Air-sensitive Research Articles

Novel P,N-Containing Cyclophane with a Chiral Hydrophobic Cavity

Macrocycles containing aromatic or heterocyclic units within the macrocyclic core draw an increasing attention for the last few decades.[1] The aromatic units, being rigid building blocks, allow the design and synthesis of molecular cavities with defined spatial characteristics, and also serve as binding sites for hosts capable of interacting with their π-electron systems.[1b-d] On the other side heterocyclic rings are also of special interest for the construction of cyclophane-type molecules[2] because the presence of donor heteroatoms provides means for the incorporation of a binding site for transition metals within the macrocyclic structure. Macrocycles formed both by the aromatic and the heterocyclic units with three-coordinated phosphorus atoms as donors[3] are able to provide a variety of the donoracceptor and the non-valent interactions so they are of interest both for supramolecular chemistry (in particular as selective sensors[4]) and as unusual ligands for transition metal catalyzed reactions in organic synthesis,[5] as the geometry and well-defined position of the complexing donor centers could lead to specific catalytically active complexes.[6] However, the chemistry of cyclophane ligands containing phosphine groups as donor centers within the macrocyclic skeleton is less developed than that of their oxygen or nitrogen analogues.[3] This fact has been mainly attributed to the air sensitivity of these compounds and the poor yields obtained in their preparations by high-dilution[3,7] or template methods,[3] although the high-yield synthesis of a few types of phosphamacrocycles has been reported. [3,8] To the best of our knowledge there are no examples of P-containg cyclophanes with chiral intramolecular cavity. But we are sure that if P-containing cyclophanes, especially chiral, with a unique shape, distinct architecture, and set of functional groups become easily available from natural or synthetic sources, they would start to inspire the imagination of supramolecular chemists to devise and synthesize novel sophisticated receptors, machines, and devices,[1-3,6,8] as well as new types of molecular reactors.[9] Recently, a highly effective self-assembly process giving macrocyclic tetraphosphines with a relatively large hydrophobic prismatic or helical twisted cavities by condensation of the three-component system diamine/ formaldehyde/phosphine was discovered.[10] In the present work diamines possessing inherent chirality, namely N-alkyl-2,6-diamino-9,10-dihydro-9,10-ethanoanthracenecis-11,12-dicarboximide 2-4,[11] were used as spatially divided diamine component of the self-assembling system to prepare a novel type of P,N-containing cyclophanes with chiral intramolecular cavity.

A sample holder for measuring the magnetic properties of air-sensitive compounds

A sample holder is reported which has allowed the magnetic characterization of air-sensitive compounds to be made in a Quantum Design Magnetic Properties Measurement System as a function of the applied field (0–5 T), and at temperatures ranging from 2 to 290 K. The sample holder is in the form of a specially designed tube, which is made from high purity quartz, utilizes PTFE (polytetrafluoroethylene) plugs and is reusable. This construction also offers the benefit that no heat treatment of the holder is required during sample loading, making the sample holder suitable for thermally sensitive compounds. The application of this sample holder is demonstrated for the case of Ni(cod)2 (cod = 1,5-cyclooctadiene), a compound that decomposes when exposed to air and/or heat. This material's instability has, so far, prevented the magnetic characterization of the compound, with nickel nanoparticles, a product of the decomposition, usually being measured instead.

Soluble and Stable Zethrenebis(carboximide) and Its Quinone

Despite first being synthesized decades ago by Clar and co-workers, zethrene only recently began attracting major interest due to its potentially interesting optoelectronic properties. Poor air and light sensitivity of unsubstituted zethrene would not have aided its cause. A more convenient route to zethrene was found in the 1960’s during attempts to synthesize and isolate the unstable tetradehydrodinaphtho[10]annulene, a precursor of zethrene. This was not successfully done until last year.

β‐Diketiminate Stabilized Magnesium Hydroxide, Heterobimetallic, and Halide Complexes: Synthesis and X‐ray Structural Studies

AbstractThe controlled hydrolysis of heteroleptic magnesium amide, LMgN(SiMe3)2 (L = CH[C(Me)N(2,6‐iPr2C6H3)]2) with water afforded the corresponding hydroxide [LMg(OH)·THF]2 as air and moisture sensitive compound. The presence of a sterically bulky β‐diketiminate ligand prevents the self‐condensation reaction of this hydroxide complex. Single crystal X‐ray analysis shows that the hydroxide is dimeric in the solid state. Reaction of the magnesium amide or LMg(Me)·OEt2 with LAlMe(OH) generates the heterobimetallic species containing the Mg–O–Al moiety. Additionally, the reaction of methylmagnesiumchloride with the free ligand leads to complex L′MgCl (L′ = CH[Et2NCH2CH2N(CMe)]2). As revealed by the crystal structure, L′MgCl is a solvent free monomeric magnesium chloride complex that is analogues to the Grignard reagent.

