78 research outputs found
Synthesis and complexation properties of calix[4]arene glycoconjugates
Pripravljena su tri nova, u vodi topljiva derivata kaliks[4]arena 1ā3 s amidnim veznim mjestima za katione. U strukturu kaliksarena ugraÄene su glukozne jedinice kao neutralni hidrofilni fragmenti koji omoguÄuju topljivost u vodi. Sinteza spojeva provedena je nizom reakcija, iz polaznog p-tert-butilkaliks[4]aren. Vezanje glukoznih jedinica je provedeno bakrom kataliziranom cikloadicijom alkina i azida, a amidne skupine uvedene su koriÅ”tenjem standardnih sintetskih tehnika u kaliksarenskoj kemiji. Spojevi se razlikuju po vrsti amidnog veznog mjesta (sekundarni ili tercijarni) te položaju i broju glukoznih podjedinica. Provedena su istraživanja kompleksiranja alkalijskih kationa u vodi, metanolu i formamidu kako bi se stekao uvid u utjecaj solvatacije te intra- i intermolekulskih vodikovih veza na ravnoteže odgovarajuÄih reakcija. Konstante stabilnosti kompleksa stehiometrije 1:1 odreÄene su pomoÄu UV spektrofotometrijskih i mikrokalorimetrijskih titracija, pri Äemu su po prvi puta takva istraživanja provedena s neutralnim kaliksarenskim ligandima u vodi. Kalorimetrijskim mjerenjima odreÄene su i pripadne reakcijske entalpije i entropije. Vrijednosti konstanti ravnoteže reakcija kompleksiranja smanjuju se u nizu otapala metanol > formamid > voda, Å”to se može povezati s razlikom u jakosti solvatacije kationa u tim otapalima. Konstante stabilnosti kationskih kompleksa s prireÄenim spojevima uglavnom padaju u nizu Na+ > K+ > Li+ > Rb+, dok za najveÄi Cs+ kompleksiranje nije primijeÄeno. NajveÄe konstante stabilnosti imaju kompleksi derivata s tercijanim amidnim veznim mjestom i osam glukoznih jedinica na donjem obodu, pri Äemu se taj derivat pokazao vrlo efikasnim (logK ā 5) i selektivnim receptorom za vezanje Na+ u vodi. Svi dobiveni rezultati detaljno su obrazloženi i raspravljeni, od sintetskih puteva za dobivanje pojedinih receptora do utjecaja njihove strukture i otapala na termodinamiÄku stabilnost kompleksa tih spojeva s alkalijskim kationima.Three novel water-soluble calix[4]arene derivatives bearing amide binding sites for metal cati-ons were prepared. Glucose units were embedded in their structures as neutral hydrophilic frag-ments which enable solubility in water. Syntheses were performed through a series of reactions starting from p-tert-butylcalix[4]arene. Glycosylation was carried out using copper catalyzed alkyne azide cycloaddition, whereas amide groups were introduced using standard techniques in calixarene chemistry. The compounds differed in the type of cation-binding site (secondary or tertiary amide) as well as position and number of glucose units. Complexation of the prepared ligands with alkali metal cations in water, methanol and formamide was studied in order to get insight into the effect of solvation as well as intra- and intermolecular hydrogen bonds on the equilibria of the corresponding reactions. Stability constants of 1:1 complexes were determined by means of UV spectrophotometric and microcalorimetric titrations. Calorimetric measure-ments provided also reaction enthalpies and entropies. It should be noted that such studies were for the first time undertaken with neutral calixarens in aqueous solutions. The complexation reaction equilibrium constants decreased in the solvent order: methanol > formamide > water, which could be accounted for by considering the differences in solvation of cations in these solvents. In most cases the stability constants of the complexes decreased in the cation order: Na+ > K+ > Li+ > Rb+, whereas no complexation was observed in the case of the largest Cs+. The highest stability constants corresponded to tertiary-amide derivative bearing eight glucose units at the lower rim, and this derivative was proven to be capable of remarkably efficient (log K ā 5) and pronouncedly selective binding of sodium cation in water. All the obtained results were thoroughly discussed with respect to the developed synthetic routes, as well as the influ-ence of solvation and ligands structural characteristics on the thermodynamic stability of their complexes with alkali metal cations
Mikroskopski model za raÄunanje poÄetnog broja ekscitona u sudarima atomskih jezgara
