Strong Hydrogen Bond Donor Research Articles

Anion-Templated Supramolecular C3 Assembly for Efficient Inclusion of Charge-Dispersed Anions into Hydrogen-Bonded Networks

The binding properties and conformational adaptability of a known nitrate/sulfate receptor N,N'-3-azapentane-1,5-bis[3-(1-aminoethylidene)-6-methyl-3H-pyran-2,4-dione] (L) toward various charge-dispersed monoanions (HSO(3)(-), ClO(4)(-), IO(4)(-), PF(6)(-), and SbF(6)(-)) are considered. These anions template the folding of three HL(+) species through a self-assembly process into a new hollow supramolecular trication. During the self-assembly, all strong hydrogen-bond donors of the podand become coordinatively saturated by interactions with the oxo functionalities from other HL(+) molecules. In that way, only the weak hydrogen-bond-donating groups in the exterior part of the receptor are accessible for anion binding. The investigated anions are accommodated in the hydrophobic pockets of the isomorphous hydrogen-bonded frameworks, which serve as a basis for selective crystallization from the highly competitive anion/solvent systems. This behavior is discussed in terms of size and geometry of the anions as well as the receptor's coordination capabilities to provide the most favorable surroundings for guest inclusion both in solution and in the solid state.

Self-Assembly of Pt(II) Spherical Complexes via Temporary Labilization of the Metal–Ligand Association in 2,2,2-Trifluoroethanol

Thermodynamically controlled platinum(II) spherical complexes were synthesized via temporary labilization of inert Pt(II)-pyridine bonds by the addition of the strong hydrogen-bond donor 2,2,2-trifluoroethanol (TFE), which weakens the pyridine-metal interaction. The platinum complex was stably trapped after removal of TFE and showed higher acid durability than its palladium counterpart.

Photoinduced Rearrangement of Aromatic N-Chloroamides to Chloroaromatic Amides in the Solid State: Inverted ΠN–ΣN Occupational Stability of Amidyl Radicals

We report a solid-state photochemical rearrangement reaction by which aromatic N-chloroamides exposed to UV light or sunlight are rapidly and efficiently converted to chloroaromatic amides. The course, the intermediate (nascent chlorine vs dichlorine) and the outcome of the reaction depend on the excitation (exposure time, wavelength, and intensity) and on inherent structural factors (the directing role of the substituents and, as demonstrated by the different reactivity of two polymorphs of N-chlorobenzanilide, the supramolecular structure). The photolysis of the chloroamides provides facile photochemical access to arylamidyl radicals as intermediates, which in the absence of strong hydrogen bond donors are stabilized in the reactant crystals by C-H/N-Cl···π interactions, thus, providing insight into their structure and chemistry. Thorough theoretical modeling of the factors determinant to the stability and the nature of the spin-hosting orbital evidenced that although the trans-Π(||) state (Np spin) of the amidyls is normally preferred over the trans-Σ(⊥) configuration (Nsp(2) spin), stabilization by aromatic conjugation, steric and geometry factors, as well as by electronic effects from the substituents can decrease the Π-Σ gap in these intermediates significantly, resulting in similar and, in the case of the orthogonal amide-phenyl disposition, even reversed population of the unpaired electron in the two orbitals. Quantitative correlation established that the inverted occupational spin stability and the Π(N)-Σ(N) crossover are collectively facilitated by the conformation, valence angle, and disposition of the amide group relative to the aromatic system. The stabilization and detection of a trans-Σ(⊥) radical was experimentally accomplished by steric locking of the orthogonal trans-amide conformation with double ortho-tert-butyl substitution at the phenyl ring. The effects of the single para-phenyl substituents on the relative occupational stability of the arylamidyl radical states point out to non-Hammett behavior. By including cumulative electronic effects from multiple substitutions, four distinct families of the aromatic amidyl radicals were identified. The Π(∥) state is the most stable structure of the N-phenylacetamidyl radical and of most of the substituted arylamidyls, although the Σ(⊥) and Π(⊥) states can also be stabilized by introducing tert-butyl and nitro groups, respectively.

