Absence Of Solvent Research Articles

Polyether from a biobased Janus molecule as surfactant for carbon nanotubes

A new polyether (PE) was prepared from a biobased Janus molecule, 2-(2,5-dimethyl-1H-pyrrol-1-yl)-1,3- propanediol (serinol pyrrole, SP). SP was synthesized with very high yield (about 96%) and high atom efficiency (about 80%) by reacting a biosourced molecule, such as serinol, with 2,5-hexanedione in the absence of solvent or catalyst. The reaction of SP with 1,6-dibromohexane led to PE oligomers, that were used as surfactants for multiwalled carbon nanotubes (MWCNT), in ecofriendly polar solvents such as acetone and ethyl acetate. The synergic interaction of aromatic rings and oxyalkylene sequences with the carbon allotrope led to dramatic improvement of surfactant efficiency: only 24% of SP based PE was extracted with ethyl acetate from the adduct with MWCNT, versus 98% of a typical pluronic surfactant. Suspensions of MWCNT-PE adducts in ethyl acetate were stable for months. High resolution transmission electron microscopy revealed a film of oligomers tightly adhered to MWCNT surface.

Advances in organometallic synthesis with mechanochemical methods.

Solvent-based syntheses have long been normative in all areas of chemistry, although mechanochemical methods (specifically grinding and milling) have been used to good effect for decades in organic, and to a lesser but growing extent, inorganic coordination chemistry. Organometallic synthesis, in contrast, represents a relatively underdeveloped area for mechanochemical research, and the potential benefits are considerable. From access to new classes of unsolvated complexes, to control over stoichiometries that have not been observed in solution routes, mechanochemical (or 'M-chem') approaches have much to offer the synthetic chemist. It has already become clear that removing the solvent from an organometallic reaction can change reaction pathways considerably, so that prediction of the outcome is not always straightforward. This Perspective reviews recent developments in the field, and describes equipment that can be used in organometallic synthesis. Synthetic chemists are encouraged to add mechanochemical methods to their repertoire in the search for new and highly reactive metal complexes and novel types of organometallic transformations.

Extended Gas-Phase Trapping Followed by Surface-Induced Dissociation of Noncovalent Protein Complexes.

Mass spectrometry has emerged as a useful tool in the study of proteins and protein complexes. It is of fundamental interest to explore how the structures of proteins and protein complexes are affected by the absence of solvent and how this alters with increasing time in the gas phase. Here we demonstrate that a range of protein and protein complexes can be confined within the Trap T-wave region of a modified Waters Synapt G2S instrument, including monomeric (β-lactoglobulin), dimeric (β-lactoglobulin and enolase), tetrameric (streptavidin, concanavalin A, and pyruvate kinase), and pentameric (C-reactive protein) complexes, ranging in size up to 237 kDa. We demonstrate that complexes can be confined within the Trap region for varying lengths of time over the range 1-60 s and with up to 86% trapping efficiency for 1 s trapping. Furthermore, using model systems, we show that these noncovalent complexes can also be fragmented by surface-induced dissociation (SID) following trapping. SID reveals similar dissociation patterns over all trapping times studied for unactivated protein complexes, suggesting that any conformational changes occurring over this time scale are insufficient to cause substantial differences in the SID spectra of these complexes. Intentional alteration of structure by cone activation produces a distinct SID spectrum, with the differences observed being conserved, in comparison to unactivated complex, after trapping. However, subtle differences in the SID spectra of the activated complex are also observed as a function of trapping time.

Zeolite Catalysts for Phenol Benzoylation with Benzoic Acid: Exploring the Synthesis of Hydroxybenzophenones

In this paper, we report on the reaction of phenol benzoylation with benzoic acid, which was carried out in the absence of solvent. The aim of this reaction is the synthesis of hydroxybenzophenones, which are important intermediates for the chemical industry. H-beta zeolites offered superior performance compared to H-Y, with a remarkably high conversion of phenol and high yields to the desired compounds, when using a stoichiometric amount of benzoic acid. It was found that the reaction mechanism did not include the intramolecular Fries rearrangement of the primary product phenyl benzoate, but indeed, the bimolecular reaction between phenyl benzoate and phenol mainly contributed to the formation of hydroxybenzophenones. The product distribution was greatly affected by the presence of Lewis-type acid sites in H-beta; it was suggested that the interaction between the aromatic ring and the electrophilic Al3+ species led to the preferred formation of o-hydroxybenzophenone, because of the decreased charge density on the C atom at the para position of the phenolic ring. H-Y zeolites were efficient than H-beta in phenyl benzoate transformation into hydroxybenzophenones.

