Visual masking: past accomplishments, present status, future developments

Visual masking, throughout its history, has been used as an investigative tool in exploring the temporal dynamics of visual perception, beginning with retinal processes and ending in cortical processes concerned with the conscious registration of stimuli. However, visual masking also has been a phenomenon deemed worthy of study in its own right. Most of the recent uses of visual masking have focused on the study of central processes, particularly those involved in feature, object and scene representations, in attentional control mechanisms, and in phenomenal awareness. In recent years our understanding of the phenomenon and cortical mechanisms of visual masking also has benefited from several brain imaging techniques and from a number of sophisticated and neurophysiologically plausible neural network models. Key issues and problems are discussed with the aim of guiding future empirical and theoretical research

Selective complexation of divalent cations by a cyclic α,β-peptoid hexamer: a spectroscopic and computational study

We describe the qualitative and quantitative analysis of the complexation properties towards cations of a cyclic peptoid hexamer composed of alternating α- and β-peptoid monomers, which bear exclusively chiral (S)-phenylethyl side chains (spe) that have no noticeable chelating properties. The binding of a series of monovalent and divalent cations was assessed by 1H NMR, circular dichroism, fluorescence and molecular modelling. In contrast to previous studies on cations binding by 18-membered α-cyclopeptoid hexamers, the 21-membered cyclopeptoid cP1 did not complex monovalent cations (Na+, K+, Ag+) but showed selectivity for divalent cations (Ca2+, Ba2+, Sr2+ and Mg2+). Hexacoordinated C-3 symmetrical complexes were demonstrated for divalent cations with ionic radii around 1 Å (Ca2+ and Ba2+), while 5-coordination is preferred for divalent cations with larger (Ba2+) or smaller ionic radii (Mg2+)

Data analysis in the determination of stoichiometries and stability constants of complexes

The determination of stoichiometries and stability constants of complexes by means of UV-visible spectrophotometry applying traditional methods does not evaluate the quality of the values obtained, since the classic application of these methods does not provide coverage intervals. However, the use of chemometric techniques in different steps of the application of these methods makes it possible to obtain not only a real value of the characteristics of the complexes but a validation of such a value. In this paper a methodology is proposed that combines some traditional methods, three different regression models (LMSR, LSR and LSPR) and a small number of mathematical algorithms. This methodology is able to estimate, in a simple and rigorous way, the stoichiometry and stability constant of a complex and its corresponding uncertainties