Novel potentiometric application for the determination of amprolium HCl in its single and combined dosage form and in chicken liver

Three novel amprolium HCl(AMP)-selective electrodes were investigated with 2-nitrophenyl octylether as a plasticiser in a polymeric matrix of polyvinyl chloride(PVC). Sensor I was fabricated using potassium tetrakis(4-chlorophenyl) borate(Tp ClPB) as a cationic exchanger without incorporation of an ionophore.Sensor Ⅱ used 2-hydroxy propyl β-cyclodextrin as an ionophore while sensor Ⅲ used p-tert-butylcalix[8]arene as an ionophore. The three proposed sensors showed Nernestian response slopes of 29.2±0.8,29.3±0.6 and 30.2±0.4 m V/decade over the concentration range from 10–6 to 10–2 mol L_(-1),respectively. The proposed sensors displayed useful analytical characteristics for the determination of AMP in bulk powder, different pharmaceutical formulations, and chicken liver and in the presence of ethopabate. The proposed method was validated according to ICH guidelines for its linearity, accuracy,precision and robustness.     

Electrosynthesis of hydroquinonethioethers using electrochemical oxidation of hydroquinone in the presence of thiouracil derivatives

Electrochemical oxidation of hydroquinone(1a) has been studied in the presence of 6-methyl-2-thiouracil(3a) and 6-propyl-2-thiouracil(3b) as nucleophiles in a DMF/buffer mixture,using cyclic voltammetry and controlled-potential coulometry.The results indicated that the p-quinone(2a) derived from 1a participates in a 1 4-Michael addition reaction with the thiouracil derivatives(3a–b) to form the corresponding hydroquinonethioether derivatives(6a–6b).The electrosynthesis of these compounds(6a–b) has been successfully performed on carbon rod electrodes in an undivided cell in good yield and purity.     

Porous core–shell CoMn_2O_4 microspheres as anode of lithium ion battery with excellent performances and their conversion reaction mechanism investigated by XAFS

Porous core–shell CoMn_2O_4 microspheres of ca. 3–5 μm in diameter were synthesized and served as anode of lithium ion battery. Results demonstrate that the as-synthesized CoMn_2O_4 materials exhibit excellent electrochemical properties. The CoMn_2O_4 anode can deliver a large capacity of 1070 mAh g~(–1) in the first discharge, a reversible capacity of 500 mAh g~(–1) after 100 cycles with a coulombic efficiency of 98.5%at a charge–discharge current density of 200 mA g~(–1), and a specific capacity of 385 mAh g~(–1) at a much higher charge-discharge current density of 1600 mA g~(–1). Synchrotron X–ray absorption fine structure(XAFS) techniques were applied to investigate the conversion reaction mechanism of the CoMn_2O_4 anode.The X–ray absorption near edge structure(XANES) spectra revealed that, in the first discharge–charge cycle, Co and Mn in CoMn_2O_4 were reduced to metallic Co and Mn when the electrode was discharged to 0.01 V, while they were oxidized respectively to CoO and MnO when the electrode was charged to 3.0 V.Experiments of both XANES and extended X–ray absorption fine structure(EXAFS) revealed that neither valence evolution nor phase transition of the porous core–shell CoMn_2O_4 microspheres could happen in the discharge plateau from 0.8 to 0.6 V, which demonstrates the formation of solid electrolyte interface(SEI) on the anode.     

RELATION BETWEEN GEOGRAPHICAL DISTRIBUTION OF LIVER CANCER AND CLIMATE-AFLATOXIN B_1 IN CHINA

This paper analyses, for the first time in China, the relationship between the data on climate (temperature and humidity) in the country, aflatoxin, hepatitis B and primary liver cancer mortality, by using the methods of geographical epidemiology and generalized factor analysis, and also approaches the characteristics of the geographical distribution of liver cancer in China from a climate-mould viewpoint. The authors come to the conclusion that climate is an important environmental condition that determines the differences in the distributions of liver cancer in different areas, and that aflatoxin B_1 is one of the main carcinogenic factors of liver cancer.     

