Addition of lithium ethyl fluoroacetate to cis and trans α,β-epoxyaldehydes. Access to C2 fluorinated butyrolactones

The aldolisation reaction of lithium ethyl fluoroacetate with cis and trans α,β-epoxyaldehydes in their racemic forms proceeds with good C₃-OH diastereoselectivity and much less at the C₂-F carbon atom. A two-step reaction on the major aldol compounds (iodination, lactonisation) led to racemic functionalised C₂ fluorinated lactones, possessing a C₂/C₃cis relationship between the fluorine and hydroxyl groups.     

Survival of Freeze-dried Leuconostoc mesenteroides and Lactobacillus plantarum Related to Their Cellular Fatty Acids Composition during Storage

Lactic acid bacteria strains Lactobacillus plantarum CWBI-B534 and Leuconostoc ssp. mesenteroïdes (L. mesenteroïdes) Kenya MRog2 were produced in bioreactor, concentrated, with or without cryoprotectants. In general, viable population did not change significantly after freeze-drying (p?>?0.05). In most cases, viable population for cells added with cryoprotectants was significantly lower than those without (p?16:0), palmitoleic (C_16:1), stearic (C_18:0), oleic (C_18:1), linoleic (C_18:2), and linolenic (C_18:3) acids were identified. Four of them, C_16:0, C_16:1, C_18:0, and C_18:1, make up more than 94% or 93% of the fatty acids in L. mesenteroides and L. plantarum, respectively, with another one, namely, C18:3, making a smaller (on average 5–6%, respectively) contribution. The C_18:2 contributed very small percentages (on average?≤?1%) to the total in each strain. C_16:0 had the highest proportion at most points relative to other fatty acids. Moisture content and water activity (a _w) increased significantly during the storage period. It was observed that C_16:1/C_16:0, C_18:0/C_16:0 and C_18:1/C_16:0 ratios for freeze-dried L. mesenteroides or L. plantarum, with or without cryoprotectants, did not change significantly during the storage period. According to the packaging mode and storage temperatures, C_18:2/C_16:0 and C_18:3/C_16:0 ratios for freeze-dried L. mesenteroides and L. plantarum with or without cryoprotectants decreased as the storage time increased. However, a higher C_18:2/C_16:0 or C_18:3/C_16:0 ratio for L. mesenteroides and L. plantarum was noted in the freeze-dried powder held at 4 °C or under vacuum and in dark than at 20 °C or in the presence of oxygen and light.     

Basicity of bisperhalophenyl aurates toward closed-shell metal ions: metallophilicity and additional interactions

The interaction of bisperhalophenyl aurates [AuR₂]^? (R?=?C₆F₅, C₆F₃Cl₂, and C₆Cl₅) with the closed-shell Ag⁺, Cu⁺, and Tl⁺ ions has been studied theoretically and compared with the experimentally known X-ray diffraction crystal structures. Initially, the aurates have been fully optimized at MP2 level of theory in a D _2h symmetry. The analysis of the basicity of the three aurates [AuR₂]^? (R?=?C₆F₅, C₆F₃Cl₂ and C₆Cl₅) against Ag⁺ ions in a C _2v symmetry has been calculated in point-by-point bsse-corrected interaction energy analysis at HF and MP2 levels of theory. Taking into account the experimental observation of additional interactions between the heterometals and C _ipso atoms at the perhalophenyl rings or halogen atoms at the ortho position of the perhalophenyl rings, dinuclear models of the type [AuR₂]^?···Ag⁺ (R?=?C₆Cl₅, and C₆F₅); [AuR₂]^?···Cu⁺ (R?=?C₆F₅, and C₆Cl₅) and [AuR₂]^?···Tl⁺ (R?=?C₆F₅, and C₆Cl₅) with a C _2v , C ₂ , and C _s symmetries have been optimized at DFT-B3LYP level. The interaction energies have been computed through bsse-corrected single point HF and MP2 calculations. The energy stabilization provided and the heterometal preference have been analyzed and compared with the experimental results.     

Microwave spectra of tetrahydroselenophene-α13C, -β13C and molecular ring structure

Microwave spectra of isotopic species α-¹³C and β-¹³C of tetrahydroselenophene molecules have been investigated and rotational constants determined: A = 5608.98 Mc, B = 2819.532 Mc, C = 2022.624 Mc forα-¹³C isotopic species and A = 5695.94 Mc, B = 2770.714 Mc, C = 2009.166 Mc for β-¹³C isotopic species. The r_s-ring structure was found to be Se-C₂ = 1.963 Å, C₂-C₃ = 1.549 Å, C₃-C₄ = 1.527 Å, ∠C₅SeC₂ = 90° 44', ∠SeC₂C₃ = 104° 58', ∠C₂C₃C₄ = 106° 52', the angle of twist = 29° 44'.     