Self-Assembly, Crystal Structure and Analysis of Intermolecular Interactions of the Supramolecular Compound Based on Hexamolybdochromate(III), Sulfate and Piperazine

A new supramolecular compound based on Anderson-B hexamolybdochromate, (H2Pz)3[Cr(OH)6Mo6O18H](SO4)2·12H2O (1) (Pz = piperazine) was synthesized and characterized by elemental analysis, IR spectroscopy, and single-crystal X-ray diffraction (Mo Kα). The compound crystallizes in monoclinic system, P21/c space group with a = 13.5708(6) A, b = 17.3711(8) A, c = 22.2387(9) A, β = 110.631(2)°; V = 4906.3(4) A3, Z = 4, Dc = 2.290 g/cm3, F(000) = 3364.0; μ = 1.905, S = 1.033. The final R = 0.0398 and wR = 0.0971. The H2pz2+ ions and sulfate anions in 1 are arranged through hydrogen bonds into a hexagonal network in [202] plane and hexamolybdochromates anions (CrMo6) fill in the hexagonal vacancies. The networks stack in such a way that each anion links two sulfate ions from adjacent networks via hydrogen bonds with short (CrMo6)O···OSO3 distances of 2.637–2.697 A. A lot of hydrogen bonds are formed between water molecules, sulfate, H2pz2+ ions and CrMo6 anions, which are the dominating force constructing the supramolecular structure. Hirshfeld surface analysis of 1 gives us the details of intermolecular interactions in the crystals of 1 in a visual manner and shows that the CrMo6 anion acts as a stronger hydrogen bond donor than as an acceptor.

Urea/thiourea derivatives and Zn(II)-DPA complex as receptors for anionic recognition—A brief account

This review covers few examples of anion complexation chemistry, with a special focus on urea/thiourea-based receptors and Zn(II)-dipicolyl amine-based receptors. This article specially focuses on structural aspects of the receptors and the anions for obtaining the desire specificity along with an efficient receptor–anion interaction. Two types of receptors have been described in this brief account; first one being the strong hydrogen bond donor urea/thiourea derivatives, which binds the anionic analytes through hydrogen bonded interactions; while, the second type of receptors are coordination complexes, where the coordination of the anion to the metal centre. In both the cases the anion binding modulate the energy gap between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) and thereby the spectroscopic response. Appropriate choice of the signalling unit may allow probing the anion binding phenomena through visual detection. Efficient design of a receptor for anionic analyte involves delicate balance of various factors and influences.

The role of weak hydrogen bonds in chiral recognition

Chiral recognition has been studied in neutral or ionic weakly bound complexes isolated in the gas phase by combining laser spectroscopy and quantum chemical calculations. Neutral complexes of the two enantiomers of lactic ester derivatives with chiral chromophores have been formed in a supersonic expansion. Their structure has been elucidated by means of IR-UV double resonance spectroscopy in the 3 μm region. In both systems described here, the main interaction ensuring the cohesion of the complex is a strong hydrogen bond between the chromophore and methyl-lactate. However, an additional hydrogen bond of much weaker strength plays a discriminative role between the two enantiomers. For example, the 1:1 heterochiral complex between R-(+)-2-naphthyl-ethanol and S-(+) methyl-lactate is observed, in contrast with the 1:1 homochiral complex which lacks this additional hydrogen bond. On the other hand, the same kind of insertion structures is formed for the complex between S-(±)-cis-1-amino-indan-2-ol and the two enantiomers of methyl-lactate, but an additional addition complex is formed for R-methyl-lactate only. This selectivity rests on the formation of a weak CHπ interaction which is not possible for the other enantiomer. The protonated dimers of Cinchona alkaloids, namely quinine, quinidine, cinchonine and cinchonidine, have been isolated in an ion trap and studied by IRMPD spectroscopy in the region of the ν(OH) and ν(NH) stretch modes. The protonation site is located on the alkaloid nitrogen which acts as a strong hydrogen bond donor in all the dimers studied. While the nature of the intermolecular hydrogen bond is similar in the homochiral and heterochiral complexes, the heterochiral complex displays an additional weak CHO hydrogen bond located on its neutral part, which results in slightly different spectroscopic fingerprints in the ν(OH) stretch region. This first spectroscopic evidence of chiral recognition in protonated dimers opens the way to the study of the complexes of Cinchona alkaloids involved in enantioselective catalysis. These examples show how secondary hydrogen bonds controlled by stereochemical factors govern molecular recognition processes.

