Condensation Agent Research Articles

Preparation of Polyarylates from Dihydroxyaceto-phenones by the Solution Polycondensation with TsCl/DMF/Py as a Condensing Agent

The polyesterification of a mixture of equal parts of isophthalic and terephthalic acids with 2,4-dihydroxybenzophenone (2,4-DHBP) and several dihydroxyacetophenones (DHAPs), from which polyesters of high molecular weight have not been prepared, was studied. Based on favorable results of two-stage copolycondensation with bisphenols first and then with 2,4-DHBP, factors such as dropwise addition of DHAPs, mol-% of them used in the initial stage, and the temperature in the subsequent stage were examined in a two-stage polycondensation. Favorable results were obtained by longer period of addition, initial reaction of 50–70 mol-%, and lowering the temperature to 60°C. The relationship between the temperature and the distribution of resulting oligomers determined by GPC was also examined. The copolymers obtained exhibited the glass transition temperatures and polymer melting points in the ranges of 165–183°C and of 280–310°C, respectively. Most of them were soluble in DMF, chloroform, cyclohexanone, and THF.

Hyperbranched Aromatic Polyamides Prepared by Direct Polycondensation

Hyperbranched aromatic polyamides and copolymers were prepared by direct polycondensation in the presence of condensation agents. Three strategies were described: (1) self-polycondensation of AB x-type monomers, (2) copolymerization of AB2 and AB monomers and (3) polymerization of A2 and B3 monomers. The self-polycondensation of AB x monomers proceeded without gelation to form soluble powdery polymers. The degree of branching of the hyperbranched polyamides was greatly influenced by the structure of the monomers. Copolymerization of AB2 and AB monomers allowed control of the branching density of the resulting polymers. Spectroscopic measurements revealed that the copolymers were composed of five kinds of repeating units. The good solubility and adequate solution viscosity of the copolymers allowed the preparation of transparent yellow films by casting the copolymer solution onto a glass plate. The polymerization of A2 and B3 monomers was also investigated as a novel route to prepare hyperbranched polyamides without using AB x-type monomers. Gelation during the polymerization could be avoided by the optimization of the reaction conditions. The structure and properties of the resulting polymers were compared with the hyperbranched polyamide prepared from the corresponding AB2 monomer.

Phosphodiester and phosphorothioate oligonucleotide condensation and preparation of antisense nanoparticles

Protamine is a cationic peptide with a molecular mass of approx. 4000 Da that is able to condense DNA. In the present study it was used to complex antisense oligonucleotides (ODNs) and to form solid particles with initial diameters of 90–150 nm. The reaction was very rapid and occurred by simple mixing of diluted solutions of the polycation with the oligonucleotide. The aggregation was dependent on the oligonucleotide chain length and the protamine/ODN mass ratio. Particle formation required a minimal chain length of nine nucleotides and a mass ratio of 0.5:1. The particle surface charge and the number of particles depended on the mass ratio. With increasing amounts of the peptide, the number of particles and the ζ potential increased. Both negatively and positively charged particles improved the stability of oligonucleotides against DNase I digestion. Above a mass ratio of 2.5:1 no degradation was found. The uptake of unbound rhodamine-labelled ODNs and its complexes with protamine was determined with Vero cells under in vitro cell culture conditions at 37°C and 4°C. At 37°C the cellular uptake increased with increasing mass ratio. The internalized oligonucleotides were localized in the cytoplasm and in the nucleus of the cells. When Vero cells were treated with these samples at 4°C for 4 h, no fluorescence could be detected inside the cells. Therefore, our data indicate an energy dependent endocytotic uptake mechanism. In contrast, spermine and spermidine, which are also known condensation agents, did not aggregate with oligonucleotides into nanoparticles under the same conditions.

