Metal Complexation for the Rational Design of Gemcitabine Formulations in Cancer Therapy

Nanoformulation of chemotherapies represents a promising strategy to enhance outcomes in cancer therapy. Gemcitabine is a chemotherapeutic agent approved by the Food and Drug Administration for the treatment of various solid tumors. Nevertheless, its therapeutic effectiveness is constrained by its poor metabolic stability and pharmacokinetic profile. Nanoformulations of gemcitabine in lipid and polymer nanocarriers usually lead to poor loading capability and an inability to effectively control its release profile due to the physicochemical characteristics of the drug and matrices. Here, we propose metal-gemcitabine complexation with biorelevant metal cations as a strategy to alter the properties of gemcitabine in a noncovalent manner, paving the way for the development of novel nanoformulations. A speciation study on gemcitabine and Mn2+, Zn2+, and Ca2+ was performed with the aim of investigating the extent of the interaction between the drug and the proposed metal cations, and selecting the best conditions of temperature, pH, and drug-to-metal molar ratio that optimize such interactions. Also, a series of density functional theory calculations and spin-polarized ab initio molecular dynamics simulations were carried out to achieve insights on the atomistic modalities of these interactions. Mn2+-gemcitabine species demonstrated the ability to maintain gemcitabine's biological activity in vitro. The scientific relevance of this study lies in its potential to propose metal-gemcitabine as a valuable strategy for developing nanoformulations with optimized quality target product profiles. The work is also clinically relevant because it will lead to improved treatment outcomes, including enhanced efficacy and pharmacokinetics, decreased toxicity, and new clinical possibilities for this potent therapeutic molecule.

Structure and size of complete hydration shells of metal ions and inorganic anions in aqueous solution

The structures of nine hydrated metal ions in aqueous solution have been redetermined by large angle X-ray scattering to obtain experimental data of better quality than those reported 40-50 years ago. Accurate M-OI and M-(OI-H)⋯OII distances and M-OI(H)⋯OII bond angles are reported for the hydrated magnesium(II), aluminium(III), manganese(II), iron(II), iron(III), cobalt(II), nickel(II), copper(II) and zinc(II) ions; the subscripts I and II denote oxygen atoms in the first and second hydration sphere, respectively. Reported structures of hydrated metal ions in aqueous solution are summarized and evaluated with emphasis on a possible relationship between M-OI-OII bond angles and bonding character. Metal ions with high charge density have M-OI-OII bond angles close to 120°, indicative of a mainly electrostatic interaction with the oxygen atom in the water molecule in the first hydration shell. Metal ions forming bonds with a significant covalent contribution, as e.g. mercury(II) and tin(II), have M-OI-OII bond angles close to 109.5°. This implies that they bind to one of the free electron pairs in the water molecule. Comparison of M-O bond distances of hydrated metal ions in the solid state with one hydration shell, and in aqueous solution with in most cases at least two hydration shells, shows no significant differences. On the other hand, the X-O bond distance in hydrated oxoanions increases by ca. 0.02 Å in aqueous solution in comparison with the corresponding X-O distance in the solid state. A linear correlation is observed between volume, calculated from the van der Waals radius of the hydrated ion, and the ionic diffusion coefficient in aqueous solution. This correlation strongly indicates that monovalent metal ions, except lithium and silver(I), and singly-charged monovalent oxoanions have a single hydration shell. Divalent metal ions, bismuth(III) and the lanthanoid(III) and actinoid(III) ions have two hydration shells. Trivalent transition and tetravalent metal ions have two full hydration shells and portion of a third one. Doubly charged oxoanions have one well-defined hydration shell and an ill-defined second one.

