Aqueous Iodine Research Articles

Simulations of the Iodine Interphase Transport Effect on the Oscillating Bray−Liebhafsky Reaction

The effect of the iodine interphase transport originated from physical processes, such as pressure decrease, vigorous stirring, and/or an inert gas bubbling, on the dynamics of the oscillating Bray−Liebhafsky reaction is studied. Some new experiments were made at 60 °C that confirmed the possibility of suppressing oscillations by means of the iodine vapor removal from the reaction solution. It has been proved that the iodine vaporization is governed by the first-order kinetics with respect to the concentration of aqueous iodine, and a critical rate constant for iodine escape causing inhibition of the oscillatory mode was determined. The experiments were confronted with the models proposed by Kolar-Anić and Schmitz with co-workers. Both the models studied reflect the observed phenomenon. A simulation based on the latest model shows very good semiquantitative agreement with experiment, needing only a minor modification of the rate constants suggested by Kolar-Anić et al.

ChemInform Abstract: Kinetics and Mechanisms of the Oxidation of Hydrazine by Aqueous Iodine.

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Kinetics and Mechanisms of the Oxidation of Hydrazine by Aqueous Iodine

Kinetics for the reactions of I2 with excess N2H5+/N2H4 and I- are measured by the loss of I3- over a wide range of acidity from pH 0.35 to 8.0 at 25.0 °C, μ = 0.50 M. Pseudo-first-order rate constants increase by factors of more than 107 with increase of pH, hydrazine, and buffer concentrations. Below pH 1, I2 reacts directly with N2H5+ which has a relative reactivity that is 2.4 × 107 times smaller than N2H4 (the dominant reactant at pH ≥ 1). Kinetic evidence for IN2H4+ as a steady-state species is found below pH 3. From pH 3.5 to 6.3, rate constants are measured by stopped-flow methods and at higher pH by pulsed−accelerated-flow methods. A multistep mechanism is proposed where I2 reacts rapidly with N2H4 to form an I2N2H4 adduct (KA = 2.0 × 104 M-1) that is present in appreciable concentrations above pH 6. The adduct undergoes general base-assisted deprotonation accompanied by loss of I- in the rate-determining step. Subsequent intermediates react rapidly with another I2 to form N2 as a final product. ...

Misacylated Transfer RNAs Having a Chemically Removable Protecting Group.

The 4-pentenoyl group and a number of derivatives have been studied as protecting groups for N(alpha) of the aminoacyl moiety in misacylated tRNAs. The unsubstituted 4-pentenoyl group itself was found to function as efficiently as any of the derivatives studied. Four different N-(4-pentenoyl)aminoacyl-tRNA(CUA)s were prepared and shown to undergo deprotection readily upon admixture of aqueous iodine; the derived misacylated tRNAs all functioned well as suppressors of a nonsense codon in an in vitro protein biosynthesizing system. Also prepared were four N(alpha)-(4-pentenoyl)aspartyl-tRNA(CUA)s that were protected on the side chain carboxylate as the nitroveratryl ester. Following treatment with aqueous iodine, the misacylated suppressor tRNAs incorporated the aspartate derivatives into position 27 of dihydrofolate reductase by suppression of a UAG codon in the mRNA. The suppression yields were significantly better than those obtained when side chain protection was absent. The resulting "caged proteins" were inactive, but full catalytic potential was restored by irradiation under conditions sufficient to effect deprotection of the side chain carboxylate moiety.

Synthesis of phosphopeptides via global phosphorylation on the solid phase: Resolution of H-phosphonate formation

The formation of the H-phosphonate by-products from the ‘global’ phosphorylation of a Thr-containing peptide resin using both di-t-butyl and dibenzylN,N-diethylphosphoramidite was identified to result from 1H-tetrazolemediated cleavage of thet-butyl or benzyl from the intermediate dialkyl phosphite triester and re-arrangement of the resultant hydroxy phosphite diester to the H-phosphonate form. This side reaction was rectified by the use of aqueous iodine for the oxidation step in which the H-phosphonate is oxidised to the benzyl phosphorodiester which, on acidolytic treatment, gives the desired dihydrogen phosphate.

