13-Hydroxyacenaphato[1,2-b]quinolizinium bromide as a new flouorescence indicator

13-Hydroxyacenaphtho[1,2-b]quinolizinium bromide (13-HQBr)was selected as a fluorescence indicator to determine basic compounds in non-aqueous media. This compound possesses an acidic phenolic hydroxyl group. It presents varying absorption (ROH, 408, 430 nm; RO(-) 456, 478 nm) and excitation spectra (ROH, 425 nm; RO, 471 nm) depending on the pH of the media, but the same emission fluorescence spectrum (ROH = RO(-), 526 nm) at different pH in buffered aqueous solutions. However, in acidic non-aqueous media (acetic, formic and trifluoroacetic acids), it can be observed that the fluorescence emission spectra differ for the ionized (lambda(em) = 530 nm) and non-ionized (lambda(em) = 440, 470 nm) forms. The fluorescence intensity at the characteristic peaks depends on the acid-base equilibria in the ground and excited states. Therefore, this property could be used to evaluate the concentration of basic compounds, showing a good linearity range between fluorescence intensity and basic sample concentration.     

An insight into the aromaticity of fullerene anions: experimental evidence for diamagnetic ring currents in the five-membered rings of C(60)(6-) and C(70)(6-)

Reduction of the two "closed" [6,6] methanofullerenes, [6,6]C(61)H(2) (1) and [6,6]C(71)H(2) (5), to the corresponding hexaanions with lithium metal causes the bridgehead-bridgehead bonds to open, at least partially, and this change gives rise to diamagnetic ring currents in the resulting homoconjugated six-membered rings (6-MRs). These new ring currents shield the overlying hydrogen atoms on the methylene bridge and induce upfield shifts of 1.60 and 0.11 ppm in their (1)H NMR resonances, respectively. Analogous reduction of the already "open" [5,6]methanofullerenes, [5,6]C(61)H(2) (2) and [5,6]C(71)H(2) (3 and 4), only slightly enhances the shielding of the hydrogen atoms over the homoconjugated 6-MRs (upfield shifts of 0.13, 0.68, and 0.14 ppm, respectively) but leads to exceptionally strong diamagnetic ring currents in the homoconjugated five- membered rings (5-MRs), as evidenced by dramatic shielding of the hydrogen atoms situated over them (upfield shift of 5.01, 6.78, and 1.63 ppm, respectively). The strongest shielding is seen for the hydrogen atom sitting over the 5-MR at the pole of C(71)H(2)(6)(-) (delta = -0.255 ppm) indicating that the excess charge density is concentrated at the poles.     

Scrambling of autoinducing precursor peptides investigated by infrared multiphoton dissociation with electrospray ionization and Fourier transform ion cyclotron resonance mass spectrometry

Two synthetic precursor peptides, H₂N-CVGIW and H₂N-LVMCCVGIW, involved in the quorum sensing of Lactobacillus plantarum WCFS1, were characterized by mass spectrometry (MS) with electrospray ionization and 7-T Fourier transform ion cyclotron resonance (ESI-FTICR) instrument. Cell-free bacterial supernatant solutions were analyzed by reversed-phase liquid chromatography with ESI-FTICR MS to verify the occurrence of both pentapeptide and nonapeptide in the bacterial broth. The structural characterization of both protonated peptides was performed by infrared multiphoton dissociation using a continuous CO₂ laser source at a wavelength of 10.6 μm. As their fragmentation behavior cannot be directly derived from the primary peptide structure, all anomalous fragments were interpreted as neutral loss of amino acids from the interior of both peptides, i.e., loss of V, G, VG and M, MC, V, CC, from H₂N-CVGIW and H₂N-LVMCCVGIW, respectively. Mechanisms of this scrambling are proposed. FTICR MS provides accurate masses of all fragment ions with very low absolute mass errors (<1.6 ppm), which facilitated the reliable assignment of their elemental compositions. The resolving power was more than sufficient to resolve closely isobaric product ions with routine subparts per million mass accuracies. Only the occurrence of pentapeptide was found in the cell-free culture of L. plantarum, grown in Waymouth’s medium broth, with a low content of 5.2?±?2.6 μM by external calibration. Most of it was present as oxidized H₂N-CVGIW, that is, the soluble disulfide pentapeptide with a level tenfold higher (i.e., 50?±?4 μM, n?=?3).

A molecularly imprinted polymer for the determination of neopterin

A molecularly imprinted polymer (MIP) for the specific retention of neopterin has been developed. A set of 6 polymers was prepared by radical polymerization under different experimental condition using methacrylic acid as functional monomer and ethylene glycol dimethacrylate as crosslinker, with the aim to understand their influence on the efficiency of the MIP. The performance of each MIP was tested in batch experiments via their binding capacity. The MIP prepared in the presence of nickel ions in dimethylsulfoxide-acetonitrile mixture (P4) exhibited the highest binding capacity for neopterin (260 μmol per gram of polymer). A selectivity study with two other pteridines demonstrated the polymer P4 also to possess the best selectivity.

