The analysis of the absorption spectra of model compounds of tyrosine and phenylalanine residues by means of fourth-derivative spectrophotometry is able to separate the contribution of the two chromophores, thus allowing the study of each one. Fourth-derivative analysis resolves the two main vibrational bands of tyrosine, giving rise to two peaks which are sensitive to changes in the environment of the phenolic ring. The parameters obtained from the fourth-derivative spectra were found to depend on the strength of the hydrogen bonds formed by the O H group of tyrosine, as well as on the heterogeneity of tyrosine environments. It is also shown that the fourth-derivative tyrosine peaks are not perturbed by broad bands, such as that arising from ionized tyrosine chromophores. The peaks arising from the phenylalanine model, although less sensitive than those of tyrosine, were found to depend on the polarity of the environment. As a check of the method, it is applied to the study of tyrosine and phenylalanine residues of calf thymus histone H1 and bovine pancreatic ribonuclease A.The near-ultraviolet absorption spectrum of aromatic residues in proteins contains a vast amount of information that is masked by the large width of the absorption bands as compared with the small changes that occur on varying the local environment of the chromophores [I, 21. Several methods of difference spectrophotometry and derivative spectrophotometry have been developed in an effort to obtain as much information as possible from the absorption spectra [2-41, but at present the majority of such information remains unresolved.This communication reports the application of the fourthderivative method to the analysis of the absorption spectra of tyrosine and phenylalanine residues. The main advantages of using fourth-derivative spectroscopy have been pointed out by Butler [5] : (a) the maxima of the fourth-derivative curves are located at nearly the same position as in the original spectrum ; (b) the fourth-derivative analysis can reveal the presence of constituent bands that are not apparent in the original spectrum ; (c) the amplitude of the fourth-derivative curve approaches an inverse fourth-power dependence on the half-width of the original band, thus selecting the narrow bands.We first applied this method to model compounds of tyrosine and phenylalanine residues in different solvents, in order to simulate the various types of environments of these residues in proteins. The conclusions obtained were then applied to the study of conformational changes of calf thymus histone H I and ribonuclease A from bovine pancreas. These proteins are well-suited to be used as a test for the fourthderivative method. The H1 molecule contains only one tyrosine residue and one phenylalanine residue, and RNase A contains six tyrosines and three phenylalanines. Both proteins MATERIALS A N D METHODSThe following solvents of spectroscopic quality were purchased from Xpectrix (Barcelona, Spain) : acetonitrile,

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This study assessed the technical feasibility of formulating lightweight aggregates (LWA) from municipal solid waste incinerator bottom ash (IBA) and residual biomass. Weathered IBA (WIBA) particles larger than 8 mm contain a mixture of calcium-rich compounds and other silicates mainly composed of glass and synthetic and natural ceramics, with low contents of heavy metals and soluble salts. Unfired LWA were formulated with the particle size fraction of WIBA larger than 8 mm and rice husk (RH) used as the bloating agent. Rapid sintering of the unfired spherical pellets at 1,100ºC for 5 min produced some cohesive sintered LWA, whose porosity, apparent particle density, water absorption, and compressive strength directly correlated with the percentage of RH added. The fired LWA formulated with 5 wt.% of RH showed the highest bloating index (115%) and porosity (53%) and the lowest apparent particle density (0.61 Mg•m-3) and compressive strength (1.4 MPa). The addition of more than 5 wt.% of RH increased the internal temperature of the sintered aggregates and decreased the viscosity of the molten glassy materials, resulting in the collapse of the inner structure. Consequently the porosity decreased and the apparent density of the particles increased, thereby shrinking the volume of the fired LWA. According to the standard leaching test (EN 12457-4), both the unfired precursor and the sintered aggregates showed concentrations of heavy metals and metalloids in the leachates that were well below the safety limits established for their reuse as secondary materials.

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Alkali-activated binders (AABs) stand out as a promising alternative to replace ordinary Portland cement (OPC) due to the possibility of using by-products and wastes in their manufacturing. This paper assessed the potential of weathered bottom ash (WBA) from waste-to-energy plants and PAVAL® (PV), a secondary aluminium recycling process by-product, as precursors of AABs. WBA and PV were mixed at weight ratios of 98/2, 95/5, and 90/10. A mixture of waterglass (WG) and NaOH at different concentrations (4 and 6 M) was used as the alkaline activator solution. The effects of increasing NaOH concentration and PV content were evaluated. Alkali-activated WBA/PV (AA-WBA/PV) binders were obtained. Selective chemical extractions and physicochemical characterization revealed the formation of C-S-H, C-A-S-H, and (N,C)-A-S-H gels. Increasing the NaOH concentration and PV content increased porosity and reduced compressive strength (25.63 to 12.07 MPa). The leaching potential of As and Sb from AA-WBA/PV exceeded the threshold for acceptance in landfills for non-hazardous waste.