Ab initio study of the cooperativity between NH···N and NH···C hydrogen bonds in H3N–HNC–HNC complex

Ab initio calculations at the MP2/aug-cc-pVTZ level have been performed to study the cooperativity of hydrogen bonds in homoclusters (HNC–HNC–HNC and HNC–HNC–HNC–HNC) and heteroclusters (H₃N–HNC–HNC and H₃N–HNC–HNC–HNC). The cooperative energies in the HNC–HNC–HNC and H₃N–HNC–HNC trimers are –2.05 and –2.56 kcal/mol, respectively. The result shows that the cooperativity in the heterotrimer is larger than that in the homotrimer. A similar result also happens in the tetramers. The energy decomposition scheme indicates that orbital interaction is a major contribution to the cooperative energy of N···HN hydrogen bond, whereas the electrostatic and orbital interactions to that of C···HN hydrogen bond. The effect of HNC chain length on the strength of N···HN hydrogen bond has also been considered at the MP2/aug-cc-pVDZ level. It is indicated that the interaction energy of N···HN hydrogen bond trends to be a fixed value when the HNC number tends to be infinite, and the strength of N···HN hydrogen bond is regulated mainly through the electrostatic and polarization interactions although the charge transfer interaction also has an effect on it.     

Comparison of aromatic NH···π, OH···π, and CH···π interactions of alanine using MP2, CCSD, and DFT methods

A comparison of the performance of various density functional methods including long‐range corrected and dispersion corrected methods [MPW1PW91, B3LYP, B3PW91, B97‐D, B1B95, MPWB1K, M06‐2X, SVWN5, ωB97XD, long‐range correction (LC)‐ωPBE, and CAM‐B3LYP using 6‐31+G(d,p) basis set] in the study of CH···π, OH···π, and NH···π interactions were done using weak complexes of neutral (A) and cationic (A⁺) forms of alanine with benzene by taking the Møller–Plesset (MP2)/6‐31+G(d,p) results as the reference. Further, the binding energies of the neutral alanine–benzene complexes were assessed at coupled cluster (CCSD)/6‐31G(d,p) method. Analysis of the molecular geometries and interaction energies at density functional theory (DFT), MP2, CCSD methods and CCSD(T) single point level reveal that MP2 is the best overall performer for noncovalent interactions giving accuracy close to CCSD method. MPWB1K fared better in interaction energy calculations than other DFT methods. In the case of M06‐2X, SVWN5, and the dispersion corrected B97‐D, the interaction energies are significantly overrated for neutral systems compared to other methods. However, for cationic systems, B97‐D yields structures and interaction energies similar to MP2 and MPWB1K methods. Among the long‐range corrected methods, LC‐ωPBE and CAM‐B3LYP methods show close agreement with MP2 values while ωB97XD energies are notably higher than MP2 values. © 2010 Wiley Periodicals, Inc. J Comput Chem 2010     

Weak H-bonds. Comparisons of CH···O to NH···O in proteins and PH···N to direct P···N interactions

Whereas CH···O H-bonds are usually weaker than interpeptide NH···O H-bonds, this is not necessarily the case within proteins. The nominally weaker CH···O are surprisingly strong, comparable to, and in some cases stronger than, the NH···O H-bonds in the context of the forces that hold together the adjacent strands in protein β-sheets. The peptide NH is greatly weakened as proton donor in certain conformations of the protein backbone, particularly extended structures, and forms correspondingly weaker H-bonds. The PH group is a weak proton donor, but will form PH···N H-bonds. However, there is a stronger interaction in which P can engage, in which the P atom, not the H, directly approaches the N electron donor to establish a direct P···N interaction. This approach is stabilized by the same sort of electron transfer from the N lone pair to the P-H σ* antibond that characterizes the PH···N H-bond.     

