PEGylation of porous silicon using click chemistry

Porous silicon has received considerable interest in recent years in a range of biomedical applications, with its performance determined by surface chemistry. In this work, we investigate the PEGylation of porous silicon wafers using click chemistry. The porous silicon wafer surface chemistry was monitored at each stage of the reaction via photoacoustic Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, whereas sessile drop contact angle and model protein adsorption measurements were used to characterize the final PEGylated surface. This work highlights the simplicity of click-chemistry-based functionalization in tailoring the porous silicon surface chemistry and controlling protein-porous silicon interactions.     

Stress-induced chemical detection using flexible metal-organic frameworks

In this work we demonstrate the concept of stress-induced chemical detection using metal-organic frameworks (MOFs) by integrating a thin film of the MOF HKUST-1 with a microcantilever surface. The results show that the energy of molecular adsorption, which causes slight distortions in the MOF crystal structure, can be converted to mechanical energy to create a highly responsive, reversible, and selective sensor. This sensor responds to water, methanol, and ethanol vapors, but yields no response to either N2 or O2. The magnitude of the signal, which is measured by a built-in piezoresistor, is correlated with the concentration and can be fitted to a Langmuir isotherm. Furthermore, we show that the hydration state of the MOF layer can be used to impart selectivity to CO2. Finally, we report the first use of surface-enhanced Raman spectroscopy to characterize the structure of a MOF film. We conclude that the synthetic versatility of these nanoporous materials holds great promise for creating recognition chemistries to enable selective detection of a wide range of analytes.     

Three new pseudohalide bridged dinuclear Zn(II) Schiff base complexes: Synthesis,crystal structures and fluorescence studies

Three new dinuclear Zn(II) complexes [Zn(L)(μ_1,1-N₃)Zn(L)(N₃)] · 1.5H₂O (1), [Zn(L)(μ_1,1-NCO)Zn(L)(NCO)] · 1.5H₂O (2) and [Zn(L)(μ_1,1-NCS)Zn(L)(NCS)(OH₂)] (3) have been synthesized from a potentially tetradentate N₂O₂-donor Schiff base ligand LH, [LH = (OCH₃)(OH)C₆H₃CHN(CH₂)₂N(CH₃)₂], which is the condensation product of o-vanillin and 2-dimethylaminoethylamine. All the three complexes 1, 2 and 3 have been characterized by elemental analysis, IR and ¹H NMR spectroscopy, TGA and fluorescence studies. Finally, their structures have been established by the single crystal X-ray diffraction method. Structural studies reveal that in complexes 1, 2 and 3 the two Zn(II) centers are held together by a μ₂-phenolato oxygen atom and also by an end-on pseudohalide nitrogen (azide for 1; cyanate for 2; thiocyanate for 3) atom. Among the two deprotonated Schiff base ligands present in each complex, one acts as a tetradentate ligand (N₂O₂ donor set) while the other acts as a tridentate ligand (N₂O donor set), having a non-coordinated methoxy group. All the synthesized complexes display intraligand ¹(π–π^∗) fluorescence and can potentially serve as photoactive materials.     

An electrochemiluminescence-based competitive displacement immunoassay for the type-2 brevetoxins in oyster extracts

A new competitive electrochemiluminescence-based immunoassay for the type-2 brevetoxins in oyster extracts was developed. The assay was verified by spiking known amounts of PbTx-3 into 80% methanol extracts of Gulf Coast oysters. We also provide preliminary data demonstrating that 100% acetone extracts, aqueous homogenates, and the clinical matrixes urine and serum can also be analyzed without significant matrix interferences. The assay offers the advantages of speed ( 2 h analysis time); simplicity (only 2 additions, one incubation period, and no wash steps before analysis); low limit of quantitation (conservatively, 50 pg/mL = 1 ng/g tissue equivalents); and a stable, nonradioactive label. Due to the variety of brevetoxin metabolites present and the lack of certified reference standards for liquid chromatography-mass spectrometry confirmation, a true validation of brevetoxins in shellfish extracts is not possible at this time. However, our assay correlated well with another brevetoxin immunoassay currently in use in the United States. We believe this assay could be useful as a regulatory screening tool and could support pharmacokinetic studies in animals and clinical evaluation of neurotoxic shellfish poisoning victims.     

Reactions of the rhenium fragment (η-C5Me5)Re(CO)2 with chlorinated ethylenes: Coordination and C-Cl bond activation

Photochemical reactions of the dinitrogen complex Cp^∗Re(CO)₂N₂ with tetrachloroethylene and trichloroethylene yield the coordination complexes Cp^∗Re(CO)₂(η²-tetrachloroethylene) (1) and Cp^∗Re(CO)₂(η²-trichloroethylene) (2), respectively. Complex 1 reacts thermally in polar organic solvents to produce the C-Cl bond activation product cis-Cp^∗Re(CO)₂(C₂Cl₃)Cl (3). All complexes were isolated and characterized by IR, ¹H and ¹³C NMR spectroscopies and mass spectrometry. Complex 3 was also characterized by X-ray crystallography.     

