CP Spectra Research Articles

Clinical profile and associated comorbidities of cerebral palsy in children visiting Orotta National Referral Hospital, Eritrea: a cross-sectional study

BackgroundCerebral Palsy (CP) is one of the most common physical disabilities in children. This study aimed to explore the clinical spectrum of CP at Orotta National Referral and Teaching Hospital, including CP subtypes, gross motor function, patterns of associated comorbidities, and possible risk factors in children aged 2 to 12 years.MethodsA hospital-based cross-sectional study was conducted from January to April 2022 in 153 children with suspected motor symptoms. The Surveillance of CP in Europe (SCPE) decision tree was used as an inclusion criteria guideline and the evaluation of the participants was done using a standardized questionnaire and clinical examination. Descriptive statistics, chi-square test, and logistic regression were employed to statistically analyze the data.ResultsEighty-four children who fulfilled the clinical criteria were included in the study. The median age was 5-years [IQR: 3.8] with an equal distribution of males and females. Quadriplegic CP was the most common subtype (51.2%) followed by unilateral (hemiplegic) CP (22.6%), and dyskinetic CP (14.3%). Most children had severe gross motor impairment GMFCS level IV-V and females were almost three times more likely to have GMFCS level IV/V than males (AOR: 2.70; CI: 1.08–6.72; p-value = 0.033.) More than half (52.4%) of the neonates either did not cry within five minutes and/or needed breathing resuscitation, 55.3% had to be admitted to the NICU with a median of 5 days’ hospital stay. Between the first week of birth and the first year of life, 28.6% had trouble feeding, 26.2% had an infection, 10.7% had difficulty breathing, 20.2% had seizures and 6% had jaundice. Feeding problems (64.3%), speech problems of some sort (91.7%), and epilepsy (46.4%) were the most commonly associated comorbidities with CP.ConclusionsThe clinical profile of the CP patients was found to be dominated by the spastic subtype and moderate to severe disability. Since perinatal risk factors were found to be dominant, strengthening maternal and child healthcare systems is recommended to minimize incidents of preventable risk factors and the burden of the disability.

Effect of a single methyl substituent on the electronic structure of cobaltocene studied by computationally assisted MATI spectroscopy.

Metallocenes represent archetypical organometallic compounds playing key roles in various fields of fundamental and applied chemistry. Many of their unique properties arise from low ionization energies (IE) which can be tuned by introducing substituents into the rings. Here we report the first mass-analyzed threshold ionization (MATI) spectrum of a methylmetallocene, (Cp')(Cp)Co (Cp' = η5-C5H4Me, Cp = η5-C5H5). The presence of a single Me group allows us to study the "pure" effect of methylation without the mutual influence of substituents. The MATI technique provides an extremely high accuracy in determining the adiabatic IE of (Cp')(Cp)Co which equals 5.2097(6) eV. The effect of a Me group on the IE of cobaltocene appears to be 36% stronger than that in bis(η6-benzene)chromium. The MATI spectrum of (Cp')(Cp)Co shows a rich vibronic structure from which vibrational frequencies of the free ion are determined. This information provides a solid basis for testing the quality of quantum chemical calculations. Various levels of the DFT and coupled cluster computations are used to describe the structural and electronic transformations accompanying the detachment of an elctron from (Cp')(Cp)Co. New aspects of the methyl substituent influence on the potential energy surfaces, as well as on the inhomogeneous changes in charge density and electrostatic potential caused by ionization, are discussed.

Tapping into the native Pseudomonas bacterial biofilm structure by high-resolution multidimensional solid-state NMR

