Synthesis and Reactivity of Main Group Complexes for Applications in Small Molecule Activation

The work described in this thesis is focused on the preparation of a series of novel main group complexes, featuring unusual structural and bonding situations, and the study of their reactivity toward small molecules. The new zinc complexes dimphZnBu (V-2) and dimphZnCl2Li(THF)3 (V-3), supported by a diiminophenyl (dimph) ligand were prepared. The reaction of complex V-3 with LiHBEt3 resulted in hydride transfer to the C=N imine group to give an unusual zinc dimer (V-7). The latter transformation occurs via formation of compound (ɳ1(C),ĸ1(N)- 2,6-(2,6-iPr2C6H3N=CH)2C6H3)2Zn (V-5) which can be also accessed by reduction of V-7 with KC8. Diiminophenyl (dimph) proved to be an excellent ligand platform to stabilise a low-valent phosphorus centre. The resultant compound dimphP (VI-2), which can be rationalised as an imino-stabilised phosphinidene or benzoazaphopshole, shows remarkable chemical stability toward water and oxygen. VI-2 reacts with excess strong acid HCl to generate the P(III) chloride (dimHph)PCl (VI-6). Surprisingly, substitution of the chloride under some nucleophilic (KOBut) and electrophilic conditions (Me3SiOTf) regenerates the parent compound VI-2 by proton removal from the weakly acidic CH2N position. A related species (dimH2ph)P (VI-10) is produced upon thermal rearrangement of the hydride (dimHph)PH (VI-9). The molecular structure and reactivity of compounds VI-2 and other related compounds are also discussed. The reduction of the O,C,O-chelated phosphorus (III) chloride (VI-16) ( O,C,O = 2,6-bis[(2,6-diisopropyl)phenoxyl]phenyl) with KC8 or PMe3 resulted in the formation of a cyclic three-membered phosphorus compound (VI-18). The intermediacy of phosphinidene VI-17 was confirmed by trapping experiments and a VT 31P{1H} NMR study. The reaction of in-situ generated phosphinidene with either PhSiH3 or HBpin resulted in the formation of an unprecedented phosphine (VI-23). The treatment of VI-16 with two equivalents of DippNHC carbene led to ArP(Cl)NHC product (VI-24). The germylone dimNHCGe (dimNHC = diimino N-Heterocyclic Carbene, VII-8) was successfully prepared by the reduction of germanium cation (VII-7) with KC8. The molecular structure of VII-8 was unambiguously established, using NMR spectroscopy and single-crystal X-ray diffraction analysis. The reactivity of VII-8 was investigated. VII-8 is inactive towards butadiene but undergoes an oxidative cyclization with tetrachloro-o-benzoquinone to give a tetragermanium derivative. VII-8 undergoes oxidation addition of CH3I and PhI, followed by an unusual migration of the Me and Ph groups from germanium to the carbene ligand. Related chemistry takes place upon protonation with dry HCl, which results in the migration of the hydride to the carbene ligand

Binding mechanism and SERS spectra of 5-fluorouracil on gold clusters

The adsorption behaviour of the 5-fluorouracil (5FU) on small gold clusters AuN with N = 6, 8, 20 was evaluated by means of density functional theory using the PBE-D3 functional in combination with a mixed basis set, i.e. cc-pVDZ-PP for gold atoms and cc-pVTZ for non-metal elements. The binding energies between 5FU and gold clusters were determined in the range of 16–24 and 11–19 kcal/mol in gas-phase and aqueous media, respectively. The corresponding Gibbs energies were found to be around -7 to -10 kcal/mol in vacum and sigificantly reduced to -1 to -6 kcal/mol in water solution, indicating that both the association and dissociation processes are likely spontaneous. An analysis on the charge density difference tends to confirm the existence of a charge transfer from the 5FU molecule to Au atoms. Analysis of the surface-enhanced Raman scattering (SERS) spectra of 5FU adsorbed on the Au surfaces shows that the stretching vibrations of N−H and C=O bonds play a major role in the SERS phenomenon. A mechanism for the drug releasing from the gold surfaces is also proposed. The process is triggered by either the low pH in cancerous tumors or the presence of cysteine residues in protein matrices

Combination of Domain Knowledge and Deep Learning for Sentiment Analysis of Short and Informal Messages on Social Media

