A novel surface modification procedure for the creation of sulfhydryl-terminated alkanethiol monolayers that can be used for the attachment of biomolecules onto gold surfaces is described. A self-assembled monolayer of the amine-terminated alkanethiol 11-mercaptoundecylamine (MUAM) is reacted with the heterobifunctional cross-linker N-succinimidyl S-acetylthiopropionate (SATP) in order to create a protected sulfhydryl-terminated monolayer. This monolayer can then be deprotected in an alkaline solution to create an active sulfhydryl surface. Compounds that have been modified to contain a maleimide moiety can be easily attached onto the sulfhydryl-derivatized gold surface. In a second attachment strategy, the sulfhydryl-terminated monolayer is reacted with 2,2‘-dipyridyl disulfide to form disulfide bonds on the surface. These disulfide bonds are then used in a thiol−disulfide exchange reaction with free sulfhydryls in order to attach biomolecules, such as thiol-modified DNA or cysteine-containing polypeptides, onto the surface. In contrast to the maleimide-attached monolayers, the disulfide-immobilized species can be cleaved in the presence of dithiothreitol (DTT) in order to regenerate the free sulfhydryl surface. Polarization modulation FTIR reflection−absorption spectroscopy (PM-FTIRRAS) has been used to characterize these surface reactions, and fluorescence “wash off” measurements provided an estimate of 1.5 × 1012 molecules/cm2 for the surface coverage of DNA immobilized using a thiol−disulfide exchange reaction. Surface plasmon resonance (SPR) imaging measurements were employed to monitor in situ hybridization onto DNA arrays fabricated using this surface immobilization reaction.

Electrochemical impedance spectroscopy, Fourier transform infrared reflection-absorption spectroscopy, and cyclic voltammetry were employed to characterize polyelectrolyte multilayers (PEMs) fabricated with poly-(styrenesulfonate) as the polyanion and the polypeptides poly-L-histidine, poly-L-lysine, and poly-L-arginine as polycations. The layer-by-layer electrostatic assembly was produced onto alkanethiol-modified gold surfaces. The frequency response reveals that the effect of the number of layers seems to be related to a progressive reduction in the active area of the PEM-modified electrodes. The active area after the deposition of seven layers can be lower than 10% of its original value. The film surface is then inhomogeneous with respect to the transport of the electroactive species and has spots through which transport is quite favored. These structural features of the PEM have been taken into account in the theoretical model of ion transport and very good agreement with the experimental impedance results has been found.

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The physical, chemical and nutritional properties of Persea americana fruits variety 'Hass' produced in the Algarve region were studied. Edible and non-edible parts of the fruits (pulp, seeds and peel) were compared considering their possible contribution to improve the sustainability of the food and pharmaceutical industries. The nutritional contents evaluated were moisture, ash, proteins, fat, total soluble solids and acidity. It were also evaluated the contents of bioactive compounds (phenolics, flavonoids, carotenoids, ascorbic acid and vitamin E) and their influence in the antioxidant activity exhibited by the fruit material. The results of the analysis demonstrated that the Algarvian avocado has physical and chemical characteristics comparable or superior to avocados from other growing regions around the world namely, Mexico and California. With regard to the contents of bioactive compounds, the pulp of the Algarvian avocado proved to be rich in carotenoids (0.815±0.201 mg/100g), phenolic compounds (410.2±69.0 mg/100g) and flavonoids (21.9±1.0 mg/100g). The skin was superior to the pulp in the contents of all these compounds with 2.585±0.117 mg/100g of carotenoids, 679.0±117.0 mg/100g of total phenolics and 44.3±3.1 mg/100g of flavonoids. The seed, in turn, was the part of the fruit with the highest total phenolic content (704.0±130.0 mg/100g) and flavonoids (47.97±2.69 mg/100g). Regarding the concentration of vitamins C and E, the highest values were found in the pulp (5.36±1.77 mg/100g of vitamin E) and skin (4.1±2.7 mg/100g of vitamin C). The extracts obtained from the seeds demonstrated higher in vitro DPPH• assay antioxidant activity (43%) than those obtained from the skin (35%) and the fruit pulp (23%). The contents of carotenoids, phenolic compounds and flavonoids found in the non-edible parts of the Algarvian avocado demonstrated that these byproducts could be an interesting inexpensive raw material for the food and cosmetic industries.

