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Two polymorphic species of the [Fe(5-Br-salEen)2]ClO4 compound were obtained, each of them being selectively recovered after evaporation of the solvent at a controlled rate. While polymorph 1a is formed during slow evaporation, fast evaporation favors polymorph 1b. The importance of the evaporation rate was recognized after detailed studies of the reaction temperature, solvent evaporation rate and crystallization temperature effects. The complex in the new polymorphic form 1a showed an abrupt spin crossover at 172 K with a small 1 K hysteresis window and over a narrow 10 K range. 57Fe Mössbauer spectroscopy and differential scanning calorimetry, complemented by X-ray studies for both the high-spin and low-spin forms, were used to further characterize the new polymorphic phase 1a. Both polymorphs are based on the same Fe(iii) complex cation hydrogen bonded to the perchlorate anion. These units are loosely bound in the crystals via weak interactions. In the new polymorph 1a, the hydrogen bonds are stronger, while the weak hydrogen and halogen bonds, as well as π-π stacking, create a cooperative network, not present in 1b, responsible for the spin transition profile.

In this work, we demonstrate that n-alkanes coil when mixed with perfluoroalkanes, changing their conformational equilibria to more globular states, with a higher number of gauche conformations. The new coiling effect is here observed in fluids governed exclusively by dispersion interactions, contrary to other examples in which hydrogen bonding and polarity play important roles. FTIR spectra of liquid mixtures of n-hexane and perfluorohexane unambiguously reveal that the population of n-hexane molecules in all-trans conformation reduces from 32% in the pure n-alkane to practically zero. The spectra of peffluorohexane remain unchanged, suggesting nanosegregatiori of the hydrogenated and fluorinated chains. Molecular dynamics simulatiOns support this analysis. The new solvophobic effect is prone to have a major impact on the structure, organization, and therefore thermodynamic properties and phase equilibria of, fluids involving mixed hydrogenated and fluorinated chains. Fundacao para a Ciencia e Tecnologia [UID/NAN/50024/2013, UID/QUI/0100/2013, SFRH/BPD/81748/2011]

This work presents the use of N-phenylamides as models for the study of self-association and intermolecular interactions. Obtaining the crystal of N-phenyltrifluoroacetamide allowed its diffraction and inclusion in the series to be studied. The N-phenylamides with H, CH3, (CH3)3, Ph, CF3, CCl3 and CBr3 substituents were used together with the supramolecular cluster approach to obtain topological and energetic data and to verify differences in crystalline packing. Analyzes were carried out through several tools including theoretical calculations at the ωB97X-D/cc-pVDZ level, molecular electrostatic potential (MEP), quantum theory of atoms in molecules (QTAIM) and NMR. After the use of the tools, it was observed that the more energetic dimers were governed mainly by the hydrogen bond NH···O. Through the energy data, it was possible to propose crystallization mechanisms. Growth through chains in the early stages has been observed for almost all compounds, mainly due to the NH···O interaction, which helps to anchor molecules. Significant differences were observed between proposed mechanisms. For the solution study, 1H NMR spectroscopy was used in order to obtain the variation of the chemical displacements as a function of the concentration. By monitoring the amide hydrogen, it was possible to obtain the association constants of the molecules (Ka). The correlation of Ka data with the hydrogen bond strength (GNH···O) showed a good trend, showing a direct relationship between experimental and theoretical data. Este trabalho apresenta a utilização de N-fenilamidas como modelos para o estudo da autoassociação e de interações intermoleculares. A obtenção do cristal do composto N-feniltrifluoracetamida permitiu a difração do mesmo e inclusão na série a ser estudada. As N-fenilamidas com substituintes H, CH3, (CH3)3, Ph, CF3, CCl3 e CBr3 foram utilizadas juntamente com a abordagem do cluster supramolecular, a fim de se obterem dados topológicos e energéticos e de se verificarem as diferenças no empacotamento cristalino. Foram realizadas análises através de diversas ferramentas, incluindo cálculos teóricos no nível ωB97X-D/cc-pVDZ, potencial eletrostático molecular (MEP), teoria quântica dos átomos em moléculas (QTAIM) e RMN. Após o emprego das ferramentas, observou-se que os dímeros mais energéticos formados nos arranjos foram regidos, principalmente, pela ligação de hidrogênio NH···O. Através dos dados energéticos, foi possível propor mecanismos de cristalização. O crescimento através de fitas, nos primeiros estágios, foi observado para quase todos os compostos, principalmente, devido à interação NH···O, que ajuda a ancorar as moléculas. Diferenças significativas foram observadas entre os mecanismos propostos. Para o estudo em solução, utilizou-se a espectroscopia de RMN de 1H com o intuito de se obterem as variações dos deslocamentos químicos em função da concentração. Monitorando-se a ressonância do hidrogênio da amida, foi possível obter as constantes de associação das moléculas (Ka). A correlação dos dados de Ka com a força da ligação de hidrogênio (GNH···O) apresentou uma boa tendência, mostrando uma relação direta entre dados experimentais e teóricos.

