1. Hydrolytic decomposition of corncobs to sugars and derivatives using subcritical waterMaja Čolnik, Mihael Irgolič, Amra Perva, Mojca Škerget, 2025, original scientific article Abstract: Corncobs are a widespread and renewable by-product of corn cultivation that are typically considered waste or low-value material. Corncobs contain hemicellulose, cellulose, and lignin, which can be converted into valuable products using suitable techniques. Subcritical water is increasingly used as a green medium for the extraction of valuable components from biomass, as it has many advantageous properties (high yield, pure extracts, shorter times) compared to other organic solvents. For this reason, subcritical water was used in this study to extract valuable components from corncobs at different temperatures (150–250 °C) and reaction times (10–60 min). During the decomposition of corncobs, numerous valuable products are formed in the aqueous phase depending on the temperature and reaction time. In addition to sugars and their derivatives, phenolic compounds were also formed, which are of great importance in numerous applications. It was found that at low temperatures (150–170 °C) the hemicellulose in the corncobs begins to decompose and, in particular, the sugars (glucose, xylose, arabinose, and galactose) are initially formed in the aqueous phase. Higher temperatures (200 and 250 °C) are more favorable for the decomposition of corncobs into valuable components. The yield of sugars increases with temperature due to the degradation of the cellulose content of the lignocellulosic biomass. At the same time, several new valuable products (furfural, 5-hydroxymethylfurfural (5-HMF), 1,3-dihydroxyacetone, levulinic acid, and formic acid as well as phenolic components) are formed through the degradation of lignin and the further degradation of sugars. The most important products are certainly the furfurals, which are central platform compounds. The highest furfural content was reached at 200 °C and 60 min and accounted for almost half of all components in the aqueous phase (472.01 ± 5.64 mg/g dry extract). These biomass-derived sugars and derivatives can be used in the production of fuels, pharmaceuticals, biodegradable polymers, and surfactants.
Keywords: corncobs, subcritical water, biomass, valuable compounds, sugar derivates
Published in DKUM: 07.02.2025; Views: 0; Downloads: 9
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2. Optimiranje postopkov formulacije farmacevtskih učinkovin v porozne polimerne nosilce : magistrsko deloTeja Cesar, 2024, master's thesis Abstract: Namen magistrske naloge je bil optimizirati formulacijo polimernih nosilcev kot sistemov za dostavo farmacevtskih učinkovin. Cilj je bil izboljšati topnost izbranih farmacevtskih učinkovin ter doseči podaljšano sproščanje v simuliranih telesnih tekočinah. Polimerni nosilci so obetavni na področju razvoja sistemov s formuliranimi zdravili, saj lahko z ustrezno prilagoditvijo njihovih fizikalno-kemijskih lastnosti dosežemo izboljšano formuliranje in sproščanje farmacevtskih učinkovin.
V sklopu laboratorijskega dela smo sintetizirali plastovite polimerne nosilce, v katere smo uspešno formulirali dve različni farmacevtski učinkovini z različno polarnostjo. Izbrana polimera sta bila hitozan in alginat. S procesom superkritičnega penjenja smo izdelali tudi porozne polimerne nosilce, kjer smo kot začetni polimer uporabili polikaprolakton. Kot farmacevtski učinkovini smo izbrali ketoprofen in klindamicin hidroklorid. Izbrali smo ju glede na njuno topnost v telesnih tekočinah. Ketoprofen se uporablja za zdravljenje akutne bolečine in je slabo topen, medtem ko je klindamicin hidroklorid bolj topen v telesnih tekočinah in se uporablja kot antibiotik.
Karakterizacijo formuliranih polimernih nosilcev z vsebnostjo farmacevtskih učinkovin smo izvedli z vrstično elektronsko mikroskopijo in tehniko oslabljenega totalnega odboja infrardeče spektroskopije s Fourierjevo transformacijo. Z in vitro testiranjem sproščanja smo prikazali spreminjanje vsebnosti formuliranih farmacevtskih učinkovin v polimernih nosilcih glede na čas sproščanja, pridobljene vzorce smo analizirali s tekočinsko kromatografijo visoke ločljivosti in z UV-Vis spektrofotometrijo.
