Scavenging of superoxide anion radical and hydroxyl radical by novel thiazolyl‐thiazolidine‐2,4‐dione compounds

The antioxidant behavior of a series of new synthesized substituted thiazolyl‐thiazolidine‐2,4‐dione compounds (TZDs) was examined using chemiluminescence and electron paramagnetic resonance spin trapping techniques. 5,5‐Dimethyl‐1‐pyrroline‐N‐oxide (DMPO) was used as the spin trap. The reactivity of TZDs with superoxide anion radical (O) and hydroxyl radical (HO^?) was evaluated using potassium superoxide/18‐crown‐6 ether dissolved in dimethylsulfoxide, and the Fenton‐like reaction (Fe²⁺ + H₂O₂), respectively. The results showed that TZDs efficiently inhibited light emission from the O generating system at a concentration of 0.05–1 mmol L^?1 (5–94% reductions were found at 1 mmol L^?1 concentration). The TZD compounds showed inhibition of HO^?‐dependent DMPO–OH spin adduct formation from DMPO (the amplitude decrease ranged from 8 to 82% at 1 mmol L^?1 concentration). The findings showed that examined TZDs had effective activities as radical scavengers. Copyright © 2009 John Wiley & Sons, Ltd.     

Studies on the antioxidant activities of some new chromone compounds

Recent reviews evidence that the naturally occurring compounds containing the chromone skeleton exhibit antiradical activities, providing protection against oxidative stress. The antioxidant activities of 13 new synthesized chromonyl‐2,4‐thiazolidinediones, chromonyl‐2,4‐imidazolidinediones and chromonyl‐2‐thioxoimidzolidine‐4‐ones were evaluated using in vitro antioxidant assays, including superoxide anion radical (), hydroxyl radical (), 2,2‐diphenyl‐1‐picryl‐hydrazyl free radical (DPPH^?) scavenging capacity and total antioxidant capacity ferric ion reducing activity. Superoxide anion radical was produced using potassium superoxide/18‐crown‐6‐ether dissolved in dimethylsulfoxide, and the Fenton‐like reaction (Fe(II) + H₂O₂) was a generator of hydroxyl radicals. Chemiluminescence, spectrophotometry, electron paramagnetic resonance (EPR) and 5,5‐dimethyl‐1‐pyrroline‐N‐oxide (DMPO) as the spin trap were the measurement techniques. The results showed that the majority of the chromone derivatives tested showed a strong scavenging effect towards free radicals, similar to the chemiluminescence reaction with superoxide anion radical with a high activity, inhibition of the DMPO‐OOH radical EPR signal (24–58%), the DMPO‐OH radical EPR signal (4–75%) and DPPH radical EPR signal (6–100%) at 1 mmol/L. Several of the examined compounds exhibited the high reduction potentials. The results obtained show that the new synthesized chromone derivatives may directly scavenger reactive oxygen species and thus may play a protective role against oxidative damage. Copyright © 2014 John Wiley & Sons, Ltd.     

Studies on the antioxidant activity of some thiazolidinedione,imidazolidinedione and rhodanine derivatives having a flavone core

A series of flavonyl‐2,4‐thiazolidinedione, imidazolidinedione and rhodanine derivatives were tested for their antioxidant activity as scavengers of oxygen free radicals. Free radical scavenging activities, including superoxide anion radical , hydroxyl radical (HO^?) and 2,2′‐diphenyl‐1‐picrylhydrazyl free radical have been evaluated using chemiluminescence, electron paramagnetic resonance and spin trapping with 5,5‐dimethyl‐1‐pyrroline‐1‐oxide as a spin trap. Potassium superoxide in dimethylsulfoxide and 18‐crown‐6 ether were used for the production of . Hydroxyl radical was generated using the Fenton reaction. Ten of the eleven examined compounds exhibited decrease in chemiluminescence, but there were large differences in the decrease, ranging from 16% to 89%; also, two of these compounds increased light emission by about 200%. On the contrary, all compounds tested exhibited 30–68% scavenging HO^? and 25–96% scavenging the DPPH^? radical respectively. Possible mechanisms are proposed to explain the results. Copyright © 2014 John Wiley & Sons, Ltd.     