We have here elucidated the crystal structures of five nostoclide analogues. A common feature in all compounds is a substituent at the para -position of the benzylidene group. Compounds with either bromine ( 3 ) or hydroxyl ( 4 ) as para -substituent crystallizes with Z’ = 2 as result of conformerism. It was also observed that Z' > 1 in the compound with a para -dimethylamino substituent ( 1 ). However, its four crystallographically independent molecules are conformationally similar. They are not related by crystallographic symmetry due to the offset packing of their C–H … O C nonclassical hydrogen bonded double chains. This compound ( 1 ) has also crystallized in a chiral space group (P2 1 ) despite the lack of a stereocenter. Such enantiomorphism phenomenon is related to the presence of only one of the two mirror benzyl conformations with phenyl ring at the equatorial position opposite the lactone oxygen atom. The molecular mean plane of nostoclide analogues has been featured by high level of planarity, except in the brominated compound where two twisted conformations occurred due to rotations on the single bond axis into benzylidene group. The benzyl conformation has been the greatest difference between the two crystallographically independent molecules of the para -hydroxylated compound ( 4 ). The crystal packing of the compounds is marked by double catemer motif assembled through C–H … O C non-classical hydrogen bonds, although C–H … π interactions do play an important role in stabilizing the crystal packing of some compounds of the series.

Submitted by GLAUCO ALMEIDA (glaucoag@gmail.com) on 2016-03-18T14:17:37Z No. of bitstreams: 1 Glauco Garrido Almeida-TESE-REV.pdf: 3028760 bytes, checksum: f9d5fc9929fc4cee05187b360a597c04 (MD5) Approved for entry into archive by Sandra Manzano de Almeida (smanzano@marilia.unesp.br) on 2016-03-18T17:11:17Z (GMT) No. of bitstreams: 1 almeida_gg_dr_ilha.pdf: 3028760 bytes, checksum: f9d5fc9929fc4cee05187b360a597c04 (MD5) Made available in DSpace on 2016-03-18T17:11:17Z (GMT). No. of bitstreams: 1 almeida_gg_dr_ilha.pdf: 3028760 bytes, checksum: f9d5fc9929fc4cee05187b360a597c04 (MD5) Previous issue date: 2015-12-11 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Trabalhos experimentais e teóricos desenvolvidos nos últimos anos evidenciaram a capacidade de alcoóis e polialcoóis em mudar características energéticas em proteínas. No entanto, o mecanismo responsável por esse efeito não está totalmente elucidado. Tomando como exemplo o dipeptídeo de alanina, foram realizadas simulações QM/MM em água, etanol e mistura 60-40 % em volume de água-etanol. A molécula de dipeptídeo foi descrita em nível de cálculo quântico MP2/aug-cc-pVDZ. Em solução, apenas confórmeros αR e PPII foram encontrados na população de equilíbrio. A diferença de energia livre em solução αR  PPII é determinada pelo balanço entre energia interna do soluto e energia de interação. Para o dipeptídeo de alanina, qualquer fator que aumente a energia de interação soluto-solvente favorece o aumento da população de αR. Por outro lado fatores que diminuam esse valor, como a adição de etanol, aumentam a população de PPII. Os resultados indicam solvatação preferencial para o sistema, evidenciado pela formação majoritária da primeira camada de solvatação por moléculas de água (na mistura), embora seja possível encontrar moléculas de etanol em pequenas quantidades ao redor do grupo carboxílico da extremidade N-terminal e, cadeias metílicas laterais. Todavia, o comportamento parece não afetar a diferença na estabilidade de equilíbrio conformacional. Recent papers, both experimental and theoretical, have highlighted the capacity of alcohols and polyalcohol in modifying the energy landscape in proteins. However, the mechanism underlying this effect is not fully elucidated. Taking as a model-system the alanine dipeptide, QM/MM calculations were performed in water, ethanol and solution 60-40% (volume) water-ethanol. The dipeptide molecule was described by MP2/aug-cc-pVDZ level. In solution, only αR and PPII conformers were found in the conformational equilibrium population. The free energy difference in solution αR  PPII is determined by the interplay between internal energy and the interaction energy. It has been found that, for alanine dipeptide, any factor that increases the solute-solvent interaction energy also promotes an increasing on αR stability, moreover factors that decreases this value, such as the addition of ethanol molecules, increases the PPII stability. The results points to a preferential solvation behavior for the system, as evidenced by the composition of the first solvation shell in the mixture mainly populated by water molecules, although it is possible to find small concentration of ethanol molecules around the carboxyl group of the N-terminal end and around methylic side chains. However, this behavior does not seem to affect the differential conformational stability. CAPES: 99999.014630/2013-03

