Terminal OH Research Articles

31] Direct sizing of RNA fragments using RNase-generated standards

Publisher Summary Electrophoretic migration of RNA is affected by its terminal OH or P character to a sizable and variable extent, considerably more than is DNA. If not accounted for when sizing RNA, errors of up to two nucleotides can arise, even when using sequencing ladders prepared from RNA with the same sequence. Many cellular cleavage events of interest generate 3′-OH termini, yet these termini are not formed when using the standard methods of preparing RNA sequencing ladders, which all generate 2′,3′-cyclic P and 5′-OH termini. Fortunately, conditions have been found in which nuclease P1 cleaves in a highly G-specific manner and different conditions in which it cleaves in an A-preferential manner, allowing convenient preparation of the desired sequencing ladders. The key to accurate RNA size determination is to select appropriate marker ladders that not only are from the same sequence RNA but also have comparable termini. Cleavage agents commonly used to generate such ladders are sequence-specific RNases, including RNase T1 (which cleaves after G residues) and RNase A (which cleaves after C and U residues), and alkali, which cleaves after any residue.

EPR probes with well-defined, long distances between two or three unpaired electrons

The synthesis of rod- and star-shaped compounds carrying two or three spin labels as end groups is described. The unpaired electrons are 2.8-5.1 nm apart from each other. The shape-persistent scaffolds were obtained through Pd-Cu-catalyzed alkynyl-aryl coupling and Pd-Cu-catalyzed alkyne dimerization in the presence of oxygen using p-phenyleneethynylene as the basic shape-persistent building block. The spin label 1-oxyl-2,2,5,5-tetramethylpyrroline-3-carboxylic acid (4) was attached through esterification of the terminal phenolic OH groups of the scaffold.

Interfacial compositions of cationic and mixed non-ionic micelles by chemical trapping: a new method for characterizing the properties of amphiphilic aggregates

A specially synthesized arenediazonium ion bound to amphiphilic aggregates decomposes spontaneously via rate determining loss of N 2 to give a highly reactive, unselective, aryl cation intermediate. This intermediate is trapped competitively by weakly basic nucleophiles in the interfacial region of aggregates such as micelles and other association colloids. Product yields, analyzed by HPLC with UV detection, are used to estimate, simultaneously, the interfacial concentrations of a number of different nucleophiles, including water, that are commonly found at the surfaces of biomembranes and in many commercial products. Two applications of the method are discussed. First, we show that the interfacial concentrations of X − ( X=Br, Cl) increase steadily with increasing cetyltrimethylammonium halide (CTA X) and tetramethylammonium halide (TMA X) concentrations and that the interfacial concentrations of these counterions increase continuously with their aqueous phase concentrations at a constant degree of micelle ionization. Interfacial Br − and Cl − concentrations also show marked increases at their respective sphere-to-rod transitions. This steady increase in interfacial counterion concentration with increasing aqueous counterion concentration contradicts a basic assumption of the pseudophase ion exchange (PIE) model of chemical reactivity in aggregates, i.e. that the total concentrations of ions at aggregate interfaces is constant and independent of the amphiphile and salt concentrations. The consequences for the PIE model are discussed. Second, the chemical trapping reaction is used to estimate: (a) distributions of terminal OH groups of non-ionic amphiphiles in mixed non-ionic micelles composed of amphiphiles with different lengths of oligoethylene oxide chains and (b) hydration numbers of the inner layers of interfacial region next to the hydrocarbon core in these mixed micelles. Terminal OH groups distributions are well fitted by a radial one-dimensional random walk model. The average hydration number for the inner layers at 40°C is about 3, in agreement with estimates from NMR water (D 2O) self-diffusion measurements and with the hydration number of 3 for aqueous solutions of polyethylene oxide. The results suggest that the hydration states of the ethylene oxide (EO) units near the micellar core are near their minimum value. Recent and potential applications of the chemical trapping method are briefly discussed.