Hydroxyl and superoxide radical scavenging abilities of chromonyl‐thiazolidine‐2,4‐dione compounds

The oxygen free radical scavenging activities of 15 chromonyl‐thiazolidine‐2,4‐dione compounds (CTDs) were examined in chemical systems producing superoxide anion radicals, O (potasium superoxide–18‐crown‐6 ether–DMSO), and hydroxyl radicals, HO^? (a Fenton reaction: Fe(II)–H₂O₂–sodium trifluoroacetate, pH 6.15). Chemiluminescence and electron spin resonance (ESR) spectroscopy using 5,5‐dimethyl‐1‐pyrroline‐1‐oxide (DMPO) as spin trap were applied to evaluate antioxidant behaviour of CTDs towards the oxygen radicals. The results indicated that 11 of the 15 tested compounds showed a significant inhibitory effect on the chemiluminescence generated from the O‐generating system, ranging from 41 to 86%, and 13 CTDs quenched the ESR signal of the DMPO–OH spin adduct by 33–86%, at a concentration of 1 mmol L^?1. Our findings demonstrate that CTDs could be good free radical scavengers. Copyright © 2008 John Wiley & Sons, Ltd.     

6‐Methyl 3‐chromonyl 2,4‐thiazolidinedione/2,4‐imidazolidinedione/2‐thioxo‐imidazolidine‐4‐one compounds: novel scavengers of reactive oxygen species

The benefits of antioxidants on human health are usually ascribed to their potential ability to remove reactive oxygen species providing protection against oxidative stress. In this paper the free radicals scavenging activities of nine 6‐methyl 3‐chromonyl derivatives (CMs) were evaluated for the first time by the chemiluminescence, electron paramagnetic resonance, spin trapping and 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH^?) methods. The total antioxidant capacity was also measured using a ferric‐ferrozine reagent. Compounds having a hydrogen atom at the N3‐position of the β‐ring were effective in quenching CL resulted from the KO₂/18‐crown‐6‐ether system (a source of superoxide anion radical, ) in a dose‐dependent manner over the range of 0.05–1 mmol/L [IC₅₀ ranged from 0.353 (0.04) to 0.668 (0.05) mmol/L]. The examined compounds exhibited a significant scavenging effect towards hydroxyl radicals (HO^? HO^?), produced by the Fenton reaction, and this ranged from 24.0% to 61.0%, at the concentration of 2.5 mmol/L. Furthermore, the compounds examined were also found to inhibit DPPH^? and this ranged from 51.9% to 97.4% at the same concentration. In addition, the use of the total antioxidant capacity assay confirmed that CM compounds are able to act as reductants. According to the present study, CM compounds showed effective in vitro free radical scavenging activity and may be considered as potential therapeutics to control diseases of oxidative stress‐related etiology. Copyright © 2013 John Wiley & Sons, Ltd.     

Scavenging capacities of some thiazolyl thiazolidine‐2,4‐dione compounds on superoxide radical,hydroxyl radical,and DPPH radical

The scavenging effects of eighteen thiazolyl thiazolidine‐2,4‐dione compounds (TTCs) on superoxide radical , hydroxyl radical HO^?, and 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH^?) radical were evaluated by the chemiluminescence technique, electron spin resonance spectrometry (ESR) and visible spectrophotometry, respectively. The examined compounds were shown to have 27–59% scavenging ability, 19–69% HO^? scavenging activity and 2–32% DPPH^? scavenging ability. This property of the tested compound seems to be important in the prevention of various diseases of free radicals etiology. Copyright © 2009 John Wiley & Sons, Ltd.     

Superoxide anion radical scavenging property of catecholamines

The direct effect of the four catecholamines (adrenaline, noradrenaline, dopamine and isoproterenol) on superoxide anion radicals () was investigated. The reaction between 18‐crown‐6‐ether and potassium superoxide in dimethylsulfoxide was used as a source of . The reactivity of catecholamines with was examined using chemiluminescence, reduction of nitroblue tetrazolium and electron paramagnetic resonance spin‐trapping techniques. 5,5‐Dimethyl‐1‐pyrroline‐N‐oxide was included as the spin trap. The results showed that the four catecholamines were effective and efficient in inhibiting chemiluminescence accompanying the potassium superoxide/18‐crown‐6‐ether system in a dose‐dependent manner over the range 0.05–2 mm in the following order: adrenaline > noradrenaline > dopamine > isoproterenol, with, IC₅₀ = 0.15 ± 0.02 mm 0.21 ± 0.03 mm , 0.27 ± 0.03 mm and 0.50 ± 0.04 mm , respectively. The catecholamines examined also exhibited a strong scavenging effect towards when evaluated this property by the inhibition of nitroblue tetrazolium reduction (56–73% at 1 m concentration). A very similar capacity of scavenging was monitored in the 5,5‐dimethyl‐1‐pyrroline‐N‐oxide spin‐trapping assay. The results suggest that catecholamines tested may involve a direct effect on scavenging radicals. Copyright © 2013 John Wiley & Sons, Ltd.     

