Glycine Ethyl Ester Research Articles

Origin of the α-Effect in Aminolysis of Y-Substituted Phenyl Diphenylphosphinates: Ground-state Versus Transition-state Contribution

Figure 1. Bronsted-type plot for reactions of 2,4-dinitrophenyl diphenylphosphinate (1a) with primary amines in 80 mol% H2O/20 mol% DMSO at 25 ± 0.1 C. The identity of amines: 1 = ethylamine, 2 = ethylenediamine, 3 = ethanolamine, 4 = benzylamine, 5 = glycylglycine, 6 = hydrazine, 7 = glycine ethyl ester, 8 = 1,2-diaminopropane-H, 9 = trifluoroethylamine. The kinetic data were taken from ref. 22 except for the reaction of 1a with hydrazine, 6. Nucleophiles possessing one or more nonbonding electron pairs at the atom α to the nucleophilic site have often been reported to exhibit abnormally higher reactivity than would be expected from their basicity. Accordingly, these nucleophiles and the enhanced reactivity were termed as α-nucleophiles and the α-effect, respectively. Numerous studies have been performed to investigate the origin of the α-effect. Some theories advanced to explain the cause of the α-effect are: (1) destabilization of the groundstate (GS) due to repulsion of the nonbonding electron pairs, (2) stabilization of transition state (TS) including general acid/base catalysis, (3) thermodynamic product stability, (4) solvent effects. However, the origin of the α-effect is not clearly understood. Particularly, solvent effects on the α-effect remain controversial. Recent calculations have shown that the α-effect is present in gas-phase reactions. Thus, solvent effect has been suggested to be unimportant for the αeffect. However, our systematic study has revealed that solvent effect on the α-effect is significantly important. The evidence provided was that the α-effect is strongly dependent on solvent compositions for reactions of aryl acetates, benzoates and thionobenzoates with butane-2,3-dione monoximate (an α-nucleophile) and 4-chlorophenoxide (a reference nucleophile) in DMSO-H2O mixtures of varying compositions, e.g., the magnitude of the α-effect increases as the DMSO content in the medium increases up to ca. 50 mol% DMSO and then decreases thereafter (a bell-shaped α-effect profile). Dissection of the α-effect into GS and TS contributions through combination of the kinetic data with our calorimetric data has led us to conclude that GS destabilization is mainly responsible for the increasing α-effect up to ca. 50 mol% DMSO, while differential TS stabilization contributes to the decreasing αeffect in the DMSO-rich region. We have also reported that TS stabilization through general acid/base catalysis plays an important role for the α-effect found in reactions of Y-substituted phenyl benzoates with hydrazine and glycylglycine. Our study has been extended to reactions of Y-substituted phenyl diphenylphosphinates (1a-f) with hydrazine and glycine ethyl ester (Scheme 1) to investigate the origin of the α-effect (e.g., GS and TS contributions).

Slightly Viscous Amino Acid Ionic Liquids: Synthesis, Properties, and Calculations

Slightly viscous N-alkyl-substituted glycine ester ionic liquids were prepared via alkylation of glycine ethyl esters with appropriate haloalkanes followed by anion exchange with lithium bis(trifluoromethanesulfonyl)amide. These ionic liquids have been characterized by IR, NMR, elemental analysis, thermal stability, phase behavior, viscosity, and density. Compound 9 crystallizes in the monoclinic system, P2(1)/c. The viscosities of the N,N,N-trialkyl-substituted glycine ester ionic liquids (6, 8, 10) are in the approximately 200 to 400 cP range at 25 degrees C. While exhibiting liquid characteristics analogous to the traditional heterocyclic ionic liquids, these new liquids are much less viscous than known amino acid ionic liquids. The correlation of viscosity and temperature was determined. To understand the influence of the alkyl and ester-substituted groups on viscosity, the electronic distributions and the electrostatic potential surfaces of the glycine-based cations, including glycine (Gly(+)), glycine ethyl ester (GlyET(+)), N,N-dimethyl glycine (DMGly(+)), N,N-dimethyl glycine ethyl ester (DMGlyET(+)), N,N-dimethyl-N-propyl glycine ethyl ester (DMPGlyET(+)), N,N-dimethyl-N-3-fluoropropyl glycine ethyl ester (DMPFGlyET(+)), and N-butyl-N,N-dimethyl glycine ethyl ester (DMBGlyET(+)) cations have been investigated and analyzed. The possible effects on the viscosity coming from the intermolecular interactions arising from Coulomb interactions, hydrogen bonding, polarizability effects, and van der Waals interactions are considered.

