Composition and antioxidant activity of essential oil of pimento (Pimenta dioica (L) Merr.) from Jamaica

The composition and antioxidant activity of the essential oil obtained through hydrodistillation of pimento berry [Pimenta dioica (L.) Merr] samples, namely P1 and P2, sourced from Jamaica, were studied. The chemical composition was analysed by GC and GC-MS methods. The antioxidant activities of the oils were evaluated in terms of their free-radical-scavenging activity against 1,1-diphenyl-2-picrylhydrazyl (DPPH), 2,2'-azinobis (3-ethylbenzothiazoline-6-sulphonic acid) diammonium salt (ABTS) radical cation and superoxide anion (?[image omitted]). Total phenolic content, total reducing power and metal-chelating capacity of the oils were also estimated. Forty-five constituents were identified. The major compound identified was eugenol (74.71%, 73.35%), followed by methyl eugenol (4.08%, 9.54%) and caryophyllene (4.90%, 3.30%). The antioxidant assays showed that the oils possess very high radical scavenging activities (DPPH IC(50) 4.82 ± 0.08, 5.14 ± 0.11 μg mL(-1), ABTS IC(50) 2.27 ± 0.16, 2.94 ± 0.03 μg mL(-1), superoxide IC(50) 17.78 ± 1.31, 20.65 ± 0.82 μg mL(-1)). The metal chelating capacities (IC(50) 83.62 ± 2.10, 101.77 ± 1.01 μg mL(-1)) and reducing power were also very high. The results show that the essential oils possess significant antioxidant activity which is comparable to that of pure eugenol. Therefore the oil can be utilised as a natural antioxidant which gives good flavour as well as health benefits.     

In vitro antimycobacterial activity and HPLC-DAD screening of phenolics from Ficus benjamina L. and Ficus luschnathiana (Miq.) Miq. leaves

The total phenolic content (Folin-Ciocalteu) of the leaves of Ficus benjamina and Ficus luschnathiana was evaluated and screened by HPLC-DAD. Ficus luschnathiana crude extract (CE) presented phenolic content higher than that of F. benjamina (149.92?±?3.65 versus 122.63?±?2.79?mg of GAE). Kaempferol (1.63?±?0.16?mg?g(-1) dry weight of CE) and chlorogenic acid (17.77?±?0.57?mg?g(-1) of butanolic fraction) were identified and quantified in F. benjamina, whereas rutin (1.39?±?0.20?mg?g(-1)), caffeic (1.14?±?0.13?mg?g(-1)) and chlorogenic (3.73?±?0.29?mg?g(-1)) acids were quantified in the CE of F. luschnathiana. Additionaly, rutin (15.55?±?1.92?mg?g(-1)) and quercetin (3.53?±?0.12?mg?g(-1)) were quantified in ethyl acetate and butanolic fractions, respectively. Antimycobacterial activity of CEs and fractions was evaluated against Mycobacterium smegmatis by broth microdilution method. Ethyl acetate fraction from F. benjamina and n-butanol fraction from F. luschnathiana displayed the highest inhibitory activity (MIC?=?312.50?μg?mL(-1) and 156.25?μg?mL(-1), respectively). Further studies are required to identify the compounds directly related to antimycobacterial activity.     

Dereplication coupled with in vitro antioxidant assay of two flavonoid glycosides from Diospyros peregrina fruit

Diospyros peregrina is an edible seasonal fruit found in coastal West Bengal, India. The fruits have been reported to possess a significant antioxidant activity. In this study, the aim was to isolate the lead compound responsible for the above-mentioned activity. The aqueous extract of D. peregrina fruit was subjected to dereplication coupled with an in?vitro 1,1-diphenyl-2-picryl-hydrazyl (DPPH) radical scavenging assay. The n-butanol fraction of the aqueous extract of D. peregrina fruit exhibited significant antioxidant activity (IC(50), 131.10?μg?mL(-1)) as compared with the parent extract (IC(50), 285.15?μg?mL(-1)). The n-butanol fraction was subjected to silica gel column chromatographic separation coupled with a chemo-autographic study of column eluents, employing ethanolic DPPH as a spraying reagent. Two bioactive flavonoid glycosides, namely luteoline-4'-methyl-ether-7-O-glucoside and quercetin-3-O-(glucosyl)-glucoside, were identified to exhibit IC(50) values of 74.04 and 65.78?μg?mL(-1), respectively in the DPPH assay.     