We present a multidimensional magic-angle spinning (MAS) solid-state NMR (ssNMR) study to characterize native Pseudomonas fluorescens colony biofilms at natural abundance without isotope-labelling. By using a high-resolution INEPT-based 2D 1H–13C ssNMR spectrum and thorough peak deconvolution at the 1D ssNMR spectra, approximately 80/134 (in 1D/2D) distinct biofilm chemical sites were identified. We compared CP and INEPT 13C ssNMR spectra to differentiate signals originating from the mobile and rigid fractions of the biofilm, and qualitatively determined dynamical changes by comparing CP buildup behaviors. Protein and polysaccharide signals were differentiated and identified by utilizing FapC protein signals as a template, a biofilm forming functional amyloid from Pseudomonas. We identified several biofilm polysaccharide species such as glucose, mannan, galactose, heptose, rhamnan, fucose and N-acylated mannuronic acid by using 1H and 13C chemical shifts obtained from the 2D spectrum. To our knowledge, this study marks the first high-resolution multidimensional ssNMR characterization of a native bacterial biofilm. Our experimental pipeline can be readily applied to other in vitro biofilm model systems and natural biofilms and holds the promise of making a substantial impact on biofilm research, fostering new ideas and breakthroughs to aid in the development of strategic approaches to combat infections caused by biofilm-forming bacteria.

Cerebral palsy in children: subtypes, motor function and associated impairments in Addis Ababa, Ethiopia

BackgroundAlthough, there is no population-level data in Ethiopia, a previous retrospective hospital-based study identified CP as the most common developmental disability in children. The overall aim of this study is to describe the clinical spectrum of CP in Tikur Anbessa Specialized Hospital in Addis Ababa, including CP subtype, gross and fine motor function, presence and pattern of associated impairments, and possible risk factors in children aged 2 to 18 years.MethodsA hospital-based descriptive cross-sectional study conducted- July – September of 2018 among 207 children with suspected motor symptoms. The Surveillance of CP in Europe (SCPE) decision tree was used as a guideline for inclusion and evaluation was by standardized questionnaire and clinical examination. Descriptive, bivariate and multivariate statistical analyses, Chi-square test, crudes association and adjusted odds ratio with 95% confidence interval employed.ResultOne hundred seventy four children who fulfilled the clinical criteria were included. Half (50.6%) were under the age of 5 years with a mean age of 5.6 (SD 3.6) years; 55.2 were male. The majority had bilateral spastic CP (60.4%) followed by unilateral spastic CP 21.8%, dyskinetic CP 10.4%, and ataxic CP 3.4%; 4% were unclassifiable. Of the children, 95.4% had speech difficulty, 87.4% learning disabilities, 60.9% epilepsy, 24.7% visual impairment and 8.6% hearing impairment. On gross motor function (GMFCS) and manual ability (MACS) classification systems, 75.3% of the children had level IV and V functional impairment. More than 80% of the mothers had complications during delivery Half of the neonates did not cry immediately after birth,44% were resuscitated with bag mask ventilation at birth and 64% immediately admitted to NICU. During the first month of life, 50% had infection, 62% had trouble feeding, 49.4% had difficulty breathing, 35% had seizure and 13.8% had jaundice.ConclusionThe severe forms of CP predominate; most children are dependent on their parents for routine activities of daily living and cannot communicate well. Multidisciplinary care approaches and focused functional habilitation services are needed. Causal relationships cannot be drawn from these data but findings make a strong argument for improving maternal and child health care.

Coenopopulation Structures of Various Plant Species in Yakutia

This research work details analysis of the coenopopulation structure of 13 plants of various species in Yakutia and compares them with the characteristic spectra types of their species. The structure of plant coenopopulations was investigated from 2003 to 2019 in Central Yakutia. The left-sided and centered ontogenetic spectra are found in perennial plants with simple ontogenesis and shallow rejuvenation which were studied. The left-sided spectrum is the basic structure of these coenopopulations. The centered ontogenetic spectrum is largely found in unfavorable growing conditions under the impact of grazing and trampling by cattle and horses. This rule applies to the CP structure of Veronica incana which is an evergreen chamaephyte and for which the seasonal anthropogenic load contributes to the mechanical vegetative reproduction of its species, resulting in stable left-sided CP spectra. The ontogenetic spectra of the studied plants coincide with the characteristic spectra of the species and are considered stable.

