Broadband adiabatic inversion experiments for the measurement of longitudinal relaxation time constants

Accurate measurements of longitudinal relaxation time constants (T₁) in solid-state nuclear magnetic resonance (SSNMR) experiments are important for the study of molecular-level structure and dynamics. Such measurements are often made under magic-angle spinning conditions; however, there are numerous instances where they must be made on stationary samples, which often give rise to broad powder patterns arising from large anisotropic NMR interactions. In this work, we explore the use of wideband uniform-rate smooth-truncation pulses for the measurement of T₁ constants. Two experiments are introduced: (i) BRAIN-CPT1, a modification of the BRAIN-CP (BRoadband Adiabatic-INversion-Cross Polarization) sequence, for broadband CP-based T₁ measurements and (ii) WCPMG-IR, a modification of the WURST-CPMG sequence, for direct-excitation (DE) inversion-recovery experiments. A series of T₁ constants are measured for spin-1/2 and quadrupolar nuclei with broad powder patterns, such as ¹¹⁹Sn (I = 1/2), ³⁵Cl (I = 3/2), ²H (I = 1), and ¹⁹⁵Pt (I = 1/2). High signal-to-noise spectra with uniform patterns can be obtained due to signal enhancements from T₂ ^eff-weighted echo trains, and in favorable cases, BRAIN-CPT1 allows for the rapid measurement of T₁ in comparison to DE experiments. Protocols for spectral acquisition, processing, and analysis of relaxation data are discussed. In most cases, relaxation behavior can be modeled with either monoexponential or biexponential functions based upon measurements of integrated powder pattern intensity; however, it is also demonstrated that one must interpret such T₁ values with caution, as demonstrated by measurements of T₁ anisotropy in ¹¹⁹Sn, ²H, and ¹⁹⁵Pt NMR spectra.

Unraveling the Rapid Performance Decay of Layered High-Energy Cathodes: From Nanoscale Degradation to Drastic Bulk Evolution

Lithium-rich layered oxides are promising cathode candidates because of their exceptional high capacity. The commercial application of these high-energy cathodes, however, is thwarted by the undesired rapid performance decay during cycling. Surface degradation has been widely considered to correlate with the performance decay of the cathodes, whereas, in this work, we demonstrate that the degradation of Li-rich high-energy Li_1.2Ni_0.13Mn_0.54Co_0.13O₂ (HENMC) cathode material not only takes place at surfaces but also proceeds from its internal structure. In addition to demonstrating the surface reconstruction and the formation of a cathode-electrolyte interphase (CEI) layer of cycled HENMC cathode, this study uncovers the irreversible bulk phase transition from a Li-excess monoclinic ( C2/ m) solid solution into a conventional "layered" ( R3̅ m) phase, accompanied by complete loss of Li⁺ from the TM layers during cycling. Furthermore, the internal grains of HENMC bear lattice distortions, leading to the formation of "nano-defect" domains, which could limit the Li⁺ diffusion inside the grains. More prominently, the layered-to-spinel transition in the form of large spinel grains ( Fd3̅ m), hundreds of nanometers across, is discovered, and their detailed atomic arrangement is studied. The findings suggest that, instead of attributing the overall capacity fade to the surface degradation, these drastic bulk evolutions would be the main degradation mechanisms at the source of the rapid failure of Li-rich cathodes.

Spatially resolved surface valence gradient and structural transformation of lithium transition metal oxides in lithium-ion batteries