Recent progress in fluorinated electrolytes for improving the performance of Li–S batteries

Lithium–sulfur(Li–S) batteries represent a "beyond Li-ion" technology with low cost and high theoretical energy density and should fulfill the ever-growing requirements of electric vehicles and stationary energy storage systems. However, the sulfur-based conversion reaction in conventional liquid electrolytes results in issues like the so-called shuttle effect of polysulfides and lithium dendrite growth, which deteriorate the electrochemical performance and safety of Li–S batteries. Optimization of conventional organic solvents(including ether and carbonate) by fluorination to form fluorinated electrolytes is a promising strategy for the practical application of Li–S batteries. The fluorinated electrolytes, owing to the high electronegativity of fluorine, possesses attractive physicochemical properties, including low melting point,high flash point, and low solubility of lithium polysulfide, and can form a compact and stable solid electrolyte interphase(SEI) with the lithium metal anode. Herein, we review recent advancements in the development of fluorinated electrolytes for use in Li–S batteries. The effect of solvent molecular structure on the performance of Li–S batteries and the formation mechanism of SEI on the cathode and anode sides are analyzed and discussed in detail. The remaining challenges and future perspectives of fluorinated electrolytes for Li–S batteries are also presented.     

Chemistry of1,16–Dihydroxytetraphenylene and 2,3,9,10–Tetrakis(trimethylsilyl)pentacene

Recently, four tetraphenylenols, as well as several non–substituted and substituted 2,3,9,10–tetrakis(trimethylsilyl)pentacenes were realized in our laboratories. In this presentation, the synthesis, hydrogen bonding properties, and chiral recognition studies of (S)–1,16–dihydroxytetraphenylene (1) and its (R)–enantiomer will be delineated. 1,16–Bis(diphenylphosphino)tetraphenylene (2) was also realized from 1 and was employed in the formation of a stable platinum complex. The synthesis…     

Identification of in vitro and in vivo metabolites of 12β-hydroxylveratroylzygadenine associated with neurotoxicity by using HPLC–MS/MS

Metabolism study was carried out on 12b-hydroxylveratroylzygadenine(VOG) that is a cevine-type alkaloid existing in Veratrum nigrum L. and a neurotoxic component. In order to better understand the potential mechanism of neurotoxicity of VOG, this study measured VOG-induced DNA damage in the cerebellum and cerebral cortex of mice after 7 days repetitive oral dose by using single-cell gel electrophoresis(Comet assay). High performance liquid chromatography-tandem mass spectrometry(LC–MS/MS) was developed and applied to separate and identify in vitro and in vivo metabolites of VOG for investing the possible relationship of metabolism and neurotoxicity. In vitro experiment was carried out using rat liver microsomes, while the in vivo study was conducted on rats. The obtained results indicated that VOG might cause DNA damage in cerebellum and cerebral cortex of mice in a dosedependent manner. Hydrolysis of ester bond and O-demethylation were proposed to be the main in vivo metabolic pathways of VOG, while the major in vitro metabolic pathways were proposed as methyl oxidation to aldehyde, dehydrogenation, hydrolysis of ester bond, hydrolysis of ester bond together with acetylation, and methoxylation. O-Demethylation reaction was likely to be associated with reactive oxygen species production, leading to the DNA damage.     

HPLC-DAD data coupled with second-order calibration method applied to food analysis: Simultaneous determination of six benzoylurea insecticides in various fruit samples by selecting time region of chromatogram

This work presents a novel application of second-order calibration based on self-weighted alternating trilinear decomposition(SWATLD)algorithm for analyzing the HPLC-DAD data.The proposed method makes it possible to simultaneously determine teflubenzuron,hexaflumuron,flufenoxuron,chlorfluazuron,diflubenzuron and benzoylurea in different fruit samples,i.e.pear,apple and banana,in the selected time region of chromatogram.The concentration,elution time and spectral information of these benzoylurea insecticides are selectively extracted from complex matrices even in the presence of unknown interferences.The root-mean-square error of prediction(RMSEP)and figures of merit,including sensitivity(SEN),selectivity(SEL)and limit of detection(LOD)are employed to access the performance of the method.The LODs obtained for these insecticides are within the range 0.017–0.26 ppm in pears,0.039–0.33 ppm in apples,0.041–0.44 ppm in bananas,respectively.Such a chemometrics-based protocol holds great potential to be extended as a promising alternative for more practical applications in food safety and quality monitoring.     

