In the present study, an efficient method with a high overall yield for preparing phytosphingosin... more In the present study, an efficient method with a high overall yield for preparing phytosphingosine and an analogue was developed. Starting with commercially available 2,3;5,6-di-O-isopropylidene-D-mannofuranose, a variety of lipid moieties were incorporated to obtain phytosphingosine and an analogue. Through an eight-step manipulation, phytosphingosine was obtained with an overall yield of 57%.
Coherence transfer Sensitivity bandwidth Double cross-polarization Magic-angle spinning a b s t r... more Coherence transfer Sensitivity bandwidth Double cross-polarization Magic-angle spinning a b s t r a c t
A fundamental understanding of the mechanism of fiber formation requires a detailed knowledge of ... more A fundamental understanding of the mechanism of fiber formation requires a detailed knowledge of fiber morphology. However due to the limitation of current techniques, the crystallization behavior is still not fully understood. Modern solid state NMR techniques enable one to approach this subject from different aspects. In this work we conducted detailed studies of the morphology of as-spun PET (poly
Rh(PPh 3 ) 3 Cl was immobilized on a (OEt) 3 Si(CH 2 ) 3 PPh 2 modified MCM-41 to form a stable h... more Rh(PPh 3 ) 3 Cl was immobilized on a (OEt) 3 Si(CH 2 ) 3 PPh 2 modified MCM-41 to form a stable hydrogenation catalyst. The morphology of the catalyst was characterized by X-ray absorption spectroscopy. The EXAFS results indicates that the immobilized Rh catalyst has an average Rh-O s (O s is a surface oxygen) and Rh-Si bond distances of 2.01 Å and 3.15 Å, respectively, suggesting that monomeric Rh complex bonds to the MCM-41 surface. However, the structure of the immobilized Rh complex is not retained after hydrogenation of cyclohexene at 75 • C under 150 psi of H 2 . After the reaction, the presence of Rh-Rh contribution with average bond distance of 2.68 Å and coordination number of 1.3 and the missing contribution with bond distance of 3.85 Å suggest that the reaction induces the coalescence of Rh complex to form dimeric Rh species. However, formation of trace amount of Rh metal clusters cannot be ruled out because rather small characteristic peak for the missing Rh-Rh shell may be covered by noise.
This work establishes a general protocol for synthesizing phytosphingosines with various lengths ... more This work establishes a general protocol for synthesizing phytosphingosines with various lengths of lipid chains. The synthetic strategy included the Wittig reaction and olefin cross-metathesis as key steps. Combining these two C-C bond formation methods provide rapid access to adequately protected phytosphingosine backbones. Ó 2007 Elsevier Ltd. All rights reserved. 8 1 2 Figure 1. Retrosynthesis and steps involved in the synthesis of phytosphingosine analog 2 from D-lyxose.
Serine/threonine kinase Akt plays a central role in the regulation of cell survival and prolifera... more Serine/threonine kinase Akt plays a central role in the regulation of cell survival and proliferation. Hence, the search for Akt specific inhibitors constitutes an attractive strategy for anticancer therapy. We have previously demonstrated that the proto-oncogene TCL1 coactivates Akt upon binding to its Plekstrin Homology Domain, and we proposed a model for the structure of the complex TCL1:Akt2-PHD. This model led to the rational design of Akt-in, a peptide inhibitor spanning the A ß-strand of human TCL1 that binds Akt2 PH domain and inhibits the kinase activation.
Nix protein is a BH3-only pro-apoptotic mitochondrial protein. Here we reported the 1H, 13C and 1... more Nix protein is a BH3-only pro-apoptotic mitochondrial protein. Here we reported the 1H, 13C and 15N resonance assignments of zebrafish Nix protein for further understanding the structure and function relationship.