Identification of an Additional Metal-Binding Site in Human Dipeptidyl Peptidase III

Dipeptidyl peptidase III (DPP III, EC 3.4.14.4) is a monozinc metalloexopeptidase that hydrolyzes dipeptides from the N-terminus of peptides consisting of three or more amino acids. Recently, DPP III has attracted great interest from scientists, and numerous studies have been conducted showing that it is involved in the regulation of various physiological processes. Since it is the only metalloenzyme among the dipeptidyl peptidases, we considered it important to study the process of binding and exchange of physiologically relevant metal dications in DPP III. Using fluorimetry, we measured the Kd values for the binding of Zn2+, Cu2+, and Co2+ to the catalytic site, and using isothermal titration calorimetry (ITC), we measured the Kd values for the binding of these metals to an additional binding site. The structure of the catalytic metal's binding site is known from previous studies, and in this work, the affinities for this site were calculated for Zn2+, Cu2+, Co2+, and Mn2+ using the QM approach. The structures of the additional binding sites for the Zn2+ and Cu2+ were also identified, and MD simulations showed that two Cu2+ ions bound to the catalytic and inhibitory sites exchanged less frequently than the Zn2+ ions bound to these sites.

Study on ionic association behavior in sodium nitrate solution

Raman spectroscopy combined with component analysis and molecular dynamics simulation were used to study chemical species and their transformation in aqueous sodium solutions. Study shows that the characteristic vibrational frequency of nitrate ions (ν₁-NO₃^-) blue-shifted from 1043.9 to 1046.9 cm^-1, and the full width at half maximum increased from 6.8 to 10.8 cm^-1 as the concentration increasing. When water/salt molar ratio (WSR) > 30, the relative concentration (RC) of free hydrated ions and solvent shared ion pair accounts for the vast majority, and there is almost no contact ion pair in solution. When WSR less than 30, due to the continuous reduction of the number of water molecules, the hydrated water molecules around the sodium ions and nitrate ions begin to decrease, and solvent shared ion pair or contact ion pair gradually forms. Sodium ions and nitrate ions mainly exist in a monodentate coordination. When WSR > 160, both the relative concentration of contact ion pair and complex structure is close to 0. This work proves that a lower RC of complex structure in solution, a smaller supersaturation of the solution is achieved, meaning aqueous sodium nitrate solution is easier to nucleate crystals.

Balanced Interfacial Ion Concentration and Migration Steric Hindrance Promoting High-Efficiency Deposition/Dissolution Battery Chemistry

The solid-liquid transition reaction lays the foundation of electrochemical energy storage systems with high capacity, but realizing high efficiency remains a challenge. Herein, in terms of thermodynamics and dynamics, this work demonstrates the significant role of both interfacial H⁺ concentration and Mn²⁺ migration steric hindrance for the high-efficiency deposition/dissolution chemistry of zinc-manganese batteries. Specially, the introduction of formate anions can buffer the generated interfacial H⁺ to stabilize interfacial potential according to the Nernst equation, which stimulates high capacity. Compared with acetate and propionate anions, the formate anion also provides high adsorption density on the cathode surface to shield the electrostatic repulsion due to the small spatial hindrance. Particularly for the solvated Mn²⁺ , the formate-anion-induced lower energy barrier of the rate-determining step during the step-by-step desolvation process results in lower polarization and higher electrochemical reversibility. In situ tests and theoretical calculations verify that the electrolyte with formate anions achieve a good balance between ion concentration and ion-migration steric hindrance. It exhibits both the high energy density of 531.26 W h kg^-1  and long cycle life of more than 300 cycles without obvious decay.

