Pub Date : 2011-11-30DOI: 10.2174/1874383801105010026
N. Ilayaraja, S. Krishnan, G. Ravindran, N. Renganathan
Different mole ratio of triethylamine HF (Et3.nHF, n= 3, 4 and 5) adducts were prepared and 1 H and 19 F NMR spin-lattice relaxation was measured at various temperatures for these three adducts. From this data the bond length and dipole properties of these three adducts were studied. These three adducts can be readily identified by 19 F NMR chemical shifts.
{"title":"NMR Studies of Complexes of Fluorides of Triethylamine","authors":"N. Ilayaraja, S. Krishnan, G. Ravindran, N. Renganathan","doi":"10.2174/1874383801105010026","DOIUrl":"https://doi.org/10.2174/1874383801105010026","url":null,"abstract":"Different mole ratio of triethylamine HF (Et3.nHF, n= 3, 4 and 5) adducts were prepared and 1 H and 19 F NMR spin-lattice relaxation was measured at various temperatures for these three adducts. From this data the bond length and dipole properties of these three adducts were studied. These three adducts can be readily identified by 19 F NMR chemical shifts.","PeriodicalId":88758,"journal":{"name":"The open spectroscopy journal","volume":"5 1","pages":"26-36"},"PeriodicalIF":0.0,"publicationDate":"2011-11-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"68070749","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2011-05-20DOI: 10.2174/1874383801105010013
N. Islam
A new algorithm for evaluating the atomic size is suggested by entailing the atomic spectroscopic data-the wave number. The basic tenet of the present method is (i) to convert a multi-electron atom system to a hydrogenic atom to invoke the Bohr model for the mechanism of electron transition, and (ii) to use the experimental atomic spectroscopic data of multi electron systems to determine the atomic radii. The estimated set of size data appears to satisfy the entire 'sine qua non' of sizes of atoms of the periodic table. Relativistic effect appears to have been significantly included in the suggested algorithm for evaluating the atomic radii. The express periodicity of periods and groups of periodic table exhibited by the computed atomic radii, d and f block contraction and the manifestation of the relativistic effect in the sizes of lanthanoids and actinoids etc speak volume of the efficacy of the present method in computing atomic size. Furthermore, as a validity test, the size data evaluated in the present work have been exploited to calculate some physical descriptors of the real world like equilibrium inter nuclear distances of a good number of hetero nuclear diatomics. We have noted the surprisingly close agreement between the theoretical and the experimental equilibrium inter-nuclear distances.
{"title":"Spectroscopic Evaluation of the Atomic Size","authors":"N. Islam","doi":"10.2174/1874383801105010013","DOIUrl":"https://doi.org/10.2174/1874383801105010013","url":null,"abstract":"A new algorithm for evaluating the atomic size is suggested by entailing the atomic spectroscopic data-the wave number. The basic tenet of the present method is (i) to convert a multi-electron atom system to a hydrogenic atom to invoke the Bohr model for the mechanism of electron transition, and (ii) to use the experimental atomic spectroscopic data of multi electron systems to determine the atomic radii. The estimated set of size data appears to satisfy the entire 'sine qua non' of sizes of atoms of the periodic table. Relativistic effect appears to have been significantly included in the suggested algorithm for evaluating the atomic radii. The express periodicity of periods and groups of periodic table exhibited by the computed atomic radii, d and f block contraction and the manifestation of the relativistic effect in the sizes of lanthanoids and actinoids etc speak volume of the efficacy of the present method in computing atomic size. Furthermore, as a validity test, the size data evaluated in the present work have been exploited to calculate some physical descriptors of the real world like equilibrium inter nuclear distances of a good number of hetero nuclear diatomics. We have noted the surprisingly close agreement between the theoretical and the experimental equilibrium inter-nuclear distances.","PeriodicalId":88758,"journal":{"name":"The open spectroscopy journal","volume":"5 1","pages":"13-25"},"PeriodicalIF":0.0,"publicationDate":"2011-05-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"68070709","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2011-03-01DOI: 10.2174/1874383801105010001
Fotis Nifiatis
The singlet oxygen photosensitizing efficiencies of the ortho-, meta-, and para-substituted free-base and zinc (II) tetraarylporphyrins have been investigated on the basis of the heavy atom effect, electronegativity, and spatial orbital overlap. Both the endocyclic and exocyclic heavy atom effects have been exploited to induce various degrees of spin-orbit coupling. The ground state and the lowest singlet excited electronic state of the porphyrins have been studied using optical absorption and fluorescence emission spectroscopic techniques. The experimental data suggest that implementation of the halogen substituent effect to enhance the photosensitizing properties of a chromophore from the excited triplet state should be done cautiously, as it may have negative implications.