Layered lithium transition metal oxides are one of the most important types of cathode materials in lithium-ion batteries (LIBs) that possess high capacity and relatively low cost. Nevertheless, these layered cathode materials suffer structural changes during electrochemical cycling that could adversely affect the battery performance. Clear explanations of the cathode degradation process and its initiation, however, are still under debate and not yet fully understood. We herein systematically investigate the chemical evolution and structural transformation of the LiNi_xMn_yCo_1-x-yO₂ (NMC) cathode material in order to understand the battery performance deterioration driven by the cathode degradation upon cycling. Using high-resolution electron energy loss spectroscopy (HR-EELS) we clarify the role of transition metals in the charge compensation mechanism, particularly the controversial Ni²⁺ (active) and Co³⁺ (stable) ions, at different states-of-charge (SOC) under 4.6 V operation voltage. The cathode evolution is studied in detail from the first-charge to long-term cycling using complementary diagnostic tools. With the bulk sensitive ⁷Li nuclear magnetic resonance (NMR) measurements, we show that the local ordering of transition metal and Li layers (R3[combining macron]m structure) is well retained in the bulk material upon cycling. In complement to the bulk measurements, we locally probe the valence state distribution of cations and the surface structure of NMC particles using EELS and scanning transmission electron microscopy (STEM). The results reveal that the surface evolution of NMC is initiated in the first-charging step with a surface reduction layer formed at the particle surface. The NMC surface undergoes phase transformation from the layered structure to a poor electronic and ionic conducting transition-metal oxide rock-salt phase (R3[combining macron]m → Fm3[combining macron]m), accompanied by irreversible lithium and oxygen loss. In addition to the electrochemical cycling effect, electrolyte exposure also shows non-negligible influence on cathode surface degradation. These chemical and structural changes of the NMC cathode could contribute to the first-cycle coulombic inefficiency, restrict the charge transfer characteristics and ultimately impact the cell capacity.

Ultra-wideline 14N solid-state NMR as a method for differentiating polymorphs: glycine as a case study

¹⁴N solid-state NMR is useful for differentiating polymorphs and chemically distinct nitrogen-containing compounds. A case study of glycine is presented.

Broadband adiabatic inversion pulses for cross polarization in wideline solid-state NMR spectroscopy

Efficient acquisition of ultra-wideline solid-state NMR powder patterns is a continuing challenge. In particular, when the breadth of the powder pattern is much larger than the cross-polarization (CP) excitation bandwidth, transfer efficiencies suffer and experimental times are greatly increased. Presented herein is a CP pulse sequence with an excitation bandwidth that is up to ten times greater than that available from a conventional spin-locked CP pulse sequence. The pulse sequence, broadband adiabatic inversion CP (BRAIN-CP), makes use of the broad, uniformly large frequency profiles of chirped inversion pulses, to provide these same characteristics to the polarization transfer process. A detailed theoretical analysis is given, providing insight into the polarization transfer process involved in BRAIN-CP. Experiments on spin-1/2 nuclei including (119)Sn, (199)Hg and (195)Pt nuclei are presented, and the large bandwidth improvements possible with BRAIN-CP are demonstrated. Furthermore, it is shown that BRAIN-CP can be combined with broadband frequency-swept versions of the Carr-Purcell-Meiboom-Gill experiment (for instance with WURST-CPMG, or WCPMG for brevity); the combined BRAIN-CP/WCPMG experiment then provides multiplicative signal enhancements of both CP and multiple-echo acquisition over a broad frequency region.

Optimized excitation pulses for the acquisition of static NMR powder patterns from half-integer quadrupolar nuclei

Various amplitude- and phase-modulated excitation pulses for the observation of static NMR powder patterns from half-integer quadrupolar nuclei have been generated using the optimal control routines implemented in SIMPSON 2.0. Such pulses are capable of both excitation of the central transition and signal enhancement by population transfer from the satellites. Enhancements in excess of 100% have been achieved for the central transition of the spin-3/2 (87)Rb nucleus compared with a selective pi/2 pulse. These pulses are shown to be relatively insensitive to changes in RF power and transmitter offsets, and can achieve a more uniform signal enhancement than double-frequency sweeps (DFS), resulting in more accurate spectral lineshapes. We also investigate the possibility of "calibration-free" optimized pulses for general use on half-integer quadrupoles with unknown interaction parameters. Such pulses could prove extremely useful for studying low abundance or insensitive nuclei for which experimental optimization of the DFS scheme may be difficult. We demonstrate that a pulse optimized for an arbitrary spin-3/2 system can function well on multiple samples, and can also excite the central transition of higher spin numbers, albeit with a smaller enhancement. The mechanism by which these optimized pulses achieve the signal enhancement is highly complex and, unlike DFS, involves a non-linear excitation of the satellite transition manifold, as well as the generation and manipulation of significant multiple-quantum coherences.

