A novel approach to the retrieval of structural and dynamic information from residual dipolar couplings using several oriented media in biomolecular NMR spectroscopy

The interpretation of residual dipolar couplings in terms of molecular properties of interest is complicated because of difficulties in separating structural and dynamic effects as well as the need to estimate alignment tensor parameters a priori. An approach is introduced here that allows many of these difficulties to be circumvented when data are acquired in multiple alignment media. The method allows the simultaneous extraction of both structural and dynamic information directly from the residual dipolar coupling data, in favorable cases even in the complete absence of prior structural knowledge. Application to the protein ubiquitin indicates greater amplitudes of internal motion than expected from traditional (15)N spin relaxation analysis.     

Magnetically Induced Alignment of Natural Products for Stereochemical Structure Determination via NMR

Anisotropic NMR has gained increasing popularity to determine the structure and specifically the configuration of small, flexible, non‐crystallizable molecules. However, it suffers from the necessity to dissolve the analyte in special media such as liquid crystals or polymer gels. Generally, small degrees of alignment are also caused by an anisotropic magnetic susceptibility of the molecule, for example, induced by aromatic moieties. For this mechanism, the alignment can be predicted via density functional theory. Here we show that both residual dipolar couplings and residual chemical shift anisotropies can be acquired from natural products without special sample preparation using magnetically induced alignment. On the two examples of the novel natural product gymnochrome G and the alkaloid strychnine, these data, together with the predicted alignment, yield the correct configuration with high certainty.     

Determination of spin-spin couplings from ultrahigh resolution 3D NMR spectra obtained by optimized random sampling and multidimensional Fourier transformation

An example of precise evaluation of backbone scalar J couplings using random sampling of evolution time space in 3D NMR experiments is presented. The recorded spectrum, due to violation of the Nyquist theorem limitation, exhibits ultrahigh resolution in indirect dimensions compared to standard NMR experiment acquired at the same time. The obtained results enable simple and accurate evaluation of scalar and residual dipolar couplings from a single multidimensional NMR experiment.     

On line photochemically induced excitation-emission-kinetic four-way data: analytical application for the determination of folic acid and its two main metabolites in serum by U-PLS and N-PLS/residual trilinearization (RTL) calibration

The determination of folic acid and its two main serum metabolites, 5-methyltetrahydrofolic acid and tetrahydrofolic acid, has been accomplished using four-way data modelled by the third-order multivariate calibration methods unfolded and N-dimensional partial least-squares (U-PLS and N-PLS), in combination with the separate procedure known as residual trilinearization (RTL). The four-way data were acquired by following the photochemical reaction of these compounds by on line irradiation with a UV lamp. The excitation-emission matrices (EEMs) were recorded as a function of the irradiation time, using a fast scanning spectrofluorimeter. The method achieves selectivity from the different rates at which the corresponding photoproducts of the folic acid derivatives are formed and degraded. Several N-dimensional chemometric algorithms were used and the method was applied to the determination of these compounds in serum samples. The best algorithms to perform the multivariate calibration were U-PLS and N-PLS in combination with the separate residual trilinearization procedure, achieving the second-order advantage. The approach allows minimizing or eliminating traditionally time-consuming sample pre-treatments and can facilitate quantifying an analyte in its native environment.     

Relaxation of Chain Extension of Amorphous PET Fiber Above the Glass Transition Temperature

The average relaxation time for segmental orientation is considerably shorter than that for chain extension1,2, due to the difference of the ability to move between segments and chains. So in certain time intervals, an almost total relaxation of the segmental orientation can take place with little relaxation of global chain extension. Under the controlled conditions1,3, high global chain orientation but nearly random segmental orientation (GOLR) state can be achieved. Through the hot shrinka…     

Constitutive modeling of polymers accounting for their hyperelasticity,plasticity, creep and viscoelastic relaxation

The hyperelastic Yeoh model has been generalized to account for creep, plasticity and viscoelasticity of polymers. The general tensorial model developed is applied to several rheometric situations: the tensile test used to measure the stress-strain curve in tension, as well as the creep and recovery tests. The resulting equations are compared to the experimental results acquired in the present work for several monolithic synthetic fibers used as specimens. The comparison revealed that the proposed phenomenological rheological constitutive equation is capable of reproducing the experimental data with a uniformly valid set of physical parameters. Moreover, it was possible to accurately predict the residual plastic deformation of the fibers.     

