Tuning of Aggregation Enhanced Emission and Solid State Emission from 1,8-Naphthalimide Derivatives: Nanoaggregates, Spectra, and DFT Calculations.

Four new 1,8-naphthalimide based compounds, 4-(1,3-dioxo-1H,3H-benzo[de]isoquinolin-2-ylmethyl)-benzoic acid (LH), 4-(1,3-dioxo-1H,3H-benzo[de]isoquinolin-2-ylmethyl)-benzoic acid methyl ester (LMe), 4-(1,3-dioxo-1H,3H-benzo[de]isoquinolin-2-ylmethyl)-benzoyl chloride (LCl), and 4-(1,3-dioxo-1H,3H-benzo[de]isoquinolin-2-ylmethyl)-benzoic acid hydrazide (LN) are synthesized and characterized using spectral data and X-ray crystallography. They form nanoaggregates in aqueous-DMF solution and exhibited aggregation enhanced emission. The nanoaggregates are characterized using their scanning electron and atomic force microscopy images. The emission intensity follows the order as LH > LMe > LCl > LN. Their photophysical properties are recorded both in solution and in the solid-state and are correlated with the nature of benzoic acid derivatives owing to the combinatorial effect of π-π stacking and intermolecular and intramolecular interactions. The density functional theory calculations empower the understanding of their molecular and cumulative electronic behaviors. Antiparallel dimeric interactions in the solid-state extend a herringbone arrangement to LH and 2D channel and stair-like arrangement for LCl and LN, respectively.

Comparison of the Effect of Addition of Cyanoacrylate, Epoxy Resin, and Gum Arabic on Surface Hardness of Die Stone.

PURPOSE: To observe the effects of incorporating cyanoacrylate, epoxy resins, and gum arabic on the abrasion resistance of type IV gypsum die materials. MATERIALS AND METHODS: Forty specimens were prepared and divided into four groups (10 specimens in each group), namely group A (control), group B (die stone mixed with cyanoacrylate), group C (die stone mixed with epoxy resin), group D (die stone mixed with gum arabic). All the specimens were subjected to abrasion testing, wear volume analysis, Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscope (SEM) analysis. RESULTS: Abrasion testing showed maximum wear in the control group and minimum wear in the gum arabic group. Intergroup differences were statistically significant (p < 0.001). The largest mean difference was between control and gum arabic. The lowest was between cyanoacrylate and the control group. The mean wear volume was lowest in the gum arabic group (4.23 mm(3) ) and highest in the control group (6.78 mm(3) ). The FT-IR graphs of the gum arabic models showed the presence of CH2 , which is responsible for its binding activity. SEM revealed that the irregular particles of gum arabic display an interlocking arrangement. This jigsaw puzzle pattern results in stronger physical bond formation. CONCLUSION: Observations from this study showed that the addition of gum arabic increases resistance to abrasion in type IV gypsum. Cyanoacrylates are good adhesives as well, but a major drawback is that they have very low resistance to chemical action with water and physical actions such as sunlight. Epoxy resins are powerful adhesives, but they attain their full efficiency when cured with heat. Cyanoacrylate and epoxy resin displayed poor physical bonding, primarily because of inhomogeneity.

Anticancer activity of two ruthenium(II)-DMSO-chalcone complexes: Comparison of cytotoxic, pro-apoptotic and antimetastatic potential.

PURPOSE: Recently, we reported the synthesis and characterization of two complexes of general formula cis-[Ru(S-DMSO)3(R-CO-CH=CH-R')Cl] (R = 2-hydroxyphenyl for both, R' = thiophene (1), 3-methyl thiophene (2)) that showed remarkable topoisomerase II inhibition and strong binding with DNA. The aim of this study was the investigation of cytotoxic properties of these complexes against a panel of human tumor cell lines, with elucidation of their anticancer mechanisms in HeLa cells. METHODS: Characterization of anticancer activity of the investigated ruthenium complexes 1 and 2 included analysis of cytotoxicity by MTT assay. Cell cycle phase disruption of HeLa cells treated with complexes 1 and 2 was analyzed by flow cytometry after propidium iodide (PI) staining. Annexin V-FITC/PI double staining and further flow cytometry analysis and acridine orange (AO)/ethidium bromide (EB) double staining and fluorescent microscopy were used to determine the apoptotic potential of the investigated ruthenium complexes. The inhibitory effect on gelatinases (MMP-2 and MMP-9) as an indication of possible antimetastatic potential was also analyzed using gelatine zymography. RESULTS: The 50% cell growth inhibition (IC50) values of the investigated complexes ranged between 22.9 and 76.8 µM, with complex 2 being more cytotoxic. Both complexes induced G2 phase cell cycle arrest and apoptosis in HeLa cells. Inhibitory effect of complex 2 on MMP-2 activity was detected. CONCLUSIONS: This work revealed the potential of the investigated Ru(II)-DMSO-chalcone complexes as anticancer agents with cytotoxic and pro-apoptotic activity and indicated complex 2 as leading compound for further chemical modifications and anticancer research.