Molecular structure of hexafluorobicyclo [2.2.0]hexa-2,5-diene (hexafluoro-dewar-benzene) in the vapour phase

Hexafluoro-Dewar-benzene has been studied by the electron-diffraction method. A model with C_2v symmetry gives excellent agreement between experimental and theoretical data. The structural parameters with error limits are (cf. Fig. 1): r(C₁-C₄)= 1.598 ±0.017 Å, r(C₁-C₂) = 1.505 ±0.005 Å, r(C₂-C₃) = 1.366 ± 0.015 Å, r(C₁-F₁) = 1.328±0.015 Å, r(C₂-F₂) = 1.319±0.007 Å, ∠F₁C₁C₄ = 118.7±0.7°, ∠F₂C₂C₃ = 133.6±0.7°, τ= 121.8±2.0°, and δ = -7.5±2.0°. Molecular orbital calculations by the CNDO/2 method gave τ = 119.8° and δ = ?4.2°.     

Stereoselective synthesis of α-C-glycosides of N-acetylgalactosamine

Attempts to synthesise α-C-glycosides of N-acetylgalactosamine by selective deprotection at C-2′ of allyl α-C-galactoside 1 and subsequent amination failed, but opened the way to α-C-talopyranosides. The synthesis of α-C-glycosides of N-acetylgalactosamine was performed from allyl α-C-glucopyranoside 9, which was regioselectively deprotected, stereoselectively aminated at C-2′, and finally epimerised at C-4′.     

Single crystal Raman study of potassium oxalate monohydrate,K2C2O4. H2O,and potassium oxalate monodeuterate,K2C2O4. D2O

Raman spectra of poly crystalline and single crystal K₂C₂O₄. H₂O and K₂C₂O₄. D₂O have been recorded at room temperature. From an earlier neutron diffraction study it is known that the space group is C⁶₂h. The water molecule occupies a C₂ site and the oxalate ion a C₁ site. The assigned water vibrations show small factor group splitting between g modes (Raman active) and u modes (IR active). The internal oxalate vibrations are found to have wavenumbers in good agreement with those reported from Raman studies of other oxalates.     

Molecular weight dependence of stress relaxation of commercial polyisobutylene

Stress relaxation measurements in simple extension of three commercial samples of polyisobutylene (PIB) of different viscosity molecular weights (1.1, 1.7 and 2.3 × 10⁶) have been made at stretch ratios (λ) up to about 2. Data obtained at 3° and 50° have been reduced at 25°. As already found previously, instantaneous stress-strain relationship can be expressed by the Mooney-Rivlin equation. The coefficient C₁ and C₂, obtained by two linear plotting procedures show for each sample behaviour already reported viz. a decrease of C₁ with time for short times and a delay of the decrease of C₂ about three decades of time later. C₁ and C₂ both show a marked dependence on molecular weight: the C₂ behaviour is as expected in terms of a tentative molecular interpretation given previously, whereas the C₁ dependence is somewhat unexpected. The latter behaviour could be attributed, however, to the influence of the unknown molecular weight distributions of the samples.     

Ionic Liquids and Water: Hydrophobicity vs. Hydrophilicity

Many chemical processes rely extensively on organic solvents posing safety and environmental concerns. For a successful transfer of some of those chemical processes and reactions to aqueous media, agents acting as solubilizers, or phase-modifiers, are of central importance. In the present work, the structure of aqueous solutions of several ionic liquid systems capable of forming multiple solubilizing environments were modeled by molecular dynamics simulations. The effect of small aliphatic chains on solutions of hydrophobic 1-alkyl-3-methylimidazolium bis(trifluoromethyl)sulfonylimide ionic liquids (with alkyl = propyl [C₃C₁im][NTf₂], butyl [C₄C₁im][NTf₂] and isobutyl [iC₄C₁im][NTf₂]) are covered first. Next, we focus on the interactions of sulphonate- and carboxylate-based anions with different hydrogenated and perfluorinated alkyl side chains in solutions of [C₂C₁im][C_nF_2n+1SO₃], [C₂C₁im][C_nH_2n+1SO₃], [C₂C₁im][CF₃CO₂] and [C₂C₁im][CH₃CO₂] (n = 1, 4, 8). The last system considered is an ionic liquid completely miscible with water that combines the cation N-methyl-N,N,N-tris(2-hydroxyethyl)ammonium [N_{1 2OH 2OH 2OH}]⁺, with high hydrogen-bonding capability, and the hydrophobic anion [NTf₂]^–. The interplay between short- and long-range interactions, clustering of alkyl and perfluoroalkyl tails, and hydrogen bonding enables a wealth of possibilities in tailoring an ionic liquid solution according to the needs.     