ChemInform Abstract: Dibisyl(fluorenylidene)stannene: Evidence of Its Formation.

Abstract The dibisyl(flourenylidene)stannene 4 , obtained by dehydro-chlorination or -fluorination of the corresponding chloro- or fluoro-stannanes 5 and 6 by tert-butyllithium is an extremely air-sensitive compound. It has not been isolated, but identified by trapping reactions by lithio compound and water.

Chain‐Type Lithium Rare‐Earth Nitridosilicates – Li5Ln5Si4N12 with Ln = La, Ce

AbstractThe quaternary lithium rare‐earth nitridosilicates Li5Ln5Si4N12 with Ln = La, Ce were synthesized at moderate temperatures below 900 °C in closed tantalum ampoules employing liquid lithium as a flux. Thereby, nitridosilicate substructures with a low degree of condensation were obtained. The air and moisture sensitive title compounds are the first representatives of quaternary lithium rare‐earth nitridosilicates and crystallize in space group P$\bar {4}$b2 [Li5La5Si4N12: a = 1104.28(16), c = 557.30(11) pm, Z = 2, R1 = 0.0498, 873 data, 56 parameters; Li5Ce5Si4N12: a = 1097.78(16), c = 551.43(11) pm, Z = 2, R1 = 0.0334, 748 data, 56 parameters]. The nitridosilicate substructure consists of infinite nonbranched zweier single‐chains of vertex sharing SiN4 tetrahedra running parallel to [001]. The chains exhibit a stretching factor fS = 0.981 for La and 0.977 for Ce, respectively. The two crystallographically independent Li+ sites are each coordinated by four nitrogen atoms. Lattice energy calculations (MAPLE) and EDX measurements confirmed the electrostatic bonding interactions and the chemical compositions. For the La containing compound 7Li solid‐state MAS NMR investigations are reported.

Analytical Characterization of ALD Thin Film Precursors

Moore's Law compliance necessitates the use of high dielectric constant (k) (e.g. Hf, Ti, Zr, Ta) and low-k (e.g. silane chemistries) material thin films in place of traditional Si/SiO2 films. Chemical precursors of these films require characterization of trace-level impurities to avoid device failure. The reporting limits listed on precursor Certificates of Analysis require analytical methods such as inductively coupled plasma - mass spectrometry (ICP-MS) ion chromatography (IC) and gas chromatography - mass spectrometry (GC-MS), for determination of trace elements, chloride and precursor purity, respectively. Analytical challenges associated with characterizing these materials include precursor volatility, air and moisture sensitivity, parent element ICP-MS matrix effects and ICP-MS elemental and molecular interferences. In addition, sample preparation methods preceding the analyses must decompose the sample yet preserve the integrity and quantity of the analytes present in the original samples. This paper will describe analytical methods designed to meet these analytical challenges.

Properties stability and biodegradation behaviors of soy protein isolate/poly (vinyl alcohol) blend films

The objective of this work was to investigate the color, transparency, water sensitivity and mechanical properties stability in air under photo-oxidative degradation influencing consumer acceptance and biodegradation behaviors in soil of soy protein isolate (SPI)/poly (vinyl alcohol) (PVA) blend packaging films during 30 days. The results showed that PVA could dilute the yellow color and make the SPI-based films less darkness in application and the transparency of SPI/PVA films at various stages of degradation was improved. The addition of PVA decreased the ability of SPI protein molecules to absorb water and enhanced the mechanical properties of blend films comparing to pure SPI film in 30 days. Aerobic biodegradation of films in soil proved that the PVA compound interacting with protein imposed negative effects on biodegradation of blend films prolonging their decomposing time. The SPI/PVA blend films decomposed into small fragments of less complex molecules along with surface completely digested after 30 days.

