The effects of low level microwaves on the fluidity of photoreceptor cell membrane

Due to the extensive use of electromagnetic fields in everyday life, more information is required for the detection of mechanisms of interaction and the possible side effects of electromagnetic radiation on the structure and function of the organism.In this paper, we study the effects of low-power microwaves (2.45 GHz) on the membrane fluidity of rod photoreceptor cells. The retina is expected to be very sensitive to microwave irradiation due to the polar character of the photoreceptor cells [Biochim. Biophys. Acta 1273 (1995) 217] as well as to its high water content [Stud. Biophys. 81 (1981) 39].     

Synthesis and magnetic properties comparison of M-Cu(II) and M-VO(II) Schiff base-porphyrazine complexes: what is the mechanism for spin-coupling?

Dimetallic Schiff base-porphyrazine (pz) compounds, denoted 1[M(1); M(2); R], have been prepared, where metal ion M(1) is incorporated into the pz core, and metal ion M(2) is bound to a bis(5-tert-butylsalicylidenimine) chelate built onto two amino nitrogens attached to the pz periphery; R is a solubilizing group (either propyl (Pr) or 3,4,5-trimethoxyphenyl (TMP)) attached to the remaining carbons of the pz periphery. The synthesis of 1[Cu; Cu; R], 1[Cu; VO; R], 1[ClMn; Cu; Pr], and 1[ClMn; VO; Pr] is discussed, the crystal structures of 1[Cu; Cu; TMP] and 1[ClMn; VO; Pr] are presented, and the magnetic properties of these compounds are compared. The pattern of ligand-mediated exchange coupling in these complexes is startling: for the Cu-M(2) complexes 1[Cu; VO; R] and 1[Cu; Cu; R], 2 x 10(2) < or = |J(Cu-VO)/J(Cu-Cu)|; for the ClMn-M(2) complexes 1[ClMn; Cu; Pr] and 1[ClMn; VO; Pr], J(ClMn-VO)/J(ClMn-Cu) approximately 1/3, an inverse ratio from that of the Cu-M(2) complexes, but with lesser discrimination. This coupling pattern is explained in terms of a novel orientation relative to the M(1)-M(2) direction: the "square-planar" Schiff base ligand set of M(2) is rotated in-plane by 45 degrees relative to the effectively coplanar pz ligand set of M(1).     

Reactivity of conjugated and unconjugated pterins with singlet oxygen (O2(1Deltag)): physical quenching and chemical reaction

Pterins (PTs) belong to a class of heterocyclic compounds present in a wide range of living systems. They participate in relevant biological functions and are involved in different photobiological processes. We have investigated the reactivity of conjugated PTs (folic acid [FA], 10-methylfolic acid [MFA], pteroic acid [PA]) and unconjugated PTs (PT, 6-hydroxymethylpterin [HPT], 6-methylpterin [MPT], 6,7-dimethylpterin [DPT], rhamnopterin [RPT]) with singlet oxygen (1O2) in aqueous solutions, and compared the efficiencies of chemical reaction and physical quenching. The chemical reactions between 1O2, produced by photosensitization, and PT derivatives were followed by UV-visible spectrophotometry and high-performance liquid chromatography, and corresponding rate constants (k(r)) were evaluated. Whenever possible, products were identified and quantified. Rate constants of 1O2 total quenching by the PT derivatives investigated were obtained from steady-state 1O2 luminescence measurements. Results show that the behavior of conjugated PTs differs considerably from that of unconjugated derivatives, and the mechanisms of 1O2 physical quenching by these compounds and of their chemical reaction with 1O2 are discussed in relation to their structural features.     

