Phase separation, aggregation, and complexation of triton-X100 and bovine serum albumin mixture: A combined cloud point and UV-visible spectroscopic approaches.

Phase separation and aggregation behaviour of triton X-100 (TX-100) and bovine serum albumin (BSA) mixture were investigated using cloud point and UV-visible spectroscopic techniques. The effects of various hydrotropes (HYTs) - namely, sodium salicylate (SS), sodium benzoate (SB), glycerol (Glyc), and 4-aminobenzoic acid (4-ABA) - on the cloud point (CP) of TX-100 + BSA were determined. The obtained CP values for the mixed system in the presence of HYTs followed the order: The measured critical micellization concentration (CMC) values of the TX-100 + BSA mixture were found to be significantly altered with varying amounts of BSA. The calculated free energy of clouding and micellization indicated the non-spontaneous nature of the phase transition and the spontaneous association of the TX-100 + BSA mixture. The non-spontaneity of phase separation decreased with increasing concentrations of HYTs. The enumerated values of ∆Hco and ∆Sco were consistently recorded as negative and positive magnitudes, respectively, in all aqueous HYTs media. The clouding process occurred due to a combination of hydrophobic and electrostatic interactions. The binding constant of the mixed system was determined employing the UV-vis spectroscopic method using the Benesi-Hildebrand equation.

Interaction between gastric enzyme pepsin and tetradecyltrimethylammonium bromide in presence of sodium electrolytes: Exploration of micellization behavior.

Pepsin is a proteolytic enzyme used in the treatment of digestive disorders. In this study, we investigated the physicochemical properties of the tetradecyltrimethylammonium bromide (TTAB) and pepsin protein mixture in various sodium salt media within a temperature range of 300.55-320.55 K with 5 K intervals. The conductometric study of the TTAB+pepsin mixture revealed a reduction in the critical micelle concentration (CMC) in electrolyte media. The micellization of TTAB was delayed in the presence of pepsin. The CMC of the TTAB + pepsin mixture was found to depend on the concentrations of electrolytes and protein, as well as the temperature variations. The aggregation of the TTAB+pepsin mixture was hindered as a function of [pepsin] and increasing temperatures, while micellization was promoted in aqueous electrolyte solutions. The negative free energy changes (∆Gm0) indicated the spontaneous aggregation of the TTAB+pepsin mixture. Changes in enthalpy, entropy, molar heat capacities, transfer properties, and enthalpy-entropy compensation variables were calculated and illustrated rationally. The interaction forces between TTAB and pepsin protein in the experimental solvents were primarily hydrophobic and electrostatic (ion-dipole) in nature. An analysis of molecular docking revealed hydrophobic interactions as the main stabilizing forces in the TTAB-pepsin complex.

Physicochemical parameters and modes of interaction associated with the micelle formation of a mixture of tetradecyltrimethylammonium bromide and cefixime trihydrate: effects of hydrotropes and temperature.

The interaction between an antibiotic drug (cefixime trihydrate (CMT)) and a cationic surfactant (tetradecyltrimethylammonium bromide (TTAB)) was examined in the presence of both ionic and non-ionic hydrotropes (HTs) over the temperature range of 300.55 to 320.55 K. The values of the critical micelle concentration (CMC) of the TTAB + CMT mixture were experienced to have dwindled with an enhancement of the concentrations of resorcinol (ReSC), sodium benzoate (NaBz), sodium salicylate (NaS), while for the same system, a monotonically augmentation of CMC was observed in aq. 4-aminobenzoic acid (PABA) solution. A gradual increase in CMC, as a function of temperature, was also observed. The values of the degree of counterion binding (ß) for the TTAB + CMT mixture were experienced to be influenced by the concentrations of ReSC/NaBz/NaS/PABA and a change in temperature. The micellization process of TTAB + CMT was observed to be spontaneous (negative standard Gibbs free energy change (ΔG0m)) at all conditions studied. Also, the values of standard enthalpy change (ΔH0m) and entropy change (ΔS0m) were found negative and positive, respectively (with a few exceptions), for the test cases indicating an exothermic and enthalpy-entropy directed micellization process. The recommended interaction forces between the components in the micellar system are electrostatic and hydrophobic interactions. In this study, the values of ΔC0m were negative in aqueous NaBz, ReSC, and PABA media, and positive in case of NaS. An excellent compensation scenario between the enthalpy and entropy for the CMT + TTAB mixed system in the investigated HTs solutions is well defined in the current work.