Cure Degree Estimation of Photocurable Coatings by DSC and Differential Photocalorimetry

Radiation-curable coatings have acquired importance, because they are environmentally-friendly (no solvent emission)and require low energy for curing, when compared to other conventional heat-curable products. UV-curable coatings performance depends on the cure quality. Suitable methods were evaluated to estimate the degree of cure applying quantitative techniques, such as differential scanning calorimetry (DSC) and differential photocalorimetry (DPC), in order to determine the residual heat of curing in UV-cured films. The results of the DPC technique showed better sensibility than DSC technique, although the use of suitable pans for the case of clear coats must be considered. This revised version was published online in July 2006 with corrections to the Cover Date.     

Employing the fluorescence anisotropy and quenching kinetics of tryptophan to hunt for residual structures in denatured proteins

Residual structures in denatured proteins have acquired importance in recent years owing to their role as protein-folding initiation sites. Locating these structures in proteins has proved quite formidable, requiring techniques like NMR. Here in this report, we take advantage of the ubiquitous presence of tryptophan residues in residual structures to hunt for their presence using steady-state fluorescence spectroscopy. The surface accessibility and rotational dynamics of tryptophan in putative residual structures among ten different proteins, namely glucagon, melittin, subtilisin carlsberg, myelin basic protein, ribonuclease T₁, human serum albumin, barstar mutant, bovine serum albumin, lysozyme and Trp-Met-Asp-Phe-NH₂ peptide, was studied using steady state fluorescence quenching and anisotropy, respectively. Five proteins, namely ribonuclease T₁, bovine serum albumin, melittin, barstar and hen egg white lysozyme appear likely to possess tryptophan(s) in hydrophobic clusters based on their reduced bimolecular quenching rates and higher steady-state anisotropy in proportion to their chain length. We also show that the fluorescence emission maximum of tryptophan is insensitive to the presence of residual structures.     

De novo peptide sequencing using exhaustive enumeration of peptide composition

We introduce the use of a peptide composition lookup table indexed by residual mass and number of amino acids for de novo sequencing of polypeptides. Polypeptides of 1600 Daltons (Da) or more can be sequenced effectively through exhaustive compositional analysis of MS/MS spectra obtained by unimolecular decomposition (without CID) in a MALDI TOF/TOF despite a fragment mass accuracy of 50 mDa. Peaks are referenced against the lookup table to obtain a complete profile of amino acid combinations, and combinations are assembled into series of increasing length. Concatenating the differences between successive entries in compositional series yields peptide sequences that can be scored and ranked according to signal intensity. While the current work involves measurements acquired on MALDI TOF-TOF, such general treatment of the data anticipates extension to other types of mass analyzers.     

Z-restored spin-echo 13C 1D spectrum of straight baseline free of hump, dip and roll

A pulse sequence of z-restored spin echo, -pi-beta-tau-pi-tau-, employing a pi pulse in the middle of the delay (2tau) to form a spin echo and the two pi pulses together to restore the residual longitudinal magnetization back to + z direction, is described. (13)C spectra of organic compounds provide a wealth of structural information; however, (13)C 1D spectra acquired using reverse geometry probes can have significant baseline humps or rolls because of pulse ring-down within the coil. The baseline distortions are especially apparent in spectra acquired using cryogenically enhanced probes. The baseline problem may be alleviated by extending the delay between the last pulse and the starting point of acquisition. However, uses of long delay times introduce large negative first-order phase corrections which themselves produce baseline roll. The prescribed experiment can be used to completely remove the hump, roll or dip in the baseline of the (13)C spectrum and at the same time obtain sensitivity similar to the experiment of a single beta pulse. We believe that this experiment will be of general applications in acquiring high-quality (13)C NMR data with reverse geometry probes and spectral interpretation.     

