(1)H-Detected IPAP DEPT-INADEQUATE and IPAP RINEPT-INADEQUATE for the measurement of long-range carbon-carbon coupling constants

The sensitivity of cryoprobes, which are rapidly becoming available, have brought about the possibility of measurement of (13)C, (13)C coupling constants at the natural abundance of (13)C using tens rather than hundreds of milligrams of compounds. This relatively recent development lays the foundation for a more routine use of the (13)C, (13)C long-range coupling constants in the conformational analysis of molecules. We have designed novel (1)H-detected INADEQUATE experiments optimized for long-range (13)C, (13)C correlations and the measurement of long-range coupling constants. These experiments incorporate refocusing of (1)J(CH) coupling constants prior to the formation of DQ coherences and (1)H-decoupling during the long carbon-carbon evolution intervals. Such modifications significantly enhance their performance over (1)H-detected INADEQUATE experiments currently in use for mapping the one-bond (13)C, (13)C correlations. (1)H or (13)C polarization is used a starting point in long-range correlation (1)H-detected IPAP DEPT-INADEQUATE or RINEPT-INADEQUATE experiments. These correlation experiments were modified yielding in-phase (IP) or antiphase (AP) (13)C, (13)C doublets in F(1). Procedures were developed for their editing yielding accurate values of small (13)C, (13)C coupling constants. The methods are illustrated using mono- and disaccharide samples and compared with related (13)C-detected experiments by means of the measurement of interglycosidic (13)C, (13)C coupling constants of a disaccharide.     

The nu(12) Band of CH(3)SiD(3)

The lowest frequency degenerate fundamental band of CH(3)SiD(3) (v(12) = 1 <-- 0) centered around 418 cm(-1) was measured in order to investigate the vibration-torsion-rotation interactions in a symmetric-top molecule with a single torsional degree of freedom. The spectrum was recorded at an instrumental resolution of 0.004 cm(-1) using a Bomem Fourier transform spectrometer. The temperature and pressure of the sample were 180 K and 2 Torr, respectively. Because of the Coriolis coupling between the torsional stack with one quantum of the silyl rock excited and the corresponding stack for the ground vibrational state, torsional splittings are measured that are substantially larger than expected simply from the observed increase in the barrier height. Due to the local nature of the Coriolis perturbation, the significantly enhanced torsional splittings are confined to a few (K, varsigma) rotational series; here varsigma = -1, 0, 1 labels the torsional sublevels. The current measurements of the nu(12) band and frequencies from previously reported studies in the ground vibrational state were fitted to within experimental uncertainty using an effective Hamiltonian which was used for the analyses of similar spectra in CH(3)SiD(3) and CH(3)CD(3). Spectroscopic parameters characterizing the states v(12) = 0 and 1 and their interactions were determined, including several Coriolis-coupling constants. Copyright 2000 Academic Press.     

Double core hole creation and subsequent Auger decay in NH3 and CH4 molecules

Energies of the hollow molecules CH(4)(2+) and NH(3)(2+) with double vacancies in the 1s shells have been measured using an efficient coincidence technique combined with synchrotron radiation. The energies of these states have been determined accurately by high level electronic structure calculations and can be well understood on the basis of a simple theoretical model. Their major decay pathway, successive Auger emissions, leads first to a new form of triply charged ion with a core hole and two valence vacancies; experimental evidence for such a state is presented with its theoretical interpretation. Preedge 2-hole-1-particle (2h-1p) states at energies below the double core-hole states are located in the same experiments and their decay pathways are also identified.     

Hyperfine Level Dependence of the Pressure Broadening of CH(3)I Rotational Transitions in the v(6) = 1 Vibrational State

We studied the hyperfine components of the (J = 10-9, Kl = 9) rotational transition in the v(6) = 1 excited vibrational state of CH(3)I, using collinear infrared and mm-wave radiations. The Doppler-free double-resonance technique allowed an accurate determination of the collisional broadening parameters for all the hyperfine components. An evident dependence on the F quantum number was observed and this result is perfectly consistent with a theoretical model allowing calculations of collisional broadening and coupling for the hyperfine components. Copyright 2000 Academic Press.     

Selection rules for multiple quantum NMR excitation in solids: derivation from time-reversal symmetry and comparison with simulations and (13)C NMR experiments.

