Termička relaksacija i kvantno tuneliranje magnetizacije u Mn12-acetatu

The dependence of the magnetic moment m on the temperature T and the magnetic field H in a synthesized molecular magnet Mn12-acetate has been measured using a SQUID magnetometer. The splitting of zero-field cooled (ZFC) and field-cooled (FC) m(T) curves below the so-called blocking temperature TB (≈ 3.6 K at H = 0) was observed. By measuring the time relaxation of m, it was found that it tended to the same value with the same relaxation time (≈ 560 s at 3 K) for both ZFC and FC processes. This indicates spin freezing below TB and the single molecule process in the explored temperature range (2 K <T < 4 K). The dependence of TB on applied H was also investigated. The decreasing of TB with increasing H can be explained in the frame of barrier reduction in the applied field.Mjerili smo ovisnost magnetskog momenta m sintetiziranog molekulskog magneta Mn12-acetat o temperaturi T i magnetskom polju H pomoću SQUID magnetometra. Ispod tzv. temperature kočenja TB (≈ 3.6 K pri H = 0) primijetili smo razdvajanje krivulja m(T) za uzorak hlađen bez polja (ZFC) i hlađen u polju (FC). Mjerenja vremenske relaksacije m pokazuju da m teži istim vrijednostima s jednakim relaksacijskim vremenima (≈ 560 s na 3 K) za oba procesa, ZFC i FC. Narečeno ukazuje na zamrzavanje spinova ispod temperature kočenja TB (≈ 3.5 K) i jednočestičnu prirodu procesa u istraživanom temperaturnom području (2 K <T < 4 K). Istraživali smo i ovisnost TB o primijenjenom polju H. Pad TB s povećanjem H objašnjavamo sniženjem bedema u primijenjenom polju

Thermal relaxation and quantum tunnelling of the magnetization in Mn_12-acetate

The dependence of the magnetic moment m on the temperature T and the magnetic field H in a synthesized molecular magnet Mn_12-acetate has been measured using a SQUID magnetometer. The splitting of zero-field cooled (ZFC) and field-cooled (FC) m(T) curves below the so-called blocking temperature TB ( ≈ 3.6 K at H = 0) was observed. By measuring the time relaxation of m, it was found that it tended to the same value with the same relaxation time ( ≈ 560 s at 3 K) for both ZFC and FC processes. This indicates spin freezing below TB and the single molecule process in the explored temperature range (2 K < T < 4 K). The dependence of TB on applied H was also investigated. The decreasing of TB with increasing H can be explained in the frame of barrier reduction in the applied field

Termička relaksacija i kvantno tuneliranje magnetizacije u Mn12-acetatu

The dependence of the magnetic moment m on the temperature T and the magnetic field H in a synthesized molecular magnet Mn12-acetate has been measured using a SQUID magnetometer. The splitting of zero-field cooled (ZFC) and field-cooled (FC) m(T) curves below the so-called blocking temperature TB (≈ 3.6 K at H = 0) was observed. By measuring the time relaxation of m, it was found that it tended to the same value with the same relaxation time (≈ 560 s at 3 K) for both ZFC and FC processes. This indicates spin freezing below TB and the single molecule process in the explored temperature range (2 K <T < 4 K). The dependence of TB on applied H was also investigated. The decreasing of TB with increasing H can be explained in the frame of barrier reduction in the applied field.Mjerili smo ovisnost magnetskog momenta m sintetiziranog molekulskog magneta Mn12-acetat o temperaturi T i magnetskom polju H pomoću SQUID magnetometra. Ispod tzv. temperature kočenja TB (≈ 3.6 K pri H = 0) primijetili smo razdvajanje krivulja m(T) za uzorak hlađen bez polja (ZFC) i hlađen u polju (FC). Mjerenja vremenske relaksacije m pokazuju da m teži istim vrijednostima s jednakim relaksacijskim vremenima (≈ 560 s na 3 K) za oba procesa, ZFC i FC. Narečeno ukazuje na zamrzavanje spinova ispod temperature kočenja TB (≈ 3.5 K) i jednočestičnu prirodu procesa u istraživanom temperaturnom području (2 K <T < 4 K). Istraživali smo i ovisnost TB o primijenjenom polju H. Pad TB s povećanjem H objašnjavamo sniženjem bedema u primijenjenom polju

