Structure and Dynamics of Inhomogeneities in Aqueous Solutions of Graft Copolymers of N-Isopropylacrylamide with Lactide (P(NIPAM-graft-PLA)) by Spin Probe EPR Spectroscopy.

Coil-to-globule transition and dynamics of inhomogeneities in aqueous solutions of graft copolymers of NIPAM with different content of oligolactide groups were studied using spin probe continuous wave EPR spectroscopy. The technique of the suppressing of TEMPO as spin probe by spin exchange with Cu2+ ions was applied. This approach allowed us to detect individual EPR spectra of the probe in collapsed globules and estimate its magnetic and dynamic parameters reliably. The formation of inhomogeneities at temperatures lower than the volume phase transition temperature measured via transmission, and differential scanning calorimetry was fixed. An increase in oligolactide content in copolymers leads to the formation of looser globules, allowing for the exchange of the probe molecules between the globules and the external solution.

Inhomogeneities in PNIPAM Aqueous Solutions: The Inside View by Spin Probe EPR Spectroscopy.

Coil to globule transition in poly(N-isopropylacrylamide) aqueous solutions was studied using spin probe continuous-wave electronic paramagnetic resonance (CW EPR) spectroscopy with an amphiphilic TEMPO radical as a guest molecule. Using Cu(II) ions as the "quencher" for fast-moving radicals in the liquid phase allowed obtaining the individual spectra of TEMPO radicals in polymer globule and observing inhomogeneities in solutions before globule collapsing. EPR spectra simulations confirm the formation of molten globules at the first step with further collapsing and water molecules coming out of the globule, making it denser.

Solute Diffusion into Polymer Swollen by Supercritical CO2 by High-Pressure Electron Paramagnetic Resonance Spectroscopy and Chromatography.

High-pressure electron paramagnetic resonance (EPR) was used to measure translational diffusion coefficients (Dtr) of a TEMPONE spin probe in poly(D,L-lactide) (PDLLA) and swollen in supercritical CO2. Dtr was measured on two scales: macroscopic scale (>1 µm), by measuring spin probe uptake by the sample; and microscopic scale (<10 nm), by using concentration-dependent spectrum broadening. Both methods yield similar translational diffusion coefficients (in the range 5-10 × 10-12 m2/s at 40-60 °C and 8-10 MPa). Swollen PDLLA was found to be homogeneous on the nanometer scale, although the TEMPONE spin probe in the polymer exhibited higher rotational mobility (τcorr = 6 × 10-11 s) than expected, based on its Dtr. To measure distribution coefficients of the solute between the swollen polymer and the supercritical medium, supercritical chromatography with sampling directly from the high-pressure vessel was used. A distinct difference between powder and bulk polymer samples was only observed at the start of the impregnation process.

Local Delivery of Pirfenidone by PLA Implants Modifies Foreign Body Reaction and Prevents Fibrosis.

Peri-implant fibrosis (PIF) increases the postsurgical risks after implantation and limits the efficacy of the implantable drug delivery systems (IDDS). Pirfenidone (PF) is an oral anti-fibrotic drug with a short (<3 h) circulation half-life and strong adverse side effects. In the current study, disk-shaped IDDS prototype combining polylactic acid (PLA) and PF, PLA@PF, with prolonged (~3 days) PF release (in vitro) was prepared. The effects of the PLA@PF implants on PIF were examined in the rabbit ear skin pocket model on postoperative days (POD) 30 and 60. Matching blank PLA implants (PLA0) and PLA0 with an equivalent single-dose PF injection performed on POD0 (PLA0+injPF) served as control. On POD30, the intergroup differences were observed in α-SMA, iNOS and arginase-1 expressions in PLA@PF and PLA0+injPF groups vs. PLA0. On POD60, PIF was significantly reduced in PLA@PF group. The peri-implant tissue thickness decreased (532 ± 98 µm vs. >1100 µm in control groups) approaching the intact derma thickness value (302 ± 15 µm). In PLA@PF group, the implant biodegradation developed faster, while arginase-1 expression was suppressed in comparison with other groups. This study proves the feasibility of the local control of fibrotic response on implants via modulation of foreign body reaction with slowly biodegradable PF-loaded IDDS.

New Insight into the Mechanism of Drug Release from Poly(d,l-lactide) Film by Electron Paramagnetic Resonance.