Chain stopper engineering for hydrogen bonded supramolecular polymers

Supramolecular polymers are linear chains of low molar mass monomers held together by reversible and directional non-covalent interactions, which can form gels or highly viscous solutions if the self-assembled chains are sufficiently long and rigid. The viscosity of these solutions can be controlled by adding monofunctional compounds, which interact with the chain extremities: chain stoppers. We have synthesized new substituted ureas and thioureas and tested them as chain stoppers for a bis-urea based supramolecular polymer. In particular, the bis-thiourea analogue of the bis-urea monomer is shown not to form a supramolecular polymer, but a good chain stopper, because it is a strong hydrogen bond donor and a weak acceptor. Moreover, all substituted ureas tested reduce the viscosity of the supramolecular polymer solutions, but the best chain stopper is obtained when two hydrogen bond acceptors are placed in the same relative position as for the monomer and when no hydrogen bond donor is present.

2-Chloro-N-[4-chloro-2-(2-chlorobenzoyl)phenyl]acetamide

In the title compound, C15H10Cl3NO2, an intra­molecular N—H⋯O hydrogen bond forms a six-membered ring and enforces an almost coplanar conformation for the acetamido group, the central benzene ring and the bridging carbonyl C—C(=O)—C group: the dihedral angles between the benzene ring and the acetamide and carbonyl C—C(=O)—C planes are 7.06 (11) and 7.17 (12)°, respectively. The dihedral angle between the two benzene rings is 67.43 (9)°. Because a strong hydrogen-bond donor is involved in the intra­molecular inter­action, the crystal packing is determined by weak C—H⋯O and C—H⋯Cl inter­actions.

Iminothiol/thiourea tautomeric equilibrium in thiourea lipids impacts DNA compaction by inducing a cationic nucleation for complex assembly

Our research on lipidic vectors for transfection led us to develop thiourea lipids able to interact with DNA. Hence, we developed a series of lipopolythioureas based on the strong hydrogen bond donor ability of thiourea. More recently we have reported a branched hydroxylated bis-thiourea derivative with interesting transfecting properties. The last step of the syntheses involved a strong acidic condition, leading to an unstable product upon storage. Therefore we designed a new synthesis in mild acidic conditions. Though they exhibit the same mass, the lipids obtained in the two different conditions differ by their interaction with DNA. We therefore explored the physicochemical properties of these two lipids by different means that we describe in this article. In order to insure easier and reliable 13C-NMR studies of the thiourea group we have designed the synthesis of the corresponding 13C-labeled thiourea lipids. We have thus shown that when the lipid was submitted to mildly acidic medium; only the thiourea group was observed; while a thiourea/charged and/or uncharged iminothiol tautomeric equilibrium formed when the last step of the synthesis was submitted to low pH. NMR experiments showed that this tautomeric equilibrium could not form in polar solvents. However, UV experiments on the liposomal form of the lipopolythiourea showed the presence of the tautomers. Lipid/DNA interaction consequently differed according to the acidic treatment applied. Eventually, these results revealed that on this particular thiourea lipid, electrostatic interactions due to cationic thioureas are likely to be responsible for DNA compaction and that this tautomeric form of the thiourea could be stabilised by hydrogen bonds in a supramolecular assembly. Nevertheless, this does not reflect a general thiourea lipid/DNA interaction as other thiourea lipids that are able to compact DNA do not undergo an acidic treatment during the final stage of their synthesis.

