Studies on the plasticization efficiency of deep eutectic solvent in suppressing the crystallinity of corn starch based polymer electrolytes

A series of polymer electrolytes composed of corn starch (CS), lithium bis(trifluoromethanesulfonyl)imide (LITFSI) and deep eutectic solvent (DES) were fabricated by solution casting technique. The DES was synthesized from a mixture of choline chloride and urea at a molar ratio of 1:2. The addition of DES is crucial in enhancing the room temperature ionic conductivity by increasing the amorphous elastomeric phase in CS:LITFSI matrix. The ionic transport mechanism is improved and appreciable amount of ion conducting polymer electrolytes is produced. The highest ionic conductivity achieved for the polymer electrolyte composition CS:LiTFSI:DES (14 wt.%:6 wt.%:80 wt.%) is 1.04 × 10⁻³ S cm⁻¹. The anomalies that were observed with the addition of DES upon formation of neutral ion multiples were visually revealed by the SEM micrographs. The possible dipole-dipole interaction between the constituents was visualized by the FTIR spectroscopy upon change in cage peaks.     

Alkyl-methylimidazolium ionic liquids affect the growth and fermentative metabolism of Clostridium sp

In this study, the effect of ionic liquids, 1-ethyl-3-methylimidazolium acetate [EMIM][Ac], 1-ethyl-3-methylimidazolium diethylphosphate [EMIM][DEP], and 1-methyl-3-methylimidazolium dimethylphosphate [MMIM][DMP] on the growth and glucose fermentation of Clostridium sp. was investigated. Among the three ionic liquids tested, [MMIM][DMP] was found to be least toxic. Growth of Clostridium sp. was not inhibited up to 2.5, 4 and 4 g L⁻¹ of [EMIM][Ac], [EMIM][DEP] and [MMIM][DMP], respectively. [EMIM][Ac] at <2.5 g L⁻¹, showed hormetic effect and stimulated the growth and fermentation by modulating medium pH. Total organic acid production increased in the presence of 2.5 and 2 g L⁻¹ of [EMIM][Ac] and [MMIM][DMP]. Ionic liquids had no significant influence on alcohol production at <2.5 g L⁻¹. Total gas production was affected by ILs at ?2.5 g L⁻¹ and varied with type of methylimidazolium IL. Overall, the results show that the growth and fermentative metabolism of Clostridium sp. is not impacted by ILs at concentrations below 2.5 g L⁻¹.     

Modeling interactions between a β‐O‐4 type lignin model compound and 1‐allyl‐3‐methylimidazolium chloride ionic liquid

Aiming at understanding the molecular mechanism of the lignin dissolution in imidazolium‐based ionic liquids (ILs), this work presents a combined quantum chemistry (QC) calculation and molecular dynamics (MD) simulation study on the interaction of the lignin model compound, veratrylglycerol‐β‐guaiacyl ether (VG) with 1‐allyl‐3‐methylimidazolium chloride ([Amim]Cl). The monomer of VG is shown to feature a strong intramolecular hydrogen bond, and its dimer is indicated to present important π‐π stacking and intermolecular hydrogen bonding interactions. The interactions of both the cation and anion of [Amim]Cl with VG are shown to be stronger than that between the two monomers, indicating that [Amim]Cl is capable of dissolving lignin. While Cl^– anion forms a hydrogen‐bonded complex with VG, the imidazolium cation interacts with VG via both the π‐π stacking and intermolecular hydrogen bonding. The calculated interaction energies between VG and the IL or its components (the cation, anion, and ion pair) indicate the anion plays a more important role than the cation for the dissolution of lignin in the IL. Theoretical results provide help for understanding the molecular mechanism of lignin dissolution in imidazolium‐based IL. The theoretical calculations on the interaction between the lignin model compound and [Amim]Cl ionic liquid indicate that the anion of [Amim]Cl plays a more important role for lignin dissolution although the cation also makes a substantial contribution.     

