Chemical Shift Ratio Research Articles

Can MRI chemical shift imaging replace thymic biopsy in myasthenia gravis patients?

BackgroundMyasthenia gravis is a neuromuscular junction autoimmune condition characterized by muscle weakness. Many people with myasthenia gravis have thymic abnormalities, such as thymic lymphoid hyperplasia and thymic tumors, therefore, the thymus plays a significant role in the disease. The imaging properties of thymic hyperplasia and thymoma on CT and conventional MRI are very similar, yet, MRI has recently revealed promising capability by adding novel sequences. Chemical shift MRI was demonstrated to consistently distinguish thymic hyperplasia from thymus gland tumors. The aim of this study was to determine the value of chemical shift MRI imaging in characterizing thymic lesions in patients diagnosed with myasthenia gravis and its ability to differentiate thymic hyperplasia from thymoma.ResultsMRI showed that thymic lymphoid hyperplasia was more common to be convex in shape while thymoma was more likely to be round or irregular (P = 0.004). Paired comparison between histopathology and chemical shift MRI showed that MRI had 90% sensitivity and 100% specificity in detecting thymoma with overall diagnostic accuracy 93.3% (P = 0.5). MRI chemical shift ratio showed 100% sensitivity by using > 0.85 as a cut off value for diagnosis of thymoma, with specificity 83.3% (P = 0.0001). There was statistically significant difference in chemical shift ratio between thymic lymphoid hyperplasia and thymoma groups, as thymoma group had a higher chemical shift ratio of 1.06 ± 0.06 compared to 0.48 ± 0.13 in thymic hyperplasia group (P = 0.0001).ConclusionMRI chemical shift imaging with chemical shift ratio offers a highly sensitive and specific tool in assessment of thymus lesions in myasthenia gravis patients and it can differentiate between thymic hyperplasia and thymoma using cutoff value of > 0.85, hence, unwarranted invasive procedures as thymic biopsy or thymectomy can be avoided and proper management could be planned.

Reply to "Quantitative MRI of the Thymus: Chemical-Shift Ratio, Signal Intensity Index, and Apparent Diffusion Coefficient Value".

AJR 2016; 206:W98 0361–803X/16/2066–W98 © American Roentgen Ray Society Reply to “Quantitative MRI of the Thymus: Chemical-Shift Ratio, Signal Intensity Index, and Apparent Diffusion Coefficient Value” My coauthors and I are grateful to Dr. Karabulut for his interest in our Structured Review article titled “Pitfalls in the Imaging and Interpretation of Benign Thymic Lesions: How Thymic MRI Can Help” [1] and his excellent comments. We agree with most of the comments and would like to add the following. First, Dr. Karabulut is correct that the initially electronically published article very unfortunately had a mistyped equation for the calculation of the chemical-shift ratio (CSR), with the denominators exchanged. This error was rapidly discovered and corrected within a few days, so the CSR equation is now correctly displayed as follows:

Determination of a cutoff attenuation value on single-phase contrast-enhanced CT for characterizing adrenal nodules via chemical shift MRI.

This study aims to determine the optimal cutoff attenuation value on single-phase contrast-enhanced CT(CECT) at which chemical shift MRI (CSMRI) yields sufficient accuracy to replace the standard CT adrenal protocol for the diagnosis of adrenal adenomas. Between January 2010 and December 2014, a total of 49 patients (age: 20-81years; 23 men and 26 women) with 60 adrenal tumors (48 adenomas and 12 non-adenomas) who underwent both CECT in portal venous phase and CSMRI were included in the study. Attenuation on portal venous phase CECT, adrenal-to-spleen chemical shift ratio (ASR), and signal-intensity index (SII) were obtained for each adrenal mass. Among different cutoff values on CECT (from <70 to <120HU), the diagnostic accuracies for those lesions measuring <80HU were the highest and most similar to dedicated adrenal CT. The sensitivities and specificities of SII were up to 96% (25/26) and 100% (7/7) for those measuring <80HU, but reduced to 73% (16/22) and 80% (4/5) for those ≥80HU. The overall sensitivities and specificities for diagnosing adrenal adenoma using SII vs. ASR were 85% (41/48) and 92% (11/12) vs. 71% (34/48) and 100% (12/12), respectively. CSMRI may replace CT adrenals in the work-up of patients with adrenal nodules below 80HU on single-phase CECT, hence reducing radiation exposure and iodinated contrast administration. Adrenal nodules greater than 80HU cannot be accurately diagnosed by CSMRI. CT adrenal protocol remains the appropriate investigative modality in those cases.