13 C CP/MAS solid-state NMR spectroscopy has been utilized to analyze six steroid compounds, name... more 13 C CP/MAS solid-state NMR spectroscopy has been utilized to analyze six steroid compounds, namely testosterone (Tes), hydrocortisone (Cor), trans-dehydroandrosterone (Adr), prednisolone (Prd), prednisone (Pre) and estradiol (Est). Among them, Tes displays a doublet pattern for all residues, whereas Prd, Pre and Est, exhibit exclusively singlets. For Cor and Adr, the 13 C spectra contain both doublet and singlet patterns. The 13 C doublet signal, with splittings of 0.2-1.5 ppm, are ascribed to local differences in the ring conformations associated with polymorphism. We have assigned all of the 13 C resonances to the different residues in these steroid compounds on the basis of solution NMR data. The C-7, C-8, C-10, C-15 and C-16 residues of Tes, Cor and Adr consistently give rise to singlets or doublets with splittings of less than 0.5 ppm, indicating similar local conformations. Accompanying hydration and dehydration processes, a reversible phase transformation between δ-and α-crystal forms has been observed in Tes, corresponding to singlet and doublet 13 C patterns, respectively. To further characterize the ring conformations in the α-form, we have successfully extracted chemical shift tensor elements for the 13 C doublets. It is demonstrated that 13 C solid-state NMR spectroscopy provides a reliable and sensitive means of characterizing polymorphism in steroids.
Rh(PPh3)3Cl was immobilized on a (OEt)3Si(CH2)3PPh2 modified MCM-41 to form a stable hydrogenatio... more Rh(PPh3)3Cl was immobilized on a (OEt)3Si(CH2)3PPh2 modified MCM-41 to form a stable hydrogenation catalyst. The morphology of the catalyst was characterized by X-ray absorption spectroscopy. The EXAFS results indicates that the immobilized Rh catalyst has an average Rh–Os (Os is a surface oxygen) and Rh–Si bond distances of 2.01Å and 3.15Å, respectively, suggesting that monomeric Rh complex bonds to the
Seven-membered iminocyclitols with diverse diastereomers were prepared starting with d- and l-ser... more Seven-membered iminocyclitols with diverse diastereomers were prepared starting with d- and l-serines and employing ring-closing olefin metathesis and dihydroxylation reaction sequence. The iminocyclitols were assayed for glycosidase inhibition and compound 20 was found to be a competitive inhibitor for β-glucosidase with Ki 26.3μM.
This work establishes a general protocol for synthesizing phytosphingosines with various lengths ... more This work establishes a general protocol for synthesizing phytosphingosines with various lengths of lipid chains. The synthetic strategy included the Wittig reaction and olefin cross-metathesis as key steps. Combining these two C-C bond formation methods provide rapid access to adequately protected phytosphingosine backbones. Ó 2007 Elsevier Ltd. All rights reserved. 8 1 2 Figure 1. Retrosynthesis and steps involved in the synthesis of phytosphingosine analog 2 from D-lyxose.
Solid-state 1 H/ 13 C cross-polarization/magic angle spinning (CP/MAS) NMR spectroscopy has been ... more Solid-state 1 H/ 13 C cross-polarization/magic angle spinning (CP/MAS) NMR spectroscopy has been applied to two steroid compounds: dehydroepiandrosterone (DHEA) and spironolactone (SPI), to analyze their conformations at the atomic level. In the absence of lipid, the high-resolution 13 C CP/MAS NMR signals of DHEA and SPI in a powder form reveal multiple patterns, with splittings of 30-160 Hz, indicating the existence of multiple conformations. In the mimic lipid environment formed by mixing 1,2-dimyristoylsn-glycero-3-phosphocholine (DMPC) and 1,2-diheptanoyl-sn-glycero-3-phosphocholine (DHPC) in a molar ratio 3:1, the resulting DHEA and SPI spectra revealed mostly singlet patterns, suggesting that these steroids undergo a conformational change leading to a specific conformation in the lipid environment. Evidence from chemical shift isotropy and anisotropy analysis indicates that DHEA might adopt conformations subtly different from that seen in solution and in the powder form. In conclusion, we demonstrate by solid-state NMR that the structures of DHEA and SPI may adopt slightly different conformations in different chemical environments.