Efficient functionalization of 2',5'-oligoadenylates with sulfur.

To derivatize the 2'-terminus of 2',5'-oligoadenylates with a thiol group, the reaction of periodate-oxidized nucleotide and 2',5'-oligonucleotide with aminothiols was explored. Two separate synthetic approaches were employed, both of which relied upon the use of S-protected thiols. In one approach, 5'AMP was oxidized with sodium periodate to dialdehyde, which was reacted with cystamine hydrochloride. Sodium cyanoborohydride reduction of the unisolated intermediate animal gave compound 4. The second approach involved reaction of S-(2-tetrahydropyranyl)cysteamine with the dialdehyde obtained by periodate oxidation of 5'AMP to yield, after reduction with Na(CN)BH3, the S-protected adduct 3. Intermediate 3 could be oxidized with aqueous iodine to give disulfide 4. Disulfide 4, obtained by either of the above routes, was reduced with dithiotreitol (DTT) to the thiol 5. This same reaction sequence was applied to 2-5A tetramer monophosphate, p5'A2'[p5'A2']2p5'A (6a), to give via 6b the 2'-terminal-modified derivative 6c. Aqueous iodine oxidation of 6c provided the disulfide 7, which reacted with DTT to give quantitative conversion to product, the free thiol 8. Both the disulfide 7 and the S-tetrahydropyranyl-protected derivative (6c) were bound effectively to the 2-5A-dependent RNase L of mouse L cells with IC50 values of 1 x 10(-9) M for 7 and 8 x 10(-10) M for 6c, not significantly different from the corresponding value for the parent unmodified 2-5A (6a) itself.

Oligo-2'-fluoro-2'-deoxynucleotide N3'-->P5' phosphoramidates: synthesis and properties

Uniformly modified oligodeoxyribonucleotide N3'-->P5' phosphoramidates containing 2'-fluoro-2'-deoxy-pyrimidine nucleosides were synthesized using an efficient interphase amidite transfer reaction. The 3'-amino group of solid phase-supported 2'-fluoro-2'-deoxynucleoside was used as an acceptor and 5'-diisopropylamino phosphoramidite as a donor of a phosphoramidite group in the tetrazole-catalyzed exchange reaction. Subsequent oxidation with aqueous iodine resulted in formation of an internucleoside phosphoramidate diester. The prepared oligo-2'-fluoro-nucleotide N3'-->P5' phosphoramidates form extremely stable duplexes with complementary nucleic acids: relative to isosequential phosphodiester oligomers, the melting temperature Tm of their duplexes with DNA or RNA was increased approximately 4 or 5 degrees C per modification respectively. Moreover, these compounds are highly resistant to enzymatic hydrolysis by snake venom phosphodiesterase and they are 4-5 times more stable in acidic media (pH 2.2-5.3) than the parent oligo-2'-deoxynucleotide N3'-->P5' phosphoramidates. The described properties of the oligo-2'-fluoronucleotide N3'-->P5' phosphoramidates suggest that they may have good potential for diagnostic and antisense therapeutic applications.

Kinetics and Mechanisms of the Oxidation of Hydroxylamine by Aqueous Iodine

Kinetics and Mechanisms of the Oxidation of Hydroxylamine by Aqueous Iodine

Synthesis of double-tailed (perfluoroalkyl)alkyl phosphosugars: new components for drug-carrying and -targeting systems

