Weak NH Research Articles

Electronic structure, vibrational spectral and intervening orbital interactions studies of NLO material: Guanidinium 4-nitrobenzoate

Single crystals of guanidinium 4-nitrobenzoate (GPNB) have been grown by slow evaporation method. Grown crystals were characterized by FT-IR, FT-Raman, UV–Vis absorption and UV–Vis transmission spectroscopies. Crystal defects and surface morphology were studied by etching method. Dielectric properties of the crystal such as dielectric constant, dielectric loss and AC electrical conductivity as function of frequency (50Hz–5MHz) at two temperatures (35°C and 100°C) were measured. The frequency and temperature dependence of dielectric behaviour were investigated. The equilibrium geometry, vibrational spectral analysis, intramolecular charge transfer interactions using NBO method, first order hyperpolarizability, molecular electrostatic potential and frontier molecular orbital analysis for GPNB have been studied using density functional theory at B3LYP/cc-pVTZ level. Vibrational spectral study reveals the presence of moderate and weak NH⋯O bonds in GPNB. NBO analysis also confirms the presence of intramolecular NH⋯O hydrogen bonding and investigates the stability as well as the intervening orbital interactions. The electronic absorption spectrum of the gas and water phases of GPNB were simulated using time dependent density functional theory and NBO transitions for the three lowest excited states were assigned and studied.

Combination of X-ray crystallography and theoretical study to evaluate the effect of N[sbnd]H⋯O[dbnd]P versus N[sbnd]H⋯O[dbnd]C hydrogen bonds on the N[sbnd]H stretching frequencies

Two new CCl3C(O)NHP(O)X compounds [X=NH(CH2)3NH (1) and NHCH2C(CH3)2CH2NH (2)] were synthesized and characterized by spectroscopic methods and X-ray crystallography. In each of 1 and 2, the phosphoryl and carbonyl groups are gauche relative to one another and the P atom is in a tetrahedral environment. The 1,3-diazaphosphorinane moiety adopts conformation between chair and envelope with the PO in an equatorial position. In the structure 1, the asymmetric unit contains one molecule; whereas, the asymmetric unit of 2 is composed of two independent molecules. In the crystal packing of 1 and 2, the NH⋯O hydrogen bonds lead to two-dimensional arrangements along (−101) plane for 1 and (010) plane for 2. In order to precise assignments of different NH units stretching frequencies in compounds 1 and 2, quantum chemical calculations were performed, with B3LYP method using 6-311++G(d,p) basis set. Theoretical procedure was performed for the individual molecule (monomer) and also for the hydrogen-bonded clusters of the molecules. In the H-bonded molecules, the effect of hydrogen bonds formation and their strengths in different NH⋯OP and NH⋯OC units were considered to close the theoretical frequencies of absorption bands to the real values. It is found that the stronger NH⋯OP hydrogen bond creates more changes in the NH stretching frequency than the weaker NH⋯OC hydrogen bond makes. The natural bond orbital analysis showed a positive character for H atom and a negative character for N and O atoms. The hydrogen bond formation was studied by the AIM method through the Laplacian analysis.

In Vitro and In Vivo Evaluation of a Sulfenamide Prodrug of Basic Metformin

In the present study, a previously described sulfenamide prodrug of a basic antidiabetic drug, metformin, was evaluated further. This sulfenamide prodrug was designed to improve the permeability and consequently the oral absorption and bioavailability (F) of the highly water-soluble metformin. Bioactivation of the prodrug was mediated by reduced glutathione, but it has been reported that sulfenamide prodrugs can also be bioactivated by other endogenous thiols like cysteine, and free thiol-containing proteins. Consistent with earlier findings for a sulfenamide prodrug of a weakly acid drug, linezolid, the permeability studies indicated that the metformin prodrug was also prematurely bioactivated on the apical surface of the Caco-2 cell monolayer. Nevertheless, the bioavailability of metformin was increased by approximately 25% after oral administration of the prodrug in rats, most probably because of better oral absorption. This indicates that the sulfenamide prodrug approach may be used to improve the moderate oral bioavailability of metformin, which may help to decrease the uncomfortable gastrointestinal adverse effects associated with metformin therapy as the daily doses of metformin can be reduced. Furthermore, the present study confirms that the applicability of the sulfenamide prodrug approach can be successfully extended from weak NH acids to very basic guanide-type drugs.

