Enhanced nonlinear magnetic resonance signals via square wave dipolar fields

This report introduces a new approach that enhances nonlinear solution magnetic resonance signals from intermolecular dipolar interactions. The resulting signals can theoretically be as large as the full equilibrium magnetization. Simple, readily implemented pulse sequences using square-wave magnetization modulation simultaneously refocus all even order intermolecular multiple quantum coherences, leading to a substantial net signal enhancement, complex nonlinear dynamics, and improved structural sensitivity under realistic conditions.     

Theoretical formalism and experimental verification of line shapes of NMR intermolecular multiple-quantum coherence spectra

Although the theories and potential applications of intermolecular multiple-quantum coherences (iMQCs) have been under active investigations for over a decade, discussion of iMQC NMR signal formation was mainly confined in the time domain. In this paper, a full line-shape theory was developed to describe iMQC signals in the frequency domain. Relevant features of the line shape, such as peak height, linewidth, and phase, were investigated in detail. Predictions based on the theory agree well with experimental and simulated results. Since radiation-damping effects always couple with iMQCs in highly polarized liquid-state NMR systems, and strongly radiation-damped signals have many spectral characteristics similar to those of iMQCs, a detailed comparison was also made between them from different spectral aspects. With detailed comparison of peak height, linewidth, and phase, this work demonstrates that the iMQC and radiation-damping phenomena result from two completely different physical mechanisms despite that both present similar signal features and coexist in highly polarized liquid-state NMR systems.     

Feasibility of Ultrafast High‐Resolution Spectroscopy in the Analysis of Molecular‐Mobility‐Restricted Samples in Deuterium‐Free Environments

The feasibility of ultrafast high‐resolution intermolecular multiple‐quantum coherence (UF‐iMQC) spectroscopy for the direct analysis of molecular‐mobility‐restricted samples that are not suitable for magic‐angle spinning, such as a jelly, hand soap, and marrow, is presented. Most components could be directly detected in their original state within 1 min without the need for tedious sample preparation processes. When we use conventional liquid nuclear magnetic resonance (NMR) method to study these systems, the spectral information could not be retrieved owing to the intrinsic inhomogeneous magnetic fields caused by sample inhomogeneity. In addition, the possibility for UF‐iMQC‐based quantifications is shown. The examples presented in this paper demonstrate the potential of UF iMQC NMR for food safety inspection, for quality testing of daily‐life supplies, or in assisting medical diagnosis.     

Polymerization behaviour of 2,5-dimethylene- 2,5-dihydrofuran

Spontaneous homopolymerization of 2,5-dimethylene-2,5-dihydrofuran (DDF) was studied. The polymerization rates in two different initial monomer concentrations of DDF were analyzed with the first-order and second-order kinetics, and the homopolymerization of DDF was found to obey the first-order kinetics. The Arrhenius plot of the apparent rate constants at 30, 40, 50, and 60° gave an overall activation energy of 68.0 kJ/mol for the polymerization of DDF. From the comparison of the apparent rate constants at –78° and the time (the so-called half-life time) to decrease in half the monomer concentration for DDF with the corresponding values for p-xylylene (QM), DDF was found to be a less reactive monomer than QM. The copolymerizations of DDF with vinyl monomers such as acrylonitrile (AN), α-chloroacrylonitrile (CIAN), diethyl fumarate (DEF), and fumaronitrile (FN) were carried out in chloroform at 50° in the presence of AIBN to obtain the monomer reactivity ratios r₁(DDF) = 30.0 ± 3.0 and r₂ (AN) = 0 for the DDF-AN system, r₁ (DDF) = 1.55 ± 0.2 and r₂(CIAN) = 0 for the DDF-CIAN system, r₁(DDF) = 3.88 ± 0.2 and r₂(DEF) = 0 for the DDF-DEF system, and r₁(DDF) = 2.41 ± 0.1 and r₂ (FN) = 0 for the DDF-FN system, respectively. As the monomer reactivity ratios of r₂ for all systems were zero, Q and e values of DDF were calculated from the combination of two r₁ (DDF) values of any two copolymerization systems to be the 7.64 to 6.63 ×10²¹ range for Q and the –0.70 to –6.31 range for e, indicating that DDF is a highly conjugative and electron-donating monomer. © 1995 John Wiley & Sons, Inc.     

