Chitosan/dialdehyde cellulose hydrogels with covalently anchored polypyrrole: Novel conductive, antibacterial, antioxidant, immunomodulatory, and anti-inflammatory materials.

In this work, conductive composite hydrogels with covalently attached polypyrrole (PPy) nanoparticles are prepared. Hydrogels are based on partially re-acetylated chitosan soluble at physiological pH without any artificial structural modifications or need for an acidic environment, which simplifies synthesis and purification. Low-toxic and sustainable dialdehyde cellulose (DAC) was used for crosslinking chitosan and covalent anchoring of PPy colloidal particles. The condensation reaction between DAC and PPy is reported for the first time and improves not only the anchoring of PPy particles but also control over the properties of the final composite. The soluble chitosan and PPy particles are shown to act in synergy, which improves the biological properties of the materials. Prepared composite hydrogels are non-cytotoxic, non-irritating, antibacterial, can capture reactive oxygen species often related to excessive inflammation, have conductivity similar to human tissues, enhance in vitro cell growth (migration assay), and have immunomodulatory effects related to the stimulation of neutrophils and macrophages. The covalent attachment of PPy also strengthens the hydrogel network. The aldol condensation as a method for PPy covalent anchoring thus presents an interesting possibility for the development of advanced biomaterials in the future.

The essential role of symmetry in understanding 3He chemical shifts in endohedral helium fullerenes.

The 3He atom is an excellent NMR probe, particularly when enclosed in endohedral helium fullerenes. The 3He chemical shift, δ(3He), in fullerenes spans a range from ca. -50 to +10 ppm, and changes sensitively between different cages, isomers, and external substituents. Reduction of the fullerenes to anions changes the δ(3He) dramatically and unexpectedly, particularly for the most symmetric and also the most abundant C60 and C70 cages. While the 3He atom is shielded by ∼43 ppm upon charging the He@C60 to He@C606-, it is correspondingly deshielded by ∼37 ppm in the He@C70/He@C706- pair. Here, we show that such puzzling differences in δ(3He) relate to the high symmetry of the host fullerene cages. While similar shielding is induced at the 3He atom by the core orbitals of different cages, the symmetry of the cage allows or quenches large paramagnetic, i.e., deshielding orbital interactions of frontier orbitals upon charging of the cage, which is directly responsible for the large observed chemical shift range of endohedral 3He.

Exact Two-Component TDDFT with Simple Two-Electron Picture-Change Corrections: X-ray Absorption Spectra Near L- and M-Edges of Four-Component Quality at Two-Component Cost.

X-ray absorption spectroscopy (XAS) has gained popularity in recent years as it probes matter with high spatial and elemental sensitivities. However, the theoretical modeling of XAS is a challenging task since XAS spectra feature a fine structure due to scalar (SC) and spin-orbit (SO) relativistic effects, in particular near L and M absorption edges. While full four-component (4c) calculations of XAS are nowadays feasible, there is still interest in developing approximate relativistic methods that enable XAS calculations at the two-component (2c) level while maintaining the accuracy of the parent 4c approach. In this article we present theoretical and numerical insights into two simple yet accurate 2c approaches based on an (extended) atomic mean-field exact two-component Hamiltonian framework, (e)amfX2C, for the calculation of XAS using linear eigenvalue and damped response time-dependent density functional theory (TDDFT). In contrast to the commonly used one-electron X2C (1eX2C) Hamiltonian, both amfX2C and eamfX2C account for the SC and SO two-electron and exchange-correlation picture-change (PC) effects that arise from the X2C transformation. As we demonstrate on L- and M-edge XAS spectra of transition metal and actinide compounds, the absence of PC corrections in the 1eX2C approximation results in a substantial overestimation of SO splittings, whereas (e)amfX2C Hamiltonians reproduce all essential spectral features such as shape, position, and SO splitting of the 4c references in excellent agreement, while offering significant computational savings. Therefore, the (e)amfX2C PC correction models presented here constitute reliable relativistic 2c quantum-chemical approaches for modeling XAS.

Enzyme-Catalyzed Polymerization Process: A Novel Approach to the Preparation of Polyaniline Colloidal Dispersions with an Immunomodulatory Effect.