Variation in supramolecular arrangements of hydrazones, o-H2NC6H4CMe[dbnd]NNHC6H4X (X[dbnd]H, o-, m- and p-NO2), derived from o-aminoacetophenone and phenylhydrazines

The crystal structures of four hydrazones, 1, derived from phenylhydrazines, XC6H4NHNH2 (XH, o-NO2, m-NO2 or p-NO2) with 2-aminoacetophenone are reported, as is the mono hydrochloride, (2: Xm-NO2), of (1: Xm-NO2). Consistent strong intramolecular hydrogen bonds in 1 are of the type, NH(amino)⋯N(hydrazono), while (1: Xm-NO2) portrays an additional NH(hydrazono)⋯O(nitro), intramolecular hydrogen bond. Of interest, different sets of strong intermolecular interactions are found even among the nitro derivatives, 1. In (1: Xo-NO2), the strongest intermolecular interactions are NH(amino)⋯O(nitro) hydrogen bonds, while in (1: Xm-NO2 and p-NO2), both NH(hydrazono)⋯O(nitro) and NH(amino)⋯N(amino) are present. These strong intermolecular hydrogen bonds coupled with different combinations of some of CH⋯O, ππ stacking interactions and NO⋯π generate different supramolecular arrays for (1: X=nitro): 2-D, 2-D and 3-D, respectively for (1: Xo-NO2), for (1: Xm-NO2) and (1: Xp-NO2). In (1: XH), the major intermolecular interactions are NH(hydrazono)⋯N(amino hydrogen bonds: these, supplemented by weaker NH⋯π and CH⋯π interactions, generate a two-dimensional array.While significant changes in the intermolecular interactions result on formation of the salt, (2: Xm-NO2) from (1: Xm-NO2), the strong NH(amino)⋯N(hydrazono) intramolecular hydrogen bonds persist. Strong intermolecular hydrogen bonds found in (2: Xm-NO2) are of the types NH⋯Cl (both hydrazone and amine), NH(amino)⋯O(nitro): these coupled with weaker CH⋯O, NO⋯π, and ππ generate a three dimensional array.

Crystal and Vibrational Analysis of a Novel Alcohol Derivate from Chlorthalidone: Ethyl-Chlorthalidone

The crystal structure of the novel alcohol deri- vate from chlorthalidone, ethyl-chlorthalidone (2-chloro-5- (1-ethyl-3-oxo-1-isoindolinyl)benzenesulfonamide hydrated), C16H15ClN2O4S.H2O, was determined by X-ray diffraction at 295 K. This molecule crystallized in an orthorhombic space group Pca21 with a = 7.928(2) A ˚ ,b = 10.920(2) A ˚ , c = 19.459(4) A ˚ , a = b = c = 90. This compound is stabilized by intra and intermolecular NHO and OHO hydrogen bonds. These interactions which involve water molecules of the network give rise to a two-dimensional (2-D) array parallel to the (110) direction. The three- dimensional design of the compound is observed through weak NH��� O hydrogen bonds (N2-H2A��� O4). The NMR study was a complementary tool for crystal characterization. The spectra analysis clearly shows that signs of ethyl group atoms appear in strong field whereas the others atoms were identified in weak magnetic field (above of 140 ppm). The vibrational spectra present bands in the region of 2890-2940 cm -1 which can be assigned as symmetric and asymmetric modes of CH2 and CH3 groups. These results are in agreement with the crystal data which indicate the pres- ence of ethyl group in this molecule.

Influence of drought and total phosphorus on diel pH in wadeable streams: Implications for ecological risk assessment of ionizable contaminants