Pulse FT NMR of non-equilibrium states of half-integer spin quadrupolar nuclei in single crystals

For quadrupolar nuclei with spin quantum numbers equal to 3/2, 5/2 and 7/2, the intensities of the NMR transitions in a single crystal are examined as a function of the rf excitation flip angle. Single-quantum NMR intensities are calculated using density matrix theory beginning under various non-equilibrium conditions and are compared with those determined experimentally. As a representative spin-3/2 system, the flip-angle dependence of the (23)Na NMR intensities of a single crystal of NaNO(3) was investigated beginning with the inversion of the populations associated with one of the satellite transitions. Subsequently, the populations of both satellite transitions were inverted using highly frequency-selective hyperbolic secant pulses. Calculated and experimental intensities are in good agreement. As an example of a spin-5/2 system, the flip-angle dependence of the (27)Al NMR transition intensities was determined using a single crystal of sapphire, Al(2)O(3), starting under different nuclear spin population conditions. The experimental trends mimicked those predicted by the density matrix calculations but the agreement was not as good as for the spin-3/2 case. Some SIMPSON simulations were also carried out to confirm the results generated by our density matrix calculations. The theoretical flip-angle behavior of the NMR transition intensities obtained from a spin-7/2 spin system is also discussed.

NMR line shapes from AB spin systems in solids — The role of antisymmetric spin–spin coupling

NMR parameters such as indirect nuclear spin–spin coupling (J), nuclear magnetic shielding (σ), direct dipolar coupling (D), and electric field gradient (V) are properly described by second-rank tensors. Each may be decomposed into isotropic, symmetric, and antisymmetric components; the number of these three components which may be nonzero is a distinguishing attribute of each interaction tensor. The rank-1 antisymmetric portion of J (Janti) holds the distinction of remaining the only nonzero part of these fundamental NMR interaction tensors which has never been observed experimentally. Accordingly, effects from Janti are usually ignored, but it is important to consider when this is valid. An experimental strategy for observing Janti in powdered samples of tightly coupled homonuclear spin pairs, based on ideas originally presented by Andrew and Farnell ( Mol. Phys. 1968, 15, 157 ), is described. The theory of Andrew and Farnell is extended to powder samples, and methods for analyzing NMR spectra from powdered samples are presented. It is found that, in certain rare cases, Janti has the potential to affect the NMR line shapes from AB spin systems, but that even in these systems, the most intense features of the spectra are not affected and may be analyzed independently of Janti. Furthermore, Janti will only have an observable effect on the NMR spectra when its magnitude is comparable with that of Jiso and with the difference in chemical shifts (in Hz) between the two sites. Finally, the first experimental attempts to measure Janti are reported, and experimental proof that no elements of Janti(119Sn,119Sn) in hexa(p-tolyl)ditin are larger than 2900 Hz is given. The benefits of modern double-quantum filtering NMR pulse sequences in isolating effects from Janti are also illustrated.

Acetylenic Carbon-13 Chemical Shift Tensors for Diphenylacetylene and (η2-Diphenylacetylene)Pt(PPh3)2: A Solid-State NMR and Theoretical Study

The structure of (eta2-diphenylacetylene)Pt(PPh3) (2), as well as those of its dichloromethane and benzene solvates, is determined via X-ray crystallography. An investigation of the chemical shift (CS) tensors of the 13C-labeled carbons in Ph13C13CPh and (eta2-Ph13C13CPh)Pt(PPh3)2.(C6H6) is carried out via analysis of 13C NMR spectra from stationary solid samples. The principal components of the CS tensors as well as their orientations with respect to the 13C,13C internuclear vector are determined. DFT calculations of these CS tensors are in close agreement with the experimental values. For diphenylacetylene (tolane), the orientations and principal-component magnitudes of the alkynyl carbon CS tensors are comparable to those for other alkynyl carbons, although the CS tensor is not axially symmetric in this case. Coordination to platinum causes a change in the CS tensor orientation and a net increase in the isotropic chemical shift, resulting from a significant increase in two principal components (delta11 and delta33) while the third (delta22) decreases only slightly. The measured carbon CS tensors in the platinum complex bear a striking similarity to those of the alkenyl carbons in trans-Ph(H)C=C(H)Ph, and a short theoretical discussion of these observations is presented.

Smoking in urban African Americans: behaviors, gender differences, and motivation to quit

OBJECTIVE

This study describes smoking behaviors and gender differences, and correlates these factors with motivation to quit smoking among African-American smokers at a community-based health center.

DESIGN

A 62-item survey assessed depression, hassles, readiness to change, and demographics.

METHODS

Participants (N = 81) were interviewed in an adult clinic waiting room.