Immobilization of DNA on Self-Assembled Monolayer

We attempted the immobilization of DNA onto self-assembled monolayer (SAM) which contains the intercalated for DNA. Anthryl moieties were attached to the terminal OH groups in SAM of 1-Mercapt-11-undecanol (MU-SAM) by esterification. In the case of the SAM containing anthryl moieties (Anth-SAM), surface plasmon resonance measurement indicates that the adsorption of DNA onto the SAM was observed in an aqueous DNA solution, and the DNA remained on the surface even after rinsing. Although the adsorption of DNA onto MU-SAM was also observed, little DNA remained on the SAM after rinsing. These results indicate that the anthracene which was attached to the SAM can interact with DNA because the binding ability was increased by introduction of anthracene moieties to the SAM.

Arenediazonium Salts: New Probes of the Compositions of Association Colloids. 7. Average Hydration Numbers and Cl- Concentrations in the Surfactant Film of Nonionic C12E5/Octane/Water Macroemulsions: Temperature and NaCl Concentration Effects

A surface-active arenediazonium ion, 4-hexadecyl-2,6-dimethylbenzenediazonium ion, 16-ArN2+, was used as a chemical trapping probe of the concentrations of weakly basic nucleophiles in the surfactant film between the aqueous and oil domains of opaque relatively long-lived C12E5/octane/water macroemulsions as a function of temperature and added NaCl. The results demonstrate that the chemical trapping method “sees” the composition of the oligooxyethylene or interfacial layer on the aqueous side of the surfactant film. Product yields from trapping of the available nucleophiles, H2O, the terminal OH group of C12E5, and Cl-, were used to estimate average hydration numbers of all aggregates present in the macroemulsions as a function of increasing temperature and added NaCl. At 19.9 °C, the average hydration number in the macroemulsions is 2.5, compared to a 70% larger value of 4.2 in C12E6 micelles at 20 °C obtained previously by chemical trapping. Average hydration numbers decrease with increasing temperature...

The synthesis and crystal structure of two novel 3D open-framework zinc phosphates UiO-21 and UiO-22

Two open-framework zinc phosphate materials denoted by UiO-21 and UiO-22 have been prepared by hydrothermal methods and characterised by single crystal X-ray diffraction. UiO-21, Zn 7(PO 4) 6N 6C 12H 34, crystallises in the trigonal space group R-3 (No. 148) with a=13.7249(2) Å, c=15.3316(1) Å, V=2501.13(5) Å 3 and Z=3. The structure has the zeolite topology CHA with double six-ring units stacked in an AABBCC stacking sequence. At the centre of each double six-ring unit there is a zinc atom octahedrally coordinated to six out of the 12 oxygen atoms in the unit. Each cage of the structure contains two 1-(2-aminoethyl)piperazine molecules, each of which being disordered over three positions around the trigonal axis. Each molecule is doubly protonated to compensate for the negative charge of the zinc phosphate framework. There are no hydrogen bonding interactions between the organic templates and the inorganic framework. UiO-22, Zn 4(PO 4) 3(OH)N 3C 6H 17, crystallises in the triclinic space group P-1 with a=5.2697(1) Å, b=12.1400(2) Å, c=13.9161(3) Å, α=115.439(1)°, β=98.392(1)°, γ=91.157(1)°, V=791.91(3) Å 3 and Z=2. The structure consists of vertex sharing PO 4 and ZnO 4 tetrahedra and is of the interrupted type by having terminal Zn–OH bonds and trigonally coordinated oxygen atoms. The structure can be viewed as built from columns of edge-sharing three and four rings running along [1 0 0] which interconnects into a framework exhibiting a two-dimensional eight and 12-ring channel system. Terminal OH groups are located in the staggered eight-ring channel running along [0 0 1]. In the 12-ring channel running along [1 0 0] there are highly disordered organic templates, probably 1-(2-aminoethyl)piperazine molecules that are doubly protonated in order to compensate for the negative charge of the zinc phosphate framework. The disordered nature of the organic templates in UiO-21 and UiO-22 indicates that the organic molecules play the role as space fillers in the crystallisation of these phases.

