The effect of organic ligand modification on protein corona formation of nanoscale metal organic frameworks

Nanoscale metal organic frameworks (NMOFs) have been widely reported in biomedical field for their unique porous structure and tunable multifunctionality. However, when administrated in vivo, the protein corona will be formed on the surface of NMOFs, significantly affecting their biodistribution, pharmacokinetics and drug release. Few studies paid attention to the protein corona formation process and its influencing factors of NMOFs. As a well-established strategy for altering structure features of NMOFs, the organic ligand modification may have effect on the protein corona formation process, which is to be investigated. In this study, the zirconium (Zr)-based UIO66 was chosen as model NMOFs, the organic ligand of which was modified with amino group (-NH₂) or carboxyl group (-COOH) to synthesize UIO66-NH₂ and UIO66-2COOH, respectively. Bovine serum albumin (BSA) was chosen as model protein to investigate the protein corona formation process of NMOFs. The current results showed that the -COOH modification remarkably enhanced the BSA adsorption on NMOFs while -NH₂ slightly decreased the protein binding affinity. These differences may be ascribed to the two different dominate protein corona formation modes, i.e., surface coating mode and porous embedded mode. The protein corona formation did not affect the crystal phase of NMOFs but increased the content of α-helix of BSA. Ultimately, upon protein corona formation, the cellular uptake of NMOFs was significantly affected. We believe our study will provide a new research paradigm to the design and applications of NMOFs.     

Changing the volume of a giant macrocycle: the swelling of the macrocycle with organic solvents

The novel tetrahedral macrocycles 1a-1c have been synthesized. Macrocycles 1a and 1c were revealed to have the property to increase in volume in solution by complexation between the macrocycle and the solvent molecules.     

Effect of the macrocycle chemical modification on the tetraphenylporphin basic properties

Russian Journal of General Chemistry - Basic properties of tetraphenylporphin and its derivatives with electron-donor and electron-acceptor substituents in the position 4 of meso-aryl fragments are...     

The influence of the macroring structure on the solvation of nonplanar porphyrins in organic solvents

An analysis of the calorimetric data and X-ray structure and fluorescence characteristics revealed the existence of a linear correlation between the enthalpies of solution of saddle-shaped nonplanar porphyrins (H₂P) in various solvents and the parameters of molecule nonplanarity in the crystalline state and in solution. This correlation is explained by a decrease in the energy of the crystal lattice of saddle-shaped nonplanar porphyrins compared with other distortion types. The deviation from the planar structure of macrocyclic compounds weakly influences the character of their solvation by organic solvents. Acid-base interaction accompanied by the formation of H-bonded associates of nonplanar H₂P with coordinating solvents decreases the relative solvation of their molecules by 5–10 kJ/mol. The extracoordination ability of nonplanar zinc porphyrinates is weakened compared with their planar analogues.     

Effect of the chemical modification of the tetrapyrrole macrocycle on the reactivity of porphyrins in complexation with Pt4+ and Pd2+ cations

The reactions of 5,10,15,20-tetraphenylporpine, 5,10,15-triphenyl-20-(4-hexadecanoxyphenyl)porphine, 5,10,15,20-tetra-(4-butoxyphenyl)porphine, and 2,3,7,8,12,13,17,18-ocaethylporphine with H₂PtCl₆ in boiling phenol and with PdCl₂ in boiling dimethylformamide are studied by spectrophotometry. Due to a strong electronic effect of the substituents, the reactivity of the tetrapyrrole macrocycle during porphyrinate formation changes by more than two orders of magnitude. Platinum(II) 5,10,15-triphenyl-20-(4-hexadecanoxyphenyl)porphinate and palladium(II) 5,10,15,20-tetra-(4-butoxyphenyl)porphinate have been synthesized and identified for the first time.     