a b s t r a c tThe effect of peel and seed removal, two commonly practiced procedures either at home or by the processing industry, on the physicochemical properties, bioactive compounds contents and antioxidant capacity of tomato fruits of four typical Portuguese cultivars (cereja, chucha, rama and redondo) were appraised. Both procedures caused significant nutritional and antioxidant activity losses in fruits of every cultivar. In general, peeling was more detrimental, since it caused a higher decrease in lycopene, bcarotene, ascorbic acid and phenolics contents (averages of 71%, 50%, 14%, and 32%, respectively) and significantly lowered the antioxidant capacity of the fruits (8% and 10%, using DPPH and b-carotene linoleate model assays, correspondingly). Although seeds removal favored the increase of both color and sweetness, some bioactive compounds (11% of carotenoids and 24% of phenolics) as well as antioxidant capacity (5%) were loss. The studied cultivars were differently influenced by these procedures. The fruits most affected by peeling were those from redondo cultivar (À66% lycopene, À44% b-carotene, À26% ascorbic acid and À38% phenolics). Seeds removal, in turn, was more injurious for cereja tomatoes (À10% lycopene, À38% b-carotene, À25% ascorbic acid and À63% phenolics). Comparatively with the remaining ones, the rama fruits were less affected by the trimming procedures.

The effect of organic and conventional agricultural systems on the physicochemical parameters, bioactive compounds content, and sensorial attributes of tomatoes (''Redondo'' cultivar) was studied. The influence on phytochemicals distribution among peel, pulp and seeds was also accessed. Organic tomatoes were richer in lycopene (+20%), vitamin C (+30%), total phenolics (+24%) and flavonoids (+21%) and had higher (+6%) in vitro antioxidant activity. In the conventional fruits, lycopene was mainly concentrated in the pulp, whereas in the organic ones, the peel and seeds contained high levels of bioactive compounds. Only the phenolic compounds had a similar distribution among the different fractions of both types of toma-toes. Furthermore, a sensorial analysis indicated that organic farming improved the gustative properties of this tomato cultivar.K e y w o r d s :

This study intended to evaluate the influence of different postharvest cooling conditions in the physicochemical, antioxidant activity and microbiological contamination of tomato cultivars namely: Cereja, Chucha, Rama and Redondo. Pink fruits were kept for 15 days under three different storage temperatures (6ºC, 12ºC and 25ºC) during which their weight loss, total soluble solids, pH, color, titrable acidity, lycopene and ascorbic acid contents, total phenolics and antioxidant activity were evaluated every three days. Counts of colony forming units of coliform bacteria, yeasts and molds and the presence of Escherichia coli, were determined before and after 15 days of storage. All studied parameters revealed that temperature and storage duration caused statistically significant differences in nutritional values of every cultivar. It was observed an increase in the lycopene concentration and antioxidant activity with temperature and storage duration. The phenolic and ascorbic acid contents showed a slight increase during storage at every temperature. Microbial contamination was only found in cultivars that grew in direct contact with the soil (Chucha and Redondo) and bacterial population increased exponentially with storage temperature. Our results indicate that the ideal temperature to maintain optimal physiological, biochemical and microbiological profiles of the cultivars studied is 12ºC and that the cv. Rama fruit is the most suited for consumption in natura.

The reaction between the arginine's guanidino group and α-dicarbonyl functionalities was used to develop a novel surface modification chemistry. The first modification step consists of the electrostatic adsorption of a poly-l-arginine layer onto ionizable alkanethiol modified gold surfaces. The strongly basic character of the guanidino group of the arginine residues (pK a > 12) guarantees the robust attachment of the polypeptide to negatively charged gold surfaces until very high pH. By varying the pH of the solution from which poly-l-arginine is electrostatically adsorbed, it is possible to control the amount deposited. The availability of the surface guanidino groups of the poly-l-arginine layer for further derivatization with α-dicarbonyl reaction probes, yielding stable heterocyclic condensation adducts, is demonstrated. In addition, the reaction with the heterobifunctional reagent p-azidophenyl glyoxal (APG) provides a surface terminated with a photosensitive aryl azide group which was employed for the photochemical immobilization of proteins to the surface. The application of this surface modification chemistry to immobilize antibodies is demonstrated.