1,427,535 research outputs found
Tight Binding of a Dimeric Derivative of Vancomycin with Dimeric l-Lys-d-Ala-d-Ala
No full textThe ligand/receptor pair consisting of a synthetic
dimeric derivative of vancomycin (V), linked at the
C
terminus by p-xylylenediamine
(V-CONHCH2C6H4CH2NHCO-V),
and a dimeric derivative of
l-Lys-d-Ala-d-Ala,
[CH2CONεH(Nα-Ac)-l-Lys-d-Ala-d-Ala-CO2-]2,
provides a new system with which to study the influence of
divalency
on the strength of binding. A competitive assay using affinity
capillary electrophoresis (ACE) has been developed
and used to estimate the dissociation constant of the divalent complex
(≈ 1.1 nM) and the enhancement in
binding (∼103) relative to the corresponding monomeric
interaction between unmodified monomeric vancomycin
and
diacetyl-l-Lys-d-Ala-d-Ala
Synthesis of [l-Ala-1]RA-VII, [d-Ala-2]RA-VII, and [d-Ala-4]RA-VII by Epimerization of RA-VII, an Antitumor Bicyclic Hexapeptide from <i>Rubia</i> Plants, through Oxazoles
No full textThree epimers of a natural cyclic hexapeptide RA-VII were prepared via formation of oxazoles
from thioamides or thioimidates of RA-VII followed by hydrolysis. They are the epimers at l-Ala-1, d-Ala-2,
and d-Ala-4, respectively. The one having l-Ala-1 adopted trans-cis-trans-trans-trans-trans (t-c-t-t-t-t) amide
configurations in the crystal, a type-VI β-turn for residues 1−4 stabilized by one intramolecular hydrogen
bond between Ala-4 NH and l-Ala-1 C = O, and in CDCl3 existed as a mixture of six conformers, of which
the major conformer was very similar to that in the crystal, but quite different from that of RA-VII in solution.
The second epimer, having d-Ala-2 had in the crystalline state t-t-t-t-c-t amide configurations, a γ-turn at
Tyr-3 stabilized by two intramolecular hydrogen bonds between d-Ala-2 NH and Ala-4 C = O and between
Ala-4 NH and d-Ala-2 C = O, and existed in CDCl3 as a single conformer, the structure of which was very
similar to its crystal structure, and to the crystal structure of peptide 25 except for the backbone and the
side chains at residues 1 and 2. The third epimer, having d-Ala-4 had t-c-t-t-c-t amide configurations in the
crystal, a type-VI β-turn for residues 1−4 as observed in the first epimer, and in CDCl3 existed in three
conformers, of which the major one was similar to that in the crystal but different from that of RA-VII in
solution. The three epimers showed very weak cytotoxicity on P-388 leukemia cells, which may be because
of their conformational differences from the active conformation of RA-VII
Synthesis of [l-Ala-1]RA-VII, [d-Ala-2]RA-VII, and [d-Ala-4]RA-VII by Epimerization of RA-VII, an Antitumor Bicyclic Hexapeptide from <i>Rubia</i> Plants, through Oxazoles
No full textThree epimers of a natural cyclic hexapeptide RA-VII were prepared via formation of oxazoles
from thioamides or thioimidates of RA-VII followed by hydrolysis. They are the epimers at l-Ala-1, d-Ala-2,
and d-Ala-4, respectively. The one having l-Ala-1 adopted trans-cis-trans-trans-trans-trans (t-c-t-t-t-t) amide
configurations in the crystal, a type-VI β-turn for residues 1−4 stabilized by one intramolecular hydrogen
bond between Ala-4 NH and l-Ala-1 C = O, and in CDCl3 existed as a mixture of six conformers, of which
the major conformer was very similar to that in the crystal, but quite different from that of RA-VII in solution.
The second epimer, having d-Ala-2 had in the crystalline state t-t-t-t-c-t amide configurations, a γ-turn at
Tyr-3 stabilized by two intramolecular hydrogen bonds between d-Ala-2 NH and Ala-4 C = O and between
Ala-4 NH and d-Ala-2 C = O, and existed in CDCl3 as a single conformer, the structure of which was very
similar to its crystal structure, and to the crystal structure of peptide 25 except for the backbone and the
side chains at residues 1 and 2. The third epimer, having d-Ala-4 had t-c-t-t-c-t amide configurations in the
crystal, a type-VI β-turn for residues 1−4 as observed in the first epimer, and in CDCl3 existed in three
conformers, of which the major one was similar to that in the crystal but different from that of RA-VII in
solution. The three epimers showed very weak cytotoxicity on P-388 leukemia cells, which may be because
of their conformational differences from the active conformation of RA-VII
Synthesis of [l-Ala-1]RA-VII, [d-Ala-2]RA-VII, and [d-Ala-4]RA-VII by Epimerization of RA-VII, an Antitumor Bicyclic Hexapeptide from <i>Rubia</i> Plants, through Oxazoles
No full textThree epimers of a natural cyclic hexapeptide RA-VII were prepared via formation of oxazoles
from thioamides or thioimidates of RA-VII followed by hydrolysis. They are the epimers at l-Ala-1, d-Ala-2,
and d-Ala-4, respectively. The one having l-Ala-1 adopted trans-cis-trans-trans-trans-trans (t-c-t-t-t-t) amide
configurations in the crystal, a type-VI β-turn for residues 1−4 stabilized by one intramolecular hydrogen
bond between Ala-4 NH and l-Ala-1 C = O, and in CDCl3 existed as a mixture of six conformers, of which
the major conformer was very similar to that in the crystal, but quite different from that of RA-VII in solution.
