Design of a new porphyrin-based compound and investigation of its photosensitive properties for antibacterial photodynamic therapy.

Considering the increasing number of pathogens resistant to commonly used antibiotics as well as antiseptics, there is an urgent need for antimicrobial approaches that can effectively inactivate pathogens without the risk of establishing resistance. An alternative approach in this context is antibacterial photodynamic therapy (APDT). APDT is a process that involves bacterial cell death using appropriate wavelength light energy and photosensitizer and causes the production of reactive oxygen species inside or outside the microbial cell depending on the penetration of light energy. In our study, a new porphyrin compound 4,4'-methylenebis(2-((E)-((4-(10,15,20-triphenylporphyrin-5-yl)phenyl)imino)methyl)phenol) (SP) was designed and synthesized as photosensitizer and its structure was clarified by NMR (13C and 1H) and mass determination method. Photophysical and photochemical properties were examined in detail using different methods. Singlet oxygen quantum yields were obtained as 0.48 and 0.59 by direct and indirect methods, respectively. Antibacterial activity studies have been conducted within the scope of biological activity and promising results have been obtained under LED light (500-700 nm, 265 V, 1500 LM), contributing to the antibacterial photodynamic therapy literature.

A Series of Biguanide Ligands and Their Cu(II) Complexes: Cholinesterase Inhibitory and Antimicrobial Properties.

In this work, a series of biguanide hydrochloride salts and their Cu(II) complexes were synthesized and screened for their acetyl/butyryl choline esterase inhibitory and antimicrobial properties. The structures of the synthesized compounds were characterised by common spectroscopic and analytical methods. Biguanide compounds showed considerably lower inhibitory activity compared to the reference drugs donepezil and galantamine. On the other hand, complexation of the biguanide compounds with Cu(II) resulted in dramatic increase in the inhibitory activity. The Cu(II) complexes showed AChE inhibitory activity with the IC50 values of 21.29±0.95-82.53±0.20 µM and those values are comparable to that of donepezil (IC50 : 18.54±1.03 µM). The synthesised compounds were also screened for their antimicrobial activity towards gram positive (+) and gram negative (-) bacteria. Compounds (12.50 mg/mL) showed important antibacterial properties with inhibition zones of 8-28 mm diameter against gram-positive and gram-negative microorganisms. Compounds A03 and A08 exhibited more antimicrobial properties towards E. coli than standard antibiotics amikacin and gentamicin.

New 1,2,3-triazoles and their oxime derivatives: AChE/BChE enzyme inhibitory and DNA binding properties.

1,2,3-Triazole compounds (1a-3a) and their oxime derivatives (1b-3b) were synthesized. The structures of these synthesized compounds were characterized using common spectroscopic methods. Crystal structures of the compounds 3, 2b and 3b were determined by single crystal X-ray diffraction studies. The acetylcholinesteras (AChE) and butyrylcholinesterase (BChE) cholinesterase inhibitor (ChEI) and DNA/calf serum albumin (BSA) binding properties of the compounds were examined. DNA binding studies have shown that compounds interact with DNA through 1,2,3-triazole and oxime groups. When the binding constant Kb values were compared, it was revealed that compound 3b (Kb = 4.6 × 105 M-1) with oxime in its structure binds more strongly than the others. In addition, in vitro BSA binding studies showed that compounds 1b and 3b exhibited higher binding affinity. These results confirm that the quenching is due to the formation of a compound resulting from the static quenching mechanism, rather than being initiated by a dynamic mechanism. Likewise, when the enzyme activity of the compounds was examined, the compounds exhibited high inhibitory activity against AChE. The highest activity was observed for compounds 2b and 3b (8.6 ± 0.05 and 4.8 ± 0.052 µM). It was observed that the compounds were not selective with respect to BChE. Communicated by Ramaswamy H. Sarma.

Hydrazide Schiff base Compound Containing Triphenylphosphonium Units for Fluorescence Sensing of Al3+ and its real Sample Applications.