Synthesis and characterization of Ru(II)-DMSO-Cl-chalcone complexes: DNA binding, nuclease, and topoisomerase II inhibitory activity.

The complexes of type cis-[Ru(S-DMSO)(3)(R-CO-CH═CH-R')Cl] (R = 2-hydroxyphenyl for all, R' = phenyl 1, naphthyl 2, anthracenyl 3, thiophene 4, 3-methyl thiophene 5) are synthesized and characterized using spectroscopic (IR, (1)H and (13)C NMR, and UV-vis) and single crystal X-ray diffraction techniques. Their crystal structures show the formation of both intermolecular and intramolecular H-bonding. The molecular assembly of complex 5 using secondary interactions provides a butterfly structure. The binding of complexes with calf thymus DNA is monitored using UV-vis spectral titrations. The binding interaction of complexes 1, 2, and 3 with DNA increases with increasing conjugation of aromatic rings. However, complexes 4 and 5 interact with DNA strongly. The emission from ethidium bromide (EB) bound DNA recorded in phosphate buffer solution (pH = 7.2) decreases by incremental addition of solution of the complexes. The complexes 4 and 5 (100 µM) bind with the minor groove of DNA and cleave double-stranded pBR322 DNA significantly even in the absence of an activator. In the presence of H(2)O(2), they cleave supercoiled DNA via oxidative pathway even at lower concentration (20 µM). Both complexes 4 and 5 inhibit topoisomerase II activity with IC(50) values of 18 and 13. These values suggest that 4 and 5 are potential topoisomerase II inhibitors as compared to some of known inhibitors like novobiocin and etoposide.

Neuroprotective Activity of a Novel Synthetic Rhodamine-Based Hydrazone against Cu2+-Induced Alzheimer's Disease in Drosophila.

A new rhodamine-based probe 3,5-di-tert-butylsalicylaldehyde rhodamine hydrazone (RHTB) has been synthesized and well characterized using spectroscopic techniques and single-crystal X-ray crystallography. Among several metal ions, it selectively detects Cu2+ ions as monitored by UV-Vis and emission spectral titrations. It displays "turn on" behavior owing to the opening of a spirolactum ring and the presence of 3,5-di-tert-butyl as an electron releasing group. Further, Cu2+ ions play a pivotal role in extracellular aggregation of Aß42 peptides. So far, we know probably that there are no promising drugs available in this regard. Hence, countering the Cu2+ ions by RHTB chelation against orally administered Cu2+ ion-induced neurotoxicity in the eye tissue of Drosophila expressing human Aß42 (amyloid-ß42) has been tested. The present study involves in vivo and in silico approaches. They reveal the therapeutic potential of RHTB against Cu2+ ion-induced Aß42 toxicity in Alzheimer's disease (AD) model of Drosophila.

Cytotoxicity of Cu(II) and Zn(II) 2,2'-bipyridyl complexes: dependence of IC50 on recovery time.