The second epimer, having d-Ala-2 had in the crystalline state t-t-t-t-c-t amide configurations, a γ-turn at
Tyr-3 stabilized by two intramolecular hydrogen bonds between d-Ala-2 NH and Ala-4 C = O and between
Ala-4 NH and d-Ala-2 C = O, and existed in CDCl3 as a single conformer, the structure of which was very
similar to its crystal structure, and to the crystal structure of peptide 25 except for the backbone and the
side chains at residues 1 and 2. The third epimer, having d-Ala-4 had t-c-t-t-c-t amide configurations in the
crystal, a type-VI β-turn for residues 1−4 as observed in the first epimer, and in CDCl3 existed in three
conformers, of which the major one was similar to that in the crystal but different from that of RA-VII in
solution. The three epimers showed very weak cytotoxicity on P-388 leukemia cells, which may be because
of their conformational differences from the active conformation of RA-VII
Synthesis of [l-Ala-1]RA-VII, [d-Ala-2]RA-VII, and [d-Ala-4]RA-VII by Epimerization of RA-VII, an Antitumor Bicyclic Hexapeptide from <i>Rubia</i> Plants, through Oxazoles
No full textThree epimers of a natural cyclic hexapeptide RA-VII were prepared via formation of oxazoles
from thioamides or thioimidates of RA-VII followed by hydrolysis. They are the epimers at l-Ala-1, d-Ala-2,
and d-Ala-4, respectively. The one having l-Ala-1 adopted trans-cis-trans-trans-trans-trans (t-c-t-t-t-t) amide
configurations in the crystal, a type-VI β-turn for residues 1−4 stabilized by one intramolecular hydrogen
bond between Ala-4 NH and l-Ala-1 C = O, and in CDCl3 existed as a mixture of six conformers, of which
the major conformer was very similar to that in the crystal, but quite different from that of RA-VII in solution.
The second epimer, having d-Ala-2 had in the crystalline state t-t-t-t-c-t amide configurations, a γ-turn at
Tyr-3 stabilized by two intramolecular hydrogen bonds between d-Ala-2 NH and Ala-4 C = O and between
Ala-4 NH and d-Ala-2 C = O, and existed in CDCl3 as a single conformer, the structure of which was very
similar to its crystal structure, and to the crystal structure of peptide 25 except for the backbone and the
side chains at residues 1 and 2. The third epimer, having d-Ala-4 had t-c-t-t-c-t amide configurations in the
crystal, a type-VI β-turn for residues 1−4 as observed in the first epimer, and in CDCl3 existed in three
conformers, of which the major one was similar to that in the crystal but different from that of RA-VII in
solution. The three epimers showed very weak cytotoxicity on P-388 leukemia cells, which may be because
of their conformational differences from the active conformation of RA-VII
Design, Synthesis, and Characterization of a High-Affinity Trivalent System Derived from Vancomycin and l-Lys-d-Ala-d-Ala
No full textA trivalent derivative of vancomycin, tris(vancomycin carboxamide), [C6H3-1,3,5-(CONHC6H4-4-CH2NHCOV)3 (RtV3; V = vancomycin)], binds an analogous trivalent derivative of d-Ala-d-Ala, R‘tL‘3, (C6H3-1,3,5-[CONεH(Nα-Ac)-l-Lys-d-Ala-d-Ala]3) in water with a dissociation constant that is approximately 4 ×
10-17 M, as estimated by HPLC using a competitive assay against Nα,ε-diacetyl-l-Lys-d-Ala-d-Ala (L). This
binding is one of the tightest known for low molecular weight organic species. The dissociation of RtV3·R‘tL‘3
in the presence of an excess of L could be followed by HPLC. The kinetics of dissociation are quite different
from those of monovalent tight-binding systems such as avidin and biotin. In particular, the rate of dissociation
of the aggregate RtV3·R‘tL‘3 is rapid in the presence of monovalent L at concentrations greater than the value
of the dissociation constant for the complex of L with V; by contrast, the rate of dissociation of biotin·avidin
is independent of the concentration of biotin. Two mechanisms by which the dissociation may occur are
postulated and discussed. Calorimetric measurements for the trivalent system indicate that the enthalpy of
association is ∼−40 kcal/mol, about three times that of V + L, and thus the entropy of association is ∼−18
kcal/mol, approximately 4.5 times that of V + L
State of America\u27s Libraries Report 2023
No full textIl s\u27agit du rapport 2023 de l\u27Association Américaine des Bibliothèques (ALA en anglais pour American Libraries Association). Ce rapport insiste sur les capacités d\u27adaptation des bibliothécaires américains alors qu\u27une offensive ,sans précédente, de censure touchent ces institutions. Le rapport a produit un top 13 des livres les plus censurés en 2022
Uvodnik [v angleščini]
No full textThe winter issue of Volume 11 presents a selection of seven different research articles on Japanese, Tetun Dili, Sylheti Bangla, Pahari, and Saraiki language. The rise of the Covid-19 pandemic, of which continuation unfortunately still allows many to collect data for research, has prompted us to publish several other interesting studies. This compilation brings to the readers the following topics.
