1. The stability of metal complexes is affected by factors such as the nature of the central metal ion, the coordinating ligand, and the presence of ring structures. The charge, size, and ionization energy of the metal ion influence stability, as do the size, charge, and basic strength of the ligand.
2. Chelation, where a multidentate ligand bonds to the metal ion at multiple sites, generally enhances stability. Five-membered rings formed by chelation are most stable due to reduced strain. An increase in the number of chelate rings or delocalized π-electrons in ring structures also increases stability.
3. Other factors like forced ligand configurations, the solvent environment, and
Classification Of Mechanisms, Ligand Substitution In Octahedral Complexes Without Breaking Metal-ligand Bond, Substitution Reaction In Square Planar Complexes, Factors Which Affect The Rate Of Substitution, Trans Effect (Labilizing Effect), Theories and applications Of Trans Effect
Classification Of Mechanisms, Ligand Substitution In Octahedral Complexes Without Breaking Metal-ligand Bond, Substitution Reaction In Square Planar Complexes, Factors Which Affect The Rate Of Substitution, Trans Effect (Labilizing Effect), Theories and applications Of Trans Effect
This Presentation describes about the evidence of metal ligand bonding in a molecule. In this presentation various evidences are explained. Learn and grow.
A brief introduction to lanthanide elements is given.
Order .ppts like this at <https://www.fiverr.com/anikmal/teamup-with-you-to-prepare-the-best-presentation>
Along with their physical and chemical properties are also shown. Helpful for quick understanding on lanthanide series.
This Presentation describes about the evidence of metal ligand bonding in a molecule. In this presentation various evidences are explained. Learn and grow.
A brief introduction to lanthanide elements is given.
Order .ppts like this at <https://www.fiverr.com/anikmal/teamup-with-you-to-prepare-the-best-presentation>
Along with their physical and chemical properties are also shown. Helpful for quick understanding on lanthanide series.
Introduction:
RNA interference (RNAi) or Post-Transcriptional Gene Silencing (PTGS) is an important biological process for modulating eukaryotic gene expression.
It is highly conserved process of posttranscriptional gene silencing by which double stranded RNA (dsRNA) causes sequence-specific degradation of mRNA sequences.
dsRNA-induced gene silencing (RNAi) is reported in a wide range of eukaryotes ranging from worms, insects, mammals and plants.
This process mediates resistance to both endogenous parasitic and exogenous pathogenic nucleic acids, and regulates the expression of protein-coding genes.
What are small ncRNAs?
micro RNA (miRNA)
short interfering RNA (siRNA)
Properties of small non-coding RNA:
Involved in silencing mRNA transcripts.
Called “small” because they are usually only about 21-24 nucleotides long.
Synthesized by first cutting up longer precursor sequences (like the 61nt one that Lee discovered).
Silence an mRNA by base pairing with some sequence on the mRNA.
Discovery of siRNA?
The first small RNA:
In 1993 Rosalind Lee (Victor Ambros lab) was studying a non- coding gene in C. elegans, lin-4, that was involved in silencing of another gene, lin-14, at the appropriate time in the
development of the worm C. elegans.
Two small transcripts of lin-4 (22nt and 61nt) were found to be complementary to a sequence in the 3' UTR of lin-14.
Because lin-4 encoded no protein, she deduced that it must be these transcripts that are causing the silencing by RNA-RNA interactions.
Types of RNAi ( non coding RNA)
MiRNA
Length (23-25 nt)
Trans acting
Binds with target MRNA in mismatch
Translation inhibition
Si RNA
Length 21 nt.
Cis acting
Bind with target Mrna in perfect complementary sequence
Piwi-RNA
Length ; 25 to 36 nt.
Expressed in Germ Cells
Regulates trnasposomes activity
MECHANISM OF RNAI:
First the double-stranded RNA teams up with a protein complex named Dicer, which cuts the long RNA into short pieces.
Then another protein complex called RISC (RNA-induced silencing complex) discards one of the two RNA strands.
The RISC-docked, single-stranded RNA then pairs with the homologous mRNA and destroys it.
THE RISC COMPLEX:
RISC is large(>500kD) RNA multi- protein Binding complex which triggers MRNA degradation in response to MRNA
Unwinding of double stranded Si RNA by ATP independent Helicase
Active component of RISC is Ago proteins( ENDONUCLEASE) which cleave target MRNA.
DICER: endonuclease (RNase Family III)
Argonaute: Central Component of the RNA-Induced Silencing Complex (RISC)
One strand of the dsRNA produced by Dicer is retained in the RISC complex in association with Argonaute
ARGONAUTE PROTEIN :
1.PAZ(PIWI/Argonaute/ Zwille)- Recognition of target MRNA
2.PIWI (p-element induced wimpy Testis)- breaks Phosphodiester bond of mRNA.)RNAse H activity.