The fate of proteins in outer space

It is well established that any properly conducted biophysical studies of proteins must take appropriate account of solvent. For water-soluble proteins it has been an article of faith that water is largely responsible for stabilizing the fold, a notion that has recently come under increasing scrutiny. Further, there are some instances when proteins are studied experimentally in the absence of solvent, as in matrix-assisted laser desorption/ionization or electrospray mass spectrometry, for example, or in organic solvents for protein engineering purposes. Apart from these considerations, there is considerable speculation as to whether there is life on planets other than Earth, where conditions including the presence of water (both in liquid or vapor form and indeed ice), temperature and pressure may be vastly different from those prevailing on Earth. Mars, for example, has only 0.6% of Earth's mean atmospheric pressure which presents profound problems to protein structures, as this paper and a large corpus of experimental work demonstrate. Similar objections will most likely apply in the case of most exoplanets and other bodies such as comets whose chemistry and climate are still largely unknown. This poses the question, how do proteins survive in these different environments? In order to cast some light on these issues we have conducted a series of molecular dynamics simulations on protein dehydration under a variety of conditions. We find that, while proteins undergoing dehydration can retain their integrity for a short duration they ultimately become disordered, and we further show that the disordering can be retarded if superficial water is kept in place on the surface. These findings are compared with other published results on protein solvation in an astrobiological and astrochemical setting. Inter alia, our results suggest that there are limits as to what to expect in terms of the existence of possible extraterrestrial forms as well to what can be achieved in experimental investigations on living systems despatched from Earth. This finding may appear to undermine currently held hopes that life will be found on nearby planets, but it is important to be aware that the presence of ice and water are by themselves not sufficient; there has to be an atmosphere which includes water vapor at a sufficiently high partial pressure for proteins to be active. A possible scenario in which there has been a history of adequate water vapor pressure which allowed organisms to prepare for a future dessicated state by forming suitable protective capsules cannot of course be ruled out.

Tracking molecular resonance forms of donor-acceptor push-pull molecules by single-molecule conductance experiments.

The ability of molecules to change colour on account of changes in solvent polarity is known as solvatochromism and used spectroscopically to characterize charge-transfer transitions in donor–acceptor molecules. Here we report that donor–acceptor-substituted molecular wires also exhibit distinct properties in single-molecule electronics under the influence of a bias voltage, but in absence of solvent. Two oligo(phenyleneethynylene) wires with donor–acceptor substitution on the central ring (cruciform-like) exhibit remarkably broad conductance peaks measured by the mechanically controlled break-junction technique with gold contacts, in contrast to the sharp peak of simpler molecules. From a theoretical analysis, we explain this by different degrees of charge delocalization and hence cross-conjugation at the central ring. Thus, small variations in the local environment promote the quinoid resonance form (off), the linearly conjugated (on) or any form in between. This shows how the conductance of donor–acceptor cruciforms is tuned by small changes in the environment.

ChemInform Abstract: An Efficient Three‐Component, One‐Pot Synthesis of Quinazolines under Solvent‐Free and Catalyst‐Free Condition.

An efficient green protocol for the synthesis of quinazolines in the absence of solvent and catalyst has been developed. 2,4-Disubstituted quinazolines have been synthesized from three-component one-pot reactions of 2-aminoaryl ketones, orthoesters, and ammonium acetate. The present method has advantages of operational simplicity, substrate generality, clean reaction, high yields (76–94%), and moderate reaction time. The plausible mechanism of the reaction has been proposed based on the spectral characterization and single crystal X-ray analysis of isolated intermediate.