Al3+ excess in the body can cause many diseases. The development of chemosensors for the detection of Al3+ is therefore highly desirable. A hydrazide Schiff base compound containing triphenylphosphonium units (ER) was prepared and used as fluorescence turn-on sensor for the sensing of Al3+. Detection of Al3+ among various metals has been achieved successfully through the formation of Al3+-ligand coordination complexes. To detect Al3+, the "turn on" property of the fluorogenic chemosensor was investigated. Fluorescence sensing studies were carried out in CH3OH-Water (v/v, 9/1, pH 7.0) at λem = 528 nm. The LOD for sensing of Al3+ was found to be 0.129 µM. Using Job's graph, the stoichiometric ratio of ER- Al3+ was determined to be 1:1. The binding constant was determined to be 1.7 × 107 M-1 between Al3 + and the chemosensor ER. Finally, the determination of Al3+ in real herbal teas was carried out by using the sensing function of the chemosensor ER.

New sulfonamide derivatives based on 1,2,3-triazoles: synthesis, in vitro biological activities and in silico studies.

Eight new hybrid constructs containing a series of sulfonamide and 1,2,3-triazole units were designed and synthesized. Anticancer, antioxidant and cholinesterase activities of these hybrid structures were investigated. In our design, the Cu(I)-catalyzed click reaction between N,4-dimethyl-N-(prop-2-yn-1-yl)benzenesulfonamide (6) and aryl azides 8a-h was used. Antioxidant activity values of 9f (IC50: 229.46 ± 0.001 µg/mL) and 9h (IC50: 254.32 ± 0.002 µg/mL) hybrid structures were higher than BHT (IC50: 286.04 ± 0.003 µg/mL) and lower than Ascorbic acid (IC50: 63.53 ± 0.001 µg/mL) and α-Tocopherol (IC50: 203.21 ± 0.002 µg/mL). We determined that the cytotoxic effects of hybrid constructs 9d (IC50: 3.81 ± 0.1084 µM) and 9g (IC50: 4.317 ± 0.0367 µM) against A549 and healthy cell line (HDF) are much better than standard cisplatin (IC50: 6.202 ± 0.0705 µM). It was determined that the AChE inhibitory activities of all synthesized compounds were much better than Galantamine used as a standard. In particular, 9c (IC50: 13.81 ± 0.0026 mM) had ten times better activity than the standard Galantamine (IC50: 136 ± 0.008 mM). The ADMET properties of the molecules have been thoroughly examined and met the criteria for drug-like substances. They also have a high oral absorption rate, as they can effectively cross the blood-brain barrier and are easily absorbed in the gastrointestinal tract. In vitro experiments were confirmed by in silico molecular docking studies.Communicated by Ramaswamy H. Sarma.

A Novel Donepezil-Caffeic Acid Hybrid: Synthesis, Biological Evaluation, and Molecular Docking Studies.

A novel donepezil-caffeic acid (DP-CA) hybrid molecule was designed, synthesis, and investigated by molecular modeling. Its biological activity and protective effect were investigated by the IR spectroscopy, 1H and 13C NMR spectroscopy, and mass spectrometry. DP-CA was highly active against acetylcholine esterase and inhibited it at the micromolar concentrations. Fluorescence and UV-Vis spectroscopy studies showed strong binding of DP-CA to DNA. Moreover, DP-CA exhibited protective effects against H2O2-induced toxicity in U-118 MG glioblastoma cells. Finally, molecular docking showed a high affinity of DP-CA in all concentrations, and the active 4EY7 site exhibited essential residues with polar and apolar contacts. Taken together, these findings indicate that DP-CA could be a prospective multifunctional agent for the treatment of neurodegenerative diseases.

The biguanide-sulfonamide derivatives: synthesis, characterization and investigation of anticholinesterase inhibitory, antioxidant and DNA/BSA binding properties.