On the problem of differentiation of acetone adsorption species on the silica gel: molecular models of adsorption complexes

In the framework of the cluster approach ab initio calculations of the adsorption complexes of acetone molecule with an isolated terminal OH group of a silica gel (S1), with the fragment including hydrogen-bonded OH group (S2) and with two separated terminal OH groups simulating bifurcated acetone interaction (S3) were carried out. It is found that the difference between the stability of acetone complexes S1 and S2 is insignificant, and it is concluded that the bifurcated acetone interaction could result in a more stable adsorption form of acetone with the silica gel.

Recognition of alpha-amino acids bearing various C=NOH functions by nitric oxide synthase and arginase involves very different structural determinants.

Several alpha-amino acids bearing a C=NOH function separated from the Calpha carbon by two to five atoms have been synthesized and tested as substrates or inhibitors of recombinant nitric oxide synthases (NOS) I and II and as inhibitors of rat liver arginase (RLA). These include four N-hydroxyguanidines, N(omega)-hydroxy-L-arginine (NOHA) and its analogues homo-NOHA, nor-NOHA, and dinor-NOHA, two amidoximes bearing the -NH-C(CH(3))=NOH group, and two amidoximes bearing the -CH(2)-C(NH(2))=NOH group. Their behavior toward NOS and RLA was compared to that of the corresponding compounds bearing a C=NH function instead of the C=NOH function. The results obtained clearly show that efficient recognition of these alpha-amino acids by NOS and RLA involves very different structural determinants. NOS favors molecules bearing a -NH-C(R)=NH motif separated from Calpha by three or four CH(2) groups, such as arginine itself, with the necessary presence of delta-NH and omega-NH groups and a more variable R substituent. The corresponding molecules with a C=NOH function exhibit a much lower affinity for NOS. On the contrary, RLA best recognizes molecules bearing a C=NOH function separated from Calpha by three or four atoms, the highest affinity being observed in the case of three atoms. The presence of two omega-nitrogen atoms is important for efficient recognition, as in the two best RLA inhibitors, N(omega)-hydroxynorarginine and N(omega)-hydroxynorindospicine, which exhibit IC(50) values at the micromolar level. However, contrary to what was observed in the case of NOS, the presence of a delta-NH group is not important. These different structural requirements of NOS and RLA may be directly linked to the position of crucial residues that have been identified from crystallographic data in the active sites of both enzymes. Thus, binding of arginine analogues to NOS particularly relies on strong interactions of their delta-NH and omega-NH(2) groups with glutamate 371 (of NOS II), whereas binding of C=NOH molecules to RLA is mainly based on interactions of their terminal OH group with the binuclear Mn(II).Mn(II) cluster of the enzyme and on possible additional bonds between their omega-NH(2) group with histidine 141, glutamate 277, and one Mn(II) ion. The different modes of interaction displayed by both enzymes depend on their different catalytic functions and give interesting opportunities to design useful molecules to selectively regulate NOS and arginase.

HREELS, TPD and XPS study of the interaction of water with the α-Cr 2O 3(001) surface

The interaction of water with the (001) surface of α-Cr 2O 3 was examined with temperature programmed desorption (TPD), high resolution electron energy-loss spectroscopy (HREELS) and X-ray photoelectron spectroscopy (XPS). Two α-Cr 2O 3(001) surfaces were examined, both of which were grown on α-Al 2O 3(001) substrates using oxygen plasma-assisted molecular beam epitaxy (MBE). The two surfaces differed in that one was grown with α-Fe 2O 3 interlayers whereas the other was grown directly on α-Al 2O 3(001). The in-plane lattice spacing of the α-Cr 2O 3(001) surface on α-Fe 2O 3/α-Al 2O 3(001) was 2% expansively strained relative to the unstrained α-Cr 2O 3(001) surface grown directly on α-Al 2O 3(001). Both the strained and unstrained surfaces exhibited similar water TPD behavior, with the possible exception that the desorption states of water on the strained surface were shifted slightly to lower temperatures relative to those on the unstrained surface. Water adsorbs on α-Cr 2O 3(001) in both molecular and dissociative states, with the former desorbing in TPD at 295 K and the latter at 345 K. TPD uptake measurements and XPS data suggest that each surface Cr 3+ atom has the capacity to bind two water molecules, one in a molecular state and one in a dissociative state. Water in the dissociative state is comprised of two distinct OH groups based on HREELS, one of which is a terminal group with a ν(OH) mode at 3600 cm −1 and the other of which is presumably a bridging group with a ν(OH) mode at 2885 cm −1. These losses shift to 2645 and 2120 cm −1 with D 2O adsorption. The low loss energy for the bridging OH/OD group indicates its involvement in a very strong hydrogen-bonded interaction with another species, presumably the oxygen atom of the terminal OH group. This pairing behavior is likely responsible for the first-order desorption kinetics observed for the recombinative desorption state at 345 K. The hydrogen-bonding interaction is unusually strong, as exemplified by the very low ν(OH) frequency for the bridging OH group. Studies on the oxygen pre-exposed surface indicate that oxygen atoms, formed by O 2 dissociation, block the H 2O dissociative channel but do not block the molecular adsorption channel.