Tetrameric rhenium complexes with a glycine-thiourea derivative

[ReNCl2(PPhMe2)3] reacts with the glycine ethylester derivative Et2NC(S)NC(Ph)NHCH2COOEt, HL(GlyEt), in methanol under hydrolysis of the ester and formation of the tetrameric, nitrido-bridged rhenium(V) compound [{ReN{fac-L(Gly)}(PMe2Ph)}{ReN{mer-L(Gly)}(H2O)}]2. Both facial and meridional coordination has been found for the tridentate {L(Gly)}2− ligand in the building blocks of the tetramer. Syn and anti isomers with respect to the PPhMe2 ligands have been isolated and characterized by X-ray diffraction.

The synthesis and characterization of a novel biodegradable and electroactive polyphosphazene for nerve regeneration

Conductive polymers have been of great interest to the biopharmaceutical industry because of their cell adhesion and proliferation. In this paper, a novel electrically-conductive and biodegradable polyphosphazene polymer containing parent aniline pentamer (PAP) and glycine ethyl ester (GEE) as side chains was synthesized through a nucleophilic substitution reaction for its potential application in nerve regeneration. The electrical conductivity of the polymer was ~ 2 × 10 − 5 S/cm in the semiconducting region upon preliminarily protonic-doped experiment. Degradation studies carried out in phosphate-buffered saline at 37 °C showed a mass loss of ~ 50% after 70 days. In vitro cytotoxicity to the RSC96 Schwann cells was evaluated using the cell viability assay. The polymer exhibited no cytotoxicity, indicating that such a polyphosphazene polymer has potential as scaffold material in tissue engineering for peripheral nerve regeneration or other biomedical devices that require electroactivity.

Structure of [Pb(Gly-H)]+ and the Monosolvated Water and Methanol Solvated Species by Infrared Multiple-Photon Dissociation Spectroscopy, Energy-Resolved Collision-Induced Dissociation, and Electronic Structure Calculations

Infrared multiple-photon dissociation (IRMPD) spectroscopy, collision-induced dissociation mass spectrometry, and theoretical calculations are combined to provide new insights into the structure and dissociation of lead(II) complexed with the conjugate acid of the amino acid glycine ([Pb(Gly-H)](+)) in the presence and absence of solvent. Unexpectedly, these experiments show the main site of lead(II) coordination to be the deprotonated amino group of glycine, with additional coordination to the carbonyl group. In such a structure lead(II) can act as an effective conduit for proton/hydrogen shifts, making H(2)O loss competitive with that of CO in the [Pb(Gly-H)](+) complex and leading to solvent deprotonation and formation of [PbOR(Gly)](+) (R = H, CH(3)) ions when solvent is present in the complex. The structural assignments based on IRMPD spectroscopy are complemented with isotopic labeling experiments (H(2)(18)O) and experiments done on the ethyl ester of glycine.

Hydrogen bonding in blends of polyesters with dipeptide‐containing polyphosphazenes

AbstractNew biomedically erodible polymer composites were investigated. Polyphosphazenes containing the dipeptide side groups alanyl–glycine ethyl ester, valinyl–glycine ethyl ester, and phenylalanyl–glycine ethyl ester were blended with poly(lactide‐co‐glycolide) (PLGA) with lactic to glycolic acid ratios of 50 : 50 [PLGA (50 : 50)] and 85 : 15 [PLGA (85 : 15)] with solution‐phase techniques. Each dipeptide ethyl ester side group contains two NH protons that are capable of hydrogen bonding with the carbonyl functions of PLGA. Polyphosphazenes that contain only the dipeptide ethyl ester groups are insoluble in organic solvents and are thus unsuitable for solution‐phase composite formation. To ensure solubility during and after synthesis, cosubstituted polymers with both dipeptide ethyl ester and glycine or alanine ethyl ester side groups were used. Solution casting or electrospinning was used to fabricate polymer blend matrices with different ratios of polyphosphazene to polyester, and their miscibilities were estimated with differential scanning calorimetry and scanning electron microscopy techniques. Polyphosphazenes with alanyl–glycine ethyl ester side groups plus the second cosubstituent were completely miscible with PLGA (50 : 50) and PLGA (85 : 15) when processed via solution‐casting techniques. This suggests that the hydrogen‐bonding protons in alanyl–glycine ethyl ester have access to the oxygen atoms of the carbonyl units in PLGA. However, when the same pair of polymers was electrospun from solution, the polymers proved to be immiscible. Solution‐cast miscible polymer blends were obtained from PLGA (50 : 50) plus the polyphosphazene that was cosubstituted with valinyl–glycine ethyl ester and glycine ethyl ester side groups. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Synthesis of a novel biodegradable and electroactive polyphosphazene for biomedical application

