Optically and redox-active ferroceneacetylene polymers and oligomers

The palladium-catalyzed Sonogashira reaction can be used to build optically active, oligomeric 1,2,3-substituted ferrocenes up to the tetramer, as well as polymers, by sequential coupling of optically active (ee > 98 %), planar chiral iodoferroceneacetylenes and ferroceneacetylenes. (SFC)-1-Iodoferrocene-2-carbaldehyde (1) was reduced to the alcohol and methylated to give the corresponding methyl ether, which was Sonogashira-coupled with HC(triple bond)CSiEt3, resulting in (RFc)-1-(C(triple bond)CSiEt3)-2-methoxymethylferrocene (4) (79%, three steps). Orthometalation with tBuLi followed by quenching with 1,2-diodoethane gave (RFc)-1-(C(triple bond)CSiEt3)-2-methoxymethyl-3-iodoferrocene (5). Deprotection of the acetylene with nBu4NF resulted in (RFc)-1-ethynyl-2-methoxymethyl-3-iodoferrocene (6), which was Sonogashira-coupled with itself to produce an optically active polymer. Deprotection of 4 with nBu4NF and Sonogashira coupling of the product with 5 resulted in the dinuclear ferrocene 9. Deprotection of 9 and coupling with 5, followed by deprotection of the resulting acetylene 11, gave the trinuclear ferrocene 12. Another such sequence involving 11 and 5 produced a tetranuclear ferrocene 13. To study the electronic communication in such oligomers in more detail, two symmetrical, closely interrelated, trinuclear ferrocenes 18 and 19 were synthesized. The redox potentials of all the ferrocenes and the ferroceneacetylene polymer were determined by cyclic and square-wave voltammetry. All the metallocenes were investigated by UV/Vis spectroscopy. A linear relationship was found between lambdamax and l/n (n=number of ferrocene units in the oligomer). The polymer displayed two redox waves in the cyclic voltammogram, at 0.65 and 0.795 V. The corresponding mixed-valence oligoferrocene cations were synthesized from four ferroceneacetylenes, and their metal-metal charge transfer bands were examined by UV/Vis-NIR. The resonance exchange integrals Had, calculated on the basis of spectral information from the metal - metal charge transfer (MMCT) bands, were between 290 and 552 cm-1.     

Multimodal Imaging and Phototherapy of Cancer and Bacterial Infection by Graphene and Related Nanocomposites

The advancements in nanotechnology and nanomedicine are projected to solve many glitches in medicine, especially in the fields of cancer and infectious diseases, which are ranked in the top five most dangerous deadly diseases worldwide by the WHO. There is great concern to eradicate these problems with accurate diagnosis and therapies. Among many developed therapeutic models, near infra-red mediated phototherapy is a non-invasive technique used to invade many persistent tumors and bacterial infections with less inflammation compared with traditional therapeutic models such as radiation therapy, chemotherapy, and surgeries. Herein, we firstly summarize the up-to-date research on graphene phototheranostics for a better understanding of this field of research. We discuss the preparation and functionalization of graphene nanomaterials with various biocompatible components, such as metals, metal oxides, polymers, photosensitizers, and drugs, through covalent and noncovalent approaches. The multifunctional nanographene is used to diagnose the disease with confocal laser scanning microscopy, magnetic resonance imaging computed tomography, positron emission tomography, photoacoustic imaging, Raman, and ToF-SMIS to visualize inside the biological system for imaging-guided therapy are discussed. Further, treatment of disease by photothermal and photodynamic therapies against different cancers and bacterial infections are carefully conferred herein along with challenges and future perspectives.     

Thermodynamics and Spectroscopy of Halogen- and Hydrogen-Bonded Complexes of Haloforms with Aromatic and Aliphatic Amines

