First Stage Of Synthesis Research Articles

Limiting Properties of Linear Control Systems, Synthesis by LQR Methods According to Quadratic Criteria with One Variable Coefficient

The work provides a comparative analysis of the properties of optimal control systems for linear stationary single-channel objects, the distinctive feature of which is that the numerator polynomial of the object’s transfer function is Hurwitz. Systems are synthesized by two main methods of the theory of analytical design of optimal regulators (ADOR) — methods the Letov-Kalman and A. A. Krasovsky, which use quality functionals based on an integral criterion containing only two terms: the square of the object’s control signal and the square of its output coordinate with a weighting coefficient q . The limiting properties of the synthesized systems are studied at q q → ∞ . The common known property of these systems, for brevity called the Letov-Kalman and Krasovsky systems, is the property of their stability at the limiting value of the weight coefficient and, accordingly, an infinitely large increase in the total gain of these systems, which for them ensures obtaining a given value static control error. Other analyzed properties of the systems turned out to be significantly different and even mutually opposite. For example, at limiting values q q → ∞ , the coefficients of the optimal Letov-Kalman controller do not depend on the parameters of the object, while the coefficients of the Krasovsky controller, on the contrary, are determined exclusively by the parameters of the object. We also note that, unlike Letov-Kalman control systems, the time of transient processes of Krasovsky systems at q q → ∞ cannot be reduced less than a certain finite value, despite the absence of restrictions on the magnitude of the control signal. In this work, with the aim of combining in one control system the indicated positive, but contradictory properties of the analyzed systems, the so-called combined ADOR method is proposed. Its main idea is to represent the control signal of an object by two terms, which are then sequentially determined by using two main methods of the ADOR theory, and at the first stage of synthesis there is control using the Letov-Kalman method, which ensures the direct application of the combined synthesis method to unstable objects. This synthesis method, when using a quality functional with one variable weight coefficient, allows for the considered control objects of order n m 5 to design systems with given values of the static error and control time, for which overregulation does not exceed 5.2 %.

Morphology Variation of Ternary PdCuSn Nanocrystalline Assemblies and Their Electrocatalytic Oxidation of Alcohols.

Metal alloys not only increase the composition and spatial distribution of elements but also provide the opportunity to adjust their physicochemical properties. Recently, multimetallic alloy nanocatalysts have attracted great attention in energy applications and the chemical industry. This work presents the production of three ternary PdCuSn nanocrystalline assemblies with similar compositions via a one-step hydrothermal method. The shape variation of assembly units from nanosheets and nanowires to nanoparticles were realized by adjusting the percentage of Sn in metal precursors. Experimental data show that PdCuSn nanowire networks showed the best catalytic activity by virtue of their optimized morphological characteristics and microscopic electronic structure. With electrooxidation of methanol, ethanol, ethylene glycol, and glycerol at 30 °C, PdCuSn nanowire networks demonstrated catalytic activity of 1129, 2111, 2540, and 1445 mA mg-1, respectively. The catalytic activity for alcohol oxidation is attributed to the production of the electronic structure and morphology features that are most suitable. This is achieved by introducing the proper quantities of Cu and Sn components in the first stage of synthesis. This study would help with the construction of high-efficiency nanostructured alloy catalysts by regulating the electronic structure and morphology.

Monad Theory of Structural Synthesis of Mechanisms

Structural synthesis creates a structural scheme according to the given structural characteristics - the degree of abnormality of the structure S and the degree of its irrationality s. Structural scheme is created at the first stage of synthesis, containing only rotational kinematic pairs and corresponds to a given degree of abnormality, which is ensured by the ratio of structural units – plus monads, minus monads and null monads. At the second stage, the independence of structural characteristics makes it possible to bring the obtained scheme to a given degree of irrationality by downgrading the class of kinematic pairs. The proposed algorithm makes it possible to synthesize structural schemes of both normal structure and adaptive (with redundant motions), as well as indifferent (with redundant links). Monadic approach to structure research allows to formalize the structural features of the circuit and to create a knowledge base for automated design of structural circuits with given structural properties.

