On the identification of ionic species of neutral halogen dimers, monomers and pincer type palladacycles in solution by electrospray mass and tandem mass spectrometry

Electrospray (ESI) mass spectra analysis of acetonitrile solutions of a series of neutral chloro dimers, pincer type, and monomeric palladacycles has enabled the detection of several of their derived ionic species. The monometallic cationic complexes Pd[κ¹-C,κ¹-N,κ¹-S-C(CH₃S-2-C₆H₄)C(Cl)CH₂N(CH₃)₂]⁺ (1a) and [Pd[κ¹-C,κ¹-N,κ¹-S-C(CH₃S-2-C₆H₄)C(Cl)CH₂N(CH₃)₂](CH₃CN)]⁺ (1b) and the bimetallic cationic complex [κ¹-C,κ¹-N,κ¹-S-C(CH₃S-2-C₆H₄)C(Cl)CH₂N(CH₃)₂]Pd-Cl-Pd[κ¹-C,κ¹-N,κ¹-S-C(CH₃S-2-C₆H₄)C(Cl)CH₂N(CH₃)₂]⁺ (1c) were detected from an acetonitrile solution of the pincer palladacycles Pd[κ¹-C,κ¹-N,κ¹-S-C(CH₃S-2-C₆H₄)C(Cl)CH₂N(CH₃)₂](Cl) 1. For the dimeric compounds {Pd[κ¹-C,κ¹-N-C(Y-2-C₆H₄)C(Cl)CH₂N(CH₃)₂](μ-Cl)}₂ (2, Y=H and 3, CF₃), highly electronically unsaturated palladacycles [Pd[κ¹-C,κ¹-N-C(Y-2-C₆H₄)C(Cl)CH₂N(CH₃)₂]⁺ (2d, 3d) and their mono and di-acetonitrile adducts, namely, [Pd[κ¹-C,κ¹-N-C(Y-2-C₆H₄)C(Cl)CH₂N(CH₃)₂](CH₃CN)]⁺ (2e, 3e) and [Pd[κ¹-C,κ¹-N-C(Y-2-C₆H₄)C(Cl)CH₂N(CH₃)₂](CH₃CN)₂]⁺ (2f and 3f) were detected together with the bimetallic complex [Pd[κ¹-C,κ¹-N-C(Y-2-C₆H₄)C(Cl)CH₂N(CH₃)₂]-Cl-Pd[κ¹-C,κ¹-N-C(Y-2-C₆H₄)C(Cl)CH₂N](CH₃)₂]⁺ (2a, 3a) and its acetonitrile adducts [κ¹-C,κ¹-N-C(Y-2-C₆H₄)C(Cl)CH₂N(CH₃)₂](CH₃CN)Pd-Cl-Pd[ κ¹-C,κ¹-N-C(Y-2-C₆H₄)C(Cl)CH₂N(CH₃)₂]⁺ (2b, 3b) and [κ¹-C,κ¹-N-C(Y-2-C₆H₄)C(Cl)CH₂N(CH₃)₂](CH₃CN)Pd-Cl-Pd[κ¹-C, κ¹-N-C(Y-2-C₆H₄)C(Cl)CH₂N(CH₃)₂(CH₃CN)]⁺ (2c, 3c). The dimeric palladacycle {Pd[κ¹-C,κ¹-N-C(CH₃O-2-C₆H₄)C(Cl)CH₂N(CH₃)₂](μ-Cl)}₂ (4) is unique as it behaves as a pincer type compound with the OCH₃ substituent acting as an intramolecular coordinating group which prevents acetonitrile full coordination, thus forming the cationic complexes [(C₆H₄(o-CH₃O)CC(Cl)CH₂N(CH₃)₂-κO,κC,κN)Pd]⁺ (4b), [(C₆H₄(o-CH₃O)CC(Cl)CH₂N(CH₃)₂- κO,κC,κN)Pd(CH₃CN)]⁺ (4c) and [(C₆H₄ (o-MeO)CC(Cl)CH₂N(CH₃)₂-κO, κC,κN)Pd-Cl-Pd(C₆H₄(o-CH₃O)CC(Cl)CH₂N(CH₃)₂-κO,κC,κN)]⁺ (4a). ESI-MS spectra analysis of acetonitrile solutions of the monomeric palladacycles Pd[κ¹-C,κ¹-N-C(Y-2-C₆H₄)C(Cl)CH₂N(CH₃)₂](Cl)(Py) (5, Y=H and 6, Y=CF₃) allows the detection of some of the same species observed in the spectra of the dimeric palladacycles, i.e., monometallic cationic 2d-3d, 2e-3e and {Pd[κ¹-C,κ¹-N-C(Y-2-C₆H₄)C(Cl)CH₂N(CH₃)₂](Py)}⁺ (5a, 6a) and {Pd[κ¹-C,κ¹-N-C(Y-2-C₆H₄)C(Cl)CH₂N(CH₃)₂](CH₃CN)(Py)}⁺ (5b, 6b) and the bimetallic 2a, 3a, 2b, 3b, 2c and 3c. In all cationic complexes detected by ESI-MS, the cyclometallated moiety was intact indicating the high stability of the four or six electron anionic chelate ligands. The anionic (chloride) or neutral (pyridine) ligands are, however, easily replaced by the acetonitrile solvent.     

