Photo-assisted peroxymonosulfate activation via 2D/2D heterostructure of Ti3C2/g-C3N4 for degradation of diclofenac.

In this paper, a two dimensional/two dimensional (2D/2D) heterostructure of Ti3C2/g-C3N4 (T/CN) was constructed and used to activate peroxymonosulfate (PMS) for the degradation of diclofenac (DCF) in water in the presence of light illumination. Compared with single photocatalytic process by T/CN (0.040/min) and with pure g-C3N4 nanosheets in PMS system (0.071/min), 5.0 and 3.0 times enhanced activities were achieved in the T/CN-PMS system at optimum Ti3C2 (1.0 wt%) loading under light illumination (0.21/min). Moreover, the decomposing processes of DCF in T/CN-PMS system were applicable in a wide initial pH range (3∼14), therefore, overcoming the limitation of pH dependence in traditional PMS system. Based on the synergistic effect of photocatalysis and PMS oxidation processes, the 1O2 was generated as primary reactive species for the removal of DCF in T/CN-PMS system. The DCF degradation mechanism was further proposed through the results of liquid chromatography-mass spectrometry (LC-MS) and density functional theory (DFT) calculations.

Degradation of imidacloprid by UV-activated persulfate and peroxymonosulfate processes: Kinetics, impact of key factors and degradation pathway.

UV-activated persulfate (UV/PS) and peroxymonosulfate (UV/PMS) processes as alternative methods for removal of imidacloprid (IMP) were conducted for the first time. The reaction rate constants between IMP and the sulfate or hydroxyl radical were calculated as 2.33×109  or 2.42×1010 M-1 s-1, respectively. The degradation of IMP was greatly improved by UV/PS and UV/PMS compared with only UV or oxidant. At any given dosage, UV/PS achieved higher IMP removal rate than UV/PMS. The pH range affecting the degradation in the UV/PS and UV/PMS systems were different in the ranges of 6-8 and 9 to 10. SO42-, F- and NO3- had no obvious effect on the degradation in the UV/PS and UV/PMS systems. CO32- and PO43- inhibited the degradation of IMP in the UV/PS system, while they enhanced the degradation in the UV/PMS system. Algae organic matters (AOM) were used to consider the impact of the degradation of IMP for the first time. The removal of IMP were restrained by both AOM and natural organic matters. The higher removal rate of IMP demonstrated that both UV/PS and UV/PMS were suitable for treating the water containing IMP, while UV/PS was cost-effective than UV/PMS based on the total cost calculation. Finally, the degradation pathways of IMP were proposed.

Parenteral nutrition and oxidant stress in the newborn: A narrative review.

There is strong evidence that oxidant molecules from various sources contaminate solutions of parenteral nutrition following interactions between the mixture of nutrients and some of the environmental conditions encountered in clinical practice. The continuous infusion of these organic and nonorganic peroxides provided us with a unique opportunity to study in cells, in vascular and animal models, the mechanisms involved in the deleterious reactions of oxidation in premature infants. Potential clinical impacts of peroxides infused with TPN include: a redox imbalance, vasoactive responses, thrombosis of intravenous catheters, TPN-related hepatobiliary complications, bronchopulmonary dysplasia and mortality. This is a narrative review of published data.

Visible-light-driven photocatalytic activation of peroxymonosulfate by Cu2(OH)PO4 for effective decontamination.

The advanced oxidation process (AOP) based on SO4- radicals draws an increasing interest in water and wastewater treatment. Producing SO4- radicals from the activation of peroxymonosulfate (PMS) by transition metal ions or oxides may be problematic due to high operational cost and potential secondary pollution caused by metal leaching. To address this challenge, the present study reports the efficient production of SO4- radicals through visible-light-driven photocatalytic activation (VL-PCA) of PMS by using Cu2(OH)PO4 single crystal for enhanced degradation of a typical recalcitrant organic pollutant, i.e., 2,4-dichlorophenol (2,4-DCP). It took only 7 min to achieve almost 100% removal of 2,4-DCP in the Cu2(OH)PO4/PMS system under visible-light irradiation and pH-neutral condition. The 2,4-DCP degradation was positively correlated to the amount of Cu2(OH)PO4 and PMS. Both OH and SO4- radicals were responsible for enhanced degradation performance, indicated by radical scavenger experiments and electron spin resonance (ESR) measurements. The Cu2(OH)PO4 single crystal exhibited good cyclic stability and negligible metal leaching. According to density functional theory (DFT) calculations, the visible-light-driven transformation of two copper states between trigonal bipyramidal sites and octahedral sites in the crystal structure of Cu2(OH)PO4 facilitates the generation of OH and SO4- radicals from the activation of PMS and cleavage of O-O bonds. This study provides the proof-in-concept demonstration of activation of PMS driven by visible light, making the SO4- radicals-based AOPs much easier, more economical and more sustainable in engineering applications for water and wastewater treatment.

