Tough polymeric hydrogels using ion-pair comonomers.

Hydrogels with excellent mechanical properties were synthesized by radical photo-polymerization of three different types of ion-pair comonomers (IPC), without requiring any chemical cross-linking agent. Insoluble gels formed only at a specific solution concentration range, which was unique to the particular salt. The gels changed properties after one day soaking in water, becoming less stiff and more extendible, but remained stable after that. Strains of up to 4000% were measured for one salt pair and ultimate stresses of up to 2.53 MPa for another. Self-healing properties were noted along with some recovery of creep, due to the non-covalent nature of the gel. These properties arise through a combination of electrostatic and hydrophobic interactions of the polymer chains. Immersion of the gels in salt solution screened the electrostatic interactions, resulting in dissolution of the gel.

A mechanically strengthened polyacrylamide gel matrix fully compatible with electrophoresis of proteins and nucleic acids.

Polyacrylamide gel electrophoresis is a universal tool in a biochemist's toolkit for protein and nucleic acid separation and subsequent visualisation and analysis. The standard formulation of polyacrylamide gels consists of acrylamide (ACM) monomer crosslinked with bisacrylamide (MBA) which creates a gel with excellent sieving properties but which is mechanically fragile and prone to tearing during post-electrophoresis manipulations involved in visualisation and analysis. By adding a poly(ethylene oxide) macro-crosslinker to the standard gel formulation, we have created a tough gel matrix that can be used to fractionate proteins and nucleic acids by polyacrylamide gel electrophoresis. The protein and nucleic acid resolving capabilities and performance during staining and electroblotting of the tough gel matrix rivals that of conventional acrylamide/bisacrylamide gels. The tough gel matrix is resistant to tear and remarkably elastic, capable of stretching to over four times its original length before breaking, and represents a significant improvement over standard polyacrylamide gel formulations.

Hyperelastic Tough Gels through Macrocross-Linking.

The wet and soft nature of hydrogels makes them useful as a mimic for biological tissues, and in uses such as actuators and drug delivery vehicles. For many applications the mechanical performance of the gel is critical, but gels are notoriously weak and prone to fracture. Free radical polymerization is a very powerful technique allowing for fine spatial and temporal control of polymerization, but also allows for the use of a wide range of monomers and mixtures. In this work, it is demonstrated that extremely tough and extensible hydrogels can be readily produced through simple radical polymerization of acrylamide or acrylic acid with a poly(ethylene oxide) macrocross-linker. These gels, with a water content of 85%, are extremely elastic with an extension much more than 15 000% at 9 MPa true stress. They can be compressed over 98% at a stress of 17 MPa. They are notch-insensitive, and the usual trouser tear test does not work because the tear simply does not propagate. This highly extensible nature seems to be related to very long chain lengths between cross-links and efficient incorporation of chains into the network.

Antimicrobial Properties of Tris(homoleptic) Ruthenium(II) 2-Pyridyl-1,2,3-triazole "Click" Complexes against Pathogenic Bacteria, Including Methicillin-Resistant Staphylococcus aureus (MRSA).