A microscopic model for estimating n0, the initial exciton number used in calculating pre-equilibrium emission from heavy-ion reactions, is presented. The model follows the evolution of the geometrical and phase spaces during the process of fusioning of the target and the projectile. A good agreement is found between the calculated values of n0 and the empirical values extracted from fits to nucleon spectra; empirical trends of physical quantities involving n0 are reproduced. An approximate expression for calculating n0 as a function of the mass and energy of the colliding system is given.Prikazan je model pomoÄu kojeg je moguce odrediti n0, poÄetni broj eksciton a na koji se dijeli energija sudara atomskih jezgara. Taj je parametar potreban za raÄunanje predravnotežne emisije Äestica iz teskoionskih reakcija. Prikazani model slijedi evoluciju geometrijskog faznog prostora tijekom procesa fuzije jezgre mete i projektila. Dobro slaganje opaženo je izmeÄu raÄunatih vrijednosti parametara n0 i onih, dobivenih na empiriÄki naÄin analizom nukleonskih spektara iz teÅ”koionskih reakcija. Model takoÄer uspjeÅ”no reproducira trendove fizikalnih veliÄina povezanih s n 0 . U Älanku je dan izraz za raÄunanje približne vrijednosti parametra n 0 u ovisnosti o masi i energiji sudarnog sustava
An Old Story in New Light: X-Ray Powder Diffraction Provides Novel Insights into a Long-Known Organic Solid-State Rearrangement Reaction
The first in situ diffraction study of the long-known solid-state rearrangement of p-bromobenzeneazotribenzoylmethane
is reported. This proof-of-principle study demonstrates how modern laboratory
X-ray powder diffraction, accompanied by up-to-date processing tools, can be used to monitor and
describe mechanisms of organic solid-state reactions while it also underpins its necessity for structural
characterisation of in situ formed crystalline phases. (doi: 10.5562/cca2127
Soft nanotechnology: the potential of polyelectrolyte multilayers against E. coli adhesion to surfaces
PrepreÄevanje adhezije bakterij na povrÅ”ine je najbolj uÄinkovit naÄin obvladovanja rasti biofilmov. Namen te raziskave je bil analizirati anti-adhezivni potencial 5 in 50 mmol/L polielektrolitskih plasti poli(alilamin hidroklorid)/poli(natrijev 4-stirensulfonat), poli(4-vinil-N-etilpiridin bromid/ poli(natrijev 4-stirensulfonat) in poli(4-vinil-N-izobutilpiridin bromid/ poli(natrijev 4-stirensulfonat) na bakterijo E. coli. Pet zaporednih plasti polielektrolitov je bilo sestavljenih na steklenih povrÅ”inah in izpostavljenih bakterijski suspenziji. Rezultati kažejo, da 50 mmol/L poli(4-vinil-N-etilpiridin bromid/ poli(natrijev 4-stirensulfonat) najbolj uÄinkovito prepreÄi adhezijo bakterij 0,4 log bakt./mm2 (60 %), sledi mu poli(4- vinil-N-izobutilpiridin bromid/ poli(natrijev 4-stirensulfonat) 0,3 log bakt. mm-2 (47 %) in poli(alilamin hidroklorid)/ poli(natrijev 4-stirensulfonat) 0,2 log bakt. mm-2 (38 %). Ta raziskava dokazuje, da polieletrolitske plasti z kvartarne amino skupinami igrajo pomembno vlogo pri prepreÄevanju adhezije bakterij in zato predstavljajo pomembno uporabo v živilski in farmacevtski industriji ter v medicini.Preventing bacterial attachment to surfaces is the most efficient approach to controlling biofilm proliferation. The aim of this study was to compare anti-adhesion potentials of 5 and 50 mmol/L polyelectrolyte multilayers of poly(allylamine hydrochloride)/poly(sodium 4āstyrenesulfonate), poly(4-vinyl-N-ethylpyridinium bromide)/ poly(sodium 4āstyrenesulfonate), and poly(4-vinyl-N-isobutylpyridinium bromide)/poly(sodium 4āstyrenesulfonate) against Escherichia coli. Glass surface was covered with five polyelectrolyte layers and exposed to bacterial suspensions. Poly(4-vinyl-N-ethylpyridinium bromide)/poly(sodium 4āstyrenesulfonate) was the most effective against bacterial adhesion, having reduced it by 60 %, followed by poly(4-vinyl-N-isobutylpyridinium bromide)/poly(sodium 4ā styrenesulfonate) (47 %), and poly(allylamine hydrochloride)/poly(sodium 4āstyrenesulfonate) (38 %). Polyelectrolyte multilayers with quaternary amine groups have a significant anti-adhesion potential and could find their place in coatings for food, pharmaceutical, and medical industry
In vitro Investigation of the Antimicrobial Activity of a Series of Lipophilic Phenols and Naphthols
