Anion⋅⋅⋅Anion Interactions Involving σ-Holes of Perrhenate,Pertechnetate and Permanganate Anions

In this communication experimental and theoretical results are reported affording strong evidence that interactions between electron rich atoms and the metal of tetroxide anions of group 7 elements are a new case of attractive and σ-hole interactions. Single crystal X-ray analyses, molecular electrostatic potentials, quantum theory of atoms-in-molecules, and noncovalent interaction plot analyses show that in crystalline permanganate and perrhenate salts the metal in Mn/ReO₄⁻ anion can act as electron acceptors, the oxygen of another Mn/ReO₄⁻ anion can act as the donor and supramolecular anionic dimers or polymers are formed. The name matere bond (MaB) is proposed to categorize these noncovalent interactions and to differentiate them from the classical metal-ligand coordination bond.     

Characterization of Phenosafranine–Hemoglobin Interactions in Aqueous Solution

Binding of the drug phenosafranine to hemoglobin (Hb) in aqueous solutions was investigated by fluorescence, UV/vis and circular dichroism (CD) spectral methods at pH=7.4. The fluorescence data showed that fluorescence quenching of Hb by phenosafranine is the result of formation of a phenosafranine–Hb complex with a 1:1 molar ratio. Thermodynamic analysis implied that hydrophobic, electrostatic and hydrogen bond interactions are all involved in stabilizing the complex. The molecular distance (r=4.29 nm) between the donor (Hb) and acceptor (phenosafranine) was calculated according to Förster’s theory. The features of phenosafranine-induced secondary structure changes of Hb have been studied by synchronous fluorescence, CD and three-dimensional fluorescence spectroscopy. This study improves our knowledge of the interaction dynamics of phenazinium drugs to the physiologically important protein Hb.     

Reactivity of α-Amino Acids in the Reaction with Esters in Aqueous–1,4-Dioxane Media

The kinetics of the reaction of a series of α-amino acids with 4-nitrophenyl acetate, 4-nitrophenyl benzoate, and 2,4,6-trinitrophenyl benzoate in aqueous 1,4-dioxane medium has been studied. Kinetics of the reactions involving 4-nitrophenyl acetate and 2,4,6-trinitrophenyl benzoate has complied with the Brønsted dependence and revealed linear correlation between rate constant logarithm and the energy difference of the frontier orbitals of α-amino acids anions.     

Thermodynamic Studies of Amino Acid–Denaturant Interactions in Aqueous Solutions at 298.15 K

As proteins and other biomolecules consisting of amino acid residues require external additives for their dissolution and recrystallization, it is important to have information about how such additives interact with amino acids. Therefore we have studied the interactions of simple model amino acids with the additives urea and guanidine hydrochloride in aqueous solutions at 298.15 K, using vapor pressure osmometry. During the measurements, the concentration of urea was fixed as ∼2 mol⋅kg⁻¹ and that of guanidine hydrochloride was fixed as ∼1 mol⋅kg⁻¹ whereas the concentrations of amino acids were varied. The experimental water activity data were processed to get the individual activity coefficients of all the three components in the ternary mixture. Further, the activity coefficients were used to get the excess Gibbs energies of solutions and Gibbs energies for transfer of either amino acids from water to aqueous denaturant solutions or denaturant from water to aqueous amino acid solutions. An application of the McMillan-Mayer theory of solutions through virial expansion of transfer Gibbs energies was made to get pair and triplet interaction parameter whose sign and magnitude yielded information about amino acid–denaturant interactions, relative to their interactions with water. The pair interaction parameters have been further used to obtain salting constants and in turn the thermodynamic equilibrium constant values for the amino acid–denaturant mixing process in aqueous solutions at 298.15 K. The results have been explained in terms of hydrophobic hydration, hydrophobic interactions and amino acid–denaturant binding.     

Ion–Water Cooperative Interactions in Aqueous Solutions of MgCl2 by Dielectric Spectroscopy

The dielectric constant of aqueous MgCl₂ solution has been determined in the frequency range 0.2 MHz to 20 GHz at 298 K using the dielectric relaxation spectroscopy method. The behavior is well described according to four Cole-Cole terms whose evolution with composition is analyzed. The static dielectric constant and relaxation times decreases with the increasing aqueous MgCl₂ solution concentrations. Only one H-bonded water cluster with the aqueous MgCl₂ solution relaxes is reported during the cutoff relaxation time. A distinct ion–water cooperative interaction is observed, and water molecules perturbed by ion contribution on dielectric constant beyond the first hydration shell are obtained.     

