Syntheses of (E)- and (Z)-3-styrylchromones

Several (E)- and (Z)-3-styrylchromones were prepared by two different methodologies, the Wittig reaction of chromone-3-carboxaldehyde with benzylic ylides and the Knoevenagel condensation of chromone-3-carboxaldehyde with phenylacetic acids in the presence of potassium tert-butoxide under microwave irradiation. The Knoevenagel reaction followed by a decarboxylation offered an efficient and diastereoselective method for preparing (E)-3-styrylchromones in a shorter reaction time. It was also demonstrated that phenylacetic acid can also be substituted with success by phenylmalonic acid. The stereochemistry of all products was assigned by NMR experiments.     

Syntheses of (<Emphasis Type="Italic">E</Emphasis>)- and (<Emphasis Type="Italic">Z</Emphasis>)-3-styrylchromones

Several (E)- and (Z)-3-styrylchromones were prepared by two different methodologies, the Wittig reaction of chromone-3-carboxaldehyde with benzylic ylides and the Knoevenagel condensation of chromone-3-carboxaldehyde with phenylacetic acids in the presence of potassium tert-butoxide under microwave irradiation. The Knoevenagel reaction followed by a decarboxylation offered an efficient and diastereoselective method for preparing (E)-3-styrylchromones in a shorter reaction time. It was also demonstrated that phenylacetic acid can also be substituted with success by phenylmalonic acid. The stereochemistry of all products was assigned by NMR experiments. Correspondence: Artur M. S. Silva, Chemistry Department, University of Aveiro, 3810-193 Aveiro, Portugal.     

Synthesis and Characterization of Gold Nanoparticles with Surface Ligands Derived from a Primary Phosphine

Reduction of HAuCl₄ · 3H₂O with NaBH₄ in THF/H₂O in the presence of the primary phosphine PH₂Mes* (Mes* = 2,4,6-(t-Bu)₃C₆H₂) gave a mixture of ca. 1.3 nm diameter gold nanoparticles (1) and the known oligomers [Au(PHMes*)]_n (2). Nanoclusters 1 might contain phosphido (PHMes*) or phosphinidene (PMes*) surface ligands, or both; they were characterized by elemental analysis, TGA, XPS, TEM, NMR, IR, and UV–Vis spectroscopies, and by their reactions with dodecanethiol, which gave PH₂Mes*. Solid-state ³¹P-NMR cross-polarization studies of 1 and 1D (prepared using NaBD₄ and PD₂Mes* in THF/D₂O) were consistent with the presence of phosphinidene surface groups.     

Cover Feature: Chirality Transfer from an Innately Chiral Nanocrystal Core to a Nematic Liquid Crystal 2: Lyotropic Chromonic Liquid Crystals (ChemPhysChem 3/2023)

The importance of and the difference between molecular versus structural core chirality of substances that form nanomaterials, and their ability to transmit and amplify their chirality to and within a surrounding condensed medium is yet to be exactly understood. Here we demonstrate that neat as well as disodium cromoglycate (DSCG) surface-modified cellulose nanocrystals (CNCs) with both molecular and morphological core chirality can induce homochirality in racemic nematic lyotropic chromonic liquid crystal (rac-N-LCLC) tactoids. In comparison to the parent chiral organic building blocks, D-glucose, endowed only with molecular chirality, both CNCs showed a superior chirality transfer ability. Here, particularly the structurally compatible DSCG-modified CNCs prove to be highly effective since the surface DSCG moieties can insert into the DSCG stacks that constitute the racemic tactoids. Overall, this presents a highly efficient pathway for chiral induction in an aqueous medium and thus for understanding the origins of biological homochirality in a suitable experimental system.     

Effects of soft X‐ray radiation damage on paraffin‐embedded rat tissues supported on ultralene: a chemical perspective