Vanadium oxides obtained by chimie douce reactions: The influences of transition metal species on crystal structures and electrochemical behaviors in zinc-ion batteries

Rechargeable aqueous zinc-ion batteries (RAZIBs) have received increasing attention due to cost-effectiveness and inherent safety. A wide variety of advanced cathode materials have been revealed with promising performance in RAZIBs. However, these materials usually require sophisticated procedures at high temperatures, which greatly limit further practical application. Herein, a chimie douce approach is adopted to prepare vanadium oxides from V₂O₅ suspension with the addition of various transition metal cations (Mn²⁺, Zn²⁺, Ag⁺, and Fe³⁺) by simple liquid-solid mixing under ambient conditions. For the cases of Mn²⁺ and Zn²⁺, the dissolution-recrystallization process takes place leading to layered Mn_0.31V₃O₇·1.40H₂O (MnVO) and Zn_0.32V₃O₇·1.52H₂O (ZnVO). The use of Ag⁺ forms tunneled Ag_0.33V₂O₅ (AgVO), and the present of Fe³⁺ stays mainly unreacted V₂O₅. The underlying reaction chemistries are proposed, for which the pH values of precursor solutions are found to be a key factor. Among the prepared materials, layered vanadium oxides exhibit promising battery performance. Particularly, MnVO delivers 340 and 217 mAh g^-1 at 1 and 8 A g^-1, respectively. A specific capacity of 164 mAh g^-1 can be retained after 500 cycles at 1 A g^-1. By contrast, AgVO and FeVO demonstrate inferior performance with retaining only 89 and 20 mAh g^-1 after 500 cycles.

Intrinsic Dependence of Groundwater Cation Hydraulic and Concentration Features on Negatively Charged Thin Composite Nanofiltration Membrane Rejection and Permeation Behavior

Commercial nanofiltration membranes of different molecular weight cut-offs were tested on a pilot plant for the exploration of permeation nature of Ca, Mg, Mn, Fe, Na and ammonium ions. Correlation of transmembrane pressure and rejection quotient versus volumetric flux efficiency on nanofiltration membrane rejection and permeability behavior toward hydrated divalent and monovalent ions separation from the natural groundwater was observed. Membrane ion rejection affinity (MIRA) dimension was established as normalized TMP with regard to permeate solute moiety representing pressure value necessary for solute rejection change of 1%. Ion rejection coefficient (IRC) was introduced to evaluate the membrane rejection capability, and to indicate the prevailed nanofiltration partitioning mechanism near the membrane surface. Positive values of the IRC indicated satisfactory rejection efficiency of the membrane process and its negative values ensigned very low rejection affinity and high permeability of the membranes for the individual solutes. The TMP quotient and the efficiency of rejection for individual cations showed upward and downward trends along with flux utilization increase. Nanofiltration process was observed as an equilibrium. The higher the Gibbs free energy was, cation rejection was more exothermic and valuably enlarged. Low Gibbs free energy values circumferentially closer to endothermic zone indicated expressed ions permeation.

Complexation of Cyclic Glutarimidedioxime with Cerium: Surrogating for Redox Behavior of Plutonium

The complexation of cerium with glutarimidedioxime (H₂L) was studied by potentiometry, ESI-mass spectrometry, and cyclic voltammetry. Crystallization of [Ce^IV(HL)₃]⁺ from Ce³⁺ starting reactant indicated spontaneous complexation-driven oxidation. In aqueous solution, Ce³⁺ ions form three successive complexes, Ce(HL)²⁺, Ce(HL)₂⁺, and Ce(HL)₃ (where HL^- stands for the singly deprotonated ligand). The interactions of glutarimidedioxime with metal ions are dominantly electrostatic in nature, and the stability constants of the complexes are correlated to the charge density of metal ions. Extrapolations of predicted stability constant (log β) values were made from plotting effective charge and the ionic radius of the metal ion for Pu³⁺ and Pu⁴⁺. The stability constants of Pu^IV(HL)³⁺ and Pu^III(HL)²⁺ are estimated to be 27.74 and 19.75, respectively. The differences of stability constants mean that glutarimidedioxime selectively binds Pu⁴⁺ over Pu³⁺ by a factor of about 8 orders of magnitude, suggesting Pu⁴⁺ would be stabilized by chelation with glutarimidedioxime. The mechanism of reduction of Pu⁴⁺ to Pu³⁺ in acidic solution is explained by decomposition of glutarimidedioxime through acid hydrolysis rather than a chelation-driven mechanism.