MiRNA:
The Double-stranded RNAs are naturally produced in eukaryotic cells during development, and they have a key role in regulating gene expression .
Richard's aventures in two entangled wonderlandsRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
Richard's entangled aventures in wonderlandRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
Slide 1: Title Slide
Extrachromosomal Inheritance
Slide 2: Introduction to Extrachromosomal Inheritance
Definition: Extrachromosomal inheritance refers to the transmission of genetic material that is not found within the nucleus.
Key Components: Involves genes located in mitochondria, chloroplasts, and plasmids.
Slide 3: Mitochondrial Inheritance
Mitochondria: Organelles responsible for energy production.
Mitochondrial DNA (mtDNA): Circular DNA molecule found in mitochondria.
Inheritance Pattern: Maternally inherited, meaning it is passed from mothers to all their offspring.
Diseases: Examples include Leber’s hereditary optic neuropathy (LHON) and mitochondrial myopathy.
Slide 4: Chloroplast Inheritance
Chloroplasts: Organelles responsible for photosynthesis in plants.
Chloroplast DNA (cpDNA): Circular DNA molecule found in chloroplasts.
Inheritance Pattern: Often maternally inherited in most plants, but can vary in some species.
Examples: Variegation in plants, where leaf color patterns are determined by chloroplast DNA.
Slide 5: Plasmid Inheritance
Plasmids: Small, circular DNA molecules found in bacteria and some eukaryotes.
Features: Can carry antibiotic resistance genes and can be transferred between cells through processes like conjugation.
Significance: Important in biotechnology for gene cloning and genetic engineering.
Slide 6: Mechanisms of Extrachromosomal Inheritance
Non-Mendelian Patterns: Do not follow Mendel’s laws of inheritance.
Cytoplasmic Segregation: During cell division, organelles like mitochondria and chloroplasts are randomly distributed to daughter cells.
Heteroplasmy: Presence of more than one type of organellar genome within a cell, leading to variation in expression.
Slide 7: Examples of Extrachromosomal Inheritance
Four O’clock Plant (Mirabilis jalapa): Shows variegated leaves due to different cpDNA in leaf cells.
Petite Mutants in Yeast: Result from mutations in mitochondrial DNA affecting respiration.
Slide 8: Importance of Extrachromosomal Inheritance
Evolution: Provides insight into the evolution of eukaryotic cells.
Medicine: Understanding mitochondrial inheritance helps in diagnosing and treating mitochondrial diseases.
Agriculture: Chloroplast inheritance can be used in plant breeding and genetic modification.
Slide 9: Recent Research and Advances
Gene Editing: Techniques like CRISPR-Cas9 are being used to edit mitochondrial and chloroplast DNA.
Therapies: Development of mitochondrial replacement therapy (MRT) for preventing mitochondrial diseases.
Slide 10: Conclusion
Summary: Extrachromosomal inheritance involves the transmission of genetic material outside the nucleus and plays a crucial role in genetics, medicine, and biotechnology.
Future Directions: Continued research and technological advancements hold promise for new treatments and applications.
Slide 11: Questions and Discussion
Invite Audience: Open the floor for any questions or further discussion on the topic.
What is greenhouse gasses and how many gasses are there to affect the Earth.moosaasad1975
What are greenhouse gasses how they affect the earth and its environment what is the future of the environment and earth how the weather and the climate effects.
1. Factors Affecting The Stability of
Metal Complexes
Presented by
LOKESH JANGID
M.Sc. Chemistry Semester 2nd
Department of Chemistry
S.P.C. Government College Ajmer
2. Content:-
•Introduction-
•Factors affecting stability of metal complexes-:
1.Nature of the central metal ion
2.Nature of the coordinating group or ligand
3.Presence of ring structure
4. other factors-
a. Forced configuration
b. solvent effect
d. steric effect
3. What is stability-
The use of term stability without any qualification
Only means that the complex exists under suitable condition and it is
Possible to store the complex for an appreciable time.
two kinds of stability of complexes are generally considered-
1.Thermodynamic stability-
it is a measure of the extent of formation
or transformation of a complex under a given set of condition at
equilibrium.
2. Kinetic stability-
The Kinetic stability of a species refers to the
speed with which transformation leading to the attainment of
equilibrium will occure.
4. We can quantitatively determine the stability of a metal complex
With the help of following two constant-
1. Instability constant-
when a complex ion dissociates into its
Components, a constant similar to ionisation constant.𝐾𝑖 is called
dissociation constant or less frequently as instability constant
because it is a measure of extent of dissociation.
2. Stability constant-
The reciprocal of dissociation constant which
is a measure of extent of association is called Stability constant.