A series of tris(homoleptic) ruthenium(II) complexes of 2-(1-R-1H-1,2,3-triazol-4-yl)pyridine "click" ligands (R-pytri) with various aliphatic (R = butyl, hexyl, octyl, dodecyl, and hexdecyl) and aromatic (R = phenyl and benzyl) substituents was synthesized in good yields (52%-66%). The [Ru(R-pytri)3]2+(X-)2 complexes (where X- = PF6- or Cl-) were characterized by elemental analysis, high-resolution electrospray ionization mass spectrometry (HR-ESI-MS), 1H and 13C nuclear magnetic resonance (NMR) and infrared (IR) spectroscopies, and the molecular structures of six of the compounds confirmed by X-ray crystallography. 1H NMR analysis showed that the as-synthesized materials were a statistical mixture of the mer- and fac-[Ru(R-pytri)3]2+ complexes. These diastereomers were separated using column chromatography. The electronic structures of the mer- and fac-[Ru(R-pytri)3]2+ complexes were examined using ultraviolet-visible (UV-Vis) spectroscopy and cyclic and differential pulse voltammetry. The family of R-pytri ligands and the corresponding mer- and fac-[Ru(R-pytri)3]2+ complexes were tested for antimicrobial activity in vitro against both Staphylococcus aureus and Escherichia coli bacteria. Agar-based disk diffusion assays indicated that two of the [Ru(R-pytri)3](X)2 complexes (where X = PF6- and R = hexyl or octyl) displayed good antimicrobial activity against Gram-positive S. aureus and no activity against Gram-negative E. coli at the concentrations tested. The most active [Ru(R-pytri)3]2+ complexes ([Ru(hexpytri)3]2+ and Ru(octpytri)3]2+) were converted to the water-soluble chloride salts and screened for their activity against a wider range of pathogenic bacteria. As with the preliminary screen, the complexes showed good activity against a variety of Gram-positive strains (minimum inhibitory concentration (MIC) = 1-8 µg/mL) but were less effective against Gram-negative bacteria (MIC = 16-128 µg/mL). Most interestingly, in some cases, the ruthenium(II) "click" complexes proved more active (MIC = 4-8 µg/mL) than the gentamicin control (MIC = 16 µg/mL) against two strains of methicillin-resistant S. aureus (MRSA) (MR 4393 and MR 4549). Transmission electron microscopy (TEM) experiments and propidium iodide assays suggested that the main mode of action for the ruthenium(II) R-pytri complexes was cell wall/cytoplasmic membrane disruption. Cytotoxicity experiments on human dermal keratinocyte and Vero (African green monkey kidney epithelial) cell lines suggested that the complexes were only modestly cytotoxic at concentrations well above the MIC values.

Synthesis of triphenylphosphonium vitamin E derivatives as mitochondria-targeted antioxidants.

A series of mitochondria-targeted antioxidants comprising a lipophilic triphenylphosphonium cation attached to the antioxidant chroman moiety of vitamin E by an alkyl linker have been prepared. The synthesis of a series of mitochondria-targeted vitamin E derivatives with a range of alkyl linkers gave compounds of different hydrophobicities. This work will enable the dependence of antioxidant defence on hydrophobicity to be determined in vivo.

Reducing the Oxidation Level of Dextran Aldehyde in a Chitosan/Dextran-Based Surgical Hydrogel Increases Biocompatibility and Decreases Antimicrobial Efficacy.

A highly oxidized form of a chitosan/dextran-based hydrogel (CD-100) containing 80% oxidized dextran aldehyde (DA-100) was developed as a post-operative aid, and found to significantly prevent adhesion formation in endoscopic sinus surgery (ESS). However, the CD-100 hydrogel showed moderate in vitro cytotoxicity to mammalian cell lines, with the DA-100 found to be the cytotoxic component. In order to extend the use of the hydrogel to abdominal surgeries, reformulation using a lower oxidized DA (DA-25) was pursued. The aim of the present study was to compare the antimicrobial efficacy, in vitro biocompatibility and wound healing capacity of the highly oxidized CD-100 hydrogel with the CD-25 hydrogel. Antimicrobial studies were performed against a range of clinically relevant abdominal microorganisms using the micro-broth dilution method. Biocompatibility testing using human dermal fibroblasts was assessed via a tetrazolium reduction assay (MTT) and a wound healing model. In contrast to the original DA-100 formulation, DA-25 was found to be non-cytotoxic, and showed no overall impairment of cell migration, with wound closure occurring at 72 h. However, the lower oxidation level negatively affected the antimicrobial efficacy of the hydrogel (CD-25). Although the CD-25 hydrogel's antimicrobial efficacy and anti-fibroblast activity is decreased when compared to the original CD-100 hydrogel formulation, previous in vivo studies show that the CD-25 hydrogel remains an effective, biocompatible barrier agent in the prevention of postoperative adhesions.

