Effects of deformability, uneven surface charge distributions, and multipole moments on biocolloid electrophoretic migration

Liposomes have been widely used as cellular and bioparticle mimics due to their lipid bilayer structure and relative ease of production and manipulation. Such biocolloids are frequently characterized by capillary electrophoresis (CE), which promises a wealth of information about such properties as surface charge, composition, and rigidity. The applicability of this information is somewhat limited, however, since it is interpreted with colloidal theories that do not account for the unique properties of biocolloids. In this work, the effects of deformability, mobile surface charges, intrinsic polarizability, and uneven surface charge distributions are incorporated into colloidal theories in order to better model the electrophoretic behaviors of liposomes.     

Voltammetric, chronocoulometric and spectroelectrochemical studies of electropolymerized films based on Co(III/II)- and Zn(II)-4,9,16,23-tetraaminophthalocyanine: effect of high pH

Electropolymerized thin films of Co(III/II)- and Zn(II)-4,9,16,23-tetraaminophthalocyanine, immersed in solutions of relatively high pH, have been studied electro- and spectroelectrochemically. Cyclic voltammetry and chronocoulometry were used to characterize films deposited on glassy carbon electrodes. Spectroelectrochemistry and ellipsometry measurements were performed on indium tin oxide (ITO) surfaces coated with the zinc and cobalt complexes and correlated to the electrochemical information collected using glassy carbon electrodes. Studies at high pH are motivated by the efficient increase in luminol chemiluminescence at high OH⁻ concentration, and by potential application in luminescence sensors. Although the films are not removed, some structural changes occur when they are exposed to solutions of high pH. In addition, an estimation of the number of monolayers has also been calculated. The atomic diameters of cobalt and zinc are very close in value, but the estimated number of monolayers, based on cyclic voltammetric data, for a given number of electropolymerization cycles is approximately four-fold higher in the zinc-based film. This would correspond to three-fold thicker films when zinc is the central metal ion. Ellipsometry measurements have been correlated with cyclic voltammetric data to confirm that film thickness varies among the different complexes, even though the conditions of electropolymerization are the same.     

Semiquantitative Analysis of Biological Materials by Inductively Coupled Plasma–Mass Spectrometry

Semiquantitative analysis with accuracy of ±30 to 50% is a valuable tool for rapid screening of samples prior to quantitative determination of trace metals. In this study semiquantitative analysis software available with commercial inductively coupled plasma–mass spectrometry (ICP-MS) instrumentation is applied for rapid multielemental analysis, and the accuracy and precision of this semiquantitative analysis approach is evaluated with biological certified reference materials. Samples were prepared by high-pressure, high-temperature nitric acid vapor-phase digestion. For most elements the measured semiquantitative results are in the range of the certified values. With appropriate analyte solution dilution, the measured concentrations of the major elements (e.g., Ca) also agree with certified values. The accuracy is within ±10% for 28 element determinations that include 16 individual elements (Ag, As, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Rb, Sb, Sr, Tl, and Zn) and ±20% for 54 element determinations that include three more elements (Mg, V, and U) in eight certified reference materials including water. The method precision is 11 ± 11% (relative standard deviation,n= 65).     

Mild and practical method for the alpha-arylation of nitriles with heteroaryl halides

[reaction: see text] A mild and transition-metal-free method for the alpha-arylation of aliphatic nitriles with activated heteroaryl halides was developed using NaHMDS or KHMDS as base at ambient temperature. The key to the success of this method is generation of the nitrile anion in the presence of the heteroaryl halide. The method is applicable to both primary and secondary carbonitriles and a wide range of heteroaryl halides. Selective monoarylation was observed with primary carbonitriles. The operational simplicity and the mild reaction conditions add to the value of this method as a practical alternative to the preparation of alpha-heteroaryl carbonitriles.     

Conformational transitions of calixphyrin derivatives monitored by temperature-dependent NMR spectroscopy. Ab initio interpretation of the spectra

Eight meso-aryl calixphyrin derivatives were synthesized and their conformational equilibria and transitions studied with temperature-dependent NMR spectroscopy. On the basis of density functional computations, several conformer species could be identified and observed changes in chemical shifts explained. In some compounds, the aryl group rotation and porphyrin ring flipping could be monitored independently, as their NMR coalescence temperatures were well-separated. Calculated relative conformer energies, transition barriers, and isotropic shieldings agree well with the experimental data. In the meso-substituted porhyrins (calixphyrins) the sp3 carbon atoms perturb their pi-electron system and significantly modify the molecular shape and the flexibility. Even when the conjugation of the pi-electron system was destroyed by the nonplanarity, far-range electronic induction effects still exist and influence chemical shielding and molecular geometry. The aryl functional groups moderately modify the structure of the calixphyrin ring and thus can be used for fine-tuning of the mechanical and chemical properties of these compounds.     