Evaluation of the antioxidant activity of tetracycline antibiotics in vitro

Tetracyclines are the second most common antibiotic family in medicine usage. These antibiotics exhibit antioxidant potential; however, the exact mechanism remains unclear. The antiradical activity of the seven tetracyclines (TCs; tetracycline, chlortetracycline, oxytetracycline, doxocycline, methacycline, demeclocycline, minocycline) was determined using the free radical 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH^?) and hydroxyl radicals (HO^?) generated in a Fenton reaction. Electron spin resonance (ESR), ESR spin‐trapping, chemiluminescence and spectrophotometry techniques were applied. It was found that the TCs showed high DPPH antiradical activity in the range 26–96% at 2.5 mmol/L concentration. The second‐order rate constants for the reaction between HO^? and TCs were calculated, in the range (3.6–9.6) × 10⁹ L/mol/s. The tetracycline compounds also exhibited a strong decrease in light emission (range 61–85% at concentration of 1 mmol/L). This study also showed that TCs promote the generation of singlet oxygen in the presence of and Fe(II)/Fe(III) ions. Our findings suggest direct scavenging activity of the examined tetracyclines towards free radicals, and may be relevant to therapeutic strategy. Copyright © 2011 John Wiley & Sons, Ltd.     

Radical scavenging ability of some compounds isolated from Piper cubeba towards free radicals

The purpose of this study was to identify the antioxidant activity of 16 compounds isolated from Piper cubeba (CNCs) through the extent of their capacities to scavenge free radicals, hydroxyl radical (HO^?), superoxide anion radical () and 2,2‐diphenyl‐1‐picrylhydrazyl radical (DPPH^?), in different systems. Electron paramagnetic resonance (EPR) and 5,5‐dimethyl‐1‐pyrroline‐N‐oxide, DMPO, as the spin trap, and chemiluminescence techniques were applied. Using the Fenton‐like reaction [Fe(II) + H₂O₂], CNCs were found to inhibit DMPO? OH radical formation ranging from 5 to 57% at 1.25 mmol L^?1 concentration. The examined CNCs also showed a high DPPH antiradical activity (ranging from 15 to 99% at 5 mmol L^?1 concentration). Furthermore, the results indicated that seven of the 16 tested compounds may catalyse the conversion of superoxide radicals generated in the potassium superoxide/18‐crown‐6 ether system, thus showing superoxide dismutase‐like activity. The data obtained suggest that radical scavenging properties of CNCs might have potential application in many plant medicines. Copyright © 2010 John Wiley & Sons, Ltd.     

Energy transfer rate and electron–phonon coupling properties in Eu3+‐doped nanophosphors

A series of controllable emissions SrWO₄:Eu³⁺ and charge‐compensated SrWO₄: (m = 0.01 or 0.20) phosphors was successfully prepared via a simple co‐precipitation method. The energy transfer mechanism was studied based on the Huang's theory. A low magnitude of Huang‐Rhys factor (10^?2) was calculated using phonon sideband spectra. The Judd–Ofelt parameters Ω_λ (λ = 2, 4 and 6) of Eu³⁺‐activated SrWO₄ doped with charge compensation were obtained. The calculated Commission Internationale de l'Eclairage chromaticity coordinates were found to be about (0.67, 0.33) for SrWO₄: and charge‐compensated SrWO₄: phosphors, which coincided with the National Television Standard Committee system standard values for red. A white light emission was obtained under 362 nm excitation. The correlated color temperature was computed by a simple equation to characterize light sources. Thus, warm white light‐emitting diodes with higher Ra can be constructed by combining as‐prepared high efficiency, low correlated color temperature and high color purity phosphor.     