On the reactivity of the Melanocarpus albomyces laccase and formation of coniferyl alcohol dehydropolymer (DHP) in the presence of ionic liquid 1-allyl-3-methylimidazolium chloride

Some ionic liquids are able to dissolve wood, including lignin and lignocellulose, and thus they provide an efficient reaction media for modification of globally abundant wood-based polymers. Lignin can be modified with laccases (EC 1.10.3.2), multicopper oxidases, which selectively catalyze the oxidation of phenolic hydroxyl to the phenoxy radical in lignin by using oxygen as the co-substrate and an electron acceptor. Many enzymes, including laccases, retain their catalytic activity in the presence of ionic liquids. However, the enzyme activity is usually decreased in the presence of ionic liquids, and the most deactivating ionic liquids have been observed to be those dissolving wood most efficiently. In the present study the activity, pH optimum and catalyzed oxidation of coniferyl alcohol by the laccase from the ascomycete Melanocarpus albomyces was investigated in the ionic liquid 1-allyl-3-methyl-imidazolium chloride ([Amim]Cl), known to dissolve wood and expected to affect the laccase activity. Indeed, with an increasing concentration of [Amim]Cl, the activity of M. albomyces laccase decreased, and the pH range of the enzyme activity was narrowed. The pH optimum, using 2,6-dimethoxyphenol as the substrate, was shifted from 6.5 to 6.0 when the amount of [Amim]Cl was increased to 60% (m-%). It was also found that the inhibition of laccase with NaN₃ was not as severe in the ionic liquid as in water. The insoluble fraction of the dehydropolymer (DHP) formed in the presence of [Amim]Cl had clearly higher molecular weight compared to the one formed in water. DHPs formed in the absence and presence of [Amim]Cl both contained β-5, β–β, β-O-4, α-CO/β-O-4 and α-O-4/β-O-4 structures. However, in the presence of [Amim]Cl, less β-O-4, slightly less β-5 and more β–β structures were formed.     

Synthesis, structures and spectroscopic properties of palladium(II) complexes with tridentate piperidyl-containing pincer ligands

A new series of square planar palladium(II) complexes with pincer ligands, pip₂NCN⁻ (pip₂NCNH = 1,3-bis(piperidylmethyl)benzene) and pip₂NNN (2,6-bis(piperidylmethyl)pyridine), has been prepared: Pd(pip₂NCN)X (X = Cl, Br, I), [Pd(pip₂NCN)(L)](BF₄) (L = pyridine, 4-phenylpyridine), and [Pd(pip₂NNN)Cl]Cl. The X-ray crystal structures of Pd(pip₂NCN)Br, [Pd(pip₂NCN)(L)]BF₄, and [Pd(pip₂NNN)Cl]Cl confirm the tridentate coordination geometries of the pincer ligands. For the pip₂NCN⁻ complexes, each piperidyl ring adopts a chair conformation with the metal center at an equatorial position on the N(piperidyl) atom. However, one of the piperidyl groups of Pd(pip₂NNN)Cl⁺ adopts a previously unobserved coordination geometry, effectively placing the metal center at an axial position on the N(piperidyl) atom. ¹H NMR and UV-Vis absorption measurements provide additional insight into the electronic structures of these complexes. The ¹H NMR spectra of Pd(pip₂NCN)X (X = Cl, Br, I) are consistent with deshielding of the pip₂NCN⁻ ligand resonances along the Cl < Br < I series, in opposition to the relative halogen electronegativities. It is suggested that this trend is consistent with decreasing filled/filled repulsions between the dπ orbitals of the metal center and the lone pair orbitals of the halide ligands along this series. Electronic absorption spectra support the notion that ligand-to-metal charge-transfer states are stabilized in these palladium(II) complexes relative to their platinum(II) analogues.     

Influence of the phosphine arrangement on the reactivity of palladium(II) and platinum(II) polyphosphine complexes with copper(I) chloride

