Redox switching of heteropolyanions entrapped in polypyrrole films investigated by ac electrogravimetry.

In this work, the global kinetics and the exchange of protons and free solvent at the film/electrolyte interface were investigated when a PPy film doped with HPA (heteropolyanions) is polarized. The ionic and electronic transfers for the PPy-HPA system are fast because the determined values of the resistances are relatively low (a few ohms). Depending on the applied potential, the global kinetics is controlled by both the ionic and electronic transfers. The transport effects were neglected here because the prepared films were very thin. Protons play an important role in charge compensation whatever the imposed potential on the PPy-HPA film. This phenomenon results from the acidic-basic properties of the SiMo(12)O(40)(4-) reduced species. A small quantity of water was also shown to be involved in the film reaction process.

Improved frequency/voltage converters for fast quartz crystal microbalance applications.

The monitoring of frequency changes in fast quartz crystal microbalance (QCM) applications is a real challenge in today's instrumentation. In these applications, such as ac electrogravimetry, small frequency shifts, in the order of tens of hertz, around the resonance of the sensor can occur up to a frequency modulation of 1 kHz. These frequency changes have to be monitored very accurately both in magnitude and phase. Phase-locked loop techniques can be used for obtaining a high performance frequency/voltage converter which can provide reliable measurements. Sensitivity higher than 10 mVHz, for a frequency shift resolution of 0.1 Hz, with very low distortion in tracking both the magnitude and phase of the frequency variations around the resonance frequency of the sensor are required specifications. Moreover, the resonance frequency can vary in a broad frequency range from 5 to 10 MHz in typical QCM sensors, which introduces an additional difficulty. A new frequency-voltage conversion system based on a double tuning analog-digital phase-locked loop is proposed. The reported electronic characterization and experimental results obtained with conducting polymers prove its reliability for ac-electrogravimetry measurements and, in general, for fast QCM applications.

New frequency/voltage converters for ac-electrogravimetric measurements based on fast quartz crystal microbalance.

A better understanding of the mechanisms located at the solid/electrolyte interface is becoming essential to the development of new applications in the electrochemical fields. The fast quartz crystal microbalance is an attractive and powerful gravimetric sensor which can be used in the dynamic regime to determine a mass/potential transfer function. The principle is equivalent to classical electrochemical impedance measurements; the only difference is the determination of mass changes given by the quartz crystal microbalance rather than current changes following sine wave modulations of the applied potential. This function appears very well adapted to characterize ionic exchanges at the electrochemical interface. Frequency/voltage converters are the key devices in translating the microbalance frequency response in terms of a continuous voltage change. The latter allows the transfer function to be obtained via a frequency response analyzer. Different converters were tested in this work in order to improve the performances of the experimental setup.

Electrochemical impedance spectroscopy investigations of a microelectrode behavior in a thin-layer cell: Experimental and theoretical studies.

Electrochemical impedance spectroscopy experiments were performed on a microdisk electrode in a thin-layer cell using a scanning electrochemical microscope for controlling the cell geometry. Experimental data showed that when the thin-layer thickness diminished, an additional low-frequency response appeared. It was ascribed to the radial diffusion of the electroactive species and was strongly dependent on the thin-layer dimensions (both thickness and diameter). Moreover, the numerical simulation of the impedance diagrams by finite element method calculations confirmed this behavior. An equivalent circuit based on a Randles-type circuit was proposed. Thus, the diffusion was described by introducing two electrical elements: one for the spherical diffusion and the other for the radial contribution. A nonlinear Simplex algorithm was used, and this circuit was shown to fit the impedance diagrams with a good accuracy.

Mechanism for interplay between electron and ionic fluxes in KhFek[Fe(CN)6]l.mH2O compounds.