Preparation and structure of the 17-electron (η 5-C 5R 5)Mo(OH) 2(dppe) (R=Me, Et) organometallic compounds containing two gem-terminal hydroxide ligands

Oxidation of (η 5-C 5R 5)MoH 3(dppe) (R=Me, Et) by Cp 2Fe + in wet THF leads to the formation of the corresponding (η 5-C 5R 5)Mo(OH) 2(dppe). These compounds show a low-potential reversible oxidation wave. The structure of the C 5Et 5 complex has been confirmed by X-ray diffraction methods: triclinic; space group P 1 ̄ ; a=11.030(1); b=12.533(1); c=16.241 (1) Å; α=68.585(7); β=75.197(5); γ=83.991(7)°; V=2020.6(3) Å 3; Z=2; D calc=1.324 g cm −3, μ(Mo–K α )=0.441 mm −1; R 1=0.0325; wR 2=0.0875 for 415 parameters and 6823 independent reflections [ R int=0.0177] with I=2 σ( I). The molecule shows a four-legged piano-stool geometry with two terminal OH ligands in a relative trans configuration. The complex EPR properties indicate that an equilibrium mixture of various species is present in solution.

Aminoacylation at the Atomic Level in Class IIa Aminoacyl-tRNA Synthetases

The crystal structures of histidyl- (HisRS) and threonyl-tRNA synthetase (ThrRS) from E. coli and glycyl-tRNA synthetase (GlyRS) from T. thermophilus, all homodimeric class IIa enzymes, were determined in enzyme-substrate and enzyme-product states corresponding to the two steps of aminoacylation. HisRS was complexed with the histidine analog histidinol plus ATP and with histidyl-adenylate, while GlyRS was complexed with ATP and with glycyl-adenylate; these complexes represent the enzyme-substrate and enzyme-product states of the first step of aminoacylation, i.e. the amino acid activation. In both enzymes the ligands occupy the substrate-binding pocket of the N-terminal active site domain, which contains the classical class II aminoacyl-tRNA synthetase fold. HisRS interacts in the same fashion with the histidine, adenosine and α-phosphate moieties of the substrates and intermediate, and GlyRS interacts in the same way with the adenosine and α-phosphate moieties in both states. In addition to the amino acid recognition, there is one key mechanistic difference between the two enzymes: HisRS uses an arginine whereas GlyRS employs a magnesium ion to catalyze the activation of the amino acid. ThrRS was complexed with its cognate tRNA and ATP, which represents the enzyme-substrate state of the second step of aminoacylation, i.e. the transfer of the amino acid to the 3′-terminal ribose of the tRNA. All three enzymes utilize class II conserved residues to interact with the adenosine-phosphate. ThrRS binds tRNAThr so that the acceptor stem enters the active site pocket above the adenylate, with the 3′-terminal OH positioned to pick up the amino acid, and the anticodon loop interacts with the C-terminal domain whose fold is shared by all three enzymes. We can thus extend the principles of tRNA binding to the other two enzymes.

