Effect of the Composition of the Water–Dimethyl Sulfoxide Solvent on the Thermodynamics of the Formation of the [Ag(18-Crown-6)]+Complex

The effect of a water–dimethyl sulfoxide solvent (X _DMSO= 0–0.97, where X _DMSOis the mole fraction of DMSO) on the thermodynamics of complexation between Ag⁺and 18-crown-6 and the solvation of all reagents involved in this equilibrium were studied. In aqueous solutions, the complex is stable mainly because of the enthalpy contribution to _r G°. For X _DMSO> 0.3, the contributions from entropy and enthalpy become comparable in magnitude, but they are opposite in sign. In the binary solvent, the complex is most stable at X _DMSO= 0.2 to 0.3. Analysis of the enthalpy characteristics of reagent solvation showed that this solvent effect was due to the superposition of two opposite solvation contributions occurring with an increase in the DMSO concentration in the binary solvent, namely, the destabilization of the ligand solvate sphere and the formation of stable Ag⁺complexes with DMSO.     

The structure of the SF6 molecule and the SF 6 − anion excited states

The electronic and geometric structures of the ground state and a number of excited states of the SF₆ molecule and the SF ₆ ^– anion have been calculated by the discrete-variation method of the local density-functionals. The anion was found to possess a number of states stable toward the outer electron detachment, and at least one excited state stable toward dissociation. The adiabatic electron affinity (EA) was determined as 3.46 eV at the highest level of theory. This result is correlated to the high EAs of the isovalent compound SeF₆ and TeF₆; however, it does not agree with the presently accepted experimental estimate of 1.0 ± 0.2 eV for the SF₆EA value. The basic anion configuration is octahedral with a S-F bond length of 1.717 Å. The calculated limit for the highest dissociation channel of the ground state SF ₆ ^– SF ₅ ^– + F is 1.5 eV lower than the minimum of the total energy of the neutral molecule; this is in good agreement with experimental estimates.Institute for Chemical Physics, Russian Academy of Sciences, 142432 Chernogolovka. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 3, pp. 641–649, March, 1992.     

Radiolysis of [EtC5H4Mn(CO)2NO]+(PF6)– and Evolution of the Nearest Environment of the Manganese Atoms in the Complex

X-ray emission and EXAFS spectroscopies were used to examine changes in the nearest environment of manganese atoms upon radiolysis of [EtC₅H₄Mn(CO)₂NO]⁺(PF₆)^– at different energy exposures (). It was found that the initial complex loses the CO and NO ligands at = 4.5 × 10⁶ J/m². An increase in to 7.5 × 10⁶ J/m² gives rise to Mn–Mn bonds with lengths characteristic of Mn dimers. At = 9.0 × 10⁶ J/m², Mn nanoparticles are formed; they interact with the carbon atoms of EtC₅H₄ and the fluorine atoms of PF₆ anions. Further increase in = 2.6 × 10⁷ J/m² yields manganese-containing nanoparticles structured like metallic Mn; their surface atoms interact with carbon atoms formed in the disintegration of the EtC₅H₄ ligands. The formation of manganese carbides and fluorides at = 2.6 × 10⁸ J/m² reduces the content of the metal constituent in nanoparticles; this content is zero at = 4.4 × 10⁸ J/m². The final radiolysis products are manganese carbides and fluorides (or fluorocarbides).     

Density functional calculations of the structures and bond energies of Cr(CO)6 and (η6-C6H6) Cr(CO)2(CX) (X=O,S) complexes

Summary Quantum chemical calculations based on density functional theory have been performed on Cr(CO)₆, (⁶-C₆H₆)Cr(CO)₃ and (⁶-C₆H₆)Cr(CO)₂(CS) at the local and nonlocal level of theory using different functionals. Good agreement is obtained with experiment for both optimized geometries and metal-ligand binding energies. In particular, a comparison of metal-arene bond energies calculated for the (⁶-C₆H₆)Cr(CO)₃ and (⁶-C₆H₆)Cr(CO)₂(CS) complexes correlates well with kinetic data demonstrating that substitution of one CO group by CS leads to an important labilizing effect of this bond, which may be primarily attributed to a larger -backbonding charge transfer to the CS ligand as compared with CO.     

