Kinetic study of the thermal and thermo-oxidative degradations of polylactide-modified films for food packaging

In this study, the thermal degradations of some commercial polylactide (PLA) films, pure and subjected to various superficial treatments, were investigated in both inert (flowing nitrogen) and oxidative (static air) atmospheres. Degradations were carried out in a thermobalance, in the scanning mode, at various heating rates, and the obtained thermogravimetric curves were discussed and interpreted. Experiments, performed in the temperature range of 35–700 °C, showed similar behavior in both the atmospheres used. The initial decomposition temperature (T _i) and the apparent activation energy (E _a) of degradation of the differently treated PLA films were determined and compared with each other and with those of untreated PLA. The E _a of degradation was obtained by Kissinger’s method, and the values were found increased linearly as a function of crystallinity percentage (%c) as well as the T _i values. The glass transition temperature (T _g) was also determined by differential scanning calorimetry. All the investigated parameters showed dependence on different treatments made to the films. The results obtained for the degradations of PLA films were compared with each other, and a classification of thermal stability in the studied environments were made.     

Carbocyclic analogues of nucleosides from bis-(Hydroxymethyl)-cyclopentane: synthesis,antiviral and cytostatic activities of adenosine,inosine and uridine analogues

Six new carbocyclic nucleosides were prepared by constructing a purine base (in compounds 9-11) or pyrimidine base (in 6-8) on the amino groups of (+/-)-(1 beta,2 alpha,4 beta)-4-amino-1,2-cyclopentanedimethanol (4) and (+/-)-(1 beta,3 alpha,4 beta)-4-amino-1,3-cyclopentanedimethanol (5), and their activities against a variety of viruses and tumour cell lines were determined.     

Evaluation of the degree of cross-linking of cellulose-based superabsorbent hydrogels: a comparison between different techniques

Three different techniques have been applied to the evaluation of the degree of cross-linking of superabsorbent cellulose-based hydrogels obtained from water solutions of carboxymethylcellulose sodium salt (CMCNa) and hydroxyethylcellulose (HEC), chemically cross-linked with divinyl sulfone. These polyelectrolyte hydrogels are biodegradable and have the same sorption capacity as acrylate-based superabsorbents on the market. A ¹³C solid state NMR analysis was carried out on dry samples of hydrogel to obtain the degree of cross-linking, an important parameter that affects the swelling and mechanical properties of a hydrogel. Dynamic mechanical analysis was performed during the hydrogel cross-linking using a parallel plate rheometer under oscillatory deformations in order to monitor the evolution of the hydrogel viscoelastic properties during the synthesis. The value of |G*| and the slope of the stress-deformation ratio plots from uniaxial compression tests were used to evaluate the elastically effective degree of cross-linking according to classical rubber elasticity theory. Moreover, a dynamic mechanical analysis was carried out on cross-linked hydrogels at different degrees of swelling in order to investigate the influence of the swelling on the mechanical properties and the application of rubber elasticity theory to swollen hydrogels.     

A comparison of depletion versus equalization for reducing high-abundance proteins in human serum

In this work three methods to diminish the content of most highly abundant proteins in human serum have been studied and compared. Protein depletion with ACN or DTT and protein equalization with the ProteoMiner^? (PM) have been assessed by 1‐D gel electrophoresis and MS. After treatment 5, 18 and 9 major proteins within the 20 most abundant proteins in serum were identified for the ACN, DTT and PM methods, respectively. The ACN method was efficient for depleting high molecular weight proteins, over 75 KDa, resulting in 10±4% (n=3) of the total protein content remaining in the depleted serum. In addition, 75% of the proteins belonging to the group of the 20 most abundant proteins were not detected, making this depletion strategy a cheap alternative to expensive commercial tools regularly used for removing high abundance proteins from serum. The ACN extract was found rich in apolipoproteins. The dithithreitol method promotes the precipitation of proteins rich in disulfide bonds, mainly albumin, with 73±7% (n=3) of the total protein content remaining in the depleted serum, which was found rich in immunoglobulins. The PM method compresses the dynamic range of the serum proteins, rendering an extract containing 16±2% (n=3) of the total initial protein content. The extract was found to be rich in both apolipoproteins and immunoglobulins. As a general rule the DTT and PM methods provide a compression of the dynamic range of serum protein concentrations while the ACN method allows an effective depletion of the protein fraction above 72 KDa.     

NIR analysis of pharmaceutical samples without reference data: improving the calibration

Using an appropriate set of samples to construct the calibration set is crucial with a view to ensuring accurate multivariate calibration of NIR spectroscopic data. In this work, we developed and optimized a new methodology for incorporating physical variability in pharmaceutical production based on the NIR spectrum for the process. Such a spectrum contains the spectral changes caused by each treatment applied to the component mixture during the production process. The proposed methodology involves adding a set of process spectra (viz. difference spectra between those for production tablets and a laboratory mixture of identical nominal composition) to the set of laboratory samples, which span the wanted concentration range, in order to construct a calibration set incorporating all physical changes undergone by the samples in each step of the production process. The best calibration model among those tested was selected by establishing the influence of spectral pretreatments used to obtain the process spectrum and construct the calibration models, and also by determining the multiplying factor m to be applied to the process spectra in order to ensure incorporation of all variability sources into the calibration model. The specific samples to be included in the calibration set were selected by principal component analysis (PCA). To this end, the new methodology for constructing calibration sets for determining the Active Principle Ingredients (API) and excipients was applied to Irbesartan tablets and validated by application to the API and excipients of paracetamol tablets. The proposed methodology provides simple, robust calibration models for determining the different components of a pharmaceutical formulation.     