Cross‐Dehydrogenative Coupling of Tertiary Amines and Terminal Alkynes Catalyzed by Copper Nanoparticles on Zeolite

AbstractA wide range of catalysts based on supported copper nanoparticles have been prepared and tested in the cross‐dehydrogenative coupling of tertiary amines and terminal alkynes. Copper nanoparticles on zeolite Y were found to be the most effective catalyst in the presence of tert‐butyl hydroperoxide as the oxidant. Contrary to the previously reported methodologies involving copper catalysts, reactions have been accomplished without the need of an inert atmosphere and in the absence of solvent, using 1.5 mol% catalyst. A variety of tertiary amines, including aromatic, benzylic and aliphatic ones, have been coupled with both aromatic and aliphatic alkynes to furnish the corresponding propargylamines in moderate‐to‐excellent yields. The procedure has been successfully scaled‐up to 12 mmol with a high conversion (93%). Moreover, the catalyst has been reused in seven cycles maintaining a good performance. Its catalytic activity has been compared with that of an array of commercial copper catalysts, being superior as regards the conversion and minimizing the alkyne homocoupling as a side reaction. The negative filtration test points to a heterogeneous nature of the process. Based on compelling experimental evidence, a novel reaction mechanism has been delineated which outlines the essential role of free radicals and the couple copper(I)/copper(II).magnified image

Solvent-Free Microwave-Assisted Synthesis of 2,5-Dimethoxyphenylaminotriazines

The green synthesis of asymmetric star-shaped 2,5-dimethoxyphenylamino-1,3,5-triazine derivatives using microwave irradiation in the absence of solvent is described. The title compounds have been characterized, and their properties as donor–acceptor (D–A) systems have been studied by UV–vis, fluorescence spectroscopy and electrochemical studies. The formation of excimers and the aggregation of these star-shaped triazine systems have been demonstrated.

A priori calculations of the free energy of formation from solution of polymorphic self-assembled monolayers

Modern quantum chemical electronic structure methods typically applied to localized chemical bonding are developed to predict atomic structures and free energies for meso-tetraalkylporphyrin self-assembled monolayer (SAM) polymorph formation from organic solution on highly ordered pyrolytic graphite surfaces. Large polymorph-dependent dispersion-induced substrate-molecule interactions (e.g., -100 kcal mol(-1) to -150 kcal mol(-1) for tetratrisdecylporphyrin) are found to drive SAM formation, opposed nearly completely by large polymorph-dependent dispersion-induced solvent interactions (70-110 kcal mol(-1)) and entropy effects (25-40 kcal mol(-1) at 298 K) favoring dissolution. Dielectric continuum models of the solvent are used, facilitating consideration of many possible SAM polymorphs, along with quantum mechanical/molecular mechanical and dispersion-corrected density functional theory calculations. These predict and interpret newly measured and existing high-resolution scanning tunnelling microscopy images of SAM structure, rationalizing polymorph formation conditions. A wide range of molecular condensed matter properties at room temperature now appear suitable for prediction and analysis using electronic structure calculations.

Expedient Mechanosynthesis of N,N-Dialkyl Imidazoliums and Silver(I)-Carbene Complexes in a Ball-Mill.

The absence of solvent, associated with intensive mechanical agitation, allowed the first mechanosynthesis of high-value silver(I)-carbene complexes and the corresponding N,N-dialkylimidazolium precursors. This procedure gave outstanding results in terms of yield and reaction time, when compared to solution-based conditions previously described in literature, and was generalized to unprecedented compounds. Silver(I)-carbene complexes could either be obtained from N,N-dialkylimidazolium salts or directly from imidazole and alkyl halides in a one-pot two-step procedure without isolating the imidazolium intermediate. Additionally, an efficient one-pot three-step sequence, including imidazole alkylation, silver metalation, and transmetalation is reported.

Solvent Free Synthesis of Four Cationic Surfactants: Evaluation of Their Corrosion Inhibition Properties on Zinc Phosphate Conversion Coating on Mild Steel

AbstractFour cationic surfactants have been synthesized in the absence of solvent using triethylamine and four different long chain alkyl halides. Using FTIR, 1H NMR spectra and elementary analysis the chemical structure of the synthesized surfactants were confirmed. The physio-chemical properties have been evaluated using standard analytical procedures. The corrosion inhibition properties of these four surfactants as additives were evaluated on zinc phosphate conversion coating on mild steel using nano silica as accelerator. The efficacy of the surfactants as corrosion inhibitor increases with increase in the side chain length and surface activity. With the help of X-ray diffraction (XRD), Atomic force microscope (AFM) and Scanning electron microscope (SEM) the surface morphology have been studied. The protective performance of the coatings was evaluated by salt spray exposure studies.