Atomistic folding simulations of the five-helix bundle protein λ(6−85)

Protein folding is a classic grand challenge that is relevant to numerous human diseases, such as protein misfolding diseases like Alzheimer’s disease. Solving the folding problem will ultimately require a combination of theory, simulation, and experiment, with theory and simulation providing an atomically detailed picture of both the thermodynamics and kinetics of folding and experimental tests grounding these models in reality. However, theory and simulation generally fall orders of magnitude short of biologically relevant time scales. Here we report significant progress toward closing this gap: an atomistic model of the folding of an 80-residue fragment of the λ repressor protein with explicit solvent that captures dynamics on a 10 milliseconds time scale. In addition, we provide a number of predictions that warrant further experimental investigation. For example, our model’s native state is a kinetic hub, and biexponential kinetics arises from the presence of many free-energy basins separated by barriers of different heights rather than a single low barrier along one reaction coordinate (the previously proposed incipient downhill folding scenario).     

On the stability of (MX6)3− complexes in halide melts of three-valent metals

ABSTRACT

The effects of volume change at dissociation equilibrium of possible anion complexes of the (MX₆)^3? type in halide melts of trivalent metals MX3 within the statistical thermodynamics based on the MSA approximation were analysed. With the help of a simplified Akdeniz–Tosi model of a mixture of charged hard spheres of different diameters and valencies, we obtained the full system of equilibrium equations including the mass action law (MAL) and the equation of state (EoS). It was shown that the simplest approximation of the complex diameter as a tripled diameter of simple ions leads to a significant overestimation of the effects of volume changes at dissociation. It was found that the complex dissociation should be accompanied by a significant increase in density in a narrow temperature interval. It can be associated with the specific manifestation of electrolytic dissociation in the case of the trivalent metal halides’ auto-complexation.     

(η6-1,2,3-Trimethoxybenzene) tricarbonylchromium complex: regioselectivity of the deprotonation

Deprotonation of (h⁶-1,2,3-trimethoxybenzene)tricarbonyl chromium with n-BuLi occurs mainly at the C4 carbon while the use of LiTMP gives predominantly the C5-substituted product.     

Detection of a β-Chlorovinyl Complex of Platinum(IV) (an Intermediate of Hydrochlorination of Acetylene by HCl Gas) on the Surface of the Mechanically Activated Salt K2PtCl6

We have used NMR spectroscopy to detect an intermediate of catalytic hydrochlorination of acetylene on the surface of the mechanically activated solid salt K₂PtCl₆: a -chlorovinyl complex of platinum(IV).     

The diastereoselectivity of the addition of tricarbonyl-(η6-2-lithiothiophene) chromium(O) complexes on aldehydes

It has been shown that the reactions of tricarbonyl(η⁶ -2-lithiothiophene)chromium(O) with various arene carboxaldehydes yields mixtures of unequal amounts of diastereoisomers, which can be separated by flash chromatography. The structures of the products have been established by ¹H NMR spectroscopy and by independent synthesis. A novel synthesis of tricarbonyl(η⁶-thiophene)-chromium(O) (1) is described.     

Cyclization of 2-methoxy-6-(substituted benzyloxy)acetophenone hydrazones in the presence of polyphosphoric acid(PPA)

Cyclization of 2-methoxy-6-benzyloxy acetophenone hydrazone gave 3-methyl-4-meth-oxy indazole and 3-methyl-4-methoxy-7-benzyl indazole in the presence of polyphosphoric acid(PPA).The hydrazone was probably converted to 2-hydroxy-6-methoxy acetophenone hydra-zone and 2-hydroxy-3-benzyl-6-methoxy acetophenone hydrazone followed by cyclization to thecorresponding indazoles in acidic conditions.Cyelization of 2-methoxy-6-(halo or alkyl or arylbenzyloxy)acetophenone hydrazones gave similar products.Cyclization of 2-methoxy-6-(p-nitrobenzyloxy)acetophenone hydrazone gave 2-(p-nitrophenyl)-3-methyl-4-methoxy benzo-furan and 3-methyl-4-methoxy indazole while 2-methoxy-6-(m-nitrobenzyloxy)acetophenonehydrazone gave 3-methyl-4-methoxy indazole,3-methyl-4-methoxy-7-(m-nitrophenyl)indazole and3-methyl-4-(m-nitrobenzyloxy)indazole.     

Evaluation of “method uncertainty” in the calibration of piston pipettes (micropipettes) using the gravimetric method in accordance with the procedure of ISO 8655-6

The gravimetric method specified by ISO 8655-6 is a standard method for calibrating piston pipettes (micropipettes). The quality of the calibration can be assessed by uncertainty evaluation, the procedure for which is described in ISO/Technical Report (TR) 20461. However, the existence of “method uncertainty” due to ambiguity in the calibration operation, which is not described in the TR, has been found in various experiments, such as the interlaboratory comparison of CCM.FF-K4.2.2011. In this report, the “method standard uncertainty” is quantified as exp(?4.51 + 0.36 ln(V ^nom/μL) + 0.05{ln(V ^nom/μL)}²) μL for a nominal volume, V ^nom, in the range from 2 μL to 10000 μL. Furthermore, the reported values in an interlaboratory comparison are confirmed to be consistent using the quantified method standard uncertainty.     