Along the historical background of science, the hydrogen bond became widely known as the universal interaction, thus playing a key role in many molecular processes. Through the available theoretical approaches, many of these processes can be unveiled on the basis of the molecular parameters of the subject intermolecular system, such as the variation of bond length and mainly the frequency shift observed in the proton donor. Supported by the natural bond analysis (NBO) with the quantification of the hybridization contributions, the structural deformations and vibrational effects cited above are also attributed to the outcome of the intermolecular interaction strength, which consequently can be estimated by means of the quantum theory of atoms in molecules (QTAIM) as well as evaluated by the symmetry-adapted perturbation theory (SAPT). Moreover, to identify the preferential interaction sites for proton donors and acceptors, the molecular electrostatic potential (MEP) is useful in this regard.

The conformational changes of imatinib (IMT) are crucial for understanding the ligand–receptor interaction and its mechanism of action [Agofonov et al. (2014) Nature Struct Mol Biol 21:848–853]. Therefore, here we investigated the free energy conformational landscape of the free IMT base, aiming to describe the three-dimensional structures and energetic stability of its conformers. Forty-five unique conformers, within an energy window of 4.8 kcal mol−1 were identified by a conformational search in gas-phase, at the B3LYP/6-31G(d) theoretical level. Among these, the 20most stable, as well as 4 conformers resulting from optimization of experimental structures found in the two known polymorphs of IMTand in the c- Abl complex were further refined using the 6-31+G(d,p) basis set and the polarizable continuum solvation model. The most stable conformers in gas-phase and water exhibit a V-shaped structure. The major difference between the most stable free conformers and the bioactive conformers consists in the relative orientation of the pyrimidine–pyridine groups responsible for hydrogen bonding interactions in the ATP-binding pocket. The ratio of mole fractions corresponding to the two known (α and β) polymorphic forms of IMT was estimated from the calculated thermochemical data, in quantitative agreement with the existing experimental data related to their solubility. The electronic absorption spectrum of this compound was investigated in water and explained based on the theoretical TD-DFT results, considering the Boltzmann populationaveraged computed data at CAM-B3LYP/6-31+G(d,p) level of theory for the nine most stable conformers.