New derivations of selection rules for excitation and detection of multiple quantum coherences in coupled spin-1/2 systems are presented. The selection rules apply to experiments in which the effective coupling Hamiltonian used for multiple quantum excitation is both time-reversal invariant and time-reversible by a phase shift of the radiofrequency pulse sequence that generates the effective couplings. The selection rules are shown to be consequences of time-reversal invariance and time-reversibility and otherwise independent of the specific form of the effective coupling Hamiltonian. Numerical simulations of multiple quantum NMR signal amplitudes and experimental multiple quantum excitation spectra are presented for the case of a multiply (13)C-labeled helical polypeptide. The simulations and experiments confirm the selection rules and demonstrate their impact on multiple quantum (13)C NMR spectra in this biochemically relevant case.     

The utility of phase alternated pulses for the measurement of dipolar couplings in 2D-SLF experiments

The measurement of hetero-nuclear dipolar coupling using two-dimensional separated local field (SLF-2D) NMR experiments is a powerful technique for the determination of the structure and dynamics of molecules in the solid state and in liquid crystals. However, the experiment is sensitive to a number of factors such as the Hartmann–Hahn match condition, proton frequency off-set and rf heating. It is shown here that by the use of phase alternated pulses during spin-exchange the effect of rf mismatch on the dipolar coupling measurement can be compensated over a wide range of off-sets. Phase alternation together with time and amplitude modulation has also been considered and incorporated into a pulse scheme that combines spin exchange with homonuclear spin decoupling based on magic sandwich sequence and named as SAMPI4. Such time and amplitude averaged nutation experiments use relatively low rf power and generate less sample heating. One of these schemes has been applied on liquid crystal samples and is observed to perform well and yield spectra with high resolution.     

Fundamentals of synchronization in chaotic systems,concepts, and applications

The field of chaotic synchronization has grown considerably since its advent in 1990. Several subdisciplines and "cottage industries" have emerged that have taken on bona fide lives of their own. Our purpose in this paper is to collect results from these various areas in a review article format with a tutorial emphasis. Fundamentals of chaotic synchronization are reviewed first with emphases on the geometry of synchronization and stability criteria. Several widely used coupling configurations are examined and, when available, experimental demonstrations of their success (generally with chaotic circuit systems) are described. Particular focus is given to the recent notion of synchronous substitution-a method to synchronize chaotic systems using a larger class of scalar chaotic coupling signals than previously thought possible. Connections between this technique and well-known control theory results are also outlined. Extensions of the technique are presented that allow so-called hyperchaotic systems (systems with more than one positive Lyapunov exponent) to be synchronized. Several proposals for "secure" communication schemes have been advanced; major ones are reviewed and their strengths and weaknesses are touched upon. Arrays of coupled chaotic systems have received a great deal of attention lately and have spawned a host of interesting and, in some cases, counterintuitive phenomena including bursting above synchronization thresholds, destabilizing transitions as coupling increases (short-wavelength bifurcations), and riddled basins. In addition, a general mathematical framework for analyzing the stability of arrays with arbitrary coupling configurations is outlined. Finally, the topic of generalized synchronization is discussed, along with data analysis techniques that can be used to decide whether two systems satisfy the mathematical requirements of generalized synchronization. (c) 1997 American Institute of Physics.     

Improvement of spectral editing in solids: A sequence for obtaining (13)CH + (13)CH(2)-only (13)C spectra

An improved spectral editing method for solids is described which allows one to obtain a set of subspectra in roughly two-thirds the amount of time as our original CPPI editing method for the same signal to noise. This improvement is afforded by a new pulse sequence that is used to acquire a (13)CH + (13)CH(2) spectrum which has very little (13)CH(3) or nonprotonated carbon contamination. By using this new sequence the (13)CH-only subspectrum is obtained much more efficiently. Criteria for optimizing the signal to noise in the edited subspectra are discussed. Copyright 2000 Academic Press.     