Differentiation of rebound and lymphoid thymic hyperplasia from anterior mediastinal tumors with dual-echo chemical-shift MR imaging in adulthood: reliability of the chemical-shift ratio and signal intensity index.

To prospectively evaluate (a) effectiveness and limits of dual-echo chemical-shift magnetic resonance (MR) imaging for distinguishing hyperplastic thymus from anterior mediastinal tumors in adulthood by using chemical-shift ratio ( CSR chemical-shift ratio ) and signal intensity index ( SII signal intensity index ), with proposal of optimal threshold value for each, and (b) whether age affects these indexes. Study was institutional review board approved, with informed consent obtained. Ninety-two subjects (53 men, 39 women; age range, 18-84 years) were divided into a rebound and lymphoid hyperplasia group (group A, 30 patients) and a tumor group (group B, 62 patients). MR images were assessed; interrater reliability was evaluated. Differences in CSR chemical-shift ratio and SII signal intensity index were tested with the Mann-Whitney U test and the Kruskal-Wallis test. Discrimination abilities of CSR chemical-shift ratio and SII signal intensity index were evaluated with logistic regression models, and optimal cutoff points were proposed. Quantitative parameters were correlated with age by using Pearson correlation coefficients. Interreader agreement was excellent (intraclass correlation coefficient: CSR chemical-shift ratio , 0.893; SII signal intensity index , 0.898). Mean CSR chemical-shift ratio and SII signal intensity index ± standard deviation were 0.545 ± 0.162 and 46.29% ± 18.41 for group A and 1.045 ± 0.094 and -0.06% ± 4.89 for group B, respectively, with significant differences for both indexes between groups (P < .0001). No overlap was found for SII signal intensity index between groups; CSR chemical-shift ratio values overlapped in a few younger adults. Distinguishing hyperplastic thymus from tumors was better with SII signal intensity index than CSR chemical-shift ratio . Respective sensitivity, specificity, and cutoff points were 100%, 100%, and 8.92% for SII signal intensity index and 100%, 96.7%, and 0.849 for CSR chemical-shift ratio . Significant correlation was found for CSR chemical-shift ratio (r = -0.761) and SII signal intensity index (r = 0.821) with age in group A (P < .001). For group B, significant correlation with age was seen for CSR chemical-shift ratio (r = 0.702, P < .001) but not SII signal intensity index (r = -0.196, P = .127). All subjects but one in group A and none in group B had signal intensity decrease at chemical-shift MR imaging. With dual-echo chemical-shift MR imaging, SII signal intensity index and CSR chemical-shift ratio have high accuracy to distinguish thymic hyperplasia from tumors, although overlapped CSR chemical-shift ratio values can occur in early adulthood.

Low yield of chemical shift MRI for characterization of adrenal lesions with high attenuation density on unenhanced CT

To investigate the threshold unenhanced CT density of adrenal nodules at which further evaluation with chemical shift MRI is unlikely to be definitive and therefore not helpful in further characterizing some indeterminate adrenal lesions. Retrospective evaluation of 44 adrenal lesions imaged with unenhanced CT and chemical shift MRI and followed for at least 1 year. Qualitative and quantitative assessment of signal loss on chemical shift MRI was performed. Adenomas were diagnosed if the lesion measured equal or less than 10 HU on unenhanced CT; on MRI a SI index greater than 16.5% or adrenal:spleen chemical shift ratio less than 0.71 was considered diagnostic of adenoma. 31.8% (14/44), 47.7% (21/44), and 20.5% (9/44) of the adrenal lesions had an unenhanced CT attenuation density ≤10, 10-30, and >30 HU. Adrenal lesions with an unenhanced CT density 10-30 and >30 HU had a 76.2% (16/21) and a 33.3% (3/9) chance of being categorized as an adenoma using MRI SI index, respectively. Adrenal lesions with unenhanced attenuation CT density >30 HU had a 66.6% of remaining indeterminate even after evaluation with chemical shift MRI. Chemical shift MRI is reasonable for evaluating adrenal lesions with an unenhanced CT attenuation density less than 30 HU. The likelihood of chemical shift MRI detecting signal loss in lesions CT density greater than 30 HU, however, is low.

