Interaction between Potassium Phosphate Bu er Solution and Modeling Cell Membrane Investigated by Sum Frequency Generation Vibrational Spectroscopy (cited: 1)

Potassium phosphate buffer solution has been widely used in the biological experiments, which represents an important process of the interaction between ions and biomolecules, yet the in fluences of potassium phosphate on biomolecules such as the cell membrane are still poorly understood at the molecular level. In this work, we have applied sum frequency generation vibrational spectroscopy and carried out a detailed study on the interaction between potassium phosphate buffer solution (PBS) and negative 1,2-dimyristoyl-d₅₄-sn-glycero-3-[phospho-rac-(1-glycerol)] (d₅₄-DMPG) lipid bilayer in real time. The PBS-induced dynamic change in the molecular structure of d₅₄-DMPG lipid bilayer was monitored using the spectral features of CD₂, CD₃, lipid head phosphate, and carbonyl groups for the first time. It is found that K⁺ can bind to the cell membrane and cause the signal change of CD₂, CD₃, lipid head phosphate, and carbonyl groups quickly. Potassium PBS interacts with lipid bilayers most likely by formation of toroidal pores inside the bilayer matrix. This result can provide a molecular basis for the interpretation of the effect of PBS on the ion-assisted transport of protein across the membrane.     

Lateral Diffusion of Lipids and Diffusion of Water through Lipid Bilayers in the Presence of (1,1-Dimethyl-3-Oxobutyl)Phosphonates

The influence of some amphiphilic (diethyl, dipropyl, and dibutyl) esters of (1,1-dimethyl-3-oxobutyl)phosphonic acid with the regularly changing number of CH₂ groups in the hydrocarbon (hydrophobic) moiety on the lateral diffusion of dioleoyl phosphatidylcholine lipid and transmembrane diffusion of water in the oriented multibilayer system was studied by ¹H pulsed field gradient NMR at phosphonate concentrations up to 30 mol %. The shape of the ³¹P NMR spectra and the dependence of the shape of the ¹H NMR spectra on the bilayer orientation suggest that the presence of phosphonates does not affect the phase state of the system. The lamellar liquid crystalline phase remains unchanged, and phosphonate molecules become incorporated into the bilayer and have the same orientation as phospholipid molecules. The presence of phosphonates in the lipid bilayer increases the coefficients of lipid lateral diffusion and water diffusion through bilayers. This effect depends monotonically on the number of CH₂ groups in the phosphonate molecule. The most probable place for the incorporation of amphiphilic phosphonate molecules is the hydrophilic/hydrophobic interphase region of the bilayer. The molecules incorporated into the interphase disorder the bilayer and increase lateral diffusion of lipids and bilayer permeability compared with the ester-free bilayer. When the number of CH₂ groups in the ester molecule increases from diethyl to dibutyl phosphonate, the arrangement of lipid hydrocarbon tails becomes more ordered. This decreases the lipid lateral diffusion coefficient and bilayer permeability to water molecules.     

Volumetric properties of mixtures of water and methanol H/D-isotopomers between 5 and 45°C

Densities of H/D-isotopomers mixtures of water (H₂O, D₂O) and methanol (CH₃OH, CD₃OH, CH₃OD, and CD₃OD) over the full range of compositions were measured at 5, 15, 25, 35, and 45°C. Results have been used to calculate molar volumes, excess molar volumes, apparent molar volumes, and isotope effects of the mixtures. The volumetric properties are discussed in terms of the structural changes in water-methanol solutions under the influence of isotope substitution.     

Angular dependence of 1H- and 2H-NMR spectra of water and methanol absorbed in cellulose triacetate film

¹H- and ²H-NMR spectra of water (H₂O and D₂O) and methanol (CH₃OD and CD₃OH) absorbed in cellulose triacetate films have been observed as a function of the angle θ between the film surface and the magnetic field. ¹H-NMR signals of H₂O and CH₃OD are doublets and triplets due to dipole interactions, respectively. ²H-NMR signals of D₂O, CD₃OH, and CH₃OD are doublets due to quadrupole splittings. The magnitudes of these splittings change depending on θ. The analysis of the angle-dependent patterns indicates that the motionally averaged axes of the dipole and the quadrupole moments orient in the direction perpendicular to the film surface. The alignment of water and/or methanol molecules originates from the film morphology, which is anisotropic in the perpendicular direction. From the angle dependence of the chemical shift, the volume diamagnetic susceptibility of the film is estimated to be 0.44 ppm.     