Theoretical and experimental investigation of (13)C relayed (2)H-(2)H-COSY 2D experiments: application to the analysis of weakly aligned solutes

We describe new NMR 2D experiments denoted DECADENCY for DEuterium CArbon DEuterium Nuclear Correlation spectroscopY dedicated to the analysis of anisotropic deuterium spectra. They belong to the class of X-relayed Y,Y-COSY 2D experiments that was initially explored in the case of a (1)H-X-(1)H fragment (I(X)=1/2) in isotropic medium. DECADENCY 2D experiments permit to correlate the quadrupolar doublets associated with two inequivalent deuterium nuclei in an oriented CD(2) fragment through heteronuclear polarization transfers. Two kinds of pulse sequences are described here using either a double INEPT-type or DEPT-type process. DECADENCY 2D experiments provide an interesting alternative to (2)H-(2)H COSY experiments when the geminal (2)H-(2)H total coupling (scalar and dipolar) is null or too small to provide visible cross-correlation peaks. Such a situation is typically observed for geminal deuteriums in prochiral or chiral molecules dissolved in chiral liquid crystals. The efficiency of these techniques is illustrated using dideuterated prochiral molecules, the phenyl[(2)H(2)]methanol and the 1-chloro[1-(2)H(2)]nonane, both dissolved in organic solutions of poly-gamma-benzyl-l-glutamate. The advantages of each sequence are presented and discussed. It is shown that the relative sign of the quadrupolar doublets can be determined.     

Measurement of small one-bond proton-carbon residual dipolar coupling constants in partially oriented (13)C natural abundance oligosaccharide samples: analysis of heteronuclear (1)J(CH)-modulated spectra with the BIRD inversion pulse

Two 2D J-modulated HSQC-based experiments were designed for precise determination of small residual dipolar one-bond carbon-proton coupling constants in (13)C natural abundance carbohydrates. Crucial to the precision of a few hundredths of Hz achieved by these methods was the use of long modulation intervals and BIRD pulses, which acted as semiselective inversion pulses. The BIRD pulses eliminated effective evolution of all but (1)J(CH) couplings, resulting in signal modulation that can be described by simple modulation functions. A thorough analysis of such modulation functions for a typical four-spin carbohydrate spin system was performed for both experiments. The results showed that the evolution of the (1)H-(1)H and long-range (1)H-(13)C couplings during the BIRD pulses did not necessitate the introduction of more complicated modulation functions. The effects of pulse imperfections were also inspected. While weakly coupled spin systems can be analyzed by simple fitting of cross peak intensities, in strongly coupled spin systems the evolution of the density matrix needs to be considered in order to analyse data accurately. However, if strong coupling effects are modest the errors in coupling constants determined by the "weak coupling" analysis are of similar magnitudes in oriented and isotropic samples and are partially cancelled during dipolar coupling calculation. Simple criteria have been established as to when the strong coupling treatment needs to be invoked.     

Determination and assignment of heteronuclear long-range coupling constants. Methods based on semiselective INEPT

One-dimensional methods for the determination and assignment of heteronuclear ¹H-X (X = rare spin-z) coupling constants based on the semiselective polarization transfer via INEPT pulse sequence are proposed. Here the selectivity of the polarization transfer plays a positive role with respect to the sensitivity of the measurement and purity of the observed multiplets. In nonrefocused experiments the acquired antiphase multiplets enable an unambiguous assignment of long-range couplings of a preselected proton. The analysis of such multiplets is also discussed. In the refocused version the purging pulse (INEPT+) was used to provide pure in-phase multiplets. The spectral editing technique DISCO was applied to simplify the spectra and to extract the couplings from complex multiplets. Finally, the modified INEPT experiments which combine semiselective polarization transfer with selective proton decoupling are proposed.     

The new HMQC-based technique for the quantitative determination of heteronuclear coupling constants. Application for the measurement of 3J(H'(i),P(i+1)) in DNA oligomers

A new general J-HMQC-based technique is presented, which allows an accurate determination of heteronuclear coupling constants. The most important feature of this new approach includes acquisition of the two data sets with and without the additional pi(S)-pulse at the end of coupling evolution period. This enables preservation and separation of the two orthogonal terms of coupling evolution, which are manifested by in- and antiphase cross-peaks, respectively. The coupling magnitudes are evaluated by the nonlinear least-squares fitting of the ratios of integrated signal volumes for both kinds of signals. The effectiveness of the new sequence is demonstrated by determination of the 3J(H3'(i),P(i+1)) couplings in DNA octamer duplex d(GCGTACGC)(2) sample. Additionally, the ability of the new method for the measurement at the natural abundance level of 13C nuclei is presented for the beta-cyclodextrin.     