A novel approach based on convolution of the electron paramagnetic resonance (EPR) spectra was used for quantitative study of the release kinetics of paramagnetic dopants from poly(d,l-lactide) films. A non-monotonic dependence of the release rate on time was reliably recorded. The release regularities were compared with the dynamics of polymer structure changes determined by EPR, SEM, and optic microscopy. The data obtained allow for the conclusion that the main factor governing dopant release is the formation of pores connected with the surface. In contrast, the contribution of the dopant diffusion through the polymer matrix is negligible. The dopant release can be divided into two phases: release through surface pores, which are partially closed with time, and release through pores initially formed inside the polymer matrix due to autocatalytic hydrolysis of the polymer and gradually connected to the surface of the sample. For some time, these processes co-occur. The mathematical model of the release kinetics based on pore formation is presented, describing the kinetics of release of various dopants from the polymer films of different thicknesses.

Evaluation of Supercritical CO2-Assisted Protocols in a Model of Ovine Aortic Root Decellularization.

One of the leading trends in the modern tissue engineering is the development of new effective methods of decellularization aimed at the removal of cellular components from a donor tissue, reducing its immunogenicity and the risk of rejection. Supercritical CO2 (scCO2)-assisted processing has been proposed to improve the outcome of decellularization, reduce contamination and time costs. The resulting products can serve as personalized tools for tissue-engineering therapy of various somatic pathologies. However, the decellularization of heterogeneous 3D structures, such as the aortic root, requires optimization of the parameters, including preconditioning medium composition, the type of co-solvent, values of pressure and temperature inside the scCO2 reactor, etc. In our work, using an ovine aortic root model, we performed a comparative analysis of the effectiveness of decellularization approaches based on various combinations of these parameters. The protocols were based on the combinations of treatments in alkaline, ethanol or detergent solutions with scCO2-assisted processing at different modes. Histological analysis demonstrated favorable effects of the preconditioning in a detergent solution. Following processing in scCO2 medium provided a high decellularization degree, reduced cytotoxicity, and increased ultimate tensile strength and Young's modulus of the aortic valve leaflets, while the integrity of the extracellular matrix was preserved.

Performance of DFT methods in the calculation of isotropic and dipolar contributions to 14N hyperfine coupling constants of nitroxide radicals.

In the present study, we tested the widely used density functionals BP86, PBE, OLYP, TPSS, M06-L, B3LYP, PBE0, mPW1PW, B97, BHandHLYP, TPSS0, M06, M06-2X, CAM-B3LYP, ωB97x, and B2PLYP with the cc-pCVQZ basis set in calculations on a set of 23 nitroxide radicals with well-resolved 14N anisotropic hyperfine coupling (HFC) constants. The results were compared with those obtained using the B3LYP/N07D and PBE/N07D methods. The convergence of the HFC values to the complete basis set limit is briefly discussed. The best results were obtained using the M06/COSMO method, with a mean absolute deviation (MAD) of 0.4 G for the dipole-dipole contribution and MAD = 0.6 G for the contact coupling contribution (as compared to 1.1 G and 1.0 G, respectively, for the B3LYP/N07D/COSMO method and 1.7 G and 0.5 G, respectively, for the B3LYP/N07D method). The majority of the functionals yielded satisfactory results for the dipole-dipole contribution, but only the M06 functional yielded similar errors for both the dipole-dipole and isotropic contributions. The RIJCOSX and RI approximations introduced errors equal to or smaller than 0.01 G.

Femtosecond spectroscopy and TD-DFT calculations of CuCl4(2-) excited states.

Photoinduced processes of tetrahexylammonium tetrachlorocuprate [(C6H13)4N]2Cu(II)Cl4 in chloro-organic solvents were investigated by steady state photolysis and femtosecond transient absorption spectroscopy. The quantum yield of photoreduction of CuCl4(2-) was estimated to be about 1%; the process resulted in the formation of the copper(i) chlorocomplex Cu(I)Cl3(2-) and a chlorine atom. Femtosecond laser photolysis with a 422 nm, 40 fs pulse revealed a three-exponential decay of the LMCT excited state of [(C6H13)4N]2CuCl4. A global fitting SVD analysis of the femtosecond transient spectra suggested three relaxation times, ∼400 fs, ∼1.4 ps and ∼5.8 ps. Oscillations in transient absorption kinetic traces were documented for CuCl4(2-) solutions in 2-chlorobutane. The oscillation Fourier transform analysis of the oscillations and linear predictive singular value decomposition revealed peaks at 283 cm(-1) (damping time ∼600 fs) and 181 cm(-1) (damping time ∼400 fs). These peaks can be tentatively attributed to νs(Cu-Cl) symmetric stretching frequency A1 and T2 reflecting excited state vibrational coherence. Quantum chemical calculations suggest a possible scheme for relaxation pathways in CuCl4(2-). The observed transient excited state absorption bands agree semiquantitatively with the calculated transition bands of CuCl4(2-).