We measure the cytotoxicity of three metal complexes containing the 2,2'-bypyridine ligand, Cu(bpy)(NCS)(2), 1, [Cu(bpy)(2)(H(2)O)](PF(6))(2), 2, and Zn(bpy)(2)(NCS)(2), 3, toward neuroblastoma cells (SK-N-SH) and ovarian cancer cells (OVCAR-3) using two different cell assays. The cells were exposed to various concentrations of the compounds for 1 h and the percent inhibition of cell growth, I, measured for various times after exposure, i.e., as a function of the recovery time t. After developing the theory showing the relationship between I and t, the cytotoxicity data were analyzed to reveal that the two copper complexes, 1 and 2, cause the cells to divide at a slower rate than the controls during the recovery period, but the zinc complex, 3, had little or no effect on cell division during the recovery period. The usual metric for reporting cytotoxicity is IC(50), which is the concentration of agent required to inhibit cell growth to 50% of the control population. However, since IC(50) can depend on the recovery time, t, as is the case for 1 and 2, reporting IC(50) for a single recovery time can hide important information about the long-time effects of a cytotoxic agent on the health of the cell population. Mechanistic studies with the compounds revealed that the copper complexes, 1 and 2, cleave closed circular pBR322 DNA in the presence of ascorbate, while the zinc complex, 3, does not facilitate DNA cleavage under the same conditions. This difference in DNA cleavage activity may be related to the fact that Cu(II) is redox active and can readily change its oxidation state, while Zn(II) is redox inert and cannot participate in a redox cycle with ascorbate to break DNA.

Binding of urea and thiourea with a barbiturate derivative: experimental and theoretical approach.

A barbiturate derivative [1,5-dihydro-5-[5-pyrimidine-2,4(1H,3H)-dionyl]-2H-chromeno[2,3-d] pyrimidine-2,4(3H)-dione)] (L1) possesses functionalities complementary to amide and thioamide. Hence its binding with urea and thiourea, is monitored using UV-vis and fluorescence titrations as well as isothermal titration calorimetry (ITC) study. Theoretical studies on hydrogen-bonded complexes of L1-urea and L1-thiourea in the gas phase, aqueous, and DMSO medium are carried out using density functional theory (DFT) at the B3LYP/6-31G** level. The theoretical calculations support the experimental results.

Ecofriendly ruthenium-containing nanomaterials: synthesis, characterization, electrochemistry, bioactivity and catalysis.

Among transition metals, ruthenium being an in-demand element along with its complexes with multidimensional applications in biology, catalysis (especially photocatalysis), and several other aspects of industrial materials, is lacking regards for the potential aspect of its nanoparticles. In the modern synthetic scenario, green synthesis of novel ruthenium nanoparticles for the development of novel materials with potential applications has become a focus. Ru-containing nanomaterials (Ru-cNMs) combined with metals like platinum and palladium or with non-metals like phosphorus and oxygen have shown applications as an anticancer, antimicrobial, and antioxidant agents along with wide-ranging catalytic applications. Reduction of Ru salts using biomaterials including plants etc. has emerged enabling the synthesis of Ru-cNMs. In this context, authors realize that poor availability of literature in this area of research seems to be one of the major handicaps that perhaps could be limiting its attractiveness to researchers. Therefore, it was thought worthwhile to present a review article to encourage, guide, and facilitate scientific researches in green ruthenium nanochemistry embodying synthesis, characterization and biological as well as catalytic applications.

Regression of Dalton's lymphoma in vivo via decline in lactate dehydrogenase and induction of apoptosis by a ruthenium(II)-complex containing 4-carboxy N-ethylbenzamide as ligand.

A novel ruthenium(II)-complex containing 4-carboxy N-ethylbenzamide (Ru(II)-CNEB) was found to interact with and inhibit M4-lactate dehydrogenase (M4-LDH), a tumor growth supportive enzyme, at the tissue level. The present article describes modulation of M4-LDH by this compound in a T-cell lymphoma (Dalton's Lymphoma: DL) vis a vis regression of the tumor in vivo. The compound showed a dose dependent cytotoxicity to DL cells in vitro. When a non toxic dose (10 mg/kg bw i.p.) of Ru(II)-CNEB was administered to DL bearing mice, it also produced a significant decline in DL cell viability in vivo. The DL cells from Ru(II)-CNEB treated DL mice showed a significant decline in the level of M4-LDH with a concomitant release of this protein in the cell free ascitic fluid. A significant increase of nuclear DNA fragmentation in DL cells from Ru(II)-CNEB treated DL mice also coincided with the release of mitochondrial cytochrome c in those DL cells. Importantly, neither blood based biochemical markers of liver damage nor the normal patterns of LDH isozymes in other tissues were affected due to the treatment of DL mice with the compound. These results were also comparable with the effects of cisplatin (an anticancer drug) observed simultaneously on DL mice. The findings suggest that Ru(II)-CNEB is able to regress Dalton's lymphoma in vivo via declining M4-LDH and inducing mitochondrial dysfunction-apoptosis pathway without producing any toxicity to the normal tissues.

