Addition Of NaClO Research Articles

Utilização de hipoclorito de sódio na esterilização de meio de cultura para multiplicação in vitro de <i>Eucalyptus pellita </i>L.

Ultimamente, vem-se observando grande interesse na área de pesquisa em cultura de tecidos vegetais, em se descobrir novas opções que resultem na redução dos custos da micropropagação das plantas em laboratórios comerciais, de modo a torná-la mais viável economicamente. Uma opção potencialmente promissora para a redução de custos, mas que não tem recebido a devida atenção, é a perspectiva de se substituir a técnica de autoclavagem por outra mais econômica. Com esse objetivo, foram realizados dois testes utilizando um novo protocolo de preparo do meio, que consistiu na esterilização química de todos os utensílios utilizados no preparo e acondicionamento do meio de cultura, associado à adição do esterilizante ao meio em diferentes concentrações. O primeiro teste teve como objetivo observar a influência de diferentes concentrações de NaClO adicionado ao meio de cultura sobre a esterilização deste. O segundo objetivou verificar a reação dos tecidos de Eucalyptus pellita a diferentes concentrações de NaClO adicionado ao meio de cultura. A adição, ao meio de cultura, de concentrações iguais ou superiores a 0,0005% no primeiro teste e de 0,005% no segundo, permitiu completa esterilização do meio, não se tendo observado qualquer dano aos tecidos do Eucalyptus pellita, quando cultivado em meio de cultura com até a concentração máxima testada, de 0,009% de NaClO. Os resultados obtidos mostraram a viabilidade de dispensar o uso da autoclave para a esterilização de meios de cultura para esta espécie.

Biological Purification of Silicate Minerals

Bioleaching is technology applicable to iron extraction from low-grade non-metallic raw materials. Bioleaching of quartz sands and feldspars involves the action of heterotrophic bacteria. Impurities include fine – grained limonite, goethite, hematite or mica were removed by the reductive dissolution of Fe3+ in linked with the silicate mineral destruction. Heterotrophic bacteria produced organic acids that are able to solubilize Fe oxide and silicates but require organic carbon as a source of energy. Molasses is a relatively inexpensive carbon source used for various industrial fermentations and contains also other nutrients that accounted for the enhancement of iron dissolution in this study. The admixture of pigments in molasses coloured the samples, but the discoloration could be removed by the addition of NaClO following the bioleaching step. The feasibility of the bioleaching treatment has to be tested specifically to each type of silicate raw materials. The Fe content in the quartz sands and feldspar samples by the biological leaching decreased as much as 60% and by subsequent using of electromagnetic separation of feldspars, the decrease of Fe content in 74% was achieved. However, the application of magnetic separation of quartz sands after bioleaching resulted in total iron removal of 93 % and in such combined way prepared product contained 0.024 % of Fe2O3. Achieved results on iron removal point to the fact that combination of leaching and magnetic separation enables to obtain product usable in glass and ceramic industry.

Determination of the dissociation constants of some newly synthesized derivatives of 1,2,4-triazoline-3-thione in sodium hydroxide media

The behaviour of some newly synthesized derivatives of 1,2,4-triazoline-3-thione (4-butyl-5-octyl-2,4-dihydro-3 H -1,2,4-triazoline-3-thione, 4-allyl-5-octyl-2,4-dihydro-3 H -1,2,4-triazoline-3-thione, 4-phenyl-5-octyl-2,4- dihydro-3 H -1,2,4-triazoline-3-thione) was studied in aqueous sodium hydroxide solutions at different pH values with UV spectroscopy. The measurements were carried out immediately after preparation of the solutions, in the wavelength range from 190 nm to 360 nm, on a Varian Cary UV spectrophotometer. When the p H value of the solution increased from 5 to 9, the measured value of the absorbance decreased, while the absorption maximum shifted towards lower wavelengths. The dissociation constants were determined using the equation p KBH = log I + p H ( I = c (BH)/ c (B – )). The ionic strength of the solutions of 0.10 mol/dm 3 was adjusted with addition of NaClO 4 . The calculations were derived from the values of the absorbance from the spectra obtained experimentally and from the spectra reconstructed by using the method of characteristic vector analysis (CVA). The absorbance values were measured at four wavelengths, on and around the absorption maxima for each investigated compound. Also, the p KBH values were determined graphically and they were in good agreement with those obtained numerically. The obtained values of the p KBH were in the range from 7.45 to 7.54 and they were in a good agreement with the expected ones for this kind of compounds.