Internal rotation and halogen bonds in CF3I···NH3 and CF3I···N(CH3)3 probed by broadband rotational spectroscopy

The rotational spectra of CF(3)I···NH(3) and CF(3)I···N(CH(3))(3) are measured between 6.7 and 18 GHz using a chirped-pulse Fourier transform microwave spectrometer. Transitions in each spectrum are assigned to A and E species associated with ground and excited internal rotor states respectively. Rotational constants, B(0), centrifugal distortion constants, D(J), D(Jm), D(JKm), nuclear quadrupole coupling constants of the (14)N and (127)I atoms, χ(aa)(N) and χ(aa)(I), are determined for each complex. D(JK) is additionally determined for CF(3)I···NH(3). Results are presented for both (14)N and (15)N-substituted isotopologues. All data are consistent with C(3v) symmetric top structures for both complexes. The nuclear quadrupole coupling constants of iodine are determined to be -2230.030(83) MHz and -2241.61(17) MHz in CF(3)I···(14)NH(3) and CF(3)I···(14)N(CH(3))(3) respectively. The data are interpreted through a model that accounts for the internal dynamics of the complexes in order to determine the length of the halogen bond between the iodine and nitrogen atoms, r(N···I). Values of r(N···I) are thus determined to lie in the ranges 3.054 ? > r(N···I) > 3.034 ? and 2.790 ? > r(N···I) > 2.769 ? for CF(3)I···NH(3) and CF(3)I···N(CH(3))(3) respectively.     

Preparation of β-fluoro- and β,β-difluoro-histidinols

Nucleophilic attack of azide on 2-bromo-3-fluoro-3-(1-trityl-1H-imidazol-4-yl)-propan-1-ol (1a) in aprotic solvent occurs on the 2-position to give the 2-azido derivative (2a). Reduction of azide and removal of the trityl group produces β-fluorohistidinol (6a). Elimination of HBr from 1a followed by “FBr” addition to the resulting double bond gives 2-bromo-3,3-difluoro-3-(1-trityl-1H-imidazol-4-yl)-propan-1-ol (1b). Nucleophilic attack of azide followed by reduction and removal of the trityl group, as for the preparation of 6a, gives β,β-difluorohistidinol (6b). Initial attempts, under a variety of conditions, to oxidize the fluorinated histidinol precursors to carboxylic acids have not been successful.     

Synthesis and Crystal Structure of Tetraamminelithium-Rubidiumtriselenide, Li(NH3)4RbSe3, and Pentaamminesodium-Rubidiumtriselenide-Ammonia(1/3), Na(NH3)5RbSe3 · 3NH3

Summary. The ammoniates Li(NH₃)₄RbSe₃ and Na(NH₃)₅RbSe₃·3NH₃ were prepared by the reduction of Rb₂Se₅ with lithium or sodium in liquid ammonia. Single crystals were isolated and characterized by X-ray structure analysis using low temperature techniques. Both compounds contain triselenide anions Se₃^2–, which coordinate to rubidium cations forming ¹[RbSe₃]^– or ¹[Rb(NH₃)₂Se₃]^– chains. The chains are separated in the crystal structures by the homoleptic ammine complexes Li(NH₃)₄⁺ and Na(NH₃)₅⁺.     

Synthesis and biological investigation of the β-thiolactone and β-lactam analogs of tetrahydrolipstatin

The synthesis of β-thiolactone and β-lactam analogs of tetrahydrolipstatin is described from a common late-stage β-lactone derivative. These analogs, and a cis-disubstituted β-lactone analog of tetrahydrolipstatin, were screened for activity against porcine pancreatic lipase and for inhibition of cell growth of a panel of four human cancer lines.     

Preparation, characterization, and application of electrodes modified with electropolymerized one-dimensional Magnus' green salts: Pt(NH3)4 · PtCl4 and Pt(NH3)4 · PtCl6

We report the modification of various electrode surfaces with electropolymerized Magnus' green salts, [Pt(NH₃)₄ · PtCl₄] _n and [Pt(NH₃)₄ · PtCl₆] _n . The modified electrodes were prepared by cyclic scanning of the electrode potential in an aqueous solution containing Pt(NH₃)₄ ²⁺ and PtCl₄ ²⁻ or PtCl₆ ²⁻ and the supporting electrolyte. The conditions for the film deposition were studied in detail. Several surface analytical techniques, including micro-Raman scattering and X-ray diffraction, were employed to characterize the modifier film. The electrochemical behavior of the modified electrode was studied in detail and the modified electrodes display very good electrocatalytic activity in the oxidation of ascorbic acid, hydrogen peroxide, thiosulfate, and especially nitric oxide. Received: 22 April 1999 / Accepted: 30 June 1999     

Practical synthesis of β-acyl and β-alkoxycarbonyl heterocyclic sulfones

A short and efficient synthesis for β-acyl and β-alkoxycarbonyl heterocyclic sulfones containing benzothiazol (BT) and phenyltetrazol (PT) heterocyclic core is presented here. The method seems to be general and provides the desired C-nucleophiles in very good to excellent yields from readily available starting materials.     

