Using nonaqueous capillary electrophoresis to analyze several quinolones in pig kidney samples

We show the potential of nonaqueous capillary electrophoresis (NACE) for analyzing enrofloxacin (ENR), ciprofloxacin (CPR), danofloxacin (DAN), difloxacin (DIF), marbofloxacin (MAR), flumequine (FLU), and oxolinic acid (OXA) in pig kidney samples. We have studied the effects of parameters such as the composition of the organic media, the choice of electrolyte, the pH* of the background electrolyte (BGE), the addition of modifiers, and the reversal of electroosmotic flow. Separation was good with 20 mM ammonium acetate, 0.004% polycation hexadimethrine bromide (HDB), and 4% acetic acid (pH* 5.4) in methanol/acetonitrile (50:50 v/v) medium. We used a quick and simple sample preparation method, hydrochloric acid as an extractant and solid-phase extraction (SPE) with Baker C18 cartridges as the cleanup step. Recoveries for all quinolones were over 80%.     

Theory of volume phase transitions of side-chain liquid crystalline gels

We present a mean field theory to describe volume phase transitions of side-chain liquid crystalline gels. Three different uniaxial nematic phases (N(1), N(2), and N(3)) are defined by using orientational order parameter S(m) of side-chain liquid crystals (mesogens) and S(b) of backbone chains. We derive the free energy for the three nematic phases of side-chain liquid crystalline gels dissolved in isotropic solvents and calculate the swelling curve of the gel, the order parameters of a backbone chain and of side-chain liquid crystals, and the deformation of the gel as a function of temperature and an electric field. We find isotropic-nematic (N(1), N(2), and N(3)) and N(1)N(2) phase transitions of the gels, depending on the interaction between a backbone chain and a side-chain liquid crystal.     

On the number of benzenoid hydrocarbons

We present a new algorithm which allows a radical increase in the computer enumeration of benzenoids b(h) with h hexagons. We obtain b(h) up to h = 35. We prove that b(h) approximately const.kappa(h), prove the rigorous bounds 4.789 < or = kappa < or = 5.905, and estimate that kappa = 5.16193016(8). Finally, we provide strong numerical evidence that the generating function summation operator b(h)z(h) approximately A(z) log(1 - kappa z), estimate A(1/kappa) and predict the subleading asymptotic behavior. We also provide compelling arguments that the mean-square radius of gyration (h) of benzenoids of size h grows as h(2 nu), with nu = 0.64115(5).     

Phytochemical Study on Some Polyphenols of <Emphasis Type="Italic">Geranium pyrenaicum</Emphasis>

In order to continue our previous studies concerning Geranium pyrenaicum Burm. (Geraniaceae), we have performed spectrophotometric determinations and a HPLC study of some polyphenols. We have analyzed the dried Geranii pyrenaici herba (harvested from Cluj-Napoca, district of Cluj, Romania). We have established the content in flavonoids (0.316%), phenolic acids (0.099%), tannins (5.295%), and anthocyanins (12.030 mg/100 g vegetal product). We have identified and measured by HPLC the following compounds: hyperoside (21.61 μg/100 mg), ellagic acid (1810.44 μg/100 mg), isoquercitrine (11.197 μg/100 mg), and caftaric acid (76.83 μg/100 mg). We have also analyzed by HPLC a hydrolyzed sample of the same drug in which we have identified and measured: ellagic acid (4139.33 μg/100 mg), quercetol (29.65 μg/100 mg), kaempherol (41.48 μg/100 mg), and caftaric acid (20.721 μg/100 mg). __________ Published in Khimiya Prirodnykh Soedinenii, No. 4, pp. 322–324, July–August, 2005.     

Molecular relaxation processes in the salt systems containing anions of various configurations

We present in this paper a comparative analysis of the spectral and molecular-relaxation parameters of the ionic salts in the region of solid-liquid phase transition and in the molten state depending on the anion symmetry (thiocyanate (SCN-), a linear rotor, C(infinity v); nitrate (NO3-), a symmetrical top, D3h; and perrhenate (ReO4-), a spherical top, Td), size and charge of the cation, and temperature. We also present new results of the investigations on molecular relaxation in thiocyanate ion in several crown-etheric complexes.     