Technology of slip casting of celsian-slavsonite ceramics

The article considers the slip casting technology of celsian-slavsonite ceramics with the ratio of raw materials to obtain crystalline phases of ВаAl2Si2O8: SrAl2Si2O8 – 25:75. The manufacture technology of product proceeded in two stages. The first stage of synthesis was performed in a muffle furnace at a rate of temperature of 15 deg / min at a maximum firing temperature of 1200 °C with a holding time of 2 hours. Then the synthesized ceramics were grinded for 10 minutes. The second stage was to obtain a slip with the addition of surfactants (DOLAPIX PC 67). The finished slip was poured into a plaster mold. Drying of the green sample was carried out in an oven at a temperature up to 110 °C for 3 hours. Firing of the dried sample was carried out in a muffle furnace at a rate of set temperature of 15 deg / min, at a maximum firing temperature of 1250 °C for 2 hours. The fired materials were subjected to machining. The obtained data indicate that, the best sample was fired at a temperature of 1250 ° C and had the following properties: dielectric constant — 9.4, water absorption — 5.9 %, open porosity — 14.4 %, apparent density — 2.42 g/cm3, flexural strength — 19 MPa.

Synthesis of a sustainable integrated biorefinery to produce value-added chemicals from palm-based biomass via mathematical optimisation

The past decade has witnessed an increase in biomass usage for combined heat and power generation. Recent advances have been focused on utilising biomass as a raw material to produce value-added bulk chemicals in integrated biorefineries. There is also a lot of opportunities for producing fine chemicals and pharmaceuticals from intermediates derived from palm-based biomass. This work focus on the incorporation of the three pillars of sustainability while converting biomass into all promising products. A mathematical optimisation model has been developed in this work to identify the optimal products that can be produced from palm-based empty fruit bunches (EFB). These products have been evaluated in terms of economic, environmental and social aspects. A comprehensive superstructure that maps all possible products that can be produced from biomass has been developed in the first stage of synthesis. Chemical reaction pathway map (CRPM) was used to illustrate the potential pathways from raw materials to intermediates and then to the final products. An economic and sustainability model was constructed to determine the most profitable configuration and the trade-offs for implementing other sustainability elements into the integrated biorefinery. Multi-objective fuzzy optimisation approach was used to identify the optimal trade-off between gross profit and sustainability index (SI). It has been observed that the sustainability elements can be maintained with minimal compromise on economic performance while synthesising several value-added products. The robustness of the optimal solution was tested by performing sensitivity analysis on production cost, capital cost, and conversion data on processes involving less mature technologies.

Size Distribution, Mechanical and Electrical Properties of CuO Nanowires Grown by Modified Thermal Oxidation Methods.

Size distribution, Young’s moduli and electrical resistivity are investigated for CuO nanowires synthesized by different thermal oxidation methods. Oxidation in dry and wet air were applied for synthesis both with and without an external electrical field. An increased yield of high aspect ratio nanowires with diameters below 100 nm is achieved by combining applied electric field and growth conditions with additional water vapour at the first stage of synthesis. Young’s moduli determined from resonance and bending experiments show similar diameter dependencies and increase above 200 GPa for nanowires with diameters narrower than 50 nm. The nanowires synthesized by simple thermal oxidation possess electrical resistivities about one order of magnitude lower than the nanowires synthesized by electric field assisted approach in wet air. The high aspect ratio, mechanical strength and robust electrical properties suggest CuO nanowires as promising candidates for NEMS actuators.

SYNTHESIS OF ACETYL AND BENZOYL ESTERS OF XANTHORRHIZOL AND ITS OXIDATION PRODUCTS AND EVALUATION OF THEIR INHIBITORY ACTIVITY AGAINST NITRIC OXIDE PRODUCTION

Objective: Xanthorrhizol is known to have anti-inflammatory activity. However, new xanthorrhizol derivatives with improved anti-inflammatoryactivity and reduced toxicity are needed.Methods: In this study, the derivatives of xanthorrhizol were synthesized and spectroscopically characterized, and their inhibitory activities againstnitric oxide (NO) production were evaluated in RAW 264.7 macrophage cells.Results: The first stage of synthesis produced compounds 2a and 2b in 58.49% and 63.26% yields, respectively. Compounds 2a and 2b were oxidizedusing potassium permanganate, giving compounds 3a and 3b in yields of 51.92% and 43.78%, respectively. Compounds 1, 2a, 3a, and 3b alongwith diclofenac sodium (the positive control) exhibited IC50 values for NO production of 31.82, 73.85, 354.05, 97.19, and 78.43 μM, respectively. Incontrast, compound 2b did not show any inhibitory activity. Based on cytotoxicity assay, compounds 1, 2a, 2b, 3a, 3b, and diclofenac sodium had LD50values of 30.97, 65.15, 31.15, 117.86, 53.40, and 51.67 μM, respectively. The NO inhibitory activities of compounds 2a, 3a, and 3b were lower than thatof xanthorrhizol (compound 1). However, cytotoxicity tests showed that compounds 2a, 3a, and 3b had reduced toxicities compared to xanthorrhizol.Conclusion: The modification of xanthorrhizol through esterification and oxidation produced derivative compounds with weaker anti-inflammatoryactivity but reduced cytotoxicity.