RESULTS

On average, participants smoked 13 cigarettes per day. Many reported attempts to reduce smoking-related health risks: 46% switched brands, 57% reduced their smoking, and 19% smoked only on some days. Fifty-nine percent indicated depressive symptoms. For women vs men, noteworthy differences were: reduction in number of cigarettes smoked (66.7% vs 40.0%; P = .023), switching brands (58.8% vs 23.3%; P = .003), number of attempts to quit in the past year (2.7 vs 1.2; P = .034), and high concern about weight gain (52.9% vs 26.7%; P = .047). Cigarettes smoked per day was negatively correlated with motivation to quit (P = .022). Variables positively correlated with motivation to quit included: harm reduction strategies (P = .002), intention to quit in 30 days (P<.0001), and intention to quit in 6 months (P<.0001).

CONCLUSIONS

Women showed more potential indications of readiness to quit, including more attempts to quit, reductions in number of cigarette smoked, and brand switching. Knowledge of cessation barriers, gender differences, and correlates to motivation may prove useful for investigators conducting research in this population.

Documentation of smoking: role of age, gender, and ethnicity

This study assessed the role of age, gender, and ethnicity in chart documentation of smoking by primary care providers. Clinic patients (n = 304) were asked their smoking status and medical records were reviewed. Twenty-nine percent of reviewed patients were smokers, 27.6% former smokers, and 43.1% nonsmokers. Providers were more likely to document smoking among males (OR = 4.6; 95% CI = 2.2-9.5), middle-aged patients (OR = 4.0; 95% CI = 1.4-11.0), and smokers (OR = 8.1; 95% CI = 4.1-16.0). Data revealed selective documentation of smoking in males and middle-aged patients by providers, suggesting gender and age bias in the recognition and documentation of this risky behavior. We conclude that providers should screen for smoking in all patients regardless of age or gender.

Smoking cessation among African Americans: what we know and do not know about interventions and self-quitting

BACKGROUND

Many studies on cessation interventions and self-quitting have been conducted, but few have focused on African Americans. The purpose of this review was to critically evaluate the available studies and make recommendations for future research.

METHODS

Articles published from 1988 to 1998 were collected using Medline and other data bases, as well as personal communication. Studies were divided into two categories: evaluations of specific cessation interventions and examinations of self-quit behaviors and related factors. Studies were tabulated using author/year, study design/sample size, variables/results, and comments.

RESULTS

In the intervention studies, church-based programs may provide an effective location for cessation interventions, but the studies to date did not demonstrate unequivocal effectiveness. In clinic programs, there do not appear to be any interventions that are particularly effective. In community-based interventions, there were no differences for African and Caucasian Americans. With regard to self-quitting, sociodemographic variables were similarly related to cessation as in the general population, as were smoking history variables. All other categories did not contain enough information for firm conclusions to be drawn.

CONCLUSIONS

There are some interventions that appear to be useful, but little information is available on self-quitting. More research is needed on the natural history of quitting, on the social norms for smoking among African American groups, and on the conceptual dimensions of race in the context of this research.

The use of nicotine patches with minimal intervention

BACKGROUND

This paper describes a natural, prospective, open-label study designed to evaluate the impact of free nicotine patches with minimal support for smoking cessation.

METHODS

Surveys were administered to 223 participants who received nicotine patches from the American Lung Association. All participants received a 6-week supply of 15-mg/16-h transdermal nicotine patches, a self-help book Freedom from Smoking, and information about area smoking cessation classes. Follow-up telephone surveys were administered 6 weeks after the patches were distributed. Abstinence was measured through self-report exclusively.

RESULTS

The overall quit rate at 6-weeks was 21% (47/223). Among nonquitters, the mean number of cigarettes smoked per day dropped from 25 at baseline to 14 at 6 weeks. There was a significant difference in the average number of patches used by quitters and nonquitters (26 versus 11, P < 0.001).

CONCLUSIONS

Nicotine patches with minimal support can be effective in smoking cessation and smoking reduction. The availability of patches may have motivated participants to quit. Efforts to increase access to and use of nicotine patches may result in increased attempts to quit and successful quitting.