Kelvin probe force microscopy in application to biomolecular films: Frequency modulation, amplitude modulation, and lift mode

Kelvin probe force microscopy (KPFM) is a powerful technique to visualize the differences of work function in metals and lateral surface potential distribution in thin organic films. Earlier we have shown that frequency modulated-Kelvin probe force microscopy has significant advantages in both sensitivity and resolution when applied to metal and inorganic interfaces in vacuum. High resolution, high sensitivity, and performance in ambient conditions are required in order to study biologically relevant samples. In this work we compared the resolution of frequency modulation (FM-KPFM), amplitude modulation (AM-KPFM), and lift modes KPFM for imaging the local electrical surface potential of complex biomolecular films and demonstrated that FM-KPFM mode has superior resolution for biological applications. The power of the method was illustrated on pulmonary surfactant films, revealing nm spatial resolution and mV potential sensitivity in ambient air. At this level of resolution this method can provide critical insight into the molecular arrangement and function of complex biosystems in a way that other KPFM modes cannot do. Based on the observed changes in the local surface potential we discovered that excess cholesterol produces nm size electrostatic domains and change the electric fields.

Design and characterization of a magnetoelastic sensor for the detection of biological agents

This paper presents the design and development of a free-standing, magnetoelastic biosensor. The detection principle is presented and various resonance characteristics of the sensor are discussed. Experimental measurements of the sensor resonance frequencies agree with theoretical predictions. The influence of the external magnetic field on the resonance behaviour of the sensor was studied and the optimum dc magnetic fields for best sensitivity in air and in water solutions for 2000 × 400 × 15 µm (2 mm) sensors and 1000 × 200 × 15 µm (1 mm) size sensors were determined to be 75 Oe and 38 Oe, respectively. Both theoretical prediction and experimental results show that smaller sensors have greater mass sensitivity and can theoretically detect mass as small as one biological spore. The sensor platform was immobilized with JRB7 phages for specific, in vitro detection of B. anthracis spores. Real-time detection of spores suspended in water was demonstrated using a flowing system. The 1 mm and 2 mm sensors were found to have a detection limit of 104 spores ml−1 and 105 spores ml−1, respectively.

BaAuP and BaAuAs, Synthesis via Disproportionation of Gold upon Interaction with Pnictides as Bases

AbstractGold disproportinates in the presence of the Zintl phases Ba3P2 or Ba3As2 forming BaAuP and BaAuAs, respectively, and BaAu2. The air and moisture sensitive ternary compounds crystallise in the ZrBeSi type of structure, an ordered variant of AlB2: BaAuP (P63/mmc; a = 440.68(6) pm; c = 899.8(2) pm; R1 = 0.0237; 183 independent reflections); BaAuAs (P63/mmc; a = 453.53(5) pm; c = 902.7(1) pm; R1 = 0.0255; 168 independent reflections). Both compounds, which are accessible as pure phases by reacting BaP or BaAs with gold, can be classified as poor metallic conductors.

H 2 sensing properties of diode-type gas sensors fabricated with Ti- and/or Nb-based materials

A thermally oxidized TiO 2 or Nb 2O 5 film equipped with a top Pd film electrode and a bottom Ti or Nb plate electrode (Pd/MO( n)/M, MO: oxide film, M: metal plate, n: annealing temperature (°C)) has been investigated as a diode-type H 2 sensor under air or N 2 atmosphere. Pd/TiO 2( n)/Ti sensors showed relatively poor H 2 sensing properties in air, in comparison with Pd/anodic-TiO 2( n)/Ti sensors constructed with an anodized TiO 2 film equipped with a top Pd film electrode and a bottom Ti plate electrode, which were reported in our previous studies. On the other hand, Pd/Nb 2O 5( n)/Nb sensors showed relatively larger H 2 response with fast response and recovery speeds than Pd/TiO 2( n)/Ti sensors in air under high forward bias conditions. A Pd/Nb 2O 5(450)/Ti sensor, which was fabricated by radio-frequency magnetron sputtering of Nb metal on a Ti substrate followed by thermal oxidation at 450 °C, showed the largest H 2 response and relatively fast response and recovery speeds in air, among the sensors tested. In addition, H 2 response of the Pd/Nb 2O 5(450)/Ti sensor in air was much lower than that in N 2, but the logarithm of H 2 response was almost proportional to the logarithm of H 2 concentration in a wide range of H 2 concentration (10–8000 ppm) in air, and the H 2 sensitivity in air was much higher than that in N 2.

Comparison of the sensitivity of air and dielectric modes in photonic crystal slab sensors

Optical cavities provide a route to sensing through the shift of the optical resonant peak. However, effective sensing with optical cavities requires the optimization of the modal quality factor, Q, and the field overlap with the sample, f. For a photonic crystal slab (PCS) this figure of merit, M = fQ, involves two competing effects. The air modes usually have large f but small Q, whereas the dielectric modes have high-Q and small f. We compare the sensitivity of air and dielectric modes for different PCS cavity designs and account for loss associated with absorption by the sensed sample or its host liquid. We find that optimizing Q at the expense of f is the most beneficial strategy, and modes deriving from the dielectric bands are thus preferred.