a b s t r a c t 13 C cross-polarization/magic-angle spinning (CP/MAS) solid-state NMR spectroscop... more a b s t r a c t 13 C cross-polarization/magic-angle spinning (CP/MAS) solid-state NMR spectroscopy has been employed to analyze four vitamin D compounds, namely vitamin D3 (D3), vitamin D2 (D2), and the precursors ergosterol (Erg) and 7-dehydrocholesterol (7DHC). The 13 C NMR spectrum of D3 displays a doublet pattern for each of the carbon atoms, while that of Erg contains both singlet and doublet patterns. In the cases of 7DHC and D2, the 13 C spectra display various multiplet patterns, viz. singlets, doublets, triplets, and quartets. To overcome the signal overlap between the 13 C resonances of protonated and unprotonated carbons, we have subjected these vitamin D compounds to 1D 1 H-filtered 13 C CP/MAS and { 1 H}/ 13 C heteronuclear correlation (Hetcor) NMR experiments. As a result, assisted by solution NMR data, all of the 13 C resonances have been successfully assigned to the respective carbon atoms of these vitamin D compounds. The 13 C multiplets are interpreted due to the presence of s-cis and s-trans configurations in the aand b-molecular conformers, consistent with computer molecular modeling determined by molecular dynamics and energy minimization calculations. To further characterize the ring conformations in D3, we have successfully extracted chemical shift tensor elements for the 13 C doublets. It is demonstrated that 13 C solid-state NMR spectroscopy provides a robust and high sensitive means of characterizing molecular conformations in vitamin D compounds.
Simple 2D 13 C/ 15 N heteronuclear correlation solid-state NMR spectroscopy was implemented to re... more Simple 2D 13 C/ 15 N heteronuclear correlation solid-state NMR spectroscopy was implemented to resolve the 15 N resonances of the a and b anomers of three amino monosaccharides: galactosamine (GalN), glucosamine hydrochloride (GlcN), and N-acetylglucosamine (GlcNAc) labeled specifically with 13 C 1 / 15 N spin pairs. Although the 15 N resonances could not be distinguished in normal 1D spectra, they were well resolved in 2D double CP/MAS correlation spectra by taking advantage of the 13 C spectral resolution. The a and b resonances shifted apart by 3-5 ppm in their 13 C chemical shifts, and differed by 1-2 ppm in the extended 15 N dimension. Aside from this, the detection of other 13 C/ 15 N correlations over short distances was also achieved arising from the C 2 , C 3 and CO carbons present in natural abundance. 2D double CP/MAS chemical shift correlation NMR spectroscopy is a simple and powerful technique to characterize the anomeric effect of amino monosaccharides. Applications of the 2D method reveal wellresolved 15 N and 13 C chemical shifts might be useful for structural determination on carbohydrates of biological significance, such as glycopeptide or glycolipids. r 2004 Elsevier Inc. All rights reserved.