Preserved chemistry of Cretaceous gymnosperm leaves in volcanic-ash deposits. Baqueró Group, Patagonia, Argentina

Gymnosperm foliar compressions belonging to two fossil taxa, Pseudoctenis ornata (Cycadophyta) and Ginkgoites tigrensis (Ginkgophyta), are chemically characterized for the first time by semi-quantitative Fourier Transform Infrared (FTIR) spectroscopy. The specimens collected in the well-known Baqueró Group (Lower Cretaceous, Santa Cruz province, Argentina) are compressions with very well-preserved cuticles. The FTIR data are analyzed along with the available paleoenvironmental data of the Baqueró Group localities in order to interpret the volcanic activity role in the preservation of these foliar compressions and, consequently, their chemical compositions. For the spectrometric study, foliar remains are analyzed into two sample forms: compressions (including coalified mesophyll and cuticle; Cp) and cuticles (Ct). Semi-quantitative data, derived from Cp and Ct spectra, are evaluated by principal component analysis (PCA) analyzing the functional groups preserved in the mesophyll and cuticle of each fossil taxon. In general, the fossil taxa reflect similar chemical compositions between compression and cuticle sample forms revealing that P. ornata and G. tigrensis compressions underwent, during diagenesis and probably post-diagenesis, a natural oxidation process. Considering the known information on the preservation model of Squamastrobus tigrensis, a podocarp recovered also in Baqueró Group, as well as the paleoenvironments and geochemical conditions in the fossiliferous localities along with the FTIR data, two preservation models are here proposed for P. ornata and G. tigrensis. The volcanic activity was most likely involved in the exceptional preservation of the foliar cuticle characters, the transformation of the organic matter, and the oxidation undergone by G. tigrensis and P. ornata foliar remains.

Chemometric approach to the foliar cuticle of Ptilophyllum micropapillosum sp. nov. from the Springhill Formation (Lower Cretaceous, Argentina)

Ptilophyllum micropapillosum sp. nov. is a new bennettitalean frond recovered from the Lower Cretaceous Springhill Formation, Patagonia, Argentina. The foliar cuticle is herein characterized by means of light and scanning electronic microscopy along with its preserved chemistry. The aim of the chemical study is to reveal mesophyll and cuticle chemical structures (functional groups) preserved in different frond parts (apical, middle, and basal) as well as their relation with kerogen types and coal macerals. Fronds of P. micropapillosum sp. nov. are bipinnate, the abaxial epidermis has different papillae types: (1) abundant, small and simple, (2) scarce compound papillae, and (3) few big simple papillae. For the first time, plant fossil remains from the Springhill Formation are studied by semi-quantitative Fourier transform infrared (FTIR) spectroscopy. Two sample forms are included: compressions (Cp) and cuticles (Ct). Additionally, the host rock is analyzed through concentrate kerogen and entire rock samples. From these, thermal indices (Ro%, TAI, and VRE) and organic and inorganic matter characterization are derived. Semi-quantitative data (area ratios), derived from the Cp and Ct FTIR spectra, are interpreted by principal component analysis. Results indicate differences between Cp and Ct, revealing a high content of aromatic compounds in P. micropapillosum sp. nov. foliar cuticle. This is most likely attributed to the presence of aromatic monomers in cutin/cutan biomacropolymers. The chemical composition is similar among apical, middle, and basal frond parts. This fact probably implies a distinctive frond construction pattern where the energy investment and the metabolic cost are similar throughout the analyzed fronds.

Determining the Surface Structure of Silicated Alumina Catalysts via Isotopic Enrichment and Dynamic Nuclear Polarization Surface-Enhanced NMR Spectroscopy.

Isotopic enrichment of 29Si and DNP-enhanced NMR spectroscopy are combined to determine the detailed surface structure of a silicated alumina catalyst. The significant sensitivity enhancement provided by DNP is vital to the acquisition of multinuclear and multidimensional experiments that provide information on the atomic-level structure of the species present at the surface. Isotopic enrichment not only facilitates spectral acquisition, particularly given the low (1.5 wt %) Si loading, but also enables spectra with higher resolution than those acquired using DNP to be obtained. The unexpected similarity of conventional, CP, and DNP NMR spectra is attributed to the presence of adventitious surface water that forms a sufficiently dense 1H network at the silica surface so as to mediate efficient polarization transfer to all Si species regardless of their chemical nature. Spectra reveal the presence of Si–O–Si linkages at the surface (identified as Q4(3Al)–Q4(3Al)) and confirm that the anchoring of the surface overlayer with the alumina occurs through AlIV and AlV species only. This suggests the presence of Q3/Q4 Si at the surface affects the neighboring Al species, modifying the surface structure and making it less likely AlVI environments are in close spatial proximity. In contrast, Q1/Q2 species, bonded to the surface by fewer covalent bonds, have less of an effect on the surface, and more AlVI species are consequently found nearby. The combination of isotropic enrichment and DNP provides a definitive and fully quantitative description of the Si-modified alumina surface, and we demonstrate that almost one-third of the silicon at the surface is connected to another Si species, even at the low level of coverage used, lowering the propensity for the formation of Brønsted acid sites. This suggests that a variation in the synthetic procedure might be required to obtain a more even coverage for optimum performance. The work here will allow for more rigorous future investigations of structure–function relationships in these complex materials.