Metal-induced isomerization of a molecular strand containing contradictory dynamic coordination sites.

A new hydroxymethyl terminated pyrimidine-hydrazone (pym-hyz) ligand (L1) was synthesized with a central hyz-pyridine-hyz (hyz-py-hyz) motif replacing the usual hyz-pym-hyz unit, to create a molecular strand that underwent metal-induced isomerization with a minimal net change in ligand length. NMR spectroscopy showed that L1 had a horseshoe shape due to the hyz-py-hyz and pym-hyz bonds adopting transoid conformations. The ligand was successfully reacted with Pb(II), Zn(II), and Ag(I) salts in either CH3CN or CH3NO2 resulting in horseshoe-shaped M(n+)3L1A3n (where A = ClO4(-) or SO3CF3(-)) complexes in the solution phase. Crystals were grown from these solutions, the structures of which were highly dependent on the metal ion and solvent used, and were distinctly different from those seen in solution. The crystals grown from mixtures of Pb(ClO4)2·3H2O and L1 in either CH3CN or CH3NO2 resulted in the horseshoe-shaped [Pb3L1(ClO4)4(H2O)2](ClO4)2·CH3CN (1) complex or the {[Pb3L1(ClO4)4(H2O)](ClO4)2}∞·CH3NO2 (2) helical coordination polymer, respectively. The horseshoe-shaped [Pb3L1(SO3CF3)6]·CH3CN (3) complex was crystallized from a solution of Pb(SO3CF3)2·H2O and L1 in CH3CN, while the crystals grown from the solution of Zn(SO3CF3)2 and L1 in CH3CN consisted of the zigzag-shaped [Zn3L1(H2O)7](SO3CF3)6 (4) complex. The [Ag3(L1)2](SO3CF3)3 (5) double-helicate and the macrocycle-like [Ag6(L1)2](SO3CF3)6 (6) complex were crystallized from solutions of AgSO3CF3 and L1 in either CH3CN or CH3NO2, respectively.

Synthesis, physiochemical characterization, and biocompatibility of a chitosan/dextran-based hydrogel for postsurgical adhesion prevention.

An amine-functionalized succinyl chitosan and an oxidized dextran were synthesized and mixed in aqueous solution to form an in situ chitosan/dextran injectable, surgical hydrogel for adhesion prevention. Rheological characterization showed that the rate of gelation and moduli were tunable based on amine and aldehyde levels, as well as polymer concentrations. The CD hydrogels have been shown to be effective post-operative aids in prevention of adhesions in ear, nose, and throat surgeries and abdominal surgeries in vivo. In vitro biocompatibility testing was performed on CD hydrogels containing one of two oxidized dextrans, an 80 % oxidized (CD-100) or 25 % (CD-25) oxidized dextran. However, the CD-100 hydrogel showed moderate cytotoxicity in vitro to Vero cells. SC component of the CD hydrogel, however, showed no cytotoxic effect. In order to increase the biocompatibility of the hydrogel, a lower aldehyde level hydrogel was developed. CD-25 was found to be non-cytotoxic to L929 fibroblasts. The in vivo pro-inflammatory response of the CD-25 hydrogel, after intraperitoneal injection in BALB/c mice, was also determined by measuring serum TNF-α levels and by histological analysis of tissues. TNF-α levels were similar in mice injected with CD-25 hydrogel as compared to the negative saline injected control; and were significantly different (P < 0.05) as compared to the positive, lipopolysaccharide, injected control. Histological examination revealed no inflammation seen in CD hydrogel injected mice. The results of these in vitro and in vivo studies demonstrate the biocompatibility of the CD hydrogel as a post-operative aid for adhesion prevention.

Crystal structure of 4-(prop-2-yn-yloxy)-2,2,6,6-tetra-methyl-piperidin-1-ox-yl.