This paper develops a framework for the interpretation of ionic insertion/deinsertion reactions in an aqueous environment taking place in transition-metal hexacyanoferrates of the general formula K(h)[Fe(2+) (CN)(6)](l).mH(2)O, also called Prussian Blue. Three different processes were fully separated in the electrochemistry of these films. It was clearly identified that one of these electrochemical processes involves the insertion/deinsertion of H(3)O(+) (hydrated protons) through the channels of the K(h)[Fe(2+) (CN)(6)](l).mH(2)O structure to reach the film electroneutrality during the electron transfer between Everitt's Salt and Prussian Blue. The other electrochemical processes involve K(+) or H(+) (proton) exchange through the water crystalline structure existing in the channels of the K(h)[Fe(2+)(CN)(6)](l).mH(2)O structure.

Kinetic aspects of ion exchange in KhFek[Fe(CN)6]l*mH2O compounds: a combined electrical and mass transfer functions approach.

The present paper quantifies and develops the kinetic aspects involved in the mechanism of interplay between electron and ions presented elsewhere(1) for K(h)Fe(k)[Fe(CN)(6)](l)*mH(2)O (Prussian Blue) host materials. Accordingly, there are three different electrochemical processes involved in the PB host materials: H(3)O(+), K(+), and H(+) insertion/extraction mechanisms which here were fully kinetically studied by means of the use of combined electronic and mass transfer functions as a tool to separate all the processes. The use of combined electronic and mass transfer functions was very important to validate and confirm the proposed mechanism. This mechanism allows the electrochemical and chemical processes involved in the K(h)Fe(k)[Fe(CN)(6)](l)*mH(2)O host and Prussian Blue derivatives to be understood. In addition, a formalism was also developed to consider superficial oxygen reduction. From the analysis of the kinetic processes involved in the model, it was possible to demonstrate that the processes associated with K(+) and H(+) exchanges are reversible whereas the H(3)O(+) insertion process was shown not to present a reversible pattern. This irreversible pattern is very peculiar and was shown to be related to the catalytic proton reduction reaction. Furthermore, from the model, it was possible to calculate the number density of available sites for each intercalation/deintercalation processes and infer that they are very similar for K(+) and H(+). Hence, the high prominence of the K(+) exchange observed in the voltammetric responses has a kinetic origin and is not related to the amount of sites available for intercalation/deintercalation of the ions.

Thermodynamic aspects of ion intercalation in KhFek[Fe(CN)6]l*mH2O compounds: application to the Everit's Salt/Prussian blue transition.

The K(+) reversible processes for ion exchange in K(h)Fe(k)[Fe(CN)(6)](l)*mH(2)O host compounds (Prussian Blue) were thermodynamically analyzed. A thermodynamic approach was established and developed based on the consideration of a lattice-gas model where the electronic contribution to the chemical potential is neglected and the ion-host interaction is not considered. The occupation fraction of the intercalation process was calculated from the kinetic parameters obtained through ac-electrogravimetry in a previous paper. In this way, the mass potential transfer function introduces a new way to evaluate the thermodynamic aspect of intercalation. Finally, based on the thermodynamic approach, the energy used to put each K(+) ion into the host material was calculated. The values were shown to be in good agreement with the values obtained through transient techniques, for example, cyclic voltammetry. As a result, this agreement between theory and experimental data validates the thermodynamic approach considered here, and for the first time, the thermodynamic aspects of insertion were considered for mixed valence materials.

Cancer mortality in a residential cohort exposed to environmental selenium through drinking water.

Cancer mortality from 1986 to 1992 was examined in a cohort of 4419 individuals who had been residing in an area of the municipality of Reggio Emilia, northern Italy, where tap water with unusually high selenium content was accidentally supplied. Mortality for all cancers was not significantly different, both in males and in females, from that expected using death rates in the remaining municipal population as standard rates. No significant difference in mortality for site-specific cancers was observed in males, while in females a higher mortality for malignancies of the lymphatic-hematopoietic tissue overall considered and for non-Hodgkin's lymphoma was detected. Even if evaluation of the results is hampered by the low number of cancer deaths on which the analysis is based, findings of the study do not support the hypothesis of a strong inverse independent relationship between dietary intake of selenium and cancer mortality in humans.