Synthesis, luminescence and NMR studies of lanthanide (III) complexes with hexafluoroacetylacetone and phenanthroline. Part II

The paper reports the syntheses, 1H NMR spectral and luminescence spectral studies of eight-coordinate Sm, Eu, Tb, Dy and Tm complexes of the type [Ln(hfaa)3(phen)] (hfaa=hexafluoropentanedione and phen=1,10-phenanthroline). These complexes have been synthesized in high yields by modifying a method reported in literature for synthesizing similar complexes. Large up field and downfield shifts were observed in their 1H NMR spectra. The lanthanide induced chemical shifts in these paramagnetic complexes are dipolar in nature. The H(2) and H(4) proton resonances of phen of the thulium complex have been shifted to highfields which is unusual. Inter- and intra-molecular chemical shift ratios are similar for Sm and Eu complexes as these are isostructural in solution. The quantum yields (Φ=46% for Eu, 32% for Tb, 2.7% for Sm and 2.1% for Dy) of the complexes indicate that energy transfer from ligands (hfaa and phen) to Ln(III) is efficient. The luminescence in the Dy(III) complex is the least intense due to poor intramolecular energy transfer match as compared to rest of the complexes. The lanthanide ions in these complexes have low symmetry sites.

A Prospective Study on the Utility of Diffusion-Weighted and Quantitative Chemical-Shift Magnetic Resonance Imaging in the Distinction of Adrenal Adenomas and Metastases

The purpose of this study was to assess the utility of diffusion-weighted and quantitative chemical-shift magnetic resonance imaging in the differentiation of adrenal adenomas and metastases. One hundred eight patients (45 men and 63 women; mean age, 57 years) with 126 adrenal masses were prospectively evaluated by magnetic resonance imaging in this study. Signal intensity and apparent diffusion coefficient (ADC) measurements were performed on axial in- and opposed-phase T1-weighted gradient-echo images and on diffusion-weighted images, respectively. Adrenal signal intensity index (ASII), adrenal-to-spleen chemical-shift ratio (ASR), and ADC values were assessed separately. The threshold values of more than 16.5% for ASII and less than 0.71 for ASR were regarded as highly suggestive of adenoma diagnosis. We also investigated whether a cutoff value for ADC could be found in distinguishing adenomas from metastases. Final diagnoses of adrenal lesions were based on follow-up imaging, histopathologic proof, and adrenal washout study. Apparent diffusion coefficient values of adenomas and metastases were compared by using the Student t test, and ASII and ASR values of the lesions were compared by using the Mann-Whitney U test, and a P < 0.05 was accepted as statistically significant. Receiver operating characteristic curve analysis and sensitivity, specificity, positive and negative predictive values, and overall accuracies were calculated. Final analysis yielded 96 adenomas and 30 metastases. With the commonly used 16.5% threshold value for ASII, we obtained a 94.8% sensitivity, 93.3% specificity, 84.8% positive predictive value, and 97.8% negative predictive value. The overall accuracy was found as 94.4%. When we applied a 0.71 threshold value for ASR, it yielded a 91.7% sensitivity, 100% specificity, 78.9% positive predictive value, and a 100% negative predictive value. The overall accuracy was 93.6%. The mean ADC values were found to be 1.35 ± 0.19 × 10⁻³ mm²/s and 1.32 ± 0.34 × 10⁻³ mm²/s for adenomas and metastases, respectively. The difference between the groups with these ADC values was not statistically significant (P = 0.673). The receiver operating characteristic analysis could not determine a clear cutoff value for the differentiation of adenomas from metastases. We can advocate that a chemical-shift magnetic resonance imaging using quantitative parameters (ie, ASII and ASR formulas) has an important role in the distinction of adenomas from metastases. These 2 techniques seem to provide close sensitivity, specificity, and accuracy levels. But diffusion-weighted imaging using quantitative ADC measurements is not of value in this differential diagnosis because of the substantial overlapping of ADC values between adenomas and metastases.

