Conformational transitions of heteropolymers in dilute solutions

In this paper we extend the Gaussian self-consistent method to permit study of the equilibrium and kinetics of conformational transitions for heteropolymers with any given primary sequence. The kinetic equations earlier derived by us are transformed to a form containing only the mean squared distances between pairs of monomers. These equations are further expressed in terms of instantaneous gradients of the variational free energy. The method allowed us to study exhaustively the stability and conformational structure of some periodic and random aperiodic sequences. A typical phase diagram of a fairly long amphiphilic heteropolymer chain is found to contain phases of the extended coil, the homogeneous globule, the micro-phase separated globule, and a large number of frustrated states, which result in conformational phases of the random coil and the frozen globule. We have also found that for a certain class of sequences the frustrated phases are suppressed. The kinetics of folding from the extended coil to the globule proceeds through non-equilibrium states possessing locally compacted, but partially misfolded and frustrated, structure. This results in a rather complicated multistep kinetic process typical of glassy systems.Comment: 15 pages, RevTeX, 20 ps figures, accepted for publication in Phys. Rev.

Модифіковані лакофарбові матеріали прискореної повітряної сушки для захисних антикорозійних покриттів

Розроблено модифіковані лакофарбові матеріали повітряної сушки з покращеними властивостями на основі уретаналкідних та уретанмеламіноалкідних блоккополімерів, що застосовуються для створення захисних антикорозійних покриттів металевих конструкцій різного призначення. Вивчено кінетику взаємодії ізоціанатвмісних олігомерів та функціоналізованих алкідних смол при одержанні блоккополімерів-модифікаторів. Оптимізовано склад синтезованих модифікаторів з визначенням основних характеристик, що впливають на властивості лакофарбового матеріалу. Виготовлено ряд модифікованих лаків та емалей різного призначення з покращеними фізико-механічними властивостями, проведено випробування дослідної партії матеріалу на виробництві.Разработаны модифицированные лакокрасочные материалы воздушной сушки с улучшенными свойствами на основе уретаналкидных и уретанмеламиноалкидных блоксополимеров, применяющиеся для создания защитных антикоррозиционных покрытий металлических конструкций различного назначения. Изучено кинетику взаимодействия изоцианатсодержащих олигомеров и функционализированных алкидных смол при получении блок сополимеров-модификаторов. Осуществлена оптимизация составов синтезированных модификаторов с определением основных характеристик, влияющих на свойства лакокрасочного материала. Изготовлен ряд модифицированных лаков и эмалей различного назначения c улучшенными физико-механическими свойствами, проведены исследования опытной партии материала на производстве.The modified paintwork materials with forced air-drying and perfected characteristic based on the urethane-alkyd and urethane-melamine-alkyd block copolymers which are used in protective anticorrosive coatings of different metallic constructions are designed. The kinetics of isocyanate oligomers and functional alkyd resins interaction during block copolymers-modifier synthesis is studied. The synthesized modifier composition was optimized along with the determination of the main characteristics influencing upon paintwork materials’ properties. The assortment of modified varnishes and enamels for different purposes with improved physical-mechanical characteristics are made; industry investigations of the experimental batch of the materials were conducted

Exploring the limits of the geometric copolymerization model

The geometric copolymerization model is a recently introduced statistical Markov chain model. Here, we investigate its practicality. First, several approaches to identify the optimal model parameters from observed copolymer fingerprints are evaluated using Monte Carlo simulated data. Directly optimizing the parameters is robust against noise but has impractically long running times. A compromise between robustness and running time is found by exploiting the relationship between monomer concentrations calculated by ordinary differential equations and the geometric model. Second, we investigate the applicability of the model to copolymerizations beyond living polymerization and show that the model is useful for copolymerizations involving termination and depropagation reactions

Synthesis and characterization of arginine-doped heliotrope leaves with high clean-up capacity for crystal violet dye from aqueous media