Aggregation phenomena and physico-chemical properties of tetradecyltrimethylammonium bromide and protein (bovine serum albumin) mixture: Influence of electrolytes and temperature.

It is important for biological, pharmaceutical, and cosmetic industries to understand how proteins and surfactants interact. Herein, the interaction of bovine serum albumin (BSA) with tetradecyltrimethylammonium bromide (TTAB) in different inorganic salts (KCl, K2SO4, K3PO4.H2O) has been explored through the conductivity measurement method at different temperatures (300.55 to 325.55 K) with a specific salt concentration and at a fixed temperature (310.55 K) using different salts concentrations. The extent of micelle ionization (α) and different thermodynamic parameters associated with BSA and TTAB mixtures in salt solutions were calculated. Evaluation of the magnitudes of ∆Hm0 and ∆Sm0 showed that the association was exothermic and primarily an enthalpy-operated process in all cases at lower contents of BSA, but the system became endothermic, and entropy driven in the presence of K3PO4.H2O at a relatively higher concentration of BSA. The enthalpy-entropy compensation variables were determined, which explained the types and nature of interactions between TTAB and BSA in salt media. Molecular docking analysis revealed that the main stabilizing factors in the BSA-TTAB complex are electrostatic and hydrophobic interactions. These findings aligned with the significant results obtained from the conductometry method regarding the nature and characteristics of binding forces observed between BSA and TTAB.

Association behavior and physico-chemical parameters of a cetylpyridinium bromide and levofloxacin hemihydrate mixture in aqueous and additive media.

The investigation of the micellization of a mixture of cetylpyridinium bromide (CPB) and levofloxacin hemihydrate (LFH) was carried out by a conductivity technique in aqueous and aq. additive mixtures, including NaCl, NaOAc, NaBenz, 4-ABA, and urea. The aggregation behavior of the CPB + LFH mixture was studied considering the variation in additive contents and the change in experimental temperature. The micelle formation of the CPB + LFH mixture was examined from the breakpoint observed in the specific conductivity versus surfactant concentration plots. Different micellar characteristics, such as the critical micelle concentration (CMC) and the extent of counter ion bound (ß), were evaluated for the CPB + LFH mixture. The CMC and ß were found to undergo a change with the types of solvents, composition of solvents, and working temperatures. The ΔG0m values of the CPB + LFH system in aqueous and aq. additive solutions were found to be negative, which denotes a spontaneous aggregation phenomenon of the CPB + LFH system. The changes in ΔH0m and ΔS0m for the CPB + LFH mixture were also detected with the alteration in the solvent nature and solution temperature. The ΔH0m and ΔS0m values obtained for the association of the CPB + LFH mixture reveal that the characteristic interaction forces may possibly be ion-dipole, dipole-dipole, and hydrophobic between CPB and LFH. The thermodynamics of transfer and ΔH0m-ΔS0m compensation variables were also determined. All the parameters computed in the present investigation are illustrated with proper logic.

Investigation of the impacts of simple electrolytes and hydrotrope on the interaction of ceftriaxone sodium with cetylpyridinium chloride at numerous study temperatures.