Solubility and Thermodynamics of Solvation of Krypton in Mixtures of H/D Isotopomers of Water and Methanol at 101325 Pa and 278-318 K

The solubility of krypton in mixtures of H/D isotopomers of water (H₂O, D₂O) and methanol (CH₃OH, CD₃OH, CH₃OD) was studied at 101325 Pa and 278.15-318.15 K with a 10 K step. The thermodynamic characteristics of Kr solvation were calculated. The densities of mixtures of water and methanol isotopomers at the examined temperatures were calculated with an error of no more than 1 × 10^{- 5} g cm^{- 3} in the entire composition range. Both in water and aqueous methanol, krypton behaves as a structure-making component, but the alcohol solvation surrounding of the Kr atoms is more labile and more susceptible to the breaking effect of temperature.     

The H/D Exchange and Hydrogenolysis of Butane on an Alumina-Supported Nickel Catalyst

The exchange of butane with deuterium on a nickel/alumina catalyst is studied over a wide range of temperatures (50–230°) and for three hydrocarbon/deuterium ratios. The initial distribution is used to propose a reaction scheme by considering different adsorbed species such as: alkyl-(α), alkene-(α, β) and allyl-(α,β,γ) species, where α, β, and γ are different C-atoms. It is assumed that each adsorbed species can either desorb directly while exchanging one, two, and three H-atoms or undergo multiple exchange before desorption. It is shown that by reducing the activity of the catalyst a back-exchange of the fully deuterated species sets in a lower temperature; a systematic deviation of all model calculations for the estimation of the concentrations of the C₄HD₉ and C₄D₁₀ is, thus, explained. The exchange of CH₃CD₂CD₂CH₃ and CD₃CH₂CH₂CD₃ with H₂ and D₂ is also studied, and similar results are obtained as with exchanges of CH₃CD₂CH₃ and CD₃CH₂CD₃. With the help of very-high-resolution mass spectra, it is shown that the initial degree of deuteration, i. e. the degree of deuteration after one adsorption step, is 84% for the methylene and 57% for the methyl group respectively. The hydrogenolysis reactions of butane is studied in the same system between 180° and 230°. A wide range of conversion is covered, and the product distributions are fitted to kinetic equations in order to obtain the initial rate constants. On the nickel/alumina catalyst one or several C–C bonds are broken before the desorption of the species. Under the conditions used in these experiments, the surface cracking is the rate-limiting step. An isotope effect is observed for the decomposition in D₂, the production of propane being favored.     

N-demethylation of N,N-dimethylanilines by photoexcited 3-nitrochlorobenzene

The title reaction proceeds via initial electron transfer (rather than hydrogen atom transfer) from the amine to the photoexcited nitro compound, as demonstrated by methoxy substitution in the substrate and absence of CH₃/CD₃-discrimination.     

Effect of H/D isotope substitution on polarizability of methanol molecules

The electron polarizabilities (α₀·10²⁴/cm³ molec.⁻¹) were estimated from the data on refractive indices and molar volumes of H/D isotopomers of methanol at 25 °C using the Lorentz-Lorentz formula: 3.265 (CH₃OH), 3.260 (CH₃OD), 3.235 (CD₃OH), and 3.231 (CD₃OD). A relationship between the isotope effects for α₀ and volume (packing) changes in the structure of liquid methanol induced by deuterosubstitution in the methanol molecule was proposed. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1927–1928, August, 2005.     

Raman linewidth study of intermolecular interactions of methanol in aqueous solution

Isotropic Raman linewidths of the CH and CD symmetric stretching modes of methanol and methanol-d₄ have been measured as a function of concentration in normal water, in heavy water and in carbon tetrachloride. On the basis of the concentration dependence of observed linewidths, intermolecular interactions and liquid structures in the methanol—water system are discussed. It is suggested that there may be some difference in mutual affinities or abilities of hydrogen bonding in the order D₂O > H₂O > CD₃OD > CH₃OH.     

Modellrechnungen von Kraftkonstanten der Tetramethyl-Verbindungen (CH3)4−nM(CD3) n,M=Si,Ge, Sn,Pb

Fromthe experiemntal fundamental vibrational frequencies of (CH₃)₄ M, (CD₃)₄ M and (CH₃)₃ MCD₃,M=Si, Ge, Sn, Pb, and of (CH₃)₂Si(CD₃)₂ and CH₃Si(CD₃)₃ a transferable local symmetry type force field for (CH₃)_4–n M groups has been calculated. Applications involving differentM atoms and numbersn of CH₃ groups are presented.

