Microwave spectrum, conformational composition, and intramolecular hydrogen bonding of (2-chloroethyl)amine (ClCH2CH2NH2)

The microwave spectrum of (2-chloroethyl)amine, ClCH(2)CH(2)NH(2), has been investigated in the 22-120 GHz region. Five rotameric forms are possible for this compound. In two of these conformers, denoted I and II, the Cl-C-C-N chain of atoms is antiperiplanar, with different orientations of the amino group. The link of the said atoms is synclinal in the three remaining forms, III-V, which differ with respect to the orientation of the amino group. The microwave spectra of four of these conformers, I-IV, have been assigned. In two of these rotamers, III and IV, the amino group is oriented in such a manner that rare and weak five-membered N-H···Cl intramolecular hydrogen bonds are formed. The geometries of conformers I and II preclude a stabilization by this interaction. The energy differences between the conformers were obtained from relative intensity measurements of spectral lines. The hydrogen-bonded conformer IV represents the global energy minimum. This rotamer is 0.3(7) kJ/mol more stable than the other hydrogen-bonded conformer III, 4.1(11) kJ/mol more stable than II, and 5.5(15) kJ/mol more stable than I. The spectroscopic work has been augmented by quantum chemical calculations at the CCSD/cc-pVTZ and MP2/6-311++G(3df,3pd) levels of theory. The CCSD rotational constants and energy differences are in good agreement with their experimental counterparts.     

Self-assembly hexanuclear metallacontainer hosting halogenated guest species and sustaining structure of 3D coordination framework

Chloride-centered hexanuclear hydroxopyrazolate reveals potential as a receptor of halomethane and halometallate species and as a molecular building block for coordination polymers.     

Controlled supramolecular oligomerization of C3-symmetrical molecules in water: the impact of hydrophobic shielding

The supramolecular oligomerization of three water-soluble C(3)-symmetrical discotic molecules is reported. The compounds all possess benzene-1,3,5-tricarboxamide cores and peripheral Gd(III)-DTPA (diethylene triamine pentaacetic acid) moieties, but differ in their linker units and thus in their propensity to undergo secondary interactions in H(2)O. The self-assembly behavior of these molecules was studied in solution using circular dichroism, UV/Vis spectroscopy, nuclear magnetic resonance, and cryogenic transmission electron microscopy. The aggregation concentration of these molecules depends on the number of secondary interactions and on the solvophobic character of the polymerizing moieties. Hydrophobic shielding of the hydrogen-bonding motif in the core of the discotic is of paramount importance for yielding stable, helical aggregates that are designed to be restricted in size through anti-cooperative, electrostatic, repulsive interactions.     

LiB12PC, the first boron-rich metal boride with phosphorus--synthesis, crystal structure, hardness, spectroscopic investigations

We present synthesis, crystal structure, hardness, and IR/Raman and UV/Vis spectra of a new compound with the mean composition LiB₁₂PC. Transparent single crystals were synthesised from Ga, Li, B, red phosphorus and C at 1500 °C in boron nitride crucibles welded in Ta ampoules. Depending on the type of boron used for the synthesis we obtained colourless, brown and red single crystals with slightly different P/C ratios. Colourless LiB₁₂PC crystallizes orthorhombic in the space group Imma (No. 74) with a=10.188(2) Å, b=5.7689(11) Å, c=8.127(2) Å and Z=4. Brown LiB₁₂P_0.89C_1.11 is very similar, but with a lower P content. Red single crystals of LiB₁₂P_1.13C_0.87 have a larger unit cell with a=10.4097(18) Å, b=5.9029(7) Å, c=8.2044(12) Å. EDX measurements confirm that the red crystals contain more phosphorus than the other ones. The crystal structure is characterized by a covalent network of B₁₂ icosahedra connected by exohedral B? B bonds and P? P, P? C or C? C units. Li atoms are located in interstitials. The structure is closely related to MgB₇, LiB₁₃C₂ and ScB₁₃C. LiB₁₂PC fulfils the electron counting rules of Wade and also Longuet‐Higgins. Measurements of Vickers micro‐hardness (H_V=27 GPa) revealed that LiB₁₂PC is a hard material. The optical band gaps obtained from UV/Vis spectra match the colours of the crystals. Furthermore we report on the IR and Raman spectra.     

Identification of sulfoquinovosyldiacyglycerides from Phaeodactylum tricornutum by matrix-assisted laser desorption/ionization QTrap time-of-flight hybrid mass spectrometry

The pharmaceutical industry is interested in identifying novel target compounds. Due to their versatile pharmacological activities (e.g. antiviral, anti-carcinogen and immunosuppressive) sulfoquinovosyldiacylglycerides (SQDGs) are potential drug candidates. The present publication deals with the purification and structural characterization of SQDGs from three different strains of Phaeodactylum tricornutum. Besides detection of SQDGs (sn-1: C16:1/sn-2: C16:0 and sn-1: C20:5/sn-2: C16:0), two novel 2'-O-acylsulfoquinovosyldiacylglyerides (Ac-SQDGs, sn-1: C16:0/ sn-2: C16:0/2' C20:5 and sn-1: C20:5/sn-2: C16:0/2' C20:5) were identified by using matrix-assisted laser desorption/ionization (MALDI) QTrap time-of-flight (ToF) hybrid mass spectrometry (MS) with multistage MS(n). The analytical method enables the sn-position verification of fatty acids (MS(2)) as well as the confirmation of the regioposition of eicospentanoic acid at the sulfoquinovose (MS(3)).     

