Search Results

You are looking at 1 - 10 of 18 items for :

  • Author or Editor: A. Novak x
  • Chemistry and Chemical Engineering x
  • Refine by Access: All Content x
Clear All Modify Search

Abstract  

For purposes of radioimmunoanalytical determination of serum ferritin, conditions for antigen iodination and separation were searched for, which could provide a satisfactory radiochemical purity and specific activity, high immunoreactivity and stability of the resulting labeled product, necessary for an acceptable expiration of the RIA kit. Two iodination methods (chloramine and conjugation methods) were tested, and a three-step procedure was elaborated for iodination and separation by gel column chromatography. The iodinated antigen obtained —125I-placental ferritin with IRmax of about 80%,125I<8%, specific activity of about 0.6MBq/g and stability for the expiration period of 3 to 4 months — is quite satisfactory for the RIA applications.

Restricted access

Abstract  

The effect of 2,4-dichlorophenol (DCP) on the main transition and pretransition of fully hydrated (20 mass%) dipalmitoylphosphatidylcholine (DPPC) multilamellar liposomes has been studied by differential scanning calorimetry (DSC). It was observed that an increase in the molar ratio of DCP/DPPC (from 4·10-5 up to 2·10-2) causes progressive reductions in the temperature and enthalpy of the pretransition. The higher concentration of DCP eliminates the pretransition. The influence of DCP on the main transition in this molar ratio range is not drastic, but a decrease in temperature and in the enthalpy values was observed. In the molar ratio range (from 2·10-1 up to 4·10-1) the DSC scans show multiple main transition peaks instead of the characteristic single peak of the main transition. Above a DCP/DPPC molar ratio of 0.6 a new peak appears at 25°C having about the same transition enthalpy as the main transition of the pure system.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors:
F. Giordano
,
A. Rossi
,
R. Bettini
,
A. Savioli
,
A. Gazzaniga
, and
Cs. Novák

Abstract  

The thermal behavior of binary mixtures of paracetamol and a polymeric excipient (microcrystalline cellulose, hydroxypropylmethylcellulose and cross-linked poly(vinylpyrrolidone)) was investigated. The physical mixtures, ranging from 50 to 90% by mass of drug, were submitted to a heating-cooling-heating program in the 35–180C temperature range. Solid-state analysis was performed by means of differential scanning calorimetry (DSC), hot stage microscopy (HSM), micro-Fourier transformed infrared spectroscopy (MFTIR), and scanning electron microscopy (SEM). The polymeric excipients were found to address in a reproducible manner the recrystallization of molten paracetamol within the binary mixture into Form II or Form III. The degree of crystallinity of paracetamol in the binary mixtures, evaluated from fusion enthalpies during the first and second heating scans, was influenced by the composition of the mixture, the nature of the excipient and the thermal history. In particular, DSC on mixtures with cross-linked poly(vinylpyrrolidone) and hydroxypropylmethylcellulose with drug contents below 65 and75%, respectively, evidenced the presence only of amorphous paracetamol after the cooling phase. Microcrystalline cellulose was very effective in directing the recrystallization of molten paracetamol as Form II.

Restricted access

Abstract  

Racemic free mandelic acid and its methyl, ethyl, isoamyl and benzyl esters were found to form inclusion complexes with all the three studied natural cyclodextrins proved by thermoanalytical results. Differences between the solid state stability of guests were detected mainly by evolved gas analysis. Even signs of an eventual optical resolution by molecular inclusion were observed in several cases, but still not sufficiently proven. Due to the rather high volatility and low melting points of the majority of guest substances DSC technique was found to be suitable for studying the cyclodextrin complexes of mandelic acid.