Selective dephasing of OH and NH proton magnetization based on (1)H chemical-shift anisotropy recoupling

A method for selectively suppressing the signals of OH and NH protons in (1)H combined rotation and multiple-pulse spectroscopy (CRAMPS) and in (1)H-(13)C heteronuclear correlation (HETCOR) solid-state NMR spectra is presented. It permits distinction of overlapping CH and OH/NH proton signals, based on the selective dephasing of the magnetization of OH and NH protons by their relatively large (1)H chemical-shift anisotropies. For NH protons, the (14)N-(1)H dipolar coupling also contributes significantly to this dephasing. The dephasing is achieved by a new combination of heteronuclear recoupling of these anisotropies with (1)H homonuclear dipolar decoupling. Since the 180 degrees pulses traditionally used for heteronuclear dipolar and chemical-shift anisotropy recoupling would result in undesirable homonuclear dephasing of proton magnetization, instead the necessary inversion of the chemical-shift Hamiltonian every half rotation period is achieved by inverting the phases of all the pulses in the HW8 multiple-pulse sequence. In the HETCOR experiments, carefully timed (13)C 180 degrees pulses remove the strong dipolar coupling to the nearby (13)C spin. The suppression of NH and OH peaks is demonstrated on crystalline model compounds. The technique in combination with HETCOR NMR is applied to identify the CONH and NH-CH groups in chitin and to distinguish NH and aromatic proton peaks in a peat humin.     

Effective dipolar couplings determined by dipolar dephasing of double-quantum coherences

It is shown how homonuclear distances and homonuclear dipolar lattice sums between spin-1/2 nuclei can be measured by a pulsed solid-state NMR experiment under magic-angle spinning conditions. The presented technique is based on double-quantum coherence filtering. Instead of measuring a build-up of double-quantum coherence the pulse sequence is designed to dephase double-quantum coherence. This is achieved by exciting double-quantum coherence either with the help of the through-space dipolar coupling or the through-bond dipolar coupling while the dephasing relies on the through-space dipolar coupling as selected by a gamma-encoded pulse sequence from the C/R symmetry class. Since dephasing curves can be normalized on zero dephasing, it is possible to analyze the initial dephasing regime and hence determine dipolar lattice sums (effective dipolar couplings) in multiple-spin systems. A formula for the effective dipolar coupling is derived theoretically and validated by numerical calculations and experiments on crystalline model compounds for (13)C and (31)P spin systems. The double-quantum dephasing experiment can be combined with constant-time data sampling to compensate for relaxation effects, consequently only two experimental data points are necessary for a single distance measurement. The phase cycling overhead for the constant-time experiment is minimal because a short cogwheel phase cycle exists. A 2D implementation is demonstrated on [(13)C(3)]alanine.     

Structural and thermochemical properties of methyl ethyl sulfide alcohols: HOCH2SCH2CH3, CH3SCH(OH)CH3, CH3SCH2CH2OH,and radicals corresponding to loss of H atom

Sulfide alkoxy radicals are important intermediates during the partial oxidation of alkyl sulfides in atmospheric chemistry and in combustion. The atmospheric reaction sequence to formation of the alkoxy radicals includes (1) initial reaction with OH to create a radical on a carbon site, (2) the carbon radical then associates with ³O₂ to form a peroxy radical, and (3) an NO radical reacts with the peroxy radical to form an alkoxy radical (RO?) plus NO₂. This study determines structural parameters, internal rotor potentials, bond dissociation energies, and thermochemical properties (Δ_fH°, S°, and C_p(T)) of 3 corresponding alcohols HOCH₂SCH₂CH₃, CH₃SCH(OH)CH₃, and CH₃SCH₂CH₂OH of methyl ethyl sulfides studied in order to characterize the thermochemistry of the respective alkoxy radicals. The lowest energy molecular structures were calculated using the B3LYP density functional level of theory with the 6‐311G(2d,d,p) basis set. Standard enthalpies of formation (Δ_fH°₂₉₈) for the radicals and their parent molecules were calculated using B3LYP/6‐31 + G(2d,p), CBS‐QB3, M062x/6‐311 + g(2d,p), and G3MP2B3 methods. Isodesmic reactions were used to determine ?_fH° values. Internal rotation potential energy diagrams and rotation barriers were investigated using the B3LYP/6‐31 + G(d,p) level theory. The contributions for S°₂₉₈ and C_p(T) were calculated using the rigid rotor harmonic oscillator approximation based on the structures and vibrational frequencies obtained by CBS‐QB3 calculations, with contributions from torsion frequencies replaced by internal rotor contributions. Group additivity and hydrogen bond increment values were developed for estimating properties of structurally similar and larger sulfur‐containing peroxide molecules and their radicals.     