The title compound, C12H20NO2, was synthesized from 4-hy-droxy-2,2,6,6-tetra-methyl-piperidin-1-oxyl (hy-droxy-TEMPO) and propargyl bromide. The six-membered ring adopts a flattened chair conformation and carries a propyn-yloxy substituent in an equatorial orientation at the 4-position. The N-O bond length of the piperidin-1-oxyl unit is 1.289 (3) Å. In the crystal, C-H⋯O hydrogen bonds combine with unusual C-H⋯π inter-actions involving the alkyne unit as acceptor to generate a three-dimensional network.

Influence of terminal acryloyl arms on the coordination chemistry of a ditopic pyrimidine-hydrazone ligand: comparison of Pb(II), Zn(II), Cu(II), and Ag(I) complexes.

A new ditopic pyrimidine-hydrazone ligand, 6-hydroxymethylacryloyl-2-pyridinecarboxaldehyde, 2,2'-[2,2'-(2-methyl-4,6-pyrimidinediyl)bis(1-methylhydrazone)] (L2), was synthesized with terminal acryloyl functional groups to allow incorporation into copolymer gel actuators. NMR spectroscopy was used to show that L2 adopted a horseshoe shape with transoid-transoid pym-hyz-py linkages. Metal complexation studies were performed with L2 and salts of Pb(II), Zn(II), Cu(II), and Ag(I) ions in CH3CN in a variety of metal to ligand ratios. Reacting L2 with an excess amount of any of the metal ions resulted in linear complexes where the pym-hyz-py linkages were rotated to a cisoid-cisoid conformation. NMR spectroscopy showed that the acryloyl arms of L2 did not interact with the bound metal ions in solution. Seven of the linear complexes (1-7) were crystallized and analyzed by X-ray diffraction. Most of these complexes (4-7) also showed no coordination between the acryloyl arms and the metal ions; however, complexes 1-3 showed some interactions. Both of the acryloyl arms were coordinated to Pb(II) ions in [Pb2L2(SO3CF3)4] (1), one through the carbonyl oxygen donor and the other through the alkoxy oxygen donor. One of the acryloyl arms of [Cu2L2(CH3CN)3](SO3CF3)4 (2) was coordinated to one of the Cu(II) ions through the carbonyl oxygen donor. There appeared to be a weak association between the alkoxy donors of the acryloyl arms and the Pb(II) ions of [Pb2L2(ClO4)4]·CH3CN (3). Reaction of excess AgSO3CF3 with L2 was repeated in CD3NO2, resulting in crystals of {[Ag7(L2)2(SO3CF3)6(H2O)2] SO3CF3}∞ (8), the polymeric structure of which resulted from coordination between the carbonyl donors of the acryloyl arms and the Ag(I) ions. In all cases the coordination and steric effects of the acryloyl arms did not inhibit isomerization of the pym-hyz bonds of L2 or the core shape of the linear complexes.

[Fe2L3]4⁺ cylinders derived from bis(bidentate) 2-pyridyl-1,2,3-triazole "click" ligands: synthesis, structures and exploration of biological activity.

A series of metallosupramolecular [Fe2L3](BF4)4 "click" cylinders have been synthesized in excellent yields (90%-95%) from [Fe(H2O)6](BF4)2 and bis(bidentate) pyridyl-1,2,3-triazole ligands. All complexes were characterized by elemental analysis, IR, UV-vis, ¹H-, ¹³C- and DOSY-NMR spectroscopies and, in four cases, the structures confirmed by X-ray crystallography. Molecular modeling indicated that some of these "click" complexes were of similar size and shape to related biologically active pyridylimine-based iron(II) helicates and suggested that the "click" complexes may bind both duplex and triplex DNA. Cell-based agarose diffusion assays showed that the metallosupramolecular [Fe2L3](BF4)4 "click" cylinders display no antifungal activity against S. cerevisiae. This observed lack of antifungal activity appears to be due to the poor stability of the "click" complexes in DMSO and biological media.