Validation of antibody-based recognition by piezoelectric transducers through electroacoustic admittance analysis.

The development of immunosensors based on piezoelectric transducers is widely investigated due to their attractive potentialities. The quartz crystal microbalance (QCM) may give a direct response signal which characterizes the binding event between a sensitive layer, immobilized onto the surface transducer, and the analysis to be detected. However, for small biomolecules, such as some antigens, it is quite difficult to obtain an observable signal. This is mainly due to the lack of sensitivity of the commonly used QCM (5 to 10 MHz quartz crystal). Moreover, the mass estimated with the QCM response through the Sauerbrey equation and the mass which can be measured thanks to other analytical techniques, in our case an enzymatic assay, are different: the deposited mass is generally overestimated by the QCM. To validate QCM mass measurements and, therefore antigens recognition, the interactions of acoustic shear waves with a biolayer were investigated during enzyme adsorption onto the microbalance gold electrode or during the antibody/antigen binding. Electroacoustic admittance was measured around the resonance frequency of a 27 MHz quartz resonator in parallel with microbalance measurements. The parameters which characterize the quartz microbalance equivalent circuit were compared with the classical microbalance frequency. The mass overestimation, given by the microbalance, could be explained either by modification of the rheological properties of the sensitive layers and/or by an inadequacy of the assay performed.

Spread of hepatitis C virus among sexual partners of HCVAb positive intravenous drug users.

Recent studies suggest that the seroprevalence of hepatitis C virus antibodies (HCVAb) among sexual partners of those who are HCVAb positive is higher than in the general population. Moreover some studies seem to indicate that transmission of hepatitis C virus (HCV) occurs more readily when there is HIV infection in the couple. We studied the prevalence of HCVAb seropositivity among the regular sexual partners of 84 HCVAb positive intravenous drug users (IVDUs), by means of ELISA confirmed by radio immuno-adsorbent assay, 11 generation (RIBA II). The couples were subdivided into three groups: group 1: 30 HIV negative IVDUs and their HIV negative partners (HIV-/HIV-); group 2: 47 HIV positive IVDUs and their HIV negative partners (HIV+/HIV-); group 3: seven HIV positive IVDUs and their HIV positive partners (HIV+/HIV+). The seroprevalence of HCVAb among the partners of IVDUs was 28.6% in the couples of group 3, 12.8% in the couples of group 2 and no partner was positive among the couples of group 1. There was no statistically significant difference in HCV transmission between the couples who never used a condom and those who always used one. The couples of group 1 never used a condom. We found HCVAb seropositivity only in the partners who were in couples in whom HIV was present. We did not demonstrate that sexual intercourse is a means of HCV transmission because none of the HIV-/HIV- couples of group 1 used a condom and no partner was HCVAb positive.(ABSTRACT TRUNCATED AT 250 WORDS)

Magnetic water treatment for scale prevention.

A home-made magnetic device was built with permanent magnets for treating scaling waters. Its efficiency was evaluated by measuring the remaining ionic calcium at the output of the device by means of an ion selective electrode. The scaling power of the treated water was estimated through an electrochemical scaling test. Chroamperometric curves and chronoelectrogravimetric curves were plotted to obtain the scaling time and the nucleation time of the scale deposition. The variation of the efficiency of the magnetic treatment was studied when the length of treatment, the flow velocity of the scaling water in the device, the material of the pipe where the scaling water flowed were changed. An empirical relationship, which gives the value of the efficiency in function of the length of treatment and the flow velocity, was proposed. Possible mechanisms of action of the magnetic treatment were discussed.

Immunodetection by quartz crystal microbalance. A new approach for direct detection of rabbit IgG and peroxidase.