Solid-state synthesis of isostructural tetrachlorometallate salts of amodiaquine: crystal structure of [CdCl4][C20H24ClN3O

Tetrachlorometallate salts [AMDH2+][CoCl4]2− 1a and [AMDH2+][CdCl4]2− 2a (AMDH2+ = amodiaquine dication) were obtained by ball milling of amodiaquine with inorganic salts CoCl2·6H2O and CdCl2·6H2O, respectively, in the absence of solvent. Solution-based synthesis of [AMDH2+][CoCl4]2− 1b and [AMDH2+][CdCl4]2− 2b were also carried out by reaction of amodiaquine with the corresponding metal salts under reflux in methanol for 1 h. The analytical and spectroscopic data (IR, UV–Vis and NMR spectra) obtained for the compounds prepared via the two different routes are identical. The XPRD pattern of 1a closely matched the simulated pattern obtained from its reported single-crystal data. Single crystals of 2b suitable for X-ray structural analysis were obtained. The X-ray structure of 2b revealed an ionic compound with formula unit comprising of one protonated dicationic amodiaquine molecule and a tetrachlorocadmate(II) anion. The crystals are triclinic with space group P-1 and unit dimensions a = 9.3272(8) A, b = 11.1418(9) A, c = 12.482(10) A, V = 1191.89 A3, and Z = 2. The amodiaquine molecule is protonated both at the quinoline and quinuclidine nitrogen atom. Antimalarial efficacy of 1a on Plasmodium berghei-infected mice were investigated, and the results revealed an enhanced activity of the compound by significantly (p < 0.05) improving the suppression of parasitemia in established infection when compared with the controls.

Structure and dynamics of a protein-surfactant assembly studied by ion-mobility mass spectrometry and molecular dynamics simulations.

The structure and dynamics of a protein-surfactant assembly studied by ion-mobility mass spectrometry (IMS) and vacuum molecular dynamics (MD) simulations is reported. Direct evidence is provided for the ability of the surfactant dodecyl-β-D-maltoside (DDM) to prevent charge-induced unfolding of the membrane protein (PagP) in the gas-phase. Restraints obtained by IMS are used to map the surfactant positions onto the protein surface. Surfactants occupying more exposed positions at the apexes of the β-barrel structure are most in-line with the experimental observations. MD simulations provide additional evidence for this assembly organization through surfactant inversion and migration on the protein structure in the absence of solvent. Surfactant migration entails a net shift from apolar membrane spanning regions to more polar regions of the protein structure with the DDM molecule remaining attached to the protein via headgroup interactions. These data provide evidence for the role of protein-DDM headgroup interactions in stabilizing membrane protein structure from gas-phase unfolding.

Synthesis of 2H-indazolo[2,1-b]phthalazine-1,6,11(13H)-triones using 1,4-disulfo-1,4-diazabicyclo[2.2.2]octane-1,4-diium dihydrogen sulfate {DABCO(HSO3)2(HSO4)2} as a new ionic liquid catalyst

1,4-Disulfo-1,4-diazabicyclo[2.2.2]octane-1,4-diium dihydrogen sulfate {DABCO(HSO3)2(HSO4)2} as a new ionic liquid, is prepared and characterized by using different methods including FT-IR, NMR, Mass and SEM analysis as well as determination of the Hammett acidity function. This reagent can be used as an efficient catalyst for the promotion of the synthesis of 2H-indazolo[2,1-b]phthalazine-1,6,11(13H)-trione derivatives as important biologically active compounds with pharmaceutical properties. All reactions are performed in the absence of solvent using small amounts of the catalyst. Easy preparation of the catalyst, simple and easy work-up, mild reaction conditions, green process, excellent yields and short reaction times are the most important advantages this of method.

Poly(vinylpyrrolidinium) perchlorate as a new and efficient catalyst for the promotion of the synthesis of polyhydroquinoline derivatives via Hantzsch condensation

A green approach for the promotion of the synthesis of Hantzsch products using poly(vinylpyrrolidinium) perchlorate {[PVPH]ClO4} as a new modified polymeric catalyst in the absence of solvent is reported. The title catalyst is easily prepared and characterized using a variety of techniques including infrared spectra, X-ray diffraction, thermal gravimetric analysis, scanning electron microscopy, pH analysis, and Hammett acidity function. Some of the advantages of this novel synthetic method are: easy preparation of the catalyst, short reaction times, high to excellent yields of the products, simple and easy work-up procedure, and reusability of the catalyst.

Solvent Control of Surface Plasmon-Mediated Chemical Deposition of Au Nanoparticles from Alkylgold Phosphine Complexes.

