University of Chemical Technology and Metallurgy
Recent publications
165 crude oils with viscosity, density, and molecular weight variation in the range 0.54 – 24135cP; 0.746 – 1.016 g/cm³; 117–579 g/mol respectively were examined for viscosity prediction using eight available in the literature models and three more, developed in this work models. The best empirical model was that of Sinha et al., 2020 with % AAD (absolute average deviation) = 18.2 %, The ANN (artificial neural network) model for the data set of the 165 crude oils outperformed the empirical correlations with % AAD = 17.7 %. 93 crude oils with viscosity, density, molecular weight, and SARA composition data variation in the range 2.3 – 23 000cP; 0.819 – 0.992 g/cm³; 179–579 g/mol; Sat.: 26.0–79.3 %; Aro:11.9–52.8 %; Res.: 2.5–30.9; Asp.:0.1–19.6 % respectively were also examined for viscosity prediction by the available in the literature empirical correlations and another new developed empirical correlation that includes besides molecular weight and density, the crude oil saturate content. The best empirical model was that developed in this work with saturate content inclusion, that showed % AAD = 23.8 %. The ANN model for the data set of 93 crude oils again outperformed the empirical correlations with % AAD = 18.8 %. The most accurate model predicting viscosity was found the new developed in this work model on the base of a reference viscosity at a particular temperature and molecular weight with %AAD = 2.5 %.
Our study evaluated the in vitro antioxidant properties, antibacterial and antifungal activities, anti-inflammatory properties, and chemical composition of the essential oils (EOs), total phenol, and total flavonoid of wild Mentha pulegium L. This study also determined the mineral (nutritional and toxic) elements in the plant. The EOs were extracted using three techniques—hydro distillation (HD), steam distillation (SD), and microwave-assisted distillation (MAD)—and were analyzed using chromatography coupled with flame ionization (GC-FID) and gas chromatography attached with mass spectrometry detector (GC-MS). The antioxidant effects of the EOs were tested with 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ABTS (2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid), while the antibacterial and antifungal activities of the EO and methanolic extract were tested using Staphylococcus aureus, Bacillus subtilis, Pseudomonas aeruginosa, Escherichia coli, and Candida albicans. Twenty-six compounds were identified in the essential oil, representing 97.73% of the total oil, with 0.202% yield. The major components were pulegone (74.81%), menthone (13.01%) and piperitone (3.82%). Twenty-one elements, including macro- and micro-elements (Ba, Br, Ca, Cl, Co, Cr, Cs, Eu, Fe, K, Mg, Mn, Mo, Na, Rb, Sb, Sc, Sr, Th, U and Zn), were detected using neutron activation analysis (INAA) and inductively coupled plasma optical emission spectrometry (ICP-OES), with the concentration of mineral element close to the FAO recommendation. The results show that the EOs and extracts from Mentha pulegium L. had significant antimicrobial activities against the microorganisms, including five human pathogenic bacteria, one yeast (Candida albicans), and one phytopathogenic fungi. The in vivo anti-inflammatory activities of the leaf extracts were confirmed. The results indicate that the EOs and extracts from Mentha pulegium L. have promising applications in the pharmaceutical industries, clinical applications, and in medical research.
In recent years, non-wovens have become the main segment of textile production because they can find applications in different areas. Thermal insulation properties, fire resistance, and flexibility make them cost-effective and efficient insulation panels for buildings. This paper aims to study the influence of the production method and surface treatment on the thermophysical characteristics and behavior under direct fire of two polyethylene terephthalate non-woven fabrics. The fibers have been bonded with polyacrylate adhesive or thermal and coated with silicone. Infrared spectroscopy, optical microscopy, and thermal analyses were applied to compare the non-wovens’ morphology, composition, and thermal properties. It founds that the non-woven polyester with acrylic additives and adhesive bonding has a higher thermal conductivity value and high flammability with complete combustion. In contrast, thermosetting siliconized polyester materials have limited flammability with limited droplet release. The silicone-based finish protects the polyester fibers leading to self-extinguishing and stopping the complete combustion of the sample.
The endogenous hemorphins are bioactive peptides with activity on opioid receptors. They are extensively studied and summarized in numerous reviews. During the last decade, several research teams have synthesized, characterized, and pharmacologically evaluated synthetic hemorphin analogs containing unusual amino acids, D-amino acids, α-aminophosphonic acids, and their derivatives. The present review summarizes the current studies on short-chain synthetic hemorphin peptide derivates containing non-natural amino acids. This review focuses on the structure–activity relationship analysis, details on specific methods for their characterization, and the advantage of synthetic hemorphin analogs compared to endogenous peptides as potent biologically active compounds with a complex mechanism of action.
