Biomechanical effects on microRNA expression in skeletal muscle differentiation

Caroline Rhim; William E. Kraus; George A. Truskey; Caroline Rhim; William E. Kraus; George A. Truskey

doi:10.3934/bioeng.2020014

AIMS Bioengineering

2020, Volume 7, Issue 3: 147-164. doi: 10.3934/bioeng.2020014

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Research article Topical Sections

Biomechanical effects on microRNA expression in skeletal muscle differentiation

1.
Departments of Biomedical Engineering, Duke University, 101 Science Drive, Durham, NC 27708 USA
2.
Duke Molecular Physiology Institute, Duke University School of Medicine, 300 N Duke St, Durham, NC, 27701, USA

Received: 28 April 2020 Accepted: 15 June 2020 Published: 19 June 2020

We examined whether mechanical stretch affected expression of muscle-specific microRNAs (miRNAs) that regulate proliferation (miR-133a) or differentiation (miR-1, -206). Real-time quantitative RT-PCR was used to assess miRNA regulation in the murine myoblast cell line C2C12 exposed to stretch regimens that promote either proliferation (high stretch: 17%, 1 Hz) or differentiation (moderate stretch: 10%, 0.5 Hz) after adding media that promotes differentiation. Controls consisted of myoblasts cultured under static conditions. While miRNA expression was not affected by high stretch, a significant effect of stretch (P < 0.05) was seen after 4 days with the moderate stretch regimen. All three microRNAs were upregulated by stretch, with the most significant increase for miR-1. Myoblast maturation was enhanced with a moderate stretch regimen, as assessed by a higher percentage of nuclei in straited fibers and an increase in Mef2c gene expression. Correspondingly, HDAC4 protein expression, a direct target of miR-1 and repressor of Mef2, was decreased with the moderate stretch regimen. Over-expression of miR-1 abrogated the effect of stretch on miR-1, miR-133a and miR-206 levels compared to its negative control but did not alter miR-133a or miR-206 levels. Treatment with an antisense mRNA to miR-1 similarly diminished the stretch-mediated response. Results indicate that the differential response of skeletal myoblasts to moderate and high stretch cyclic stretch regimens is due, in part, to muscle specific miRNA expression.

Keywords:

Citation: Caroline Rhim, William E. Kraus, George A. Truskey. Biomechanical effects on microRNA expression in skeletal muscle differentiation[J]. AIMS Bioengineering, 2020, 7(3): 147-164. doi: 10.3934/bioeng.2020014

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Abstract

1. Introduction, definitions and preliminaries

In his survey-cum-expository review article, Srivastava ^[35] included also a brief overview of the classical $q$ -analysis versus the so-called $(p, q)$ -analysis with an obviously redundant additional parameter $p$ (see, for details, [,p. 340]). The present sequel to Srivastava's widely-cited review article ^[35], we apply the concept of $q$ -convolution in order to introduce and study the general Taylor-Maclaurin coefficient estimates for functions belonging to a new class of normalized analytic and bi-close-to-convex functions in the open unit disk, which we have defined here.

Let $\mathcal{A}$ denote the class of analytic functions of the form:

$\begin{equation} f(z) = z+\sum\limits_{n = 2}^{\infty}a_{n}\;z^{n} \qquad (z\in \Delta), \end{equation}$

(1.1)

where $\Delta$ denotes the open unit disk in the complex $z$ -plane given by

$\Delta: = \{z: z\in \mathbb{C}\qquad \text{and} \qquad |z| \lt 1\}.$

Also let $\mathcal{S}\subset \mathcal{A}$ consist of functions which are also univalent in $\Delta$ .

If the function $f$ is given by (1.1) and the function $\Upsilon \in \mathcal{A}$ is given by

$\begin{equation} \Upsilon(z) = z+\sum\limits_{n = 2}^{\infty}\psi_{n}z^{n} \qquad (z\in \Delta), \end{equation}$

(1.2)

then the Hadamard product (or convolution) of the functions $f$ and $\Upsilon$ is defined by defined by

$\begin{equation*} (f\ast \Upsilon)(z): = z+\sum\limits_{n = 2}^{\infty}a_{n}\,\psi _{n}\, z^{n} = : (\Upsilon \ast f)(z)\qquad (z\in \Delta). \end{equation*}$

For $0\leqq \alpha < 1,$ we let $S^{\ast}\left(\alpha \right)$ denote the class of functions $g\in \mathcal{S}$ which are starlike of order $\alpha$ in $\Delta$ such that

$\begin{equation*} \Re\left(\frac{zg^{{\prime}}(z)}{g(z)}\right) \gt \alpha \qquad (z\in \Delta). \end{equation*}$

We denote by $\mathcal{C}\left(\alpha \right)$ the class of functions $f\in \mathcal{S}$ which are close-to-convex of order $\alpha$ in $\Delta$ such that (see ^[10,24])

$\begin{equation*} \Re\left(\frac{zf^{\prime}(z)}{g(z)}\right) \gt \alpha \qquad (z \in \Delta), \end{equation*}$

where

$\begin{align*} g\in S^{\ast}\left(0\right) = :S^{\ast}. \end{align*}$

We note that

$S^{\ast}\left(\alpha \right) \subset \mathcal{C}\left( \alpha \right) \subset \mathcal{S}\qquad \text{and} \qquad \left\vert a_{n}\right\vert \lt n \qquad (\forall\; f\in \mathcal{S};\; n\in \mathbb{N}\setminus \{1\})$

by the Bieberbach conjecture or the De Branges Theorem (see ^[3,10]), $\mathbb{N}$ being the set of natural numbers (or the positive integers).

In the above-cited review article, Srivastava ^[35] made use of various operators of $q$ -calculus and fractional $q$ -calculus. We begin by recalling the definitions and notations as follows (see also ^[33] and [45,pp. 350–351]).

The $q$ -shifted factorial is defined, for $\lambda, q\in \mathbb{C}$ and $n \in \mathbb{N}_{0} = \mathbb{N}\cup \{0\}$ , by

$\begin{equation*} (\lambda;q)_{n} = \left\{ \begin{array}{ll} 1 & \qquad (n = 0) \\ \\ \left(1-\lambda \right) \left(1-\lambda q\right) \cdots \left( 1-\lambda q^{n-1}\right) & \qquad (n\in \mathbb{N}). \end{array} \right. \end{equation*}$

By using the $q$ -gamma function $\Gamma_{q}(z),$ we get

$\begin{equation*} \left(q^{\lambda};q\right)_{n} = \frac{\left(1-q\right)^{n}\ \Gamma _{q}\left(\lambda+n\right)}{\Gamma_{q}\left(\lambda \right)} \qquad \left(n\in \mathbb{N}_{0}\right), \end{equation*}$

where (see ^[19,33])

$\begin{equation*} \Gamma_{q}(z) = \left(1-q\right)^{1-z}\;\frac{\left(q;q\right)_{\infty}} {\left(q^{z};q\right)_{\infty}}\qquad \left(\left\vert q\right\vert \lt 1\right) . \end{equation*}$

We note also that

$\begin{equation*} \left(\lambda;q\right)_{\infty } = \prod\limits_{n = 0}^{\infty}\left( 1-\lambda q^{n}\right) \qquad \left(\left\vert q\right\vert \lt 1\right) , \end{equation*}$

and that the $q$ -gamma function $\Gamma_{q}(z)$ satisfies the following recurrence relation:

$\begin{equation*} \Gamma_{q}(z+1) = \left[z\right]_{q}\; \Gamma_{q}(z), \end{equation*}$

where $\left[\lambda\right]_{q}$ denotes the basic (or $q$ -) number defined as follows:

$\begin{equation} \lbrack \lambda]_{q}: = \left\{ \begin{array}{ll} \dfrac{1-q^{\lambda}}{1-q} &\qquad (\lambda\in \mathbb{C})\\ \\ 1+\sum\limits_{j = 1}^{\ell-1}q^{j} &\qquad (\lambda = \ell\in \mathbb{N}). \end{array} \right. \end{equation}$

