Changes In Ultraviolet Absorption Spectra Research Articles

Characterization of UV irradiated space application polymers by spectroscopic ellipsometry

AbstractMaterials deployed on long‐duration space missions such as the Hubble Space Telescope (HST) and the proposed International Space Station (ISS) are subject to high ultraviolet (UV) radiation fluences. Some UV radiation present in space has photon energy high enough to dissociate organic polymer molecular bonds. Induced chemical structure modifications can cause changes in optical, structural, and thermal properties. The present work investigates UV radiation effects on DuPont Kapton® H polyimide, polyarylene ether benzimidazole (PAEBI), and DuPont Teflon® fluorinated ethylene‐propylene (FEP). UV irradiated polymers were characterized with in situ and ex situ spectroscopic ellipsometry (SE). Ellipsometric data acquired on UV modified polymers were best modeled as an exponentially graded layer, as opposed to a single layer or linearly graded layer model. Because photon intensity decays exponentially as a function of depth into absorbing materials, an exponentially graded model should be the most physically realistic. Ellipsometric data provided information about changes in UV absorption spectra, depth of damage, and growth trends in the damaged layer.

Purification of Lac repressor protein using polymer displacement and immobilization of the protein.

Lac repressor protein was purified from E. coli BMH8117 harboring plasmid pWB1000 and E. coli K12BMH 71-18 strains. Displacement of the protein with poly(ethyleneimine) (PEI) from phosphocellulose cation exchange column was shown to be an effective elution strategy. It resulted in better recoveries and sharper elution profiles than traditional salt elution without effecting the purity of the protein. The elution is assumed to proceed via displacement of bound protein by PEI when the polymer binds to the ion exchanger. The minor impurities in the protein solution were finally removed by chromatography on immobilized metal affinity column. The repressor protein undergoes distinct conformational changes upon addition of specific inducer isopropyl-beta-D-thiogalactoside (IPTG), which is evidenced by changes in ultraviolet absorption spectrum. The protein was immobilized covalently to the Sepharose matrix. The intact biological activity of the protein after immobilization was shown by binding of genomic DNA and lac operator plasmid DNA from E. coli to the immobilized lac repressor.

Isoelectric points of some sulfonamides: determination by microelectrophoresis and by calculations involving acid-base strength.

The isoelectric points of four very slightly soluble sulfonamides were measured by microelectrophoresis of dilute suspensions as a function of pH. Ionic strength and pH were adjusted with KCl, KOH, and HCl only. The isoelectric points were also calculated from published values of acid and basic ionization constants which had been determined by potentiometric titration, and from changes in ultraviolet absorption spectra and in solubility as a function of pH. Including one sulfonamide whose isoelectric point as measured by microelectrophoresis was published, rather good agreement between the two methods was observed for all but one compound. All values were between 3.5 and 4.6, indicating that the sulfonamides function as weak acids rather than as amphoteric compounds at physiological pH.

Polymeric UV absorbers of the 2‐hydroxybenzophenone type. II. On the mechanism of the polymerization of 2‐hydroxy‐4‐(2,3‐epoxypropoxy) benzophenone with phthalic anhydride

AbstractSimultaneously with the preparation of 2‐hydroxybenzophenone light stabilizers with a reduced extractability from polypropylene, the mechanism of the propagation reaction of 2‐hydroxy‐4‐(2,3‐epoxypropoxy) benzophenone with phthalic anhydride was studied under different concentrations and temperature conditions, with tert‐amines, potassium benzoate, and potassium hydroxide being used as catalysts. If the polymerization of epoxide with anhydride is performed in melt at 125°C, an alternating copolymer is formed whether an equimolar ratio or a molar excess of anhydride with respect to epoxide has been used. Provided epoxide is present in molar excess with respect to anhydride in the reaction system, some changes in ultraviolet absorption spectra are observed in comparison with the spectra of alternating copolymers which indicate that some undesirable reactions of the orthophenolic groups of benzophenone occur simultaneously with the catalyzed polyaddition reaction, and that the polymeric stabilizer is impaired.