Double-tailed d-glycose 3- and 6-[sodium (perfluoroalkyl)alkyl phosphates] were synthesized via the hydrogen phosphonate approach. Stable double-tailed (perfluoroalkyl)alkyl hydrogenphosphonates, prepared from double-tailed (perfluoroalkyl)alkanols and PCl 3-imidazole, reacted with 1,2:3,4-di- O-isopropylidene-α- d-galactopyranose or with 1,2:5,6 -di- O-isopropylidene-α- d-glucofuranose in the presence of Me 3CCOCl as the condensing agent to give, after oxidation with aqueous iodine, the corresponding O-protected glycose phosphate diesters. O-Deisopropylidenation of the latter by aqueous trifluoroacetic acid afforded the target compound in 70% yield, based on the protected glycosides. Condensation of 1,2,3,4-tetra- O-acetyl-β- d-glucopyranose or -mannopyranose with double-tailed (perfluoroalkyl)alkyl hydrogenphosphonates or 10-eicosyl hydrogenphosphonate, via the coupling and oxidation steps described above, afforded per- O-acetylglycose phosphodiesters. O-Deacetylation with MeONa-MeOH was achieved in 65% yield based on the protected sugar. All the compounds were characterized by 19F, 1H, 13C, and 31P NMR data. Preliminary biocompatibility assays indicate a reduction of hemolytic activity when fluorinated chains are present and maximum tolerated doses of ca. 125 mg/kg body weight in mice.

Synthesis of oligodeoxynucleotides containing 2-thiopyrimidine residues--a new protection scheme.

A method is described for the incorporation of 2'-deoxy-2-thiouridine (dS2U) and 2'-deoxy-2-thiothymidine (dS2T) into oligodeoxynucleotides at predetermined positions. This requires N3 or O4-acylation of dS2U and dS2T with toluoyl chloride. These base-protected thiopyrimidines are completely stable toward the aqueous iodine oxidation reagent used in the phosphoramidite DNA synthesis method. The toluoyl protecting group is removed during the standard post-synthetic ammonia treatment. This novel protection strategy allows dS2U and dS2T to be efficiently incorporated into oligodeoxynucleotides at predetermined sites without the usual problem of desulfurization and decomposition. Several 14-mers containing the Eco-RI recognition site (dGGCGGAAXXCCGCC and dGGCGGAAXXCGCGG, where X represents dT, dS2U or dS2T) have been synthesized and characterized by base composition, thermal denaturation, CD spectroscopy and endonuclease substrate activity.

Complexation of aqueous iodine by 18-crown-6

The reaction of 18-crown-6 with aqueous iodine has been monitored by UV and visible spectrophotometry. The stability constant for the reaction has been determined as well as the spectra for the pure aqueous complex. This stability constant has been related to other equilibrium constants for the complexation of molecular iodine. The relation appears to predict correctly the stability constant for the iodine–water charge-transfer complex.

Evaluation of potential gastrointestinal contrast agents for echoplanar MR imaging

Although the diagnostic application of echoplanar imaging (EPI) has until now been limited, recent technical advances provide anatomic resolution and signal-to-noise ratios comparable to that of conventional MR imaging. The purpose of this study was to investigate approved aqueous gastrointestinal contrast agents for use in abdominal EPI. Conventional and echoplanar MR imaging experiments were performed with 1.0 Tesla whole body systems. Phantom measurements of Gastrografin, barium sulfate suspension, oral gadopentetate dimeglumine, water, and saline were performed. Signal intensity (SI) of aqueous oral barium sulfate and iodine based CT contrast agents was lower on conventional spin-echo (SE), Flash, and Turbo-Flash images than on EP images. The contrast agents exhibited higher SI on T2-weighted SE PE images and TI-time dependence on inversion recovery EP-images. The barium sulfate suspension was administered in volunteers to obtain information about bowel lumen enhancement and susceptibility artifacts. Oral administration of the aqueous barium sulfate suspension increased bowel lumen signal and reduced susceptibility artifacts. Approved aqueous gastrointestinal contrast media or flavored saline with long relaxation times may serve as safe, simple, and effective gastrointestinal contrast agents in abdominal EPI.