(1.3)

Using the definition in (1.3), we have the following consequences:

(ⅰ) For any non-negative integer $n\in \mathbb{N}_0$ , the $q$ -shifted factorial is given by

$\begin{equation*} \left[n\right]_{q}!: = \left\{ \begin{array}{ll} 1 & \qquad (n = 0) \\ \\ \prod\limits_{k = 1}^{n}[k]_{q} & \qquad (n\in \mathbb{N}). \end{array} \right. \end{equation*}$

(ⅱ) For any positive number $r$ , the generalized $q$ -Pochhammer symbol is defined by

$\begin{equation*} \left[r\right]_{q,n}: = \left\{ \begin{array}{ll} 1 & \qquad (n = 0)\\ \\ \prod\limits_{k = r}^{r+n-1}[k]_{q} & \qquad (n\in \mathbb{N}). \end{array} \right. \end{equation*}$

In terms of the classical (Euler's) gamma function $\Gamma\left(z\right)$ , it is easily seen that

$\begin{equation*} \lim\limits_{q\rightarrow 1{-}}\{\Gamma_{q}\left(z\right)\} = \Gamma\left(z\right). \end{equation*}$

We also observe that

$\begin{equation*} \lim\limits_{q\rightarrow 1{-}} \left\{\frac{\left(q^{\lambda};q\right) _{n}}{\left(1-q\right)^{n}}\right\} = \left(\lambda \right)_{n}, \end{equation*}$

where $\left(\lambda\right)_{n}$ is the familiar Pochhammer symbol defined by

$\begin{equation*} \left(\lambda \right)_{n} = \left\{ \begin{array}{ll} 1 & \qquad (n = 0) \\ \\ \lambda \left(\lambda +1\right) \cdots \left(\lambda+n-1\right) & \qquad (n\in \mathbb{N}). \end{array} \right. \end{equation*}$

For $0 < q < 1$ , the $q$ -derivative operator (or, equivalently, the $q$ -difference operator) $D_{q}$ is defined by (see ^[22]; see also ^[14,16,21])

$\begin{align*} D_{q}\left(f\ast\Upsilon\right)(z)&\; = D_{q}\left( z+\sum\limits_{n = 2}^{\infty}a_{n}\,\psi_{n}\,z^{n}\right) \\ &: = \frac{\left(f\ast\Upsilon \right)(z) -\left(f\ast\Upsilon \right)(qz)} {z(1-q)} = 1+\sum\limits_{n = 2}^{\infty}[n]_{q}\,a_{n}\, \psi_{n}\,z^{n-1}\qquad (z\in \Delta), \end{align*}$

where, as in the definition (1.3),

$\begin{equation} \left[n\right]_{q} = \left\{ \begin{array}{ll} \dfrac{1-q^{n}}{1-q} = 1+\sum\limits_{j = 1}^{n-1}q^{j}&\qquad (n\in\mathbb{N})\\ \\ 0 &\qquad (n = 0). \end{array} \right. \end{equation}$

(1.4)

Remark 1. Whereas a $q$ -extension of the class of starlike functions was introduced in $1990$ in ^[20] by means of the $q$ -derivative operator $D_q$ , a firm footing of the usage of the $q$ -calculus in the context of Geometric Function Theory was actually provided and the generalized basic (or $q$ -) hypergeometric functions were first used in Geometric Function Theory in an earlier book chapter published in 1989 by Srivastava (see, for details, ^[34]; see also the recent works ^{[25,27,32,36,37,39,40,46,51,52,53,55,56,57]}).

For $\lambda > -1$ and $0 < q < 1$ , El-Deeb et al. ^[14] defined the linear operator $\mathcal{H}_{\Upsilon}^{\lambda, q}:\mathcal{A}\rightarrow \mathcal{A}$ by

$\begin{equation*} \mathcal{H}_{\Upsilon}^{\lambda,q}f(z)\ast\mathcal{M}_{q,\lambda +1}(z) = z\,D_{q}\left(f\ast\Upsilon\right)(z)\qquad (z\in \Delta), \end{equation*}$

where the function $\mathcal{M}_{q, \lambda}(z)$ is given by

$\begin{equation*} \mathcal{M}_{q,\lambda}(z) = z+\sum\limits_{n = 2}^{\infty} \frac{[\lambda]_{q,n-1}}{[n-1]_{q}!}\;z^{n}\qquad (z\in \Delta). \end{equation*}$

A simple computation shows that

$\begin{equation} \mathcal{H}_{\Upsilon}^{\lambda,q}f(z) = z+\sum\limits_{n = 2}^{\infty}\frac{ [n]_{q}!}{[\lambda +1]_{q,n-1}}\;a_{n}\psi_{n}\; z^{n}\qquad (\lambda \gt -1;\; 0 \lt q \lt 1;\; z\in \Delta). \end{equation}$

(1.5)

From the defining relation (1.5), we can easily verify that the following relations hold true for all $f\in \mathcal{A}$ :

$\begin{align} &\text{(i)} \quad [\lambda +1]_{q}\mathcal{H}_{\Upsilon }^{\lambda ,q}f(z) = [\lambda]_{q}\mathcal{H}_{\Upsilon}^{\lambda+1,q}f(z)+q^{\lambda }\,z\ D_{q}\left(\mathcal{H}_{\Upsilon }^{\lambda +1,q}f(z)\right) \qquad (z\in\Delta); \\ &\text{(ii)} \quad \mathcal{I}_{\Upsilon }^{\lambda }f(z): = \lim\limits_{q\rightarrow 1{-}}\mathcal{H}_{\Upsilon}^{\lambda ,q}f(z) = z+\sum\limits_{n = 2}^{\infty}\dfrac{n!}{(\lambda+1)_{n-1}} \,a_{n}\psi_{n}z^{m}\qquad (z\in \Delta). \end{align}$

(1.6)

Remark 2. If we take different particular cases for the coefficients $\psi_{n},$ we obtain the following special cases for the operator $\mathcal{H}_{h}^{\lambda, q}$ :

(ⅰ) For $\psi_{n} = 1$ , we obtain the operator $\mathfrak{J}_{q}^{\lambda}$ defined by Arif et al. ^[2] as follows (see also Srivastava ^[47]):

$\begin{equation} \mathfrak{J}_{q}^{\lambda}f(z) : = z+\sum\limits_{n = 2}^{\infty}\frac{[n]_{q}!} {[\lambda+1]_{q,n-1}}\;a_{n}\,z^{n}\qquad (z\in \Delta); \end{equation}$

(1.7)

(ⅱ) For

$\psi_{n} = \dfrac{(-1)^{n-1}\;\Gamma(\upsilon+1)}{ 4^{n-1}\; (n-1)! \;\Gamma(n+\upsilon)} \qquad \text{and} \qquad \upsilon \gt 0,$

we obtain the operator $\mathcal{N}_{\upsilon, q}^{\lambda}$ defined by El-Deeb and Bulboacǎ ^[12] and El-Deeb ^[11] as follows (see also ^[16]):

$\begin{align} \mathcal{N}_{\upsilon,q}^{\lambda}f(z)&: = z+\sum\limits_{n = 2}^{\infty}\frac{ (-1)^{n-1}\Gamma(\upsilon+1)}{4^{n-1}\; (n-1)! \;\Gamma(n+\upsilon)}\cdot \frac{[n]_{q}!}{[\lambda +1]_{q,n-1}}\;a_{n}\,z^{n} \\ &\; = z+\sum\limits_{n = 2}^{\infty}\frac{[n]_{q}!}{[\lambda+1]_{q,n-1}}\;\phi _{n}\,a_{n}\,z^{n} \end{align}$

(1.8)