Development of methods of determination of technological houses 3,5-dinitro- and 3,5-diaminobenzoics acids at synthesis of sodium amidotrіzоate

Ionogenic contrast preparations, Triombrast, Urographin and Trasograph containing the active pharmaceutical ingredient (APhI), sodium amidotrizoate, have a positive experience in medical diagnosis.
 Qualitative control of intermediate products of each stage of AFI to prevent the possibility of technological toxic impurities – a mixture of 3,5-dinitro- and 3,5-diaminobenzoic acids (3,5-dNBK and 3,5-dABK) in the composition of the target product for safety X-ray contrast drugs in their application is a pressing issue today.
 The aim of the work – to develop a method for determining the technological impurities of 3,5-dNBK and 3,5-dABK acids in the synthesis of amidotrizoate sodium using UV spectrophotometry, which will allow to determine these impurities without their preliminary separation both in the inter-operative process control and in the finished product.
 The objects of study are aqueous solutions of 3,5-dNBK and 3,5-dABK acids, as well as their binary mixtures. The absorption spectra of the analytes were recorded using a Specord UV VIS spectrophotometer in the ultraviolet region. Calculations of the concentrations of the investigated acids in the composition of their binary compositions were performed according to the Vierordt's method.
 It is found that the absorption maxima of aqueous solutions of 3,5-dNBK and 3,5-dABK are at wavelengths of 240 nm and 218 nm; in the experimental conditions, the molar absorption coefficient for 3,5-dinitrobenzoic acid was the same (e1240 = e1218) and was equal to 17 940 ± 150. For solutions of 3,5-diaminobenzoic acid, the molar absorption coefficients were different: for a wavelength of 218 nm, the molar e2218 = 28 890 ± 220 and at a wavelength of 240 nm e2240 = 10 770 ± 80.
 Based on the Firordt method, taking into account the molar absorption coefficients of the investigated acids, we determined mathematical formulas for the quantitative analysis of the composition of mixtures at different ratios of analytes within their total concentration 1–6·10-5 M. Spectrophotometric Vierordt's method of quantitative analysis of 3,5-dinitro- and 3,5-diaminobenzoic acids, as well as their binary mixtures in aqueous solutions can be applied in the industrial production of iodine-containing contrast agents, where in the first stages of synthesis, the corresponding nitrobenzoic acid is reduced. Strict control of the possible amount of impurities in the first stage of synthesis of sodium amidotrizoate – the main active ingredient of ionic iodine-containing X-ray contrast drugs (Triombrast, Urografin, Trasograph) – will improve the quality of the final product and will allow to reduce the final product.

SYNTHESIS AND CHARACTERIZATION OF GRAPHENE FROM COCONUT FIBER (COCOS NUCIFERA) AS ANODE MATERIALS FOR LI-ION BATTERY

Synthesis of graphene from coconut fiber conducted in two stages. The first stage is heating the powder of coconut fiber that passes 325 meshes by hydrothermal method at 200o C for 4 hours. Furthermore, the pyrolysis then treated at temperature of 1000° C for 2 hours. The grain size and surface morphology from graphene observed using SEM in the 1000X magnification. From the SEM image of graphene, it shows the pattern of several thick layers build mutual three-dimensional, forming a flake structure. Observations also show stacks of graphene structure with more big flakes forming a thick pallet. Another characterization was performed by using X-ray diffractometer (XRD), Raman Spectrometer and LCR meter. From XRD observation there is an amorphous pattern at the first stage of synthesis, after pyrolysis at 1000o C for 2 hour a peak near 2θ = 24o, 42oand 52o which corresponds to crystal indexes (002), (400) and (511) became visible. The peak at around 1350 cm-1 in the Raman is the D band. The D band is represented defects, like disruption in the sp2 bonding because of heptagon and pentagon rings, vacancies, edge effect, and etc. DC conductivity or bulk electrical conductivity of about 4.6 x 10-3 Scm-1.