Semicrystalline Polyimides Starting from AB-Type Monomers

AB-type isomeric mixture of m- and p-monomethyl 4-(4‘-aminophenoxy)phthalate (I) and its pure m-monomethyl ester isomer (II) were successfully synthesized from 4-nitrophenol and 4-nitrophthalonitrile. The polyimide was prepared via a two-step method in which the direct polycondensation reactions were carried out in N-methylpyrrolidone (NMP) in the presence of diphenyl(2,3-dihydro-2-thioxo-3-benzoxazolyl)phosphonate (DBOP) as a condensation agent. AB-type crystalline polyimides, with a glass transition temperature (Tg) of 260 °C, melting transition temperature (Tm) of 528 °C, and 10% weight loss temperature (T10) of 575 °C, can be readily obtained by thermal imidization of poly(amic acid methyl ester) films. The polyimide films prepared by thermal imidization of the isomeric poly(amic acid methyl ester)s were tough, flexible, and transparent, whereas the film prepared from the pure m-monomethyl ester precursor was brittle and opaque, indicating that the constitutional isomerism of the precursors has a sign...

ChemInform Abstract: One‐Step Preparation of 1,4‐Diketones from Methyl Ketones and α‐Bromomethyl Ketones in the Presence of ZnCl2×t‐BuOH×Et2NR as a Condensation Agent.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Interplay between folding/unfolding and helix/coil transitions in giant DNA.

It has been well established that double-stranded DNA undergoes a melting, or helix/coil, transition into a single-stranded coil state with an increase in temperature. On the other hand, it has recently been found that, at a fixed temperature, long DNA, larger than several kilobase pairs, exhibits a discrete transition, or switching, between elongated and folded states, preserving its double-stranded structure, with the addition of various condensation agents, such as alcohol, hydrophilic polymer, multivalent cation, and cationic surfactant. In the present study, we examined the interplay between the folding/unfolding transition and the helix/coil transition in individual giant DNA molecules, by observing the conformation of single molecular chains with fluorescence microscopy. The results indicate that the helix-to-coil transition tightly cooperates with the unfolding transition in DNA.

Studies on the synthesis and properties of thermotropic liquid crystalline polycarbonates. VII. Liquid crystalline polycarbonates and poly(ester-carbonate)s derived from various mesogenic groups

Three series of thermotropic liquid crystalline polycarbonates and poly(ester-carbonate)s were prepared by solution polycondensation of 4,4′-biphenyldiol (BP), 4′-hydroxybiphenyl-4-hydroxybenzoate (HHB), or 4-hydroxyphenyl-4″-hydroxybiphenyl-4′-carboxylate (HHBP), as mesogenic unit, with 1,10-bis(p-hydroxybiphenoxy)decane (N10), bisphenol A (BPA), 4,4′-dihydroxy-diphenyl ether (BPO), 4,4′-[phenylbis(oxy)]bisphenol (BPOO), methylhydroquinone (MeHQ), or phenylhydroquinone (PhHQ). One series of cholesteric poly(ester-carbonate)s were also prepared by using HHBP, the aromatic diols mentioned above and isosorbide as the chiral moiety. All polycondensations were implemented in pyridine by using triphosgene as the condensation agent. The synthesized polycarbonates were characterized by viscometer, FTIR, DSC, TGA measurements, polarizing microscopy equipped with a heating stage, and WAXD powder pattern. In this study, it was found that the liquid crystalline properties of polycarbonates strongly rely on the mesogenic unit applied. HHBP-series exhibits a wide temperature region of liquid crystalline (LC) phase even with 50% of bisphenol A (BPA), which is a V-shaped structure and usually destroys liquid crystalline properties. In addition, homopolycarbonate with HHBP structure possesses extraordinarily low phase-transition temperature and wide liquid crystalline phase range, due to its asymmetric structure. This asymmetric structure results in head-to-tail, head-to-head, and tail-to-tail random conformation of polymer chain. The isosorbide containing poly(ester-carbonate)s formed cholesteric phase, which showed homogeneous blue, green, or red Grandjean texture upon shearing in molten state and the Grandjean texture could be frozen easily while quenching the sample to the room temperature. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1852–1860, 2000