Restricted access

Abstract

Vegetable oil derived fuels for diesel engines are becoming important as alternative to petroleum diesel fuels due to their environmental friendliness and availability. Ignition quality in compression ignition (CI) engines is influenced by thermal characteristics and fuel properties. In this study, the effects of vegetable oil transesterification and vegetable oil–1-butanol-diesel blends on fuel properties, cetane number (CN) and thermal characteristics were experimentally investigated. Methyl esters (biodiesel) and 10% vegetable oil–10% 1-butanol–80% diesel blends were prepared from croton oil (CRO), coconut oil (COO) and jatropha oil (JAO). CN was measured in a CFR F-5 engine, and a thermogravimetric analysis (TG), as well as the determination of fuel properties of vegetable oils, biodiesels and blends was carried out. It can be observed for vegetable oils that they possess low volatility characteristics, low CN and high viscosity different from those of biodiesels, blends and diesel fuel. It was observed that biodiesels and blends exhibit similarities with diesel in the fuel characteristics, CN and TG curves.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors:
M. Zaharescu
,
A. Jitianu
,
A. Brãileanu
,
V. Bãdescu
,
G. Pokol
,
J. Madarász
, and
Cs. Novák

Abstract  

The hydrolysis-polycondensation of organically modified Si-alkoxides leads to the obtaining of inorganic-organic hybrid materials in which the organic moieties remain as permanent groups bonded to the inorganic network. The molecular species previously determinated by GC-MS during the gelation process have been significantly different according to the type of the alkoxide used. In the present work, thermal stability of SiO2-based inorganic-organic hybrid materials starting with TEOS (tetraethoxysilan), MTEOS (triethoxymethylsilan), VTEOS (triethoxyvinylsilan) and MTMOS (trimethoxymethylsilan) was studied. The molecular structure of the gels obtained determines differences in their thermal behaviour. Gels obtained starting with MTEOS show the highest thermal stability, while gels obtained using VTEOS the lowest, among the substituted alkoxides. A particular behaviour presents the gel obtained with MTMOS that decomposes in four steps. This could be explained by the presence in the gel of some prevalent types of molecular species with different thermal stability.

Restricted access
Restricted access
Journal of Thermal Analysis and Calorimetry
Authors:
Alaize de Martins
,
A. Craveiro
,
M. Machado
,
Fernanda Raffin
,
T. Moura
,
Cs. Novák
, and
Zsuzsanna Éhen

Abstract  

Inclusion complex between the essential oil of Mentha x villosa Hudson and β-cyclodextrin, with a 1:9 mass/mass oil–β-cyclodextrin ratio was prepared by co-precipitation and kneading methods in a hydroethanolic medium. The GC/MS analysis showed a total volatile content of 99.5% in the Mentha x villosa oil. The characterization of the complex involved the analysis of the original essential oil, the surface and the total extracted oils. Among 28 detected compounds in the original essential oil, 13 are monoterpenes and 10 sesquiterpenes, furthermore, piperitenone-oxide is the major component (35.4%). 12 compounds were totally and 11 partially complexed, 3 have been adsorbed only on the surface of the β-CD and 2 have not been detected neither in the surface oil nor in the complexed oil. A 13.6% encapsulation efficiency was observed, while the total oil and volatiles retention was 15 and 77%, respectively. Non-parametric statistic analysis of the data showed that the profile of the volatiles were not significantly different comparing the original oil and the complexed oil (p>0.04). The results of thermogravimetry-mass spectrometry and XRD analysis have proven the inclusion complex formation between the essential oil and cyclodextrin.

Restricted access

Abstract  

Thermogravimetry (TG) and mass spectrometry (MS) combined techniques have been used to investigate the thermal degradation and catalytic decomposition of high-density polyethylene (HDPE) over solid acid catalysts as H-ZSM-5, Al-MCM-41 and a hybrid material with a bimodal pore size distribution (H-ZSM-5/Al-MCM-41). The silicon/aluminum ratio of all catalysts is 15. Both thermal and catalytic processes showed total conversion in a single mass loss step. Furthermore, the catalytic conversion presents average reduction of 27.4%, in the onset decomposition temperature. The kinetic parameters were calculated using non-isothermal method. These parameters do not indicate significant differences between the thermal and catalytic processes. Even though, the presence of the catalysts changes the reaction mechanism, from phase boundary controlled reaction to random nucleation mechanism. Important difference in distribution of evolved products was detected when several catalysts were used. However, in all cases the main products were alkanes (C2, C3 and C4), alkenes (C3 and C4), dienes (C4 and C5) and traces of aromatic compounds.

Restricted access