The distorted square-planar complexes [Pd(PNHP)Cl]Cl (1) (PNHP = bis[2-(diphenylphosphino)ethyl]amine), [M(P₃)Cl]Cl [P₃ = bis[2-(diphenylphosphino)ethyl]phenylphosphine; M = Pd (2), Pt (3)] and [Pt(NP₃)Cl]Cl (5) (NP₃ = tris[2-(diphenylphosphino)ethyl]amine), coexisting in the later case with a square-pyramidal arrangement, react with one equivalent of CuCl to give the mononuclear heteroionic systems [M(L)Cl](CuCl₂) [L = PNHP, M = Pd (1a); L = P₃, M = Pd (2a), Pt (3a); L = NP₃, M = Pt (5a)]. The crystal structure of 3a confirms that Pt(II) retains the distorted square-planar geometry of 3 in the cation with P₃ acting as tridentate chelating ligand, the central P atom being trans to one chloride. The counter anion is a nearly linear dichlorocuprate(I) ion. However, the five-coordinate complexes [Pd(NP₃)Cl]Cl (4), [M(PP₃)Cl]Cl (M = Pd (6), Pt (7); PP₃ = tris[2-(diphenylphosphino)ethyl] phosphine) containing three fused five-membered chelate rings undergo a ring-opening by interaction with one (4, 6, 7) and two (6, 7) equivalents of CuCl with formation of neutral MCu(L)Cl₃ [L = NP₃, M = Pd (4a); L = PP₃, M = Pd (6a), Pt (7a)] and ionic [MCu(PP₃)Cl₂](CuCl₂) [M = Pd (6b), Pt (7b)] compounds, respectively. The heteronuclear systems were shown by ³¹P NMR to have structures where the phosphines are acting as tridentate chelating ligands to M(II) and monodentate bridging to Cu(I). Further additions of CuCl to the neutral species 6a and 7a in a 1:1 ratio resulted in the achievement of the ionic complexes 6b and 7b with ions as counter anions. It was demonstrated that the formation of heterobimetallic or just mononuclear mixed salt complexes was clearly influenced by the polyphosphine arrangement with the tripodal ligands giving the former compounds. However, complexes [M(NP₃)Cl]Cl constitute one exception and the type of reaction undergone versus CuCl is a function of the d⁸ metal centre.     

Aqueous solution chemistry of dichloro[S-methylcysteine(N,S)]platinum(II) isomers and their hydrolysis products

Rate and equilibrium constants at 25 °C, pH ∼ 1, and ionic strength 0.10 for hydrolysis of the two non-equivalent chlorides of dichloro[S-methyl-l-cysteine(N,S)]platinum(II) isomers, denoted [PtCl₂(SmecysH)], and the resultant chloro-aqua species have been determined by NMR, potentiometric, and spectrophotometric methods. Though hydrolysis constants, K_h, for the two chlorides are similar (pK_h = 4-5), the rate of hydrolysis of the chloride trans to coordinated S, k_h = 3.4 × 10⁻³ s⁻¹, is 2-3 orders of magnitude faster than the k_h for the other chloride, 2.3 × 10⁻⁶ s⁻¹, and for the cancer drug cisplatin, cis-[PtCl₂(NH₃)₂], 5.2 × 10⁻⁵ s⁻¹. Relative rates of hydrolysis determined under three different experimental conditions (pH ∼ 1 in 0.10 M HNO₃, high pH in 0.10 M NaOH, and at low pH with Ag⁺ assistance) are consistent: the Cl trans to S is 100-1000 times more labile than the Cl cis to S. Potentiometric and NMR methods were also used to estimate pK_a values of all aqua species, which are comparable to values reported for corresponding aqua species derived from cisplatin.     

Immunoprecipitation on magnetic beads and liquid chromatography-tandem mass spectrometry for carbonic anhydrase II quantification in human serum

In this study, a magnetic bead-based platform amenable to high-throughput protein carbonic anhydrase II (CA II) capture is presented. The key steps in this approach involved immunoaffinity purification of the target protein from serum followed by on-bead digestion with trypsin to release a surrogate peptide. This tryptic peptide was quantified by liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) operating in multiple reaction monitoring acquisition mode. Using a synthetic peptide standard and a structural analogue free-labeled internal standard, the resulting concentration was stoichiometrically converted to CA II serum concentration. The analytical steps, such as preparation of immunobeads, protein capture, proteolysis, and calibration, were optimized. The method was validated in terms of recovery (77%), reproducibility (relative standard deviation [RSD] < 12%), and method detection limit (0.5 pmol ml⁻¹). The developed method was applied to determining the CA II in eight healthy subjects, and the concentration measured was 27.3 pmol ml⁻¹ (RSD = 65%).     