Chelate effect and thermodynamics of metal complex formation in solution: a quantum chemical study

The accuracy of quantum chemical predictions of structures and thermodynamic data for metal complexes depends both on the quantum chemical methods and the chemical models used. A thermodynamic analogue of the Eigen-Wilkins mechanism for ligand substitution reactions (Model A) turns out to be sufficiently simple to catch the essential chemistry of complex formation reactions and allows quantum chemical calculations at the ab initio level of thermodynamic quantities both in gas phase and solution; the latter by using the conductor-like polarizable continuum (CPCM) model. Model A describes the complex formation as a two-step reaction: 1. [M(H2O)x](aq) + L(aq) <==>[M(H2O)x], L(aq); 2. [M(H2O)x], L(aq) <==>[M(H2O)(x-1)L],(H2O)(aq). The first step, the formation of an outer-sphere complex is described using the Fuoss equation and the second, the intramolecular exchange between an entering ligand from the second and water in the first coordination shell, using quantum chemical methods. The thermodynamic quantities for this model were compared to those for the reaction: [M(H2O)x](aq) + L(aq) <==>[M(H2O)(x-1)L](aq) + (H2O)(aq) (Model B), as calculated for each reactant and product separately. The models were tested using complex formation between Zn(2+) and ammonia, methylamine, and ethylenediamine, and complex formation and chelate ring closure reactions in binary and ternary UO(2)(2+)-oxalate systems. The results show that the Gibbs energy of reaction for Model A are not strongly dependent on the number of water ligands and the structure of the second coordination sphere; it provides a much more precise estimate of the thermodynamics of complex formation reactions in solution than that obtained from Model B. The agreement between the experimental and calculated data for the formation of Zn(NH(3))(2+)(aq) and Zn(NH(3))(2)(2+)(aq) is better than 8 kJ/mol for the former, as compared to 30 kJ/mol or larger, for the latter. The Gibbs energy of reaction obtained for the UO(2)(2+) oxalate systems using model B differs between 80 and 130 kJ/mol from the experimental results, whereas the agreement with Model A is better. The errors in the quantum chemical estimates of the entropy and enthalpy of reaction are somewhat larger than those for the Gibbs energy, but still in fair agreement with experiments; adding water molecules in the second coordination sphere improves the agreement significantly. Reasons for the different performance of the two models are discussed. The quantum chemical data were used to discuss the microscopic basis of experimental enthalpy and entropy data, to determine the enthalpy and entropy contributions in chelate ring closure reactions and to discuss the origin of the so-called "chelate effect". Contrary to many earlier suggestions, this is not even in the gas phase, a result of changes in translation entropy contributions. There is no simple explanation of the high stability of chelate complexes; it is a result of both enthalpy and entropy contributions that vary from one system to the other.     

A kinetic template effect in the metal ion-catalysed formation of arylphosphonium salts

Tertiary phosphines react with $\text{o}$-halobenzaldimines and $\text{o}$-bromodiarylazo compounds, under mild conditions in the presence of a metal ion catalyst, with displacement of the halogen to form the related arylphosphonium salts. The corresponding $\text{o}$-haloaryl compounds do not undergo these reactions.     

Fluorination of nitroform or its salts in organic solvents

Conclusions Fluorination of nitroform and its salts with elemental fluorine in the liquid phase has been achieved only in polar solvents.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 676–677, March, 1968.     

The central ion effect on the complex formation process in aqueous organic solvents. The Jahn-Teller effect in the Cu<Superscript>2+</Superscript> solutions

The complex formation of the Ni²⁺ and Cu²⁺ ions in aqueous solutions of 16 organic solvents of different nature (hydrophilic, hydrophobic, and neutral according to the dielectric data) was studied by the electronic spectroscopy. It was shown that in the case of nickel, the solvents under study behaved similarly (except for acetonitrile), i.e., were coordinated to the metal ion through oxygen, and turned weaker than water as regards the spectrochemical series. In the case of copper, the organic solvents exhibited their pronounced hydrophilic and hydrophobic nature. This is explained by nonequivalence of the equatorial and axial positions in the coordination polyhedron of copper due to the Jahn-Teller effect.     

Inorganic salts in non-aqueous solvents: Absorption spectra of transition metal salts in dimethylformamide

Absorption spectra of Cr, Mn, Fe, Co, Ni and Cu salts have been determined in dimethylformamide. In most cases the spectra differed considerably from those in aqueous solutions. The absorption maxima and the molar absorptivities of these salts in dimethylformamide are tabulated. The spectra are strongly influenced by the presence of certain anions, the order of decreasing effect being Cl^-, Oac^-, NO₃^- and ClO₄^-.     