To prepare one electroactive and biodegradable biomaterial for biomedical application, a new synthetic strategy was developed to synthesize a novel electrically conductive biodegradable polyphosphazene polymer containing parent aniline pentamer (PAP) and glycine ethyl ester (GEE) as side chains by a nucleophilic substitution reaction. The electrical conductivity of the polymer is ∼2 × 10−5 S cm−1 in the semiconducting region upon preliminarily protonic-doped experiment. The degradation and RSC96 Schwann cells experiments in vitro prove that the polymer is biodegradable and beneficial to the cell adhesion and proliferation. The as-synthesized polymer also shows good solubility in common organic solvent and good film-forming properties. This new type of polymer has potential applications as scaffolds for neuronal and cardiovascular tissue engineering or other biomedical devices that require electroactivity.

Novel thiourea derivatives of α-amino acids and their oxorhenium(V) complexes

N-[(Dialkylamino)(thiocarbonyl)]benzimidoyl chlorides react with α-amino acid esters under formation of the corresponding N-[(dialkylamino)(thiocarbonyl)]benzamidines. Derivatives with glycine ethylester, HL(GlyOEt), cysteine methylester and S-benzyl protected cysteine ethylester, HL(S-Bzl-CysOEt), were prepared and isolated in crystalline form. The reaction with cysteine methylester yields the corresponding sulfur-bridged dimeric compound {HL(CysOMe)} 2. Starting from [ReOCl 3(PPh 3) 2], complexes of these new ligands could be obtained in two different coordination modes: monodentate coordination by only the thiourea sulfur atom or S,N,O tridentate coordination after ester hydrolysis.

The influence of side group modification in polyphosphazenes on hydrolysis and cell adhesion of blends with PLGA

Polyphosphazenes have been synthesized with tris(hydroxymethyl)amino methane (THAM) side groups and with co-substituents glycine ethyl ester and alanine ethyl ester. The THAM side group was linked to the polyphosphazene backbone via the amino function. The three pendent hydroxyl functions on each THAM side group were utilized for hydrogen bonding association with poly(glycolic–lactic acid) (PLGA). Co-substitution of the polyphosphazene with both THAM and glycine or alanine ethyl esters was employed to avoid the insolubility of the single-substituent THAM-substituted polyphosphazenes. Both poly[(tris(hydroxymethyl)aminomethane)(ethyl glycinato)phosphazene] and poly[(tris(hydroxymethyl)aminomethane)(ethyl alanato)phosphazene] (1:1 ratio of side groups) were blended with PLGA (50:50) or PLGA (85:15). DSC analysis indicated miscible blend formation, irrespective of the detailed molecular structure of the polyphosphazene or the composition of PLGA in the blend. Hydrolysis studies of the polyphosphazene:PLGA (50:50) blends indicated that the PLGA component hydrolyzed more rapidly than the polyphosphazene. Primary osteoblast cell studies showed good cell adhesion to the polymer blends during 14 days, but subsequent limited cell spreading due to increased surface roughness as the two polymers eroded at different rates.

Polyphosphazenes That Contain Dipeptide Side Groups: Synthesis, Characterization, and Sensitivity to Hydrolysis

The dipeptides alanyl-glycine ethyl ester, valinyl-glycine ethyl ester, and phenylalanyl-glycine ethyl ester were synthesized by mixed anhydride solution-phase peptide reactions. The free N-terminus was used as a reactive site for nucleophilic replacement of the chlorine atoms in poly(dichlorophosphazene). The C-terminus was protected with an ethyl ester to prevent side reactions and cross-linking. The alanyl-glycine ethyl ester replaced all the chlorine atoms in poly(dichlorophosphazene). However, replacement of all the chlorine atoms in poly(dichlorophosphazene) by valinyl-glycine ethyl ester or phenylalanyl-glycine ethyl ester polyphosphazenes was prevented by the insolubility of the partially substituted intermediates. To circumvent this problem, cosubstitution was carried out using the valinyl- or phenylalanyl esters with glycine ethyl ester or alanine ethyl ester in a 1:1 ratio. Cosubstituted polyphosphazenes with alanyl glycine ethyl ester and glycine ethyl ester or alanine ethyl ester were also sy...

