-poor alkyne. In a cell proliferation assay using A549, HT-29, and MDA-MB-231 human cancer cell lines, the palladium compound was significantly more potent than the isostructural platinum analogue and exhibited submicromolar activity on the most responsive cell line. This difference was also reflected in the inhibitory efficiency toward TrxR with IC50 values of 0.1 versus 5.4 μM for the Pd(II) and Pt(II) complexes, respectively. UV/Vis kinetic studies revealed that the Pt compound binds to selenocysteine faster than to cysteine [k = (22.9 ± 0.2)·10-3 vs (7.1 ± 0.2)·10-3 s-1]. Selective triazolato ligand exchange of the title compounds with cysteine (Hcys) and selenocysteine (Hsec)─but not histidine (His) and 9-ethylguanine (9EtG)─was confirmed by 1H, 77Se, and 195Pt NMR spectroscopy. Crystal structures of three of the four ligand exchange products were obtained, including [Pt(sec)(terpy)]PF6 as the first metal complex of selenocysteine to be structurally characterized.

Is hydrogen electronegativity higher than Pauling’s value? New clues from the13C and29Si NMR chemical shifts of [CHF3] and [SiHF3] molecules

We previously demonstrated that the δ NMR chemical shift of central NMR active atoms (A), in simple halido [AXn] (A=C, Si, Ge, Sn, Pb, Pt; Xn = combination of n halides, n = 4 or 6) derivatives, could be directly related to X radii overall sum, Σ(rL). Further correlation have also been observed for tetrahedral [AX4] (A=C, Si; X4 = combination of four halides) compounds where the X Pauling electronegativities sum,Σ(χLPau),$\Sigma (\chi _L^{{\rm{Pau}}}),$exceeds a specific value (≈12.4). In this work, we focused on these latter systems considering the H vs. X substitution. The analysis of the literature reported δ(13C) and δ(29Si) NMR chemical shift for the mono hydrogenated derivatives and in particular for [CHF3] and [SiHF3], characterized by the lowest Σ(rL) and the highestΣ(χLPau),$\Sigma (\chi _L^{{\rm{Pau}}}),$suggests a revised value for the H electronegativity ranking with respect to Pauling’s.

The fundamental flaw of the HSAB principle is revealed by a complete speciation analysis of the [PtCl(6-n)Br(n)](2-) (n = 0-6) system

Bjerrum's model of step-wise ligand exchange is extended to compute a complete speciation diagram for the [PtCl6-nBrn](2-) (n = 0-6) system including all 17 equilibrium constants concerning the Pt(IV) chlorido-bromido exchange reaction network (HERN). In contrast to what the hard soft acid base (HSAB) principle "predicts", the thermodynamic driving force for the replacement of chloride by bromide in an aqueous matrix, for each individual ligand exchange reaction present in the Pt(IV) HERN, is due to the difference in halide hydration energy and not bonding interactions present in the acid-base complex. A generalized thermodynamic test calculation was developed to illustrate that the HSAB classified class (b) metal cations Ag(+), Au(+), Au(3+), Rh(3+), Cd(2+), Pt(2+), Pt(4+), Fe(3+), Cd(2+), Sn(2+) and Zn(2+) all form thermodynamically stable halido complexes in the order F(-) ≫ Cl(-) > Br(-) > I(-) irrespective of the sample matrix. The bonding interactions in the acid-base complex, e.g. ionic-covalent σ-bonding, Π-bonding and electron correlation effects, play no actual role in the classification of these metal cations using the HSAB principle. Instead, it turns out that the hydration/solvation energy of halides is the reason why metal cations are categorized into two classes using the HSAB principle which highlights the fundamental flaw of the HSAB principle.