Relativistic calculation of indirect NMR spin-spin couplings using the Douglas-Kroll-Hess approximation

We have employed the Douglas-Kroll-Hess approximation to derive the perturbative Hamiltonians involved in the calculation of NMR spin-spin couplings in molecules containing heavy elements. We have applied this two-component quasirelativistic approach using finite perturbation theory in combination with a generalized Kohn-Sham code that includes the spin-orbit interaction self-consistently and works with Hartree-Fock and both pure and hybrid density functionals. We present numerical results for one-bond spin-spin couplings in the series of tetrahydrides CH(4), SiH(4), GeH(4), and SnH(4). Our two-component Hartree-Fock results are in good agreement with four-component Dirac-Hartree-Fock calculations, although a density-functional treatment better reproduces the available experimental data.     

Structural,electronic, elastic,thermodynamic and vibration properties of TbN compound from first principles calculations

We have predicted structural, electronic, elastic, thermodynamic and vibration characteristics of TbN, using density functional theory within generalized-gradient (GGA) apraximation. For the total energy calculation we have used the projected augmented plane-wave (PAW) implementation of the Vienna Ab initio Simulation Package (VASP). We have used to examine structure parameter in eight different structures such as in NaCl (B1), CsCl (B2), ZB (B3), Tetragonal (L1₀), WC (Bh), NiAs (B8), PbO (B10) and Wurtzite (B4). We have performed the thermodynamics properties for TbN by using quasi-harmonic Debye model. We have, also, predicted the temperature and pressure variation of the volume, bulk modulus, thermal expansion coefficient, heat capacities and Debye temperatures in a wide pressure (0–130 GPa) and temperature ranges (0–2000 K). Furthermore, the band structure, phonon dispersion curves and corresponding density of states are computed. Our results are compared to other theoretical and experimental works, and excellent agreement is obtained.     

Broken symmetry solutions of the extended Hubbard model

This paper describes a group theoretical classification of the unrestricted Hartree–Fock (UHF ) solution of the extended Hubbard model including nearest-neighbor repulsion and exchange interactions. We derived systematically all types of the broken symmetry solution with a single-order parameter for the ordering vector Q = (π,π). It is shown that there are four nonmagnetic states: a charge density wave (CDW), a charge current wave (CCW), and two bond-order waves (BOW), and five magnetic states: an ordinary antiferromagnetic state (AF), a spin current wave (SCW), two axial spin bond-order waves (ASBOW), and an helical spin bond-order wave (HSBOW). We showed that these phases can be derived naturally from the irreducible decomposition of the Fourier transformed interaction and the self-consistent field (SCF ) condition. Some numerical results are given for the half-filled case.     

Perturbational relativistic theory of electron spin resonance g-tensor

We carry out a complete treatment of the leading-order relativistic one-electron contributions, arising from the Breit-Pauli Hamiltonian, to the g-tensor of electron spin resonance spectroscopy. We classify the different terms and discuss their interpretation as well as give numerical ab initio estimates for the F2(-), Cl2(-), Br2(-), and I2(-) series, using analytical response theory calculations with a multiconfigurational self-consistent field reference state. The results are compared to available experimental data. (c) 2004 American Institute of Physics     

7-endo radical cyclizations catalyzed by titanocene(III). Straightforward synthesis of terpenoids with seven-membered carbocycles

We describe a novel procedure for the straightforward synthesis of seven-membered carbocycles via free-radical chemistry, based on titanocene(III)-catalyzed 7-endo-dig and 7-endo-trig cyclizations. This procedure has proved to be useful for the chemical preparation of terpenoids with different skeletons containing cycloheptane rings, including the first total syntheses of dauca-4(11),8-diene (2), barekoxide (3), authentic laukarlaol (81), and a valparane diterpenoid (72), as well as a substantially improved synthesis of karahanaenone (1). We also provide theoretical and experimental evidence in support of a plausible mechanism, which may rationalize the preference for the unusual 7-endo cyclization mode shown by radicals with substitution patterns characteristic of the linalyl, nerolidyl, and geranyl linalyl systems. In light of these chemical findings, we discuss the potential involvement of radical cyclizations in the biosynthesis of some terpenoids containing seven-membered carbocycles.     