A higher chromatic analogue of the image of J

We prove a higher chromatic analogue of Snaith's theorem which identifies the K-theory spectrum as the localisation of the suspension spectrum of CP^\infty away from the Bott class; in this result, higher Eilenberg-MacLane spaces play the role of CP^\infty = K(Z,2). Using this, we obtain a partial computation of the part of the Picard-graded homotopy of the K(n)-local sphere indexed by powers of a spectrum which for large primes is a shift of the Gross-Hopkins dual of the sphere. Our main technical tool is a K(n)-local notion generalising complex orientation to higher Eilenberg-MacLane spaces. As for complex-oriented theories, such an orientation produces a one-dimensional formal group law as an invariant of the cohomology theory. As an application, we prove a theorem that gives evidence for the chromatic redshift conjecture.

Correlations among 31P NMR Coordination Chemical Shifts, Ru–P Bond Distances, and Enthalpies of Reaction in Cp′Ru(PR3)2Cl Complexes (Cp′ = η5-C5H5, η5-C5Me5; PR3 = PMe3, PPhMe2, PPh2Me, PPh3, PEt3, PnBu3)

The 31P NMR spectra of CpRu(PR3)2Cl and Cp*Ru(PR3)2Cl complexes with PR3 = PMe3, PPhMe2, PPh2Me, PPh3, PEt3, PnBu3 have been measured; these data correlate with and can be used to predict Ru–P bond distances and enthalpies. Their 31P NMR coordination chemical shifts (Δ(ppm) = δcomplex – δfree) show significant linear correlations with literature values of both the enthalpies of the ligand exchange reactions to form the Ru–P bonds and the average Ru–P bond distances from crystal structures. The strong correlation between Δ(ppm) and Ru–P distance can be extended to include the first-generation Grubbs metathesis catalyst (PCy3)2Cl2Ru═C(H)Ph and four of its derivatives, (PCy3)2Cl2Ru═C(H)(p-C6H4X) (X = OCH3, CH3, Cl, Br), the four related Fischer carbenes (PCy3)2Cl2Ru═C(H)ER (ER = OEt, SPh, N(carbazole), N(pyrrolidinone)), the second-generation Grubbs catalyst (PCy3)(IMes)Cl2Ru═C(H)Ph, and its derivative (PCy3)(IMes)Cl2Ru═C(H)OEt. Other significant correlations in the Cp′Ru(PR3)2Cl complexes are found between ...

Self-Assembled Oligoanilinic Nanosheets: Molecular Structure Revealed by Solid-State NMR Spectroscopy

The products obtained during the early stages of the oxidative polymerization of aniline in the “falling pH” reaction were investigated using multinuclear solid-state magic-angle spinning (MAS) NMR combined with first-principles NMR chemical shielding calculations using the GIPAW (gauge-including projector augmented wave) method. A sample was synthesized starting from a 50:50 mixture of U–13C aniline and 15N-labeled aniline; two-dimensional 13C refocused INADEQUATE, 15N–13C double CP, 15N PDSD, and 1H–13C/15N refocused INEPT MAS NMR spectra revealed the presence of quinoneimine structural units. Structural models that are consistent with the connectivities revealed by the 13C refocused INADEQUATE and 15N–13C Double CP spectra are proposed. GIPAW chemical shift calculations are performed for model structures based on the proposed oligomeric structures; noting that the model structures do not take into account intermolecular hydrogen bonding and CH−π interactions, agreement and discrepancy to experiment are discussed.