Similarities and differences in the structures of 5-bromo-6-hydroxy-7,8-dimethylchroman-2-one and 6-hydroxy-7,8-dimethyl-5-nitrochroman-2-one.

The title compounds, C11H11BrO3, (I), and C11H11NO5, (II), respectively, are derivatives of 6-hydroxy-5,7,8-trimethylchroman-2-one substituted at the 5-position by a Br atom in (I) and by a nitro group in (II). The pyranone rings in both molecules adopt half-chair conformations, and intramolecular O-H···Br [in (I)] and O-H···O(nitro) [in (II)] hydrogen bonds affect the dispositions of the hydroxy groups. Classical intermolecular O-H···O hydrogen bonds are found in both molecules but play quite dissimilar roles in the crystal structures. In (I), O-H···O hydrogen bonds form zigzag C(9) chains of molecules along the a axis. Because of the tetragonal symmetry, similar chains also form along b. In (II), however, similar contacts involving an O atom of the nitro group form inversion dimers and generate R2(2)(12) rings. These also result in a close intermolecular O···O contact of 2.686 (4) Å. For (I), four additional C-H···O hydrogen bonds combine with π-π stacking interactions between the benzene rings to build an extensive three-dimensional network with molecules stacked along the c axis. The packing in (II) is much simpler and centres on the inversion dimers formed through O-H···O contacts. These dimers are stacked through additional C-H···O hydrogen bonds, and further weak C-H···O interactions generate a three-dimensional network of dimer stacks.

Antimicrobial properties of a chitosan dextran-based hydrogel for surgical use.

A chitosan dextran-based (CD) hydrogel, developed for use in endoscopic sinus surgery, was tested for antimicrobial activity in vitro against a range of pathogenic microorganisms. The microdilution technique was used to determine minimum inhibitory, minimum bactericidal, and minimum fungicidal concentrations. In addition, the time-kill efficacy of CD hydrogel was determined for two bacterial species. Scanning and transmission electron microscopy were carried out to elucidate the antimicrobial mechanism of this compound. CD hydrogel was found to be effective against Staphylococcus aureus, Streptococcus pyogenes, Escherichia coli, and Clostridium perfringens at its surgical concentration of 50,000 mg/liter. Minimum bactericidal concentrations ranged from 2,000 to 50,000 mg/liter. Dextran aldehyde (DA) was found to be the antimicrobial component of the CD hydrogel with MBC ranging from 2,000 to 32,000 mg/liter. S. aureus appeared to be killed at a slightly faster rate than E. coli. Candida albicans and Pseudomonas aeruginosa were more resistant to CD hydrogel and DA. Scanning and transmission electron microscopy of E. coli and S. aureus incubated with CD hydrogel and DA alone revealed morphological damage, disrupted cell walls, and loss of cytosolic contents, compatible with the proposed mode of action involving binding to cell wall proteins and disruption of peptide bonds. Motility and chemotaxis tests showed E. coli to be inhibited when incubated with DA. The antibacterial activity of CD hydrogel may make it a useful postsurgical aid at other body sites, especially where there is a risk of Gram-positive infections.

Sensitivity of silver(I) complexes of a pyrimidine-hydrazone ligand to solvent, counteranion, and metal-to-ligand ratio changes.

