Neutral Species (neutral + species)

Distribution by Scientific Domains

Selected Abstracts

Potentiometric Sensing of Neutral Species Based on a Uniform-Sized Molecularly Imprinted Polymer as a Receptor,

Rong-Ning Liang
Veränderungen auf der Spur: Ein einheitlich großes molekular geprägtes Polymer (MIP) kann als Rezeptor in einer Polymermembran eingesetzt werden, die als ionenselektive Elektrode zum potentiometrischen Nachweis neutraler Spezies genutzt wird (siehe Schema). Die Veränderungen der Bindungsstellen des MIP in der Membranphase, die durch die Analyterkennung ausgelöst werden, werden mit einem Indikator-Ion gemessen, dessen Molekülstruktur der des Analyten ähnelt. [source]

Pressure Ionization and Transitions in Dense Hydrogen

W. Ebeling
Abstract Shock experiments with fluid hydrogen have shown that a transition from insulating behavior to metal-like conductivity occurs at pressures beyond 100 GPa. This requires the development of new methods to describe the transition region of dense plasmas. The traditional approach due to Saha is based on the assumption of chemical equilibrium between charged and neutral components. This is equivalent to minimizing the free energy with respect to the composition. Here we improve an expression for the free energy developed recently to determine Hugoniot curves and isentropes in dense hydrogen and deuterium plasma in the regions of partial dissociation and partial ionization. We show that at high pressures the influence of the excluded volume occupied by neutral species is crucial for the transition to full ionization. We present curves for several thermodynamic functions for the region 5000 K < T < 20000 K and 0.6 g/cm3 < , < 1 g/cm3. The influence of the effective radii of the neutral species is crucial in the transition region. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Lanthanide Chelates Based on Diethylenetriamine Fitted with O -Benzoic Acid Pendant Arms

Daniel Imbert
Abstract A new polycarboxylate ligand H5L has been synthesized by the attachment of five benzoate subunits onto a diethylenetriamine framework. Seven pKa values have been determined by potentiometry, spectrophotometry and NMR spectroscopy as 1.9(2), 2.8(2), 3.87(5), 4.58(6), 4.87(6), 9.19(6) and 11.68(5), the first four corresponding to the carboxylic functions and the last three to amine sites. The interaction between H5L and LnIII ions in dilute aqueous solution has been examined by UV/Vis absorption and emission spectrometries, and has been found to result in monometallic complexes that are moderately stable in the pH range 3.7,7.5. Conditional stability constants at pH 5.3 are logK11 = 5.3(2), 6.6(1), 6.5(1) and 7.2(3) for La, Eu, Tb and Lu, respectively. In the case of TbIII, the stability constants for [Tb(HL)], and [Tb(H2L)] are log,111 = 22.0(2) and log,121 = 29.8(1), giving a pTb of 10.0. In the pH range 4,7, more than 90% of the TbIII ions are in the form of the neutral species [Tb(H2L)]. Lifetime determinations of the Eu(5D0) and Tb(5D4) excited levels in both H2O and D2O at pH 5.3 indicate 4.8 ± 0.5 (Eu) and 4.5 ± 0.5 (Tb) water molecules being bound in the inner coordination sphere of the LnIII. The triplet state of the ligand in water lies at around 26000 cm,1, resulting in a sizeable sensitisation of the Tb-centred luminescence (absolute quantum yield: ,abs = 10.3%), while the luminescence of EuIII is only poorly sensitised (,abs = 1.5%). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]

Novel Engineered Ion Channel Provides Controllable Ion Permeability for Polyelectrolyte Microcapsules Coated with a Lipid Membrane

Andrew R. Battle
Abstract The development of nanostructured microcapsules based on a biomimetic lipid bilayer membrane (BLM) coating of poly(sodium styrenesulfonate) (PSS)/poly(allylamine hydrochloride) (PAH) polyelectrolyte hollow microcapsules is reported. A novel engineered ion channel, gramicidin (bis-gA), incorporated into the lipid membrane coating provides a functional capability to control transport across the microcapsule wall. The microcapsules provide transport and permeation for drug-analog neutral species, as well as positively and negatively charged ionic species. This controlled transport can be tuned for selective release biomimetically by controlling the gating of incorporated bis-gA ion channels. This system provides a platform for the creation of "smart" biomimetic delivery vessels for the effective and selective therapeutic delivery and targeting of drugs. [source]

