Non-hydrolysable Phosphinic Analogues of Dipeptides

Abstract

Peptide analogues 1 in which the phosphonamide group replaces the amide function are thought to mimic the tetrahedral intermediates and transition states in peptide hydrolysis. While pepti-des 1 are potent inhibitors of some peptidases, their unsefulness is limited by rapid hydrolysis of P-N bond in aqueous media. To circumvent the instability problem we designed peptide analogues 2 with a CH₂ group inserted between the phosphorus and nitrogen atoms. Such structures are resistant to hydrolysis but it was interesting to see if they are similar enough to pepti-des to retain any affinity to enzyme active sites.     

Activated monomer propagation in cationic polymerizations

New mechanism of cationic polymerization of cyclic ethers and acetals consisting in the activated (e.g. protonated) monomer addition to the electrically neutral macromolecule e.g.: is discussed. It is shown, that when the -OH in the tail-group is more nucleophilic than monomer itself this mechanism has chances to dominate over the traditional mechanism of propagation, involving tertiary oxonium ion. Kinetics of the polymerization process, elementary reactions, competition with the tertiary oxonium ion growth are discussed. Examples are given, based on the work on ethylene oxide and epichlorohydrin polymerization, showing how to apply the theory of the activated monomer in order to avoid side reactions, namely cyclization and disproportionation of the chains.     

Organic Thermoelectric Materials as the Waste Heat Remedy

The primary reason behind the search for novel organic materials for application in thermoelectric devices is the toxicity of inorganic substances and the difficulties associated with their processing for the production of thin, flexible layers. When Thomas Seebeck described a new phenomenon in Berlin in 1820, nobody could have predicted the future applications of the thermoelectric effect. Now, thermoelectric generators (TEGs) are used in watches, and thermoelectric coolers (TECs) are applied in cars, computers, and various laboratory equipment. Nevertheless, the future of thermoelectric materials lies in organic compounds. This paper discusses the developments made in thermoelectric materials, including small molecules, polymers, molecular junctions, and their applications as TEGs and/or TECs.     

Star‐Shaped Conjugated Molecules with Oxa‐ or Thiadiazole Bithiophene Side Arms

Star‐shaped conjugated molecules, consisting of a benzene central unit symmetrically trisubstituted with either oxa‐ or thiadiazole bithiophene groups, were synthesized as promising molecules and building blocks for application in (opto)electronics and electrochromic devices. Their optical (E_g(opt)) as well as electrochemical (E_g(electro)) band gaps depended on the type of the side arm and the number of solubilizing alkyl substituents. Oxadiazole derivatives showed E_g(opt) slightly below 3 eV and by 0.2 eV larger than those determined for thiadiazole‐based compounds. The presence of alkyl substituents in the arms additionally lowered the band gap. The obtained compounds were efficient electroluminophores in guest/host‐type light‐emitting diodes. They also showed a strong tendency to self‐organize in monolayers deposited on graphite, as evidenced by scanning tunneling microscopy. The structural studies by X‐ray scattering revealed the formation of supramolecular columnar stacks in which the molecules were organized. Differences in macroscopic alignment in the specimen indicated variations in the self‐assembly mechanism between the molecules. The compounds as trifunctional monomers were electrochemically polymerized to yield the corresponding polymer network. As shown by UV/Vis‐NIR spectroelectrochemical studies, these networks exhibited reversible electrochromic behavior both in the oxidation and in the reduction modes.     

Cationic copolymerization of racemic‐β‐butyrolactone with L,L‐lactide: One‐pot synthesis of block copolymers

Cationic copolymerization of racemic‐β‐butyrolactone (β‐BL) with l,l ‐lactide (LA) initiated by alcohol and catalyzed by trifluoromethanesulfonic acid proceeding by activated monomer (AM) mechanism was investigated. Although both comonomers were present from the beginning in the reaction mixture, polymerization proceeded in sequential manner, with poly‐BL formed at the first stage acting as a macroinitiator for the subsequent polymerization of LA. Such course of copolymerization was confirmed by following the consumption of both comonomers throughout the process as well as by observing the changes of growing chain‐end structure using ¹H NMR. ¹³C NMR analysis and thermogravimetry revealed the block structure of resulting copolymers. The proposed mechanism of copolymerization was confirmed by the studies of changes of ¹H NMR chemical shift of acidic proton in the course of copolymerization, providing an indication that indeed protonated species and hydroxyl groups are present throughout the process, as required for AM mechanism. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4873–4884     

Hydrogels as Scaffolds in Bone-Related Tissue Engineering and Regeneration

Several years have passed since the medical and scientific communities leaned toward tissue engineering as the most promising field to aid bone diseases and defects resulting from degenerative conditions or trauma. Owing to their histocompatibility and non-immunogenicity, bone grafts, precisely autografts, have long been the gold standard in bone tissue therapies. However, due to issues associated with grafting, especially the surgical risks and soaring prices of the procedures, alternatives are being extensively sought and researched. Fibrous and non-fibrous materials, synthetic substitutes, or cell-based products are just a few examples of research directions explored as potential solutions. A very promising subgroup of these replacements involves hydrogels. Biomaterials resembling the bone extracellular matrix and therefore acting as 3D scaffolds, providing the appropriate mechanical support and basis for cell growth and tissue regeneration. Additional possibility of using various stimuli in the form of growth factors, cells, etc., within the hydrogel structure, extends their use as bioactive agent delivery platforms and acts in favor of their further directed development. The aim of this review is to bring the reader closer to the fascinating subject of hydrogel scaffolds and present the potential of these materials, applied in bone and cartilage tissue engineering and regeneration.     

Variability of spatio-temporal patterns in non-homogeneous rings of spiking neurons

We show that a ring of unidirectionally delay-coupled spiking neurons may possess a multitude of stable spiking patterns and provide a constructive algorithm for generating a desired spiking pattern. More specifically, for a given time-periodic pattern, in which each neuron fires once within the pattern period at a predefined time moment, we provide the coupling delays and/or coupling strengths leading to this particular pattern. The considered homogeneous networks demonstrate a great multistability of various travelling time- and space-periodic waves which can propagate either along the direction of coupling or in opposite direction. Such a multistability significantly enhances the variability of possible spatio-temporal patterns and potentially increases the coding capability of oscillatory neuronal loops. We illustrate our results using FitzHugh-Nagumo neurons interacting via excitatory chemical synapses as well as limit-cycle oscillators.     

The Study of Derivatization Prior MALDI MSI Analysis—Charge Tagging Based on the Cholesterol and Betaine Aldehyde

Mass spectrometry imaging is a powerful tool for analyzing the different kinds of molecules in tissue sections, but some substances cannot be measured easily, due to their physicochemical properties. In such cases, chemical derivatization could be applied to introduce the charge into the molecule and facilitate its detection. Here, we study cholesterol derivatization with betaine aldehyde from tissue slices and evaluate how different sample preparation methods influence the signal from the derivatization product. In this study, we have tested different solutions for betaine aldehyde, different approaches to betaine aldehyde deposition (number of layers, deposition nozzle height), and different MALDI matrices for its analysis. As a result, we proved that the proposed approach could be used for the analysis of cholesterol in different tissues.