Accessing Lanthanide-to-Lanthanide Energy Transfer in a Family of Site-Resolved [LnIIILnIII′] Heterodimetallic Complexes

The ligand H₃L (6-[3-oxo-3-(2-hydroxyphenyl)propionyl]pyridine-2-carboxylic acid), which exhibits two different coordination pockets, has been exploited to engender and study energy transfer (ET) in two dinuclear [Ln^IIILn^III′] analogues of interest, [EuYb] and [NdYb]. Their structural and physical properties have been compared with newly synthesised analogues featuring no possible ET ([EuLu], [NdLu], and [GdYb]) and with the corresponding homometallic [EuEu] and [NdNd] analogues, which have been previously reported. Photophysical data suggest that ET between Eu^III and Yb^III does not occur to a significant extent, whereas emission from Yb^III originates from sensitisation of the ligand. In contrast, energy migration seems to be occurring between the two Nd^III centres in [NdNd], as well as in [NdYb], in which Yb^III luminescence is thus, in part, sensitised by ET from Nd. This study shows the versatility of this molecular platform to further the investigation of lanthanide-to-lanthanide ET phenomena in defined molecular systems.     

A novel lipopathic Cr(VI) oxidant for organic substrates: Kinetic study of oxidation of benzyl alcohol

A novel lipopathic oxidizing agent, cetyltrimethylammonium dichromate, was used for oxidation of benzyl alcohol in various organic solvents and in surfactant systems. The reaction kinetics was investigated with change in [acid], [substrate], [oxidant], [surfactant], and temperature. The rate constant values led to propose that the reaction occurs in a reversed micellar system produced by the oxidant, akin to an enzymatic environment. The rate variation with variation in [surfactant] and solvent isotope effect suggest that the path of reaction to be through the formation of an ester complex, the decomposition of which is the rate‐determining step. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 651–656, 2006     

Calixarenes in analytical and separation chemistry

Discovered in the 1940’s, [1_n]metacyclophanes with the common name calix[n]arenes which is derived from for the molecule’s shape enjoyed a remarkable interest in almost all fields of chemistry since the 1980’s, which is highlighted by several books [1–8]. Over 50 reviews concerning their synthesis, properties and applicabilities were published, many of those with emphasis on organic synthesis and structural properties are cited in ¶[P. 5–6 in 2]. Of interest for analytical chemists are reviews on calixarenes and the structurally related resorcin[n]arenes (or calix[n]resorcarenes) and calixpyrroles concerning potentiometric sensors [9–12], chromo- and fluorophores [13, 14], molecular switches [15], metal ion binding in solution [16–19], redox properties [20] and anion binding [21–24]. Other recent reviews deal with thermodynamic aspects [25], organometallic compounds [26], P-containing calixarenes [27–29], as well as molecular dynamics modeling [30–33]. It is a vital field with over 200 publications per year. Therefore, this article presents only selected results on complexation, solvent extraction and membrane transport with the emphasis on ion and molecular recognition which can be used for analytical purposes, without attempting to cover all available references.     

Electronic currents and Born-Oppenheimer molecular dynamics

Born-Oppenheimer variable separation is the mainstay of studies of chemical reactivity and dynamics. A long-standing problem of this ansatz is the absence of electronic currents in a system undergoing dynamics. I analyze the physical origin of the "missing" electronic currents in Born-Oppenheimer wavefunctions. By examining the problem within the multi-state Born-Huang ansatz, I demonstrate that electronic currents arise from the first-order non-adiabatic coupling to electronically excited states. I derive two expressions for the electronic currents induced by nuclear motion. The sum-over-the-states formula, identical to the result of "complete adiabatic" treatment of Nafie [J. Chem. Phys. 79, 4950 (1983)] leads to a transparent and intuitive physical picture of the induced currents, but is unsuitable for practical implementation in all but the simplest systems. The equivalent expression in terms of the electronic energy derivatives is straightforward to implement numerically. I present first applications of this approach to small systems of potential chemical interest.     

Four-dimensional NMR spectroscopy of a 723-residue protein: chemical shift assignments and secondary structure of malate synthase g

A four-dimensional (4-D) NMR study of Escherichia coli malate synthase G (MSG), a 723-residue monomeric enzyme (81.4 kDa), is described. Virtually complete backbone (1)HN, (15)N, (13)C, and (13)C(beta) chemical shift assignments of this largely alpha-helical protein are reported. The assignment strategy follows from our previously described approach based on TROSY triple resonance 4-D NMR spectroscopy [Yang, D.; Kay, L. E. J. Am. Chem. Soc. 1999, 121, 2571-2575. Konrat, R; Yang, D; Kay, L. E. J. Biomol. NMR 1999, 15, 309-313] with a number of modifications necessitated by the large size of the protein. A protocol for refolding deuterated MSG in vitro was developed to protonate the amides deeply buried in the protein core. Of interest, during the course of the assignment, an isoaspartyl linkage in the protein sequence was unambiguously identified. Chemical shift assignments of this system are a first step in the study of how the domains of the protein change in response to ligand binding and for characterizing the dynamical properties of the enzyme that are likely important for function.     