{"title":"Substituent Effects of Porphyrin on Singlet Oxygen Generation Quantum Yields","authors":"Fotis Nifiatis","doi":"10.2174/1874383801105010001","DOIUrl":"https://doi.org/10.2174/1874383801105010001","url":null,"abstract":"The singlet oxygen photosensitizing efficiencies of the ortho-, meta-, and para-substituted free-base and zinc (II) tetraarylporphyrins have been investigated on the basis of the heavy atom effect, electronegativity, and spatial orbital overlap. Both the endocyclic and exocyclic heavy atom effects have been exploited to induce various degrees of spin-orbit coupling. The ground state and the lowest singlet excited electronic state of the porphyrins have been studied using optical absorption and fluorescence emission spectroscopic techniques. The experimental data suggest that implementation of the halogen substituent effect to enhance the photosensitizing properties of a chromophore from the excited triplet state should be done cautiously, as it may have negative implications.","PeriodicalId":88758,"journal":{"name":"The open spectroscopy journal","volume":"5 1","pages":"1-12"},"PeriodicalIF":0.0,"publicationDate":"2011-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"68070697","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2010-09-03DOI: 10.2174/1874383801004010032
M. Ibrahim
{"title":"Effect of Physical and Chemical Treatments on the Electrical and Structural Properties of Water Hyacinth~!2010-05-18~!2010-07-26~!2010-09-03~!","authors":"M. Ibrahim","doi":"10.2174/1874383801004010032","DOIUrl":"https://doi.org/10.2174/1874383801004010032","url":null,"abstract":"","PeriodicalId":88758,"journal":{"name":"The open spectroscopy journal","volume":"4 1","pages":"32-40"},"PeriodicalIF":0.0,"publicationDate":"2010-09-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"68070640","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2010-04-22DOI: 10.2174/1874383801004010016
G. Kummerlöwe, S. Schmitt, B. Luy
Residual dipolar couplings (RDCs) are important NMR-parameters for the structure determination of organic molecules. In this article we describe how RDCs can be used to effectively transfer structural information by cross-fitting the anisotropic parameters of molecules with similar overall structure. Using the example of 5- -cholestan-3-one and cho- lesterol, it is possible to distinguish diastereomers of the compounds by cross-fitting with transferred alignment tensors, even when strongly reduced subsets of RDCs are used. It is also demonstrated that RDCs can be used for direct cross- fitting even in flexible parts of the molecules that are sufficiently similar in structure and dynamic behavior. The cross- fitting approach as a general tool is discussed in details.