Fundamental Study on Solvent Sublation Using Salphen and Its Application for Separative Determination of Trace Ni(II), Co(II) and Cu(II) in Water Samples

A solvent sublation using salphen as a ligand was studied and applied for the determination of trace Ni(II), Co(II) and Cu(II) in water samples. The fundamental study was investigated by a solvent extraction process because the solvent sublation was done by extracting the floated analytes into an organic solvent from the aqueous solution. The salphen complexes of Ni(II), Co(II) and Cu(II) ions were formed in an alkaline solution of more than pH 8 and then they were extracted into m-xylene. It was known that the each metallic ion formed 1 : 1 complex with the salphen and the logarithmic values of extraction constants for the complexes were 3.3 5.1 as an average value. Based on the preliminary study, the procedure was fixed for the separation and concentration of the analytes in samples. Various conditions such as the pH of solutions, the influence of NaClO 4 , the bubbling rate and time of N 2 gas, and the type of organic solvent were optimized. The metal-salphen complexes could be extracted into m-xylene from the solution of more than pH 8, but the pH could be shifted to acidic solution of pH 6 by the addition of NaClO 4 . In addition, the solvent sublation efficiency of the analytes was increased by adding NaClO 4 . The recovery of 97-115% was obtained in the spiked samples in which given amounts of 0.3 mg/L Ni(II), 0.8 mg/L Co(II) and 0.04 mg/L Cu(II) were added.

Influence of configuration of carboxylic acid capping ligands on the salt-induced aggregation of gold clusters

Oxalic acid (Ox) and 1,2,3,4-cyclobutanetetracarboxylic acid (CBTCA) were employed as capping ligands in the preparation of gold colloids. FTIR indicated that Ox adopted a linear configuration through one oxygen atom and one gold atom, while CBTCA adopted a bridge configuration through two oxygen atoms and two gold atoms. Ox–gold colloids exhibited aggregation upon addition of NaClO 4, while they remained as isolated particles upon NaCl. For CBTCA–gold colloids, not NaClO 4 but NaCl resulted in aggregation. The reversed results were considered to have been influenced by the different configurations of Ox and CBTCA, which were combined results of the Lewis basicity and steric hindrance of the added ions.

Silver(I) complexes of the naphthyl-azoimine function: single crystal X-ray structure of bis-[1-ethyl-2-(naphthyl-α-azo)imidazole]silver(I) perchlorate

Reaction of AgNO 3 and 1-alkyl-2-(naphthyl-(α/β)-azo)imidazole (α-/β-NaiR) in MeOH followed by the addition of NaClO 4 has isolated [Ag(α-/β-NaiR) 2](ClO 4) ( 3/ 4). The complexes are characterized by microanalytical and spectral data. Single crystal X-ray diffraction study of bis-[1-ethyl-2-(naphthyl-α-azo)imidazole]silver(I) perchlorate confirms the structure of the complex. Argentophilicity of imidazole-N and steric crowding by naphthyl groups have forced a {2+2} distorted linear geometry. The structure shows intramolecular and intermolecular H-bonding in a 1D helical framework along with face-to-face π–π interactions.

Electrocatalytic reduction of nitrate in water

Nitrate (NO 3 −) contamination of groundwater is a common problem throughout intensive agricultural areas (nonpoint source pollution). Current processes (e.g., ion exchange, membrane separation) for NO 3 − removal have various disadvantages. The objective of this study was to evaluate an electrocatalytic reduction process to selectively remove NO 3 − from groundwater associated with small agricultural communities. A commercially available ELAT (E-Tek Inc., Natick, MA) carbon cloth with a 30% surface coated Rh (rhodium) (1 μg cm −1) was tested at an applied potential of –1.5 V versus standard calomel electrode (SCE) with a Pt auxiliary electrode. Electrocatalytic reduction process (electrolysis) of NO 3 − was tested with cyclic voltammetry (CV) in samples containing NO 3 − and 0.1 M NaClO 4 −. Nitrate and NO 2 − concentrations in test solutions and groundwater samples were analyzed by ion chromatography (IC). The presence of Rh on the carbon cloth surface resulted in current increase of 36% over uncoated carbon cloths. The electrocatalysis experiments using Rh coated carbon cloth resulted in reduction of NO 3 − and NO 2 − on a timescale of minutes. Nitrite is produced as a product, but is rapidly consumed upon further electrolysis. Field groundwater samples subjected to electrocatalysis experiments, without the addition of NaClO 4 − electrolyte, also exhibited removal of NO 3 − on a timescale of minutes. Overall, results suggest that at an applied potential of –1.5 V with respect to SCE, Rh coated carbon cloth can reduce NO 3 − concentrations in field groundwater samples from 73 to 39 mg/L (16.58 to 8.82 mg/L as N) on a timescale range of 40–60 min. The electrocatalytic reduction process described in this study may prove useful for removing NO 3 − and NO 2 − from groundwater associated with nonpoint source pollution.