The Reaction of 2,5-Dimethoxy-2,5-Dihydrofuran with Dichloroketene

2,5-Dimethoxy-2,5-dihydrofuran (DDF) reacts with dichloroketene to give 7,9-dimethoxy-3,3,5,5-tetrachloro-8-oxabicyclo[4,3,0]-noan-2,4-dione (I), and methyl chloro-(2,5-dihydro-5-methoxy-2-furanylidene) acetate (II). The reactions of 2,5-dihydrofuran and 2,5-dimethoxy-tetrahydrofuran with dichloroketene were also-studied for comparison. Compound II was derived from the insertion of a molecule of dichloroketene into the C-O bond of DDF with subsequent dehydrochlorination. Compound I resulted from the cycloaddition of two molecules of dichloroketene to the C=C bond of DDF. A mechanism involving a 1,5-dipolar intermediate is proposed to account for this novel reaction.     

Traveling interface modulations in the NH3 + O2 reaction on a Rh(110) surface

A new type of traveling interface modulation has been observed in the NH(3) + O(2) reaction on a Rh(110) surface. A model is set up which reproduces the effect, which is attributed to diffusional mixing of two spatially separated adsorbates causing an excitability which is strictly localized to the vicinity of the interface of the adsorbate domains.     

Application of the forward linear prediction on high-resolution NMR spectra in inhomogeneous fields

In homogeneous fields, the advantages of forward linear prediction (LP) for processing 2D NMR data sets have long been recognized. In this paper, the forward LP method was employed to obtain high-resolution NMR spectra in inhomogeneous fields. Intermolecular multiple-quantum coherence (iMQC) signals are caused by intermolecular dipolar interactions and can be used to obtain 1D high-resolution NMR spectra from the 2D iMQC spectra acquired in inhomogeneous fields. However, when the 2D spectra are acquired with insufficient increments to save experimental time, wiggles around strong peaks and bad resolution will occur. Extending the data set by forward LP in the indirect dimension is a good way to improve spectral resolution. Compared to normal discrete Fourier transform, the forward LP method can shorten experimental time by a factor of four or more at the same level of sensitivity and resolution.     

Isolation,Detection, and Antigen‐Based Profiling of Circulating Tumor Cells Using a Size‐Dictated Immunocapture Chip

Even though the diagnostic and prognostic value of circulating tumor cells (CTCs) has been demonstrated, their clinical utility and widespread adoption have been limited. Herein, we describe a new device, size‐dictated immunocapture chip (SDI‐Chip), for efficient, sensitive, and spatially resolved capture and detection of CTCs. SDI‐Chip enables selective, frequent, and extended interaction of CTCs with hydrodynamically optimized immunocoated micropillar surfaces. CTCs with different antigen expression levels can be efficiently captured and spatially resolved around the micropillars. Capture efficiency greater than 92 % with a purity of 82 % was achieved with blood samples. CTCs were detected in non‐metastasis colorectal (CRC) patients, while none was detected from healthy volunteers. We believe that SDI‐Chip will facilitate the transition of tumor diagnosis from anatomical pathology to molecular pathology in localized CRC patients.     

Isolation,Detection, and Antigen‐Based Profiling of Circulating Tumor Cells Using a Size‐Dictated Immunocapture Chip

Even though the diagnostic and prognostic value of circulating tumor cells (CTCs) has been demonstrated, their clinical utility and widespread adoption have been limited. Herein, we describe a new device, size‐dictated immunocapture chip (SDI‐Chip), for efficient, sensitive, and spatially resolved capture and detection of CTCs. SDI‐Chip enables selective, frequent, and extended interaction of CTCs with hydrodynamically optimized immunocoated micropillar surfaces. CTCs with different antigen expression levels can be efficiently captured and spatially resolved around the micropillars. Capture efficiency greater than 92 % with a purity of 82 % was achieved with blood samples. CTCs were detected in non‐metastasis colorectal (CRC) patients, while none was detected from healthy volunteers. We believe that SDI‐Chip will facilitate the transition of tumor diagnosis from anatomical pathology to molecular pathology in localized CRC patients.     