Investigation on stress distribution of multilayered composite structure (MCS) using infrared thermographic technique

In this paper, the thermoelastic stress analysis (TSA) on a multilayered composite structure (MCS) was investigated by means of lock-in thermographic image technique (LITI). The application of thermoelastic stress analysis on MCS becomes particularly complicated due to consisting of different material components, which determines the different thermoelastic coupling response depended on material thermal-physical property. The thermoelastic coupling constants (TCC) of GFRP, medium-carbon steel and foam were obtained through thermomechanical calibration experiments, respectively. An artificial neural network was proposed to determine the component of MCS. Comparisons between finite element analysis (FEA) and LITI measurement are reported. It is found that the stress distribution of MCS can be evaluated with good accuracies using LITI measurement.     

Hadamard-Spectroscopic-Imaging-Polarization-Transfer Technique

A combined transverse-Hadamard-spectroscopic-imaging (HSI) and polarization-transfer (PT) technique is described. Using average-Hamiltonian theory, composite pulses, which perform plane rotations in the presence of chemical shift, and J coupling are described. These pulses are used as building blocks in the HSI-PT experiment. The technique is demonstrated, using INEPT as the polarization-transfer sequence in a 2 × 2 and a 4 × 2 HSI, by obtaining multivolume-localized ¹³C spectra from two different phantoms.     

顺式聚乙炔中双极化子的新电子定域态

本文用自洽迭代的方法研究了顺式聚乙炔cis-(CH)_x中双极化子的电子能谱。结果发现,除了禁带中两个在连续模型中存在的深能级电子束缚态外,还存在一些浅能级的电子束缚态。它们形成分立的能级,并分别位于导带的顶部和底部以及价带的顶部和底部。这些电子态的定域程度随着电子晶格耦合参数λ及电子相互作用U的不同而变化。 关键词：     

Internal Rotation of the Hydroxyl Group in Isopropanol and the Chirality of the Gauche Form: Fourier Transform Microwave Spectroscopy of (CH(3))(2)CHOD

The rotational spectrum of the deuterated isopropanol (CH(3))(2)CHOD has been observed by Fourier transform microwave spectroscopy and analyzed to yield tunneling splitting of 4431.4613 (17) MHz, between the antisymmetric and the symmetric gauche forms, which is much larger than the 2400 MHz estimated from the internal-rotation potential function reported in the literature. The potential function for the OH internal rotation has been examined in view of the discrepancy between the observed and estimated tunneling splitting, and it was accounted for by taking into account isotope effects on the potential constants. The deuterium quadrupole coupling effect has been included together with the Coriolis terms in the off-diagonal block of the Hamiltonian matrix for the gauche form. The deuterium quadrupole coupling constants obtained for the trans form were employed to calculate the components of the coupling constants as functions of the internal-rotation angle, and the components at around 120 degrees were compared with the values observed for the gauche form, thereby leading to unambiguous determination of the signs of the constants in the off-diagonal block; the signs are not obtainable from an ordinary analysis of the rotational spectra. The chirality of the gauche form was discussed by placing special emphasis on the effect of intermolecular interactions between two chiral molecules. Copyright 2001 Academic Press.     

Near UV Spectra of the Aniliniums: φCH+ 2CH2X, φNH+ (CH2Xa)CH2Xb and φNH+ (C2H4)2X. Long Range Interactions Involving φ and X

We have shown in preceding papers^(1–3), in a study of some specific anilinium ions such as φNH⁺ _3-n (CH₃)_n, φ₂NH⁺ ₂ and φ₃NH⁺, that varying the ammonium groups, or the medium, can lead to great changes in the intensity of the secondary transition of the chromophore^(1–4) because of a δ, π coupling involving the substituent ^(1–10) and φ. In the present work we should like to extend our experiments to more complex ions - since apart our own works the UV spectroscopy of the aniliniums is almost unknown - to study the sensitivity of the chromophore to long range interactions with X through space or through the bonds of the substituents^(11–16).