Similarities and differences of halogen and hydrogen bonding were explored via UV–Vis and ¹H NMR measurements, X-ray crystallography and computational analysis of the associations of CHX₃ (X=I, Br, Cl) with aromatic (tetramethyl-p-phenylenediamine) and aliphatic (4-diazabicyclo[2,2,2]octane) amines. When the polarization of haloforms was taken into account, the strengths of these complexes followed the same correlation with the electrostatic potentials on the surfaces of the interacting atoms. However, their spectral properties were quite distinct. While the halogen-bonded complexes showed new intense absorption bands in the UV–Vis spectra, the absorptions of their hydrogen-bonded analogues were close to the superposition of the absorption of reactants. Additionally, halogen bonding led to a shift in the NMR signal of haloform protons to lower ppm values compared with the individual haloforms, whereas hydrogen bonding of CHX₃ with aliphatic amines resulted in a shift in the opposite direction. The effects of hydrogen bonding with aromatic amines on the NMR spectra of haloforms were ambivalent. Titration of all CHX₃ with these nucleophiles produced consistent shifts in their protons’ signals to lower ppm values, whereas calculations of these pairs produced multiple hydrogen-bonded minima with similar structures and energies, but opposite directions of the NMR signals’ shifts. Experimental and computational data were used for the evaluation of formation constants of some halogen- and hydrogen-bonded complexes between haloforms and amines co-existing in solutions.     

Syneresis and crystallinity in plasticized rubbery networks and composites

We prepared polycaprolactone networks plasticized (60 wt%) with triacetin, with and without filler particles to model high-energy solid rocket propellants. Under strain and at lower temperatures these materials partially crystallize but also undesirably exude plasticizer (syneresis). We measured both properties isothermally (30°C) on the basis of molecular mobility: crystallinity with rapid-passage cw proton nuclear magnetic resonance (NMR), and syneresis with pulsed-gradient spin-echo NMR diffusion techniques, as a function of strain and time. In the gumstocks crystallinity and syneresis increase monotonically with strain and asymptotically with time. In a given specimen syneresis lags behind crystallinity but they approach the same value, suggesting that syneresis originates in expulsion of plasticizer from crystallizing regions. In the composites, crystallinity results resemble those in gum, but our diffusion data suggest that most syneresis is internal, with plasticizer accumulating in strain-debonded void regions near filler particles. © 1994 John Wiley & Sons, Inc.     

Influence of PCL and PHBV on PLLA Thermal and Mechanical Properties in Binary and Ternary Polymer Blends

PLLA, PCL and PHBV are aliphatic polyesters which have been researched and used in a wide range of medical devices, and all three have advantages and disadvantages for specific applications. Blending of these materials is an attractive way to make a material which overcomes the limitations of the individual polymers. Both PCL and PHBV have been evaluated in polymer blends with PLLA in order to provide enhanced properties for specific applications. This paper explores the use of PCL and PHBV together with PLLA in ternary blends with assessment of the thermal, mechanical and processing properties of the resultant polymer blends, with the aim of producing new biomaterials for orthopaedic applications. DSC characterisation is used to demonstrate that the materials can be effectively blended. Blending PCL and PHBV in concentrations of 5–10% with PLLA produces materials with average modulus improved by up to 25%, average strength improved by up to 50% and average elongation at break improved by 4000%, depending on the concentrations of each polymer used. PHBV impacts most on the modulus and strength of the blends, whilst PCL has a greater impact on creep behaviour and viscosity. Blending PCL and PHBV with PLLA offers an effective approach to the development of new polyester-based biomaterials with combinations of mechanical properties which cannot be provided by any of the materials individually.     

Noise and Drift Phenomena in Amperometric and Coulometric Detectors for HPLC and FIA

Abstract

Noise and drift phenomena in electrochemical detectors with solid electrodes are discussed. A relationship between the capacity of the working electrode and the noise of the detector is demonstrated in three different ways, using direct correlation of noise with capacity, time correlation functions and electrical simulation of the cell properties. Conclusions are drawn with respect to the prospects of various measures to improve the detection limit.     

Preparation and photolysis of poly-p-ethylacrylophenone and poly-p-chloroacrylophenone and their copolymers with styrene and methyl methacrylate

Poly-p-ethylacrylophenone (PPEtAP) and poly-p-chloroacrylophenone (PPClAP) and their copolymers with styrene (PEtAP/S) and (PClAP/S) and with methyl methacrylate (PEtAP/MMA) and (PClAP/MMA) were prepared. Quantum yields of main-chain scissions at 366 nm at room temperature in benzene solution are of the same order as those of the unsubstituted polyacrylophenone and its copolymers. Substitution with chlorine and ethyl group in the para position compared to the unsubstituted polyacrylophenone and its copolymers leads to an increase of the lifetime for the n–π^* excited triplet state, as is evident from the measured quenching constants of photolysis. The low-temperature emission spectra of the copolymers are similar to the spectra of the model compounds in a polymer film. For the homopolymer, however, the character of the emission spectrum changes considerably.     