One Step Preparation of 1,4-Diketones from Methyl Ketones and α-Bromomethyl Ketones in the Presence of ZnCl2 · t-BuOH · Et2NR as a Condensation Agent

One Step Preparation of 1,4-Diketones from Methyl Ketones and α-Bromomethyl Ketones in the Presence of ZnCl2 · t-BuOH · Et2NR as a Condensation Agent

Laser Trapping of an Individual DNA Molecule Folded Using Various Condensing Agents

Laser Trapping of an Individual DNA Molecule Folded Using Various Condensing Agents

A simple and mild derivatization method for hydroxyl compounds using condensation agent carbazole-9-N-(2-methyl)-acetyl-benzene-disulfonate and its application for the determination of volatile alcohols from plasma by HPLC with fluorescence detection

A simple and sensitive HPLC method for the determination of hydroxyl compounds including volatile alcohols from spiked plasma, using a fluorescent condensation agent, namely carbazole-9-N-(2-methyl)-acetyl-benzene-disulfonate (CMABS), has been developed. A mixture of alcohols and pyridine in dichloromethane was treated with CMABS to give a quantitative yield of esters. The maximum fluorescence emissions for the derivatized alcohols are at 365 nm (λex 335 nm). Studies on derivatization conditions indicate that alcohols react very fast with CMABS in presence of pyridine in dichloromethane to give the corresponding fluorescent derivatives. The method, in conjunction with a multi-step gradient, offers a baseline resolution of the common alcohol derivatives on a reversed-phase C18 column, which is more convenient and more efficient than previous methods which require the prior conversion of the carboxylic acids to the acyl chlorides. The application of this method to the analysis of volatile alcohols in plasma was also investigated. The LC separation shows good selectivity and reproducibility for alcohol derivatives. The relative standard deviations ¶(n = 5) for 100 pmol of each alcohol are < 4%. The detection limits are at the fmol level for C1–C3 alcohols and pmol level for C4–C9 alcohols.

ChemInform Abstract: Direct Condensation Reaction of Carbon Dioxide with Alcohols Using Trisubstituted Phosphine—Carbon Tetrabromide—Base System as a Condensing Agent.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Chromatin Condensation Is Confined to the Loop and Involves an All-or-None Structural Change

Using differential scanning calorimetry in combination with pulsed field gel electrophoresis, we relate here the changes in the thermal profile of rat liver nuclei induced by very mild digestion of chromatin by endogenous nuclease with the chain length distribution of the DNA fragments. The enthalpy of the endotherm at 106°C, which reflects the denaturation of the heterochromatic domains, decreases dramatically after the induction of a very small number of double-strand breaks per chromosome; the thermal transition disappears when the loops have undergone on average one DNA chain scission event. Quantitative analysis of the experimental data shows that the loop behaves like a topologically isolated domain. Also discussed is the process of heterochromatin formation, which occurs according to an all-or-none mechanism. In the presence of spermine, a strong condensation agent, only the loops that have undergone one break are able to refold, in confirmation of the extremely cooperative nature of the transition. Furthermore, our results suggest a relationship between the states that give rise to the endotherms at 90°C and 106°C and the morphologies referred to as class II and class III in a previous physicochemical study of the folding of chromatin fragments (Widom, 1986. J. Mol. Biol. 190:411–424) and support the view that the overall process of condensation follows a sequential (two-step) pathway.