{"title":"Cross-Fitting of Residual Dipolar Couplings","authors":"G. Kummerlöwe, S. Schmitt, B. Luy","doi":"10.2174/1874383801004010016","DOIUrl":"https://doi.org/10.2174/1874383801004010016","url":null,"abstract":"Residual dipolar couplings (RDCs) are important NMR-parameters for the structure determination of organic molecules. In this article we describe how RDCs can be used to effectively transfer structural information by cross-fitting the anisotropic parameters of molecules with similar overall structure. Using the example of 5- -cholestan-3-one and cho- lesterol, it is possible to distinguish diastereomers of the compounds by cross-fitting with transferred alignment tensors, even when strongly reduced subsets of RDCs are used. It is also demonstrated that RDCs can be used for direct cross- fitting even in flexible parts of the molecules that are sufficiently similar in structure and dynamic behavior. The cross- fitting approach as a general tool is discussed in details.","PeriodicalId":88758,"journal":{"name":"The open spectroscopy journal","volume":"4 1","pages":"16-27"},"PeriodicalIF":0.0,"publicationDate":"2010-04-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"68070604","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2010-04-09DOI: 10.2174/1874383801004010010
M. Ibrahim, .. Z.I.A.AL-Fifi
The aquatic plant water hyacinth is a powerful tool for mediating pollution from aquatic environment. PM3 semiempirical method and FTIR spectroscopy was used to predicate the mechanism of pollution control. First the plant is subjected to acetic acid 0.1 M for 19 hours. FTIR proves that the plant is cellulose like material. Furthermore, the acetylated plant is looks like cellulose acetate. The mechanism of acetylation is tested using PM3 method. CH 3 COOH is interacted with OH of CH 2 OH by two ways. The first is through H-bonding of CH 3 the second is through the interaction of the H-bonding of COOH. The mechanism of divalent metal removal was such that Cd as an example is coordinated with acetylated plant either through two OH of CH 2 OH or through two COOH attached with CH 2 OH.
{"title":"Mechanism of Pollution Control for Aquatic Plant Water Hyacinth","authors":"M. Ibrahim, .. Z.I.A.AL-Fifi","doi":"10.2174/1874383801004010010","DOIUrl":"https://doi.org/10.2174/1874383801004010010","url":null,"abstract":"The aquatic plant water hyacinth is a powerful tool for mediating pollution from aquatic environment. PM3 semiempirical method and FTIR spectroscopy was used to predicate the mechanism of pollution control. First the plant is subjected to acetic acid 0.1 M for 19 hours. FTIR proves that the plant is cellulose like material. Furthermore, the acetylated plant is looks like cellulose acetate. The mechanism of acetylation is tested using PM3 method. CH 3 COOH is interacted with OH of CH 2 OH by two ways. The first is through H-bonding of CH 3 the second is through the interaction of the H-bonding of COOH. The mechanism of divalent metal removal was such that Cd as an example is coordinated with acetylated plant either through two OH of CH 2 OH or through two COOH attached with CH 2 OH.","PeriodicalId":88758,"journal":{"name":"The open spectroscopy journal","volume":"4 1","pages":"10-15"},"PeriodicalIF":0.0,"publicationDate":"2010-04-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"68070595","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2010-01-13DOI: 10.2174/1874383801004010001
M. Alfonsetti, C. Testa, S. Iotti, E. Malucelli, V. Clementi, B. Barbiroli, G. Placidi, A. Sotgiu, M. Alecci
We describe the use of a transverse field RF surface coil that improves 1.5 T proton MR spectroscopy in the human calf. A 2-element figure-of-eight (FO8) transverse field RF surface coil (diameter 2R=10 cm; separation between the two linear current elements 2s=1cm) and a circular loop (CL) coil of equal diameter where built and tested with proton PRESS spectra at 1.5 T. The 1 H PRESS spectra obtained in the resting calf muscle of healthy volunteers showed that the FO8 coil allows a higher PRESS SNR (up to a factor 4.5) within a region of about 20 mm centred at about 12 mm from the coil plane, as compared to a standard CL coil. We found also a faster PRESS SNR decrease in the muscle tissue for anterior/posterior distance >20 mm using the FO8 coil. The measured PRESS SNR in the fat tissues of the calf showed a signal mostly localised within 10 mm from the coils surface and with an improved SNR (up to 5.5 times) observed in the presence of the FO8 coil as compared to the CL coil of equal diameter. The FO8 coil design can be advantageous for MRS applications, since it allows higher SNR from a small VOI positioned centrally within a relatively narrow region at a given depth in the human calf. The reported spatial SNR features of the FO8 coil design should also be useful for 1 H and 31 P MRS metabolites quantification in the human brain.