Mechanism of the N-cyclopropylimine-1-pyrroline photorearrangement

We present here a combined experimental and computational investigation into the photorearrangement of N-cyclopropylimines to yield pyrrolines. We show that the photochemistry, regiochemistry, and stereochemistry of the reaction can be understood in terms of a mechanism involving barrierless evolution in three different (S(2), S(1), S(0)) singlet states and sequential decay through two different (S(2)/S(1), and S(1)/S(0)) conical intersection funnels. We provide evidence that the reaction mechanism involves the generation of a nonequilibrated (i.e., transient) excited state diradical, whose decay can lead not only to pyrrolines but also to cyclopropylimine isomers. It is concluded that the reaction outcome depends on the details of the structure of such transient diradical and on the nature of the dynamics of its decay through the S(1)/S(0) conical intersection.     

A convergent approach to huperzine A and analogues

We describe a concise and convergent synthesis of (rac)-5-methoxy-6-azatricyclco[7.3.1.0(2,7)]trideca-2(7),3,5,11-tetraen-13-ol, which has the basic ring system of huperzine A, a potent inhibitor of acetylcholinesterase. We also describe the synthesis of the novel system 5-methoxy-6-azatricyclo[7.2.2.0(2,7)]trideca-2(7),3,5-trien-10-one and a series of related systems.     

Methanol nucleation in a supersonic nozzle

We determined the partial pressures p(Jmax), temperatures T(Jmax), monomer supersaturations S(Jmax), and characteristic times Δt(Jmax?) corresponding to the maximum nucleation rates of methanol in a supersonic nozzle. We found that T(Jmax) increased from 202.2 K to 223.7 K as p(Jmax) increased from 67.1 to 413.2 Pa, while the maximum nucleation rate J(max) changed by less than a factor of 4 over the measurement range. Our nucleation rates appear reasonably consistent with measurements in other devices and are within one order of magnitude of the nucleation rates predicted by classical nucleation theory.     

Analytical methods to determine cocaine contamination of banknotes from around the world

The presence of cocaine in a significant number of UK pounds (Xxxx), Euros (€) and North American banknotes ($) in general circulation requires appropriate tools to do determinations. This article discusses the-state-of-the-art in the analysis of cocaine on banknotes. We summarize the usual extraction methods of currency samples and compare them, especially with respect to avoiding sample damage. We critically discuss analytical methods, namely gas chromatography (GC) and liquid chromatography (LC), capillary electrophoresis (CE), immunoassay, thermal desorption tandem mass spectrometry (TD-MS²) and ion-mobility spectrometry (IMS). We also review cocaine levels on banknotes around the world and their possible relationship with drug consumption.     

Adsorption of homopolypeptides on gold investigated using atomistic molecular dynamics

We investigate the role of dynamics on adsorption of peptides to gold surfaces using all-atom molecular dynamics simulations in explicit solvent. We choose six homopolypeptides [Ala(10), Ser(10), Thr(10), Arg(10), Lys(10), and Gln(10)], for which experimental surface coverages are not correlated with amino acid level affinities for gold, with the idea that dynamic properties may also play a role. To assess dynamics we determine both conformational movement and flexibility of the peptide within a given conformation. Low conformational movement indicates stability of a given conformation and leads to less adsorption than homopolypeptides with faster conformational movement. Likewise, low flexibility within a given conformation also leads to less adsorption. Neither amino acid affinities nor dynamic considerations alone predict surface coverage; rather both quantities must be considered in peptide adsorption to gold surfaces.     

Databases for transition element bonding: metal-metal bond energies and bond lengths and their use to test hybrid, hybrid meta, and meta density functionals and generalized gradient approximations

