Thermodynamics of water/β-cyclodextrin system

The thermodynamics of β-cyclodextrin dehydration is investigated, by parallel DSC/TG experiments, on both fully and partially hydrated samples. The apparent dehydration enthalpies per mole of water are impossibly high and this fact suggests that another phenomenon, in addition to the rupture of the β-cyclodextrin/H₂O hydrogen bonds, contributes to the peak area. All the experimental evidence agrees with an ‘interaction model’ which assumes that deydration is accompanied by a slow and reversible rearrangement of the β-cyclodextrin structure.     

Comparison of three spectrophotometric methods for the determination of gamma-oryzanol in rice bran oil

A comparison of the results obtained by applying three spectrophotometric methods (at fixed wavelength, second-derivative and multicomponent analysis) to the determination of gamma-oryzanol in rice bran oil is reported.At fixed wavelength the results are more accurate when using isopropyl alcohol, rather than n-heptane, to dilute the oil samples, because the absorption bands of gamma-oryzanol are red-shifted and the absorbance, measured at lambda(max)=327 nm, is less affected by the interference of the oil "matrix" (lambda(max)=314 nm in n-heptane).However, to obtain accurate results also in oils with a low content of gamma-oryzanol, it is necessary to perform the analysis using second-derivative ((2)D330.365) or multicomponent (lambda=310-360 nm) methods. The first one fully removes the interference of oil matrix whilst the second, which needs a specific computational program to process the spectrophotometric data, furnishes evidence the presence of some unexpected interference in the analysis and/or standards which are not representative of the analysed samples, from the square root of the sum of the squared differences at each point between the linear combination of the standards and the unknown spectra (RMS error).Finally, some aspects of the chemical, spectroscopic (UV, IR) and thermoanalytical (TG, DSC) behaviour of gamma-oryzanol and the values of the parameters which enable "computation" of its UV spectra are reported.     

Triplet to ground state intersystem crossing and CIS-trans isomerization in stilbene

The T₁ ? S₀ intersystem crossing process in stilbene is considered adopting a formulation in which the isomerization coordinate can be treated separately. Energy surfaces in agreement with experimental and theoretical results are employed and pertinent spin-orbit coupling is evaluated. The calculated decay rate is in good agreement with the experimental results based on the azulene quenching effect. The qualitative feature that quantum yield for cis formation tends to be higher than the counterpart trans formation is explained. Deuterium effects are discussed and explanations for them are suggested.     

New Spermine Alkaloids from Aphelandra tetragona (VAHL) NEES

18-O-Methylchaenorpine ( 1a ) and iso-18-O-methylchaenorpine ( 1b ) two novel stereoisomeric spermine alkaloids were isolated from the roots of Aphelandra tetragona (VAHL ) NEES. Their structures were established by chemical and spectroscopic studies.     

PHOTODYNAMIC THERAPY OF B16 PIGMENTED MELANOMA WITH LIPOSOME-DELIVERED Si(IV)-NAPHTHALOCYANINE

The possibility of extending photodynamic therapy to the treatment of highly pigmented neoplastic lesions was tested by using Si(IV)-naphthalocyanine (SiNc) as a tumor-localizing agent. Si(IV)-naphthalocyanine displays intense absorbance at 776 nm (ɛ= 5 × 10⁵ M⁻¹ cm⁻¹), where melanin absorption becomes weaker. As an experimental model we selected B16 pigmented melanoma subcutaneously transplanted to C57BL mice. Upon injection of 0.5 or 1 mg kg⁻¹ of liposome-incorporated SiNc, maximal accumulation of the photosensitizer in the tumor was observed at 24 h with recoveries of 0.35 and 0.57 μg g⁻¹, respectively. However, the tumor targeting by SiNc shows essentially no selectivity, since the photosensitizer concentrations in the skin (peritumoral tissue) were very similar to those found in the tumor at all postinjection times examined by us. Irradiation of SiNc-loaded melanoma with 776 nm light from a diode laser at 24 h postinjection induces tumor necrosis and delay of tumor growth. The effect appears to be of purely photochemical nature at dose rates up to 260 mW cm⁻²; at higher dose rates, thermal effects are likely to become important.     

Ring-closure reactions through intramolecular displacement of the phenylselenonyl group by nitrogen nucleophiles: a new stereospecific synthesis of N-tosyl and N-benzoyl-1,3-oxazolidin-2-ones from beta-hydroxyalkyl phenyl selenides

A new and convenient method for the stereospecific synthesis of variously substituted 1,3-oxazolidin-2-ones from the easily available beta-hydroxyalkyl phenyl selenides is presented. After transformation into the N-tosyl or N-benzoyl carbamates, the selenides were oxidized to the corresponding selenones. The key step of the process is the ring-closure reaction, which occurs by stereospecific intramolecular nucleophilic substitution of the selenone group by the nitrogen atom of the carbamate. Enantiomerically pure 1,3-oxazolidin-2-one derivatives can be easily prepared by using enantiomerically pure beta-hydroxyalkyl phenyl selenides as starting materials.     