Rezultati so nedvoumno pokazali, da je formulacija farmacevtskih učinkovin v polimerne nosilce omogočila podaljšano sproščanje v telesnih tekočinah. Ugotovitve kažejo, da so porozni polimerni nosilci bolj primerni za sisteme dostave zdravil s podaljšanim sproščanjem v primerjavi s plastovitimi polimernimi nosilci.
Keywords: farmacevtske učinkovine, polimerni nosilci, plastoviti polimeri, superkritično penjenje, in vitro sproščanje
Published in DKUM: 03.04.2024; Views: 273; Downloads: 67
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3. Razvoj in optimizacija HPLC metode za določanje antimikrobnih substanc v suhem ekstraktu limone : magistrsko deloKlara Žvab, 2021, master's thesis Abstract: Hesperidin, eriocitrin, rutin ter kavna in klorogena kislina so antimikrobne snovi, ki jih najdemo v limoni in njenem suhem ekstraktu. Zaradi njihovih pozitivnih učinkov, predvsem na zdravje ljudi, se vse bolj pogosto uporabljajo v raznih prehrambenih dodatkih. V magistrskem delu smo razvili in optimizirali HPLC metodo, s katero identificiramo in kvantificiramo te antimikrobne snovi v suhem ekstraktu limone.
Za ločevanje spojin smo uporabili gradientno elucijo, kjer smo 0,4 % ocetni kislini postopoma dodajali vse več organske faze (metanola) pri pretoku 0,8 ml/min. Komponente v ekstraktu smo identificirali s primerjavo UV spektrov in retenzijskih časov referenčnih substanc, vsebnost komponent pa smo določili na podlagi umeritvene krivulje.
Pokazali smo linearnost metode za določevanje klorogene kisline, eriocitrina in hesperidina v območju 2,5–300 g/ml, kavne kisline v območju 1,0–300 g/ml in rutina v koncentracijskem območju 5,0–300 g/ml. Določili smo mejo zaznave (LOD), ki za vse komponente znaša 1,0 g/ml ter mejo določljivosti (LOQ), ki je 2,5 g/ml za hesperidin, eriocitrin in klorogeno kislino, 1,0 g/ml za kavno kislino ter 5,0 g/ml za rutin. Rezultati kažejo, da je metoda natančna za določevanje vseh komponent, medtem ko je točna za določevanje hesperidina in kavne kisline.
Z optimizirano metodo smo določili vsebnost posameznih antimikrobnih komponent v različnih vzorcih ekstrakta limone. Vse komponente smo zaznali v liofiliziranem suhem ekstraktu limone, v katerem sta prevladovala hesperidin (7,09 mg/g ekstrakta) in eriocitrin (3,81 mg/g ekstrakta). Visoke vsebnosti hesperidina smo zaznali tudi v liofiliziranem ekstraktu limete, kjer je ta vrednost znašala 9,74 mg/g ekstrakta. Ostale komponente so bile v teh in ostalih vzorcih zaznane v manjših količinah, nekje od 0,15 do 2,5 mg komponente/g ekstrakta.