Characterization of the superoxide anion radical scavenging activity by tetracycline antibiotics in aprotic media

The tetracycline family antibiotics are widely used as human and veterinary treatments. The drugs are effective as antibiotics and also show antimicrobial and non‐microbial action. However, the antioxidant properties of tetracyclines have not been characterized in aprotic media. To better understand their biological functions, the in vitro superoxide anion radical () scavenging activities of tetracycline, chlortetracycline, oxytetracycline, doxycycline and methacycline were characterized, along with a very efficient scavenger, tiron, in dimethyl sulphoxide (DMSO), using ultra‐weak chemiluminescence (CL). We found that tetracycline, chlortetracycline and doxycycline efficiently inhibited CL from the ‐generating system at concentration levels of 0.02–1.0 mmol/L. Methacycline and oxytetracycline were the scavengers at concentration levels of 0.01–0.1 mmol/L, whereas when their concentration was lowered the drugs were capable of generating , leading to CL enhancement. For all the data obtained in this study, the scavenging activity for the compounds tested decreased in the following order: tetracycline > doxycycline > chlortetracycline > tiron methacycline > oxytetracycline. These results indicate that the tetracycline drugs directly alter redox chemistry in aprotic media. Copyright © 2011 John Wiley & Sons, Ltd.     

4‐alkoxyethoxy‐N‐octadecyl‐1,8‐naphthalimide fluorescent sensor for human serum albumin and other major blood proteins: design,synthesis and solvent effect

A series of 4‐alkoxyethoxy‐N‐octadecyl‐1,8‐naphthalimides with intense blue fluorescence were designed and synthesized as polarity and spectrofluorimetric probes for the determination of proteins. In solvents of different polarities, the Stokes shifts of two dyes increased with increasing solvent polarity and fluorescence quantum yields decreased significantly, suggesting that electronic transiting from ground to excited states was π–π^* in character. Dipole moment changes were estimated from solvent‐dependent Stokes shift data using a solvatochromic method based on bulk solvent polarity functions and the microscopic solvent polarity parameter (). These results were generally consistent with semi‐empirical molecular orbital calculations and were found to be quite reliable based on the fact that the correlation of the solvatochromic Stokes shifts with was superior to that obtained using bulk solvent polarity functions. Fluorescence data revealed that the fluorescence quenching of human serum albumin (HSA) by dyes was the result of the formation of a Dye–HSA complex. The method was applied to the determination of total proteins (HSA + immunoglobulins) in human serum samples and results were in good agreement with those reported by the research institute. Copyright © 2012 John Wiley & Sons, Ltd.     

Radical‐scavenging activity of penicillin G,ampicillin, oxacillin,and dicloxacillin

The aim of this study was to characterize the antioxidant activity of penicillin G (PG), ampicillin (AMP), oxacillin (OX) and dicloxacillin (DOX) through their reactivity towards reactive oxygen species (superoxide anion radical, ; hydroxyl radical, HO^?; peroxyl radical, ROO^?; hydrogen peroxide, H₂O₂; DPPH^?) using various in vitro antioxidant assays with chemiluminescence (CL) and spectrophotometry as measurement techniques. In hydroxyl radical assays , PG, OX and AMP were found to inhibit the CL signal arising from the Fenton‐like reaction in a dose‐dependent manner with IC₅₀ = 0.480 ± 0.020 mM, IC₅₀ = 0.569 ± 0.021 mM, and IC₅₀ = 0.630 ± 0.019 mM, respectively. The highest reactivity of PG among the tested penicillins towards the HO radical was confirmed in the deoxyribose degradation assay. In the ABAP‐derived ROO radical assay, the radical‐scavenging ability of the test penicillins was in the following order: AMP > PG > DOX > OX. The number of reduced DPPH radicals by the drugs tested was <1 being the biggest for PG. The weak antioxidant capacity of the test penicillins was confirmed in the trolox antioxidant capacity assay (0.075 ± 0.004; 0.093 ± 0.006; 0.123 ± 0.005; 0.126 ± 0.004) for OX, AMP, DOX, PG, respectively. Use of luminol as a CL probe for estimation of penicillin reactivity towards H₂O₂ showed that only AMP was able to quench light emission; the remaining antibiotics demonstrated a strong enhancing effect. All the examined compounds showed a weak antioxidant potential when estimated using the ferric‐ferrozine assay. This study is the first to report the evaluation of test penicillins as antioxidants under the same reaction conditions.     