Herein, interactions between cetylpyridinium chloride (CPC) and ceftriaxone sodium (CTS) were investigated applying conductivity technique. Impacts of the nature of additives (e.g. electrolytes or hydrotrope (HDT)), change of temperatures (from 298.15 to 323.15 K), and concentration variation of CTS/additives were assessed on the micellization of CPC + CTS mixture. The conductometric analysis of critical micelle concentration (CMC) with respect to the concentration reveals that the CMC values were increased with the increase in CTS concentration. In terms of using different mediums, CMC did not differ much with the increase in electrolyte salt (NaCl, Na2SO4) concentration, but increased significantly with the rise of HDT (NaBenz) amount. In the presence of electrolyte, CMC showed a gentle increment with temperature, while the HDT showed the opposite trend. Obtained result was further correlated with conventional thermodynamic relationship, where standard Gibb's free energy change (ΔGmo), change of enthalpy (ΔHmo), and change of entropy (ΔSmo) were utilized to investigate. The ΔGmo values were negative for all the mixed systems studied indicating that the micellization process was spontaneous. Finally, the stability of micellization was studied by estimating the intrinsic enthalpy gain (ΔHmo,∗) and compensation temperature (Tc). Here, CPC + CTS mixed system showed more stability in Na2SO4 medium than the NaCl, while in NaBenz exhibited the lowest stability.

Reactions of diphosphine-stabilized Os3 clusters with triphenylantimony: syntheses and structures of new antimony-containing Os3 clusters via Sb-Ph bond cleavage.

The reactivity of the trimetallic clusters [Os3(CO)10(µ-dppm)] [dppm = bis(diphenylphosphino)methane] and [HOs3(CO)8{µ3-Ph2PCH2PPh(C6H4-µ2,σ1)}] with triphenylantimony (SbPh3) has been examined. [Os3(CO)10(µ-dppm)] reacts with SbPh3 in refluxing toluene to yield three new triosmium clusters [Os3(CO)9(SbPh3)(µ-dppm)] (1), [HOs3(CO)7(SbPh3){µ3-Ph2PCH2PPh(C6H4-µ2,σ1)}] (2), and [HOs3(CO)7(SbPh3)(µ-C6H4)(µ-SbPh2)(µ-dppm)] (3). [HOs3(CO)8{µ3-Ph2PCH2PPh(C6H4-µ2,σ1)}] reacts with SbPh3 (excess) at room temperature to afford [Os3(CO)8(SbPh3)(η1-Ph)(µ-SbPh2)(µ-dppm)] (4) as the sole product. A series of control experiments have also been conducted to establish the relationship between the different products. The molecular structure of each product has been determined by single-crystal X-ray diffraction analysis, and the bonding in these new clusters has been investigated by electronic structure calculations.

Physico-chemical parameters of phase separation of the mixture of BSA and triton X 100 in aqueous solutions of monohydroxy compounds.

Clouding behavior and thermodynamic properties for the TX 100 + BSA mixture were investigated in aqueous and aq. alcoholic media. In an aqueous environment, the values of cloud point (CP), at which a clear solution becomes cloudy, for TX 100 decreases with augmentation of the concentration of BSA. The reverse result was obtained in the aq. alcoholic media. In this study, we have used ethanol (EtOH), 1-propanol (1-PrOH), and 2-butanol (2-BuOH) as alcohols. The changes of CP values in alcoholic media have been obtained in the following order: CPH2O+EtOH > CPH2O+2-BuOH > CPH2O+1-PrOH. The standard free energy (∆Gco), standard enthalpy (∆Hco), and standard entropy (∆Sco) changes of clouding were derived at CP. The ΔGc0 values of TX 100 + BSA decreases in the aqueous and alcoholic media with increasing the concentration of BSA and alcohol. This process becomes endothermic in the aq. alcoholic media. Different thermodynamic properties of transfer and entropy-enthalpy compensation parameters for the phase partitioning of the TX 100 + BSA mixture have been calculated and assessed properly.

Reactions of triosmium and triruthenium clusters with 2-ethynylpyridine: new modes for alkyne C-C bond coupling and C-H bond activation.