Keywords: tekočinska kromatografija visoke ločljivosti (HPLC), validacija, hesperidin, eriocitrin, rutin, kavna kislina, klorogena kislina
Published in DKUM: 20.01.2021; Views: 1776; Downloads: 188
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4. Novel chitosan/diclofenac coatings on medical grade stainless steel for hip replacement applicationsMatjaž Finšgar, Amra Perva, Janja Stergar, Lidija Gradišnik, Uroš Maver, 2016, original scientific article Abstract: Corrosion resistance, biocompatibility, improved osteointegration, as well the prevention of inflammation and pain are the most desired characteristics of hip replacement implants. In this study we introduce a novel multi-layered coating on AISI 316LVM stainless steel that shows promise with regard to all mentioned characteristics. The coating is prepared from alternating layers of the biocompatible polysaccharide chitosan and the non-steroid anti-inflammatory drug (NSAID), diclofenac. Electrochemical methods were employed to characterize the corrosion behavior of coated and uncoated samples in physiological solution. It is shown that these coatings improve corrosion resistance. It was also found that these coatings release the incorporated drug in controlled, multi-mechanism manner. Adding additional layers on top of the as-prepared samples, has potential for further tailoring of the release profile and increasing the drug dose. Biocompatibility was proven on human-derived osteoblasts in several experiments. Only viable cells were found on the sample surface after incubation of the samples with the same cell line. This novel coating could prove important for prolongation of the application potential of steel-based hip replacements, which are these days often replaced by more expensive ceramic or other metal alloys.
Keywords: corrosion, corrosion resistance, chitosan, biocompatibility, biomaterials, biomedical materials, coatings, stainless steel
Published in DKUM: 23.06.2017; Views: 2073; Downloads: 393
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5. ADSORPCIJA IN DESORPCIJA NEKATERIH NARAVNIH SPOJIN NA RAZLIČNE ADSORBENTEZlatka Cafuta Prevolšek, 2016, undergraduate thesis Abstract: V diplomskem delu je bil izveden proces adsorpcije in desorpcije različnih komponent: (benzojske kisline, oleinske kisline, estra oleinske kisline in kvercetina) na različne nosilce. Uporabili smo naslednje nosilce: silikagel, neusilin, aerogel hidrofilen SiO2, aerogel hidrofoben MTMS 07, Amberlite IRA 420, Amberlite XAD 16. Proces adsorpcije in desorpcije je bil izveden s klasično kolonsko kromatografijo. Adsorpcijo in desorpcijo smo izvajali pri sobni temperaturi in pretoku 1 ml/min. Maso adsorbirane in desorbirane komponente smo določili z gravimetrično metodo. Z raziskovanjem smo ugotovili, da se komponente različno vežejo na adsorbent. Masa adsorbirane in desorbirane komponente je odvisna od izbire komponente, topila, časa ter pretoka. Dokazali smo, da ima vsaka komponenta različne lastnosti glede na nosilec.
Za benzojsko kislino smo dokazali, da je za adsorpcijo najprimernejši izmenjevalec amberlit IRA 420, za desorpcijo pa amberlit XAD 16. Za oleinsko kislino smo dokazali, da je prav tako za adsorpcijo najprimernejši ionski izmenjevalec Amberlite IRA 420, za desorpcijo pa Amberlite XAD 16. Za ester oleinske kisline smo dokazali, da je za adsorpcijo najprimernejši ionski izmenjevalec silikagel, za desorpcijo pa Amberlite IRA 420. Za kvercetin smo dokazali, da je za adsorpcijo najprimernejši izmenjevalec Amberlite IRA 420, za desorpcijo pa silikagel.
Dokazali smo tudi, da bi za kvercetin morali izboljšati tehniko izvedbe adsorpcije, pri desorpciji pa izbrati druga topila.