Comparison of computed tomography histogram analysis and chemical-shift magnetic resonance imaging for adrenal mass characterization

Computed tomography (CT) histogram analysis and chemical-shift magnetic resonance imaging (MRI) are currently used modalities for adrenal mass characterization. However, it is not yet clear which modality can be regarded as most sensitive in terms of adrenal mass characterization. To prospectively compare CT histogram analysis and chemical-shift MRI in the characterization of adrenal masses. Between May 2007 and November 2008, 93 patients (45 males, 48 females; mean age 56.7 years, range 22-85 years) with 109 adrenal masses prospectively underwent both unenhanced CT and chemical-shift MRI examinations. These masses consisted of 67 adenomas and 42 metastases. Histogram analysis was applied with a circular region of interest (ROI) that recorded mean attenuation, total number of pixels, number of negative pixels, and the percentage of negative pixels on unenhanced CT images for each adrenal mass. In the CT histogram analysis, a 10% negative pixel threshold for unenhanced CT was calculated. In chemical-shift MRI, signal intensity drop between in-phase and opposed-phase images was quantitatively calculated so that adrenal-to-spleen chemical-shift ratios and adrenal signal intensity indexes were determined for each of the adrenal masses. A mass was regarded as an adenoma if it contained more than 10% negative pixels by CT histogram analysis, showed an adrenal-to-spleen chemical-shift ratio of less than 0.71, and had an adrenal signal intensity index of more than 16.5% by chemical-shift MRI. The results were compared to reveal which method was most sensitive in the diagnosis of adrenal masses and whether or not a correlation exists between these two modalities. Final diagnoses were based on imaging follow-up of minimum 6 months, biopsy, surgery, and adrenal washout study. On unenhanced CT examinations, all of the 67 adenomas and 21 out of 42 metastases exhibited negative pixels. None of the metastases showed more than 10% negative pixels on CT histogram analysis. An increase in the percentage of negative pixels correlated well with a decrease in the mean CT attenuation. CT histogram analysis using a 10% negative pixel threshold gave a 91% sensitivity and 100% specificity for the diagnosis of an adenoma. On chemical-shift MRI, for an adrenal-to-spleen chemical-shift ratio of less than 0.71, a 97% sensitivity and 100% specificity were achieved, while a 97% sensitivity and 93% specificity were obtained for an adrenal signal intensity index of more than 16.5% for adenoma diagnosis. CT histogram analysis method using a 10% negative pixel threshold on unenhanced CT had a good sensitivity and perfect specificity for the differentiation of adrenal adenomas from non-adenomas. In spite of the good results obtained with the CT histogram analysis method, chemical-shift MRI using adrenal-to-spleen chemical-shift ratio and adrenal signal intensity index formulas had a higher sensitivity and could help in the characterization of adrenal masses appearing indeterminate by CT histogram analysis.

Primary mediastinal Hodgkin lymphoma and rebound thymic hyperplasia: differentiation with chemical-shift magnetic resonance imaging after treatment

A 30-year-old man complained of progressive fatigue, cough and mild intermittent fever of 3 months duration. Chest radiography showed a smoothly marginated mediastinal mass. Contrast-enhanced computed tomography (CT) scan depicted a slightly heterogeneous anterior mediastinal solid lesion with smooth margins (Fig. 1). Chemical-shift magnetic resonance (CSMR) imaging demonstrated no apparent decrease in signal intensity of the lesion on transverse T1-weighted opposed-phase images (Fig. 2b) relative to in-phase images (Fig. 2a), suggesting the absence of fat tissue component within the mass. Chemical-shift ratio (CSR), determined by comparing the signal intensity of the mass with that of the paraspinal muscle on both in-phase and opposed-phase images, was 1.035. CT and fluorodeoxyglucose positron emission tomography (FDG-PET) did not show any other apparent site of disease. CT-guided transthoracic needle core-biopsy demonstrated Hodgkin disease. The patient was treated with combined-modality therapy and underwent complete remission. Six months after the end of treatments, follow-up CT scan depicted a homogeneous soft-tissue structure with a biconvex margin in the anterior mediastinum (Fig. 3), characterized by positive attenuation values without evidence of fatty component. To differentiate hyperattenuating rebound thymic hyperplasia from recurrence of lymphoma, patient underwent CSMR. CSMR demonstrated high decrease in signal intensity of the mass on opposed-phase (Fig. 4b) relative to in-phase images (Fig. 4a), suggesting the presence of fat within tissue, and therefore the diagnosis of hyperplastic thymus. CSR was 0.585. No increase in size of the anterior mediastinal tissue was detected at follow-up CT performed at 6, 12 and 18 months. Meanwhile, patient did not undergo any treatment because neither clinical nor biochemical signs of relapse were found in this period. At present, he remains in complete remission, with a follow-up of 20 months. CSMR imaging is more sensitive than other fat-suppressed MR sequences for detecting microscopic fat within tissue. CSMR demonstrates the presence of an intravoxel mixture of fat and water in tissue, which would be indistinct at CT, by showing homogeneously decreased signal intensity on the opposed-phase images relative to the inphase images, with CSR value less than 0.7. In clinical