Flow‐injection chemiluminescence and electrogenerated chemiluminescence determination of escitalopram oxalate in tablet form

Rapid, simple and highly sensitive flow‐injection (FI) chemiluminescence (CL) and flow‐injection electrogenerated chemiluminescence (ECL) methods were developed for the determination of escitalopram oxalate (ESC), a selective serotonin reuptake inhibitor used as an antidepressant drug. The CL method was based on the CL reaction of ESC with acidic cerium(IV) and tris(2,2'‐bipyridyl)ruthenium(II) (Ru). Various experimental parameters affecting CL intensity were carefully studied and optimised. The method enabled the determination of 0.001‐50 µg/mL of ESC in bulk form with a correlation coefficient r = 0.9999. The limit of detection (LOD) was 0.01 ng/mL (S/N = 3). The ECL method was based on the ECL reaction of Ru with the drug in an acidic medium, permitting the determination of ESC in the range of 0.00001‐70 µg/mL with r = 0.9999 and LOD of 1 x 10^‐4 ng/mL. The proposed methods were applied to the determination of ESC in commercial tablets. The results were compared statistically with those obtained from a published method using t‐ and F‐tests. Copyright © 2012 John Wiley & Sons, Ltd.     

A kinetic treatment of stopped‐flow time courses for multiple chemiluminescence of the KIO4‐luminol‐Mn2+ system

Stopped‐flow time courses for chemiluminescence (CL) of the KIO₄‐luminol‐Mn²⁺system showed an instantaneous jump in initial signal followed by two distinct bands. A kinetic model of the form with ten adjustable parameters was proposed to account for CL intensity (I) versus time (t) profiles. The three terms in the model represent the three CL bands. Each band was comprised of a rise part and an exponential decay corresponding to the formation and deactivation of the CL emitter. CL bands could have originated from different CL pathways with the participation of reactive species such as O₂^?, ^?OH and ¹O₂ generated in the reactions involving IO₄^?, O₂ and Mn²⁺. Subsequent reactions of these reactive species with luminol induced CL emissions. Simulation parameters together with peak positions and intensities of the three CL bands were found to vary in different manners by changing conditions such as reagent concentration, pH and temperature. The temperature‐dependence of the rate constants yielded activation energies of 73.2 ± 2.8, 70.1 ± 2.4 and 67.2 ± 1.2 kJ?mol^‐1 for the three decay processes. Moreover, different substances exhibited a significant influence on the three CL bands and their simulation parameters. The numerous parameters and characteristics of CL emissions could serve as multiple probes for detecting analytes, making this system promising for potential analytical applications. Copyright © 2012 John Wiley & Sons, Ltd.     

NMR‐based conformation and dynamics of a tetrasaccharide‐repeating sulfated fucan substituted by different counterions

The sulfated fucan from the sea urchin Lytechinus variegatus is composed of the repetitive sequence [‐3)‐α‐l ‐Fucp‐4( )‐(1‐3)‐α‐l ‐Fucp‐2,4‐di( )‐(1‐3)‐α‐l ‐Fucp‐2( )‐(1‐3)‐α‐l ‐Fucp‐2( )‐(1‐]_n. Conformation (of rings and chains) and dynamics of this tetrasaccharide‐repeating sulfated fucan substituted by Na⁺, Ca²⁺, and Li⁺ as counterions have been examined through experiments of liquid‐state nuclear magnetic resonance spectroscopy. Scalar coupling and nuclear Overhauser effect (NOE)‐based data have confirmed that all composing units occur as ¹C₄ chair conformer regardless of the cation type, unit position within the repeating sequence, and sulfation type. Chain conformation determined by NOE signal pattern assisted by molecular modeling for a theoretical octasaccharide has shown a similar linear 3D structure for the three differently substituted forms. Data derived from spin‐relaxation measurements have indicated a contribution of counterion type to dynamics. The calcium‐based preparation has shown the highest mobility while the sodiated one showed the lowest mobility. The set of results from this work suggests that counterion type can affect the physicochemical properties of the structurally well‐defined sulfated fucan. The counterion effect seems to impact more on the structural mobility than on average conformation of the studied sulfated glycan in solution.     

Biophysical analysis of the dynamics of calmodulin interactions with neurogranin and Ca2+/calmodulin‐dependent kinase II