At the surface of non-aqueous solutions of anionic surfactants

We have determined the concentration–depth profiles of sodium dodecyl sulfate (SDS) and cesium dodecyl sulfate (CDS) in their pure solutions, by which the surface structure of those solutions are characterized. With the identical bulk concentration, more Cs ions than sodium ions are present at the topmost layer and they penetrate deeper than sodium ions into the layer formed by the heads of the anions, shielding the electrostatic repulsion among those negatively charged anions more efficiently. The distributions of the charge at the surface of each studied solution were determined from those concentration–depth profiles of surfactant ions. The charge density varies more drastically in SDS solutions than in CDS solutions when their bulk concentrations are identical. These charge density profiles exhibit a visible and direct insight into the electric charge structure of the surface of ionic surfactant solutions. The experimental findings might be helpful to the investigations on the surface structures of aqueous solutions of ionic surfactants.     

Fractional surface termination of diamond by electrochemical oxidation

The crystalline form of sp(3)-hybridized carbon, diamond, offers various electrolyte-stable surface terminations. The H-termination-selective attachment of nitrophenyl diazonium, imaged by AFM, shows that electrochemical oxidation can control the fractional hydrogen/oxygen surface termination of diamond on the nanometer scale. This is of particular interest for all applications relying on interfacial electrochemistry, especially for biointerfaces.     

Partial Molar Isentropic Compressions of Some Tetra- and Pentapeptides in Aqueous Solution: Implications for Group Additivity Schemes for Unfolded Proteins

Sound speeds have been measured for aqueous solutions of five tetrapeptides and five pentapeptides at T=298.15 K. The partial molar isentropic compressions at infinite dilution, $K_{S,2}^{\circ}$ , were derived for the peptides using conventional methods. The results were compared with those calculated using group additivity methods, with the amino acid side-chain contributions derived using $K_{S,2}^{\circ}$ data reported previously for some tripeptides of sequence gly-X-gly, where X represents an amino acid, and also for some N-acetyl amino acid amides. The tripeptides are the preferred model compounds for the estimation of the side-chain contributions to $K_{S,2}^{\circ}$ of a polypeptide. Our study also confirms that simple group additivity schemes are not feasible for the estimation of $K_{S,2}^{\circ}$ values for polypeptides and unfolded proteins.     

Aqueous Mixtures of a Trisiloxane Surfactant and Oil Studied by SANS and NMR Self-diffusion: Effect of Temperature and Oil Concentration

Samples of a poly(ethylene oxide) trisiloxane surfactant, water, and decane have been investigated using pulsed field gradient NMR (PGSE NMR) and small-angle neutron scattering (SANS) to determine the solution structure. The surfactant/water weight ratio has been kept constant at a value of 3/2, with variation of the oil (decane) content. In the neutron scattering measurements the temperature was varied from 23 °C up to the phase separation limit for these systems. The combined NMR and SANS data show that on addition of decane, the system exists as a hexagonal phase of cylindrical decane-containing micelles at all temperatures investigated. The addition of decane changes significantly the values for the structure parameters in the system, inducing an increase in periodicity of 12–15 ?. By substitution of decane with its deuterated equivalent, decane-d₂₂, it was possible to obtain detailed information on the structural organization of the oil component in this ternary mixture.     

Ag(I)/V(V) Heterobimetallic Frameworks Generated from Novel-Type {Ag(2)(VO(2)F(2))(2)(triazole)(4)} Secondary Building Blocks: A New Aspect in the Design of SVOF Hybrids

A series of new silver(I)-containing MOFs [Ag(2)(tr(2)ad)(2)](ClO(4))(2) (1), [Ag(2)(VO(2)F(2))(2)(tr(2)ad)(2)]·H(2)O (2), [Ag(2)(VO(2)F(2))(2)(tr(2)eth)(2)(H(2)O)(2)] (3), and [Ag(2)(VO(2)F(2))(2)(tr(2)cy)(2)]·4H(2)O (4) supported by 4-substituted bifunctional 1,2,4-triazole ligands (tr(2)ad = 1,3-bis(1,2,4-triazol-4-yl)adamantane, tr(2)eth = 1,2-bis(1,2,4-triazol-4-yl)ethane, tr(2)cy = trans-1,4-bis(1,2,4-triazol-4-yl)cyclohexane) were hydrothermally synthesized and structurally characterized. In these complexes, the triazole heterocycle as an N(1),N(2)-bridge links either two adjacent Ag-Ag or Ag-V centers at short distances forming polynuclear clusters. The crystal structure of compound 1 is based on cationic {Ag(2)(tr)(4)}(2+) fragments connected in a 2D rhombohedral grid network with (4,4) topology. The neighboring layers are tightly packed into a 3D array by means of argentophilic interactions (Ag···Ag 3.28 ?). Bridging between different metal atoms through the triazole groups assists formation of heterobimetallic Ag(I)/V(V) secondary building blocks in a linear V-Ag-Ag-V sequence that is observed in complexes 2-4. These unprecedented tetranuclear {Ag(2)(VO(2)F(2))(2)(tr)(4)} units (the intermetal Ag-Ag and Ag-V distances are 4.24-4.36 and 3.74-3.81 ?, respectively), in which vanadium(V) oxofluoride units possess distorted trigonal bipyramidal environment {VO(2)F(2)N}ˉ, are incorporated into 1D ribbon (2) or 2D square nets (3, 4) using bitopic μ(4)-triazole ligands. The valence bond calculation for vanadium atoms shows +V oxidation state in the corresponding compounds. Thermal stability and photoluminescence properties were studied for all reported coordination polymers.