Thymic Hyperplasia and Thymus Gland Tumors: Differentiation with Chemical Shift MR Imaging1

To prospectively evaluate chemical shift magnetic resonance (MR) imaging for differentiating thymic hyperplasia from tumors of the thymus gland. The institutional review board approved this study; informed consent was obtained and patient confidentiality was protected. The authors assessed 41 patients (17 male, 24 female; age range, 16-78 years) in whom thymic lesions were seen at chest computed tomography. Patients were assigned to a hyperplasia group (n=23) (18 patients with hyperplastic thymus associated with Graves disease and five with rebound thymic hyperplasia) and a tumor group (n=18) (seven patients with thymomas, four with invasive thymomas, five with thymic cancers, and two with malignant lymphomas). T2-weighted fast spin-echo and T1-weighted in-phase and opposed-phase MR images were obtained in all patients and visually assessed. A chemical shift ratio (CSR), determined by comparing the signal intensity of the thymus gland with that of the paraspinal muscle, was calculated for quantitative analysis. Mean CSRs for the patient groups and subgroups were analyzed by using Welch t and Newman-Keuls tests. P<.05 indicated a significant difference. The thymus gland had homogeneous signal intensity in all 23 patients in the hyperplasia group and in 12 of the 18 patients in the tumor group. The mean CSR (+/- standard deviation) was 0.614 +/- 0.130 in the hyperplasia group and 1.026 +/- 0.039 in the tumor group. Mean CSRs in the patients with a hyperplastic thymus and Graves disease, rebound thymic hyperplasia, thymoma, invasive thymoma, thymic cancer, and malignant lymphoma were 0.594 +/- 0.120, 0.688 +/- 0.154, 1.033 +/- 0.043, 1.036 +/- 0.040, 1.020 +/- 0.044, and 0.997 +/- 0.010, respectively. The difference in CSR between the hyperplasia and tumor groups was significant (P<.001). Mean CSRs in the hyperplasia subgroups were lower than those in the tumor subgroups (P<.001). All hyperplasia group patients had an apparent decrease in thymus gland signal intensity at chemical shift MR imaging; no tumor group patients had a decrease in thymus gland signal intensity. Chemical shift MR imaging can be used to differentiate thymic hyperplasia from thymic tumors.

Characterization of adrenal adenomas and metastases: correlation between unenhanced computed tomography and chemical shift magnetic resonance imaging

To evaluate the correlation of absolute attenuation values of unenhanced computed tomography (CT) with signal intensity (SI) quantitative analysis on chemical shift (CS) magnetic resonance (MR) imaging in differentiating adrenal adenomas from metastases. Forty-one adrenal masses (27 adenomas, 14 metastases) were studied with CS MR imaging and unenhanced CT. MR included T1-weighted breathhold gradient-echo in-phase (IP) and opposed-phase (OP) sequences. The SI index (SI-i) [(SIIP-SIOP/SIIP)] x 100% and chemical-shift ratio (CS-r) relative to the spleen [(SIlesion/ SIspleen)OP/(SIlesion/SIspleen)IP] were calculated for each lesion. CT absolute attenuation values were also determined. The mean attenuation value of metastases was significantly greater than that of adenomas (< 0.0001). On MR, the mean SI-i of adenomas was significantly greater than that of metastases (P < 0.0001) and no overlaps were evident. The CS-r of malignant and benign lesions overlapped considerably, and five adenomas (all with indeterminate Hounsfield Unit values at CT) were misclassified as potentially malignant. CT attenuation values were significantly correlated with both MR quantitative analyses. Since CS MR imaging and CT both depict the presence of lipids within adrenal lesions, absolute attenuation values are highly correlated with MR quantitative analysis. SI-i is the most reliable tool for differentiating adrenal adenomas from metastases, showing better accuracy than lesion-to-spleen CS-r, in particular for adenomas with indeterminate absolute attenuation values.