Climatological influences on site-specific ecohydrology are particularly germane in semiarid regions where instream flows are strongly influenced by effluent discharges. Because many traditional and emerging aquatic contaminants, such as pharmaceuticals, are ionizable, we examined diel surface water pH patterns (i.e., change in pH over a 24-h period) at 23 wadeable streams in central Texas, USA, representing a gradient of nutrient enrichment during consecutive summers of 2006 and 2007. The years of our study were characterized by decidedly different instream flows, which likely affected production:respiration dynamics and led to distinctions in diel pH patterns between 2006 and 2007. Site-specific ambient water quality criteria for NH(3) and the aquatic toxicity of the model weak base pharmaceutical sertraline were predicted using continuous water quality monitoring data from the sites. Drought conditions of 2006 significantly increased (p<0.05) diel pH changes compared to high instream flows of 2007,and the magnitude of diel pH variability was most pronounced at nutrient-enriched sites in 2006. Differences in diel pH change patterns between 2006 and 2007 affected predictions of the environmental fate and effects for model weak base pharmaceuticals and NH(3). Overall, site-specific diel pH was more variable at some sites than the difference in mean surface water pH between the 2 summers. Diel pH variability affected regulatory criteria, because 20% of the study sites in 2006 experienced greater than 5-fold differences in National Ambient Water Quality Criteria for NH(3) over 24-h periods. Our study emphasizes the potential uncertainty that diel pH variability may introduce in site-specific assessments and provides recommendations for environmental assessment of ionizable contaminants.

IR and NMR spectra, intramolecular hydrogen bonding and conformations of para-tert-butyl-aminothiacalix[4]arene in solid state and chloroform solution

It is demonstrated that dissolution of aminothiacalix[4]arene in chloroform results in transformation of 1,3-alternate conformation, adopted in single-crystal and bulk polycrystalline solids, to the pinched-cone form. This conformer is stabilised by the intramolecular hydrogen bonds of two distal amino-groups acting as H-donors with another two amino moieties that appear as H-acceptors. The H-bonds cause quite small (ca. 10–20 cm −1) red shift of the IR bands of the NH 2 stretching vibrations, which suggests rather weak NH⋯N hydrogen bonding. This latter is sufficient to stabilize the pinched-cone conformation in the chloroform solution, but the energy gap between the pinched-cone and other conformations is small, and solid-state intermolecular forces easily overcome it, leading to realisation of the 1,3-alternate conformer. The comparison of the DFT computed and experimental vibrational and NMR spectra demonstrates good quality of present quantum-chemical computations, allows complete interpretation of the spectra and reveals simple IR and NMR spectroscopic markers of the conformers of aminothiacalix[4]arenes.

Conformers of gaseous threonine†

Following an extensive search on the potential energy surfaces (PES) of the natural amino acid L-threonine (Thr) and its allotropic form L-allo-threonine (aThr), 56 and 61 conformers of Thr and aThr, respectively, have been located with the help of density functional theory (DFT). Accurate structures, relative energies, rotational as well as quartic and sextic centrifugal distortion constants, dipole moments, 14N nuclear quadrupole coupling constants, anharmonic vibrational frequencies and double-harmonic infrared intensities have been determined from ab initio electronic structure calculations for the five most stable Thr and aThr conformers. The global minimum, Thr-I, has a cyclic triple H-bond motif with strong OH ··· N, C=O ··· HO, and a weaker NH ··· OH H-bond, where the latter two involves the side chain OH, and an energetically unfavourable trans-COOH arrangement. The best relative energies of the conformers, accurate within ±1 kJ mol−1, have been determined through the first-principles composite focal-point analysis (FPA) approach. There are four and three conformers of Thr and aThr, respectively, within a relative energy of 5 kJ mol−1. Similarly to other amino acids investigated, lower levels of electronic structure theory, especially the Hartree–Fock level, are unable to determine the correct relative energies of the conformers. The rotational, the quartic and sextic centrifugal distortion, and the 14N nuclear quadrupole coupling constants as well as the anharmonic vibrational fundamentals and double-harmonic infrared intensities, all determined using DFT, should aid identification and characterization of the conformers of threonine and allo-threonine by rotational and vibrational spectroscopies, respectively. †This paper is dedicated to Professor Fritz Schaefer on the occasion of his 65th birthday.

Conformational study of 2-phenylethylamine by molecular-beam Fourier transform microwave spectroscopy

The conformational preferences of the simplest amine neurotransmitter 2-phenylethylamine have been investigated using molecular beam Fourier transform microwave (MB-FTMW) spectroscopy. Two new conformers have been observed together with the two previously reported by Godfrey et al. [J. Am. Chem. Soc., 1995, 117, 8204]. The (14)N nuclear quadrupole hyperfine structure has been resolved for all four conformers. Comparison of the experimental rotational and quadrupole coupling constants with those calculated theoretically provides a conclusive test for the identification of all conformers. The two most stable conformers present a gauche (folded) disposition of the alkyl-amine chain and are stabilised by a weak NH...pi interaction between the amino group and the aromatic ring. The other two conformers show an anti (extended) arrangement of the alkyl-amine chain. Tunnelling splittings have been observed in the spectrum of one of the anti conformers. The post expansion relative abundances in the supersonic jet have been also investigated and related to the conformer energies.