WOS: 000317788800014, PubMed ID: 24981533, beta-aminoisobutyric acid (BAIBA) has been studied in isolation conditions: in the gas phase and trapped into a cryogenic N-2 matrix. A solid sample of the compound was vaporized by laser ablation and investigated through their rotational spectra in a supersonic expansion using two different spectroscopic techniques: broadband chirped pulse Fourier transform microwave spectroscopy and conventional molecular beam Fourier transform microwave spectroscopy. Four conformers with structures of two types could be successfully identified by comparison of the experimental rotational and N-14 nuclear quadruple coupling constants with those predicted theoretically: type A, bearing an OH center dot center dot center dot N intramolecular hydrogen bond and its carboxylic group in the trans geometry (H-O-C=O dihedral similar to 180 degrees), and type B, having an NH center dot center dot center dot O bond and the cis arrangement of the carboxylic group. These two types of conformers could also be trapped from the gas phase into a cryogenic N-2 matrix and probed by Fourier transform infrared (IR) spectroscopy. In situ irradiation of BAIBA isolated in N-2 matrix of type B conformers using near-IR radiation tuned at the frequency of the O-H stretching 1st overtone (similar to 6930 cm(-1)) of these forms allowed to selectively convert them into type A conformers and into a new type of conformers of higher energy (type D) bearing an NH center dot center dot O=C bond and a O-H "free" trans carboxylic group, COMPETE-QREN-EU [PTDC/QUI-QUI/111879/2009]; Portugal-Spain Bilateral Project [E-7 CRUP-MCI 2011-E03]; Ministerio de Ciencia y Innovacion [CTQ 2006-05981/BQU, CTQ 2010-19008]; Consolider Ingenio [CSD 2009-00038]; Junta de Castilla y Leon [VA070A08]; Spain-Portugal Bilateral Project [AIB2010PT-00315], These studies were performed under projects PTDC/QUI-QUI/111879/2009 (also funded by COMPETE-QREN-EU) and the Portugal-Spain Bilateral Project E-7 CRUP-MCI 2011-E03. This work has also been supported by the Ministerio de Ciencia y Innovacion (Grant Nos. CTQ 2006-05981/BQU and CTQ 2010-19008), Consolider Ingenio 2010 (Grant No. CSD 2009-00038), Junta de Castilla y Leon (Grant No. VA070A08), and the Spain-Portugal Bilateral Project AIB2010PT-00315.

Explicit hydration of the neutral and charged cyclohexylamine and of the cyclohexyldiamine isomers in their mono- or diprotonated forms is investigated through classical molecular dynamics (MD) simulations in aqueous solutions combined with DFT calculations in amine–water complexes. The MD studies performed in the monoamines reveal that the structure of the hydration shell around the neutral amino group (NH2) is quite distinct from that around the charged one (NH3+). On average, the number of water molecules surrounding the two groups is calculated to be ∼2 and 3–4, respectively. The variation of the hydration structure prompted by the groups’ proximity is discussed based on the data found for the mono- and diprotonated diamines. To have a more detailed picture of the water molecules’ arrangement around the amino groups and of the amine–water hydrogen bonds, geometry optimisations in hydrates with up to six water molecules are carried out at the B3LYP/aug-cc-pVDZ level. Complexation energies are also comp...

The triterpenoids oleanolic (OA) and ursolic (UA) acids show non-selective antiinflamatory activity in vitro for cyclooxygenase (COX) isoforms. 3D conformations of OA and UA, with three possible orientations (1, 1' and 2) in the active site of isoforms COX, obtained by docking, were submitted to molecular dynamics. The results show that orientation 2 of the OA in COX-2 is more favorable because orientation 1 moved away from the active site. The carboxylate group of OA interact by hydrogen bonds with Ser353 and with Phe357 and Leu359, mediated by water, while hydroxyl in C-3 interact by hydrogen bond, mediated by water, with Tyr385.

It is through the application of an electronic partition approach called Symmetry-Adapted Perturbation Theory (SAPT) that the nature of hydrogen bonds and van der Waals interactions can be unveiled according to the contribution of electrostatic, charge transfer, exchange repulsion, polarization, and dispersion terms. Among these, electrostatic partition governs the formation of the hydrogen bonds, whose energies are arguably high. However, the weakness of the interaction strength is caused by dispersion forces, whose contribution decisively lead to the stabilization of complexes formed via van der Waals interactions.

