Number Of Thiol Groups Research Articles

CRUDE INULIN DERIVED FROM DAHLIA TUBER AS NANOMATERIAL AND ITS CHARACTERIZATION

Objective: Dahlia tuber (Dahlia sp.) is one of the inulin sources that could be planted in Indonesia. Inulin is fructan-based polysaccharide. Therefore, the research aimed to investigate inulin from the extract of dahlia tuber as a drug excipient, especially for nanoparticles based on inulin-cysteamine thiomer. Methods: Crude inulin was isolated from dahlia tuber using ethanol for maceration. The resulting inulin was characterized using FT-IR and oxidized using sodium periodate (NaIO4) to increase solubility. Afterward, the oxidized crude inulin was further modified by conjugation with cysteamine to produce a cationic thiomer using reductive amination. The thiomer was evaluated regarding the number of thiol groups and solubility. The nanoparticles were prepared using ionic gelation methods. The resulting nanoparticles were evaluated for particle size and zeta potential. Results: Inulin can be isolated from dahlia tuber with its content of 18.60±4.45% and carbohydrate of 61.75±0.75%. Crude inulin can be conjugated with cysteamine to generate a cationic thiomer using NaCNBH3 as a reductant, which can increase its solubility with free thiol group content of 415.21±40.39 µmol/g. Nanoparticles were generated from crude inulin-cysteamine thiomer with sodium tripolyphosphate (NaTTP), leading to a particle size of 180 nm and zeta potential of-10.8 mV. Conclusion: As a potential nanoparticulate drug delivery system, a cationic thiomer could be synthesized from inulin derived from dahlia tuber grown in Indonesia.

Stable Na-organosulfide batteries enabled by an in-situ constructed protective interphase

Sodium-organic battery is one of the most promising energy storage systems, due to the low-cost, earth-abundant Na and absence of transition metals. Organosulfide compounds through the breakage and reformation of SS bonds to achieve the redox process have emerged as high-capacity candidates for the family of organic cathodes. To understand the electrochemical properties, we investigate the three aromatic-based organosulfide compounds in which each benzene ring consists of different number of thiol groups, i.e., 4,4′-thiobisbenzenethiol (TBBT), 1,3-benzenedithiol (1,3-BDT), and 1,3,5-benzenetrithiol (BTT). It is revealed that BTT with three thiol groups can most strongly coordinate with Na cation and enter the solvation sheath. It promotes the uniform distribution of organosulfide in the anode|electrolyte interphase, effectively protecting the active Na from corrosion of polysulfides. Meanwhile, the massive NaF decomposed from concentrated NaPF6 salts renders the smooth plating of Na and avoids the repetitive exposure of fresh Na to the electrolyte. The synergism between the organosulfide and NaF-rich interphase enables the Na|BTT cell stable cycling for 200 times with the highest reversible capacity of 342.8 mAh/g and average Coulombic efficiency of 98.9 %. The work sheds light on rational design of molecular structures for high-performance Na-organic batteries.

Functionalized GO/polysulfide rubber composites with excellent comprehensive properties based interfacial optimum design

Polysulfide rubbers (PSR) have been widely used as high performance sealants to line or seal aircraft fuel tanks. In this research, liquid polysulfide oligomers-graphene oxide (LPO-GO) nanocomposite was prepared through the mild reaction between liquid polysulfide oligomers (LPO) and graphene oxide (GO) nanosheets, and was dispersed into PSR to obtain LPO-GO/PSR composites. Benefit from the grafting of polysulfide oligomer segments on the surface of GO, good dispersion of LPO-GO in PSR matrix was achieved. The mechanical properties of PSR composites were enhanced by LPO-GO. The elongation at break and tensile strength of the 0.5% LPO-GO/PSR composites were about 70% and 43% higher than that of neat PSR. The dynamic mechanical thermal analysis (DMTA) results showed that the storage modulus of PSR was increased by 206% when 0.5% of LPO-GO was added. The broadband dielectric spectroscopy (BDS) results indicated that LPO-GO was well dispersed in PSR and some phenomena of molecular chain movement in PSR matrix. Study of the reinforcing mechanism showed that a number of thiol groups and S–S bonds had been attached onto the surface of GO after being modified by LPO, which quietly promoted the dispersion of LPO-GO in PSR matrix and strengthened the interfacial interactions between LPO-GO with PSR.