Sentiment analysis has been emerging recently as one of the major natural language processing (NLP) tasks in many applications. Especially, as social media channels (e.g. social networks or forums) have become significant sources for brands to observe user opinions about their products, this task is thus increasingly crucial. However, when applied with real data obtained from social media, we notice that there is a high volume of short and informal messages posted by users on those channels. This kind of data makes the existing works suffer from many difficulties to handle, especially ones using deep learning approaches. In this paper, we propose an approach to handle this problem. This work is extended from our previous work, in which we proposed to combine the typical deep learning technique of Convolutional Neural Networks with domain knowledge. The combination is used for acquiring additional training data augmentation and a more reasonable loss function. In this work, we further improve our architecture by various substantial enhancements, including negation-based data augmentation, transfer learning for word embeddings, the combination of word-level embeddings and character-level embeddings, and using multitask learning technique for attaching domain knowledge rules in the learning process. Those enhancements, specifically aiming to handle short and informal messages, help us to enjoy significant improvement in performance once experimenting on real datasets.Comment: A Preprint of an article accepted for publication by Inderscience in IJCVR on September 201

GRAMMATICAL ERRORS IN ACADEMIC WRITING OF ENGLISH SECOND-YEAR STUDENTS

The study aimed to analyze the common grammatical errors of students in academic writing. Mixed-method research was implemented for this study. The study team gathered 110 essays from learners in the Writing Course 4 – Social Texts classroom. Then, the researchers conducted interviews with 23 learners in order to ascertain the reasons behind their grammatical errors in writing and provide suitable remedies. Participants in this research were second-year students majoring in English Studies in the Department of English Language and Culture's High-Quality Program at a Vietnamese university. The findings revealed that the errors that made up the biggest percentage of all errors were those involving the articles (25,5 %), prepositions (14,2%), and plural/singular forms (13,7 %). On the other hand, tenses (7%), passive voice (3,8%), and subject-verb agreement (1,7%) errors had the respective lowest percentages. The results of the interviews with 23 randomly selected students in this course showed that students struggled with academic writing on a number of different levels, with the root causes being a lack of vocabulary knowledge, carelessness, and uncertainty about basic grammatical structure.  Article visualizations

Reinforcement Learning With Simulated User For Automatic Dialog Strategy Optimization

In this paper, we propose a solution to the problem of formulating strategies for a spoken dialog system. Our approach is based on reinforcement learning with the help of a simulated user in order to identify an optimal dialog strategy. Our method considers the Markov decision process to be a framework for representation of speech dialog in which the states represent history and discourse context, the actions are dialog acts and the transition strategies are decisions on actions to take between states. We present our reinforcement learning architecture with a novel objective function that is based on dialog quality rather than its duration

Remarkable shifts of C(sp2)-H and O-H stretching frequencies and stability of complexes of formic acid with formaldehydes and thioformaldehydes

Thirty‐six stable complexes of formic acid with formaldehydes and thioformaldehydes were determined on the potential energy surface, in which the XCHO···HCOOH complexes are found to be more stable than the XCHS···HCOOH counterparts, with X = H, F, Cl, Br, CH3, NH2. All complexes are stabilized by hydrogen bonds, and their contribution to the total stabilization energy of the complexes increases in going from C‐H···S to C‐H···O to O‐H···S and finally to O‐H···O. Remarkably, a significant blueshift of Csp2‐H bond by 81–96 cm−1 in the Csp2‐H···O hydrogen bond has hardly ever been reported, and a considerable redshift of O‐H stretching frequency by 206–544 cm−1 in the O‐H···O/S hydrogen bonds is also predicted. The obtained results in our present work and previous literatures support that a distance contraction and a stretching frequency blueshift of C‐H bond involving hydrogen bond depend mainly on its polarity and gas phase basicity of proton acceptor, besides the rearrangement of electron density due to complex formation. Markedly, we suggest the ratio of deprotonation enthalpy to proton affinity (R c) as an indicator to prospect for classification of hydrogen bonds. The symmetry adapted perturbation theory results show a larger role of attractive electrostatic term in XO‐n as compared to that in XS‐n and the electrostatic interaction is overwhelming dispersion or induction counterparts in stabilizing XO‐n and XS‐n, with n = 1, 2, 3