Optimized labeling of 13CHD2 methyl isotopomers in perdeuterated proteins: Potential advantages for 13C relaxation studies of methyl dynamics of larger proteins

¹³CHD₂ methyl isotopomers are particularly useful to study methyl dynamics in proteins because, as compared with other methyl isotopomers, the ¹³C relaxation mechanism for this isotopomer is straightforward. However, in the case of proteins, where ()² 1, the refocused INEPT pulse sequence does not completely suppress unwanted ¹³CH₃ signals. The presence of weak ¹³CH₃ peaks is usually not a serious problem for smaller proteins because there are relatively few methyl signals and they are sharp; however, signal overlap becomes more common as the size of the protein increases. We overcome this problem by preparing a protein using a 98% D₂O cell culture medium containing 3-¹³C pyruvic acid, 50–60% deuterated at the 3-position, and 4-¹³C 2-ketobutyric acid, 98% and 62% deuterated at the 3- and 4-positions, respectively. This approach significantly reduces the population of the CH₃ isotopomer while optimizing the production of ¹³CHD₂, the isotopomer desired for ¹³C relaxation measurements. In larger proteins where the deuterium T₂ may be too short to measure accurately, we also suggest the alternative measurement of the proton T₂ of the ¹³CH₂D methyl isotopomer, because these protons are well-isolated from other protons in these highly deuterated samples.     

Syntheses and structural analyses of chiral rhenium containing amines of the formula (η-C5H5)Re(NO)(PPh3)((CH2)nNRR′) (n = 0, 1)

The reaction of the racemic chiral methyl complex (η⁵-C₅H₅)Re(NO)(PPh₃)(CH₃) (1) with CF₃SO₃H and then NH₂CH₂C₆H₅ gives [(η⁵-C₅H₅)Re(NO)(PPh₃)(NH₂CH₂C₆H₅)]⁺ ([4a-H]⁺; 73%), and deprotonation with t-BuOK affords the amido complex (η⁵-C₅H₅)Re(NO)(PPh₃)(NHCH₂C₆H₅) (76%). Reactions of 1 with Ph₃C⁺ X⁻ and then primary or secondary amines give [(η⁵-C₅H₅)Re(NO)(PPh₃)(CH₂NHRR′)]⁺ X⁻ ([6-H]⁺ X⁻; R/R′/X = a, H/NH₂CH₂C₆H₅/BF₄; a′, H/NH₂CH₂C₆H₅/PF₆; b, H/NH₂CH₂(CH₂)₂CH₃/PF₆; c, H/(S)-NH₂CH(CH₃)C₆H₅/BF₄); d, CH₂CH₃/CH₂CH₃/PF₆; e, CH₂(CH₂)₂CH₃/CH₂(CH₂)₂CH₃/PF₆; f, CH₂C₆H₅/CH₂C₆H₅/PF₆; g, -CH₂(CH₂)₂CH₂-/PF₆; h, -CH₂(CH₂)₃CH₂-/PF₆; i, CH₃/CH₂CH₂OH/PF₆ (62-99%). Deprotonations with t-BuOK afford the amines (η⁵-C₅H₅)Re(NO)(PPh₃)(CH₂NRR′) (6a-i; 99-40%), which are more stable and isolated in analytically pure form when R ≠ H. Enantiopure 1 is used to prepare (R_ReS_C)-[6c-H]⁺, (R_ReS_C)-6c, (S)-[6g-H]⁺, and (S)-6g. The crystal structures of [4a-H]⁺, a previously prepared NH₂CH₂Si(CH₃)₃ analog, [6a′,d,f,h-H]⁺, (R_ReS_C)-6c, and 6f are determined and analyzed in detail, particularly with respect to cation/anion hydrogen bonding and conformation. In contrast to analogous rhenium containing phosphines, 6a-i show poor activities in reactions that are catalyzed by organic amines.     

