Vibrational Spectroscopic and Theoretical Studies of Urea Derivatives with Biochemical Interest: N,N′-Dimethylurea,N,N,N′,N′-Tetramethylurea,and N,N′-Dimethylpropyleneurea

Abstract

Mid-infrared, far-infrared, and Raman vibrational spectroscopic studies were combined with density functional theory (DFT) calculations and normal coordinate force field analyses for N,N′-dimethylurea (DMU), N,N,N′,N′-tetramethylurea (TMU), and N,N′-dimethylpropyleneurea (DMPU: IUPAC name 1,3-dimethyltetrahydropyrimidin-2(1H)-one). The equilibrium molecular geometry of DMU (all three conformers), TMU, and DMPU and the frequencies, intensities, and depolarization ratios of their fundamental infrared (IR) and Raman vibrational transitions were obtained by DFT calculations. The vibrational spectra were fully analyzed by normal coordinate methods as well. A starting force field for DMPU was obtained by adapting corresponding force constants for DMU and TMU, resulting after refinements in the stretching force constants C=O (7.69, 7.30, 7.68 N·cm^?1), C–N (5.16, 5.55, 5.05 N·cm^?1), and C-Me (5.93, 4.00, 4.22 N·cm^?1) for DMU, TMU, and DMPU, respectively. The dominating conformer of liquid DMU was identified as trans-trans, strong intermolecular hydrogen bonding was verified in solid DMU, and weak dipole–dipole association was found in liquid TMU and in DMPU. Special attention was paid to analyzing the methyl group frequencies, which revealed deviations from local C_3v symmetry. A linear correlation was found between the CH stretching force constants and the inverse of the CH bond lengths (1/r ²). The averaged NH stretching frequencies of gaseous, dissolved, and solid urea and of DMU, with variations for hydrogen bonding of different strength, are linearly correlated to the NH stretching force constants. Characteristic skeletal vibrations were assigned for a broad variety of urea derivatives and also for pyrimidine derivatives, which all contain the N₂C=O entity. The very strong IR bands of C=O stretching (1,676 ± 40 cm^?1) and asymmetric CN₂ stretching (1,478 ± 60 cm^?1), and the very intense Raman feature of symmetric CN₂ stretching or ring breathing (757 ± 80 cm^?1), can be recognized as fingerprint bands also for the pyrimidine derivatives cytosine, thymine, and uracil, which all are nucleobases in DNA and RNA nucleotides.     

Copper(II) complexes of N-terminal protected tri- and tetra-peptides containing histidine residues

Copper(II) complexes of peptides containing two or three histidyl residues (Ac-HisGlyHis-OH, Ac-HisGlyHis-NHMe, Ac-HisHisGlyHis-OH and Ac-HisHisGlyHis-NHMe) have been studied by potentiometric, UV-Vis, EPR and CD spectroscopic measurements. The imidazole nitrogen atoms are described as the primary metal binding sites of all ligands resulting in the formation of various macrochelates in the pH range 4 to 7. The (Nim, N-, Nim)-co-ordinated [CuH-1L]0+ complexes were mainly detected in samples containing free carboxylates at the C-termini, whilst the [CuH-2L]-(0) complexes were the predominant species in slightly alkaline solution and their binding modes were described via 4N-co-ordination (Nim, N-, N-, Nim) in (7,5,6)-membered fused chelate rings. Deprotonation and co-ordination of the third amide nitrogens were detected above pH approximately 9 in all cases.     

Photoinduced electron transfer via nonbuttressed metal-metal bonds. The photochemical study of binuclear complexes with platinum-thallium bonds

The photochemistry of binuclear metal-metal bonded complexes [(NC) 5Pt-Tl(solv) x ] (solv is water or dimethylsulfoxide) has been studied in aqueous and dimethylsulfoxide solutions. Both stationary and nanosecond laser flash photolysis have been carried out on the species. The metal-metal bonded complexes have been photolyzed by irradiation into the corresponding intense MMCT absorption bands. Photoexcitation results in the cleavage of the platinum-thallium bond and the formation of a solvated thallous ion and a cyano complex of platinum(IV), [Pt(CN) 5(solv)] (-), in both cases. The species have been characterized by multinuclear NMR and optical spectroscopy. The products of the photoreaction indicate a complementary two-electron transfer occurring between platinum and thallium ions in the binuclear Pt-Tl species. Quantum yield values for the photodecomposition of the species have been determined. The intermediates of the photoinduced metal-to-metal electron transfer have been detected and characterized by optical spectroscopy. The kinetics of transient formation and decomposition have been studied, and mechanisms of the photoactivated redox reaction have been suggested.     