Detection and characterization of intermolecular multiple-quantum coherence NMR signals of IS (I=1/2; S=3/2) spin systems

Intermolecular multiple-quantum coherences (iMQCs) have some intrinsic properties different from conventional single-quantum coherences in solution NMR. In this paper, we extended our study to heteronuclear iMQCs in IS (I=1/2, S=3/2) spin systems. A sample of sodium chloride (NaCl) water solution was taken as an example. Heteronuclear COSY revamped by asymmetric Z-gradient echo detection (CRAZED) experiments were performed. One- and two-dimensional heteronuclear iMQC spectra were obtained. The quantum-mechanical treatment was used to deduce the signal expressions. Magic angle experiments validate that the signals are indeed from intermolecular dipolar interaction and insensitive to the imperfection of radio-frequency (RF) flip angles. Both experimental results and theoretical analysis indicate that heteronuclear CRAZED experiment allows coherence transfer from spin-3/2 nuclei to spin-1/2, and vice verse. Furthermore, the dependences of iMQC signal intensities on RF pulse flip angles follow the same rules as those for heteronuclear IS (I=1/2, S=1/2 or 1) spin systems.     

A square-wave wavelength modulation system for automatic background correction in carbon furnace atomic emission spectrometry

A square-wave wavelength modulation system, based on a rotating quartz chopper with four quadrants of different thicknesses, has been developed and evaluated as a method for automatic background correction in carbon furnace atomic emission spectrometry. Accurate background correction is achieved for the residual black body radiation (Rayleigh scatter) from the tube wall and Mie scatter from particles generated by a sample matrix and formed by condensation of atoms in the optical path. Intensity modulation caused by overlap at the edges of the quartz plates and by the divergence of the optical beam at the position of the modulation chopper has been investigated and is likely to be small.     

Spatially Resolved Quantification of Gadolinium(III)‐Based Magnetic Resonance Agents in Tissue by MALDI Imaging Mass Spectrometry after In Vivo MRI

Gadolinium(III)‐based contrast agents improve the sensitivity and specificity of magnetic resonance imaging (MRI), especially when targeted contrast agents are applied. Because of nonlinear correlation between the contrast agent concentration in tissue and the MRI signal obtained in vivo, quantification of certain biological or pathophysiological processes by MRI remains a challenge. Up to now, no technology has been able to provide a spatially resolved quantification of MRI agents directly within the tissue, which would allow a more precise verification of in vivo imaging results. MALDI imaging mass spectrometry for spatially resolved in situ quantification of gadolinium(III) agents, in correlation to in vivo MRI, were evaluated. Enhanced kinetics of Gadofluorine M were determined dynamically over time in a mouse model of myocardial infarction. MALDI imaging was able to corroborate the in vivo imaging MRI signals and enabled in situ quantification of the gadolinium probe with high spatial resolution.     

Development of Macrocyclic Mn(II)−Bispyridine Complexes as pH-Responsive Magnetic Resonance Imaging Contrast Agents

In this study, macrocyclic complexes of Mn (II) with pH-responsive relaxivities were developed. The ligands were based on the rigid MPi platform, which was composed of a triazacyclononane (TACN) macrocycle and two picolyl pendant arms. An aryl sulfonamide moiety introduced in the skeleton of MPi endowed the final Mn complex (Mn−MPA) with pH-sensitive relaxivities. Mn−MPA showed a ∼3-fold increase in longitudinal relaxivity associated with the protonation and decoordination of the sulfonamide group in an acidic environment. We found that it was feasible to tune the pH window of the complexes by choosing proper substituents on the aromatic ring or modifying on the picolyl pendants. Considering the good kinetic inertness, rapid and efficient response to pH stimuli, and easy modulation characteristics, Mn−MPAs can be considered ideal candidates for use as acidic microenvironment-specific MRI contrast agents.     

Ab initio program for treatment of related molecules. II. Integral transformation in extended systems

An integral transformation procedure is reported as a part of an ab initio program (named SYCETY) developed recently for spatially extended molecules. It is shown that all advantages of the program SYCETY can be kept. The procedure is especially suitable to transform the integrals to a localized basis set. By using the MBPT with localized basis the most important part of the correlation can be calculated even for large (spatially extended) systems.     

Recombination and transport processes in dye-sensitized solar cells investigated under working conditions

The transport and recombination of electrons in dye-sensitized TiO(2) solar cells were studied by analysis of the current and voltage response to a small square-wave light-intensity modulation. Solar cells were studied under working conditions by using potentiostatic and galvanostatic conditions. An increase in applied voltage, that is, from 0 V toward open-circuit voltage, was found to lead to faster electron transport at low light intensities, while it slowed transport at higher light intensities. This observation seems to be conflicting with the multiple trapping model with diffusive transport. An effective diffusion length at the maximum power point was calculated, and it was shown that it decreases with increasing light intensity.     