Synthesis of a ruthenium(II) bipyridyl complex coordinated by a functionalized Schiff base ligand: characterization, spectroscopic and isothermal titration calorimetry measurements of M2+ binding and sensing (M2+=Ca2+, Mg2+).

Bis-[methylsalicylidine-4'benzoic acid]-ethylene (LH2) complexed with cis-Ru(bpy)2Cl(2).2H2O provides a complex of composition [Ru(bpy)2L].2NH4PF6 (1), which has been characterized spectroscopically. Its binding behaviour towards Mg2+ and Ca2+ ions is monitored using 1H NMR titration, isothermal titration calorimetry (ITC) and luminescence microscopy. The luminescent ruthenium complex binds Ca2+ in a more selective manner as compared to Mg2+.

Synthesis, characterization, and supramolecular architectures of two distinct classes of probes for the visualization of endogenously generated hypochlorite ions in response to cellular activity.

Two distinct classes of compounds, (E)-2-(((3-amino-4-nitrophenyl) imino) methyl)-5-(diethylamino) phenol (SB) and 5-(diethylamino)-2-(5-nitro-1H-benzo[d]imidazol-2-yl) phenol (IM) were synthesized. SB, a bright red colored compound was crystallized in acetonitrile as a triclinic crystal system while IM, yellow colored compound crystallized as a monoclinic crystal system in dimethylformamide by vapor diffusion of diethylether. These compounds were characterized using spectroscopic techniques (IR, UV-visible, 1H, and 13C NMR), and X-ray crystallography. SB and IM displayed classical and non-classical H-bonding involving C-H…O and π…π interactions. These compounds detected hypochlorite ions in aqueous DMSO (1: 9, v/v, HEPES buffer, pH 7.4), and detection was visible via color changes by naked eye. We also performed UV-visible and fluorescence titrations, showing detection limits of 8.82 × 10-7 M for SB and 2.44 × 10-7 M for IM. The fluorometric responses from SB and IM were also studied against different ROS and anions. DFT calculations were performed to strengthen the proposed sensing mechanisms of both SB and IM. Hypochlorite, which is endogenously generated by myeloperoxidase in endosomes, was specifically visualized using SB and IM in lipopolysaccharide-treated RAW264.7 cells. These probes were also used to image the generation of hypochlorite by RAW264.7 cells during phagocytosis of non-fluorescent polystyrene beads.

An ensemble of Zn2+ with a rhodamine B-3-allylsalicylaldehyde hydrazone as novel photosensitive material: Photochromism, photopatterning, photoprinting and molecular logic gates.

An ensemble of Zn2+ with Rhodamine B-3-allylsalicylaldehyde hydrazone (1-Zn2+), has been synthesized and fully characterized using spectroscopic techniques. A solution of 1-Zn2+ in THF, displays color changes from light yellow to pink color in the presence UV light (λ, 405 nm). The process is reversible and owes to keto-enol tautomerism which allows the opening of spirolactam ring of rhodamine in the presence of UV light. It is corroborated by the appearance of a new peak at λmax = 554 nm. The ensemble, 1-Zn2+ embedded in the matrix of silica gel, displays photo patterning phenomena initiated by the conventional light sources including sunlight. It also displays photoprinting property with a laser pen (λ 405 nm) and has been displayed by a videography. The module 1-Zn2+ meets real challenges through a simple synthetic route, fast response, and as a binary data storage system with non-destructive optical identity.

Mixed-ligand Ru(II) complexes with 2,2'-bipyridine and tetradentate Schiff bases auxiliary ligands: Synthesis, physico-chemical study, DFT analysis, electrochemical and Na+ binding properties.

cis-Bis(2,2'-bipyridyl)dichlororuthenium(II)dihydrate complexed with Schiff bases salen (L1H2) and salophen (L2H2) provides complexes of compositions [Ru(L1)(bpy)2] 1 and [Ru(L2)(bpy)2] 2, respectively with cavity. The structure of these complexes characterized by spectroscopic studies were supported by their optimized geometries based on DFT calculations. Complexes 1 and 2 were then allowed to interact with methanolic solution of sodium perchlorate separately providing corresponding complexes 3 and 4 with the compositions 1.NaClO4 and 2.NaClO4, respectively. The formation constants were then evaluated by monitoring the changes in their UV-visible spectral features upon addition of different amount of sodium salts in the presence of a fixed concentration of the ruthenium complexes at a wavelength 294 nm. Emission (solution), luminescence microscopic and cyclic voltammetric studies of these complexes have also been made.