Reactivity of chloro(N-methyliminodiacetato)palladium(II) and chloro(pyridyl-2,6-dicarboxylato)palladium(II) complexes with purine based 5′-nucleotides and glutathione: antitumor activity of platinum(II)-analogs

The interaction of [Pd^II(mida)(Cl)]⁻ (1) (mida²⁻ = N-methyliminodiacetate) and [Pd^II(pydc)(Cl)]⁻ (2) (pydc²⁻ = pyridyl-2,6-dicarboxylate) with adenosine-5′-monophosphate (AMP), inosine-5′-monophosphate (IMP) and glutathione (GSH) was studied kinetically as a function of [L] (L = AMP, IMP, GSH) and [Cl⁻] and temperatures (10-35 °C) at pH 4.0. The kinetic results suggest that the reaction of 1 and 2 with the 5′-nucleotides (AMP, IMP) is characterized by the hydrolysis of chloro-complexes followed by the aquo-substitution with purine based 5′-nucleotides through its N7 atom. The reaction of 1 and 2 with GSH takes place through the direct chloride replacement with GSH. Kinetic data and activation parameters are interpreted in terms of an associative mechanism and discussed in reference to the data reported earlier. The [Pt^II(mida)(Cl)]⁻ (3) and [Pt^II(pydc)(Cl)]⁻ (4) complexes were prepared and allowed to interact with AMP and IMP and their reaction products were characterized by ¹H NMR studies. The antitumor activity of 3 and 4 was examined against MCF-7 (breast cancer), NCI-H460 (lung cancer) and SF-268 (CNS) cell lines.     

Mechanistic studies on monodentate-ligand substitution of five-coordinate trigonal-bipyramidal platinum (II) complexes with tris[2-(diphenylphosphino)ethyl]phosphine

Reaction of the five-coordinate trigonal-bipyramidal platinum(II) complex, [Pt(pt)(pp₃)](BF₄) (pt = 1-propanethiolate, pp₃ = tris[2-(diphenylphosphino)ethyl]phosphine), with I⁻ in chloroform gave the five-coordinate square-pyramidal complex with a dissociated terminal phosphino group and an apically coordinated iodide ion in equilibrium. The thermodynamic parameters for the equilibrium between the trigonal-bipyramidal and square-pyramidal geometries, [Pt(pt)(pp₃)]⁺ + I⁻ ? [PtI(pt) (pp₃)], and the kinetic parameters for the chemical exchange were obtained as follows: , ΔH⁰ = − 10 ± 2.4 kJ mol⁻¹, ΔS⁰ = − 36 ± 10 J K⁻¹ mol⁻¹, , ΔH^‡ = 34 ± 4.7 kJ mol⁻¹, ΔS^‡ = − 50 ± 21 J K⁻¹ mol⁻¹. The square-planar trinuclear platinum(II) complex was formed by bridging reaction of one of the terminal phosphino groups of trigonal-bipyramidal [PtCl(pp₃)]Cl with trans-[PtCl₂(NCC₆H₅)₂] in chloroform. From these facts, ligand substitution reactions of [PtX(pp₃)]⁺ (X = monodentate anion) are expected to proceed via an intermediate with a dissociated phosphino group. The rate constants for the chloro-ligand substitution reactions of [PtCl(pp₃)]⁺ with Br⁻ and I⁻ in chloroform approached the respective limiting values as concentrations of the entering halide ions are increased. These kinetic results confirmed the preassociation mechanism in which the square pyramidal intermediate with a dissociated phosphino group and an apically coordinated halide ion is present in the rapid pre-equilibrium.     

Synthesis and characterization of platinum(II) complexes of 2N1O-donor ligands with a pendent indole ring

The Pt(II) complexes of 2N1O-donor ligands containing a pendent indole, 3-[N-2-pyridylmethyl-N-2-hydroxy-3,5-di(tert-butyl)benzylamino]ethylindole (Htbu-iepp), and 1-methyl-3-[N-2-pyridylmethyl-N-2-hydroxy-3,5-di(tert-butyl)benzylamino]ethylindole (Htbu-miepp) (H denotes an ionizable hydrogen), were synthesized, and the structure of [Pt(tbu-iepp)Cl] (1) was determined by X-ray analysis. Complex 1 prepared in CH₃CN was revealed to have the C2 atom of the indole ring bound to Pt(II) with the Pt(II)-C2 distance of 1.981(3) Å. On the other hand, [Pt(tbu-miepp)Cl] (2) was concluded to have a phenolate coordination instead of the C2 atom of the indole ring by ¹H NMR spectra. Reaction of 1 with 1 equiv. of Ce(IV) in DMF gave the corresponding one-electron oxidized species, which exhibited an ESR signal at g = 2.004 and an absorption peak at 567 nm, indicating the formation of the Pt(II)-indole-π-cation radical species. The half-life, t_1/2, of the radical species at −60 °C was calculated to be 43 s (k_obs = 1.6 × 10⁻² s⁻¹).     