Monitoring enzyme activity using a diamagnetic chemical exchange saturation transfer magnetic resonance imaging contrast agent

Chemical exchange saturation transfer (CEST) is a new approach for generating magnetic resonance imaging (MRI) contrast that allows monitoring of protein properties in vivo. In this method, a radiofrequency pulse is used to saturate the magnetization of specific protons on a target molecule, which is then transferred to water protons via chemical exchange and detected using MRI. One advantage of CEST imaging is that the magnetizations of different protons can be specifically saturated at different resonance frequencies. This enables the detection of multiple targets simultaneously in living tissue. We present here a CEST MRI approach for detecting the activity of cytosine deaminase (CDase), an enzyme that catalyzes the deamination of cytosine to uracil. Our findings suggest that metabolism of two substrates of the enzyme, cytosine and 5-fluorocytosine (5FC), can be detected using saturation pulses targeted specifically to protons at +2 ppm and +2.4 ppm (with respect to water), respectively. Indeed, after deamination by recombinant CDase, the CEST contrast disappears. In addition, expression of the enzyme in three different cell lines exhibiting different expression levels of CDase shows good agreement with the CDase activity measured with CEST MRI. Consequently, CDase activity was imaged with high-resolution CEST MRI. These data demonstrate the ability to detect enzyme activity based on proton exchange. Consequently, CEST MRI has the potential to follow the kinetics of multiple enzymes in real time in living tissue.     

Dynamical correlations in Brownian hard rods

We analyze the time decay of small amplitude density perturbations in systems of highly packed Brownian hard rods, relaxing towards a uniform density distribution. The results of Brownian dynamics simulations and those of the deterministic dynamic density functional (DDF) theory, are contrasted with a new theoretical approach beyond the DDF assumptions. We characterize dynamical correlation modes which, having the lowest relaxation time, determine the late time evolution of the system. The spectrum of possible time decays has a continuous band structure, with pockets of discrete values, near the minima of the DDF results, where the validity of that theory appears to be well established.     

A New Method for High-Resolution NMR Spectra in Inhomogeneous Fields with Efficient Solvent Suppression

High-resolution nuclear magnetic resonance （NMR） is one of the most powerful tools for analyzing molecular structures and dynamics. Magnetic field homogeneity is required for conventional high-resolution spectra. However, there are many chemical and/or biological circumstances where the spatial homogeneities of the magnetic fields are degraded. Intense solvent signal is another obstacle for obtaining high-resolution spectra, especially in in vivo and in situ NMR spectroscopy. In this paper, a new pulse sequence based on intermolecular multiple quantum coherence （iMQC） was reported. This sequence can effectively remove the effect of magnetic field inhomogeneity and suppress the solvent signal. It can recover the spectral information such as chemical shifts, coupling constants, multiplet patterns, and relative peak areas in inhomogeneous fields. Theoretical analyses and experimental verifications are presented to demonstrate the feasibility of this method.     

Ultrasoft magnetic films investigated with Lorentz tranmission electron microscopy and electron holography.

As a tribute to the scientific work of Professor Gareth Thomas in the field of structure-property relationships this paper delineates a new possibility of Lorentz transmission electron microscopy (LTEM) to study the magnetic properties of soft magnetic films. We show that in contrast to the traditional point of view, not only does the direction of the magnetization vector in nano-crystalline films make a correlated small-angle wiggling, but also the magnitude of the magnetization modulus fluctuates. This fluctuation produces a rapid modulation in the LTEM image. A novel analysis of the ripple structure in nano-crystalline Fe-Zr-N film corresponds to an amplitude of the transversal component of the magnetization deltaMy of 23 mT and a longitudinal fluctuation of the magnetization of the order of deltaMx = 30 mT. The nano-crystalline (Fe99Zr1)1-xNx films have been prepared by DC magnetron reactive sputtering with a thickness between 50 and 1000 nm. The grain size decreased monotonically with N content from typically 100 nm in the case of N-free films to less than 10 nm for films containing 8 at%. The specimens were examined with a JEOL 2010F 200 kV transmission electron microscope equipped with a post column energy filter (GIF 2000 Gatan Imaging Filter). For holography, the microscope is mounted with a biprism (JEOL biprism with a 0.6 microm diameter platinum wire).     

An efficient method for solving the quantum liouville equation: applications to electronic absorption spectroscopy

We examine a method for solving Liouville's equation, consisting of successive application of short time propagators which are evaluated by using fast Fourier transforms. The method is examined numerically by computing electronic absorption spectra. The procedure is very efficient when applied to the study of short time dynamics of systems whose quantum degrees of freedom are spatially localized.