The strong influence of alkyl tail length on the aggregation and viscoelasticity of carboxylate gemini surfactants with a p-dibenzenediol spacer in aqueous solution

This paper reports a study on the aggregation and rheological behavior of the family of O, O’-bis(sodium 2-alkylcarboxylate)-p-dibenzenediol (referred to as C_m?₂C_m, m?=?10, 12, 14, respectively) in aqueous solution using dynamic light scattering, ¹H NMR and rheology measurements. The results showed that all three surfactants formed large network-like aggregates at low concentrations. However, C₁₀?₂C₁₀ formed small compact micelles simultaneously but neither C₁₂?₂C₁₂ nor C₁₄?₂C₁₄ did. These network-like aggregates were transformed into the wormlike micelles with increasing the surfactant concentration. The length of alkyl tails was found to strongly affect the viscoelasticity of wormlike micellar solutions. From C₁₀?₂C₁₀, C₁₂?₂C₁₂ to C₁₄?₂C₁₄ in turn, the system developed rapidly from the viscous fluid to typically viscoelastic solution and then to a solid-like gel. The scaling exponents of the concentration dependence of both zero-shear viscosity (η ₀) and plateau elastic modulus (G′_∞) greatly exceeded the theoretic predictions, showing fast micellar growth and strong entanglements between the wormlike micelles. For C₁₄?₂C₁₄ that had the longest alkyl tails in this series, the wormlike micelles formed at 140?mmol L^?1 were quite long and the micellar reptation dominated over the scission and recombination. This system yielded a viscosity as high as 2.20?×?10⁴ Pa?s at 25 °C.     

Phase behavior and solubilization of microemulsion systems containing Gemini imidazoliums and their monomeric analogues

The Gemini imidazolium surfactants with a four-methylene spacer group [C_n(Bim)₂-2Br, n?=?12, 14, 16] and their corresponding monomers [C_nmimBr, n?=?12, 14, 16] were synthesized and characterized. The phase behavior and solubilization of microemulsion systems containing C_n(Bim)₂-2Br/butan-1-ol/octane/brine as well as microemulsion systems containing C_nmimBr/butan-1-ol/octane/brine were studied and compared. The C_n(Bim)₂-2Br-based microemulsion systems have greater solubilization ability than that of the corresponding mono surfactants C_nmimBr-based systems. As the carbon chain lengths of the surfactants [C_n(Bim)₂-2Br and C_nmimBr] increase, the mass fraction of the alcohol in the interfacial layer A ^S would decrease, whereas the solubilization ability (SP*) would increase. The maximum solubilization ability (SP*) of the two microemulsion systems was attained when the oil/water mass ratio (α) approaches 0.5. The solubilization ability of both microemulsion systems would increase with increasing NaCl concentrations in aqueous phase. In C_n(Bim)₂-2Br-based microemulsion systems, the alcohol is significantly more soluble in aqueous phase than in the oleic phase. And it was noted that the alcohol is more soluble in C_n(Bim)₂-2Br-based systems than in C_nmimBr-based systems in both aqueous and oleic phases.     

Robust and easily retrievable Pd/Ti_3C_2T_x■graphene hydrogels for efficient catalytic hydrogenation of nitroaromatic compounds

Ti_3C_2T_x has been emerging as an attractive platform to prepare composite catalysts,and their assembly into integrated catalytic mate rials repre sents a key step forward toward practical applications.Howeve r,the swelling behavior of Ti_3C_2T_x leads to significant structure change,which challenges the stability of Ti_3C_2T_x-based integrated functional materials for catalytic applications.Here we report a facile synthesis of Pd/Ti_3C_2T_x■graphene hydrogels in which Pd/Ti_3C_2T_x are spatially encapsulated in the 3 D porous graphene framework.The porous interconnected structure not only affords efficient mass transfer and desirable functional accessibility to catalytic active sites,but also effectively buffers the swelling behavior of Ti_3C_2T_x.When applied for catalytic hydrogenation of nitroaromatic compounds,the mechanically robust Pd/Ti_3C_2T_x■graphene hydrogels exhibit efficient activities,easy separability,and good cyclability.This work is expected to promote the application of Ti_3C_2T_x-based functional materials for practical applications involving interactions with salt solutions,such as supercapacitors,catalysis,and water purification.     

