Photolysis of Phenylalanine in the Presence of Oxidized Carbon Nanotubes

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Photolyses at 254 nm of aqueous solutions of phenylalanine (Phe) were carried out at 25°C in the absence and presence of multiwalled carbon nanotubes (CNT). The photolyses were performed in distilled, deoxygenated water and inert Ar atmosphere or in distilled water and air atmosphere. Kinetics of the photolyses were followed by UV spectrophotometry at 220 nm. Initial rates were obtained from the plot of ΔA versus Δt, both in the presence of CNT (ΔA/Δt = p*) and in their absence (ΔA/Δt = po*). The ratio p*/ po* gave the ratio k*/ ko* of the rate constants of the photolysis in the presence and in the absence of nanotubes, respectively. The mass of nanotubes produced an exponential attenuation of the photolytic decomposition of Phe with minor formation of tyrosine and an attenuation constant κ of the shielding effect of the nanotubes against the photolytic degradation of the amino acid. The results show the effects of CNT on the photolysis of Phe and support the previously observed attenuation effect of carbons on the denaturalizatoion of amino acids and proteins. It is concluded that carbons produce a shielding effect on the photolysis, absorbing the photons and decreasing substantially their denaturalization while at the same time excites the active sites of the carbon for the insertion reaction of the organic moiety.

Section: Results and Discusionsupporting

confidence: 82%

Section: Results and Discusionmentioning

confidence: 99%

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Effect of mass of pristine carbon nanotubes on the photolysis of phenylalanine

Humeres

Souza

Debacher

et al. 2018

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“…[18][19][20] In all cases, the thiolysis proceeded through the oxidized intermediate, while reaction with amine took place through the primary product episulfide. These results suggest the possibility of a double functionalization of the matrix through an amino-thiolysis reaction if both reactive sites would be near enough as assumed by the primary mechanism.…”

Section: Selective Reactivity Of So 2 Reduction Intermediates Insertementioning

confidence: 99%

“…Several other electrophiles could react, allowing an extensive surface functionalization and generating modified graphenes with miscellaneous physical‐chemical properties. The reactivities of several carbons modified with SO 2 , including MPGO and nanotubes, with respect to the basic hydrolysis, thiolysis, aminolysis, reaction with alkyl halides, and photolysis of phenylalanine and t ‐butanol have already been studied. XPS spectra after the reaction calculated by the atom inventory method, assuming reactions already described in the literature, showed that thiol and t ‐butanol moieties were inserted via oxidized intermediates, while in aminolysis, only the non‐oxidized intermediate was involved.…”

Section: Introductionmentioning

confidence: 99%

Interconversion and selective reactivity of sulfur dioxide reduction intermediates inserted on graphene oxide

Smaniotto

Humeres

Debacher

et al. 2016

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Graphene oxide, MPGO, was obtained by oxidation of graphite microparticles by a H 2 SO 4 /KMnO 4 /H 2 O 2 mixture followed by thermal exfoliation. Non-thermal plasma treatment of MPGO under SO 2 atmosphere resulted in the insertion of the oxidized intermediates only. Refluxing this material in CS 2 (46°C) showed sulfur elimination and interconversion of the oxidized into non-oxidized intermediates with an energetic barrier of ΔG ‡ = 25.81 kcal mol À1 without decarboxylation. The episulfide content in modified MPGO increases with respect to the oxidized intermediates when increasing temperature. Modification of MPGO with SO 2 at 630°C presented exclusively the non-oxidized intermediate. These results support the hypothesis that there are two major reactions with different energetic demand in the SO 2 reduction on carbons: desulfurization and decarboxylation. The selectivity of thiolysis and aminolysis towards the intermediates inserted in the MPGO matrix allowed the aminothiolysis of a sample containing both intermediates with the insertion of the amino group on the episulfide site followed by an intramolecular thiolysis with double functionalization of the matrix.

Mechanism of the desulfurization route of the reduction of SO₂ on carbons. Dimerization of Disulfur and Tetrasulfur

Humeres,

Correia,

Debacher

et al. 2024

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The desulfurization of carbons modified with SO2 was studied as a dispersion in boiling cyclohexane (81°C) using activated carbon (mAC) and graphene oxide (mGO), modified by SO2. The steady‐state species in the carbon matrix after the catalytic reduction of SO2 was considered a trisulfane. For mAC, there was a burst of a sulfur species identified as S2 by UV spectrum with a maximum at 217 nm (εM at 217 nm = 2.56 × 103) that showed a second‐order decay of absorbance with = 47.29 M‐1·sec‐1 (= 18.1 kcal·mol‐1). The product was postulated to be S4. No other consecutive reaction was observed because of the possible adsorption of S4 in the carbon matrix. The desulfurization of mGO was shown by XPS and the kinetics were a second‐order decay up to 16 min ( 18.41 M‐1·sec‐1;= 18.8 kcal·mol‐1) followed by a second‐order increase of absorbance with = 3.84 M‐1·sec‐1 (= 19.9), where the product showed a double maximum at 260‐285 nm typical of S8. These results are consistent with a mechanism of consecutive thermodynamically favorable dimerizations of S2 and S4 and with the desulfurization mechanism that has been previously postulated.