Chemical composition and antioxidant activity of the essential oil and various extracts of Haplophyllum robustum Bge

This study was designed to examine the chemical composition and in vitro antioxidant activity of the essential oil and various extracts of Haplophyllum robustum. GC-MS analysis of the oil resulted in the identification of 30 compounds, representing 99.2% of the oil; 1,8-cineole (38.1%), myrcene (10.7%), α-pinene (8.5%), 4-terpineol (7.0%) and sabinene (6.1%) were the main components. The antioxidant potential of the oil and extracts was evaluated using three separate methods: inhibition of the free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH), β-carotene-linoleic acid assay and reducing power systems. The essential oil of the plant was able to reduce the stable free radical DPPH with an IC(50) of 72.0?±?1.2?μg?mL(-1) (the IC(50) for ascorbic acid was determined as 5.8?±?0.4?μg?mL(-1)). The essential oil also showed strong reducing power. The level of total phenolics was highest in the essential oil (179.5?±?2.1?μg?mg(-1)).     

Antioxidant, nitric oxide scavenging and malondialdehyde scavenging activities of essential oils from different chemotypes of Zataria multiflora

The antioxidant, nitric oxide (NO) scavenging and malondialdehyde (MDA) scavenging activities of different Zataria multiflora (ZM) chemotype essential oils (EOs) were investigated. The main components are: ZM1 (carvacrol, p-cymene), ZM2 (carvacrol, p-cymene), ZM3 (carvacrol, p-cymene), ZM4 (linalool), ZM5 (carvacrol, p-cymene, thymol), ZM6 (thymol, carvacrol, p-cymene, γ-terpienene), ZM7 (thymol, p-cymene, γ-terpienene) and ZM8 (carvacrol, linalool, p-cymene, thymol). The antioxidant capacities were estimated to be 863?±?55, 619?±?27, 876?±?32, 38?±?9, 649?±?50, 595?±?40, 696?±?41 and 618?±?9?μg ascorbic acid equivalents per millilitre for ZM1 to ZM8, respectively. The NO scavenging values were estimated to be 54?±?1.2, 50?±?1.4, 63?±?1, 0.60?±?0.1, 53?±?0.7, 53?±?1.5, 38?±?1.1 and 46.5?±?3?μg ascorbic acid equivalents per millilitre for ZM1 to ZM8, respectively. The MDA scavenging values were estimated to be 19?±?1, 9?±?1, 24?±?1, 1.6?±?0.6, 12?±?1, 11.7?±?1, 10?±?1 and 12.5?±?1.3?μg ascorbic acid equivalents per millilitre for ZM1 to ZM8, respectively. Among these EOs, ZM3 with carvacrol and p-cymene had higher antioxidant, NO scavenging and MDA scavenging properties.     

Photoprotecting action and phytochemical analysis of a multiple radical scavenger lipophilic fraction obtained from the leaf of the seagrass Thalassia testudinum

The apolar fraction F1 of Thalassia testudinum was chemically characterized by gas chromatography-mass spectrometry, which led to the identification of 43 metabolites, all of them reported for the first time in the genus Thalassia. More than 80% of the F1 composition was constituted by aromatic metabolites including the major components 1,1-bis(p-tolyl)ethane (6.0%), 4,4'-diisopropylbiphenyl (4.8%) and a 1,1-bis(p-tolyl)ethane isomer (4.7%). This lipophilic fraction was assayed for its antioxidant effects and skin protective action. In vitro assays showed that F1 strongly scavenged DPPH* (IC(50) 312.0 ± 8.0 μg mL(-1)), hydroxyl (IC(50) 23.8 ± 0.5 μg mL(-1)) and peroxyl radical (IC(50) 6.6 ± 0.3 μg mL(-1) ), as well as superoxide anion (IC(50) 50.0 ± 0.7 μg mL(-1)). Also, F1 markedly inhibited the spontaneous lipid peroxidation (LPO) in brain homogenates (IC(50) 93.0 ± 6.0 μg mL(-1)) and the LPS-stimulated nitrite generation on RAW624.7 macrophages (58.6 ± 3.2%, 400 μg mL(-1)). In agreement with these findings, its topical application at 250 and 500 μg cm(-2) strikingly reduced skin damage on mice exposed to acute UVB radiation by 45% and 70%, respectively and significantly attenuated the LPO developed following the first 48 h after acute exposure to UVB irradiation, as manifested by the decreased malondialdehide level and by the increased of reduced gluthatione content. Our results suggest that F1 may contribute to skin repair by attenuating oxidative stress due to its antioxidant activity.     