The reaction of the trimetallic clusters [H2Os3(CO)10] and [Ru3(CO)10L2] (L = CO, MeCN) with 2-ethynylpyridine has been investigated. Treatment of [H2Os3(CO)10] with excess 2-ethynylpyridine affords [HOs3(CO)10(µ-C5H4NCH=CH)] (1), [HOs3(CO)9(µ3-C5H4NC[double bond, length as m-dash]CH2)] (2), [HOs3(CO)9(µ3-C5H4NC[double bond, length as m-dash]CCO2)] (3), and [HOs3(CO)10(µ-CH[double bond, length as m-dash]CHC5H4N)] (4) formed through either the direct addition of the Os-H bond across the C[triple bond, length as m-dash]C bond or acetylenic C-H bond activation of the 2-ethynylpyridine substrate. In contrast, the dominant pathway for the reaction between [Ru3(CO)12] and 2-ethynylpyridine is C-C bond coupling of the alkyne moiety to furnish the triruthenium clusters [Ru3(CO)7(µ-CO){µ3-C5H4NC[double bond, length as m-dash]CHC(C5H4N)[double bond, length as m-dash]CH}] (5) and [Ru3(CO)7(µ-CO){µ3-C5H4NCCHC(C5H4N)CHCHC(C5H4N)}] (6). Cluster 5 contains a metalated 2-pyridyl-substituted diene while 6 exhibits a metalated 2-pyridyl-substituted triene moiety. The functionalized pyridyl ligands in 5 and 6 derive via the formal C-C bond coupling of two and three 2-ethynylpyridine molecules, respectively, and 5 and 6 provide evidence for facile alkyne insertion at ruthenium clusters. The solid-state structures of 1-3, 5, and 6 have been determined by single-crystal X-ray diffraction analyses, and the bonding in the product clusters has been investigated by DFT. In the case of 1, the computational results reveal a rare thermodynamic preference for a terminal hydride ligand as opposed to a hydride-bridged Os-Os bond (3c,2e Os-Os-H bond).

A new synthetic route for the preparation of [Os3(CO)10(µ-OH)(µ-H)] and its reaction with bis(diphenylphosphino)methane (dppm): syntheses and X-ray structures of two isomers of [Os3(CO)8(µ-OH)(µ-H)(µ-dppm)] and [Os3(CO)7(µ3-CO)(µ3-O)(µ-dppm)].

The triosmium cluster [Os3(CO)10(µ-OH)(µ-H)] containing bridging hydride and hydroxyl groups at a common Os-Os edge was obtained in good yield (ca. 75%) from the hydrolysis of the labile triosmium cluster [Os3(CO)10(NCMe)2] in THF at 67 °C. [Os3(CO)10(µ-OH)(µ-H)] reacts with dppm at 68 °C to afford the isomeric clusters 1 and 2 with the general formula [Os3(CO)8(µ-OH)(µ-H)(µ-dppm)] that differ by the disposition of bridging dppm ligand. Cluster 1 is produced exclusively from the reaction of [Os3(CO)10(µ-OH)(µ-H)] with dppm in CH2Cl2 at room temperature in the presence of added Me3NO. Heating cluster 1 at 81 °C furnishes 2 in a process that likely proceeds by the release of one arm of the dppm ligand, followed by ligand reorganization about the cluster polyhedron and ring closure of the pendent dppm ligand. The oxo-capped [Os3(CO)7(µ3-CO)(µ3-O)(µ-dppm)] (3) has been isolated starting from the thermolysis of either 1 or 2 at 139 °C. Reactions of [Os3(CO)10(µ-dppm)] with ROH (R = Me, Et) in the presence of Me3NO at 80 °C furnish [Os3(CO)8(µ-OH)(µ,η1,κ1-OCOR)(µ-dppm)] (4, R = Me; 5, R = Et). Clusters 1-5 have been characterized by a combination of analytical and spectroscopic studies, and the molecular structure of each product has been established by X-ray crystallography. The bonding in these products has been examined by electronic structure calculations, and cluster 1 is confirmed as the kinetic product of substitution, while cluster 2 represents the thermodynamically favored isomer.