Adsorption properties of synthesised polystyrol-polyanyline composites

In this paper, the results of the study of the possibility of creating a polymeric composite material based on crosslinked polystyrene granules (polymer matrix – ”host”) and polyaniline (a polymer – ”guest”) were presented and the results of the adsorption study of silver ions on the surface of the synthesized polymer composite were presented. Under conditions of suspension polymerization, we synthesized micro-sized polystyrene-divinylbenzene PST–DVB granules (the first stage of synthesis), and then by the method of chemical oxidation polycondensation of aniline under the action of ammonium peroxodisulfate polyaniline particles of the composite PST–PAn were synthesized which were synthesized by us (the second stage of synthesis) in the presence in acidic aqueous solution of sodium dodecylbenzenesulfonate granules of copolymer of styrene with divinylbenzene. The average diameter of the granules of the copolymer (PST–DVB), according to granulometric analysis, had numerical values within the range of 100–650 μm. Based on the IR spectroscopic studies of the chemical structure of the samples obtained, we conclude that there is a possibility of formation of partially penetrating polymer networks in synthesized composites (PAn-crosslinked polystyrene) and the presence of interactions between macromolecular polymer chains. Obviously, aniline penetrates from the solution into a polymeric polystyrene net (swelling process) and then aniline is polymerized by the action of ammonium peroxodisulfate, forming semipermeable spatial networks of these polymers. The processes of adsorption of silver ions on composite granules are investigated. The method of CEM using a raster microscope REMMA-102-02 shows the presence of adsorbed silver on the surface of the granules. The content of silver ions in AgNO 3 solution before and after adsorption on the surface of synthesized polymeric composites (potentiometric titration method) was determined and the mechanism of adsorption of silver on the surface of a polyaniline adsorbent was discussed. Keywords: polyaniline, polystyrene, composite, adsorption of Ag + .

Plasma-arc sputtering for synthesis of Pt/CeO2 and Pd/CeO2 nanosystems

Plasma-arc (PA) sputtering method was applied for synthesis of Pt/CeO2 and Pd/CeO2 nanoparticles. PA represents a joint sputtering of a graphite electrode with various metals (Ce with Pt or Pd). This novel approach allows obtaining highly dispersed metals and ceria on the first stage of synthesis. The thermal treatment of an initial composite in air at 600°C-1000°C results in the burnt of a carbon shell and formation of CeO2 with a fluorite-type structure. XPS and TEM analysis showed that Pd and Pt species are stabilized in the ionic form due to strong interaction with ceria. Obtained nanoparticles have a high potential of application as catalysts for efficient low temperature CO oxidation.

A general strategy for direct synthesis of reduced graphene oxide by chemical exfoliation of graphite

In this work, a first stage of synthesis to obtain reduced graphene oxide (rGO) using an efficient chemical exfoliation method from graphite was studied. An ammonium hydroxide and a nitric-sulfuric acid mixture were used for in situ oxidation and partial-reduction of graphite. Flakes with a thickness of 3 nm were observed by using AFM, suggesting the presence of ten or less graphene layers. The average C/O atomic percentage ratio obtained was 4.27, which is similar to those results obtained by conventional reduction processes associated with using hydrazine. In addition, a graphitic nitrogen functionalization was observed during the proposed process. Besides that, the precursor of rGO suspension obtained remained stable for six months. Therefore, the present study showed a less aggressive and dangerous chemistry route in order to rGO production than others previously reported works.