Transformations of N-arylpropiolamides to indoline-2,3-diones and acids via C≡C triple bond oxidative cleavage and C(sp^2)–H functionalization

A new palladium-catalyzed oxidative conversion of N-arylpropiolamides and H2O to various indoline-2,3-diones and acids through the C≡C triple bond cleavage and C(sp2)–H functionalization is described,which is promoted by a cooperative action of catalytic CuBr2,2,2,6,6-tetramethyl-1-piperidinyloxy(TEMPO)and O2.The method provides a practical tool for transformations of alkynes by means of a C–H functionalization strategy,which enables the formation of one C–C bond and multiple C–O bonds in a single reaction with high substrates compatibility and excellent functional group tolerance.     

Analysis of silicon-based integrated photovoltaic–electrochemical hydrogen generation system under varying temperature and illumination

Last decade witnessed tremendous research and development in the area of photo-electrolytic hydrogen generation using chemically stable nanostructured photo-cathode/anode materials. Due to intimately coupled charge separation and photo-catalytic processes, it is very difficult to optimize individual components of such system leading to a very low demonstrated solar-to-fuel efficiency(SFE) of less than 1%.Recently there has been growing interest in an integrated photovoltaic–electrochemical(PV–EC) system based on Ga As solar cells with the demonstrated SFE of 24.5% under concentrated illumination condition.But a high cost of Ga As based solar cells and recent price drop of poly-crystalline silicon(pc-Si) solar cells motivated researchers to explore silicon based integrated PV–EC system. In this paper a theoretical framework is introduced to model silicon-based integrated PV–EC device. The theoretical framework is used to analyze the coupling and kinetic losses of a silicon solar cell based integrated PV–EC water splitting system under varying temperature and illumination. The kinetic loss occurs in the range of 19.1%–27.9% and coupling loss takes place in the range of 5.45%–6.74% with respect to varying illumination in the range of 20–100 m W/cm~2. Similarly, the effect of varying temperature has severe impact on the performance of the system, wherein the coupling loss occurs in the range of 0.84%–21.51% for the temperature variation from 25 to 50 °C.     

A boronate-based ratiometric fluorescent probe for fast selective detection of peroxynitrite

Given that peroxynitrite (ONOO^?) is profoundly associated with health and diseases, a new fluorescent probe ABT was designed and synthesized for detection of ONOO^?. ABT manifested not only ratiometric fluorescence signals simultaneously in response to concentrations of ONOO^? (within 10?s), but high selectivity and sensitivity towards ONOO^? over other physiological relevant species (detection limit?=?26.3?nM). Moreover, ABT worked in a broad pH range with biological relevance. Thus, ABT could be used to quantitative detection of ONOO^? concentration and has the potential to efficiently monitor ONOO^? in living organisms.     

Fluorescent probe for the imaging of superoxide and peroxynitrite during drug-induced liver injury

Drug-induced liver injury (DILI) is an important cause of potentially fatal liver disease. Herein, we report the development of a molecular probe (LW-OTf) for the detection and imaging of two biomarkers involved in DILI. Initially, primary reactive oxygen species (ROS) superoxide (O₂˙⁻) selectively activates a near-infrared fluorescence (NIRF) output by generating fluorophore LW-OH. The C C linker of this hemicyanine fluorophore is subsequently oxidized by reactive nitrogen species (RNS) peroxynitrite (ONOO⁻), resulting in cleavage to release xanthene derivative LW-XTD, detected using two-photon excitation fluorescence (TPEF). An alternative fluorescence pathway can occur through cleavage of LW-OTf by ONOO⁻ to non-fluorescent LW-XTD-OTf, which can react further with the second analyte O₂˙⁻ to produce the same LW-XTD fluorescent species. By combining NIRF and TPEF, LW-OTf is capable of differential and simultaneous detection of ROS and RNS in DILI using two optically orthogonal channels. Probe LW-OTf could be used to detect O₂˙⁻ or O₂˙⁻ and ONOO⁻ in lysosomes stimulated by 2-methoxyestradiol (2-ME) or 2-ME and SIN-1 respectively. In addition, we were able to monitor the chemoprotective effects of tert-butylhydroxyanisole (BHA) against acetaminophen (APAP) toxicity in living HL-7702 cells. More importantly, TPEF and NIRF imaging confirmed an increase in levels of both O₂˙⁻ and ONOO⁻ in mouse livers during APAP-induced DILI (confirmed by hematoxylin and eosin (H&E) staining).