Effect of the central metal ion on the cleavage of DNA by [M(TPA)Cl]ClO4 complexes (M = Co, Cu and Zn, TPA = tris(2-pyridylmethyl)amine): An efficient artificial nuclease for DNA cleavage

[M(TPA)Cl]ClO₄·nH₂O complexes (1: M = Co^II, n = 0; 2: M = Cu^II, n = ½; 3: M = Zn^II, n = 0) where TPA = tris(2-pyridylmethyl)amine, were synthesized and structurally characterized. The molecular structure of [Cu(TPA)Cl]ClO₄·½H₂O was determined by single crystal X-ray crystallography. In aqueous solution, the complex ions [M(TPA)Cl]⁺ (M = Co^II or Cu^II) are hydrolyzed to the corresponding aqua species [M(TPA)(H₂O)]²⁺. In contrast to the TBP [Cu(TPA)(H₂O)]²⁺, the corresponding TBP cobalt(II) species showed severe distortion towards tetrahedral geometry. The interactions of the three complexes with DNA have been investigated at pH 7.0 (1.0 mM Tris-Cl buffer) and 37 °C. Significant DNA cleavages were obtained for complexes 1 and 2, whereas complex 3 did not show any detectable cleavage for DNA. Under pseudo Michaelis-Menten kinetic conditions, the kinetic parameters k_cat and K_M were determined as k_cat = 6.59 h⁻¹ and K_M = 2.20 × 10⁻⁴ M for 1 and the corresponding parameters for 2 are k_cat = 5.7 × 10⁻² h⁻¹ and K_M = 6.9 × 10⁻⁵ M, and the reactivity of the complexes in promoting the cleavage of DNA decreases in the order 1 > 2 ? 3. The rate enhancements for the DNA cleavage by 1 and 2 correspond to 1.8 × 10⁸ and 1.6 × 10⁶, respectively, over the non-catalyzed DNA. The reactivity of the two complexes was discussed in relation to other related artificial nucleases.     

α-Rhamnosidase and β-glucosidase expressed by naringinase immobilized on new ionic liquid sol-gel matrices: Activity and stability studies

Novel ionic liquid (IL) sol-gel materials development, for enzyme immobilization, was the goal of this work. The deglycosylation of natural glycosides were performed with α-l-rhamnosidase and β-d-glucosidase activities expressed by naringinase. To attain that goal ILs with different structures were incorporated in TMOS/Glycerol sol-gel matrices and used on naringinase immobilization.The most striking feature of ILs incorporation on TMOS/Glycerol matrices was the positive impact on the enzyme activity and stability, which were evaluated in fifty consecutive runs. The efficiency of α-rhamnosidase expressed by naringinase TMOS/Glycerol@ILs matrices increased with cation hydrophobicity as follows: [OMIM] > [BMIM] > [EMIM] > [C₂OHMIM] > [BIM] and [OMIM] ≈ [E₂-MPy] ? [E₃-MPy]. Regarding the imidazolium family, the hydrophobic nature of the cation resulted in higher α-rhamnosidase efficiencies: [BMIM]BF₄ ? [C₂OHMIM]BF₄ ? [BIM]BF₄. Small differences in the IL cation structure resulted in important differences in the enzyme activity and stability, namely [E₃-MPy] and [E₂-MPy] allowed an impressive difference in the α-rhamnosidase activity and stability of almost 150%. The hydrophobic nature of the anion influenced positively α-rhamnosidase activity and stability. In the BMIM series the more hydrophobic anions (PF₆⁻, BF₄⁻ and Tf₂N⁻) led to higher activities than TFA. SEM analysis showed that the matrices are shaped lens with a film structure which varies within the lens, depending on the presence and the nature of the IL.The kinetics parameters, using naringin and prunin as substrates, were evaluated with free and naringinase encapsulated, respectively on TMOS/Glycerol@[OMIM][Tf₂N] and TMOS/Glycerol@[C₂OHMIM][PF₆] and on TMOS/Glycerol. An improved stability and efficiency of α-l-rhamnosidase and β-glucosidase expressed by encapsulated naringinase on TMOS/Glycerol@[OMIM][Tf₂N] and TMOS/Glycerol@[C₂OHMIM][PF₆] were achieved. In addition to these advantageous, with ILs as sol-gel templates, environmental friendly processes can be implemented.     

