Showing papers by "University of Perugia published in 1974"
TL;DR: In this paper, the authors review various definitions of aromaticity in common use and to survey their applications in heterocyclic chemistry, concluding that the characteristics of an aromatic compound are easy to define from a qualitative viewpoint.
Abstract: Publisher Summary This chapter discusses aromaticity of heterocycles. At a time when the validity of the concept of aromaticity is questioned, increasingly, it seems appropriate to review various definitions in common use and to survey their applications in heterocyclic chemistry. From a qualitative viewpoint the characteristics of an aromatic compound are easy to define. A compound is said to be aromatic if it is cyclic and unsaturated with an enhanced stability over simple olefinic compounds. The characteristic aromatic reactivity of the type described is clearly a matter of degree and is difficult to assess quantitatively. From a simple consideration of pyridine, which reacts less readily with electrophiles but more readily with nucleophiles at the ring carbon atoms than does benzene, it soon becomes apparent that attempts to discuss even relative aromatic character using kinetic criteria is fraught with difficulties; this is apart from the fundamental objection that chemical reactivity is not solely a function of ground-state stability.
104 citations
TL;DR: In this paper, the effect of the degree of crystallinity of zirconium phosphate on its ion-exchange properties and electrical conductivity, the dependence of its selectivity for large cations on steric hindrance and the catalytic effect of small amounts of sodium ions on the exchange of large hydrated cations are discussed.
85 citations
TL;DR: Results indicate that more than one enzyme is probably involved in the Ca2+‐medialed exchange of nitrogenous bases, and shows differences for the three substrates when various factors are changed during incubation.
Abstract: — The calcium-dependent incorporation of choline, ethanolamine and L-serine into the phospholipids of isolated rat brain microsomes has been studied in vitro, and various properties of the incorporation have have been examined. The optimum pH for the incorporation of each base was found to vary inversely with the Ca2- concentration. Conversely, the optimal Ca2 + concentration for the exchange of the bases increased with decreasing pH values. The enzymic system for the incorporation of ethanolamine appeared to be saturated by two substrate concentrations, i.e. 0-2 and 1-7-2-0 mM. At low ethanolamine concentration (0-2 mM] much less incorporation of the base occurred into the alkenylacyl- and alkylacyl-derivatives of ethanolamine phosphoglycerides compared to that into the diacyl species, whereas the difference becomes smaller at a high substrate concentration (1-7 mM). At pH 81 and 2 mM-Ca2+ the apparent Km of ethanolamine at low substrate concentration was 80 × 10-5 M, and this value increased to 16-2 × 10-4.viat 10mM-Ca2+ concentration. At similar pH the Km values for choline and L-serine were 5.88 × 10-4M and 40 × 10-4 M at 2 mM- and 10mM-Ca2 + concentrations, respectively. The properties of the enzyme system show differences for the three substrates when various factors are changed during incubation. These and other results indicate that more than one enzyme is probably involved in the Ca2+-medialed exchange of nitrogenous bases.
67 citations
TL;DR: Results obtained indicate that growth factors and esteroprotease activity are associated in the same intracellular particles, suggesting a possible role of the enzyme in the maturation of native molecules of growth factors, as described for proinsulin-insulin conversion.
35 citations
TL;DR: The circadian rhythm of the rat body temperature is abolished in rats kept either in constant dark or light or blinded, and most likely the circadian rhythm is not related to changes in patterns of motor activity.
31 citations
TL;DR: In this article, computer simulation of the lanthanide induced shifts has been applied to study conformational preferences in the 2-formyl and 2-acetyl derivatives of furan, thiophene, selenophene and tellurophene derivatives.
28 citations
TL;DR: It is concluded that the cytidine-dependent system for ethanolamine plasmalogen and phosphatidylethanolamine synthesis is concentrated prevalently in the neuronal cells, as compared to glia.
Abstract: The de novo synthesis of ethanolamine plasmalogen in isolated neuronal and glial cells from adult rabbit brain cortex was investigated in vitro, using labeled cytidine-5′-diphosphate ethanolamine as lipid precursor. The neuronal cell enriched fraction was found to possess a twofold ethanolaminephosphotransferase activity (EC 2.7.8.1), as compared to the glial fraction. The neuronal/glial ratio was similar both in the absence and in the presence of saturating alkenylacyl glycerol. Under the most favorable conditions, rates of 31 nmoles and 16 nmoles ethanolamine plasmalogen/mg protein/30 min were obtained for neurons and glia, respectively. Several kinetic properties of the phosphotransferase were found to be similar both in neurons and glia, e.g., Km of cytidine-5′-diphosphate ethanolamine, pH optimum, need for divalent cations; the Km value for alkenylacyl glycerol was twofold higher in glia (4 mM) than in neurons (2 mM). The neuronal/glial ratio for the phosphatidylethanolamine synthesizing activity was 2, 4.5, and 6 on using diacyl glycerols prepared from ox heart, ox brain, and soybean, respectively. It is concluded that the cytidine-dependent system for ethanolamine plasmalogen and phosphatidylethanolamine synthesis is concentrated prevalently in the neuronal cells, as compared to glia.