A green, nature-friendly synthesis of polyaniline colloidal particles based on enzyme-assisted oxidation of aniline with horseradish peroxidase and chitosan or poly(vinyl alcohol) as steric stabilizers was successfully employed. Physicochemical characterization revealed formation of particles containing the polyaniline emeraldine salt and demonstrated only a minor effect of polymer stabilizers on particle morphology. All tested colloidal particles showed in vitro antioxidation activity determined via scavenging of 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals. In vitro, they were able to reduce oxidative stress and inhibit the production of reactive oxygen species by neutrophils and inflammatory cytokines by macrophages. The anti-inflammatory effect observed was related to their antioxidant activity, especially in the case of neutrophils. The particles can thus be especially advantageous as active components of biomaterials modulating the early stages of inflammation. In addition to the immunomodulatory effect, the presence of intrinsically conducting polyaniline can impart cell-instructive properties to the particles. The approach to particle synthesis that we employed─an original one using environmentally friendly and biocompatible horseradish peroxidase─represents a smart way of preparing conducting particles with unique properties, which can be further modified by the stabilizers used.

Dicarboxylated hyaluronate: Synthesis of a new, highly functionalized and biocompatible derivative.

Sequential periodate-chlorite oxidation of sodium hyaluronate to 2,3-dicarboxylated hyaluronate (DCH), a novel biocompatible and highly functionalized derivative bearing additional pair of COOH groups at C2 and C3 carbons of oxidized ᴅ-glucuronic acid units, is investigated. The impact of various reaction parameters (time, oxidizer concentration, and molar amount) on DCH's composition, molecular weight, degree of oxidation, and cytotoxicity are investigated to guide the synthesis of DCH derivatives of desired properties. Subsequently, fully (99%) and partially (70%) oxidized DCH derivatives were compared to untreated sodium hyaluronate in terms of anticancer drug cisplatin loading efficacy, carrier capacity, drug release rates, and cytotoxicity towards healthy and cancerous cell lines. DCH derivatives were found to be superior in every aspect, having nearly twice the carrier capacity, significantly slower release rates, and higher efficacy. DCH is thus a highly interesting hyaluronate derivative with an adjustable degree of oxidation, molecular weight, and great potential for further modifications.

One-step synthesis of gold nanoparticles for catalysis and SERS applications using selectively dicarboxylated cellulose and hyaluronate.

Properties and applications of gold nanoparticles (AuNPs) depend on their characteristics which are intrinsically connected to the reducing and capping agents used in their synthesis. Although polysaccharides are commonly used for Au salt reduction, the control over the result is often limited. Here, the selectively dicarboxylated cellulose (DCC) and hyaluronate (DCH) with adjustable composition and molecular weight are used for the first time as reducing and capping agents for AuNPs preparation in an environmental friendly one-step synthesis. Mechanism of reduction and structure-function relationships between the composition of oxidized polysaccharides and properties of formed AuNPs are elucidated and the variances in the macromolecular architecture of dicarboxypolysaccharides are applied to guide the growth of AuNPs. While the homogenous structure and high density of carboxyl groups of fully-oxidized DCC induced isotropic growth of small and uniform AuNPs with good catalytic performance (d = ~20 nm, TOF = 7.3 min-1, k = 1.47 min-1), the lower stabilizing potential and slower reduction rates of the DCH induced the anisotropic growth of larger polyhedral ~50 nm nanoparticles, which increased the Surface-Enhanced Raman Scattering efficacy (9× stronger Raman signals on average compared to AuDCC). The use of dicarboxypolysaccharides with adjustable composition and properties thus introduced a new degree of freedom for the preparation of AuNPs with desired properties.

Comparison of dialdehyde polysaccharides as crosslinkers for hydrogels: The case of poly(vinyl alcohol).

A little is known about the link between the macromolecular architecture of dialdehyde polysaccharides (DAPs), their crosslinking capabilities, and the properties of resulting hydrogels. Here, DAPs based on cellulose, dextrin, dextran, and hyaluronate were compared as crosslinkers for poly(vinyl alcohol), PVA. The swelling, network parameters, viscoelastic properties, porosity, and cytotoxicity of PVA/DAP hydrogels were investigated concerning the crosslinker structure, molecular weight, aldehyde group density per macromolecule, and the size of spontaneously formed crosslinker nano-assemblies. Generally, crosslinkers based on linear polysaccharides (cellulose, hyaluronate) performed more reliably, while the presence of branching could be both beneficial (dextran) but also detrimental (dextrin) at lower crosslinker concentrations. For example, the hydrogel swelling differed by up to one-third (600 vs. 400%) and storage modulus even by up to one half (~7000 vs. ~3500 Pa) depending on crosslinker structure and properties. These differences were rationalized by variances in crosslinking modes derived based on obtained data.