A number of new biguanidine-sulfonamide derivatives (1-16) were synthesized and their structures were characterized by spectroscopic and analytical methods. Crystal structures of the compounds 1, 4, 8, 10 and 14 were determined by single crystal X-ray diffraction studies. X-ray crystallographic data showed the π-electron delocalization through the biguanide units. The AChE and BChE cholinesterase inhibitor, DPPH antioxidant and DNA/BSA binding properties of the synthesized compounds were evaluated. Results of cholinesterase inhibitory properties have shown that the compounds containing electron-withdrawing (-F, -Cl) groups have higher AChE/BChE inhibitory and antioxidant activities. Compound 3 showed higher BChE inhibitory activity than tacrine with IC50 value of 28.4 µM. The compounds interact with DNA via minor groove binding mode. The compounds with a naphthyl group in its structure strongly binds with DNA/BSA biomolecules.Communicated by Ramaswamy H. Sarma.

Pyrene, Anthracene, and Naphthalene-Based Azomethines for Fluorimetric Sensing of Nitroaromatic Compounds.

Special attention is given to the development of rapid and sensitive detection of nitroaromatic explosives for homeland security and environmental concerns. As part of our contribution to the detection of nitroaromatic explosives, fluorescent materials (A), (B) and (C) were synthesized from the reaction of 1,2-diaminocyclohexane with pyrene-1-carbaldehyde, anthracene-9-carbaldehyde and 2-hydroxy-1-naphthaldehyde, respectively. The structures of the prepared fluorescent azomethine probes were confirmed using FTIR, 1H-NMR and 13C-NMR spectroscopies. The basis of the study is the use of the synthesized materials as fluorescent probes in the photophysical and fluorescence detection of some nitroaromatic explosives. Emission increases occurred due to aggregation caused by π-π stacking in synthesized azomethines. To measure the nitroaromatic detection capabilities of fluorescence probes, fluorescence titration experiments were performed using the photoluminescence spectroscopy. It was observed that compound A containing pyrene ring provided the best emission intensity-increasing effect due to aggregation with the lowest LOD value (14.96 µM) for the sensing of 4-nitrophenol. In compounds B and C, nitrobenzene with the lowest LOD (16.15 µM and 23.49 µM respectively) caused the most regular emission increase, followed by picric acid.

Synthesis, characterization and docking studies of benzenesulfonamide derivatives containing 1,2,3-triazole as potential inhibitor of carbonic anhydrase I-II enzymes.

Carbonic Anhydrases (CAs) are an important family of metalloenzymes that contain zinc (Zn2+) ions in their active site and catalyze the conversion of carbon dioxide to bicarbonate and proton and found in all living organisms. Sulfonamides are well-known inhibitors of CAs isoenzymes. In this study, a series of benzenesulfonamide derivatives (9a-h) containing 1,2,3-triazole-moiety were designed, synthesized and their structures were characterized by spectroscopic methods. In addition, molecular structures of compounds 5a, 5 b, 9e and 9f were elucidated by X-ray diffraction technique. To investigate drug similarity of 9a-h compounds, Lipinski's five rules (ADMET: absorption, distribution, metabolism, excretion and toxicity) were carried out by in silico studies. According to results, the compounds showed drug-like properties. Docking studies were applied to determine the scores, interactions and binding modes of compounds 9a-h against hCA I and hCA II enzymes. Compound 9c (-5.13 kcal/mol docking score) against hCA I enzyme and 9 h (-5.32 kcal/mol docking score) against hCA II enzyme showed potent inhibitory properties. The binding interactions of the compounds with the carbonic anhydrases were examined by docking studies.Communicated by Ramaswamy H. Sarma.

Design, synthesis, biological evaluation and molecular docking of cyclic biguanidine compounds as cholinesterase inhibitors.