Effects of water and ion-exchanged counterion on the FTIR spectra of ZSM-5. I. NaH-ZSM-5:: H-bonding with OH groups of zeolite and formation of H +(H 2O) n

A dried (773 K, Ar, 1 h) NaH-ZSM-5 sample (Si/Al = 20, Na/Al = 0.5) showed two sharp O–H vibrations at 3745 cm −1 (SiOH, terminal OH) and at 3612 cm −1 [Si(OH)Al, bridged OH], a weak, wide band at 3300–3200 cm −1 due to H-bonded OH and three characteristic (T–O–T) vibrations at 1268, 975 and 834 cm −1 due to external asymmetric ( ν as ext), internal asymmetric ( ν as int) and internal symmetric ( ν sym int) stretching lattice vibrations, respectively. The value of 975 cm −1 obtained here for the charge-sensitive ν as int of the ZSM-5, was in good accordance with earlier results gained for bare Cu +, Cu +–CO or Cu 2+ containing ZSM-5. The broadening of the 975 cm −1 band to 1010–990 cm −1 indicated an incomplete ion-exchange of H + by Na + obtained during the preparation of NaH-ZSM-5 from H-ZSM-5. Depending on the amount, water markedly influenced almost the whole FTIR spectra of NaH-ZSM-5, increasing more or less the intensities of the ν as ext, ν as int and ν sym int bands. At high H 2O concentration, the H 2O ligands in the aquacomplex completely screened the positive charge of Na + ions. As a result, the perturbation effect on ν as int disappeared, since ν as int blueshifted to 1010 cm −1. Strongly H-bonded interactions with Fermi resonance and the formation of H +(H 2O) n was highly suggested by the FTIR spectra at medium and high concentration of H 2O, respectively. Even at higher temperatures, a part of silanol OH groups revealed unusually strong interactions with H 2O molecules retained probably by the Na + cations. The 880 cm −1 band attributed to out-of-plane OH bending mode and the ν as int and ν sym int bands varied in relation to each other, in three different stages.

Synthesis and characterisation of main-chain oligomeric cyclopalladated azobenzene complexes

In this paper we report the synthesis of main-chain oligomeric cyclopalladated azobenzene complexes. The approach we followed was focused on the synthesis of difunctional azo-ligands substituted properly with terminal polymerisable OH groups, synthesis of cyclopalladated monomers and polycondensation reaction with acid chlorides as comonomers. In this way, using the interfacial method, two soluble cyclopalladated oligomers P1 and P2 were synthesised.

Conceptually new sulfone analogues of the hormone 1alpha, 25-dihydroxyvitamin D(3): synthesis and preliminary biological evaluation.

A conceptually new series of vitamin D(3)-like nonfluorinated and fluorinated 16-ene side chain tert-butyl sulfones 3-7 has been synthesized. Even though these novel C,D-ring side chain analogues of the hormone 1alpha,25-dihydroxyvitamin D(3) (1,1,25D(3)) lack a terminal OH group, thought previously to be essential for high biological activity, they are highly antiproliferative and, in several cases, transcriptionally active in vitro but desirably noncalcemic in vivo. The side chain sulfone group may be binding to the nVDR as a hydrogen-bond acceptor, in contrast to the hydrogen-bond donor function of the 25-OH group of natural 1,25D(3).

Isolation and characterization of novel neutral glycolipids from Thermoplasma acidophilum

Several novel neutral glycolipids (GL-1a, GL-1b, GL-2a, GL-2b and GL-2c) were isolated from Thermoplasma acidophilum by high-performance liquid chromatography using phenylboronic acid-silica and preparative thin-layer chromatography. The tentative structures of these lipids were characterized by the combination of gas–liquid chromatography, the methylation procedure, and 1H-NMR and FAB-mass spectrometries. The lipophilic portion of the neutral glycolipids was composed of a simple molecular species named caldarchaeol (dibiphytanyl-diglycerol tetraether). The sugar moieties of these glycolipids were composed of gulose and glucose which formed monosaccharide residues on one side or both sides of the core lipids. Gulose was attached to the terminal glycerol OH group of the core lipid with a β-configuration and glucose being attached with an α-configuration. The proposed structure of GL-1a was gulosylcaldarchaeol and that of GL-1b was glucosylcaldarchaeol. The structures of GL-2a, GL-2b, and GL-2c were the analogs of the caldarchaeol derivatives attached by a variety of gulosyl residues or glucosyl residues on both sides of the terminal OH groups.