Pharmacotherapy of smoking cessation

Tobacco use is the number one cause of preventable diseases in the United States. Smoking accounts for more than 400,000 deaths yearly and 30% of all cancer deaths. Primary care physicians have access to 70% of smokers, approximately 60% of whom are perceived to be in excellent health. Recent advances in the pharmacotherapy of nicotine addiction, including nicotine nasal spray, nicotine inhaler, bupropion hydrochloride, and over-the-counter transdermal nicotine patches, have increased the treatment options physicians can offer to smokers. Physicians, especially those in primary care specialties, should familiarize themselves with these products to improve efforts to help their patients stop smoking. This article reviews scientific data on the efficacy of approved medications, benefits, adverse effects, and appropriate use of these products. We also discuss nicotine addiction and treatment for special populations, including women, ethnic minorities, light smokers, and patients with cardiovascular and pulmonary diseases.

Effects of a replication of a multicomponent model for preventing adolescent pregnancy in three Kansas communities

CONTEXT

A significant amount of attention has been devoted to the complex issue of teenage pregnancy and to programs for reducing pregnancy among adolescents. Careful evaluations of such programs are needed to ascertain what strategies will be most effective at reducing teenage pregnancy.

METHODS

A pretest-posttest comparison group design was used to analyze the effects of a comprehensive multicomponent school and community intervention on estimated pregnancy rates and birthrates among young people in three Kansas communities: Geary County, Franklin County and selected neighborhoods of Wichita.

RESULTS

There were high levels of program activity in all three communities during the intervention period, including teacher training and sexuality education for students. Survey respondents rated highly such project interventions as the extension of school-linked clinic hours to accommodate student schedules and support groups established in middle schools. Between 1994 and 1997, the proportions of adolescents reporting that they had ever had sex decreased significantly among all ninth and 10th graders in Geary County, from 51% to 38% among females and from 63% to 43% among males. In Franklin County, more males in grades 11 and 12 reported using condoms in 1996 (55%) than had done so in 1994 (39%). Age at first intercourse remained relatively stable in Franklin and Geary counties during the intervention period. The estimated pregnancy rate among adolescents aged 14-17 decreased between 1994 and 1997 in Geary Country, while it increased in comparison areas. The estimated pregnancy rates among 14-17-year-olds decreased in both Franklin County and its comparison communities. The birthrate declined both in one target area of Wichita and in its comparison area from 1991-1993 to 1994-1996. Over the same time period, the birthrate increased in a second target area of Wichita, while it decreased in the comparison community.

CONCLUSIONS

This evaluation of a comprehensive multicomponent program for adolescent pregnancy prevention contributes to our understanding of this model and its replicability in diverse communities. Ongoing program evaluation is important for developing initiatives and for refining strategies so they respond to local conditions.

Evaluating a statewide partnership for reducing risks for chronic diseases

We describe a case study evaluation of Kansas LEAN, a statewide partnership with the mission of reducing risks for chronic diseases through dietary and exercise modification. We used a case study design to examine five primary questions related to process and outcome: (a) were the goals of the partnership important to constituents? (process), (b) were constituents satisfied with the partnership (process), (c) were community or systems changes (new or modified programs, policies, or practices) facilitated by partnership efforts (outcome)?, (d) were these changes important to the partnership's mission (outcome)?, and (e) what critical events helped facilitate community changes (outcome)? several measurement instruments--a monitoring and feedback system, constituent surveys, and semistructured interviews--were used to address key evaluation questions. Kansas LEAN is a strong statewide partnership with involvement from key representatives throughout Kansas. It is an ongoing, comprehensive health promotion program that plans and implements multiple components, in a variety of settings, to create awareness, behavior change, and a supportive environment. Kansas LEAN has facilitated several important community or systems changes related to its mission. We conclude with a discussion of the challenges of evaluating partnerships that seek to reduce risks for chronic diseases.

Using empowerment theory in collaborative partnerships for community health and development

Models of community empowerment help us understand the process of gaining influence over conditions that matter to people who share neighborhoods, workplaces, experiences, or concerns. Such frameworks can help improve collaborative partnerships for community health and development. First, we outline an interactive model of community empowerment that describes reciprocal influences between personal or group factors and environmental factors in an empowerment process. Second, we describe an iterative framework for the process of empowerment in community partnerships that includes collaborative planning, community action, community change, capacity building, and outcomes, and adaptation, renewal, and institutionalization. Third, we outline activities that are used by community leadership and support organizations to facilitate the process of community empowerment. Fourth, we present case stories of collaborative partnerships for prevention of substance abuse among adolescents to illustrate selected enabling activities. We conclude with a discussion of the challenges and opportunities of facilitating empowerment with collaborative partnerships for community health and development.