3‐(Triphenyl­phospho­ranyl­idene)pentane‐2,4‐dione and dieth­yl 2‐(triphenyl­phospho­ranyl­idene)malonate

The title ylides, 3‐(triphenyl­phospho­ranyl­idene)pentane‐2,4‐dione, C₂₃H₂₁O₂P, (I), and diethyl 2‐(triphenyl­phospho­ranyl­idene)malonate, C₂₅H₂₅O₄P, (II), differ in the conformations adopted by their extended ylide moieties. In (I), one carbonyl O atom is syn and the other is anti with respect to the P atom, the ylide group is nearly planar, with a maximum P—C—(C=O) angle of 18.2 (2)°, and the P—C, C—C and C=O bond lengths are consistent with electronic delocalization involving the O atoms. In (II), both carbonyl O atoms are anti and the ester groups are twisted out of the plane of the near trigonal ylide C atom, reducing delocalization, the largest P—C—(C=O) angle being 30.2 (2)°.     

Combined on-line transmission FTIR measurements and BTEM analysis for the kinetic study of a consecutive reaction in aqueous-organic phase medium

Combined on-line transmission FTIR spectroscopy and band-target entropy minimization (BTEM) analysis were employed in order to monitor and analyze the kinetics of the alkaline hydrolysis reaction of diethyl phthalate (DEP) in aqueous-ethanol solvent mixture. This reaction is irreversible and involves two consecutive steps with the formation of the observable mono-ion intermediate species. The pure component mid-FTIR spectra of the reactive species involved in this reaction, namely DEP, mono-ion intermediate and di-ion product were successfully reconstructed using BTEM. Their corresponding concentrations were also calculated and subsequently employed to derive the kinetic rate parameters. The effect of temperature and the solvent mixture compositions on these two consecutive reaction steps were also discussed. The temperature variation study showed that both reaction rate coefficients increased with temperature. Both rate coefficients were also affected by the solvent mixture compositions and reached minimum values at certain water-ethanol solvent composition (circa 60% (v/v)). This study shows the utility of combined on-line transmission FTIR spectroscopy and chemometric techniques for the present, rather complex, consecutive organic reaction. Moreover, the present type of approach could facilitate better understanding of a wide variety of organic reactions that are performed in aqueous and mixed aqueous-organic solvents.     

Crystal Structure of Bis(5,17-dihydroxy-3,7,15,19,25,26-hexa-azatricyclo(19.3.1.19,13)hexacosa-1(25),2,7,9(26),10,12,14,19,21,23-decaene-μ1,2-perchlorato barium) diperchlorate: a Schiff-Base Macrocyclic Complex Derived from 2,6-Diformylpyridine and 1,3-Diaminopropan-2-ol

Abstract  

The title complex, [Ba(L1)(μ_1,2-ClO₄)]₂(ClO₄)₂ (where L1 = 5,17-dihydroxy-3,7,15,19,25,26-hexa-azatricyclo(19.3.1.19,13)hexacosa-1(25),2,7,9(26),10,12,14,19,21,23-decaene), was synthesised by a Schiff base condensation of 2,6-diformylpyridine with 1,3-diaminopropan-2-ol in dry methanol using barium(II) as template ion. The complex was characterised by IR, ¹H NMR, mass spectrometry, elemental analysis and X-ray crystallography. The structure was solved in the triclinic space group P [`\text1] {\bar{\text{1}}} with a = 8.4587(9), b = 8.7360(9), c = 17.7722(19) ?, α = 79.786(2), β = 88.780(2), γ = 83.048(2)°, V = 1283.0(2) ?³, Z = 1 and R1 = 0.0433. The macrocycle is folded and the complex dimerises via perchlorate anions which bridge the barium ions, and this interaction is supported by hydrogen bonding between neighbouring alcohol groups. The dimers are further linked into chains via intermolecular O–H···OClO₃ hydrogen bonds.     

Protonated Bis(quinuclidine) Included in Channel Thiourea-Bromide and Ribbons Thiourea-Iodide Lattice: New Thiourea Inclusion Compounds

Host-guest supramolecular complexes are of special interest for understanding the chemistry in low dimensional spaces. The molecular recognition involved in the formation of such structures sometimes may be a relevant model for the kind of organized system usually found in living organisms. Matrix effects and anisotropic features which are habitual of the chemistry in restricted spaces also appear as useful for the development of new material of scientific and technological importance (Takemoto and Sonoda, 1984). Urea and thiourea clathrates constitute interesting systems in which the matrix being structured by hydrogen bond interactions has a relatively high liability to structural changes caused by the interaction with the host (Lehn, 1996). The syntheses and crystal structure of two novel ternary inclusion compounds having protonated bis (quinuclidine) as a guest into anionic thiourea-bromide and thiourea-iodide hosts are reported: (thiourea₂[quinuclidine₂H]⁺Br^?), 1 and (thiourea₂[(quinuclidine₂H)⁺]₂(I^?)₂), 2. In the two structures thiourea molecules interact with each other via N–H....S hydrogen bonds to produce ribbon-like arrangements. In structure 1 these ribbons do not contain the halogen and define two non intersecting sets running along the a and b axis, linked through N–H....Br hydrogen bonds having the external halide ions as acceptors. This ribbon-crossover defines a channel structure along c with a cavity cross section of ca. 5.85 × 15.50 Å. In structure 2, ribbons contain iodide anions as well, bridging thiourea dimers into parallel 1D structures which align their flat side parallel to the (110) set of planes leaving a free spacing of ca. 8.25 Å.