Synthesis and Structure of N,N’-Butylene-N,N’-hexylenebis(2-oxy-1-naphthaldimine)

The title compounds were synthesized in the reaction of 2-hydroxy- 1-naphthaldehyde and corresponding aliphatic diamines. Standard TGA and DSC procedures were applied to characterize both compounds 1 and 2. The stereochemistry of the compounds in solid state was determined by the single crystal X-ray diffraction. Compound 1: C26H24N2O2, orthorhombic, space group Pbca, a = 8.142(2) Å, b = 9.097(3) Å, c = 28.812(8) Å, R = 0.032. Compound 2: C28H28N2O2, orthorhombic, space group Pbcn, a = 23.738(2) Å, b = 8.9933(8) Å, c = 10.4206(8) Å, R = 0.038. The molecules of both compounds 1 and 2 have an imposed centre of inversion in the middle of the aliphatic chain bridging two naphthaldimine moieties. The well known crystallographic D2h bond length pattern as well as quinoid effects were observed in the fused ring system in both cases. In both Schiff bases, the N−H⋅⋅⋅O type of intramolecular hydrogen bond was established. An additional intermolecular three-centre hydrogen bond links the molecules in 1

HPLC Monitoring of Acid Catalyzed Conversion of 7-Ethyltryptophol to Methyl Ester of Etodolac

Small scale experimental model for the preparation of methyl ester of etodolac, the key intermediate in the synthesis of nonsteroidal drug etodolac, is thoroughly investigated in order to define the key parameters needed for its large scale production. Oxa-Pictet-Spengler reaction of 7-ethyltryptophol and methyl 3-oxopentanoate with inorganic acids as catalysts was monitored over time using HPLC method with UV detection. HPLC method for the simultaneous determination of 7-ethyltryptophol and the product was developed first. The conversion of 7-ethyltryptophol to etodolac precursor was performed using different molar equivalents of acid (1-5 with respect to the β-ketoester) and starting 7-ethyltryptophol of different degrees of purity. Kinetic profiles and optimal reaction times were in each case defined and key parameters selected

Thermal relaxation and quantum tunnelling of the magnetization in Mn_12-acetate

The dependence of the magnetic moment m on the temperature T and the magnetic field H in a synthesized molecular magnet Mn_12-acetate has been measured using a SQUID magnetometer. The splitting of zero-field cooled (ZFC) and field-cooled (FC) m(T) curves below the so-called blocking temperature TB ( ≈ 3.6 K at H = 0) was observed. By measuring the time relaxation of m, it was found that it tended to the same value with the same relaxation time ( ≈ 560 s at 3 K) for both ZFC and FC processes. This indicates spin freezing below TB and the single molecule process in the explored temperature range (2 K < T < 4 K). The dependence of TB on applied H was also investigated. The decreasing of TB with increasing H can be explained in the frame of barrier reduction in the applied field

Rapid Identification of Unknown Impurities in 3-Bromo-5-(trifluoromethyl)aniline by LC-SPE/NMR

Identification of unknown pharmaceutical impurities is an essential part in the drug development process. In the present study, we developed and applied liquid chromatography (LC) – solid-phase extraction (SPE) / nuclear magnetic resonance (NMR) methodology with cryoprobe for identification and structural characterization of unknown impurities in 3-bromo-5-(trifluoromethyl)aniline. The three main impurities were separated and isolated by LC-SPE system. After multiple trapping, isolated impurities were eluted from the SPE cartridges with deuterated acetonitrile and one- and two-dimensional homo- and heteronuclear NMR spectra were recorded. The structures of the unknown impurities were determined by detailed inspection of NMR spectra and by mass spectrometric (MS) analysis. The results of the present preliminary study demonstrated that LC-SPE/NMR can be used for rapid impurity profiling of 3-bromo-5-(trifluoromethyl)aniline. This work is licensed under a Creative Commons Attribution 4.0 International License