UV photostability of metal phthalocyanines in organic solvents

Kinetic studies of photochemical reactions induced by UV radiation in solutions of metal phthalocyanines have been carried out to determine the factors which might have influenced the stability of photosensitized phthalocyanines. Complexes of the molecular type Mpc, M'(2)pc, and Lnpc(2) (where M = Li, Mg, Fe, Co, Zn, Pb; M'= Tl; Ln = rare earth; pc = phthalocyanine ligand, C(32)H(16)N(8)(2-)) were investigated in DMF, DMSO, and pyridine. Progressive decay of the phthalocyanine macrocycle due to absorption of UV light was observed. Phthalimide found in the final photolysis product may indicate some chemically bonded oxygen involved in the solid phthalocyanine material. Fluorescence lifetimes determined for the studied compounds (2.91-5.98 ns) have shown no particular relation to the stability of the excited macrocyclic system. The bonding strength of the photosensitized phthalocyanine moiety appears to rely on typical chemical factors, rather than on the properties of the excited states. Kinetics of the degradation process has proved to depend on the molecular structure of the complex and seems to be controlled by interactions of the macrocycle bridging nitrogen atoms with the solvent molecules. The use of electron acceptor solvents such as DMSO may enhance the molecular stability of phthalocyanines excited by UV radiation. Sandwich-type rare earth diphthalocyanines dissolved in DMSO displayed the highest photostability.     

Dynamic study of metal-ion incorporation into porphyrins based on the dynamic characterization of metal ions and on sitting-atop complex formation.

We succeeded in the detection of the sitting-atop (SAT) copper(II) complex of TPP (5,10,15,20-tetraphenylporphyrin) in acetonitrile (AN) as a solvent with a very low Br?nsted basicity, where two pyrrolenine nitrogens in the Cu(II)-SAT complex coordinate to the metal ion and two protons still remain on the pyrrole nitrogens. The structure parameters around the copper(II) ion in the Cu(II)-SAT complex, as determined by a fluorescent EXAFS method, suggest an axially elongated and equatorially distorted six-coordinate geometry. We measured the rates of the formation reaction of the SAT complexes for a series of transition metal(II) ions in AN using the stopped-flow technique. We propose the mechanism where there is a rapid deformation equilibrium of the porphyrin ring prior to the rate-determining step of the bond rupture of a coordinated solvent molecule on the metal(II) ion. Furthermore, we measured the rates of the deprotonation reaction of the Cu(II)-SAT complex by some Br?nsted bases and indicated that the rate-determining step is the attack of the base on the proton of the pyrrole nitrogen in the SAT complex. Finally, a unified mechanism relevant to the porphyrin metalation mechanism has been proposed.     

The atomization of metal chelates in chlorinated organic solvents in flame spectrometry

A study of the influence of organic solvents, particularly chlorinated hydrocarbons, on the atomization of metal-organic compounds is described. The results obtained show that chlorine and its compounds play in the flame an important role in the atomization of metal chelates. Increased amounts of chlorine in the solvent first reduce the absorption, which reaches a minimum, but then increases again, reaching the starting value at a defined amount of chlorine.     

Nonideal behavior of alkylammonium salts in organic solvents at elevated temperatures

Osmometric vapor-pressure-lowering measurements on toluene, butylbenzene, chlorobenzene, and chloronaphthalene solutions of several secondary, tertiary, and quaternary long-chain (at least five carbon atoms per chain) alkylammonium chlorides, bromides, thiocyanates, nitrates, and perrhenates in the temperature range between 50–130°C show an appreciable amount of molecular association. The extent (number of aggregated units) and/or the degree (size of aggregated units) of aggregation decreases with the number of carbon atoms per chain, the polarity of the solvent, and the temperature, but increases with the size of the anions and the solute concentration. The data were treated quantitatively in terms of activity coefficients via the Gibbs-Duhem relation and also in terms of specific oligomer formation. The latter treatment shows the salts to form a dimer and one (exceptionally two) higher oligomer, for which the association constants have been calculated.     