Redox regulation of calcium signaling in cancer cells by ascorbic Acid involving the mitochondrial electron transport chain.

Previously, we have reported that ascorbic acid regulates calcium signaling in human larynx carcinoma HEp-2 cells. To evaluate the precise mechanism of Ca(2+) release by ascorbic acid, the effects of specific inhibitors of the electron transport chain components on mitochondrial reactive oxygen species (ROS) production and Ca(2+) mobilization in HEp-2 cells were investigated. It was revealed that the mitochondrial complex III inhibitor (antimycin A) amplifies ascorbate-induced Ca(2+) release from intracellular stores. The mitochondrial complex I inhibitor (rotenone) decreases Ca(2+) release from intracellular stores in HEp-2 cells caused by ascorbic acid and antimycin A. In the presence of rotenone, antimycin A stimulates ROS production by mitochondria. Ascorbate-induced Ca(2+) release in HEp-2 cells is shown to be unaffected by catalase. The results obtained suggest that Ca(2+) release in HEp-2 cells caused by ascorbic acid is associated with induced mitochondrial ROS production. The data obtained are in line with the concept of redox signaling that explains oxidant action by compartmentalization of ROS production and oxidant targets.

UV-Vis identification and DFT-assisted prediction of structures of Cu(II)-alkyl chlorocomplexes.

The structures of paramagnetic copper complexes, the products of photolysis of tetrachlorocuprates of quaternary ammonium in frozen solvents, earlier denoted as 1-Cu and 2-Cu, were established on the basis of comparison of experimental and theoretical UV-vis spectra. UV-vis spectra of photolysis products were registered at 77-116 K. Comparison with the EPR data in this temperature range allowed to assign photolysis products bands in the vis spectrum either to 1-Cu or to 2-Cu. Model structures for 1-Cu and 2-Cu were proposed. TD-DFT calculated spectra of model compounds along with CuCl(4)(2-) anion are in excellent agreement with the experiment. The comparison of UV-vis and EPR data and results of TD-DFT calculations evidence that 1-Cu and 2-Cu are paramagnetic organochlorocuprates(II) with general formulas Cu(II)Cl(2)R and Cu(II)Cl(3)R, respectively, where R is (-C(6)H(12))N(+)(C(6)H(13))(3).

Cu(II)-alkyl chlorocomplexes: stable compounds or transients? DFT prediction of their structure and EPR parameters.

DFT calculations were used for studying the structure and reactivity of organocuprates(II) usually considered as intermediates with very weak Cu-C bond. It was found that calculated principal g-tensor values of model compounds RCu(II)Cl(2(-)) are similar to the experimentally found values for organocopper product of photolysis of quaternary ammonium tetrachlorocuprates. The calculations confirm that the most of organocuprates(II) could be stable at ambient conditions, and short lifetimes of organocuprates(II) in solutions or soft matrices are caused by their high reactivity in various bimolecular processes; the rate of those may be close to the rate of diffusion controlled reactions. The charges, spin densities, and d-orbital populations of the Cu atom in them are typical for bivalent copper complexes. Natural bond orbital analysis of organochlorocuprates(II) confirms the formation of polar σ-bond between copper and carbon atoms.

Formation of active catalysts in the system: chlorocuprates-CCl4-n-C10H22.

Transformations of anionic Cu(II) chlorocomplexes have been studied under conditions of catalytic exchange reactions between carbon tetrachloride and n-alkanes. It was shown that chlorocuprates are just precursors and are easily reduced to the genuine catalysts, that is, to the respective Cu(I) complexes. Both the composition and the geometric structure of the precursor (CuCl(4)(2-)) and, probably, the active site (CuCl(3)(2-)) have been investigated by several techniques (UV-vis spectroscopy, electron spin resonance (ESR), extended X-ray absorption fine structure (EXAFS), X-ray absorption near-edge structure (XANES), and static magnetic measurements). The dependence of the metathesis velocity on the [Cl-]/[Cu] ratio was found to exhibit a maximum most likely corresponding to the highest content of trichlorocuprite CuCl(3)(2-).