Electronic structures of 3d -metal mononitrides

Zhijian Wu
Abstract Bond distances, vibrational frequencies, electron affinities, ionization potentials, and dissociation energies of the title molecules in neutral, positively, and negatively charged ions were studied by use of density functional methods B3LYP, BLYP, BHLYP, BPW91, and B3PW91. The calculated results are compared with experiments and previous theoretical studies. It was found that the calculated properties are highly dependent on the functionals employed, in particular for the dissociation energy and vibrational frequency. For neutral species, pure density functional methods BLYP and BPW91 have relatively good performance in reproducing the experimental bond distance and vibrational frequency. For cations, hybrid exchange functional methods B3LYP and B3PW91 are good in predicting the dissociation energy. For both neutral and charged species, BHLYP tends to give smaller dissociation energy. © 2005 Wiley Periodicals, Inc. J Comput Chem 27: 267,276, 2006 [source]

Photophysics in Motionally constrained Bioenvironment: Interactions of Norharmane with Bovine Serum Albumin,

Arabinda Mallick
ABSTRACT Steady-state photophysics of norharmane (NHM), a bioactive alkaloid, has been studied in the presence of a model transport protein, bovine serum albumin (BSA). The emission spectrum undergoes a remarkable change upon addition of BSA to the aqueous solution of NHM in buffer. Addition of BSA leads to a marked increase in the fluorescence anisotropy of the neutral species of NHM, although the fluorescence anisotropy for the cationic species is almost invariant to BSA addition, suggesting that the neutral species is located in a motionally restricted environment of BSA, whereas the cationic species remains in the bulk aqueous phase. The binding constant (K) and free energy change (,G) for the probe-protein binding have been calculated from the fluorescence data. Light has been thrown on the action of urea on protein-bound NHM. The denaturation study suggests that the protein, in its native form, binds with NHM. Polarity of the microenvironment around the probe has been determined from a comparison of the fluorescence properties of the two prototropic species of NHM in water-dioxane mixture with varying composition. [source]

The Ever-Surprising Chemistry of Boron: Enhanced Acidity of Phosphine,Boranes

Marcela Hurtado Dr.
Abstract The acidity-enhancing effect of BH3 in gas-phase phosphine,boranes compared to the corresponding free phosphines is enormous, between 13 and 18 orders of magnitude in terms of ionization constants. Thus, the enhancement of the acidity of protic acids by Lewis acids usually observed in solution is also observed in the gas phase. For example, the gas-phase acidities (GA) of MePH2 and MePH2,BH3 differ by about 118,kJ,mol,1 (see picture). The gas-phase acidity of a series of phosphines and their corresponding phosphine,borane derivatives was measured by FT-ICR techniques. BH3 attachment leads to a substantial increase of the intrinsic acidity of the system (from 80 to 110,kJ,mol,1). This acidity-enhancing effect of BH3 is enormous, between 13 and 18 orders of magnitude in terms of ionization constants. This indicates that the enhancement of the acidity of protic acids by Lewis acids usually observed in solution also occurs in the gas phase. High-level DFT calculations reveal that this acidity enhancement is essentially due to stronger stabilization of the anion with respect to the neutral species on BH3 association, due to a stronger electron donor ability of P in the anion and better dispersion of the negative charge in the system when the BH3 group is present. Our study also shows that deprotonation of ClCH2PH2 and ClCH2PH2,BH3 is followed by chloride departure. For the latter compound deprotonation at the BH3 group is found to be more favorable than PH2 deprotonation, and the subsequent loss of Cl, is kinetically favored with respect to loss of Cl, in a typical SN2 process. Hence, ClCH2PH2,BH3 is the only phosphine,borane adduct included in this study which behaves as a boron acid rather than as a phosphorus acid. [source]