η(6)-Hexahelicene Complexes of Iridium and Ruthenium: Running along the Helix

The first η(6)-complexes of iridium and ruthenium coordinated to helicenes have been obtained. Hexahelicene (1), 2,15-dimethylhexahelicene (2), and 2,15-dibromohexahelicene (3) react with [Cp*IrCl(2)](2) and AgBF(4) in CD(3)NO(2) to afford quantitatively the complexes [Cp*Ir(η(6)-1)][BF(4)](2) (4A), [Cp*Ir(η(6)-2)][BF(4)](2) (5A), and [Cp*Ir(η(6)-3)][BF(4)](2) (6A), respectively. In all cases, the final thermodynamic products are similar, and they exhibit coordination between the 12 e(-) metal fragment [IrCp*](2+) and the terminal ring of the helicene. Monitoring the reaction by NMR shows formation of intermediates, some of which have been fully characterized in solution. These intermediates exhibit the metal fragment coordinated to the internal rings. We have also synthesized the bimetallic complex [(Cp*Ir)(2)(μ(2)-η(6):η(6)-2)][BF(4)](4) (7), achieving coordination between two units [IrCp*](2+) and the helicene 2. Following an analogous methodology, we have prepared the complex [(η(6)-cymene)Ru(η(6)-2)][BF(4)](2) (8), which has been studied by X-ray diffraction, confirming the preferential binding to the terminal aromatic ring.     

Halogenation of the Hexaphosphabenzene Complex [(Cp*Mo)2(μ,η6:η6-P6)]: Snapshots on the Reaction Progress

The oxidation of [(Cp*Mo)₂(μ,η⁶:η⁶-P₆)] ( 1 ) with halogens or halogen sources was investigated. The iodination afforded the ionic complexes [(Cp*Mo)₂(μ,η³:η³-P₃)(μ,η¹:η¹:η¹:η¹-P₃I₃)][X] (X=I₃⁻, I⁻) ( 2 ) and [(Cp*Mo)₂(μ,η⁴:η⁴-P₄)(μ-PI₂)][I₃] ( 3 ), while the reaction with PBr₅ led to the complexes [(Cp*Mo)₂(μ,η³:η³-P₃)(μ-Br)₂][Cp*MoBr₄] ( 4 ) [(Cp*MoBr)₂(μ,η³:η³-P₃)(μ,η¹-P₂Br₃)] ( 5 ) and [(Cp*Mo)₂(μ-PBr₂)(μ-PHBr)(μ-Br)₂] ( 6 ). The reaction of 1 with the far stronger oxidizing agent PCl₅ was followed via time- and temperature-dependent ³¹P{¹H} NMR spectroscopy. One of the first intermediates detected at 193 K was [(Cp*Mo)₂(μ,η³:η³-P₃)(μ-PCl₂)₂][PCl₆] ( 8 ) which rearranges upon warming to [(Cp*Mo)₂(μ-PCl₂)₂(μ-Cl)₂] ( 9 ), [(Cp*MoCl)₂(μ,η³:η³-P₃)(μ-PCl₂)] ( 10 ) and [(Cp*Mo)₂(μ,η⁴:η⁴-P₄)(μ-PCl₂)][Cp*MoCl₄] ( 11 ), which could be isolated at room temperature. All complexes were characterized by single-crystal X-ray diffraction, NMR spectroscopy and their electronic structures were elucidated by DFT calculations.     

Potential energy mapping of the excited-states of (η6-arene)Cr(CO)3 complexes: the evolution toward CO-loss or haptotropic shift processes

The potential energy profiles of the optically accessible excited states of two model (η(6)-arene)Cr(CO)(3) systems were explored using Time-Dependent Density Functional Theory. Two photochemical reactions were investigated, CO-loss and the haptotropic or ring-slip of the arene ligand. In both cases the photochemical reaction requires the surmounting of a small thermal barrier in the lowest energy excited state. In the case of (η(6)-benzene)Cr(CO)(3) only one excited state is populated following 400 nm excitation and this leads to the release of CO. The calculated energy barrier to this process is 13 kJ mol(-1). In the case of (η(6)-thiophenol)Cr(CO)(3) two excited states are accessible one leading to CO-loss while the other results in the ring-slip process. The calculated barrier to the ring-slip process is 11 kJ mol(-1). The calculations are consistent with the results of picosecond time-resolved infrared studies.     