Accurate X-ray Absorption Spectra near L- and M-Edges from Relativistic Four-Component Damped Response Time-Dependent Density Functional Theory.

The simulation of X-ray absorption spectra requires both scalar and spin-orbit (SO) relativistic effects to be taken into account, particularly near L- and M-edges where the SO splitting of core p and d orbitals dominates. Four-component Dirac-Coulomb Hamiltonian-based linear damped response time-dependent density functional theory (4c-DR-TDDFT) calculates spectra directly for a selected frequency region while including the relativistic effects variationally, making the method well suited for X-ray applications. In this work, we show that accurate X-ray absorption spectra near L2,3- and M4,5-edges of closed-shell transition metal and actinide compounds with different central atoms, ligands, and oxidation states can be obtained by means of 4c-DR-TDDFT. While the main absorption lines do not change noticeably with the basis set and geometry, the exchange-correlation functional has a strong influence with hybrid functionals performing the best. The energy shift compared to the experiment is shown to depend linearly on the amount of Hartee-Fock exchange with the optimal value being 60% for spectral regions above 1000 eV, providing relative errors below 0.2% and 2% for edge energies and SO splittings, respectively. Finally, the methodology calibrated in this work is used to reproduce the experimental L2,3-edge X-ray absorption spectra of [RuCl2(DMSO)2(Im)2] and [WCl4(PMePh2)2], and resolve the broad bands into separated lines, allowing an interpretation based on ligand field theory and double point groups. These results support 4c-DR-TDDFT as a reliable method for calculating and analyzing X-ray absorption spectra of chemically interesting systems, advance the accuracy of state-of-the art relativistic DFT approaches, and provide a reference for benchmarking more approximate techniques.

Behaviour of Titanium Dioxide Particles in Artificial Body Fluids and Human Blood Plasma.

The growing application of materials containing TiO2 particles has led to an increased risk of human exposure, while a gap in knowledge about the possible adverse effects of TiO2 still exists. In this work, TiO2 particles of rutile, anatase, and their commercial mixture were exposed to various environments, including simulated gastric fluids and human blood plasma (both representing in vivo conditions), and media used in in vitro experiments. Simulated body fluids of different compositions, ionic strengths, and pH were used, and the impact of the absence or presence of chosen enzymes was investigated. The physicochemical properties and agglomeration of TiO2 in these media were determined. The time dependent agglomeration of TiO2 related to the type of TiO2, and mainly to the type and composition of the environment that was observed. The presence of enzymes either prevented or promoted TiO2 agglomeration. TiO2 was also observed to exhibit concentration-dependent cytotoxicity. This knowledge about TiO2 behavior in all the abovementioned environments is critical when TiO2 safety is considered, especially with respect to the significant impact of the presence of proteins and size-related cytotoxicity.

Oxidized polysaccharides for anticancer-drug delivery: What is the role of structure?

Study provides an in-depth analysis of the structure-function relationship of polysaccharide anticancer drug carriers and points out benefits and potential drawbacks of differences in polysaccharide glycosidic bonding, branching and drug binding mode of the carriers. Cellulose, dextrin, dextran and hyaluronic acid have been regioselectively oxidized to respective dicarboxylated derivatives, allowing them to directly conjugate cisplatin, while preserving their major structural features intact. The structure of source polysaccharide has crucial impact on conjugation effectiveness, carrier capacity, drug release rates, in vitro cytotoxicity and cellular uptake. For example, while branched structure of dextrin-based carrier partially counter the undesirable initial burst release, it also attenuates the cellular uptake and the cytotoxicity of carried drug. Linear polysaccharides containing ß-(1→4) glycosidic bonds and oxidized at C2 and C3 (cellulose and hyaluronate) have the best overall combination of structural features for improved drug delivery applications including potentiation of the cisplatin efficacy towards malignances.

Design of dialdehyde cellulose crosslinked poly(vinyl alcohol) hydrogels for transdermal drug delivery and wound dressings.