Investigation on the coordination modes: Syntheses, characterization and crystal structures of diorganotin (IV) dichloride with 4(5)-imidazoledithiocarboxylic acid

A series of diorganotin (IV) complexes of the types of R₂SnCl(SSCC₃H₃N₂) (R = CH₃1, ⁿBu 2, C₆H₅3 and C₆H₅CH₂4), R₂Sn(SSCC₃H₃N₂)₂ (R = CH₃5, ⁿBu 6, C₆H₅7 and C₆H₅CH₂8) and R₂Sn(SSCC₃H₂N₂) (R = CH₃9, ⁿBu 10, C₆H₅11 and C₆H₅CH₂12) have been obtained by reactions of 4(5)-imidazoledithiocarboxylic acid with diorganotin (IV) dichlorides in the presence of sodium ethoxide. All complexes are characterized by elemental, IR, ¹H, ¹³C and ¹¹⁹Sn NMR spectra analyses. Also, the complexes 1, 7 and 9 are characterized by X-ray crystallography diffraction analyses, which reveal that the complex 1 is monomeric structure with five-coordinate tin (IV) atom, the complex 7 is monomeric structure with six-coordinate tin (IV) atom and the complex 9 is one-dimensional chain with five-coordinate tin (IV) atom.     

Solution-phase disproportionation equilibria for monosubstituted Pentakis- (arylisocyanide)cobalt(I) complexes by proton-NMR studies

Equilibrium constants, K_dis, for the solvent- dependent, solution-phase disproportionation equilibria of monosubstituted pentakis(arlisocyanide)cobalt(I) complexes: 2[Co(CNR)₄L]⁺?[Co(CNR)₃L₂]⁺ + [Co(CNR)₅]⁺, K_dis = $\text{[Co(CNR)}{}_3\text{L}{}_2\text{][Co(CNR)}{}_5\text{]}\text{[Co(CNR)}{}_4\text{L]}{}^2$ are measured by planimeter-integration of proton- NMR spectra at ambient temperature. The complexes, [Co(CNR)₄L]ClO₄, R = 2,6-Me₂C₆H₃, L = P(C₆H₅)₃, P(C₆H₄Cl-p)₃, P(OC₆H₅)₃, P(OC₆H₄Cl-p)₃; R = o-MeC₆H₄, L = P(C₆H₄Cl-p)₃, P(OC₆H₅)₃, P(OC₆H₄Cl-p)₃; R = 2,4,6-Me₃C₆H₂, L = P(C₆H₅)₃; R = 2,6-Et₂C₆H₃, L = P(C₆H₅)₃; are investigated in the deuterated solvents, CDCl₃, CD₃CN, (CD₃)₂CO, C₅D₅N, CD₃NO₂, and (CD₃)₂SO. Disproportionation seems to occur in all [Co(CNR)₄L]⁺, but NMR study is facilitated by utilizing equivalent alkyl protons (i.e., Me-groups) on the RNC ligands.Correlation of K_dis values with steric-hindrance of the RNC in sets of complexes with the same P-ligand is evident in all solvents: K_dis decreases with increased steric-hindrance in RNC. The K_dis values for complexes with the same RNC and analogous triarylphosphine, triarylphosphite ligands (i.e., PR₃, P(OR)₃, same R) are approximately equal. The K_dis values for complexes of P-ligands with Cl-substituent are significantly larger than K_dis values for complexes with the corresponding unsubstituted P-ligands (e.g., [Co(CNR)₄P(C₆H₄Clp)₃]ClO₄vs. [Co(CNR)₄P(C₆H₅)₃]ClO₄) in (CD₃)₂CO and C₅D₅N solution, but are smaller in CDCl₃ and CD₃CN, and approximately equal in CD₃NO₂ and (CD₃)₂SO. Properties of the solvents are also considered.     

Intramolecular activation of pendant alkenyl group as a tool for modification of the zirconocene framework

The diphenyl zirconocene [(η⁵-C₅H₅){η⁵-C₅H₄CMe₂(CH₂)₂CHCH₂}ZrPh₂] (2) was readily obtained from the corresponding zirconocene dichloride 1 and two equivalents of phenyllithium. Upon thermal treatment at 80 °C, complex 2 released benzene, with concomitant activation of the pendant double bond and formation of intramolecularly α-tethered zirconaindane [(η⁵-C₅H₅){η⁵,η¹,η¹-C₅H₄CMe₂(CH₂)₂CHCH₂C₆H₄}Zr] (3). Both Zr-C σ-bonds in 3 easily undergo nucleophilic reactions with two equivalents of HCl or one equivalent of Cl₂PPh giving rise to zirconocene dichlorides with pendant phenyl group [(η⁵-C₅H₅){η⁵-C₅H₄CMe₂(CH₂)₄Ph}ZrCl₂] (4) or with 1-phenylphosphindolinyl moiety [(η⁵-C₅H₅){η⁵-C₅H₄CMe₂(CH₂)₂cyclo-CHCH₂C₆H₄P(Ph)}ZrCl₂] (5), respectively.     

