Cholesteric Molecular Tweezer Artificial Receptor for Rapid and Highly Selective Detection of Ag+ in Food Samples

Chiral cholesteric molecular tweezer 7a was synthesized, and its recognition properties for Ag⁺, Al³⁺, Ca²⁺ etc., were investigated by UV and fluorescence spectra. The results showed that in ethanol/Tris (1/1, v/v, pH 7.0) buffer solution, the host molecular tweezer 7a had a specific recognition ability for Ag⁺, the detection limit was up to 1 × 10⁻⁶ mol/L, and other metal ions had little effect on Ag⁺ recognition. At the same time, the naked-eye detection of Ag⁺ was realized by the light red color of the complex solution. Furthermore, the mechanism of recognition of Ag⁺ by molecular tweezer 7a was studied by a nuclear magnetic titration test and computer molecular simulation, and a rapid detection method of Ag⁺ using host molecular tweezer 7a was established. Through the determination of Ag⁺ in milk powder, quinoa and other food samples, it was proved that this novel method had a good application prospect for the detection of Ag⁺ in food.     

Host-guest complexation-37 : Synthesis and binding properties of a transacylase partial mimic with imidazole and benzyl alcohol in place

The design and 30-step synthesis of a transacylase partial mimic is described. The target catalyst combines a macrocyclic binding site, a hydroxymethyl group, and an imidazole group organized to act cooperatively through their attachment to a quaterphenyl support structure. The binding site is composed of three cyclic urea units in a tripod arrangement, rigidified by their incorporation into a macrocycle along with two anisyl and one m-xylyl spacer units. The binding and catalytic sites are complementary to amino acid ester salts. The host catalyst collects and orients through complexation the guest substrate to provide substantial rate enhancements for transacylation of amino ester salts. The free energies are reported for the host in CDCl₃ binding the picrate salts of Li⁺, Na⁺, K⁺, Rb⁺,Cs⁺, NH₄⁺, CH₃NH₃⁺ and t-BuNH₃⁺.     

Polarographic reduction of aldehydes and ketones: Part XXIII. Electroreduction of 1-methylpyridiniumcarboxaldehydes

All three isomeric 1-methylpyridiniumcarboxaldehydes are present in aqueous solutions predominantly in the hydrated form (PyCH(OH)₂). At pH smaller than about 7, the protonated form of the free aldehyde is reduced in two one-electron steps following the sequence H⁺, e, H⁺, e. At pH greater than about 8 the free aldehydic form is reduced in two one-electron steps following the sequence, e, H⁺, e, H⁺. Up to pH about 10 the reducible species is formed by dehydration of PyCH(OH)₂, at higher pH by elimination of hydroxide ion from PyCH(OH)O⁻.The increase in polarographic reduction current between pH about 8 and 10 is due to a base-catalyzed dehydration, involving a rate-determining formation of PyCH(OH)O⁻. The polarographic dissociation curve (i₁ vs. pH) is in this case shifted to lower pH-values when compared with the conditional dissociation curve ([PyCH(OH)₂] vs. pH). Such behavior shows that the effective reduction of the conjugate base of an electroinactive acid (PyCH(OH)₂) occurs.The increase in polarographic reduction current at pH smaller than about 1 is due to an acid-catalyzed dehydration involving formation of PyCH(OH)(OH₂⁺). The rate of protonation governs the limiting current, since the increase in current with increasing acidity occurs in a region one to two acidity units higher than pK₁ values obtained spectrophotometrically, using acidity functions H_C(OH)2. The free carbonyl species produced by dehydration is reduced following a sequence H⁺, e, H⁺, e.     

Calculation of the potential energy curves for the low-lying doublet and quartet states of the CN radical

The potential energy curves of the low-lying X²Σ⁺, A²π_i, B²Σ⁺,⁴Σ⁺, and ⁴π states of CN are calculated by the MC SCF (CAS SCF) method. Their vibrational levels and the molecular constants obtained are in good agreement with those determined in our recent experimental analysis of the CN (B²Σ⁺-X²Σ⁺) emission spectrum. several intensity anomalies in the observed spectrum are ascribed to perturbations between the B²Σ⁺ and ⁴π states with the following vibrational quantum numbers: (υ_B, υ_π)=(9,x), (11, x+2), (12, x+3), (14, x+6), (17, x+11), and (18, x+13), where x = 0 is the most probable assignment. Likewise, the perturbations between the B²Σ⁺ and ⁴Σ⁺ states with (υ_B, υ_Σ) = (11, y), (13, y+3) are interpreted as y = 8±1.     