Digestive Ripening of Au Nanoparticles Using Multidentate Ligands.

The efficiency of multidentate ligands as digestive ripening (DR) agents for the preparation of monodisperse Au nanoparticles (NPs) was investigated. This systematic investigation was performed using ligands possessing one, two, or three thiol moieties as ligands/DR agents. Our results clearly establish that among the different ligands, monodentate ligands and the use of temperature in the range of 60-120 °C offer the best conditions for DR. In addition, when DR was carried out at lower temperatures (e.g., 60 °C), the NP size increased as the number of thiol groups per ligand increased. However, in the case of ligands possessing two and three thiol moieties, when they were heated with polydispersed particles at higher temperatures (120 or 180 °C), the etching process dominated, which affected the quality of the NPs in terms of their monodispersity. We conclude that the temperature-dependent strength of the interaction between the ligand headgroup and the NP surface plays a vital role in controlling the final particle sizes.

Cationic Thiolated Poly(aspartamide) Polymer as a Potential Excipient for Artificial Tear Formulations.

Dry eye disease is a relatively common ocular problem, which causes eye discomfort and visual disorders leading to a decrease in the quality of life. The aim of this study was to find a possible excipient for eye drop formulations, which is able to stabilize the tear film. A cationic thiolated polyaspartamide polymer, poly[(N-mercaptoethylaspartamide)-co-(N-(N′,N′-dimethylaminoethyl)aspartamide)] (ThioPASP-DME), was used as a potential vehicle. Besides satisfying the basic requirements, the chemical structure of ThioPASP-DME is similar to those of ocular mucins as it is a protein-like polymer bearing a considerable number of thiol groups. The solution of the polymer is therefore able to mimic the physiological properties of the mucins and it can interact with the mucus layer via disulphide bond formation. The resultant mucoadhesion provides a prolonged residence time and ensures protective effect for the corneal/conjunctival epithelium. ThioPASP-DME also has an antioxidant effect due to the presence of the thiol groups. The applicability of ThioPASP-DME as a potential excipient in eye drops was determined by means of ocular compatibility tests and through examinations of the interactions with the mucosal surface. The results indicate that ThioPASP-DME can serve as a potential eye drop excipient for the therapy of dry eye disease.

Thiol modification of silicon-substituted hydroxyapatite nanocrystals facilitates fluorescent labelling and visualisation of cellular internalisation.

Calcium phosphates are used widely as orthopaedic implants and in nanocrystalline form to enable the transfer of genetic material into cells. Despite widespread use, little is known about their fate after they have crossed the cell membrane. Here we present a method of surface modification of silicon-substituted hydroxyapatite (SiHA) through a silane group, which enables the engraftment of a fluorescent dye to facilitate real-time biological tracking. Surface modification of the nanocrystal surface was undertaken using (3-mercaptopropyl)trimethoxysilane (MPTS), which presented a thiol for the further attachment of a fluorophore. Successful modification of the surface was demonstrated using zeta potential measurements and fluorescence microscopy and the number of thiol groups at the surface was quantified using Ellman's reagent. In vitro experiments using the fluorescently modified particles enabled the discrimination of the calcium phosphate particulate from other biological debris following internalisation by a population of MC3T3 (pre-osteoblast) cells and the particles were shown to maintain fluorescence for 24 hours without quenching. The successful modification of the surface of SiHA with thiol groups offers the tantalising possibility of the intracellular growth factor delivery.

Rheological properties of cysteine-containing elastin-like polypeptide solutions and hydrogels.