Hydrogen bond energies of fifteen dimers were calculated using the large basis set 6-311++G(3df,3pd), at Hartree-Fock (HF) level including Møller-Plesset (MP2) calculations. The procedure for obtaining such energies were based on the dimer's energy rise provoked by increasing in intermolecular distance of the system component units. Deviations from a strictly linear hydrogen bond were investigated and rotational barriers were also computed allowing the calculation of the second order attractive interactions. In order to provide a more objective definition of hydrogen bond, a lower energy limit was proposed in place of the merely empirical parameters employed in the classical definition

HYDROGEN BOND STUDY BY AB INITIO CALCULATIONS FOR DIMERS FORMED FROM H2O, NH3, HF, HCl AND HBr MONOMERS. Hydrogen bond energies of fifteen dimers were calculated using the large basis set 6-311++G(3df,3pd), at HartreeFock (HF) level including Moller-Plesset (MP2) calculations. The procedure for obtaining such energies were based on the dimer’s energy rise provoked by increasing in intermolecular distance of the system component units. Deviations from a strictly linear hydrogen bond were investigated and rotational barriers were also computed allowing the calculation of the second order attractive interactions. In order to provide a more objective definition of hydrogen bond, a lower energy limit was proposed in place of the merely empirical parameters employed in the classical definition.

Adesão é um parâmetro físico-químico que pode promover inovações em materiais à base de cimento Portland. Este conceito, entretanto, ainda requer evidência experimental para propiciar mais desenvolvimentos neste assunto. Este trabalho tem demonstrado como diferentes substâncias podem promover diferentes forças de adesão após a avaliação do grau de hidratação e a resistência mecânica de materiais cementícios não reativos. As substâncias capazes de produzir ligações de hidrogênio tridimensionais como, por exemplo, a água, foram as mais eficazes para produzir amostras cementícias com melhor resistência mecânica. Isso significa que a água não é importante somente por causa de seu papel na hidratação do cimento, mas também porque ela desenvolve adesão entre as superfícies cementícias hidratadas. Mais que especular sobre o entendimento fundamental na adesão de materiais cementícios à base de cimento Portland, este artigo tem a intenção de estimular a discussão como aproveitar a água confinada entre as superfícies cementícias hidratadas como um nanoadesivo interno, até agora pouco explorado, mas ao mesmo tempo com tendência de fornecer materiais de alto desempenho. Adhesion is a physical-chemical parameter able to render innovations to Portland cement-based materials. However, this concept still lacks experimental evidence to underlie further developments in this subject. This work has demonstrated how distinct substances can impart different adhesion forces after evaluating the hydration degree and the mechanical strength of non-reactive cementitious materials. The substances capable of making tridimensional hydrogen bonds, such as water, for instance, were the most effective in providing cementitious samples with improved bending strength. It implies that water is not only important because of its role in cement hydration, but also because it develops adhesion between hydrated cementitious surfaces. More than speculating the fundamental understanding on adhesion in Portland cement-based materials, the present paper intends to stimulate thinking on how to take the benefits of the water confined between the hydrated cementitious surfaces as an in-built nanoadhesive, so far little explored, but at the same time so prone to yield high performance materials.