2,3-Dialdehyde cellulose (DAC) was used as an efficient and low-toxicity crosslinker to prepare thin PVA/DAC hydrogel films designed for topical applications such as drug-loaded patches, wound dressings or cosmetic products. An optimization of hydrogel properties was achieved by the variation of two factors - the amount of crosslinker and the weight-average molecular weight (Mw) of the source PVA. The role of each factor to network parameters, mechanical, rheological and surface properties, hydrogel porosity and transdermal absorption is discussed. The best results were obtained for hydrogel films prepared using 0.25 wt% of DAC and PVA with Mw = 130 kDa, which had a high porosity and drug-loading capacity (high water content), mechanical properties allowing easy handling, best adherence to the skin from all tested samples and improved transdermal drug-delivery. Hydrogel films are biocompatible, show no cytotoxicity and have no negative impact on cell growth and morphology in their presence. Furthermore, hydrogels do not support cell migration and attachment to their surface, which should ensure easy removal of hydrogel patches even from wounded or damaged skin after use.

Towards Accurate Predictions of Proton NMR Spectroscopic Parameters in Molecular Solids.

The factors contributing to the accuracy of quantum-chemical calculations for the prediction of proton NMR chemical shifts in molecular solids are systematically investigated. Proton chemical shifts of six solid amino acids with hydrogen atoms in various bonding environments (CH, CH2 , CH3 , OH, SH and NH3 ) were determined experimentally using ultra-fast magic-angle spinning and proton-detected 2D NMR experiments. The standard DFT method commonly used for the calculations of NMR parameters of solids is shown to provide chemical shifts that deviate from experiment by up to 1.5 ppm. The effects of the computational level (hybrid DFT functional, coupled-cluster calculation, inclusion of relativistic spin-orbit coupling) are thoroughly discussed. The effect of molecular dynamics and nuclear quantum effects are investigated using path-integral molecular dynamics (PIMD) simulations. It is demonstrated that the accuracy of the calculated proton chemical shifts is significantly better when these effects are included in the calculations.

Experimental and Theoretical Evidence of Spin-Orbit Heavy Atom on the Light Atom 1 H†NMR Chemical Shifts Induced through H⋠⋠⋠I- Hydrogen Bond.

Invited for the cover of this issue is the group of Michal Straka and Martin Dracínský (IOCB Prague, Czech Academy of Sciences). The image depicts a neutron star, which is used to represent the relativistic effects between a heavy element and a hydrogen atom reported in this work. Read the full text of the article at 10.1002/chem.202001532.

Relativity or aromaticity? A first-principles perspective of chemical shifts in osmabenzene and osmapentalene derivatives.

We have studied the magnetic response properties and aromaticity of osmium metallacycles by means of scalar-relativistic (1c) and fully relativistic (4c) density functional theory computations. For osmabenzene, whose aromatic character is controversial, a topological analysis of the current density has revealed the presence of a unique σ-type Craig-Möbius magnetic aromaticity. We show that the partially filled osmium valence shell induces a large paratropic current, which may interfere with certain methods commonly used to analyze aromaticity, in particular NICS. Further, we show that the extreme deshielding of the light atoms in the vicinity of the osmium atoms in osmapentalene derivatives is not a consequence of aromaticity but can be explained by paramagnetic couplings between σOs-C bonding orbitals and the π*Os orbitals. We demonstrate that variations in the orientation of the induced magnetic currents through the molecule dictates the alternating signs of the spin-orbit contribution to the NMR chemical shift.

Experimental and Theoretical Evidence of Spin-Orbit Heavy Atom on the Light Atom 1 H†NMR Chemical Shifts Induced through H⋠⋠⋠I- Hydrogen Bond.

Spin-orbit (SO) heavy-atom on the light-atom (SO-HALA) effect is the largest relativistic effect caused by a heavy atom on its light-atom neighbors, leading, for example, to unexpected NMR chemical shifts of 1 H, 13 C, and 15 N nuclei. In this study, a combined experimental and theoretical evidence for the SO-HALA effect transmitted through hydrogen bond is presented. Solid-state NMR data for a series of 4-dimethylaminopyridine salts containing I- , Br- and Cl- counter ions were obtained experimentally and by theoretical calculations. A comparison of the experimental chemical shifts with those calculated by a standard DFT methodology without the SO contribution to the chemical shifts revealed a remarkable error of the calculated proton chemical shift of a hydrogen atom that is in close contact with the iodide anion. The addition of the relativistic SO correction in the calculations significantly improves overall agreement with the experiment and confirms the propagation of the SO-HALA effect through hydrogen bonds.

Biocompatible dialdehyde cellulose/poly(vinyl alcohol) hydrogels with tunable properties.