Density and Sound Velocity Studies of Aqueous Solutions of Tetradecyltrimethylammonium Nitrate at Different Temperatures

The density and ultrasound velocity of aqueous solutions of tetradecyltrimethylammonium nitrate were measured in the temperature range of 15 to 35°C in 5°C intervals. The concentration range covered the premicellar and micellar regimes. By assuming a pseudophase separation model for the micellar system, we applied the densitometric data to estimate the apparent molar volumes and the apparent thermal expansibility coefficients of the surfactant in monomeric and micellar forms. Ultrasound velocity and density data enabled us to estimate the isentropic compressibility of the surfactant in both forms. The results are compared with relevant literature data for alkyltrimethylammonium bromides.     

Use of Nitrogen-Doped Carbon Nanodots for the Photocatalytic Fluoroalkylation of Organic Compounds

The use of amine-rich N-doped carbon nanodots (NCNDs) for the photochemical radical perfluoroalkylation of organic compounds is reported. This operationally simple approach occurs under mild conditions producing valuable new C−C bonds. The chemistry is driven by the ability of NCNDs to directly reach an electronically excited state upon light absorption, thereby successively triggering the formation of reactive radical species from simple perfluoroalkyl iodides. Preliminary mechanistic studies are also reported.     

Engineering the structure and magnetic properties of crystalline solids via the metal-directed self-assembly of a versatile molecular building unit

We report the supramolecular chemistry of several metal complexes of N-(4-pyridyl)benzamide (NPBA) with the general formula [Ma(NPBA)2AbSc], where M = Co2+, Ni2+, Zn2+, Mn2+, Cu2+, Ag+; A = NO3-, OAc-; S = MeOH, H2O; a = 0, 1, 2; b = 0, 1, 2, 4; and c = 0, 2. NPBA contains structural features that can engage in three modes of intermolecular interactions: (1) metal-ligand coordination, (2) hydrogen bonding, and (3) pi-pi stacking. NPBA forms one-dimensional (1-D) chains governed by hydrogen bonding, but when reacted with metal ions, it generates a wide variety of supramolecular scaffolds that control the arrangement of periodic nanostructures and form 1- (2-4), 2- (5), or 3-D (6-10) solid-state networks of hydrogen bonding and pi-pi stacking interactions in the crystal. Isostructural 7-9 exhibit a 2-D hydrogen bonding network that promotes topotaxial growth of single crystals of their isostructural family and generates crystal composites with two (11) and three (12) different components. Furthermore, 7-9 can also form crystalline solid solutions (M,M')(NPBA)2(NO3)2(MeOH)2 (M, M' = Co2+, Ni2+, or Zn2+, 13-16), where mixtures of Co2+, Ni2+, and Zn2+ share the same crystal lattice in different proportions to allow the formation of materials with modulated magnetic moments. Finally, we report the effects that multidimensional noncovalent networks exert on the magnetic moments between 2 and 300 K of 1-D (4), 2-D (5), and 3-D (7, 8, 10, and 13-16) paramagnetic networks.     

Ultrasound-assisted method for determination of chemical oxygen demand

A method for determination chemical oxygen demand (COD) assisted by use of ultrasound has been successfully evaluated for the first time. The method uses instrumentation simpler and cheaper and, in some instances, safer than that used by previous methods for the same purpose. The new device used for sonication is an all-glass cylindrical sonotrode that can be introduced directly into the reaction mixture. Use of this device enables more efficient interaction between sample and ultrasonic energy. The optimized experimental conditions are high ultrasonic power (55% amplitude, 0.9-second pulses each second), high sulfuric acid concentration (>60%), and a sonication time of 2 min. Under these conditions the method has limitations similar to those of the official COD method with regard to the type of organic compound. It works adequately with easily oxidized organic matter (potassium hydrogen phthalate and dextrose) and other organic compounds difficult to oxidize by conventional methods (e.g. phenol and acetic acid) but the COD values obtained with volatile compounds and difficult organic matter are poor. Chloride is tolerated up to a concentration of 7000 mg L(-1) without any masking agent. Gasification of the sample is recommended to improve results; use of air and argon resulted in no significant differences - bubbling with air during sonication resulted in COD values for certified materials and real wastewater samples statistically identical with the certified COD values and those obtained by the classic (open reflux) method. The use of ultrasound energy for COD determination thus seems to be an interesting and promising alternative to conventional oxidation methods used for the same purpose.     

A chiroptical molecular switch with distinct chiral and photochromic entities and its application in optical switching of a cholesteric liquid crystal

Two new structurally related photoswitches are described, in which azobenzene photochromism is combined with the chirality of a 2,2'-dihydroxy-1,1'-binaphthyl unit. In system 1 the chiral binaphthyl moiety is bridged by a methylene tether, locking the biaryl chirality while in system 2 the biaryl core is unbridged and has considerable conformational flexibility. Both compound are capable of inducing cholesteric liquid crystalline phases and proved to be good photoswitches both in solution and in a liquid crystalline matrix. Compound 2 is capable of completely reversing the liquid crystalline chirality which is unique for a chiroptical molecular switch where the switching unit and the chiral moiety are separate entities.