A survey of the experimental equilibrium constants in solution for the mixed complexes of 4f ions with acidic (chelating) and O-donor organophosphorus ligands published in the period between 1954 and 2022 is presented. These data are widely used in both analytical and solvent extraction chemistry. Important data evaluation criteria involved the specification of the essential reactions, process conditions and the correctness of techniques and calculations used, as well as appropriate equilibrium analysis of experimental data. Higher-quality data have been evaluated, compiled and presented herein, providing a synoptic view of the unifying theme in this area of research, i.e., synergism.
Galantamine is a natural alkaloid witha proved antioxidant activity, which easily passes the blood-brain barrier. This makes it a reliable drug for the treatment of many human brain diseases.In this paper we report the results of quantum chemical calculations of the dissociationenthalpies of O-H and C-H bonds in galantamine. The results clearly show the propensity of galantamine to react with radicals in the living organisms.This includes an assessment of the stability of O-H and C-H bonds in it, as well as their acidity.In addition, hydride ion abstraction reactions such as occur with nicotine-amid-adenine-dinucleotide (NAD) are discussed here.
In order to study the purification of hydrogen and its separation from gas mixtures by adsorption, different models describing the adsorption equilibrium of gas mixtures have been tested; seven of them have been compared with experimental multi-component data obtained from the literature. The measurements include three-component mixtures of hydrogen, nitrogen, and methane. All the models used in this study are purely predictive; such models are competitive isotherm models which use only the previously obtained coefficients of the single-component isotherms. A mathematical description of each model is developed and discussed. Based on the results of numerical experiments, an analysis of how best to apply the Sips multi-component approach and the Ideal Adsorbed Solution theory is developed. A discussion on the ability and accuracy of the different models to describe the multi-component adsorption equilibria is developed. Based on this research, the Jovanovic model, which best reproduces the experimental results of the adsorption equilibrium in all cases, can be recommended as the most appropriate to use.
A novel highly water-soluble 1,8-naphthalimide with pH and viscosity-sensing fluorescence was synthesized and investigated. The synthesized compound was designed as a molecular device in which a molecular rotor and molecular “off-on” switcher were integrated. In order to obtain a TICT driven molecular motion at C-4 position of the 1,8-naphthalimide fluorophore, a 4-methylpiperazinyl fragment was introduced. The molecular motion was confirmed after photophysical investigation in solvents with different viscosity; furthermore, the fluorescence-sensing properties of the examined compound were investigated in 100% aqueous medium and it was found that it could be used as an efficient fluorescent probe for pH. Due to the non-emissive deexcitation nature of the TICT fluorophore, the novel system showed low yellow–green emission, which represented “power-on”/“rotor-on” state. The protonation of the methylpiperazine amine destabilized the TICT process, which was accompanied by fluorescence enhancement indicating a “power-on”/“rotor-off” state of the system. The results obtained clearly illustrated the great potential of the synthesized compound to serve as pH- and viscosity-sensing material in aqueous solution.
Endogenous hemorphins are being intensively investigated as therapeutic agents in neuropharmacology, and also as biomarkers in mood regulation, inflammation and oncology. The datasets collected herein report physicochemical parameters of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine membranes in the presence of VV-hemorphin-5 (Val-Val-Tyr-Pro-Trp-Thr-Gln) and analogues, modified at position 1 and 7 by the natural amino acid isoleucine or the non-proteinogenic 2-aminoisobutyric, 2,3-diaminopropanoic or 2,4-diaminobutanoic amino acids. These peptides have been previously screened for nociceptive activity and were chosen accordingly. The present article contains fluorescence spectroscopy data of Laurdan- and di-8-ANEPPS- labelled large unilamellar vesicles (LUV) providing the degree of hydration and dipole potential of lipid bilayers in the presence of VV-hemorphin-5 analogues. Lipid packing is accessible from Laurdan intensity profiles and generalized polarization datasets reported herein. Data presented on fluorescence intensity ratios of di-8-ANEPPS dye provide dipole potential values of phosphatidylcholine-valorphin membranes. Vesicle size and electrophoretic mobility datasets included refer to the effect of valorphins on the size distribution and ζ-potential of POPC LUVs. Investigation of physicochemical properties of peptides such as diffusion coefficients and heterogeneous rate constant relates to elucidation of transport mechanisms in living cells. Voltammetric data of valorphins are presented together with square-wave voltammograms of investigated peptides for calculation of their heterogeneous electron transfer rate constants. Datasets from the thermal shape fluctuation analysis of quasispherical ‘giant’ unilamellar vesicles (GUV) are provided to quantify the influence of hemorphin incorporation on the membrane bending elasticity. Isothermal titration calorimetric data on the thermodynamics of peptide-lipid interactions and binding affinity of valorphin analogues to phosphatidylcholine membranes are reported. Data of frequency-dependent deformation of GUVs in alternating electric field are included together with the values of the specific electrical capacitance of POPC-valorphin membranes. Datasets reported in this article can underlie the formulation and implementation of peptide-based strategies in pharmacology and biomedicine.