Synthesis and surface activities of organic solvent-soluble fluorinated surfactants

A variety of fluorinated surfactants soluble in organic solvent were prepared, including C₈F₁₇SO₂NHC_nH_2n+1 (n = 2, 4, 6, 8, 10), C₈F₁₇SO₂NHR (R = C₆H₁₁, C₆H₅), C₈F₁₇SO₂N(C_nH_2n+1)₂ (n = 1, 2, 3, 4) and C₈F₁₇SO₂NH(CH₂)_nNHO₂SC₈F₁₇ (n = 6, 10). Their surface activities in various organic solvents were determined by surface tension measurement. The results showed that these fluorinated surfactants can reduce the surface tension of both polar and non-polar organic solvents. In general, organic solvents with strong polarity or long alkyl chain are beneficial to increase the surface activity of these polar fluorinated surfactants. By comparing fluorinated surfactants with the same fluorocarbon segment and connecting group, C₈F₁₇SO₂N(C_nH_2n+1)₂ (n = 1, 2, 3, 4) showed lower surface activity in organic solvents than C₈F₁₇SO₂NHC_nH_2n+1 (n = 2, 4, 6, 8) with an equal carbon number of the solvophilic group. Through surface tension vs. concentration curves given for N-octyl perfluorooctanesulfonamide in various organic solvents, a break point like the critical micelle concentration of ordinary surfactants in aqueous solutions was observed, and the effect of the different types of organic solvents on adsorption and aggregation behavior was also studied.     

Preparation and protonation of 2-pyrimidyl- and 2-pyrazylpalladium(II) complexes

The oxidative addition of 2-chloropyrimidine or 2-chloropyrazine to [Pd(PPh₃)₄] yields a mixture of trans-[PdCl(C₄H₃N₂-C²)(PPh₃)₂] (I) and [PdCl(μ-C₄H₃N₂-C²,N¹)(PPh₃ (II) (C₄H₃N₂ = 2-pyrimidyl or 2-pyrazyl group). The mononuclear complexes I are quantitatively converted into the binuclear species II upon treatment with H₂O₂. The reaction of II with HCl gives the N-monoprotonated derivatives cis-[PdCl₂(C₄H₄N₂-C²)(PPh₃)] (III), from which the cationic complexes trans-[PdCl(C₄H₄N₂-C²)(L) (L = PPh₃, IV; PMe₂Ph, V; PEt₃, VI) can be prepared by ligand substitution reactions. Reversible proton dissociation occurs in solution for III–VI. The low-temperature ¹H NMR spectra of trans-[PdCl(C₄H₄N₂-C²)(PMe₂Ph)₂]ClO₄ show that the heterocyclic moiety undergoes restricted rotation around the PdC² bond and that the 2-pyrazyl group is protonated predominantly at the N¹ atom. These results and the ¹³C NMR data for the PEt₃ derivatives are interpreted on the basis of a significant d_π → π^★ back-bonding contribution to the palladium—carbon bond of the protonated ligands.     

Vibrational spectra of N-2′-methyl-propyliden-propan-2-amine: conformational analysis and influence of the nitrogen hybridization

Infrared and Raman spectra of the (CH₃)₂C^2′HC^1′HNCH(CH₃)₂ aldimine (NPP) and of two deuterated derivatives at C^1′ and C^2′ in the liquid, solid and solution phases have been recorded and assigned between 4000 and 130 cm⁻¹. NPP adopts the E configuration and two conformers at the C_sp2 and N sides are in equilibrium. Some vibrational modes are specifically assigned to the anticlinal (ac) or synperiplanar (sp) conformers at the C_sp2 side. The ac(C_sp2) form is dominant in the pure liquid whilst the sp(C_sp2) form is favoured in the solid and in chloroform. The vibrational dynamics of the isopropyl group on both sides of the CN bond are partially similar to that of the (CH₃)₂CHCHO aldehyde on the one hand and of the (CH₃)₂CHNH₂ amine on the other hand. When moving from the amine to the corresponding aldimine, changes about νNC and wCC₂ modes (at the N side) are related to electronic and geometrical effects as a consequence of the nitrogen hybridization change from sp₃ to sp₂.     