IS ADRENALECTOMY A NECESSARY COMPONENT OF RADICAL NEPHRECTOMY? UCLA EXPERIENCE WITH 511 RADICAL NEPHRECTOMIES

We determine the incidence and characteristics of adrenal involvement in localized and advanced renal cell carcinoma, and evaluate the role of adrenalectomy as part of radical nephrectomy. The records of 511 patients undergoing radical nephrectomy with ipsilateral adrenalectomy for renal cell carcinoma at our medical center between 1986 and 1998 were reviewed. Mean patient age was 63.2 years (range 38 to 85), and 78% of the subjects were males and 22% were females. Patients were divided into subgroups of 164 with localized (stage T1-2 tumor, group 1) and 347 with advanced (stage T3-4N01M01, group 2) renal cell carcinoma. Staging of tumors was performed according to the 1997 TNM guidelines. A retrospective review of preoperative computerized tomography (CT) of the abdomen was performed. Radiographic findings were subsequently compared to postoperative histopathological findings to assess the predictive value of tumor characteristics and imaging in determining adrenal metastasis. Of the 511 patients 29 (5.7%) had adrenal involvement. Average size of the adrenal tumor was 3.86 cm. (standard deviation 1.89). Tumor stage correlated with probability of adrenal spread, with T4, T3 and T1-2 tumors accounting for 40%, 7.8% and 0.6% of cases, respectively. Upper pole intrarenal renal cell carcinoma most likely to spread was local extension to the adrenal glands, representing 58.6% of adrenal involvement. In contrast, multifocal, lower pole and mid region renal cell carcinoma tumors metastasized hematogenously, representing 32%, 7% and 4% of adrenal metastasis, respectively. The relationship between intrarenal tumor size (mean 8.9 cm., range 3 to 17) and adrenal involvement (independent of stage) was not statistically significant. Renal vein thrombus involvement was demonstrated in 8 of 12 cases (67%) with left and 2 of 9 (22%) with right adrenal involvement. Preoperative CT demonstrated 99.6% specificity, 99.4% negative predictive value, 89.6% sensitivity and 92.8% positive predictive value for adrenal involvement by renal cell carcinoma. With a low incidence of 0.6%, adrenal involvement is not likely in patients with localized, early stage renal cell carcinoma and adrenalectomy is unnecessary, particularly when CT is negative. In contrast, the 8.1% incidence of adrenal involvement with advanced renal cell carcinoma supports the need for adrenalectomy. Careful review of preoperative imaging is required to determine the need for adrenalectomy in patients at increased risk with high stage lesions, renal vein thrombus and upper pole or multifocal intrarenal tumors. With a negative predictive value of 99.4%, negative CT should decrease the need for adrenalectomy. In contrast, positive findings are less reliable given the relatively lower positive predictive value of this imaging modality. Although such positive findings may raise suspicion of adrenal involvement, they may not necessarily indicate adrenalectomy given the low incidence, unless renal cell carcinoma with risk factors, such as high stage, upper pole location, multifocality and renal vein thrombus, is present.

Mixed-ligand lanthanide complexes—X. Interaction of trivalent lanthanides with 1,10-phenanthroline and thiocyanate in alcohol

The interaction of trivalent lanthanide thiocyanates and phen in ethanol results in the formation of the complexes of the type [Ln(phen) 3(SCN) 3], where Ln = La, Pr, Nd, Sm and Eu; and [Ln(phen) 3 (SCN) 3(H 2O)], where Ln = Dy, Ho, Er and Yb. The complexes have been characterized by elemental analyses, molar conductance, IR spectra and thermal analyses. The complexes behave as non-electrolytes in methanol. TGA showed the presence of coordinated water in the case of the heavier lanthanides making them ten-coordinate. The NMR spectra of the complexes of La, Pr, Nd, Sm, Eu and Yb have been studied in DMSO- d 6 and pyridine- d 5. The complexes do not dissociate in DMSO and retain their coordination number. The chemical shift ratios are constant for different phen protons which indicates dipolar nature of the shift. Pyridine coordinates without displacing any ligand and increases the coordination number of the lighter lanthanides from nine to ten.