Synthesized 2,4,5-Triphenylimidazole as Precursor of Organic Light Emitting Diode (OLED) Material

Current research based on fluorescent organic material has many advantages. One of advantages fluorescent organic material is as OLED (Organic Light Emitting Diode) based devices. OLED compound is rigid conjugated organic molecules. 2,4,5-triphenylimidazole (3) was synthesized by microwave assisted organic synthesis method. The first stage of synthesis is the synthesis of bibenzoyl (2) produced from the solventless oxidation reaction of benzoin (1) by atmospheric oxygen using MAOS (Microwave Assisted Organic Synthesis) method with chemical yields of 99.18% and melting point of bibenzoyl is 94-95 °C, and the FTIR spectrum showed the lost of -OH group peak at 3425.51 cm-1 and the strengthening of group C=O peak at 1672.25 cm-1. compound (3) was synthesized from the reactions between compound (2), benzaldehyde, ammonium acetate and acetic acid glacial by MAOS method with chemical yields of 69.04%. Melting point of compound (3) is 267-268°C and FTIR spectrum showed -NH group peak at 3038.53 cm-1 and C-N group peak at 1209.51 cm-1. Result of elucidation by 1H-NMR measurements of compound (3) showed a typical signal of -NH proton at chemical shifts of 9.31 ppm and the phenyl protons in the chemical shifts range of 7.46 to 7.94 ppm. UV-Vis and fluorescence spectra shown compound (3) has a potential as precursor compound of Organic Light Emitting Diode material.

A model for the proteolytic regulation of LpxC in the lipopolysaccharide pathway of Escherichia coli

Lipopolysaccharide (LPS) is an essential structural component found in Gram-negative bacteria. The molecule is comprised of a highly conserved lipid A and a variable outer core consisting of various sugars. LPS plays important roles in membrane stability in the bacterial cell and is also a potent activator of the human immune system. Despite its obvious importance, little is understood regarding the regulation of the individual enzymes involved or the pathway as a whole. LpxA and LpxC catalyze the first two steps in the LPS pathway. The reaction catalyzed by LpxA possesses a highly unfavourable equilibrium constant with no evidence of coupling to an energetically favourable reaction. In our model the presence of the second enzyme LpxC was sufficient to abate this unfavourable reaction and confirming previous studies suggesting that this reaction is the first committed step in LPS synthesis. It is believed that the protease FtsH regulates LpxC activity via cleavage. It is also suspected that the activity of FtsH is regulated by a metabolite produced by the LPS pathway; however, it is not known which one. In order to investigate these mechanisms, we obtained kinetic parameters from literature and developed estimates for other simulation parameters. Our simulations suggest that under modest increases in LpxC activity, FtsH is able to regulate the rate of product formation. However, under extreme increases in LpxC activities such as over-expression or asymmetrical cell division then FtsH activation may not be sufficient to regulate this first stage of synthesis.

Direct synthesis and mechanism of the formation of mixed metal Fe2Ni-MIL-88B

The direct synthesis of Fe3-MIL-88B and Fe2Ni-MIL-88B was analyzed using different characterization techniques including UV-vis, IR, and Raman spectroscopies and XRD. It was found that single metal Fe3-MOF-235 seeds which were formed from the first stage of synthesis are precursors for the formation of MIL-88B. Fe3-MOF-235 seeds formed in the first stage of synthesis were then transformed to Fe3-MIL-88B in the case of single metal, and to mixed Fe2Ni-MIL88B in the case of mixed metal synthesis. In the both cases of Fe3-MIL-88B and Fe2Ni-MIL-88B, the FeCl4− anion is a key feature for the formation of MOF-235. An anion-mediated mechanism for the formation of the MOF-235 structure is also suggested.

Application of a voltammetric method for investigation the formation mechanisms of silver nanoparticles in multicomponent solutions

A voltammetric method has been tested for the investigation of the kinetics of formation of silver nanoparticles in two systems: (a) silver(I) triflourineacetate, methylcellosolve, butyl acetate, toluene and methyl methacrylate with methacrylic acid copolymer; and (b) silver nitrate, sodium citrate, poly-N-vinyl-2-pirrolydone, sodium borohydride. It could be established for the first system that the formation rate of metal nanoparticles from silver triflourineacetate solutions depends on the dielectric constant and complexing ability of the solvent. The formation of silver particles proceeds faster in methylcellosolve than in other solvents. The butyl acetate addition to the solution contributes to the complex stability of methylcellosolve with silver triflourineacetate and decelerates the formation process of particles. It could be shown that nitrogen purging of solutions containing poly-N-vinyl-2-pirrolydone affects the silver-ion concentration in the first stage of synthesis and accelerates the formation process of nanoparticles for the second system. The spherical silver nanoparticles which are formed at the first stage of the synthesis are destroyed after starting the UV–irradiation. Then new silver nanoparticles (triangular prisms) are formed.