New Compounds in Rare Earth-Trels-Tetrels Systems:Syntheses,Structures, Their Rich Chemistry and Physical Properties

Intermetallic compounds constitute a very large fraction of inorganic compounds. Understanding these compounds with respect to their structures, chemical bonding, and physical properties is very important to fundamental materials science. The so-called Zintl phase (valence compound) subset of these has been of interest to many investigators for many years, and some understanding of this class of compounds has greatly broadened our views of chemical bonding^[1-3].Some progress has been achieved for compounds between alkali metals and the triels Ga, In, Tl^[4] Besides some structural reports^[5-9], ternary systems of rare earth-trels-tetrels are especially lack of broad and further exploration. Here we report more than ten new compounds characterized in these systems. The as cast samples were synthesized by High Frequency melting method inside Ar-glovebox followed by annealing in silica tubes. Lattice parameter refinements were done from powder data using Si as an internal standard. The structures were determined either from single crystal or from powder XRD full profile refinements. The physical properties of the compounds will be discussed together with their structures and bonding features. The compounds show, depending on compositions, metallic Zintl phase, magnetic ordering, heavy Fermion behaviour or other phase transitions. The compounds have both rich structural chemistry and physical properties.     

A Convenient and Easy-controlled Method for Preparation of 7,10-Bis(2,2,2-trichloroethyloxycarbonyl)-10-deacetyl Baccatin Ⅲ

Introduction The complex natural product paclitaxel(Tax-olR, 1a), first isolated from Taxus brevifolia[1], has an excellent clinical activity against ovarian and breast cancers[2] and shows promising results in the treatment of other cancers[3]. The structure-activity relationships(SAR) of taxoid derivatives have been extensively studied to search for the analogues bearing better physical, chemical and biological properties. One example is the discovery of TaxotereR(1b). The structures of Taxol and Taxotere are shown in Scheme 1.     

Graft copolymers having hydrophobic backbone and hydrophilic branches. XXIII. Particle size control of poly(ethylene glycol)-coated polystyrene nanoparticles prepared by macromonomer method

Monodisperse polymeric nanospheres, which consist of polystyrene cores and poly(ethylene glycol) (PEG) branches on their surfaces, were prepared by the dispersion copolymerization of styrene (St) with PEG macromonomers that had a methacryloyl (MMA-PEG) or p-vinylbenzyl (St-PEG) end group in various organic solvent/water media. Electron spectroscopy for chemical analysis (ESCA) of the nanosphere surfaces indicated that PEG macromonomer chains were favorably located on their surfaces. The morphologies of the nanospheres were observed via a scanning electron micrograph (SEM), and particle sizes were estimated by a submicron particle analyzer. When both the concentration of macromonomers and molecular weight were higher, small nanospheres in diameter were obtained. Larger nanospheres in diameter were obtained using macromonomers with low molecular weight at lower concentration. The functions that correlate the diameter (D_n) on different concentration units were D_n = K[St]^0.64[MMA-PEG]^{−0.53±0.01}[I]^−0.49 and D_n = K[St]^0.80[St-PEG]^{−0.69±0.01}[I]^−0.22, where [I], [St], [MMA-PEG], and [St-PEG] are initiator, styrene, MMA-PEG, and St-PEG macromonomer concentration in feed, respectively. When the reaction parameters such as the molecular weight of the macromonomers were properly chosen, the particle size could be controlled in a range from ca. 80 to 3100 nm. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2155–2166, 1999     

Supercooled water's thermodynamic behaviour and a conflict between Arrhenius relaxation and configurational entropy

