Electrospun chitosan-coated fibers of poly(L-lactide) and poly(L-lactide)/poly(ethylene glycol): preparation and characterization

Fibrous poly(L-lactide) (PLLA) and bicomponent PLLA/poly(ethylene glycol) mats were prepared by electrospinning and then were coated with chitosan. The presence of chitosan coating was proved by scanning electron microscopy and by fluorescence microscopy. On contact with blood, the chitosan coating led to changes in erythrocyte shape and in their aggregation. The haemostatic activity of the mats increased with increasing chitosan content. Microbiological studies against Staphylococcus aureus revealed that the chitosan coating imparts antibacterial activity to the hybrid mats. The combined haemostatic and antibacterial activities render these novel materials suitable for wound-healing applications.     

Novel electrospun poly(ε-caprolactone)-based bicomponent nanofibers possessing surface enriched in tertiary amino groups

For the first time preparation of electrospun poly(ε-caprolactone) (PCL) based nanofibers possessing surface enriched in tertiary amino groups is shown. For that purpose the pair PCL and poly(ε-caprolactone)-b-poly[(2-dimethylamino)ethyl methacrylate] (PCL-b-PDMAEMA) diblock copolymers was used. PCL-b-PDMAEMA copolymers were synthesized using a combination of ring-opening polymerization and atom transfer radical polymerization (ATRP). Nanofibers with mean diameters ranging from 400 to 800 nm were obtained. Their morphology was evaluated by scanning electron (SEM) and atomic force microscopy (AFM). It was found that the morphology of the fibers depended on the weight ratio between the partners and the length of the PDMAEMA-block in the copolymers. The enrichment of the fiber surface in tertiary amino groups was studied by X-ray photoelectron spectroscopy (XPS). Increasing the copolymer content and the length of the PDMAEMA-block led to increase of the amount of tertiary amino groups on the fiber surface. The AFM analyses of the mechanical properties of the fiber surface showed that increasing the copolymer content led to decrease of the surface stiffness. The increase of the copolymer content led also to decrease of the melting temperature and the crystallinity degree in respect to PCL from the (co)polymer as determined by differential scanning calorimetry.     

In search of cyclohexane-like Sn6(12-): synthesis of Li2Ln5Sn7 (Ln = Ce, Pr, Sm, Eu) with an open-chain heptane-like Sn7(16-) instead

The title compounds were prepared by direct reactions of the corresponding elements at high temperature. They are isostructural and crystallize in the chiral orthorhombic space group P212121 (Li2Ce5Sn7: a = 6.273(1), b = 13.839(2), and c = 17.467(2) A; Li2Pr5Sn7: a = 6.241(1), b = 13.762(2), and c = 17.367(1) A; Li2Sm5Sn7: a = 6.262 (1), b = 13.809(1), and c = 17.432(1) A; Li2Eu5Sn7: a = 6.165(1), b = 13.562(2), and c = 17.128(1) A). The structure contains isolated Sn7 oligomers that resemble the carbon core of an open-chain heptane molecule C7H16. Although these heptamers are stacked along the a axis at a distance that is comparable to the distances within the heptamer, electronic structure calculations show that this intermolecular contact is nonbonding for a formal charge of 16- or higher per heptamer. A hypothetical lower charge of 14-, on the other hand, leads to positive and substantial bond-overlap population that would result in branched infinite chains of infinity[Sn714-]. Magnetic measurements of the Ce and Pr compounds indicate a 3+ oxidation state for the rare-earth cations and, therefore, 17 available electrons from the cations per formula unit. According to four-probe conductivity measurements, the compounds are metallic.     

FT-IR microscopy characterization of sol–gel layers prior and after glucose oxidase immobilization for biosensing applications

Micro-Attenuated Total Reflection (ATR) Fourier Transform Infrared spectroscopy was used to investigate sol–gel layers for biosensing applications prior and after glucose oxidase (GOD) immobilization. The changes occurring in sol–gel infrared spectrum after GOD immobilization were clearly evidenced confirming the retaining of the enzyme activity. Moreover, micro-ATR experimental technique allowed us to investigate the spatial distribution of enzyme concentration. The non-destructive nature of our approach also enabled to monitor the time stability of sol–gel layers and of embedded GOD. The temporal evolution of some peaks in infrared spectra of these sol–gel layers was compared with absorption and steady-state fluorescence measurements. The results reported here confirm that micro-ATR infrared spectroscopy can be usefully employed for a non- or minimally invasive detailed characterization of supports for enzyme immobilization.     

Fiber-optic glucose biosensor based on glucose oxidase immobilised in a silica gel matrix

A monolithic silica gel matrix with entrapped glucose oxidase was constructed as a bioactive element in an optical biosensor for glucose determination. Physicochemical and biochemical characterizations of the catalytic matrix were performed, and the intrinsic fluorescence of immobilised glucose oxidase (GOD) was investigated in the UV and visible range by performing steady state and time course measurements. In all cases, the silica gel matrix proved to be a suitable support for optical biosensing owing to its superior optical properties (e.g., high transmittance and reliable fluorescence and GOD absorption spectra after immobilisation). From steady state measurements, calibration curves were obtained as a function of glucose concentration. When time course measurements were performed, the silica gel support displayed a larger linear calibration range and higher sensitivity than other immobilisation systems. In addition, a glucose optical biosensor was developed and characterised using as catalytic element GOD immobilised on a gel disk bound to a bundle of optical fibres.     