Mechanism of the Conformational Transitions in 6-Hydroxymethyl-7,8-dihydropterin Pyrophosphokinase as Revealed by NMR Spectroscopy,

6-Hydroxymethyl-7,8-dihydropterin pyrophosphokinase (HPPK) catalyzes the transfer of pyrophosphate from ATP to 6-hydroxymethyl-7,8-dihydropterin (HP), leading to the biosynthesis of folate cofactors. HPPK undergoes dramatic conformational changes during its catalytic cycle, and the conformational changes are essential for enzymatic catalysis. Thus, the enzyme is not only an attractive target for developing antimicrobial agents but also an excellent model system for studying the catalytic mechanism of enzymatic pyrophosphoryl transfer as well as the role of protein dynamics in enzymatic catalysis. In the present study, we report the NMR solution structures of the binary complex HPPK*MgAMPCPP and the ternary complex HPPK*MgAMPCPP*DMHP, where alpha,beta-methyleneadenosine triphosphate (AMPCPP) and 7, 7-dimethyl-6-hydroxypterin (DMHP) are the analogues of the substrates ATP and HP, respectively. The results suggest that the three catalytic loops of the binary complex of HPPK can assume multiple conformations in slow exchanges as evidenced by multiple sets of NMR signals for several residues in loops 2 and 3 and the very weak or missing NH cross-peaks for several residues in loops 1 and 3. However, the ternary complex shows only one set of NMR signals, and the cross-peak intensities are rather uniform, suggesting that the binding of the second substrate shifts the multiple conformations of the binary complex to an apparently single conformation of the ternary complex. The NMR behaviors and conformations of the binary complex HPPK*MgAMPCPP are significantly different from those of HPPK in complex with Mgbeta,gamma-methyleneadenosine triphosphate (MgAMPPCP). It is suggested that the conformational properties of the binary substrate complex HPPK*MgATP be represented by those of HPPK*MgAMPCPP, because MgAMPCPP is a better MgATP analogue for HPPK with respect to both binding affinity and bound conformation.

Characterization of Weak NH−π Intermolecular Interactions of Ammonia with Various Substituted π-Systems

Among the several weak intermolecular interactions pervading chemistry and biology, the NH-pi interaction is one of the most widely known. Nevertheless its weak nature makes it one of the most poorly understood and characterized interactions. The present study details the results obtained on gas-phase complexes of ammonia with various substituted pi systems using both laser vibrational spectroscopy and ab initio calculations. The spectroscopic measurements carried out by applying one-color resonant two-photon ionization (R2PI) and IR-vibrational predissociation spectroscopy in the region of the NH stretches yield the first experimental NH stretching shifts of ammonia upon its interaction with various kinds of pi-systems. The experiments were complemented by ab initio calculations and energy decompositions, carried out at the second-order Møller-Plesset (MP2) level of theory. The observed complexes show characteristic vibrational spectra which are very similar to the calculated ones, thereby allowing an in-depth analysis of the interaction forces and energies. The interaction energy of the conformers responsible for the observed vibrational spectra has the maximum contribution from dispersion energies. This implies that polarizabilities of the pi-electron systems play a very important role in governing the nature and geometry of the NH-pi interaction. The larger polarizability of ammonia as compared to water and the tendency to maximize the dispersion energy implies that the characteristics of the NH-pi interactions are markedly different from that of the corresponding OH-pi interactions.

Ion transport versus gas conduction: function of AMT/Rh-type proteins

Although lipid membranes exhibit some permeability to the weak base NH 3, organisms have developed specialized proteins that increase and regulate the NH 3 fluxes across cellular membranes. In humans, the Rh glycoproteins, such as the erythrocyte-specific RhAG and the liver and kidney homologs RhBG and RhCG, are involved in the passage of NH 3. Rh glycoproteins have distant relatives, called ammonium transporters (AMTs), in archae and bacteria. The crystal structures of AMTs show that the proteins are homo-trimers and that the center of each monomer forms a pore. AMT/Rh proteins have also been identified in plants. In contrast to the human Rh glycoproteins, these AMTs specifically transport NH 4 + or co-transport NH 3/H +. Hence, they can transport against NH 3 gradients. The molecular determinants for the different transport mechanisms within proteins of the same family are currently unclear. The functional differences between AMT/Rh transporters are likely to be an evolutionary adaptation to different ammonium and nitrogen requirements in bacteria, plants and animals.