Reactivity of a new family of diamido-diamine cyclam-based zirconium complexes in ethylene polymerization

Compounds of general formula [(^∗Bn₂Cyclam)ZrCl₂] (^∗Bn = 4-^tBuC₆H₄CH₂, (4) and 4-CF₃C₆H₄CH₂, (5)) were synthesised using Zr(CH₂SiMe₃)₂Cl₂(Et₂O)₂ and the corresponding ligand precursors 1,8-(4-^tbutylbenzyl)-1,4,8,11-tetraazacyclotetradecane (H₂(4-^tBuBn)₂Cyclam), (4a), and 1,8-(4-trifluoromethylbenzyl)-1,4,8,11-tetraazacyclotetradecane (H₂(4-CF₃Bn)₂Cyclam), (5a). Complexes 4 and 5, in addition to other [(^∗Bn₂Cyclam)ZrCl₂] compounds previously described by some of us (^∗Bn = PhCH₂, (1), 3,5-Me₂C₆H₃CH₂, (2) and 3,5-^tBu₂C₆H₃CH₂, (3)) were tested in the polymerization of ethylene in the presence of MAO. System 4/MAO presents the highest activity (2790 g PE molZr⁻¹ h⁻¹ atm⁻¹). The polymers formed are slight to moderately branched polyethylenes with a percentage of branching ranging between 1.2% and 3.3%. The melting points obtained by differential scanning calorimetry (DSC) ranging from 128 to 140 °C, are consistent with rather high average molecular weight polymers with crystallinity close to 50%.     

Synthesis and solid-state structures of (triphos)iridacyclopentadiene complexes as models for vinylidene intermediates in the [2 + 2 + 1] cyclotrimerization of alkynes

The iridium 1,1,1-tris(diphenylphosphinomethyl)ethane (triphos) complexes [{κ²(C¹,C⁴)-CRCRCRCR}{CH₃C(CH₂PPh₂)₃}Ir(NCMe)]BF₄ (2-NCMe, R = CO₂Me) and [{κ²(C¹,C⁴)-CRCRCRCR}{CH₃C(CH₂PPh₂)₃}Ir(CO)]BF₄ (2-CO, R = CO₂Me) serve as models for proposed iridium-vinylidene intermediates of relevance to the [2 + 2 + 1] cyclotrimerization of alkynes. The solid-state structures of 2-NCMe, 2-CO, and [κ²(C¹,C⁴)-CRCRCRCR]{CH₃C(CH₂PPh₂)₃}Ir(Cl) (2-Cl), were determined by X-ray crystallography.     

An improved formula for evaluating electrical capacitance using the dissipation factor

Background and aims

The measurement of electrical capacitance in root–soil system (C_R) is a useful method for estimating the root system size (RSS) in situ; however, C_R–RSS regressions are often poor. It was hypothesized that this weak relationships could be partly due to the variable energy-loss rate, indicated by the dissipation factor (DF).

Methods

The values of C_R and the associated DF were measured in six plant species grown in quasi-hydroponic pumice medium, arenosol and chernozem soil. The dielectric properties of the plant growth media were also recorded. A modified root–soil capacitance, C_DF, was calculated from each C_R/DF pair according to the formula C_DF = C_R·(DF/DF_mean)^α by estimating α with a standard nonlinear minimization of the sum of squared residuals for C_DF–RSS regressions.

Results

The capacitive behavior of the medium improved (mean DF decreased) but fluctuated increasingly as the substrate became more complex. The mean DF values in plant–substrate systems were chiefly determined by the plant and were the most variable in chernozem soil. This strengthening substrate effect on C_R measurements appeared as a decreasing trend in the R² values obtained for the C_R–RSS regressions. The regression slope was influenced by plant species and medium, while the y-intercept differed only between substrate types. The proposed use of C_DF in place of C_R could significantly improve the R² of C_DF–RSS regressions, particularly in chernozem soil (R² increased by 0.07–0.31).

Conclusions

The application of C_DF will provide more reliable and accurate RSS estimations and more efficient statistical comparisons. The findings are worth considering in future investigations using the root capacitance method.

     

Synthesis, reactivity, and structures of dialuminum complexes containing linked ketiminate ligands

Linked bis(ketimine) (1) can be prepared with the reaction of excess 2,4-pentanedione and 4,4′-methylene-bis(2,6-diisopropylaniline) in methanol in the presence of catalytic amount of formic acid. The dialuminum alkyl complexes containing the linked bis(ketiminate) dianionic ligands, [OC(Me)CHC(Me)N(2,6-ⁱPr₂C₆H₂-4)AlR₂]₂CH₂ (2, R = Me; 3, R = Et), were prepared by a reaction of 2 equiv AlR₃ with [OC(Me)CHC(Me)NH(2,6-ⁱPr₂C₆H₂-4)]₂CH₂ in methylene chloride. Reactions of 2 with 2 and 4 equiv of I₂ gave corresponding aluminum iodo complexes 4 and 5, respectively. Treatment of 5 with 2 equiv of AgBF₄, however, gave a diboron complex, [OC(Me)CHC(Me)N(2,6-ⁱPr₂C₆H₂-4)BF₂]₂CH₂ (6), in 18% isolated yield. All new complexes have been characterized by ¹H and ¹³C NMR spectroscopy and complexes 2, 3, and 6 are also confirmed by X-ray diffraction.     