Acute Evaluation of Transthoracic Impedance Vectors Using ICD Leads

Minute ventilation (MV) has been proven to be very useful in rate responsive pacing. The aim of this study was to evaluate the feasibility of using implantable cardioverter-defibrillator (ICD) leads as part of the MV detection system. At implant in 10 patients, the transthoracic impedance was measured from tripolar ICD, tetrapolar ICD, and atrial lead vectors during normal, deep, and shallow voluntary respiration. MV and respiration rate (RespR) were simultaneously measured through a facemask with a pneumotachometer (Korr), and the correlations with impedance-based measurements were calculated. Air sensitivity was the change in impedance per change in respiratory tidal volume, ohms (Omega)/liter (L), and the signal-to-noise ratio (SNR) was the ratio of the respiratory and cardiac contraction components. The air sensitivity and SNR in tripolar ICD vector were 2.70 +/- 2.73 ohm/L and 2.19 +/- 1.31, respectively, and were not different from tetrapolar. The difference in RespR between tripolar ICD and Korr was 0.2 +/- 1.91 breaths/minute. The regressed correlation coefficient between impedance MV and Korr MV was 0.86 +/- 0.07 in tripolar ICD. The air sensitivity and SNR in tripolar and tetrapolar ICD lead vectors did not differ significantly and were in the range of the values in pacemaker leads currently used as MV sensors. The good correlations between impedance-based and Korr-based RespR and MV measurements imply that ICD leads may be used in MV sensor systems.

A Stable Homodinuclear Biscobalt(III)–Schiff Base Complex for Catalytic Asymmetric 1,4‐Addition Reactions of β‐Keto Esters to Alkynones

Two metal cooperation: A homodinuclear Co(2)-Schiff base complex Co(2)(OAc)(2)-1 promoted the asymmetric 1,4-addition of beta-keto esters to alkynones under solvent-free conditions in air (see scheme). The reactions proceeded without air or moisture sensitivity in high yields and with high enantioselectivities (99-91% ee) at room temperature under highly concentrated conditions (neat-20 M) with 0.1-2.5 mol % catalyst loading.

Detection of Campylobacter Bacteria in Air Samples for Continuous Real-Time Monitoring of Campylobacter Colonization in Broiler Flocks

Improved monitoring tools are important for the control of Campylobacter bacteria in broiler production. In this study, we compare the sensitivities of detection of Campylobacter by PCR with feces, dust, and air samples during the lifetimes of broilers in two poultry houses and conclude that the sensitivity of detection of Campylobacter in air is comparable to that in other sample materials. Profiling of airborne particles in six poultry houses revealed that the aerodynamic conditions were dependent on the age of the chickens and very comparable among different poultry houses, with low proportions of particles in the 0.5- to 2-microm-diameter range and high proportions in the 2- to 5-microm-diameter range. Campylobacter could also be detected by PCR in air samples collected at the hanging stage during the slaughter process but not at the other stages tested at the slaughterhouse. The exploitation of airborne dust in poultry houses as a sample material for the detection of Campylobacter and other pathogens provides an intriguing possibility, in conjunction with new detection technologies, for allowing continuous or semicontinuous monitoring of colonization status.

Graphical Abstract: Eur. J. Inorg. Chem. 2/2009

AbstractThe cover picture shows the X‐ray crystal structures of new benzo‐anellated N‐heterocyclic germylene complexes with nickel(0) and molybdenum(0). The low bathochromic shift of the valence vibration of CO in the trans position of the germylene ligands of fac‐(bnNHGe)3Mo(CO)3 indicates weak donor properties, the relatively short Mo–GeII bonds indicate stabilization by back‐bonding. The ligand properties contrast strongly with those of the homologous N‐heterocyclic carbene ligand (bnNHC) because of the different electronic structures, which can also be recognised from the photoelectron spectrum of the germylene ligand. The GeII electron lone pair is bound firmly, and according to quantum chemical calculations represents only the third band, whereas in bnNHC the lone electron pair is the HOMO. The extreme air and moisture sensitivity of the NHGe complexes is in sharp contrast with the background, depicting the Baltic Sea with the small island Greifswalder Oie at the seaside entrance to the site of one of the oldest universities in northern Europe. Details are discussed in the article by T. Veszprémi, J. Heinicke et al. on p. 221 ff. We thank Prof. Dr. Martin Köckerling (Rostock) and Dr. Lutz Wolf (Kahla) for support in designing this picture.