Determination of alcohols using condensation agent carbazole-9-acetyl-benzene-disulfonate by high performance liquid chromatography with pre-column fluorescence derivatization

A sensitive LC method for the determination of alcohols, using fluorescent condensation agent carbazole-9-N-acetylbenzne-disulfonate(CABS), has been developed. A mixture of alcohols and triethylamine catalyst in dichloromethane or chloroform is treated with CABS to give quantitative yields of esters. Emission maximum for the derivatized alcohols is 365 nm (λex 335 nm). The labeled derivatives are very stable, no significant decomposition is observed after heating in 40% at 40°C for 24 h. The method, in conjunction with a multigradient program, offers baseline resolution of common alcohol derivatives on a reversed-phase C18 column. Studies on derivatization conditions indicate that primary and secondary alcohols react very fast with CABS in the presence of triethylamine in dichloromethane or chloroform to give the corresponding fluorescent derivatives. This method is more convenient and more efficient than previous methods which require prior conversion of carboxylic acids to acyl chlorides. The separation of alcohol derivatives has good reproducibility and the rsd's (n=5) for 50 pmol of each alcohol are 4%. Detection limits are at the fmol level.

Syntheses of Soluble Tert-Butyl substituted Poly(p-Oxybenzoate)s

Soluble poly( p-oxybenzoate)s (POBs) were synthesized by direct solution polycondensation using thionyl chloride and pyridine as condensation agents starting from tert-butyl substituted p-hydroxybenzoic acids (3- tert-butyl-4-hydroxybenzoic acid (BuHB) and 3, 5-di- tert-butyl-4-hydroxybenzoic acid (Bu2HB)). Tert-butyl substituted homopolymers (homo-POBs) had poor solubility in organic solvents, whereas solubility of resulting copolymers (co-POBs) was improved in comparison with that of homo-POBs. In particular, the co-POBs with the weight average molecular weight ( Mωw) value of 20 000 from BuHB/Bu2HB in the monomer feed ratio of 40/60–50/50 were soluble in various organic solvents such as tetrahydrofuran, chloroform, N, N-dimethylformamide, and 10 wt% loss and glass transition temperatures of co-POBs in nitrogen were at 375 °C and 190 °C, respectively.

Derivatization of alcohols using acridone-9- N-acetyl-benzene-disulfonate as a condensation agent and its application for the determination of volatile alcohols in human plasma by liquid chromatography with fluorescence detection

A sensitive liquid chromatographic (LC) method for the determination of alcohols including the volatile alcohols from spiked plasma, using the fluorescent condensation agent, acridone-9- N-acetyl-benzene-disulfonate (AABS), has been developed. A mixture of alcohols and triethylamine in dichloromethane or chloroform is treated with AABS to give a quantitative yield of esters. Emission maxima for the derivatized alcohols are at 435 nm ( λ ex 404 nm). The labeled derivatives are very stable, no remarkable decomposition is observed after heating in 15% acetonitrile solution (pH 6.5) at 40°C for 24 h. The method, in conjunction with a multi-gradient program, offers a baseline resolution of the common alcohol derivatives on a reversed-phase C 18 column. Studies on derivatization conditions indicate that alcohols react very fast with AABS in the presence of triethylamine in dichloromethane or chloroform to give the corresponding fluorescent derivatives. The established method for the analysis of alcohol derivatives is more convenient and more efficient than previous methods which require the prior conversion of the carboxylic acids to the acyl chlorides. The application for the analysis of volatile alcohols in spiked human plasma is also investigated. The LC system shows good selectivity and reproducibility for volatile alcohols from spiked plasma. The relative standard deviations ( n=5) for 50 pmol of each alcohol are <4%. The detection limits are at the fmol level. The method is also suitable for the determination of other alcohols in various matrices.

CARBAZOLE-9-N-ACETYL-N-HYDROXYSUCCINIMIDE (CAHS) AS PRE-COLUMN DERIVATIZATION AGENT FOR FLUORIMETRIC DETECTION OF AMINO COMPOUNDS WITH LIQUID CHROMATOGRAPHY

A simple and sensitive LC method for the determination of amino compounds, using carbazole-N-acetyl-N-hydroxy-succinimide (CAHS) as condensation agent, has been developed.A mixture of amines is treated with CAHS, in the presence of triethylamine catalyst in non-aqueous acetonitrile or in the presence of 0.2 M borate buffer at pH 8.0–9.0 in 40% (v/v) of acetonitrile solution, to give quantitative yields of amides. Emission maximum for the derivatized amines is 365 nm (λex 335 nm). Studies on derivatization conditions indicate that amines react very fast with CAHS under proposed conditions. The method, in conjunction with a multi-step gradient, offers baseline resolution of common amine derivatives on a reversed-phase C18 column. Derivatization reaction is more convenient and more efficient than previous methods which require prior conversion of carboxylic acids to acyl chlorides. The LC separation of amine derivatives has good reproducibility. The established method is also suitable for the determination of other amines in various biological fluids.