Antioxidant and anticancer activity of fresh corm extract from Romulea tempskyana (Iridaceae)

The antioxidant and anticancer properties of a medicinal plant, Romulea tempskyana (R. tempskyana) (Iridaceae) were investigated. The fresh corm water extract of R. tempskyana significantly increased cell viability against H(2)O(2) cytotoxicity(.) The extract also showed high inhibition of the lipid peroxidation activity (78.20%), reducing power (IC(50) 64.99?μg?mL(-1)) activity and hydroxyl (IC(50) 38.66?μg?mL(-1)), superoxide (IC(50) 25.99?μg?ml(-1)) and DPPH (IC(50) 19.88?μg?mL(-1)) radical scavenging activity. On the other hand, treatment of the cells with higher extract concentration showed the anticancer activity inducing cytotoxicity. The extract significantly affected Hepatoma G2 and H1299 cell proliferation (IC(50); 103.79 and 88.15?μg?mL(-1)). The amount of MDA (2-fold and 2.5-fold) and activities of several cellular antioxidant enzymes, including Se-GSPx (30%, 15%), non-Se-GSH-Px (11%, 16%) and GST (17%, 23%) increased in Hepatoma G2 and H1299 cells treated with IC(50) concentrations of extract, respectively. These findings suggest that R. tempskyana extract exhibits antioxidant and carcinogenesis-reducing potential.     

Composition of essential oil and antioxidant capacity of Centaurea drabifolia Sm. subsp. detonsa (Bornm.) Wagenitz, endemic to Turkey

In this study, composition of essential oil and antioxidant capacity of Centaurea drabifolia subsp. detonsa were investigated. The antioxidant capacity of the methanolic extract was evaluated by various methods including measuring the total phenolic content, total antioxidant capacity, free radical scavenging activity (DPPH assay), β-carotene/linoleic acid bleaching assay and ferric and cupric ion reducing power assay. The composition of essential oil was identified by using gas chromatography-mass spectrometry. Totally, 41 compounds were described in the essential oil. Germacrene D (44.829%) was determined as the major compound of the essential oil. The total phenolic content, total antioxidant capacity, inhibition rate of oxidation of linoleic acid, IC(50) (in DPPH assay) and EC(50) (in reducing power) value were found to be 40.454?mg?GAE/g, 100.840?mg?AAE/g, 65.639%, 39.584?μg?mL(-1) and 0.603?mg?mL(-1), respectively. The results indicated that the extract of C. drabifolia subsp. detonsa has strong antioxidant properties and this species can be used as a natural antioxidant in food processing and pharmaceutical industries.     

Polyphenol contents and antioxidant activity of Brassica nigra (L.) Koch. leaf extract

Profound research has been done on the medicinal value of Brassica nigra (BN) seeds, and the leaves of the plant have been investigated in this study. The methanol extracts of the leaves were subjected to several in?vitro studies. The antioxidant activity of methanol extract was demonstrated with a wide range of concentration, 10-500?μg?mL(-1), and the antioxidant activity increased with the increase in concentration. Total phenol content was found to be 171.73?±?5.043 gallic acid equivalents and the total flavonoid content 7.45?±?0.0945 quercetin equivalents. Further quantification and identification of the compounds were done by HPTLC and GC-MS analyses. The predominant phenolic compounds determined by HPTLC were gallic acid, followed by quercetin, ferulic acid, caffeic acid and rutin. The free radical quenching property of BN leaf extract suggests the presence of bioactive natural compounds.     

