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2.
Summary Hydrophobic character is usually expressed in terms of the partition coefficient in 1-octanol-water (log P o/w). However, measurement of this coefficient is often problematic. Retention in micellar liquid chromatography is mainly due
to hydrophobic interactions and can also be used as an index of hydrophobicity. A hydrophobicity scale was established with
retention data for o-phthalaldehyde (OPA)-N-acetyl-L-cysteine (NAC) amino acid derivatives, using the glycine derivative as reference. Since the
OPA-NAC derivatives only differ in the nature of R 1 in the amino acid (R 1CH (COOH)NH 2), in the absence of electrostatic interactions the hydrophobic character of the substituent was responsible for retention.
Linear relationships were obtained between log of the ratio k′ of amino acid derivatives: k′ of the glycine derivative for a given mobile phase, and log P
o/w for the R 1 substituent. Good correlations were also found for phenylthiohydantoin amino acid derivatives. 相似文献
3.
Summary Hydrophobic character is usually expressed in terms of the partition coefficient in 1-octanol-water (log P O/W). However, measurement of this coefficient is often problematic. Retention in micellar liquid chromatography is mainly due
to hydrophobic interactions and can also be used as an index of hydrophobicity. A hydrophobicity scale was established with
retention data for o-phthalaldehyde (OPA)-N-acetyl-L-cysteine (NAC) amino acid derivatives, using the glycine derivative as reference. Since the
OPA-NAC derivatives only differ in the nature of R 1 in the amino acid (R 1CH(COOH)NH 2), in the absence of electrostatic interactions the hydrophobic character of the substituent was responsible for retention.
Linear relationships were obtained between log of the ratio k′ of amino acid derivatives: k′ of the glycine derivative for a given mobile phase, and log P
O/W for the R 1 substituent. Good correlations were also found for phenylthiohydantoin amino acid derivatives. 相似文献
5.
In this paper we report on the synthesis and solution conformation of a new set of structurally related polycationic branched chain polypeptides (poly[Lys(X
i
-dl-Ala
m
)]) with hydrophobic (Ile, Nle, Val) or cationic (Arg) amino acids at the N-terminal end of the side chains as well as their cytotoxic effect on murine bone marrow derived macrophages. Solution conformation of the polypeptides was studied with circular dichroism spectroscopy under different conditions (pH, ionic strength). The results of these comparative studies indicate that a) polypeptides could adopt an ordered (mainly helical) conformation at physiological pH and salt concentration (pH 7.4, 0.2 M NaCl); b) the nature of side chain terminal amino acid (X) could determine under which conditions the ordered structure was formed. Thus, the solution conformation of branched polypeptides could be modulated by the selection of amino acid X under physiological conditions. All polypeptides with hydrophobic amino acid at the terminal position were essentially non-toxic on macrophages, whereas the polypeptide with terminal Arg proved to be markedly cytotoxic. 相似文献
6.
N-Tritylamino acids activated with DCC/HOBt, were coupled with various amino acid derivatives without racemization. The trityl group was split off quantitatively in 10% CCl 3COOH monohydrate or CH 2ClCOOH in CH 2Cl 2. Under these conditions detritylation of N-Trt-Trp-Gly-NH 2 proceeds without formation of an oxindole derivative and side alkylation products, even in the absence of a scavenger. Dipeptide derivatives 1 and 2 exhibited magnetic asymmetry, attributed to steric factors. 相似文献
7.
β-Amino esters were obtained in up to 78% yield with 72:28–96:4 diastereomeric ratios by the reaction of the chiral titanium enolate of menthyl esters, prepared using the TiCl 4/Et 3N reagent system with prochiral imines. A representative syn-β-amino ester derivative has been used for the resolution of racemic mandelic acid to obtain a sample with >99% ee in a single step. A representative syn-β-amino ester was converted to the corresponding N-deprotected amino ester using the Pd–C/HCOOH reagent system, and then to the corresponding β-amino acid using the glacial CH 3COOH/HCl reagent system, and to the corresponding β-lactam derivative with partial epimerization by the reaction using C 2H 5MgBr. 相似文献
8.
A glassy carbon electrode modified with per‐6‐amino‐β‐cyclodextrin (β‐CDNH 2) and functionalized single‐walled carbon nanotubes (SWCNT‐COOH) was elaborated. This structure was investigated for the detection of dopamine acid (DA) in presence of ascorbic acid (AA). The sensor behavior was studied by cyclic voltammetry, square wave voltammetry and electrochemical impedance spectroscopy. The analysis results show that the electrode modification with CD derivative improves the sensitivity and selectivity of the DA recognition; the electrochemical response was further improved by introduction of SWCNT‐COOH. The sensor shows good and reversible linear response toward DA within the concentration range of 7×10 ?7–10 ?4 M with a detection limit of 5×10 ?7 M. 相似文献
9.