Thiophosphorylated cavitand: structure and affinity towards soft metal ions

The iiii stereoisomer of the tetrathiophosphonate-calix[4]resorcinarene host 1 exhibited excellent extraction properties towards soft metal ions, with a better affinity for Ag⁺ (91%), than for Tl⁺ (38%) and Hg²⁺ (16%). The extraction of other picrate salts (Cu²⁺, Ni²⁺, Co²⁺, Zn²⁺, Cd²⁺, Pb²⁺) was not detected. The stoichiometry and the structure of the Hg²⁺, Tl⁺ and Ag⁺ complexes were studied by NMR in solution and gave respectively 1:1, 1:1 and 1:2 host-guest complexes. The formation of the self-assembled 1₂·(AgPic)₄ complex was independent on the anion and only observed with silver(I) ion.     

Spectrophotometric determination of osmium : O-Aminophenol-p-sulphonic acid as a reagent

o-Aminophenol-p-sulphonic acid is suggested as a very sensitive reagent for spectrophotometric determination of osmium (VI) and (VIII) at pH 2 5–4. The absorption maximum is at 440 mμ and the optimum concentration range is from 2 to 8 p p m of osmium Moderate amounts of Pd⁺², lr⁺⁴, WO₄^-2, Cr⁺³, Zn⁺², Zr⁺⁴, Mg⁺², Ba⁺² and Sr⁺² do not interfere     

Thermal quenching of characteristic luminescence. II

A model proposed earlier to explain the dependence of the quenching temperature (T_q) of a given luminescent center on the host lattice is extended to luminescent centers bearing a formally effective charge. Predictions from this model are compared with experimental data. The agreement is satisfactory. It turns out that effectively charged centers with charge-transfer excitation (e.g., Eu³⁺, WO^2?₄) do not have a high value of T_q, whereas those with Rydberg excitation (e.g., Tl⁺, Tb³⁺) can have a high value of T_q, especially if the host lattice is rigid.     

Ligase-Independent Cloning of Amylase Gene from a Local Bacillus subtilis Isolate and Biochemical Characterization of the Purified Enzyme

Five hundred ninety-seven bacterial isolates from Turkish hot spring water sources were screened for their ability to produce extracellular α-amylase. Among them, a high enzyme-producing Bacillus subtilis isolate, A28, was selected, and its α-amylase gene was cloned and expressed in Escherichia coli by a ligase-independent method. α-Amylase from the recombinant strain was purified to homogeneity by Q-Sepharose anion exchange and Sephacryl S-100 gel filtration chromatographies. The final yield of the enzyme was about 22.5 % of the initial activity, with a 16.4-fold increase in specific activity compared with the culture lysate. The optimum temperature and pH of the enzyme were 70 °C and 6.0, respectively. The enzyme was highly active at acidic-neutral pH range of 4.5–7.0. The amy28 α-amylase retained 100 % of its activity after incubation at 50 °C for 90 min. Co⁺², Cu²⁺, Fe²⁺, Fe³⁺, Ni⁺², and Zn⁺² caused significant inhibition in enzyme activity, which was not affected by Na⁺, Mg²⁺, Li⁺, and Ba²⁺. The activity was inhibited about 70 % upon treatment of the enzyme with 10 mM ethylenediaminetetraacetic acid. However, Ca²⁺ ions known as high temperature stabilizer for other amylases did not stimulate the activity of the enzyme. Due to pH stability and thermostability of the recombinant amylase, this enzyme may be suitable in starch processing, brewing, and food industries.     

Systéme lymphocytaire et résistance relative de la souris consanguine a Trypanosoma brucei brucei

The distribution of B-(Ig⁺) and T-(Thy1.2⁺, Lyt1⁺, Lyt2⁺) lymphocyte subsets in murine lymphoid organs was analysed by immunofluorescence (FACS) on cell suspensions throughout a primary infection of C3H/He (susceptible) and CBA/Ca (subtolerant) inbred mice with metacyclic Trypanosoma brucei brucei EATRO 1125.A direct correlation was observed between (1) the level of first-peak parasitaemia, (2) its subsequent control by the host and (3) survival time.In the course of the infection, the overall population of spleen and lymph node lymphocytes was subject to polyclonal activation whilst the proportion of differenciated B and T subsets decreased accordingly.     