Preparation and evaluation of inclusion complexes of diacerein with β-cyclodextrin and hydroxypropyl β-cyclodextrin

The objective of this research was to improve the aqueous solubility, dissolution rate and, consequently, bioavailability of diacerein, along with avoiding its side effect of diarrhea, by complexation with β-cyclodextrin (β-CD) and HP-β-cyclodextrin (HP-β-CD). Phase solubility curve was classified as an A_N type for both the CDs, which indicated formation of complex of diacerein with β-CD and HP-β-CD in 1:1 stoichiometry and demonstrating that both CDs are proportionally less effective at higher concentrations. The complexes were prepared by kneading method and were evaluated to study the effect of complexation on aqueous solubility and rate of dissolution in phosphate buffer (pH 6.8). Based on the dissolution profile HP-β-CD was selected for preparing fast disintegrating tablet of diacerein which was compared with marketed formulation (MF-J). The HP-β-CD complex was probed for Fourier transform infrared spectroscopy, differential scanning calorimetry, and powder X-ray diffraction studies which evidenced stable complex formation and increase in amorphousness of diacerein in complex. In brief, the characterization studies confirmed the inclusion of diacerein within the non-polar cavity of HP-β-CD. HP-β-CD complex showed improved in vitro drug release profile compared to pure drug and similar to that of marketed formulation respectively.     

Synthesis of N-(2-chloroethyl)isatins and their β-ethyleneacetals and β-thiosemicarbazones

The nitrogen atoms of isatin, its 5-bromoderivative, and their -ethyleneacetals are alkylated by 1,2-dichloroethane in K₂CO₃–DMF and LiH(NaH)-DMF.Institute of Biological Protection of Plants and Institute of Chemistry of the Moldovan Academy of Sciences, Kishinev 2058. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 907–909, July, 1999.     

Stereochemistry in alkylations of dianions of β-hydroxysulfoxides and β-hydroxysulfones

Alkylations of dianions of β-hydroxysulfoxides and β-hydroxysulfones have been found to be affected by chelation of a Li cation with a sulfinyl group and by coordination of the cation with tetrahydrofuran rather than a sulfonyl group, respectively.     

Tetranuclear copper complexes with new β-diketone and β-iminoketone-containing ligands

Novel tetranuclear copper complexes, Cu4(OH)2(ClO4)3 (HA)·H2O (1) and Cu4(ClO4)5(H3B)·3H2O (2), were synthesized by reacting 1,5-bis(1-phenyl-3-methyl-5-pyrazolone-4)-1 ,5-pentanedione with 1,3-propanediamine and 2-hydroxyl-1,3-propanediamine in the presence of a template reagent copper ion. New [2+2] type open cyclic multidentate ligands are also obtained from the reaction (H4A and H6B stand for new compounds from 1,3-propanediamine and 2-hydroxyl-1,3-propanediamine, respectively). They each contain five C = O, three C = N and one NH2 groups. The complexes were characterized by elemental analyses, conductivity, FT-i.r. (micro-i.r., deconvolution technique), FAB-MS, e.s.r., electronic spectra and extended X-ray absorption fine structure (EXAFS). Copper ions in (1) are basically four coordinate with tetragonal geometry. The average coordination bond distances of Cu–N and Cu–O are 1.91 Å and 2.05 Å. In (2), copper ions are primarily five coordinate with square-based pyramidal geometry. The average coordination bond distances of Cu–N and Cu–O are 1.93Å and 2.08Å. Four copper atoms in molecules may be arranged tetragonally. Both the ligand field and the coordination bonds in complex (1) are stronger than those in (2). Investigations on variable temperature susceptibilities show that some antiferromagnetic exchange interaction exist in the complexes. The plots of –1 versus T obey the Curie-Weiss law only at low temperature. Preliminary results of a bioassay indicate that the two complexes have some antitumour activity in vitro.     

ZnSO4·CO(NH2)2·2H2O和MgCl2·NH4Cl·6H2O的热分解动力学研究

采用TG-DSC研究了ZnSO4·CO(NH2)2·2H2O和MgCl2·NH4Cl·6H2O的热分解反应,并对其中的脱水过程及部分分解过程进行了动力学计算,由Fridman、Ozawa-Flynn-Wall、ASTME698三种方法得出峰温时的活化能值与指前因子值,通过优化选择出了热分解过程最佳机理函数.     

