Magnetic properties of six-coordinated high-spin cobalt(II) complexes: Theoretical background and its application

In this contribution we study and analyse the influence of the different parameters involved in the magnetic susceptibility of six-coordinated high-spin Co(II) complexes. We propose an empirical expression to fit the magnetic susceptibility of polycrystalline samples of mononuclear Co(II) complexes with an axial distortion, the variable parameters being Δ (axial distortion), α (orbital reduction factor) and λ (spin–orbit coupling). This expression avoids solving the 12 × 12 matrix associated to the distortion of the ⁴T_1g term. In order to take into account the magnetic coupling (J) in the polynuclear Co(II) complexes, a perturbational approach is proposed to describe their magnetic susceptibility in the whole temperature range (2–300 K) as a function of J, Δ, α and λ. This approach is valid in the limit of the weak magnetic coupling as compared to the spin–orbit coupling, |J/λ| < 0.1. The model allows the treatment of each cobalt(II) ion in axial symmetry as an effective spin S_eff = 1/2. That causes a drastic reduction of the matrix size of the polynuclear compounds from 12ⁿ × 12ⁿ to 2ⁿ × 2ⁿ, n being the number of Co(II) ions in the complex. The main advantage of the model is to make possible the fit of the magnetic susceptibility data of those polynuclear Co(II) complexes whose high nuclearity involved intractable matrices.     

Origin of magnetization tunneling in single-molecule magnets as determined by single-crystal high-frequency EPR

We review an extensive body of single-crystal high-frequency electron paramagnetic resonance (HFEPR) data in order to determine the transverse spin Hamiltonian parameters that control the tunneling of the direction of magnetization in a variety of integer and half-integer-spin single-molecule magnets (SMMs). The SMMs studied are members of the following families: S = 9/2 [Mn₄O₃Cl]⁶⁺; S = 5 [Mn₃NiO₄]⁶⁺; S = 6 [Mn₃ZnO₄]⁶⁺; and S = 4 [Ni₄(OR)₄]⁴⁺. HFEPR spectra for the half-integer S = 9/2 Mn₄ complexes that have C₃ symmetry do not provide measurable evidence for transverse spin Hamiltonian terms. This finding is consistent with the relatively large coercive field seen in the magnetization hysteresis loops for these complexes. On the other hand, a low symmetry S = 9/2 complex exhibits a much faster rate of ground-state magnetization tunneling, in agreement with HFEPR spectra for a powder sample that gives a rhombic zero-field splitting (ZFS) parameter of E = 0.140 cm^?1. The S = 5 Mn₃Ni systems exhibit magnetization tunneling that is much faster than seen for the high-symmetry S = 9/2 Mn₄ complexes. This can be attributed to their integer-spin ground states. Like the C₃ symmetry Mn₄ SMMs, the HFEPR spectra for high-symmetry Mn₃Ni complexes do not provide measurable evidence for transverse ZFS terms. However, the spectra exhibit broad peaks, suggesting distributions in the local molecular environments brought about by disordered solvate molecules. This disorder likely explains the fast tunneling in the high-symmetry S = 5 Mn₃Ni systems, though one cannot rule out fourth- (and higher-) order interactions that cannot be detected by HFEPR due to the broad resonances. The one S = 6 Mn₃Zn complex shows an even faster rate of tunneling compared to the isostructural S = 5 Mn₃Ni complex. Finally, the S = 4 [Ni(hmp)(dmb)Cl]₄ complex provides unique insights into the origin of fourth- (and higher-) order interactions found for many SMMs on the basis of analysis using a giant spin Hamiltonian (GSH) approximation. We conclude that the fourth-order anisotropy found for the S = 4 ground state of [Ni(hmp)(dmb)Cl]₄ originates from the second-order ZFS interactions associated with the individual Ni^II ions, but only as a result of higher-order processes that occur via S-mixing between the ground state and higher-lying (S < 4) spin-multiplets. The S-mixing is relatively strong in this system because of comparable exchange and anisotropy energy scales. The relatively fast tunneling is a direct consequence of this S-mixing, as opposed to any intrinsic fourth-order (spin–orbit) anisotropy associated with Ni^II.     