Synthesis of cyclopentadienyl ruthenium(II) complexes containing tethered functionalities

The reaction of [C₅H₄(CH₂)_nX]Tl (1: n = 2, X = NMe₂, OMe, CN; n = 3, X = NMe₂) with [(η⁶-C₆H₆)RuCl(μ-Cl)]₂, 2, afforded the sandwich compounds [{η⁵-C₅H₄(CH₂)_nX}Ru(η⁶-C₆H₆)]PF₆, 3, and [η⁵-C₅H₄(CH₂)_nX]₂Ru, 4. Photolytic cleavage of 3 in acetonitrile afforded the tethered products [{η⁵:κN-C₅H₄(CH₂)_nX}Ru(CH₃CN)₂]PF₆, 5.     

Indium complexes incorporating bidentate substituted pyrrole ligand: Synthesis, characterization, and ring-opening polymerization of ε-caprolactone

The reactions of InCl₃ with two and three equivalents of lithium (2-dimethylaminomethyl)pyrrolate (1) in diethyl ether solutions afford In[C₄H₃N(CH₂NMe₂)]₂Cl (2) and In[C₄H₃N(CH₂NMe₂)]₃ (3) in 92% and 50% yield, respectively. Subsequent reactions of 2 with MeLi and Li(CCPh) yield In[C₄H₃N(CH₂NMe₂)]₂Me (4) and In[C₄H₃N(CH₂NMe₂)]₂(CCPh) (5), respectively. All compounds were confirmed by ¹H and ¹³C NMR spectroscopy and compounds 3, 4, and 5 were further characterized by single-crystal X-ray crystallography. Compounds 2, 3, and 4 showed moderate catalytic activity toward the ring-opening polymerization of ε-caprolactone.     

Mononuclear and tetranuclear palladacycles with terdentate [C,N,N] and [C,N,O] Schiff base ligands. C-H versus C-Br activation reactions

Reaction of the Schiff base ligands 2-Br-4,5-(OCH₂O)C₆H₂C(H)NCH₂CH₂NMe₂ (a) and 4,5-(OCH₂CH₂)C₆H₃C(H)NCH₂CH₂NMe₂ (b) with Pd(OAc)₂ or K₂[PdCl₄] leads to the mononuclear cyclometallated compounds [Pd{2-Br-4,5-(OCH₂O)C₆HC(H)NCH₂CH₂NMe₂-C6,N,N}(OCOMe)] (1a) and [Pd{4,5-(OCH₂CH₂)C₆H₂C(H)NCH₂CH₂NMe₂-C6,N,N}(Cl)] (1b), derived from C-H activation at the C6 carbon. Treatment of a with Pd₂(dba)₃ gave [Pd{4-5-(OCH₂O)C₆H₂C(H)NCH₂CH₂NMe₂-C2,N,N}(Br)] (2a), via C-Br activation.The metathesis reaction of 1a with aqueous sodium chloride gave [Pd{2-Br-4,5-(OCH₂O)C₆HC(H)NCH₂CH₂NMe₂-C6,N,N}(Cl)] (3a), with exchange of the acetate group by a chloride ligand. Treatment of the cyclometallated monomers 1a-3a with PPh₃ in a 1:1 molar ratio yielded the mononuclear complexes [Pd{2-Br-4,5-(OCH₂O)C₆HC(H)NCH₂CH₂NMe₂-C6,N}(L)(PPh₃)] (L: OAc, 4a; Cl, 5a) and [Pd{4-5-(OCH₂O)C₆H₂C(H)NCH₂CH₂NMe₂-C2,N}(Br)(PPh₃)] (6a), with Pd-NMe₂ bond cleavage. However, treatment of a solution of 3a or 2a with silver trifluoromethanesulfonate, followed by reaction with PPh₃ in acetone yielded the cyclometallated complexes [Pd{2-Br-4,5-(OCH₂O)C₆HC(H)NCH₂CH₂NMe₂-C6,N,N}(PPh₃)][CF₃SO₃] (7a) and [Pd{4-5-(OCH₂O)C₆H₂C(H)NCH₂CH₂NMe₂-C2,N,N}(PPh₃)][CF₃SO₃] (8a), respectively, where the Pd-NMe₂ bond was retained.The reaction of the ligands 2-Br-4,5-(OCH₂O)C₆H₂C(H)N(2′-OH-5′-^tBuC₆H₃) (c) and 4,5-(OCH₂CH₂)C₆H₃C(H)N(2′-OH-5′-^tBuC₆H₃) (d) with Pd(OAc)₂ gave the tetranuclear complexes [Pd{2-Br-4,5-(OCH₂O)C₆HC(H)N(2′-O-5′-^tBuC₆H₃)-C6,N,O}]₄ (1c) and [Pd{4,5-(OCH₂CH₂)C₆H₂C(H)N(2′-O-5′-^tBuC₆H₃)-C6,N,O}]₄ (1d), respectively. Treatment of 1c with PPh₃ in 1:4 molar ratio, gave the mononuclear species [Pd{2-Br-4,5-(OCH₂O)C₆HC(H)N(2′-(O)-5′-^tBuC₆H₃)-C6,N,O}(PPh₃)] (2c) with opening of the polynuclear structure after P-O_bridging bond cleavage.The structure of compounds 2a, 1c and 1d has been determined by X-ray diffraction analysis.     