Synthesis and reaction of selenocarbamic acid sodium and potassium salts and organo-germanium, -tin,and -lead esters

Sodium 2 and potassium selenocarbamates 3 were found to be synthesized in moderate to good yields by the reaction of carbamoyl chlorides with sodium and potassium selenides. The salts 2 and 3 reacted with alkyl halides and organo-germanium, -tin, and -lead chlorides to give the corresponding esters 7–9 in good yields.     

Tricalixarenes and pentacalixarenes: synthesis and complexation studies

Tricalix[4]arene 4, tricalix[5]arene 14, and pentacalix[4]arene 10 have been synthesized from O-alkylcalixarene mono- and dialdehydes by a two-step conversion to the corresponding monoethynyl ketones or diethynyl ketones followed by aryne trimerization in refluxing DMF containing a dialkylamine. The tricalixarenes 4 and 14 were converted, in turn, to calixarenes 6 and 16, which carry OH groups on the lower rim and methylenes as the bridging moieties to the benzene ring. Complexation studies with the tricalix[5]arene 16 show that it forms (a) a 1:3 complex with N,N-dimethylethylenediamine in which each calixarene unit contains a molecule of the amine, (b) a 1:1 complex with tris(aminomethyl)amine in which each calixarene unit contains one of the three arms of the guest, and (c) a 1:1 complex with C60 in which the guest presumably resides in the cavity provided by the three calixarene units acting cooperatively.     

Monomeric and polymeric copper and zinc tripyrrins

Neutral transition metal complexes of different alpha,omega-dimethyltripyrrins TrpyMX with M = Cu(II) and Zn(II) have been prepared with a variety of anionic halogeno and pseudohalogeno ligands X, and have been studied with respect to coordination modes and structural distortion. Only four- and five-coordinate species have been observed throughout the series. All four-coordinate species display unstrained, but distorted tetrahedral or strained and distorted square-planar coordination environments for zinc(II) and copper(II) species, respectively, thus following the expectations from simple ligand field arguments. Five-coordinate species do not form easily and were observed either in donor solvents or in the solid as 1D coordination polymers with distorted trigonal-bipyramidal coordination and different topologies.     

Adsorption and Mobility of Water and Benzene Molecules in Carbon and Polymer Adsorbents

The correlation between the adsorption and the mobility of adsorbed molecules was analyzed. The peculiarities of molecular mobility in microporous adsorbents with relatively rigid (active carbons) and non-rigid (polymer super-crosslinked and methacrylate sorbents) structure were studied using pulsed nuclear magnetic resonance (NMR) techniques. It was shown that the translational behavior of water and benzene in pores are connected with the specific adsorption mechanism. The NMR data allowed analyzing the changes of molecular state in the processes of adsorption. Diffusional properties of water molecules in the super-crosslinked polystyrenes and active carbons with relatively rigid framework are similar and differ from that in methacrylate polymer sorbents. Moreover, the results of NM relaxation measurements allowed analyzing the porous structure over the scale of pore sizes, while the scale of the self-diffusion measurements comprises the areas of different porosity. The NMR data agree well with the data of adsorption measurements and complement them. Dedication: This work is devoted to memory of the professor W. Schirmer.     

Kinetics and mechanisms of chlorine dioxide and chlorite oxidations of cysteine and glutathione

Chlorine dioxide oxidation of cysteine (CSH) is investigated under pseudo-first-order conditions (with excess CSH) in buffered aqueous solutions, p[H+] 2.7-9.5 at 25.0 degrees C. The rates of chlorine dioxide decay are first order in both ClO2 and CSH concentrations and increase rapidly as the pH increases. The proposed mechanism is an electron transfer from CS- to ClO2 (1.03 x 10(8) M(-1) s(-1)) with a subsequent rapid reaction of the CS* radical and a second ClO2 to form a cysteinyl-ClO2 adduct (CSOClO). This highly reactive adduct decays via two pathways. In acidic solutions, it hydrolyzes to give CSO(2)H (sulfinic acid) and HOCl, which in turn rapidly react to form CSO3H (cysteic acid) and Cl-. As the pH increases, the (CSOClO) adduct reacts with CS- by a second pathway to form cystine (CSSC) and chlorite ion (ClO2-). The reaction stoichiometry changes from 6 ClO2:5 CSH at low pH to 2 ClO2:10 CSH at high pH. The ClO2 oxidation of glutathione anion (GS-) is also rapid with a second-order rate constant of 1.40 x 10(8) M(-1) s(-1). The reaction of ClO2 with CSSC is 7 orders of magnitude slower than the corresponding reaction with cysteinyl anion (CS-) at pH 6.7. Chlorite ion reacts with CSH; however, at p[H+] 6.7, the observed rate of this reaction is slower than the ClO2/CSH reaction by 6 orders of magnitude. Chlorite ion oxidizes CSH while being reduced to HOCl, which in turn reacts rapidly with CSH to form Cl-. The reaction products are CSSC and CSO3H with a pH-dependent distribution similar to the ClO2/CSH system.     

