On tuning the fluorescence emission of porphyrin free bases bonded to the pore walls of organo-modified silica.

A sol-gel methodology has been duly developed in order to perform a controlled covalent coupling of tetrapyrrole macrocycles (e.g., porphyrins, phthalocyanines, naphthalocyanines, chlorophyll, etc.) to the pores of metal oxide networks. The resulting absorption and emission spectra intensities in the UV-VIS-NIR range have been found to depend on the polarity existing inside the pores of the network; in turn, this polarization can be tuned through the attachment of organic substituents to the tetrapyrrrole macrocycles before bonding them to the pore network. The paper shows clear evidence of the real possibility of maximizing fluorescence emissions from metal-free bases of substituted tetraphenylporphyrins, especially when these molecules are bonded to the walls of functionalized silica surfaces via the attachment of alkyl or aryl groups arising from the addition of organo-modified alkoxides.

Crossed and linked histories of tetrapyrrolic macrocycles and their use for engineering pores within sol-gel matrices.

The crossed and linked histories of tetrapyrrolic macrocycles, interwoven with new research discoveries, suggest that Nature has found in these structures a way to ensure the continuity of life. For diverse applications porphyrins or phthalocyanines must be trapped inside solid networks, but due to their nature, these compounds cannot be introduced by thermal diffusion; the sol-gel method makes possible this insertion through a soft chemical process. The methodologies for trapping or bonding macrocycles inside pristine or organo-modified silica or inside ZrO2 xerogels were developed by using phthalocyanines and porphyrins as molecular probes. The sizes of the pores formed depend on the structure, the cation nature, and the identities and positions of peripheral substituents of the macrocycle. The interactions of the macrocyclic molecule and surface Si-OH groups inhibit the efficient displaying of the macrocycle properties and to avoid this undesirable event, strategies such as situating the macrocycle far from the pore walls or to exchange the Si-OH species by alkyl or aryl groups have been proposed. Spectroscopic properties are better preserved when long unions are established between the macrocycle and the pore walls, or when oligomeric macrocyclic species are trapped inside each pore. When macrocycles are trapped inside organo-modified silica, their properties result similar to those displayed in solution and their intensities depend on the length of the alkyl chain attached to the matrix. These results support the prospect of tuning up the pore size, surface area, and polarity inside the pore cavities in order to prepare efficient catalytic, optical, sensoring, and medical systems. The most important feature is that research would confirm again that tetrapyrrolic macrocycles can help in the development of the authentic pore engineering in materials science.

Improvement of Fucosylated Oligosaccharides Synthesis by α-L-Fucosidase from Thermotoga maritima in Water-Organic Cosolvent Reaction System.

The effects of water activity (aw), pH, and temperature on transglycosylation activity of α-L-fucosidase from Thermotoga maritima in the synthesis of fucosylated oligosaccharides were evaluated using different water-organic cosolvent reaction systems. The optimum conditions of transglycosylation reaction were the pH range between 7 and 10 and temperature 90-95 °C. The addition of organic cosolvent decreased α-L-fucosidase transglycosylation activity in the following order: acetone > dimethyl sulfoxide (DMSO) > acetonitrile (0.51 > 0.42 > 0.18 mM/h). However, the presence of DMSO and acetone enhanced enzyme-catalyzed transglycosylation over hydrolysis as demonstrated by the obtained transglycosylation/hydrolysis rate (rT/H) values of 1.21 and 1.43, respectively. The lowest rT/H was calculated for acetonitrile (0.59), though all cosolvents tested improved the transglycosylation rate in comparison to a control assay (0.39). Overall, the study allowed the production of fucosylated oligosaccharides in water-organic cosolvent reaction media using α-L-fucosidase from T. maritima as biocatalyst.

Spectroscopic studies and molecular modelling of the aflatoxin M1-bovine α-lactalbumin complex formation.

Since the high incidence of aflatoxin M1 (AFM1) in milk and dairy products poses a serious risk to human health, this work aimed to investigate the complex formation between bovine α-lactalbumin (α-La) and AFM1 using different spectroscopic methods coupled with molecular docking studies. Fluorescence spectroscopy measurements demonstrated the AFM1 addition considerably reduced the α-La fluorescence intensity through a static quenching mechanism. The results indicated on the endothermic character of the reaction, and the hydrophobic interaction played a major role in the binding between AFM1 and α-La. The binding site stoichiometric value (n = 1.32) and a binding constant of 2.12 × 103 M-1 were calculated according to the Stern-Volmer equation. The thermodynamic parameters ΔH, ΔS and ΔGb were determined at 93.58 kJ mol-1, 0.378 kJ mol-1 K-1 and -19.17 ±â€¯0.96 kJ mol-1, respectively. In addition, far-UV circular dichroism studies revealed alterations in the α-La secondary structures when the α-La-AFM1 complex was formed. An increased content of the α-helix structures (from 35 to 40%) and the ß-sheets (from 16 to 19%) were observed. Furthermore, protein-ligand docking modelling demonstrated AFM1 could bind to the hydrophobic regions of α-La protein. Overall, the gathered results confirmed the α-La-AFM1 complex formation.