     

United atom force field for phospholipid membranes: Constant pressure molecular dynamics simulation of dipalmitoylphosphatidicholine/water system

We refined the united atom field for the simulations of phospholipid membranes. To validate this potential we performed 1000-ps constant pressure simulation of a dipalmitoylphosphatidicholine (DPPC) bilayer at T=50° C. The average area per head group (61.6±0.6) Ų obtained in our simulation agrees well with the measured one of (62.9±1.3) Ų. The calculated S_CD order parameters for the Sn-2 hydrocarbon tail also display a good agreement with the experiment. The conformations of head groups in our simulations of the liquid crystal phase are different than the ones observed in the crystal structure. ©1999 John Wiley & Sons, Inc. J Comput Chem 20, 531–545, 1999     

Crossed Molecular Beam Study of H+CH4 and H+CD4 Reactions: Vibrationally Excited CH3/CD3 Product Channels

We study the H+CH₄/CD₄→H₂/HD+CH₃/CD₃ reactions using the time sliced velocity map ion imaging technique. Ion images of the CH₃/CD₃ products were measured by the (2+1) resonance enhanced multi-photon ionization (REMPI) detection method. Besides the CH₃/CD₃ products in the ground state, ion images of the vibrationally excited CH₃/CD₃ products were also observed at two collision energies of 0.72 and 1.06 eV. It is shown that the angular distribution of the products CH₃/CD₃ in vibrationally excited states gradually vary from backward scattering to sideways scattering as the collision energy increases. Compared to the CH₃/CD₃ products in the ground state, the CH₃/CD₃ products in vibrationally excited states tend to be more sideways scattered, indicating that larger impact parameters play a more important role in the vibrationally excited product channels.     

Conformational Analysis of the 1,3‐Oxaphosphorinanes Formed from α,β‐Unsaturated Aldehydes and the (Hydroxymethyl)phosphines RP(CH2OH)2 (R = Ph or CH2OH)

Equimolar reactions of cinnamaldehyde or its 3,5‐dimethoxy‐4‐hydroxy derivative (sinapaldehyde) with RP(CH₂OH)₂ (R = Ph or CH₂OH) were studied in MeOH or CD₃OD at room temperature by NMR spectroscopy. In MeOH, nucleophilic attack of the phosphine at the C?C bond, with concomitant loss of CH₂O, affords the tertiary phosphine HOCH₂P(R)CH(Ar)CH₂CHO ( 3 ) that rapidly converts mainly into a 1,3‐oxaphosphorinane derivative ( 5 ) formed as a mixture of four diastereomers. Conformational analysis reveals that the Ar group in these is exclusively in an equatorial position while the OH and R groups can be equatorial‐oriented or axial‐oriented. In CD₃OD, 1,3‐oxaphosphorinanes monodeuterated in the C5 position are obtained as a mixture of eight diastereomers where the dominate diastereomers have an axial D‐atom. Diastereomeric ratios depend on the nature of the Ar and R groups.     

Reactions of [CH3]+ and [CD3]+ with alcohols

The reactions of [CH₃]⁺ and [CD₃]⁺ with a number of C₁ to C₅ alcohols were studied at approximately thermal energies (0.1 eV) using a tandem Dempster ion cyclotron resonance mass spectrometer. Branching ratios obtained under single collision conditions are reported for [CH₃]⁺ and [CD₃]⁺ with methanol, perdeutero methanol, ethanol, allyl alcohol, 1-propanol, 2-propanol, perdeutero-2-propanol, 1-butanol, 2-butanol, t-butanol, cyclopentanol and 1-pentanol. The results are examined in terms of the mechanism of reactions and indicate that upon progression to larger alcohols, the formation of a long-lived adduct becomes less important in determining the reaction products.     

Effect of strongly interacting solutes on group rotational correlation functions in ethanol

Proton magnetic relaxation rates of solutions of LiCl and LiI in isotopically labelled ethanols CH₃CD₃OD, CD₃CH₂OD and CD₃CD₂OH have been measured as functions of temperature and concentration mostly at v=30 MHz, where 21. The data were reduced in a way that revealed that CH₃ and CH₂ relaxation curves contained a residuum from the slow motion of the OH group in many cases. Thus, the rotational time correlation function of the CH₃ and CH₂ groups contain a residuum term stemming from the slow motion within the same molecule. The data show a threshold of the rotational energy which has to be exceeded in order to make the effect observable.     

