Involving Hydrogen Bonds Research Articles

Molecular modeling and imaging of initial stages of cellulose fibril assembly: evidence for a disordered intermediate stage.

The remarkable mechanical strength of cellulose reflects the arrangement of multiple β-1,4-linked glucan chains in a para-crystalline fibril. During plant cellulose biosynthesis, a multimeric cellulose synthesis complex (CSC) moves within the plane of the plasma membrane as many glucan chains are synthesized from the same end and in close proximity. Many questions remain about the mechanism of cellulose fibril assembly, for example must multiple catalytic subunits within one CSC polymerize cellulose at the same rate? How does the cellulose fibril bend to align horizontally with the cell wall? Here we used mathematical modeling to investigate the interactions between glucan chains immediately after extrusion on the plasma membrane surface. Molecular dynamics simulations on groups of six glucans, each originating from a position approximating its extrusion site, revealed initial formation of an uncrystallized aggregate of chains from which a protofibril arose spontaneously through a ratchet mechanism involving hydrogen bonds and van der Waals interactions between glucose monomers. Consistent with the predictions from the model, freeze-fracture transmission electron microscopy using improved methods revealed a hemispherical accumulation of material at points of origination of apparent cellulose fibrils on the external surface of the plasma membrane where rosette-type CSCs were also observed. Together the data support the possibility that a zone of uncrystallized chains on the plasma membrane surface buffers the predicted variable rates of cellulose polymerization from multiple catalytic subunits within the CSC and acts as a flexible hinge allowing the horizontal alignment of the crystalline cellulose fibrils relative to the cell wall.

Extremely strong temperature-dependent Davydow-splitting effects in the polarized IR spectra of the hydrogen bond: Pyrazole and quinolin-2(1H)-one crystals

Polarized IR spectra were recorded in the spectral range of the νN–H and νN–D proton stretching vibration bands for the isotopically neat and isotopically diluted crystals of pyrazole (Pzl) and quinolin-2(1H)-one (2HQ). The spectra measured in the temperature range of 77–293K have shown that temperature extremely strongly influenced the magnitude of the Davydow-splitting effects in the crystalline spectra. Two different competing vibrational Davydow-coupling mechanisms involving hydrogen bonds, i.e., the ‘tail-to-head’ and the ‘side-to-side’, were responsible for the generation of the temperature effects in the polarized spectra.

Inter-hydrogen bond coupling in crystals with molecular chains in their lattices investigated by polarized IR spectroscopy: 4-Bromo-3,5-dimethylpyrazole and 3,4-dimethoxyphenylacetic acid

We report the results of the experimental and theoretical studies of the polarized IR crystalline spectra of 4-bromo-3,5-dimethylpyrazole (4Br35DMPz) and 3,4-dimethoxyphenylacetic acid (34DMPAA) as well as the spectra of their deuterium-bonded analogues. The results of model calculations of the temperature impact exerted on to the band shapes measured in the X–H- and X–D bond stretching vibration regions, performed on the basis of the “strong-coupling” model, are also shown. These studies confirm a direct relationship between the spectral properties in IR and the electronic structure of the associating molecules in the crystals. Two different competing exciton coupling mechanisms involving hydrogen bonds, the “tail-to-head” (TH) in 4Br35DMPz and the “side-to-side” coupling in 34DMPAA, were recognized. The molecular electronic structure determines the relative contribution of each individual vibrational exciton coupling mechanism in the spectra generation. It also strongly influences the temperature-induced evolution of the Davydov-splitting effects in the crystalline spectra. Dynamical co-operative interactions responsible for a non-random distribution of protons and deuterons in the crystal hydrogen bonds can also be identified in the investigated systems.

