Colorimetric and fluorimetric pH sensing using polydiacetylene embedded within PVC-PCL nanofibers

The applicability of model polydiacetylenes (PDAs) in hydrogen ions sensitive optodes was tested. Nanofibers mats were electrospun using a mixture of polyvinyl chloride (PVC) and polycaprolactone (PCL) together with 10, 12-tricosadiynoic acid (TCDA) or 10,12-pentacosadiynoic acid (PCDA). After the polymerization the mats were applied in colorimetric and fluorimetric pH sensors. The PDAs were formed by photopolymerization with a UV lamp (254 nm), resulting in a change of mats color from white to dark blue. The morphology of both fiber mats is similar (SEM images), and the average diameters of fibers were estimated as equal to 228±73 and 248±61 nm for TCDA and PCDA, respectively. As the pH increases, the color of the fiber mat changes from blue to red and the process can be followed visually. The result obtained by computer image analysis showed a sigmoidal increase in the intensity of red and a decrease in the intensity of blue color with increasing pH. A similar sigmoidal response is observed for the dependence of the emission intensity on the pH. Changes in the recorded signal occur in the pH range from 7 to 8.5 or from 8 to 9.5 for mats with TCDA and PCDA, respectively. Both readout modes can be successfully used for pH sensing with proposed nanofibrous mats in the range of pH close to the physiological pH range.     

Geometric quantization, reduction and decomposition of group representations

We consider a Hamiltonian action of a connected group G on a symplectic manifold (P, ω) with an equivariant momentum map and its quantization in terms of a K?hler polarization which gives rise to a unitary representation of G on a Hilbert space . If O is a co-adjoint orbit of G quantizable with respect to a K?hler polarization, we describe geometric quantization of algebraic reduction of J ⁻¹(O). We show that the space of normalizable states of quantization of algebraic reduction of J ⁻¹(O) gives rise to a projection operator onto a closed subspace of on which is unitarily equivalent to a multiple of the irreducible unitary representation of G corresponding to O. This is a generalization of the results of Guillemin and Sternberg obtained under the assumptions that G and P are compact and that the action of G on P is free. None of these assumptions are needed here. Dedicated to Vladimir Igorevich Arnold     

Linear gradings of polynomial algebras

Let k be a field, let be a finite group. We describe linear -gradings of the polynomial algebra k[x ₁, ..., x _m ] such that the unit component is a polynomial k-algebra.      

Alkaline-Earth Metal Mediated Benzene-to-Biphenyl Coupling

Complex [(^DIPePBDI)Ca]₂(C₆H₆), with a C₆H₆²⁻ dianion bridging two Ca²⁺ ions, reacts with benzene to yield [(^DIPePBDI)Ca]₂(biphenyl) with a bridging biphenyl²⁻ dianion (^DIPePBDI=HC[C(Me)N-DIPeP]₂; DIPeP=2,6-CH(Et)₂-phenyl). The biphenyl complex was also prepared by reacting [(^DIPePBDI)Ca]₂(C₆H₆) with biphenyl or by reduction of [(^DIPePBDI)CaI]₂ with KC₈ in presence of biphenyl. Benzene-benzene coupling was also observed when the deep purple product of ball-milling [(^DIPPBDI)CaI(THF)]₂ with K/KI was extracted with benzene (DIPP=2,6-CH(Me)₂-phenyl) giving crystalline [(^DIPPBDI)Ca(THF)]₂(biphenyl) (52 % yield). Reduction of [(^DIPePBDI)SrI]₂ with KC₈ gave highly labile [(^DIPePBDI)Sr]₂(C₆H₆) as a black powder (61 % yield) which reacts rapidly and selectively with benzene to [(^DIPePBDI)Sr]₂(biphenyl). DFT calculations show that the most likely route for biphenyl formation is a pathway in which the C₆H₆²⁻ dianion attacks neutral benzene. This is facilitated by metal-benzene coordination.     

The properties of gold catalysts precursors adsorbed on the MCM-41 materials modified with Mn and Fe oxides

Silica mesoporous materials modified with manganese and iron were obtained by the hydrothermal method. Gold was introduced to pure and modified silica materials by the direct hydrothermal and impregnation methods. Nitrogen adsorption/desorption studies evidenced formation of the materials with large total surface area and mesoporous structure. Unmodified silica materials showed regular pore arrangement. The uniform porous structure was distorted in the iron or manganese containing samples. XRD, UV-Vis/DRS spectroscopy and temperature programmed reduction studies revealed changes of the nature of transition metal oxide and gold species on the different preparation stages. The oxide species after drying were strongly dispersed and partially incorporated to the silica framework. High temperature treatment led to the formation of extraframework Mn and Fe oxide species. Complex processes of gold deposition were observed during hydrothermal synthesis and impregnation of modified silica materials. The increase of the size of gold species was observed during calcination. The presence of transition metal oxides decreased sintering of gold crystallites.     