Titanium-based composites have potential applications in the aeronautical industry as multifunctional materials and/or magnetic shape memory composites (MSMCs). In this work, gas-atomized recycled pure iron (1–5 μ) and fine magnetic iron oxide (<1 μ-Fe3O4) were used as reinforcements for pure titanium (VWR) Two types of composites were fabricated by using a powder metallurgy-combined method: sintering + forging. Two types of processes were carried out at two different sintering temperatures (600 °C and 850 °C). As known, the Ti-Fe eutectic temperature is ~750 °C. Increasing of the pure iron to 45 wt% gives rise to the formation of Ti-Fe intermetallic in the composites. As a result, mechanical properties of the sintered forging composites were considerably improved. Electrical and thermal behaviour and magnetic permeability were measured. The microstructure analyses and the diffusion mechanism at the Ti-Fe interface are also investigated by using scanning electron microscopy (SEM).
The novel PAMAM perylene tetracarboxydiimide 5 was synthesized via PAMAM divergent strategy, involves initial Michael addition of aminofunctional core 3 with methyl acrylate followed by exhaustive amidation of the resulting ester 4 with a large excess of ethylenediamine to afford the fluorescent dendrimer 5 with reactive amine groups of its periphery, The chosen fluorophore units are suitable donor–acceptor pair for light-harvesting materials which was in agreement with their good antibacterial activity.
252 literature sources and about 5000 crude oil assays were reviewed in this work. The review has shown that the petroleum characterization can be classified in three categories: crude oil assay; SARA characterization; and molecular characterization. It was found that the range of petroleum property variation is so wide that the same crude oil property cannot be measured by the use of a single standard method. To the best of our knowledge for the first time the application of the additive rule to predict crude oil asphaltene content from that of the vacuum residue multiplied by the vacuum residue TBP yield was examined. It was also discovered that a strong linear relation between the contents of C5-, and C7-asphaltenes in crude oil and derived thereof vacuum residue fraction exists. The six parameter Weibull extreme function showed to best fit the TBP data of all crude oil types, allowing construction of a correct TBP curve and detection of measurement errors. A new SARA reconstitution approach is proposed to overcome the poor SARA analysis mass balance when crude oils with lower density are analyzed. The use of a chemometric approach with combination of spectroscopic data was found very helpful in extracting information about the composition of complex petroleum matrices consisting of a large number of components.
Gunshot residue (GSR) is a material formed during firearm discharge with a specific spheroidal/noncrystalline morphology and chemical composition. The examination of gunshot residue by SEM/EDS is an important tool in forensic studies and presents supporting evidence in criminal investigations. This study is aimed at exploring the number of particles characteristic of GSR identified by SEM/EDS as a function of time, gun caliber, the number of shots, and weather conditions. Firearms typically used in criminal cases in Kosovo were studied, and the experiments were conducted outdoors in the summer and winter seasons. Nine people made different numbers of shots from one to nine and followed a common office routine. An optimized and validated SEM/EDS protocol was applied with a sensitivity of 95%, a bias of −5%, a repeatability of 2% (RSD), a within-lab reproducibility of 2% (RSD), and an expanded uncertainty of the number of GSR particles of 6% at coverage factor k = 2. The results showed that GSR particles could be identified by SEM/EDS five to seven hours after shooting, depending on the weapon used and number of produced shots. The results will benefit forensic scientists by providing a supportive tool for hypothesizing the time interval between firearm discharge and GSR sampling.