Application of multivariate curve resolution to the voltammetric data Factor analysis ambiguities in the study of weak consecutive complexation of metal ion with ligand

Different techniques for factor analysis (FA) have been applied in the study of weak consecutive complexes of Cd(II) propanoate by analysing experimental matrices obtained from four electroanalytical techniques: normal pulse polarography (NPP), reverse normal pulse polarography (RNPP), differential pulse polarography (DPP) and differential pulse anodic stripping voltammetry (DPASV). All experiments were performed at a constant temperature, 25 ± 1 °C, in aqueous solutions having a constant cadmium ion concentration (10 and 20 μM), varying propanoate concentrations in the range 10–400 mM, a constant c(propanoic acid)-to- c(sodium propanoate) ratio (1: 50), and a constant ionic strength (2 M), obtained by addition of NaClO 4. From the experimental signals using DeFord and Hume's model, to calculate the experimental F 0 function model identification, β i estimates and corresponding standard error of stability constants were obtained using conventional fitting of polynomial (univariate hard modelling) to the experimental data, together with the recently proposed evolving polynomial fitting and optimized least squares extrapolation of F i functions. The same experimental data matrices were analysed by multivariate soft modelling approach using the following FA techniques: principal component analysis (PCA), evolving factor analysis (EFA) and constrained alternating least squares (ALS) optimization of individual and global (augmented) data matrices.

Nitrification monitoring in activated sludge by oxygen uptake rate (OUR) measurements

A simple measuring system was developed that yields information about the presence of NH + 4 and NO − 2 nitrogen in mixed liquor samples. In addition, it allows monitoring of the rate of both NH + 4 and NO − 2 oxidation simultaneously with the carbon substrate oxidation using OUR measurements. The method is based on the subsequent addition of NaClO 3 and allylthiourea, selective inhibitors of Nitrobacter and Nitrosomonas respectively, to the mixed liquor sample in a closed batch respirometer. The presented method is valuable for detailed monitoring of the nitrification process in a reactor: it is simple, inexpensive, robust and generally applicable for nitrifying reactor systems. The measurement of NH + 4 and NO − 2 oxidation rates enables the operator to detect the presence of NH + 4 and NO − 2 species. This allows action to be taken to improve the performance of the system. The method is validated on a SBR. It is indicated that optimal SBR phase scheduling can be based on such OUR measurements.

Voltammetry of Plastocyanin at a Graphite Electrode: Effects of Structure, Charge, and Electrolyte.

Comparative voltammetric studies on Anabaena variabilis plastocyanin (positively charged at neutral pH) and spinach and poplar plastocyanins (negatively charged at neutral pH) have been undertaken at an edge-plane graphite electrode as a function of ionic strength, pH, and Mg(2+) concentration at 3 degrees C. The aim was to provide a more detailed understanding of the influence of the electrode-protein (solution) interfacial characteristics, as well as the variation of the formal potential with both the nature of the plastocyanin species and the pH. As might be expected, some of the interfacial properties associated with the positive charge on A. variabilis plastocyanin are the opposite of those observed with the negatively charged plastocyanins. For example, the linear diffusion component of the mass transport process for A. variabilis plastocyanin under the conditions of cyclic voltammetry is decreased and the radial diffusion component is increased by the addition of Mg(2+), whereas the reverse occurs with poplar and spinach plastocyanins. The voltammetrically determined reversible potentials for A. variabilis plastocyanin are considerably less positive than those for spinach and poplar plastocyanins, in agreement with values calculated from chemically based redox studies. Ionic strength effects, as determined by addition of NaClO(4) over the concentration range 0.005-0.20 M, are negligible for all three proteins. The addition of Mg(2+) causes a significant shift in the reversible potential toward more positive values for spinach and poplar plastocyanin but only a small positive shift for A. variabilis plastocyanin. The difference is attributed to a specific binding effect. The addition of Mg(2+) also dramatically alters the pH dependence of the reversible potential, indicating that the equilibrium between the protonated and unprotonated forms of reduced plastocyanin is modified by binding of Mg(2+) to the protein. It is concluded that the effects of biologically relevant redox-inactive cations such as Mg(2+) or Ca(2+) have to be considered carefully in studies of the redox chemistry of metalloproteins.