27 citations
01 Jun 1974
27 citations
TL;DR: In this paper, a procedure for direct gas chromatographic analysis of volatile constituents present in the headspace above wines has been developed Samples of wine and its headspace were conditioned for specified times and temperatures so as to reach air-liquid equilibrium in a special large syringe (2000 ml).
Abstract: A procedure for direct gas chromatographic analysis of volatile constituents present in the headspace above wines has been developed Samples of wine (100 ml) and its headspace were conditioned for specified times and temperatures so as to reach air-liquid equilibrium in a special large syringe (2000 ml) designed in our laboratory The headspace volatiles were collected directly, freed from water and ethanol in a short trap packed with Porapak Q connected to the syringe The vapour passed from the syringe to the precolumn through a container holding the internal standard under strictly defined conditions of temperature, pressure and flow rate The elution of volatiles from the traps was accomplished directly into the oven of the gas chromatograph The operating parameters of the system are discussed This procedure allows the qualitative (and quantitative) determination of different volatile compounds present in the headspace above wines The factors which influence the air-liquid partition of volatile compounds present in wine are also examined
24 citations
TL;DR: In this paper, the composition and the solid phase percentages at the various stages of exchange were investigated to study the large hysteresis loop found for the Li/K system.
23 citations
TL;DR: In three synthetic unleaded fuels at constant total aromatics the type of aromatic present strongly affected the PAH emissions: it seems that simple aromatic hydrocarbons, such as benzene or xylene, produce less PAH than C 9 and C 10 hydrocarbon.
01 Aug 1974
TL;DR: In this paper, the spectral properties of solid selenophene at different temperatures have been measured using polarized radiation and a tentative hypothesis for the space group of the crystalline selenophhene has been given.
Abstract: Infrared spectra of solid selenophene at different temperatures, have been measured using polarized radiation. Just below the freezing point the selenophene molecule has a noticeable degree of ring-rigidity, allowing for a definite location in sites of lower symmetry than the molecular one. Dichroic behaviour of IR lines in the solid state enables us to attribute the bands to the relative symmetry species and give a tentative hypothesis for the space group of the crystalline selenophene.
TL;DR: The application of untreated urine and plasma, the possibility of identifying with accuracy the carbohydrates present in the samples and the rapidity of the procedure make this method particularly suitable for the screening of carbohydrate anomalies.
TL;DR: In this paper, the polarographic reduction in acetonitrile (ACN) of π-C3H5Co(CO)3 and of the phosphinic derivatives was discussed and the reduction mechanism was discussed.
TL;DR: The dipole moments of compounds of the four series C6H5SM(CH3)3, m- and p-ClC6H4SM( CH3)4, [(CH 3)3M]2S (M = C, Si, Ge, Sn, Pb) have been measured as mentioned in this paper.
TL;DR: In this article, a synthese d'analogues fluores en 2,3 ou 4 des [1]benzothiopyrano[4,3-b]indoles cancerogenes and des 6H[1]bensothio-thiochromanones correspondantes.
TL;DR: No changes in the sequential methylation pathway for lecithin synthesis in the liver were observed after acute ethanol ingestion, and an increase in the Kennedy pathway was found in vitro in the homogenates and microsomal fractions prepared from the ethanol-treated rats.
TL;DR: È stata dimostrata la capacità di culture primarie di fegato embrionale di sintetizzare fosvitina in vitro dopo trattamento con estrogeni.
Abstract: E stata dimostrata la capacita di culture primarie di fegato embrionale di sintetizzare fosvitina in vitro dopo trattamento con estrogeni.
TL;DR: In this paper, the fluorescence quenching of fluorene, dibenzofuran, and Dibenzothiophen by aliphatic amines and aromatic nitriles (electron acceptors) has been studied in different solvents.
TL;DR: I'ultrastruttura nel neurosecreto delle fibre nervose decorrenti fra i fasci ghiandolari faringei di soggetti digiuni da 7 gg e di sogsgetti utilizzati nel momento dell'assunzione del cibo.
Abstract: In esemplari di Dugesia lugubris e stata esaminata I'ultrastruttura nel neurosecreto delle fibre nervose decorrenti fra i fasci ghiandolari faringei di soggetti digiuni da 7 gg e di soggetti utilizzati nel momento dell'assunzione del cibo. Nei digiuni il neurosecreto e abbondante in vicinanza delle propaggini ghiandolari e molto scarso in prossimita dei corpi delle ghiandole. Negli alimentati il neurosecreto e scarso a livello delle propaggini ed abbondante in prossimita dei corpi ghiandolari. In base a questi rilievi si avanza l'ipotesi che esista una precisa correlazione fra neurosecreto e secreto ghiandolare.