Mutagenic effect, antioxidant and anticancer activities of six medicinal plants from Burkina Faso

The antiproliferative activities of six medicinal plant extracts from Burkina Faso were evaluated in order to justify their traditional use for the treatment of cancer. The SOS chromotest method was used in vitro on Escherichia coli PQ37 to evaluate the mutagenic effect of the plant extracts. The DPPH method was used to evaluate the antioxidant activity of each plant. The antiproliferative activity was evaluated by MTS method on normal cells (Vero and MCR5) and cancer cells (KB) in contact with the extracts for 72?h. The results showed that the studied plants are not genotoxic. Lantana ukambensis and Acacia macrostachya induced a very significant antiproliferative effect against cancer cells with 94% and 95%, respectively. They also developed a strong antioxidant activity. The IC?? values were 5.96?±?0.40?μg?mL?1 for L. ukambensis and 4.30?±?0.26?μg?mL?1 for A. macrostachya. These two plants are therefore potential sources for isolating new antioxidant and anticancer molecules.     

Geissoschizine methyl ether, a corynanthean-type indole alkaloid from Uncaria rhynchophylla as a potential acetylcholinesterase inhibitor

Geissoschizine methyl ether (1), a newly discovered strong acetylcholinesterase (AChE) inhibitor, along with six weakly active alkaloids, vallesiachotamine (2), hisuteine (3), hirsutine (4), isorhynchophylline (5), cisocorynoxeine (6) and corynoxeine (7) have been isolated from Uncaria rhynchophylla. Geissoschizine methyl ether (1) inhibited 50% of AChE activity at concentrations of 3.7?±?0.3?μg?mL(-1) while the IC(50) value of physostigmine as a standard was 0.013?±?0.002?μg?mL(-1). The mode of AChE inhibition by 1 was reversible and non-competitive. In addition, molecular modelling was performed to explore the binding mode of inhibitor 1 at the active site of AChE.     

Chemical composition of essential oil and in vitro antioxidant activities of the essential oil and methanol extracts of Eucalyptus loxophleba

This study was designed to examine the chemical composition of the essential oil and the antioxidant activity of the essential oil and methanol extracts of Eucalyptus loxophleba Benth. subsp. The chemical composition of the essential oil of the leaves of E. loxophleba was analysed by GC and GC/MS. The main constituents of the oil were found to be 1,8-cineole (39.4%), methyl amyl acetate (19.8%) and aromadendrene (10%). Antioxidant activities of the samples were determined by two different test systems namely DPPH and β-carotene/linoleic acid. In the DPPH system, the highest radical-scavenging activity was shown by the polar subfraction of the methanol extract (15.2?±?1.7?μg?mL?1). Also, in the second case, the inhibition capacity (%) of the polar subfraction (94.1?±?1.3) was found to be stronger. In addition, the amounts of total phenol components in the polar subfraction (273.0?±?2.6?μg?mg?1) and nonpolar subfraction (146.3?±?2.5?μg?mg?1) were determined.     

Niobium(V) oxynitride: synthesis, characterization, and feasibility as anode material for rechargeable lithium-ion batteries

The decomposition reaction of niobium(V) oxytrichloride ammoniate to the oxynitride of niobium in the 5+ oxidation state was developed in a methodological way. By combining elemental analysis, Rietveld refinements of X-ray and neutron diffraction data, SEM and TEM, the sample compound was identified as approximately 5?nm-diameter particles of NbO(1.3(1))N(0.7(1)) crystallizing with baddeleyite-type structure. The thermal stability of this compound was studied in detail by thermogravimetric/differential thermal analysis and temperature-dependent X-ray diffraction. Moreover, the electrochemical uptake and release by the galvanostatic cycling method of pure and carbon-coated NbO(1.3(1))N(0.7(1)) versus lithium was investigated as an example of an Li-free transition-metal oxynitride. The results showed that reversible capacities as high as 250 and 80?A?h kg(-1) can be reached in voltage ranges of 0.05-3 and 1-3?V, respectively. Furthermore, a plausible mechanism for the charge-discharge reaction is proposed.     