We propose a data set of bond lengths for 8 selected transition metal dimers (Ag(2), Cr(2), Cu(2), CuAg, Mo(2), Ni(2), V(2), and Zr(2)) and another data set containing their atomization energies and the atomization energy of ZrV, and we use these for testing density functional theory. The molecules chosen for the test sets were selected on the basis of the expected reliability of the data and their ability to constitute a diverse and representative set of transition element bond types while the data sets are kept small enough to allow for efficient testing of a large number of computational methods against a very reliable subset of experimental data. In this paper we test 42 different functionals: 2 local spin density approximation (LSDA) functionals, 12 generalized gradient approximation (GGA) methods, 13 hybrid GGAs, 7 meta GGA methods, and 8 hybrid meta GGAs. We find that GGA density functionals are more accurate for the atomization energies of pure transition metal systems than are their meta, hybrid, or hybrid meta analogues. We find that the errors for atomization energies and bond lengths are not as large if we limit ourselves to dimers with small amounts of multireference character. We also demonstrate the effects of increasing the fraction of Hartree-Fock exchange in multireference systems by computing the potential energy curve for Cr(2) and Mo(2) with several functionals. We also find that BLYP is the most accurate functional for bond energies and is reasonably accurate for bond lengths. The methods that work well for transition metal bonds are found to be quite different from those that work well for organic and other main group chemistry.     

Computational study of the effect of confinement within microporous structures on the activity and selectivity of metallocene catalysts for ethylene oligomerization

The effect of confinement within some zeolitic structures on the activity and selectivity of metallocene catalysts for the ethylene oligomerization has been investigated using grand canonical Monte Carlo simulations (GCMC). The following zeolite (host) frameworks displaying different pore sizes, have been studied as solid hosts: mazzite (MAZ), AIPO-8 (AET), UTD-1F (DON), faujasite (FAU), and VPI-5 (VFI). Intermediates and transition states involved in the ethylene trimerization reaction catalyzed by a Ti-based catalyst [(η(5)-C(5)H(4)CMe(2)C(6)H(5))TiCl(3)/MAO] have been used as sorbates (guests). We have demonstrated linear correlations with slope a(H,j) between the adsorption enthalpy and the molecular volume V(m) of the sorbates, each holding for a given microporous host below a host-specific threshold V(mmax,j). Beyond this maximal molecular volume, the adsorption vanishes due to steric exclusion. a(H,j) increases, and V(mmax,j) decreases with decreasing host pore size, in line with the confinement concept. We moreover showed that, in the limit of vanishing loading (Henry regime), the enthalpies and entropies of adsorption in a given host are linearly correlated. We have defined a host-specific confinement compensation temperature a(j), which refers to a temperature where the stabilizing adsorption enthalpic interactions are canceled out against the loss in entropy. However, calculated a(j) are much larger than the operating temperatures. With a setup microkinetic model, we predict that the activity and selectivity of the confined Ti-catalyst in ethylene oligomerization can be significantly altered with respect to homogeneous phase conditions, since the adsorption free energies of transition states and intermediates also become functions of a(H,j) and V(m). We have applied this theory to predict the optimum host pore size to get maximum α-octene production, instead of α-hexene, which is primarily produced in the homogeneous phase. We also predict a significantly increased activity for confined catalysts.     

Reaction Pathways and Convexity of the Potential Energy Surface: Application of Newton Trajectories

The reaction path is an important concept of theoretical chemistry. We employ the definitions of the intrinsic reaction coordinate (IRC), the gradient extremal (GE), and the Newton trajectory (NT). The usual imagination in chemistry is that a minimum energy path is in a convex region of the potential energy surface. We describe different schemes of convexity to handle the situation. It comes out that NTs are the best ansatz for the problem: NTs, which monotonically increase (or monotonically decrease), are automatically strictly pseudo-convex throughout, and they go throughout along a valley between minimum and saddle point.     

Formation of ultracold Rb2 molecules in the v' = 0 level of the a(3)Σ+(u) state via blue-detuned photoassociation to the 1(3)Π(g) state

We report on the observation of blue-detuned photoassociation in Rb(2), in which vibrational levels are energetically above the corresponding excited atomic asymptote. (85)Rb atoms in a MOT were photoassociated at short internuclear distance to levels of the 1(3)Π(g) state at a rate of approximately 5 × 10(4) molecules s(-1). We have observed most of the predicted vibrational levels for all four spin-orbit components; 0(+)(g), 0(-)(g), 1(g), and 2(g), including levels of the 0(+)(g) outer well. These molecules decay to the metastable a(3)Σ(+)(u) state, some preferentially to the v' = 0 level, as we have observed for photoassociation to the v' = 8 level of the 1(g) component.