Solid-state 19 F NMR in combination with fast magic angle spinning at a speed of 35 kHz has been ... more Solid-state 19 F NMR in combination with fast magic angle spinning at a speed of 35 kHz has been applied to examine the morphology of poly(vinylindene fluoride) samples by effectively suppressing dipolar interactions of the same order. A Lorentzian lineshape fitting analysis applied to the fast magic angle spinning spectrum was able to determine accurately the relative contents for the various domains: crystalline phase, 41%; amorphous regions, 54%; defect segments, 5%; with^3% error limits. Chemical shift anisotropies were also retrieved from sideband intensities: the amorphous component showed rather small anisotropy compared to that of the crystalline domain. Phase separation, in terms of the crystalline and non-crystalline domains, was distinguished by 2D spin exchange experiments, where cross-peaks were found not to be caused by chain conformation reorientations, but instead by spin diffusion. Evidence of the spin diffusion behavior mediated by unsuppressed homonuclear dipolar interactions has allowed us to examine molecular proximity under fast MAS conditions. ᭧
The role of water of hydration in proton relaxation in tissues as exemplified by hydrated collage... more The role of water of hydration in proton relaxation in tissues as exemplified by hydrated collagen in beef tendon was studied as a function of temperature from -40" to 37°C by using cross-relaxation spectroscopy. Experimental data were fitted to a simple binary spin-bath model. The outcome of this procedure allows the construction of a semi-quantitative depiction of proton relaxation in a heterogeneous system and its change as one of the water fractions freezes at about -10 to -2O"C, a transition observed by NMR and confirmed independently by differential scanning calorimetry. Such physical depiction provides a crude but insightful interpretation of the role "bound" water plays in proton relaxation. This may be important in shedding light on the mechanism of tissue relaxation and its role in MRI diagnosis, particularly for those diseases such as liver cirrhosis where the water-macromolecular interaction plays a prominent role.
Solid-state 13 Cf 1 Hg cross-polarization/magic angle spinning spectroscopy (CP/MAS) has been uti... more Solid-state 13 Cf 1 Hg cross-polarization/magic angle spinning spectroscopy (CP/MAS) has been utilized to extract the molecular structure information of Taxol, which is an anti-tumor therapeutic medicine extracted from the yew bark. The 13 C signals have chemical shift values quite consistent with those measured in solution phase, and the overall chemical shift range is over 200 ppm. Notably, most of the 13 C resonances of the taxane ring have two clearly resolved spectral components except the resonance peaks of C-15, C-16 and C-17, which are located at the central part of the taxane ring. On the basis of our NMR data, we propose that these doublets originate from two slightly different molecular conformations of the taxane ring and still the central part of the ring remains structurally similar. Furthermore, it is demonstrated that the 13 C chemical shift difference deduced from the doublet splittings can serve as a direct measure of the structural difference between the two conformations, which could possibly correlate with the anti-tumor activity of Taxol.
In the present study, an efficient method with a high overall yield for preparing phytosphingosin... more In the present study, an efficient method with a high overall yield for preparing phytosphingosine and an analogue was developed. Starting with commercially available 2,3;5,6-di-O-isopropylidene-D-mannofuranose, a variety of lipid moieties were incorporated to obtain phytosphingosine and an analogue. Through an eight-step manipulation, phytosphingosine was obtained with an overall yield of 57%.
Coherence transfer Sensitivity bandwidth Double cross-polarization Magic-angle spinning a b s t r... more Coherence transfer Sensitivity bandwidth Double cross-polarization Magic-angle spinning a b s t r a c t
A fundamental understanding of the mechanism of fiber formation requires a detailed knowledge of ... more A fundamental understanding of the mechanism of fiber formation requires a detailed knowledge of fiber morphology. However due to the limitation of current techniques, the crystallization behavior is still not fully understood. Modern solid state NMR techniques enable one to approach this subject from different aspects. In this work we conducted detailed studies of the morphology of as-spun PET (poly
Rh(PPh 3 ) 3 Cl was immobilized on a (OEt) 3 Si(CH 2 ) 3 PPh 2 modified MCM-41 to form a stable h... more Rh(PPh 3 ) 3 Cl was immobilized on a (OEt) 3 Si(CH 2 ) 3 PPh 2 modified MCM-41 to form a stable hydrogenation catalyst. The morphology of the catalyst was characterized by X-ray absorption spectroscopy. The EXAFS results indicates that the immobilized Rh catalyst has an average Rh-O s (O s is a surface oxygen) and Rh-Si bond distances of 2.01 Å and 3.15 Å, respectively, suggesting that monomeric Rh complex bonds to the MCM-41 surface. However, the structure of the immobilized Rh complex is not retained after hydrogenation of cyclohexene at 75 • C under 150 psi of H 2 . After the reaction, the presence of Rh-Rh contribution with average bond distance of 2.68 Å and coordination number of 1.3 and the missing contribution with bond distance of 3.85 Å suggest that the reaction induces the coalescence of Rh complex to form dimeric Rh species. However, formation of trace amount of Rh metal clusters cannot be ruled out because rather small characteristic peak for the missing Rh-Rh shell may be covered by noise.