Activation of the silent secondary metabolite production by introducing neomycin-resistance in a marine-derived Penicillium purpurogenum G59

Introduction of neomycin-resistance into a marine-derived, wild-type Penicillium purpurogenum G59 resulted in activation of silent biosynthetic pathways for the secondary metabolite production. Upon treatment of G59 spores with neomycin and dimethyl sulfoxide (DMSO), a total of 56 mutants were obtained by single colony isolation. The acquired resistance of mutants to neomycin was testified by the resistance test. In contrast to the G59 strain, the EtOAc extracts of 28 mutants inhibited the human cancer K562 cells, indicating that the 28 mutants have acquired the capability to produce bioactive metabolites. HPLC-photodiode array detector (PDAD)-UV and HPLC-electron spray ionization (ESI)-MS analyses further indicated that diverse secondary metabolites have been newly produced in the bioactive mutant extracts. Followed isolation and characterization demonstrated that five bioactive secondary metabolites, curvularin (1), citrinin (2), penicitrinone A (3), erythro-23-O-methylneocyclocitrinol (4) and 22E-7α-methoxy-5α,6α-epoxyergosta-8(14),22-dien-3β-ol (5), were newly produced by a mutant, 4-30, compared to the G59 strain. All 1–5 were also not yet found in the secondary metabolites of other wild type P. purpurogenum strains. Compounds 1–5 inhibited human cancer K562, HL-60, HeLa and BGC-823 cells to varying extents. Both present bioassays and chemical investigations demonstrated that the introduction of neomycin-resistance into the marine-derived fungal G59 strain could activate silent secondary metabolite production. The present work not only extended the previous DMSO-mediated method for introducing drug-resistance in fungi both in DMSO concentrations and antibiotics, but also additionally exemplified effectiveness of this method for activating silent fungal secondary metabolites. This method could be applied to other fungal isolates to elicit their metabolic potentials to investigate secondary metabolites from silent biosynthetic pathways.

Bioactive terpenes from marine-derived fungi

Marine-derived fungi continue to be a prolific source of secondary metabolites showing diverse bioactivities. Terpenoids from marine-derived fungi exhibit wide structural diversity including numerous compounds with pronounced biological activities. In this review, we survey the last five years’ reports on terpenoidal metabolites from marine-derived fungi with particular attention on those showing marked biological activities.

General cooperative effects of single atom ligands on a metal: a195Pt NMR chemical shift as a function of coordinated halido ligands’ ionic radii overall sum

An inverse linear relationship between the experimentally observed¹⁹⁵Pt NMR signals and the overall sum of coordinated halido X ligands’ ionic radii was discovered in Pt(ii) and Pt(iv) complexes.

Accurate prediction of 195Pt NMR chemical shifts for a series of Pt(ii) and Pt(iv) antitumor agents by a non-relativistic DFT computational protocol

Exhaustive benchmark DFT calculations reveal that the non-relativistic GIAO-PBE0/SARC-ZORA(Pt)∪6-31+G(d)(E) computational protocol predicts accurate ¹⁹⁵Pt NMR chemical shifts for a wide range of square planar Pt(ii) and octahedral Pt(iv) anticancer agents.

Three new glucosides from a cold-adapted fungal strain Mucor sp

Two new naphthaline glucosides, 2-hydroxy-3-methoxy-8-methyl-1-O-β-d-glucopyranosylnaphthaline (1) and 1-hydroxy-3-methoxy-8-methyl-2-O-β-d-glucopyranosylnaphthaline (2), together with one new isocoumarin glucoside, 3-(3,3-dichloro-2-hydroxylpropyl)-6-methoxy-8-O-β-d-glucopyranosyl-1H-isochromen-1-one (3), were isolated from a cold-adapted fungal strain Mucor sp. (No. XJ07027-5). Their structures were characterized by detailed analyses of IR, MS, 1D- and 2D-NMR spectra. Among them, 2 showed moderate cytotoxic activity against five tumor cells (A-549, HL-60, MCF-7, SMMC-7721, and SW480).