Molecular dynamics study of a new metastable allotropic crystalline form of gallium—supertetrahedral gallium

A new metastable crystalline form of gallium has been computationally designed using density functional calculations with imposing periodic boundary conditions. The geometric and electronic structures of the predicted new allotrope were calculated on the basis of a diamond lattice in which all carbon atoms are replaced by gallium Ga₄ tetrahedra. This form does not have any imaginary phonons, thus it is a metastable crystalline form of gallium. The new form of gallium is a metal and shows high plasticity and low-melting temperature. Molecular dynamics simulations show that this form of gallium will melt at about 273 K with a sharp increase in temperature in the system during the melting process from 273 to 1800 K. This melting process is very different from conventional melting, where temperature stays the same until complete melting. That unusual melting can be explained by the fact that supertetrahedral gallium is a metastable structure that has an excess of strain energy released during melting. If made this new material may find many useful applications as a new low density metal with stored internal energy. © 2019 Wiley Periodicals, Inc.     

On the anatomy of multi-spin magnon and single spike string solutions

We study rigid string solutions rotating in AdS₅×S⁵${\mathit{AdS}}_5\times S^5$ background. For particular values of the parameters of the solutions we find multispin solutions corresponding to giant magnons and single spike strings. We present an analysis of the dispersion relations in the case of three spin solutions distributed only in S⁵$S^5$ and the case of one spin in AdS₅${\mathit{AdS}}_5$ and two spins in S⁵$S^5$. The possible relation of these string solutions to gauge theory operators and spin chains are briefly discussed.     

Novel Electrospun Nanofibers Composed of Polyelectrolyte Complexes

A simple method to obtain novel nanofibers composed of polyelectrolyte complexes (PECs) has been proposed. It consists of the electrospinning of a mixed homogeneous solution of polyelectrolyte partners, and the formation of PEC during the electrospinning. This was achieved by careful choice of the composition of the spinning solutions. Chitosan was the polycationic partner, with either a weak polyacid [poly(acrylic acid), PAA] as a counterpart or a strong one [poly(2‐acrylamido‐2‐methylpropanesulfonic acid), PAMPS]. The fibrous mats were composed of nanofibers with mean diameters of ca. 100 nm. They retained their integrity over the pH range which is typical of the corresponding PEC.

     

Anionic polymerization of lactones initiated by alkali graphitides. II. Changes in the KC24 structure during polymerization of lactones

The structural changes in the potassium graphitide KC₂₄ in its interaction with ?-caprolactone, γ-butyrolactone and pivalolactone are examined by profilometric measurement and electron scanning microscopy. The interaction of KC₂₄ with a nonpolymerizable lactone-γ-butyrolactone proceeds without delamination of the graphitide. The polymerization of ?-caprolactone and pivalactone in the interlayer spaces of KC₂₄ leads to destruction of the initiators structure. An increase in the temperature and monomer concentration enhances the delamination of the graphitide.     

Heavy-metal aromatic and conjugated species: rings, oligomers, and chains of tin in Li(9)(-)(x)EuSn(6+)(x), Li(9)(-)(x)CaSn(6+)(x), Li(5)Ca(7)Sn(11), Li(6)Eu(5)Sn(9), LiMgEu(2)Sn(3), and LiMgSr(2)Sn(3)

The title compounds were synthesized from the elements by heating the corresponding mixtures at high temperature. Their structures were determined from single-crystal X-ray diffraction. Li(9)(-)(x)()EuSn(6+)(x)(), Li(9)(-)(x)()CaSn(6+)(x)(), Li(5)Ca(7)Sn(11), and Li(6)Eu(5)Sn(9) contain columns of stacked aromatic pentagons of Sn(5)(6)(-) that are analogous to the cyclopentadienyl anion C(5)H(5)(-). The pentagons are separated with Ca(2+) or Eu(2+) in the columns and resemble a polymeric metallocene. In addition to the columns, the isostructural Li(9)(-)(x)()EuSn(6+)(x)() and Li(9)(-)(x)()CaSn(6+)(x)() contain isolated tin atoms and bent tin trimers while Li(5)Ca(7)Sn(11) and Li(6)Eu(5)Sn(9) contain flat zigzag hexamers and flat zigzag infinite chains of tin, respectively. The isostructural LiMgEu(2)Sn(3) and LiMgSr(2)Sn(3) do not contain columns of pentagons but only flat zigzag infinite chains of tin. The aromaticity of the pentagons and the conjugation of the pi-systems of the hexamers and the infinite chains are discussed. The title compounds are also characterized by magnetic and conductivity measurements.