Novel an arginine-modified Heliotrope leaf (Arg@HL) was used as adsorbent for the crystal violet (CV) dye adsorption in a batch process. The physicochemical and morphological composition of Arg@HL were characterized by field-emission-scanning-electron-microscopy (FE-SEM), Fourier transforms infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC). The experiments were carried out to investigate the factors that influence the dye uptake by the adsorbent, such as the contact time under agitation, adsorbent amount, initial dye concentration, temperature and pH of dye solution. The optimum conditions of adsorption were found on the batch scale as followed: CV concentration of 20 mg center dot L-1, an amount of 0.75 g center dot L-1 of the adsorbent, 90 min contact time, 6 pH and 25 degrees C temperature for Arg@HL. The results confirmed a second-order model explaining the dye crystal violet's adsorption's kinetics by Arg-Heliotrope leaves. The Langmuir model effectively defines the adsorption isotherms. The results revealed that the Arg@HL has the potential to be used as a low-cost adsorbent for the removal of CV dye from aqueous solutions

Transient Optical Characterisation of Donor-Acceptor Block Copolymers for Use in Solar Cells

This thesis presents a study of photo-active, semiconducting block copolymers for use in molecular solar cells. Current state-of-the-art organic devices utilise blends of two (or more) materials that are co-deposited from a common solution; the resulting structures formed are determined by material properties and deposition conditions, but often result in configurations that are detrimental to device performance. An answer to this problem comes in the form of the block copolymer; using these materials, devices can be formed from a single material active layer. In addition, the counterbalance of forces within films of block copolymer can lead to nano-scale self-assembly that allows for a strong degree of control over layer equilibrium morphology. Such control will be an important step forward in the evolution of molecular solar cells. The main body of this work is concerned with the study of the photo-physics of photo-conductive block copolymers, especially the generation of free charge. First, an investigation is made into the inherent structure-function relationship in block copolymers. A varying chain length is seen to drastically affect the photoluminescence quenching and yield of long-lived charges. Photovoltaic devices made using these materials show a peak efficiency of 0.11% and correlate with the spectroscopic results, subject to a trade off between charge generation and transport/collection. In a second investigation, the effects of post-fabrication annealing on block copolymer films are considered; studies on annealed samples lead to the conclusion that domain crystallinity is a significant factor in determining the yields of long-lived charge carriers. It is found that these yields are comparable with those of a standard blend (that achieve 75% photon to electron conversion efficiency). Annealing leads to increases in photovoltaic device performance over unannealed samples, although additional control over active layer morphology is necessary for these materials to attain their potential. Following this, a comparative study is made between a block copolymer and a similarly composed blend formed from well studied polyfluorene copolymers. Further advantages of block copolymers are highlighted, including the stability of morphologies generated under different deposition conditions. Finally, a novel tool set is introduced using a block copolymer sample to emphasise the experiments potential with regard to studying interfacial photophysical effects