Oxidation of azo and anthraquinonic dyes by peroxymonosulphate activated by UV light.

The photochemical degradation of two azo and two anthraquinonic dyes was performed using potassium peroxymonosulphate (Oxone®) activated by UV radiation. The fast decolourization of all dyes was observed within 6 min of UV irradiation, with corresponding dye decays higher than 80%. The kinetic rate constants of the dyes' decay were determined, along with the energetic efficiency of the photochemical treatment, taking into account the influence of a few anions commonly present in real wastewaters (i.e., chloride, nitrate, carbonate/bicarbonate and phosphate ions). Chloride and carbonate/bicarbonate ions enhanced dye degradation, whereas phosphate ions exerted an inhibitory effect, and nitrates did not have a predictable influence. The dye decolourization was not associated with efficient mineralization, as suggested by the lack of a significant total organic carbon (TOC) decrease, as well as by the low concentrations of a few detected low molecular weight by-products, including nitrate ions, formaldehyde and organic acids. High molecular weight by-products were also detected by mass spectrometry analysis. The investigated process may be proposed as a convenient pre-treatment to help dye degradation in wastewater during combined treatment methods.

Removal of trace level amounts of twelve sulfonamides from drinking water by UV-activated peroxymonosulfate.

Trace levels of residual antibiotics in drinking water may threaten public health and become a serious problem in modern society. In this work, we investigated the degradation of twelve sulfonamides (SAs) at environmentally relevant trace level concentrations by three different methods: ultraviolet (UV) photolysis, peroxymonosulfate (PMS) oxidation, and UV-activated PMS (UV/PMS). Sulfaguanidine, sulfadiazine, sulfamerazine, sulfamethazine, sulfathiazole, sulfamethoxydiazine, and sulfadimethoxine were be effectively removed by direct UV photolysis and PMS oxidation. However, sulfanilamide, sulfamethizole, sulfamethoxazole, sulfisoxazole, and sulfachloropyridazine were not completely degraded, despite prolonging the UV irradiation time to 30min or increasing the PMS concentration to 5.0mg·L-1. UV/PMS provided more thorough elimination of SAs, as demonstrated by the complete removal of 200ng·L-1 of all SAs within 5min at an initial PMS concentration of 1.0mg·L-1. UV/PMS promoted SA decomposition more efficiently than UV photolysis or PMS oxidation alone. Bicarbonate concentration and pH had a negligible effect on SA degradation by UV/PMS. However, humic acid retarded the process. Removal of 200ng·L-1 of each SA from a sample of sand-filtered effluent from a drinking water treatment plant (DWTPs) was quickly and completely achieved by UV/PMS. Meanwhile, about 41% of the total organic carbon (TOC) was eliminated. Scavenging experiments showed that sulfate radical (SO4-) was the predominant species involved in the degradation. It is concluded that UV/PMS is a rapid and efficient method for removing trace-level SAs from drinking water.

Catalytic degradation of Acid Orange 7 by manganese oxide octahedral molecular sieves with peroxymonosulfate under visible light irradiation.

In this paper, the photodegradation of Acid Orange 7 (AO7) in aqueous solutions with peroxymonosulfate (PMS) was studied with manganese oxide octahedral molecular sieves (OMS-2) as the catalyst. The activities of different systems including OMS-2 under visible light irradiation (OMS-2/Vis), OMS-2/PMS and OMS-2/PMS/Vis were evaluated. It was found that the efficiency of OMS-2/PMS was much higher than that of OMS-2/Vis and could be further enhanced by visible light irradiation. The catalyst also exhibited stable performance for multiple runs. Results from ESR and XPS analyses suggested that the highly catalytic activity of the OMS-2/PMS/Vis system possible involved the activation of PMS to sulfate radicals meditated by the redox pair of Mn(IV)/Mn(III) and Mn(III)/Mn(II), while in the OMS-2/PMS system, only the redox reaction between Mn(IV)/Mn(III) occurred. Several operational parameters, such as dye concentration, catalyst load, PMS concentration and solution pH, affected the degradation of AO7.