Muon spin relaxation study of manganese hydroxy squarate

Muon spin relaxation has been used to study the magnetic phase transition and spin dynamics above T_c in Mn₂(OH)₂(C₄O₄). These studies confirm previous findings of a transition to long range order, providing a more accurate determination of T_c = 12.5 K as well as indicating short range order at temperatures above the phase transition. The muon measurements are insensitive to the presence of a small quantity of manganese carbonate in the sample that tend to dominate bulk magnetic susceptibility experiments.     

Synthesis,chiral resolution,and determination of novel furan lignan derivatives with potent anti-tumor activity

A kind of racemic furan lignans were synthesized via a novel route, and two optical isomers were obtained through a selective hydrolization. The absolute configurations were determined by circular dichroism spectroscopy after separated through a preparative column. The different activities of isomers and the racemates were evaluated on QGY-7701 and HeLa cell lines, and compound 2c showed the best activity on QGY-7701 and HeLa cell lines with IC₅₀ 12 μM and 13 μM, respectively.     

Gellan gel beads containing magnetic nanoparticles: An effective biosorbent for the removal of heavy metals from aqueous system

This study describes an efficient adsorbent consisting of magnetic Fe₃O₄ and gellan gum, which couples magnetic separation with ionic exchange for heavy metal removal. Adsorption kinetics analysis showed that the adsorption capacities were in an order of Pb²⁺ > Cr³⁺ > Mn²⁺. Different experimental parameters studies indicated that adsorbent dosage, initial metal concentration, temperature and initial pH played important roles in adsorption process. Additionally, the Freundlich model gave a better fit to the experimental data than the Langmuir model. Chemical analysis of calcium ions released into the bulk solutions demonstrated that carboxyl group is critical for binding Pb²⁺, Mn²⁺ and Cr³⁺. Furthermore, a high desorption efficiency was obtained by sodium citrate.     

Tuning magnetic properties using targeted structural distortion: New additions to a family of Mn6 single-molecule magnets

We report the synthesis and magnetic properties of three hexametallic Mn clusters: [Mn₆O₂(Et-sao)₆(O₂C-Naphth)₂(EtOH)₄(H₂O)₂] (1) (HO₂C-Naphth = 1-naphthoic acid, Et-saoH₂ = 2-hydroxyphenylpropanone oxime), [Mn₆O₂(Et-sao)₆(O₂C-Anthra)₂(EtOH)₄(H₂O)₂] · 0.66EtOH · 0.33H₂O (HO₂C-Anthra = anthracene-9-carboxylic acid) (2 · 0.66EtOH · 0.33H₂O) and [Mn₆O₂(Et-sao)₆(O₂CPhCCH)₂(EtOH)₄(H₂O)₂] · 1.7EtOH · 0.3H₂O (HO₂CPhC  CH = 4-ethynylbenzoic acid) (3 · 1.7EtOH · 0.3H₂O). Clusters 1–3 exhibit ferromagnetic exchange between all six Mn^III centres resulting in S = 12 ground spin states. Ac magnetic susceptibility and single crystal micro-SQUID measurements on 1–3 confirm SMM behaviour with barriers to magnetisation reversal of 60.12 (1), 60.10 (2) and 66.79 (3) K.     

Dinuclear manganese complexes containing 1,4-dimethyl-1,4,7-triazacyclononane ligands as well as carboxylato and oxo bridges

The reaction of 1,4-dimethyl-1,4,7-triazacyclononane (L-Me₂) with MnCl₂ · 4H₂O in acetonitrile gives, in the presence of sodium formate, hydrogen peroxide, triethylamine and KPF₆, the dinuclear Mn(III)–Mn(IV) complex cation [(L-Me₂)₂Mn₂(O)₂(OOCH)]²⁺ (1) which crystallises as the hexafluorophosphate salt.The analogous reaction with sodium benzoate, however, yields the dinuclear Mn(III)–Mn(III) complex cation [(L-Me₂)₂Mn₂(O)(OOCC₆H₅)₂]²⁺ (2), isolated also as the hexafluorophosphate salt.In the case of sodium acetate, both cations, the Mn(III)–Mn(IV) complex [(L-Me₂)₂Mn₂(O)₂(OOCCH₃)]²⁺ (3) and the known Mn(III)–Mn(III) complex [(L-Me₂)₂Mn₂(O)(OOCCH₃)₂]²⁺ (4) are available, depending upon the molar ratio.The single-crystal X-ray structure analyses show for the green crystals of [1][PF₆]_1.5[Cl]_0.5 · 1.5 H₂O and [3][PF₆]₂ · (CH₃)₂CO, a Mn–Mn distance of 2.620(2) and 2.628(4) Å, respectively, while for the red-violet crystal of [4][PF₆]₂, a Mn–Mn distance of 3.1416(8) Å is observed.All four compounds show catalytic activity for the oxidation of isopropanol with hydrogen peroxide in water and in acetonitrile to give acetone in the presence of oxalic or ascorbic acid as co-catalysts.     

