L-metiyonin L-metiyoninyum hidrojen maleate (LMLMHM), L-metiyonin pikrat(LMP), L-metiyonin L-metiyoninyum pikrat (L-MMP) moleküllerinin moleküler yapı parametreleri, titreşim dalga sayıları, 1H NMR ve 13C NMR kimyasal kaymaları yoğunluk fonksiyoneli (DFT) B3LYP ve PBEPBE yöntemi ile 6- 311++G(d,p) temel seti kullanılarak hesaplanmıştır. Bu üç molekülün Geometrik parametreleri, titreşim verileri, NMR kimyasal kaymaları, bildirilen deneysel bulgularla uyumlu olduğu gözlemlendi. Moleküler içi ve moleküler arası yük transferi ile konjugatif etkileşimler, doğal bağ orbital analizi (NBO) ve Sınır Moleküler Orbitalleri (FMO) analizi kullanılarak araştırıldı. İlgili bileşiklerin elektrofilik ve nükleofilik bölgeleri, Moleküler Elektrostatik Potansiyel (MEP) yüzeyler kullanılarak bulundu. Doğrusal olmayan optik özellikler (NLO), aynı teori seviyelerinde dipol moment, ortalama kutuplanabilirlik, yönelime bağlı kutuplanabilirlik ve birinci mertebeden yüksek kutuplanabilirlik parameteleri kullanılarak incelenmiştir. LMLMHM, LMP ve L-MMP molekülleri için minimum enerjili yapılar esas alınarak DFT//B3LYP-PBEPBE/6-311++G(d,p) yöntemiyle titreşim frekansları hesaplanmıştır. Elde edilen teorik verilerin deneysel titreşim frekansları karşılaştırıldığında aralarında iyi bir uyum olduğu görülmektedir. Komplekslerin HOMO ve LUMO enerjileri değerleri yaklaşık olarak 2 eV olarak hesaplanmıştır. Bu fark ne kadar büyük olursa kompleksin kimyasal sertliğide orantılı olarak artacaktır. Hesaplanan teorik veriler açısından, kimyasal olarak en kararlı kompleks, LMLMHM en kararsız kompleks ise L-MMP olarak bulunmuştur. Buradan, HOMO'dan LUMO'ya bir elektron geçişi oluşturmak için gereken enerji L-MMP kompleksi için en yüksekken LMLMHM kompleksi için en düşüktür. Metiyoninyum kompleksleri için antibağ, bağ, ve eşlenmemiş elektron orbitalleri arasında gerçekleşen yüksek enerjili etkileşmeler DFT//B3LYP-PBEPBE/6-311++G(d,p) yöntemi kullanılarak elde edilmiştir. Hesaplanan yüksek enerjili etkileşmeler, kompleksler içerisinde gerçekleşen yük aktarım geçişlerine neden olduğu tespit edilmiştir. Bu sebeple, ortaya çıkan yük hareketliliği en yüksek olan molekül LMP, en düşük olan ise LMLMHM molekülüdür. Metiyoninyum komplekslerinin kararlı yapıları temel alınarak, dipol moment (μ), ortalama kutuplanabilirlik (<α>), yönelime bağlı kutuplanabilirlik (Δα) ve birinci mertebeden statik yüksek kutuplanabilirlik (<β>) parametreleri, teorik olarak B3LYP - PBEPBE metodları ve 6-311++G(d,p) temel seti kullanılarak incelendi. Kurumsal hesaplamalar, söz konusu komplekslerin doğrusal olmayan bir optik malzeme olarak kullanılma potansiyeline sahip olduğunu göstermektedir.
Methionine and its derivatives are generally used in medicinal and industrial applications. A major advantage of methionine moiety in applications is that two sulphurcontaining proteinogenic amino acids. Up to now, the researchers have tended to focus on the crystal structure of methionine derivatives or salt complexes [. A considerable amount of literature has been published on polymer and organic nonlinear optical materials. Among recently developed organic molecular and nonlinear crystal materials, stand out in the view of their second order nonlinearity and high laser damage threshold in the pulsed regime. It is interesting to note that the donor and acceptor groups of amino acids are a majör influence data on the second order nonlinearity because of providing the ground state charge asymmetry for the related molecule. The result from several studies suggest that amino acids have a pivotal role in nonlinear optical (NLO) applications as they contain a proton donor carboxylic acid (COOH) group and the proton acceptor amino (NH2) group in them. The molecular structure parameters, vibrational wavenumbers, 1H NMR and 13C NMR chemical shifts of L-methionine L-methioninium hydrogen maleate (LMLMHM), L-methionine pikrat( LMP) , L-methionine L-methioninium pikrat were carried out by using density functional theory (DFT) B3LYP and PBEPBE method using 6- 311++G(d,p) basis set. The complete structural analysis such as geometric parameters, vibrational datas, NMR chemical shifts of three molecules were in good agreement with reported experimental findings. The stability of the molecule arising from charge transfer and hyperconjugative interaction were researched using Natural Bonding Orbital (NBO), and Frontier Molecular Orbital (FMO) analysis. The electrophilic and nucleophilic sides of methioninium derivates were investigated by using molecular electrostatic potential. The nonlinear optical features (NLO) were investigated from the dipole, polarizability and hyperpolarizability values at the same theory levels.. Vibration frequencies for LMLMHM, LMP and L-MMP molecules were calculated using the DFT//B3LYP-PBEPBE/6-311++G(d,p) method based on the minimum energy structures. When the experimental vibration frequencies of the obtained theoretical data are compared, it is seen that there is a good agreement between them. The HOMO and LUMO energies of the complexes were calculated as approximately 2 eV. The larger this difference, the higher the chemical hardness of the complex will be proportionally. In terms of the calculated theoretical data, the most chemically stable