$(\upsilon \gt 0;\;\lambda \gt -1;\;0 \lt q \lt 1;\ z\in \Delta),$

where

$\begin{equation} \phi_{n}: = \frac{(-1)^{n-1}\;\Gamma(\upsilon+1)}{4^{n-1}\; (n-1)! \;\Gamma (n+\upsilon)} \qquad (n \in \mathbb{N}\setminus\{1\}); \end{equation}$

(1.9)

(ⅲ) For

$\psi_{n} = \left(\dfrac{n+1}{m+n}\right)^{\alpha}, \quad \alpha \gt 0 \qquad \text{and} \qquad n \in \mathbb{N}_0,$

we obtain the operator $\mathcal{M}_{m, q}^{\lambda, \alpha}$ defined by El-Deeb and Bulboacǎ (see ^[13,43]) as follows:

$\begin{equation} \mathcal{M}_{m,q}^{\lambda,\alpha}f(z): = z+\sum\limits_{n = 2}^{\infty }\left(\frac{m+1}{m+n}\right)^{\alpha}\cdot \frac{[n]_{q}!} {[\lambda+1]_{q,n-1}}\;a_{n}\, z^{n}\qquad (z\in \Delta) ; \end{equation}$

(1.10)

(ⅳ) For

$\psi_{n} = \dfrac{\rho^{n-1}}{(n-1)!}\;e^{-\rho} \qquad \text{and} \qquad \rho \gt 0,$

we obtain a $q$ -analogue of the Poisson operator defined in ^[30] by

$\begin{equation} \mathcal{I}_{q}^{\lambda,\rho}f(z): = z+\sum\limits_{n = 2}^{\infty}\frac{ \rho^{n-1}}{(n-1)!}\;e^{-\rho}\cdot \frac{[n]_{q}!}{[\lambda +1]_{q,n-1}}\; a_{n}\,z^{n}\qquad (z\in \Delta); \end{equation}$

(1.11)

(ⅴ) For

$\psi_{n} = \binom{m+n-2}{n-1}\; \theta^{n-1}\left(1-\theta \right)^{m}\qquad \left(m\in \mathbb{N};\; 0\leqq \theta \leqq 1\right),$

we get a $q$ -analogue $\Psi_{q, \theta}^{\lambda, m}$ of the Pascal distribution operator as follows (see ^[15]):

$\begin{equation} \Psi_{q,\theta}^{\lambda,m}f(z): = z+\sum\limits_{n = 2}^{\infty} \binom{m+n-2}{n-1}\theta^{n-1}\left(1-\theta \right)^{m}\cdot \frac{[n]_{q}!}{[\lambda+1]_{q,n-1}}\;a_{n}\; z^{n} \end{equation}$

(1.12)

$(z\in \Delta).$

If $f$ and $F$ are analytic functions in $\Delta$ , we say that the function $f$ is subordinate to the function $F$ , written as $f(z)\prec F(z)$ , if there exists a Schwarz function $s$ , which is analytic in $\Delta$ with $s(0) = 0$ and $\left\vert s(z)\right\vert < 1$ for all $z\in \Delta$ , such that

$f(z) = F\big(s(z)\big) \qquad (z\in \Delta).$

Furthermore, if the function $F$ is univalent in $\Delta$ , then we have the following equivalence (see, for example, ^[7,28])

$\begin{equation*} f(z)\prec F(z)\; \Longleftrightarrow \; f(0) = F(0)\qquad \text{and} \qquad f(\Delta)\subset F(\Delta). \end{equation*}$

The Koebe one-quarter theorem (see ^[10]) asserts that the image of $\Delta$ under every univalent function $f\in \mathcal{S}$ contains the disk of radius $\dfrac{1}{4}$ . Therefore, every function $f\in \mathcal{S}$ has an inverse $f^{-1}$ which satisfies the following inequality:

$\begin{equation*} f\big(f^{-1}(w)\big) = w\qquad \left(\left\vert w\right\vert \lt r_{0}\left(f\right); \;r_{0}\left(f\right) \geqq \frac{1}{4}\right) , \end{equation*}$

where

$\begin{align*} g(w) & = f^{-1}(w) = w-a_{2}w^{2}+\left(2a_{2}^{2}-a_{3}\right) w^{3}-\left( 5a_{2}^{3}-5a_{2}a_{3}+a_{4}\right) w^{4}+\cdots \\ & = w+\sum\limits_{n = 2}^{\infty}A_{n}\; w^{n}. \end{align*}$

A function $f\in \mathcal{A}$ is said to be bi-univalent in $\Delta$ if both $f$ and $f^{-1}$ are univalent in $\Delta$ . Let $\Sigma$ denote the class of normalized analytic and bi-univalent functions in $\Delta$ given by (1.1). The class $\Sigma$ of analytic and bi-univalent functions was introduced by Lewin ^[26], where it was shown that

$f\in \Sigma \;\Longrightarrow\;\left\vert a_{2}\right\vert \lt 1.51.$

Brannan and Clunie ^[4] improved Lewin's result to the following form:

$f\in \Sigma \;\Longrightarrow\; \left\vert a_{2}\right\vert \lt \sqrt{2}$

and, subsequently, Netanyahu ^[29] proved that

$f\in \Sigma \;\Longrightarrow\;\left\vert a_{2}\right\vert \lt \frac{4}{3}.$

It should be noted that the following functions:

$f_{1}(z) = \dfrac{z}{1-z},\quad f_{2}(z) = \dfrac{1}{2}\log\left(\dfrac{1+z}{1-z}\right) \qquad \text{and} \qquad f_{3}(z) = -\log (1-z),$

together with their corresponding inverses given by

$f_{1}^{-1}(w) = \dfrac{w}{1+w}, \quad f_{2}^{-1}(w) = \dfrac{e^{2w}-1}{e^{2w}+1} \qquad \text{and} \qquad f_{3}^{-1}(w) = \dfrac{e^{w}-1}{e^{w}},$

are elements of the analytic and bi-univalent function class $\Sigma$ (see ^[14,48]). A brief history and interesting examples of the analytic and bi-univalent function class $\Sigma$ can be found in (for example) ^[5,48].

Brannan and Taha ^[6] (see also ^[48]) introduced certain subclasses of the bi-univalent function class $\Sigma$ similar to the familiar subclasses $S^{\ast }\left(\alpha \right)$ and $K\left(\alpha \right)$ of starlike and convex functions of order $\alpha \; \left(0\leqq \alpha < 1\right)$ , respectively (see ^[5]). Indeed, following Brannan and Taha ^[6], a function $f\in \mathcal{A}$ is said to be in the class $S_{\Sigma}^{\ast }\left(\alpha \right)$ of bi-starlike functions of order $\alpha \; \left(0 < \alpha \leqq 1\right)$ , if each of the following conditions is satisfied:

$\begin{equation*} f\in \Sigma \qquad \text{and}\qquad \left\vert \arg\left(\frac{zf^{\prime}(z)}{ f(z)}\right)\right\vert \lt \frac{\alpha \pi}{2}\qquad (z\in \Delta) \end{equation*}$

and

$\begin{equation*} \left\vert \arg\left(\frac{z\mathcal{F}^{\prime}(w)}{\mathcal{F}(w)}\right\vert\right) \lt \frac{\alpha \pi }{2} \qquad (w\in \Delta), \end{equation*}$

where the function $\mathcal{F}$ is the analytic extension of $f^{-1}$ to $\Delta$ , given by

$\begin{equation} \mathcal{F}(w) = w-a_{2}w^{2}+\left( 2a_{2}^{2}-a_{3}\right) w^{3}-\left( 5a_{2}^{3}-5a_{2}a_{3}+a_{4}\right) w^{4}+\cdots \qquad (w\in \Delta). \end{equation}$

(1.13)

A function $f\in A$ is said to be in the class $K_{\Sigma}^{\ast }\left(\alpha \right)$ of bi-convex functions of order $\alpha \; \left(0 < \alpha \leqq 1\right)$ , if each of the following conditions is satisfied:

$\begin{equation*} f\in \Sigma ,\quad \text{with}\quad \left\vert \arg\left(1+\frac{ zf^{\prime \prime }(z)}{f^{\prime}(z)}\right) \right\vert \lt \frac{\alpha \pi }{2} \qquad (z\in \Delta) \end{equation*}$

and

$\begin{equation*} \left\vert \arg\left(1+\frac{zg^{\prime \prime}(w)}{g^{\prime}(w)} \right) \right\vert \lt \frac{\alpha \pi }{2}\qquad (w\in \Delta). \end{equation*}$

The classes $S_{\Sigma}^{\ast}\left(\alpha \right)$ and $K_{\Sigma}\left(\alpha \right)$ of bi-starlike functions of order $\alpha$ in $\Delta$ and bi-convex functions of order $\alpha \; \left(0 < \alpha \leqq 1\right)$ in $\Delta$ , corresponding to the function classes $S^{\ast}\left(\alpha \right)$ and $K\left(\alpha \right)$ , were also introduced analogously. For each of the function classes $S_{\Sigma}^{\ast}\left(\alpha \right)$ and $K_{\Sigma}\left(\alpha \right)$ , non-sharp estimates on the first two Taylor-Maclaurin coefficients $\left\vert a_{2}\right\vert$ and $\left\vert a_{3}\right\vert$ are known (see ^[6,35,48]). In fact, this pioneering work by Srivastava et al. ^[48] happens to be one of the most important studies of the bi-univalent function class $\Sigma$ . It not only revived the study of the bi-univalent function class $\Sigma$ in recent years, but it has also inspired remarkably many investigations in this area including the present paper. Some of these many recent papers dealing with problems involving the analytic and bi-univalent functions such as those considered in this article include ^{[1,9,17,23,48]}, and indeed also many other works (see, for example, ^[38,44,54]).

Sakar and Güney ^[31] introduced and studied the following class:

$\mathcal{T}_{\Sigma}\left( \lambda,\beta \right) \;\; \left(0\leqq \lambda \leqq 1;\; 0\leqq \beta \lt 1\right).$

In the same way, we define the following subclass of bi-close-to-convex functions $\mathcal{H}_{\Sigma}^{q, \lambda }\left(\eta, \beta, \Upsilon \right)$ as follows.

Definition 1. For $0\leqq \eta < 1$ and $0\leqq \beta \leqq 1, \;$ a function $f\in \Sigma$ has the form (1.1) and the function $\Upsilon$ given by (1.2), the function $f$ is said to be in the class $\mathcal{H}_{\Sigma}^{q, \lambda}\left(\eta, \beta, \Upsilon\right)$ if there exists a function $g \in \mathcal{S}^{\ast}$ such that

$\begin{equation} \Re\left(\frac{z\left(\mathcal{H}_{\Upsilon}^{\lambda ,q}f(z)\right) ^{{\prime }}+\beta z^{2}\left( \mathcal{H}_{\Upsilon }^{\lambda ,q}f(z)\right)^{\prime\prime}}{\left(1-\beta \right) \mathcal{H}_{\Upsilon }^{\lambda,q}g(z)+\beta z\left(\mathcal{H}_{\Upsilon }^{\lambda,q}g(z)\right)^{\prime}}\right) \gt \eta \qquad (z\in \Delta) \end{equation}$

(1.14)

and

$\begin{equation} \Re\left(\frac{z\left(\mathcal{H}_{\Upsilon}^{\lambda,q}\mathcal{F }(w)\right)^{{\prime}}+\beta z^{2}\left(\mathcal{H}_{\Upsilon}^{\lambda ,q}\mathcal{F}(w)\right) ^{^{{\prime \prime }}}}{\left(1-\beta \right) \mathcal{H}_{\Upsilon }^{\lambda,q}\mathcal{G}(w)+\beta z\left(\mathcal{H} _{\Upsilon }^{\lambda ,q}\mathcal{G}(w)\right)^{{\prime}}}\right) \gt \eta \qquad (w\in \Delta), \end{equation}$

(1.15)

where the function $\mathcal{F}$ is the analytic extension of $f^{-1}$ to $\Delta$ , and is given by (1.13), and $\mathcal{G}$ is the analytic extension of $g^{-1}$ to $\Delta$ as follows:

$\begin{equation} \mathcal{G}(w) = w-b_{2}w^{2}+\left(2b_{2}^{2}-b_{3}\right)w^{3}-\left( 5b_{2}^{3}-5b_{2}b_{3}+b_{4}\right) w^{4}+\cdots \qquad (w\in \Delta). \end{equation}$

(1.16)

We note that, if $b_{n} = a_{n}\; \; (n\in \mathbb{N}\setminus\{1\})$ , $\mathcal{S}_{\Sigma }^{q, \lambda}\left(\eta, \beta, \Upsilon\right)$ becomes the class of bi-starlike functions satisfying the following inequalities:

$\begin{equation} \Re\left(\frac{z\left(\mathcal{H}_{\Upsilon}^{\lambda ,q}f(z)\right)^{{\prime}}+\beta z^{2}\left(\mathcal{H}_{\Upsilon }^{\lambda ,q}f(z)\right) ^{\prime \prime}}{\left( 1-\beta \right) \mathcal{H}_{\Upsilon }^{\lambda ,q}f(z)+\beta z\left( \mathcal{H}_{\Upsilon }^{\lambda ,q}f(z)\right)^{\prime}}\right) \gt \eta \qquad (z\in \Delta). \end{equation}$

(1.17)

and

$\begin{equation} \Re\left(\frac{z\left(\mathcal{H}_{\Upsilon}^{\lambda ,q}\mathcal{F }(w)\right) ^{{\prime}}+\beta z^{2}\left(\mathcal{H}_{\Upsilon}^{\lambda ,q}\mathcal{F}(w)\right)^{\prime \prime}}{\left(1-\beta \right) \mathcal{H}_{\Upsilon}^{\lambda,q}\mathcal{F}(w)+\beta z\left( \mathcal{H} _{\Upsilon }^{\lambda ,q}\mathcal{F}(w)\right)^{\prime}}\right) \gt \eta \qquad (w\in \Delta). \end{equation}$

(1.18)

Remark 3. Each of the following limit cases when $q\rightarrow 1{-}$ is worthy of note.

(ⅰ) Putting $q\rightarrow 1{-}$ , we obtain

$\lim\limits_{q\rightarrow 1{-}}\mathcal{H}_{\Sigma }^{q,\lambda}\left(\eta,\beta,h\right) = : \mathcal{P}_{\Sigma}^{\lambda}\left(\eta,\beta,h\right),$

where $\mathcal{P}_{\Sigma}^{\lambda }\left(\eta, \beta, \Upsilon \right)$ represents the functions $f\in \Sigma$ that satisfy (1.14) and (1.15) with $\mathcal{H}_{\Upsilon}^{\lambda, q}$ replaced by $\mathcal{I}_{\Upsilon}^{\lambda}$ as in (1.6).

(ⅱ) Putting

$\psi_{n} = \dfrac{(-1)^{n-1}\Gamma(\upsilon+1)}{ 4^{n-1}\; (n-1)! \;\Gamma(m+\upsilon)}\qquad (\upsilon \gt 0),$

we obtain the class $\mathcal{B}_{\Sigma}^{q, \lambda} \left(\eta, \beta, \upsilon\right)$ representing the functions $f\in \Sigma$ that satisfy (1.14) and (1.15) with $\mathcal{H}_{\Upsilon}^{\lambda, q}$ replaced by $\mathcal{N}_{\upsilon, q}^{\lambda}$ as in (1.8).