Effect of the metal dilution on the thermal and light-induced spin transition in [FexMn1−x(bpp)2](NCSe)2: When T(LIESST) reaches T1/2

The thermal and light-induced spin transition in [Fe_xMn_1?x(bpp)₂](NCSe)₂ (bpp = 2,6-bis(pyrazol-3-yl)pyridine) has been investigated by magnetic susceptibility, photomagnetism and diffuse reflectivity measurements. These complexes display a thermal spin transition and exhibit the light-induced excited spin state trapping (LIESST) effect at low temperature. For each mixed-crystal system, the thermal spin transition temperature, T_1/2, and the relaxation temperature of the photo-induced high-spin state, T(LIESST), have been systematically determined. It appears that T_1/2 decreases with the metal dilution while T(LIESST) remains unchanged, suggesting that the two interconversion processes are controlled by different factors; i.e. the photomagnetic properties are governed at the molecular scale and the thermal spin crossover regime is affected by both the ligand field and crystal packing effects. For highly metal-diluted complex with x < 0.2, it is found that when T_1/2 reaches the T(LIESST), the complex remains HS on the whole range of temperature.     

A new fused tetracyclic heterocyclic antioxidant from Serratia sp. PAMC 25557

A new fused tetracyclic heterocyclic compound, (4bR,10bR)-4b-hydroxy-10b,12-dihydrodibenzo[c,h][2,6]naphthyridine-5,11(4bH,6H)-dione (1), and a known compound, butyl 2-[(benzoyloxy)methyl]benzoate, spatozoate 2, were isolated from the broth culture of Serratia sp. PAMC 25557. The structure of 1 was determined by analyzing spectroscopic data. Compound 1 did not exhibit antimicrobial activity against Escherichia coli, Staphylococcus aureus, or Candida albicans. In addition, up to 100 μg/ml compound 1 did not show any toxicity against Artemia salina larvae. However, compound 1 showed DPPH free radical scavenging activity (IC₅₀ = 16.7 ± 0.34 μg/ml). This was the first report of spatozoate isolation from bacterial sources.     

Synthesis,crystal structure and magnetic properties of the spin crossover system [Fe(pq)3]2+

Three new compounds formulated (ClO₄)₂[Fe(pq)₃] (1), (BF₄)₂[Fe(pq)₃] · EtOH (2) and {(ClO₄)[MnCr(C₂O₄)₃][Fe(pq)₂(H₂O)₂]} (3), where pq is 2,2′-pyridylquinoline, have been synthesised and characterised. Despite the different crystal packing exhibited by 1 and 2, the cationic species [Fe(pq)₃]²⁺ are structurally quite similar. At 293 K, the Fe–N bond lengths are characteristic of the iron(II) in the high-spin state. In contrast to 1, 2 undergoes a continuous spin transition. Indeed, at 95 K its structure experiences a noticeable change in the Fe–N bonds and angles, i.e. the Fe–N bonds shorten by 0.194 Å on the average. The magnetic behaviour confirms that 1 is fully high-spin in the 4–300 K temperature range while 2 shows a spin transition centred at T_1/2 = 150 K. The corresponding enthalpy, entropy and interaction parameter are ΔH = 7.49 kJ mol^?1, ΔS = 50 J K^?1 mol^?1and Γ = 1.35 kJ mol^?1. Compound 3 has been obtained as a microcrystalline powder. The magnetic properties of 3 point at the occurrence of ferromagnetic coupling below 100 K and the onset of a ferromagnetic ordering below 10 K (Weiss constant equal to 6.8 K). The Mössbauer spectra of 3 show the occurrence of a magnetic order at T ? 4.2 K.     