TL;DR: Catecholamine plasma concentrations and urinary excretion were measured together with plasma renin activity in ten patients with essential hypertension and in five normal control subjects before and after a frusemide challenge and Oxprenolol suppressed the response of noradrenaline and plasma renIn activity to frusemides in all cases.
Abstract: 1. Catecholamine plasma concentrations and urinary excretion were measured together with plasma renin activity in ten patients with essential hypertension and in five normal control subjects before and after a frusemide challenge. 2. The same procedure was repeated in the same subjects 3–4 days later after pretreatment with oxprenolol. 3. Noradrenaline plasma concentrations and urinary excretion increased significantly after frusemide in all cases, returning to normal values at 30 and 60 min. Adrenaline plasma concentrations and urinary excretion were unchanged. 4. Plasma renin activity increased significantly in seven patients with hypertension and normal renin basal values, remaining unchanged in three hypertensive patients with low-renin basal values. 5. Oxprenolol suppressed the response of noradrenaline and plasma renin activity to frusemide in all cases.
TL;DR: In this article, the authors showed that the reaction mechanism is the same as that in toluene in dichloromethane, acetone, acetonitrile, isopropyl ether and n-hexane, and the solvent and temperature effects on the α/1α ratio further confirm the nature of the proposed intermediates.
TL;DR: In this paper, Li/K exchange of crystalline zirconium phosphate in molten LiNO 3 KNO 3 mixtures at 300°C has been investigated and it was shown that the large hysteresis loop between the forward and reverse isotherms is related to the formation of different phases in the two processes.
Abstract: Li/K exchange of crystalline zirconium phosphate in molten LiNO 3 KNO 3 mixtures at 300°C has been investigated. For the forward process the exchange occurs with the formation of an immiscible ZrLiK(PO 4 ) 2 phase having an interlayer distance of 7·6 A, whereas the reverse process occurs without a decrease of the interlayer distance. The large hysteresis loop between the forward and reverse isotherms is therefore related to the formation of different phases in the two processes. It was also found that by heating Zr(LiPO 4 ) 2 (7·6 A) at ∼500°C the phase Zr(LiPO 4 ) 2 (7·0 A) was again obtained. On the basis of these results and of those previously obtained for Na/K exchange in molten salt and in aqueous media, some general considerations for the alkali-alkali metal ion exchange processes of crystalline zirconium phosphate are reported.
01 Jun 1974
TL;DR: In this paper, the polarized infrared spectra of a single crystal of CuenCl 2 have been measured and a vibrational assignment is suggested on the basis of group frequencies, polarization behavior and application of the oriented gas model, where the latter is applicable, in addition to isotopomer shifts of Cu(en-Nd 4 )Cl 2 and Raman spectra.
Abstract: ]The polarized infrared spectra of a single crystal of CuenCl 2 have been measured. A vibrational assignment is suggested on the basis of group frequencies, polarization behaviour and application of the oriented gas model, where the latter is applicable, in addition to isotopomer shifts of Cu(en-Nd 4 )Cl 2 and Raman spectra.
TL;DR: The ion exchange behavior of crystalline ZrNaH(PO 4 ) 2 5H 2 O towards alkali metal ions has been investigated in this article, where it was found that, in the pH range 3-5, hydrogen ion is not exchanged and only Na+alkali metal ion exchanges take place Forward and reverse Na + -K +, Na +-Li +, K + -Li + and Na + −C + ion exchange isotherms have been determined and discussed comparatively with the results obtained previously with fully-substituted alkali ion ionic
Abstract: The ion exchange behaviour of crystalline ZrNaH(PO 4 ) 2 5H 2 O towards alkali metal ions has been investigated It was found that, in the pH range 3–5, hydrogen ion is not exchanged and only Na + -alkali metal ion exchanges take place Forward and reverse Na + -K + , Na + -Li + , K + -Li + and Na + -Cs + ion exchange isotherms have been determined and discussed comparatively with the results obtained previously with fully-substituted alkali metal ionic form of zirconium phosphate The exchanges occur with phase transitions and small hysteresis loops have been observed between the isotherms of the two opposite processes The sequence of decreasing alkali metal ion preference is K + > Cs + > Na + > Li + and a very high selectivity towards K + or Cs + ion has been found Thus, differently from Zr(HPO 4 ) 2 H 2 O, the monosodium form exhibits preference for large cations and this different behaviour may be due to the large difference in the interlayer distances of the two ionic forms (7·56 and 11·8 A respectively) The uptake of large ions by enlarged crystalline zirconium phosphate discloses new practical applications for such an exchanger