New κ-PNN′- and κ-PNN′O-polydentate ligands: Synthesis, coordination and structural studies

The three-step synthesis of new mixed P/N/N′/O-donor ligands C₆H₃(OH){2-NHC(O)CH₂NCHC₆H₄PPh₂}(4-CH₃) 3a·HH and C₆H₄(OH){3-NHC(O)CH₂NCHC₆H₄PPh₂} 3b·HH, by Schiff base condensation of the 1° amines C₆H₃(OH){2-NHC(O)CH₂NH₂}(4-CH₃) 2a or C₆H₄(OH){3-NHC(O)CH₂NH₂} 2b with C₆H₄(CHO)(2-PPh₂) in refluxing EtOH, is described. Reaction of 1 equiv. of 3a·HH or 3b·HH with MCl₂(cod) (M = Pt, Pd; cod = cycloocta-1,5-diene) affords the κ²-PN-chelate complexes MCl₂(3a·HH) (M = Pd 4a; M = Pt 4b) and MCl₂(3b·HH) (M = Pt 4c). The dichlorometal(II) complexes 4d and 4e, bearing instead a pendant 4-phenolic group, were similarly prepared (in >90% yield). Chloro-bridge cleavage of [Pd(μ-Cl)(η³-C₃H₅)]₂ with 3a·HH or 3b·HH gave the monocationic κ²-PN-chelate complexes [Pd(η³-C₃H₅)(3a·HH)]Cl 5a or [Pd(η³-C₃H₅)(3b·HH)]Cl 5b, respectively. Elimination of cod, and single CH₃ protonation, from Pt(CH₃)₂(cod) upon reaction with 1 equiv. of 3a·HH or 3b·HH in C₇H₈ at room temperature afforded the neutral complexes C₆H₃(OH){2-NC(O)CH₂NCHC₆H₄PPh₂Pt(CH₃)}(4-CH₃) 6a and C₆H₄(OH){3-NC(O)CH₂NCHC₆H₄PPh₂Pt(CH₃)} 6b, respectively bearing a monoanionic (3a·H⁻ or 3b·H⁻) κ³-PNN′-tridentate ligand. Amide and phenol deprotonation were readily achieved, using KO^tBu as base, to give high yields of the κ⁴-PNN′O-tetradentate complexes C₆H₃(O){2-NC(O)CH₂NCHC₆H₄PPh₂Pd}(4-CH₃) 7a and C₆H₃(O){2-NC(O)CH₂NCHC₆H₄PPh₂Pt}(4-CH₃) 7b bearing the dianionic ligand 3a²⁻. All new compounds have been characterised by multinuclear NMR, FTIR, mass spectroscopy and microanalysis. Single crystal X-ray studies have been performed on compounds 1b·1.5CH₂Cl₂, 3b·HH·0.5Et₂O, 6b·CHCl₃ and 7b·0.5Et₂O.     

Solvent and electrolyte effects in enhancing the identification of intramolecular electronic communication in a multi redox-active diruthenium tetraferrocenoate complex, a triple-sandwiched dicadmium phthalocyanine and a ruthenocene-containing β-diketone