New molecular architectures containing low-valent cluster centres with di- and trimetalated 2-vinylpyrazine ligands: synthesis and molecular structures of Ru5(CO)15(µ5-C4H2N2CH[double bond, length as m-dash]CH)(µ-H)2 and Ru8(CO)24(µ7-C4H2N2CH[double bond, length as m-dash]C)(µ-H)3.

Reaction of 2-vinylpyrazine with Ru3(CO)12 results in multiple C-H bond activations to afford penta- and octa-ruthenium clusters, Ru5(CO)15(µ5-C4H2N2CH[double bond, length as m-dash]CH)(µ-H)2 (2) and Ru8(CO)24(µ7-C4H2N2CH[double bond, length as m-dash]C)(µ-H)3 (3), in which a Ru3 sub-unit is linked to Ru2 and Ru5 centres via di- and tri-metalated 2-vinylpyrazine ligands, exhibiting novel coordination modes including the loss of ring aromaticity in 2. The bonding of 2 and the mechanism for the fluxional behaviour of the hydrides have been examined by electronic structure calculations.

Mixed-valence dimolybdenum complexes containing hard oxo and soft carbonyl ligands: synthesis, structure, and electrochemistry of Mo2(O)(CO)2(µ-κ2-S(CH2)nS)2(κ2-diphosphine).

Mixed-valence dimolybdenum complexes Mo2(O)(CO)2{µ-κ2-S(CH2)nS}2(κ2-Ph2P(CH2)mPPh2) (n = 2, 3; m = 1, 2) (1-4) have been synthesized from one-pot reactions of fac-Mo(CO)3(NCMe)3 and dithiols, HS(CH2)nSH, in the presence of diphosphines. The dimolybdenum framework is supported by two thiolate bridges, with one molybdenum carrying a terminal oxo ligand and the second two carbonyls. The dppm (m = 1) products exist as a pair of diastereomers differing in the relative orientation of the two carbonyls (cis and trans) at the Mo(CO)2(dppm) center, while dppe (m = 2) complexes are found solely as the trans isomers. Small amounts of Mo(CO){κ3-S(CH2CH2S)2}(κ2-dppe) (5) also result from the reaction using HS(CH2)2SH and dppe. The bonding in isomers of 1-4 has been computationally explored by DFT calculations, trans diastereomers being computed to be more stable than the corresponding pair of cis diastereomers for all. The calculations confirm the existence of Mo[triple bond, length as m-dash]O and Mo-Mo bond orders and suggest that the new dimeric compounds are best viewed as Mo(v)-Mo(i) mixed-valence systems. The electrochemical properties of 1 have been investigated by CV and show a reversible one-electron reduction associated with the Mo(v) centre, while two closely spaced irreversible oxidation waves are tentatively assigned to oxidation of the Mo(i) centre of the two isomers as supported by DFT calculations.

Experimental and computational preference for phosphine regioselectivity and stereoselective tripodal rotation in HOs3(CO)8(PPh3)2(µ-1,2-N,C-η1,κ1-C7H4NS).