This issue opens with Saki AMANO’s paper “Polysemy of ‘Common Language’ and the Modern Japanese Nation: The Universalization of a ‘Standard Language’ to correct ‘Dialects’?”. The author examines the term futsūgo (common language) over two periods and explains the shift from the populace’s everyday commonplace language to a unified national language.
In the next paper “From Native-speaker Likeness to Self-representation in Language: Views from the Acquisition of Japanese Transitive and Intransitive Verbs”, ITO Hideaki considers the degree to which a language user’s own will is recognized in language education. The author demonstrates that the usage-centric acquisition process can create opportunities for language users to make expressive choices focused on what they wish to say.
The third article is Nastja PAHOR’s paper “Corpus analysis of the collocations of the transitive verbs owaru and oeru”, in which the author approaches the transitivity of Japanese verbs from the corpus perspective. Semantical analysis of collocations in combination with the morphological analysis of co-occurring verbs reveals some interesting findings.
After the first three papers that focus on Japanese, the fourth one brings some new insights into Tetun Dili. Andrei A. AVRAM in his paper “Contact-induced variation in Tetun Dili phonology” analyzes Portuguese influence on Tetun Dili phonology, and demonstrates that the intricacies of inter-speaker variation cannot be merely reduced to variation between more Portuguese-like phonology and a more Tetun-Dili-like one.
Arpita GOSWAMI’s paper “Marked Geminates as Evidence of Sonorants in Sylheti Bangla: An Optimality Account” analyzes the universal concept that sonorants are marked geminates in the gemination process of Sylheti Bangla, and proposes a hierarchy of the constraints for analyzing the gemination processes in SHB. Besides, the author illustrates some additional constraints found to be necessary.
The following article “Stop Voicing and F0 Perturbation in Pahari” presents the findings of Nazia RASHID, Abdul Qadir KHAN, Ayesha SOHAIL, and Bilal Ahmed ABBASI. The authors investigate the perturbation effect of the voicing of initial stops on the fundamental frequency of the following vowels in Pahari.
Last but not least, “Word Stress system of the Saraiki language” is an article by Firdos ATTA, who presents an Optimality-Theoretic analysis of Saraiki word stress. The author concludes that Saraiki has a trochaic stress system and falls in the category of quantity-sensitive languages. This paper also indicates further research work on word stress at the sentence level.
Editors and Editorial board wish the regular and new readers of the ALA journal a pleasant read full of inspiration, and a rise of new research ideas inspired by these papers
Predgovor (v angleščini)
No full textIn these strange days of a limited physical and social contact due to the worldwide pandemic we are especially grateful for the existence of the parallel virtual world, which goes beyond human shortcomings. Our work continued without any obstructions and we are pleased to announce the summer ALA issue of the year 2020. In it we offer six research articles that extend over a broad linguistic area and include languages of the far East Asia, namely Mandarin Chinese, Japanese, Korean, and Vietnamese.
The issue opens with the WU Jiayi’s article “Contextual Conditions and Constraints in Chinese Dangling Topics: Syntax-Discourse Interface Analysis”, in which the author revisits dangling topics in Mandarin Chinese from the semantic and syntactic view, and evolves their findings to the hypothesis concerning language typology.
The second article on Chinese is Tina ČOK’s “Lexical Aspect Classification for Unrelated Languages: A Case Study on Slovenian and Chinese Lexical Aspect”, in which the author analyzes Chinese and Slovenian verb aspect to show that deeper cognitive differences effect our perception of reality, and upon her findings proposes an upgraded general classification of verb types.