A series of cyclic biguanidine derivatives (E01-E16) was designed, synthesized, characterized by FTIR, NMR, elemental analysis and evaluated as cholinesterase [acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE)] inhibitory effects for the treatment of Alzheimer's disease (AD). The cyclic biguanidine derivatives (E01-E16) were obtained as hydrochloride salt from one-pot reaction of 2-cyanoguanidine, p-substitute aniline derivatives and cyclohexanone/4-ethylcyclohexanone in the acidic medium. The crystal structures of compounds E13 and E16 were determined by XRD studies. The in vitro acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) inhibitory assessment of the compounds revealed that compounds showed considerable inhibitory activity. The substitute groups on the phenyl rings have an impact on the inhibitory activity of the compounds. Compound E08, containing an ester group on the phenyl ring, showed the highest inhibitory activity against BuChE (IC50: 97.97 ± 0.13 µM) compared to other compounds. According to the docking result, compound E08 exhibited higher binding affinity (-10.17 kcal/mol) against BuChE than the standard drug tacrine (-7.02 kcal/mol). Compound E08 was orientated towards the active site of the enzyme BuChE.Communicated by Ramaswamy H. Sarma.

Photophysical and Fluorescence Nitroaromatic Sensing Properties of Methylated Derivative of a Pamoic Acid Ester.

Rapid and selective detection of nitroaromatic explosives is very important for public safety, life, and environmental health. Current instrumental techniques suffer from high cost and poor site used. In order to investigate fluorescence sensing of nitroaromatics, we prepare a new small fluorescence probe derived from pamoic acid. This study covers the synthesis of Pamoic acid based [diisopropyl 4,4'-methylenebis(3-methoxy-2-naphthoate)] (2) material and characterization of its structure. The methylation of Pamoic acid ester, which we have successfully synthesized in our previous studies, was carried out in this study. Determination of the photophysical and fluorescent nitroaromatic detection properties of the compound forms the basis of the study. Structural characterization of the synthesized compound [diisopropyl 4,4'-methylenebis(3-methoxy-2-naphthoate)] (2) was characterized using spectroscopic methods. In addition, Molecular structure of the synthesized compound was determined by single crystal X-ray diffraction studies. In the final step, compounds [diisopropyl 4,4'-methylenebis(3-hydroxy-2-naphthoate)] (1) and [diisopropyl 4,4'-methylenebis(3-methoxy-2-naphthoate)] (2) were tested as fluorescent probes for the detection of some nitroaromatic explosives. It is seen that Nitrobenzene provides the best quenching effect on the compound [diisopropyl 4,4'-methylenebis(3-hydroxy-2-naphthoate)] (1) containing the -OH group, with lowest the limit of detection (LOD) value. It was observed that Picric acid provided the best quenching effect with lowest the limit of detection (LOD) value in the compound [diisopropyl 4,4'-methylenebis(3-methoxy-2-naphthoate)] (2) obtained by methylation of the -OH group in the compound [diisopropyl 4,4'-methylenebis(3-hydroxy-2-naphthoate)] (1).

Estimation of Excited-State Geometries of Benzene and Fluorobenzene through Vibronic Analyses of Absorption Spectra.

The parameters used in theoretical modeling of vibrational patterns within Franck-Condon (FC) approximation can be adjusted to match the vibrationally well-resolved experimental absorption spectrum of molecules. These simulation parameters can then be used to reveal the structural changes occurring between the initial and final states assuming the harmonic oscillator approximation holds for both states. Such a theoretical approach has been applied to benzene and fluorobenzene to disclose the first excited-state geometries of both compounds. The carbon-carbon bond length of benzene in the 1B2u state has been calculated as 1.430 Å, which is in very good agreement with the experimental bond length of 1.432 Å. The FC spectral fit method has been exploited to reveal the 1B2 state of fluorobenzene as well. Commonly employed density functional theory (DFT) and time-dependent DFT methods have been used to calculate the ground- and excited-state geometries of both compounds, respectively. The comparison of geometrical parameters and vibrational frequencies at the relevant states shows that frequently used hybrid functionals perform quite well in the ground state, whereas their performances drop considerably while predicting the excited-state properties. Among the hybrid functionals studied, TD-B3LYP with 6-31+G(d) basis set can be chosen to calculate the excited-state properties of molecules, albeit with much less anticipation of accuracy from the performance that B3LYP usually shows at the ground state.