Kinetics and Mechanism of the Hydrolysis of Benzyl Ether Bonds in Aqueous–Organic Media

Russian Journal of Physical Chemistry A - Kinetic parameters (rate constant, energy of activation, and entropy of activation) of the acid-catalyzed hydrolysis of the benzyl ethers...     

Asymmetric Transfer Hydrogenation of ω-Bromo Acetophenones in Aqueous Media

Optical active ω-bromophenylethanols are useful building blocks for synthesis of various pharmaceuticals such as α1-, β2-, and β3- adrenergic receptor agonists, which are always obtained though a biotransformative pathway and using boron reagent with rigorous conditions . To our knowledge, the metal-catalysed transfer hydrogenation is seldom applied in this [1] reaction. Recently we have developed a water-soluble chiral Ru-complex and applied successfully in transfer hydrogenation of ω-br…     

Henry Reaction in Aqueous Media：Chemoselective Addition of Aldehydes

The chemoselective addition of aldehydes in aquoues medium was obtained under mild condition using improved Henry reaction.     

Enhanced Macroanion Recognition of Superchaotropic Keggin Clusters Achieved by Synergy of Anion–π and Anion–Cation Interactions

Keggin clusters are the most widely used polyoxometalate building blocks for the construction advanced materials, but effective methods for precisely recognizing the isostructural analogues of Keggins are still limited. In this study we employed the zwitterionic molecule 4,4′-dipyridyl N,N′-dioxide as a recognition receptor to specifically bind to the three Keggin analogues PW₁₂O₄₀³⁻, PMo₁₂O₄₀³⁻, and SiW₁₂O₄₀⁴⁻, which separately co-assembled into three different types of spherical charged colloids of different sizes. The recognition phenomena were confirmed by electrochemical methods and their crystallization behavior. Compared with solely anion–cation interaction-driven systems, the synergism with the anion–π interactions between the superchaotropic Keggins and the electron-deficient pyridine rings is believed to enhance the recognition. This observation is intriguing as the long-range solution assembly of Keggins is mainly driven by short-range anion–π interactions. Our results show that the little-noticed hydration shell of Keggins is significantly influenced by the superchaotropic effect, leading to differentiated binding affinity to the receptors and more obvious recognition phenomena between tungsten/molybdenum Keggin analogues.     

Molecular Interactions of L-Histidine in an Aqueous Buffer Solution in the Temperature Range of 288–313 K

Russian Journal of Physical Chemistry A - The behavior of L-histidine (His) in an aqueous buffer solution (pH 7.4) is studied via densimetry and differential scanning calorimetry. The densities and...     

Determination of Organic Compounds in Aqueous–Organic and Dispersed Media Using Electrochemical Methods of Analysis

Journal of Analytical Chemistry - We considered capabilities of electrochemical analysis for the determination of organic compounds in aqueous-organic and dispersed media. The main factors...     

Zinc–Proline Complex: An Efficient,Reusable Catalyst for Direct Nitroaldol Reaction in Aqueous Media

Zinc–proline complex is an effective homogeneous catalyst for the nitroaldol reaction to afford 2‐nitro alcohols in high yields at room temperature in water. The catalyst is reused for several cycles with consistent activity.     

Lipase-Catalyzed Condensation Reaction of 4-Nitrobenzaldehyde with Acetyl Acetone in Aqueous–Organic Cosolvent Mixtures and in Nearly Anhydrous Media

The nature of the product(s) in lipase-catalyzed reaction of acetyl acetone with 4-nitrobenzaldehyde was found to depend upon the source of lipase and the reaction medium. Mucor javanicus lipase was found to give 70% aldol with 80% enantiomeric excess in anhydrous t-amyl alcohol. A 2:2 adduct was formed by the dimerization of the aldol along with an unsaturated cyclic ether as the side products in varying proportions depending upon the reaction medium and the lipase used.

[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.]     

One-Pot Synthesis of Tetrahydrobenzo-[b]-pyran Derivatives in Aqueous Media

In modem organic chemical research, 4H-benzo-[b]-pyran and their derivatives have attracted strong interest due to their useful biological and pharmacological properties. Herein, we report a clean one-pot synthesis of 2-amino-3-cyano-4-aryl-7,7-dimethyl-5-oxo-4H-5,6,7,8-tetrahydro-benzo-[b]-pyrans from aromatic aldehyde, malononitrile and 5,5-dimethyl-1,3-cyclohexadione using hexadecyl trimethyl ammonium bromide (HTMAB) as the catalyst. This method provides several advantages such as high yield, simple work-up procedure and environmental friendliness. All the products were characterized by 1H NMR and IR analyses.     

