Multi-technique structural analysis of zinc carboxylates (soaps).

A series of medium- and long-chain zinc carboxylates (zinc octanoate, zinc nonanoate, zinc decanoate, zinc undecanoate, zinc dodecanoate, zinc pivalate, zinc stearate, zinc palmitate, zinc oleate, and zinc azelate) was analyzed by ultra-high-field Zn NMR spectroscopy up to 35.2 T, as well as C NMR and FTIR spectroscopy. We also report the single-crystal X-ray diffraction structures of zinc nonanoate, zinc decanoate, and zinc oleate-the first long-chain carboxylate single-crystals to be reported for zinc.

Nano- to microscale three-dimensional morphology relevant to transport properties in reactive porous composite paint films.

The quantitative evaluation of the three-dimensional (3D) morphology of porous composite materials is important for understanding mass transport phenomena, which further impact their functionalities and durability. Reactive porous paint materials are composites in nature and widely used in arts and technological applications. In artistic oil paintings, ambient moisture and water and organic solvents used in conservation treatments are known to trigger multiple physical and chemical degradation processes; however, there is no complete physical model that can quantitatively describe their transport in the paint films.

Review of the use of NMR spectroscopy to investigate structure, reactivity, and dynamics of lead soap formation in paintings.

Heavy metal carboxylate or soap formation is a widespread deterioration problem affecting oil paintings and other works of art bearing oil-based media. Lead soaps are prevalent in traditional oil paintings because lead white was the white pigment most frequently chosen by old masters for the paints and in some cases for the ground preparations, until the development of other white pigments from approximately the middle of the 18th century on, and because of the wide use of lead-tin yellow. In the latter part of the 19th century, lead white began to be replaced by zinc white.

Molecular dynamics of palmitic acid and lead palmitate in cross-linked linseed oil films: Implications from deuterium magnetic resonance for lead soap formation in traditional oil paintings.

Many oil paintings, dating from the 15th century to the present, are affected by the formation of heavy-metal carboxylates (soaps) that alter the structural integrity and appearance of the works. Through transport phenomena not yet understood, free fatty acids formed from oils used as binders migrate through the paint film and react with heavy-metal ions that are constituents of pigments and/or driers, forming metal carboxylates. The local molecular dynamics of fatty acids and metal carboxylates are factors influencing material transport in these systems.

Elemental and Molecular Segregation in Oil Paintings due to Lead Soap Degradation.

The formation of Pb, Zn, and Cu carboxylates (soaps) has caused visible deterioration in hundreds of oil paintings dating from the 15th century to the present. Through transport phenomena not yet understood, free fatty acids in the oil binding medium migrate through the paint and react with pigments containing heavy metals to form soaps. To investigate the complex correlation among the elemental segregation, types of chemical compounds formed, and possible mechanisms of the reactions, a paint sample cross-section from a 15th century oil painting was examined by synchrotron X-ray techniques.

DNP-enhanced ultrawideline Pb solid-state NMR spectroscopy: an application to cultural heritage science.

Dynamic nuclear polarization (DNP) is used to enhance the (ultra)wideline Pb solid-state NMR spectra of lead compounds of relevance in the preservation of cultural heritage objects. The DNP SSNMR experiments enabled, for the first time, the detection of the basic lead carbonate phase of the lead white pigment by Pb SSNMR spectroscopy. Variable-temperature experiments revealed that the short T' relaxation time of the basic lead carbonate phase hinders the acquisition of the NMR signal at room temperature.

Coordination geometry of lead carboxylates - spectroscopic and crystallographic evidence.

Despite their versatility, only a few single-crystal X-ray structures of lead carboxylates exist, due to difficulties with solubility. In particular, the structures of long-chain metal carboxylates have not been reported. The lone electron pair in Pb(ii) can be stereochemically active or inactive, leading to two types of coordination geometries commonly referred to as hemidirected and holodirected structures, respectively.

207Pb and 119Sn solid-state NMR and relativistic density functional theory studies of the historic pigment lead-tin yellow type I and its reactivity in oil paintings.

Lead soaps (lead carboxylates) have been detected in traditional oil paintings in layers containing the pigment lead-tin yellow type I (LTY-I). LTY-I has been used by artists from at least the second quarter of the 15th century until the first half of the 18th century. Soap formation can lead to protrusions in paint layers and increased transparency, causing the paint support to become visible.

Nuclear magnetic resonance spectra and (207)Pb chemical-shift tensors of lead carboxylates relevant to soap formation in oil paintings.

Soap formation in traditional oil paintings occurs when heavy-metal-containing pigments, such as lead white, 2PbCO3·Pb(OH)2, and lead tin yellow type I, Pb2SnO4, react with fatty acids in the binding medium. These soaps may form aggregates that can be 100-200 μm in diameter, which swell and protrude through the paint surface, resulting in the degradation of the paint film and damage to the integrity of the artwork. The factors that trigger soap formation and the mechanism(s) of the process are not yet well understood.