Investigation of Chemosensing and Color Properties of Schiff Base Compounds Containing a 1,2,3-triazole Group.

A series of Schiff base compounds (ER1-ER5) containing a 1,2,3-triazole and carboxylic acid groups were synthesized and their chemosensory properties towards anions (I-, CO32-, SO42-, NO2-, NO3-, CH3COO-, ClO3-, CNO-, N3-) and cations (Al3+, Ag+, Co2+, Cr3+, Cu2+, Fe3+, Hg2+, Mn2+, Ni2+, Zn2+, Cd2+, Pb2+). The compounds were also used as fluorescence probs for the detection of nitroaromatic compounds. The structural characterization of the synthesized compounds was elucidated using methods such as FT-IR, UV, FL, LC-MS, MALDI-TOF MS, 1H(13C) NMR. The effect of substitute groups (-CH3, -OCH3, -OH, -Cl and -Br) on the synthesized Schiff bases (ER1-ER5) on the chemosensory properties were compared. As the groups changed, the sensor and quenching effects of the molecule against anions and cations changed. Compound ER3 having methoxy (OCH3) group exhibited selective sensor properties against Fe3+ ion while compound ER5 with a chloride substitute (Cl) group showed selectivity for Cr3+ ion under 254 nm UV-lamp. The substitute effect was also observed for the sensing of anions. Under 254 nm UV-lamp, ER2 having the -OH group has a selective sensing property for CNO- and ER4 with the bromide (Br) group exhibited selectivity for N3- ion. The synthesized Schiff base compounds were also tested as fluorescence probs for the sensing of some nitroaromatic explosives.

Synthesis, Biological Evaluation and Docking Study of Mono- and Di-Sulfonamide Derivatives as Antioxidant Agents and Acetylcholinesterase Inhibitors.

Mono(M1-M5)- and di(DM1-DM5)-sulfonamide derivatives were synthesized by the reaction of 4-iodobenzenesulfonyl chloride compound and aniline derivatives in basic medium. The structures of sulfonamide derivatives were characterized by spectroscopic and X-ray diffraction methods. All compounds were screened for acetylcholinesterase (AChE) inhibitory studies and 2,2-diphenyl-1-picrylhydrazil (DPPH) radical scavenging activities. Among the compounds tested, compound M1 showed the best activity against both AChE (IC50 =42.09 µg/mL for AChE) and DPPH (IC50 =9.94 µg/mL for DPPH). By placing compounds at the active site of AChE, their binding energies and modes were determined. Docking studies were performed in order to investigate binding interaction between the synthesized compounds and AChE. The most active M1 compound showed its low CDOCKER energy (-65,834 kcal/mol).

Enzyme Inhibition Properties and Molecular Docking Studies of 4-Sulfonate Containing Aryl α-Hydroxyphosphonates Based Hybrid Molecules.

In this study, a series of new hybrid molecules containing two important functional groups on the same skeleton were designed. 4-Hydroxybenzaldehyde and its two different derivatives were converted into their respective sulphonates by interacting with tosylchloride and methanesulfonyl chloride. Then, the desired molecules were synthesized by adding diethoxyphosphonate to the aldehyde group. Also, novel synthesis of hybrid compounds (4a-c and 5a-c) were tested toward some metabolic enzymes like carbonic anhydrase I and II isoenzymes (hCA I and hCA II) and acetylcholinesterase (AChE) enzyme. The synthesis of hybrid compounds (4a-c and 5a-c) showed Ki values of in range of 25.084±4.73-69.853±15.19 nM against hCA I, 32.325±1.67-82.761±22.73 nM against hCA II and 1.699±0.25 and 3.500±0.91 nM against AChE. For these compounds, compound 4c showed maximum inhibition effect against hCA I and hCA II isoenzymes and compound 5b showed maximum inhibition effect against AChE enzyme. By performing docking studies of the most active compounds for their binding modes and interactions were determined.