Spectrophotometric determination of titanium with tannin and thioglycollic acid and its application to titanium-treated steels and ferrous and non-ferrous alloys

A sensitive spectrophotometric method for the determination of titanium by formation of its complex with tannin and thioglycollic acid at pH 4 has been developed. The intense yellow colour is measured at 400 nm and the system obeys Beer's law over the range 0.2-5 ppm titanium in the solution measured. The method is applicable to titanium-treated steels, stainless steels, permanent magnet alloys and duralumin alloys. The interference of Co, Ni, Cr, Mn, V, Mo and W can be eliminated by prior separation of titanium by controlled addition of cupferron in the presence of thioglycollic acid (TGA). Copper can be quantitatively separated by precipitation with TGA and determined complexometrically with EDTA, with PAN as indicator. Niobium interferes even in traces.     

Vibrational spectra of anhydrous and monohydrated caffeine and theophylline molecules and crystals

Density functional theory and classical molecular dynamics simulations are used to investigate the vibrational spectra of caffeine and theophylline anhydrous and monohydrate molecules and those of their crystalline anhydrous and monohydrated states, with emphasis in the terahertz region of the spectra. To better understand the influence of water in the monohydrate crystal spectra, we analyze the vibrational spectra of water monomer, dimer, tetramer, and pentamer, and also those of liquid water at two different temperatures. In small water clusters, we observe the progressive addition of translational and librational modes to the terahertz region of the spectra. The water spectra predicted by rigid and flexible water models is examined with classical molecular dynamics, and the respective peaks, especially in the terahertz region, are compared with those found in the small clusters. Similar analysis done for caffeine and theophylline monohydrate molecules using density functional theory clearly shows the presence of water modes in the librational states and in the water stretching region. Molecular dynamics of caffeine and theophylline anhydrous and monohydrate crystals reveal the influence of vibrations from the molecule-molecule (caffeine or theophylline) crystal stacks and those from the water-molecule interactions found in the monohydrate molecules and new modes from molecule-molecule, water-molecule, and water-water hydrogen bonding interactions arising from collective effects in the crystal structure. Findings illustrate challenges of terahertz technology for the detection of specific substances in condensed phases.     

Synthesis and structures of trifluoromethyl-, fluoro-, and azido-substituted hexabenzylhexaazaisowurtzitanes and isolation of a novel hexaazaisowurtzitane-based polycycle

The first hexabenzylhexaazaisowurtzitane cage compounds with trifluoromethyl and azide groups, as well as those with fluorine atoms in the 3- and 4-positions, have been prepared and fully characterized. A study of the substituent influence on the benzene ring regarding the formation of the hexaazaisowurtzitane polycycle in either the 2- or 4-position with CF(3), F, and N(3) revealed an interesting difference. In all cases with CF(3), F, and N(3) substituents in the 4-position, the corresponding hexabenzylhexaazaisowurtzitanes were isolated. The corresponding hexabenzylhexaazaisowurtzitanes were also formed when these substituents were in the 2-position; however, in addition with azide in 2-position a novel type of polycycle was isolated and identified. (15)N NMR data and crystal structures of hexabenzylhexaazaisowurtzitane derivatives were obtained and are discussed in detail.     

Robust and straightforward chemo-enzymatic enantiopure dipeptide syntheses and diketopiperazines thereof

We have explored the scope of the synthetic route towards d-phenylglycyl diketopiperazines, involving a penicillin acylase catalysed formation of d-phenylglycyl dipeptides of l-amino acids with functional groups in the side chain. The synthesis of dipeptides from serine, threonine, glutamic acid, glutamine and methionine was successful. In contrast, aspartic acid, asparagine and cysteine only afforded trace amounts of dipeptides while no dipeptide was detected with arginine, lysine and tyrosine. Isolated dipeptide yields varied from 10% to 76%. The dipeptides were successfully converted into their corresponding enantiopure diketopiperazines by chemical esterification and cyclization under alkaline conditions, in 35–43% yield. In the case of glutamic acid, the procedure yielded the diketopiperazine with an esterified side chain. Remarkably with glutamine, the amide function in the side chain was transformed into an ester moiety, resulting in the same diketopiperazine as with glutamic acid.     