Characterization and electrochemical properties of a nickel film/carbon paper electrode prepared by a filtered cathodic vacuum arc technique

SEM spectrum of bare CP in low magnification (A), bare CP of cross-sectional views (B), bare CP in high magnification (C), Ni/CP in high magnification (D) and EDS spectrum of bare CP (E) and Ni/CP electrode (F).

Magnetodielectric properties of La0.67Sr0.33MnO3 and Ba0.7Sr0.3TiO3 thin film heterostructures

The paper discuses synthesis and magnetodielectric properties of La0.67Sr0.33MnO3 (LSMO), Ba0.7Sr0.3TiO3 (BST), and BST/LSMO thin film heterostructures. The XRD spectra are determined for confirmation of the crystal structure of LSMO, BST and formation of a pure bi-phase composite. The paper presents variation of Cp and tanδ as a function of frequency between 100 Hz to 1 MHz and applied magnetic field up to 0.6 T. The observed variation of Cp, tanδ, magnetocapacitance and impedance spectra are analyzed in terms of a possible equivalent circuit model. The present analysis shows that the method of impedance spectra could be used to separate out the possible contributions.

Diffusion of Chlorin-p6 Across Phosphatidyl Choline Liposome Bilayer Probed by Second Harmonic Generation

We have investigated the diffusion of the photosensitizer Chlorin-p(6) (Cp(6)) across a egg lecithin lipid bilayer at different pH by the Second Harmonic Generation (SHG) method. Cp(6) has three ionizable carboxylic acid groups, and consequently, neutral and several ionic forms of Cp(6) are expected to be present in the pH range 3-8. The absorption spectra of Cp(6) get considerably modified in the presence of liposomes as the pH is decreased indicating that the drug liposome binding is pH dependent. The first pK(a) of interconversion (D-C) has been identified at pH ~7.0 by fluorescence measurement in an earlier work. In this work, the second pK(a) of interconversion (C-B) has been identified at pH ~4.8 by the hyper-Rayleigh scattering method. At acidic pH (3, 4, and 5), where species A, B, and C are dominant, the addition of liposomes to a Cp(6) solution generates an instantaneous rise (less than 1 s) in the second harmonic (SH) signal followed by decays whose time constants ranged from ten to hundreds of seconds. The instantaneous rise is attributed to the adsorption of Cp(6) to the outer lipid bilayer, and the decay is attributed to the diffusion of the neutral and charged (A and B) species of the drug. The observed fast and slow time constants for diffusion in the pH range 3-5 are attributed to the neutral (A) and ionic form (B) of Cp(6), respectively. At pH 6, the intensity of the generated SH signals on the addition of liposome reduced, and at physiological pH, it was too weak to be detected. These results are consistent with previous studies that show that the interaction between Cp(6) and egg-PC liposomes is pH dependent. At lower pH due to the presence of the hydrophobic species (A and B) of Cp(6), its interaction with liposomes is strong, and at higher pH, the abundance of the negatively charged hydrophilic species (C and D) decreases the interaction with the like charged liposomes. We have also studied the effect of increasing the bilayer rigidity by decreasing the temperature of the medium or by incorporating 50 mol % cholesterol in the lipid bilayer and observed that lowering of temperature has more profound effect on the diffusion rates. The characteristics of the SH signal changed significantly when liposomes incorporating 50 mol % cholesterol were used at a low (3 °C) temperature. Under these conditions, the SH signal consisted of an instantaneous (<1s) followed by a slower rise (10-90s), and then, it decayed on a much longer time scale. This slow rise of the SH signal at pH 3 and 4 may be attributed to the temperature dependent adsorption of the anionic species (B) of Cp(6) with the liposomes. Further investigations are required in order to understand clearly the pH dependent diffusion of this drug across lipid bilayers.

BPS spectrum of supersymmetricCP(N−1)theory withZNtwisted masses

We revisit the BPS spectrum of the supersymmetric CP(N-1) two-dimensional model with Z_N-symmetric twisted masses m_l (l=0,1, ..., N-1). A related issue we address is that of the curves of marginal stability (CMS) in this theory. Previous analyses were incomplete. We close the gap by exploiting a number of consistency conditions. In particular, we amend the Dorey formula for the BPS spectrum. Our analysis is based on the exact Veneziano--Yankielowicz-type superpotential and on the strong-coupling spectrum of the theory found from the mirror representation at small masses, |m_l| << \Lambda . We show that at weak coupling the spectrum, with necessity, must include N-1 BPS towers of states, instead of just one, as was thought before. Only one of the towers is seen in the quasiclassical limit. We find the corresponding CMS for these towers, and argue that in the large-N limit they become circles, filling out a band on the plane of a single mass parameter of the model at hand. Inside the CMS, N-1 towers collapse into N stable states.