O presente trabalho traz a determinação da estrutura dos compostos 5-bromoisatina-3- tiossemicarbazona, sendo a obtenção e síntese do composto 5-bromoisatina-3-tiossemicarbazona já é conhecida e publicada, 5-bromosalicilaldeídotiossemicarbazona e do complexo 5-bromosalicilaldeídotiossemicarbazonato- (piridina) de níquel II [Ni(5-Br-SalTSC)py] caracterizados por análise espectroscópicas na região do infravermelho e ultravioleta-visível sendo que, no complexo também realizou-se a análise termogravimétrica. Obteve-se a estrutura cristalina/molecular do composto 5-bromoisatina-3-tiossemicarbazona que apresenta moléculas de acetonitrila como solvato de cristalização. O composto cristalizou em um sistema monoclínico e pertence ao grupo espacial C2/C. A cela elementar apresenta constantes a= 20,017(4)Å, b= 12,352(2)Å e c= 13,190(5)Å e β=129,258(2)°.Na cela elementar estão presentes oito fórmulas elementares (Z=8). O índice de discordância para I>2(I) é igual a R1=0,0392 e wR2=0,1036 e para todos os dados R1=0,0522 e wR2=0,1036. Ainda sobre a estrutura deste composto cabe ressaltar que esta apresenta diversas interações intermoleculares entre as destacam-se N-H···S e as N-H···O, onde as moléculas do composto formam uma rede polimérica planar. Também obteve-se a estrutura cristalina/ molecular do complexo 5-bromosalicilaldeídotiossemicabazonato(piridina) de níquel(II) [Ni(5-Br-SalTSC)py] que apresenta geometria quadrado planar distorcida, e cristalizou em um sistema monoclínico, grupo espacial P21/c, Z=4 a= 12, 2448(4)Å, b= 4,11340(10)Å e c= 31,1340(11)Å e = 112,470(10)°. O índice de discordâncias para I>2(I) igual R1= 0,0232 e wR2= 0,0507 e para todos os dados R1= 0,0336 e wR2= 0,0555. O complexo [Ni(5-Br-SalTSC)py] apresenta ligações de hidrogênio do tipo N-H···N e C-H···S que resultam em um polímero de coordenação. The present work brings obtainment of the compounds 5-bromoisatin-3-thiosemicarbazone, 5- bromosalicylaldehydethiosemicarbazone of the complex [Ni(5-BrSalTSC)py] characterized by spectroscopy infrared and spectroscopy ultraviolet-visible in the complex was made analysis thermogravimetric. The structure crystalline/molecular of the compound 5-bromoisatin-3-thiosemicarbazone which present a molecule of acetonitrile of solvate of crystallization. The compound crystallized in a monoclinic system belonging at the space group C2/c. The unit cell present constant a= 20,017(4)Å, b = 12,352(2)Å e c=13,190(5)Å and β=129,258(2)º. In the cell unit are present eight elementaries formulas (Z=8). The discordance indexes to I>2(I) are equal the R1= 0,0392 and wR2=0,1036 and to all the data R1=0,0522 and wR2=0,1036. It is important underline which the structure has several interactions intermolecular including the interactions N-H···S and NH···O in the which the molecules of the compound builds a planar polymer network. The structure - crystalline/molecular of complex 5-bromosalicylaldehydethiosemicarbazonate(pyridine) of Nickel (II) was obtained has distorted square planar geometry and crystallized in a monoclinic system, space group P21/c and Z=4 it has a=12,2448(4)Å, b= 4,11340(10)Å and c= 31,1340(11)Å and = 112,6470(10)Å and the cell unit present discordance indexes to I2(I) equal R1=0,0232 e wR2=0,0507 and to all the data R1= 0,0336 and wR2=0,0555. The complex [Ni(5-Br-SalTSC)py] present hydrogen bonds N-H···N and C-H···S which result in a coordination polymer.

Hydrogen bonds formed through the interaction between a high electronic density center (lone electron pairs, π or pseudo-π bonds) and proton donors cause important electronic and vibrational phenomena in many systems. However, it was demonstrated that proton donors interact with hydrides, such as alkali and alkaline earth metals (BeH2, MgH2, LiH and NaH), what yields a new type of interaction so-called dihydrogen bonds. The characterization of these interactions has been performed at light of the Quantum Theory of Atoms in Molecules (QTAIM), by which the electronic densities ρ are quantified and the intermolecular regions are characterized as closed-shell interactions through the analysis of the Laplacian field ∇2ρ.

B3LYP/6-31G(d,p) calculations were used to determine the optimized geometries of the C2H4O-C2H2 and C2H4S-C2H2 heterocyclic hydrogen-bonded complexes. Results of structural, rotational, electronic and vibrational parameters indicate that the hydrogen bonding is non-linear due to the pi bond of the acetylene interacting with the hydrogen atoms of the methyl groups of the three-membered rings. Moreover, the theoretical investigation showed that the non-linearity is much more intriguing, since there is a structural disjunction on the acetylene within the heterocyclic system.

B3LYP/6-31G(d,p) calculations were used to determine the optimized geometries of the C2H4O-C2H2 and C2H4S-C2H2 heterocyclic hydrogen-bonded complexes. Results of structural, rotational, electronic and vibrational parameters indicate that the hydrogen bonding is non-linear due to the pi bond of the acetylene interacting with the hydrogen atoms of the methyl groups of the three-membered rings. Moreover, the theoretical investigation showed that the non-linearity is much more intriguing, since there is a structural disjunction on the acetylene within the heterocyclic system.

