• Article close
• English close
• Kemija u Industriji close

In this paper, a review of reactions with benzotriazole as synthetic auxiliary is given. In contrast to most other azoles, benzotriazole reacts with phosgene in molar ratio 1:1 yielding carboxylic acid chloride (BtcCl, 1), which readily reacts with nucleophiles giving reactive compounds. These products can be easily transformed into carbamates, ureas, semicarbazides, carbazides, sulfonylureas, sulfonylcarbazides, nitroalkanic acid esters, etc. In addition, benzotriazole was used in the synthesis of various heterocyclic compounds: benzoxazine, kinazoline, triazinetrione, hydantoin and oxadiazine derivatives. The reaction of chloride 1 with amino acids enabled the use of benzotriazole in peptide chemistry, with triple role of benzotriazolecarbonyl group as N-protecting, N-activating, and both N-protecting/C-activating group. N-(1-benzotriazolecarbonyl)-amino acids 25 are starting compounds in the synthesis of various amino acid, di- and tripeptide derivatives, hydantoic acids and hydroxyureas.Benzotriazole was also applied in the preparation of polymer-drug and thiomer-drug conjugates, polymeric prodrugs with drugs covalently bound to the polymeric carriers. Such macromolecular prodrugs may offer many advantages compared to other drug delivery systems such as increased drug solubility, prolonged drug release, increased stability. It is also possible to accumulate the drug at the site of the pathological process and to minimize its toxicity. In this paper, the binding of drugs from various therapeutic groups (mostly nonsteroidal, anti-inflammatory drugs) to polymersof polyaspartamide type by the benzotriazolide method is described.

Polyketides and non-ribosomal peptides represent a large class of structurally diverse natural products much studied over recent years because the enzymes that synthesise them, the modular polyketide synthases (PKSs) and the non-ribosomal peptide synthetases (NRPSs), share striking architectural similarities that can be exploited to generate "un-natural" natural products. PKS and NRPS proteins are multifunctional, composed of a co-linear arrangement of discrete protein domains representing each enzymic activity needed for chain elongation using either carboxylic acid or amino acid building blocks. Each domain is housed within larger modules which form the complex. Polyketide and peptide antibiotics, antifungals, antivirals, cytostatics, immunosuppressants, antihypertensives, antidiabetics, antimalarials and anticholesterolemics are in clinical use. Of commercial importance are also polyketide and peptide antiparasitics, coccidiostatics,animal growth promoters and natural insecticides.Polyketides are assembled through serial condensations of activated coenzyme-A thioester monomers derived from simple organic acids such as acetate, propionate and butyrate. The choice of organic acid allows the introduction of different chiral centres into the polyketide backbone. The active sites required for condensation include an acyltransferase (AT), an acyl carrier protein (ACP) and a ß-ketoacylsynthase (KS). Each condensation results in a ß-keto group that undergoes all, some or none of a series of processing steps. Active sites that perform these reactions are contained within the following domains; ketoreductase (KR), dehydratase (DH) and an enoylreductase (ER). The absence of any ß-keto processing results in the incorporation of a ketone group into the growing polyketide chain, a KR alone gives rise to a hydroxyl moiety, a KR and DH produce an alkene, while the combination of KR, DH and ER domains lead to complete reduction to an alkane. Most often, the last module contains the thioesterase domain (TE) responsible for the release of linear polyketide chain from the enzyme and final cyclisation. After assembly, the polyketide backbone typically undergoes post-PKS modifications such as hydroxylation(s), methylation(s) and glycosylation(s) to give the final active compound.Non-ribosomal peptides are assembled by the so-called "multiple carrier thio-template mechanism". Three domains are necessary for an elongation module: an adenylation (A) domain that selects the substrate amino acid, analogous to a polyketide AT domain, and activates it as an amino acyl adenylate; a peptidyl carrier protein (PCP) that binds the co-factor 4-phosphopantetheine to which the activated amino acid is covalently attached, analogous to the ACP of a PKS; and a condensation (C) domain that catalyzes peptide bond formation, again analogous to the KS in modular PKSs. The NRPSs also contain a (Te) domain located at the C-terminal of the protein which is essential for release of linear, cyclic or branched cyclic peptides. Auxiliary activities can further enlarge the structural diversity of the peptide especially common are epimerization domains (Epim) that convert the thioester-bound amino acid from an L- to D- configuration.There has been a lot of interest in the last few years in generating new compounds for the production of novel drugs by manipulating the programming of such clusters in vitro (e.g. the idea of combinatorial biosynthesis). However, an important barrier to the progress is the fact that most changes made by in vitro methods result in very low yields or no detectable product. A possible solution to the yield problem would be the generation of novel clusters by homologous recombination in vivo, because this would favour more closely related sequences and should reduce problems caused by non-functional incompatible junctions.The Unified Modeling Language (UML) was used to define the platform independent integral generic program packages, CompGen and ClustScan, which are under development to model these processes in silico. The heart of CompGen is a specially structured database, based on BioSQL v1.29, which connects the biosynthetic order of synthase/synthetase enzymes to the sequences of the component polypeptides. The additional linkage to the gene sequences allows the integration of DNA sequence with product structure. The database contains sequences of the well-characterised PKS/NRPS clusters, and non-annotated sequenced clusters whose structure and functionis yet unknown, to act as building blocks for the production of novel products. It is easy to add custom sequences to the database and to annotate them by the use of propriety protein profiles designed by Pfam database and HMMER. One function of the program is the ability to generate virtual recombinants between clusters. This can be done using a recombination model (with optional parameters) to predict sites for homologous recombination or by user defined recombination sites (e.g. to model in vitro genetic manipulation such as module replacement). The program predicts the linear polyketide structure of the resulting "un-natural" natural products with a chemical description using isomeric SMILES. Molecular modelling of the subsequent spontaneous cyclisation process produces structures for a virtual compound database for further molecular modelling studies using PASS and CDD technology. An optional "reverse genetics" module analyses a given chemical structure to see if it could be produced by a novel PKS/NRPS synthesis cluster and suggests the DNA sequence of a suitable cluster based on building blocks derived from clusters contained in the database.Overall, the CompGen allows in silico generation of the database of novel "un-natural" natural chemical compounds that can be used for in silico screening using PASS or CDD technology. The other integral generic program package, ClustScan, will recognise and annotate new gene clusters from microbial genome sequencing projects or in metagenomes of soil and/or marine microorganisms.