Synthesis, in vitro anticancer activity and in silico study of new disubstituted thiazolidinedione derivatives

Thiazolidinediones are known to have antidiabetic activity, but new activities are being discovered every year; among these, their anticancer activity has received the most attention. In this study, we synthesized three new disubstituted thiazolidinediones and assayed their cytotoxicity against six tumor cell lines, as well as against normal cells. Cytometry studies and molecular modeling were also performed to elucidate the mechanism of cytotoxicity. Of the three new thiazolidinediones synthesized, (5Z)-5-(3-bromo-benzylidene)-3-(4-nitrobenzyl)-thiazolidine-2,4-dione (LPSF/SF-13) exhibited the most promising activity; it was selectively cytotoxic against leukemia, lymphoma, glioblastoma, and hepatocarcinoma cell lines without being toxic to normal cells. Apoptosis was the main cell death process induced by this compound, although it also induced necrosis. Furthermore, molecular modeling studies showed that LPSF/SF-13 had good affinity for peroxisome proliferator-activated receptor γ; binding to the receptor involved hydrogen bonds with Arg288 and Ser342 residues (bond distances of 3.1 and 2.8 A, respectively), as well as a π-bonding interaction with His449. We concluded that LPSF/SF-13 is a promising compound for in vivo and combination therapy studies against cancer.

Phosphanchalkogenide und ihre Metallkomplexe. II. Komplexe einiger Gold(I)-Halogenide mit Diphosphanmonochalkogeniden [1] / Phosphane Chalcogenides and their Metal Complexes. II. Gold(I) Halide Complexes of some Diphosphane Monochalcogenides

We report the crystal structures of 19 gold(I) complexes with diphosphane monochalcogenide ligands, general formula (PP)EAuHal (PP = diphosphane, E = chalcogen, Hal = halogen). For PP = bis(diphenylphosphano)methane (dppm): 1, dppmOAuCl as its diisopropyl ether solvate; 2, dppmOAuI as its dichloromethane solvate; 3, dppmSAuCl as its dichloromethane hemisolvate; 4, dppmSAuI; 5, dppmSeAuBr as a 1:1 adduct with dppmSe2; 6, dppmSeAuI. Compound 3 is isotypic to the known structure of dppmSeAuCl. Most of the structures have an E-P…P-Au torsion angle close to zero, which, especially for the larger E atoms, facilitates a close intramolecular approach of E and Au. The packing of 1-3 involves hydrogen bonds from the methylene hydrogens. For PP = 1,2-bis(diphenylphosphano)ethane (dppe): 7, dppeOAuBr and 8, dppeOAuI, both as their hemihydrates; 9, dppeSAuBr; 10, dppeSAuI. All four compounds crystallise with two independent molecules of the gold complex, between which short Au…Au contacts are observed; the molecules of 7 and 8 are further linked by hydrogen bond systems […P=O…H-O-H…O=P…]. Compounds 7 and 8 form an isotypic series with their known chloride analogue, as do 9 and 10. For PP = 1,2- bis(diphenylphosphano)benzene (dppbz): 11, dppbzOAuCl; 12, dppbzOAuBr; 13, dppbzSAuBr; 14, dppbzSAuI, 16, dppbzSeAuBr and 17, dppbzSeAuI, all as their isotypic dichloromethane disolvates; 15, dppbzSeAuCl (isotypic to 13). The absolute E-P…P-Au torsion angles are all in the range 50 - 70°; short intramolecular E…Au contacts are observed. The packing of 11-17 shows few notable short contacts. For PP = cis-1,2-bis(diphenylphosphano)ethene (cisdppen): 18, cisdppenSAuCl; 19, cisdppenSAuBr. Both compounds crystallise with two independent molecules, and in both cases the molecules display considerable differences in configuration. The packing of 18 involves short H…Cl and that of 19 short H…S contacts. For PP = 1,8-bis(diphenylphosphano)naphthalene (dppn), an inversion-symmetric gold(III) complex (dppnSeAu)2Cl2 20, with a central four-membered ring Au2Se2, was obtained instead of the expected isomeric gold(I) derivative by formal insertion of gold into a P-Se bond; it crystallised as a deuterochloroform hexasolvate.