Novel micelles from graft polyphosphazenes as potential anti-cancer drug delivery systems: Drug encapsulation and in vitro evaluation

In this study, a new class of amphiphilic methoxy-poly(ethylene glycol) grafted polyphosphazene with glycine ethyl ester side groups (PPP-g-PEG/GlyEt) was synthesized and characterized. An anti-cancer agent doxorubicin (DOX) was encapsulated into polymeric micelles derived from those copolymers, which exhibited considerably strong impact on micelle morphology: turned the rod-like and spherical drug free micelles into spheres and vesicles respectively. The in vitro release behavior of those drug-loaded micelles exhibits a sustained release manner and is affected by drug content. Cytotoxicity assay against adriamycin-resistant human breast cancer MCF-7 cell line showed that drug-loaded micelles based on PPP-g-PEG/GlyEt micelles can effectively suppress cell proliferation and the cytotoxicity was both time and concentration related, an enhanced cytotoxicity was observed either with increasing drug concentration or with prolonged incubation time. Moreover, flow cytometry results revealed a particle size dependency in cellular uptake of drug-loaded micelles. These findings suggest that the present copolymers can encapsulate water insoluble anti-cancer agents and contribute to improve drug sensitivity of adriamycin-resistant cell line.

Efficient protocol to quinazolino[3,2-d][1,4]benzodiazepine-6,9-dione via Staudinger-aza-Wittig cyclization: application to synthesis of Asperlicin D

Tandem Staudinger and intramolecular aza-Wittig reactions followed by cyclodehydration of the linear N-[N-(2-azidobenzoyl)-2-aminobenzoyl]glycine ethyl ester furnished the tetracyclic quinazolino[3,2-d][1,4]benzodiazepine-6,9-dione ring system found in some biologically active natural alkaloids. This method was successfully implemented to synthesize asperlicin D from a linear peptide containing ester and azido terminal groups.

Stereoselective Formation of Fused Tricyclic Amines from Acyclic Aldehydes by a Cascade Process Involving Condensation, Cyclization, and Dipolar Cycloaddition

The preparation of tricyclic amines from acyclic precursors is described using a cascade of tandem reactions involving condensation of an aldehyde with a primary amine, cyclization (with displacement of a halide), and then in situ deprotonation or decarboxylation to give an azomethine ylide or nitrone followed by intramolecular dipolar cycloaddition. The methodology is straightforward, and the aldehyde precursors are prepared easily and quickly in high yield using nitrile alkylations followed by DIBAL-H reduction. The relative ease of reaction of various substrates with different tether lengths between the aldehyde and the halide or dipolarophile has been studied. Several primary amines including simple amino acids such as glycine, alanine, and phenylalanine and derivatives such as glycine ethyl ester and also hydroxylamine have been investigated. High yields are obtained in the formation of different tricyclic ring sizes; the dipolar cycloaddition necessarily creates a five-membered ring, and we have investigated the formation of five- and six-membered rings for the other two new ring sizes. In all cases, yields are high (except when using glycine when the tether to the terminal alkene dipolarophile leads to a six-membered ring), and most efficient is the formation of the tricyclic product in which all five-membered rings are formed. Examples with an alkyne as the dipolarophile were also successful. In all the reactions studied, the products are formed with complete regioselectivity and remarkably with complete stereoselectivity. The key step involves the formation of three new rings and potentially up to four new stereocenters in a single transformation. The power of the chemistry was demonstrated by the synthesis of the core ring systems of the alkaloids (+/-)-scandine and (+/-)-myrioneurinol and the total syntheses of the alkaloids (+/-)-aspidospermine, (+/-)-quebrachamine, and (+/-)-aspidospermidine.

Synthesis of Purine- and Pyrimidine-Containing Polyphosphazenes: Physical Properties and Hydrolytic Behavior

We report here the first examples of poly(organophosphazenes) with side groups derived from the purines guanine and adenine and the pyrimidine cytosine. Polymers with these purines or pyrimidines as the only side groups proved difficult to synthesize by macromolecular substitution techniques because of the insolubility of the intermediate products. Therefore, cosubstitution reactions of the poly(dichlorophosphazene) with glycine ethyl ester, alanine ethyl ester, or diethylene glycol methyl ether, followed by the respective purine or pyrimidine, were utilized. Each pair of side groups was incorporated into the polyphosphazene in a 1:1 ratio. 31P NMR spectroscopy verified the replacement of all the chlorine atoms, while 1H and 13C NMR techniques confirmed the presence and ratio of the different side group. DRIFT spectroscopy indicated that the attachment of the purines or pyrimidines was via the primary amino functionality. Glass transition temperatures ranged from −28 to −15 °C for the mixed-substituent po...

