Rüdiger Fründ

The Chemical Nature of Nitrogen in Native Soil Organic Matter

H. Knicker, R. Frtind and H.-D. Ltidemann Institut for Biophysik und physikalische Biochemie der Universit~it, W-8400 Regensburg, FRG Fossil fuels and soil organic matter (SOM) together contain approximately five times more carbon than the biota and the atmosphere. Of this, soil organic matter accounts for about 30 % of the carbon present. In addition, SOM has an average carbon/nitrogen ratio of 10/1 and contains a huge fraction of the total ni- trogen available for plant growth [1]. Taking into account that the abundance of nitrogen in the earths crust is much lower than that of carbon, this is a signif- icant fraction of the total nitrogen acces- sible to the biosphere. Under natural soil conditions, without the addition of miner- al fertilizers, SOM provides the majority of the nitrogen necessary for plant growth. It is also thought to be respon- sible for the interaction between agricul- tural biocides and the soil [5-7]. The chemical structure of this ubiquitous material, SOM, and especially the chem- ical nature of the nitrogen are thus of great and general importance. The mo- lecular structure of the nitrogen- containing fraction is, however, still a matter of controversy [2-4]. Structural models based on partial chem- ical analysis claim that a significant part of the nitrogen is present in the form of heteroaromatic structures, while NMR- spectroscopic studies on lSN-enriched composts and recent humic material found approximately 85 % of the signal intensity in the amide/peptide region of chemical shift and no signals in the range typical for heteroaromatic nitrogen. A major fraction of the native soil organic matter has been in the soil for several hundred to several thousand years [8, 9]. Compared to these time spans, laboratory-produced material has been fermented for at most 1 year, and it could be argued that heteroaromatic structures are only produced after much longer fermentation periods. This criti- cism may be overcome by the study of lsN-CPMAS spectra of soil organic mat- ter with natural lSN levels. This has not been achieved hitherto, because the low natural abundance (0.4 %) and the small gyromagnetic ratio of the 15N nucleus and therefore its low sensitivity in NMR experiments appeared to make this experiment an impossible one. The most abundant 14N-isotope (99.6 %) cannot be studied by high-resolution NMR because its large nuclear quadrupole moment leads to very broad and unresolved signals, especially in solid-state NMR [101. In previous systematic studies on 15N- enriched composts and organic soil extracts [11] our group optimized all spectral parameters for the ~sN-CPMAS experiment. A crude estimate showed that it should be possible to obtain 15N spectra with a tolerable signal-to-noise ratio after the accumulation of approximately one million transients. In the present paper we report on the first successful results of such experiments. Six German soils were studied as detailed in Table 1. In Figs. 1 and 2 some of the spectra obtained are shown. They fully corrobo- rate the conclusions drawn from the stud- ies of short-term composting exper-

Enzymatic co-polymerization of lignin with low-molecular mass compounds

The oxidoreductive enzyme laccase (E.C.1.10.3.2.) isolated from a culture medium of white-rot fungus Trametes versicolor transformed lignin preparations solubilized in a dioxane-H2O (7:3) mixture. The obvious net result of lignin transformation was an increase in molecular mass. A superoxide radical was found in the reaction mixture during lignin incubation with laccase. It appeared that a change in the reaction medium or in the lignin molecule instigated by laccase could lead to polymerization after the lignin molecules had crossed a dialysis membrane and were separated from the enzyme. Two possible mechanisms are suggested, either diffusion of an activated oxygen species or diffusion of primed lignin molecules. Laccase was able to co-polymerize lignin with low-molecular-mass compounds of different origins, particularly with aromatics containing either carboxyl or isocyanate groups, as well as acrylamide — an aliphatic monomer containing a vinyl group.