Target Binding to S100B Reduces Dynamic Properties and Increases Ca2 +-Binding Affinity for Wild Type and EF-Hand Mutant Proteins

Mutations in the second EF-hand (D61N, D63N, D65N, and E72A) of S100B were used to study its Ca^2 + binding and dynamic properties in the absence and presence of a bound target, TRTK-12. With ^D63NS100B as an exception (^D63NK_D = 50 ± 9 μM), Ca^2 + binding to EF2-hand mutants were reduced by more than 8-fold in the absence of TRTK-12 (^D61NK_D = 412 ± 67 μM, ^D65NK_D = 968 ± 171 μM, and ^E72AK_D = 471 ± 133 μM), when compared to wild-type protein (^WTK_D = 56 ± 9 μM). For the TRTK-12 complexes, the Ca^2 +-binding affinity to wild type (^WT + TRTKK_D = 12 ± 10 μM) and the EF2 mutants was increased by 5- to 14-fold versus in the absence of target (^{D61N + TRTK}K_D = 29 ± 1.2 μM, ^{D63N + TRTK}K_D = 10 ± 2.2 μM, ^{D65N + TRTK}K_D = 73 ± 4.4 μM, and ^{E72A + TRTK}K_D = 18 ± 3.7 μM). In addition, R_ex, as measured using relaxation dispersion for side‐chain ¹⁵N resonances of Asn63 (^D63NS100B), was reduced upon TRTK-12 binding when measured by NMR. Likewise, backbone motions on multiple timescales (picoseconds to milliseconds) throughout wild type, ^D61NS100B, ^D63NS100B, and ^D65NS100B were lowered upon binding TRTK-12. However, the X-ray structures of Ca^2 +-bound (2.0 Å) and TRTK-bound (1.2 Å) ^D63NS100B showed no change in Ca^2 + coordination; thus, these and analogous structural data for the wild-type protein could not be used to explain how target binding increased Ca^2 +-binding affinity in solution. Therefore, a model for how S100B–TRTK‐12 complex formation increases Ca^2 + binding is discussed, which considers changes in protein dynamics upon binding the target TRTK-12.     

Rational enhancement of the coordination capability of Ru(III)(salen)-nitronyl nitroxide building block: A step towards 2p–3d–4d magnetic edifices

The reaction of [Ru(salen)(PPh₃)Cl] and the 5-imidazol-substituted nitronyl nitroxide radical (NIT-(5)ImH) yields the [Ru(salen)(PPh₃)(NIT-(5)ImH)](ClO₄) (1) complex which has been characterized by single crystal X-ray diffraction. This analysis reveals that the Ru(III) ion is coordinated to a tetradentate salen^2? ligand in equatorial positions while one PPh₃ ligand and one NIT-(5)ImH radical are coordinated in axial positions. This led to Ru^III ions in tetragonally elongated octahedral geometry. From the magnetic point of view ferromagnetic intramolecular interaction (J₁ = +2.47 cm^?1) have been found between the Ru(III) ion and the coordinated NIT-(5)ImH while no significant intermolecular antiferromagnetic interactions are observed at low temperature leading to a ground spin state S = 1. The absence of intermolecular magnetic interaction is explained by considering the crystal packing of (1) where the [Ru(salen)(PPh₃)(NIT-(5)ImH)]⁺ moieties are relatively well isolated. This has to be compared with the situation observed in the previously reported [Ru(salen)(PPh₃)-(NIT)]⁺ compound (2) where ferromagnetic Ru^III–NIT interaction were identified and the crystal packing generate intermolecular antiferromagnetic interactions that complicated the study. The analysis of this compound confirms the rather isotropic g values that were found of (2) and of [Ru(salen)(PPh₃)(N₃)], (3) a radical-free analogue. Moreover it is also a step towards extended structures based on Ru^III–NIT moieties since this compound possesses a free bischelating site likely to coordinate additional metallic ions.     

Lanthanide-containing and bridged polyoxometalate chains: Syntheses,crystal structures and magnetic properties

Two lanthanide-decorated polyoxometalates K[Ln₂(α-SiW₁₁O₃₉)(H₂O)₁₁] (Ln = La, Ce) have been successfully synthesized and characterized with single-crystal X-ray diffraction, IR spectroscopy and thermogravimetric analysis. The two compounds have analogy structures, which consist of one-dimensional chains based on [α-SiW₁₁O₃₉]⁸⁻ building blocks. The chains are further connected to a two-dimensional layer by potassium ions. The magnetic studies of compound 1 demonstrate a ferromagnetic interaction in 1.     