Hyperbranched polylysines: Mechanism of formation

To gain insight into the mechanism treating formation of hyperbranched polylysines through the polymerization of N ɛ-carbobenzoxylysine N-carboxyanhydride under conditions of the reductive removal of a N ɛ-carbobenzoxy group, hyperbranched polylysine has been synthesized with the use of trifluoroacetic acid as a terminator in the polymerization of N-carboxyanhydride. The structure of the polymers is studied by capillary electrophoresis, low-pressure gel-permeation chromatography, circular dichroism, and enzymatic hydrolysis with trypsin. At the first stage of synthesis, a low-molecular-mass strongly branched core of the polymer is formed. At the second stage, polylysine chains are grafted via one point onto amino groups of N-terminal lysine moieties of the low-molecular-mass core through their carboxyl ends.

Preparation of 5A zeolite monolith granular extrudates using kaolin: Investigation of the effect of binder on sieving/adsorption properties using a mixture of linear and branched paraffin hydrocarbons

A zeolite monolith extrudates using kaolin is synthesized, and effect of binders on sieving/adsorption properties of the prepared zeo- lite is reported. The monolith extrudates of 4A zeolite powder produced as the precursor of 5A zeolite in the first stage of synthesis pro- cess was prepared using different percentages of kaolin powder and carboxymethylcellulose (CMC) as binding agent. The average particle size distribution of produced 4A zeolite was between 20 and 40 US standard mesh sizes equivalent to 0.841 mm and 0.420 mm, respectively. The extrudate was calcined at 600 � C, and the kaolin content of extrudates was converted to type A zeolite through ion exchange by immersing the extrudates in caustic soda solution. The 4A zeolite extrudate samples were converted to 5A type through ion exchange process using calcium chloride solution. The 5A zeolite samples were characterized using XRD, SEM, and EDX instrumental analytic methods. Sieving test was carried out using samples of 5A zeolite and a special cut of kerosene containing C10-C13 saturated hydrocarbons using a simple dead-end fixed bed. Results show that the highest purity of 5A zeolite, highest rate of calcium ion exchange, and best sieving results are obtained when 30 wt% of binder (kaolin) is used, and use of small amounts of CMC as an organic binder along with inorganic kaolin binder has a pro- found effect on the adsorption properties of the synthesized 5A zeolite. This profound effect is attributed to de-clogging of the cylindrical pores due to CMC gasification in final calcinations of the extrudates.

Synthesis of nanocrystalline magnesium diboride (MgB 2) metallic superconductor by mechano-chemical reaction and post-annealing

MgB 2 is recently discovered superconducting compound with a record-breaking transition temperature ( T c = 39 K) for a conventional metallic superconductor. Nanocrystallinity can improve its electrical properties by strong pinning. In the present work we report the results of the synthesis of nanocrystalline MgB 2 superconducting compound by mechano-chemical reaction followed by post-annealing. The first stage of synthesis was carried out from elemental crystalline Mg and amorphous B powders by controlled mechanical alloying (CMA) in the magneto-mill Uni-Ball-Mill 5. X-ray diffraction studies reveal that the nucleation of small amount of MgB 2 is initiated after two-step milling for combined 100 h under protective helium gas. Further reaction to form MgB 2 is accelerated by subsequent annealing of the milled powder at various temperatures. X-ray diffraction shows formation of a well-developed nanocrystalline MgB 2 after annealing of the pre-nucleated powder at the 630–650 °C range for a few hours.

Study of the Properties of Electrodeposited Polypyrrole Films

Experimental and theoretical methods have been used for characterization of the properties of polypyrrole films. The AFM studies show that the morphology of polypyrrole (PPy) films on polycrystalline gold electrodes at the first stages of synthesis depends on the structure of the metal surface. It was established that mobility of anions depends remarkably on the rate of electrodeposition of the polymer film. If PPy film was deposited at relatively low current density, mobility of ClO-4 anion was not high enough to guarantee electroneutrality during redox cycling and cations take part in this process especially when Li+ cations were replaced by more mobile К+ cations. Semiempirical (AM1 and PM3) quantum-chemical methods were used for theoretical studies. It was established that different size and charge of the anions together with the variation in doping levels give rise to a different optimal conformation of oligopyrrole cations which, in turn, define the resulting polymer to be either all-anti (common linear chains) or all-syn (formation of helical structures) or a combination of the two.