Metal complexation studies were performed with AgSO(3)CF(3) and AgBF(4) and the ditopic pyrimidine-hydrazone ligand 6-(hydroxymethyl)pyridine-2-carboxaldehyde (2-methylpyrimidine-4,6-diyl)bis(1-methylhydrazone) (1) in both CH(3)CN and CH(3)NO(2) in a variety of metal-to-ligand ratios. The resulting complexes were studied in solution by NMR spectroscopy and in the solid state by X-ray crystallography. Reacting either AgSO(3)CF(3) or AgBF(4) with 1 in either CH(3)CN or CH(3)NO(2) in a 1:1 metal-to-ligand ratio produced a double helicate in solution. This double helicate could be converted into a linear complex by increasing the metal-to-ligand ratio; however, the degree of conversion depended on the solvent and counteranion used. Attempts to crystallize the linear AgSO(3)CF(3) complex resulted in crystals with the dimeric structure [Ag(2)1(CH(3)CN)(2)](2)(SO(3)CF(3))(4) (2), while attempts to crystallize the AgSO(3)CF(3) double helicate from CH(3)CN resulted in crystals of another dimeric complex, [Ag(2)1(SO(3)CF(3))(CH(3)CN)(2)](2)(SO(3)CF(3))(2)·H(2)O (3). The AgSO(3)CF(3) double helicate was successfully crystallized from a mixture of CH(3)CN and CH(3)NO(2) and had the structure [Ag(2)1(2)](SO(3)CF(3))(2)·3CH(3)NO(2) (4). The linear AgBF(4) complex could not be isolated from the double helicate in solution; however, crystals grown from a solution containing both the AgBF(4) double helicate and linear complexes in CH(3)CN had the structure [Ag(2)1(CH(3)CN)(2)](BF(4))(2) (5). The AgBF(4) double helicate could only be crystallized from CH(3)NO(2) and had the structure [Ag(2)1(2)](BF(4))(2)·2CH(3)NO(2) (6).

4,5-Dihydro-cyclo-penta-[b]thio-phen-6-one.

The title compound, C(7)H(6)OS, crystallizes with two similar mol-ecules, 1 and 2, in the asymmetric unit. Both mol-ecules are essentially planar with r.m.s. deviations of 0.0193 and 0.0107 Šfor the planes through the nine non-H atoms of mol-ecules 1 and 2, respectively. The thio-phene and 4,5-dihydro-cyclo-penta-dienone rings are inclined at 2.40 (13)° in 1 and 0.64 (13)° in 2. In the crystal structure π-π [3.6542 (17) Å] and C-H⋯π contacts stack the mol-ecules into columns in an inverse fashion along the b axis. An extensive series of C-H⋯O hydrogen bonds links the columns, generating an extended network structure.

6-Hy-droxy-7,8-dimethyl-chroman-2-one.

The title compound, C(11)H(12)O(3), is essentially planar, with an r.m.s. deviation of 0.179 Šfrom the mean plane through the 14 non-H atoms in the mol-ecule. The benzene ring and the pyranone mean plane are inclined at 13.12 (6)° to one another and the pyran-one ring adopts a flattened chair conformation. In the crystal, O-H⋯O hydrogen bonds and C-H⋯O contacts form R(1) (2)(6) rings and link mol-ecules into chains along b. Additional C-H⋯O contacts generate inversion dimers, with R(2) (2)(8) ring motifs, and form sheets parallel to (-102) which are linked by C-H⋯π interactions.

5,6-Dimethyl-1,2,9,10-tetra-hydro-pyrano[3,2-f]chromene-3,8-dione.

The title mol-ecule, C(14)H(14)O(4), lies on a twofold rotation axis that bis-ects the central benzene ring, with only one half-mol-ecule in the asymmetric unit. The pyran-one systems adopt distorted twist- boat conformations, with the two methyl-ene C atoms displaced by 0.537 (1) and 0.163 (2) Šfrom the best-fit plane through the remaining five C and O atoms (r.m.s. deviation = 0.073 Å). In the crystal, bifurcated C-H⋯(O,O) hydrogen bonds link pairs of adjacent mol-ecules in an obverse fashion, stacking mol-ecules along c. These contacts are further stabilized by very weak π-π inter-actions between adjacent benzene rings with centroid-centroid distances of 4.1951 (4) Å. Additional C-H⋯O contacts link these stacks, giving a three-dimensional network.

Metal ion-controlled self-assembly using pyrimidine hydrazone molecular strands with terminal hydroxymethyl groups: a comparison of Pb(II) and Zn(II) complexes.