Efficient Photocatalytic Degradation of Gaseous Benzene and Toluene over Novel Hybrid PIL@TiO2/m-GO Composites

In this work, the PIL (poly ionic liquid)@TiO2 composite was designed with two polymerized ionic liquid concentrations (low and high) and evaluated for pollutant degradation activity for benzene and toluene. The results showed that PIL (low)@TiO2 composite was more active than PIL (high)@TiO2 composites. The photodegradation rate of benzene and toluene pollutants by PIL (low)@TiO2 and PIL (high)@TiO2 composites was obtained as 86% and 74%, and 59% and 46%, respectively, under optimized conditions. The bandgap of TiO2 was markedly lowered (3.2 eV to 2.2 eV) due to the formation of PIL (low)@TiO2 composite. Besides, graphene oxide (GO) was used to grow the nano-photocatalysts’ specific surface area. The as-synthesized PIL (low)@TiO2@GO composite showed higher efficiency for benzene and toluene degradation which corresponds to 91% and 83%, respectively. The resultant novel hybrid photocatalyst (PIL@TiO2/m-GO) was prepared and appropriately characterized for their microstructural, morphology, and catalytic properties. Among the studied photocatalysts, the PIL (low)@TiO2@m-GO composite exhibits the highest activity in the degradation of benzene (97%) and toluene (97%). The ultimate bandgap of the composite reached 2.1 eV. Our results showed that the as-prepared composites hold an essential role for future considerations over organic pollutants.

Raman and ab initio analyses of ion pairs in concentrated K[B(OH)4] droplets

In this study, microscopic Raman spectroscopy and Ab initio quantum chemical calculation were used to determine the structural details of ion pairs and their transformation in concentrated K[B(OH)₄] droplets. The Raman experiment shows that the v_sym-B(OH)₄^- undergoes a downward shift with the decrease of WSR. The contact ion pairs (CIPs) change to solvent shared ion pairs when the molar water-to-solute ratio (WSR) is bigger than 6; CIPs are the dominant species when 1.33 < WSR < 6, where K⁺ bonds to [B(OH)₄^-] in bidentate form (CIP-II); the CIPs quickly dehydrate and associate to triple ion pairs (TIPs) when WSR < 5. Raman experiment and ab initio quantum chemical calculation show that TIPs are mainly present in "anionic" type such as {[B(OH)₄^-]K⁺[B(OH)₄^-](H₂O)_n}, where K⁺ bonds to two [B(OH)₄^-] in bidentate or/and tridentate form (TIP-a-II or/and TIP-a-III). When WSR <1.33, most TIPs convert to complex clusters such as chain-like structure. The remaining TIPs associate to six-membered ring structure [B₃O₃(OH)₄^-] and the relative content increases from 0 to 20% when the WSR ranges from 1.33 to 0.55.

Ab-initio investigation on ion-associated species and association process in Li[B(OH)4] solution

In this paper, the factors determining the spectroscopic characteristics of v_sym-B(OH)₄^- band including coupling effect, hydrogen bonding effect, and direct contact effect in Li[B(OH)₄] solutions are investigated by using ab initio calculation. The coupling effect between the liberations of water and [B(OH)₄^-] has a larger effect on v_sym-B(OH)₄^- in solvent-shared ion pair (SIP) and monodentate contact ion pair (MCIP), but the smaller effect in bidentate contact ion pair (BCIP). Water molecule tends to hydrate to the middle position between the first sphere of B(OH)₄^- and outer-sphere of [Li(H₂O)₄⁺] and has a different effect on v_sym-B(OH)₄^- in ion pairs. The direct contact effect and polarization effect lead to 19.7 cm^-1 red shift of v_sym-B(OH)₄^- in MCIP, and 0.4 cm^-1 blue shift in BCIP. The association process in Li[B(OH)₄] solution was also introduced by using Raman spectral evolution of v_sym -B(OH)₄^- in the dehydration process.