Enhanced electrochemical resolution of anodic processes is possible in the presence of [N(ⁿBu)₄][B(C₆F₅)₄], 1, as supporting electrolyte over that obtained in the presence of [N(ⁿBu)₄][PF₆]. By changing the anion of the supporting electrolyte to a salt having [B(C₆F₅)₄]⁻, anions, electrochemical processes of especially cationic analytes can benefit. Thus, the redox chemistry of 0.5 mmol dm⁻³ solutions of [Ru₂(μ-FcCOO)₄·(CH₃CH₂OH)₂][PF₆], 2, Fc = ferrocenyl, in CH₂Cl₂/[N(ⁿBu)₄][B(C₆F₅)₄] were found to involve four well-resolved ferrocenyl-based electrochemical reversible redox processes as well as reduction of Ru^III-Ru^II. At 1.0 mmol dm⁻³ concentrations of 2, or in the presence of [N(ⁿBu)₄][PF₆], the four ferrocenyl processes coalesced into only two waves as a result of (Fc⁺)?() ion paring. Seventeen of the possible 18 one-electron transfer processes of the biscadmium trisphthalocyaninato complex [Cd₂{Pc(C₆H₁₃)₈}₃], 3, could be observed in THF/[N(ⁿBu)₄][B(C₆F₅)₄], but the electrochemical window of CH₂Cl₂/[N(ⁿBu)₄][B(C₆F₅)₄] only allowed detection of 15 of these processes. Although reduction processes were unaffected, THF solvation leading to species such as (3ⁿ⁺)(THF)_x with 1 ? n ? 4 and x ? 1 as well as ion pair formation of the type (3ⁿ⁺)?() prevented good resolution of oxidation processes. The CH₂Cl₂/[N(ⁿBu)₄][B(C₆F₅)₄] system also allowed detection of reversible one-electron transfer ferrocenyl (Fc/Fc⁺) and ruthenocenyl-based (Rc/Rc⁺) processes for both enol and keto isomers of the β-diketone FcCOCH₂CORc, 4, Rc = ruthenocenyl. In CH₃CN/[N(ⁿBu)₄][PF₆], the ruthenocenyl moiety was oxidised to a Ru^IV species.     

Biotic and abiotic methane releases from Lake Biwa sediment slurry

To determine the rate and mechanism of CH₄ production in Lake Biwa sediment, slurry was prepared and incubated. Surface sediment (sed) slurry (1.5–6cm) showed a CH₄ release rate (4.9–9.5nmolg-dry-sed^–1 day^–1) higher than that observed in the 5- to 10-cm sediment slurry (0.2–2nmolg-dry-sed^–1 day^–1). Methane release from the surface (1.5–6cm) sediment slurry was biotic and was inhibited by addition of 2-bromoethanesulfonate (BES, an inhibitor of CH₄ production), whereas that from 5- to 10-cm sediment slurry was abiotic. The addition of BES, HNO₃, and O₂ showed no effect on the CH₄ release rate from the 5- to 10-cm sediment slurry. In addition, tracers (NaH¹³CO₃, ¹³CH₃COONa) were not incorporated into the released CH₄. However, ¹³C of CH₄ released from the 5- to 10-cm sediment slurry (–74.0 ± 0.6) indicated that this CH₄ was produced by bacterial metabolism in the past, stored by adsorption on the surface of clay minerals in the sediment, and then released abiotically by desorption from the sediment slurry as a result of a decrease in hydraulic pressure and CH₄ concentration in the pore water. This CH₄ stored by adsorption could be extracted by autoclaving. In the sediment below 5cm, bacterial activity for CH₄ production ceased, possibly because of the limitated availability of H₂. To clarify the mechanism of CH₄ production in the sediment, biotic CH₄ production and the abiotic CH₄ release found here should be estimated separately.     

Effect of soil characteristics on sequential reduction and methane production in sixteen rice paddy soils from China, the Philippines, and Italy

The potentials for sequential reduction of inorganic electron acceptors and production of methane have been examined in sixteen rice soils obtained from China, the Philippines, and Italy. Methane, CO₂, Fe(II), NO ₃ ^- , SO ₄ ² , pH, E_h, H₂ and acetate were monitored during anaerobic incubation at 30 °C for 120 days. Based on the accumulation patterns of CO₂ and CH₄, the reduction process was divided into three distinct phases: (1) an initial reduction phase during which most of the inorganic electron acceptors were depleted and CO₂ production was at its maximum, (2) a methanogenic phase during which CH₄ production was initiated and reached its highest rate, and (3) a steady state phase with constant production rates of CH₄ and CO₂. The reduction phases lasted for 19 to 75 days with maximum CO₂ production of 2.3 to 10.9 mol d^-1 g^-1 dry soil. Methane production started after 2 to 87 days and became constant after about 38--68 days (one soil >120 days). The maximum CH₄ production rates ranged between 0.01 and 3.08 mol d^-1 g^-1. During steady state the constant CH₄ and CO₂ production rates varied from 0.07 to 0.30 mol d^-1 g^-1 and 0.02 and 0.28 mol d^-1 g^-1, respectively. Within the 120 d of anaerobic incubation only 6--17% of the total soil organic carbon was released into the gas phase. The gaseous carbon released consisted of 61--100% CO₂, <0.1--35% CH₄, and <5% nonmethane hydrocarbons. Associated with the reduction of available Fe(III) most of the CO₂ was produced during the reduction phase. The electron transfer was balanced between total CO₂ produced and both CH₄ formed and Fe(III), sulfate and nitrate reduced. Maximum CH₄ production rate (r = 0.891) and total CH₄ produced (r = 0.775) correlated best with the ratio of soil nitrogen to electron acceptors. Total nitrogen content was a better indicator for available organic substrates than the total organic carbon content. The redox potential was not a good predictor of potential CH₄ production. These observations indicate that the availability of degradable organic substrates mainly controls the CH₄ production in the absence of inorganic electron acceptors.     