Abstract A comparison was made among five precolumn derivatization techniques for amino acid analysis using reverse-phase high-performance liquid chromatography (HPLC). All chromatographic analyses were conducted using the same instrumentation and a C 18 Ultrasphere ODS column (5 μm, 250 × 4.6 mm). The precolumn derivatization methodologies studied included the formation of OPA ( o-phthaldialdehyde), DANSYL (dimethylaminonaphthalenesulphonyl), DABSYL (dimethylaminoazobenzenesulphonyl), PTH (phenylthiohydantoin), and PTC (phenylthiocarbamyl) derivatives. The derivatization procedures were evaluated for simplicity, time required, and derivative stability. HPLC analyses of the amino acid derivatives were compared in terms of resolution, sensitivity, reproducibility, and time of analysis. 相似文献
10.
d-Mannose was treated with dry acetone in the presence of conc. H 2SO 4 to afford 2,3:5,6-di- O-isopropylidene-α- d-mannofuranoside. Treating the latter with ethyl chloroacetate gave carboethoxymethyl 2,3:5,6-di- O-isopropylidene-α- d-mannofuranoside, which was hydrolyzed with N 2H 4 · H 2O to afford the acid hydrazide derivative. Treating of the acid hydrazide with acylated amino acides, via the azide-coupling method afforded the corresponding O-glycopeptides. Reaction of the glycopeptide methyl esters with N 2H 4 · H 2O afforded the corresponding hydrazides, which were coupled with the amino acid methyl esters to afford the dipeptides. Deprotection
was carried out by using 70% AcOH. The prepared O-glycopeptides were tested for antiviral activity against hepatitis B virus and showed moderate activities. 相似文献
11.
The Raman spectra of serine [α-amino-β-hydroxypropionic acid; HOCH 2CH(NH 3) +COO −] and 3,3-dideutero-serine [HOCD 2CH(NH 3) +COO −] in aqueous solution were studied in the range 4000–300 cm −1. The data obtained for the deuterated compound are novel and provide compelling evidence that previously reported assignments for the undeuterated amino acid should be revised. 相似文献
12.
Summary.
d-Mannose was treated with dry acetone in the presence of conc. H 2SO 4 to afford 2,3:5,6-di- O-isopropylidene-α- d-mannofuranoside. Treating the latter with ethyl chloroacetate gave carboethoxymethyl 2,3:5,6-di- O-isopropylidene-α- d-mannofuranoside, which was hydrolyzed with N 2H 4 · H 2O to afford the acid hydrazide derivative. Treating of the acid hydrazide with acylated amino acides, via the azide-coupling method afforded the corresponding O-glycopeptides. Reaction of the glycopeptide methyl esters with N 2H 4 · H 2O afforded the corresponding hydrazides, which were coupled with the amino acid methyl esters to afford the dipeptides. Deprotection
was carried out by using 70% AcOH. The prepared O-glycopeptides were tested for antiviral activity against hepatitis B virus and showed moderate activities. 相似文献
13.
The polyesterifications of cinnamylsuccinic acid with 1,4-tetramethylene glycol in both equimolar and non-equimolar ratios were investigated over the range of 130–180°C in the absence and the presence of p-toluenesulphonic acid as catalyst. The kinetic equations were: d[COOH]/dt = k 1[COOH][OH] 2 and d[COOH]/dt = k 2[COOH] 2 for uncatalyzed and acid-catalyzed polyesterifications, respectively. The apparent rate constants for uncatalyzed and acid-catalyzed reactions were evaluated by using the method of least squares for various values of initial molar ratios between [OH] and [COOH]. The activation parameters were also calculated. 相似文献
14.
The reaction of 2,3-diaminonaphthalene with dimedone gave 3-[(3-amino-2-naphthyl)amino]-5,5-dimethylcyclohex-2-en-1-one that reacts with alloxan to afford a product of addition at the enamine moiety. The latter is converted to a spiro derivative on heating in CF 3COOH, or undergoes condensation with 2,6-di- tert-butyl- p-benzoquinone to give a benzophenazinone derivative with a sterically hindered phenol substituent. 相似文献
15.
