Rheology of a lyotropic mesophase through a stress-relaxation experiment

We report on the first rheological study of the structural relaxations in a nematic liquid crystalline phase. Linear dynamic and transient shear experiments were applied to a polydomain nematic phase of the CTAB/water system: a liquid crystalline mixture composed of 28 wt% CTAB at 35 degrees C. The decay of the shear modulus, G(t), was analyzed using the CONTIN inverse Laplace transform to obtain a distribution of relaxation times which were compared with ones from the usual fitting procedure based on a generalized Maxwell model. The behavior of the nematic lyotropic structure of the CTAB/water system is characterized by the presence of both slow and fast relaxation times. These were interpreted as being due to a progressive loss of the lyotropic domain orientation and to the breaking/reforming process of the cylindrical aggregates, respectively.     

In Situ Amperometric Detection of Vesicles and Microgel Phases in an Aggregating System: Calcium Alginate

In situ amperometric characterization of an aggregating system in terms of molecular adsorption and single microparticle interactions at the electrode interface is demonstrated using a model system: alginate/Ca(II) in an aqueous electrolyte solution. Recording of chronoamperometric curves of oxygen reduction at the dropping mercury electrode is designed for detection of dip‐shaped signals of individual gel microparticles. By addition of Ca(II) decrease of alginate adsorption is accompanied by appearance of signals indicating vesicle type association of alginate molecules and microparticles of gel phase. AFM imaging provided evidence of initial stage in calcium alginate gel formation.     

Imaging intracellular viscosity by a new molecular rotor suitable for phasor analysis of fluorescence lifetime

The arsenal of fluorescent probes tailored to functional imaging of cells is rapidly growing and benefits from recent developments in imaging strategies. Here, we present a new molecular rotor, which displays strong absorption in the green region of the spectrum, very little solvatochromism, and strong emission sensitivity to local viscosity. The emission increase is paralleled by an increase in emission lifetime. Owing to its concentration-independent nature, fluorescence lifetime is particularly suitable to image environmental properties, such as viscosity, at the intracellular level. Accordingly, we demonstrate that intracellular viscosity measurements can be efficiently carried out by lifetime imaging with our probe and phasor analysis, an efficient method for measuring lifetime-related properties (e.g., bionalyte concentration or local physicochemical features) in living cells. Notably, we show that it is possible to monitor the partition of our probe into different intracellular regions/organelles and to follow mitochondrial de-energization upon oxidative stress.     

Redox and electrocatalytic properties of mimochrome VI, a synthetic heme peptide adsorbed on gold

Mimochrome VI (MC-VI) is a synthetic heme peptide containing a helix-heme-helix sandwich motif designed to reproduce the catalytic activity of heme oxidases. The thermodynamics of Fe(III) to Fe(II) reduction and the kinetics of the electron-transfer process for MC-VI immobilized through hydrophobic interactions on a gold electrode coated with a nonpolar SAM of decane-1-thiol have been determined through cyclic voltammetry. Immobilization slightly affects the reduction potential of MC-VI, which under these conditions electrocatalytically turns over molecular oxygen. This work sets the premise for the exploitation of totally synthetic mimochrome-modified electrode surfaces for clinical and pharmaceutical biosensing.     

Some spectral synthesis results by the analytic semigroup method

In 1980, J. Esterle proved the Wiener theorem forL ¹ (—) by a completely new method using analytic semigroup techniques. We show here how to extend the method in two different ways. First, it is shown that spectral synthesis for points on the real line is also provided by analytic semigroup techniques. Second, Esterle's proof may also be adapted to provide Wiener theorem for some elementary hypergroups. Eine überarbeitete Fassung ging am 24. 4. 2001 ein     

Hydrothermal growth and structural studies of Si(1-x)Ge(x)O2 single crystals

The substitution of germanium in the α-quartz structure is a method investigated to improve the piezoelectric properties and the thermal stability of α-quartz. Growth of α-quartz type Si(1-x)Ge(x)O(2) single crystals was performed using a temperature gradient hydrothermal method under different experimental conditions (pressure, temperature, nature of the solvent, and the nutrient). To avoid the difference of dissolution kinetics between pure SiO(2) and pure GeO(2), single phases Si(1-x)Ge(x)O(2) solid solutions were prepared and used as nutrients. The influence of the nature (cristobalite-type, glass) and the composition of this nutrient were also studied. Single crystals were grown in aqueous NaOH (0.2-1 M) solutions and in pure water. A wide range of pressures (95-280 MPa) and temperatures (315-505 °C) was investigated. Structures of single crystals with x = 0.07, 0.1, and 0.13 were refined, and it was shown that the structural distortion (i.e., θ and δ) increases with the atomic fraction of Ge in an almost linear way. Thus, the piezoelectric properties of Si(1-x)Ge(x)O(2) solid solution should increase with x, and this material could be a good candidate for technological applications requiring a high piezoelectric coupling factor or high thermal stability.     

On some measurements of thermal diffusivity by means of thermal-wave propagation in wires

Summary By means of a new experimental technique based on a non-steady-state method,i.e. on the propagation properties of thermal waves, we have measured the thermal diffusivityD of a copper wire by changing properly its boundary conditions in order to ascertain whether the values ofD were independent of the surface heat losses. Temperature oscillations at the fixed frequency of 0.0121 Hz were excited at one end of the specimen which was in nitrogen atmosphere at different pressures ranging from ∼10⁻² mTorr to 220 mTorr. The temperatures of the far end of the specimen and the walls of the container had the same constant value of 0°C, while the temperature gradient between the average value of the oscillating temperatures and this constant temperature was changed from 2°C to 12°C for each pressure by adjusting the heater power. By operating in this way it was possible to change either the heat losses due to conduction and convection or those due to radiation. The major cause of error came from the uncertainty in the measurements of the phase shift between the thermal oscillations detected at the two fixed points of the specimen which introduces in the evaluation ofD an error of about 2%. The experimental values obtained for the thermal diffusivity in these different boundary conditions were in any case comprised within this uncertainty sinceD=(1.17±0.02) cm²s⁻¹, in good agreement with the literature. The results so far obtained show that the experimental method has the great advantage of giving the thermal diffusivity and, therefore, the thermal conductivity of a solid without the necessity of taking particular care in insulating the specimen.