Aromatic character of planar boron-based clusters revisited by ring current calculations

The planarity of small boron-based clusters is the result of an interplay between geometry, electron delocalization, covalent bonding and stability. These compounds contain two different bonding patterns involving both sigma and pi delocalized bonds, and up to now, their aromaticity has been assigned mainly using the classical (4N + 2) electron count for both types of electrons. In the present study, we reexplored the aromatic feature of different types of planar boron-based clusters making use of the ring current approach. B3(+/-), B-4(2-), B-5(+/-), B-6, B-7(-), B-8(2-), B-9(-), B-10(2-), B-11(-), B-12, B-13(+), B-14(2-) and B-16(2-) are characterized by magnetic responses to be doubly sigma and pi aromatic species in which the pi aromaticity can be predicted using the (4N + 2) electron count. The triply aromatic character of B-12 and B-13(+) is confirmed. The pi electrons of B-18(2-), B-19(-) and B-20(2-) obey the disk aromaticity rule with an electronic configuration of [1 sigma(2)1 pi(4)1 delta(4)2 sigma(2)] rather than the (4N + 2) count. The double aromaticity feature is observed for boron hydride cycles including B@B5H5+, Li7B5H5 and M@BnHnq clusters from both the (4N + 2) rule and ring current maps. The double pi and sigma aromaticity in carbon-boron planar cycles B7C-, B8C, B6C2, B9C-, B8C2 and B7C3- is in conflict with the Huckel electron count. This is also the case for the ions B11C5+/- whose ring current indicators suggest that they belong to the class of double aromaticity, in which the pi electrons obey the disk aromaticity characteristics. In many clusters, the classical electron count cannot be applied, and the magnetic responses of the electron density expressed in terms of the ring current provide us with a more consistent criterion for determining their aromatic character

An Experimental Study of the Server-based Unfairness Solutions for the Cross-Protocol Scenario of Adaptive Streaming over HTTP/3 and HTTP/2

منذ إدخال HTTP / 3 ، ركز البحث على تقييم تأثيره على البث التكيفي الحالي عبر HTTP (HAS). من بين هذه الأبحاث ، نظرًا لبروتوكولات النقل غير ذات الصلة ، حظي الظلم عبر البروتوكولات بين HAS عبر HTTP / 3 (HAS / 3) و HAS عبر HTTP / 2 (HAS / 2) باهتمام كبير. لقد وجد أن عملاء HAS / 3 يميلون إلى طلب معدلات بت أعلى من عملاء HAS / 2 لأن النقل QUIC يحصل على عرض نطاق ترددي أعلى لعملائه HAS / 3 من TCP لعملائه HAS / 2. نظرًا لأن المشكلة تنشأ من طبقة النقل ، فمن المحتمل أن حلول الظلم المستندة إلى الخادم يمكن أن تساعد العملاء في التغلب على مثل هذه المشكلة. لذلك ، في هذه الورقة ، تم إجراء دراسة تجريبية لحلول الظلم القائمة على الخادم لسيناريو البروتوكول المتقاطع لـ HAS / 3 و HAS / 2. تظهر النتائج أنه على الرغم من فشل حل توجيه معدل البت في مساعدة العملاء على تحقيق العدالة ، فإن حل تخصيص النطاق الترددي يوفر أداءً فائقًا.Since the introduction of the HTTP/3, research has focused on evaluating its influences on the existing adaptive streaming over HTTP (HAS). Among these research, due to irrelevant transport protocols, the cross-protocol unfairness between the HAS over HTTP/3 (HAS/3) and HAS over HTTP/2 (HAS/2) has caught considerable attention. It has been found that the HAS/3 clients tend to request higher bitrates than the HAS/2 clients because the transport QUIC obtains higher bandwidth for its HAS/3 clients than the TCP for its HAS/2 clients. As the problem originates from the transport layer, it is likely that the server-based unfairness solutions can help the clients overcome such a problem. Therefore, in this paper, an experimental study of the server-based unfairness solutions for the cross-protocol scenario of the HAS/3 and HAS/2 is conducted. The results show that, while the bitrate guidance solution fails to help the clients achieve fairness, the bandwidth allocation solution provides superior performance