Practical Synthesis of 2'-5'-Linked Oligoadenylates (2-5A Oligomers)

A general, facile synthesis of 2'-5'-linked oligonucleotides (2-5A oligomers ) has been achieved based on the second-order regioselective protection of adenosine, one-pot formation of the 2'5' internucleotide linkage, and O-selective phosphorylation of N-unblocked nucleosides. Standard t- butyldimethylsilylation of 5'-O-p-methoxytrityladenosine followed by careful recrystallization from a mixture of triethylamine , methanol, ethyl acetate and ether (4 : 4 : 5 : 100 v/v) gives the 3',5'-di-O-protected adenosine in high yield. Magnesium alkoxide -mediated condensation of the 2'-O-free adenosine with o-chlorophenyl p-nitrophenyl phosphorochloridate followed by 2',3'-di-O-t-butyldimethylsilyladenosine produces the N-free and fully O-protected adenylyl (2'-5')adenosine. The resulting adenylyl dimer, after removal of the 5'-O-trityl protector, is elongated to the protected trimeric compound through a similar reaction sequence. Deprotection of the product furnishes the 2-5A core. Condensation of the 5?-0-detritylated core and bis (2,2,2-trichloroethyl) phosphorochloridite assisted by 2,6-lutidine and subsequent oxidation with aqueous iodine produces, after deblocking, 2-5A 5'-monophosphate (p5'A2'p5'pA2'p5'A). The 2-5A 5'-monophosphate is converted into 2-5A 5'-triphosphate (ppp5'A2'p5'A2'p5'A) by reaction with N,N'-carbonyldiimidazole in the presence of triethylamine followed by tributylammonium diphosphate. This procedure allows ready synthesis of 2-5A oligomers and related compounds on a multigram scale.

Effect of topical antimicrobial treatment on aerobic bacteria in the stratum corneum of human skin

The efficacy of antimicrobial agents applied topically to the skin surface in eradicating coagulase-negative staphylococci (CNS) residing in the stratum corneum underlying the surface was examined. Glabrous skin was sampled with a 26-cm2 contact plate containing Trypticase soy agar. Five antiseptic solutions and four antimicrobial ointments were evaluated. The antiseptic solutions (10% povidone-iodine, 2% aqueous iodine, 2% tincture of iodine, 70% ethanol, and 0.5% chlorhexidine-ethanol) were applied for 15 s with a gauze sponge. The antimicrobial ointments (iodophor, silver sulfadiazine, mupirocin, and a triple-antibiotic ointment containing neomycin, polymyxin, and bacitracin) were applied and covered for 6 h with gauze. After treatment, the surface was sampled, 15 to 25 keratinized layers were subsequently removed by sequential stripping with cellophane tape, and the stratum corneum was sampled. All agents were effective in eradicating CNS from the surface (80 of 88 trials). However, only 2% iodine (17 of 20 trials), iodophor (8 of 12), mupirocin (6 of 10), and the triple-antibiotic ointment (9 of 11) eradicated CNS from the stratum corneum reliably (greater than or equal to 50% of trials). The stratum corneum was repopulated with resident flora within 24 h of treatment with 2% iodine (4 of 4 trials), iodophor (6 of 7), or mupirocin (5 of 6), but repopulation occurred in only 1 of 7 trials with the triple-antibiotic ointment. Topical treatment of skin with antimicrobial agents usually eradicates CNS from the skin surface but may not eradicate CNS from the stratum corneum. Only the triple-antibiotic ointment eradicated CNS from the stratum corneum and prevented repopulation with resident flora.

Interaction of iodide and iodate with granitic fracture-filling minerals

An emprical study has been conducted to determine the ability of common granitic fracture-filling minerals to remove aqueous iodine species from solution. The two iodine species studied were iodide and iodate. The effect on measured sorption of the initial iodide or iodate concentration in solution, the total dissolved solids in solution and the solution volume to solid weight ratio were determined using a statistically designed experimental technique. It was concluded that iodide was not significantly sorbed by chemical interaction with the fracture-filling minerals used. Iodate sorption was observed under a variety of conditions with a number of the minerals. The significant coefficients required to solve the polynomial equation describing the observed sorption were determined.