The site preference for ligand substitution in the benzothiazolate-bridged cluster HOs3(CO)10(µ-1,2-N,C-η1,κ1-C7H4NS) (1) has been investigated using PPh3. 1 reacts with PPh3 in the presence of Me3NO to afford the mono- and bisphosphine substituted clusters HOs3(CO)9(PPh3)(µ-1,2-N,C-η1,κ1-C7H4NS) (2) and HOs3(CO)8(PPh3)2(µ-1,2-N,C-η1,κ1-C7H4NS) (3), respectively. 2 exists as a pair of non-interconverting isomers where the PPh3 ligand is situated at one of the equatorial sites syn to the edge-bridging hydride that shares a common Os-Os bond with the metalated heterocycle. The solid-state structure of the major isomer establishes the PPh3 regiochemistry at the N-substituted osmium center. DFT calculations confirm the thermodynamic preference for this particular isomer relative to the minor isomer whose phosphine ligand is located at the adjacent C-metalated osmium center. 2 also reacts with PPh3 to give 3. The locus of the second substitution occurs at one of the two equatorial sites at the Os(CO)4 moiety in 2 and gives rise to a pair of fluxional stereoisomers where the new phosphine ligand is scrambled between the two equatorial sites at the Os(CO)3P moiety. The molecular structure of the major isomer has been determined by X-ray diffraction analysis and found to represent the lowest energy structure of the different stereoisomers computed for HOs3(CO)8(PPh3)2(µ-1,2-N,C-η1,κ1-C7H4NS). The fluxional behavior displayed by 3 has been examined by VT NMR spectroscopy, and DFT calculations provide evidence for stereoselective tripodal rotation at the Os(CO)3P moiety that serves to equilibrate the second phosphine between the two available equatorial sites.

Alkyne activation and polyhedral reorganization in benzothiazolate-capped osmium clusters on reaction with diethyl acetylenedicarboxylate (DEAD) and ethyl propiolate.

The reactivity of the face-capped benzothiazolate clusters HOs3(CO)9[µ3-C7H3(R)NS] (1a, R = H; 1b, R = 2-CH3) with alkynes has been investigated. 1a reacts with DEAD at 67 °C to furnish the isomeric alkenyl clusters Os3(CO)9(µ-C7H4NS)(µ3-EtO2CCCHCO2Et) (2a and 3a). X-ray crystallographic analyses of 2a and 3a have confirmed the stereoisomeric relationship of these products and the regiospecific polyhedral expansion that follows the formal transfer of the hydride to the coordinated alkyne ligand in HOs3(CO)9(µ-C7H4NS)(η2-DEAD). The significant structural differences between the two isomers, as revealed by the solid-state structures, derives from the regiospecific cleavage of one of the three Os-Os bonds in the intermediate alkenyl cluster Os3(CO)9(µ-C7H4NS)(η1-EtO2CCCHCO2Et), which follows hydride transfer to the coordinated alkyne ligand in the pi compound HOs3(CO)9(µ-C7H4NS)(η2-DEAD). Control experiments confirm the reversibility of the reaction leading to the formation of 2a and 3a. Whereas heating either isomer in refluxing THF or benzene affords a binary mixture containing 2a and 3a, thermolysis in refluxing toluene leads to the activation of the alkenyl ligand and formation of the new cluster Os3(CO)9(µ-C7H4NS)(µ3-EtO2CCCH2) (4). 4 was independently synthesized from 1a and ethyl propiolate at room temperature. The computed mechanisms that account for the formation of 2a and 3a are presented, along with the mechanism for the reaction of 1a with ethyl propiolate to give 4.

Electrocatalytic proton reduction catalysed by the low-valent tetrairon-oxo cluster [Fe4(CO)10(κ(2)-dppn)(µ4-O)](2-) [dppn = 1,1'-bis(diphenylphosphino)naphthalene].