Keywords: adsorpcija, desorpcija, benzojska kislina, oleinska kislina, ester oleinske kisline, kvarcetin
Published in DKUM: 14.10.2016; Views: 2333; Downloads: 141
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6. RAZVOJ IN VALIDACIJA ANALIZNE METODE B PO STANDARDU SIST EN ISO 7887:2012 ZA DOLOČANJE BARVE VODEMarjeta Umek, 2016, undergraduate thesis Abstract: Namen diplomskega dela je razvoj in validacija metode B po standardu SIST EN ISO 7887:2012 Kakovost vode – Pregled in določevanje vode. V laboratoriju NLZOH Novo mesto smo se glede na spremembe zahtev zakonodaje, naročnikov in akreditacijske presoje odločili izvesti ponovno validacijo, saj se z leti parametri spreminjajo. Dodali so standard za preverjanje točnosti valovnih dolžin, primerjali so pH in barvo in pregledali vpliv interferenc. Določili smo LOD in LOQ, delovno območje, povprečje, standardno deviacijo in RSD. Preverili smo pravilnost in natančnost metode ter določili merilno negotovost. Metoda se uporablja za vse tipe vod naravne in odpadne vode. Pri realnih vzorcih različnih tipov vod smo s spektrofotometrom Agilent 8453 UV/VIS izmerili absorpcijo pri treh različnih valovnih dolžinah 436 nm, 525 nm in 620 nm, pri katerih smo izračunali realno barvo vode. Glede na rezultate validacije smo ocenili, da je metoda primerna za rutinsko določanje barve vode.
Keywords: validacija, merilna negotovost, absorbanca, barva vode
Published in DKUM: 25.07.2016; Views: 2811; Downloads: 233
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7. Phase equilibira of permethrin and dicofol with carbon dioxidePetra Kotnik, Amra Perva, Mojca Škerget, Željko Knez, 2005, original scientific article Abstract: The solubilities of pesticides (permethrin and dicofol) in CO2 were measured by a static-analytic method at pressures ranging from 10.0 MPa to 25.0 MPa andtemperatures of 293.2 K, 303.2 K, and 313.2 K. Due to the nonconventional shape of some solubility isotherms, solid-liquid transitions of pesticides under pressure of CO2 were determined using a modified capillary method. Sincethe solubilities depend on solvent density, the experimental binary solid-fluid equilibrium data were correlated as a function of solvent density by two different models.
Keywords: chemical processing, high pressure technology, CO2, pesticides, phase equilibria, solubility
Published in DKUM: 01.06.2012; Views: 2097; Downloads: 36
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8. Phase equilibria of vanillins in compressed gasesŽeljko Knez, Mojca Škerget, Amra Perva, 2007, original scientific article Abstract: Solid-liquid phase transitions of vanillin, ethylvanillin, o-vanillin and o-ethylvanillin in compressed hydrocarbons (isobutane and propane), fluorinated hydrocarbons (R23, R134a and R236fa) and sulphur hexafluoride (SF6) were determined with a modified capillary method in a pressure range between 0.1 and 31.0 MPa. Equilibrium solubilities of vanillins in compressed fluorinated hydrocarbons were determined at temperatures 313.2 and 333.2 K and over a pressure range between 1.1 and 26.0 MPa with a static-analytic method. Experimental solubility data were correlated by a density-based Chrastil model. Results showed that phase equilibria of vanillins in investigated compressed gases are influenced by the type of alchoxy group (methoxy or ethoxy) and the position of OH group (ortho or para), bound to the aromatic ring of solute, as well as the molecular structure of the gas. Three phase SLG curves in p,T-projections mainly exhibited temperature minimums and negative slopes dp/dT, with a maximum melting point depression between 9 and 21 K; all systems with SF6 exhibited a continuous positive slope dp/dT of approximately 4.5 MPa/K. SLG curves with a temperature maximum at low pressure were observed for systems of o-vanillins with R23. Solubilities of o-vanillins in R23 and R236fa were higher in comparison with p-vanillins, whereas, in the case of R134a, the solubilities were influenced by the alchoxy group bound on aromatic ring: vanillin and o-vanillin with methoxy group are more soluble than vanillins with ethoxy group (ethylvanillin and o-ethylvanillin). The highest solubility of all four vanillins was observed in R236fa.
Keywords: solid-liquid-gas equilibria, melting point depression, solubility, vanilin isomers, hydrocarbons, fluorinated hydrocarbons, SF6
Published in DKUM: 31.05.2012; Views: 2120; Downloads: 95
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