我们描述了一个横向场射频表面线圈的使用，提高了1.5 T质子磁共振光谱在人小腿。2元8字图(FO8)横向场射频表面线圈(直径2R=10 cm;两个线性电流元件(2s=1cm)和一个直径相等的环形线圈(CL)之间的分离，并在1.5 t下使用质子PRESS光谱进行测试。在健康志愿者静息的小腿肌肉中获得的1 H PRESS光谱表明，与标准CL线圈相比，FO8线圈在距离线圈平面约12 mm的约20 mm区域内允许更高的PRESS信噪比(高达4.5倍)。我们还发现，使用FO8线圈在前后距离bbb20 mm时，肌肉组织的PRESS信噪比下降更快。在犊牛脂肪组织中测量的PRESS信噪比显示，信号主要定位在距离线圈表面10毫米范围内，并且与相同直径的CL线圈相比，在FO8线圈存在时观察到的信噪比(高达5.5倍)有所改善。FO8线圈设计对于MRS应用是有利的，因为它可以从位于人体小腿给定深度的相对狭窄区域中心的小VOI获得更高的信噪比。所报道的FO8线圈设计的空间信噪比特征也可用于人脑中1h和31p MRS代谢物的量化。
{"title":"Improved 1.5 T Magnetic Resonance Spectroscopy in the Human Calf with a Spatially Selective Radio Frequency Surface Coil","authors":"M. Alfonsetti, C. Testa, S. Iotti, E. Malucelli, V. Clementi, B. Barbiroli, G. Placidi, A. Sotgiu, M. Alecci","doi":"10.2174/1874383801004010001","DOIUrl":"https://doi.org/10.2174/1874383801004010001","url":null,"abstract":"We describe the use of a transverse field RF surface coil that improves 1.5 T proton MR spectroscopy in the human calf. A 2-element figure-of-eight (FO8) transverse field RF surface coil (diameter 2R=10 cm; separation between the two linear current elements 2s=1cm) and a circular loop (CL) coil of equal diameter where built and tested with proton PRESS spectra at 1.5 T. The 1 H PRESS spectra obtained in the resting calf muscle of healthy volunteers showed that the FO8 coil allows a higher PRESS SNR (up to a factor 4.5) within a region of about 20 mm centred at about 12 mm from the coil plane, as compared to a standard CL coil. We found also a faster PRESS SNR decrease in the muscle tissue for anterior/posterior distance >20 mm using the FO8 coil. The measured PRESS SNR in the fat tissues of the calf showed a signal mostly localised within 10 mm from the coils surface and with an improved SNR (up to 5.5 times) observed in the presence of the FO8 coil as compared to the CL coil of equal diameter. The FO8 coil design can be advantageous for MRS applications, since it allows higher SNR from a small VOI positioned centrally within a relatively narrow region at a given depth in the human calf. The reported spatial SNR features of the FO8 coil design should also be useful for 1 H and 31 P MRS metabolites quantification in the human brain.","PeriodicalId":88758,"journal":{"name":"The open spectroscopy journal","volume":"4 1","pages":"1-9"},"PeriodicalIF":0.0,"publicationDate":"2010-01-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"68070585","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2009-09-10DOI: 10.2174/1874383800903010065
V. Ropars, P. Barthe, Chihao Wang, Wenlung Chen, D. Tzou, Anne Descours, Loïc Martin, M. Noguchi, D. Auguin, C. Roumestand
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 s-strand of human TCL1 that binds Akt2 PH domain and inhibits the kinase activation. In the present report, we used NMR spectroscopy to determine the 3D structure of the peptide free in solution and bound to Akt2-PHD. NMR chemical shift mapping was used to determine the imprint of Akt-in on the PH domain; whereas peptide Ala-scanning revealed which peptide residues were involved in the interaction. Together with the solution structure of Akt2-PHD, these results allowed us to dock Akt-in on the PH domain. The docked complex suggests that while Akt-in binds Akt2-PHD in a region overlapping the binding site of TCL1, its mode of interaction is markedly different. Moreover, the affinity was disappointingly low, contrary to that published previously. Besides providing a description of the interaction between Akt-in an Akt2 PH domain, the present work brings additional clues on the putative peptide mode of action. Instead of behaving as an analog of PtdIns, as previously suggested, Akt-in might act as an "allosteric" inhibitor, maintaining the full-length kinase in its "closed" inactive conformation, rather than disturbing the membrane anchorage of its "open" active conformation.