Hydrogen-bonding molecular ruler surfactants as probes of specific solvation at liquid/liquid interfaces

Resonance-enhanced, second harmonic generation (SHG) is used to measure the electronic structure of solutes sensitive to specific solvation adsorbed to liquid/liquid and liquid/solid interfaces. Here, specific solvation refers to solvent-solute interactions that are directional and localized. N-methyl-p-methoxyaniline (NMMA) is a solute whose first allowed electronic transition wavelength remains almost constant (approximately 315 nm) in non-hydrogen-bonding solvents regardless of solvent polarity. However, in hydrogen-bond-accepting solvents such as dimethylsulfoxide, NMMA's absorbance shifts to longer wavelengths (320 nm), whereas in hydrogen-bond-donating solvents (e.g., water), the absorbance shifts to shorter wavelengths (approximately 300 nm). SHG experiments show that at alkane/silica interfaces, surface silanol groups serve as moderately strong hydrogen-bond donors as evidenced by NMMA's absorbance of 307 nm. At the carbon tetrachloride/water interface, NMMA absorbance also shifts to slightly shorter wavelengths (298 nm) implying that water molecules at this liquid/liquid interface are donating strong hydrogen bonds to the adsorbed NMMA solutes. In contrast, experiments using newly developed molecular ruler surfactants with NMMA as a model hydrophobic solute and a hydrophilic, cationic headgroup imply that, as NMMA migrates across an aqueous/alkane interface, it carries with it water that functions as a hydrogen-bond-accepting partner.

Selectivity patterns in micellar electrokinetic chromatography: Characterization of fluorinated and aliphatic alcohol modifiers by micellar selectivity triangle

The usefulness of the micellar selectivity triangle (MST) for prediction and interpretation of separation patterns in micellar electrokinetic chromatography (MEKC) separations is presented. In addition, we demonstrate the capability of controlling selectivity properties of micelles through addition of organic modifiers with known solvation properties as predicted by MST. The examples are modification of the hydrogen bond donor (HBD) micelle of lithium perfluorooctanesulfonate, the hydrogen bond acceptor (HBA) micelle of tetradecyltrimethylammonium bromide, and the sodium dodecyl sulfate micelles with intermediate hydrogen bonding properties with two hydrophobic organic modifiers. One is an aliphatic alcohol, n-pentanol that can act as both a HBA and a HBD; by contrast, the other organic modifier is a fluorinated alcohol, hexafluoroisopropanol that is a strong HBD modifier and would enhance the hydrogen bond donor strength of micelles. A test sample composed of 20 small organic solutes representing HBA, HBD, and non-hydrogen bond aromatic compounds was carefully selected. The trends in retention behavior of these compounds in different micelles are consistent with the selectivity patterns predicted by the MST scheme. To the best of our knowledge, this is the first report on the unique selectivity of fluorinated alcohols as modifiers in MEKC. These results demonstrate the usefulness of the MST scheme for identifying pseudo-phases with highly similar or different selectivities and can serve as a guide for judicious selection of modifiers to create pseudo-phases with desired selectivity behavior on a rational basis.

Diphenylmethane-based anion receptors bearing bis(p-toluenesulfonyl urea) groups

Diphenylmethane-based receptors (1) bearing urea units were prepared for anion recognition. Analogous anion receptors based on biphenyl (2), diphenylsulfide (3), cyclophane (4) and phenyl (5) were also synthesized as control compounds. Their anion recognition ability was evaluated by 1H-NMR spectroscopy in CDCl3 at 297 K. The association constants for the complexation between receptors and anions are strongly dependent on the framework of the receptors and the urea moiety substituent. The much stronger binding of a chloride anion by the diphenylmethane-based receptor (1a) having two p-toluenesulfonyl urea groups was observed. It is rationalized by the stronger hydrogen bond donor strength of the p-toluenesulfonyl urea group and the moderate flexibility of the diphenylmethane framework and is explained in terms of the complex geometry.