Significant impact of divalent metal ions on the fidelity,sugar selectivity,and drug incorporation efficiency of human PrimPol

Human PrimPol is a recently discovered bifunctional enzyme that displays DNA template-directed primase and polymerase activities. PrimPol has been implicated in nuclear and mitochondrial DNA replication fork progression and restart as well as DNA lesion bypass. Published evidence suggests that PrimPol is a Mn²⁺-dependent enzyme as it shows significantly improved primase and polymerase activities when binding Mn²⁺, rather than Mg²⁺, as a divalent metal ion cofactor. Consistently, our fluorescence anisotropy assays determined that PrimPol binds to a primer/template DNA substrate with affinities of 29 and 979 nM in the presence of Mn²⁺ and Mg²⁺, respectively. Our pre-steady-state kinetic analysis revealed that PrimPol incorporates correct dNTPs with 100-fold higher efficiency with Mn²⁺ than with Mg²⁺. Notably, the substitution fidelity of PrimPol in the presence of Mn²⁺ was determined to be in the range of 3.4 × 10⁻² to 3.8 × 10⁻¹, indicating that PrimPol is an error-prone polymerase. Furthermore, we kinetically determined the sugar selectivity of PrimPol to be 57–1800 with Mn²⁺ and 150–4500 with Mg²⁺, and found that PrimPol was able to incorporate the triphosphates of two anticancer drugs (cytarabine and gemcitabine), but not two antiviral drugs (emtricitabine and lamivudine).     

Purification and biochemical characterization of angiotensin I-converting enzyme (ACE) from ostrich lung: The effect of 2,2,2-trifluoroethanol on ACE conformation and activity

This work reports the purification and biochemical characterization of angiotensin I-converting enzyme (ACE) from ostrich (Struthio camelus) lung. The molecular weight of the purified enzyme was approximately evaluated to be 200 kDa and the maximum enzyme activity was observed at pH 7.5. The enzyme activity was increased by detergents of Triton X-100 (0.01%), cetyltrimethylammonium bromide (CTAB) (0.1 and 1 mM) and sodium dodecyl sulfate (SDS) (0.1 mM), while decreased by Triton X-100 (1% and 10%) and SDS (1 mM and 10 mM). The secondary and tertiary structure and activity of ACE in the absence and presence of trifluoroethanol (TFE) were investigated using circular dichroism, fluorescence quenching and UV–visible spectroscopy, respectively. Our results revealed that TFE stabilizes ACE at low concentrations, while acts as a denaturant at higher concentration (20%). The K_m, K_cat and K_cat/K_m values of ostrich ACE towards FAPGG were 0.8 × 10^?4 M, 59,240 min^?1 and 74 × 10⁷ min^?1 M^?1, respectively. The values of IC₅₀ and K_i for captopril were determined to be 36.5 nM and 16.6 nM, respectively. In conclusion, ostrich lung ACE is a new enzyme which could be employed as a candidate for studying ACE structure and its natural or synthetic inhibitors.     

Pencitrin and pencitrinol,two new citrinin derivatives from an endophytic fungus Penicillium citrinum salicorn 46

Two new citrinin derivatives, pencitrin (1) and pencitrinol (2), and a known compound citrinin (3), together with its two known dimers, penicitrinone A (4), penicitrinone E (5), were isolated from an endophytic fungus P. citrinum 46 derived from Salicornia herbacea Torr. by adding CuCl₂ into fermentation medium. The structures of these compounds were elucidated by detailed spectroscopic analysis, and the absolute configurations of 1, 4, and 5 were determined by comparison of quantum chemical time-dependent density functional theory (TDDFT) calculated and electronic circular dichroism (ECD) spectra. Compound 1 exhibited potent cytotoxic activities towards A549 human lung cancer cells and HepG2 human liver cancer cells with IC₅₀ values of 23.73 ± 3.61 and 35.73 ± 2.15 μM, respectively, whereas compound 5 showed moderate cytotoxic activities towards A549 and HepG2 cancer cells with IC₅₀ values of 40.47 ± 4.52 and 53.57 ± 3.24 μM, respectively. The results from the current research highlighted the effectiveness and usefulness of the pipeline to discover novel bioactive fungal secondary metabolites by modification of the culture media.     