Carbohydrate radicals: from ethylene glycol to DNA strand breakage.

Radiation-induced DNA strand breakage results from the reactions of radicals formed at the sugar moiety of DNA. In order to elucidate the mechanism of this reaction investigations were first performed on low molecular weight model systems. Results from studies on deoxygenated aqueous solutions of ethylene glycol, 2-deoxy-d-ribose and other carbohydrates and, more relevantly, of d-ribose-5-phosphate have shown that substituents can be eliminated from the ß-position of the radical site either proton and base-assisted (as in the case of the OH substituent), or spontaneously (as in the case of the phosphate substituent). In DNA the C(4') radical undergoes strand breakage via this type of reaction. In the presence of oxygen the carbon-centred radicals are rapidly converted into the corresponding peroxyl radicals. Again, low molecular weights models have been investigated to elucidate the key reactions. A typical reaction of DNA peroxyl radicals is the fragmentation of the C(4')-C(S') bond, a reaction not observed in the absence of oxygen. Although OH radicals may be the important direct precursors of the sugar radicals of DNA, results obtained with poly(U) indicate that base radicals may well be of even greater importance. The base radicals, formed by addition of the water radicals (H and OH) to the bases would in their turn attack the sugar moiety to produce sugar radicals which then give rise to strand breakage and base release. For a better understanding of strand break formation it is therefore necessary to investigate in more detail the reactions of the base radicals. For a start, the radiolysis of uracil in oxygenated solutions has been reinvestigated, and it has been shown that the major peroxyl radical in this system undergoes base-catalysed elimination of [Formula: see text], a reaction that involves the proton at N(l). In the nucleic acids the pyrimidines are bound at N(l) to the sugar moiety and this type of reaction can no longer occur. Therefore, with respect to the nucleic acids, pyrimidines are good models only in acid solutions where the [Formula: see text] elimination reaction is too slow to compete with the bimolecular reactions of the peroxyl radicals. Moreover, the long lifetime of the radical sites on the nucleic acid strand may allow reactions to occur which are kinetically of first order, and which cannot be studied in model systems at ordinary dose rates. It is therefore suggested to extend model system studies to low dose rates and to oligonucleo-tides. Such studies might eventually reveal the key reactions in radical-induced DNA degradation.

Synthesis, photochemistry, DNA cleavage/binding and cytotoxic properties of fluorescent quinoxaline and quinoline hydroperoxides.

Novel fluorescent quinoxaline and quinoline hydroperoxides were shown to perform dual role as both fluorophores for cell imaging and photoinduced DNA cleaving agents. Photophysical studies of newly synthesized quinoxaline and quinoline hydroperoxides showed that they all exhibited moderate to good fluorescence. Photolysis of quinoxaline and quinoline hydroperoxides in acetonitrile using UV light above 350nm resulted in the formation of corresponding ester compounds via γ-hydrogen abstraction by excited carbonyl chromophore. Single strand DNA cleavage was achieved on irradiation of newly synthesized hydroperoxides by UV light (⩾350nm). Both hydroxyl radicals and singlet oxygen were identified as reactive oxygen species (ROS) responsible for the DNA cleavage. Further, we showed quinoline hydroperoxide binds to ct-DNA via intercalative mode. In vitro biological studies revealed that quinoline hydroperoxide has good biocompatibility, cellular uptake property and cell imaging ability. Finally, we showed that quinoline hydroperoxide can permeate into cells efficiently and may cause cytotoxicity upon irradiation by UV light.

Ciprofloxacin oxidation by UV-C activated peroxymonosulfate in wastewater.

This work aimed at demonstrating the advantages to use sulfate radical anion for eliminating ciprofloxacin residues from treated domestic wastewater by comparing three UV-254nm based advanced oxidation processes: UV/persulfate (PDS), UV/peroxymonosulfate (PMS) and UV/H2O2. In distilled water, the order of efficiency was UV/PDS>UV/PMS>UV/H2O2 while in wastewater, the most efficient process was UV/PMS followed by UV/PDS and UV/H2O2 mainly because PMS decomposition into sulfate radical anion was activated by bicarbonate ions. CIP was fully degraded in wastewater at pH 7 in 60min for a [PMS]/[CIP] molar ratio of 20. Nine transformation products were identified by liquid chromatography-high resolution-mass spectrometry allowing for the establishment of degradation pathways in the UV/PMS system. Sulfate radical anion attacks prompted transformations at the piperazinyl ring through a one electron oxidation mechanism as a major pathway while hydroxyl radical attacks were mainly responsible for quinolone moiety transformations as a minor pathway. Sulfate radical anion generation has made UV/PMS a kinetically effective process in removing ciprofloxacin from wastewater with the elimination of ciprofloxacin antibacterial activity.