Enhancing solution-phase supramolecular interactions between monomeric porphyrins and [60]fullerene by simple chemical modification

The supramolecular interactions of N-methylporphyrin and iridium porphyrin with C₆₀ in toluene solution were investigated using NMR spectroscopy and absorption spectroscopy. Our results demonstrate that both the N-methylation and iridium metalation of porphyrin are effective means to enhance the binding affinity to C₆₀, resulting in 1:1 complexation for N-methylporphyrin/C₆₀ and 2:1 complexation for iridium porphyrin/C₆₀.     

The structure of the nickel—8-quinolinol complex in some organic solvents

The ultraviolet and visible absorption spectra of the nickel—8-quinolinol complex in chloroform are significantly affected by traces of water. Absorption spectra of the complex in mixed solvents, e.g. dioxane—water, dioxane—methanol and chloroform-methanol, and in chloroform solution containing water, pyridine, or 8-quinolinol are compared. An addition compound is formed in which the mole ratio of the nickel-8-quinolinol complex to the solvent or the base is 1:1 or 1:2. Polymerization occurs by mutual interaction between the nickel-8-quinolinol complexes. A degree of polymerization of 2.2 was obtained; this indicates that the binuclear compound predominates. The structure of the nickel—8-quinolinol complex in organic solvents is discussed.     

The influence of ZnO-Sensor modification by porphyrins on to the character of sensor response to volatile organic compounds

The influence of modification of semi conductive ZnO and SnO₂ sensors by porphyrins and their metal complexes on the parameters of sensor response to volatile organic compounds, ethanol, acetone and benzene, was analyzed. The concentration of volatile organic compounds (c _i ) varied in the range of 1–200 ppm. The sensor response was characterized by specific sensitivity γ _i = 100ΔR _i /R ₀ c _i , where ΔR _i = R _i − R ₀, R _i and R ₀ are measurable and initial resistance of the sensitive sensor layer correspondingly. It was established that the modification of sensors by porphyrins caused changes in sensor response and first of all decrease of ZnO sensor temperature at which the threshold of sensitivity is achieved (as used at this method c _i ^min = 0.1 ppm) from 300 to 100°C. It also caused a change in sing of the parameter γ, which was of importance for creating “electronic nose” sensor systems. It was shown also, that the modification of ZnO sensor by metal complexes of porphyrin did not change sensor response parameters.     

Electrochemistry of metal phthalocyanines in organic solvents at variable pressure

High-pressure electrochemical investigations of representative metallophthalocyanines in solution are reported. The selected systems were ZnPc, CoPc, FePc, and CoTNPc (Pc = phthalocyanine, TNPc = tetraneopentoxyphthalocyanine) in several donor solvents and (for CoTNPc) dichlorobenzene, with [Bu(4)N][ClO(4)] as supporting electrolyte and a conventional Pt electrode referred to Ag(+)(CH(3)CN)/Ag. Electrode reaction volumes deltaV(cell) for CoTNPc and ZnPc show that consecutive ring reductions result in progressive increases in electrostriction of solvent in accordance with Drude-Nernst theory. Reductions of the metal center in CoTNPc and CoPc, however, result in much less negative values of deltaV(cell) than would be expected by analogy with ring reductions of the same charge type. This is attributable to loss of axial ligands following the insertion of antibonding 3d(z)2 electrons on going from Co(III) to low-spin Co(II) and then Co(I). In the same vein, rate constants for reduction of Co(III) centers to Co(II) were an order of magnitude slower than those for other metal center or phthalocyanine ring reductions because of Franck-Condon restrictions. The volumes of activation deltaV(el) were invariably positive for all the electrode reactions and in most cases were roughly equal to the volumes of activation for reactant diffusion deltaV(diff)(), indicating predominant rate control by solvent dynamics rather than by activation in the manner of transition-state theory for which negative deltaV(el) values are expected. For CoTNPc and CoPc in donor solvents, the deltaV(cell) and deltaV(el) data are consistent with the assignments of the successive reduction steps made for CoTNPc in DMF by Nevin et al. (Inorg. Chem. 1987, 26, 570).