Claudius Mundoma

STRUCTURE AND STABILITY OF AMINOIMINOMETHANESULFONIC ACID

Abstract The crystal structure of aminoiminomethanesulfonic acid (AIMSOA), (NH 2 ) 2 CSO 3 , was determined by X-ray crystallography. The molecular geometry about the central C atom of this zwitterionic species was found to be strictly planar. The tetrahedral S atom was characterized by three nearly equivalent S–O bonds. The unusually high value for the calculated density of 1.948 g cm −3 indicated extremely efficient packing of the (NH 2 ) 2 CSO 3 molecules in the crystal lattice. Correlation was made between stability of (NH 2 ) 2 CSO 3 and aminoiminomethanesulfinic acid (AIMSA) (NH 2 ) 2 CSO 2 in aqueous solution. A number of unexpected differences were observed in their reactivities, stabilities and decomposition products.

Purification and biochemical characterization of Brazil nut (Bertholletia excelsa L.) seed storage proteins.

Brazil nut storage proteins, 2S albumin, 7S vicilin, and an 11S legumin, were purified using column chromatography. Analytical ultracentrifugation of the purified albumin, vicilin, and legumin proteins, respectively, registered sedimentation coefficients of 1.8, 7.1, and 11.8 S. Under reducing conditions, the major polypeptide bands in 2S albumin were observed at 6.4, 10-11, and 15.2 kDa. The 7S globulin was composed of one 12.6 kDa, two approximately 38-42 kDa, and two approximately 54-57 kDa polypeptides, whereas the 11S globulin contained two major classes of polypeptides: approximately 30-32 and approximately 20-21 kDa. The 7S globulin stained positive when reacted with Schiff reagent, indicating that it is a glycoprotein. The estimated molecular mass and Stokes radius for 2S albumin and 7S and 11S globulins were 19.2 kDa and 20.1 A, 114.8 kDa and 41.1 A, and 289.4 kDa and 56.6 A, respectively. Circular dichroism spectroscopic analysis indicated the secondary structure of the three proteins to be mainly beta-sheets and turns. Emission fluorescence spectra of the native proteins registered a lambda(max) at 337, 345, and 328 nm for 2S albumin and 7S and 11S globulins, respectively. When probed with anti-Brazil nut seed protein rabbit polyclonal antibodies, 7S globulin exhibited higher immunoreactivity than 2S albumin and 11S globulin.

Oxyhalogen–sulfur chemistry Oxidation of2-aminoethanethiolsulfuric acid by iodate in acidicmedium

The oxidation of 2-aminoethanethiolsulfuric acid, AETSA, by iodate has been studied in highly acidic media. The reaction is very slow and shows some clock-reaction characteristics in which iodine is formed after some induction period. The oxidation of AETSA involves the oxidation of only one of the sulfur atoms to SO 4 2- . The other sulfur atom remains attached to the carbon chain as a sulfonic acid (taurine). The stoichiometry of the reaction is: IO 3 - +H 2 NCH 2 CH 2 S–SO 3 H+H 2 O→ H 2 NCH 2 CH 2 SO 3 H+I - +SO 4 2- +2H + . The reaction of I 2 and AETSA was found to be slow and autoinhibitory as the I - formed combines with the remaining I 2 to form the relatively unreactive triiodide ion, I 3 - . The second-order rate constant for the reaction between I 2 and AETSA was determined as 16.7±2.3 M -1 s -1 .

Oxyhalogen–sulfur chemistry: Kinetics and mechanism of the oxidation of a Bunte salt 2-aminoethanethiolsulfuric acid by chlorite

Spectrophotometric and 1H NMR methods have been used to study the kinetics and mechanism of oxidation of the Bunte salt, 2-aminoethanethiol sulfuric acid, H2NCH2CH2S-SO3H (AETSA) by chlorite in mildly acidic media. The reaction is characterized by a long quiescent induction period followed by rapid and autocatalytic production of chlorine dioxide. The formation of chlorine dioxide is much more pronounced in stoichiometric excess of chlorite. The stoichiometry of the reaction in excess chlorite just before formation of chlorine dioxide was determined to be: 2ClO2− + H2NCH2CH2S–SO3H → ClNHCH2CH2SO3H + SO4−2 + Cl− + H+, while in excess AETSA the stoichiometry was: 3ClO2− + 2H2NCH2CH2S–SO3H + 2H2O → 2NH2CH2CH2SO3H + 2SO4−2 + 3Cl− + 4H+. Although the products in excess chlorite also included pure taurine and dichlorotaurine, monochlorotaurine was the dominant species at pH 1–3. This Bunte salt showed a facile S–S bond cleavage after a single S-oxygenation step on the inner sulfur atom. The sulfoxide is quite stable but there was no experimental evidence for the existence of the sulfone-sulfonic acid. Sulfate production was almost quantitative for the oxidation of only one of the sulfur atoms. Further reaction of the taurine occurred only on the nitrogen atom with no cleavage of the C–S bond. A 21-reaction kinetics scheme model gave reasonable agreement with experiment.