Relaxation compensated and intensity recovered dynamics of cross polarization in the frame of reciprocity relation

Abstract Through combing the scheme of TORQUE (by Tekely et al.) with cross depolarization (CDP), we derived a relaxation compensated and intensity recovered Hartmann–Hahn CP dynamics in the frame of reciprocity relation. As a result, the CP dynamics of TORQUE (CPT1ρQ(t)) emerges from the T1ρ damped dynamics and upon normalization of the intensities by the reciprocity relation, it is perfectly symmetric with respect to the CDP(t). Along with an enhancement factor of CP defined as η(t) = [ 1 - CDP ( t ) ] ( γ I / γ S ) and a scaling factor between two peak intensities, λ ( t ′ ) = PI CP ( t ′ ) /PIT1ρQ(t′), this method provides a convenient, robust, and quantitative measure of CP spectra.

Erratum: Large-Nsolution of the heteroticN=(0,2)two-dimensionalCP(N−1)model [Phys. Rev. D77, 125017 (2008)

We continue explorations of non-Abelian strings, focusing on the solution of a heterotic deformation of the CP(N-1) model with an extra right-handed fermion field and N=(0,2) supersymmetry. This model emerges as a low-energy theory on the worldsheet of the BPS-saturated flux tubes (strings) in N=2 supersymmetric QCD deformed by a superpotential of a special type breaking N=2 supersymmetry down to N=1. Using large-N expansion we solve this model to the leading order in 1/N. Our solution exhibits spontaneous supersymmetry breaking for all values of the deformation parameter. We identify the Goldstino field. The discrete Z_{2N} symmetry is shown to be spontaneously broken down to Z_2; therefore, the worldsheet model has N strictly degenerate vacua (with nonvanishing vacuum energy). Thus, the heterotic CP(N-1) model is in the deconfinement phase. We can compare this dynamical pattern, on the one hand, with the N=(2,2) CP(N-1) model which has N degenerate vacua with unbroken supersymmetry, and, on the other hand, with nonsupersymmetric CP(N-1) model with split quasivacua and the Coulomb/confining phase. We determine the mass spectrum of the heterotic CP(N-1) model in the large-N limit.

Synthesis, Electrochemistry, and Reactivity of Half-Sandwich Ruthenium Complexes Bearing Metallocene-Based Bisphosphines

The bimetallic complexes CpRu(P−P)X [Cp = η5-C5H5; X = Cl, H; P−P = dppf (1,1′-bis(diphenylphosphino)ferrocene), dppr (1,1′-bis(diphenylphosphino)ruthenocene), dppo (1,1′-bis(diphenylphosphino)-osmocene), dippf (1,1′-bis(diisopropylphosphino)ferrocene), dcpf (1,1′-bis(dicyclohexylphosphino)ferrocene)], Cp*Ru(P−P)X [Cp* = η5-C5Me5; X = Cl, H; P−P = dppf, dippf, dppomf (1,1′-bis(diphenylphosphino)octamethylferrocene), dppc (1,1′-bis(diphenylphosphino)cobaltocene)], [Cp*Ru(P−P)X]+ (X = H, CCPh; P−P = dppc+), and [Cp*Ru(P−P)L]2+ (L = CH3CN, t-BuCN; P−P = dppc+) have been synthesized. Most of the chloride and hydride complexes have been studied by cyclic voltammetry. The X-ray structures of [Cp*Ru(dppc)CH3CN][PF6]2 and [Cp*Ru(dppc)CCPh][PF6] have been determined. Protonation of [Cp*Ru(dppc)CCPh]+ gives the vinylidene complex [Cp*Ru(dppc)CCHPh]2+. The Co(III/II) potential of the dppc+ ligand undergoes a cathodic shift upon coordination in [Cp*Ru-(dppc)H]+ and an anodic shift upon coordination in [Cp*Ru(dppc)CH3CN]2+. The 1H NMR spectrum of Cp*Ru(dppc)H is consistent with its formulation as a Co(II)/Ru(II) complex. As gauged by their reactivity toward iminium cations, the hydride complexes are poor hydride donors; proton and electron transfer are dominant. CpRu(dippf)H and CpRu(dcpf)H deprotonate iminium cations with acidic α-hydrogens. Cp*Ru(dppc)H is oxidized by the N-(benzylidene)pyrrolidinium cation, giving [Cp*Ru-(dppc)H]+ and the vicinal diamine 1,2-bis(N-pyrrolidino)-1,2-diphenylethane. Most of the hydride complexes give trans-dihydride cations upon protonation; an exception is [Cp*Ru(dppc)H]+, which forms a dihydrogen complex [Cp*Ru(dppc)(H2)]2+ with surprising kinetic stability. This dihydrogen complex is more acidic and less thermodynamically stable than its dihydride isomer. The H2 ligand in [Cp*Ru(dppc)-(H2)]2+ is readily replaced by nitriles; the reaction with t-BuCN occurs by a dissociative mechanism.