Theoretical investigation of the low-lying electronic states of the alkaline hydride BeH2+ ion: Potential energy curves, spectroscopic constants, vibrational levels, and transition dipole functions

The structure and spectroscopic properties of the alkaline hydride BeH²⁺ ion have been investigated using an ab initio approach based on nonempirical pseudopotentials and parameterized l-dependent polarization potentials. The adiabatic potential energy curves and their spectroscopic constants for the ground and seventeen excited electronic states, dissociating into Be⁺(2s, 2p, 3s, 3p, 3d, 4s, 4p, and 4d) + H⁺ and Be²⁺ + H(1s and n = 2), of ²??⁺, ²??, and ²?? symmetries have been determined. As no experimental data are available, our results are discussed and compared with the few existing theoretical calculations. A very good agreement has been found with the previous theoretical data for the ground state; however many potential energy curves for the higher excited states are presented here, for the first time. Numerous avoided crossings between electronic states for ²??⁺ and ²?? symmetries have been localized and analyzed. Their existence is related to the interaction between the electronic states and to the charge transfer process between the two ionic systems Be²⁺H and Be⁺H⁺. In addition, we have calculated the vibrational energy level spacings of the bound electronic states. Furthermore, the adiabatic transition dipole functions from the X ²??⁺ and 2²??⁺ states to the higher excited states of ²??⁺ and ²?? symmetries have been evaluated and compared with the available theoretical work. This study represents the necessary initial step towards the investigation of the charge transfer processes in collision between Be⁺-H⁺ and Be²⁺-H.     

High resolution studies of the origins of polyatomic ions in inductively coupled plasma-mass spectrometry,Part I. Identification methods and effects of neutral gas density assumptions,extraction voltage,and cone material

Common polyatomic ions (ArO⁺, NO⁺, H₂O⁺, H₃O⁺, Ar₂⁺, ArN⁺, OH⁺, ArH⁺, O₂⁺) in inductively coupled plasma-mass spectrometry (ICP-MS) are identified using high mass resolution and studied using kinetic gas temperatures (T_gas) determined from a dissociation reaction approach. Methods for making accurate mass measurements, confirming ion identifications, and correcting for mass bias are discussed. The effects of sampler and skimmer cone composition and extraction voltage on polyatomic ion formation are also explored. Neutral species densities at several locations in the extraction interface are estimated and the corresponding effects of the T_gas value are calculated. The results provide information about the origins of background ions and indicate possible locations for their formation or removal.     

Solvent extraction and self-assembly of nanosized aggregates of p-tert-butyl thiacalix[4]arenes tetrasubstituted at the lower rim by tertiary amide groups and monocharged metal cations in the organic phase

New p-tert-butyl thiacalix[4]arenes functionalized with morpholide and pyrrolidide groups at the lower rim in cone, partial cone, and 1,3-alternate conformations were synthesized, and their receptor properties for monocharged cations (alkali metal and silver ions) were studied using the picrate extraction method and dynamic light scattering (DLS). To evaluate the ability of the p-tert-butyl thiacalix[4]arene derivatives to recognize metal ions, liquid-liquid extraction of their picrate salts has been carried out in a mutually saturated water-dichloromethane system. The degrees of extraction and the extraction constants for monocharged metal cations (Li⁺, Na⁺, K⁺, Cs⁺) have been determined. The ability of the systems, consisting of host and guest molecules, to self-assembly was proved by DLS using a Zetasizer Nano ZS particle size analyzer. It was shown that all the investigated thiacalix[4]arenes are able to form nanoscale particles with silver cations under the experimental conditions. The pyrrolidide derivative in the cone conformation showed both self-association and aggregation processes with lithium cations. The degree of extraction for all the investigated systems that formed nanoscale aggregates in the organic phase was more than 67% and the extraction constants, log K_ex determined by the picrate extraction method, more than 6.     

The colours of simple salts of the violurate anion

Salts of the violurate anion with the alkali and alkaline earth metals, the d¹⁰ ions Zn²⁺ and Cd²⁺, Mn²⁺, Pb²⁺, Ag⁺ and the lanthanides show a variety of spectacular colours in the solid state. The metal ions have no intrinsic absorption in the visible region (apart from the weak spin-forbidden bands of Mn²⁺) and do not normally show charge-transfer absorption. The colours are ascribed to the n→π* transition of the violurate anion. As confirmation of this assignment the visible absorption of the K⁺ salt is shown to be polarized perpendicular to the plane of the violurate anion. Low temperature (∼20 K) absorption spectra of the Na⁺, K⁺ and Rb⁺ salts are reported.     