Complementary interference method for determining optical parameters of liquid crystals

ABSTRACT

Wedge cells of small apex angle, filled with liquid crystals, were used to determining optical characteristics as functions of temperature for three liquid crystalline mixtures recently produced and a reference nematic. The interference fringes appearing in polarised monochromatic light (of sodium yellow line) normally incident on the cell were exploited to measure the ordinary and extraordinary refractive indices in the reflection mode and birefringence in the transmission mode. The measurements were repeated using Abbe's refractometer for 6CHBT as the reference to verifying the precision. Additionally the order parameter was computed from birefringence as a function of temperature. The results confirm the usefulness of the method and provide the properties of two nematic liquid crystals of small and large birefringence and one smectic liquid crystal of medium birefringence, recently produced. The experimental systems served also to investigating phase transition between the liquid crystals and the isotropic liquid at near-clearing temperature.     

A Single Methylene Group in Oligoalkylamine‐Based Cationic Polymers and Lipids Promotes Enhanced mRNA Delivery

The development of chemically modified mRNA holds great promise as a new class of biologic therapeutics. However, the intracellular delivery and endosomal escape of mRNA encapsulated in nanoparticles has not been systematically investigated. Here, we synthesized a diverse set of cationic polymers and lipids from a series of oligoalkylamines and subsequently characterized their mRNA delivery capability. Notably, a structure with an alternating alkyl chain length between amines showed the highest transfection efficiency, which was linked to a high buffering capacity in a narrow range of pH 6.2 to 6.5. Variation in only one methylene group resulted in enhanced mRNA delivery to both the murine liver as well as porcine lungs after systemic or aerosol administration, respectively. These findings reveal a novel fundamental structure–activity relationship for the delivery of mRNA that is independent of the class of mRNA carrier and define a promising new path of exploration in the field of mRNA therapeutics.     

The aza-Pudovik reaction accelerated in external constant magnetic field

The aza-Pudovik reaction of N-benzyl aromatic and aliphatic aldimines with dimethyl H-phosphonate was found to be accelerated significantly when carried out in an external magnetic field. Its conversion rates were analyzed and compared with those obtained during the aza-Pudovik reaction carried out under standard conditions. Magnetic acceleration was found to have a similar degree as in that observed in the Kabachnik–Fields reaction. However, the formation of the starting imines was found not to be susceptible to constant magnetic field–no acceleration was observed.     

Clustering analysis of different hop varieties according to their essential oil composition measured by GC/MS

This study describes the analysis of total hops essential oils from 18 cultivated varieties of hops, five of which were bred in Lithuania, and 7 wild hop forms using gas chromatography-mass spectrometry. The study sought to organise the samples of hops into clusters, according to 72 semi-volatile compounds, by applying a well-known method, k-means clustering analysis and to identify the origin of the Lithuanian hop varieties. The bouquet of the hops essential oil was composed of various esters, terpenes, hydrocarbons and ketones. Monoterpenes (mainly β-myrcene), sesquiterpenes (dominated by β-caryophyllene and α-humulene) and oxygenated sesquiterpenes (mainly caryophyllene oxide and humulene epoxide II) were the main compound groups detected in the samples tested. The above compounds, together with a-muurolene, were the only compounds found in all the samples. Qualitative and quantitative differences were observed in the composition of the essential oils of the hop varieties analysed. For successful and statistically significant clustering of the data obtained, expertise and skills in employing chemometric analysis methods are necessary. The result is also highly dependent on the set of samples (representativeness) used for segmentation into groups, the technique for pre-processing the data, the method selected for partitioning the samples according to the similarity measures chosen, etc. To achieve a large and representative data set for clustering analysis from a small number of measurements, numerical simulation was applied using the Monte Carlo method with normal and uniform distributions and several relative standard deviation values. The grouping was performed using the k-means clustering method, employing several optimal number of clusters evaluation techniques (Davies-Bouldin index, distortion function, etc.) and different data pre-processing approaches. The hop samples analysed were separated into 3 and 5 clusters according to the data filtering scenario used. However, the targeted Lithuanian hop varieties were clustered identically in both cases and fell into the same group together with other cultivated hop varieties from Ukraine and Poland.     

Reversible Carbon–Carbon Bond Breaking and Spin Equilibria in Bis(pyrimidinenorcorrole)

Reversible homolytic dissociation of the bis(pyrimidinenorcorrole) σ‐dimer was elucidated by means of variable temperature ESR and ¹H NMR spectroscopy, mass spectrometry, and optical spectrocopy. Dehydrogenation of the σ‐dimer yielded another dimer displaying a singlet–triplet equilibrium in solution, strong NIR absorption (1570 nm), and a narrow electrochemical HOMO–LUMO gap (0.74 V).