Fully reduced granulin-B is intrinsically disordered and displays concentration-dependent dynamics

Granulins (Grns) are a family of small, cysteine-rich proteins that are generated upon proteolytic cleavage of their precursor, progranulin (Pgrn). All seven Grns (A-G) contain 12 conserved cysteines that form 6 intramolecular disulfide bonds, rendering this family of proteins unique. Grns are known to play multi-functional roles, including wound healing, embryonic growth, and inflammation and are implicated in neurodegenerative diseases. Despite their manifold functions, there exists a dearth of information regarding their structure-function relationship. Here, we sought to establish the role of disulfide bonds in promoting structure by investigating the fully reduced GrnB (rGrnB). We report that monomeric rGrnB is an intrinsically disordered protein (IDP) at low concentrations. rGrnB undergoes dimerization at higher concentrations to form a fuzzy complex without a net gain in the structure-a behavior increasingly identified as a hallmark of some IDPs. Interestingly, we show that rGrnB is also able to activate NF-κB in human neuroblastoma cells in a concentration-dependent manner. This activation correlates with the observed monomer-dimer dynamics. Collectively, the presented data establish that the intrinsic disorder of rGrnB governs conformational dynamics within the reduced form of the protein, and suggest that the overall structure of Grns could be entirely dictated by disulfide bonds.

Nonlinear dynamics in the oxidations of substituted thioureas I: The reaction of 4-methyl-3-thiosemicarbazide with acidic iodate [1]

The substituted thiourea, 4-methyl-3-thiosemicarbazide, was oxidized by iodate in acidic medium. In high acid concentrations and in stoichiometric excess of iodate, the reaction displays an induction period followed by the formation of aqueous iodine. In stoichiometric excess of methylthiosemicarbazide and high acid concentration, the reaction shows a transient formation of aqueous iodine. The stoichiometry of the reaction is: 4IO + 3CH3NHC(S)NHNH2 + 3H2O 4I− + 3SO + 3CH3NHC(O)NHNH2 + 6H+ (A). Iodine formation is due to the Dushman reaction that produces iodine from iodide formed from the reduction of iodate: IO + 5I− + 6H+ 3I2(aq) + 3H2O (B). Transient iodine formation is due to the efficient acid catalysis of the Dushman reaction. The iodine produced in process B is consumed by the methylthiosemicarbazide substrate. The direct reaction of iodine and methylthiosemicarbazide was also studied. It has a stoichiometry of 4I2(aq) + CH3NHC(S)NHNH2 + 5H2O 8I− + SO + CH3NHC(O)NHNH2 + 10H+ (C). The reaction exhibits autoinhibition by iodide and acid. Inhibition by I− is due to the formation of the triiodide species, I, and inhibition by acid is due to the protonation of the sulfur center that deactivates it to further electrophilic attack. In excess iodate conditions, the stoichiometry of the reaction is 8IO + 5CH3NHC(S)NHNH2 + H2O 4I2 + 5SO + 5CH3NHC(O)NHNH2 + 2H+ (D) that is a linear combination of processes A and B.

Oxyhalogen–sulfur chemistry: non-linear oxidation of 2-aminoethanethiolsulfuric acid (AETSA) by bromate in acidic medium

The reaction between bromate and 2-aminoethanethiolsulfuric acid, H2NCH2CH2S—SO3H (AETSA), has been studied in high acid environments. The stoichiometry in excess AETSA is BrO3–+ H2NCH2CH2S—SO3H + H2O → H2NCH2CH2SO3H + SO42–+ 2H++ Br–. In excess BrO3– the stoichiometry is: 7BrO3–+ 5H2NCH2CH2S—SO3H → 5Br(H)NCH2CH2SO3H + 5SO42–+ Br2+ 3H++ H2O. The reaction displays clock reaction characteristics in which there is initial quiescence followed by a sudden and rapid formation of Br2(aq). The oxidation proceeds by successive addition of oxygen on the inner sulfur atom followed by cleavage of the S—S bond to form taurine and SO42–. The Br2(aq) and the HOBr in solution oxidize the taurine to form a mixture of monobromotaurine and dibromotaurine. Computer simulations of a proposed 13-step reaction scheme produced a reasonable fit to the experimental data.

Benefits and Dangers of Nanotechnology: Health and Terrorism

The first goal in this paper is to discuss the fundamental principles, applications, advantages, and disadvantages of nanotechnology with a view of promoting the importance and validity of nanotechnology in the developed countries as well as the emerging developing countries in Africa and elsewhere. The second goal is intended to provoke critical thinking, analysis, medical applications, environmental and economic issues or implications involving nanotechnology. The third goal is to discuss the potential security threat that would pose world peace, should nanotechnology, nanodevices, nanomaterials fall into the wrong hands.