Synthesis and transformations of S- and N-substituted 2-mercaptobenzothiazoles

2-Mercaptobenzothiazole reacts with alkyl halides and hydrazine hydrate in the thiol form, and with formaldehyde in the thione form. The alkylation of 2-mercaptobenzothiazolidin-3-yl-methanol has been performed with sulfoalkyl halides and with propan-1,3-sultone. A number of new 2-hydrazinobenzothiazoles derivatives have been synthesized.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 40–43, January 1984.     

The fate and behavior of glufosinate-enantiomers and their metabolites in open-field soil and weeds

In this study, a chiral method based on high performance liquid chromatography–Q-Exactive Orbitrap Mass Spectrometry was developed to determine glufosinate stereoisomers and three metabolites in weed. Fortified recoveries in weed and soil samples were from 78.6 to 94.3 %, with relative standard deviations of less than 9.8 % and fortified values ranging from 0.04 to 40 mg/kg for the glufosinate enantiomers and 0.08–8 mg/kg for three metabolites. When glufosinate was given at the peak of weed growth in three orchards, it was mostly distributed and degraded in the weeds, with little remaining in the soil. The two glufosinate enantiomers degraded rapidly in the weeds and soils, with half-lives ranging from 0.7 to 3.1 days. The degradation of glufosinate enantiomers in Guizhou and Hunan weeds was enantioselective, with l-glufosinate being preferentially degraded. In Hainan weed, the degradation rate of the two enantiomers was nearly the same. In open field soils, glufosinate enantiomers were almost non-enantioselective. 3-methylphosphinico-propionic acid (MPP) was the primary glufosinate metabolite in weeds and soils, accounting for up to 14 % of the parent. N-acetyl-glufosinate (NAG) was relatively low, with less than 1 % of the parent glufosinate metabolized into 2-methylphosphinico-acetic acid (MPA).     

Electron beam modification and crosslinking: Influence of nitrile and carboxyl contents and level of unsaturation on structure and properties of nitrile rubber

The structural changes of nitrile rubber with varying nitrile contents, hydrogenated nitrile rubber and carboxylated nitrile rubber in the presence and absence of a polyfunctional monomer, namely trimethylolpropane triacrylate, at different doses of electron beam irradiation, were investigated with the help of FTIR spectroscopy (in the attenuated total reflectance mode), dynamic mechanical thermal analysis and sol–gel analysis. Solid-state NMR with gated high power decoupling technique was used to understand the mechanism of crosslinking of the irradiated samples. The allylic radicals generated in the butadiene chains react to form intermolecular crosslinkages. There was a significant decrease in the concentration of olefinic groups for the nitrile rubber on irradiation. This was also affirmed by the increase in the carbon resonances due to C–C linkages from the NMR technique, indicating more crosslinkages. The spectroscopic crosslink densities were determined and the results were compared with the swelling measurements. The variation in the crosslink clustering for rubbers with different acrylonitrile contents was explained using the NMR technique. The increase in crosslinking was also revealed by the increase in the percent gel content and dynamic storage moduli with radiation doses. The lifetime of spurs formed and the critical dose, an important criterion for overlapping of spurs, were determined for both the grafted and the ungrafted nitrile rubbers of different grades and compared using a mathematical model. The ratio of scissioning to crosslinking for nitrile rubber was determined using Charlesby–Pinner equation. The mechanical properties had also been studied for both the modified and the unmodified systems.     

Bocdene and mocdene derivatives of catechols and catecholamines

[reaction in text] Catechols react chemoselectively, in the presence of either alcohols, 1,2-diols, or simple phenols, with tert-butyl propynoate and with methyl propynoate to give 2-Boc-ethylidene (Bocdene) and 2-Moc-ethylidene (Mocdene) acetals, respectively, in 96-100% yields within 30 min at room temperature, provided that 150 mol % of DMAP is added. Cleavage of these acetals with pyrrolidine readily takes place (at room temperature!) in 95-100% yields. By taking advantage of the features of Bocdene acetals, novel catecholamine-related phosphate mimetics have been prepared.