New PCT probes featuring N-phenylmonoaza-18-crown-6 and aryl/pyridyl oxadiazoles: optical spectral studies of solvent effects and selected metal ions

Aryl/pyridyl oxadiazole chromophores 6, 8 and 10, carrying N-phenyl aza-18-crown-6 have been synthesized as new photo-induced charge transfer (PCT) probes. While, the absorption spectra of the hosts experienced a slight negative solvatochromism, however the emission bands were dramatically red shifted (Stokes shifts up to 178 nm) in solvents of increasing polarity. Among the metal ions tested, Li⁺, Na⁺, K⁺ and Mg²⁺ did not appreciably perturbed the optical properties of the hosts. On the other hand, Ba²⁺ and to a lesser extent Ca²⁺ induced marked blue shifts in both the absorption and emission spectra of the hosts. The magnitude of cation induced spectral blue shifts corresponded with the increasing acceptor strength of the attached aryl/pyridyl groups in the host molecules. The blue shifts and the stability constants were found to follow the order Ba²⁺ > Ca²⁺ ? Mg²⁺ > Na⁺ > Li⁺ > K⁺. Competitive experiments performed with a matrix of ions also revealed superior binding affinity of Ba²⁺ with all the hosts examined. Noteworthily, the deep yellow solution (λ_max, 386 nm) of the host 10 was completely bleached (λ_max, 320 nm), in the company of Ba²⁺ thereby allowing the naked eye detection of this ion.     

Probing the interaction of alkali and transition metal ions with bradykinin and its des-arginine derivatives via matrix-assisted laser desorption/ionization and postsource decay mass spectrometry

The complexes of the peptides (Pep) bradykinin (RPPGFSPFR), des-Arg¹-bradykinin, and des-Arg⁹-bradykinin with the metal (M) ions Na⁺, K⁺, Cs⁺, Cu⁺, Ag⁺, Co²⁺, Ni²⁺, and Zn²⁺ are generated in the gas phase by matrix-assisted laser desorption/ionization and the structures of the corresponding [Pep + M⁺]⁺ or [Pep − H⁺ + M²⁺]⁺ cations are probed by postsource decay (PSD) mass spectrometry. The PSD spectra depend significantly on the metal ion attached; moreover, the various metal ions respond differently to the presence or absence of a basic arginine residue. The Na⁺ and K⁺ adducts of all three peptides mainly produce N-terminal sequence ions upon PSD; the fragments observed point out that these metal ions are anchored by the PPGF segment and not the arginine residue(s). In contrast, the adducts of Cu⁺ and Ag⁺ show a strong dependence on the position of Arg; complexes of des-Arg¹-Pep (which contains a C-terminal Arg) produce primarily y_n ions whereas those of des-Arg⁹-Pep generate exclusively a_n and b_n ions. These trends are consistent with Cu⁺ ligation by Arg’s guanidine group. The [Pep + Cs⁺]⁺ ions mainly yield Cs⁺; a second significant fragmentation occurs only if a C-terminal arginine is present and involves elimination of this arginine’s side chain plus water. This reaction is rationalized through a salt bridge mechanism. The most prominent PSD products from [Pep − H⁺ + Co²⁺]⁺ and [Pep − H⁺ + Ni²⁺]⁺ contain at least one phenylalanine residue, revealing a marked preference for these divalent metal ions to bind to aromatic rings; the fragmentation patterns of the complexes further suggest that Co²⁺ and Ni²⁺ bind to deprotonated amide nitrogens. The coordination chemistry of Zn²⁺ combines features found with the divalent Co²⁺/Ni²⁺ as well as the monovalent Cu⁺/Ag⁺ transition metal ions. Generally, the structure and fragmentation behavior of each complex reflects the intrinsic coordination preferences of the corresponding metal ion.     

Heterometric micro-determination of traces of iron in thiocyanate solutions by titration with nitron

Traces of ferric iron were determined heterometrically in concentrated solutions of potassium thiocyanate by titration with nitron. The solutions could contain 99.9% of the following cations: Ca⁺², Ba⁺², Mg⁺², Zn⁺², Cr⁺³, Al⁺³, Mn⁺². Cd⁺², Th⁺⁴, Ce⁺³ or 99% of Ni⁺², Pb⁺², Cu⁺², Mo⁺⁶, v⁺⁵ and W. A titration usually lasted 5 min and in most cases the error was ca. 1%. The molar ratio of [Fe] : [nitron] was always equal to 1 : 6.6.     