Ion−Oligomer Interactions in Poly(ethylene glycol)400/(LiCl)x Electrolyte Complexes

By reacting metallic lithium with 1-chlorobutane we obtained a very anhydrous LiCl that allowed us to prepare 10 poly(ethylene glycol)/(LiCl)x complexes (0≤ x ≤ 1.40665) using a reaction protocol that does not require added solvents. The interactions between Li+ and Cl- ions and poly(ethylene glycol) (PEG) ligands in the polymer electrolytes were investigated by mid and far FT-IR spectroscopy. Results revealed that (a) the PEG chains assume a TGT type conformation; (b) Li+ ions are coordinated by ethereal oxygens of the PEG ligand; (c) at an Li/O molar ratio less than 0.036, Cl- ions form hydrogen bonding cages with the terminal OH groups of PEG chains; (d) at an Li/O molar ratio greater than 0.036, Cl- ions are present both in hydrogen bonds and as “free anions” along PEG chains. Conductivity measurements made at different temperatures showed that these systems conduct ionically, with two distinct conductivity regions detected. The possible correlation between the conductivity and the structure of these ...

Fluoropolyethers end-capped by polar functional groups. I. Kinetic approach to the reaction of hydroxy-terminated fluoropolyethers with cycloalyphatic and aromatic diisocyanates

Urethane reactions of cycloaliphatic and aromatic diisocyanates with hydroxy-terminated fluoropolyethers (FPEs) of various molecular weights and structure, at NCO : OH = 2, have been studied by monitoring, by IR analysis, the rate of decrease in NCO absorbance at 2264–2268 cm−1. Different diisocyanates have been tested, among them the following: 4,4′-dicyclohexylmethane diisocyanate (H12MDI); 5-isocyanato-1,3,3-trimethylcyclohexylmethyl isocyanate or isophorone diisocyanate (IPDI); 2,4-toluene diisocyanate (TDI). Ethyl acetate (EA), methyl isobutyl ketone (MIBK), and hexafluoroxylene (HFX) have been used as solvents in presence of dibutyltin dilaurate (DBTDL) or 1,4-diazabicyclo[2.2.2]octane (DABCO) as catalysts. These reactions gave rise to NCO-end-capped FPE–oligourethanes. Preliminary solubility tests for HO-terminated FPEs in various solvents made it possible to select proper candidates for carrying out reaction in homogeneous conditions at high concentrations of reagents (30–50% w/w). The second-order kinetic mechanism was shown to be valid. Positive deviations from linearity for the second-order kinetics around 40–80% conversion, found for most of the FPE diols, were attributed to the autocatalysis of the isocyanate–hydroxyl reaction by the arising urethane groups. Uncatalyzed reactions with cycloaliphatic diisocyanates are very slow at 40°C. The tertiary amine DABCO is a much less effective catalyst than DBTDL. FPEs having terminal OH groups separated from the perfluorinated main molecular chain by (OCH2CH2)n segments (n = 1–2) are generally more reactive than FPEs with end CH2OH groups. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 557–570, 1999

Fluoropolyethers end‐capped by polar functional groups. I. Kinetic approach to the reaction of hydroxy‐terminated fluoropolyethers with cycloalyphatic and aromatic diisocyanates