FTIR studies of molecular disorder in long chain n-alkanes: chain tilt and chain end disorder

Successive heat annealing and cooling of the extended chain form of C₁₉₈H₃₉₈ leads to a “perfecting” of the chains, on the evidence of FTIR data. A similar sample of CD₃(CD₂)₁₁(CH₂)₁₉₂(CD₂)₁₁CD₃ allows the deuterated end segments to be analysed separately. It is shown that the end segments develop better register, while the chain interior is scarcely affected by annealing. The alignment of chain ends coincides with the development of chain tilt (from SAXS data), the tilt angle increasing as the chain ends become more “defect-free” to a figure close to the maximum values obtained for polyethylene.     

Reaction of tris(hydroxymethyl)phosphine and cinnamaldehyde in methanol

Reaction of tris(hydroxymethyl)phosphine with excess cinnamaldehyde in CH₃OH or CD₃OD, followed using NMR, proceeds via several phosphorus-containing intermediates, multiple transformations of organic parts, and with the solvent H/D isotope effect on products. In both solvents, one CH₂OH group of tris(hydroxymethyl)phosphine is readily replaced by the cinnamaldehyde moiety to give the primary product, a 1,3-oxaphosphorinane derivative. Slower replacement of the second CH₂OH group leads to a mixture of aliphatic and heterocyclic phosphine intermediates in a ratio of ~4:1 in CH₃OH and ~1:1 in CD₃OD; both intermediates contain alcohol and aldehyde groups and convert rapidly into intra- and intermolecular hemiacetals. The hemiacetals of the aliphatic phosphine rearrange further into an unsymmetrical trialkylphosphine oxide, whereas the hemiacetals of the heterocyclic phosphine react with the third mole of cinnamaldehyde to replace the third CH₂OH group of tris(hydroxymethyl)phosphine. All intermediates and products are formed as mixtures of stereoisomers.     

Interpretation of infrared intensities of propane and deutero-propanes by electrooptical parameters

The interpretation of IR intensities of CH₃CH₂CH₃, CD₃CH₂CD₃ and CH₃CD₂CH₃ in terms of bond parameters (electrooptical parameters, e.o.p. s) is discussed. Sets of e.o.p. s derived from a previous study on methanes and ethanes are used as starting points to derive more complete sets of e.o.p. s which fit the intensities of propane very well. The intensities from ethanes have been used as a constraint on the e.o.p. s of CH₃ groups. The results are discussed and compared with values from quantum mechanics for the derivatives of the molecular dipole moment. Since the parameters derived in this work predict satisfactorily the IR intensities of polyethylene, they should form a good starting set for the interpretation of the intensities of n-paraffins.     

Controlled radical polymerization of 2‐hydroxyethyl methacrylate with a hydrophilic ruthenium complex and the synthesis of amphiphilic random and block copolymers with methyl methacrylate

A hydrophilic ruthenium complex with ionic phosphine ligands { 1 : RuCl₂[P(3‐C₆H₄SO₃Na)(C₆H₅)₂]₂} induced controlled radical polymerization of 2‐hydroxyethyl methacrylate (HEMA) in methanol under homogeneous conditions; the initiator was a chloride (R‐Cl) such as CHCl₂COPh. The number‐average molecular weights of poly(HEMA) increased in direct proportion to monomer conversion, and the molecular weight distributions were relatively narrow (M_w/M_n = 1.4–1.7). A similar living radical polymerization was possible with (MMA)₂‐Cl [(CH₃)₂C(CO₂CH₃)CH₂C(CH₃)(CO₂CH₃)Cl] as an initiator coupled with amine additives such as n‐Bu₃N. In a similar homogeneous system in methanol, methyl methacrylate (MMA) could also be polymerized in living fashion with the R‐Cl/ 1 initiating system. Especially for such hydrophobic polymers, the water‐soluble ruthenium catalyst was readily removed from the polymers by simple washing with an aqueous dilute acid. This system can be applied to the direct synthesis of amphiphilic random and block copolymers of HEMA and MMA. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2055–2065, 2002     

Secondary kinetic isotope effects: Deuterium abstraction by chlorine atoms from the CD3 group in CD3CH2Cl,CD3CHDCl,and CD3CD2Cl

The occurrence and magnitude of secondary kinetic isotope effects in the gas phase has been determined for deuterium abstraction from the CD₃ group in CD₃CH₂Cl, CD₃CHDCl, and CD₃CD₂Cl by photochemically generated ground-state chlorine atoms. Over the temperature range 10–94°C a discernible “inverse” kinetic isotope effect is observed. Both the pre-exponential factors and activation energies decrease with deuterium substitution in the vicinal chloromethyl group. The opposing trends result in a net effect close to unity.