The rheological properties of cysteine-containing elastin-like polypeptide (Cys-ELP) solutions and Cys-ELP hydrogels are reported. The Cys-ELP solutions exhibit a surprisingly high apparent viscosity at low shear rate. The high viscosity is attributed to the formation of an interfacial cross-linked "skin" at the sample surface, rather than the bulk of the Cys-ELP solution. At higher shear rate, the interfacial cross-linked film breaks, and its influence on the viscosity of the Cys-ELP solution can be ignored. Cys-ELP hydrogels are formed by mixing Cys-ELP and hydrogen peroxide (H(2)O(2)). At fixed concentration of Cys-ELP, the gelation time can be tuned by the concentration of H(2)O(2). Cys-ELP hydrogels have the typical characteristics of covalent cross-linked networks, as the storage moduli are larger than the loss moduli and are independent of frequency in dynamic oscillatory frequency sweep experiments. The plateau moduli obtained from linear frequency sweep experiments are much lower than those estimated from the number of thiol groups along the Cys-ELP chain, indicating that only a small fraction of thiols form elastically active cross-links. From the small value of the fraction of elastically active cross-links, the Cys-ELP hydrogel is concluded to be an inhomogenous network. Under steady shear, a 2.5 wt % Cys-ELP hydrogel shear thickens at shear rates lower than that necessary for fracture.

Raman Response of Dithiolated Nanoparticle Linkers

We report on a study of the overall surface-enhanced Raman scattering (SERS) response from several thiol-terminated molecules located at interstitial sites between Ag nanoparticles. Multiplexing of the SERS signal was demonstrated along with its dependence of the molecular length, regiochemistry, and the number of thiol groups. The data collected establish pathways for the rational design of the SERS reporters and multiplexed sensory applications.

Tuning the geometry of shape-restricted DNA molecules on the functionalized Si(1 1 1)

Designing a well-defined and stable interface between biomolecules and semiconductor surfaces is of great importance for current and future biosensing and bioelectronic applications. The well-characterized chemistry, stability, and easily tunable electronic properties of silicon substrate make it a practical platform for this type of interface. It has been established in our previous work that a robust, covalent attachment between thiol-DNA molecules of a pre-designed geometrical shape and a modified silicon surface can be achieved. This work focuses on using this binding model and altering the distance between the DNA molecules and silicon surface by strategically placing thiol linkers within the pre-determined geometric design of the rectangularly shaped DNA. The statistical analysis of the height profiles of DNA molecules attached to the surface, as determined by AFM, provides specific insight into how the construction of the DNA molecules affects the binding distance. A comparison between two thiol-DNA molecules with different numbers of thiol groups placed either within the rectangular shape or anchored to the free loop of the same geometric design suggest that the average distance of these molecules to the functionalized silicon surface can be changed by approximately 0.5 nm.

Characterization of Hyaluronic Acid-Poly(Ethylene Oxide) Hydrogel Dependent upon Poly(Ethylene Oxide)

Characterization of an hyaluronic acid (HA)-poly(ethylene oxide) (PEO) hydrogel was performed by changing the number of side arms in a PEO molecule. Verification of grafting chemistry and mechanical strength, as well as swelling behaviors and surface morphologies of the HA-PEO hydrogels were analyzed by employing different x-linking molecular weights (MW) of PEO ranging from 1.7 to 5.0 kDa at a fixed low MW HA in the hydrogel network. Methacrylation to the HA successfully obtained via Michael type reaction between the methacrylate arm groups in HA and the thiol end groups in PEO was observed by XPS. Hydrogel formation was markedly dependent upon the numbers of thiol groups in the PEO molecule. Furthermore the lower MW PEO-based HA hydrogel demonstrated stronger mechanical properties but lower water absorption and the smaller pore sizes on its surface and cross section.

The influence of the Si(OC2H5)4/(CH3O)3Si(CH2)3SH ratio on the structure-adsorption characteristics of xerogels formed and accessibility of functional groups in their surface layers

It was shown for the example of the Si(OC2H5)4/(CH3O)3Si(CH2)3SH system that successively increasing the fraction of tetraethoxysilane in it (from 1: 1 to 5: 1 (mol)) successively decreased the content of 3-mercaptopropyl groups in xerogels synthesized by the sol-gel method (in the presence of methanol as a solvent and fluorine ions as a catalyst) from 5.0 to 1.9 mmol/g, whereas the specific surface area of such xerogels simultaneously increased from 13 to 631 m2/g. The sorption volume of pores also increased, their mean diameter varying insignificantly. The mean diameter of pores (2.2–2.5 nm) was close to the boundary between meso-and micropores, which was in agreement with the form of nitrogen adsorption isotherms (type I according to the IUPAC classification). It was shown by scanning electron microscopy that virtually nonporous xerogels formed at a 1: 1 ratio between alkoxysilanes consisted of spherical partially united particles 2.5–3 μm in diameter. All the 3-mercaptopropyl groups of this and other samples were, however, accessible to silver(I) ions. It follows that these groups are situated in the surface layer of xerogels. The number of thiol groups per 1 nm2 of the surface of nonporous xerogels was 1.7–7.0 groups/nm2 and depended on the ratio between reacting alkoxysilanes and s sp.