{"title":"Structural Studies of the Complex Between Akt-in and the Akt2-PH Domain Suggest that the Peptide Acts as an Allosteric Inhibitor of the Akt Kinase","authors":"V. Ropars, P. Barthe, Chihao Wang, Wenlung Chen, D. Tzou, Anne Descours, Loïc Martin, M. Noguchi, D. Auguin, C. Roumestand","doi":"10.2174/1874383800903010065","DOIUrl":"https://doi.org/10.2174/1874383800903010065","url":null,"abstract":"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 s-strand of human TCL1 that binds Akt2 PH domain and inhibits the kinase activation. In the present report, we used NMR spectroscopy to determine the 3D structure of the peptide free in solution and bound to Akt2-PHD. NMR chemical shift mapping was used to determine the imprint of Akt-in on the PH domain; whereas peptide Ala-scanning revealed which peptide residues were involved in the interaction. Together with the solution structure of Akt2-PHD, these results allowed us to dock Akt-in on the PH domain. The docked complex suggests that while Akt-in binds Akt2-PHD in a region overlapping the binding site of TCL1, its mode of interaction is markedly different. Moreover, the affinity was disappointingly low, contrary to that published previously. Besides providing a description of the interaction between Akt-in an Akt2 PH domain, the present work brings additional clues on the putative peptide mode of action. Instead of behaving as an analog of PtdIns, as previously suggested, Akt-in might act as an \"allosteric\" inhibitor, maintaining the full-length kinase in its \"closed\" inactive conformation, rather than disturbing the membrane anchorage of its \"open\" active conformation.","PeriodicalId":88758,"journal":{"name":"The open spectroscopy journal","volume":"3 1","pages":"65-76"},"PeriodicalIF":0.0,"publicationDate":"2009-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"68070546","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2009-04-24DOI: 10.2174/1874383800903010052
J. Muñoz, J. Bravo, M. Calzada
This work is aimed at studying emission spectra and morphological characteristics of surface wave discharges generated with Ar/He and Ar/N2 gas mixtures at atmospheric pressure with powers ranging from 80 to 400 W. In both cases, power density is higher than that found with pure Ar, although these changes are due to different discharge features. Kinetic processes can be derived from the analysis of plasma-emitted spectra. We also provide evidence of variations in the external aspect of discharges (filamentation and contraction) related to changes in thermal conductivity in gas mixture.