Determination of the chemical composition and in vitro antioxidant activities of essential oil and methanol extracts of Echinophora platyloba DC

This study was designed to examine the chemical composition and in vitro antioxidant activity of essential oil and methanol extracts of Echinophora platyloba from Iran. Gas chromatography (GC) and GC/MS (mass spectrometry; MS) analysis of the essential oil resulted in the identification of 29 compounds, which comprised 97.4% of the oil. The main constituents were found to be: (Z)-β-ocimene (26.7%), Δ-3-carene (16.2%) and limonene (6.6%). Antioxidant activities of the essential oil and the methanolic extracts from E. platyloba were evaluated using three different test systems, namely 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging, β-carotene-linoleic acid bleaching and reducing power assays. In the DPPH system, the highest radical-scavenging activity was shown by the polar sub-fraction of methanol extract (71.2 ± 1.11 μg mL(-1)). Also in the second case, the relative inhibition capacity (%) of the essential oil (68.0 ± 1.14%) was found to be the stronger one. In addition, the amounts of total phenol components in the polar sub-fractions of methanolic extract (67.5 ± 0.48 μg mg(-1)), nonpolar sub-fractions of methanol extract (35.3 ± 0.12) and the oil (83.3 ± 0.24 μg mg(-1)) were determined.     

In vitro evaluation of the anti-proliferative activities of the wood essential oils of three Cedrus species against K562 human chronic myelogenous leukaemia cells

There are four kinds of Cedar: Cedrus libani naturally occurring in Lebanon, Syria and Turkey, Cedrus atlantica in Morocco and Algeria, Cedrus brevefolia in Cyprus Island and Cedrus deodara which is distributed in Himalayan Mountains. Wood essential oils obtained from C. libani, C. atlantica and C. deodara were tested for the inhibition of K562 cell proliferation and for the induction of erythroid differentiation. The wood essential oils of C. libani, C. atlantica and C. deodara inhibited the proliferation of the K562 cell line exhibiting IC(50) values 23.38?±?1.7, 59.37?±?2.6 and 37.09?±?1.4?μg?mL(-1), respectively. Meanwhile, C. libani wood oils induced a percentage of erythroid differentiation of 15?±?2% at concentration 5?μg?mL(-1). Cedrus deodara wood oil indicated a percentage of erythroid differentiation of 20?±?2% at concentration 25?μg?mL(-1) and C. atlantica wood oils showed a percentage of erythroid differentiation of 12?±?1.8% at concentration 10?μg?mL(-1).     

4-[2-(4,6-二甲氧基-2-嘧啶氧基)苄胺基]苯甲酸正丙酯的合成和晶体结构

2-甲砜基-4,6二甲氧基嘧啶和N-(4-丙氧羰基苯基)-2-羟基苄胺在四氢呋喃溶液中反应, 生成标题化合物4-[2-(4,6-二甲氧基-2-嘧啶氧基)苄胺基]苯甲酸正丙酯,并测定了其晶体结构。该化合物分子式为C23H25N3O5,晶体属单斜晶系,空间群为P2/n,晶胞参数为a = 14.8504(8),b = 9.4420(4),c = 16.3129(9) 牛 = 104.881(1)埃琕 = 2210.6(2) 3,Z = 4,Dc = 1.272 g/cm3,F(000) = 896.00,(MoK? = 0.91 cm-1,R = 0.051,wR = 0.118,获得19761衍射数据,其中独立衍射点5004个。经元素分析、IR、MS和HNMR等对化合物的结构进行了表征。在分子结构中,各有3个不同的共轭平面。嘧啶环和苯环(C(7) C(12)),及苯环(C(14) C(19))的夹角分别为99.18 , 164.15埃?个苯环之间的夹角为94.93啊;衔锍世啻焦瓜蟆?     

Synthesis,Crystal Structure and Anti-fungal Activity of 2-(4-Chlorophenyl)-(1,3-dimethyl-2,3-dihydro-1H)-perimidine

The title compound 2-(4-chlorophenyl)-1,3-dimethyl-2,3-dihydro-1H-perimidine(C_(19)H_(17)ClN_2) was synthesized and characterized by elemental analysis, ~1H NMR, HRMS and single-crystal X-ray diffraction. The crystal of the title compound belongs to orthorhombic system,space group Pnma with a = 11.385(2), b = 12.170(2), c = 11.210(2) ?, V = 1553.2(5) ?~3, Z = 4, Dc =1.321 g/cm~3, m(Mo-Ka) = 0.244 mm~(-1), F(000) = 648, S = 1.309, R = 0.0400 and w R(I 2s(I)) =0.1065. X-ray diffraction results showed that the molecular structure is highly symmetric and the new-formed N-heterocyclic ring is non-planar. In addition, the biological experiment showed that the title compound showed inhibitory activities against fungi with varied potencies.     