Analysis and approximate integral-balance solutions of a non-linear diffusion model of wood impregnation by methacrylate have been developed in two cases: (i) Dirichlet boundary condition assuming instantaneous saturation of the wood surface contacting the liquid bath and (ii) Relaxing Dirichlet boundary conditions accounting for the fact that instantaneous saturation is unphysical and takes some time to be established.KeywordsDiffusionWood impregnationNon-linear diffusivityApproximate solutionsRelaxing boundary conditions
The emergence of diverse peptide derivatives has been due to constant efforts to find a specific peptide with pronounced biological activity for effective application as a therapeutic. Spinorphin-peptide products have been reported to possess various applications and properties. In the present study, spinorphin peptides with a rhodamine residue and a modification in the amino acid backbone were synthesized by a solid-phase method using Fmoc chemistry. The results obtained from the spectral and electrochemical techniques used: Scanning electron microscopy (SEM), UV-vis, fluorescence, infrared spectroscopy (IR), and voltammetry were used to elucidate the structural characteristics and some physicochemical properties to gain insight into their behavior in the solid state and in aqueous solutions with different pHs. Both Rh-S5 and Rh-S6 had compound anticonvulsant effect comparable to Rh-S against psychomotor seizures at the highest dose of 20 μg. Furthermore, Rh-S6 showed a strong ability to inhibit seizure propagation and had a similar threshold to Rh-S against the intravenous pentylenetetrazol induced clonic seizure in mice; one of the three hybrid spinorphin analogs tested when screened for anticonvulsant activity. Biological tests against several bacterial pathogens such as Staphylococcus aureus, Escherichia coli, and Bacillus cereus showed similar results to negative control of the new peptide derivatives. The compounds also showed weak activity against Candida albicans fungus. The antioxidant testing results revealed more than 50% activity by reviewing the radical deterrence capabilities of 2,2-diphenyl-1-picrylhydrazyl (DPPH). The results are indicative of the ongoing search for universal antimicrobial agents with pronounced synergism when used simultaneously as anticonvulsant, antibacterial, and antifungal agents.
The present paper reviews and analyses different models that could be used to describe the adsorption equilibrium of pure gases. The adsorption equilibrium of hydrogen, nitrogen and methane is characterised and modelled. Several thermodynamic conceptions have been selected and tested for the calculation of physico-chemical parameters. The model of Dubinin has been selected to estimate the pseudo-saturation vapour pressure. The best results for the molar volume of the adsorbate have been obtained by using Do’s equation. Eight models, namely Langmuir, Freundlich, Sips, Toth, Jovanovic, UNILAN, OBMR and Potential Theory, describing the adsorption equilibrium of pure gases, have been tested and compared with experimental data obtained from the literature at three different temperatures (283 K, 298 K and 313 K). In order to determine the best fit, the correlation coefficient and the standard errors for each parameter have been used to evaluate the data. All the models used in this study, except for Freundlich’s equation in the case of nitrogen or methane adsorption, are in good agreement between experiment and modelling for the adsorption isotherms.
Ace naphthene as a primary material was nitrated and further reacted by various processes such as oxidation, imidation and amination in order to obtain dyad 5. The dyad 5 fluoresces in solvents of different polarity and the emission is shifted bathochromically with increasing the solvent polarity due to ICT enhancement, The fluorescent enhancement is greatest in case of chloroform (ФF = 0.48) on excitation at 420 nm,The influences of the pH on dyad 5 were also investigated, The results can be considered as representing off–on-off states. Dyad 5 executes two input XNOR logic gates, towards H+ and HO− ions, “off–on-off” switching behavior between H+ and HO− ions was observed, The synthesized compounds were tested for antimicrobial activity of Gram-positive and Gram-negative bacteria, The compounds tested have a good antibacterial activity as compared with standard compound (Gentamycin).
An alternative method for kinematic and power analysis of compound gear train is presented, which uses the torques and lever analogy of a given gear train. The method combines the accuracy of the Willis analytical method with the clarity of the graphic method of Kutzbach. Unlike these methods, the torque method allows determining not only the gear ratio, but the magnitude and direction of power flows, and hence the determination of efficiency of a given compound planetary gear train. The application of the method is illustrated with example of novel arrangement of complex nine-speed change-gear. Structural, kinematic, and power (efficiency) analysis are made. A software for these analysis facilitation is developed. A numerical example is presented and discussed.
An overview of all possible structural schemes of two-carrier planetary gear trains (PGTs) with two compound and four external shafts is made. One of possible application of these PGTs is as change-gears. A few cases of this application are presented and investigated through the torque method. Kinematical possibilities of PGTs in question as function of parameters of component simple PGTs are discussed.
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285 members
Petar Todorov
  • Department of Organic Chemistry
Jordan Hristov
  • Department of Chemical Engineering
Juliana G. Javorova
  • Department of Applied Mechanics
Rayna Bryaskova
  • Department Polymer Engineering
Lachezar Radev
  • Department of Fundamental Chemical Technology
8, St. Kliment Ohridski Blvd, 1756, Sofia, Sofia, Bulgaria
Head of institution
Prof. Senia Terzieva
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