Nitrozobenzenska biblioteka: Model za proučavanje selektivnosti dimerizacije nitrozo-azodioksida u čvrstom stan

Cross-linking of nitroso benzenes to heterodimers (azodioxides), in the case when they are not sterically crowded with large groups in ortho-position, was studied by NMR, UV-VIS, and Raman spectroscopy as well as by powder X-ray crystallography. Dimerization of nitroso compounds to azodioxides can, in principle, be used for the construction of novel supramolecular structures. As a preliminary investigation, the selectivity of nitrosobenzenes to form dimers in the solid state was studied. Observations by NMR and vibrational spectroscopy show that selectivity for cross-linking is quite different in the solid state from that in solution. This is explained by a considerable influence of packing factors in the former. Selectivities for cross- -linking in the solid state in a complex chemical library of monomers were formulated and measured using simple spectroscopic and diffraction methods. For every member of such a nitrosobenzene chemical library it is possible to measure and, using the Tanimoto similarity coefficients, calculate two selectivity parameters, chemical selectivity and packing selectivity. While packing selectivity is correlated with total dipole moments of nitroso monomer molecules, chemical selectivity is in correlation with the x-component of the molecular dipole, i.e., the axis that is nearly collinear with the C-N bond in nitroso group. The method developed in this work could, in principle, be proposed for more general use in investigations of similar chemical libraries with binary combined components.Dimerizacija različito supstituiranih nitrozobenzena, do koje dolazi kristalizacijom, rabljena je kao model za kvantificiranje reaktivnosti i selektivnosti u čvrstome stanju. Predloženi parametri selektivnosti dobiveni su na temelju IR spektroskopije i difrakcije X-zraka na prahu za kemijsku biblioteku nitrozobenzena supstituiranih u m- i p- položaju

27. hrvatski skup kemičara i kemijskih inženjera

U Velom Lošinju je od 5. do 8. listopada 2021. godine u organizaciji Hrvatskoga kemijskog društva i Hrvatskoga društva kemijskih inženjera i tehnologa održan 27. hrvatski skup kemičara i kemijskih inženjera s međunarodnim sudjelovanjem (27. HSKIKI) te mini-simpozij Vladimir Prelog. Skup je održan pod visokim pokroviteljstvom Predsjednika Republike Hrvatske g. Zorana Milanovića te Hrvatskog sabora kao i pod pokroviteljstvom Hrvatske akademije znanosti i umjetnosti, Ministarstva znanosti i obrazovanja, Ministarstva zaštite okoliša i energetike, Primorsko-goranske županije, grada Malog Lošinja, Sveučilišta u Zagrebu, Sveučilišta u Rijeci, Instituta Ruđer Bošković, Agencije za odgoj i obrazovanje, Hrvatskog inženjerskog saveza, Akademije tehničkih znanosti Hrvatske i Hrvatske gospodarske komore. Hrvatski skup kemičara i kemijskih inženjera ima više od 50 godina dugu tradiciju te se održava kontinuirano svake dvije godine. Prva konferencija organizirana je u Zagrebu 1969. godine. Unatoč teškom i izazovnom vremenu uzrokovanom pandemijom COVID-19 uspjeli smo organizirati konferenciju uživo i susreli smo se u respektabilnom broju. Tako je 27. HSKIKI bio izvrsno posjećen te je okupio oko 530 sudionika. Skup je privukao znanstvenike i stručnjake sa sveučilišta, istraživačkih instituta i industrije, kako iz Hrvatske tako i iz inozemstva, uz znatan udio mlađe populacije, studenata diplomskih i doktorskih studija te poslijedoktoranada. U nastavnoj sekciji je sudjelovalo i oko 30 nastavnika iz svih krajeva Hrvatske