Efficient & Novel Approaches to Relay Chirality in the Synthesis of Planar Chiral Metallocenes

Abstract Intermolecular and intramolecular dynamic kinetic resolution were detected for organocobalt complexed diynes prepared from the complexation of an alkyne to dicobalt hexacarbonyl, Co2(CO)6 and subsequent manipulation of the carbocationic charge generated at the carbon α– to the alkyne moiety via to the prior treatment with a Co2(CO)6– stabilised enyne, propargylic alcohol and alkynyl radical in a interesting departure from the Nicholas reaction. Diastereomeric ratios of up to 1:0 in favour of the anti diastereoisomer and yields of up to 67% were observed. Ether and ester linked diynes were synthesised from secondary terminal propargylic alcohols. On heating with (η5– cyclopentadienyl)bis(triphenylphosphine)cobalt(I), new chiral transition metal complexes were formed with high diastereomeric ratios in greater than 70% yield displaying in some cases four elements of chirality; central carbon chirality, chiral–at–metal chirality, conformational propeller phosphine chirality and conformational atropisomerism. Using mainly two representative examples the first a 7,5–membered cyclic lactone and the second a 5,5–membered cyclic ether complex the origins of chirality were explored which indicated the central carbon chirality relayed its stereochemical information to the stereogenic transition metal center thus resulting in a opposite configuration to the remote central carbon element of chirality i.e. (SC,RCo). Due to the unique properties of the 7,5–membered cyclic lactone complex a relatively stable major conformation propeller isomer of triphenylphosphine was found to be locked in space e.g. (SC,RCo,P). NMR analysis showed the presence of a dynamic equilibrium as three minor peaks of approximate equal intensity were observed which could be conformational atropisomers arising from hindered rotation between two interacting aromatics as a result of conformational flexibility inherent of the lactone architecture e.g. (P,aR), (R,aS), (M,aR), (M,aS). With respect to the 5,5–membered cyclic ether complex using a chiral ether diyne in a oxidative cyclisation reaction was found to result in chirality being relayed from the carbon stereogenic center to the chiral–at–metal stereocenter. As with the lactone complexes, an opposite configuration was observed. However, with respect to the conformation of triphenylphosphine it appeared to be non selective upon initial complexation. Recrystallisation gave an enriched (M) propeller conformational isomer which allowed the configurational stability of the chiral metal center to be measured which suggested that a mechanism did exist for epimerisation at metal but occurred only at an ambient temperature over several hours. Chiral metallocyclopentadiene complexes were treated with a selection of isocyanides and found to give novel planar chiral (η5–cyclopentadienyl)(η4–iminocyclopentadiene)cobalt metallocenes in good yields >60% yield and in some cases a diastereomeric ratio of up to 5:1. The isocyanide insertion reaction was in some cases complementary to the results observed for the isocyanides isoelectronic equivalent carbon monoxide which gave similar planar chiral (η5– cyclopentadienone)(η5–cyclopentadienyl)cobalt metallocenes. Preliminary results suggests because the isocyanide is smaller, in the diastereomeric transition state it is less discriminating compared to the chiral–at–metal complexes which are highly diastereoselective with respect to the configuration at metal. The methodology was extended to a non racemic example and found which gave a diastereomeric ratio of 2:1 and 92% yield. *[N.B.: Additional data was attached to this thesis at the time of its submission. Please refer to the author for further details.

Relative Dissatisfaction and Its Impact on Employees’ Intention to Quit

This study aims at showing the factors of relative job dissatisfaction and the influence of those factors on employee intention to quit. The study has conducted a field survey of 143 respondents from different famous private sector companies of Bangladesh. The findings of this study are that most of the factors of relative job dissatisfaction lead to employee intention to quit. Such as:  in the expectation of more pay and better working conditions employees intend to quit the job or organization, similarly employees possess the intention to quit when they want to lessen their workload or to get good supervision. Likewise, employees possess the intention to quit the job or organization in case of getting sound retirement benefits. On the other hand, employees are not found to possess the intention to quit the organization or job in order to get and accept more challenging jobs. The findings of this study will help manager and concerned authorities to be aware about the factors of relative job dissatisfaction of an employee as well as to take care about the factors that lead the employees to possess the intention to quit the organization which is similarly harmful for any organization as the real turnover. Keywords: Relative dissatisfaction, turnover intention, factors, turnover

Facile One-Pot Synthesis of NiCo₂Se₄-RGO on Ni Foam for High Performance Hybrid Supercapacitors

A facile, innovative synthesis for the fabrication of NiCo2Se4-rGO on a Ni foam nanocomposite via a simple hydrothermal reaction is proposed. The as-prepared NiCo2Se4-rGO@Ni foam electrode was tested through pxrd, TEM, SEM, and EDS to characterize the morphology and the purity of the material. The bimetallic electrode exhibited outstanding electrochemical performance with a high specific capacitance of 2038.55 F g-1 at 1 A g-1. NiCo2Se4-rGO@Ni foam exhibits an extensive cycling stability after 1000 cycles by retaining 90% of its initial capacity. A superior energy density of 67.01 W h kg-1 along with a high power density of 903.61 W kg-1 further proved the high performance of this electrode towards hybrid supercapacitors. The excellent electrochemical performance of NiCo2Se4-rGO@Ni foam can be explained through the high electrocatalytic activity of NiCo2Se4 in combination with reduced graphene oxide which increases conductivity and surface area of the electrode. This study proved that NiCo2Se4-rGO@Ni foam can be utilized as a high energy density-high power density electrode in energy storage applications