(ⅲ) Putting

$\psi_{n} = \left(\dfrac{n+1}{m+n}\right)^{\alpha}\qquad (\alpha \gt 0;\; m\geqq \mathbb{N}_0),$

we obtain the class $\mathcal{L}_{\Sigma}^{\lambda, q} \left(\eta, \beta, m, \alpha \right)$ consisting of the functions $f\in \Sigma$ that satisfy (1.14) and (1.15) with $\mathcal{H} _{\Upsilon}^{\lambda, q}$ replaced by $\mathcal{M}_{m, q}^{\lambda, \alpha }$ as in (1.10).

(ⅳ) Putting

$\psi_{n} = \dfrac{\rho^{n-1}}{(n-1)!}\;e^{-\rho }\qquad (\rho \gt 0),$

we obtain the class $\mathcal{M}_{\Sigma}^{q, \lambda}\left(\eta, \beta, \rho \right)$ representing the functions $f\in \Sigma$ which satisfy the inequalities in (1.14) and (1.15) with $\mathcal{H}_{\Upsilon}^{\lambda, q}$ replaced by $\mathcal{I}_{q}^{\lambda, \rho}$ as in (1.11).

(ⅴ) Putting

$\psi_{n} = \binom{m+n-2}{n-1}\; \theta^{n-1}\left(1-\theta \right)^{m}\qquad \left(m\in \mathbb{N};\; 0\leqq \theta \leqq 1\right),$

we get the class $\mathcal{W}_{\Sigma}^{q, \lambda}\left(\eta, \beta, m, \theta \right)$ of the functions $f\in \Sigma$ which satisfy the inequalities in (1.14) and (1.15) with $\mathcal{H}_{\Upsilon}^{\lambda, q}$ replaced by $\Psi_{q, \theta}^{\lambda, m}$ occurring in (1.12).

Using the Faber polynomial expansion of functions $f\in \mathcal{A}$ which have the normalized form (1.1), the coefficients of its inverse map may be expressed as follows (see ^[18]):

$\begin{equation} \mathcal{F}(w) = f^{-1}(w) = w+\sum\limits_{n = 2}^{\infty}\frac{1}{n}\; K_{n-1}^{-n}(a_{2},a_{3},\cdots)\;w^{n} = w+\sum\limits_{n = 2}^{\infty}A_{n}\;w^{n}, \end{equation}$

(1.19)

where

$\begin{align} \mathcal{K}_{n-1}^{-n}(a_{2},a_{3},\cdots) & = \frac{(-n)!}{(-2n+1)!\; (n-1)!} a_{2}^{n-1} \\ &\qquad +\frac{(-n)!}{(2(-n+1))!\; (n-3)!}\;a_{2}^{n-3}\;a_{3} \\ &\qquad +\frac{(-n)!}{(-2n+3)!\; (n-4)!}\;a_{2}^{n-4}\;a_{4} \\ &\qquad +\frac{(-n)!}{ (2(-n+2))!\; (n-5)!}\;a_{2}^{n-5}\;\left[a_{5}+\left(-n+2\right)a_{3}^{2}\right] \\ &\qquad +\frac{(-n)!}{(-2n+5)!\; (n-6)!}\;a_{2}^{n-6} \left[a_{6}+\left(-2n+5\right) a_{3}\;a_{4}\right] \\ &\qquad +\sum\limits_{j\geqq 7}a_{2}^{n-j}U_{j} \end{align}$

(1.20)

such that $U_{j}$ with $7\leqq j\leqq n$ is a homogeneous polynomial in the variables $a_{2}, a_{3}, \cdots, a_{n}$ . Here such expressions as (for example) $(-n)!$ are to be interpreted symbolically by

$\begin{equation*} (-n)!\equiv \Gamma(1-n): = (-n)(-n-1)(-n-2)\cdots \qquad \big(n\in \mathbb{N}_0\big). \end{equation*}$

In particular, the first three terms of $\mathcal{K}_{n-1}^{-n}$ are given by

$\begin{align*} \mathcal{K}_{1}^{-2} = -2a_{2}, \end{align*}$

$\begin{align*} \mathcal{K}_{2}^{-3} = 3\left(2a_{2}^{2}-a_{3}\right) \end{align*}$

and

$\begin{align*} \mathcal{K}_{3}^{-4} = -4\left(5a_{2}^{3}-5a_{2}a_{3}+a_{4}\right). \end{align*}$

In general, an expansion of $\mathcal{K}_{m}^{-n} \; (n\in \mathbb{N})$ is given by (see ^{[1,8,41,42,47,49,50]})

$\begin{equation*} \mathcal{K}_{m}^{-n} = na_{m}+\frac{n\left(n-1\right)}{2}\;\mathcal{D}_{m}^{2}+ \frac{n!}{3!\;\left(n-3\right)!}\;\mathcal{D}_{m}^{3}+\cdots+\frac{n!}{m!\left( n-m\right)!}\;\mathcal{D}_{m}^{m}, \end{equation*}$

where

$\mathcal{D}_{m}^{n} = \mathcal{D}_{m}^{n}(a_{2},a_{3},a_{4},\cdots)$

and, alternatively,

$\begin{equation*} \mathcal{D}_{m}^{n}(a_{2},a_{3},\cdots,a_{m+1}) = \sum\limits_{i_1,\cdots,i_m}\left(\frac{n!}{ i_{1}!\;\cdots\; i_{m}!}\right)\;a_{2}^{i_{1}}\;\cdots\; a_{m+1}^{i_{m}}, \end{equation*}$

where $a_{1} = 1$ and the sum is taken over all non-negative integers $i_{1}, \cdots, i_{m}$ satisfying the following constraints:

$i_{1}+i_{2}+\cdots+i_{m} = n$

and

$i_{1}+2i_{2}+\cdots+mi_{m} = m.$

Evidently, we have

$\begin{equation*} \mathcal{D}_{m}^{m}(a_{2},a_{3},\cdots,a_{m+1}) = a_{2}^{m}. \end{equation*}$

The following Lemma will be needed to prove our results.

The Carathéodory Lemma. (see ^[10]) If $\phi \in \mathfrak{P}$ and

$\phi(z) = 1+\sum\limits_{n = 1}^{\infty}c_{n}\;z^{n},$

then

$|c_{n}|\leqq 2 \qquad (n \in \mathbb{N}).$

This inequality is sharp for all positive integers $n$ . Here $\mathfrak{P}$ is the family of all functions $\phi,$ which analytic and have positive real part in $\Delta,$ with $\phi(0) = 1$ .

2. A set of main results

In this section, we apply the above-described Faber polynomial expansion method, we derive bounds for the general Taylor-Maclaurin coefficients of functions in $\mathcal{H}_{\Sigma}^{q, \lambda}\left(\eta, \beta, \Upsilon \right)$ .

Theorem 1. Let the function $f$ given by (1.1) belong to the class $\mathcal{H}_{\Sigma}^{q, \lambda}\left(\eta, \beta, \Upsilon \right)$ . Suppose also that

$0\leqq \eta \lt 1,\quad 0\leqq \beta \leqq 1,\quad \lambda \gt -1 \qquad \mathit{\text{and}} \qquad 0 \lt q \lt 1.$

If $a_{k} = 0$ for $2\leqq k\leqq n-1,$ then

$\begin{equation*} \left\vert a_{n}\right\vert \leqq \frac{2\left(1-\eta \right) [\lambda +1]_{q,n-1}}{n\left[1+\left(n-1\right)\beta\right] \ [n]_{q}!\,\psi _{n}} +1. \end{equation*}$

Proof. If $f\in \mathcal{H}_{\Sigma }^{q, \lambda }\left(\eta, \beta, \Upsilon \right)$ , then there exists a function $g(z)$ , given by

$g(z): = z+\sum\limits_{n = 2}^{\infty}b_{n}\;z^{n}\in S^{\ast},$

such that

$\begin{equation*} \Re\left(\frac{z\left(\mathcal{H}_{\Upsilon}^{\lambda ,q}f(z)\right)^{\prime}+\beta z^{2}\left( \mathcal{H}_{\Upsilon }^{\lambda ,q}f(z)\right)^{\prime \prime}}{\left(1-\beta \right) \mathcal{H}_{\Upsilon}^{\lambda,q}g(z)+\beta z\left(\mathcal{H}_{\Upsilon }^{\lambda,q}g(z)\right)^{{\prime}}}\right) \gt \eta \qquad (z\in \Delta). \end{equation*}$