A benzimidazolyl terpyridine-Fe2+ system and its recognition driven molecular model of a traffic light.

A new benzimidazolyl terpyridyl ligand (BIT) selectively detects Fe2+, F- and CN- ions in acetonitrile. The Fe2+ complex [Fe(H-BIT)2]·(ClO4)4 (1) displays the fast and selective detection of 2,4,6-trinitrophenol (TNP) with strong binding (log ß = 8.51 ± 0.24) and a low limit of detection (1.4 × 10-7 M) among several nitroaromatics. The color of complex 1 changes from purple to red, yellow, and green upon the separate addition of 2,4,6-trinitrophenol and tetrabutylammonium salts of fluoride and cyanide, respectively. The overall color changes thus display a model of a traffic light. The structures of BIT, 1 and [Fe(BIT)2]·(TNP)2 (2) have been well characterized using spectroscopic techniques and single crystal X-ray crystallography.

Emission switching of ferrocenyl Schiff bases and a representative ruthenium complex in alkaline DMSO: absorption, electrochemical and microstructural studies.

N,N'-Bis(4-ferrocenyl)-p-phenylene/octamethylene-diimines (L1/L2) and a representative Ru(II) complex [Ru(DMSO)2Cl2L1].2H2O were prepared and characterized which showed many fold enhancement in their luminescence in alkaline dimethylsulfoxide (DMSO) solution. Spectral and electrochemical properties of these compounds have been studied. Microstructure (SEM) of L1 and its complex showed single-phase porous material of crystal size approximately 1 microm.

Synthesis, structures, nuclease activity, cytotoxicity, DFT and molecular docking studies of two nitrato bridged homodinuclear (Cu-Cu, Zn-Zn) complexes containing 2,2'-bipyridine and a chalcone derivative.

Nitrato briged dinuclear complexes of type [Cu2(L)2(bpy)2(NO3)](NO3)·4H2O, 1 and [Zn2(L)2(bpy)2(NO3)](NO3)·4H2O, 2 (L=deprotonated form of free ligand LH, [1-(2-hydroxyphenyl)-3-(9-anthracenyl) propenone; bpy=2,2'bipyridine] are synthesized and characterized using a battery of physicochemical techniques and X-ray crystallography. A distorted square pyramidal geometry is assigned to them with N2O3 coordination core around the metal ion. The co-ligand L binds the metal ions through its O,O' atoms in anti-syn mode. The metal centers in complexes 1 and 2 are separated via bridging nitrato group at a distance of 6.073Å and 5.635Å respectively. Their structures and absorption spectra are supported by the computational studies using density functional theory (DFT) and TD-DFT. Both complexes exhibit nuclease activity and cleave supercoiled (form I) DNA. The complex 1 preferentially binds major groove of DNA and follows an oxidative pathway whereas complex 2 binds with minor groove of DNA via hydrolytic pathway. Both complexes inhibit topoisomerase I relaxation activity with IC50 values of 7 and 35µM. Molecular docking studies support the groove binding and topoisomerase I binding of the complexes. The complex 1 showed a significant cytotoxicity against HeLa cell lines (a cervical cancer cell lines) in vitro with IC50 value calculated as 2.9±0.021µM as compared to 28.2±0. 044µΜ for complex 2. Complex 2 induces the cell apoptosis at a later-stage as compared to complex 1. The cell apoptosis and topoisomerase inhibition by complexes enable them to be potential candidates as future anticancer drugs.

Mixed ligand complexes of Cu(II)/Zn(II) ions containing (m-)/(p-) carboxylato phenyl azo pentane 2,4-dione and 2,2'-bipyridine/1,10 phenanthroline: Synthesis, characterization, DNA binding, nuclease and topoisomerase I inhibitory activity.