Guided ion beam studies of the reactions of O+, O 2 + , N+ and N 2 + with silane

Guided ion beam mass spectrometry is used to measure the cross sections as a function of kinetic energy for reaction of SiH₄ with O⁺(⁴S), O ₂ ⁺ (²Π_g,v=0), N⁺(³P), and N ₂ ⁺ (²Σ _g ⁺ ,v=0). All four ions react with silane by dissociative charge-transfer to form SiH _m ⁺ (m=0?3), and all but N ₂ ⁺ also form SiXH _m ⁺ products where (m=0?3) andX=O, O₂ or N. The overall reactivity of the O⁺, O ₂ ⁺ , and N⁺ systems show little dependence on kinetic energy, but for the case of N ₂ ⁺ , the reaction probability and product distribution relies heavily on the kinetic energy of the system. The present results are compared with those previously reported for reactions of the rare gas ions with silane [13] and are discussed in terms of vertical ionization from the 1t ₂ and 3a ₁ bands of SiH₄. Thermal reaction rates are also provided and dicussed.     

A highly selective pyrene based fluorescent sensor toward Hg detection

A new pyrene-containing fluorescent sensor has been synthesized from 2,3,3-trimethylindolenine. Spectroscopic and photophysical properties of sensor are presented. The large change in fluorescence intensity (I/I₀ = 0.13) at 381 nm and affinity to Hg²⁺ over other cations such as K⁺, Na⁺, Ca²⁺, Mg²⁺, Pb²⁺, and Cu²⁺ make this compound a useful chemosensor for Hg²⁺ detection in hydrophilic media. The sensor (6.0 × 10⁻⁶ M) displays significant fluorescence quenching upon addition of Hg²⁺ in pH 7.4 HEPES buffer without excimer formation. Job’s plot analysis shows the binding stoichiometry to be 2:1 (host/guest).     

Cluster Formation of 1-Butanol–Water Mixture Leading to Phase Separation

Microscopic structures of 1-butanol (1-BuOH)–water mixtures in the presence and absence of salts are studied through the mass spectrometric analysis of clusters generated from the fragmentation of liquid droplets. The analysis of cluster structures provides information on the phase separation of 1-BuOH–water mixtures from the microscopic viewpoint. In a saturated solution of 1-BuOH in water, 1-BuOH exists as hydrated 1-BuOH clusters and self-associated 1-BuOH clusters. With further addition of 1-BuOH, a 1-BuOH rich phase is generated. When the salt (LiCl, NaCl, MgCl₂, etc.) coexists in the 1-BuOH–water mixtures, the cation is preferentially solvated by the 1-BuOH to form M ⁺(1-BuOH) _m or M ²⁺(1-BuOH) _m clusters: M ⁺ = Li⁺, Na⁺, Mg²⁺ = Mg²⁺, etc., m = 1, 2, 3, ... Since the formation of M ⁺(1-BuOH) _m corresponds to an increase of the self-associated 1-BuOH clusters in water, the presence of the salt induces the phase separation at lower 1-BuOH concentrations.     

Heavy metal complexation by N-acyl(thio)urea-functionalized cavitands: synthesis, extraction and potentiometric studies

The synthesis and binding properties of resorcinarene-based cavitands functionalized with N-acylthiourea moieties towards different cations are described. Extraction studies with metal (Pb²⁺, Cu²⁺, Ag⁺, Hg²⁺, Cd²⁺, Eu³⁺, Fe³⁺, K⁺, Na⁺, and Ca²⁺) picrates and the incorporation in ion selective electrodes (ISEs), show that there is more than a 40% increase of the Ag⁺ extraction for N-acylthiourea ionophores (2, 3, and 8) in comparison with N-benzoyl-N′-benzylthiourea (9). Ionophore 8, which has a C₃ chain between the platform and the ionophore, extracts two times more Cu²⁺ than the more rigid one (2). Stoichiometry studies showed for ligand 2 a ligand/metal ratio of 1:1, while for model compound 9 a ratio of 1:2 was found. Potentiometric studies of electrodes revealed that cavitands 2, 3, and 8 induce a significantly different selectivity pattern compared to the cation-exchanger used, as well as model compound 9. Especially, a considerable enhancement of the selectivity towards Ag⁺ and Pb²⁺ over K⁺, Ca²⁺, and Na²⁺ ions was observed.