A Spectroscopic Study of the Reduction of Geometrically Restrained Viologens

Abstract A small series of N,N,-dimethyl-4,4,-bipyridinium dication derivatives (commonly known as viologens) has been synthesized and fully characterized; a short dialkoxy tether attached at the 3,3,-positions is used to alter the central dihedral angle. These angles were determined by both single-crystal X-ray diffraction and by computational studies made for the dication, radical cation, and neutral species in a solvent reservoir. The dihedral angle derived for the dication controls the first reduction potential, whereas the geometry of the resultant ,-radical cation determines the magnitude of the second reduction potential. The optical absorption spectra recorded for the various species, and especially those of the radical cations, and the EPR spectral parameters of the ,-radical cations also depend on the molecular geometry. In particular, the central dihedral angle influences the spin density distribution around the aromatic nucleus and, by way of comparison to the parent viologen, it has been possible to resolve the angle dependence from the inherent inductive effect of the strap. These results are considered in terms of the degree of electronic communication between the two aromatic rings, as controlled by the length of the tether. [source]

Study of Intramolecular Competition between Carboxylate and Phosphonate for PtII with the Aid of a Novel Tridentate Carboxylato-Thioether-Phosphonato Ligand

Matthieu Hamel Dr.
Abstract The tridentate dianionic ligand 2-[2,-(hydroxyisopropoxyphosphoryl)phenylsulfanyl]benzoate (L2,) reacts with cis -[Pt(NH3)2(H2O)2]2+ to form an S,O-chelate in which the O-coordinated group is either carboxylate or phosphonate, depending on the degree of protonation of the complex. Carboxylate appears to be the stronger ligand, and the stoichiometric reaction between cis -[Pt(NH3)2(H2O)2]2+ and L2, yields the neutral species [Pt(L)(NH3)2], with L bound by sulfanyl and carboxylate groups, both in solution and in the solid state. Upon protonation of [Pt(L)(NH3)2], the stronger basicity of the carboxylate causes the Pt coordination to switch from carboxylate to phosphonate, and the uncoordinated carboxylate group becomes protonated. In methanolic solution, the first-order kinetics of this rearrangement could be observed by 31P,NMR spectroscopy. Both complexes,the carboxylate-bound neutral complex [Pt(L)(NH3)2],H2O (triclinic, P (no.,2), a=9.529(6), b=9.766(6), c=12.299(7),Å, ,=106.91(2), ,=101.71(2), ,=102.05(2)°, Z=2) and the perchlorate salt of the phosphonate-bound complex [Pt(LH)(NH3)2]ClO4,H2O (monoclinic, P21/c (no.,14), a=12.095(2), b=14.046(2), c=14.448(2),Å, ,=95.55(2)°, Z=4),were characterized by X-ray crystallography. [source]

Radical Ions from 3,3,,,,3,,,,-Tris(butylsulfanyl)-2,2,:5,,2,:5,,2,,,,5,,,,2,,,,:5,,,,,2,,,,-sexithiophene: An Experimental and Theoretical Study of the p - and n -Doped Oligomer

CHEMPHYSCHEM, Issue 11 2003
Angelo Alberti Dr.
Abstract The 3,3,,,,3,,,,-tris(butylsulfanyl)-2,2,:5,,2,:5,,2,,,,5,,,,2,,,,:5,,,,,2,,,,-sexithiophene 1 was investigated through spectroscopic (NMR, EPR, UV/Vis-NIR), electrochemical, spectroelectrochemical and theoretical (DFT) studies. The charged species obtained upon its oxidation and reduction were characterised, showing that 1 can exist in at least five different oxidation states, that is, a neutral species, a radical cation, a dication, a radical anion, and a dianion. The long term stability of the radical cation 1+. was evidenced by the 1H NMR study in the presence of small quantities of trifluoroacetic acid (TFA). This approach allowed a comparison of the relative broadening of proton signals of 1, induced by the electron exchange process with traces of radical cation 1+., and the hfc (hyperfine coupling) constants obtained from the EPR study and DFT calculations. In the radical cation, all of the heterocyclic sulphur atoms are not significantly involved in the delocalisation of the unpaired electron, whereas the opposite holds for the radical anion. Time-dependent DFT calculations reproduced well the wavelengths of the optical transitions observed in the spectroelectrochemical experiments for all the five oxidation states and support the formation of the dianion 12,. [source]