A novel triply bridged dinuclear manganese (III) complex containing the [Mn 2O(OAc) 2] 2+ core: synthesis, crystal structure and properties of [Mn 2(μ-O)(μ-OAc) 2(bpea) 2](ClO 4) 2

The reaction of Mn(O 2CCH 3) 3 ·2H 2O with the ligand N, N-bis(2-pyridylmethyl)ethylamine (bpea) in a 1:1 ratio in methanol followed by the addition of NaClO 4 afforded the title compound [Mn 2O(O 2CCH 3) 2(bpea) 2](ClO 4) 2 ( 1) in 75% yield. Compound 1 was characterized by using several physical methods including single-crystal X-ray diffractometry. Compound 1·0.5H 2O crystallizes in the orthorhombic space group Pbca (No. 61) with a = 38.780(2), b = 22.058(4), c = 19.719(5) A ̊ , V = 16 868(8) A ̊ 3 and Z = 16. There are two independent equivalents of compound 1 in the crystallographic asymmetric unit and there is a single unique water molecule in the crystal lattice. Both manganese atoms in each of the independent dinuclear units are in the +3 oxidation state and they are bridged by one oxo ligand (O 2−) and two acetate groups. Each manganese atom is also bound to one facially-coordinating tridentate bpea ligand, with the aliphatic nitrogen donor situated trans to an acetate oxygen atom. Deviations from idealized octahedral symmetry at each manganese center are consistent with expectations for a d 4 electronic configuration. Compound 1 has an average Mn…Mn separation of 3.11 Å and an average Mn(μ-O)Mn angle of 122.7°. The electronic absorption spectrum of 1 in CH 3CN is very similar to other compounds that contain the {Mn 2(μ-O)(μ-O 2CCH 3) 2} 2+ core. A cyclic voltammogram of 1 in CH 3CN exhibits an oxidation wave (III,III to III,IV) at +0.66 V and a reduction wave (III,III to III,II) at −0.39 V versus the ferrocene/ferrocenium (Fc/Fc +) couple. The IR spectrum of 1 reveals two strong bands at 1566 and 1432 cm −1 corresponding to the bridging acetate groups present in the compound. The X-band electron paramagnetic resonance (EPR) spectrum of 1 in dry CH 3CN at 77 and 4 K is featureless. Compound 1 disproportionates in an H 2O/CH 3CN solvent mixture to give the (III,IV) binuclear species [Mn 2O 2(O 2CCH 3)(bpea) 2] 2+, which displays a characteristic 16-line g = 2 EPR signal.

Synthesis and Characterization of Mononuclear Octahedral Titanium(IV) Complexes Containing Ti:O, Ti(O2), and Ti(OCH3)x (x = 1-3) Structural Units

The oxidation of [(Me 3 tacn)Ti III Br 3 ] (where Me 3 tacn is 1,4,7-trimethyl-1,4,7-triazacyclononane) in water with Na 2 [S 2 O 8 ] yields upon addition of NaClO 4 yellow-orange [(Me 3 tacn)Ti IV Br 3 ]ClO 4 (1). The series [(Me 3 tacn)Ti IV Br x (OCH 3 ) (3-x) )] + (x=2 (2); x=1 (3); x=0 (4)) has been synthesized by oxidation reactions of [(Me 3 tacn)TiBr 3 ] with air in acetonitrile/methanol mixtures and methanol as solvents

Synthesis of aquanitrato(1-methyl-2,2′-bipyridin-3-yl-ium)-palladium(II) perchlorate hydrate

Treatment of [Pd(bpyMeH)Cl 2]/(bpyMeH  1-methyl-2,2′-bipyridin-3-yl-ium) with 2 mol of AgNO 3 in water yields a solution of [Pd(bpyMeH)(H 2O) 2] 2+ and NO 3 −, which on evaporation forms [Pd(bpyMeH)(ONO 2) 2]. Addition of NaClO 4 to a solution of [Pd(bpyMeH)(H 2O) 2] 2+ and NO 3 − yields [Pd(bpyMeH)(H 2O)(ONO 2)]ClO 4 · H 2O.