High-throughput screening system for identifying phototoxic potential of drug candidates based on derivatives of reactive oxygen metabolites.

PURPOSE: The present study aimed to develop a high-throughput screening strategy for predicting the phototoxic potential of pharmaceutical substances, using a derivatives-of-reactive-oxygen-metabolites (D-ROM) assay. METHODS: The assay conditions of the D-ROM assay were optimized with a focus on screening run time, sensitivity, solvent system, and reproducibility. The phototoxic potentials of 25 model compounds were assessed by the D-ROM assay, as well as by other screening systems for comparison, including the reactive oxygen species (ROS) assay, the DNA-photocleavage assay, and the 3T3 neutral red uptake phototoxicity test (3T3 NRU PT). RESULTS: Some phototoxic drugs tended to yield D-ROM when exposed to simulated sunlight (250 W/m(2)), whereas D-ROM generation was negligible for non-phototoxic chemicals. Compared with the ROS assay, the assay procedure for the D-ROM assay was highly simplified with a marked reduction in screening run time. Comparative experiments also demonstrated that D-ROM data were related to the outcomes of the DNA-photocleavage assay and the 3T3 NRU PT, with prediction accuracies of 76 and 72%, respectively. CONCLUSION: The D-ROM assay has potential for identifying the phototoxic potential of a large number of new drugs as a 1st screening system in the early stages of drug discovery.

Chlorine-catalyzed ozone destruction: Cl atom production from ClOOCl photolysis.

Recent laboratory measurements of the absorption cross sections of the ClO dimer, ClOOCl, have called into question the validity of the mechanism that describes the catalytic removal of ozone by chlorine. Here we describe direct measurements of the rate-determining step of that mechanism, the production of Cl atoms from the photolysis of ClOOCl, under laboratory conditions similar to those in the stratosphere. ClOOCl is formed in a cold-temperature flowing system, with production initiated by a microwave discharge of Cl(2) or photolysis of CF(2)Cl(2). Excimer lasers operating at 248, 308, and 352 nm photodissociate ClOOCl, and the Cl atoms produced are detected with time-resolved atomic resonance fluorescence. Cl(2), the primary contaminant, is measured directly for the first time in a ClOOCl cross section experiment. We find the product of the quantum yield of the Cl atom production channel of ClOOCl photolysis and the ClOOCl absorption cross section, (phisigma)(ClOOCl) = 660 +/- 100 at 248 nm, 39.3 +/- 4.9 at 308 nm, and 8.6 +/- 1.2 at 352 nm (units of 10(-20) cm(2) molecule(-1)). The data set includes 468 total cross section measurements over a wide range of experimental conditions, significantly reducing the possibility of a systematic error impacting the results. These new measurements demonstrate that long-wavelength photons (lambda = 352 nm) are absorbed by ClOOCl directly, producing Cl atoms with a probability commensurate with the observed rate of ozone destruction in the atmosphere.

In vitro evaluation of the effectiveness of bleaching agents activated by different light sources.

PURPOSE: This study evaluated the efficacy of tooth whitening and color stability at different time periods after treatment. MATERIALS AND METHODS: Blocks obtained from human molars were divided into 15 groups (n = 5) by bleaching agents: 35% hydrogen peroxide (Whiteness HP and Opalescence Xtra) and 37% carbamide peroxide (Whiteness Super); and light sources: halogen lamp and plasma arc lamp (bleach mode), LED/diode laser, argon laser, and no light source. The efficacy of bleaching was measured using a spectrophotometer. Six bleaching sessions were performed (times 1 to 6). The specimens were submitted to another reading 7, 15, and 30 days after the end of bleaching (times 7, 8, and 9). The results were submitted to ANOVA followed by Tukey test and polynomial regression (p < 0.05). RESULTS: Carbamide peroxide significantly differed from hydrogen peroxide, presenting low reflectance values. Activated versus non-activated bleaching did not differ significantly for any gel tested, except for Whiteness HP activated by argon laser, which presented the lowest mean reflectance values. The results obtained with hydrogen peroxide revealed a decrease in reflectance values one month after the end of treatment. For carbamide peroxide, this decrease was not observed. CONCLUSION: The halogen lamp presented the same or higher efficacy than non-activated bleaching, which had a longer gel contact period. When hydrogen peroxide was used, a decrease in reflectance values was observed 30 days after the end of bleaching.