Complexation of Manganese with Glutarimidedioxime: Implication for Extraction Uranium from Seawater

The molecule of glutaroimidedioxime, a cyclic imidedioxime moiety that can form during the synthesis of the poly(amidoxime)sorbent and is reputedly responsible for the extraction of uranium from seawater. Complexation of manganese (II) with glutarimidedioxime in aqueous solutions was investigated with potentiometry, calorimetry, ESI-mass spectrometry, electrochemical measurements and quantum chemical calculations. Results show that complexation reactions of manganese with glutarimidedioxime are both enthalpy and entropy driven processes, implying that the sorption of manganese on the glutarimidedioxime-functionalized sorbent would be enhanced at higher temperatures. Complex formation of manganese with glutarimidedioxime can assist redox of Mn(II/III). There are about ~15% of equilibrium manganese complex with the ligand in seawater pH(8.3), indicating that manganese could compete to some degree with uranium for sorption sites.

Hydration and ion pair formation in aqueous Y(3+)-salt solutions

Raman spectra of aqueous yttrium perchlorate, triflate (trifluoromethanesulfonate), chloride and nitrate solutions were measured over a broad concentration range (0.198-3.252 mol L(-1)). The spectra range from low wavenumbers to 4200 cm(-1). A very weak mode at 384 cm(-1) with a full width at half height at 50 cm(-1) in the isotropic spectrum suggests that the Y(3+)- octa-aqua ion is thermodynamically stable in dilute perchlorate solutions (∼0.5 mol L(-1)) while in concentrated perchlorate solutions outer-sphere ion pairs and contact ion pairs are formed. The octa-hydrate, [Y(OH2)8](3+) was also detected in a 1.10 mol L(-1) aqueous Y(CF3SO3)3 solution. Furthermore, very weak and broad depolarized modes could be detected which are assigned to [Y(OH2)8](3+)(aq) at 100, 166, 234 and 320 cm(-1) confirming that a hexa-hydrate is not compatible with the hydrated species in solution. In yttrium chloride solutions contact ion pair formation was detected over the measured concentration range from 0.479-3.212 mol L(-1). The contact ion pairs in YCl3(aq) are fairly weak and disappear with dilution. At a concentration <0.2 mol L(-1) almost all complexes have disappeared. In YCl3 solutions, with additional HCl, chloro-complexes of the type [Y(OH2)8-nCln](+3-n) (n = 1,2) are formed. The Y(NO3)3(aq) spectra were compared with a spectrum of a dilute NaNO3 solution and it was concluded that in Y(NO3)3(aq) over the concentration range from 2.035-0.198 mol L(-1) nitrato-complexes [Y(OH2)8-n(NO3)ln](+3-n) (n = 1,2) are formed. The nitrato-complexes are weak and disappear with dilution <0.1 mol L(-1). DFT geometry optimizations and frequency calculations are reported for both the yttrium-water cluster in the gas phase and the cluster within a polarizable continuum model in order to implicitly describe the presence of the bulk solvent. The bond distance and angle for the square antiprismatic cluster geometry of [Y(OH2)8](3+) with the polarizable dielectric continuum is in good agreement with data from recent structural experimental measurements. The DFT frequency of the Y-O stretching mode of the [Y(OH2)8](3+) cluster, in a polarizable continuum, is at 372 cm(-1) in satisfactory agreement with the experimental value.