Biological activity of different adamantane derivatives and their application has been described in various reviews. Similarly, many reviews deal with biological activity and application of guanidine compounds. However, up to now no review has been made concerning the guanidine derivatives of adamantane and other polycycles, compounds which incorporate both of these moieties in the same molecule. Therefore, a literature survey of polycyclic guanidine derivatives is here provided and their application as potential pharmacophores stressed. Biološka aktivnost različitih adamantanskih derivata i njihova primjena opisane su u brojnim preglednim člancima. Isto tako, mnogi revijalni članci opisuju biološku aktivnost i primjenu gvanidinskih spojeva. Međutim do sada nije načinjen pregled koji bi se bavio gvanidinskim derivatima adamantana i drugih policikla, tj. spojevima koji sadrže obje navedene podjedinice u istoj molekuli. U ovom radu bit će stoga dan pregled policikličkih derivata gvanidina, i to s naglaskom na njihovu primjenu kao potencijalnih farmakofora.

Radikale, kemijske vrste s nesparenim elektronima, obično se smatra vrlo nestablinima, tako da ih se može pri - praviti samo pod posebnim uvjetima i proučavati samo pomoću posebnih, vrlo skupih, instrumenata. Također ih se smatra štetnima te neprimjerenima za pokuse u školi. Ipak, radikali imaju ključnu ulogu u biološkim susta - vima. Zahvaljujući nesparenim elektronima, obično su živo obojani, tako da se njihovo nastajanje često može opaziti golim okom. Ovdje je opisano nekoliko jednostavnih reakcijâ s biološki najvažnijim radikalom, semikinonom. Lako ih je izvesti u školskom laboratoriju uporabom male količine jeftinih i bezopasnih tvari. Jednostavnim promatranjem tih reakcijâ dade se naučiti mnogo toga o kemiji (slob odnih) radikala