The increase in the time- and temperature-dependent heat capacity, C_p, in the glass–liquid transition range of water has been investigated using earlier data [G.P. Johari, A. Hallbrucker, E. Mayer, Nature 330 (1987) 552], new computation of the manner of C_p increase in the glass–liquid transition range and theoretical views. The investigation shows that the temperature dependence of structural relaxation time of water in the 136–148 K range remains non-Arrhenius, like the dielectric relaxation time [G.P. Johari, J. Chem. Phys. 105 (1996) 7079] and the self-diffusion coefficient [R.C. Smith, B.D. Kay, Nature 398 (1999) 788]. Theoretical reasons for the broadening of the heat-capacity endotherm are given and verified by computation. Analysis shows that for an Arrhenius-type relaxation-dynamics, the configurational entropy of a liquid will remain constant on its cooling, which violates the consequences of the third law of thermodynamics. When the relaxation time is taken as 10² s at T_g and as 10⁻¹⁴ s at infinite temperature for analysing a liquid's relaxation [K. Ito, C.T. Moynihan, C.A. Angell, Nature 398 (1999) 492; R. Richert, C.A. Angell, J. Chem. Phys. 108 (1998) 9016], the Arrhenius energy becomes unjustifiably proportional to the T_g of a liquid. In its glass transition features, water is not as analogous with molten silica as is believed.     

Calixarenes in analytical and separation chemistry

Discovered in the 1940's, [1n]metacyclophanes with the common name calix[n]arenes which is derived from for the molecule's shape enjoyed a remarkable interest in almost all fields of chemistry since the 1980's, which is highlighted by several books [1-8]. Over 50 reviews concerning their synthesis, properties and applicabilities were published, many of those with emphasis on organic synthesis and structural properties are cited in [P. 5-6 in 2]. Of interest for analytical chemists are reviews on calixarenes and the structurally related resorcin[n]arenes (or calix[n]resorcarenes) and calixpyrroles concerning potentiometric sensors [9-12], chromo- and fluorophores [13, 14], molecular switches [15], metal ion binding in solution [16-19], redox properties [20] and anion binding [21-24]. Other recent reviews deal with thermodynamic aspects [25], organometallic compounds [26], P-containing calixarenes [27-29], as well as molecular dynamics modeling [30-33]. It is a vital field with over 200 publications per year. Therefore, this article presents only selected results on complexation, solvent extraction and membrane transport with the emphasis on ion and molecular recognition which can be used for analytical purposes, without attempting to cover all available references.     

Thermodynamic study of interfacial tension between oil and aqueous phases composed of ionic liquids and brine

The first fundamental step in determining the physicochemical properties of an equilibrium system is to determine the activity coefficient of electrolyte and non-electrolyte ions. Based on understanding the importance of activity coefficient in thermodynamic systems in this study, in order to predict interfacial tension between oil and aqueous phases composed of ionic liquids and brine, a modified thermodynamic equation based on concentration and coefficient of activity of ionic liquids is defined. For this study, the Extended UNIQUAC model is desired and its adjustable parameters are optimized with Genetic + PSO algorithm. The modified model has practical features such as investigating the effect of concentrations of salts in the water of oil fields formation on the interfacial tension of the system, investigating the effect of concentrations of various organic compounds such as ionic liquids on the interfacial tension of the system and investigating the interaction energy between organic and inorganic ions. In this study, the optimization of the modified thermodynamic equation to predict the interfacial tension of solutions containing [C₈Py][Cl], [C₁₈Py][Cl], [C₁₂mim][Cl] and [C₁₈mim][Cl] with the presence of brine and distilled water is investigated. Also, the effect of ionic strength of the solution in 32 equilibrium systems on interfacial tension is investigated. According to the optimization results of this study, the design of a computer program can be considered to predict the interfacial tension with the presence of ionic liquids and salts.     