Rhodium-catalyzed asymmetric ring opening of oxabicyclic alkenes with sulfur nucleophiles

The synthesis of 2-sulfanyl-1,2-dihydro-naphthalen-1-ols is described. This methodology is based on rhodium catalysis and enables various thiols to undergo an asymmetric SN2' ring opening of oxabenzonorbornadiene. Under the reaction conditions ([Rh(COD)Cl](2) (2.5 mol %), (S)-(R)-PPF-P(t)Bu(2) (6 mol %), AgOTf (7 mol %), NH(4)I (1.7 equiv), galvinoxyl (5 mol %), THF, 85 degrees C), aryl- and alkyl-sulfide adducts are obtained in good to excellent yield and in high enantiomeric excess (>90% ee).     

Nordesferriferrithiocin. Comparative Coordination Chemistry of a Prospective Therapeutic Iron Chelating Agent(1)

Nordesferriferrithiocin, NDFFTH(2), is a derivative of the siderophore desferriferrithiocin, DFFTH(2), in which the methyl group is substituted by a hydrogen atom. Both compounds show high oral activity as possible drugs for the treatment of iron overload. While DFFTH(2) is significantly toxic, NDFFTH(2) exhibits a lower toxicity and offers a much better therapeutic window than other orally active iron chelators. In this study, complexes of DFFTH(2) and NDFFTH(2) with various trivalent metals have been synthesized and characterized. Five isomers (the maximum possible) have been observed in the case of [Co(DFFT)(2)](-) in solution, as proved by (1)H-NMR measurements. Although normally labile, complexes of Al(3+) ([Al(DFFT)(2)](-)) have been separated by HPLC. In general, DFFTH(2) forms kinetically inert complexes whereas complexes of NDFFTH(2) tend to isomerize quickly in solution, as indicated by CD spectroscopy of separated HPLC fractions of [Cr(NDFFT)(2)](-). The most stable isomers of the aluminum complexes of both ligands have been characterized by X-ray crystallography; K[Al(DFFT)(2)] crystallizes from methanol/diethyl ether in the orthorhombic space group P2(1)2(1)2 with a = 11.238(3) ?, b = 31.719(11) ?, c = 7.684(2) ?, V = 2739.2(24) ?(3), and Z = 4. This isomer has the mer-(N,O-Lambda)(S,S) configuration, while K[Al(NDFFT)(2)] crystallizes from methanol/diethyl ether in the space group P6(1) (a = 21.269(8) ?, c = 9.643(3) ?, V = 3777.8(42) ?(3), Z = 6) and has the same coordination geometry. The solution thermodynamics of the Al(3+), Ga(3+), and Fe(3+) complexes have been studied by spectrophotometric titration. The stability constants (log K) are 23.6(1), 29.2(3), and 31.04(3), respectively, for the DFFTH(2) complexes and 22.0(1), 27.8(2), and 29.09(3), respectively, for the NDFFTH(2) complexes. Cyclic voltammograms of both iron complexes have been recorded in water at a carbon disk working electrode and in DMF at a graphite working electrode. The reduction waves measured in DMF indicate no reversibility whereas in water a quasi-reversible reduction is observed. The reduction potentials (E(1/2)'s) in water are -166 mV for [Fe(DFFT)(2)](-) and -97 mV for [Fe(NDFFT)(2)](-) versus NHE. These potentials are well in the range for biological reductants, which makes possible an in vivo reduction mechanism for the iron removal from the siderophore.     

Iminophosphines: synthesis, formation of 2,3-dihydro-1H-benzo[1,3]azaphosphol-3-ium salts and N-(pyridin-2-yl)-2-diphenylphosphinoylaniline, coordination chemistry and applications in platinum group catalyzed Suzuki coupling reactions and hydrosilylations