Covalent sidewall functionalization of single-walled carbon nanotubes by amino acids

Single-walled carbon nanotubes (SWNTs) with amino acids covalently attached to their side walls, viz., “nanotube-aminoacids,” have been prepared starting from colloidal solutions of fluorinated SWNTs (F-SWNTs) and amino acids in o-dichlorobenzene and heating at 80–150 °C in the presence of pyridine. The syntheses were carried out with the F-SWNTs of approximately 2: 1 (C: F) stoichiometry and several natural α-aino acids with both pro-tected and unprotected carboxyl groups, such as glycine ethyl ester hydrochloride, L-serine ethyl ester hydrochloride, l-cysteine, and trans-4-hydroxy-l-proline. The nanotube-aminoacids have been characterized by Raman and FTIR spectroscopy, atomic force, scanning, and transmission electron microscopies, and thermal gravimetric analysis (TGA). Based on TGA data, the degree of sidewall functionalization in the synthesized SWNT derivatives was estimated to be in the range from one of 32 to one of 8 carbon atoms, depending on the amino acid nature and reaction conditions used. The amino acid-functionalized SWNTs, prepared in this work by simple and inexpensive one-step method, can be valuable precursors for peptide synthesis and targeted drug delivery, design and fabrication of nanocomposites and fibers, and other biomedical and engineering applications.

Effect of amino acids and amino acid derivatives on crystallization of hemoglobin and ribonuclease A

Determination of the appropriate conditions for protein crystallization remains a highly empirical process. Preventing protein aggregation is necessary for the formation of single crystals under aggregation-prone solution conditions. Because many amino acids and amino acid derivatives offer a unique combination of solubility and stabilizing properties, they open new avenues into the field of protein aggregation research. The use of amino acids and amino acid derivatives can potentially influence processes such as heat treatment and refolding reactions. The effect of the addition of several amino acids, such as lysine, and several amino acid derivatives, such as glycine ethyl ester and glycine amide, on the crystallization of equine hemoglobin and bovine pancreatic ribonuclease A has been examined. The addition of these amino acids and amino acid derivatives expanded the range of precipitant concentration in which crystals formed without aggregation. The addition of such additives appears to promote the crystallization of proteins.

Calixarene-based chiral phase-transfer catalysts derived from cinchona alkaloids for enantioselective synthesis of α-amino acids

The synthesis of the first calixarene-based chiral phase-transfer catalysts derived from cinchona alkaloids has been achieved in two steps from p- tert-butylcalix[4]arene. The catalytic efficiency of the chiral calix[4]arenes 3a– c was evaluated by carrying out the phase-transfer alkylation of N-(diphenylmethylene)glycine ethyl ester with benzyl bromide. Various factors that affect the chemical yield and enantioselectivity were also examined. Benzylation of glycine imine 4 using calix[4]arene-based dimeric catalyst 3a as a chiral phase-transfer catalyst in toluene/CHCl 3 mixture (7:3 v/v) at 0 °C gave the best enantioselectivities and yields in the presence of aqueous NaOH.