Number of thiol groups rather than the size of the aggregates determines the hardness of cold set whey protein gels

Variation of protein concentration during heating resulted in the formation of protein aggregates with clearly different structural and chemical characteristics. Heating conditions were chosen such that differences in the degree of aggregation were excluded. Acid induced gelation of dispersions of these aggregates resulted in gels with clearly different hardness. Although gel hardness seemed to correlate with the different structural aggregate features as reported before in literature, the differences in hardness could for the most part be cancelled by blocking of the thiol groups. Application of thiol-blocked protein aggregates enabled us to make a distinction between the effect of structural- and chemical-properties of the aggregates. Formation of larger disulfide cross-linked protein structures paralleled the increase in gel hardness and dominated the effect of structural characteristics on mechanical properties of cold-set gels. In addition, the effect of the presence of native non-aggregated protein on the final gel properties can be excluded, since in our gel-experiments most protein (>95%) participated in the formation of a protein network. Therefore, we can conclude that the hardness of cold set whey protein gels is determined by the number of thiol groups rather than by the size of the aggregates or other structural features.

Complexation Properties of the Metallothionein Fragment Lys-Cys-Thr-Cys-Cys-Ala [56-61] MT I with Zinc and Cadmium Using Square Wave Voltammetry

An electrochemical study using square wave voltammetry of the complexing properties of the peptide Lys-Cys-Thr-Cys-Cys-Ala [56–61] MT 1 (FT), a part of the metallothionein structure, with cadmium and zinc was performed. The applied technique allows one to obtain well-defined peaks corresponding to the free metal ions as well as providing evidence that different forms of coordination of Cd(II) and Zn(II) with the peptide exist. FT is capable of complexing Cd2+and Zn2+ separately in a concentration equal to FT, obtaining complexes with a ratio of 1:1. However, the total metal ion concentration bound to the FT is higher when both cations are simultaneously present. The maximum total concentration that can be complexed with FT is a ratio of [Zn]:[Cd]:[FT] like 0.6:1.0:1.0 which leads to the ratio of Zn4Cd7S21, comparable to that of the metallothionein structure. The coordination of Cd(II) with FT not only depends on the Cd:FT ratio, but also on the proportion in which Zn(II) is added. However, the Zn(II) complexes are not affected by the presence of Cd-FT complexes in solution. The complexation equilibrium was investigated going from acid to basic solutions and viceversa. From the slopes of the variation Ep=f (pH), the number of thiol groups at which the cations are bound were evaluated. This study allows us to enable comparisons between the behavior of [Zn]:[Cd]:[FT] with that of Cd,Zn metallothioneins.

Role of free thiol groups in the biological activities of stonustoxin, a lethal factor from stonefish ( Synanceja horrida) venom

Stonustoxin (SNTX) is a two-subunit protein purified from the venom of a stonefish, Synanceja horrida. It has potent lethal activity and is also a membrane pore-forming cytolysin. The role of thiol groups in the biological activities of SNTX was investigated. Both the hemolytic and lethal activities of SNTX were potentiated by the reducing agent, dithiothreitol (DTT). The hemolytic activity of SNTX was sensitive to the modification of thiol groups by 5,5′-dithiobis(2-nitrobenzoic acid) (DTNB). The loss of haemolytic activity correlated with the number of thiol groups that were titrated with DTNB. Thiol modification of SNTX with DTNB also inhibited its lethality. These inhibitory effects of thiol modification could be reversed by reduction with DTT. It was also found that the haemolytic activity of SNTX could not be inhibited by cholesterol. These observations indicate that free thiol groups play an important role in the haemolytic activity and lethality of SNTX but unlike other thiol-activated cytolysins, SNTX was not inhibited by cholesterol. Thus, SNTX may represent a new class of cytolytic toxin.