Physicochemical properties of collagen sheet from bovine femur.

PURPOSE: In the present study collagen sheets were prepared from the spongy part of the bovine femur and characterized from the physicochemical point of view. METHODS: The physicochemical properties of the collagen sheets were studied using scanning electronic microscopy (SEM) and thermogravimetrical analysis (TGA). RESULTS: The SEM studies showed that the collagen sheets are porous and exhibit a fibrous nature. The TGA study revealed that the collagen sheets are a two-phase system containing a protein and a mineral phase. In order to determine the collagen type present in the sample, the sheets were dissolved and studied by circular dichroism (CD) and electrophoresis techniques. The results obtained showed that the nature of the collagen is type I. CONCLUSIONS: The type I collagen sheets from bovine femur isolated in this study are proposed as a biomaterial for medical applications, for example, as an osteoinductive material or they could be used as a bone substitute.

Circular dichroism of pig and bovine lactadherins and their affinity for the pig zona pellucida.

We have purified and characterized pig and bovine milk lactadherins. Studies by circular dichroism spectroscopy indicate that the two proteins present a similar folding pattern. Results have been discussed in terms of their affinity for pig zona pellucida in order to use these proteins as analogs of pig sperm lactadherin in gamete studies.

Determination of the secondary structure of Kluyveromyces lactis beta-galactosidase by circular dichroism and its structure-activity relationship as a function of the pH.

The secondary structure of Kluyveromyces lactis beta-galactosidase was determined by circular dichroism. It is mainly a beta-type protein, having 22% beta-turns, 14% parallel beta-sheet, 25% antiparallel beta-sheet, 34% unordered structure, and only 5% alpha-helix. The structure-activity relationship as a function of the pH was also studied. The pH conditions leading to the highest secondary structure content (100% ellipticity) of the enzyme was found at pH 7.0; at pH 6.5-7.0, the percent ellipticity decreased slightly, suggesting little structural change, but the activity decreased significantly, probably because of variations in critical residues. On the other hand, at pH's above 7.0, a more noticeable change in ellipticity was observed due to structural changes; the CD analysis showed a small increase in the helical content toward higher pH, whereas the maximum activity was found at pH 7.5, meaning that the changes produced in the secondary structure at this pH favored the interaction between the enzyme and the substrate.

Binding energetics of the inhibitor cystatin to the cysteine proteinase actinidin.

The binding energetics of actinidin to chicken cystatin was determined from fluorometric titrations at different temperatures. It is shown that the association of actinidin with cystatin is both enthalpically and entropically driven, with a negative change in the heat capacity. The molecular basis of these contributions are analyzed within the framework of surface-area models, using a 3D model of the actinidin-cystatin complex, which was obtained using the x-ray structure of the homologous complex papain-stefin B as template.

Antimicrobial activity and hydrophobicity of edible whey protein isolate films formulated with nisin and/or glucose oxidase.

The use of edible antimicrobial films has been reported as a means to improve food shelf life through gradual releasing of antimicrobial compounds on the food surface. This work reports the study on the incorporation of 2 antimicrobial agents, nisin (N), and/or glucose oxidase (GO), into the matrix of Whey protein isolate (WPI) films at pH 5.5 and 8.5. The antimicrobial activity of the edible films was evaluated against Listeria innocua (ATCC 33090), Brochothrix thermosphacta (NCIB10018), Escherichia coli (JMP101), and Enterococcus faecalis (MXVK22). In addition, the antimicrobial activity was related to the hydrophobicity and water solubility of the WPI films. The greatest antibacterial activity was observed in WPI films containing only GO. The combined addition of N and GO resulted in films with lower antimicrobial activity than films with N or GO alone. In most cases, a pH effect was observed as greater antimicrobial response at pH 5.5 as well as higher film matrix hydrophobicity. WPI films supplemented with GO can be used in coating systems suitable for food preservation.

Stability parameters for one-step mechanism of irreversible protein denaturation: a method based on nonlinear regression of calorimetric peaks with nonzero deltaCp.

Thermal transitions of many proteins have been found to be calorimetrically irreversible and scan-rate dependent. Calorimetric determinations of stability parameters of proteins which unfold irreversibly according to a first-order kinetic scheme have been reported. These methods require the approximation that the increase in heat capacity upon denaturation deltaCp is zero. A method to obtain thermodynamic parameters and activation energy for the two-state irreversible process N --> D from nonlinear fitting to calorimetric traces is proposed here. It is based on a molar excess heat capacity function which considers irreversibility and a nonzero constant deltaCp. This function has four parameters: (1) temperature at which the calorimetric profile reaches its maximal value (Tm), (2) calorimetric enthalpy at Tm (deltaHm), (3) deltaCp, and (4) activation energy (E). The thermal irreversible denaturation of subtilisin BPN' from Bacillus amyloliquefaciens was studied by differential scanning calorimetry at pH 7.5 to test our model. Transitions were found to be strongly scanning-rate dependent with a mean deltaCp value of 5.7 kcal K(-1)mol(-1), in agreement with values estimated by accessible surface area and significantly higher than a previously reported value.