K= 1/𝐾𝑖. Higher the value of stability constant greater is the
stability of the complexes.
5. Factors affecting stability of metal complexes
1. Nature of central
metal ion
a. Size and charge
b. Ionization energies
c. Class a and class b
metals
2. Nature of
coordinating group
or ligand
a. size and charge
b. base strength
c. ligand concentration
3. Presence of ring
structure
a. Chelate effect
b. size of chelate ring
c. Number of chelate
ring
d. Entropy effect
4. Other factors
a. forced configuration
b solvent effect
c. Steric effect
6. Factors affecting stability of metal complexes-
1. Nature of the central metal ion-
a. Size and charge:
the relative stabilities of many complexes can be
explained on the basis of a simple electrostatic model. more stable
complexes expected to be formed by the combination of oppositely
charged ions. moreover, greater the charge and smaller the ions ,
greater the stability of the complexes. Smaller ions are favoured
because their centers can be closer. the following hydroxo
complexes which show a gradual increase in their stability with
the increase in the charge of the metal ion.
KLiOH =2 KMgOH
+2 = 102 KYOH
+2 = 107 KThOH
+3 =1010
As the value of stability constant increases it indicates that the
complexes become more and more stable.
7. b. Ionization energy:
the electronegativity , covalent nature and
ionic radii can all be related to the ionization energies of atoms.
it is found that the stability constant for the metal complexes with a
ligand increases with the ionization energies of the metallic species.
c. The ions with high polarizability gives complexes with higher
stability constant and also ions with high electronegativity gives
stabler complexes.
d. Class a and class b metal-
metals can be divided into two classes
as class a (hard acid) and class b (soft acid).
8. Class b metals
.less electropositive metals like Pt, Pd, Hg, Pb and
Rh belong to class b metals.
Class b metals prefer ligands in which the donor
atom is less electronegative i.e.one of the heavier
element of group VA ,VIAand VIIA.
. Class b metal complexes is attributed to the
covalent metal ligand bonds and to the transfer
of electron density from the metal to the ligand
through 𝜋 bonding by making use of d- electrons
present in the metal atoms.
. The most stable complexes of class b metals are
formed with ligand such as P𝑀𝑒3 , 𝑆2− , 𝐼− which
have vacant d- orbitals or the ligand such as CO ,
CNˉ Which have vacant molecular orbital of low
energy.
Class a metals-
. More electropositive metals like Na, Ca,
lanthanides, Ti and Fe belong to class a.
.class a metals form the most stable complexes
with ligands Having more electronegative donor
atoms like N,O or F.
. The stability of class a metal complexes is
attributed to the ionic bonding.
Class a and class b metals:
9. 2. Nature Of the coordinating group or ligand-
Nature of the ligand or important characteristics of ligand
affects to determine the stability of the compounds is
explained in the following manner-
a. Size and Charge:
Ligands with less charge and large size are less stable and
form less stable coordination compounds. Ligands with higher
charge have small size and form more stable compounds.
large size →Less Stable ←Less Charge
Small size → More stable ← More Charge
10. b. Base strength-
Calvin and Wilson suggested that the higher basic character or
strength of the ligand, higher will be the stability of coordination compounds. It is
defined that a strong base or higher basic strength of the ligand means it forms
more stable compounds or its donating tendency of electron to central metal ion
is higher.
e.g.- Aromatic diamines form unstable coordination compounds while
aliphatic diamines form stable coordination compounds. Ligands like NH3, CN- etc
have more basic character that means they form more stable compounds.
11. c. Ligand Concentration:
Some coordination complexes exist in aqueous solution only in presence of
higher concentration of coordination group. In some cases aqueous molecules
show greater coordinating tendency than the coordinating group which is
originally present.
e.g. in presence of highly concentrated solution of SCN- (thiocynate ion), the Co2+
metal ion
forms a stable blue colored coordination complex but on dilution in aqueous medium the blue
complex is destroyed and a pink aqua complex [Co(H2O)6]2+ is formed and then by further
addition of ligand (SCN-) pink colour disappears.
[Co(SCN)4]2−
+ H2O → [Co(H2O)6]2+
+ + 4SCNˉ
Blue Pink
The colour change indicates that there is a competition between H2O/SCN- in
formation of complex with Co(II) ion.
12. 3. Presence of ring structure (chelation)-
a. Chelate Effect:
The process of forming metal chelate by the attachment of multidentate ligand
with central metal ion in which ligand act as chelating agent is known as
chelation. Chelation is expressed by the following unidentate and bidentate
ligand reaction.
M + 2L→ ML2 K=[ML2]/[M][𝐿]2
M + L-L → M-L-L or K=
[𝑀−𝐿−𝐿]
𝑀 [𝐿−𝐿]
Multidentate ligands form more stable coordination compounds than
monodentate ligands. Following factors are of great importance in chelate
formation.
