13C

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1 - Ab initio and DFT studies on tautomerism of 5-methyl cytosine in gaseous phase
K. Zare M. Monajjemi E. Zahedi H. Aghaie

Ab initio and DFT methods have been used to study the seven tautomeric forms of 5-methylcytosine molecule.The related tautomer in gas phase have been studied at HF/6-31G, HF/6-31G* and B3LYP/6-31G* levels oftheory. The structures,enthalpies,entropies,Gibbs free energies أکثر

Ab initio and DFT methods have been used to study the seven tautomeric forms of 5-methylcytosine molecule.The related tautomer in gas phase have been studied at HF/6-31G, HF/6-31G* and B3LYP/6-31G* levels oftheory. The structures,enthalpies,entropies,Gibbs free energies,relative tautomerization energies of tautomersand tautomeric equilibrium constants were compared and analyzed along with full geometry optimization. Thecalculations showed that the Oxo-amino(6), Oxo-imino(7) and Hydroxy-amino(4) tautomers are the most stablein the gas phase. The results are in a good agreement with the available experimental data. The entropy effecton the Gibbs free energy of the 5-methylcytosine bases is very small and it has a little significance on thetautomeric equilibria of pyrimidine bases.Therefore the enthalpic term is dominant in the determination of theequilibrium constants. 13C-NMR studies have been carried out for these tautomers and the results arediscussed.We have also evaluated the hybridation coefficient for bonds and hetero atom LPS in the aromaticring for the stable tautomers. Natural Bond Orbital Theory (NBO) calculation showed that the stable tautomersmust be considered aromatic. تفاصيل المقالة

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2 - Ab Initio Quantum Chemical Studies of 15N and 13C NMR Shielding Tensors in Serine and Complexes of Serine- nH2O: Investigation on Strength of the CαH…O Hydrogen bonding in the Amino Acid Residue.
M. Monajjemi T. Karimkeshteh F. Mollaamin

In this paper, the hydrogen bonding (HB) effects on the NMR chemical shifts of selected atoms in serineand serine-nH2O complexes (from one to ten water molecules) have been investigated with quantummechanical calculations of the 15N and 13C tensors. Interaction with wat أکثر

In this paper, the hydrogen bonding (HB) effects on the NMR chemical shifts of selected atoms in serineand serine-nH2O complexes (from one to ten water molecules) have been investigated with quantummechanical calculations of the 15N and 13C tensors. Interaction with water molecules causes importantchanges in geometry and electronic structure of serine.For the compound studied, the most important intermolecular interaction between serine and watermolecules employ different geometrical models of numerous N…H and C-H…O bonds in the crystallinestructures. These interactions have been approximated by explicitly adding the nearest neighbors into thecalculations.At present, quantum chemistry is almost universally applicable to the interpretation of physical andchemical properties of various compoundsChemical shift calculations, geometry optimization and energies have been performed with ab initiomethod at HF/6-31G* and HF/6-31G** levels with GIAO methods.There is strong evidence that intermolecular effects are important in determining the 15N chemical shiftsof free amino acid residue to assign principal axes of the tensors and some systematic trends appear fromthe analysis of the calculated values.Formation of each interaction (in ten orientations) results in a shift of the bridging hydrogen's chemicalshifts of N…H bond that indicate the most stabilized compound.The CαH…O bond plays an important role in the interactions of amino acids residue upon the structureand function of a protein.Despite the finding of numerous CαH…O contacts in proteins, major questions remain about theirimportance. Thus it is the strength of this binding that is of most importance in understanding the possiblefactor that the CαH…O H-bond may play in the folding of proteins.This paper represents comparison between theoretical and experimental values of NMR resonances, andcalculations of HF/6-31G** level produce results in better agreement with the experimental data. تفاصيل المقالة

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3 - Solvent Effect on the Molecular Structure, Chemical Reactivity and Spectroscopy Properties of Z-Ligustilide: A Main Active Component of Multitude Umbelliferae Medicinal Plants
Mahmoud Osanloo Reza Ghiasi

In this investigation, the structural, electronic properties, 13C and 1H NMR parameters and firsthyperpolarizability of Z-Ligustilide were explored. As well, the solvent effect on structural parameters, frontier orbital energies, electronic transitions, and 13C and 1H N أکثر

In this investigation, the structural, electronic properties, 13C and 1H NMR parameters and firsthyperpolarizability of Z-Ligustilide were explored. As well, the solvent effect on structural parameters, frontier orbital energies, electronic transitions, and 13C and 1H NMR parameters was illustrated based on Polarizable Continuum Model (PCM).These consequences specify that the polarity of solvents participates on the structures and spectroscopic properties of Z-Ligustilide.NBO analysis was used to examining of the hybridation of atoms, atomic charges and their second order stabilization energy within the molecule. تفاصيل المقالة

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4 - A review of 13C NMR spectra of drimane sesquiterpenes
Sylvia Awino Opiyo