The weak bases NH3 and trimethylamine inhibit the medium and slow afterhyperpolarizations in rat CA1 pyramidal neurons

The weak bases NH(3) and trimethylamine (TMeA), applied externally, are widely used to investigate the effects of increasing intracellular pH (pH(i)) on neuronal function. However, potential effects of the compounds independent from increases in pH(i) are not usually considered. In whole-cell patch-clamp recordings from rat CA1 pyramidal neurons, bath application of 1-40 mM NH(4)Cl or TMeA HCl reduced resting membrane potential and input resistance, inhibited the medium and slow afterhyperpolarizations (AHPs) and their respective underlying currents, mI(ahp) and sI(ahp), and led to the development of depolarizing current-evoked burst firing. Examined in the presence of 1 microM TTX and 5 mM TEA with 10 mM Hepes in the recording pipette, NH(3) and TMeA increased pH(i) and the magnitudes of depolarization-evoked intracellular [Ca(2+)] transients, Ca(2+)-dependent depolarizing potentials, and inward Ca(2+) currents but reduced the slow AHP and sI(ahp). When internal H(+) buffering power was raised by including 100 mM tricine in the patch pipette, the effects of NH(3) and TMeA to increase pH(i) and augment Ca(2+) influx were attenuated whereas the reductions in the slow AHP and sI(ahp) (as well as membrane potential and input resistance) were maintained. The findings indicate that increases in pH(i) contribute to the increases in Ca(2+) influx observed in the presence of NH(3) and TMeA but not to the reductions in membrane potential, input resistance or the magnitudes of AHPs. The results have implications for the interpretation of data from experiments in which pH(i) is manipulated by the external application of NH(3) or TMeA.

Relation between Intramolecular NH···S Hydrogen Bonds and Coordination Number in Mercury(II) Complexes with Carbamoylbenzenethiol Derivatives

A novel series of bis(carbamoylthiophenolato)mercury(II) complexes, [Hg(S-RNHCOC6H4)2] (1, R = 2-t-Bu; 2, R = 2-CH3; 3, R = 2-C6H5CH2; 4, R = 4-t-Bu), and a tetrakis(carbamoylthiophenolato)mercury(II) complex, (NEt4)2[Hg-(S-2-CH3NHCOC6H4)4] (5), were synthesized and characterized by 1H NMR, IR, 199Hg NMR, and crystallographic analyses. The bis(carbamoylthiophenolato)mercury complexes 1-3 do not have intramolecular NH...S hydrogen bonds between the amide NH group and the sulfur atom coordinated to mercury, whereas the tetrakis(thiophenolato)mercury complex 5 does have an intramolecular NH...S hydrogen bond. A relatively weak NH...S hydrogen bond in 5 can be seen in the 1H NMR spectra and the IR spectra in chloroform and in the solid state. The 199Hg NMR spectra in bis(carbamoylthiophenolato)mercury complexes 1-4 show a downfield shift, with an increase in the flow of electrons to mercury(II) from the oxygen atom due to the intramolecular Hg...O bonding interaction. Conversely, the 199Hg NMR spectra in 5 show a high-field shift with a decrease in the flow of electrons to mercury(II) from the sulfur atom due to the intramolecular NH...S hydrogen bond.