Solubilized dialdehyde cellulose (DAC), an efficient crosslinking agent for poly(vinyl alcohol) (PVA), provides less toxic alternative to current synthetic crosslinking agents such as glutaraldehyde, while simultaneously allowing for the preparation of hydrogels with comparably better characteristics. PVA/DAC hydrogels prepared using 0.5, 1 and 1.5 wt% of DAC were analyzed in terms of mechanical, swelling and cytotoxicity characteristics. Materials properties of PVA/DAC hydrogels range from stiff substances to soft viscoelastic gels capable of holding large amounts of water. Superior mechanical properties, porosity and surface area in comparison with analogical PVA/glutaraldehyde hydrogels were observed. Biological studies showed low toxicity and good biocompatibility of PVA/DAC hydrogels. Potential of PVA/DAC in mesh-controlled release of biologically active compounds was investigated using ibuprofen, rutin and phenanthriplatin. Hydrogel loaded with anticancer drug phenantriplatin was found effective against alveolar cancer cell line A549 under in vitro conditions.

Selectively Oxidized Cellulose with Adjustable Molecular Weight for Controlled Release of Platinum Anticancer Drugs.

The synthesis of selectively oxidized cellulose, 2,3-dicarboxycellulose (DCC), is optimized for preparation of highly oxidized material for biological applications, which includes control over the molecular weight of the product during its synthesis. Conjugates of DCC and cisplatin simultaneously offer a very high drug binding efficiency (>90%) and drug loading capacity (up to 50 wt %), while retaining good aqueous solubility. The adjustable molecular weight of the DCC together with variances in drug feeding ratio allows to optimize cisplatin release profiles from delayed (<2% of cisplatin released during 6 h) to classical burst release with more than 60% of cisplatin released after 24 h. The release rates are also pH-dependent (up to 2 times faster release at pH 5.5 than at pH 7.4), which allows to exploit the acidic nature of tumor microenvironment. Extensive in vitro studies were performed on eight different cell lines for two cisplatin-DCC conjugates with different release profiles. In comparison with free cisplatin, both cisplatin-DCC conjugates demonstrated considerably lower cytotoxicity toward healthy cells. Conjugates with burst release profiles were found more effective against prostate cell lines, while DCC conjugates with slower release were more cytotoxic against ovarian and lung carcinoma cell lines. In vivo studies indicated a significantly longer survival rate, a reduction in tumor volume, and a higher accumulation of platinum in tumors of mice treated with the cisplatin-DCC conjugate in comparison to those treated by free cisplatin.

Spectroscopic and Computational Evidence of Intramolecular AuI ⋠⋠⋠H+ -N Hydrogen Bonding.

Despite substantial evidence of short Au⋅⋅⋅H-X contacts derived from a number of X-ray structures of AuI compounds, the nature of AuI ⋅⋅⋅H bonding in these systems has not been clearly understood. Herein, we present the first spectroscopic evidence for an intramolecular AuI ⋅⋅⋅H+ -N hydrogen bond in a [Cl-Au-L]+ complex, where L is a protonated N-heterocyclic carbene. The complex was isolated in the gas phase and characterized with helium-tagging infrared photodissociation (IRPD) spectra, in which H+ -N-mode-derived bands evidence the intramolecular AuI ⋅⋅⋅H+ -N bond. Quantum chemical calculations reproduce the experimental IRPD spectra and allow to characterize the intramolecular Au⋅⋅⋅H+ -N bonding with a short rAu⋅⋅⋅H distance of 2.17 Šand an interaction energy of approximately -10 kcal mol-1 . Various theoretical descriptors of chemical bonding calculated for the Au⋅⋅⋅H+ -N interaction provide strong evidence for a hydrogen bond of moderate strength.

Reactive Dimerization of an N-Heterocyclic Plumbylene: C-H Activation with PbII.

The N-heterocyclic plumbylene [Fe{(η5 -C5 H4 )NSiMe3 }2 Pb:] is in equilibrium with an unprecedented dimer in solution, whose formation involves the cleavage of a strong C-H bond and concomitant formation of a Pb-C and an N-H bond. According to a mechanistic DFT assessment, dimer formation does not involve direct PbII insertion into a cyclopentadienyl C-H bond, but is best described as an electrophilic substitution. The bulkier plumbylene [Fe{(η5 -C5 H4 )NSitBuMe2 }2 Pb:] shows no dimerization, but compensates its electrophilicity by the formation of an intramolecular Fe-Pb bond.