Probing isotope shifts in 103Rh and 195Pt NMR spectra with density functional theory

Zero-point vibrationally averaged (rg(0)) structures were computed at the PBE0/SDD/6-31G* level for the [Pt(35)Cln(37)Cl5-n(H2(18)O)](-) (n = 0-5), cis-Pt(35)Cln(37)Cl4-n(H2(18)O)(H2(16)O) (n = 0-4), fac-[Pt(35)Cln(37)Cl3-n(H2(18)O)(H2(16)O)2](+) (n = 0-3), [Pt(35)Cln(37)Cl5-n((16/18)OH)](2-) (n = 0-5), cis-[Pt(35)Cln(37)Cl4-n((16/18)OH)2](2-) (n = 0-4), fac-[Pt(35)Cln(37)Cl3-n((16/18)OH)3](2-) (n = 0-3), cis-[Pt(35)Cln(37)Cl2-n((16/18)OH)4](2-) (n = 0-2), [Pt(35)Cln(37)Cl1-n((16/18)OH)5](2-) (n = 0-1), [Rh(35)Cln(37)Cl5-n(H2O)](2-) (n = 0-5), cis-[Rh(35)Cln(37)Cl4-n(H2O)2](-) (n = 0-4), and fac-Rh(35)Cln(37)Cl3-n(H2O)3 (n = 0-3) isotopologues and isotopomers. Magnetic shielding constants, computed at the ZORA-SO/PW91/QZ4P/TZ2P level, were used to evaluate the corresponding (35/37)Cl isotope shifts on the (195)Pt and (103)Rh NMR spectra, which are known experimentally. While the observed effects are reproduced reasonably well computationally in terms of qualitative trends and the overall order of magnitude (ca. 1 ppm), quantitative agreement with experiment is not yet achieved. Only small changes in M-Cl and M-O bonds upon isotopic substitution, on the order of femtometers, are necessary to produce the observed isotope shifts.

(35/37)Cl and (16/18)O isotope resolved 195Pt NMR: unique spectroscopic 'fingerprints' for unambiguous speciation of [PtCl(n)(H2O)(6-n)](4-n) (n = 2-5) complexes in an acidic aqueous solution

At high magnetic fields the 128.8 MHz (195)Pt NMR of all the species in the series [PtCl(n)(H(2)O)(6-n)](4-n) (n = 2-6) display unique (35/37)Cl isotope effects resulting in a unique 'fine-structure' of each individual resonance, which constitutes an unambiguous spectroscopic 'fingerprint' characteristic of the structure of the octahedral platinum(IV) complex, provided (195)Pt NMR are recorded at optimum magnetic field homogeneity and carefully controlled temperature (293 ± 0.1 K). The detailed (195)Pt resonance fine-structure observed experimentally can readily be accounted for by an isotopologue and isotopomer model for each complex, showing particularly noticeable differences between stereoisomer pairs such as the cis/trans- and fac/mer-complexes. Moreover partial isotopic (18)O enrichment of the coordinated water molecules in the series [Pt(35/37)Cl(n)(H(2)(16/18)O)(6-n)](n-2) (n = 2-6) confirms this model. This technique can thus be considered a novel, direct spectroscopic method of chemical speciation of appropriate platinum(IV) complexes in solution without reference to accurate chemical shifts of authentic members of such a series. These effects are interpreted qualitatively in terms of the high sensitivity of (195)Pt NMR shielding to very small and subtle Pt-(35/37)Cl and Pt-(16/18)OH(2) bond displacements. Preliminary work shows this also applied to the corresponding bromido-complexes.

Computational study and molecular orbital analysis of NMR shielding, spin-spin coupling, and electric field gradients of azido platinum complexes