Conformational Determinants of the Activity of Antiproliferative Factor Glycopeptide

The antiproliferative factor (APF) involved in interstitial cystitis is a glycosylated nonapeptide (TVPAAVVVA) containing a sialylated core 1 α-O-disaccharide linked to the N-terminal threonine. The chemical structure of APF was deduced using spectroscopic techniques and confirmed using total synthesis. The synthetic APF provided a platform to study amino acid modifications and their effect on APF activity, based on which a structure-activity relationship (SAR) for APF activity was previously proposed. However, this SAR model could not explain the change in activity associated with minor alterations in the peptide sequence. Presented is computational analysis of 14 APF derivatives to identify structural trends from which a more detailed SAR is obtained. The APF activity is found to be dictated by the close interplay between carbohydrate-peptide and peptide-peptide interactions. The former involves hydrogen bond and hydrophobic interactions, and the latter is dominated by hydrophobic interactions. The highly flexible hydrophobic peptide adopts collapsed conformations separated by low energy barriers. APF activity correlates with hydrophobic clustering associated with amino acids 4A, 6V, and 8V. Peptide conformations are highly sensitive to single point mutations, which explain the experimental trends. The presented SAR will act as a guide for lead optimization of more potent APF analogues of potential therapeutic utility.

Evaluation of arsenic effects in Vicia faba by FTIR and FTNIR spectroscopy

Arsenic is an ubiquitous and highly toxic metalloid widely distributed in the environment through both natural and anthropogenic pathways (Liu et al., 2004) and its presence in food composites is a matter of concerns to the well being of both humans and animals. In fact, As has been recently found in drinking water (network and groundwater) in some Italian regions, including Lazio (Central Italy), at concentration ranging between 25 and 80 μg L-1, higher than the limits set by law (10 μg L- 1) where Arsenic-contaminated groundwaters are often used in agriculture to irrigate crops for food and animal consumption; this determines that arsenic can enter human food chain. Inorganic or organic species of the metalloid arsenic occur in the environment. Either inorganic or organic As occurs in the environment and inorganic forms (iAs) are more toxic than the organic ones (oAs). Most of the human health effects of arsenic have been established based on epidemiologic studies, which have shown a significant association between the consumption of arsenic through drinking water and cancers of the skin, lung, bladder, liver, and kidney, neurologic disease, cardiovascular disease, as well as other non-malignant diseases. Arsenic is not an essential element for plants and its over-concentration in soils can generate toxicity phenomena. Its translocation from soil to plant constitutes one of the main human exposure ways. In this research we evaluated the effects of As exposure on Vicia faba seedlings by means of infrared (FTIR) and near infrared (FTNIR) spectroscopy to investigate molecular modifications caused by the interactions of plant with As. Both techniques showed relevant molecular modifications depending on As exposure. Molecular modifications evidenced by FTIR spectroscopy were mainly related to modified structures involving methyl groups of polysaccharides proteins and lipids, resulting better evidenced in meristem root samples. However, seconds derivative FTIR spectra did not show modification of the secondary structure of proteins. The molecular modifications shown by FTNIR spectroscopy were mainly related to the bands of hydroxyl groups with carboxylic and methyl groups, involving hydrogen bonds between carbohydrates and nucleic acids and lipids. These molecular and structural modifications are determined by the direct introduction of As within the plant biomolecules.

Water-soluble bis(4′-[2,2,2-tris(hydroxymethyl)ethoxy]-2,2′:6′,2″-terpyridine)metal complexes