Calmodulin (CaM) functions depend on interactions with CaM‐binding proteins, regulated by . Induced structural changes influence the affinity, kinetics, and specificities of the interactions. The dynamics of CaM interactions with neurogranin (Ng) and the CaM‐binding region of /calmodulin‐dependent kinase II (CaMKII_290−309) have been studied using biophysical methods. These proteins have opposite dependencies for CaM binding. Surface plasmon resonance biosensor analysis confirmed that and CaM interact very rapidly, and with moderate affinity ( ). Calmodulin‐CaMKII_290−309 interactions were only detected in the presence of , exhibiting fast kinetics and nanomolar affinity ( ). The CaM–Ng interaction had higher affinity under ‐depleted ( and k ₋₁ = 1.6 × 10⁻¹s⁻¹) than ‐saturated conditions ( ). The IQ motif of Ng (Ng₂₇₋₅₀) had similar affinity for CaM as Ng under ‐saturated conditions ( ), but no interaction was seen under ‐depleted conditions. Microscale thermophoresis using fluorescently labeled CaM confirmed the surface plasmon resonance results qualitatively, but estimated lower affinities for the Ng ( ) and CaMKII_290−309( ) interactions. Although CaMKII_290−309 showed expected interaction characteristics, they may be different for full‐length CaMKII. The data for full‐length Ng, but not Ng₂₇₋₅₀, agree with the current model on Ng regulation of /CaM signaling.     

Spectroscopic investigations of Er(3+) :CdO-Bi(2) O(3) -B(2) O(3) glasses

This article reports on the optical properties of Er³⁺ ions doped CdO–Bi₂O₃–B₂O₃ (CdBiB) glasses. The materials were characterized by optical absorption and emission spectra. By using Judd–Ofelt theory, the intensity parameters Ω_λ (λ = 2, 4, 6) and also oscillatory strengths were calculated from the absorption spectra. The results were used to compute the radiative properties of Er³⁺:CdBiB glasses. The concentration quenching and energy transfer from Yb³⁺–Er³⁺ were explained. The stimulated emission cross‐section, full width at half maximum (FWHM) and FWHM × values are also calculated for all the Er³⁺:CdBiB glasses. Copyright © 2011 John Wiley & Sons, Ltd.     

Isotope labeling to determine the dynamics of metabolic response in CHO cell perfusion bioreactors using MALDI‐TOF‐MS

The steady‐state operation of Chinese hamster ovary (CHO) cells in perfusion bioreactors requires the equilibration of reactor dynamics and cell metabolism. Accordingly, in this work we investigate the transient cellular response to changes in its environment and their interactions with the bioreactor hydrodynamics. This is done in a benchtop perfusion bioreactor using MALDI‐TOF MS through isotope labeling of complex intracellular nucleotides (ATP, UTP) and nucleotide sugars (UDP‐Hex, UDP‐HexNAc). By switching to a ¹³C₆ glucose containing feed media during constant operation at 20 × 10⁶ cells and a perfusion rate of 1 reactor volume per day, isotopic steady state was studied. A step change to the ¹³C₆ glucose medium in spin tubes allowed the determination of characteristic times for the intracellular turnover of unlabeled metabolites pools, (≤0.56 days), which were confirmed in the bioreactor. On the other hand, it is shown that the reactor residence time (1 day) and characteristic time for glucose uptake (0.33 days), representative of the bioreactor dynamics, delayed the consumption of ¹³C₆ glucose in the bioreactor and thus the intracellular ¹³C enrichment. The proposed experimental approach allowed the decoupling of bioreactor hydrodynamics and intrinsic dynamics of cell metabolism in response to a change in the cell culture environment. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:1630–1639, 2017     

Nanodiamond‐Embedded p‐Type Copper(I) Oxide Nanocrystals for Broad‐Spectrum Photocatalytic Hydrogen Evolution

Copper(I) oxide (Cu₂O) is an attractive photocatalyst because of its abundance, low toxicity, environmental compatibility, and narrow direct band gap, which allows efficient light harvesting. However, Cu₂O exhibits poor photocatalytic performance and photostability because of its short electron diffusion length and low hole mobility. Here, it is demonstrated that nanodiamond (ND) can greatly improve the photocatalytic hydrogen evolution reaction (HER) of the p‐type photocatalyst Cu₂O nanocrystals by nanocomposition. Compared with pure Cu₂O nanocrystals, this composite shows a tremendous improvement in HER performance and photostability. HER rates of 100.0 mg NDs‐Cu₂O nanocrystals are 1597 and 824 under the simulated solar light irradiation (AM 1.5, 100 mW cm^?2) and visible light irradiation (420–760 nm, 77.5 mW cm^?2), respectively. The solar‐to‐hydrogen conversion efficiency of this composite is 0.85%, which is nearly ten times higher than that of pure Cu₂O. The quantum efficiency of the composite is high, with values of 0.17% at and 0.23% at . The broad spectral response of ND provides numerous carriers for the subsequent reactions. The electron‐donating ability of ND and suitable band structures of the two components promote electron injection from ND to Cu₂O. These results suggest the broad applicability of ND to ameliorate the photoelectric properties of semiconductors.