Detection of Simulated Chest Lesions with Normal and Reduced Radiation Dose: Comparison of Conventional Screen-film Radiography and a Flat-panel X-ray Detector Based on Amorphous Silicon

RATIONALE AND OBJECTIVES The authors compared a solid-state amorphous silicon (a-Si) detector and screen-film radiography (SFR) with regard to the detection of simulated pulmonary lesions. Evaluation of the impact of a dose reduction of 50% with this digital flat-panel detector was of special interest. METHODS A self-scanning flat-panel detector, based on a-Si technology with 143 x 143 microm pixel size, 1 k x 1 k matrix and 12-bit digital output was used. An asymmetric state-of-the-art screen-film system was compared with a-Si images taken at the same dose as SFR-images and at a dose reduced by 50%. An anthropomorphic chest phantom was superimposed by templates containing nodules, linear structures, reticular, and micronodular opacities in a random distribution. Receiver operating characteristic analysis was performed for 23,040 observations made by four independent observers. Students t test (95% confidence-level) was used for statistical analysis. RESULTS Receiver operating characteristic analysis showed that a-Si images taken at the same dose as SFR-images were significantly superior to SFR with respect to the detectability of lines (P = 0.01) and micronodular opacities (P < 0.01). For the other objects and the a-Si images taken at a reduced dose, it yielded no statistically significant differences between both imaging modalities. CONCLUSIONS The results of this phantom study indicate that a-Si detector technology holds promise in terms of dose reduction in chest radiography without loss of diagnostic accuracy compared with SFR.

Transformation of lignin-related compounds with laccase in organic solvents

Abstract The extracellular laccase (benzenediol: oxygen oxidoreductase, EC 1.10.3.2) of Trametes versicolor was isolated from culture medium and immobilized by entrapment of the enzyme in a solvent-resistant hydrophilic matrix like Sepharose-CL-6B. The gel-enzyme association has been shown to be stable in water containing organic solvents. The efficiency of the immobilized laccase in different organic solvents was comparable with the activity shown in a buffered aqueous system. The immobilized laccase in organic solvents showed a good stability and a high tolerance to elevated temperatures. Water-insoluble organosolv lignin (OL), dissolved in dioxane/water, was readily converted by immobilized laccase from Trametes versicolor . The transformed lignin showed an increase in phenolic groups, changes in the quantity of conjugated elements, and a significant modification of both the aliphatic and aromatic carbon moieties of the lignin molecule. The changes in the lignin molecule were analyzed by UV-, IR-spectroscopy, and 13 C-NMR solid-state spectroscopy. High-performance size exclusion chromatography (HPSEC) of the lignin transformed with the laccase—Sepharose complex revealed a pronounced increase in weight-average molecular weight. Polymerization of the lignin in the organic solvent proved to be 4 times more effective than polymerization of the same compound in an aqueous system. Water-insoluble organosolv lignin as well as a variety of lignin-related aromatics, solubilized in dioxane-H 2 O (7 : 3), was readily converted by laccase preparation either in batch or in continuous flow column. Reaction of laccase with the solubilized lignin generates in the reaction media reduced oxygen species able to reduce the cytochrome c. For the first time it is now possible to perform enzymatically catalyzed reactions with lignin in an organic solvent. This is a first step towards an enzymatically derivatization of lignin, the formation of polymer blends on the basis of lignin by an enzymatically catalyzed reaction.

Amorphous silicon, flat-panel, x-ray detector versus screen-film radiography: effect of dose reduction on the detectability of cortical bone defects and fractures.