A series of homoleptic metal complexes containing the pentaerythritol-functionalized ligand 1 (4′-(2,2,2-tris(hydroxymethyl)ethoxy)-2,2′:6′,2″-terpyridine) has been synthesized. In MeOH and under microwave conditions, the 2,2,2-tris(hydroxymethyl)ethoxy substituent is cleaved and replaced by a methoxy group originating from the solvent. This has been confirmed from the single crystal structure of [Zn(2)2][PF6]2 (2=4′-methoxy-2,2′:6′,2″-terpyridine). The complexes [Zn(1)2][OAc]2, [Fe(1)2]Cl2 and [Co(1)2][PF6]2 were therefore prepared under mild conditions; [Co(1)2][PF6]2 readily oxidizes to [Co(1)2][PF6]3; the conversion of the paramagnetic [Co(1)2]2+ to diamagnetic [Co(1)2]3+ is readily monitored by 1H NMR spectroscopy. The homoleptic complexes are hygroscopic and are highly soluble in water; the most soluble is [Zn(1)2][OAc]2 (71mmoldm−3). Structural data for 1, [Zn(1)2][PF6]2, 4{[Zn(1)2][PF6]2}·3MeCN, [Zn(1)(OAc-O)2]·2MeOH and 2{[Co(1)2][PF6]3}·1.5MeCN·1.5H2O confirm that dominant packing forces involve hydrogen bonds between pendant 2,2,2-tris(hydroxymethyl)ethoxy units.

An investigation on hydrogen bonding between 3-methylindole and ethanol using trilinear decomposition of fluorescence excitation–emission matrices

The multi-state fluorescence characteristics of 3-methylindole (MI) make its spectra rich in chemical information and the spectral interpretation rather challenging. The trilinear decomposition method could be appropriate for this task and provide a deeper insight into the hydrogen bonding to MI. Taking the excitation fluorescence spectra together with the emission counterparts to formulate a three-way data array and solving the data array using the Alternating Trilinear Decomposition (ATLD) algorithm is beneficial for studying hydrogen bonding to MI in several aspects. Firstly, making full use of the excitation spectra could guarantee that the experimentally collected data contain sufficient information necessary for investigating signals originated from the weak interactions buried in the strong interaction background. Secondly, the resolution of a three-way data array could theoretically guarantee the uniqueness of the resolved component spectra with actual physical meaning. Thirdly, the ATLD algorithm resolves spectra of complex mixture and determines the spectra of corresponding individual components of different states without disturbing the complex chemical equilibrium involved. The hydrogen bonding interaction of MI with other molecules has been studied using the ATLD algorithm. A detailed investigation has been undertaken for the 1La and 1Lb states as the lowest excited singlet states which dominate the fluorescence emission of MI depending on the effect of other molecules and the surrounding microenvironment. The hydrogen bonding between indole derivatives and other molecules has been examined and some association constants involving hydrogen bond formation have been estimated and compared with theoretical simulation results or experimental observations of previous researchers.

Systematic investigation on the interaction of bovine serum albumin with ZnO nanoparticles using fluorescence spectroscopy

Zinc oxide (ZnO) nanoparticles with average size of ∼7.5nm were synthesized to investigate their interaction with bovine serum albumin (BSA) at different temperatures. Fluorescence quenching, synchronous and polarization spectroscopy along with UV–vis absorption, circular dichroism and resonance light scattering spectroscopy techniques were used to establish the interaction mechanism between ZnO and BSA. The obtained results confirmed that the ZnO nanoparticles (NPs) quench the fluorophore of BSA by forming ground state complex in the solution. The fluorescence quenching data was also used to determine binding sites and binding constants at different temperatures. The calculated thermodynamic parameters (ΔG°, ΔH°, and ΔS°) suggest that the binding process occurs spontaneously by involving hydrogen bond and van der Waals interactions. The synchronous fluorescence spectra reveal that the microenvironment close to both the tyrosine and tryptophan residues of BSA is perturbed and that the hydrophobicity of both the residues is increased in the presence of ZnO NPs. Resonance light scattering, circular dichroism, and fluorescence polarization spectra suggest the formation of BSA–ZnO complex and conformational changes in BSA. The calculated distance between the BSA and ZnO NPs suggests that the energy transfer from excited state of BSA to ZnO NPs occurs with high efficiency.