Computer‐Assisted 3D Structure Elucidation of Natural Products using Residual Dipolar Couplings

An enhanced computer‐assisted procedure for the determination of the relative configuration of natural products, which starts from the molecular formula and uses a combination of conventional 1D and 2D NMR spectra, and residual dipolar couplings (RDCs), is reported. Having already the data acquired (1D/2D NMR and RDCs), the procedure begins with the determination of the molecular constitution using standard computer‐assisted structure elucidation (CASE) and is followed by fully automated determination of relative configuration through RDC analysis. In the case of moderately flexible molecules the simplest data‐explaining conformational model is selected by the use of the Akaike information criterion.     

Effect of Glass Transition Temperature of Pressure Sensitive Adhesives on Light Leakage in LCD Panel

Pressure-sensitive adhesives (PSA), which mainly are made of acrylic polymers, have been used to fix optical films to liquid crystal display (LCD) cells to prevent contraction or expansion of the optical film under high temperature and high humidity conditions, while residual stress on the polarizing film is generated and light-leakage results from it in the peripheral area of an LCD panel. In this work, we prepared two different kinds of PSAs and tested light leakage with respect to T_g, verifying that T_g would have an effect on light leakage. We calculated their T_g values using the Fox equation and investigated them by DSC. Rheological properties of the PSAs were also acquired by a rotational rheometer which confirm the relation between T_g and dynamic moduli (G′ and G″). It was found that the higher the T_g, the less is an amount of light leaked.     

Comparison of PLS and kinetic models for a second-order reaction as monitored using ultraviolet visible and mid-infrared spectroscopy

A second-order reaction between benzophenone and phenylhydrazine to give benzophenone phenylhydrazone was followed using UV/vis and mid-infrared spectroscopic probes. Established kinetic (hard) and partial least squares (soft) modelling chemometrics methods were applied to both datasets in order to compare the information acquired with each probe. To this purpose, an experimental design with 25 samples and a test set with 5 samples were used to build a partial least squares calibration model to predict the concentration profiles of the compounds present in the reaction vessel. In addition, multivariate kinetic modelling was also performed on the spectroscopic data. Using a guess of the rate constant, concentration profiles were estimated. The profiles are then used to calculate the estimated spectroscopic profile, which is compared to the data acquired experimentally. The residual is minimised and the rate constant estimated; this procedure is iterated until convergence. A total of four profiles were obtained for each compound, corresponding to two sets of probes and two sets of models. The results were compared and discussed. It is shown that several different spectroscopic techniques can be used in reaction monitoring, with increasing benefits in terms of information and interpretation of the results. The profiles obtained agreed well which was also demonstrated when comparing the different rate constants obtained.     

Development and validation of an analytical method for determination of endocrine disruptor, 2,4-D, in paddy field water

The acidic herbicides are an important class of chemical compounds that are used to control a variety of weeds that threaten many crops. Owing to their low microbial activity levels, the acidic herbicides exhibit a residual activity remaining for periods of up to several months in soils and water. The principal objective of this study was to develop an analytical method based on liquid–liquid and solid‐phase extraction followed by HPLC, for the determination of 2,4‐D in paddy field water. The residues were verified via tandem mass spectrometry (MS/MS) in negative‐ion electrospray ionization (ESI) mode. Linearity was good over a concentration range of 1–100 µg/L with a correlation coefficient (r²) of 0.999. The mean recovery rates of triplicate results ranged from 85.2 to 90.85%. The limits of detection and quantitation were 0.4 and 1.0 µg/L, respectively. The method proposed herein was applied to field samples acquired from Hampyung and Sunchang counties, Republic of Korea. The analyte was detected at a concentration range of 6.8–12.8 and 3.55–24.0 µg/L, respectively. Copyright © 2010 John Wiley & Sons, Ltd.     