Preparation and characterization of triply-bridged dinuclear copper(II) complexes containing the [Cu 2(μ-OH)(μ-X)(μ-OAc)] + core (X = Cl, Br), and the crystal structure of [Cu 2(OH)Cl(OAc)(bpy) 2](ClO 4) · H 2O

Synthetic procedures are described that allow access to complexes containing the cation [Cu 2(μ-OH)(μ-X)(μ-O 2CMe)(bpy) 2] + (X = Cl, Br). Reaction mixtures consisting of CuX 2, bpy, OH −, MeCO 2 − and ClO 4 − (X = Cl −) in MeOH/H 2O give blue solutions from which the products [Cu 2(OH)Cl(O 2CMe)(bpy) 2](ClO 4) · H 2O ( 1) and [Cu 2(OH)Br(O 2CMe)(bpy) 2]Br · H 2O ( 4) can be obtained in good yield. Complex 1 may also be prepared from the known complexes [Cu 2(OH)(H 2O)(O 2CMe)(bpy) 2](ClO 4) 2 ( 2) and Cu 2(OH) 2(bpy) 2 (ClO 4) 2 ( 3). Complex 1 crystallizes in monoclinic space group P2 1/ n with (at − 175°C) a = 8.434(1), b = 16.074(2), c = 9.430(1) Å, β = 98.09(1)°, Z = 2 and V = 1265.83 Å 3. The structure was solved by direct methods (MULTAN) and refined to values of conventional indices R( R w) of 3.38 (3.54)% using 1499 unique reflections with F > 2.33σ( F). The structure of the cation consists of a triply-bridged pair of five-coordinate copper(II) atoms. One of the bridging ligands is a syn, syn η 1: η 1: μ 2 acetate group, the others being the Cl − and OH − ions; a terminal bpy molecule completes five-coordination at each metal. The Cu…Cu separation is 2.957(1) Å. The metal coordination geometry is best described as distorted square-pyramidal with the Cl − ligand occupying the apical site for each metal. The oxygen atom of the water molecule is hydrogen-bonded to the OH − hydrogen. Recrystallization of 1 from warm water yields 3 in 20% yield; addition of NaClO 4 to the solution increases the yield to 40%. Complex 1 in warm water containing one equiv. of NaClO 4 and one equiv. of NaOH also gives 3 (yield 73%). The thermal decomposition, room temperature μ eff values, and electronic and IR spectra of 1 and 4 are discussed interms of the nature of bonding and structure of 1.

The anodic behaviour of iron in ethanol—water solutions in the presence and absence of NaClO 4 as the supporting electrolyte

The anodic behaviour of iron in ethanol—water solutions and the effect of NaClO 4 have been investigated on the basis of potentiostatic polarization curves and electrochemical impedance plots. The influence of the water content in ethanol (6–80 vol.%) on the anodic polarization curves without a supporting electrolyte is to increase the anodic current density monotonically with potential. Furthermore, for a given potential, the current density is higher when the water content is increased. In the presence of NaClO 4 the polarization curves shift towards more high current in the low anodic potential range. Thus, addition of NaClO 4 not only increases the conductivity of ethanol solutions in its role as a supporting electrolyte, but it also modifies the electrochemical process significantly.

The synthesis and reaction kinetics of some Co(IIl) and Cr(III) chloro complexes of 1,4,8-Triazaoctane (2,3-tri) and the isolation of chiral trans-dichloro [CoCl 2(NH 3)(2,3-tri)] ClO 4