Mapping Paratope on Antithrombotic Antibody 6B4 to Epitope on Platelet Glycoprotein Ibalpha via Molecular Dynamic Simulations

Binding of platelet receptor glycoprotein Ibα (GPIbα) to the A1 domain of von Willebrand factor (vWF) is a critical step in both physiologic hemostasis and pathologic thrombosis, for initiating platelet adhesion to subendothelium of blood vessels at sites of vascular injury. Gain-of-function mutations in GPIbα contribute to an abnormally high-affinity binding of platelets to vWF and can lead to thrombosis, an accurate complication causing heart attack and stroke. Of various antithrombotic monoclonal antibodies (mAbs) targeting human GPIbα, 6B4 is a potent one to inhibit the interaction between GPIbα and vWF-A1 under static and flow conditions. Mapping paratope to epitope with mutagenesis experiments, a traditional route in researches of these antithrombotic mAbs, is usually expensive and time-consuming. Here, we suggested a novel computational procedure, which combines with homology modeling, rigid body docking, free and steered molecular dynamics (MD) simulations, to identify key paratope residues on 6B4 and their partners on GPIbα, with hypothesis that the stable hydrogen bonds and salt bridges are the important linkers between paratope and epitope residues. Based on a best constructed model of 6B4 bound with GPIbα, the survival ratios and rupture times of all detected hydrogen bonds and salt bridges in binding site were examined via free and steered MD simulations and regarded as indices of thermal and mechanical stabilizations of the bonds, respectively. Five principal paratope residues with their partners were predicted with their high survival ratios and/or long rupture times of involved hydrogen bonds, or with their hydrogen bond stabilization indices ranked in top 5. Exciting, the present results were in good agreement with previous mutagenesis experiment data, meaning a wide application prospect of our novel computational procedure on researches of molecular of basis of ligand-receptor interactions, various antithrombotic mAbs and other antibodies as well as theoretically design of biomolecular drugs.

Pharmacophore, QSAR, and Binding Mode Studies of Substrates of Human Cytochrome P450 2D6 (CYP2D6) Using Molecular Docking and Virtual Mutations and an Application to Chinese Herbal Medicine Screening

The highly polymorphic human cytochrome P450 2D6 (CYP2D6) metabolizes about 25% of currently used drugs. In this study, we have explored the interaction of a large number of substrates (n = 120) with wild-type and mutated CYP2D6 by molecular docking using the CDOCKER module. Before we conducted the molecular docking and virtual mutations, the pharmacophore and QSAR models of CYP2D6 substrates were developed and validated. Finally, we explored the interaction of a traditional Chinese herbal formula, Fangjifuling decoction, with CYP2D6 by virtual screening. The optimized pharmacophore model derived from 20 substrates of CYP2D6 contained two hydrophobic features and one hydrogen bond acceptor feature, giving a relevance ratio of 76% when a validation set of substrates were tested. However, our QSAR models gave poor prediction of the binding affinity of substrates. Our docking study demonstrated that 117 out of 120 substrates could be docked into the active site of CYP2D6. Forty one out of 117 substrates (35.04%) formed hydrogen bonds with various active site residues of CYP2D6 and 53 (45.30%) substrates formed a strong π-π interaction with Phe120 (53/54), with only carvedilol showing π-π interaction with Phe483. The active site residues involving hydrogen bond formation with substrates included Leu213, Lys214, Glu216, Ser217, Gln244, Asp301, Ser304, Ala305, Phe483, and Phe484. Furthermore, the CDOCKER algorithm was further applied to study the impact of mutations of 28 active site residues (mostly non-conserved) of CYP2D6 on substrate binding modes using five probe substrates including bufuralol, debrisoquine, dextromethorphan, sparteine, and tramadol. All mutations of the residues examined altered the hydrogen bond formation and/or aromatic interactions, depending on the probe used in molecular docking. Apparent changes of the binding modes have been observed with the Glu216Asp and Asp301Glu mutants. Overall, 60 compounds out of 130 from Fangjifuling decoction matched our pharmacophore model for CYP2D6 substrates. Fifty four out of these 60 compounds could be docked into the active site of CYP2D6 and 24 of 54 compounds formed hydrogen bonds with Glu216, Asp301, Ser304, and Ala305 in CYP2D6. These results have provided further insights into the factors that determining the binding modes of substrates to CYP2D6. Screening of high-affinity ligands for CYP2D6 from herbal formula using computational models is a useful approach to identify potential herb-drug interactions.

