PTh-silica

Hydrophobicity - Before plasma treatment, silica powder is highly hydrophilic and immediately sinks in water. After plasma film deposition, the material floats on water for several hours. A significant reduction in polarity and in surface energy compared to untreated silica is found, down to the range of 28.4-47.7 mJ/m2. The water penetration into powder beds of untreated and plasma-treated silica is shown in Fig. 7. The untreated silica absorbs water very fast, whereas the plasma-treated silicas show a significantly decreased water penetration rate. The lowest rate is found for the polythiophene-coated silica (PTh-silica). 

Amount of deposited material - The difference in weight loss between coated and untreated silica corresponds to the weight of the plasma-polymerized film deposited on the surface. For the plasma-treated silicas, decomposition of the coating starts at 265°C for poly acetylene, 200°C for polypyrrole, and 225°C for poly thiophene, and is complete at 600°C. Between 265 and 600°C, PA-silica shows 6 wt% weight loss, and PPy- and PTh-silicas show 4.5 wt% and 5 wt% loss, respectively. 

In all the cases of poly acetylene, polythiophene, and polypyrrole coating, the amount of plasma-film deposition was different, caused by the difference in the structure of the three different monomers and their reactivity during the plasma process. PPy- and PTh-silica are more hydrophobic than PA-silica, probably due to the presence of different chemical moieties in the complex film structure deposited onto the silica surface. 

Sample codes SU S-SBR reinforced with untreated silica SPA S-SBR with PA-silica SPPy S-SBR with PPy-silica SPTh S-SBR with PTh-silica ST S-SBR with silanized silica... 

The Payne effect of S-SBR compounds filled with untreated silica, PA-, PPy-, and PTh-silicas, and silane-modified silica are shown Fig. 17. 

Compounds containing PA-silica, PTh-silica, or silane-treated silica show the lowest reinforcement parameters in this series. This indicates a good dispersion of the polymer and a low degree of filler-filler interaction, as also shown by the Payne effect values. 

Most conspicuous is the steep tensile curve for the S-SBR sample containing PTh-silica. The PTh-silica gives the best improvement in tensile properties in terms of tensile strength, modulus at 100%, and modulus at 300%, but elongation at break is lower. The PA- and PPy-silicas as well as the silane-treated silica result in only a slight... 

The blends containing PA-silica and PTh-silica (samples SEPA and SEPTh, respectively) show the highest Payne effect values of all samples. The silane-modified silica shows the lowest filler-filler interaction compared to all other silicas. 

Sample codes SEU SBR/EDPM reinforced with untreated silica SEPA SBR/EDPM with PA-silica SEPPy SBR/EDPM with PPy-silica SEPTh SBR/EDPM with PTh-silica SET SBR/EDPM with silanized silica... 

The plasma polymerization onto silica was carried out after charging 100 g of dried silica Ultrasil VN3 into the reactor, pumping down to 13 Pa and introducing plasma gasses or monomer vapors for further plasma polymerization. The conditions for the preparation of plasma-polymerized acetylene (PA), pyrrole (PPy) and thiophene (PTh) are presented in Table 2. 

PTH-amino acids may be separated with a liquid-solid adsorption system consisting of small-particle silica gel (particle diameter, 5 pm) in a 50-cm column eluted with methylene chloride-dimethyl sulfoxide-rerr.-butanol in various ratios. The separation of a number of PTH-amino acids on Merkosorb SI-60 (5 pm) with methylene chloride-dimethyl sulfoxide-rerr.-butanol (125 0.1 1.0) is illustrated in Fig.4.3. Absorption is measured at 260 nm. Amounts of less than 1 nmole of each amino acid derivative can be... 

The use of ligand exchange has been examined for the analysis of PTH (phenylthio-hydantoin) amino acids separated on silica gel plates [92]. The method is an extension of the procedure developed for organophosphate pesticides [84]. The chromatoplate is sprayed with a solution of palladium(II) chloride and calcein. Palladium complexes with calcein to form a non-fluorescent chelate. However, in the presence of many sulfur-containing compounds, such as PTH-amino acids, the palladium is displaced from the complex liberating free calcein which gives an intense fluorescence. This method is capable of determining 0.1-nmole amounts of PTH-amino acids. 

Figure 6.8 Experimental variation of the retention of 23 phenylthiohydantoin (PTH) derivatives of amino acids with mobile phase composition in RPLC. Mobile phase mixtures of acetonitrile and 0.05M aqueous sodium nitrate buffer (pH — 5.81). All mobile phases contain 3% THF. Stationary phase ODS silica. Solutes D = aspartic acid C-OH = cysteic acid E = glutamic acid N = asparagine S = serine T = threonine G = glycine H = histidine Q = glutamine R = arginine A = alanine METS = methionine sulphone ABA = a-aminobutyric acid Y = tyrosine P = proline V = valine M = methionine NV = norvaline I = isoleucine F = phenylalanine L = leucine W = tryptophan K = lysine. Figure taken from ref. [610]. Reprinted with permission.

Using one-dimensional chromatography on alumina, polyamide, and silica gel, difficulties are encountered in resolving Leu/Ile and Glu/Asp pairs as well as other combinations of PTH-amino adds (e.g., Phe/Val/Met/Thr). The most common solvents used on polyamide plates are n-heptane-n-butanol-acetic add (40 30 9), toluene-n-pentane-acetic acid (60 30 35), ethylene chloride-acetic add (90 16), and ethylacetate-n-butanol-acetic add (35 10 1), and... 

Phenylthiohydantoin derivatization offers a special value because it is actually performed during Edman degradation, the sequencing technique mostly used for the determination of the primary structure of proteins and peptides. PTH derivatives are separated in many different stationary phases, in either normal- or re-versed-phase mode and are mostly detected at 254 nm [8,9]. Using radiolabeled proteins, sequencing of proteins down to the 1-100-pmol range can be achieved. The formed derivatives are basic and thus interact strongly with base silica materials. RP separations are mostly carried out in acidic conditions with the addition of appropriate buffers (sodium acetate mostly, but... 

The DNP-amino acids, after separation into individual spots on the chromatographic plate, can be eluted from the scraped off area by adding 4 ml of water to the material in a small tube. The tube is heated at 50° in a water bath for 15 minutes and centrifuged to clear the solution. The color is read against known standards at 360 nm. Direct estimation of DNP-, PTH-, and DANS-amino acids separated on the thin-layer plate can be performed by fluorescence and fluorescence quenching techniques (P8). It is also possible to convert unmodified amino acids, separated on a silica gel G chromatographic plate, into DNP-amino acids by in situ conversion as was described in Section 4.7.18. The DNP-derivatives can then be developed in the second dimension and the spots analyzed quantitatively. 

Five solvent systems useful for the chromatographic separation of 32 PTH-amino acids on silica gel G thin layers with one-dimensional runs are listed in Table 44 of the textbook by Pataki (P7). According to Cherbuliez et al. (C3, C3a, C5), when three chromatograms are run simultaneously in one dimension on silica gel G plates with the following solvent systems (a) chloroform isopropanol water (28 8 1),... 

HPLC finally provided a practical means to separate and directly identify all 20 PTH derivatives. Generally, all involve gradients of aqueous sodium acetate at pH 4 against acetonitrile, on C-18 silica columns. HPLC also greatly reduced the amount of sample required, shifting efforts back to the degradation end of the equation for increasing sensitivity. 

In the same idea, it is worth mentioning that the electrochemical behavior of PTh grown by a template electrosynthesis in a silica sol-gel matrix is rather different from the one of a classical PTh... 

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