The reaction of 2,3-tri with CrCl 3·6H 2O 1, dehydrated in boiling DMF, results in the formation of mer-CrCl 3(2,3-tri) and anation of hydrolysed solutions of mer-MCl 3(2,3,-tri) (M=Co, Cr) with 6 M HCl containing HClO 4, forms trans-dichloro- mer-[MCl 2(2,3-tri)(OH 2)]ClO 4·H 2O (M=Cr, Co; I, II). trans-Dinitro- mer-[Co(NO 2) 2(NH 3)(2,3-tri)] ClO 4 crystallises from the reaction between mer-Co(NO 2) 3(2,3-tri) and aqueous 7 M ammonia, on addition of NaClO 4·H 2O, and trans-dichloro- mer-[CoCl 2(NH 3)(2,3-tri)]ClO 4 ( III) can be isolated by treatment of the dinitro with 12 M HCl. Reaction of mer-CoCl 3(2,3-tri) with C 2O 4 2 −, followed by addition of aqueous NH 3 and NaClO 4·H 2O results in the isolation of racemic mer-[Co(ox)(NH 3)(2,3-tri)]ClO 4· H 2O. This complex was resolved into its enantiomeric forms and treatment of these with SOCl 2/MeOH/ HClO 4 gave the chiral forms of trans-dichloro- mer- [CoCl 2(NH 3)(2,3-tri)]ClO 4 ( R or S at the see-NH center). The rates of loss of the first chloro ligand from these dichloro complexes have been measured spectrophotometrically in 0.1 M HNO 3 over a 15 K temperature range to give the following kinetic parameters; ( I) k H(298)=7.25 × 10 −5 s −1, E a=78.5 kJ mol −1, δ S 298 #= −69 J K −1 mol −1; ( II) k H(298)=4.00 × 10 −3 s −1, E a=89.9, δ S 298 #= +87.5; ( III) k H(298)=3.09 × 10 −4 s −1, E a=103, δ S 298 #=+27. Treatment of the dichloro cations with Hg 2+/HNO 3 results in the generation of mer- M(2,3-tri)(OH 2) 3 3+ (M=Cr, Co; IV, V) and trans- diaqua- mer-Co(NH 3)(2,3-tri)(OH 2) 2 3+ ( VI). The Co( III) cations isomerise to the fac configuration with ( V) K isom(298) μ=1.0 M)=2.97 × 10 −5 s −1, E a=115, δ S 298 #=+46. ( VI) K isom(298) (μ=1.0 M)=4.13 × 10 −5 s −1, E a=113, δ S 298 #=+52.

The effect of salts on the kinetics of iron release from N-terminal and C-terminal monoferrictransferrins

The kinetics of iron release from N-terminal and C-terminal monoferric human transferrins has been studied using EDTA as the accepting chelate. In the absence of added salts iron release from the N-terminal site is more facile but the relative lability can be reversed by the addition of NaClO 4, NaCl and LiCl. The results indicate that both anions and cations can affect the lability of the two sites. Since the relative lability of the two monoferrictransferrins is affected by fairly moderate concentrations of NaCl and NaClO 4 we suggest that the ionic composition serum may play an important role in determining the observed distribution of iron among the sites. A new method for the preparation of N-terminal monoferrictransferrin is described.

The importance of the ionic strength of sucrose gradients in the determination of the sedimentation coefficient of poorly iodinated or newly synthesized thyroglobulin

The sedimentation rate of thyroglobulin from iodine-sufficient or iodine-deficient rats was examined in sucrose gradients prepared in buffers of different ionic strengths at pH 6.8. Iodine deficiency was obtained by feeding rats a low iodine diet for 15–18 weeks, alone or with addition of NaClO 4 or propylthiouracil for 7 days. The poorly iodinated in vivo 125I-labeled or in vitro 14C-labeled thyroglobulins sedimented in a symmetrical approx. 18-S peak in sucrose gradients made in phosphate-NaCl buffer with ionic strength of 0.40 and similarly in the same buffer with ionic strength of 0.15 for less poorly iodinated thyroglobulin. In sucrose gradients made in 0.01 M phosphate buffer all thyroglobulins with an iodine content lower than 0.1% showed heterogeneity. This consisted in the appearance of a new 14–16-S species, the amount of which was inversely related to thyroglobulin iodine content and which was likely an unfolded form of approx. 18 S. Unfolding of the approx. 18-S into the 14–16-S species was partially reversible. The unfolded 14–16-S form was easily dissociated into approx. 12-S subunits. The results indicated that dissociation of thyroglobulin into subunits is probably preceded by unfolding of the molecule. Low sedimentation coefficients of poorly iodinated thyroglobulins reported by several investigators are related to environmental factors such as the ionic strength of the buffer at a near neutral pH used to make the sucrose gradients.