This work establishes a general protocol for synthesizing phytosphingosines with various lengths ... more This work establishes a general protocol for synthesizing phytosphingosines with various lengths of lipid chains. The synthetic strategy included the Wittig reaction and olefin cross-metathesis as key steps. Combining these two C-C bond formation methods provide rapid access to adequately protected phytosphingosine backbones. Ó 2007 Elsevier Ltd. All rights reserved. 8 1 2 Figure 1. Retrosynthesis and steps involved in the synthesis of phytosphingosine analog 2 from D-lyxose.
Serine/threonine kinase Akt plays a central role in the regulation of cell survival and prolifera... more Serine/threonine kinase Akt plays a central role in the regulation of cell survival and proliferation. Hence, the search for Akt specific inhibitors constitutes an attractive strategy for anticancer therapy. We have previously demonstrated that the proto-oncogene TCL1 coactivates Akt upon binding to its Plekstrin Homology Domain, and we proposed a model for the structure of the complex TCL1:Akt2-PHD. This model led to the rational design of Akt-in, a peptide inhibitor spanning the A ß-strand of human TCL1 that binds Akt2 PH domain and inhibits the kinase activation.
Nix protein is a BH3-only pro-apoptotic mitochondrial protein. Here we reported the 1H, 13C and 1... more Nix protein is a BH3-only pro-apoptotic mitochondrial protein. Here we reported the 1H, 13C and 15N resonance assignments of zebrafish Nix protein for further understanding the structure and function relationship.
13 C CP/MAS solid-state NMR spectroscopy has been utilized to analyze six steroid compounds, name... more 13 C CP/MAS solid-state NMR spectroscopy has been utilized to analyze six steroid compounds, namely testosterone (Tes), hydrocortisone (Cor), trans-dehydroandrosterone (Adr), prednisolone (Prd), prednisone (Pre) and estradiol (Est). Among them, Tes displays a doublet pattern for all residues, whereas Prd, Pre and Est, exhibit exclusively singlets. For Cor and Adr, the 13 C spectra contain both doublet and singlet patterns. The 13 C doublet signal, with splittings of 0.2-1.5 ppm, are ascribed to local differences in the ring conformations associated with polymorphism. We have assigned all of the 13 C resonances to the different residues in these steroid compounds on the basis of solution NMR data. The C-7, C-8, C-10, C-15 and C-16 residues of Tes, Cor and Adr consistently give rise to singlets or doublets with splittings of less than 0.5 ppm, indicating similar local conformations. Accompanying hydration and dehydration processes, a reversible phase transformation between δ-and α-crystal forms has been observed in Tes, corresponding to singlet and doublet 13 C patterns, respectively. To further characterize the ring conformations in the α-form, we have successfully extracted chemical shift tensor elements for the 13 C doublets. It is demonstrated that 13 C solid-state NMR spectroscopy provides a reliable and sensitive means of characterizing polymorphism in steroids.
Rh(PPh3)3Cl was immobilized on a (OEt)3Si(CH2)3PPh2 modified MCM-41 to form a stable hydrogenatio... more Rh(PPh3)3Cl was immobilized on a (OEt)3Si(CH2)3PPh2 modified MCM-41 to form a stable hydrogenation catalyst. The morphology of the catalyst was characterized by X-ray absorption spectroscopy. The EXAFS results indicates that the immobilized Rh catalyst has an average Rh–Os (Os is a surface oxygen) and Rh–Si bond distances of 2.01Å and 3.15Å, respectively, suggesting that monomeric Rh complex bonds to the
Seven-membered iminocyclitols with diverse diastereomers were prepared starting with d- and l-ser... more Seven-membered iminocyclitols with diverse diastereomers were prepared starting with d- and l-serines and employing ring-closing olefin metathesis and dihydroxylation reaction sequence. The iminocyclitols were assayed for glycosidase inhibition and compound 20 was found to be a competitive inhibitor for β-glucosidase with Ki 26.3μM.