Mechanism of the reaction of radicals with peroxides and dimethyl sulfoxide in aqueous solution.

The reactions of methyl and methylperoxyl radicals derived from dimethyl sulfoxide (DMSO) with hydrogen peroxide, peroxymonocarbonate (HCO4 (-)), and persulfate were studied. The major reaction observed for the hydroperoxides was the abstraction of the hydrogen atom by the radicals. The radicals interact with a lone pair of electrons on the peroxide to produce methanol and formaldehyde. Furthermore, the results indicate that in RO2H and RO2R', electron-withdrawing groups cause a considerable increase in the reactivity of the peroxides towards the radicals and not only towards nucleophiles. The HO2 (.)/O2 (.-) and CO3 (.-) radicals react with DMSO to produce methyl radicals. Thus, the formation of the (.)CH3 radicals in the presence of DMSO is not proof of the formation of the (.)OH radicals in the system. These reactions must be considered when radical processes, such as in biological and catalytic systems, are studied. Especially, the plausible role of HCO4 (-) ions in biological systems as a source of oxidative stress cannot be overlooked.

Enhanced radical-scavenging activity of naturally-oriented artepillin C derivatives.

More than two-fold augmentation in the radical-scavenging activity of artepillin C could be achieved via altering the O-H bond dissociation enthalpy of artepillin C by means of structural modifications.

Oxidation and inactivation of SERCA by selective reaction of cysteine residues with amino acid peroxides.

The oxidative modification of proteins plays an important role in a wide range of pathological processes and aging. Proteins are modified by numerous biologic oxidants including hydrogen peroxide, peroxynitrite, singlet oxygen, and oxygen- and nitrogen-centered radicals. More recently, an additional class of physiologically important oxidants has been identified, peptide and protein peroxides. The latter react quite rapidly and selectively with protein cysteine residues. The sarco/endoplasmic reticulum Ca-ATPase (SERCA) is reversibly regulated through NO-dependent S-glutathiolation of specific cysteine residues. The irreversible oxidation of these cysteine residues could, therefore, impair NO-dependent muscle relaxation. Here, we show that specific protein-derived (amino acid) peroxides react selectively with a subset of the 22 reduced cysteine residues of SERCA1, including a peptide-containing Cys674 and Cys675, where Cys674 (in SERCA2) represents one of the targets for NO-dependent S-glutathiolation. Out of 11 tested amino acid, peptide, and protein peroxides, those derived from free tryptophan and free tyrosine showed the highest reactivity towards SERCA, while no oxidation under similar experimental conditions was detected through hydrogen peroxide. Among the peroxides from tryptophan, those of free tryptophan showed a significantly higher reactivity as compared to those from N- and C-terminally blocked tryptophan. Quantitative HPLC-MS/MS analysis demonstrated that the highest reactivity of the tryptophan-derived peroxides was observed for Cys774 and Cys938, cysteine residues, which are embedded within the transmembrane domains of SERCA1. This unusual reactivity of transmembrane domains cannot be solely rationalized by the hydrophobicity of the oxidant, as the peroxide from dl-tryptophan shows considerable higher reactivity as compared to the one derived from N-acetyl-tryptophan methyl ester. Our data demonstrate a potential role of peptide- and protein-derived peroxides as important mediators of oxidative stress in vivo, which may cause a selective oxidation of Cys residues leading to inactivation of membrane proteins.

Study of benzylperoxy radical using laser photolysis: ultraviolet spectrum, self-reaction, and reaction with HO2 kinetics.