Coupling Reaction of Carbonyl Compounds Mediated by Gallium Metal in Aqueous Media

A simple and effective pinacol coupling of various aromatic aldehydes mediated by gallium in good yields has been carried out. The reaction is highly effective in water in the prurience of KOH or HCl and was strongly affected by the steric environ-ment surrounding the carbonyl group. Aliphaflc aldehydes, ke-tones and aromatic ketones appear inert under the same reac-tion conditions.     

3-Mercaptopropionic Acid Capped Gold Nanoclusters: Quantized Capacitance in Aqueous Media

IntroductionAnextensiveresearchinterest1,2 inmonolayerprotectedgoldclusters (MPCs)hasariseneversincethemilestonere portofBrustetal.3TheparticularlyinterestingpropertyoftheMPCscoreisitssmallcapacitance (sub attofarad ,aF) ,whichcausesthatsingleelectrontransfersto/fromthecoreleadingtoreadilymeasurablechangesinitselectronicpoten tial.Thatis ,theelectrochemicalchargingoftheMPCscorebecomesaquantizedprocess .However,usualalkanethiolateMPCsarenotwater soluble,resultinginthelimitationoftheirpote…     

Clean,One‐Pot Synthesis of Naphthopyran Derivatives in Aqueous Media

A general and practical one‐pot synthesis of naphthopyran derivatives using hexadecyltrimethylammonium bromide (HTMAB) as catalyst (10 mol%) is described. This method provides several advantages such as neutral conditions, high yields and simple workup procedure. The catalyst is low cost, facile, active, environmentally friendly, and reusable. In addition, water is chosen as a green solvent.     

Catalytic Polarographic Waves of 2,2′-Bipyridine Cobalt Complexes in Aqueous Media

Abstract

The electrochemical reduction of 2,2′-bipyridine (bipy) complexes of cobalt (II), [Co(bipy)₃]²⁺, in aqueous medium has been studied with dc tast, normal pulse polarography and controlled-potential coulometry. The cathodic wave in the process [Co(bipy)₃]²⁺/[Co(bipy)₃]⁺ shows catalytic character in the presence of hydrogen ions. The rate constant of the parallel chemical reaction was found to be 2.2 × 10⁴ M^?1. s^?1.     

Azobenzene–Hemicyanine Conjugated Polymeric Chemosensor for the Rapid and Selective Detection of Cyanide in Pure Aqueous Media

A water-soluble polymeric probe was designed and synthesized that can be used for the colorimetric selective detection of cyanide ions in pure aqueous media. In particular, P1, a water-soluble random terpolymer (P1) of N,N′-dimethylacrylamide, 2-((E)-4-((E)-(4-((2-(acryloyloxy)ethyl)(methyl)amino)phenyl)diazenyl)styryl)-1,3,3-trimethyl-3H-indol-1-ium (M1), and N-(4-benzoylphenyl)acrylamide was synthesized via traditional free-radical polymerization. Upon the addition of CN⁻ ions to a P1 solution, a macroscopically detectable color change of the solution from brick red to light yellow took place, which was associated with a low limit of analyte detection (1.23 μM). Notably, P1 exhibited excellent selectivity toward CN⁻ over other anions and biothiols, which may be present in the medium. Such highly selective colorimetric response to CN⁻ by P1 originated from the nucleophilic attack of CN⁻ anions onto the electron-deficient polarized CN bonds of P1's indolium moieties, resulting in the perturbation of the intramolecular charge transfer process occurring within the probe via destruction of the polymer's extended π-conjugation. P1 was also immobilized on a quartz slide by spin coating and then exposed to ultraviolet light. The resulting polymeric film displayed a rapid response to CN⁻ consisting in a distinct color change, extending the scope of the usefulness of P1 as a cyanide-ion probe beyond the solution phase. © 2019 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 124–131     

Dual Responsive Regulation of Host–Guest Complexation in Aqueous Media to Control Partial Release of the Host

The regulation of the concentration of a wide range of small molecules is ubiquitous in biological systems because it enables them to adapt to the continuous changes in the environmental conditions. Herein, we report an aqueous synthetic system that provides an orchestrated, temperature and pH controlled regulation of the complexation between the cyclobis(paraquat-p-phenylene) host ( BBox ) and a 1,5-dialkyloxynaphthalene ( DNP ) guest attached to a well-defined dual responsive copolymer composed of N-isopropylacrylamide as thermoresponsive monomer and acrylic acid as pH-responsive monomer. Controlled, partial release of the BBox , enabling control over its concentration, is based on the tunable partial collapse of the copolymer. This colored supramolecular assembly is one of the first synthetic systems providing control over the concentration of a small molecule, providing great potential as both T and pH chromic materials and as a basis to develop more complex systems with molecular communication.