This work establishes a general protocol for synthesizing phytosphingosines with various lengths ... more This work establishes a general protocol for synthesizing phytosphingosines with various lengths of lipid chains. The synthetic strategy included the Wittig reaction and olefin cross-metathesis as key steps. Combining these two C-C bond formation methods provide rapid access to adequately protected phytosphingosine backbones. Ó 2007 Elsevier Ltd. All rights reserved. 8 1 2 Figure 1. Retrosynthesis and steps involved in the synthesis of phytosphingosine analog 2 from D-lyxose.
Solid-state 1 H/ 13 C cross-polarization/magic angle spinning (CP/MAS) NMR spectroscopy has been ... more Solid-state 1 H/ 13 C cross-polarization/magic angle spinning (CP/MAS) NMR spectroscopy has been applied to two steroid compounds: dehydroepiandrosterone (DHEA) and spironolactone (SPI), to analyze their conformations at the atomic level. In the absence of lipid, the high-resolution 13 C CP/MAS NMR signals of DHEA and SPI in a powder form reveal multiple patterns, with splittings of 30-160 Hz, indicating the existence of multiple conformations. In the mimic lipid environment formed by mixing 1,2-dimyristoylsn-glycero-3-phosphocholine (DMPC) and 1,2-diheptanoyl-sn-glycero-3-phosphocholine (DHPC) in a molar ratio 3:1, the resulting DHEA and SPI spectra revealed mostly singlet patterns, suggesting that these steroids undergo a conformational change leading to a specific conformation in the lipid environment. Evidence from chemical shift isotropy and anisotropy analysis indicates that DHEA might adopt conformations subtly different from that seen in solution and in the powder form. In conclusion, we demonstrate by solid-state NMR that the structures of DHEA and SPI may adopt slightly different conformations in different chemical environments.
a b s t r a c t 13 C cross-polarization/magic-angle spinning (CP/MAS) solid-state NMR spectroscop... more a b s t r a c t 13 C cross-polarization/magic-angle spinning (CP/MAS) solid-state NMR spectroscopy has been employed to analyze four vitamin D compounds, namely vitamin D3 (D3), vitamin D2 (D2), and the precursors ergosterol (Erg) and 7-dehydrocholesterol (7DHC). The 13 C NMR spectrum of D3 displays a doublet pattern for each of the carbon atoms, while that of Erg contains both singlet and doublet patterns. In the cases of 7DHC and D2, the 13 C spectra display various multiplet patterns, viz. singlets, doublets, triplets, and quartets. To overcome the signal overlap between the 13 C resonances of protonated and unprotonated carbons, we have subjected these vitamin D compounds to 1D 1 H-filtered 13 C CP/MAS and { 1 H}/ 13 C heteronuclear correlation (Hetcor) NMR experiments. As a result, assisted by solution NMR data, all of the 13 C resonances have been successfully assigned to the respective carbon atoms of these vitamin D compounds. The 13 C multiplets are interpreted due to the presence of s-cis and s-trans configurations in the aand b-molecular conformers, consistent with computer molecular modeling determined by molecular dynamics and energy minimization calculations. To further characterize the ring conformations in D3, we have successfully extracted chemical shift tensor elements for the 13 C doublets. It is demonstrated that 13 C solid-state NMR spectroscopy provides a robust and high sensitive means of characterizing molecular conformations in vitamin D compounds.