Communication: The highest frequency hydrogen bond vibration and an experimental value for the dissociation energy of formic acid dimer

The highest frequency hydrogen bond fundamental of formic acid dimer, ν(24) (B(u)), is experimentally located at 264 cm(-1). FTIR spectra of this in-plane bending mode of (HCOOH)(2) and band centers of its symmetric D isotopologues (isotopomers) recorded in a supersonic slit jet expansion are presented. Comparison to earlier studies at room temperature reveals the large influence of thermal excitation on the band maximum. Together with three B(u) combination states involving hydrogen bond fundamentals and with recent progress for the Raman-active modes, this brings into reach an accurate statistical thermodynamics treatment of the dimerization process up to room temperature. We obtain D(0) = 59.5(5) kJ/mol as the best experimental estimate for the dimer dissociation energy at 0 K. Further improvements have to wait for a more consistent determination of the room temperature equilibrium constant.

Chemistry of Aqueous Silica Nanoparticle Surfaces and the Mechanism of Selective Peptide Adsorption

Control over selective recognition of biomolecules on inorganic nanoparticles is a major challenge for the synthesis of new catalysts, functional carriers for therapeutics, and assembly of renewable biobased materials. We found low sequence similarity among sequences of peptides strongly attracted to amorphous silica nanoparticles of various size (15-450 nm) using combinatorial phage display methods. Characterization of the surface by acid base titrations and zeta potential measurements revealed that the acidity of the silica particles increased with larger particle size, corresponding to between 5% and 20% ionization of silanol groups at pH 7. The wide range of surface ionization results in the attraction of increasingly basic peptides to increasingly acidic nanoparticles, along with major changes in the aqueous interfacial layer as seen in molecular dynamics simulation. We identified the mechanism of peptide adsorption using binding assays, zeta potential measurements, IR spectra, and molecular simulations of the purified peptides (without phage) in contact with uniformly sized silica particles. Positively charged peptides are strongly attracted to anionic silica surfaces by ion pairing of protonated N-termini, Lys side chains, and Arg side chains with negatively charged siloxide groups. Further, attraction of the peptides to the surface involves hydrogen bonds between polar groups in the peptide with silanol and siloxide groups on the silica surface, as well as ion-dipole, dipole-dipole, and van-der-Waals interactions. Electrostatic attraction between peptides and particle surfaces is supported by neutralization of zeta potentials, an inverse correlation between the required peptide concentration for measurable adsorption and the peptide pI, and proximity of cationic groups to the surface in the computation. The importance of hydrogen bonds and polar interactions is supported by adsorption of noncationic peptides containing Ser, His, and Asp residues, including the formation of multilayers. We also demonstrate tuning of interfacial interactions using mutant peptides with an excellent correlation between adsorption measurements, zeta potentials, computed adsorption energies, and the proposed binding mechanism. Follow-on questions about the relation between peptide adsorption on silica nanoparticles and mineralization of silica from peptide-stabilized precursors are raised.

Charge effect of foreign metal ions and the crystal growth process in hybridized metal–organic frameworks

A paddle-wheel-type Cu metal-organic framework CuHTPO involving hydrogen bonds in the network is utilized to obtain composite systems with different metal ions of Zn(2+) and Tb(3+). The framework stability and crystal transformation are affected by the charges of foreign cations.

Application of terahertz spectroscopy and molecular modeling in isomers investigation: Glucose and fructose

Terahertz spectra of glucose and fructose have been measured by terahertz time-domain spectroscopy (THz-TDS) at room temperature. Because they have the same molecular formula, the differences of the THz spectra can be attributed to their molecular structures and the arrangement of molecules in unit cell. In this paper, gaseous-state theory has been employed to simulate the isolated molecule of these two isomers. The results indicate that experimental THz spectral features (0.5–4.0THz) of glucose and fructose arise from the mixture of intramolecular and intermolecular modes, involving hydrogen bonds and covalent bonds, and with the intermolecular modes dominating.