RATIONALE AND OBJECTIVES The purpose of this phantom study was to assess the diagnostic performance of a self-scanning, solid-state amorphous silicon (a-Si) detector in skeletal radiography using different exposure parameters. METHODS A flat-panel detector (15 cm x 15 cm), based on a-Si technology with 143 microm x 143 microm pixel size, 1k x 1k matrix, and 12 bit digital output was used. State-of-the-art screen-film radiography (SFR; speed 400, detector dose 2.5 microGy) was compared with a-Si images taken at doses that were equivalent to a speed of 400, 800, 1,250, and 1,600, respectively. A total of 232 segments of long tubular deer-bones (femur, tibia, humerus, radius) had 110 artificial fractures and 112 cortical defects simulating osteolytic lesions. Receiver operating characteristic analysis was performed for 9,280 observations made by four independent observers. Two-tailed Students paired t test was used for statistical analysis (95% confidence level). RESULTS Receiver operating characteristic analysis yielded equivalent results of the a-Si and SFR system. Even at the lowest dose there were no statistically significant differences between both imaging modalities with respect to the detectability of fractures and cortical defects. CONCLUSIONS The results of this study indicate that a-Si detector technology holds promise in terms of dose reduction in skeletal radiography without loss of diagnostic accuracy.

Visualization of the IXth to XIIth Cranial Nerves Using 3-Dimensional Constructive Interference in Steady State, 3-Dimensional Magnetization-Prepared Rapid Gradient Echo and T2-Weighted 2-Dimensional Turbo Spin Echo Magnetic Resonance Imaging Sequences

Objective. The purpose of this study was to evaluate the visibility of the IXth to XIIth cranial nerves using different magnetic resonance sequences. Thirty healthy volunteers underwent magnetic resonance imaging at 1.5 T using 3‐dimensional constructive interference in steady state (CISS) sequence (TR = 17 ms, TE = 8.08 ms, α= 70°), 3‐dimensional magnetization‐prepared rapid gradient echo (MP‐RAGE) sequence (TR = 11.08 ms, TE = 4.3 ms, α= 15°), and T2‐weighted (w) 2‐dimensional turbo spin echo (TSE) sequence (TR = 4000 ms, TE = 102 ms, α= 180°, slice thickness = 2 mm). Visibility of the IXth to XIIth cranial nerves in each sequence was evaluated by consensus of 2 radiologists using an evaluation scale from 1 (excellently visible) to 5 (not visible). A correlation with anatomic specimens was made. The 3‐dimensional CISS sequence provides best resolution of the IXth to XIIth cranial nerves and their relation to surrounding structures. Additional information is given by the 3‐dimensional MP‐RAGE when nerves are surrounded by soft tissues. Using the T2w 2‐dimensional TSE sequence, even whole nerves cannot be visualized due to intersection gap and partial volume effects. However, even in 3‐dimensional high‐resolution sequences, segments of nerves are not always visualized. A combination of 3‐dimensional CISS and 3‐dimensional MP‐RAGE proved to be useful to visualize the IXth to XIIth cranial nerves, whereas the 2‐dimensional technique failed. Further investigations using 3‐dimensional MP‐RAGE with contrast medium should be performed in the case of abnormality.

Comparison of two-dimensional gradient echo, turbo spin echo and two-dimensional turbo gradient spin echo sequences in MRI of the cervical spinal cord anatomy

The aim of this study was to assess the detectability and distinguishability of the cervical spinal cord, the anterior and posterior spinal roots and of the internal anatomy of the cord (distinction of grey and white matter). For this purpose 20 healthy volunteers were examined using a 1.5 T MR unit with 20 mT/m gradient strength and a dedicated circular polarized neck array coil. Three T2* weighted (w). 2D gradient echo sequences, two T2 w. 2D turbo spin echo (TSE) sequences and one T2 w. 2D turbo gradient spin echo (TGSE) sequence were compared. The multiecho 2D fast low angle shot (FLASH) sequence with magnetization transfer saturation pulse (me FLASH+MTS) yielded the best results for liquor/compact bone, liquor/spinal cord and grey/white matter contrast, as found with regions of interest (ROI) analysis. The single echo 2D FLASH sequence was significantly poorer than the two me FLASH+/-MTS sequences. Two-dimensional TGSE as well as 2D TSE with a 256 matrix and with a 512 matrix yielded the poorest results. In the visual analysis the contrast between liquor and compact bone, liquor and cord as well as liquor and roots was best with me FLASH+MTS, whereas grey/white matter distinction was best using me FLASH-MTS. In conclusion, we would therefore recommend the inclusion of an axial T2* w. multiecho 2D spoiled gradient echo sequence with magnetization transfer saturation pulse and gradient motion rephasing in a MR imaging protocol of the cervical spine.