Conformational change of the [formula omitted] repressor induced with the inducer

The repressor of the lac operon in Escherichia , coli undergoes a distinct conformational change upon addition of a specific inducer isopropyl-β-D-thiogalactoside (IPTG), which is evidenced by changes in ultraviolet absorption spectrum, sedimentation coefficient and in circular dichroism spectrum. The significance of the conformational change reported here is discussed in relation to the allosteric properties of the repressor.

Intracellular mechanisms for the decomposition of a lipid peroxide. I. Decomposition of a lipid peroxide by metal ions, heme compounds, and nucleophiles.

Linoleic acid hydroperoxide was prepared. Two types of mechanisms for its decomposition were found. The hydroperoxide was rapidly decomposed by certain transition metal ions, heme, and hemoprotein to a complex range of products, the decomposition being accompanied by changes in ultraviolet absorption spectra. The production of radical oxidizing species may account for these products. It was also found that the hydroperoxide could be decomposed by nucleophiles presumably in a nonradical reaction to a hydroxy acid without any change in ultraviolet spectra.The kinetics, the pH dependence, and the effects of metal-complexing agents, inhibitors, and hydrogen donors on the catalytic activity of the metal ions and heme compounds were also investigated.

Studies on Soft Drinks (IV)

As previously reported, the decrease in recoveries of dehydroacetic acid was observed in citric acid solution allowed to stand at 25 and 37°C for several months.This time, the changes in ultraviolet absorption spectra were investigated on continuous heating of dehydroacetic acid in citric acid solution.As the result, upon continued heating, absorption maxima of dehydroacetic acid at 224 and 307mμ were found to decrease in their intensities while the newly appeared absorption maximum at 249mμ increased in its intensity. And these phenomena were found to be irreversible.From these facts, it was concluded that the decrease in recoveries of dehydroacetic acid in citric acid solution could not be attributed to the successive decomposition or degradation of dehydroacetic acid but that it was caused by the transformation of dehydroacetic acid to the substance having the absorption maximum at 249mμ.After 34 hours' heating, whole dehydroacetic acid were transformed into this substance in the citric acid solution, but mold-static activity of this solution for Aspergillus niger still remained in strength from 1/100 to 1/10 of the original solution.

Change in ultraviolet absorption spectrum of H-meromyosin induced by its binding with substrate and competitive inhibitor.

Change in ultraviolet absorption spectrum of H-meromyosin induced by its binding with substrate and competitive inhibitor.

Spectral analysis of the intramolecular heterogeneity of λ DNA

The internal heterogeneity of base composition of DNA derived from λ bacteriophages has been detected by studies of the changes in ultraviolet absorption spectrum that occur during the course of thermal denaturation. Results obtained for the internal heterogeneity of λ c I-857 DNA are consistent with results obtained by shearing methods. Results obtained with deletion mutants of λ are consistent with the known locations of the deletions in the chromosome. In the case of the b 2 deletion, it appears possible to detect heterogeneity of base composition within the b 2 region. The method gives results which complement those obtained by shearing; it is also applicable to phage DNA of permuted base sequence, which cannot be studied by shearing methods.

核酸の構造におよぼすγ線照射の影響-I

The effect of γ-irradiation on the constituent components of nucleic acid was examined as the first step for studying the effect of γ-irradiation on its structure. In the present study, nucleic acid bases, nucleosides, nucleotides, and ribose, were γ-irradiated mostly in aqueous solution and in the presence of air, and the irradiation effect on those substances were examined by measuring the change in ultraviolet absorption spectrum, and the amounts of ammonia formed and ribose, phosphate, bases, and nucleosides liberated. Results obtained were as follows: 1) Ammonia was formed when solutions of bases, nucleosides, and nucleotides were ir-radiated with doses above 105R (Table 2). 2) On irradiating with doses above 106R, bases and ribose were liberated from nucleo-sides (Table 4). However, from nucleotides, corresponding nucleosides and ribose were not liberated, but bases and ribose-5-phosphate were liberated. 3) By irradiation with a dose of 2×106R, 70% of ribose was decomposed (Fig. 4). From the results mentioned above, it may be concluded that whenγ-irradiation with doses above 105R, the nucleotide is affected in several ways; deamination, scission of glyco-sidic bond between sugar and base and of ester bond between sugar and phosphate, and des-truction of base ring.

Physiochemical properties and quantitative determination of thiamine monophosphate disulfide.