Charge-remote fragmentations are energy-dependent processes

Fast atom bombardment-produced [M + Na]⁺ ions of tristearoylglycerol and [M ? H]^? ions of stearic or nervonic acid undergo charge-remote fragmentations (CRFs) to produce one series of product ions reflecting C _n H_2n+2 losses, whereas electrospray ionization-produced ions fragment to give two series of product ions reflecting C _n H_2n+2 and C _n H_2n+1 losses. These results and those from previous studies show that the mechanisms and energetics of CRFs are complex and unsettled. We demonstrate that several pathways are simultaneously involved in CRFs, and the preference for certain pathways (by C _n H_2n+1 and C _n H_2n+2 losses) is determined by the internal energy of the compound itself and the ionization and activation energies that are applied to it.     

Observations on the swelling of cross-linked poly(dimethylsiloxane) networks by solvents

The Flory Huggins Solvent parameter (χ) previously published for a range of solvents and a cross-linked silicone polymer, have been recalculated using the original swelling data, but including a term representing the loss of configurational entropy consequent on crosslinking. From the Shore hardness of the polymer, the Young’s modulus E was calculated. E = 6(C₁ + C₂), where C₁ and C₂ are the parameters from the Mooney Rivlin equation for the elastic deformation of an elastomer. Since C₁ is related to M_c, the average molecular weight between crosslinks, revised χ values could be calculated for various values of C₂/C₁. These showed that for good solvents for the silicone polymer, the values published previously were too high.     

Probing the exohedral magnetic properties of C20 derivatives by through space NMR shieldings (TSNMRS)

The through space NMR shieldings (TSNMRS) of dodecahedrane C₂₀H₂₀, of the isomeric hydrocarbons C₂₀H₁₂, of the ions C₂₀H₁₂²⁺ and C₂₀H₁₂^2?, of the fluxional fullerene C₂₀ and of its dication C₂₀²⁺ have been ab initio calculated employing the NICS concept on basis of MP2/6-31G1 geometries and visualized as iso-chemical-shielding/deshielding surfaces (ICSSs). TSNMRS values were employed to study the exohedral magnetic properties of the compounds studied. Hereby, the curved π-conjugation in the compounds studied could be quantified.     

Gas phase electron diffraction study of basketene,C10H10

A gas phase electron diffraction study of the cage hydrocarbon, basketene, is reported. A least squares treatment of molecular intensities has been carried out in terms of a geometrically consistent r_α structure. The mean amplitude values and shrinkage corrections have been calculated using the force field parameters estimated from the data on simpler molecules.Structure refinement of the C_2v molecular model yields the following parameter values (bond lengths, r_a, in nm; angles, r_α in degrees): <C₂—C_3, C₄—C₅?_av 0.1609(14); C₃—C₄ 0.1563(6); C₉C₁₀ 0.1360(9); C₁—C₁₀ 0.1511(13); C₁—C₂ 0.1517(9); <C-H>_av. 0.1092(8); <C₃C₄C₇ 88.5(1.0); dihedral angle C₃C₄C₇/C₃C₅C₇ 153.8(1.0). Parenthesized are three times the standard deviation values, 3σ.In addition to the geometric parameters listed, the mean amplitudes for all bonded and C· C nonbonded distances have been determined by the least squares method. All the other amplitudes (C· H and H· H) have been fixed at the values estimated from the spectral data.Comparison of the results obtained with the literature data on similar polycyclic molecules points to the stronger internal strain in the basketene molecule.     

Morphological Changes of Cationic Gemini Surfactants 14-s-14 (s=4,5,6) in the Presence of Additives

The effect of adding aliphatic alcohols (C₄OH, C₅OH, C₆OH) and corresponding amines (C₄NH₂, C₅NH₂, C₆NH₂) on a series of dicationic gemini surfactants with the general formula C₁₄H₂₉(CH₃)₂N⁺?C(CH₂)_s?CN⁺(CH₃)₂C₁₄H₂₉, 2Br^? (14-s-14; s=4,5,6), in the absence and presence of KNO₃, has been studied by viscosity measurements at 303.15?K. As the chain length of the additive increased, the viscosity increased with increasing additive concentration and the extent of the effect followed the sequence: C₆OH>C₅OH>C₄OH; C₆NH₂>C₅NH₂>C₄NH₂. The simultaneous presence of salt and additives showed an increase in ?? _r values due to a synergistic effect. However, for equal chain lengths in the additives, the effect was greater for the n-alcohols. The tendency for the micelles to grow from spherical to rod-like structures is mainly influenced by the spacer chain length. At 303.15?K, the micellar growth was more pronounced for the shorter spacer, i.e. s being 4, which can be interpreted in terms of the short spacer having a higher tendency for micellar growth. Contrary to the cationic geminis, no effect was observed with a conventional surfactant of equal chain length, TTAB, even in the presence of KNO₃ at the same concentration used for the geminis.