Theoretical Study on the Reaction of FeS+(6∑+,4Ф)with COS in the Gas Phase

The possible reaction mechanisms of FeST(6∑+and 4Ф states)with COS in the gas phase have been studied by using density functional theory at the B3LYP/TZVP and B3LYP/6-311+G*levels:the O/S exchange reaction(FeS++COS=FeO++CS2),O-transfer reaction(FeS++COS=FeSO++CS)and S-transfer reaction(FeS++COS=FeS2++CO).The calculation results show that the large barriers(205.7 and 310.1 kJ/mol)and the small probability of forming the preceding intermediate indicate a much lower efficiency of the O/S exchange and the O-transfer reactions and their corresponding products may not be observed experimentally.FeS2+,the product of S-transfer reaction,is predicted to be the main product.But the reactivity of the 6∑+ground state of FeS+toward COS is lower than the earlier transition metal sulfide cations MS+(M=Sc,Ti and V),although it has more reaction channels and different mechanisms.     

Method of the selection of the g(α) function based on the reduced-time plot

A method for the selection of the g(α) function describing the thermal decomposition of solids based on the reduced-time plot is proposed. This method allows more objective selection of the g(α) function best describing the experimental results from a mathematical point of view, when compared to the graphical method applied up to the present. With the use of variously defined values of reduced time, this method was applied to the investigation of the kinetics of the isothermal decomposition of CaCO₃ under nitrogen. The listing of a computer program enabling the carrying out of calculations and the making of plots is given.     

Structure of the silver imidodi(sulphuryl fluoride)-benzene solvate AgN(SO2F)2·C6H6

The structure of the monobenzene solvate of silver imidodi(sulphuryl fluoride), AgN(SO₂F)₂ · C₆H₆, was determined from single crystal X-ray data. The asymmetric unit contains one quarter of the formula unit with the silver and nitrogen atoms lying at the intersection of two mirror planes; the sulphur and one of the oxygen atoms, O(2), lie on the same mirror plane. The remaining substituent at sulphur is in a general position that must be occupied equally by oxygen and fluorine and is designated as O/F (1). The bonding between silver and benzene is of a new type, in which each benzene is symmetrically η²-coordinated (Ag-C 2.490(7) Å) to each of two silver atoms to give infinite chains parallel to the c axis. A weak C(1)-H(1) ṫ O/F(1) hydrogen bond (C ṫ O/F 3.47 Å) was located, which cross-links these chains in the b direction, and probably accounts for the fact that the more electronegative fluorine atom predominantly occupies the general position.     

Photochemistry of metalmetal bonded complexes.: IV. Breaking of the metalmetal bond and decoupling of the two 1,4-diaza-1,3-butadiene (= R-DAB) fragments of bis(1-t-butylimino-2-t-butylaminoethane) (= t-Bu-IAE) during the photochemical conversion of Mo2(CO)6(t-Bu-IAE) into Mo2(CO)6(t-Bu-DAB)2

The complex Mo₂(CO)₆(t-Bu-IAE) (I) (bis(1-t-butylimino-2-t-butylaminoethane) which contains a MoMo bond and a tetradentate 10e donor ligand t-Bu-IAE, consisting of two CC coupled t-Bu-DAB (t-BuNCHCHNBu-t) ligands has been irradiated into its σ → σ^* transition. The photolysis yields Mo₂(CO)₆(t-Bu-DAB)₂ (II), a complex in which the MoMo bond is broken and the uncoupled t-Bu-DAB ligands act as 6e (σ-N,μ²-N′,η²-CN′) donors.     

Migration of the η1:η6-C6H5Cr(CO)3 ligand into the cyclopentadienyl ring during metallation of the η5-C5H5(CO)2Fe η1:η6-C6H5Cr(CO)3 binuclear complex

It was found that the ¹⁶-C₆H₅Cr(CO)₃ ligand migrates into the cyclopentadienyl ring when the ⁵-C₅H₅(CO)₂Fe ¹⁶-C₆H₅Cr(CO)₃ binuclear complex is metallated with BuⁿLi. Under the same conditions, no migration of the phenyl ligand in the ⁵-C₅H₅(CO)₂Fe ¹-C₆H₅ complex was observed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 325–326, February, 1994.