Fundamentals of multilevel mesomechanics of nanostructural transitions in erythrocyte membranes and their destructions in interaction with stress hormones

Stress hormones (cortisol, adrenaline, noradrenaline) are capable for nonspecific binding with erythrocyte membranes thus initiating structural-phase transitions in them. The binding constants for cortisol, adrenaline and noradrenaline are respectively 1.23·106, 6.3·106 and 1.7·106 M−1. The amount of bound hormones varies in the range 10∼10-10∼n mole/mg of protein. The binding involves hydrogen bonds, hydrophobic bonds and electrostatic bonds. Active groups of hormones (amino-, imino-, methylamine-, keto- and hydroxy-groups) interact simultaneously with CO- and NH-groups of both proteins and phospholipids. These processes underlie structural-phase transitions in an erythrocyte membrane in its interaction with stress hormones. The structural-phase transitions result in complex protein-lipid domains of increasing structural order in the membrane. At the same time, water dipoles are displaced from the domains to adjacent regions and promote membrane loosening. The membrane microviscosity thus greatly increases in the regions of both protein-lipid interactions and lipid-lipid interactions. The increase in erythrocyte membrane viscosity hampers the motion of erythrocytes through capillaries, and as a certain critical threshold is approached, this contributes to the development of tissue hypoxia. The mesomechanics of structural-phase transitions and destruction in external fields of biological membranes and nanostructured solids are qualitatively alike.

Backscattering Interferometry: An Alternative Approach for the Study of Hydrogen Bonding Interactions in Organic Solvents

Intermolecular interactions involving hydrogen bonds are responsible for catalysis and recognition. Traditional methods used to study hydrogen-bonding interactions are generally limited to relatively large volumes and high substrate concentrations. Backscattering Interferometry (BSI) provides a microfluidic platform to study these interactions in nonaqueous media at micromolar to nanomolar concentrations in picoliter volumes by monitoring changes in the refractive index.

The sorption of benzocaine from aqueous solution by nylon 6 powder.

Abstract The sorption of benzocaine by nylon 6 powder from aqueous solution has been examined under varying environmental conditions. The extent of sorption increases with increase in electrolyte concentration, and with pH up to about pH 4. Increasing temperature reduces the amount of drug sorbed. In all cases, the sorption isotherms were linear over the concentration ranges studied, and can be described by a simple distribution law which allows the effects of ionic strength and pH to be predicted. The interaction is believed to involve hydrogen bond formation between benzocaine and the amide groups of the nylon after penetration of the polymer matrix by the drug.

Cation–anion interactions involving hydrogen bonds: Syntheses and crystal structures study of hexafluorotitanate(IV) salts with pyridine and methyl substituted pyridines

Fluorotitanates (LH) 2[TiF 6]· nH 2O ( 1: R = pyridine, n = 1, 2: R = 2-picoline, n = 2, 3: R = 2,6-lutidine, n = 0, 4: R = 2,4,6-collidine, n = 0) and (LH)[TiF 5(H 2O)] ( 3a: L = 2,6-lutidine) have been synthesized by the reaction of pyridine or corresponding methyl substituted pyridines and titanium dioxide dissolved in hydrofluoric acid. The crystal structures of ionic compounds 1, 2, 3, 3a and 4 have been determined by single-crystal X-ray diffraction analysis. The hydrogen bonding led to the formation of discrete (LH) 2[TiF 6] units ( 4), chains ( 1– 3), and layers ( 3a). The additional π– π interactions present in 1, 2, and 4 results in chain structures of 1 and 4 and in a layer structure of 2. The [TiF 6] 2− and [TiF 5(H 2O)] − anions were observed by 19F NMR spectroscopy in aqueous solutions of 1, 2, 3, 3a and 4.