Radiation damage is an important aspect to be considered when analysing biological samples with X‐ray techniques as it can induce chemical and structural changes in the specimens. This work aims to provide new insights into the soft X‐ray induced radiation damage of the complete sample, including not only the biological tissue itself but also the substrate and embedding medium, and the tissue fixation procedure. Sample preparation and handling involves an unavoidable interaction with the sample matrix and could play an important role in the radiation‐damage mechanism. To understand the influence of sample preparation and handling on radiation damage, the effects of soft X‐ray exposure at different doses on ultralene, paraffin and on paraffin‐embedded rat tissues were studied using Fourier‐transform infrared (FTIR) microspectroscopy and X‐ray microscopy. Tissues were preserved with three different commonly used fixatives: formalin, glutaraldehyde and Karnovsky. FTIR results showed that ultralene and paraffin undergo a dose‐dependent degradation of their vibrational profiles, consistent with radiation‐induced oxidative damage. In addition, formalin fixative has been shown to improve the preservation of the secondary structure of proteins in tissues compared with both glutaraldehyde and Karnovsky fixation. However, conclusive considerations cannot be drawn on the optimal fixation protocol because of the interference introduced by both substrate and embedding medium in the spectral regions specific to tissue lipids, nucleic acids and carbohydrates. Notably, despite the detected alterations affecting the chemical architecture of the sample as a whole, composed of tissue, substrate and embedding medium, the structural morphology of the tissues at the micrometre scale is essentially preserved even at the highest exposure dose.     

Oligosaccharide Analogues of Polysaccharides,Part 22 , Synthesis of Cyclodextrin Analogues Containing a Buta‐1,3‐diyne‐1,4‐diyl or a Butane‐1,4‐diyl Unit

The peracetylated hexaamylose (maltohexaose) 18 was obtained by an improved acetolysis of cyclomaltohexaose (α‐cyclodextrin, α‐CD, 16 ), and transformed into the benzyl‐ and 4‐chlorobenzyl‐protected thioglycosides 22 and 23 , respectively (Scheme 2). Sequential chain elongation of 22 and 23 by glycosidation of the C‐ethynylated glucosides 9 and 11 gave the α‐anomeric heptaglycosides 24 and 26 , respectively, and their anomers 25 and 27 (Scheme 3). These were transformed into the glycosyl acceptors 28 , 30 , and 31 . Glycosidation of 28 and 30 by 13 and 15 , respectively, led to the benzyl‐protected octasaccharides 32 (αα₅α) and 33 (βα₅α), and to the chlorobenzylated analogues 34 (αα₅α) and 35 (βα₅α), while glycosidation of 31 led to the 4‐chlorobenzyl‐protected analogues 36 (αα₅β) and 37 (βα₅β) (Scheme 4). Hay coupling of O‐Bn‐ and O‐Ac‐protected linear octaoses 32 (αα₅α) and 33 (βα₅α) led to the cyclooctaamylose (γ‐cyclodextrin) analogues 38 and 43 , respectively (Scheme 5). Similarly, the 4‐chlorobenzyl‐protected analogues 34 and 35 gave 39 and 44 , and the anomeric linear precursors 36 and 37 provided the cyclootaamylose analogues 48 and 50 , respectively (Scheme 6). The influence of the constitution and configuration of the linear precursors on the rate and yield of the cyclisation was relatively weak. Deprotection and hydrogenation of 38 and 43 yielded the γ‐CD analogues 42 (αα₅α) and 47 (βα₅α), where one glycosidic O‐atom is replaced by a butanediyl group, while FeCl₃‐promoted dechlorobenzylation of 39 and 44 did not affect the butadiyne moiety and afforded the acetyleno γ‐CD's 40 (αα₅α) and 45 (βα₅α), respectively. Similarly, deprotection of 48 and 50 afforded the acetyleno γ‐CD analogues 49 (αα₅β) and 51 (βα₅β), respectively, which contain one butanediyl moiety instead of a glycosidic O‐atom. MM3* Force‐field calculations evidence the strong influence of the configuration and constitution of the new γ‐CD analogues on the shape of the cavity.     

New Calix[4]arene—Fluoresceine Conjugate by Click Approach—Synthesis and Preparation of Photocatalytically Active Solid Lipid Nanoparticles

New fluorescent systems for photocatalysis, sensors, labeling, etc., are in great demand. Amphiphilic ones are of special interest since they can form functional colloidal systems that can be used in aqueous solutions. A new macrocycle platform for click chemistry and its adduct with o-propargylfluoresceine was synthesized and characterized using modern physical techniques. Nanosized solid lipid nanoparticles (SLNs) from the calixarene—fluoresceine adduct were synthesized through the solvent injection technique and well-characterized in the solution and in solid state using light-scattering and microscopy methods. The maximum fluorescence intensity of the SLNs was found to be in the pH range from 7 to 10. The Förster resonance energy transfer (FRET) efficiency from SLNs to rhodamine 6g was found to be 97.8%. Finally, pure SLNs and the FRET system SLNs—Rh6G were tested in model photocatalytic ipso oxidative hydroxylation of phenylboronic acid under blue LED light. The SLNs—Rh6G system was found to be the best, giving an almost qualitative phenol yield, which was shown by HPLC-UV analysis.     