The following article entitled “The New Chinese Corpus of Literary Texts Litchi” by Mateja PETROVČIČ, Radovan GARABÍK, and Ľuboš GAJDOŠ presents a newly launched corpus of Chinese literary texts Litchi, and exemplifies the variety of its benefits.
Furthermore, Petra JAKLIN “The Many Meanings of the Japanese Causative:Widening the Pragmatic Take on the -(sa)seru Causative Sentence” is an article in which the author revisits the range of possible interpretations and meanings carried by Japanese causative sentences, and supports her conclusions with comparisons to English and Croatian structures.
HWANG Yoong Hee’s article “Normative Forms and Synthetic Structure of Japanese in the Incubation Period of L2: Subject to Sentence-final Forms in Longitudinal Discourse Data of Korean Returnee Sisters’ Japanese” focuses on L2 Japanese sentence-final forms and their change mechanism in case of Korean returnees.
Last but not least, “Examining the Part-of-speech Features in Assessing the Readability of Vietnamese Texts” is an article by An-Vinh LUONG, Diep NGUYEN, and Dien DINH that discusses the present state of research on text readability in Vietnamese and proposes an improved model on estimating readability of texts and consequently their classification.
Editors and Editorial board wish the regular and new readers of the ALA journal a pleasant read full of inspiration.
EditorsIn these strange days of a limited physical and social contact due to the worldwide pandemic we are especially grateful for the existence of the parallel virtual world, which goes beyond human shortcomings. Our work continued without any obstructions and we are pleased to announce the summer ALA issue of the year 2020. In it we offer six research articles that extend over a broad linguistic area and include languages of the far East Asia, namely Mandarin Chinese, Japanese, Korean, and Vietnamese.
The issue opens with the WU Jiayi’s article “Contextual Conditions and Constraints in Chinese Dangling Topics: Syntax-Discourse Interface Analysis”, in which the author revisits dangling topics in Mandarin Chinese from the semantic and syntactic view, and evolves their findings to the hypothesis concerning language typology.
The second article on Chinese is Tina ČOK’s “Lexical Aspect Classification for Unrelated Languages: A Case Study on Slovenian and Chinese Lexical Aspect”, in which the author analyzes Chinese and Slovenian verb aspect to show that deeper cognitive differences effect our perception of reality, and upon her findings proposes an upgraded general classification of verb types.
The following article entitled “The New Chinese Corpus of Literary Texts Litchi” by Mateja PETROVČIČ, Radovan GARABÍK, and Ľuboš GAJDOŠ presents a newly launched corpus of Chinese literary texts Litchi, and exemplifies the variety of its benefits.
Furthermore, Petra JAKLIN “The Many Meanings of the Japanese Causative:Widening the Pragmatic Take on the -(sa)seru Causative Sentence” is an article in which the author revisits the range of possible interpretations and meanings carried by Japanese causative sentences, and supports her conclusions with comparisons to English and Croatian structures.
HWANG Yoong Hee’s article “Normative Forms and Synthetic Structure of Japanese in the Incubation Period of L2: Subject to Sentence-final Forms in Longitudinal Discourse Data of Korean Returnee Sisters’ Japanese” focuses on L2 Japanese sentence-final forms and their change mechanism in case of Korean returnees.
Last but not least, “Examining the Part-of-speech Features in Assessing the Readability of Vietnamese Texts” is an article by An-Vinh LUONG, Diep NGUYEN, and Dien DINH that discusses the present state of research on text readability in Vietnamese and proposes an improved model on estimating readability of texts and consequently their classification.
Editors and Editorial board wish the regular and new readers of the ALA journal a pleasant read full of inspiration.
Editor
3D Structure of the Complex of MDL 63,246 with the Cell Wall Model Peptide Ac<sub>2</sub>-Lys-d-Ala-d-Ala
No full textThe complex between the glycopeptide MDL 62,346 and the model
cell wall analog
Ac2-Lys-d-Ala-d-Ala was studied by NMR spectroscopy in DMSO solution. A complete
assignment of proton and carbon resonances
was achieved, and the data were compared with the results observed for
the free glycopeptide. NOE buildup rates
were determined to calculate interproton distances which were used as
constraints to model the 3D structure of the
complex. Molecular dynamics simulations were performed in DMSO to
gain further insight into the stability of the
complex and the dynamical behavior of structural features. The
structure of the glycopeptide backbone and the
attractive interactions in the intermolecular interface are very well
defined. The complex is stabilized by the formation
of five intermolecular hydrogen bonds between the glycopeptide and the
tripeptide
- …