Kinetics and Mechanism of Oxidation of Melibiose and Cellobiose by Alkaline Aqueous Iodine Solution

Kinetics and Mechanism of Oxidation of Melibiose and Cellobiose by Alkaline Aqueous Iodine Solution

Mechanistic studies with positive iodine: Kinetics of oxidation of thiocyanate ion by iodine monochloride and aqueous iodine in perchloric acid medium

AbstractKinetics of oxidation of thiocyanate ion (NCS−) by iodine monochloride and iodine has been studied in aqueous perchloric acid medium. The rates of oxidations followed the rate laws: Variations in ionic strength and dielectric constant of the medium had little effects on the rates of reactions with both the oxidants. Mechanisms consistent with the observed rate laws have been suggested. Rate limiting steps have been identified and the constants of some of these steps have been evaluated by varying [NCS−] at each temperature. Activation parameters were computed from the Arrhenius plots. The rate constants predicted from the rate law as [NCS−], and [H+], varied in iodine monochloride oxidation, are in good agreement with the experimental values providing support to the proposed mechanism.

Aqueous Iodine Adsorption Properties of Activated Carbon Samples Made from Yallourn Brown Coal Activated with CO2 under the Condition of Chemical Reaction Controlling Step

The properties of iodine adsorption on activated carbons were investigated. The activated carbons were prepared from Yallourn brown coal char by activating with carbon dioxide under the conditions of chemical reaction rate-controlling step at 800°C in the atmosphere of PCO2, /PCO=9.0, 2.3 and 1.0, respectively. The iodine adsorption from an aqueous KI-I2 solution of 0.2 mol. of KI and 0.02 mol. of I2 per cubic decimeter was measured at 25°C for more than 120 hours. Dubinin-Radushkevich's equation was applied to elucidate the adsorption characteristics of activated carbons and a parameter Wo in the equation was estimated.From these results, it is suggested that the micropore volume Wo increases with the decrease of PCO2/PCO ratio in the activation process of Yallourn brown coal char.

ChemInform Abstract: Triphenylmethanesulfenyl Group. A New Protecting Group for the Uracil Residue in Oligoribonucleotide Synthesis.

The selective protection of the N3-imido group of uridine with triphenymethanesulfenyl group is described. This group could be introduced selectively onto the N3-position of the uracil moiety of 3′,5′-O-(tetraisopropyldisiloxane-1,3-diyl)uridine in a good yield and removed very easily by treatment with aqueous iodine.

Interaction of lodine with nonionic surfactant and polyethylene glycol in aqueous potassium lodide solution

AbstractWhen a nonionic surfactant, such as hexaoxyethylene glycol dodecyl ethers (6ED) is added to an aqueous iodine solution in the presence of potassium iodide, some spectral changes corresponding to the interaction of iodine‐potassium iodide mixture with 6ED are found above the critical micelle concentration (CMC) of 6ED. The absorption maximum bands of complexes formed between 6ED and iodine are significantly different from those formed between 6ED and iodine‐potassium iodide mixture in aqueous solution. The complexes of iodic compounds (such as iodine, triiodide ion and polyiodide ion) with 6ED show absorption bands at 390 nm, 370 nm and 385 nm which are assigned to an interaction between iodine‐6ED, triiodide ion‐6ED and polyiodide ion‐6ED, respectively.When the concentration of polyethylene glycol (PEG, MW=200–600) becomes high in aqueous triiodide ion solution, the maximum absorption wavelength of triiodide ion solution also shifts toward 370 nm, similar to that of the triiodide ion‐6ED complex.If it is assumed that the absorbance between I3− and the EO chain in 6ED is the same as that between I3− and the EO chain of PEG, the concept of effective EO number can be applied to explain the behavior in the absorption spectra among I3−, 6ED and PEG. Here, the effective EO number is defined as the product of EO chain length and concentration of each 6ED and PEG in the complexes.The effective EO number and concentration of PEG decrease in the triiodide ion‐PEG complex as the molecular weight of PEG becomes large. Moreover, the effective EO number and concentration of 6ED are lower than those of PEG at all maximum absorption wavelengths.