Polilaktidna kiselina (PLA) i bakterijska nanoceluloza (BNC) zbog svoje biorazgradljivosti, biokompatibilnosti i netoksičnosti imaju velik potencijal za primjenu u biomedicini. Cilj ovog rada bio je pripraviti i ispitati biokompozit PLA/BNC. Istražen je utjecaj BNC-a na morfološku strukturu, kemijski sastav, toplinska svojstva, toplinsku postojanost i hidrofobnost PLA te zasijavanje i rast stanica biokompozita PLA/BNC primjenom pretražnog elektronskog mikroskopa (SEM), infracrvene spektroskopije (FTIR), diferencijalne pretražne kalorimetrije (DSC) i termogravimetrijske analize (TGA) te određivanjem kontaktnog kuta i metodom MTT. Dodatkom BNC-a u PLA dolazi do pomaka staklišta (Tg) prema nižim temperaturama, što ukazuje na veću pokretljivost amorfne faze PLA te porasta stupnja kristalnosti zbog nukleacijskog učinka celuloze. Početak toplinske razgradnje pomaknut je na niže temperature u odnosu na čisti PLA, što ukazuje na smanjenje toplinske postojanosti PLA dodatkom BNC-a. Biokompozit PLA/BNC pokazuje poroznu, vlaknastu strukturu. Test zasijavanja stanica pokazao je da je biokompozit PLA/BNC pogodan za prihvaćanje i rast humanih stanica, pa je prema tome potencijalno primjenjiv u regenerativnoj medicini i tkivnom inženjerstvu. Ovo djelo je dano na korištenje pod licencom Creative Commons Imenovanje 4.0 međunarodna. Polylactic acid (PLA) and bacterial nanocellulose (BNC) are promising materials in medicine due to their biodegradability, biocompatibility, and non-toxicity. The aim of this work was to prepare and characterize the PLA/BNC biocomposite. Morphology, chemical composition, thermal properties, thermal stability, hydrophobicity and cell seeding, and growth of the PLA/BNC biocomposite were characterized by means of scanning electron microscopy (SEM), Fourier transform infrared spectra (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), contact angle, and MTT method. DSC showed that the glass transition temperature (Tg) of PLA decreased with the addition of BNC due to higher mobility of amorphous PLA phase. The degree of crystallinity increased due to nucleation effect of cellulose. With the addition of BNC, the thermal stability of biocomposite decreased. The PLA/BNC biocomposite exhibited a porous, fibrous structure. The cell seeding test showed the PLA/BNC biocomposite to be suitable for growth of human cells, and therefore, potentially applicable in regenerative medicine and tissue engineering. This work is licensed under a Creative Commons Attribution 4.0 International License.

The development of Croatian chemistry from the end of the Second World War to the establishment of the Republic of Croatia is outlined. Briefly discussed is the founding and development of the Chemistry Department of the Faculty of Natural Sciences and Mathematics, and the Rugjer Bošković Institute. Also presented is the postwar structure and organization of the chemical-technological study at the Technical Faculty and later at the Faculty of Technology. The chemical lectures and research in chemistry at the Faculty of Nutrition and Biotechnology, Faculty of Pharmacy and Biochemistry, Faculty of Medicine, Faculty of Veterinary Medicine, Facultyof Agronomy and Faculty of Forestry are reviewed. This article follows logically our first article in this series entitled Croatian Chemistry in the 20th Century. I. From the Turn of the Century to May 8,th 1945 (Kem. Ind. 56 (2007) 403–416).

