Determination of sunset yellow and tartrazine using silver and poly (L-cysteine) composite film modified glassy carbon electrode

Silver and poly(L-cysteine) composite film modified glassy carbon electrode (PLC/Ag/GCE) has been fabricated via cyclic voltammetry and used for investigation of the electrochemical behavior of sunset yellow (SY) and tartrazine (TT). A pair of anodic peak at 0.760 V (vs. Ag/AgCl) and cathodic peak at 0.701 V (vs. Ag/AgCl) for SY and an anodic peak at 1.013 V (vs. Ag/AgCl) of TT are observed in pH 4.5 phosphate buffer solution. Based on the two well-resolved anodic peaks of SY and TT, a novel electrochemical method has been successfully developed for simultaneous determination of SY and TT using differential pulse voltammetry. Under the optimized experimental conditions, the linear range for the determination of SY and TT are 5.00×10-7 –3.00×10-4 mol L-1 and 7.50×10-7–7.50×10-4 mol L-1, respectively with detection limits of 7.50×10-8 mol L-1 and 2.50×10-7 mol L-1, respectively. The proposed method has been applied for simultaneous determination SY and TT in beverage with satisfactory results

Energetic frustrations in protein folding at residue resolution: a homologous simulation study of Im9 proteins.

Energetic frustration is becoming an important topic for understanding the mechanisms of protein folding, which is a long-standing big biological problem usually investigated by the free energy landscape theory. Despite the significant advances in probing the effects of folding frustrations on the overall features of protein folding pathways and folding intermediates, detailed characterizations of folding frustrations at an atomic or residue level are still lacking. In addition, how and to what extent folding frustrations interact with protein topology in determining folding mechanisms remains unclear. In this paper, we tried to understand energetic frustrations in the context of protein topology structures or native-contact networks by comparing the energetic frustrations of five homologous Im9 alpha-helix proteins that share very similar topology structures but have a single hydrophilic-to-hydrophobic mutual mutation. The folding simulations were performed using a coarse-grained Gō-like model, while non-native hydrophobic interactions were introduced as energetic frustrations using a Lennard-Jones potential function. Energetic frustrations were then examined at residue level based on φ-value analyses of the transition state ensemble structures and mapped back to native-contact networks. Our calculations show that energetic frustrations have highly heterogeneous influences on the folding of the four helices of the examined structures depending on the local environment of the frustration centers. Also, the closer the introduced frustration is to the center of the native-contact network, the larger the changes in the protein folding. Our findings add a new dimension to the understanding of protein folding the topology determination in that energetic frustrations works closely with native-contact networks to affect the protein folding

Nonnative Energetic Frustrations in Protein Folding at Residual Level: A Simulation Study of Homologous Immunoglobulin-like β-Sandwich Proteins

Nonnative interactions cause energetic frustrations in protein folding and were found to dominate key events in folding intermediates. However, systematically characterizing energetic frustrations that are caused by nonnative intra-residue interactions at residual resolution is still lacking. Recently, we studied the folding of a set of homologous all-α proteins and found that nonnative-contact-based energetic frustrations are highly correlated to topology of the protein native-contact network. Here, we studied the folding of nine homologous immunoglobulin-like (Ig-like) β-sandwich proteins, and examined nonnative-contact-based energetic frustrations Gō-like model. Our calculations showed that nonnative-interaction-based energetic frustrations in β-sandwich proteins are much more complicated than those in all- α proteins, and they exhibit highly heterogeneous effects on the folding of secondary structures. Further, the nonnative interactions introduced distinct correlations in the folding of different folding-patches of β-sandwich proteins. Taken together, a strong interplay might exist between nonnative-interaction energetic frustrations and the protein native-contact networks, which ensures that β-sandwich domains adopt a common folding mechanism

Validation of the variable temperature protein folding simulation method.

<p>A) Temperature changes in a variable temperature folding simulation of protein G B1 domain (protein enter 2GB1). B) Comparison of protein residual φ-value distributions derived from the constant temperature simulation and those from the variable temperature simulation, using the conventional Gō-like model for protein G B1 domain. C) Comparison of residual φ-value distributions derived from the constant temperature simulation and those from the variable temperature simulation, using the frustrated Gō-like model for protein G B1 domain. D) Comparison of residual φ-value distributions derived from the constant temperature simulation and those from the variable temperature simulation, using the frustrated Gō-like model for a Im7 domain (SCOP ID d1ayia_).</p

Sequence alignment of the five selected Im9 domains selected from SCOP.

<p>The abbreviations reads <b>Im9</b>: d1emva_, <b>D51A</b>: d2gyka1, <b>E41A</b>: d1fr2a_, <b>H5A</b>: d1bxia_, <b>R75A</b> :d1emvax.</p

Representative native contact number between secondary structures of E41A.

<p>Representative native contact number between secondary structures of E41A.</p

Apparent folding free energy changes for the five Im9 domain structures.

<p>A) <b>Im9</b>. B) <b>H5A</b>. C) <b>E41A</b>. D) <b>D51A</b>. E) <b>R75A</b>.</p

Representative native contact number between secondary structures of E41A.

<p>Representative native contact number between secondary structures of E41A.</p

The effects of energetic frustrations introduced at different locations.

<p>Comparison of residual φ-value distributions derived from the conventional Gō-like and those from the frustrated Gō-like model for the five Im9 domains; the difference in residual φ-value changes can be ascribed to the difference of the local environments of the mutation centers. A) <b>Im9</b>. B) <b>H5A</b>. C) <b>E41A</b>. D) <b>D51A</b>. E) <b>R75A</b>.</p