Transition Metal Complexes of N‐Heterocyclic Germylenes (Eur. J. Inorg. Chem. 2/2009)

AbstractThe cover picture shows the X‐ray crystal structures of new benzo‐anellated N‐heterocyclic germylene complexes with nickel(0) and molybdenum(0). The low bathochromic shift of the valence vibration of CO in the trans position of the germylene ligands of fac‐(bnNHGe)3Mo(CO)3 indicates weak donor properties, the relatively short Mo–GeII bonds indicate stabilization by back‐bonding. The ligand properties contrast strongly with those of the homologous N‐heterocyclic carbene ligand (bnNHC) because of the different electronic structures, which can also be recognised from the photoelectron spectrum of the germylene ligand. The GeII electron lone pair is bound firmly, and according to quantum chemical calculations represents only the third band, whereas in bnNHC the lone electron pair is the HOMO. The extreme air and moisture sensitivity of the NHGe complexes is in sharp contrast with the background, depicting the Baltic Sea with the small island Greifswalder Oie at the seaside entrance to the site of one of the oldest universities in northern Europe. Details are discussed in the article by T. Veszprémi, J. Heinicke et al. on p. 221 ff. We thank Prof. Dr. Martin Köckerling (Rostock) and Dr. Lutz Wolf (Kahla) for support in designing this picture.

Stability and Reversibility of Lithium Borohydrides Doped by Metal Halides and Hydrides

In an effort to develop reversible metal borohydrides with high hydrogen storage capacities and low dehydriding temperature, doping LiBH4 with various metal halides and hydrides has been conducted. Several metal halides such as TiCl3, TiF3, and ZnF2 effectively reduced the dehydriding temperature through a cation exchange interaction. Some of the halide doped LiBH4 are partially reversible. The LiBH4 + 0.1TiF3 desorbed 3.5 wt % and 8.5 wt % hydrogen at 150 and 450 °C, respectively, with subsequent reabsorption of 6 wt % hydrogen at 500 °C and 70 bar observed. XRD and NMR analysis of the rehydrided samples confirmed the reformation of LiBH4. The existence of the (B12H12)−2 species in dehydrided and rehydrided samples gives insight into the resultant partial reversibility. A number of other halides, MgF2, MgCl2, CaCl2, SrCl2, and FeCl3, did not reduce the dehydriding temperature of LiBH4 significantly. XRD and TGA-RGA analyses indicated that an increasing proportion of halides such as TiCl3, TiF3, and ZnCl2 from 0.1 to 0.5 mol makes lithium borohydrides less stable and volatile. Although the less stable borohydrides such as LiBH4 + 0.5TiCl3, LiBH4 + 0.5TiF3, and LiBH4 + 0.5ZnCl2 release hydrogen at room temperature, they are not reversible due to unrecoverable boron loss caused by diborane emission. In most cases, doping that produced less stable borohydrides also reduced the reversible hydrogen uptake. It was also observed that halide doping changed the melting points and reduced air sensitivity of lithium borohydrides.

Evaluating the effects of historical land cover change on summertime weather and climate in New Jersey: Land cover and surface energy budget changes

The 19th‐century agrarian landscape of New Jersey (NJ) and the surrounding region has been extensively transformed to the present‐day land cover by urbanization, reforestation, and localized areas of deforestation. This study used a mesoscale atmospheric numerical model to investigate the sensitivity of the warm season climate of NJ to these land cover changes. Reconstructed 1880s‐era and present‐day land cover data sets were used as surface boundary conditions for a set of simulations performed with the Regional Atmospheric Modeling System (RAMS). Three‐member ensembles with historical and present‐day land cover were compared to examine the sensitivity of surface air and dew point temperatures, rainfall, and the individual components of the surface energy budget to these land cover changes. Mean temperatures for the present‐day landscape were 0.3–0.6°C warmer than for the historical landscape over a considerable portion of NJ and the surrounding region, with daily maximum temperatures at least 1.0°C warmer over some of the highly urbanized locations. Reforested regions, however, were slightly cooler. Dew point temperatures decreased by 0.3–0.6°C, suggesting drier, less humid near‐surface air for the present‐day landscape. Surface warming was generally associated with repartitioning of net radiation from latent to sensible heat flux, and conversely for cooling. While urbanization was accompanied by strong surface albedo decreases and increases in net shortwave radiation, reforestation and potential changes in forest composition have generally increased albedos and also enhanced landscape heterogeneity. The increased deciduousness of forests may have further reduced net downward longwave radiation.