Asymptotic neutrality of diatomic molecules

We use the no-binding theorem of Thomas-Fermi theory to prove that a large diatomic molecule is almost neutral. That is to say, that if the total nuclear charge isZ then the numberN of electrons required for the diatomic molecule to be stable satisfies . In contrast to the atomic case the emphasis here is on the lower bound onN. Our analysis will imply a new bound on the size of the molecule. These results are proved in the Born-Oppenheimer approximation. We also give bounds onN which hold for allZ by a very elementary method, not assuming the Born-Oppenheimer approximation.Work supported by a Danish Research Academy fellowship and U.S. National Science Foundation grant PHY-85-15288-A03Adress from September 1989: Department of Mathematics, The University of Michigan, Ann Arbor, Michigan 48109 USA     

Wetting of regularly structured gold surfaces

In this study we report results for a systematic study of the wetting of structured gold surfaces formed by electrodeposition through monolayer templates of close-packed uniform submicrometer spheres. Removal of the template after deposition leaves a regular hexagonal array of sphere segment pores where the depth of the pores and, thus, the topography of the surface are controlled by the thickness of gold deposited through the template. We find that, as the thickness of the porous film increases up to the radius of the pores, the apparent contact angle for water on the surface increases from 70 degrees on the flat surface to more that 130 degrees , and then with increasing thickness above the radius of the pores the apparent contact angle decreases back toward 70 degrees . We show that these changes in the apparent contact angle agree with the model of Cassie and Baxter for nonwetted surfaces even though the gold itself is hydrophilic. We also show that the apparent contact angle is independent of the diameter of the pores over the range 400-800 nm. This is the first reported example showing the change of a hydrophilic surface (theta; < 90 degrees ) into a hydrophobic surface (theta; > 90 degrees ) purely by control of the surface topography. The role of the pore shape and size in stabilizing the nonwetting (Cassie-Baxter) droplet on the surface is discussed.     

Application of headspace solid-phase microextraction (HS-SPME) and comprehensive two-dimensional gas chromatography (GC x GC) for the chemical profiling of volatile oils in complex herbal mixtures

The coupling of headspace solid-phase microextraction (HS-SPME) with comprehensive two-dimensional gas chromatography (GC x GC) was shown to be a powerful technique for the rapid sampling and analysis of volatile oils in complex herbal materials. When compared to one-dimensional (1-D) GC, the improved analytical capabilities of GC x GC in terms of increased detection sensitivity and separation power were demonstrated by using HS-SPME/GC x GC for the chemical profiling (fingerprinting) of essential/volatile oils contained in herbal materials of increasing analytical complexity. More than 20 marker compounds belonging to Panax quinquefolius (American ginseng) can be observed within the 2-D contour plots of ginseng itself, a mixture of ginseng and another important herb (P. quinquefolius/Radix angelicae sinensis), as well as a mixture of ginseng and three other herbs (P. quinquefolius /R. angelicae sinensis/R. astragali/R. rehmanniae preparata). Such analytical capabilities should be important towards the authentication and quality control of herbal products, which are receiving increasing attention as alternative medicines worldwide. In particular, the presence of Panax in the herb formulation could be readily identified through its specific peak pattern in the 2-D GC x GC plot.     

Phase-transfer-catalyzed alkylation of guanidines by alkyl halides under biphasic conditions: a convenient protocol for the synthesis of highly functionalized guanidines

An operationally straightforward and efficient method for the alkylation of carbamate-protected guanidines with various alkyl halides and mesylates is described. This protocol proceeds via deprotonation of the acidic N-carbamate hydrogen of the guanidine under biphasic conditions using a catalytic amount of a tetrabutylammonium salt as a phase-transfer catalyst. In this manner, highly functionalized guanidines can be obtained. The reaction is tolerant of a wide range of functional groups on both the alkyl halide and guanidine component. In addition, the reaction is sufficiently mild such that simple aqueous workup and filtration through a short silica gel column yields the substituted guanidines in high purity. In conjunction with the EDCI-mediated guanylation of disubstituted thioureas with amines, phase-transfer catalyzed alkylation of guanidines via a one-pot, three-component synthesis of substituted guanidines was achieved.     

The synthesis and crystal structure of [NiL(NCS)2] (L=3-hydroxyethyl-1,3,5,8,12-pentaazacyclotetradecane)

The reaction of H2CO and H2NCH2CH2OH with the nickel(II) complex of 1,9-diamino-3,7-diazanonane (2,3,2-tet) in the presence of Et3N gives the nickel(II) complex of the macrocycle 3-hydroxyethyl-1,3,5,8,12-pentaazacyclotetradecane (L), which can be readily isolated as the perchlorate salt. The reaction of KCNS with the perchlorate salt in aqueous solution gives [NiL(NCS)2] and the crystal structure of this complex has been determined. The complex is octahedral and trans with the two N-bonded thiocyanates in the axial sites with Ni-NCS bond lengths of 2.106 and 2.145AÅ. The equatorial sites are occupied by N2, N5, N8 and N12 with Ni-N bond distances of 2.053 to 2.076AÅ, which are typical for octahedral nickel(II) complexes. The ligand has a trans III configuration of the sec-NH centres, leading to chair six-membered rings and gauche five-membered rings. The hydroxyethyl group on N3 is axial. There is no evidence for hydrogen-bonding interactions involving the hydroxyethyl group in the crystal lattice.     

