Part two: Analytical optimisation of a procedure for lead detection in milk by means of bismuth-modified screen-printed electrodes

This work reports the optimisation of a new analytical method for lead ion detection in milk; the electrochemical detection scheme is based on the method that was described in Part I [1]. It features the use of a disposable, environmentally friendly bismuth film electrode to replace the traditionally used (toxic) mercury one while here we report an arduous development of sample treatment so that the simple device can be applied as a screening tool in many settings. For this purpose, a milk pre-treatment procedure by means of wet digestion with HCl, HClO₄, and H₂O₂ combined with an ultrasonic treatment was developed. The detection of lead ions in treated milk was then carried out using a disposable screen-printed electrode modified with Nafion^® and an “in situ” bismuth film, with the analysis being performed in anodic stripping voltammetry mode. The analytical method developed allows the detection of milk contaminated with lead ions at a concentration of 20 μg Kg⁻¹ (legal limit) and it can be proposed as a screening method for routine analysis of lead ions in milk with the advantage of employing inexpensive and portable instrumentation. Moreover, dedicated software supported by a portable instrument introduces procedures that are essential to avoid distortion from ambient lead contamination and also makes it possible for an unskilled operator to carry out each step of the analysis.     

Preparation,characterization, and binding profile of imprinted semi-IPN cryogel composite for aluminum

Human body is greatly exposed to aluminum due to its high abundance in the environment. This nonessential metal is a threat to the patients of chronic renal disorders, as it is easily retained in their plasma and quickly accumulates in different tissues. Thus, there is great need to remove it from the aqueous environment. In this study, Al³⁺ imprinted semiinterpenetrating polymer network (semi-IPN)-based cryogel composite was prepared and applied for the purification of environmental and drinking water samples from aluminum. Poly (2-hydroxyethyl methacrylate) (pHEMA) discs were produced via cryogenic treatment and imprinted semi-IPN was introduced to the 3-(trimethoxysilyl) propyl acrylatemodified macroporous cryogel discs. The adsorption properties and selectivity of the aluminum (III) imprinted semi-IPN cryogel composite were studied in detail. The imprinted semi-IPN cryogel composite showed good selectivity towards aluminum (III) ions with the imprinting factor (IF) of 76.4 in the presence of competing copper (II), nickle (II), and iron (III) ions. The maximum adsorption capacity of 271 μmol g^-1 was obtained for aluminum (III) at pH 7.0 within 10 min using imprinted semi-IPN cryogel composite. The good selectivity and reusability of aluminum (III)-imprinted semi-IPN cryogel composite makes this material an eligible candidate for the purification of drinking water from aluminum (III) leaving important minerals remained in the water.     

Complexes with metal-carbon bonds,part III(1). Preparation and properties of binuclear diarylplatinum(II) compounds

Summary Reaction ofcis-PtCl₂(R₂S)₂, where R=Et, n-Pr or i-Pr, with an excess of PhLi orp-tolylLi in ether yielded the dimeric [PtR₂(R₂S)]₂ complexes where R=Ph orp-tolyl. Usingtrans-PtCl₂(R₂S)₂ under the same conditions with PhLi, both [PtPh₂(Et₂S)]₂ and PtPh₂(Et₂S)₂ were isolated.The dimericcis-[PtR₂(Et₂S)]₂ complexes reacted with a range of neutral ligands to give PtR₂L₂ where L=Et₂S, Me₂S, PPh₃, t-BuNC, 0.5 (bipyridine) or pyridine. With CO, thecis-PtR₂(Et₂S)(CO) compounds were formed. Thecis-Pt(C₆F₅)₂(Et₂S)₂ complex reacted stepwise with PPh₃ and both Pt(C₆F₅)₂(Et₂S)(PPh₃) and Pt(C₆F₅)₂(PPh₃)₂ were isolated.     

Conformational analysis of furanoid epsilon-sugar amino acid containing cyclic peptides by NMR spectroscopy,molecular dynamics simulation,and X-ray crystallography: evidence for a novel turn structure