13. b. Size of chelate Rings :-
The stability of chelate is depending on the size of chelate ring. The stability
of coordination complex increases with number of chelate ring. It is found that
4-membered rings are unstable and rare than 5-membered rings which are
common and stable. For chelate (saturated chelate) rings the following is the
decreasing order of stability with increasing ring size-
Five membered > Six membered > Seven membered
The stability of metal chelates decrease by increasing the chelate size.
the higher membered rings are uncommon due to-
(i) strain set up in the heterocyclic ring.
(ii) possibility of a long chain multidentate ligand bonding to more
than one atom, giving the formation of the polynuclear complexes
rather than the chelate complexes.
14. in general it has been observed that saturated ligand form 5
membered rings give the most stable product. e.g. complexes with
ethylenediamine and C2O2
2-. Fig
15. But unsaturated ligands (those with double bonds) form very stable
metal complexes containing six membered rings. This is because
in such complexes 𝜋 electron density is delocalised and spread
over the ring which is thus stabilised by resonance. Examples are
acetyl acetone complexes with metals fig. 2
16. c. Number of chelate Rings:
Increase in the number of rings increase the stability of
compounds. Stability constant of complexes with metal(II) ions
No. of rings
formed
Ligand
0 NH3 3.7 5.3 7.8 12.6
1 en 7.7 10.9 14.5 20.2
2 trien 7.8 11.0 14.1 20.2
3 tren 8.8 12.8 14.o 18.3
5 penen 11.2 15.8 19.3 22.4
stability constants for complexes with
Fe(II) Co(II) Ni(II) Cu(II)
trien : triethylene tetraamine NH2CH2CH2NHCH2CH2NHCH2CH2NH2
tren : triaminoethylamine (H2NCH2CH2)3N
penen : tetrakis (aminoethyl) ethylenediamine (H2NCH2CH2)2NCH2CH2N(CH2CH2NH2)2
17. d. Entropy Effect –
the chief factor responsible for the stability of the chelate
ring is the entropy change. Considering the electronic effect of the
donor atom to be the same in the monodentate and the bidentate
ligands, it can be seen that the dissociation of a monodentate from
the complex will be higher than that in the chelating bidentate.
The dissociation of the M-L bond in monodentate will release
The ligand completely from the coordination sphere of the metal,
So that it can be easily swept off by the solvent. but the dissociation
Of one M-L bond for the bidentate ligand does not release the ligand
Completely (for which simultaneous dissociation at both ends is
required).hence the stability constant for metal chelate must be
Higher.
[Co(NH3)6]3++ 3en → [𝐶𝑜 𝑒𝑛 3]2++ 6NH3
18. 4. Other factors-
a. Forced configuration-
ligands like porphyrin and phthalcyanine
Which have completely fused planar ring system form extraordinarily
Stable complexes with metal ions that tend to give planar complexes
e.g. Cu2+ complex with phthalocyanine is very stable. Similarly trien
Forms very stable complexes with Ni(II) and Cu(II).
These ligands impose planar configurations
Even on metal ions that have no tendency
to form planar complexes with unidentate
Ligands. for e.g. 𝐵𝑒2+and 𝑍𝑛2+ion normally
Form tetrahedral complexes but when they
Combine with these polydentate ligands they
Are forced to assume planner configuration.
Therefore these complexes are less stable.
Copper(II) Pthalocynine complex
19. b. Nature of the solvent-
solvent with low dielectric constant and low dipole
moment are expected to increase the stability and the stability
constant.
further, a donor solvent will tend to form its own complexes
with the metal ions, so that the incoming ligand will face a competition
with the solvent molecules to get attached with the metal ions. Hence
strongly donor solvents decrease the stability constants of the metal
complexes.
20. c. Steric effect-
In some cases the clashing of groups on two coordinated
ligands will result in distortion of bond angles and a decrease in stability is
the phenomenon of F-strain, described by Brown [27], as applied to
coordination compounds.
As steric effect is decreasing, the stability of a complex is increasing.
Due to steric effect in Ni(II) complexes with 2-methyl 8- hydroxy quinoline
are less stable than complexes with 8-hydroxy quinoline because of the
steric hindrance caused by the methyl
group adjacent to the site of coordination.
Similarly complexes of ethylene diamine are more stable than its
tetramethyl derivatives
21. Reference:-
Theoretical principles of inorganic chemistry by G.S.MANKU
(Tata McGraw-HILL Publication)
Coordination chemistry by GURDEEP R. CHATWAL, MAHINDRA S.YADAV,
Mrs. M. Arora
(Campus books publication)