Expression of deuterium-isotope-labelled protein in the yeast Pichia pastoris for NMR studies

Deuterium isotope labelling is important for NMR studies of large proteins and complexes. Many eukaryotic proteins are difficult to express in bacteria, but can be efficiently produced in the methylotrophic yeast Pichia pastoris. In order to facilitate NMR studies of the malaria parasite merozoite surface protein-1 (MSP1) complex and its interactions with antibodies, we have investigated production of the MSP1-19 protein in P. pastoris grown in deuterated media. The resulting deuteration patterns were analyzed by NMR and mass spectrometry. We have compared growth characteristics and levels of heterologous protein expression in cells adapted to growth in deuterated media (95% D₂O), compared with expression in non-adapted cells. We have also compared the relative deuteration levels and the distribution pattern of residual protiation in protein from cells grown either in 95% D₂O medium with protiated methanol as carbon source, or in 95% D₂O medium containing deuterated methanol. A high level of uniform C deuteration was demonstrated, and the consequent reduction of backbone amide signal linewidths in [¹H/¹⁵N]-correlation experiments was measured. Residual protiation at different positions in various amino acid residues, including the distribution of methyl isotopomers, was also investigated. The deuteration procedures examined here should facilitate economical expression of ²H/¹³C/¹⁵N-labelled protein samples for NMR studies of the structure and interactions of large proteins and protein complexes.     

Synthesis, characterization, and structural studies of mercury(II) complexes of new bidentate phosphorus ylide

The reaction of Ph₂PCH₂CH₂PPh₂ (dppe) with BrCH₂C(O)C₆H₄NO₂ (1:1.05 molar ratio) in acetone produces a mixture of the new monophosphonium salt [Ph₂PCH₂CH₂PPh₂CH₂C(O)C₆H₄NO₂]Br (1) and the diphosphonium salt [NO₂C₆H₄C(O)CH₂PPh₂CH₂CH₂PPh₂CH₂C(O)C₆H₄NO₂]Br₂ (2). Compound 2 was insoluble in acetone and thus easily separated from the solution of 1. Further, by reacting both the mono- and diphosphonium salts with the appropriate bases the bidentate phosphorus ylides, [Ph₂PCH₂CH₂PPh₂CHC(O)C₆H₄NO₂] (3) and [NO₂C₆H₄C(O)CHPPh₂CH₂CH₂PPh₂CHC(O)C₆H₄NO₂] (4) were obtained. The reaction of ligand 3 with mercury(II) halides in dry methanol leads to the formation of the P,P-coordinated monomeric complexes {HgX₂(Ph₂PCH₂CH₂PPh₂CHC(O)C₆H₄NO₂)₂} [X = Cl (5), Br (6), I (7)]. The structure of complex 7 being unequivocally determined by single crystal X-ray diffraction techniques. Characterization of these species was also performed by elemental analysis, IR spectroscopy and ¹H, ³¹P, and ¹³C NMR techniques. These analyses being consistent with a 2:1 stoichiometry ylide/Hg(II) for compounds 5 through 7. Results obtained from theoretical studies are also consistent with a product in which two ylides are coordinated to the Hg(II) center through their phosphine groups, being this product the most stable among all the possible products.     

Rotational diffusion tensor of nucleic acids from 13C NMR relaxation

Rotational diffusion properties have been derived for the DNA dodecamer d(CGCGAATTCGCG)₂ from ¹³C R₁ and R₁ measurements on the C₁, C₃, and C₄ carbons in samples uniformly enriched in ¹³C. The narrow range of C-H bond vector orientations relative to the DNA axis make the analysis particularly sensitive to small structural deviations. As a result, the R₁/R₁ ratios are found to fit poorly to the crystal structures of this dodecamer, but well to a recent solution NMR structure, determined in liquid crystalline media, even though globally the structures are quite similar. A fit of the R₁/R₁ ratios to the solution structure is optimal for an axially symmetric rotational diffusion model, with a diffusion anisotropy, D_||/D, of 2.1±0.4, and an overall rotational correlation time, (2D_||+4D)^–1, of 3.35 ns at 35 °C in D₂O, in excellent agreement with values obtained from hydrodynamic modeling.