Moreover, by using the Faber polynomial expansion, we have

$\begin{align} &\frac{z\left(\mathcal{H}_{\Upsilon }^{\lambda,q}f(z)\right)^{\prime} +\beta z^{2}\left(\mathcal{H}_{\Upsilon}^{\lambda ,q}f(z)\right) ^{\prime \prime}}{\left(1-\beta \right) \mathcal{H}_{\Upsilon }^{\lambda ,q}g(z)+\beta z\left(\mathcal{H}_{\Upsilon }^{\lambda ,q}g(z)\right)^{\prime}} \\ &\qquad = 1+\sum\limits_{n = 2}^{\infty}\Bigg(\left[1+\beta \left(n-1\right) \right]\; \frac{[n]_{q}!}{[\lambda+1]_{q,n-1}}\,\psi _{n}\left(na_{n}-b_{n}\right) \\ &\qquad \qquad \qquad +\sum\limits_{t = 1}^{n-2}\dfrac{[n,q]!} {[\lambda +1,q]_{n-1}}\,\psi _{n}\left[1+\left(n-t-1\right)\beta \right] \\ &\qquad \qquad \qquad \qquad \cdot K_{t}^{-1}\left[\left( 1+\beta \right) b_{2},\left(1+2\beta \right) b_{3},\cdots, \left(1+t\beta \right) b_{t+1}\right] \\ &\qquad \qquad \qquad \qquad \cdot \left[\left(n-t\right)\ a_{n-t}-b_{n-t}\right] \Bigg) z^{n-1}\qquad (z\in \Delta). \end{align}$

(2.1)

Also, for the inverse map $\mathcal{F} = f^{-1},$ there exists a function $\mathcal{G}(w)$ , given by

$\mathcal{G}(w) = w+\sum\limits_{n = 2}^{\infty}B_{n}\;w^{n}\in S^{\ast},$

such that

$\begin{equation*} \Re\left(\frac{z\left( \mathcal{H}_{\Upsilon }^{\lambda ,q}\mathcal{F }(w)\right) ^{{\prime }}+\beta z^{2}\left( \mathcal{H}_{\Upsilon }^{\lambda ,q}\mathcal{F}(w)\right) ^{{{\prime \prime }}}}{\left( 1-\beta \right) \mathcal{H}_{\Upsilon }^{\lambda ,q}\mathcal{G}(w)+\beta z\left( \mathcal{H} _{\Upsilon }^{\lambda ,q}\mathcal{G}(w)\right) ^{{\prime }}}\right) \gt \eta \qquad (w\in \Delta), \end{equation*}$

the Faber polynomial expansion of the inverse map $\mathcal{F} = f^{-1}$ is given by

$\mathcal{F}(w) = w+\sum\limits_{n = 2}^{\infty}A_{n}\;w^{n},$

so we have

$\begin{align} &\frac{z\left(\mathcal{H}_{\Upsilon}^{\lambda,q}\mathcal{F}(w)\right) ^{\prime}+\beta z^{2}\left(\mathcal{H}_{\Upsilon}^{\lambda,q}\mathcal{ F}(w)\right)^{\prime \prime}}{\left(1-\beta \right) \mathcal{H} _{\Upsilon }^{\lambda ,q}\mathcal{G}(w)+\beta z\left(\mathcal{H}_{\Upsilon }^{\lambda ,q}\mathcal{G}(w)\right)^{\prime}} \\ &\qquad = 1+\sum\limits_{n = 2}^{\infty}\Bigg(\left[1+\beta \left(n-1\right)\right]\;\frac{[n]_{q}!}{[\lambda +1]_{q,n-1}}\,\psi _{n}\left(nA_{n}-B_{n}\right) \\ &\qquad \qquad +\sum\limits_{t = 1}^{n-2}\frac{[n]_{q}!}{[\lambda +1]_{q,n-1}}\psi _{n}\left[1+\left(n-t-1\right) \beta \right] \\ &\qquad \qquad \qquad \cdot K_{t}^{-1}\left[\left( 1+\beta \right) B_{2},\left( 1+2\beta \right) B_{3},\cdots,\left(1+t\beta \right) B_{t+1}\right] \\ &\qquad \qquad \qquad \cdot \left[\left(n-t\right) A_{n-t}-B_{n-t}\right] \Bigg)\; w^{n-1}\qquad (w\in \Delta). \end{align}$

(2.2)

Now, since

$\begin{equation*} f\in \mathcal{H}_{\Sigma}^{q,\lambda}\left(\eta,\beta,\Upsilon \right) \qquad \text{and}\qquad \mathcal{F} = f^{-1}\in \mathcal{H}_{\Sigma}^{q,\lambda }\left(\eta,\beta,\Upsilon \right) , \end{equation*}$

there are the following two positive real part functions:

$\begin{equation*} U(z) = 1+\sum\limits_{n = 1}^{\infty}c_{n}\;z^{n} \end{equation*}$

and

$\begin{equation*} V(w) = 1+\sum\limits_{n = 1}^{\infty}d_{n}\;w^{n}, \end{equation*}$

for which

$\begin{equation*} \Re\big(U(z)\big) \gt 0\qquad \text{and} \qquad \Re\big( V(w)\big) \gt 0 \qquad (z,w\in \Delta), \end{equation*}$

so that

(2.3)

and

$\begin{align} &\frac{z\left(\mathcal{H}_{\Upsilon }^{\lambda ,q}\mathcal{F}(w)\right) ^{{\prime }}+\beta z^{2}\left(\mathcal{H}_{\Upsilon }^{\lambda ,q}\mathcal{ F}(w)\right)^{\prime \prime}}{\left(1-\beta \right) \mathcal{H} _{\Upsilon }^{\lambda ,q}\mathcal{G}(w)+\beta z\left(\mathcal{H}_{\Upsilon }^{\lambda ,q}\mathcal{G}(w)\right)^{\prime}} = \eta +\left(1-\eta \right)\; V(w) \\ &\qquad = 1+\left(1-\eta \right)\sum\limits_{n = 1}^{\infty}d_{n}\;w^{n}. \end{align}$

(2.4)

Now, under the assumption that $a_{k} = 0$ for $0\leqq k\leqq n-1,$ we obtain $A_{n} = -a_{n}.$ Then, by using (2.1) and comparing the corresponding coefficients in (2.3), we obtain

$\begin{equation} \left[1+\beta \left(n-1\right)\right] \;\frac{[n]_{q}!}{[\lambda+1]_{q,n-1} }\,\psi_{n}\left(na_{n}-b_{n}\right) = \left(1-\eta \right)\; c_{n-1}. \end{equation}$

(2.5)

Similarly, by using (2.2) in the Eq (2.4), we find that

$\begin{equation} \left[1+\beta \left(n-1\right) \right]\; \frac{[n]_{q}!}{[\lambda +1]_{q,n-1} }\,\psi_{n}\left(nA_{n}-B_{n}\right) = \left(1-\eta \right)\; d_{n-1}, \end{equation}$

(2.6)

$\begin{equation} \left[1+\beta \left(n-1\right) \right]\; \frac{[n]_{q}!}{[\lambda +1]_{q,n-1} }\,\psi_{n}\left(na_{n}-b_{n}\right) = \left(1-\eta \right) \;c_{n-1} \end{equation}$

(2.7)

and

$\begin{equation} -\left[ 1+\beta \left(n-1\right) \right] \frac{[n]_{q}!}{[\lambda +1]_{q,n-1}}\,\psi_{n}\left(-na_{n}-B_{n}\right) = \left(1-\eta \right)\; d_{n-1}. \end{equation}$

(2.8)

Taking the moduli of both members of (2.7) and (2.8) for

$\left\vert b_{n}\right\vert \leqq n\qquad \text{and} \qquad \left\vert B_{n}\right\vert \leqq n,$

and applying the Carathéodory Lemma, we conclude that

$\begin{equation*} \left\vert a_{n}\right\vert \leqq \frac{2\left(1-\eta \right) [\lambda +1]_{q,n-1}}{n\left[1+\left(n-1\right) \beta \right] \; [n]_{q}!\,\psi_{n}} +1, \end{equation*}$

which completes the proof of Theorem 1.