Molecular sensing behavior of the first Mn(I)-compound of di-2-pyridylketone-p-nitrophenylhydrazone (dpknph), fac-[Mn(CO)3(dpknph)Br]

The reaction between [Mn(CO)₅Br] and di-2-pyridylketone-p-nitrophenylhydrazone (dpknph) in diethyl ether under ultrasonic conditions gave fac-[Mn(CO)₃(dpknph)Br] in good yield. Optical and thermodynamic measurements on fac-[Mn(CO)₃(dpknph)Br] in non-aqueous polar solvents revealed reversible interconversion between two intense charge transfer absorption bands due to π-π* (dpk), followed by dpk → nitro intraligand charge transfer transition (ILCT), mixed with metal ligand charge transfer transition (MLCT) due to . In non-polar solvents, a single absorption band appeared. Extinction coefficients of 46 200 ± 2000 and 28 400 ± 2000 M⁻¹ cm⁻¹ were calculated in DMSO for the low- and high-energy electronic states of fac-[Mn(CO)₃(dpknph)Br] using excess NaBF₄. Changes in enthalpy (ΔH^ø) of +14.0 and −12.1 kJ mol⁻¹, entropy (ΔS^ø) of +28.65 and −64.30 J mol⁻¹ K⁻¹, and free energy (ΔG^ø) of +5.48 and +7.08 kJ mol⁻¹ at 298 K were calculated for the interconversion between the high and low energy electronic states of fac-[Mn(CO)₃(dpknph)Br]. These results allow for the use of these systems (fac-[Mn(CO)₃(dpknph)Br] and surrounding solvent or solute molecules) as optical sensors for a variety of physical and chemical stimuli that include metal ions. Group 12 metal ions in concentrations as low as 1.00 × 10⁻⁹ M can be detected and determined using fac-[Mn(CO)₃(dpknph)Br] in dmso in the presence and absence of NaBH₄.     

Nitrite reduction by Co(II) and Mn(II) substituted myoglobins: towards understanding necessary components of Mb nitrite reductase activity

Nitrite reduction to nitric oxide by heme proteins is drawing increasing attention as a protective mechanism to hypoxic injury in mammalian physiology. Here we probe the nitrite reductase (NiR) activities of manganese(II)- and cobalt(II)-substituted myoglobins, and compare with data obtained previously for the iron(II) analog wt Mb^II. Both Mn^IIMb and Co^IIMb displayed NiR activity, and it was shown that the kinetics are first order each in [protein], [nitrite], and [H⁺], as previously determined for the Fe^II analog wt Mb^II. The second order rate constants (k₂) at pH 7.4 and T = 25 °C, were 0.0066 and 0.015 M^− 1 s^− 1 for Co^IIMb and Mn^IIMb, respectively, both orders of magnitude slower than the k₂ (6 M^− 1 s^− 1) for wt Mb^II. The final reaction products for Mn^IIMb consisted of a mixture of the nitrosyl Mn^IIMb(NO) and Mn^IIIMb, similar to the products from the analogous NiR reaction by wt Mb. In contrast, the products of NiR by Co^IIMb were found to be the nitrito complex Co^IIIMb(ONO⁻) plus roughly an equivalent of free NO. The differences can be attributed in part to the stronger coordination of inorganic nitrite to Co^IIIMb as reflected in the respective M^IIIMb(ONO⁻) formation constants K_nitrite: 2100 M^− 1 (Co^III) and <~0.4 M^− 1 (Mn^III). We also report the formation constants (3.7 and 30 M^− 1, respectively) for the nitrite complexes of the mutant metmyoglobins H64V Mb^III(NO₂⁻) and H64V/V67R Mb^III(ONO⁻) and a K_nitrite revised value (120 M^− 1) for the nitrite complex of wt metMb. The respective K_nitrite values for the three ferric proteins emphasize the importance of a H-bonding residue, such as His64 in the Mb^III distal pocket or the Arg67 in H64V/V67R Mb^III, in stabilizing nitrite coordination. Notably, the NiR activities of the corresponding ferrous Mbs follow a similar sequence suggesting that nitrite binding to these centers are analogously affected by the H-bonding residues.     

Does scope for growth change as a result of salinity stress in the amphipod Gammarus oceanicus?