The 62-electron oxo-capped tetrairon butterfly cluster, Fe4(CO)10(κ(2)-dppn)(µ4-O) (1) {dppn = 1,8-bis(diphenylphosphino)naphthalene}, undergoes reversible one-electron oxidation and reduction events to generate the 61- and 63-electron radicals [Fe4(CO)10(κ(2)-dppn)(µ4-O)](+) (1+) and [Fe4(CO)10(κ(2)-dppn)(µ4-O)](-) (1-) respectively. Addition of a second electron affords the 64-electron cluster [Fe4(CO)10(κ(2)-dppn)(µ4-O)](2-) (1(2-)) which has more limited stability but is stable within the time frame of the electrochemical experiment. While 1 and 1(-1) are inactive as proton reduction catalysts, dianionic 1(2-) is active for the formation of hydrogen from both CHCl2CO2H and CF3CO2H. This occurs via two separate mechanistic cycles branching at the mono-protonated species [Fe4(CO)10(κ(2)-dppn)(µ4-O)H](-) (1H-) resulting from the rapid protonation of 1(2-). This intermediate then undergoes competing protonation and reduction events leading to EECC and ECEC catalytic cycles respectively with 1- being pivotal to both. In order to understand the nature of [Fe4(CO)10(κ(2)-dppn)(µ4-O)](2-) (1(2-)) and its protonated products density functional theory (DFT) calculations have been employed. Theoretical calculations reveal that the cluster core remains intact in 1(2-), but the two consecutive one-electron reductions lead to an expansion of one of the trigonal-pyramids of this trigonal-bipyramidal cluster. The two-electron reduced cluster 1(2-) protonates at dppn-bound iron, accompanied by a wingtip-hinge iron-iron bond scission, and then reacts with a second proton to evolve hydrogen.

Bioinspired Hydrogenase Models: The Mixed-Valence Triiron Complex [Fe3(CO)7(µ-edt)2] and Phosphine Derivatives [Fe3(CO)7-x (PPh3) x (µ-edt)2] (x = 1, 2) and [Fe3(CO)5(κ2-diphosphine)(µ-edt)2] as Proton Reduction Catalysts.

The mixed-valence triiron complexes [Fe3(CO)7-x (PPh3) x (µ-edt)2] (x = 0-2; edt = SCH2CH2S) and [Fe3(CO)5(κ2-diphosphine)(µ-edt)2] (diphosphine = dppv, dppe, dppb, dppn) have been prepared and structurally characterized. All adopt an anti arrangement of the dithiolate bridges, and PPh3 substitution occurs at the apical positions of the outer iron atoms, while the diphosphine complexes exist only in the dibasal form in both the solid state and solution. The carbonyl on the central iron atom is semibridging, and this leads to a rotated structure between the bridged diiron center. IR studies reveal that all complexes are inert to protonation by HBF4·Et2O, but addition of acid to the pentacarbonyl complexes results in one-electron oxidation to yield the moderately stable cations [Fe3(CO)5(PPh3)2(µ-edt)2]+ and [Fe3(CO)5(κ2-diphosphine)(µ-edt)2]+, species which also result upon oxidation by [Cp2Fe][PF6]. The electrochemistry of the formally Fe(I)-Fe(II)-Fe(I) complexes has been investigated. Each undergoes a quasi-reversible oxidation, the potential of which is sensitive to phosphine substitution, generally occurring between 0.15 and 0.50 V, although [Fe3(CO)5(PPh3)2(µ-edt)2] is oxidized at -0.05 V. Reduction of all complexes is irreversible and is again sensitive to phosphine substitution, varying between -1.47 V for [Fe3(CO)7(µ-edt)2] and around -1.7 V for phosphine-substituted complexes. In their one-electron-reduced states, all complexes are catalysts for the reduction of protons to hydrogen, the catalytic overpotential being increased upon successive phosphine substitution. In comparison to the diiron complex [Fe2(CO)6(µ-edt)], [Fe3(CO)7(µ-edt)2] catalyzes proton reduction at 0.36 V less negative potentials. Electronic structure calculations have been carried out in order to fully elucidate the nature of the oxidation and reduction processes. In all complexes, the HOMO comprises an iron-iron bonding orbital localized between the two iron atoms not ligated by the semibridging carbonyl, while the LUMO is highly delocalized in nature and is antibonding between both pairs of iron atoms but also contains an antibonding dithiolate interaction.

Hydrogenase biomimetics: Fe2(CO)4(µ-dppf)(µ-pdt) (dppf = 1,1'-bis(diphenylphosphino)ferrocene) both a proton-reduction and hydrogen oxidation catalyst.