Drug-induced liver injury (DILI) is an important cause of potentially fatal liver disease.     

Aza-BODIPY based probe for photoacoustic imaging of ONOO− in vivo

The effective detecting ONOO⁻ variations in vivo is of great importance to well understand the complex pathophysiological processes. We reported here a photoacoustic (PA) probe AZB-1 for imaging ONOO⁻ in vivo. AZB-1 showed an originally strong photoacoustic signal at 660 nm. And its PA signal can be turned off by shutting the ICT effect caused by the conjugated electron withdrawing group at 2-position of the aza-BODIPY core. Moreover, the probe was successfully employed to imaging ONOO⁻ variations in inflammatory mice models. Wisely utilized this strategy may serve as powerful platforms for the preparation of novel PA chemosensors.     

Enzyme-activated near-infrared fluorogenic probe with high-efficiency intrahepatic targeting ability for visualization of drug-induced liver injury

Hepatotoxicity is a serious problem faced by thousands of clinical drugs, and drug-induced liver injury (DILI) caused by chronic administration or overdose has become a major biosafety issue. However, the near-infrared (NIR) fluorescent probes currently used for liver injury detection still suffer from poor liver targeting ability and low sensitivity. Enzyme-activated fluorogenic probes with powerful in situ targeting ability are the key to improving the imaging effect of liver injury. Herein, we rationally designed a leucine aminopeptidase (LAP) activated fluorogenic probe hCy-CA-LAP, which greatly improved the hepatocyte-targeting capability by introducing a cholic acid group. The probe hCy-CA-LAP is converted into a high-emission hCy-CA fluorophore in the presence of LAP, showing high selectivity, high sensitivity and low detection limit (0.0067 U mL⁻¹) for LAP, and successfully realizes the sensitive detection of small fluctuations of LAP in living cells. Moreover, the probe can achieve effective in situ accumulation in the liver, thereby achieving precise imaging and evaluation of two different types of drug-induced hepatotoxicity in vivo. Therefore, the probe hCy-CA-LAP may be a potential tool for exploring the roles of LAP and evaluating the degree of DILI.

We rationally designed a leucine aminopeptidase (LAP) activated fluorogenic probe hCy-CA-LAP with high hepatocyte-targeting ability for accurate and sensitive imaging of DILI.     

Amphiphilic peroxynitrite decomposition catalysts in liposomal assemblies

Background: Peroxynitrite (ONOO⁻), a toxic biological oxidant, has been implicated in many pathophysiological conditions. The water-soluble porphyrins 5,10,15,20-tetrakis(N-methyl-4′-pyridyl)porphinato iron(III) (FeTMPyP) and manganese(III) (MnTMPyP) have recently emerged as potential drugs for ONOO⁻ detoxification, and FeTMPyP has demonstrated activity in models of ONOO⁻ related disease states. We set out to develop amphiphilic analogs of FeTMPyP and MnTMPyP suitable for liposomal delivery in sterically stabilized liposomes (SLs).Results: Three amphiphilic iron porphyrins (termed 1a-c) and three manganese porphyrins (termed 2a-c) bound to liposomes and catalyzed the decomposition of ONOO⁻. The polyethylene-glycol-linked metalloporphyrins 1b and 2b proved the most effective of these catalysts, rapidly decomposing ONOO⁻ with second-order rate constants (k_cat) of 2.9 × 10⁵ M⁻¹s⁻¹ and 5.0 × 10⁵ M⁻¹ s⁻¹, respectively, in dimyristoylphosphatidylcholine liposomes. Catalysts 1b and 2b also bound to SLs, and these metal loporphyrin-SL constructs efficiently catalyzed ONOO⁻ decomposition (k_cat ≈ 2 × 10⁵ M⁻¹ s⁻¹). The analogous metalloporphyrins 1a and 2a, which are not separated from the vesicle membrane surface by polyethylene glycol linkers, were significantly less effective (k_cat ≈ 3.5 × 10⁴ M⁻¹ s⁻¹).Conclusions: For these amphiphilic analogs of FeTMPyP and MnTMPyP, the polarity of the environment of the metalloporphyrin headgroup is intimately related to the efficiency of the catalyst; a polar aqueous environment is essential for effective catalysis of ONOO⁻ decomposition. Thus, catalysts 1b and 2b react rapidly with ONOO⁻ and are potential therapeutic agents that, unlike their water-soluble TMPyP analogs, could be administered as liposomal formulations in SLs. These SL-bound amphiphilic metalloporphyrins may prove to be highly effective in the exploration and treatment of ONOO⁻ related disease states.     