2-Propanephosphonic acid anhydride (T3P)-mediated segment coupling and head-to-tail cyclization of sterically hindered peptides

In the course of comparing the effectiveness of an HOAt-derived coupling reagent (HAPyU) and a phosphonic acid-based condensation agent (T3P) by cyclization of model sequences, we found that T3P was a superior reagent with regard to conversion of the linear peptide into the stereochemically intact cyclic monomer when sterically hindered amino acids are found at the cyclization site.

Synthesis and Properties of Thermally Resistant Poly(amide-imide)s

A series of poly(amide-imide)s has been synthesized by the direct polycondensation of biphenyl imide containing diacids with aromatic diamines using triphenylphosphite (TPP) as the condensation agent in a N-methyl-2-pyrrolidone (NMP)-pyridine solution containing 3.5 wt% LiCl. The direct polycondensation was markedly facilitated to give high-molecular-weight (0.24<ηinh<2.38) of poly(amide-imide)s in quantitative yield. The thermal properties of the obtained poly(amide-imide)s were examined by DSC and TGA. The synthesized poly(amide-imide)s possessed glass transition temperature in the range of 285–337°C. The poly(amide-imide)s exhibited excellent thermal stabilities and had 10% weight loss at the temperature in the range of 475–597°C under nitrogen atmosphere. With the exception of polymer BP-2 series, the poly(amide-imide)s showed good solubility in NMP, N,N-dimethylformamide (DMF), and dimethyl sulfoxide (DMSO).

Peptides by activation of amino acids with CO on (Ni,Fe)S surfaces: implications for the origin of life.

In experiments modeling volcanic or hydrothermal settings amino acids were converted into their peptides by use of coprecipitated (Ni,Fe)S and CO in conjunction with H2S (or CH3SH) as a catalyst and condensation agent at 100 degreesC and pH 7 to 10 under anaerobic, aqueous conditions. These results demonstrate that amino acids can be activated under geochemically relevant conditions. They support a thermophilic origin of life and an early appearance of peptides in the evolution of a primordial metabolism.

Structopendant unsaturated cellulose esters via acylation in homogeneous lithium chloride/N,N‐dimethylacetamide solutions

Novel acylation reactions of cellulose were accomplished with a series of unsaturated carboxylic acids or their respective anhydrides including crotonic acid (CRA), methacrylic acid (MAA), vinyl acetic acid (VAA), fumaric acid monoethyl ester (FAME), and cinnamic acid (CINA) in lithium chloride (LiCl)/dimethylacetamide (DMAc) homogeneous solutions. The acylation reactions were conducted at room temperature using dicyclohexylcarbodiimide (DCC) as a condensation agent and 4-dialkyl-aminopyridine (4-[N,N-dimethylamino-] or 4-pyrrolidino-pyridine, DMAP or PP) as a catalyst. A reaction mechanism is proposed based on experimental evidence. The acylated cellulose derivatives obtained from CRA, MAA, or their anhydrides exhibit poor solubility in organic solvents. Side reactions, e.g., the Michael addition, likely occur at the high temperatures required for reaction of these acyl groups. However, acylation of cellulose with VAA, FAME, and CINA is facile with derivatives readily soluble in DMSO. The structures of these derivatized celluloses were characterized with FTIR and 1H-NMR spectroscopy and degrees of substitution were calculated. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 293–305, 1997