Rate constants for the gas-phase reactions of OH and O3 with β-ocimene, β-myrcene, and α- and β-farnesene as a function of temperature

The rate constants for the gas-phase reactions of hydroxyl radicals and ozone with the biogenic hydrocarbons β-ocimene, β-myrcene, and α- and β-farnesene were measured using the relative rate technique over the temperature ranges 313-423 (for OH) and 298-318 K (for O?) at about 1 atm total pressure. The OH radicals were generated by photolysis of H?O?, and O? was produced from the electrolysis of O?. Helium was used as the diluent gas. The reactants were detected by online mass spectrometry, which resulted in high time resolution, allowing large amounts of data to be collected and used in the determination of the Arrhenius parameters. The following Arrhenius expressions have been determined for these reactions (in units of cm3 molecules?1 s?1): for β-ocimene + OH, k = (4.35(-0.66)(+0.78)) × 10?11 exp[(579 ± 59)/T]; for β-ocimene + O?, k = (3.15(-0.95)(+1.36)) × 10?1? exp[-(626 ± 110)/T]; for β-myrcene + O?, k = (2.21(-0.66)(+0.94)) × 10?1? exp[-(520 ± 109)/T]; for α-farnesene + OH, k(OH) = (2.19 ± 0.11) × 10?1? for 23-413 K; for α-farnesene + O?, k = (3.52(-2.54)(+9.09)) × 10?12 exp[-(2589 ± 393)/T]; for β-farnesene + OH, k(OH) = (2.88 ± 0.15) × 10?1? for 323-423 K; for β-farnesene + O?, k = (1.81(-1.19)(+3.46)) × 10?12 exp[-(2347 ± 329)/T]. The Arrhenius parameters here are the first to be reported. The reactions of α- and β-farnesene with OH showed no significant temperature dependence. Atmospheric residence times due to reactions with OH and O? were also presented.     

Isoiridomyrmecin rich essential oil from Nepeta erecta Benth. and its antioxidant activity

The essential oil composition of the aerial parts of Nepeta erecta Benth. (Family: Lamiaceae) from Uttarakhand, India was analysed by capillary gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). A total of 34 constituents were identified representing 94.6% of the oil composition. Oxygenated monoterpenes (74.0%) constituted the major proportion of the oil, dominated by isoiridomyrmecin (70.6%) as a single major constituent. Other significant constituents were caryophyllene oxide (9.6%), β-Bourbonene (2.0%), humulene epoxide II (1.7%) and linalool (1.0%). The in?vitro antioxidant activity (AOA) was assessed using β-Carotene bleaching assay, reducing power, 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging and inhibition of lipid peroxidation methods. The oil was found to exhibit AOA by inhibiting β-Carotene bleaching (54.6?±?2.52%) and by scavenging DPPH free radical (IC(50)?=?0.74?±?0.12?mg?mL(-1)). The AOA of the essential oil of N. erecta and its major compound isoiridomyrmecin has not been reported so far.     

Isostructural dinuclear phenoxo-/acetato-bridged manganese(II), cobalt(II), and zinc(II) complexes with labile sites: kinetics of transesterification of 2-hydroxypropyl-p-nitrophenylphosphate