---

Riassunto Utilizzando una tecnica sperimentale che consente di determinare in fili metallici sia la diffusività termicaD sia il coefficienteμ di perdita superficiale mediante la misura diretta del ritardo di fase e dell'attenuazione di un'onda termica tra due punti fissi del campione, ci si è proposti di analizzare alcuni risultati ottenuti recentemente in un campione di rame, variando opportuamente le condizioni al contorno. In particolare, ci si è voluti assicurare che la diffusività termica non risultasse dipendente dal valore del coefficiente di perdita superficiale. Le misure sono state eseguite alla frequenza fissa di 0.0121 Hz in atmosfera di azoto, a pressioni diverse comprese tra ∼10⁻² mTorr e 220 mTorr. L'estremità lontana del campione e le pareti del contenitore erano tenuti costantemente alla stessa temperatura (0°C), mentre il gradiente termico era sistematicamente variato tra 2°C e 12°C, in corrispondenza di ciascuna pressione. Operando in questo modo, si potevano variare opportunamente sia la conduzione sia l'irraggiamento del calore dalla superficie laterale del campione nel mezzo circostante. In queste misure, la causa predominante di errore viene dalla misura dello sfasamento delle due onde, che introduce nella valutazione diD un'incertezza del 2%. I valori sperimentali ottenuti nelle diverse condizioni prima ricordate risultano, in ogni caso, compresi entro i limiti di questa incertezza, poichéD=(1.17±0.02) cm²/s, in ottimo accordo con i dati della letteratura. Questo risultato dimostra pertanto che la diffusività termica, determinata con questo metodo dinamico, risulta effettivamente indipendente dalla quantità di calore transmesso dal campione nel mezzo circostante, consentendo pertanto piú agevoli determinazioni della conducibilità termica dei solidi, noti la densità ed il calore specifico.

---

Резюме С помощью новой экспериментальной техники, основанной на нестационарном методе, т.е. на свойствах распространения тепловых волн, мы измеряем коэффициент температуропроводностиD медного провода, посредством измения граничных условий, чтобы выяснить независимость величинD от поверхностных потерь тепла. Температурные осцилляции при фиксированной частоте 0.0121 Гц возбуждаются на одном конце образца, который помеЩен в атмосферу азота при различных давлениях в области от ∼10⁻² мтор до 220 мтор. Температуры другого конца образца и стенок контейнера являются постояннюми 0°C, тогда как градиент температуры между средним значением осциллирующей темпертурой и этой постоянной температурой изменяется от 2°C до 12°C для каждого значения давления, за счет регулировки мощности нагревателя. Этот метод позволяет изменять тепловые потери, обусловленные либо проводимостью и конвекцией, либо излучением. Основная причина ошибок проистекает из неопределенности в измерениях фазового сдвига между тепловыми осцилляциями, заререгистрированными в двух фиксированных точках образца. Ошибка при измерении составляет около 2%. Экспериментальные значения, полученные для коэффициента температуропроводности при различных граничных условиях,D=(1.17±0.02) см⁻²с⁻¹, хорошо согласуются с данными в литературе. Полученные результаты показывают, что предложенный экспериментальный метод обладает большим преимуществом при определении температуропроводности и, следовательно, теплопроводности твердых тел, не уделяя особого внимания изоляции образца.

---

---

To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.

---

This research was supported by the Consiglio Nazionale delle Ricerche, Rome (Italy).

---

Some preliminary results were presented at the ?LXVII Congresso della Società Italiana di Fisica?, Pisa, October 1981.     

Electron transfer and electrocatalytic properties of the immobilized methionine80alanine cytochrome c variant

The M80A variant of yeast iso-1-cytochrome c (cytc), which features a noncoordinating Ala residue in place of the axial heme iron Met ligand, was chemisorbed on a gold electrode coated with 4-mercaptopyridine or carboxyalkanethiol self-assembled monolayers (SAM) and investigated by cyclic voltammetry at varying conditions of temperature, pH, and O2 concentration. The E degrees ' value (standard reduction potential for the heme Fe(III)/Fe(II) couple) of M80A cytc on both SAMs is of approximately -200 mV (vs the standard hydrogen electrode, SHE) at pH 7, which is more than 400 mV lower than that of native cytochrome c in the same conditions. The thermodynamics of Fe(III) to Fe(II) reduction and the kinetics of heterogeneous electron transfer (ET) are dominated by the presence of a hydroxide ion as the sixth axial heme iron ligand above pH 6. On both SAMs, protonation of the bound hydroxide ion is mainly responsible for the changes in these parameters at low pH, since the distances of ET between the heme and the electrode are found to be independent of pH in the range of 5-11. The invariance of the electrochemical features up to pH 11 indicates that no changes in heme iron coordination occur at high pH, at variance with native cytc. Most notably, immobilized M80A cytc is found to act as an efficient biocatalyst for O2 reduction from pH 5 to 11.0. This finding makes M80A cytc a suitable candidate as a constituent of a biocatalytic interface for O2 biosensing and opens the way for the exploitation of engineered cytochrome c in the bio-based detection of chemicals of environmental and clinical interest.