FLAT-PANEL X-RAY DETECTOR USING AMORPHOUS SILICON TECHNOLOGY : REDUCED RADIATION DOSE FOR THE DETECTION OF FOREIGN BODIES

RATIONALE AND OBJECTIVES The authors evaluate a new flat-panel x-ray detector (FD) with respect to foreign body detection and reduction of radiation dose compared with screen-film radiography. METHODS Flat-panel x-ray detector is based on amorphous silicon technology and uses a 1 k x 1 k photo-detector matrix with a pixel size of 143 x 143 microns and 12-bit digital output. A thallium-dotted cesium iodide scintillation layer converts x-rays into light. An ex vivo experimental model was used to determine the detectability of foreign bodies. Foreign bodies with varying sizes were examined: glass with and without addition of lead, bone, aluminium, iron, copper, gravel fragments, and graphite. Four hundred observation fields were examined using conventional radiography (speed, 400; system dose: 2.5 microGy) as well as FD with a simulated speed of 400, 800, 1200, and 1600, corresponding to a detector dose of 2.5 microGy, 1.25 microGy, 0.87 microGy, and 0.625 microGy, respectively. Four independent radiologists performed receiver operating characteristic analysis of 8000 observations. RESULTS Flat-panel x-ray detector with a simulated speed of 400 was significantly superior (P = 0.012) to screen-film radiography (speed, 400). At a simulated speed of 800 and 1200 FD yielded results equivalent to screen-film radiography. Flat-panel x-ray detector was significantly inferior to screen-film radiography at a simulated speed of 1600 (P = 0.012). CONCLUSIONS Flat-panel x-ray detector technology allows significant reduction in radiation dose compared with screen-film radiography without loss of diagnostic accuracy.

Comparison of 2D and 3D MRI of the optic and oculomotor nerve anatomy

A total of 30 healthy volunteers underwent magnetic resonance imaging (MRI) with T1 weighted (w.) 3D magnetization prepared rapid gradient echo (MP-RAGE), T2 w. 2D turbo spin echo (TSE) and T2* w. 3D constructive interference in steady state (CISS) sequences to evaluate the detectability of the optic, oculomotor, trochlear and abducens nerves. CISS yielded the best results for the trochlear and abducens nerve, MP-RAGE for the optic chiasm and tract. The optic and oculomotor nerves were very well detectable using both CISS and MP-RAGE without any statistically significant difference between the two.

Comparison of 2-D turbo spin echo and 3-D gradient echo sequences for the detection of the trigeminal nerve and branches anatomy

The aim of this study was to assess the detectability of the trigeminal nerve and its branches using T1 weighted (w.) 3-D magnetization prepared rapid gradient echo (MP-RAGE), T2* w. 3D CISS and T2 w. 2-D turbo spin echo MR sequences. Thirty healthy volunteers were examined for this purpose using a 1.5 Tesla MR unit. The detectability of the trigeminal nerve and Gassers Ganglion, i.e. structures that are surrounded by liquor was best using 3-D CISS. In the case of the ophthalmic, maxillary and mandibular nerves, the T1 w. 3-D MPRAGE was significantly better than T2* w. CISS and T2 w. 2-D turbo spin echo. The latter yielded the poorest results. We conclude that both high resolution T2* w. and T1 w. 3-D sequences are necessary in order to detect the liquor-surrounded trigeminal nerve and its soft tissue-surrounded branches. We would therefore recommend the inclusion of constructive interference in steady state (CISS) and MP-RAGE in a MR imaging protocol of the trigeminal nerve and its branches.