95Mo NMR spectral studies on seven-coordinate molybdenum(II) isocyanide complexes

The 95Mo NMR spectra of a series of seven-coordinate molybdenum(II) isocyanide complexes of the types [Mo(CNR) 7- n L n ](PF 6) 2 (R = CH 3, CHMe 2, CMe 3, C 6H 11, CH 2Ph; L = py, bpy, Me 2bpy, phen, dppe, P-n-Bu 3; n = 0,1,2) [Mo(CNC-Me 3) 6X]PF 6 (X = Cl, Br, I) and [{Mo(CNCMe 3) 4(NN)} 2(μ-CN)](PF 6) 3 (NN = bpy, Me 2bpy, phen) have been studied. The 95Mo chemical shift range for this group of complexes is about 1100 ppm. An increase in the size of the R group attached to the isocyanide ligand generally tends to shield the 95Mo nucleus. Replacement of the isocyanide ligand with a phosphorus ligand also increases the shielding, whereas the replacement of isocyanide with a heterocyclic nitrogen donor leads to deshielding by 800–900 ppm. This group of complexes shows a normal halogen dependence, i.e. replacement of Cl − by Br − and I − increases the shielding of the 95Mo nucleus. The cyano-bridged cations [{Mo(CNCMe 3) 4(NN)} 2(μ-CN)] 3+ (NN = bpy, Me 2bpy, or phen) show two 95Mo NMR signals, one for the molybdenum coordinated to the carbon of the bridging CN and one for the N-coordinated molybdenum. Comparison of the chemical shifts and linewidths of the cyano-bridged species with those of the corresponding mononuclear molybdenum(II) complexes [Mo(CNCMe 3) 5(NN)](PF 6) 2 leads to the assignment of the more deshielded signal to the N-coordinated molybdenum. The 14N and 31P NMR spectra for these complexes have also been measured, as have the 13C NMR spectra of the pairs of complexes [Mo(CNCMe 3) 5(NN)](PF 6) 2 and [{Mo(CNCMe 3) 4(NN)} 2(μ-CN)](PF 6) 3 (NN = bpy or phen). The 183W NMR spectra for [W(CNR) 5(bpy)](PF 6) 2 (R = CMe 3 and CH 2Ph), show that the δ( 183W)/δ( 95Mo) chemical shift ratios for isocyanide complexes are different from the ratio found for M 0 and M VI.

X-Ray Photoelectron and Anger Electron Spectroscopic Studies of Chemical Shifts in Amorphous Ge–Se System

The chemical shifts of the Ge 3d, 3p3/2,1/2 and Se 3d, 3p3/2,1/2 photoelectron lines were measured for the amorphous Ge–Se system and those of the Ge photoelectron lines are corrected for Auger parameter shifts. According to the valence shell potential model, the ratio of the chemical shift in the amorphous Ge–Se system to that in stoichiometric GeSe2 can be approximated by the ratio of the Ge–Se bond number in the Ge–Se system to that in GeSe2. The chemical shift ratios evaluated from the experimental results reveal bond structures at non-stoichiometric compositions. In the excess-Ge range, GeSe is composed of atomic clusters of three-fold co-ordinated Ge and Se atoms, and Ge2Se3 contains atomic clusters of Se3Ge–GeSe3 units. In the excess-Se range, GeSe3 includes GeSe4 tetrahedral units, and Se–Se chains and/or Se8 rings.

Conformational analysis of 2-butanone and 3-methyl-2-butanone using lanthanide shift reagents

Lanthanide-induced 13C and 1H NMR chemical shift ratios of 2-butanone and 3-methyl-2-butanone have been determined using the shift reagent Yb(fod) 3. The induced shift data were analyzed to derive the conformational populations for these ketone-lanthanide chelate complexes. For 2-butanone, the cis conformation (methyl eclipsing the carbonyl) was found to be more stable than the gauche conformation (hydrogen eclipsing the carbonyl). The equilibrium constant for cis conformation ⇋ gauche conformation is 0.7 at 37°C. For 3-methyl-2-butanone, however, no conclusion can be drawn from our data. Possible reasons for this difficulty are discussed.