Isolation,identification, and bioactivity of microbial metabolites of cyclopamine and its congeners

The biotransformation of cyclopamine (1) and its congeners (2, 3 and 4) by Cunninghamella echinulata (ACCC 30369) was investigated. The chemical structures of two new congeners (2 and 4) and nine new metabolites were elucidated by 1D NMR (¹H, ¹³C and DEPT), 2D NMR (COSY, HMBC, HSQC and NOESY) and HRESIMS analyses and further confirmed by X-ray diffraction studies. Among these compounds, 2 and 4 showed moderate cytotoxicity in HepG2 cells (2, IC₅₀ = 8.03 ± 1.92 μM) and A549 cells (4, IC₅₀ = 10.19 ± 2.18 μM). Conversely, the cytotoxicity of the nine metabolites was sharply reduced. Similar to 1, compound 4 induced a cyclopia phenotype in zebrafish embryos at 20 μM. Moreover, compound 4 was more stable than 1 in an acidic environment.     

Metal ion dependence of DNA cleavage by SepMI and EhoI restriction endonucleases

Most of type II restriction endonucleases show an absolute requirement for divalent metal ions as cofactors for DNA cleavage. While Mg²⁺ is the natural cofactor other metal ions can substitute it and mediate the catalysis, however Ca²⁺ (alone) only supports DNA binding. To investigate the role of Mg²⁺ in DNA cleavage by restriction endonucleases, we have studied the Mg²⁺ and Mn²⁺ concentration dependence of DNA cleavage by SepMI and EhoI. Digestion reactions were carried out at different Mg²⁺ and Mn²⁺ concentrations at constant ionic strength. These enzymes showed different behavior regarding the ions requirement, SepMI reached near maximal level of activity between 10 and 20 mM while no activity was detected in the presence of Mn²⁺ and in the presence of Ca²⁺ cleavage activity was significantly decreased. However, EhoI was more highly active in the presence of Mn²⁺ than in the presence of Mg²⁺ and can be activated by Ca²⁺. Our results propose the two-metal ion mechanism for EhoI and the one-metal ion mechanism for SepMI restriction endonuclease. The analysis of the kinetic parameters under steady state conditions showed that SepMI had a K_m value for pTrcHisB DNA of 6.15 nM and a V_max of 1.79 × 10^?2 nM min^?1, while EhoI had a K_m for pUC19 plasmid of 8.66 nM and a V_max of 2 × 10^?2 nM min^?1.     

Stimuli responsive polymorphism of C12NO/DOPE/DNA complexes: Effect of pH,temperature and composition

N,N-dimethyldodecylamine-N-oxide (C₁₂NO) is a surfactant that may exist either in a neutral or cationic protonated form depending on the pH of aqueous solutions. Using small angle X-ray diffraction (SAXD) we observe the rich structural polymorphism of pH responsive complexes prepared due to DNA interaction with C₁₂NO/dioleoylphosphatidylethanolamine (DOPE) vesicles and discuss it in view of utilizing the surfactant for the gene delivery vector of a pH sensitive system. In neutral solutions, the DNA uptake is low, and a lamellar L_α phase formed by C₁₂NO/DOPE is prevailing in the complexes at 0.2 ≤ C₁₂NO/DOPE < 0.6 mol/mol. A maximum of ~ 30% of the total DNA volume in the sample is bound in a condensed lamellar phase L_α^C at C₁₂NO/DOPE = 1 mol/mol and pH 7.2. In acidic conditions, a condensed inverted hexagonal phase H_II^C was observed at C₁₂NO/DOPE = 0.2 mol/mol. Commensurate lattice parameters, a_HC ≈ d_LC, were detected at 0.3 ≤ C₁₂NO/DOPE ≤ 0.4 mol/mol and pH = 4.9–6.4 suggesting that L_α^C and H_II^C phases were epitaxially related. While at the same composition but pH ~ 7, the mixture forms a cubic phase (Pn3m) when the complexes were heated to 80 °C and cooled down to 20 °C. Finally, a large portion of the surfactant (C₁₂NO/DOPE > 0.5) stabilizes the L_α^C phase in C₁₂NO/DOPE/DNA complexes and the distance between DNA strands (d_DNA) is modulated by the pH value. Both the composition and pH affect the DNA binding in the complexes reaching up to ~ 95% of the DNA total amount at acidic conditions.