The aprotic and protic bi- and multidentate iminophosphines 2-Ph₂PC₆H₄N=CR¹R² (R¹=H, R²=Ph=2a; R¹=Me R²=Ph=2b; R¹=H, R²=2-thienyl=2c; R¹=H, R²=C₆H₄-2-PPh₂=2d; R¹=H, R²=C₆H₄-2-OH=2e, R¹=H, R²=C₆H₄-2-OH-3-Bu^t=2f; R¹=H, R²=CH₂C(O)Me=2g) have been prepared by the acid catalyzed condensation of 2-(diphenylphosphino)aniline with the corresponding aldehyde–ketone. Iminophosphine 2d can be reduced with sodium cyanoborohydride to give the corresponding amino-diphosphine 2-Ph₂PC₆H₄N(H)CH₂C₆H₄-2-PPh₂ (2h). In the presence of a stoichiometric quantity of acid, 2-(diphenylphosphino)aniline reacts in an unexpected manner with benzaldehyde, salicylaldehyde, or acetophenone to give the corresponding 2,3-dihydro-1H-benzo[1,3]azaphosphol-3-ium salts and with pyridine-2-carboxaldehyde to give N-(pyridin-2-ylmethyl)-2-diphenylphosphinoylaniline, the latter of which has been characterized by single-crystal X-ray crystallography, as its palladium dichloride derivative. The attempted condensation of 2-(diphenylphosphino)aniline with pyridine-2-carboxaldehyde to give the corresponding pyridine-functionalized iminophosphine resulted in an unusual transformation involving the diastereoselective addition of two equivalents of aldehyde to give 1,2-dipyridin-2-yl-2-(o-diphenylphosphinoyl)phenylamino-ethanol, which has been characterized by a single-crystal X-ray structure determination. The bidentate iminophosphine 2-Ph₂PC₆H₄N=C(H)Ph reacts with [(cycloocta-1,5-diene)PdClX] X=Cl, Me) to give [Pd{2-Ph₂PC₆H₄N=C(H)Ph}ClX] and the imino-diphosphine 2-Ph₂PC₆H₄N=C(H)C₆H₄-PPh₂ reacts with [(cycloocta-1,5-diene)PdClMe] to give [Pd{2-Ph₂PC₆H₄N=C(H)C₆H₄---PPh₂}ClMe] and each has been characterized by single-crystal X-ray crystallography. The monobasic iminophosphine 2-Ph₂PC₆H₄N=C(Me)CH₂C(O)Me reacts with [Ni(PPh₃)₂Cl₂] in the presence of NaH to give the phosphino–ketoiminate complex [Ni{2-Ph₂PC₆H₄N=C(Me)CHC(O)Me}Cl], which has been structurally characterized. Mixtures of iminophosphines 2a–h and a palladium source catalyze the Suzuki cross coupling of 4-bromoacetophenone with phenyl boronic acid. The efficiency of these catalysts show a marked dependence on the palladium source, catalysts formed from [Pd₂(OAc)₆] giving consistently higher conversions than those formed from [Pd₂(dba)₃] and [PdCl₂(MeCN)₂]. Catalysts formed from neutral bi- and terdentate iminophosphines 2a–d gave significantly higher conversions than those formed from their monobasic counterparts 2e–f. Notably, under our conditions the conversions obtained with 2a–c compare favorably with those of the standards; catalysts formed from tris(2-tolyl)phosphine and tris(2,4-di-tert-butylphenyl)phosphite and a source of palladium. In addition, mixtures of [Ir(COD)Cl]₂ and 2a–h are active for the hydrosilylation of acetophenone; in this case catalysts formed from monobasic iminophosphines 2e–f giving the highest conversions.     

Conversion of Allylic Alcohols into Allylic Nitromethyl Compounds via a Palladium-Catalyzed Solvolysis: An Enantioselective Synthesis of an Advanced Carbocyclic Nucleoside Precursor(1)

A two-step reaction sequence to homoallylic nitro compounds from allylic alcohols is presented. Ethoxy carbonylation of the alcohols with ethyl chloroformate provides the corresponding allylic ethyl carbonates in high yields. Exposure of these substrates to catalytic palladium(0) in CH(3)NO(2) initiates a reaction sequence, ionization-decarboxylation-nitromethylation, that culminates with the formation of nitroalkenes. The regio- and stereochemical outcomes of the nitromethyl allylation reaction can be explained by the behavior of the transient pi-allylpalladium complexes. This methodology serves as a centerpiece for the synthesis of an important carbocyclic nucleoside intermediate.     

A detailed analysis of pseudorotation in PH4F

Summary Pentacoordinated molecules are thought to undergo intramolecular isomerization by the widely accepted Berry pseudorotation mechanism. Through our investigations, we have found that the actual pseudorotation for the PH₄F system is more complex than that envisioned by Berry. The potential energy surface of PH₄F is mapped out at the RHF/6-311G(d, p) level. According to the Berry mechanism, this system is expected to have two minima and two maxima; however, the system actually has two transition states and one global minimum. The minimum energy path from the highest transition state is followed to the second transition state, which in turn has a minimum energy path leading to the global minimum. Along the path between the two transition states there is a branching region. This portion of the potential energy surface is probed extensively.Dedicated to Prof. Klaus Ruedenberg