Ultraviolet absorption study of aqueous mixtures of monohydric alcohols: Water structural effects

Summary The ultraviolet absorption spectra of aqueous mixtures of methanol, ethanol, 1- and 2-propanol in the spectral region (190÷210) nm were measured as a function of alcohol concentration in the entire cosolvent mole fraction. The ultraviolet absorption coefficient exhibits, for all the systems investigated, an anomalous behaviour which occurs in the water-rich region (mole fraction of cosolventx ₂<0.1) and which for each alcohol shows the existence of a solvent composition,x ₂ ^*, corresponding to which the association state of the alcohol molecules changes. This behaviour is in line with the prediction of a liquid-clathrate-hydrate model and with the conclusions drawn from recent results on compressibility data.

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Riassunto è stato misurato lo spettro di assorbimento di soluzioni acquose di metanolo, etanolo, 1-e 2-propanolo, nell'intervallo spettrale (190÷210) nm, in funzione della temperatura e della frazione molare,x ₂, di cosolvente. L'assorbanza delle miscele esaminate mostra un comportamento anomalo nella regione ricca in acqua (x ₂<0.1). In questo modo si individua, per ciascun alcool, un valorex ₂ ^* della frazione molare in corrispondenza del quale cambia lo stato di associazione delle molecole di alcool. Tale comportamento è in accordo con le conclusioni tratte da un recente studio sulla compressibilità di miscele acqua-alcool etilico e con l'ipotesi dell'esistenza nelle miscele esaminate di strutture locali simili a quelle di un clatrato idrato.

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Резюме Измеряются ультрафиолетовые спектры поглощения в водных смесях метанола, этанола, 1- и 2-пропанола в спектральной области (190÷210) нм, как функция температуры и молярной доли,x ₂, сорастворителя. Коэффициент ультрафиолетового поглощения для всех исследованных систем обнаруживает аномальное поведение, которое имеет место в области с большим слдержанием воды (мольная доля сорастворителяx ₂<0.1) и которое для каждого из спиртов указывает на существование значения молярной долиx ₂ ^* растворителя, при котором происходит изменение состояния связи молекул спирта. Это поведение согласуется с предсказаниями о существовании локальной структуры в исследованных смесях и с выводами из недавних исследований сжимаем ости водных смесей спиртов.

     

Effect of head group size, temperature and counterion specificity on cationic micelles

The critical micelle concentration (cmc) and ionisation degree (α), of micelles of cetyltrimethylammonium bromide (CTABr), cetyltrimethylammonium chloride (CTACl), cetyltripropylammonium bromide (CTPABr) and cetyltripropylammonium chloride (CTPACl) have been measured over a narrow temperature range at 2 degree intervals using electrical conductivity. CTPACl and CTPABr are very soluble in water and were measured in the temperature range 275.15-323.15K. The Krafft temperatures for CTABr and for CTACl are 293.15K and 284.15K, respectively and established a lower temperature limit for our studies on these two surfactants. The cmc vs temperature curves have a smooth minimum near room temperature and α linearly increases with temperature. The changes of cmc and α with temperature are smaller than those associated with the modification of head group size or counterion nature. Using these results, basic thermodynamic quantities associated with the phenomena of micellization have been evaluated. Thermodynamic properties of the surfactant solutions were discussed in terms of temperature dependence of the free energy, enthalpy and entropy of micellization. A close similarity between the effects of change in temperature on protein folding and micellization process appears from the data.     

On the structure of alkali halide solutions

Summary The adiabatic compressibility of NaCl, NaBr and NaI water solutions has been determined by measuring the sound velocity as a function of both concentration and temperature. A simple model has been employed to interpret the data in terms of size of hydration shells. Reasonably good agreement has been found with neutron and X-ray diffraction results.

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Riassunto La compressibilità adiabatica delle soluzioni acquose di NaCl, NaBr ed NaI è stata misurata determinando la velocità del suono in funzione di temperatura e concentrazione. Per interpretare i dati è stato impiegato un modello semplice che tiene conto delle sfere di idratazione degli ioni. Tale modello risulta in soddisfacente accordo con i dati ricavati da un esperimento di diffrazione di raggi X e neutroni.

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Резюме Определяется адиабатическая сжимаемость водньх растворов NaCl, NaBr и NaI, используя измерения зависимостей скорости звука от концентрации и температурь. Предлагается простая модель для интерпретации данньих в терминах размера сферьі гидратации. Получется хошее согласие с результатами дифракции нейтронов и рентгеновских лучей.