Microscopic Picture of the Aqueous Solvation of Glutamic Acid

We present molecular dynamics simulations of glutamic acid and glutamate solvated in water, using both density functional theory (DFT) and the Gromos96 force field. We focus on the microscopic aspects of the solvation-particularly on the hydrogen bond structures and dynamics-and investigate the influence of the protonation state and of the simulation method. Radial distribution functions show that the hydrogen bonds are longer in the force field systems. We find that the partial charges of the solutes in the force field simulations are lower than the localized electron densities for the quantum simulations. This lower polarization decreases the hydrogen bond strength. Protonation of the carboxylate group renders glutamic acid a very strong and stable hydrogen bond donor. The donated hydrogen bond is shorter and lives longer than any of the other hydrogen bonds. The solute molecules simulated by the force field accept on average three more hydrogen bonds than their quantum counterparts. The life times of these bonds show the opposite result: the residence times are much longer (up to a factor 4) in the ab initio simulations.

Cocrystals of Piroxicam with Carboxylic Acids

A crystal engineering method was used to investigate cocrystal formation of piroxicam with pharmaceutically acceptable carboxylic acids. Forming cocrystals of piroxicam can potentially result in solid forms with increased bioavailability. A total of 50 unique cocrystals containing piroxicam and a guest carboxylic acid were identified in screening experiments. Each of the 23 guest molecules tested formed at least one cocrystal with piroxicam. In addition, the three known polymorphs of piroxicam were observed. Raman data for the piroxicam cocrystals can be sorted into three distinct groups based on spectral similarity. These groups are differentiated by the piroxicam tautomer present in the cocrystal and the presence or absence of a strong hydrogen bond donor interacting with piroxicam's amide carbonyl group. X-ray powder diffraction data revealed six isostructural piroxicam cocrystals. Single-crystal structure determination revealed that this isostructural series is a host−guest system in which the piroxic...

(η5-Cyclopentadienyl)(2-naphthylethynyl)(triphenylphosphine-κP)nickel(II)

The title compound, [Ni(C₅H₅)(C₁₂H₇)(C₁₈H₁₅P)], does not contain strong hydrogen-bond donors or acceptors and the primary interactions are limited to those of the weak C-H...π(arene) type and mainly involving the arene rings.

Polysulfonylamine. CLXXVIII Onium‐Salze des Benzol‐1,2‐di(sulfonyl)amins (HZ): Eine zweite Kristallform des Ammonium‐Salzes NH4Z·H2O und Kristallstruktur des Bis(triphenylphosphoranyliden)ammonium‐Salzes [Ph3PNPPh3

AbstractPolysulfonylamines. CLXXVIII. Onium Salts of Benzene‐1,2‐di(sulfonyl)amine (HZ): A Second Crystal Form of the Ammonium Salt NH4Z·H2O and Crystal Structure of the Bis(triphenylphosphoranylidene)ammonium Salt [Ph3PNPPh3]ZA dimorphic form of NH4Z·H2O, where Z− is N‐deprotonated ortho‐benzenedisulfonimide, has been obtained and structurally characterized (previously known form 1A: monoclinic, P21/c, Z′ = 1; new polymorph 1B: monoclinic, P21/n, Z′ = 1). Both structures are dominated by an abundance of classical hydrogen bonds N+–H/O–H···O=S/OH2, whereby the anionic N− function does not act as an acceptor. The major difference between the dimorphs arises from the topology of the hydrogen bond network, which is two‐dimensional in 1A, leading to a packing of discrete lamellar layers, but three‐dimensional in 1B. Moreover, the latter network is reinforced by a set of weak C–H··O/N hydrogen bonds, whereas the layered structure of 1A displays only one independent C–H···O bond, providing a link between adjacent layers. The compound [Ph3PNPPh3]Z (2, monoclinic, P21/c, Z′ = 1) is the first structurally authenticated example of an ionic Z− derivative in which the cation contains neither metal bonding sites nor strong hydrogen bond donors. This structure exhibits columns of anions, surrounded by four parallel columns of cations, giving a square array. The large cations are associated into a three‐dimensional framework via weak C–H···C(π) interactions and an offset face‐to‐face phenyl interaction, while the anions occupy tunnels in this framework and are extensively bonded to the surrounding cations by C–H···O/N− hydrogen bonds and C–H···C(π) interactions.