Five groups of phenols/naphthols (42 compounds in total) were synthesized and screened against Gram-positive StaphylococcusĀ aureus and Bacillus subtilis, Gram-negative Escherichia coli and Klebsiella pneumoniae, and the fungus Candida albicans. WhereasĀ compounds were found inactive against Gram-negative bacteria, potent activities against Gram-positive bacteria were observed.Ā The activities correlate with the ability of molecules to form quinone methides, suggesting potential new modes of action.KEYWORDSĀ Antimicrobial activity, phenols, naphthols, quinone methides
Investigations of Thermally Controlled Mechanochemical Milling Reactions
Mechanochemical milling reactions have received much attention recently as a green and highly efficient path toward various relevant materials. Control over the fundamental reaction parameters in the milling procedure, such as temperature and pressure of the reactor, is still in its infancy, and the vast majority of milling reactions are done by controlling just the basic parameters such as frequency and milling media weight. We demonstrate here how milling under controlled, prolonged, and variable heating programs accomplished in a new milling reactor introduces a new level of mechanochemical reactivity beyond what can be achieved by conventional mechanochemical or solution procedures and also reduces the time and energy costs of the milling process. The methodology is demonstrated on four varied systems: CāC bond-forming Knoevenagel condensation, selective CāN bond formation for amide/urea synthesis, selective double-imine condensation, and solid-state formation of an archetypal open metal-organic framework, MOF-74. The potential of this methodology is best demonstrated on the one-pot selective synthesis of four complex products containing combinations of amide, amine, or urea functionalities from the same and simple acyl azide and diamine reactants. Principal control over this enhanced reactivity and selectivity stemmed from the application of specific heating regimes to mechanochemical processing accomplished by a new, in-house developed mechanochemical reactor. As even a moderate increase in temperature strongly affects the selectivity and the rate of mechanochemical reactions, the results presented are in line with recent challenges of the accepted theories of mechanochemical reactivity
FEASIBILITY OF ALPHA-BLOCKERS IN CHRONIC CATEGORY III PROSTATITIS
ElektroniÄkim pretraživanjem putem interneta na adresi: http://www.ncbi.nlm.nih.gov/pubmed/ izdvojene su randomizirane studije s kontrolnom skupinom na placebu radi ispitivanja uÄinkovitosti djelovanja alfa-blokatora na kroniÄni prostatitis tipa III s tegobama definiranim s pomoÄu simptomskog skora NIH-CPSI. Od 13 odabranih studija tri su iskljuÄene zato Å”to nisu rabile NIH-CPSI, tri zato Å”to su bile na kineskom jeziku i dvije zato Å”to su bile u formi kongresnog sažetka. Analizirano je pet studija s ukupno 563 bolesnika, a metodoloÅ”ka kvaliteta studija po Jadadu iznosila je Äetiri ili pet jedinica. Uporijebljeni alfa-blokatori bili su alfuzosin, terazosin, tamsulozin i doksazosin u trajanju od 6 tjedana do 6 mjeseci. UÄinak lijeÄenja alfa-blokatorima bio je izraženiji u bolesnika s kroniÄnim prostatitisom tipa III s visokim vrijednostima NIH-CPSI i izraženijim tegobama mokrenja, koji su manje selektivne alfa-blokatore alfuzosin, terazosin i doksazosin primali 3ā6 mjeseci.Studies were identified on internet by searching on address: http://www.ncbi.nlm.nih.gov/pubmed/ with criteria that studies should be placebo-controlled and randomized in trials of alpha-blockers in chronic category III prostatitis evaluated by symptom-score NIH-CPSI. From 13 clinical studies three were excluded because of not using NIH-CPSI, three were in Chinese language and two were congress abstracts. Analysed were five studies with four or five Jadad scale including 563 patients. Alpha-blockers alfuzosin, terazosin, tamsulosin and doxazosin have been used through 6 weeks and 6 months. Better results were accomplished by less selective alpha-blockers alfuzosin, terazosin and doxazosin through 3ā6 months in patients having higher NIH-CPSI score and higher voiding score
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