Simple 2D 13 C/ 15 N heteronuclear correlation solid-state NMR spectroscopy was implemented to re... more Simple 2D 13 C/ 15 N heteronuclear correlation solid-state NMR spectroscopy was implemented to resolve the 15 N resonances of the a and b anomers of three amino monosaccharides: galactosamine (GalN), glucosamine hydrochloride (GlcN), and N-acetylglucosamine (GlcNAc) labeled specifically with 13 C 1 / 15 N spin pairs. Although the 15 N resonances could not be distinguished in normal 1D spectra, they were well resolved in 2D double CP/MAS correlation spectra by taking advantage of the 13 C spectral resolution. The a and b resonances shifted apart by 3-5 ppm in their 13 C chemical shifts, and differed by 1-2 ppm in the extended 15 N dimension. Aside from this, the detection of other 13 C/ 15 N correlations over short distances was also achieved arising from the C 2 , C 3 and CO carbons present in natural abundance. 2D double CP/MAS chemical shift correlation NMR spectroscopy is a simple and powerful technique to characterize the anomeric effect of amino monosaccharides. Applications of the 2D method reveal wellresolved 15 N and 13 C chemical shifts might be useful for structural determination on carbohydrates of biological significance, such as glycopeptide or glycolipids. r 2004 Elsevier Inc. All rights reserved.
Solid-state 19 F NMR in combination with fast magic angle spinning at a speed of 35 kHz has been ... more Solid-state 19 F NMR in combination with fast magic angle spinning at a speed of 35 kHz has been applied to examine the morphology of poly(vinylindene fluoride) samples by effectively suppressing dipolar interactions of the same order. A Lorentzian lineshape fitting analysis applied to the fast magic angle spinning spectrum was able to determine accurately the relative contents for the various domains: crystalline phase, 41%; amorphous regions, 54%; defect segments, 5%; with^3% error limits. Chemical shift anisotropies were also retrieved from sideband intensities: the amorphous component showed rather small anisotropy compared to that of the crystalline domain. Phase separation, in terms of the crystalline and non-crystalline domains, was distinguished by 2D spin exchange experiments, where cross-peaks were found not to be caused by chain conformation reorientations, but instead by spin diffusion. Evidence of the spin diffusion behavior mediated by unsuppressed homonuclear dipolar interactions has allowed us to examine molecular proximity under fast MAS conditions. ᭧
The role of water of hydration in proton relaxation in tissues as exemplified by hydrated collage... more The role of water of hydration in proton relaxation in tissues as exemplified by hydrated collagen in beef tendon was studied as a function of temperature from -40" to 37°C by using cross-relaxation spectroscopy. Experimental data were fitted to a simple binary spin-bath model. The outcome of this procedure allows the construction of a semi-quantitative depiction of proton relaxation in a heterogeneous system and its change as one of the water fractions freezes at about -10 to -2O"C, a transition observed by NMR and confirmed independently by differential scanning calorimetry. Such physical depiction provides a crude but insightful interpretation of the role "bound" water plays in proton relaxation. This may be important in shedding light on the mechanism of tissue relaxation and its role in MRI diagnosis, particularly for those diseases such as liver cirrhosis where the water-macromolecular interaction plays a prominent role.
Solid-state 13 Cf 1 Hg cross-polarization/magic angle spinning spectroscopy (CP/MAS) has been uti... more Solid-state 13 Cf 1 Hg cross-polarization/magic angle spinning spectroscopy (CP/MAS) has been utilized to extract the molecular structure information of Taxol, which is an anti-tumor therapeutic medicine extracted from the yew bark. The 13 C signals have chemical shift values quite consistent with those measured in solution phase, and the overall chemical shift range is over 200 ppm. Notably, most of the 13 C resonances of the taxane ring have two clearly resolved spectral components except the resonance peaks of C-15, C-16 and C-17, which are located at the central part of the taxane ring. On the basis of our NMR data, we propose that these doublets originate from two slightly different molecular conformations of the taxane ring and still the central part of the ring remains structurally similar. Furthermore, it is demonstrated that the 13 C chemical shift difference deduced from the doublet splittings can serve as a direct measure of the structural difference between the two conformations, which could possibly correlate with the anti-tumor activity of Taxol.
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