NADP-malate dehydrogenase from Zea mays leaves: Amino acid composition and thiol content of active and inactive forms

NADP-malate dehydrogenase (L-malate: NADP + oxidoreductase, E.C. 1.1.1.82) was purified from the leaves of Zea mays L. and its subunit molecular weight, amino acid composition and the changes in number of thiol groups during activation were determined. The amino acid composition we found differed from that reported earlier for the Z. mays enzyme but was very similar to that reported for the enzyme isolated from pea leaves. The maize enzyme contains fewer methionine residues (3 compared to 5 in pea) but a greater total number of cysteine residues (6 compared to 3 in pea). In its inactive form (oxidised) the enzyme contained 2 thiols per subunit of which only 1 reacts with 5,5′-dithiobis(2-nitrobenzoic acid) when the enzyme is in its native form. During activation by dithiothreitol two disulphide bonds are reduced per subunit to give 4 new thiol groups. We conclude that NADP-malate dehydrogenase from leaves of the C 4 plant Z. mays is very similar to the enzyme from the C 3 plant pea. However, apparently two disulphide bonds are reduced during the reductive activation of the Z. mays enzyme in vitro compared with 1 disulphide bond for the pea enzyme.

Reductases for Aromatic Aldehydes and Ketones from Rabbit Liver<subtitle>Purification and Characterization</subtitle>

Four aldehyde reductases, F1, F2, F3, and F4, were isolated from rabbit liver cytosol to homogeneity by various chromatographic techniques. F2 is an aldehyde reductase with a molecular weight of 32,000, which resembled aldehyde reductases of human liver and pig kidney in properties. It was inhibited in a noncompetitive way by alpha-ketoglutarate and oxaloacetate with Ki values of 4 x 10(-5) M. The other three enzymes were NADPH-dependent aromatic aldehyde-ketone reductases. F1 and F3 were monomeric enzymes with molecular weights of 38,000 and 29,000, respectively. F4 showed a molecular weight of 78,000 on gel filtration, but sodium dodecyl sulfate gel electrophoresis revealed two different subunits with molecular weights of 26,000 and 24,000. The molar ratio of NADPH : F1, F2, or F3 binding was 1 : 1, whereas that of NADPH:F4 binding was 3 : 1. The number of thiol groups in order molecule of F1, F2, F3, and F4, was 4, 4, 4, and 5, respectively. The enzyme activity of F3 was inhibited by addition of an equal mole amount of PCMB. Only F4 was inhibited by metal chelating agents. F1 also catalyzed the interconversion of 3(17)-keto and 3(17) beta-hydroxysteroids, whereas F3 catalyzed oxidoreduction of some 3 alpha-hydroxysteroids of the 5 alpha-series. These results suggest that F1 and F3 are 3(17) beta-hydroxysteroid dehydrogenase and 3 alpha-hydroxysteroid dehydrogenase, respectively. Endogenous substrates for F4 could not be identified in this work. F1 showed the lowest Km value for reduction of aldehydes and ketones among the four reductases. It has been suggested that F1 is the primary enzyme responsible for the reduction of endogeneous aldehydes and xenobiotic aldehydes and ketones in vivo.

Determination of the number of cross-links in a protein gel from its mechanical and swelling properties.

AbstractThe relation between the chemical structure of a protein and the physical properties of a heat‐set gel of that protein has been investigated. The physical properties of the gel are determined by means of mechanical experiments in which the viscoelastic properties of the gel are determined in terms of the storage shear modulus, the loss modulus and the stress‐strain curve. The storage shear modulus defined the solid (elastic) character of the gel. The chemical structure of the protein and the nature of the solvent determine the nature and number of cross‐links in the gel. The cross‐links in gels formed by heating concentrated solutions of ovalbumin in 6M urea solutions were found to be disulfide bridges and the mechanical properties of these ovalbumin/urea gels approximated those of an ideal rubber. The latter finding enables one to calculate the number of cross‐links per ovalbumin molecule from the value of the storage modulus, using the classical theory of rubber elasticity. This theory, together with the Flory‐Huggins lattice model, can also be used to calculate the number of cros‐links per ovalbumin molecule from the swelling behavior of ovalbumin/urea gels. The number of cross‐links per ovalbumin molecule calculated from these two types of experiments are in mutual agreement and correspond with the number of thiol groups in ovalbumin. We conclude, thereforee, that theories of polymer physics can be used to relate the chemical structure of a protein to the physical properties of its gel.