The ultraviolet absorption spectrum of benzylperoxy radical and the kinetics of the reactions 2C(6)H(5)CH(2)O(2) --> products (I) and C(6)H(5)CH(2)O(2) + HO(2) --> products (II) are studied. Experiments are carried out using the laser photolysis technique with time-resolved UV-visible absorption spectroscopy over the temperature range 298-353 K and the pressure range 50-200 Torr. The UV spectrum is determined relative to the known cross section of the ethylperoxy radical C(2)H(5)O(2) at 250 nm. Using factor analysis, the spectrum obtained is refined and the concentrations of the main absorbing species are extracted. The kinetic parameters are determined by analyzing and simulating the temporal profiles of the species concentrations and the experimental optical densities in the spectral region 220-280 nm. These are obtained using the recent UV spectra of the absorbing species existing in our mechanism. The Arrhenius expressions for reactions I and II are (cm(3).molecule(-1).s(-1)) k(I) = 2.50 x 10(-14)e(1562/)(T) and k(II) = 5.70 x 10(-14)e(1649/)(T). Our results are discussed and compared to literature data.

Pro-oxidant effects of extremely low frequency electromagnetic fields in the land snail Helix aspersa.

Pro-oxidant effects of extremely low frequency (ELF) 50-Hz magnetic fields were investigated in the land snail Helix aspersa exposed both in short-term laboratory treatments and under field conditions by maintaining the organisms in the proximity of a power line for up to 2 months. Oxidative perturbations were investigated as individual antioxidants (catalase, glutathione reductase, glutathione S-transferases, and total glutathione) and total scavenging capacity toward peroxyl radicals and hydroxyl radicals. Accumulation of lipid peroxidation products, destabilization of lysosomal membranes, and loss of DNA integrity were also evaluated as markers of cell damage. The overall results indicated an oxidative challenge caused by ELF magnetic fields with particularly prompt and sensitive responses for catalase, glutathione reductase, and the overall capability to neutralize peroxyl radicals. Cell injuries occurred to different extents according to duration and intensity of electromagnetic exposure and confirmed complex cause-effect relationships between pro-oxidant factors, efficiency of antioxidant defenses, and the onset of oxidative toxicity. This study highlights the importance of a multimarker approach for detecting a wide panel of biological responses, the necessity of investigating the long-term effects of early oxidative responses, and the role of ELF in enhancing susceptibility to other forms of pathologies or diseases.

Stable spiro-endoperoxides by sunlight-mediated photooxygenation of 1,2-O-alkylidene-5(E)-eno-5,6,8-trideoxy-alpha-D-xylo-oct-1,4-furano-7-uloses.

Sunlight-mediated photooxygenation of 3-O-acetyl and 3-O-methyl derivatives of 1,2-O-alkylidene-5(E)-eno-5,6,8-trideoxy-alpha-D-xylo-oct-1,4-furano-7-uloses (1a-e) in carbon tetrachloride solution gave stable 4,7-epidioxy derivatives in 4R (2a-e) and 4S (3a-e) configurations. The presence of an endo alkyl, on the 1,2-O-alkylidene group and its size, resulted in an increase of the yield of the 4S isomers. 3-O-acetyl derivatives yielded products as a mixture of C-7 anomers, whereas 3-O-methyl derivatives gave pure single stereoisomers.

Effect of light energy on peroxide tooth bleaching.

BACKGROUND: Light-activated bleaching is a method of tooth whitening. The authors conducted a study to compare the whitening effects and tooth temperature changes induced by various combinations of peroxide bleaches and light sources. METHODS: The authors randomly assigned 250 extracted human teeth halves into experimental groups (n = 10). A placebo gel (control), a 35 percent hydrogen peroxide or a 10 percent carbamide peroxide bleach was placed on the tooth surface and was irradiated with no light (control); a halogen curing light; an infrared, or IR, light; an argon laser; or a carbon dioxide, or CO2, laser. Color changes were evaluated immediately, one day and one week after treatment using a value-oriented shade guide and an electronic dental color analyzer. The outer enamel and inner dentin surface temperatures were monitored before and immediately after each 30-second application of light using a thermocouple thermometer. RESULTS: Color and temperature changes were significantly affected by an interaction of the bleach and light variables. The application of lights significantly improved the whitening efficacy of some bleach materials, but it caused significant temperature increases in the outer and inner tooth surfaces. The IR and CO2 laser lights caused the highest tooth temperature increases. CONCLUSIONS: Dentists performing an in-office bleaching technique with the use of an additional light source to accelerate tooth whitening should consider the specific bleaching agent being used, as well as the potential risks of heating teeth. CLINICAL IMPLICATIONS: A specific combination of bleach and light that demonstrates good color change and little temperature rise should be selected for in-office tooth bleaching.