Bottom-up approaches to nanofabrication are of great interest because they can enable structural control while minimizing material waste and fabrication time. One new bottom-up nanofabrication method involves excitation of the surface plasmon resonance (SPR) of a Ag surface to drive deposition of sub-15 nm Au nanoparticles from MeAuPPh3. In this work we used density functional theory to investigate the role of the PPh3 ligands of the Au precursor and the effect of adsorbed solvent on the deposition process, and to elucidate the mechanism of Au nanoparticle deposition. In the absence of solvent, the calculated barrier to MeAuPPh3 dissociation on the bare surface is <20 kcal/mol, making it facile at room temperature. Once adsorbed on the surface, neighboring MeAu fragments undergo ethane elimination to produce Au adatoms that cluster into Au nanoparticles. However, if the sample is immersed in benzene, we predict that the monolayer of adsorbed solvent blocks the adsorption of MeAuPPh3 onto the Ag surface because the PPh3 ligand is large compared to the size of the exposed surface between adsorbed benzenes. Instead, the Au-P bond of MeAuPPh3 dissociates in solution (Ea = 38.5 kcal/mol) in the plasmon heated near-surface region followed by the adsorption of the MeAu fragment on Ag in the interstitial space of the benzene monolayer. The adsorbed benzene forces the Au precursor to react through the higher energy path of dissociation in solution rather than dissociatively adsorbing onto the bare surface. This requires a higher temperature if the reaction is to proceed at a reasonable rate and enables the control of deposition by the light induced SPR heating of the surface and nearby solution.

Gas Phase Studies of N-Heterocyclic Carbene-Catalyzed Condensation Reactions.

N-Heterocyclic carbenes (NHCs) catalyze Umpolung condensation reactions of carbonyl compounds, including the Stetter reaction. These types of reactions have not heretofore been examined in the gas phase. Herein, we explore the feasibility of examining these reactions in the absence of solvent. A charge-tagged thiazolylidene catalyst is used to track the reactions by mass spectrometry. We find that the first Umpolung step, the addition of the NHC catalyst to a carbonyl compound to form the "Breslow intermediate", does not readily proceed in the gas phase, contrary to the case in solution. The use of acylsilanes in place of the carbonyl compounds appears to solve this issue, presumably because of a favorable Brook rearrangement. The second addition reaction, with enones, does not occur under our gas phase conditions. These reactions do occur in solution; the differential reactivity between the condensed and gas phases is discussed, and calculations are used to aid in the interpretation of the results.

PERFORMANCE OF LOOFA-IMMOBILIZED Rhizopus oryzae IN THE ENZYMATIC PRODUCTION OF BIODIESEL WITH USE OF OLEIC ACID IN n-HEXANE MEDIUM

The performance of loofa-immobilized Rhizopus oryzae (as a whole-cell biocatalyst) in the synthesis of methyl oleate was evaluated using oleic acid as a model substrate. The activities of the cell-bound lipase in terms of the esterification and hydrolysis reactions were found to be higher for the immobilized cells as compared with those of the free cells. The time to reach equilibrium for methyl oleate synthesis was 12 h in the presence of n-hexane (hexane:oleic acid ratio 9:1(v/v)), and the yield was 80%. In the absence of solvent, equilibrium was reached after 48 h and the yield was only 30%. The moisture repellency and the hydrophilic properties of loofa sponge make this natural fiber a good candidate for cell-enzyme immobilization, especially for lipases as the interfacial enzyme.

On the C60 Fullerene Adduct with Pentacene: Synthesis and Stability

C60 fullerene and pentacene were reacted under mild conditions in toluene, yielding the monoadduct, which was characterized by electronic absorption and Fourier transform infrared (FT-IR) spectroscopy. The C60/pentacene adduct was studied by thermogravimetric analysis and its experimental composition was found in line with the theory for a 1:1 molar adduct. The decomposition temperature of the C60/pentacene monoadduct was found to be 404°C. The decomposition implies a retro Diels–Alder reaction, yielding back C60, which was recognized by FT-IR spectroscopy, while pentacene underwent decomposition and vaporization at 404°C. When an equimolar mixture of C60 and pentacene was heated in a differential scanning calorimeter in absence of solvents, the formation of monoadduct occurred at 380°C, but above 400°C it was decomposed back to reactants.