Human tryptophan transfer ribonucleic acid synthetase. Composition, function of thiol groups, and structure of thiol peptides.

Human tryptophanyl-tRNA synthetase resembles its counterpart in Escherichia coli in quaternary structure (alpha2), but differs in molecular weight, amino acid composition, the number of thiol groups, and the relationship of the thiol groups to enzyme activity. Nevertheless, one of the thiol groups resides in a heptapeptide sequence homologous to a heptapeptide sequence containing a thiol group in the E. coli enzyme. Each subunit of the enzyme has 6 half-cystine residues, and four thiol groups are readily titrated with 5,5'-dithiobis(2-nitrobenzoic acid). Titration of these four thiol groups inactivates the enzyme, and the inactivation is partially reversible by reduction with dithiothreitol. One thiol group reacts rapidly unless L-tryptophan, ATP, and Mg2+ are present together.

The nature of inactivation of rat muscle 5'-adenylate aminohydrolase by fluorodinitrobenzene

1. The inactivation of rat skeletal muscle AMP deaminase by Dnp-F (1-fluoro-2,4-dinitrobenzene) is accompanied by the arylation of thiol, amino and phenolic hydroxyl groups. 2. The number of thiol groups that react with Dnp-F is about 12; this is the number that reacts with Nbs2 [5,5'-dithiobis-(2-nitrobenzoic acid)] and N-ethylmaleimide without loss of enzyme activity, and it appears to be the same thiol groups that all three reagents attack. 3. Dinitrophenylation of these reactive SH groups is not the cause of inactivation, since active N-ethylmaleimide-substituted enzyme is also inactivated by Dnp-F.4. Complete inactivation of the N-ethylmaleimide-treated AMP deaminase occurs when about six tyrosine and two lysine residues are dinitrophenylated. 5. Since the treatment of Dnp-enzyme with 2-mercaptoethanol restores much of the enzyme activity, inactivation of AMP deaminase by Dnp-F is probably largely due to modification of tyrosine residues. 6. The kinetic properties of the Dnp-enzyme indicate that a marked decrease in V occurs only after extensive enzyme modification. The decreased activity after slight inactivation results from modification of Km.

Characterisation of Escherichia coli cell surface by isoelectric equilibrium analysis

A characterisation of the lipopolysaccharide (outermost) layer of Escherichia coli cells has been made by isoelectric equilibrium analysis. Unmodified E. coli cells show a surface isoelectric point (pI) of 5.6. Cells treated with ethyleneimine in order to esterify the carboxyl groups are isoelectric at pH 8.55. When amino groups are blocked the bacterial surface has a pI of 3.85. An analysis of these results suggests that the ionisable groups occurring in the isoelectric zone i.e. the zone amenable to investigation by the isoelectric equilibrium method are: carboxyl groups and amino groups of polysaccharide and protein components. The carboxyl groups have a p K between 3.2 and 4.5 and the amino groups have a p K of 7.5. ε-Amino groups, phenolic hydroxyl groups and guanidyl groups do not occur, and phosphate and amino groups of the phospholipid complex are not detected. The number of thiol groups in the isoelectric zone has been determined using 6,6′-dithiodinicotinic acid. The number of anionogenic and cationogenic groups has been determined. From the density of the negative charges on the surface it is estimated that the isoelectric zone might extend up to 60 Å below the cell surface. The data discussed in this paper relate to the outermost layer of the bacterial cell wall composed of lipopolysaccharide-phospholipid-protein complex. Since reactive groups of the phosphilipid component of the complex have not been detected in the isoelectric zone, it is suggested that the arrangement of lipopolysaccharide phospholipid protein complex is such that the phospholipids are located at a depth of more than 60 Å from the bacterial surface.