Biodetection is one of the most important challenges for the twenty-first century: many fields are concerned, mainly environmental and medical. The quartz crystal microbalance (QCM) may offer great possibilities for this purpose: a direct response signal, which characterizes the binding event between a sensitive layer, immobilized onto the surface transducer, and the analyte to be detected, can be obtained. However, for the detection of small biomolecules such as antigens, it is quite difficult to obtain an observable signal that corresponds directly to the binding event. In general, this is owing to the lack of mass sensitivity of the commonly used QCM, with 5- to 10-MHz quartz crystals. For improving this mass sensitivity, a 27-MHz quartz resonator was developed and incorporated in a flow-through microcell. Two biospecies, IgG rabbit and peroxidase enzyme, were studied with this ultra-sensitive QCM in terms of specificity, detection limit, and calibration curve.

Influence of the supersaturation on the nucleation-growth process of scale electrodeposition by in situ observation through a transparent quartz crystal microbalance.

An original technique allowed three in situ measurements to be obtained simultaneously, i.e. electrochemical and mass measurements and a microscope image of the interface between electrode and solution. The nucleation-growth process of CaCO3 deposition was investigated by varying different parameters which influenced the supersaturation coefficient, the Ca2+ concentration, pH and convection of the carbonically pure water near the substrate. The results showed that the variation of the scaling rate was due, for the two first cases, to an influence of the nucleation process whereas for the last case, the kinetics of scale deposition were modified by a shift of the growth rate.

[Preoperative radiotherapy in cancer of the rectum. Our 5-year experience]. / La radioterapia preoperatoria nel cancro del retto. La nostra esperienza di 5 anni.

Since 1990, 41 patients with rectal carcinoma have been submitted to preoperative radiotherapy, which induced a shrinkage of the tumor, favouring its surgical resection. Besides, in 3 cases the operative specimens were tumor free, and a higher incidence of A and B 1 categories was found. Surgical results have been compared with an analogous group of 20 patients, where surgery was performed as a first procedure, then followed by radiotherapy in 9. No increase of postoperative complications was observed. While analysis of follow-up results demonstrates a decrease of tumour recurrence in patients with preoperative radiotherapy, no difference in survival was registered, because of the development of extra-pelvic metastases.

Median artery and superficial palmar branch of the radial artery in the carpal tunnel.

In the carpal tunnel there are the flexor muscle tendons, their sheaths, and the median nerve. Because its walls are inflexible, any thickening of its components that reduce its area may compress the median nerve. There are many reasons for nerve compression, including persistence of the median artery into adult life. We dissected the arteries in the carpal tunnel of 102 hands of 51 adult cadavers of both sexes, age range 23-77 years, and injected latex into 42 hands. In the carpal tunnel we sought the median artery and the superficial palmar branch of the radial artery. We found the median artery in 23 of 102 cases (23%), and its calibre ranged from 0.7 to 2.7 mm, mean (SD) 1.6 (0.5) mm. In 16 cases it made up part of the superficial palmar arch. The superficial palmar branch of the radial artery was partly responsible for the distal irrigation of the hand in 48 cases (47%); and in three hands (3%) it passed through the carpal tunnel. The external diameters of these vessels were 1.8, 1.9, and 1.8 mm, respectively. These arteries might cause compression of the median nerve and consequently the carpal tunnel syndrome.

Perforating branches: important contribution to the formation of the dorsal metacarpal arteries.

The perforating branches that originate from the deep palmar arch of the hand have been studied to provide a complete anatomical description of these vessels and assess their importance in the blood collateral pathway of the hand. We injected latex into the arteries of 50 cadaveric hands of 25 adults, of both sexes, all of Brazilian origin. These were dissected under a stereoscopic microscope. The perforating branch of the second interosseous space originated from the deep palmar arch in 80% of the cases, and it corresponded to the radial artery passing through the second space in 16%; the one of the third interosseous space originated from the deep palmar arch in 76% of the cases and from the palmar metacarpal artery of the third interosseous space in 16%; the one of the fourth interosseous space originated from the deep palmar arch in half the cases, from the deep palmar branch of the ulnar artery in 14%, and from the palmar metacarpal artery of this space in 18%. The perforating branch of the second space anastomosed with the second dorsal metacarpal artery (DMA) in 60% of the cases and formed it in 10%; the one of the third space anastomosed with the third DMA in 20% and formed it in 64%; the one of the fourth space anastomosed with the fourth DMA in 8% and formed it in 78%. These vessels are an important anastomotic pathway between the dorsal carpal network and the deep arteries of the hand and are important in the supply to the dorsum.