Constraints on fallout melt glass formation from a near-surface nuclear test

We present major element and actinide composition data from a population of fallout glass samples produced from a single near-surface nuclear detonation. Glass major element compositions indicate that composition of local geology is a primary control on bulk fallout chemical composition. Uranium isotope compositions indicate that vaporized, residual fuel was incorporated into the melts prior to solidification, likely within seconds, and are consistent with two-component mixing between naturally-occurring uranium and residual uranium fuel. Model ages of the residual fuel in fallout are systematically inaccurate, biased towards older ages, and are consistent with two-component mixing between naturally-occurring daughter nuclides in local sediment and decay-derived daughter nuclides from residual nuclear fuel. Multiple processes such as mixing, agglomeration of melted sediment-derived droplets, and incorporation of condensates must all occur within the timescale between sediment melting and melt solidification.     

Birefringence techniques for the characterization of residual stresses in injection-moulded micro-lens arrays

The presence or absence of residual stresses is a major concern in the injection moulding of plastic products used in precision optical and medical applications. Micro-lens arrays are critical components of LED displays that are produced by micro-injection moulding. Due to their small size, residual stresses in these micro-lens arrays are difficult to measure and characterize. The birefringence method was used in this paper to evaluate residual stresses in injection-moulded micro-lens arrays and the finite element simulation method was also employed to predict their distribution. Comparable results from both experiments and simulation were obtained. It is found that the mould temperature is the most significant processing parameter. The value of maximum residual stress is smaller when the mould temperature is higher. The birefringence method is applicable and efficient for the measurement of residual stress in injection-moulded plastic micro-optics.     

Homonuclear Decoupling in 1H NMR of Solids by Remote Correlation

The typical linewidths of ¹H NMR spectra of powdered organic solids at 111 kHz magic-angle spinning (MAS) are of the order of a few hundred Hz. While this is remarkable in comparison to the tens of kHz observed in spectra of static samples, it is still the key limit to the use of ¹H in solid-state NMR, especially for complex systems. Here, we demonstrate a novel strategy to further improve the spectral resolution. We show that the anti-z-COSY experiment can be used to reduce the residual line broadening of ¹H NMR spectra of powdered organic solids. Results obtained with the anti-z-COSY sequence at 100 kHz MAS on thymol, β-AspAla, and strychnine show an improvement in resolution of up to a factor of two compared to conventional spectra acquired at the same spinning rate.     

Cathodic reactivity of platinum interface in the presence of tetramethylammonium salts. A pro-base cathode material?

The cathodic charging of platinum and platinized platinum surfaces has been shown to occur to the great extent in the presence of a large palette of tetramethylammonium salts (TMAX) dissolved in dry dimethylformamide (DMF). The role of residual moisture and that of OH⁻ generated at low potential were underlined. Thus, the electrical charging stoichiometry can reach one electron per platinum atom according to a process which appeared to be quasi reversible (X=BF₄ or ClO₄). The paper stresses on dramatic surface structural changes acquired progressively during several reduction/oxidation cycles or in the course of macroelectrolyses.     

Heterogeneous nature of human complement factor B: an electrophoretic approach for the analysis of its oligosaccharide chain structure and its physiological breakdown products

Factor B is a glycoprotein which plays an essential role in the alternative pathway of complement activation. It carries the proteolytic activity of the convertases, and its physiological breakdown products Ba and Bb have some effects on the cells of the immune system. Human factor B exhibits a microheterogeneity and five isoforms are present in serum. The nature and origin of the microheterogeneity was investigated by using electrophoretic techniques. Treatments of factor B with neuraminidase and glycopeptidase F show that this microheterogeneity is mainly due to differences in its sialic acid content, varying from seven to eleven residues per molecule, and resulting in different oligosaccharide structures. However, deglycosylated factor B reveals a residual, nonallotypic variation in the Bb region of the polypeptide backbone. We confirm the presence of four asparagine-linked oligosaccharide chains of the complex type in native factor B, two of which are located in the Ba fragment, and the two others in the Bb fragment. The prevalent isoform of the native protein carries two sialic acid residues per oligosaccharide chain. Biosynthesis experiments show that the microheterogeneity of secreted factor B from HepG2 cells is acquired during the processing of its glycans. However, in vitro-secreted factor B is more heterogeneous than the serum protein. We propose a structural model for the microheterogeneity of the native protein and its physiological fragments. We discuss as well the feasibility of electrophoretic techniques to deal with microheterogeneity analysis.