A simple synthesis of (R)-3-aminooctanoic acid (D-BAOA) from (S)-1-octyn-3-ol

A simple substrate-controlled asymmetric synthesis of (R)-3-aminooctanoic acid (D-BAOA) is described. The present method involves the conversion of commercially available (S)-1-octyn-3-ol into the protected propargylic amine, with complete inversion of configuration, and the successive transformation of the (phenylseleno)acetylene intermediate into the Se-phenyl selenocarboxylate, which is then easily converted into the carboxylic group. The phthalimido group was eventually removed by treatment with hydrazine hydrate.     

Nanostructured ruthenium on γ-Al2O3 catalysts for the efficient hydrogenation of aromatic compounds

Free and trioctylamine (TOA)-stabilized ruthenium nanoparticles have been prepared by decomposition of the metal precursor Ru(η⁶-cycloocta-1,3,5-triene)(η⁴-cycloocta-1,5-diene) under mild conditions (room temperature, hydrogen atmospheric pressure). The nanoparticles have been deposited on γ-Al₂O₃ supports having different surface area. The resulting systems are active in the hydrogenation of methyl benzoate to methyl cyclohexanoate with a reaction rate decreasing in the order Ru(TOA)/γ-Al₂ O₃ (high surface area, catalyst D) > Ru(TOA)/γ-Al₂O₃ (catalyst C) > Ru/γ-Al₂O₃ (high surface area, catalyst B) > Ru/γ-Al₂O₃ (catalyst A). Catalysts A-D are long lived and can be reused without loss of activity; they are considerably more active than a commercial ruthenium on γ-Al₂O₃ sample. High Resolution Transmission Electron Microscopy analyses of such systems show that the nanoparticles are homogeneously dispersed on the support and that the size distribution decreases in the order catalyst A, 2.9 nm > catalyst B, 2.8 nm > catalyst C, 2.4 nm > catalyst D, 2.3 nm. Based on the easy hydrogenation of the aromatic ring to the cyclohexane derivative, an efficient synthesis of 4-carbomethoxyformylcyclohexane, important starting material in the preparation of pharmaceutical products, from the largely available methyl 4-formylbenzoate, has been set up in the presence of catalyst D.     

Comparison of collisional activation by the ‘boundary effect’ vs. ‘tickle’ excitation in an ion trap mass spectrometer

It has been shown previously that collisional activation in an ion trap mass spectrometer can be achieved by storing parent ions within a narrow zone extending close to the theoretical boundaries β_r = 0 or β_z = 0 of the stability diagram. This procedure can be used for obtaining collision-induced dissociation of selected parent ions without the need to apply a precisely tuned resonant ‘tickle’ potential between the end-cap electrodes. In this investigation a comparison was made between the two methods (‘tickle’ and ‘boundary’) of activation based on the efficiency of parent-to-daughter conversion and on the relative abundance of daughter ions for a model system (the m/z 91/92 ratio for n-butylbenzene). The data show that, under conditions of maximum efficiency, a comparable amount of internal energy is present in the ions after activation with the two methods. However, with the ‘tickle’ technique it is possible to increase the internal energy of the parent ions even further, although at the expense of the efficiency, whereas in the case of the “boundary” activation, the conditions for optimum efficiency almost coincide with those for maximum activation and a drastic loss of ions follows any attempt to overcome these limits. It is also found that at any given q_z value used for storing and activating parent ions the permitted mass difference between parent and fragment ions is greater with ‘boundary’ than with ‘tickle’ excitation.     

Aflatoxin M1 determination in raw milk using a flow-injection immunoassay system

A flow-injection immunoassay (FI-IA) method with amperometric detection for aflatoxin M1 (AFM1) determination in milk has been developed. The first step consists in an incubation of the sample containing AFM1 (Ag) with fixed amounts of anti-AFM1 antibody (Ab) and of the tracer (Ag^*, AFM1 covalently coupled to HRP) until equilibrium is reached. In this mixture a competition occurs between Ag and Ag^* for the Ab. The mixture is then injected into a flow system where the separation of the free tracer (Ag^*) and the antibody-bound tracer (AbAg^*) is performed in a column with immobilized Protein G. The antigen–antibody complexes are retained in the column due to the high affinity of the Protein G for the antibody. The activity of the eluted enzyme label is then amperometrically detected.

The immunoassay was optimised relative to conditions for antibody–antigen incubation (pH, incubation time, ionic strength, temperature) and enzymatic label detection. This method showed a dynamic concentration range between 20 and 500 ppt AFM1, a low detection limit (11 ppt), good reproducibility (RSD < 8%) and a high throughput (six samples per hour in triplicate). Different milk samples were analysed and the results were in good agreement with those obtained by HPLC using the AOAC 2000.08 method.