Effects of the Intramolecular NH···S Hydrogen Bond in Mononuclear Platinum(II) and Palladium(II) Complexes with 2,2‘-Bipyridine and Benzenethiol Derivatives

A series of complexes, [M(bpy)(SAr)2] (M = platinum(II) or palladium(II), bpy = 2,2'-bipyridine, SAr = 2- or 4-(acylamino)benzenethiolate, or 2-(alkylcarbamoyl)benzenethiolate), were synthesized and characterized on the basis of 1H NMR, IR, and electrochemical properties. The structures of [Pt(bpy)(S-2-Ph3CCONHC6H4)2] (1) and [Pt(bpy)(S-2-t-BuNHCOC6H4)2] (3) were determined by X-ray analysis. The complexes have intramolecular NH...S hydrogen bonds between the amide NH group and the sulfur atom. A weak NH...S hydrogen bond in these complexes and [Pd(bpy)(S-2-Ph3CCONHC6H4)2] (4) is detected from the 1H NMR spectra and the IR spectra in chloroform and in the solid state. [Pt(bpy)(S-2-Ph3CCONHC6H4)2] (1) exhibits a remarkably high-energy-shifted lowest-energy band in UV-visible spectra and has a positively shifted oxidation potential. The blue-shift of 42 nm and the positive shift of +0.24 V, as compared to those of [Pt(bpy)(SC6H5)2), are due to the effect of the NH...S hydrogen bond.

Weak intramolecular interactions in perchlorate salts of Λ-β 1-[Co( R, R-picchxn)( R-aa)] 2+ [picchxn= N, N′-di(2-picolyl)-1,2-diaminocyclohexane; aa=phenylalaninato(1−), tyrosinato(1−)] and their diastereoisomeric equilibration in solution

Single-crystal X-ray structures and high-resolution solution NMR studies of Λ-β 1-[Co( R, R-picchxn)( R-phe)](ClO 4) 2 · H 2O and Λ-β 1-[Co( R, R-picchxn)( R-tyr)](ClO 4) 2 · 2H 2O (pheH=phenylalanine, tyrH=tyrosine) are reported. In the former, the aromatic side group of the phenylalanine ligand is extended, as is found in related halide salts. In the tyrosine analogue, the aromatic ring adopts a conformation such that a weak intramolecular NH–π interaction with a NH group of the tetradentate ligand is stabilized. The interaction is rather weak and is not particularly favoured in solution, as revealed by 1H NMR. The β 1 complex of phenylalanine is not the thermodynamically stable diastereoisomer. Equilibration experiments give a mixture of Λ-β 1, Λ-β 2 and Δ-α diastereoisomers in D 2O solution, the α diastereoisomer being more stable than either of the β complexes by about 1 kJ mol −1 at 298.2 K. Intramolecular π–π and NH–π interactions are responsible for the stabilization of the α complex, demonstrating the significance of the cooperative effects of such interactions. The ternary cobalt complexes described in this study could act as simple model systems for investigating the discriminatory effects of analogous weak interactions that occur in a complex biological setting.

Hydration of neurotransmitters: a computational and spectroscopic study of a noradrenaline analogue, 2-amino-1-phenyl-ethanol

Singly and multiply hydrated clusters of the noradrenaline analogue, 2-amino-I-phenyl-ethanol (APE) have been studied using a combination of resonant two-photon ionization time of flight spectroscopy (R2PI-TOF), infrared ion-dip spectroscopy and ab initio quantum chemical calculation. Singly hydrated clusters populate two distinct structures: the water molecule either hydrogen-bonds to the ethanol group in the extended AG conformer (leaving the intramolecular OH → N hydrogen bond intact) or inserts into the intramolecular hydrogen bond in the (distorted) ethanolamine side chain (promoting a weak NH → O bond). The observed doubly and triply hydrated clusters both display insertion structures only, with the water molecules arrayed as linear chains, hydrogen bonded to the functional groups of the side-chain and again promoting a weak NH → O bond along the distorted ethanolamine side-chain. The infrared spectrum of the 1:4 cluster of APE, which is very similar to that of the corresponding cluster of ephedrine, includes new features in the ‘window region’ (3500–3700 cm−1), indicating the onset of a three-dimensional assembly. Comparisons with ab initio computed spectra favour a structure that incorporates a cyclic water tetramer linked to the two functional groups on the ethanolamine side-chain.