This article is the second part of a series dealing with organometallic and bioorganometallic chemistry. In the first part of this series a short review on the history and development of these disciplines was given, emphasizing the importance and scope of bioorganometallic chemistry as a new field dealing with conjugates of organometallics and biomolecules (DNA, PNA, amino acids, peptides...). From the variety of biorganometallics, syntheses and properties of simple conjugates of ferrocene with natural amino acids/peptides were elaborated inter alia. This material is the basis for the second part in which ferrocene amino acids are described. The introduction presents nonproteinogenic alicyclic and aromatic amino acids as the models for the title compounds. Naturally occurring amino acids labelled with ferrocene moiety mostly retain properties of the biomolecules included. Contrary to these ω-ferrocenylamino acids, one could imagine specific amino acids with inserted ferrocene core belonging to either homo- or heterodisubstituted type. The central part of this article is devoted to our investigations of the second type - H2N-(CH2)m-Fn-(CH2)n-COOH. The general rational procedure for synthesis of these compounds and of their N- and/or C-protected derivatives via the azide intermediates N3-CO-(CH2)m- Fn-(CH2)n-COOMe has been described. In the solid state derivatives of ferrocene amino acids contain intermolecular hydrogen bonds giving dimeric structures, three-dimensional networks or endless helical chains. The solutions of homologues Ac-NH-(CH2)m-Fn-(CH2)n-COOMe in nonpolar solvents are dominated by open form conformers. Compounds containing 2–3 ferrocene cores connected by amide, imide and oxalamide spacers were prepared by oligomerization of 1'-aminoferrocene-1-carboxylic acid (Fca) or by its condensation with the appropriate reagents. Similar to natural amino acids, ferrocene amino acids are water-soluble substances with high melting points, insoluble in organic solvents.

Cilj ovog rada bio je razviti tri metode temeljene na umjetnoj inteligenciji za modeliranje trostruke adsorpcije iona teških metala {Pb2+, Hg2+, Cd2+, Cu2+, Zn2+, Ni2+, Cr4+} na različitim adsorbatima {aktivni ugljen, kitozan, danski treset, treset Heilongjiang, ugljik glave suncokreta i ugljik stabljike suncokreta). Rezultati pokazuju da se regresija potpornih vektora (SVR) pokazala nešto boljom, preciznijom, stabilnijom i bržom od regresije potpornih vektora najmanjih kvadrata (LS-SVR) i umjetnih neuronskih mreža (ANN). Za procjenu kinetike trostrukog adsorpcijskog sustava višekomponentnog sustava preporučuje se model SVR. Ovo djelo je dano na korištenje pod licencom Creative Commons Imenovanje 4.0 međunarodna. The aim of this work was to develop three artificial intelligence-based methods to model the ternary adsorption of heavy metal ions {Pb2+, Hg2+, Cd2+, Cu2+, Zn2+, Ni2+, Cr4+} on different adsorbates {activated carbon, chitosan, Danish peat, Heilongjiang peat, carbon sunflower head, and carbon sunflower stem). Results show that support vector regression (SVR) performed slightly better, more accurate, stable, and more rapid than least-square support vector regression (LS-SVR) and artificial neural networks (ANN). The SVR model is highly recommended for estimating the ternary adsorption kinetics of a multicomponent system. This work is licensed under a Creative Commons Attribution 4.0 International License.

It is of great challenge and significance to recycle activated carbon (AC), yet still with various problems in operation. Here, we have performed a simulation on the regeneration of AC by using an indirect heating method with an unsteady cylindrical heat transfer model. The result has shown that the optimal parameters for a regeneration tube of outer diameter Φ = 108 with wall thickness 4 mm were: heating in the tube for 30 min at a surrounding temperature of 550 °C. In these conditions, a temperature of 417.5 °C could be obtained at the centre of the cylindrical tube, reaching the temperature required for AC regeneration. The experimental values obtained in our laboratory were consistent with the simulation, providing significant references for scaling up pilot plant of AC regeneration.

Rad se bavi razvojem pojma elementa od antičkih vremena (Empedoklo, Aristotel) preko razdoblja alkemije i rane kemije (Paracelsus, Petar Bono, Boyle) te početaka moderne kemije (Lavoisier, Mendeljejev) do suvremenih shvaćanja utemeljenih na atomskoj teoriji. Pokazuje se da pojam elementa ima dva značenja, elementarne (jednostavne) tvari i elementa u užem smislu; dok se prvi pojam razvijao prateći napredak metoda kemijske analize, za razumijevanje drugog pojma, pojma elementa, bilo je nužno steći dublji uvid u narav kemijskih promjena.