Hydrogen-bonded complexes formed by the interaction of the heterocyclic molecules C2H4O and C2H5N with HF, HCN, HNC and C2H2 have been studied using density functional theory. The hydrogen bond strength has been analyzed through electron density charge transfer from the proton acceptor to the proton donor. The density charge transfer has been estimated using different methods such as Mulliken population analysis, CHELPG, GAPT and AIM. It has been shown that AIM-estimated charge transfer correlates very well with the hydrogen bond energy and the infrared bathochromic effect of the proton donor stretching frequencies.

The purpose of this work is to study theoretically stereoelectronic aspects of the interaction between heme and artemisinin in the transitional heme-artemisinin complex. Through semi-empirical calculations using the PM3 method, the potential energy barrier of artemisinin rotation relative to heme in the heme-artemisinin complex was studied in vacuum and in the partially solvated state. The minimum heat of formation obtained for the complex with and without water molecules is -702.39 and -100.86 kcal mol-1, respectively, which corresponds to the dihedral angle C-Fe-O1-O2 of 43.93º and 51.90º around the iron-oxygen O1 bond, respectively. The water molecules bind to heme via 13 hydrogen bonds and O-H•••O and 6 C-H•••O interactions, which accounts for -67.23 kcal mol-1. It is observed that the inclusion of water molecules does not affect significantly the stability of the heme-artemisinin complex.

Two ortho-iodoallyloxybenzoates, methyl 4-O-allyl-2,3-di-O-benzyl-6-O-(2-iodobenzoyl)- alpha-D-glucopyranoside (3) and methyl 4-O-allyl-2,3-di-O-benzyl-6-O-(2-iodobenzoyl)- alpha-D-galactopyranoside (4) were synthesized in seven conventional steps from methyl alpha-D-glucopyranoside and methyl alpha-D-galactopyranoside, respectively. Bu3SnH-mediated aryl radical cyclization of 3 provided exclusively the hydrogenolysis product 12. The reaction of 4 gave the reduced uncyclized product 13 and only traces of 4A, resulting from 11-endo aryl radical cyclization. In previous papers we described that in similar Bu3SnH-mediated radical reaction of ortho-iodoallyloxybenzamides, analogs of 3 and 4, we obtained macrolactams resulting from 11-endo cyclization. An hypothesis to explain the differences is presented. It was assumed that in the aryl radical formed from iodobenzamides there is a suitable conformation to cyclization, which is stabilized by an intramolecular hydrogen bond.

In the present work, we analyzed the accuracy of distinct theoretical methods to reproduce the solid state structures of cyclodextrins. The a, b and g-cyclodextrins (CD) were considered and also their hydrates with included water molecules: a-CD.2H2O, b-CD.10H2O and g-CD.12H2O. The geometries were fully optimized using Molecular Mechanics (MM2), semiempirical (AM1 and PM3) and ab initio (HF/3-21G) methods and quantitatively compared with experimental data from X ray diffraction. The results obtained from the classical MM2 method were in best agreement with the experiment. The semiempirical and ab initio structures were also in satisfactory accordance with the experimental data. In general, the PM3 method was found to be more suitable than the AM1 to describe the CD geometries, mainly when the intramolecular hydrogen bonds are considered.