If we set

$\psi_{n} = \dfrac{(-1)^{n-1}\Gamma (\upsilon+1)}{4^{n-1}\;(n-1)!\;\Gamma (n+\upsilon)}\qquad (\upsilon \gt 0)$

in Theorem 1, we obtain the following special case.

Corollary 1. Let the function $f$ given byt (1.1) belong to the class $\mathcal{B}_{\Sigma}^{q, \lambda}\left(\eta, \beta, \upsilon \right)$ . Suppose also tha

$0\leqq \eta \lt 1,\quad 0\leqq \beta \leqq 1,\quad \lambda \gt -1,\quad \upsilon \gt 0\qquad \mathit{\text{and}} \qquad 0 \lt q \lt 1.$

If $a_{k} = 0$ for $2\leqq k\leqq n-1,$ then

$\begin{equation*} \left\vert a_{n}\right\vert \leqq \frac{2\left(1-\eta \right)[\lambda +1]_{q,n-1}}{n\left[1+\left( n-1\right) \beta \right] \; [n]_{q}!\;\phi_{n}} +1, \end{equation*}$

where $\phi_{n}$ is given by (1.9).

Upon putting

$\psi_{n} = \left(\dfrac{n+1}{m+n}\right)^{\alpha} \qquad (\alpha \gt 0;\; m\in \mathbb{N}_0)$

in Theorem 1, we obtain the following result.

Corollary 2. Let the function $f$ given by (1.1) belong to the class $\mathcal{L}_{\Sigma}^{q, \lambda}\left(\eta, \beta, m, \alpha \right)$ . Suppose also that

$0\leqq \eta \lt 1,\quad 0\leqq \beta \leqq 1,\quad \lambda \gt -1,\quad \alpha \gt 0,\quad m\in \mathbb{N}_0 \qquad \mathit{\text{and}} \qquad 0 \lt q \lt 1.$

If $a_{k} = 0$ for $2\leqq k\leqq n-1,$ then

$\begin{equation*} \left\vert a_{n}\right\vert \leqq \frac{2\left(1-\eta \right) \left( m+n\right)^{\alpha}\;[\lambda +1]_{q,n-1}}{n\left[1+\left(n-1\right) \beta \right] \; [n]_{q}!\,\left(n+1\right)^{\alpha}}+1. \end{equation*}$

If we take

$\psi_{n} = \dfrac{\rho^{n-1}}{(n-1)!}\;e^{-\rho}\qquad (\rho \gt 0)$

in Theorem 1, we obtain the following special case.

Corollary 3. Let the function $f$ given by (1.1) belong to the class $\mathcal{M}_{\Sigma}^{q, \lambda}\left(\eta, \beta, \rho \right)$ . Suppose also that

$0\leqq \eta \lt 1,\quad 0\leqq \beta \leqq 1,\quad\lambda \gt -1,\quad \rho \gt 0 \qquad \mathit{\text{and}} \qquad 0 \lt q \lt 1.$

If $a_{k} = 0$ for $2\leqq k\leqq n-1,$ then

$\begin{equation*} \left\vert a_{n}\right\vert \leqq \frac{2\left(1-\eta \right)\;(n-1)!\;[\lambda +1]_{q,n-1}}{n\left[1+\left(n-1\right) \beta \right] \; [n]_{q}!\;\rho ^{n-1}\;e^{-\rho }}+1. \end{equation*}$

Upon setting

$\psi_{n} = \binom{m+n-2}{n-1}\ \theta^{n-1}\;\left(1-\theta \right)^{m}\qquad \left(m\in\mathbb{N};\; 0\leqq \theta \leqq 1\right)$

in Theorem 1, we are led to the following result for the above-defined class $\mathcal{W}_{\Sigma}^{q, \lambda}\left(\eta, \beta, m, \theta\right)$ .

Corollary 4. Let the function $f$ given by (1.1) belong to the following class $:$

$\mathcal{W}_{\Sigma}^{q,\lambda}\left(\eta,\beta,m,\theta \right)$

$(0\leqq \eta \lt 1;\; 0\leqq \beta \leqq 1;\;\lambda \gt -1;\; 0 \lt q \lt 1;\; m\in \mathbb{N};\; 0\leqq\theta \leqq 1).$

If $a_{k} = 0$ for $2\leqq k\leqq n-1,$ then

$\left\vert a_{n}\right\vert \leqq \frac{2\left(1-\eta\right) [\lambda +1]_{q,n-1}}{n\left[1+\left(n-1\right)\beta \right] \; [n]_{q}!\; \binom{m+n-2}{n-1}\; \theta^{n-1}\;\left(1-\theta \right)^{m}}+1.$

In particular, if we let $g(z) = f(z)$ , we obtain the class $\mathcal{S}_{\Sigma }^{q, \lambda}\left(\eta, \beta, \Upsilon \right)$ , which is a subclass of $\mathcal{H}_{\Sigma }^{q, \lambda}\left(\eta, \beta, \Upsilon\right)$ . We then give the next theorem, which involves the coefficients of this subclass of the analytic and bi-starlike functions in $\Delta$ .

Theorem 2. Let the function $f$ given by (1.1) belong to the class $\mathcal{S}_{\Sigma}^{q, \lambda}\left(\eta, \beta, \Upsilon \right)$ . Suppose also that

$\gamma \geqq 1,\quad \eta \geqq 0,\quad \lambda \gt -1, \quad 0\leqq\beta \lt 1 \qquad \mathit{\text{and}} \qquad 0 \lt q \lt 1.$

Then

$\begin{equation} \left\vert a_{2}\right\vert \leqq \left\{ \begin{array}{ll} \frac{2\left( 1-\eta \right) [\lambda +1]_{q}}{\left( 1+\beta \right) \ [2]_{q}!\,\psi _{2}}& \qquad \left(0\leqq \eta \lt 1-\frac{\left( 1+\beta \right) ^{2}\ \left( [2]_{q}!\right) ^{2}\,[\lambda +2]_{q}\ \psi _{2}^{2}}{ 2\left( 1+2\beta -\beta ^{2}\right) \ [3]_{q}!\,[\lambda +1]_{q}\ \psi _{3}} \right) \\ \\ \sqrt{\frac{2\left( 1-\eta \right) [\lambda +1]_{q,2}}{\left( 1+2\beta -\beta ^{2}\right) \ [3]_{q}!\,\psi _{3}}} &\qquad \left(1-\frac{\left(1+\beta \right)^{2}\ \left([2]_{q}!\right)^{2}\,[\lambda +2]_{q}\ \psi_{2}^{2}}{ 2\left(1+2\beta -\beta ^{2}\right) \ [3]_{q}!\,[\lambda +1]_{q} \psi_{3}} \leqq \eta \lt 1\right) \end{array} \right. \end{equation}$