Can an OH radical form a strong hydrogen bond? A theoretical comparison with H2O

In this study, we apply UCCSD/6-31++G** to investigate the ability of an OH radical acting as a hydrogen bond acceptor with HF, HCl, and H(2)O (HO...HX; X=F, Cl, OH) or as a hydrogen bond donor with H(2)O and H(2)S (OH...XH(2); X=O and S). We also replace OH with H(2)O and make a fair comparison between them. Additionally, the counterpoise method (CP) has been used to examine the effect of basis set superposition error (BSSE). Our results reveal that OH is a stronger hydrogen bond donor but a weaker hydrogen bond acceptor than H(2)O. This conclusion is independent of the correction for BSSE and can be rationalized by the NBO analysis, the results of which indicate that OH radical has a lower n(O) and sigma*(O-H) in energy than that of H(2)O.

2-Amino-4,6-dimethoxypyrimidin-1-ium 1-methyl-5-sulfamoyl-1H-pyrazole-4-carboxylate

In the title compound, C6H10N3O2+·C5H6N3O4S−, the pyrimidinium cation acts as a strong hydrogen-bond donor via the NH2 and NH groups, with the carboxyl­ate groups of the pyrazole group acting as the acceptors. These hydrogen bonds lead to fused R22(8) rings, which form sheets parallel to the [10\overline 1] plane

Solvatochromism in Binary Solvent Mixtures by Means of a Penta‐tert‐butyl Pyridinium N‐Phenolate Betaine Dye

AbstractThe solvatochromic behavior of a penta‐tert‐butyl prydinium N‐phenolate betaine dye was studied using UV‐visible spectrophotometry in several binary mixture solvents. The solvent polarity parameter, ET (1) (kcal. mol−1) was calculated from the position of the longest‐wavelength intramolecular charge transfer absorption band of this penta‐tert‐butyl betaine dye.For binary solvent mixtures, all plots of ET (1) versus the mole fraction of a more polar component are nonlinear owing to preferential solvation of the probe by one component of the binary solvent mixture.In the computation of ET (1) it was assumed that the two solvents mixed interact to form a common structure with an ET (1) value not always intermediate between those of the two solvents mixed. The results obtained are explained by the strong synergism observed for some of the binary mixtures with strong hydrogen bond donors (HBD) solvents such as alcohols.

Interpretation of the dissolution of insoluble peptide sequences based on the acid-base properties of the solvent.

The dissolution process of model insoluble peptide sequences was investigated in view of the electron acceptor (AN) and electron donor (DN) solvent properties. The Alzheimer's disease-inducing (1-42) Abeta-amyloid peptide and its (1-21) fragment, the (66-97) transmembrane bradykinin B2 receptor sequence, and the strongly aggregated VVLGAAIV were selected as models of insoluble peptides. Solvents presenting similar AN and DN values failed, despite their polarities, to dissociate peptide chains (free in solution or bound to a polymer). The maximum solubility of these aggregated sequences was attained in solvents presenting the highest possible (AN-DN) values (in positive or negative mode). The AN-DN values ranged from approximately -20 to +80 and, notably, the lowest dissociation power was ascribed to solvents presenting values of approximately +40. The strong hydrogen bond donor water is located in this region, indicating that, for dissociation of specific insoluble segments, the solvent should appropriately combine its acid/base strength with the potential for van der Waals interactions. We also observed a sequence-dependent pH effect on peptide solubility confirmed through circular dichroism spectroscopy. This approach also revealed a complex but, in many cases, consistent influence of peptide conformation on its solubility degree, even when structure-inducing solvents were added. In conclusion, the random method of selecting solvents to dissolve insoluble and intractable peptide sequences, still in use by some, could be partially supplanted by the strategy described herein, which may be also applicable to other solute dissociation processes.