Three-dimensional structure determination of N-(p-Tolyl)-dodecylsulfonamide from powder diffraction data and validation of structure using solid-state NMR spectroscopy.

The three-dimensional structure, conformation, and packing of molecules in the solid state are crucial components used in the optimization of many technologically useful materials properties. Single-crystal X-ray diffraction is the traditional and most effective method of determining 3-D structures in the solid state. Obtaining single crystals that are sufficiently large and free of imperfections is often laborious, time-consuming, and, occasionally, impossible.

Elucidation of the chain conformation in a glassy polyester, PET, by two-dimensional NMR.

The chain conformation of glassy poly(ethylene terephthalate) (PET) was characterized by two-dimensional double-quantum nuclear magnetic resonance (NMR). In amorphous carbon-13-labeled PET, the statistics of the O-13CH2-13CH2-O torsion angle were determined, on the basis of the distinct shapes of the two-dimensional NMR patterns of trans and gauche conformations. In crystalline PET, the trans content is 100 percent, but in the amorphous PET it is only 14 percent (+/-5 percent).

A simple model for deuterium cross-polarization magic-angle spinning nuclear magnetic resonance at the interphases of amorphous materials.

The structure and composition of the interphase at the boundary of two immiscible phases has long been the subject of experimental and theoretical studies in polymer science. Cross-polarization between protons and deuterons offers the potential for elucidating the composition of the interphase if one of the immiscible phases is deuterated. A prerequisite for such an analysis is the establishment of an experimental protocol for reliable spin counting in 1H-2H cross-polarization magic-angle spinning (CP-MAS) spectroscopy.

EPR and 1H and 13C dynamic nuclear polarization studies of a molecularly doped polymer: bisphenol A polycarbonate doped with trianisylamine and trianisylaminium perchlorate.

We have investigated the EPR and DNP behavior of a molecularly doped polymer modeling those used to transport electronic charge in electrophotography. The EPR spectra show no evidence of the superexchange reported for a closely related system based on tri-p-tolylamine. The difference may be due to larger charge-transfer matrix elements in the latter system.

Sodium ion binding in human serum.

The amount of sodium ion binding in human sera and in dialyzed human sera was estimated from standard-addition titrations with an ion-selective electrode and from measurements of 23Na nuclear magnetic resonance (NMR) linewidth. For the untreated sera, maximum binding was 1% (1.4 mmol/L) as indicated by NMR; virtually no binding was found via the titration method.

Human conjugated bilirubin--isolation, biosynthesis, and direct molecular characterization.

We prepared human conjugated bilirubin by isolation from fresh gall bladder bile and by biosynthesis using liver homogenates. The isolation protocol was modified after Lucassen (doctoral thesis, Univ. Utrecht, 1961), and the in vitro synthesis was done with fresh liver homogenates in the presence of D-glucaro-1,4-lactone (a glucuronidase inhibitor).

Proton and carbon-13 nuclear magnetic resonance studies of rhodopsin-phospholipid interactions.

Proton and carbon-13 nuclear magnetic resonance (1H and 13C NMR) spectra of rhodopsin-phospholipid membrane vesicles and sonicated disk membranes are presented and discussed. The presence of rhodopsin in egg phosphatidylcholine vesicles results in homogeneous broadening of the methylene and methyl resonances. This effect is enhanced with increasing rhodopsin content and decreased by increasing temperature.

Light-regulated permeability of rhodopsin:egg phosphatidylcholine recombinant membranes.

Purified rhodopsin was incorporated into phospholipid bilayers of egg phosphatidylcholine to give recombinant membrane vesicles, which were examined by proton and phosphorus nuclear magnetic resonance spectroscopy. Increased rhodopsin content in the membranes appears to progressively inhibit the molecular motions of the methyl, methylene, and phosphate groups of the phospholipid molecules. This indicates that regions of the rhodopsin molecule interact in a manner that affects the phospholipids from the aqueous interface to the bilayer midline.

Proton relaxation and charge accumulation during oxygen evolution in photosynthesis.

The water proton spin-spin (transverse) relaxation rate of chloroplast suspensions has been measured after each of a series of 2.4 musec light flashes. The sequence of relaxation rates shows a damped oscillatory pattern with a period of four and peaks after the 3rd, 7th, 11th, and 15th flashes.

Water proton relaxation as a monitor of membrane-bound manganese in spinach chloroplasts.

First measurements of proton relaxation on chloroplast membranes are presented here. Experiments show that the water proton spin-lattice relaxation rate in chloroplast thylakoid membrane suspensions can be used to monitor membrane-bound manganese. The relaxation effect is reduced to 0.