Hydration and ion pair formation in common aqueous La(III) salt solutions--a Raman scattering and DFT study

Raman spectra of aqueous lanthanum perchlorate, triflate (trifluorosulfonate), chloride and nitrate solutions were measured over a broad concentration (0.121-3.050 mol L(-1)) range at room temperature (23 °C). A very weak mode at 343 cm(-1) with a full width at half height at 49 cm(-1) in the isotropic spectrum suggests that the nona-aqua La(III) ion is thermodynamically stable in dilute perchlorate solutions (∼0.2 mol L(-1)) while in concentrated perchlorate solutions outer-sphere ion pairs and contact ion pairs are formed. The La(3+) nona-hydrate was also detected in a 1.2 mol L(-1) La(CF3SO3)3(aq). In lanthanum chloride solutions chloro-complex formation was detected over the measured concentration range from 0.5-3.050 mol L(-1). The chloro-complexes in LaCl3(aq) are fairly weak and disappear with dilution. At a concentration <0.1 mol L(-1) almost all complexes disappeared. In LaCl3 solutions, with additional HCl, a series of chloro-complexes of the type [La(OH2)(9-n)Cln](+3-n) (n = 1-3) were formed. The La(NO3)3(aq) spectra were compared with a spectrum of a 0.409 mol L(-1) NaNO3(aq) and it was concluded that in La(NO3)3(aq) over the concentration range from 0.121-1.844 mol L(-1), nitrato-complexes, [La(OH2)(9-n)(NO3)n](+3-n) (n = 1, 2) were formed. These nitrato-complexes are quite weak and disappear with dilution <0.01 mol L(-1). DFT geometry optimizations and frequency calculations are reported for a lanthanum-nona-hydrate with a polarizable dielectric continuum in order to take the solvent into account. The bond distances and angles for the cluster geometry of [La(OH2)9](3+) with the polarizable dielectric continuum are in good agreement with data from recent structural experimental measurements and high quality simulations. The DFT frequency of the La-O stretching mode at 328.2 cm(-1), is only slightly smaller than the experimental one.

A Raman spectroscopic investigation of speciation in La2(SO4)3(aq)

Raman spectroscopic speciation studies were conducted of aqueous solutions of La(ClO₄)₃, La₂(SO₄)₃, and Na₂SO₄ in water and heavy water, in the terahertz frequency region (40–1400 cm⁻¹) and down to low concentrations (0.000263 mol L⁻¹).

Metal-ion effects on the polarization of metal-bound water and infrared vibrational modes of the coordinated metal center of Mycobacterium tuberculosis pyrazinamidase via quantum mechanical calculations

Mycobacterium tuberculosis pyrazinamidase (PZAse) is a key enzyme to activate the pro-drug pyrazinamide (PZA). PZAse is a metalloenzyme that coordinates in vitro different divalent metal cofactors in the metal coordination site (MCS). Several metals including Co²⁺, Mn²⁺, and Zn²⁺ are able to reactivate the metal-depleted PZAse in vitro. We use quantum mechanical calculations to investigate the Zn²⁺, Fe²⁺, and Mn²⁺ metal cofactor effects on the local MCS structure, metal–ligand or metal–residue binding energy, and charge distribution. Results suggest that the major metal-dependent changes occur in the metal–ligand binding energy and charge distribution. Zn²⁺ shows the highest binding energy to the ligands (residues). In addition, Zn²⁺ and Mn²⁺ within the PZAse MCS highly polarize the O–H bond of coordinated water molecules in comparison with Fe²⁺. This suggests that the coordination of Zn²⁺ or Mn²⁺ to the PZAse protein facilitates the deprotonation of coordinated water to generate a nucleophile for catalysis as in carboxypeptidase A. Because metal ion binding is relevant to enzymatic reaction, identification of the metal binding event is important. The infrared vibrational mode shift of the C=Nε (His) bond from the M. tuberculosis MCS is the best IR probe to metal complexation.

Vibrational spectroscopic studies and DFT calculations on NaCH3CO2(aq) and CH3COOH(aq)

NaCH₃CO₂(aq) and CH₃COOH(aq) were studied using Raman and infrared spectroscopy over a large concentration range, in the terahertz region and up to 4000 cm⁻¹. Band assignments for CH₃CO₂⁻(aq) and CH₃COOH(aq) were carried out under guidance of DFT frequencies.