Metal complexes of type [Cu(L1H)2(bpy)] (1), [Zn(L1H)2(bpy)] (2), [Cu(L2H)2(bpy)] (3) and [Cu(L2H)2(Phen)] (4) (L1H2=3-[N'-(1-acetyl-2-oxo-propylidene)-hydrazino]-benzoic acid, L2H2=4-[N'-(1-acetyl-2-oxo-propylidene)-hydrazino]-benzoic acid, bpy=2,2'-bipyridine, Phen=1,10 phenanthroline) are synthesized and characterized using spectroscopic techniques (FT-IR, (1)H NMR, (13)C NMR, electronic absorption and emission) and elemental analysis data. The assembly of the complexes involving intramolecular H-bonding is displayed using corresponding crystal structure. Binding of the complexes separately with Calf Thymus DNA is monitored using UV-vis spectral titrations. The displacement of ethidium bromide (EB) bound to DNA by the complexes, in phosphate buffer solution (pH∼7.2) is monitored using fluorescence spectral titrations. Nuclease activity of the complexes follow the order 4>3>1>2. The gel electrophoretic mobility assay measurement in presence of minor groove binder 4',6-diamidino-2-phenylindole (DAPI), suggests that complexes preferably bind with the minor groove of DNA. Topoisomerase I inhibitory activity of the complexes 3 and 4 inhibit topoisomerase I activity with IC50 values of 112 and 87µM respectively.

A smart switchable module for the detection of multiple ions via turn-on dual-optical readout and their cell imaging studies.

A module switchable as a function of multi-stimuli response has been designed. The module displays sequential logic gate-based detection of multiple ions (Fe(3+), Hg(2+), CN(-) and S(2-)) at ppm levels via a "turn on" signature which potentially meets real-world-challenges through a simple synthetic route, a fast response, water based-activity, naked-eye visualization, regenerative-action, high selectivity and multiple readout for precise analysis. Living cell imaging of Fe(3+) and Hg(2+) has also been carried out in HeLa cell lines.

Mixed-ligand Ru(II) complexes with 2,2'-bipyridine and aryldiazo-beta-diketonato auxillary ligands: synthesis, physico-chemical study and antitumour properties.

The complexes of Ru(II)-2,2'-bipyridyl with substituted diazopentane-2,4-diones (L1H-L5H) were synthesized and characterized by elemental analyses, conductance, FAB (fast atom bombardment) mass and spectral (IR, UV/Vis (UV/visible), NMR) studies. Molecular geometry optimization of the complexes was also made. None of the complexes luminesce. However, facilitated oxidation of Ru(II) to Ru(III) was evidenced from their lower reduction potential data. The ligands and their complexes were tested for their antitumour activity against a variety of tumour cell lines. Though activity is found to vary with the type of tumour cell lines used, yet complex 5 with naphtyldiazopentane-2,4-dione as co-ligand was found to be a potential compound as it showed in general significant activity against all cell lines studied.

Pentacoordinated Cu(II)/Zn(II) complexes bearing macrocyclic skeleton: synthesis, spectroscopic and molecular structure optimization studies.

2,6-Diacetylpyridine and 1,2-diaminoethane in the presence of copper(II) and zinc(II) chlorides containing a few drops of acetic acid were condensed into compositions [CuLH2]2.2HCl.H2O (1), [Cu2LPyz]2.2HCl.4CH3COCH3 (2) [CuZnLPyz]2.2HCl.2CH3COCH3.10H2O (3) and [ZnL'Cl]3.3HCl.3H2O (4) substantiated by elemental analyses, IR, UV-vis, 1H NMR and FAB mass spectral data. Demetallation of a Ni(II) complex (isolated as above) afforded macrocyclic skeleton LH4, whereas L' symbolizes a skeleton of the ligand containing only ethylenediamine and 2,6-diacetylpyridine. Molecular structure optimization using MM2 force field calculations for the complexes revealed distorted square pyramidal geometry around Cu(II) centers in complexes 1 and 2 and tetrahedral geometry around Cu(II) and Zn(II) centers with different degrees of distortion in complex 3 whereas three Zn(II) atoms (each in distorted square pyramidal geometry) attached via Cl bridges form a cyclic structure in complex 4. In complexes 1 and 2,Cu-Cu = 2.63-2.66 angstroms indicated the possibility of coupling between the two Cu(II) centers which has been supported by lower magnetic moment as well as ESR spectra showing half-field signal.