New imino-methoxy derivatives: design, synthesis, characterization, antimicrobial activity, DNA interaction and molecular docking studies.

Four new diarylmethylamine imine compounds (5a-5d) were prepared in order to examine their DNA binding properties, antimicrobial activity and molecular docking. The compounds were characterized by the common spectroscopic and analytic methods. Furthermore, solid-state structure of compounds 5a and 5c were determined by single-crystal X-ray diffraction studies. The compounds were then investigated for their DNA binding properties employing UV absorption, fluorescence spectroscopy under the physiological pH condition Tris-HCl buffer at pH 7.4. The compounds 5a-5d showed moderate binding constants with Kb values of 3.56 ± 0.3 × 104, 2.18 ± 0.2 × 105, 1.44 ± 0.3 × 105 and 2.56 ± 0.3 × 104 M-1, respectively. The molecular dockings were performed to investigate the ligand-DNA interactions. The in-silico DNA-compound interaction studies showed that the compounds interact with DNA in groove binding mode. Antimicrobial activity studies of imine compounds were tested against E. coli as bacteria, S. typhimurium, S. aureus, B. cereus, B. subtilis, and C. albicans as fungi. While all compounds show moderate activity against bacteria, no activity against fungi has been investigated.Communicated by Ramaswamy H. Sarma.

N-substituted benzenesulfonamide compounds: DNA binding properties and molecular docking studies.

Benzenesulfonamide-based imine compounds 5-8 were prepared and screened for their binding properties to the FSdsDNA. The structures of synthesized compounds were elucidated by the spectroscopic and analytical methods. Compounds 5-8 were screened for their interactions with the FSdsDNA. Compound 8 showed the highest binding affinity to the FSdsDNA with intrinsic binding constant of 3.10 × 104 M-1. The compounds caused the quenching of the DNA-EB emission indicating displacement of EB (ethidium bromide) from the FSdsDNA. Finally, the binding interactions between the DNA and binder molecules 5-8 were examined by the molecular docking studies. The compounds locate approximately same region of the minor groove of DNA via hydrogen bonding contacts between the sulfonamide oxygen atoms and the DG10/DG16 nucleotides of DNA.Communicated by Ramaswamy H. Sarma.

How to Predict Excited State Geometry by Using Empirical Parameters Obtained from Franck-Condon Analysis of Optical Spectrum.

Excited state geometries of molecules can be calculated with highly reliable wavefunction schemes. Most of such schemes, however, are applicable to small molecules and can hardly be viewed as error-free for excited state geometries. In this study, a theoretical approach is presented in which the excited state geometries of molecules can be predicted by using vibrationally resolved experimental absorption spectrum in combination with the theoretical modelling of vibrational pattern based on Franck-Condon approximation. Huang-Rhys factors have been empirically determined and used as input for revealing the structural changes occurring between the ground and the excited state geometries upon photoexcitation. Naphthalene molecule has been chosen as a test case to show the robustness of the proposed theoretical approach. Predicted 1B2u excited state geometry of the naphthalene has similar but slightly different bond length alternation pattern when compared with the geometries calculated with CIS, B3LYP, and CC2 methods. Excited state geometries of perylene and pyrene molecules are also determined with the presented theoretical approach. This powerful method can be applied to other molecules and specifically to relatively large molecules rather easily as long as vibrationally resolved experimental spectra are available to use.

Manganese(II) complexes derived from acyclic ligands having flexible alcohol arms: structural chracterization and SOD and catalase mimetic studies.