Sugar amino acids (SAAs) are useful building blocks for the design of peptidomimetics and peptide scaffolds. The three-dimensional structures of cyclic hybrid molecules containing the furanoid epsilon-SAA III and several amino acids were elucidated to study the preferred conformation of such an epsilon-SAA and its conformational influence on the backbone of cyclic peptides. NMR-based molecular dynamics simulations and empirical calculations of the cyclic tetramer 1, consisting of two copies of the SAA residue and two amino acids, revealed that it is conformationally restrained. The two SAA residues adopt different conformations. One of them forms an unusual turn, stabilized by an intraresidue nine-member hydrogen bond. The methylene functionalities of the other SAA residue are positioned in such a way that an intraresidue H bond is not possible. The X-ray crystal structure of 1 strongly resembles the solution conformation. Molecular dynamics calculations in combination with NMR analysis were also performed for compounds 2 and 3, which contain the RGD (Arg-Gly-Asp) consensus sequence and were previously shown to inhibit alpha(IIb)beta(3)-receptor-mediated platelet aggregation. The biologically most active compound 2 adopts a preferred conformation with the single SAA residue folded into the nine-member H bond-containing turn. Compound 3, containing an additional valine residue, as compared with compound 2, is conformational flexible. Our studies demonstrate that the furanoid epsilon-SAA III is able to introduce an unusual intraresidue hydrogen bond-stabilized beta-turn-like conformation in two of the three cyclic structures.     

Synthese und chemie von 4R-silacyclohexa-2,5-dienen und 4R-silacyclohexa-2,4-dienen

The 1(Z),4(Z)-1,5-dilithium-3R-3-methoxypenta-1,4-dienes, available by cleavage of 1,1-di-n-butyl-4R-4-methoxy-1-stannacyclohexane-2,5-dienes with n-BuLi in ether, react with dichlorosilanes (R′R″ SiCl₂; R′, R″ = H, alkyl, aryl, alkoxy) to give 1R′,1R″,4R-4-methoxy-1-silacyclohexa-2,5-dienes.Claevage of the ether group with BBr₃, BCl₃ or PCl₃ gives 6-chloro(bromo)-1-silacyclohexa-2,4-dienes or 1,5-dichloro-1-silacyclohexane-2,4-dienes, respectively.Ether cleavage of 4R-4-methoxy-1-silacyclohexa-2,5-dienes with sodium results in the formation of 4R-1-silacyclohexadienyl anions, which can be hydrolyzed to give 1-silacyclohexa-2,4-dienes which reach further with trichloromethylsilane to give 6-trimethylsilyl-1-silacyclohexa-2,4-dienes.Phase transfer-catalyzed conversion of 1-chlorosilacyclohexadienes into the fluoro derivatives as well as further substitution reactions of 1-chlorosilacyclohexadienes are described.The ¹H NMR, ¹³C NMR, IR and mass spectra of the silacyclohexadienes are discussed.     

Determination of polybutylene terephthalate polycondensation equilibrium constant using a batch reactor

The PBT polycondensation equilibrium constant at 255°C was determined using a batch reactor. Starting from a Polybutylene terephthalate (PBT) prepolymer having a degree of polymerisation of 12.7, equilibrium experiments were performed in the range of 1 to 50 mbar. The equilibrium degree of polymerisation (i) was determined indirectly using dilute solution viscometry of a solution of 1 weight % PBT in m - cresol. The degree of polymerisation of PBT obtained at equilibrium in the range of 1 to 50 mbar at 255°C as a function of the BDO partial pressure (mbar) could be expressed by: i = 111.47 − 86.18 exp(−1.14 equation/tex2gif-stack-1.gif). The equilibrium solubility of 1,4 butanediol (BDO) in the PBT melt was derived form the BDO partial pressure using the Flory - Huggins theory. The PBT polycondensation reaction equilibrium constant was related to the degree of polymerisation by the equation: in the range i = 26 − 100. The PBT polycondensation equilibrium constant at high degrees of polymerisation is in line with literature data and thermodynamics.     

INDUCTION and DISAPPEARANCE OF THYMINE DIMERS IN HUMAN SKIN EXPOSED TO UVB RADIATION: FLOW CYTOMETRIC MEASUREMENTS IN REPLICATING and NONREPLICATING EPIDERMAL CELLS

We have earlier reported on determining UV-induced DNA damage in murine epidermal cell suspensions by flow cytometric analysis of the fluorescence from a fluorescein isothiocyanate-labeled antibody (H3) directed against thymine dimers (T>2-M-phase cells can further be distinguished from cell doublets by pulse-shape discrimination. Thus, T>(i.e. G₀-G₁, S or G₂-M phases) can be determined after in vivo exposure of human skin to environmentally relevant UVB (280–315nm) doses. The method was applied to measure the decrease of T>0-G₁ phase) and replicating cells (S phase or G₂-M phase) from seven volunteers exposed to twice their minimal erythema dose. The reduction in the average T>0-G₁ cells and 70% (ranging between 37% and 100%) for the S + G₂-M cells. The difference was statistically highly significant. Determination of individual DNA repair capacities with this method can become a convenient diagnostic tool for patients with DNA repair disorders, or it may even be used to identify individuals with low repair proficiencies and increased risk of developing skin cancers.