Urethane reactions of cycloaliphatic and aromatic diisocyanates with hydroxy-terminated fluoropolyethers (FPEs) of various molecular weights and structure, at NCO : OH = 2, have been studied by monitoring, by IR analysis, the rate of decrease in NCO absorbance at 2264–2268 cm−1. Different diisocyanates have been tested, among them the following: 4,4′-dicyclohexylmethane diisocyanate (H12MDI); 5-isocyanato-1,3,3-trimethylcyclohexylmethyl isocyanate or isophorone diisocyanate (IPDI); 2,4-toluene diisocyanate (TDI). Ethyl acetate (EA), methyl isobutyl ketone (MIBK), and hexafluoroxylene (HFX) have been used as solvents in presence of dibutyltin dilaurate (DBTDL) or 1,4-diazabicyclo[2.2.2]octane (DABCO) as catalysts. These reactions gave rise to NCO-end-capped FPE–oligourethanes. Preliminary solubility tests for HO-terminated FPEs in various solvents made it possible to select proper candidates for carrying out reaction in homogeneous conditions at high concentrations of reagents (30–50% w/w). The second-order kinetic mechanism was shown to be valid. Positive deviations from linearity for the second-order kinetics around 40–80% conversion, found for most of the FPE diols, were attributed to the autocatalysis of the isocyanate–hydroxyl reaction by the arising urethane groups. Uncatalyzed reactions with cycloaliphatic diisocyanates are very slow at 40°C. The tertiary amine DABCO is a much less effective catalyst than DBTDL. FPEs having terminal OH groups separated from the perfluorinated main molecular chain by (OCH2CH2)n segments (n = 1–2) are generally more reactive than FPEs with end CH2OH groups. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 557–570, 1999

Heterogenizing Homogeneous Catalysis Using Molecular Self-Assembly of Long Alkane Chain Phosphines Bound to Rh(I) Complexes

Long alkane chain hydrocarbons terminated with OH and PPh2 groups, HO−(CH2)n−PPh2 (n = 10−12) were self-assembled on inorganic oxide surfaces via acid−base hydrolysis of surface-anchored [Si]−NEt2 groups with terminal OH moieties and subsequently used to covalently anchor Rh(I) complexes. Similar thin films can also be prepared from [Si]−NEt2 and RhCl(1,5-C8H12)[PPh2(CH2)nOH]. The functionalized surfaces were characterized using solid-state NMR, contact angle goniometry, ellipsometry, X-ray photoelectron spectroscopy, and FT-IR. The self-assembled organometallic thin films were found to be highly active in catalyzing hydrogenation of tolan. Surface-bound Rh(I) catalyst is stable and can be recycled, while the homogeneous analogue decomposes under similar catalytic reaction conditions.

Arenediazonium Salts: New Probes of the Interfacial Compositions of Association Colloids. 5.1−4 Determination of Hydration Numbers and Radial Distributions of Terminal Hydroxyl Groups in Mixed Nonionic CmEn Micelles by Chemical Trapping

An aggregate-bound long tail arenediazonium ion, 4-hexadecyl-2,6-dimethylbenzenediazonium ion, 16-ArN2+, was used as a chemical trapping reagent to estimate the hydration state and terminal hydroxyl, OH, group distributions within the interfacial region of sets of binary mixed nonionic micelles of oligooxyethylene alkyl monoether, CmEn, surfactants: C10E4/C12E6, C10E4/C16E8, C10E5/C16E8, C12E6/C16E8, and C10E5/C12E5. 16-ArN2+ decomposes spontaneously to generate an aryl cation that is trapped by water and by the terminal OH groups of the two nonionic surfactants to give phenol and alkyl aryl ethers as products. Quantitative analyses of product yields by HPLC were used to estimate the hydration numbers and relative number densities of the terminal OH groups of the two surfactants in the two inner layers of the interfacial region adjacent to the micellar core. The thickness of one layer is set equal to the length of one ethylene oxide unit. The radial distributions of terminal OH groups and ethylene oxide units in the mixed micelles are described by using a simple radial one-dimensional random walk model without adjustable parameters. The calculated ratios of terminal OH groups in the two inner layers are in excellent agreement with those obtained from experimental product yields. The calculated hydration numbers of the inner two layers ranged between 1.8 and 3.5, depending upon oligooxyethylene chain length, mixed micelle composition, and temperature. The average hydration number of the inner two layers is about 3 at 18 °C.