A prominent dissociation path for electrospray generated tryptic peptide ions is the dissociation of the peptide bond linking
the second and third residues from the ammo-terminus. The formation of the resulting b 2 and y
n−2 fragments has been rationalized by specific facile mechanisms. An examination of spectral libraries shows that this path
predominates in diprotonated peptides composed of 12 or fewer residues, with the notable exception of peptides containing
glutamine or glutamic acid at the N-terminus. To elucidate the mechanism by which these amino acids affect peptide fragmentation,
we synthesized peptides of varying size and composition and examined their MS/MS spectra as a function of collision voltage
in a triple quadrupole mass spectrometer. Loss of water from N-terminal glutamic acid and glutamine is observed at a lower
voltage than any other fragmentation, leading to cyclization of the terminal residue. This cyclization results in the conversion
of the terminal amine group to an imide, which has a lower proton affinity. As a result, the second proton is not localized
at the N-terminus but is readily transferred to other sites, leading to fragmentation near the center of the peptide. Further
confirmation was obtained by examining peptides with N-terminal pyroglutamic acid and N-acetyl peptides. Peptides with N-terminal
proline maintain the trend of forming b 2 and y
n−2 because their ring contains an imine rather than imide and has sufficient proton affinity to retain the proton at the N-terminus. 相似文献
16.
The [C 7H 10NO 3] + ion in the normal mass spectrum of 2-ethoxycarbonyl-5-oxo-2-pyrrolidinepropanoic acid was shown to correspond to a mixture of two isomeric structures. By decreasing the ionizing electron energy, the one containing a CH 2CH 2COOH group becomes dominant. The proportion of the concentrations of the two isomeric ions was calculated by comparing their daughter ion spectra (obtained by linked scan at constant B/E) with the analogous spectra of a derivative partially labelled by deuterium at the carboxyl and amide groups. 相似文献
17.
The paper describes methods for the synthesis and isolation of solid phases of the individual stereoisomeric Pd(II) bis(amino
acid) complexes with serine (SerH = NH 2C*H(CH 2OH)COOH, α-amino-β-hydroxypropionic acid), threonine (ThrH CH 3C*H(OH)C*H(NH 2)COOH, threo-α-amino-β-hydroxybutyric acid), and allothreonine (alloThrH is erythro-α-amino-β-hydroxybutyric acid): cis-[Pd(S-Ser)2], trans-[Pd(R-Ser)(S-Ser)], cis-[Pd(S-Thr) 2], trans-[Pd(S-Thr) 2], trans-[Pd(R-Thr)(S-Thr)], and cis-[Pd(R-alloThr)(S-alloThr)] (R, S are the absolute configurations of the asymmetric C* atom connected to the NH 2 group). The synthesized compounds were characterized by elemental analysis, IR and NMR ( 1H and 13C) data, and X-ray diffraction analysis. 相似文献
18.
Kinetics and mechanism of the reaction of Cr(VI) with oxalic acid have been studied in presence and absence of H 2SO 4, HClO 4, and CH 3COOH by monitoring the formation of Cr(III)-oxalic acid complex at 560 nm. The effect of total [oxalic acid], [Cr(VI)], [H 2SO 4], [HClO 4], and [CH 3COOH] on the reaction rate was determined at 30°C. Formation of carbon dioxide was also confirmed. The oxidation rate increases with [oxalic acid] and [CH 3COOH] while it decreases with [H 2SO 4], [HClO 4], and pH. The rate law governing the oxidation of oxalic acid over a wide range of conditions is rate= k1 Kes1 [oxalic acid] T [Cr(VI)] T 1+ Kes1 [oxalic acid] T, where only undissociated oxalic acid is kinetically active. Kinetic evidence for the formation of a Cr(VI)(SINGLEBOND)oxalic acid 1:1 complex has been obtained and the equilibrium constant for their formation has been determined. The 1:1 complex exists most likely in an open chain form. The rate-limiting step of the oxidation reaction involves the breaking of the C(SINGLEBOND)C bond in the 1:2 complex. Oxidizing ability of Cr(VI) species have been discussed. Mechanism with the associated reaction kinetics is assigned. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 335–340, 1998 相似文献
19.
Abstract Non-enzymic methods for the phosphorylation of proteins are reviewed with respect to type of reagent, protein source, reactive site (N[sbnd], O[sbnd] or S[sbnd]), extent of reaction, and effect on physical properties, functionality and biological properties. Experimental procedures are given to illustrate the most important methods. Some enzymic methods are included for comparison. The evidence for phosphorylation of specific amino acid residues, such as serine, threonine, histidine or lysine, is critically assessed. Conclusions are drawn regarding the status of phosphorylation as a synthetic method for modifying proteins. 相似文献
20.
Structure of a Stable Dipolar Compound from 2,2-Dimethyl-3-dimethylamino-2 H-azirine and Benzoylisothiocyanate. Benzoylisothiocyanate and 2,2-dimethyl-3-dimethylamino-2 H-azirine ( 1 ) react to given the dipolar compound 4,4-dimethyl-2-thiazolin-5-dimethylimminium-2-benzcarboxamidate ( 2 ), whose structure has been proved by X-ray analysis. Compound 2 , upon addition of water, yields the thiourea derivative 3 , whereas by acid catalyzed hydrolysis the thiazolinone derivative 4 is formed. The dipolar structure 2 is also existent in organic solvents like dimethylsulfoxide or chloroform. 相似文献
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