Time-resolved luminescence detection of peroxynitrite using a reactivity-based lanthanide probe

Peroxynitrite (ONOO⁻) is a powerful and short-lived oxidant formed in vivo, which can react with most biomolecules directly. To fully understand the roles of ONOO⁻ in cell biology, improved methods for the selective detection and real-time analysis of ONOO⁻ are needed. We present a water-soluble, luminescent europium(iii) probe for the rapid and sensitive detection of peroxynitrite in human serum, living cells and biological matrices. We have utilised the long luminescence lifetime of the probe to measure ONOO⁻ in a time-resolved manner, effectively avoiding the influence of autofluorescence in biological samples. To demonstrate the utility of the Eu(iii) probe, we monitored the production of ONOO⁻ in different cell lines, following treatment with a cold atmospheric plasma device commonly used in the clinic for skin wound treatment.

Reactivity-based europium(iii) probe displays excellent selectivity for peroxynitrite (ONOO⁻), enabling its time-resolved luminescence detection in living cells.     

A high‐throughput glutathione trapping assay with combined high sensitivity and specificity in high‐resolution mass spectrometry by applying product ion extraction and data‐dependent neutral loss

Reactive metabolites are thought to play a pivotal role in the pathogenesis of some drug‐induced liver injury (DILI) and idiosyncratic adverse drug reactions (IADRs), which is of concern to patient safety and has been a cause of drugs being withdrawn from the market place. To identify drugs with a lower propensity for causing DILI and/or IADRs, high‐throughput assays to capture reactive metabolites are required in pharmaceutical industry for early drug discovery risk assessment. We describe the development of an assay to detect glutathione adducts with combined high sensitivity, enhanced specificity, and rapid data analysis. In this assay, compounds were incubated with human liver microsomes and a mixture of 1:1 of GSH (γ‐GluCysGly): GSX(γ‐GluCysGly‐¹³C₂¹⁵N) in a 96‐well plate format. UPLC‐UV and LTQ Orbitrap XL were employed to detect GSH‐adducts using the following mass spectrometry setups: (a) selected ion monitoring (SIM) at m/z of 274 ± 3 Da in negative mode with in‐source fragmentation (SCID), which enables simultaneously monitoring two characteristic product ions of m/z 272.0888 (γ‐glutamyl‐dehydroalanyl‐glycine) and 275.0926 (γ‐glutamyl‐dehydroalanyl‐glycine‐¹³C₂¹⁵N); (b) full scan mode for acquisition of exact mass of glutathione adducts; (c) data‐dependent MS² scan through isotopic matching (M:M + 3.00375 = 1:1) for monitoring neutral loss fragments (144 Da from dehydroalanyl‐glycine) and for structural information of glutathione adducts. This approach was qualified using eight compounds known to form GSH conjugates as reported in the literature. The high sensitivity and specificity were demonstrated in identifying unique CysGly adducts in the case of clozapine, diclofenac, and raloxifene and in identifying GSH‐adducts of fragmented parent molecules in the case of amodiaquine and troglitazone. In addition, LC‐UV chromatograms in the presence or absence of GSH/GSX allowed for identification of the rearranged glutathione adducts without aforementioned characteristic fragment ions. Implement of this assay in drug discovery small molecule programs has successfully guided drug design.     

Saxifraganoids A and B,two novel cucurbitane triterpenoid glycosides from Saxifraga umbellulata var. pectinata

Two novel cucurbitane triterpenoid glycosides, named saxifraganoids A (1) and B (2), were isolated from Saxifraga umbellulata var. pectinata. Their structures including absolute configurations were elucidated based on the analysis of spectroscopic data (1D, 2D NMR and HRMS), and single-crystal X-ray diffraction. Compound 1 represents the first example of cucurbitane triterpenoid with a Δ¹⁷⁽²⁰⁾, and compound 2 contained an unusual N-acetylglucosamine at C-16. The protective effects against liver injury induced by carbon tetrachloride (CCl₄) in the human embryonic-liver L-02 cells of these two compounds were evaluated.     