pH‐Dependent Chloride Transport by Pseudopeptidic Cages for the Selective Killing of Cancer Cells in Acidic Microenvironments

Acidic microenvironments in solid tumors are a hallmark of cancer. Inspired by that, we designed a family of pseudopeptidic cage‐like anionophores displaying pH‐dependent activity. When protonated, they efficiently bind chloride anions. They also transport chloride through lipid bilayers, with their anionophoric properties improving at acidic pH, suggesting an H⁺/Cl^? symport mechanism. NMR studies in DPC micelles demonstrate that the cages bind chloride within the lipid phase. The chloride affinity and the chloride‐exchange rate with the aqueous bulk solution are improved when the pH is lowered. This increases cytotoxicity towards lung adenocarcinoma cells at the pH of the microenvironment of a solid tumor. These properties depend on the nature of the amino‐acid side chains of the cages, which modulate their lipophilicity and interactions with the cell membrane. This paves the way towards using pH as a parameter to control the selectivity of cytotoxic ionophores as anticancer drugs.     

Selective Separation of Oxy-PAH from n-Alkanes and PAH in Complex Organic Mixtures Extracted from Airborne PM2.5

A fast and simple fractionation method was optimized to selectively separate oxy-PAH from polycyclic aromatic hydrocarbons (PAH) and n-alkanes contained in solvent extracted organic matter (SEOM) from atmospheric particles with an aerodynamic diameter ≤2.5 μm (PM_2.5). Samples were collected in Mexico City. Multivariate parameters were adjusted on a standard mixture, and on SEOM spiked with pure standard mixture solutions: type and amount of phase; packing densities; type, proportion and amount of solvents, and elution flow rates were tested under several elution schemes. Cyanopropylsilyl-bonded phase material was the selected stationary phase. The separation method was applied to real samples of SEOM (2.6, 5.6 and 8.5 mg) spiked with n-alkanes, PAH and oxy-PAH. n-Alkanes overlapped with PAH due to an excess of n-alkanes in real samples overloading the capacity of the stationary phase. Oxy-PAH was separated totally from n-alkanes and PAH. Mean recoveries ± confidence intervals (95%) for n-alkanes ranged from 53 ± 17% (n-tetracontane) to 101 ± 11% (n-hexacosane); for PAH from 58 ± 5% (phenanthrene) to 85 ± 9% (benzo[k]fluoranthene); and for oxy-PAH from 68 ± 12% (9,10-dihydrobenzo[a]pyren-7(8H)one) to 108 ± 9% (1,2-benzopyrone). This method is an efficient fractionation procedure to be applied to oxy-PAH, PAH and n-alkanes in complex organic mixtures extracted from PM_2.5.     

Homo‐ and Copolymerization of Butadiene Catalyzed by an Bis(imino)pyridyl Vanadium Complex

Summary: The bis(imino)pyridyl vanadium(III ) complex [VCl₃{2,6‐bis[(2,6‐iPr₂C₆H₃)NC(Me)]₂(C₅H₃N)}] activated with different aluminium cocatalysts (AlEt₂Cl, Al₂Et₃Cl₃, MAO) promotes chemoselective 1,4‐polymerization of butadiene with activity values higher than classical vanadium‐chloride‐based catalysts. The polymer structure depends on the nature of the cocatalyst employed. The MAO‐activated complex was also found to be active in ethylene‐butadiene copolymerization, producing copolymers with up to 45 mol‐% of trans‐1,4‐butadiene. Crystalline polyethylene and trans‐1,4‐poly(butadiene) segments were detected in these copolymers by DSC and ¹³C NMR spectroscopy.

     

Structural and spectroscopic study of 5,7-dihydroxy-flavone and its complex with aluminum

The structure, stability and molar absorptivity of the complex formed between AlCl(3) and 5,7-dihydroxy-flavone in methanol were investigated using UV-Vis spectroscopy and the AM1 method. The molar ratio method and Job's method of continuous variation were applied to ascertain the stoichiometric composition of the complex in methanol at constant ionic strength. A 1:2 complex was indicated by both methods. The molar absorptivity and stability constant of the complex were determined using a simple and accurate procedure that requires solutions having the ligand and metal ion in the stoichiometric proportion. The high stability constant demonstrates that the complexation reaction is total. The structure of this complex, obtained by the quantum semi-empirical AM1 method, indicates that two classes of metal-ligand interactions are involved in the formation of the metal complex: (a) two simple covalent bonds between the aluminum atom and the oxygen atoms of o-hydroxyl groups of 5,7-dihydroxy-flavone; (b) two stronger Coulombic interactions between the aluminum atom and the carbonyl oxygen atoms of the ligand.