Variability of the 15N chemical shielding tensors in the B3 domain of protein G from 15N relaxation measurements at several fields. Implications for backbone order parameters

We applied a combination of 15N relaxation and CSA/dipolar cross-correlation measurements at five magnetic fields (9.4, 11.7, 14.1, 16.4, and 18.8 T) to determine the 15N chemical shielding tensors for backbone amides in protein G in solution. The data were analyzed using various model-independent approaches and those based on Lipari-Szabo approximation, all of them yielding similar results. The results indicate a range of site-specific values of the anisotropy (CSA) and orientation of the 15N chemical shielding tensor, similar to those in ubiquitin (Fushman, et al. J. Am. Chem. Soc. 1998, 120, 10947; J. Am. Chem. Soc. 1999, 121, 8577). Assuming a Gaussian distribution of the 15N CSA values, the mean anisotropy is -173.9 to -177.2 ppm (for 1.02 A NH bond length) and the site-to-site CSA variability is +/-17.6 to +/-21.4 ppm, depending on the method used. This CSA variability is significantly larger than derived previously for ribonuclease H (Kroenke, et al. J. Am. Chem. Soc. 1999, 121, 10119) or recently, using "meta-analysis" for ubiquitin (Damberg, et al. J. Am. Chem. Soc. 2005, 127, 1995). Standard interpretation of 15N relaxation studies of backbone dynamics in proteins involves an a priori assumption of a uniform 15N CSA. We show that this assumption leads to a significant discrepancy between the order parameters obtained at different fields. Using the site-specific CSAs obtained from our study removes this discrepancy and allows simultaneous fit of relaxation data at all five fields to Lipari-Szabo spectral densities. These findings emphasize the necessity of taking into account the variability of 15N CSA for accurate analysis of protein dynamics from 15N relaxation measurements.     

Electric and hydrodynamic stretching of DNA-polymer conjugates in free-solution electrophoresis

The conjugation of an uncharged polymer to DNA fragments makes it possible to separate DNA by free-solution electrophoresis. This end-labeled free-solution electrophoresis method has been shown to successfully separate ssDNA with single monomer resolution up to about 110 bases. It is the aim of this paper to investigate in more detail the coupled hydrodynamic and electrophoretic deformation of the ssDNA-label conjugate at fields below 400 V/cm. Our model is an extension of the theoretical approach originally developed by Stigter and Bustamante [Biophys. J. 75, 1197 (1998)] to investigate the problems of a tethered chain stretching in a hydrodynamic flow and of the electrophoretic stretch of a tethered polyelectrolyte. These two separate models are now used together since the charged DNA is "tethered" to the uncharged polymer (and vice versa), and the resulting self-consistent model is used to predict the deformation and the electrophoretic velocity for the hybrid molecule. Our theoretical and experimental results are in good qualitative agreement.     

Synthesis of 2-Mercapto- and 2-Hydroxy-Substituted Diphenylphosphines for use as Dianionic Bidentate Ligands and Polydentate Ligand Precursors

Abstract

As part of our studies into the synthesis of polydentate phosphine-containing ligands, we have investigated the preparation of the phosphines (4; X[dbnd]O) and (4; X[dbnd]S). These are of interest both as potential dianionic bidentate ligands and as useful precursors of more complex polydentate ligand systems. A synthesis of the thiol system (4; X[dbnd]S) from 1,2-dinitrobenzene has been previously reported [1], but the observation [2], that 2-bromoaryl esters of phosphoric acid rearrange to give esters of arylphosphonic acids in the presence of alkyl lithiums, led us to consider whether a similar type of rearrangement might provide a convenient approach to both (4; X[dbnd]S) and (4; X[dbnd]O).     

Correlations between phase behaviors and ionic conductivities of (ionic liquid + alcohol) systems

To understand the basic properties of ionic liquids (ILs), we examined the phase behavior and ionic conductivity characteristics using various compositions of different ionic liquids (1-ethyl-3-methylimidazolium hexafluorophosphate [emim] [PF6] and 1-benzyl-3-methylimidazolium hexafluorophosphate [bzmim] [PF6]) in several different alcohols (ethanol, propanol, 1-butanol, 2-butanol, and hexanol). We conducted a systematic study of the impact of different factors on the phase behavior of imidazolium-based ionic liquids in alcohols. Using a new experimental method with a liquid electrolyte system, we observed that the ionic conductivity of the ionic liquid/alcohol was sensitive to the surrounding temperature. We employed Chang et al.’s thermodynamic model [Chang et al. (1997, 1998) [21], [22]] based on the lattice model. The obtained co-ordinated unit parameter from this model was used to describe the phase behavior and ionic conductivities of the given system. Good agreement with experimental data of various alcohol and ILs systems was obtained in the range of interest.