1. The ultraviolet absorption spectrum of thiamine monophosphate disulfide (TMPDS) changed with pH like thiamine, the isosbestic points being at 239 and 277mμ.2. pKa1, pKa2, and pKb were obtained from the titration curve. The pKa value obtained from the change in ultraviolet absorption spectrum with pH was almost the same as that obtained from titration, and the isoelectric point was 3.96. This value well corresponded to the properties of solubility and stability.3. It was hardly soluble in organic solvents. The solubility in water at 30° was 4.94% (w/v) at pH 7.0 and 4.50% (w/v) at pH 3.86.4. It could be separated from the related compounds by thin layer chromatography using pyridine-acetic acid-water as a solvent system.5. The anhydrate of TMPDS was hygroscopic, forming a stable powder-like material with 4-8 molecules of water in 24 hours.6. The stability of TMPDS solution (1-10mg/ml) after heating at various pH levels for 1-2 hours was greatest at pH 4 below 70°, but it was hydrolyzed at above 80°. It was unstable to light.7. The ultraviolet absorption spectrum and fluorescence spectrum of the thiochrome phosphate obtained by cysteine reduction and BrCN oxidation at pH 13.0 were the same as those of thiochrome obtained from thiamine. The recovery was more than 98%.8. The total thiamine value can be determined by measuring the ultraviolet absorbance and fluorometry in alkaline solution obtained by BrCN oxidation after cysteine reduction. Thiamine disulfide and free thiamine can be determined by fluorometry of the isobutanol extract of this solution. Thiamine monophosphate and free thiamine can be determined by ultraviolet absorbance and the fluorometry of the alkaline solution obtained by BrCN oxidation of the solution without cysteine reduction. Free thiamine can be determined by fluorometry of the isobutanol extract of this solution. TMPDS can be determined from each value thus obtained.9. TMPDS in the blood can be determined with 95% recovery by combined use of cysteine reduction and Takadiastase hydrolysis.

Immunochemical studies on myosin. II. Cardiac myosin.

Abstract 1. 1. Heterogeneous antisera have been obtained consistently from rabbits that were injected with skeletal-muscle myosin purified by several different procedures. Cardiac muscle has been investigated, consequently, as a possible source of immunochemically pure myosin which could be used to obtain the homogeneous antisera required for unambiguous localizations of myosin and the meromyosins by fluorescent antibody techniques. 2. 2. The similarity of chicken cardiac myosin and actomyosin to their skeletal-muscle counterparts was established on the bases of their differential solubilities in sal solutions, changes in ultraviolet absorption spectra resulting from ammonium sulfate fractionation, and enzyme activities. These characteristics were correlated with results of gel-diffusion analyses of the purified proteins and their antisera. 3. 3. The results showed that antisera to cardiac myosin are also immunochemically heterogeneous, and that the heterogeneity is caused by a contaminant of myosin that is, or is associated with, actomyosin.

Inactivation of tulare apple mosaic virus by o-quinones

Purified Tulare apple mosaic virus (TAMV) preparations lost infectivity rapidly when exposed to chlorogenic acid and tyrosinase. Tyrosinase alone did not inactivate TAMV. The amount of virus inactivated in oxidizing chlorogenic acid solutions was directly proportional to the substrate concentration, the enzymatic activity, and the interval of exposure to oxidation. The rate of virus inactivation closely paralleled the formation of the o-quinone of chlorogenic acid. o-Benzoquinone, tetrachloro- o-benzoquinone, and tetrabromo- o-benzoquinone isolated by chemical procedures each caused immediate and total inactivation of TAMV while their catecholic equivalents had no effect. When approximately 1 μg of tetrachloroquinone was present for every 34 μg of virus, total inactivation occurred, but few or no changes were detected in the virus ultraviolet (UV) absorption spectrum, serological activity, sedimentation in sucrose density-gradient tubes, or solubility in acetate buffer. At virus to quinone ratios between 17:1 and 0.7:1 virus inactivation was accompanied by changes in UV absorption spectrum, the rate of serological reaction, the rate of sedimentation, and the location of visible zones in sucrose density-gradient tubes and solubility of virus pellets in acetate buffer. Each of the changes determined was consistent with the hypothesis that a virus-quinone complex was formed at the higher quinone concentrations. However, the evidence indicates that o-quinones cause loss of infectivity without affecting some of the biophysical properties of the virus. Inactivation of TAMV by exposure to tetrasubstituted o-quinones suggests that oxidation reduction reactions are directly involved in the loss of biological activity. This was supported by inactivation of TAMV by exposure to silver oxide.