(195)Pt, (14)N, and (15)N NMR data for five azido (N(3)(-)) complexes are studied using relativistic density functional theory (DFT). Good agreement with experiment is obtained for Pt and N chemical shifts as well as Pt-N J-coupling constants. Calculated (14)N electric field gradients (EFGs) reflect experimentally observed trends for the line broadening of azido (14)N NMR signals. A localized molecular orbital analysis of the nitrogen EFGs and chemical shifts is performed to explain some interesting trends seen experimentally and in the first-principles calculations: (i) (14)N NMR signals for the Pt-coordinating (N(α)) nuclei in the azido ligands are much broader than for the central (N(β)) or terminal (N(γ)) atoms. The N(β) signals are particularly narrow; (ii) compared to N(γ), the N(α) nuclei are particularly strongly shielded; (iii) N(β) nuclei have much larger chemical shifts than N(α) and N(γ) ; and (iv) The Pt-N(α) J-coupling constants are small in magnitude when considering the formal sp hybridization of N(α). It is found that for N(α) a significant shielding reduction due to formation of the dative N(α)-Pt bond is counterbalanced by an increased shielding from spin-orbit (SO) coupling originating at Pt. Upon coordination, the strongly delocalized π system of free azide localizes somewhat on N(β) and N(γ). This effect, along with rehybridization at N(α) upon bond formation with Pt, is shown to cause a deshielding of N(γ) relative to N(α) and a strong increase of the EFG at N(α). The large 2p character of the azide σ bonds is responsible for the particularly high N(β) chemical shifts. The nitrogen s-character of the Pt-N(α) bond is low, which is the reason for the small J-coupling. Similar bonding situations are likely to be found in azide complexes with other transition metals.

35Cl/37Cl isotope effects in 103Rh NMR of [RhCl(n)(H2O)(6-n)](3-n) complex anions in hydrochloric acid solution as a unique 'NMR finger-print' for unambiguous speciation

A detailed analysis of the (35)Cl/(37)Cl isotope effects observed in the 19.11 MHz (103)Rh NMR resonances of [RhCl(n)(H(2)O)(6-n)](3-n) complexes (n=3-6) in acidic solution at 292.1K, shows that the 'fine structure' of each (103)Rh resonance can be understood in terms of the unique isotopologue and in certain instances the isotopomer distribution in each complex. These (35)Cl/(37)Cl isotope effects in the (103)Rh NMR resonance of the [Rh(35/37)Cl(6)](3-) species manifest only as a result of the statistically expected (35)Cl/(37)Cl isotopologues, whereas for the aquated species such as for example [Rh(35/37)Cl(5)(H(2)O)](2-), cis-[Rh(35/37)Cl(4)(H(2)O)(2)](-) as well as the mer-[Rh(35/37)Cl(3)(H(2)O)(3)] complexes, additional fine-structure due to the various possible isotopomers within each class of isotopologues, is visible. Of interest is the possibility of the direct identification of stereoisomers cis-[RhCl(4)(H(2)O)(2)](-), trans-[RhCl(4)(H(2)O)(2)](-), fac-[RhCl(3)(H(2)O)(3)] and mer-[RhCl(3)(H(2)O)(3)] based on the (103)Rh NMR line shape, other than on the basis of their very similar δ((103)Rh) chemical shift. The (103)Rh NMR resonance structure thus serves as a novel and unique 'NMR-fingerprint' leading to the unambiguous assignment of [RhCl(n)(H(2)O)(6-n)](3-n) complexes (n=3-6), without reliance on accurate δ((103)Rh) chemical shifts.

[Pt@Pb12]2– — A challenging system for relativistic density functional theory calculations of 195Pt and 207Pb NMR parameters

We report computations of NMR chemical shifts and indirect spin-spin coupling constants (J couplings) for the [Pt@Pb12]2– “superatom”. The system is strongly influenced by relativistic effects. The Pt–Pb coupling constant is predicted to be negative, with its magnitude being in reasonable agreement with experiment. Pt and Pb chemical shifts also agree reasonably well with experiment. The Pb shielding tensor is strongly anisotropic, with a large deshielding principal component dominated by magnetic coupling between frontier orbitals of the cluster that resemble atomic g orbitals. The NMR parameters are sensitive to approximations made in the computations and require the inclusion of spin-orbit coupling in the theoretical model to achieve reliable results. Computing the NMR parameters of the compact [Pt@Pb12]2– system with its many electrons proves to be a challenging test case for relativistic density functional methods.