PREPARATION OF GLUCOSYL-SUBSTITUTED POLYPHOSPHAZENE HYDROGELS

Two kinds of polyphosphazenes,that bear α-D-glucosyl side groups together with methoxyethoxy or ethyl glycinato as cosubstituent groups,have been synthesized and characterized by IR and ~1H-NMR analyses.They were examined in order to investigate their possible use as matrix for glucose-sensitive insulin delivery basing on the specific interaction of glucose with lection. Briefly, the polymers were prepared via nucleophilic displacement of the reactive chlorines of polydichlorophosphazene with diisopropylidene D-glucose at first, and subsequently with methoxyethanol (polymer a) or glycine ethyl ester (polymer b) to substitute the residual P-Cl. After filtration and dialysis, the purified polymers were then treated with 90% trifluoroacetic acid to remove isopropylidene groups to get glucosyl groups. The formation of aggregates of glucosyl-substituted polyphosphazenes physically crosslinked by Concanavalin A (Con A) was studied by monitoring the transmittance at 360 nm of dilute polymeric aqueous solutions. Hydrogels were made by mixing concentrated glucosyl-substituted polyphosphazene aqueous solution with Con A aqueous solution. Different polyphosphazenes with various compositions of α-D-glucosyl side group and methoxyethoxy or ethyl glycinato side group combinations were obtained by adjusting the feeding dose of the nucleophiles. And their hydrophilicity differed from each other for the methoxyethoxy group is hydrophilic, and the ethyl glycinato group is hydrophobic, which would affect the formation of hydrogel and the drug release thereof in different way. In the deprotection reaction, the treating time needed to be prolonged to complete the hydrolysis of isopropylidene groups, however, it would cause significant cleavage of polyphosphazene backbones and degradation of cosubstituted ethyl glycinato groups (while almost no effect to methoxyethoxy) in the strong acidic condition. As a result, the deprotection ratio of glucoses was maintained at about 60% in this study to avoid remarkable decrease in molecular weight, and at the same time, the remained diisopropylidene D-glucosyl groups were considered biocompatible and might play a role in balancing polymeric hydrophilicity/hydrophobicity. Con A is one of the most widely used lectins in studying the interaction of specific saccharide with protein, particularly, for nonreducing D-mannosyl and D-glucosyl residues. For both polymers a and b, their dilute solutions rapidly turned turbid when Con A was mixed into, and turbidity increased with increasing the concentration of polymeric solutions and the content of glucosyl side groups in the polymers due to the formation of more and larger aggregates. The aggregates could be dissociated by addition of free glucose, and transmittance of the solution increased. On the other hand, it has been found that the transmittance data of solutions of polymer a mixed with Con A were much larger that those of polymer b, even if they had the similar amount of glucosyl side groups and the same polymeric concentration. One possible reason for this phenomenon was that polymer b could not dissolve well in water due to the presence of hydrophobic ethyl glycinato side groups, and the interaction between Con A and glucosyl groups was hindered. Thus, hydrogels were made from polymer a and Con A by increasing the polymeric concentration above 10 wt%. Higher concentrations of glucosyl-substituted polyphosphazene, more hydrophilic co-substituted side groups and higher amounts of glucosyl side groups would be in favor of hydrogel formation. This hydrogel can be a potential matrix for glusoce-sensitive insulin delivery.

Interaction between Proteins and Polyphosphazene Derivatives Having a Galactose Moiety

For tissue engineering applications, it is necessary to balance the need for specific biological interactions with the need to prevent unfavorable nonspecific interactions. For this purpose, novel poly[(organo)phosphazenes] were synthesized having galactose and/or poly(ethylene glycol) (PEG) side chains. The synthesis was described previously. Here, we investigate the human serum albumin (HSA) adhesion to these polymers using surface plasmon resonance (SPR). We could conclude that the incorporation of PEG reduced the protein adsorption. The influence of the galactose moieties was investigated using SPR and a sugar-lectin binding assay. The interaction between a lectin (Peanut agglutinin, PNA or Ricinus communis-agglutinin, RCA) and the polyphosphazene derivatives was evaluated. Type IIA polymers, having aminohexyl-galactose, phenylalanine ethyl ester, and glycine ethyl ester side chains, were capable of binding with the lectin. As the amount of galactose was increased, the extent of the galactose specific lectin binding was also increased (higher RU or absorbance). PEG containing polymers failed to bind specifically with the lectin. The presence of PEG, either as a spacer or as additional chains, interfered with the establishment of contact between the galactose and the binding site on the lectin. The adsorption of PNA or RCA to these types of polymers was attributed to nonspecific interactions. SPR was also used to determine rate and equilibrium constants. In addition the effect of the addition of water soluble polyphosphazenes on the enzymatic cleavage of o-nitrophenyl-beta-D-galactopyranoside was investigated. The galactose moieties were not available as inhibitors because of the presence of PEG.

Role of Carboxyl Groups in the Secondary Structure and Function of Sturgeon Gonadotropin

Role of Carboxyl Groups in the Secondary Structure and Function of Sturgeon Gonadotropin Free negatively charged carboxyl groups were selectively modified (neutralised) in sturgeon (Acipenser güldenstädti Br.) gonadotropic hormone (GTH) α and β subunits. Eleven free carboxyl groups, three in the α and eight in the β subunit, were neutralised by reaction with glycine ethyl ester. Investigation of reassociated α-β dimers (recombinants) comprising one or both modified subunits showed that specific hormonal activity was completely lost while immunoreactivity was lowered in comparison with that of the standard α-β dimer. CD-spectroscopy of the modified subunits did not indicate any considerable changes in their spatial structure. A conclusion was made that free COOH groups of GTH were important as bearers of the negative charge necessary for the hormone activity on the level of the hormone-specific membrane receptors.