Factors Determining Job Turnover: A Study on Some Leading Private and Public Sector Companies of Bangladesh

What causes job turnover? Why do some people frequently change their jobs? The answer is, ‘definitely some factors are responsible for this’. This article aimed at identifying the factors which lead to job turnover in Bangladesh. In order to collect data for this study a comprehensive questionnaire was distributed to 150 employees of different private and public organizations in Bangladesh, of them 143 usable responses were received (drop-out rate: 5 percent). The results showed that the main factors for which people quit their jobs were Work load and supervision, Retirement benefits, Administration, Pay and facilities, Job Challenges, Job Availability and performance. The suggestion of this study was that, the organizations experienced excessive rate of job turnover should consider the said factors employee retention and maintenance. Keywords: job turnover, commitment, intention to quit, job dissatisfaction, organization

Street Vending as an Alternative to Self-employment and a Way to Income Generation in Bangladesh

This study aimed at visualizing the role of the street vendors as a way to self-employment and income generation in Bangladesh. It was based on the survey of 152 street vendors in different areas of Dhaka. It administered a well structured questionnaire to collect the primary information and to picture the overall street vending scenario in order to show the contribution of the street vendors in self-employment and income generation of Bangladesh. The findings of the study showed that the street vendors are playing a significant role in the economic development of the country through creating the self-employment opportunities, income generation and saving a specific portion from among their income. Since for this street vending, both the vendors and the local community faced several problems the paper finally suggested that, a well management and formalization system of street vending can enrich the overall street vending scenario of the city and can bring a good prospect for the economy. Keywords: Street vendors, street vending, street vending scenario, social status

Ultrasensitive and Highly Selective Ni₃Te₂ as a Nonenzymatic Glucose Sensor at Extremely Low Working Potential

Developing Nonenzymatic glucose biosensors has recently been at the center of attention owing to their potential application in implantable and continuous glucose monitoring systems. In this article, nickel telluride nanostructure with the generic formula of Ni3Te2 has been reported as a highly efficient electrocatalyst for glucose oxidation, functional at a low operating potential. Ni3Te2 nanostructures were prepared by two synthesis methods, direct electrodeposition on the electrode and hydrothermal method. The electrodeposited Ni3Te2 exhibited a wide linear range of response corresponding to glucose oxidation exhibiting a high sensitivity of 41.615 mA cm-2 mM-1 and a low limit of detection (LOD) of 0.43 µM. The hydrothermally synthesized Ni3Te2, on the other hand, also exhibits an ultrahigh sensitivity of 35.213 mA cm-2 mM-1 and an LOD of 0.38 µM. The observation of high efficiency for glucose oxidation for both Ni3Te2 electrodes irrespective of the synthesis method further confirms the enhanced intrinsic property of the material toward glucose oxidation. In addition to high sensitivity and low LOD, Ni3Te2 electrocatalyst also has good selectivity and long-term stability in a 0.1 M KOH solution. Since it is operative at a low applied potential of 0.35 V vs Ag|AgCl, interference from other electrochemically active species is reduced, thus increasing the accuracy of this sensor

Immersive Horizons: Exploring the Transformative Power of Virtual Reality Across Economic Sectors

open access articleThe scholarly discourse surrounding the manifold advantages, applications, and limitations of implementing Virtual Reality (VR) in the contemporary milieu has burgeoned over time. VR holds immense potential, attracting fervent interest from governmental and private entities alike. Nevertheless, the existing body of literature pertaining to the expanding utilization of VR in diverse economic sectors remains scant. Therefore, the primary objective of this study is to furnish a comprehensive literature review encompassing VR applications across various economic domains while elucidating concerns surrounding its integration within engineering education. A total of 108 publications were extracted from prominent databases such as Scopus, Elsevier, Science Direct, and Google Scholar, with a subsequent review of 51 relevant works. These scrutinized journals were published between 2015 and 2022 and were predominantly authored in English. The reviewed publications encompassed VR applications in education, robotics, healthcare, transportation, sports, agriculture, governance, security, and media. The study’s findings unveiled significant advancements in VR implementation within engineering education, medical training, cognitive augmentation, aircraft assembly, governance, and diverse other spheres. Notwithstanding these achievements, impediments to VR deployment were identified, stemming from financial exigencies, cultural and conventional norms, with scant evidence of VR’s prevalence in underdeveloped nations, given that all the assessed research originated from developed economies. Additionally, the limitations of this review encompassed a small sample size and a narrowly focused demographic in the examined articles. Nevertheless, despite these constraints, the research highlights substantial progress in VR utilization over the preceding decade

A poised fragment library enables rapid synthetic expansion yielding the first reported inhibitors of PHIP(2), an atypical bromodomain

Research into the chemical biology of bromodomains has been driven by the development of acetyl-lysine mimetics. The ligands are typically anchored by binding to a highly conserved asparagine residue. Atypical bromodomains, for which the asparagine is mutated, have thus far proven elusive targets, including PHIP(2) whose parent protein, PHIP, has been linked to disease progression in diabetes and cancers. The PHIP(2) binding site contains a threonine in place of asparagine, and solution screening have yielded no convincing hits. We have overcome this hurdle by combining the sensitivity of X-ray crystallography, used as the primary fragment screen, with a strategy for rapid follow-up synthesis using a chemically-poised fragment library, which allows hits to be readily modified by parallel chemistry both peripherally and in the core. Our approach yielded the first reported hit compounds of PHIP(2) with measurable IC50 values by an AlphaScreen competition assay. The follow-up libraries of four poised fragment hits improved potency into the sub-mM range while showing good ligand efficiency and detailed structural data