NMR Studies of the Thermal Degradation of a Perfluoropolyether on the Surfaces of γ-Alumina and Kaolinite

Solid-state nuclear magnetic resonance (NMR) methods are used to follow the thermal degradation of Krytox 1506, a common perfluoropolyether, following adsorption onto the surfaces of gamma-Al2O3 and a model clay (kaolinite). The alumina studies are complemented with thermogravimetric analysis (TGA) to follow the degradation process macroscopically. Molecular-level details are revealed through 19F magic-angle spinning (MAS), 27Al MAS, and 19F --> 27Al cross-polarization MAS (CPMAS) NMR. The CPMAS results show the time-dependent formation of probable VIAl(O6 - nFn) (n = 1, 2, 3) species in which the fluorine atoms are selectively associated with octahedrally coordinated aluminum atoms. For the alumina system, the changes in peak shapes of the CP spectra over time suggest the early formation of catalytically active degradation products, which in turn lead to the formation of additional perfluoropolyether degradation products. Similar to the alumina system, the kaolinite system also displays new resonances in both the 27Al MAS and 19F --> 27Al CPMAS spectra after thermal treatment at 300 degrees C for up to 20 h but reveals a more distinct species at -15.5 ppm that forms at the expense of an initial species (3 ppm), which is in greater abundance at shorter heating times.

Towards uniform enhancement in solid-state cross polarization magnetic angle spinning NMR: A scheme incorporating cross polarization with rotational resonance

A recently proposed experimental scheme for achieving uniform cross polarization enhancement of low-gamma nuclear species in solids under magic angle spinning, termed quantitative cross polarization (QUCP) [Hou et al., Chem. Phys. Lett. 421, 356 (2006)], is described, supported with comprehensive theoretical analysis, numerical simulation, and experimental investigation with both uniformly labeled and naturally abundant solids. This method combines cross polarization with dipolar-assisted rotational resonance (DARR) [Takegoshi et al., Chem. Phys. Lett. 344, 631 (2001)] broadband homonuclear recoupling technique to achieve quantitative CP spectra under fast magic angle spinning. In addition to the correct and systematical interpretation on the phenomenon we reported in the previous Letter, a number of general guidelines for performing QUCP experiments are presented in this work. It is firmly established that while the enhancement factor in QUCP depends on the CP contact time, uniform enhancement can nevertheless be realized for all types of carbon group. For natural abundance samples, the polarization transfer rate is generally slower than that in labeled samples, but quasi-equilibrium among dilute spins in the mixing period can always be reached and uniform enhancement can be achieved albeit the DARR irradiation time needed can be much longer. For labeled samples, the time gain of QUCP experiment is almost the same as that of conventional CP. For natural abundance samples, it is generally much better than single-pulse experiment. Various representative systems, including uniformly (13)C-labeled DL-alanine and (13)C, (15)N labeled L-tyrosine, as well as naturally abundant alanine, tyrosine, and monoethyl fumarate, are used to verify the validity of our theoretical analysis and numerical simulation and to demonstrate the utility and advantages of the present approach.