A determinação de estruturas tridimensionais de quelatos com metais pesados e de alguns potencialmente úteis agentes quelantes, é uma ferramenta muito importante no estudo de complexos que poderão agir como antídotos na intoxicação por ingestão de metais pesados. Um conhecimento detalhado destes complexos é exigido para auxiliar na modelagem de estruturas moleculares e na determinação de procedimentos que sejam mais efetivos na neutralização dos processos, desenvolvidos por indivíduos com intoxicação crônica por metais pesados. Aqui serão reportados os resultados de um estudo sistemático de complexos [TlMe2L], onde L = 2-mercapto-3-piridina ácido carboxílico (I), 6-mercapto-3-piridinametoxicarboxilato (II), 2-mercapto-3-piridina-metoxicarboxilato (III), 6-mercapto-3-piridina-etoxicarboxilato (IV) e 2-mercapto-3-piridina-etoxicarboxilato (V). O estudo dos arranjos supramoleculares destes complexos mostra que, apesar das diferenças na simetria dos grupos espaciais e os substituintes nos ligantes, o empacotamento no cristal são similares. Os complexos formam polimeros infinitos em uma, duas e três dimensões, baseadas em interações TI - S, T1 - N e T1 - O e ligações de hidrogênio. Existem várias formas de correções dos dados de difração de raios X em monocristais. Durante o processamento das intensidades coletadas realizam-se várias correções, tais como de Lorentz, polarização, absorção e eventualmente correção por deterioração da amostra. A correção por absorção é fortemente recomendada para cristais que possuem fortes absorvedores em sua forma estrutural. Foram estudados os efeitos da absorção dos raios X em amostras cristalinas e uma comparação dos resultados obtidos ao aplicar os diferentes métodos de correções por absorção disponíveis. Constatou-se que após serem realizados diferentes formas de correção por absorção, houve diferenças significativas nas figuras de mérito, picos e vales de densidade de carga residual e parâmetros de deslocamentos anisotrópicos. Já nos ângulos e distâncias de ligações não foram observados mudanças significativas. The determination of the three-dimensional structures of heavy-metal chelates and of some potentially useful chelating agents is a very important to01 in the study of complexes that may act as antidotes against poisoning by ingestion of heavy metals. A detailed knowledge of these complexes is expected to assist in the design of molecular structures and procedures that are more effective in counteracting the life threatening processes inevitably developed by individuals with chronic heavy-metal intoxication. Within this framework a series of dimethylthallium(III) complexes were studied. Here we present complexes of the type [TlMe2L], where L=2-mercapto-3- pyridine carboxylic acid(I), 6-mercapto-3-pyridine-methoxycarboxylate(II), 2-mercapto-3-pyridine-methoxycarboxylate(III), 6-mercapto-3-pyridineethoxycarboxylate(IV) and 2-mercapto-3-pyridine-ethoxycarboxylate(V). The study of the supramolecular arrangement of these complexes shows that, in spite of the differences in space group symmetry and substituents in the ligand, the crystals packing are remarkably similar. The complexes form infinite polymers in one, two and three dimensions, based upon TI-S, T1-0 e T1-N covalent bonds and intermolecular secondary interactions. The complexes also present strong hydrogen bond intermolecular interactions. There are many forms of corrections to the data collected in a single crystal X-ray diffration experiment. During the data reduction many corrections take place, such as: Lorentz, polarization, absorption and eventualy corrections for the deterioration of the sample. The absorption correction is strongly recommended for crystals with strong absorbers in its structural form. The effect of the absorption of the X rays has been studied in crystalline samples, as well as a comparison between the result obtained from the different available methods of absorption corrections. This work that showed different forms of absorption correction, made significant differences in the merit figures, peak and hole of residual charge density, as well as the anisotropic displacements parameters. Bonds distances and angles, on the other hand, did not change significantly.

The structure and hydration of the HNP-3 have been derived from molecular dynamics data using root mean square deviation, radial and energy distributions. Three antiparallel beta sheets were found to be preserved. 15 intramolecular hydrogen bonds were identified together with 36 hydrogen bonds on the backbone and 35 on the side chain atoms. From the point of view of the hydration dynamics, the analysis shows a high solvent accessibility of the monomer and attractive interactions with water molecules.

A very short-strong hydrogen bond (20kcal/mol) is found in the monoanion of certain dicarboxylic acids derived from maleic and dialkylmalonic acids. Certain aromatic diamines that are known as proton sponge have exceptionally high basicity (pKa) and are only monoprotonated with strong acids like percloric acid. The closed proximity between the two basic centers provokes a strong steric interaction that is relieved upon protonation. Similar effects are found in dicarboxylic acids (hydrogen maleate and hydrogen dialkylmalonates) that present a very short distance between the two oxygens and a short-strong hydrogen bond.