{"title":"Surface Wave Discharges Generated with Ar/He and Ar/N2 Gas Mixturesat Atmospheric Pressure","authors":"J. Muñoz, J. Bravo, M. Calzada","doi":"10.2174/1874383800903010052","DOIUrl":"https://doi.org/10.2174/1874383800903010052","url":null,"abstract":"This work is aimed at studying emission spectra and morphological characteristics of surface wave discharges generated with Ar/He and Ar/N2 gas mixtures at atmospheric pressure with powers ranging from 80 to 400 W. In both cases, power density is higher than that found with pure Ar, although these changes are due to different discharge features. Kinetic processes can be derived from the analysis of plasma-emitted spectra. We also provide evidence of variations in the external aspect of discharges (filamentation and contraction) related to changes in thermal conductivity in gas mixture.","PeriodicalId":88758,"journal":{"name":"The open spectroscopy journal","volume":"3 1","pages":"52-57"},"PeriodicalIF":0.0,"publicationDate":"2009-04-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"68070523","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2009-03-18DOI: 10.2174/1874383800903010043
S. Konorov, H. G. Schulze, C. Addison, C. Haynes, R. Turner, M. Blades
Transient absorption measurements of excited states in DNA and LNA were performed using a femtosecond pump-probe arrangement with excitation at 266 nm and absorption monitored at 400 nm while varying the sample tem- perature between 5 °C and 70 °C. Samples consisted of adenine monophosphate monomer, polyadenine 12-mer in single- stranded form, and polyadenine 12-mer in hybridized form. Excited states decayed in a biphasic manner with short-lived ( 1) and long-lived ( 2) components, while the monomer had only a 'single' short-lived decay time. Temperature increases increased absorption intensities and reduced 1 until they approached those of the monomer at high temperatures (where stacking is minimal). These results suggest that the initial excitation in stacked regions is cooperative and involves several bases and that the number of bases involved is reduced with increasing temperature. In contrast, increasing temperatures had little effect on 2 while absorption intensities decreased, suggesting that very few, perhaps only two, stacked bases are involved and that their number is reduced at higher temperatures. We found no clear evidence of melting point transitions indicating that those excited states probed with our arrangement were not dependent on base pairing. Our results are con- sistent with and strengthen an emerging consensus model of excited state dynamics in DNA wherein a UV photon is ab- sorbed collectively by electronically coupled and thus well-stacked intrachain bases. This collective excitation results in a Frenkel exciton that is delocalized over these bases, and the Frenkel exciton then decays rapidly to a long-lived, lower en- ergy, dark intrachain exciplex.
{"title":"Temperature-Dependent Excited State Absorption in DNA and LNA Oligomers Supports an Emerging Model of Excited State Dynamics in DNA","authors":"S. Konorov, H. G. Schulze, C. Addison, C. Haynes, R. Turner, M. Blades","doi":"10.2174/1874383800903010043","DOIUrl":"https://doi.org/10.2174/1874383800903010043","url":null,"abstract":"Transient absorption measurements of excited states in DNA and LNA were performed using a femtosecond pump-probe arrangement with excitation at 266 nm and absorption monitored at 400 nm while varying the sample tem- perature between 5 °C and 70 °C. Samples consisted of adenine monophosphate monomer, polyadenine 12-mer in single- stranded form, and polyadenine 12-mer in hybridized form. Excited states decayed in a biphasic manner with short-lived ( 1) and long-lived ( 2) components, while the monomer had only a 'single' short-lived decay time. Temperature increases increased absorption intensities and reduced 1 until they approached those of the monomer at high temperatures (where stacking is minimal). These results suggest that the initial excitation in stacked regions is cooperative and involves several bases and that the number of bases involved is reduced with increasing temperature. In contrast, increasing temperatures had little effect on 2 while absorption intensities decreased, suggesting that very few, perhaps only two, stacked bases are involved and that their number is reduced at higher temperatures. We found no clear evidence of melting point transitions indicating that those excited states probed with our arrangement were not dependent on base pairing. Our results are con- sistent with and strengthen an emerging consensus model of excited state dynamics in DNA wherein a UV photon is ab- sorbed collectively by electronically coupled and thus well-stacked intrachain bases. This collective excitation results in a Frenkel exciton that is delocalized over these bases, and the Frenkel exciton then decays rapidly to a long-lived, lower en- ergy, dark intrachain exciplex.","PeriodicalId":88758,"journal":{"name":"The open spectroscopy journal","volume":"3 1","pages":"43-51"},"PeriodicalIF":0.0,"publicationDate":"2009-03-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"68069478","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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