Classical and non-classical iron hydrides: synthesis,NMR characterisation,theoretical investigation and X-ray crystal structure of the iron(IV) dihydride 〚Cp*Fe(dppe)(H)2〛+BF4–

Protonation of Cp*Fe(dppe)H (1; Cp* = η⁵-C₅Me₅, dppe = Ph₂PCH₂CH₂PPh₂) by HBF₄Et₂O at –80 °C in diethylether affords the dihydrogen complex 〚Cp*Fe(dppe)(η²-H₂)〛⁺BF₄^– (2⁺BF₄^–) in 90% yield. Its PF₆^– salt analogue (2⁺PF₆^–) is obtained in 94% yield by reaction between the 16-electron derivative 〚Cp*Fe(dppe)〛⁺PF₆^– (3⁺PF₆^–) with H₂ gas at –80 °C. The presence of a bound dihydrogen ligand in 2⁺ is indicated by a short T₁ minimum values consistent with a H–H distances of 0.98(1) Å. For the partially deuterated derivative 2⁺–d₁, the observed J_HD value of 27.0 Hz confirms the presence of the coordinated dihydrogen ligand, which displays an H–H separation of 0.97(1) Å, in complete agreement with the distance calculated using the T₁ static rotation model. Variable temperature NMR study shows the gradual, complete and irreversible transformation of the dihydrogen complex into its classical dihydride isomer trans-〚Cp*Fe(dppe)(H)₂〛⁺ (4⁺). Thermal solid state reaction (–20 °C, 48 h) of 2⁺BF₄^– gives quantitatively 4⁺BF₄^–, whereas 4⁺PF₆^– is obtained by simple contact of H₂ with a solution of 3⁺PF₆^– in THF at room temperature. The crystal structure of 4⁺BF₄^– has been determined and shows a transoid arrangement of hydride ligands, consistent with the formulation of 4⁺ as an iron(IV) dihydride. DFT calculations on both dihydride and dihydrogen isomers of 〚Cp*Fe(dppe)H₂〛⁺ indicate that 4⁺ is more stable than 2⁺ by 0.19 eV, while this energy difference is reversed in the case of 〚CpFe(dpe)H₂〛⁺ (dpe = H₂PCH₂CH₂PH₂). The preference for the dihydride form in the case of 〚Cp*Fe(dppe)H₂〛⁺ and of the dihydrogen one in the case of 〚CpFe(dpe)H₂〛⁺ is due to the larger π-donor and σ-acceptor abilities of the 〚Cp*Fe(dppe)〛⁺ fragment, as compared to the 〚CpFe(dpe)〛⁺ unit.     

Ultraviolet B Light-induced Nitric Oxide/Peroxynitrite Imbalance in Keratinocytes—Implications for Apoptosis and Necrosis

Elevation of nitric oxide (NO˙) can either promote or inhibit ultraviolet B light (UVB)-induced apoptosis. In this study, we determined real-time concentration of NO˙ and peroxynitrite (ONOO⁻) and their role in regulation of membrane integrity and apoptosis. Nanosensors (diameter 300–500 nm) were used for direct in situ simultaneous measurements of NO˙ and ONOO⁻ generated by UVB in cultured keratinocytes and mice epidermis. An exposure of keratinocytes to UVB immediately generated ONOO⁻ at maximal concentration of 190 nm followed by NO^˙ release with a maximal concentration of 91 nm . The kinetics of UVB-induced NO˙/ONOO⁻ was in contrast to cNOS agonist stimulated NO˙/ONOO⁻ from keratinocytes. After stimulating cNOS by calcium ionophore (CaI), NO˙ release from keratinocytes was followed by ONOO⁻ production. The [NO˙] to [ONOO⁻] ratio generated by UVB decreased below 0.5 indicating a serious imbalance between cytoprotective NO˙ and cytotoxic ONOO⁻—a main component of nitroxidative stress. The NO˙/ONOO⁻ imbalance increased membrane damage and cell apoptosis was partially reversed in the presence of free radical scavenger. The results suggest that UVB-induced and cNOS-produced NO˙ is rapidly scavenged by photolytically and enzymatically generated superoxide (O₂˙⁻) to produce high levels of ONOO⁻, which enhances oxidative injury and apoptosis of the irradiated cells.