Metal complexation studies were performed with the ditopic pyrimidine-hydrazone (pym-hyz) strand 6-hydroxymethylpyridine-2-carboxaldehyde (2-methyl-pyrimidine-4,6-diyl)bis(1-methylhydrazone) (1) and Pb(ClO(4))(2)·3H(2)O, Pb(SO(3)CF(3))(2)·H(2)O, Zn(SO(3)CF(3))(2), and Zn(BF(4))(2) to examine the ability of 1 to form various supramolecular architectures. X-ray crystallographic and NMR studies showed that coordination of the Pb(II) salts with 1 on a 2:1 metal/ligand ratio in CH(3)CN and CH(3)NO(2) resulted in the linear complexes [Pb(2)1(ClO(4))(4)] (2), [Pb(2)1(ClO(4))(3)(H(2)O)]ClO(4) (3), and [Pb(2)1(SO(3)CF(3))(3)(H(2)O)]SO(3)CF(3) (4). Two unusually distorted [2 × 2] grid complexes, [Pb1(ClO(4))](4)(ClO(4))(4) (5) and [Pb1(ClO(4))](4)(ClO(4))(4)·4CH(3)NO(2) (6), were formed by reacting Pb(ClO(4))(2)·6H(2)O and 1 on a 1:1 metal/ligand ratio in CH(3)CN and CH(3)NO(2). These grids formed despite coordination of the hydroxymethyl arms due to the large, flexible coordination sphere of the Pb(II) ions. A [2 × 2] grid complex was formed in solution by reacting Pb(SO(3)CF(3))(2)·H(2)O and 1 on a 1:1 metal/ligand ratio in CH(3)CN as shown by (1)H NMR, microanalysis, and ESMS. Reacting the Zn(II) salts with 1 on a 2:1 metal/ligand ratio gave the linear complexes [Zn(2)1(H(2)O)(4)](SO(3)CF(3))(4)·C(2)H(5)O (7) and [Zn(2)1(BF(4))(H(2)O)(2)(CH(3)CN)](BF(4))(3)·H(2)O (8). (1)H NMR studies showed the Zn(II) and Pb(II) ions in these linear complexes were labile undergoing metal ion exchange. All of the complexes exhibited pym-hyz linkages in their cisoid conformation and binding between the hydroxymethyl arms and the metal ions. No complexes were isolated from reacting either of the Zn(II) salts with 1 on a 1:1 metal/ligand ratio, due to the smaller size of the Zn(II) coordination sphere as compared to the much larger Pb(II) ions.

6-Hy-droxy-5,7,8-trimethyl-chroman-2-one.

The title compound, C(12)H(14)O(3), consists of a chromanone unit with an -OH substituent at the 4-position and methyl substituents on the remaining C atoms of the aromatic ring. The fused pyran-one ring adopts a distorted envelope conformation with the methyl-ene group adjacent to the carbonyl carbon as the flap atom. The crystal structure is stabilized by classical O-H⋯O hydrogen bonds and weak C-H⋯O and C-H⋯π inter-actions, generating a three-dimensional network.

N-(1-Acryloyl-2,2,6,6-tetra-methyl-piperidin-4-yl)acryl-amide.

The title compound, C(15)H(24)N(2)O(2), crystallizes with two unique mol-ecules, (I) and (II), in the asymmetric unit, differing in the orientation of the acryloyl units with respect to the piperidine rings. The acryl-amide units are essentially planar in both mol-ecules (r.m.s. deviations = 0.042 and 0.024 Å, respectively), as are the C(3)N chains of the acryloyl units. The carbonyl O atoms of the acryloyl systems lie significantly out of these planes, viz. by -0.171 (9) Šfor molecule (I) and by 0.33 (1) Šfor molecule (II). The acryl-amide and acryloyl planes are inclined at 68.7 (4)° and 59.8 (3)° in the two mol-ecules. The piperidine rings each adopt twist boat conformations. In the crystal, strong N-H⋯O hydrogen bonds link the mol-ecules into zigzag C(4) chains along b. Additional C-H⋯O contacts result in the formation of stacks along a.