Using the dinucleating phenol-based ligand 2,6-bis[3-(pyridin-2-yl)pyrazol-1-ylmethyl]-4-methylphenol] (HL(2)), in its deprotonated form, the six new dinuclear complexes [M(II)(2)(L(2))(μ-O(2)CMe)(2)(MeCN)(2)][PF(6)] (M = Mn (2a), Co (3a), Zn (4a)) and [M(II)(2)(L(2))(μ-O(2)CMe)(2)(MeCN)(2)][BPh(4)] (M = Mn (2b), Co (3b), Zn (4b)) have been synthesized. Crystallographic analyses on 2b·2MeCN, 3b·2MeCN, and 4b·2MeCN reveal that these complexes have closely similar μ-phenoxo bis(μ-carboxylato) structures. The physicochemical properties (absorption and ESI-MS spectral data, 2a,b, 3a,b, and 4a,b; (1)H NMR, 4a,b) of the cations of 2a-4a are identical with those of 2b-4b. Each metal ion is terminally coordinated by a pyrazole nitrogen and a pyridyl nitrogen from a 3-(pyridin-2-yl)pyrazole unit and a solvent molecule (MeCN). Thus, each metal center assumes distorted-octahedral M(II)N(3)O(3) coordination. Temperature-dependent magnetic studies on Mn(II) and Co(II) dimers reveal the presence of intramolecular antiferromagnetic (J = -8.5 cm(-1)) for 2b and ferromagnetic exchange coupling (J = +2.51 cm(-1)) for 3b, on the basis of the Hamiltonian H = -JS(1)·S(2). The exchange mechanism is discussed on the basis of magneto-structural parameters (M···M distance). Spectroscopic properties of the complexes have also been investigated. The pH titration and kinetics of phosphatase (transesterification) activity on 2-hydroxypropyl-p-nirophenylphosphate (HPNP) were studied in MeOH/H(2)O (33%, v/v) with 2a-4a, due to solubility reasons. This comparative kinetic study revealed the effect of the metal ion on the rate of hydrolysis of HPNP, which has been compared with what we recently reported for [Ni(II)(2)(L(2))(μ-O(2)CMe)(2)(MeOH)(H(2)O)][ClO(4)] (1a). The efficacy in the order of conversion of substrate to product (p-nitrophenolate ion) follows the order 4a > 3a > 2a > 1a, under identical experimental conditions. Notably, this trend follows the decrease of pK(a) values of M(II)-coordinated water (7.95 ± 0.04 and 8.78 ± 0.03 for 1a, 7.67 ± 0.08 and 8.69 ± 0.06 for 2a, 7.09 ± 0.05 and 8.05 ± 0.06 for 3a, and 6.20 ± 0.04 and 6.80 ± 0.03 for 4a). In this work we demonstrate that the stronger the Lewis acidity (Z(eff)/r) of the metal ion, the more acidic is the M(II)-coordinated water and the greater is the propensity of the metal ion to catalyze hydrolysis of the activated phosphate ester HPNP. Notably, the observed k(2) values (M(-1) s(-1)) for Mn(II) (2a, 0.152), Co(II) (3a, 0.208), and Zn(II) (4a, 0.230) complexes (1a, 0.058; already reported) linearly correlate with Z(eff)/r values of the metal ion. In each case a pseudo-first-order kinetic treatment has been done. Kinetic data analysis of complexes 2a-4a were also done following Michaelis-Menten treatment (catalytic efficiency k(cat)/K(M) values 0.170 M(-1) s(-1) for 2a, 0.194 M(-1) s(-1) for 3a and 0.161 M(-1) s(-1) for 4a; for 1a the value is 0.089 M(-1) s(-1)). Temperature-dependent measurements were done to evaluate kinetic/thermodynamic parameters for the hydrolysis/transesterification of HPNP and yielded comparable activation parameters (E(a) (kJ mol(-1)): 71.00 ± 4.60 (1a; reported), 67.95 ± 5.71 (2a), 62.60 ± 4.46 (3a), 67.80 ± 3.25 (4a)) and enthalpy/entropy of activation values (ΔH(?) (kJ mol(-1)) = 68.00 ± 4.65 (1a; reported), 65.40 ± 5.72 (2a), 60.00 ± 4.47 (3a), 65.29 ± 3.26 (4a); ΔS(?) (J mol(-1) K(-1)) = -109.00 ± 13 (1a; reported), -107.30 ± 16 (2a), -122.54 ± 14 (3a), -104.67 ± 10 (4a)). The E(a) values for all the complexes are comparable, suggesting a closely similar reaction barrier, meaning thereby similar course of reaction. The ΔS(?) values are consistent with an associative process. Positive ΔH(?) values correspond to bond breaking of the activated complex as a result of nucleophilic attack at the phosphorus atom, releasing cyclic phosphate and p-nitrophenolate ion. These data have helped us to propose a common mechanistic pathway: deprotonation of a metal-bound species to form the effective nucleophile, binding of the substrate to the metal center(s), intramolecular nucleophilic attack on the electrophilic phosphorus atom with the release of the leaving group, and possibly regeneration of the catalyst.