(2.9)

and

$\begin{equation} \left\vert a_{3}\right\vert \leqq \left\{ \begin{array}{ll} \frac{2\left(1-\eta \right) [\lambda +1]_{q,2}}{\left( 1+2\beta -\beta ^{2}\right) \ [3]_{q}!\,\psi _{3}} &\quad \left(0\leqq \eta \lt 1-\frac{\left(1+\beta \right)^{2}\ \left( [2]_{q}!\right)^{2}\,[\lambda +2]_{q}\ \psi _{2}^{2}}{2\left(1+2\beta -\beta ^{2}\right) \ [3]_{q}!\,[\lambda +1]_{q}\ \psi _{3}}\right) \\ \\ \frac{\left(1-\eta \right)}{\left(1+2\beta \right)}\left(\tfrac{ [\lambda +1]_{q,2}}{[3]_{q}!\,\psi_{3}}+\tfrac{2\left(1-\eta\right) [\lambda +1]_{q}^{2}}{\left([2]_{q}!\right)^{2}\ \psi_{2}^{2}}\right) &\quad \left(1-\tfrac{\left(1+\beta \right)^{2}\ \left([2]_{q}!\right) ^{2}\,[\lambda +2]_{q}\ \psi_{2}^{2}}{2\left(1+2\beta -\beta ^{2}\right) \ [3]_{q}![\lambda +1]_{q}\ \psi _{3}}\leqq \eta \lt 1\right). \end{array} \right. \end{equation}$

(2.10)

Proof. Putting $n = 2$ and $n = 3$ in (2.5) and (2.6), we have

$\begin{equation} \left( 1+\beta \right) \ \frac{[2]_{q}!}{[\lambda +1]_{q}}\,\psi _{2}a_{2} = \left( 1-\eta \right) c_{1}, \end{equation}$

(2.11)

$\begin{equation} \left[ 2\left( 1+2\beta \right) \ a_{3}-\left(1+\beta \right)^{2}a_{2}^{2} \right] \frac{[3]_{q}!}{[\lambda +1]_{q,2}}\,\psi_{3} = \left( 1-\eta \right) c_{2}, \end{equation}$

(2.12)

$\begin{equation} -\left( 1+\beta \right) \ \frac{[2]_{q}!}{[\lambda +1]_{q}}\,\psi _{2}a_{2} = \left( 1-\eta \right) d_{1} \end{equation}$

(2.13)

and

$\begin{equation} \left[ -2\left( 1+2\beta \right) \ a_{3}+\left(3+6\beta -\beta ^{2}\right) a_{2}^{2}\right] \frac{[3]_{q}!}{[\lambda +1]_{q,2}}\,\psi _{3} = \left( 1-\eta \right) d_{2}. \end{equation}$

(2.14)

From (2.11) and (2.13), by using the Carathéodory Lemma, we obtain

$\begin{align} \left\vert a_{2}\right\vert & = \frac{\left( 1-\eta \right) [\lambda +1]_{q}\left\vert c_{1}\right\vert }{\left( 1+\beta \right) [2]_{q}!\psi _{2} } = \frac{\left( 1-\beta \right) [\lambda +1]_{q}\left\vert d_{1}\right\vert }{ \left( 1+\gamma +2\eta \right) [2]_{q}!\psi _{2}} \\ &\leq \frac{2\left( 1-\eta \right) [\lambda +1]_{q}}{\left( 1+\beta \right) [2]_{q}!\psi _{2}}. \end{align}$

(2.15)

Also, from (2.12) and (2.14), we have

$\begin{equation*} 2\left(1+2\beta -\beta ^{2}\right) \ \frac{[3]_{q}!}{[\lambda +1]_{q,2}} \,\psi _{3}a_{2}^{2} = \left( 1-\beta \right) \left( c_{2}+d_{2}\right). \end{equation*}$

Thus, by using the Carathéodory Lemma, we obtain

$\begin{equation} \left\vert a_{2}\right\vert \leqq \sqrt{\frac{2\left( 1-\beta \right) [\lambda +1]_{q,2}}{\left( 1+2\beta -\beta ^{2}\right) \ [3]_{q}!\,\psi _{3}} }. \end{equation}$

(2.16)

From (2.15) and (2.16), we obtain the desired estimate on the coefficient $\left\vert a_{2}\right\vert$ as asserted in (2.9).

In order to find the bound on the coefficient $\left\vert a_{3}\right\vert,$ we subtract (2.14) from (2.12), so that

$\begin{equation*} 4\left(1+2\beta \right) \ \frac{[3]_{q}!}{[\lambda +1]_{q,2}}\,\psi _{3}\left( a_{3}-a_{2}^{2}\right) = \left( 1-\eta \right) \left( c_{2}-d_{2}\right), \end{equation*}$

that is,

$\begin{equation} a_{3} = a_{2}^{2}+\frac{\left(1-\eta \right) \left( c_{2}-d_{2}\right) [\lambda +1]_{q,2}}{4\left(1+2\beta \right)\; [3]_{q}!\; \psi_{3}}. \end{equation}$

(2.17)

Now, upon substituting the value of $a_{2}^{2}$ from (2.16) into (2.17) and using the Carathéodory Lemma, we find that

$\begin{equation} \left\vert a_{3}\right\vert \leqq \frac{2\left( 1-\beta \right) [\lambda +1]_{q,2}}{\left( 1+2\beta -\beta ^{2}\right) \ [3]_{q}!\;\psi _{3}}. \end{equation}$

(2.18)

Moreover, upon substituting the value of $a_{2}^{2}$ from (2.11) into (2.12), we have

$\begin{equation*} a_{3} = \frac{\left(1-\eta \right)}{2\left(1+2\beta \right)}\left(\frac{ [\lambda+1]_{q,2}\ c_{2}}{[3]_{q}!\psi_{3}}+\frac{\left(1-\eta \right) [\lambda+1]_{q}^{2}c_{1}^{2}}{\left([2]_{q}!\right)^{2}\psi_{2}^{2}} \right). \end{equation*}$

Applying the Carathéodory Lemma, we obtain

$\begin{equation} \left\vert a_{3}\right\vert \leqq \frac{\left( 1-\eta \right) }{\left( 1+2\beta \right) }\left(\frac{[\lambda +1]_{q,2}\ }{[3]_{q}!\psi _{3}}+ \frac{2\left(1-\eta \right) [\lambda +1]_{q}^{2}}{\left([2]_{q}!\right) ^{2}\psi_{2}^{2}}\right). \end{equation}$

(2.19)

Finally, by combining (2.18) and (2.19), we have the desired estimate on the coefficient $\left\vert a_{3}\right\vert$ as asserted in (2.10). The proof of Theorem 2 is thus completed.

3. Conclusions

In our present investigation, we have made use of the concept of $q$ -convolution with a view to introducing a new class of analytic and bi-close-to-convex functions in the open unit disk. For functions belonging to this analytic and bi-univalent function class, we have derived estimates for the general coefficients in their Taylor-Maclaurin series expansions in the open unit disk. Our methodology is based essentially upon the Faber polynomial expansion method. We have also presented a number of corollaries and consequences of our main results.

In his recently-published review-cum-expository review article, in addition to applying the $q$ -analysis to Geometric Function Theory of Complex Analysis, Srivastava ^[35] pointed out the fact that the results for the $q$ -analogues can easily (and possibly trivially) be translated into the corresponding results for the $(p, q)$ -analogues (with $0 < q < p \leqq 1$ ) by applying some obvious parametric and argument variations, the additional parameter $p$ being redundant. Of course, this exposition and observation of Srivastava [,p. 340] would apply also to the results which we have considered in our present investigation for $0 < q < 1$ .

Acknowledgements

The authors received no funding for the investigation leading to the completion of this article.

Conflict of interest

The authors declare that there is no conflict of interest in respect of this article.

Acknowledgments

The authors would like to thank Cindy Cheng and Stephen Morton for their assistance, and Dr. H.S. Kim from the UNC Department of Cell Biology for oligonucleotide synthesis. We would also like to acknowledge funding from the National Institutes of Health (NIH) grant AR55195 and the McChesney Foundation.

Author contributions

C.R. conceived of the research, designed and performed experiments, analyzed results and wrote the manuscript draft. W.E.K. analyzed results and edited the manuscript. G.A.T. Conceived of the research with C.R., obtained funding, analyzed results, and edited the manuscript.

Conflict of interest

All authors declare no conflicts of interest.

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