Physiological performance (feeding, metabolism, growth and excretion) across a broad range of salinity (5-30 psu) were determined for the benthic amphipod Gammarus oceanicus, a species of marine origin inhabiting brackish waters of the southern Baltic Sea. Feeding rates decreased with increasing salinity, whereas the nutritive absorption efficiency increased. Faeces production and ammonia excretion rates decreased strongly from the lowest to the highest salinity by 60% and 58%, respectively. Increasing salinity was accompanied by a reduction in the metabolic rate from 438 J g^− 1 dry wt d^− 1 (5.1 mW g^− 1) at 5 psu to 245 J g^− 1 (2.8 mW g^− 1) at 30 psu. Individuals were able to maintain a positive energy balance at all experimental salinities. The greatest values for scope for growth were recorded at the environmental salinity (7 psu) with a mean of 769 J g^− 1 dry wt d^− 1 (8.7 mW g^− 1).     

Probing valence and spin situations in selective ruthenium-iminoquinonoid frameworks. An experimental and DFT analysis

The ruthenium-iminoquinone complexes, [Ru(tpm)(Cl)(Q)]⁺ [tpm = tris(1-pyrazolyl)methane, Q = 3,5-di-tert-butyl-N-aryl-1,2-benzoquinonemonoimine, where aryl = C₆H₅, [1]⁺; m-(OCH₃)₂C₆H₃, [2]⁺; m-(Cl)₂C₆H₃, [3]⁺] have been synthesized. The sensitive bond distances of “Q” in [1](ClO₄) and [2](ClO₄), C-O: 1.294(8), 1.281(2) Å; C-N: 1.352(8), 1.335(2) Å; and C-C(meta): 1.366(10)/1.367(9) Å, 1.364(2)/1.353(2) Å, respectively, and other analytical as well as theoretical (DFT) events suggest the valence configuration of [Ru^III(tpm)(Cl)(Q_Sq⁻)]⁺ for [1]⁺-[3]⁺. The paramagnetic [1]⁺-[3]⁺ show sharp ¹H NMR spectra with strikingly small J of 1.8-3.0 Hz. The DFT calculations on [1]⁺ predict that the triplet (S = 1) state exists above (1004 cm⁻¹) the singlet (S = 0) ground state. [1]⁺ exhibits μ = 2.2 BM at 300 K which diminishes to 0.3 BM near 2 K due to the steady decrease in the ratio of triplet to singlet population with the lowering of temperature. [1]⁺-[3]⁺ exhibit one oxidation and two successive reductions each in CH₃CN. Experimental and DFT analyses collectively establish the valence configurations at the non-innocent {Ru-Q} interface along the redox chain as [(tpm)(Cl)Ru^III(Q_Q^o)]²⁺ ([1]²⁺-[3]²⁺) → [(tpm)(Cl)Ru^III(Q_Sq⁻)]⁺ ([1]⁺-[3]⁺) → [(tpm)(Cl)Ru^II(Q_Sq⁻)] ↔ [(tpm)(Cl)Ru^III(Q_Cat)] (1-3) → [(tpm)(Cl)Ru^II(Q_Cat)]⁻ ([1]⁻-[3]⁻). The spectral features of [1]ⁿ-[3]ⁿ (n = +2, +1, 0) have been addressed based on the TD-DFT calculations on [1]ⁿ.     

Formation of a wrapped DNA-protein interface: experimental characterization and analysis of the large contributions of ions and water to the thermodynamics of binding IHF to H' DNA