Functionalization of biodegradable polymers by itaconic anhydride

Předložená diplomová práce se zabývá přípravou biodegradabilního termosenzitivního triblokového kopolymeru na bázi polyethylenglykolu, kyseliny polymléčné a polyglykolové (PLGA-PEG-PLGA) a dále pak především jeho modifikací anhydridem kyseliny itakonové (ITA), který dodá kopolymeru jak reaktivní dvojné vazby tak i funkční karboxylové skupiny důležité pro reakci s biologicky aktivními látkami. Hlavním cílem bylo optimalizovat reakční podmínky pro dosažení nejvyššího stupně navázání ITA na polymer za vzniku ITA/PLGA-PEG-PLGA/ITA. Uvedený kopolymer je po vytvoření heterogenního kompozitu např. s hydroxyapatitem vhodný pro biomedicíncké aplikace především v oblasti tkáňového inženýrství jako dočasná náhrada či fixace tvrdých tkání (kostí). V teoretické části uvedené práce jsou na základě literární rešerše obecně popsány hydrogely, jejich rozdělení, síťování a degradace. Stručně jsou rozepsány fyzikální a chemické vlastnosti a syntéza jednotlivých biomateriálů použitých při syntéze, anhydridu kyseliny itakonové a jejich kopolymerů. Experimentální část popisuje detailně syntézu PLGA-PEG-PLGA kopolymeru polymerací za otevření kruhu pomocí vakuové linky a Schlenkových technik. Byla sledována i kinetika polymerace s navržením nejvhodnějších podmínek syntézy. Uvedený kopolymer byl následně modifikován anhydridem kyseliny itakonové opět katalytickou reakcí za otevření kruhu. V důsledku optimalizace reakčních podmínek byl sledován vliv teploty, rozpouštědla, času a čistoty vstupních látek. Výsledný ITA/PLGA-PEG-PLGA/ITA kopolymer byl charakterizován pomocí 1H NMR, FT-IR a GPC metody. Byly sledovány kinetiky polymerace PLGA-PEG-PLGA kopolymeru a to z přesublimované a nepřesublimované kyseliny polymléčné a polyglykolové. V obou případech probíhala kinetika reakcí bez přítomnosti rozpouštědla při 130 °C po dobu 3 hodin s konverzí asi 90 %. Delší čas neměl vliv na růst konverze. U kinetiky z nepřesublimovaných monomerů byl sledován během několika prvních minut prudký nárůst konverze a pak již byl průběh konstantní, na čase nezávislý. Výsledná polydisperzita kopolymeru byla 1,26 a molekulová hmotnost 7155 g/mol. Optimálních podmínek bylo dosaženo u polymerace z přesublimovaných monomerů, kdy byl nárůst konverze do hodnoty 88 % získané během 2,5 hodin téměř lineární (polymerace byla živá) a poté byl progres konstantní. Byl získán přesně definovaný PLGA-PEG-PLGA kopolymer o molekulové hmotnosti 7198 g/mol a polydisperzitě 1,20. Nejlepších podmínek při syntéze ITA/PLGA-PEG-PLGA/ITA kopolymeru bylo dosaženo reakcí bez přítomnosti rozpouštědla při 110 °C po dobu 1,5 hodiny s přesublimovaným anhydridem kyseliny itakonové, kdy bylo na původní kopolymer navázáno 76.6 mol. %. Výsledná molekulová hmotnost kopolymeru (5881 g/mol) s polydisperzitou 1,37 stanovená pomocí GPC se shodovala s vypočítanou molekulovou hmotností z 1H NMR i s teoretickou molární hmotností (Mn(teor)/Mn(GPC)/Mn(NMR) = 1/0,89/0,96).Presented diploma thesis describes preparation of biodegradable termosensitive triblock copolymer based on poly(ethylene glycol), poly(lactic acid) and poly(glycolic acid) (PLGA-PEG-PLGA) that was subsequently modified by itaconic anhydride (ITA), which gives copolymer both reactive double bonds and functional carboxylic acid groups essential for the reaction with biological active material. The general goal was optimizing reaction conditions in order to reach the highest yield of ITA end-capped to polymer resulting in ITA/PLGA-PEG-PLGA/ITA copolymer. Prepared functionalized copolymer as a component of heterogeneous composite e.g. with hydroxyapatite might be suitable for biomedical application in the field of tissue engineering as a temporary replacement or adhesive of hard tissues (bones). In the theoretical part, hydrogels, their separation, crosslinking and degradation mechanism are generally described together with physico-chemical properties and the synthesis of the individual used biomaterials and their copolymers, itaconic anhydride and its functionalization. The experimental part describes in detail the synthesis of PLGA-PEG-PLGA copolymer via ring opening polymerization (ROP) using vacuum line and Schlenk’s techniques. Kinetics of the ROP was measured and optimization of polymerization conditions was suggested. Prepared thermosensitive copolymer was additionally modified by itaconic anhydride via catalytic ring-opening reaction. Optimization of ITA functionalization conditions were evaluated in terms of effect temperature, time, ITA purification and presence of the solvent effect. Successful end-capping of PLGA-PEG-PLGA copolymer by ITA was precisely characterized by means of 1H NMR, FT-IR and GPC methods. Kinetics of PLGA-PEG-PLGA copolymerization from unsublimated (neat) and sublimated (purified) D,L-lactide and glycolide were studied. In both cases the synthesis proceeded in a bulk at 130 °C for 3 hours with conversion approximately of 90 %. Prolonged polymerization period had no effect on the increase of conversion. In the case of ROP using unsublimated monomers, a rapid increase of monomer conversion was observed during first few minutes, followed by constant progress. Resulting copolymer displayed molecular weight of 7155 g/mol and narrow polydispersity index of 1.26. Optimal conditions were reached when sublimated monomers were polymerized. First, increase of conversion up to 88 % was nearly linear (living polymerization) to 2.5 hours, after that a plateau was observed. Well-defined PLGA-PEG-PLGA copolymer with molecular weight of 7198 g/mol and narrow polydispersity index of 1.20 was obtained. Optimal conditions for synthesis of ITA/PLGA-PEG-PLGA/ITA copolymer were reached with sublimated itaconic anhydride in a bulk at the temperature of 110 °C with total reaction time of 1.5 hours. As a result 76.6 mol. % of ITA was end-capped to the original PLGA PEG PLGA copolymer. Resulting molecular weight of ITA/PLGA-PEG-PLGA/ITA copolymer (5881 g/mol) with polydispersity index of 1.37 found by GPC correlated well with Mn calculated from 1H NMR and a theoretical Mn (Mn(theor)/Mn(GPC)/Mn(NMR) = 1/0.89/0.96).