Drimane sesquiterpenes are important group of phytochemicals with a wide range of medicinal properties including antibacterial, antifungal, anti-inflammatory, antioxidant, antiplasmodial, antileishmanial, molluscicidal, antifeedant and insecticidal features. Due to thei أکثر

Drimane sesquiterpenes are important group of phytochemicals with a wide range of medicinal properties including antibacterial, antifungal, anti-inflammatory, antioxidant, antiplasmodial, antileishmanial, molluscicidal, antifeedant and insecticidal features. Due to their wide range of medicinal activities, scientists are prompted to continuously search for novel drimane sesquiterpenes since most of the currently available anti-infective agents have drawbacks such as drug resistance and side effects. Structure determination of new compounds relies on accurate interpretation of spectroscopic data which is quite challenging but can be simplified by comparison with the data of known related compounds from the reliable databases. A large number of drimane sesquiterpenes have been examined by 13C NMR spectroscopy but such data are scattered in the literature making it hard for researchers to use them. This paper provides a review on previously reported drimane sesquiterpenes and a compilation of their 13C NMR data. It also provides a brief discussion on the substituent effect on the 13C shielding of the drimane sesquiterpenes. تفاصيل المقالة

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5 - Plant sink-source relationships and carbon isotopic labeling techniques . Taher Barzegar* and Fatemhe Nekounam
Taher Barzegar Fatemhe Nekounam

10.30495/ijpp.2016.539827

The concept of source and sink strength is presently well-recognized and accepted by the scientiﬁc community as a pertinent approach describing the mechanisms of carbohydrate partitioning into the different and competing organs at a whole plant or canopy scales. Sink&nd أکثر

The concept of source and sink strength is presently well-recognized and accepted by the scientiﬁc community as a pertinent approach describing the mechanisms of carbohydrate partitioning into the different and competing organs at a whole plant or canopy scales. Sink–source relationships have a clear role in the size of sink organs. Besides the effect on organ size, sink/source ratio might also affect photosynthesis. Crop biomass productivity is closely related to source and sink capacities and the balance between them. Determination of the carbon balance of a whole plant and relation between source and sink were studied by carbon isotopic labeling techniques. Techniques using 14C or 13C have been used for many years to study the allocation of carbohydrates produced by photosynthesis between different parts of the plant. This method also allows calculation of the proportion of the total carbon accumulated in each sink that was supplied by all source leaves, as well as the growth contribution from each source leaf to the main plant sinks. These data are vital to determine the productivity of each source leaf. تفاصيل المقالة

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6 - مطالعه الکتروشیمیایی رفتار خوردگی داغ پوشش نفوذی آلومینایدی روی سوپر آلیاژ اینکونل 713C
اسماعیل طاهری مهدی وردیان

در این پژوهش، مقاومت به خوردگی داغ پوشش نفوذی آلومینایدی اعمال شده روی سوپر آلیاژ اینکونل 713C به روش الکتروشیمیایی مورد بررسی قرار گرفت. در این رابطه، آزمایش های پلاریزاسیون پتانسیودینامیک در دمای 750 درجه سانتیگراد و تحت شرایط اتمسفری در دو نوع نمک مذاب انجام شد. نمک أکثر

در این پژوهش، مقاومت به خوردگی داغ پوشش نفوذی آلومینایدی اعمال شده روی سوپر آلیاژ اینکونل 713C به روش الکتروشیمیایی مورد بررسی قرار گرفت. در این رابطه، آزمایش های پلاریزاسیون پتانسیودینامیک در دمای 750 درجه سانتیگراد و تحت شرایط اتمسفری در دو نوع نمک مذاب انجام شد. نمک اول حاوی 70% سولفات سدیم و 30% کلرید سدیم و نمک دوم حاوی 70% سولفات سدیم، 25% کلرید سدیم و 5% پنتا اکسید وانادیوم بود. همچنین، ترکیب فازی و ریزساختار پوشش ها و محصولات خوردگی با روش های پراش پرتو ایکس و میکروسکوپ الکترونی روبشی مجهز به طیف سنج تفکیک انرژی بررسی شد. نتایج نشان داد که در حضور ترکیبات وانادیوم قدرت حفاظت کنندگی پوشش بیشتر است و در منحنی پلاریزاسیون آندی پوشش یک ناحیه وسیع با جریان تقریبا ثابت مشاهده می شود. در این محیط، یک لایه متراکم از محصولات خوردگی مشاهده شد. در غیاب وانادیوم، نمونه پوشش دار و بدون پوشش سرعت خوردگی مشابهی نشان دادند اما در محیط حاوی وانادیوم سرعت خوردگی نمونه ها کمتر بود. در این حالت پوشش ها رفتار فعال آندی از خود نشان دادند. محصولات خوردگی در محیط عاری از وانادیوم به صورت متخلخل و ناپیوسته مشاهده شدند. تفاصيل المقالة

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