     

Modulation of hydrophobic effect by cosolutes

This work concerns a comparison of the hydration properties and self-association behavior in aqueous solution of three biologically relevant simple molecules: tert-butyl alcohol (TBA), trimethylamine-n-oxide (TMAO), and glycine betaine (GB). These molecules were used as a model to study hydrophobic behavior in water solutions. In particular, water perturbation induced by TBA, TMAO, and GB molecules was studied as a function of the solute molar fraction X(2) (0 < X(2) < 0.04) by Raman spectra of water in the fundamental OH-stretching region (3,800-2,800 cm(-1)). Furthermore, possible hydrophobic clustering of these molecules was investigated by studying the behavior of the alkyl CH stretching band in the 3,100-2,900 cm(-1) frequency region as a function of X(2). To establish the existence of a correlation between the effects of these three solutes on the micellization process and changes in the properties of the solvent, the behavior of the critical micelle concentration of sodium dodecyl sulfate was also investigated as a function of the added amount of TBA, TMAO, and GB. On the whole, these data show that there is no direct correlation between a solute's effect on the water structure and its effect on micelle or protein stability. Results indicate that, while TBA starts to self-aggregate at approximately X(2) = 0.025, both TMAO and GB do not exhibit any significant self-aggregation up to the highest concentration considered. In addition, nonadditive perturbations of the H-bonded networks of solvent water are observed in the case of TBA solutions, but are absent in both the TMAO and GB cases. The absence of these nonlinear effects in TMAO and GB water solutions allow for tracing the microscopical mechanism of the neutrality of these osmolytes toward hydrophobic effects. This confers the compatibility to these two osmolytes, which can be accumulated at high concentrations without interfering with biochemical processes in the cell.     

ISS protocol for EPR tooth dosimetry

The accuracy in Electron Paramagneetic Resonance (EPR) dose reconstruction with tooth enamel is affected by sample preparation, dosimetric signal amplitude evaluation and unknown dose estimate. Worldwide efforts in the field of EPR dose reconstruction with tooth enamel are focused on the optimization of the three mentioned steps in dose assessment. In the present work, the protocol implemented at ISS in the framework of the European Community Nuclear Fission Safety project “Dose Reconstruction” is presented. A combined mechanical–chemical procedure for ground enamel sample preparation is used. The signal intensity evaluation is carried out with powder spectra simulation program. Finally, the unknown dose is evaluated individually for each sample with the additive dose method. The unknown dose is obtained by subtracting a mean native dose from the back-extrapolated dose. As an example of the capability of the ISS protocol in unknown dose evaluation, the results obtained in the framework of the 2nd International Intercomparison on EPR tooth enamel dosimetry are reported.     

Structure, stability, and activity of myoglobin adsorbed onto phosphate-grafted zirconia nanoparticles

The adsorption of myoglobin (Mb) onto phosphate grafted-zirconia (ZrO2-P) nanoparticles was studied in terms of conformational studies and thermal stability, determined by circular dichroism (CD), differential scanning calorimetry (DSC), and atomic force microscopy (AFM). The changes in protein structure have been correlated with the catalytic activity of free and adsorbed Mb. CD and DSC studies indicate marked rearrangements in Mb structure upon adsorption onto phosphate-grafted zirconia nanoparticles. These structural rearrangements of Mb could be responsible for the loss of catalytic activity observed for the adsorbed Mb. In particular, the conformational changes due to the adsorption process induced a reduction of kcat and KM. AFM measurements indicate that the interaction with the grafted-zirconia nanoparticles also affects the morphology of the bound protein, inducing the nucleation of prefibrillar-like aggregates.     

Structure of water-in-oil microemulsions of AOT by infrared spectroscopy

Summary The structure of water in water/AOT/n-heptane reverse micelles has been studied as a function of the [H₂O]/[AOT] ratio (W) by using the absorption IR due to O−H stretching modes in the 3800–3000 cm⁻¹ range. The results show that the IR spectra can be expressed as a sum of contributions from bound- and bulk-like water. The fraction of water in the two ?regions? within the water pool was evaluated as a function ofW. The ?bound? water region seems to hold 3.5 water molecules (corresponding to 7 O−H oscillators) per AOT molecule and its formation is nearly complete atW>6. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.     

EFFECT OF MID-UV RADIATION ON DNA-Cu2+ COMPLEX: ABSORPTION AND CIRCULAR DICHROISM STUDY

Abstract— When DNA is complexed with Cu²⁺ ions it becomes sensitized to mid-UV light. Irradiation of the complex at 310 ± 10 nm produces marked changes in absorption and circular dichroism spectra in addition to those in melting profiles of irradiated samples. These variations show conformational changes in DNA structure due to a photoreduction of some copper sites in the DNA-Cu²⁺ complex. In addition to this effect an irreversible damage in DNA structure could be invoked to explain the observed behaviour. These facts can be related to the presence in DNA-Cu²⁺ complex of a small absorption band extending up to mid-UV range while the absorption of DNA is negligible in this spectral range.