Structural thermal and textural studies on cobalt oxide/alumina supported catalysts

CoO/Al₂O₃ catalysts containing amounts of cobalt ranging form 2 to 20% were prepared atpH 11 from neutral mesoporous alumina composed of γ-Al₂O₃ and poorly crystalline boehmite, and were then dried at 80?C. X-ray diffraction, DTA and TG techniques were used to study the structural changes produced upon thermal treatment up to 700?C. Soaking of the alumina in cobalt ammine complex solutions for a period of 10 days (the time required for equilibrium) resulted in a series of catalyst samples (I–V). Another sample (III-a) was soaked for a period of 5 days only in order to study the effect of the soaking time upon the equilibrium conditions. Cobalt aluminate (CoAl₂O₄) bands were characterized in all catalyst samples except III-a. They increased in intensity with increasing cobalt content. Surface species appeared in samples heated to 80?C, and others persisted at 150?C. Heating to temperatures above 200?C resulted in the formation of cobalt oxides, due to decomposition of the surface compounds. DTA and TG studies showed that this was more pronounced at higher concentrations of cobalt. Samples heated at 500?C and above did not undergo any further structural changes, except that the boehmite in the support was converted to γ-Al₂O₃. The variations in the surface parameters followed the same pattern as found previously [1], demonstrating that the catalyst samples are mesoporous, with retention of two ranges of pore size in most cases.     

Molecular structure of 6-methyleneoxytetracycline hydrobromide

The structure of 4(dimethylamino)-1, 4, 4a, 5, 5a, 6, 11, 12a-octahydro-3, 5, 10, 12, 12a-pentahydroxy-6-methylene-1, 11-dioxo-2-naphthacenecarboxamide hydrobromide salt was determined by an X-ray analysis. One methacycline cation and one bromide anion were found in the asymmetric unit of an orthorhombic cell, space group P2₁2₁2₁,a 9.580(1),b 12.147(2),c 18.735(3) å,V2180.0(5) å³, Z4,D _c 1.59 g cm^–3, (MoK) 19.15 cm^–1. The structure was solved and refined toR(F) 0.062 andR _w(F) 0.064 by a full matrix least-squares procedure. The conformation of the methacycline cation is found to be similar to that reported for 6-demethyl-7-chlorotetracycline hydrochloride trihydrate.     

Chemistry of Thiobenzoates: Syntheses, Structures, and NMR Spectra of Salts of [M(SOCPh)(3)](-) (M = Zn, Cd, Hg)

The salts (Ph(4)E)[M(SOCPh)(3)] (M = Zn, Cd, or Hg; E = P or As) are produced by the reaction of Zn(NO(3))(2).6 H(2)O, Cd(NO(3))(2).4H(2)O or HgCl(2) with Et(3)NH(+)PhCOS(-) and (Ph(4)E)X (E = P, X = Br; E = As, X = Cl) in aqueous MeOH in the ratios M(II):PhCOS(-):Ph(4)E(+) = 1:>/=3:>/=1. The crystal structures of (Ph(4)P)[Zn(SOCPh)(3)] (1), (Ph(4)As)[Cd(SOCPh)(3)] (2) and (Ph(4)P)[Hg(SOCPh)(3)] (3) have been determined by single-crystal X-ray diffraction experiments. Crystal data for 1: triclinic; space group P&onemacr;; Z = 2; a = 10.819(2) ?, b = 13.219(3) ?, c = 15.951(3) ?; alpha = 101.75(2) degrees, beta = 97.92(1) degrees, gamma = 109.18(2) degrees. Crystal data for 2: triclinic; space group P&onemacr;; Z= 2; a = 10.741(2) ?, b = 13.168(2) ?, c = 15.809(2) ?; alpha = 101.00(1) degrees, beta = 97.65(1) degrees, gamma = 109.88(1) degrees. Crystal data for 3: monoclinic; space group P2(1)/n; Z = 4; a = 13.302(2) ?, b = 14.276(2) ?, c = 21.108(2) ?; beta = 90.92(1) degrees. The compounds 1 and 2 are isomorphous and isostructural. In the anions [M(SOCPh)(3)](-) the metal atoms have trigonal planar coordination by three sulfur atoms. The metal atoms are further more weakly coordinated intramolecularly to one (M = Hg) or two (M = Zn, Cd) thiobenzoate oxygen atom(s). Using the Bond Valence approach it is found that the contribution of M.O bonding to the total bonding is in the order Cd > Zn > Hg. The metal ((113)Cd, (199)Hg) NMR signals of [M(SOCPh)(3)](-) (M = Cd, Hg) are more shielded than those found for MS(3) kernels in thiolate complexes, a difference attributed to the M(.)O bonding in the thiobenzoate complexes. The (113)Cd resonance of [Cd(SOCPh)(3)](-) in dilute solution is in the region anticipated from dilution data for [Na(Cd{SOCPh}(3))(2)](-).