Fe2(CO)4(µ-dppf)(µ-pdt) catalyses the conversion of protons and electrons into hydrogen and also the reverse reaction thus mimicing both types of binuclear hydrogenase enzymes.

Bio-inspired hydrogenase models: mixed-valence triion complexes as proton reduction catalysts.

Mixed-valence triiron complexes Fe(3)(CO)(7-x)(PPh(3))(x)(µ-edt)(2) (x = 0-2) have been prepared and are shown to act as proton reduction catalysts. Catalysis takes place via an ECEC mechanism with a reduced overpotential of ca. 0.45 V for Fe(3)(CO)(7)(µ-edt)(2) as compared to the corresponding diiron complex.

Cluster chemistry in the Noughties: new developments and their relationship to nanoparticles.

Over the past decade, the chemistry of low-valent transition metal clusters has again come to the fore, primarily as a result of the development of nanochemistry and the realization that large clusters are on the cusp of the nano-domain. This perspective focuses on these recent developments in low-valent transition metal cluster chemistry, specifically looking at cluster-nanoparticles, the use of small and medium sized clusters as nanoparticle precursors, the development of clusters as homogeneous catalysts and hydrogen uptake and storage systems, together with fundamental discoveries relating to novel transformations that can take place within the cluster framework.

Tetranuclear group 7/8 mixed-metal and open trinuclear group 7 metal carbonyl clusters bearing bridging 2-mercapto-1-methylimidazole ligands.

The reactivity of group 7 metal dinuclear carbonyl complexes [M(2)(CO)(6)(mu-SN(2)C(4)H(5))(2)] (1, M = Re; 2, M = Mn) toward group 8 metal trinuclear carbonyl clusters were examined. Reactions of 1 and 2 with [Os(3)(CO)(10)(NCMe)(2)] in refluxing benzene furnished the tetranuclear mixed-metal clusters [Os(3)Re(CO)(13)(mu(3)-SN(2)C(4)H(5))] (3) and [Os(3)Mn(CO)(13)(mu(3)-SN(2)C(4)H(5))] (4), respectively. Similar treatment of 1 and 2 with Ru(3)(CO)(12) yielded the ruthenium analogs [Ru(3)Re(CO)(13)(mu(3)-SN(2)C(4)H(5))] (5), and [Ru(3)Mn(CO)(13)(mu(3)-SN(2)C(4)H(5))] (6), but in the case of 2 a secondary product [Mn(3)(CO)(10)(mu-Cl)(mu(3)-SN(2)C(4)H(5))(2)] (7) was also formed. Compounds have a butterfly core of four metal atoms with the M (Mn or Re) at a wingtip of the butterfly and containing a noncrystallographic mirror plane of symmetry. This result provides a potential method for the synthesis of a series of new group 7/8 mixed metal complexes containing a bifunctional heterocyclic ligand. Compound 7 is a unique example of a 54-electron trimanganese complex having bridging 2-mercapto-1-methylimidazolate and chloride ligands. Interestingly, the reaction of 1 with Fe(3)(CO)(12) at 70-75 degrees C furnished the tri- and dirhenium complexes [Re(3)(CO)(10)(mu-H)(mu(3)-SN(2)C(4)H(5))(2)] (8) and [Re(2)(CO)(6)(N(2)C(4)H(5))(mu-SN(2)C(4)H(5))(2)] (9), respectively instead of the expected formation of the mixed-metal clusters. The former is an interesting example of a 52-electron trirhenium-hydridic complex containing bridging 2-mercapto-1-methylimidazolate ligand, while the latter can be viewed as a 1-methylimidazole adduct of 1 . No mixed Fe-Re complexes were produced in this reaction. The molecular structures of the new compounds and were established by single-crystal X-ray diffraction analyses and the DFT studies of compounds , and are reported.