complex was found to be LMLMHM and the most unstable complex was L-MMP. From here, the energy required to create an electron transition from HOMO to LUMO is highest for the L-MMP complex and lowest for the LMLMHM complex. High-energy interactions between antibond, bond, and unpaired electron orbitals for methioninium complexes were obtained using the DFT//B3LYP-PBEPBE/6-311++G(d,p) method. It has been determined that the calculated high-energy interactions cause charge transfer transitions within the complexes. For this reason, the molecule with the highest charge mobility is LMP, and the one with the lowest is LMLMHM. Based on the stable structures of methioninium complexes, dipole moment (μ), average polarizability (<α>), orientation dependent polarity (Δα) and first order static high polarizability (<β>) parameters were theoretically investigated using B3LYP – PBEPBE 6-311++G(d,p) methods. The computational finding suggests that mentioned compounds have a potential to be used as a nonlinear optical materials. A few study have reported for organic methioninium derivatives about its synthesis and characterization. L-methionine L-methioninium hydrogen maleate (LMLMHM) molecule is synthesized by S. Natarajan et al. and the crystal form of LMLMHM molecule is experimentally characterized its some thermal and electronic properties by using FT-IR, UV-Vis and thermal spectroscopies . LMP is synthesized by V.V . Ghazaryan et al. Also L-LMP molecule is synthesized by K.Anithaet al. To the best of our knowledge, quantum chemical calculations investigations for LMLMHM, LMP nad L- LMP have not been reported up to now. In this thesis, we aim to model theoretical spectroscopic studies (XRD, IR and NMR), as well as the NLO and NBO analysis on some methionionıum containing compounds. Additionally, MEP, FMO energies and molecular charges of tis moleules are investigated by using quantum chemical calculations. The molecular geometry parameters of LMLMHM, LMP and L-LMP were fully optimized by usingdensity functional theory (DFT) employing Becke's three-parameter exchange functional in conjunction with the Lee-Yang-Parr correlation functional (B3LYP) and the recommended version of the Perdew-Burke-Ernzerhof functional (PBEPBE) [18] in conjunction with 6-311++G(d,p) basis set without any constraint with the help of standard gradient procedure implemented within Gaussian 03W program . All the geometric parameters were allowed to relax and all the calculations converged to an optimized geometry which corresponds to a true energy minimum revealed by the lack of imaginary frequencies in the vibrational mode calculation. The vibrational wavenumbers of three molecules were calculated with B3LYP/6-311++G(d,p) and PBEPBE/6- 311++G(d,p) levels of theory. The vibrational wavenumbers values, were computed by DFT levels, contain well-known systematic discrepancies. Thus the scaling factor of 0.960 was used for both theory levels in order to repair discrepancies between experimental and theoretical results [21]. DFT theory levels were also used to determine molecular geometric parameters, NMR chemical shifts, NLO, NBO, MEP, FMO and molecular charges. The structural, spectroscopic, electronic and nonlinear optical properties of Lmethionine L-methioninium hydrogen maleate (LMLMHM), L-methionine pikrat( LMP) and L-methionine L-methioninium pikrat (L-MMP) are investigated by theapplication of the B3LYP and PBEPBE levels with the 6-311++G(d,p) basis set. All moleules were optimized in ground state by density functional theory levels, and obtained structural parameters are in good agreement with reported XRD results. NH..O and OH...O hydrogen bonding interactions are supposed from the small changes of bond lengths and bond angles. The calculated vibration wavenumbers and approximate descriptions of normal modes were investigated by using B3LYP and PBEPBE functional. In IR calculations, the N–H stretching vibration modes appear in different regions of the vibration spectra. This difference is derived from the hydrogen bonding interactions, i.e., the NH vibration mode without the hydrogen bonding interactions appears in high wavenumbers. In other words, hydrogen bonding interactions reduce the wavenumber of the mentioned vibration mode. The vibration peak (C=O, C=N, C=C, OH, and NH) moieties may be contribute to the nonlinear optical activity of some methioninum compounds. 1H and 13C NMR spectra simulated for whole molecules give results in the expected regions. The reported and the calculated isotropic chemical shifts are found to be in good agreement with the exception of N H protons shift. The reason of this discrepancy can be shown due to the intra- or inter-molecular hydrogen bonding. These hydrogen bonding interactions are also proved by the NBO analysis. From MEP and Mulliken charges, the electrophilic and nucleophilic regions are demonstrated, and the formation of hydrogen bonding interactions is explained. The energy gap between HOMO and LUMO has been found to be appropriate for charge transfer interactions within this three molecules. Obtained large α and β values indicate that the methioninum compounds are good candidate for nonlinearopticalmaterials.
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