Studies of phase transformations in nitrates and nitrites II. Changes in ultra-violet absorption spectra accompanying thermal transformations in the crystals

Changes in ultra-violet absorption spectra have been measured for nitrates and nitrites of the alkali metals and for ammonium, silver and thallous nitrates, in relation to thermal transformations in these solids. A gradual shift of absorption bands is found to accompany thermal expansion of all the crystals. More abrupt changes in absorption spectra are observed at transformation points from one crystal structure to another; in many instances these two effects of temperature can be correlated. In cases where crystal structures are known, shifts in absorption maxima due to changes in temperature have been interpreted. in relation to changes in the distances between cations and anions. By means of the techniques described, ultra-violet absorption spectroscopy provides a sensitive means for studying various thermodynamic effects in phase transformations. Thus with ammonium nitrate, hysteresis with both superheating and supercooling is observed for the transitions IV ^ III ( T c ~ 32 °C) and III ^ II ( T c ~ 88 °C), but not II ^ I ( T c ~ 125 °C). With potassium nitrate during cyclic changes of temperature a (metastable) crystal form III appears. With potassium nitrite, a new crystal transformation showing hysteresis ( T c ~ 40 °C) is readily detected by ultra-violet spectroscopy.

Studies of phase transformations in nitrates and nitrites I. Changes in ultra-violet absorption spectra on melting

Ultra-violet absorption spectra of ions in crystals are sensitive to their environment of neighbouring ions. This fact is utilized to study melting processes in nitrates and nitrites, with particular reference to changes in the average shell of nearest neighbours around any ion, on passing from crystal to melt. For the nitrates of sodium, potassium, rubidium, caesium, thallium and silver, for ammonium nitrate and for the nitrites of sodium and potassium this shell appears to contract on melting, which is attributed to the formation of association complexes in the melt. For the two crystal hydrates HNO 3 . H 2 O and HNO 3 . 3H 2 O, corresponding changes are observed, suggesting that the structure and absorption spectra correspond with the ions (OH 3 )+ and NO - 3 in the crystals, likewise giving rise to tighter association complexes on melting. Pure nitric acid on the other hand behaves in a manner more closely similar to isopropyl nitrate.

Changes in ultra-violet absorption spectra of deoxyribonucleic acid by treatment with bromine.

IN 1947, a procedure was developed1 for the determination of pyrimidine nucleoside in which bromination and prolonged acid hydrolysis precede the performance of Bial reaction. More recently, it was also shown that marked changes in ultra-violet absorption spectra, particularly disappearance of selective absorption of cytosine, uracil and their nucleosides, occurred before and after the bromination of the compounds2. While studying the effects of bromine on the chemical nature of nucleic acids, we have also found that the maximal absorption of deoxyribonucleic acid shows a decrease with increasing bromination period. In further experiments, it has also been demonstrated that acid hydrolysis of brominated deoxyribonucleic acid results in a loss of selective absorption without significant loss of phosphorus.

Photooxidation of crystalline ribonuclease in the presence of methylene blue

The photochemical action of methylene blue on ribonuclease resulted in a complete inactivation when 3 moles of oxygen was taken up per mole of enzyme. At this level of oxidation, the only chemical change observed was the photooxidation of 3 moles of histidine out of the total of 4. Up to 50 % inactivation, the decrease of histidine was found to be proportional to the decrease in enzymatic activity, in asmuchas the photooxidation of 0.5 mole of histidine resulted finally in a 52% inactivation. No changes in relative viscosity and optical rotation of ribonuclease could be noted up to 2.5 moles of oxygen uptake per mole of enzyme, whereas the decrease in enzymatic activity at this point amounted to 95%. Changes in ultraviolet absorption spectrum during the photooxidation of ribonuclease were in agreement with the changes observed in amino acid composition. Ribonuclease does not possess any sulfhydryl groups. Addition of reducing agents to the photoinactivated enzyme did not restore its activity. The possible significance of histidine to the catalytic activity of ribonuclease is discussed.