Comparison of the reactivity of β-thiolactones and β-lactones toward ring-opening by thiols and amines

An investigation into the comparative reactivity of simple β-lactones and β-thiolactones toward a thiol and a primary amine is reported. A simple 3-mercaptomethyl-2-oxetanone is found to undergo rearrangement in the presence of aqueous base to give the corresponding thietane-3-carboxylic acid rather than the 3-hydroxymethyl-2-thietanone. Implications for the use of β-thiolactones in bioorganic and medicinal chemistry are discussed.     

On the Cl···N halogen bond: a rotational study of CF3Cl···NH3

The rotational spectra of six isotopologues (CF(3)(35)Cl···(14)NH(3), CF(3)(37)Cl···(14)NH(3), CF(3)(35)Cl···(15)NH(3), CF(3)(37)Cl···(15)NH(3), CF(3)(35)Cl···(14)ND(3) and CF(3)(37)Cl···(14)ND(3)) of the CF(3)Cl···NH(3) adduct have been investigated and analyzed by pulsed jet Fourier transform microwave spectroscopy. Rotational, centrifugal distortion and quadrupole ((35)Cl, (37)Cl, (14)N) coupling constants have been precisely obtained. The two subunits of the complex are held together via a Cl···N halogen bond interaction. Information on the internal dynamics and on the dissociation energy of the complex is provided.     

SH···N and SH···P blue-shifting H-bonds and N···P interactions in complexes pairing HSN with amines and phosphines

Quantum calculations at the MP2/aug-cc-pVDZ level examine complexes pairing HSN with aliphatic amines and phosphines. Complexes are cyclic and contain two attractive interactions. The first is a SH···N/P H-bond in which the S-H covalent bond contracts and shifts its stretching frequency to the blue, more so for amines than for phosphines. The second interaction is different for the amines and phosphines. The amines engage in a NH···N H-bond comparable in strength to the aforementioned SH···N interaction. In contrast, the second interaction in the phosphine complexes is a direct N···P attraction without an intervening H. This interaction is due in part to opposite partial charges on the N and P atoms, as well as covalent forces generated by charge transfer effects.     

Synthesis and characterization of di- and trivalent pyrazolylborate β-diketonates and cyanometalates

The syntheses, structures, and magnetic properties of a series of di- and trivalent hydridotris(3,5-dimethylpyrazol-1-yl)borate (Tp*) cyanomanganates are described. Treatment of tris(acetylacetonate)manganese(III) [Mn(acac)(3)] with KTp* and tetra(ethyl)ammonium cyanide affords [NEt(4)][(Tp*)Mn(II)(κ(2)-acac)(CN)] (1), as the first monocyanomanganate(II) complex; attempted oxidation of 1 with iodine affords {(Tp*)Mn(II)(κ(2)-acac(3-CN))}(n) (2) as a one-dimensional chain and bimetallic {[NEt(4)][(Tp*)Mn(II)(κ(2)-acac(3-CN))](2)(μ-CN) (3) as the major and minor products, respectively. A fourth complex, [NEt(4)][(Tp*)Mn(II)(η(2)-acac(3-CN))(η(1)-NC-acac)] (4), is obtained via treatment of Mn(acac(3-CN))(3) with KTp* and [NEt(4)]CN, while [NEt(4)](2)[Mn(II)(CN)(4)] (5) was prepared from manganese(II) trifluoromethanesulfonate and excess [NEt(4)]CN. Tricyanomanganate(III) complexes, [cat][(Tp*)Mn(III)(CN)(3)] [cat = NEt(4)(+), 7; PPN(+), 8], are prepared via sequential treatment of Mn(acac(3-CN))(3) with KTp*, followed by [NEt(4)]CN, or [cat](3)[Mn(III)(CN)(6)] with (Tp*)SnBu(2)Cl. Magnetic measurements indicate that 1, 2, and 4 contain isotropic Mn(II) (S = (5)/(2); g = 2.00) centers, and no long-range magnetic ordering is found above 1.8 K. Compounds 7 and 8 contain S = 1 Mn(III) centers that adopt singly degenerate spin ground states without orbital contributions to their magnetic moments.