Comparative assessment of zinc ions sorption and retention by prospective unconventional soil additives

Mining, combustion of coal and waste, and steel processing are the main industrial activities that trigger the emission of large amounts of Zn, which reach the soil and pose a risk to its services, functions, and groundwater quality. A frequently associated process is soil acidification, reducing soil's ability to retain incoming toxic metals. The soil treatments with reactive, low-cost, and locally available materials might be a straightforward approach to decreasing the mobility of toxic metals and alleviating the environmental risks. This study aimed to compare Zn ions sorption and retention by several unconventional soil additives (seashell waste, bone char, and red mud) against the performance of acidic soil. Batch experiments of Zn ions sorption were initially performed using solutions with different Zn concentrations, followed by the determination of sorbed Zn stability in an acidic medium. The waste materials exhibited higher pH values and superior Zn sorption capacities with respect to the soil. The desorption experiment exposed different mechanisms of Zn ions fixation by studied materials. While the substantial amounts of Zn sorbed by seashells, red mud, as well as soil were released in the scope of the ion exchange and carbonate fraction, sensitive to pH decrease, the bone char preserved Zn in more stable fractions. The investigated waste materials can potentially prevent Zn leaching through the soil profile, with the bone char demonstrating the most significant capability for long-term retention performance

Design of nanoplatforms for electrochemical sensing of biomolecules

Nanomaterials exhibit unique chemical, physical and electronic properties that are different from their bulk counterparts, due to their small size, high surface area and specifically arranged architecture. Nanoscale metal oxides in combination with carbonaceous or other nanomaterials, utilized as modifiers of various types of working electrodes, serve as the basis for the development of electroanalytical procedures for the detection of various compounds. Electrochemical sensors that we are being developed are distinguished by high selectivity, sensitivity, low detection limit and thorough real-world sample analysis. Three types of biosensors: non-enzymatic, enzymatic and immuno-biosensors, were developed. Here we present synthesis nanoplatforms and their applications in electrochemical sensing of various biomolecules: a) (Zn,Fe)3O4 for glucose detections, b) amidase/CeO2/GNR for paracetamol monitoring, c) dandelion-like MnO2 for determination of L-dopa and d) citric acid-capped gallium oxyhydroxide for homocysteine impedimetric immunosensing. The design of these materials was analysed by complementary technics (XRPD, SEM, TEM, SQUID, DLS) to determine their (micro)structural properties and correlate them with electroanalytical performance. During the development, sensors’ overall output had to be assessed in detail, especially real-world sample performance and the capability of potential commercialization. Unique electrochemical sensors based on nanomaterials, developed in our group, open new avenues for the design and fabrication of high-performance sensors with great sensitivity to different biomolecules