Fully On-Line Hyphenation of an Experimental OPLC Separation Unit with Diode-Array Detection and Mass-Spectrometry (OPLC-DAD-MS) for Analysis of Xanthine Compounds

JPC – Journal of Planar Chromatography – Modern TLC - The newly developed experimental OPLC separation unit 100 (OSU 100) has been used for fully on-line multiple hyphenation using the...     

Gene network and canonical pathway analysis in prostate cancer: a microarray study

The molecular mechanism playing a role in the development of prostate cancer (PCA) is not well defined. We decided to determine the changes in gene expression in PCA tissues and to compare them to those in non-cancerous samples. Prostate tissue samples were collected by needle biopsy from 21 PCA and 10 benign prostate hyperplasic (BPH) patients. Total RNA was isolated, cDNA was synthesized, and gene expression levels were determined by microarray method. In the progression to PCA, 738 up-regulated and 515 down-regulated genes were detected in samples. Analysis using Ingenuity Pathway Analysis (IPA) software revealed that 466 network and 423 functions-pathways eligible genes were up-regulated, and 363 network and 342 functions-pathways eligible genes were down-regulated. Up-regulated networks were identified around IL-1beta and insulin-like growth factor-1 (IGF-1) genes. The NFKB gene was centered around two up- and down-regulated networks. Up-regulated canonical pathways were assigned and four of them were evaluated in detail: acute phase response, hepatic fibrosis, actin cytoskeleton, and coagulation pathways. Axonal guidance signaling was the most significant down-regulated canonical pathway. Our data provide not only networks between the genes for understanding the biologic properties of PCA but also useful pathway maps for future understanding of disease and the construction of new therapeutic targets.     

Investigation of chiral reactions: the structural detection of new hydrogenated isocinchona alkaloids from mixtures without isolation using electrospray ionization tandem mass spectrometry

The reaction mixture for the hydrogenation of ethyl pyruvate on Pt-alumina catalyst modified with isocinchona alkaloids (alpha-ICN (I) and beta-ICN (II)) was studied by electrospray ionization tandem mass spectrometry (ESI-MS/MS). It was established that part of the chiral modifiers themselves are converted into ions of m/z 299, 305 and 309 in the course of chiral hydrogenation. The experimental data allowed the determination of the probable structure of the ions mentioned. According to ESI-MS/MS spectra the structure of the new cinchona alkaloids was assumed: tetrahydro-isocinchonines (III-VI), decahydro-isocinchonines (VII, VIII) and hydrogenated compounds of VII and VIII by scission of their C--N and C--O bonds (IX/1, IX/2, X). Fragmentation pathways are proposed for these new compounds.     

Detection of Amadori compounds by capillary electrophoresis coupled to tandem mass spectrometry

Capillary electrophoresis coupled to mass spectrometry (CE-MS) is reported for the first time as an alternative and powerful analytical method for the characterization and monitoring of N-substituted 1-amino-1-deoxyketoses (Amadori compounds). It allows rapid separation and identification of Amadori compounds, while benefiting from the well-known advantages of MS, such as specificity and sensitivity. Amadori compounds of several amino acids, such as glycine, valine, isoleucine, methionine, proline, and phenylalanine, as well as a cysteine-derived compound, were separated and/or discriminated using CE-MS/MS under standard conditions. The technique may also be useful to study the stability and degradation kinetics of other labile charged Maillard intermediates that play an important role in food and medical science.     

Comparative study of the thermal behavior of Sr–Cu–O gels obtained by sol–gel and microwave-assisted sol–gel method

Journal of Thermal Analysis and Calorimetry - In the literature data, several papers reported the synthesis by various chemical or physical methods of the SrCu2O2 (SCO) having possible applications...     

Cinchona based squaramide catalysed enantioselective Michael addition of α-nitrophosphonates to aryl acrylates: enantioselective synthesis of quaternary α-aminophosphonates

Several cinchona based squaramide catalysts were applied to the asymmetric Michael addition of α-nitroethylphosphonates to acrylic acid aryl esters, resulting in high yields and enantioselectivities. The absolute configuration of one of the quaternary α-nitrophosphonate adducts was deduced from its experimental and calculated CD spectra. The adducts were reduced to their cyclic aminophosphonates by catalytic hydrogenation.     

DIHALOCARBENE ADDITION TO ARYLSUBSTTTUTED VINYL PHOSPHATES UNDER PHASE TRANSFER CATALYTIC CONDITIONS

Abstract

Dihalocarbene addition to aryl-substituted vinyl phosphates was carried out both in solid-liquid and in liquid-liquid two phase systems. The dihalocyclopropane adducts of vinyl phosphates could be obtained in better yield using dihalocarbenes generated by the latter method and no hydrolysis of the vinyl phosphate and of the adduct occurred under these circumstances. Eighteen new vinyl phosphate-dihalocarbene adducts were synthetized and characterized.