Nutraceutic Potential of Bioactive Compounds of Eugenia dysenterica DC in Metabolic Alterations

The fruit and leaves of Eugenia dysenterica DC., locally known as cagaita, are rich in antioxidant glycosylated quercetin derivatives and phenolic compounds that have beneficial effects on diabetes mellitus, hypertension and general inflammation. We conducted a literature search to investigate the nutraceutical potentials of these phenolic compounds for treating obesity, diabetes mellitus and intestinal inflammatory disease. The phenolic compounds in E. dysenterica have demonstrated effects on carbohydrate metabolism, which can prevent the development of these chronic diseases and reduce LDL (low-density lipoprotein) cholesterol and hypertension. E. dysenterica also improves intestinal motility and microbiota and protects gastric mucosa, thereby preventing inflammation. However, studies are necessary to identify the mechanism by which E. dysenterica nutraceutical compounds act on such pathological processes to support future research.     

Synthesis,characterization, and crosslinking of novel stars comprising eight poly(isobutylene‐azeotropic‐styrene) copolymer arms with allyl or hydroxyl termini. II. Stars of eight isobutylene/styrene azeotropic copolymer arms emanating from a calix[8]arene core

Our objective was the precision synthesis of novel stars consisting of a well‐defined calix[8]arene core out of which radiate eight poly(isobutylene‐aze‐styrene) [P(IB‐aze‐St)] arms fitted with crosslinkable end groups. We reached our objective by preparing the octafunctional calixarene derivative C[8]OCH₃, inducing the living azeotropic copolymerization of IB/St charges with the C[8]OCH₃/BCl₃·TiCl₄ initiating system, and end‐quenching living IB/St copolymerizations with allyltrimethylsilane. With this strategy, we obtained stars C[8]? [P(IB‐aze‐St)? CH₂CH?CH₂]₈ of various molecular weights. The number of ? CH₂CH?CH₂ termini of the arms was 8.0 ± 0.2 by quantitative ¹H NMR analysis. The eight allyl termini were quantitatively converted to ? CH₂CH₂CH₂OH termini by hydroboration/oxidation. To confirm that the latter second‐generation stars possessed eight primary alcohol end groups, we quantitatively converted the ? CH₂OH termini to ? OSi(CH₃)₃ termini, the concentration of which was quantitated by ¹H NMR spectroscopy. According to this analysis, the stars contained 8.0 ± 0.3 hydroxyl termini. The glass‐transition temperatures of the P(IB‐aze‐St) arms increased from 59 to 65 °C as the weight‐average molecular weights of the arms increased from about 2500 to about 4300 g/mol, respectively. The α and K constants of the Mark–Houwink–Sakurada relationship and the intrinsic viscosity of a representative allyl‐telechelic star were determined and compared with a linear azeotropic IB/St copolymer of similar molecular weight. The crosslinking of C[8]? [P(IB‐aze‐St)CH₂CH₂CH₂OH]₈ stars with 4,4′‐methylene bis(phenyl) diisocyanate and 2,4‐tolylene diisocyanate in various solvents afforded tightly crosslinked films of potential interest for scratch‐resistant coatings, mar‐resistant coatings, or both. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1525–1532, 2001     

Search for γ-Emission from Isomeric Nuclei Induced by MeV Electron Beams

In this paper we study the nuclear transitions induced by incident electrons having an energy of several MeV's. We measured the cross sections for the excitation of isomeric nuclear states by 7.7 MeV electrons. The cross sections were 1.2 μb for ^111m Cd, 5.5 μb for ^113m In and 7.0 μb for ^115m In. The peak activation rates were 1.8×10⁻¹² s⁻¹ for ^111m Cd, 8.1×10⁻¹² s⁻¹ for ^113m In and 1.0×10⁻¹¹ s⁻¹ for ^115m In, for a peak power of the electron beam of 1.8×10⁶ W cm⁻². Then we describe for the first time the results of a series of experiments in which samples containing the isomeric nuclei ^166m Ho and ^186m Re have been irradiated with MeV electron beams. An upper limit of 17 mb has been determined for the cross section of electron-induced γ-emission from ^166m Ho and an upper limit of 2.2 mb has been determined for the cross section of electron-induced γ-emission from ^186m Re. This revised version was published online in July 2006 with corrections to the Cover Date.