In this work, a series of seven MnII complexes of noncyclic flexible ligands derived from 2,6-diformylpyridine and ethanolamine or alkyl-substituted ethanolamines were prepared and characterized, six structurally by single-crystal X-ray diffraction studies. The complexes are dichlorido{2,2'-[(pyridine-2,6-diyl)bis(nitrilomethanylylidene)]diethanol}manganese(II), [MnCl2(C11H15N3O2)] or [MnCl2(L1)], (2), bis{µ-2,2'-[(pyridine-2,6-diyl)bis(nitrilomethanylylidene)]diethanol}bis[dithiocyanatomanganese(II)], [Mn2(NCS)4(C11H15N3O2)2] or [Mn2(NCS)4(L1)2], (3), chlorido{1,1'-[(pyridine-2,6-diyl)bis(nitrilomethanylylidene)]bis(propan-2-ol)}manganese(II) chloride monohydrate, [MnCl(C13H19N3O2)(H2O)]Cl·H2O or [MnCl(L2)(H2O)]Cl·H2O, (4), {1,1'-[(pyridine-2,6-diyl)bis(nitrilomethanylylidene)]bis(propan-2-ol)}dithiocyanatomanganese(II), [Mn(NCS)2(C13H19N3O2)] or [Mn(NCS)2(L2)], (5), aquadichlorido{2,2'-dimethyl-2,2'-[(pyridine-2,6-diyl)bis(nitrilomethanylylidene)]bis(propan-1-ol)}manganese(II) 0.3-hydrate, [MnCl2(C15H23N3O2)(H2O)]·0.3H2O or [MnCl2(L3)(H2O)]·0.3H2O, (6), (dimethylformamide){2,2'-dimethyl-2,2'-[(pyridine-2,6-diyl)bis(nitrilomethanylylidene)]bis(propan-1-ol)}dithiocyanatomanganese(II), [Mn(NCS)2(C15H23N3O2)(C3H7NO)] or [Mn(NCS)2(L3)(DMF)], (7), and (dimethylformamide){2,2'-[(pyridine-2,6-diyl)bis(nitrilomethanylylidene)]bis(butan-1-ol)}dithiocyanatomanganese(II) dimethylformamide monosolvate, [Mn(NCS)2(C15H23N3O2)(C3H7NO)]·C3H7NO or [Mn(NCS)2(L4)(DMF)]·DMF, (8). The crystal structure of ligand L1 is also reported, but that of (5) is not. All four ligands (L1-L4) have five potential donor atoms in an N3O2 donor set, i.e. three N (pyridine/diimine donors) and two alcohol O atoms, to coordinate the MnII centre. The N3O2 donor set coordinates to the metal centre in a pentagonal planar arrangement; seven-coordinated MnII complexes were obtained via coordination of two auxiliary ligands (anions or water molecules) at the axial positions. However, in some cases, the alcohol O-atom donors remain uncoordinated, resulting in five- or six-coordinated MnII complexes. The structurally characterized complexes were tested for their catalytic scavenging of superoxide and peroxide. The results indicated that the complexes with coordinated exogenous water or chloride ligands showed higher SOD activity than those with exogenous thiocyanate ligands.

Prediction of Internal Reorganization Energy in Photoinduced Electron Transfer Processes of Molecular Dyads.

A novel theoretical methodology is proposed to estimate the magnitude of internal reorganization energy for electron transfer and charge recombination processes in donor-bridge-acceptor (D-B-A) type molecular dyads. The potential energy surface for each process is plotted for the shortest path by assuming a displaced but slightly distorted harmonic oscillator model. Structural changes occurring upon photoexcitation and ionization were exploited to calculate the activation energies needed for electron transfer reactions with the aid of involved vibrational modes. D-B-A dyads consisting of octathiophene (T8) paired with three (di)imide acceptors (naphthalene diimide (NDI), benzene diimide (BDI), and naphthalimide (NI)) were studied as model systems for theoretical calculations. It has been found that T8NDI and T8BDI possess very low activation energies for both forward electron transfer and charge recombination, and hence the rates for relevant processes should be very rapid. In contrast, the activation energies for such processes for T8NI were found to be relatively large, and free energy estimations predict that the charge recombination mechanism in T8NI falls into the inverted regime of Marcus semiclassical electron transfer theory. All of the calculated properties of the dyads are in very good agreement with the available experimental data, suggesting the suitability of the proposed theoretical approach in revealing the photoinduced electron transfer mechanisms of molecular dyads.