To characterize driving forces and driven processes in formation of a large-interface, wrapped protein-DNA complex analogous to the nucleosome, we have investigated the thermodynamics of binding the 34-base pair (bp) H′ DNA sequence to the Escherichia coli DNA-remodeling protein integration host factor (IHF). Isothermal titration calorimetry and fluorescence resonance energy transfer are applied to determine effects of salt concentration [KCl, KF, K glutamate (KGlu)] and of the excluded solute glycine betaine (GB) on the binding thermodynamics at 20 °C. Both the binding constant K_obs and enthalpy ΔH°_obs depend strongly on [salt] and anion identity. Formation of the wrapped complex is enthalpy driven, especially at low [salt] (e.g., ΔH^o_obs = − 20.2 kcal·mol^− 1 in 0.04 M KCl). ΔH°_obs increases linearly with [salt] with a slope (dΔH°_obs/d[salt]), which is much larger in KCl (38 ± 3 kcal·mol^− 1 M^− 1) than in KF or KGlu (11 ± 2 kcal·mol^− 1 M^− 1). At 0.33 M [salt], K_obs is approximately 30-fold larger in KGlu or KF than in KCl, and the [salt] derivative SK_obs = dlnK_obs/dln[salt] is almost twice as large in magnitude in KCl (− 8.8 ± 0.7) as in KF or KGlu (− 4.7 ± 0.6).A novel analysis of the large effects of anion identity on K_obs, SK_obs and on ΔH°_obs dissects coulombic, Hofmeister, and osmotic contributions to these quantities. This analysis attributes anion-specific differences in K_obs, SK_obs, and ΔH°_obs to (i) displacement of a large number of water molecules of hydration [estimated to be 1.0(± 0.2) × 10³] from the 5340 Å² of IHF and H′ DNA surface buried in complex formation, and (ii) significant local exclusion of F⁻ and Glu⁻ from this hydration water, relative to the situation with Cl⁻, which we propose is randomly distributed. To quantify net water release from anionic surface (22% of the surface buried in complexation, mostly from DNA phosphates), we determined the stabilizing effect of GB on K_obs: dlnK_obs/d[GB]  = 2.7 ± 0.4 at constant KCl activity, indicating the net release of ca. 150 H₂O molecules from anionic surface.     

The bimolecular sensitization of nitric oxide release from weak interacting ruthenium units

This work reports on the bimolecular sensitization of nitric oxide release from cis-[Ru(bpy)₂(iso)NO](PF₆)₃ (1) (iso = isoquinoline and bpy = 2,2′-bipyridine) by irradiating the MLCT transition of the chloro analog cis-[Ru(bpy)₂(iso)Cl]PF₆ (2)_. The compounds displayed peaks in the ESI-MS spectra at m/z 749.1 and m/z 578.1 ascribed, respectively, to ([1(NO⁰)−2PF₆·CH₃OH]²⁺) and ([2−PF₆]⁺). In the cyclic voltammograms, the nitrosyl complex presented two redox waves related to the NO ligand at 0.48 and −0.37 V (versus Ag/AgCl, NO^+/0/−1 processes), while the sensitizer showed two reversible waves at 0.79 and −1.46 V (versus Ag/AgCl, Ru^2+/3+ and bpy ^0/−1, respectively). The most important feature of this system is that the nitrosyl compound does not have significant absorption in the visible region, while the sensitizer has an intense band centered at 496 nm. The irradiation of an equimolar mixture of the two compounds in an ethanol:water solution (v:v) with light of λ > 500 nm leads to NO release, as probed by amperometric measurements. The variational method was applied, showing that the two compounds self-assembly in solution with a 1:1 stoichiometry. Fluorescence spectra acquired at 77 K provided the E_0-0 for the system and, from the thermodynamic cycle it was estimated that the photoinduced electron transfer between the species has a ΔG value of −1.59 eV.     

Electrochemical reduction properties of A-frame compounds and crystal structure of Pd2(dppm)2(Me)2(Br) dimer

Two series of A-frame complexes, [Pd₂(dppm)₂(R)₂(μ-X)]⁺ (R = Me and X = Cl, Br, I, H; R = Mes and X = Br, I), were investigated by cyclic voltammetry (CV). The 2-electron reduction potentials for the first series increase from I (−1.10), Br (−1.17), Cl (−1.25) to H (−1.65 V versus SCE, in CHCl₃), as well as in the second series; Br (−1.35) and I (−1.38 V versus SCE, in THF). The nature of the LUMO where the electron reduction takes place is qualitatively addressed by DFT on the corresponding model complexes [Pd₂(H₂PCH₂PH₂)₂(R)₂(μ-X)]⁺. The LUMO and (LUMO + 1) of the halide derivatives exhibit the presence of Pd d_x²-y² atomic orbitals interacting in an anti-bonding fashion with the n-donor orbitals of X⁻, P, and Me⁻, explaining in part the observed reactivity upon reduction. The X-ray structure of [Pd₂(dppm)₂(Me)₂(μ-Br)]⁺ compound exhibits the typical A-frame structure with a Pd?Pd non-bonding distance of 3.036(1) Å, and long Pd-Br bonds of 2.5623(5) and 2.5793(5) Å.