Anatomical relationships between the deep palmar arch and the deep branch of the ulnar nerve.

The relationship between the deep palmar arch (DPA) and the deep branch of the ulnar nerve (dbUN) was analysed in 60 hands from 30 formaldehyde treated cadavers of adult individuals, of both sexes, with age ranging from 21 to 70 years, in the Division of Descriptive and Topographic Anatomy of the Federal University of São Paulo (UNIFESP). The arteries were injected with neoprene latex and dissections were performed under a magnifying glass. DPA was ventral to dbUN in 50% of the cases (type I) and dorsal in 45% (type). In type I dbUN crossed the arterial arch at the following levels: in the 4th interosseous space in 17.9% of the cases, in the 3rd interosseous space in 21.4% and in the 3rd metacarpal bone in 39.3%. In type II dbUN crossed the arterial arch in the 4th metacarpal bone in 25.9% and in the 3rd intersseous space in 37%. The relationship between the nerve and the palmar metacarpal arteries was also studied. The data obtained may be of practical use in the surgery of the palmar region.

A biometric study on the relationships between the deep palmar arch and the superficial palmar arch, the distal wrist and palmar creases.

The topographical localisation of the palmar arches is important in hand surgery. The aim of this study was to contribute with biometric data on their positions and to correlate this with the size od the palm. We studied 60 hands of 30 adult fixed cadavers, of Brazilian origin, from both sexes and between the ages of 21 and 70 years. The arteries of 54 hands were injected with latex Neoprene. Before dissection the distance between distal wrist crease (DWC) and the proximal palmar digital crease of the middle finger (PDMC) was measured. Also, we recorded the distance between the DWC and the proximal and distal palmar creases (PPC, DPC). After dissecting the superficial palmar region, the distance between the superficial palmar arch (SPA) and the DWC was recorder. We then dissected the deep palmar arch (DPA). The average distance between the DPA and DWC was always measured in the midline of the palm. The average distance DWC-DPA was 33.7 +/- 2.6 mm in the female and 36 +/- 4.0 mm in the male. The difference was statistically significant. The average distance between DPA and the PPC was 24.2 +/- 3.0 mm in the female and 27.1 +/- 4.1 mm in the male; this difference was significant. In 83% of cases the DPA was proximal to the SPA and in 14.9% was distal to it. The linear regression test for the relation between DWC-PDMC and DWC-DPA was significant in the male and this fact allowed us to obtain the linear equation to predict the distance DWC-DPA. Other parameters were also considered. The results may be useful as a reference to radiologists as well as to surgeons.

Morphometric studies of the muscular branch of the median nerve.

The branch from the median nerve to the thenar muscles has a proximal and lateral (recurrent) course and is vulnerable to lesions that affect these muscles. Because of its anatomical-clinical importance, this branch was studied in 60 palmar regions from 30 cadavers of adult individuals of both sexes, aged between 23 and 77 y. It arose from the lateral branch of the median nerve in 83.3% of the cases. Its origin was distal to the flexor retinaculum in 48.3%, at the distal margin of the retinaculum in 31.6%, in the carpal tunnel in 18.3% and proximal to the retinaculum in 1.7%; it pierced the retinaculum in 15%. The point of recurrence of the branch was localised topographically to 34.6 +/- 3.6 mm from the distal wrist crease; the angle between its recurrent course and the longitudinal axis of the hand averaged 66.8 degrees. In 50% of the cases the muscular branch innervated abductor pollicis brevis (APB), opponens pollicis (OP) and the superficial head of flexor pollicis brevis (FPB), in 40% it supplied only APB and OP, and in 10% a short muscular branch gave rise to independent branches in the palm and which supplied APB, OP and the superficial head of FPB. The so called "accessory thenar branch' was found in 38.3%.