Structural, thermal and spectral studies of N-2-pyridyl-, N-2-picolyl- and N-2-(4,6-lutidyl)- N′-(3-methoxyphenyl)thioureas

N-2-pyridyl- N′-3-methoxyphenylthiourea, PyTu3OMe, triclinic, P-l, a=8.6590(16), b=8.7489(16), c=10.0540(15) A ̊ , α=90.255(9), β=66.765(8), γ=68.547(7)°, V=641.40(19) A ̊ 3 and Z=2; N-2-(3-picolyl)- N′-3-methoxyphenylthiourea, 3PicTu3OMe, triclinic, P-1, a=6.9100(9), b=12.7370(16), c=16.4710(14) A ̊ , α=107.782(6), β=91.656(7), γ=95.115(4)°, V=1372.5(3) A ̊ 3 and Z=4; N-2-(4-picolyl)- N′-3-methoxphenylthiourea, 4PicTu3OMe, monoclinic, C2/ c, a=12.5036(7), b=8.5942(5), c=25.4050(10) A ̊ , β=97.712(3)°, V=2705.3(2) A ̊ 3 and Z=8; N-2-(5-picolyl)- N′-3-methoxyphenylthiourea, 5PicTu3OMe, monoclinic, P2 1/ c, a=10.9200(4), b=15.3920(15), c=8.1150(11) A ̊ , β=92.020(5)°, V=1363.1(2) A ̊ 3 and Z=4; N-2-(6-picolyl)- N′-3-methoxyphenylthiourea, 6PicTu4OMe, triclinic, P-1, a=7.4220(16), b=9.944(3), c=10.038(3) A ̊ , α=104.815(9), β=94.452(16), γ=108.134(14)°, V=670.6(3) A ̊ 3 and Z=2 and N-2-(4,6-lutidyl)- N′-3-methoxyphenylthiourea, 4,6LutTu3OMe, orthorhombic, Pbca, a=16.3710(5), b=7.4910(6), c=24.1890(15) A ̊ , V=2966.4(3), Z=8. Intramolecular hydrogen bonding between N′H and the pyridine nitrogen and intermolecular hydrogen bonding between NH and the thione sulfur are characteristic of these thioureas except that 3PicTu3OMe has a very weak intermolecular NH⋯S interaction due to a steric effect of the methyl group.

A combined matrix-isolation infrared spectroscopy and MO study of 1-amino-2-propanol

Vibrational spectra of 1-amino-2-propanol (1AP) isolated in argon and krypton matrices at 14K and of the pure liquid at room temperature were recorded and interpreted on the basis of ab initio MO calculations undertaken at the HF-SCF and MP2 levels of theory. For the first time, five different conformational states of monomeric 1AP could be experimentally observed and their vibrational signatures obtained. The observed conformers were found to correlate well with the most stable forms predicted by the MP2 calculations, the first and second lowest energy forms corresponding to conformers which exhibit a considerably strong intramolecular OH⋯N hydrogen bond (gG′g and g′Gg′), while the less abundant forms observed in the matrices (tG′t, g′G′t and tG′g′) are characterized by having a relatively weak intramolecular NH⋯O bond. These results were reinforced by infrared solution studies of the compound in tetrachloroethylene. The experimental data obtained for the pure liquid, where OH⋯N intermolecular hydrogen bonding dominates, indicate that the preferred conformation of the monomeric unit within the aggregates is similar to conformer tG′t.

Dinuclear calcium complex with weakly NH...O hydrogen-bonded sulfonate ligands.

The novel intramolecularly NH...O hydrogen-bonded Ca(II)-aryl sulfonate complex, [Ca2(SO3-2-t-BuCONHC6H4)2(H2O)4]n(2-t-BuCONHC6H4SO3)2n (1), sulfonate anion, (HNEt3)(SO3-2-t-BuCONHC6H4) (2a), (PPh4)(SO3-2-t-BuCONHC6H4) (2b), (n-Bu4N)(SO3-2-t-BuCONHC6H4) (2c), and sulfonic acid, 2-t-BuCONHC6H4SO3H (3), were synthesized. The structures of 1, 2a, and 2b depict the presence of the formation of NH...O hydrogen bonds between the amide NH and S-O oxygen for a series of compounds as determined by IR and 1H NMR analyses both in the solid state and in the solution state. Thus, the NH...O hydrogen bonds with neutral amide groups are available for investigation of the electronic state of the O- anion. The combined data from the IR and 1H NMR spectra indicate that the sulfonic acid, sulfonate anion, and Ca(II) complex have a substantially weak intramolecular NH...O hydrogen bond between the SO3 oxygen and amide NH. In the detailed comparison with the intense NH...O hydrogen bonds for the carboxylate, weak NH...O hydrogen bonds for sulfonate is due to the strong conjugation of the SO3- group with the lower nucleophilicity.